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Unraveling the potential of microbes in decomposition of organic matter and release of carbon in the ecosystem
Abstract
Organic matter decomposition is a biochemical process with consequences affecting climate change and ecosystem productivity. Once decomposition begins, C is lost as CO2 or sequestered into more recalcitrant carbon difficult to further degradation. As microbial respiration releases carbon dioxide into the atmosphere, microbes act as gatekeepers in the whole process. Microbial activities were found to be the second largest CO2 emission source in the environment after human activities (industrialization), and research investigations suggest that this may have affected climate change over the past few decades. It is crucial to note that microbes are major contributors to the whole C cycle (decomposition, transformation, and stabilization). Therefore, imbalances in the C cycle might be causing changes in the entire carbon content of the ecosystem. The significance of microbes, especially soil bacteria in the terrestrial carbon cycle requires more attention. This review focuses on the factors that affect microorganism behavior during the breakdown of organic materials. The key factors affecting the microbial degradation processes are the quality of the input material, nitrogen, temperature, and moisture content. In this review, we suggest that to address global climate change and its effects on agricultural systems and vice versa, there is a need to double up on efforts and conduct new research studies to further evaluate the potential of microbial communities to reduce their contribution to terrestrial carbon emission.
... Microorganisms are central to nutrient cycling, breaking down organic matter into essential nutrients that can be utilized by plants and other organisms. This process, known as decomposition, is vital for sustaining life in ecosystems (Raza et al., 2023). For example, Certain bacteria, like nitrogen-fixing bacteria in the root nodules of leguminous plants, convert atmospheric nitrogen into a form usable by plants, enhancing soil fertility (Chakraborty & Kundu, 2023). ...
... • Efficient waste decomposition: Microorganisms are integral to the decomposition of organic matter, including agricultural residues. Efficient decomposition enriches the soil with organic content and contributes to water conservation by preventing the accumulation of biomass that can interfere with water availability (Raza et al., 2023). • Improved crop resilience: Microbial inoculants, such as plant growth-promoting rhizobacteria (PGPR) and mycorrhizal fungi, enhance crop resilience to environmental stressors, including water scarcity, by stimulating root development and improving overall plant tolerance to water stress (El-Saadony et al., 2022). ...
Amidst escalating climate change and food insecurity concerns, exploring the potential of microbes offers a promising and sustainable solution. This review delves into the complex interplay between microbial communities and the dual challenge of environmental crisis and food security. Ubiquitous microorganisms-from bacteria to fungi and archaea-shape our planet's ecosystems, playing a crucial role in soil health, nutrient cycling, and plant-microbe interactions. This review dissects diverse microbial habitats, highlighting their remarkable adaptability to varied environments. It then underscores the reciprocal impacts of human-induced environmental changes on microbes and their habitats. Addressing these challenges, the review presents microbes as powerful allies in mitigating climate change. Their ability to sequester carbon, reduce greenhouse gas emissions, and enhance soil fertility is explored. Innovations like biofertilizers and biopesticides demonstrate the potential of microbial technologies to revolutionize agriculture and ensure global food security. Concluding, the review emphasizes the symbiotic link between microbes and sustainable food production. Microbial technologies can adapt agriculture to changing climate conditions, addressing water scarcity and enhancing soil moisture retention. Their potential to boost productivity in both traditional and precision agriculture under diverse climatic conditions is highlighted. This review calls for the urgent recognition and harnessing of microbial power for a sustainable future. Embracing microbial technologies not only fosters environmental stewardship but also paves the way for a resilient and resource-efficient agricultural future.
... Regarding soil factors, the mycelium biomass had a positive and linear relationship with soil organic matter in truffle plantations. Different authors have shown the association between soil fungal mycelium and organic matter content and fractions (Soukupová et al., 2008;Hu et al., 2023;Raza et al., 2023). Compared to forests, long-term cultivation of agricultural land can result in decreased content of soil organic carbon (Beheshti et al., 2012). ...
The black truffle (Tuber melanosporum Vittad.) is a highly appreciated edible ectomycorrhizal fungus. It grows belowground and the mycelium and sporocarp production greatly depends on the abiotic environmental conditions. Although there is some evidence about the variables influencing the truffle mycelium at local scale, there is still a lack of knowledge on the soil and climatic patterns driving mycelium growth at broader scales. We aimed to decipher the potential environmental drivers of T. melanosporum mycelium across its westernmost natural distribution area. A paired-design experiment with truffle productive plantations and forests was set up across 10 sites. Mycelium biomass was qPCR-quantified, physicochemical soil analyses were done, and climatic data were collected to perform generalised additive modelling. Mycelium dynamics was driven by a combination of soil and climatic variables that accounted for 65.7% of mycelium variance in plantations and 53.4% in forests. Longitude, CaCO 3 , Na and Zn were related, either positively or negatively, with soil mycelium distribution in forests, while elevation, organic matter, P, Mg and B, were the main potential drivers of truffle mycelium biomass in plantations. These results strengthen our knowledge on black truffle ecology and can be applied to design management strategies for optimization of truffle mycelial biomass and sporocarp production.
... Soil bacteria constitute the largest group of microorganisms in soil, typically accounting for 70%~90% of soil microorganisms, with the richest genetic diversity [5]. They effectively promote organic material decomposition [6] and the liberation of soil mineral nutrients [7]. In addition, soil bacteria take part in in the cycling processes of carbon, nitrogen, phosphorus, potassium, and other substances, playing important roles in maintaining ecosystem energy-flow and material circulation [8,9]. ...
This study investigates the structure of soil bacterial communities in the brown mountain soils beneath the deciduous broadleaf forests of Dongling Mountain and their response to soil physicochemical properties. Aiming to provide a scientific basis for soil conservation and sustainable forest development under deciduous broadleaf forests, this research utilized high-throughput sequencing technology to examine the diversity and community structure of bacteria in soil under different tree species, alongside assessing soil physicochemical properties. The results revealed significant differences in nutrient content between the 0–20 cm and 20–40 cm soil layers. Additionally, the N:P in the brown mountain soils of Dongling Mountain was found to be below the national average, indicating potential nitrogen limitation. Dominant bacterial phylum included Actinobacteria, Proteobacteria, and Acidobacteria. The study also found that soil bacterial community structure was similar under different tree species at the same depth but varied significantly with soil depth. Furthermore, redundancy analysis (RDA) showed that the available potassium (AK), total nitrogen (TN), and ammonium nitrogen (NH4+-N) significantly influenced the structural changes in the soil bacterial community. This research highlights the characteristics of soil bacterial community structure beneath deciduous broadleaf forests and its relationship with soil physicochemical properties, offering valuable insights for regional soil ecosystem conservation and forest management.
... Notably, bacterial and archaeal communities are among the most abundant and diverse microbial communities found in soils (Singh et al., 2009), playing essential roles in soil and plant productivity, particularly within integrated agricultural systems (Pratibha et al., 2023). Indeed, both bacterial and archaeal communities contribute to nutrient cycling through the decomposition of organic residues (Raza et al., 2023), being involved in various steps of nitrogen cycling (Gubry-Rangin et al., 2010), such as ammonification and nitrification (Diao et al., 2023). In addition, these communities facilitate processes such as nitrogen fixation promotion (Sepp et al., 2023) and phosphate solubilization (Tian et al., 2021). ...
... The temperature and humidity of topsoil are more suitable for the growth of microorganisms, so the nitrogen content of topsoil is increased by decomposing litter. With the deepening of the soil layer, the soil nitrogen content decreased due to the reduction in microbial activity [45]. This also reflects that in North China, the increase in the soil nitrogen content caused by ecological restoration mainly depends on the decomposition of plant litter [26], which is different from the increase in soil nitrogen content caused by plant roots in semihumid Northwest Sichuan, China. ...
Ecological restoration can improve soil fertility and have a significant impact on the soil nitrogen cycle. Nitrogen (N) is an essential nutrient element for plant growth and development, and also an important factor limiting soil productivity. As an important part of soil nitrogen, the composition and proportion of soil organic nitrogen components can directly or indirectly affect the difficulty of soil organic nitrogen mineralization and nitrogen availability, and then affect soil fertility. However, the current studies on soil nitrogen under ecological restoration mainly focus on nitrogen accumulation and nitrogen mineralization, while there are relatively few studies on changes in soil organic nitrogen components, especially in alpine regions. Therefore, in this study, three restoration pattern of mixed forage (MG), single shrub (SA) and shrub combination (SG) that have been restored continuously for 15 years in northwest Sichuan, China, were taken as the research object, and natural sandy land (CK) without manual intervention was taken as the control. Through field sampling and laboratory analysis, the characteristics of the soil nitrogen content and its proportion to soil total nitrogen (TN) under ecological restoration in alpine sandy land in northwest Sichuan, China, were investigated, and the correlation between the nitrogen content and soil physicochemical properties was analyzed. The results showed that the three ecological restoration patterns significantly increased the contents of acylated ammonium nitrogen (AMMN), acid-lyzed amino sugar nitrogen (ASN), acid-lyzed amino acid nitrogen (AAN), acid-lyzed unknown nitrogen (HUN), acid-lyzed total nitrogen (AHN) and non-acid-lyzed nitrogen (NHN) in soil, and the change trend was consistent with that of soil TN. Ecological restoration improved soil nitrogen mineralization and storage capacity by increasing the proportion of AAN, HUN and NHN to soil TN, and the effect was most obvious in the MG pattern 20–40 cm and SG pattern 40–60 cm soil layers. In general, except ASN, the soil nitrogen content was positively correlated with the soil TN, soil water content (SWC) and soil organic carbon (SOC), and negatively correlated with the soil bulk density (BD) and pH. The results of this study will help us to understand the supply capacity of soil nitrogen under ecological restoration and provide a scientific basis for the selection of an ecological restoration mode and the improvement of the restoration effect and efficiency in alpine sandy land.
... We know different families, species and genes that are part of the soil microbial community, but there is a lack of knowledge about what are their roles and functions in the complex soil ecosystem. Soil microbes are a key factor for the soil quality and health since they are largely responsible for soil fertility, and structure, biochemical cycling and soil C sequestration, even though for the latest they can act as both sink and source [46]. The decoded of the soil microbial functions in different ecosystems could contribute for example to improve crop yield and quality in agricultural soils [35]. ...
In this introductory chapter the authors show their views on what they consider current and future fundamental issues to advance knowledge and research in Soil Science. Each of the authors gives responses to a question posed by the scientific editor of the book. Furthermore, additional data is included to show a picture corresponding to the current situation of the theme, as per different scientific searching tools.
... The addition of N can effectively alleviate microbial N limitation, while it has been shown that straw return with N fertilizer can increase the abundance of microorganisms carrying functional genes for carbohydrate decomposition [14], which agrees with our findings. This N-indued increment of KSDMs will promote strawderived organic matter and nutrient release by enhancing microbial turnover pathways [62], improving soil nutrient availability, and facilitating crop growth and development. ...
Crop residue decomposition is an important part of the carbon cycle in agricultural ecosystems, and microorganisms are widely recognized as key drivers during this process. However, we still know little about how nitrogen (N) input and rhizosphere effects from the next planting season impact key straw-decomposing microbial communities. Here, we combined amplicon sequencing and DNA-Stable Isotope Probing (DNA-SIP) to explore these effects through a time-series wheat pot experiment with four treatments: 13C-labeled maize straw addition with or without N application (S1N1 and S1N0), and no straw addition with or without N application (S0N1 and S0N0). The results showed that straw addition significantly reduced soil microbial alpha diversity in the early stages. Straw addition changed microbial beta diversity and increased absolute abundance in all stages. Growing plants in straw-amended soil further reduced bacterial alpha diversity, weakened straw-induced changes in beta diversity, and reduced bacterial and fungal absolute abundance in later stages. In contrast, N application could only increase the absolute abundance of soil bacteria and fungi while having little effect on alpha and beta diversity. The SIP-based taxonomic analysis of key straw-decomposing bacteria further indicated that the dominant phyla were Actinobacteria and Proteobacteria, with overrepresented genera belonging to Vicinamibacteraceae and Streptomyces. Key straw-decomposing fungi were dominated by Ascomycota, with overrepresented genera belonging to Penicillium and Aspergillus. N application significantly increased the absolute abundance of key straw-decomposing microorganisms; however, this increase was reduced by the rhizosphere effect. Overall, our study identified key straw-decomposing microorganisms in straw-amended soil and demonstrated that they exhibited opposite responses to N application and the rhizosphere effect.
... Additionally, the biochar provides habitat and nutrients for soil microorganisms, and biochar directly or indirectly affects microbial diversity, composition, and makeup (Mustafa et al., 2023a, b). Microbial activity significantly alters the soil pH (Raza et al., 2023b) and nutrients availability through their enzymatic activities. Therefore, the application of phosphorus solubilizing bacteria (PSB) and biochar showed positive effects for soil remediation in the past (Lai et al., 2022). ...
The growing global population has led to a heightened need for food production, and this rise in agricultural activity is closely tied to the application of phosphorus-based fertilizers, which contributes to the depletion of rock phosphate (RP) reserves. Considering the limited P reserves, different approaches were conducted previously for P removal from waste streams, while the adsorption of ions is a novel strategy with more applicability. In this study, a comprehensive method was employed to recover phosphorus from wastewater by utilizing biochar engineered with minerals such as calcium, magnesium, and iron. Elemental analysis of the wastewater following a batch experiment indicated the efficiency of the engineered biochar as an adsorbent. Subsequently, the phosphorus-enriched biochar, hereinafter (PL-BCsb), obtained from the wastewater, underwent further analysis through FTIR, XRD, and nutritional assessments. The results revealed that the PL-BCsb contained four times higher (1.82%) P contents which further reused as a fertilizer supplementation for Brassica napus L growth. PL-BCsb showed citric acid (34.03%), Olsen solution (10.99%), and water soluble (1.74%) P desorption. Additionally, phosphorous solubilizing bacteria (PSB) were incorporated with PL-BCsb along two P fertilizer levels P45 (45 kg ha−1) and P90 (90 kg ha−1) for evaluation of phosphorus reuse efficiency. Integrated application of PL-BCsb with half of the suggested amount of P45 (45 kg ha−1) and PSB increased growth, production, physiological, biochemical, and nutritional qualities of canola by almost two folds when compared to control. Similarly, it also improved soil microbial biomass carbon up to four times, alkaline and acid phosphatases activities both by one and half times respectively as compared to control P (0). Furthermore, this investigation demonstrated that waste-to-fertilizer technology enhanced the phosphorus fertilizer use efficiency by 55–60% while reducing phosphorus losses into water streams by 90%. These results have significant implications for reducing eutrophication, making it a promising approach for mitigating environmental pollution and addressing climate change.
... However, when microplastics inhibit microbial activity, the decomposition process slows down, resulting in the accumulation of organic matter and reduced CO 2 release. This can contribute to carbon sequestration and potentially impact global climate patterns (Raza et al., 2023). ...
Microplastics are so widely dispersed and abundant throughout the globe that many scientists consider them to be important markers of the recent and current time, which is known as the Plasticene. The effects of microplastics are still not fully known, though. Because microplastics are multiple stressors with a variety of physical-chemical characteristics, understanding their impact is quite complicated. Toxic chemicals are transported by microplastics in ecosystems, acting as vectors of transport. Also, many dangerous chemicals are added during polymer production to enhance their properties as well as lengthen their life, and these chemicals must have detrimental effect. To date, many significant studies have been conducted, making a good progress to understand the effect of the key plastic additives on the environment. These additives are discharged into the environment and, hence become a source of many health issues, especially, when are coupled with micro-plastics. The current study thoroughly reviewed the most toxic and dangerous chemicals used in the plastic industry, elaborating the effects on organism health. Also, it provided information about the works that explored their abundance on microplastics.
... Previous research has shown that residue cover and retention through cropping intensification can increase SOC and other soil properties (Bowman et al., 1999;Blanco-Canqui et al., 2013;Moinet et al., 2018;Raza et al., 2023). Crop residue acts as physical barrier that protects the soil beneath from factors like sunlight, wind, and rain, and these factors can promote microbial activity, and subsequently faster decomposition or loss of soil organic matter (Bertol et al., 2007;Lal, 2009;Ranaivoson et al., 2017). ...
... Plant mostly uptake the nutrients from weathering of minerals, decomposition of organic matter (OM), application of organic or inorganic nutrient sources, and rain/irrigation (Akcura et al. 2019;Raza et al. 2023). OM decomposition is the most rapid process through which nutrients become readily available to the plant in the soil like decomposition of plant litter releases tannin-acid (Chen et al. 2020). ...
Intensive cultivation is a threat to soil health. Holistic management strategies are necessary to rejuvenate soil health. Farmyard manure (FYM) application is an alternative option to rejuvenate soil health and crop productivity. A short-term field study was conducted at UAF-Pakistan to evaluate the co-application of FYM and inorganic fertilizer (Di-ammonium Phosphate; DAP) for rejuvenation of soil health and maize productivity. Treatments included four levels of phosphorus (P) at a rate of 0, 90, 120, and 150 Kg ha −1 alone and in combination with two levels of FYM with the rate of 0 and 10 tons ha −1 in two-factor randomized complete block design with three replicates. Total eight treatments were maintained as T1 (control), T2 (90 Kg ha −1 P), T3 (120 Kg ha −1 P), T4 (150 Kg ha −1 P), T5 (10 tons ha −1 FYM), T6 (90 Kg ha −1 P and 10 tons ha −1 FYM), T7 (120 Kg ha −1 and 10 tons ha −1 FYM), and T8 (150 Kg ha −1 P and 10 tons ha −1 FYM). Data analysis showed that treatment T8 significantly (P ≤ .005) improved the plant height (15.31%), cob length (21.33%), cob weight (36.92%), 1000 grains weight (4.89%), grain yield (31.21%), PUE (39%), and soil physical properties over control. Overall, we concluded integrated application of FYM and DAP increases nutrient use efficiency and maize productivity. ARTICLE HISTORY
... After a few years of implementation, these practices have been reported to result in increased SOC reserves [20][21][22][23]. Several research studies have shown that water-stable aggregate fractionation and fractionation density can be used to understand the impact of soil management practices on carbon dynamics [24,25], since aggregates are more sensitive to changes in soil management [26][27][28]. For example, Puget et al. [26] reported that macro-aggregates form due to enrichment with fresh organic matter and are recycled faster than micro-aggregates. ...
In Tunisia, climate change impacts that lead to the degradation of soil resources are considered to be a major limiting factor on socioeconomic development. These impacts are exacerbated by the intensive plowing and cultivation practices used by Tunisian farmers, which expedite the depletion of soil organic matter (SOM), leading to changes in the physio-chemical properties of soil and consequently promoting soil erosion. In fact, the decrease in soil organic carbon (SOC) stocks affects soil's fertility and the ability to regulate climate change. The objective of this study, which was conducted in Le Krib in the Siliana region of northwestern Tunisia, was to evaluate the effects of two cropping systems, consisting of durum wheat (Triticum aestivum) and oats (Avena sativa), and two types of tillage, no-till (NT) and mouldboard plowing (MP), on different soil aggregate classes (>2000 µm, 2000-250 µm, 250-180 µm, 180-53 µm and <53 µm) and soil physio-chemical properties, as well as the resulting effects on the carbon and nitrogen concentrations in these aggregates. The results showed that the carbon content of all soil aggregate classes was influenced by interactions between the previous crop and tillage regime. The clay-silt fraction had higher carbon concentrations under no-till and mouldboard plowing management. Furthermore, the previous crop and tillage type and their interactions had significant effects on nitrogen concentrations in micro-aggregates. The highest nitrogen concentrations (2846.6 ppm) were found in micro-aggregates in soils where the previous crop was durum wheat and mouldboard plowing was used, while the lowest concentrations (1297 ppm) were obtained in soils where the previous crop was oats and mouldboard plowing was used.
Tourism development influenced the ecological network of microbial communities.
Regulating mechanism of intra- and inter-domain networks was clarified.
Macrophyte coverage reduces microbial network complexity and stability.
Landscaping may promote nitrogen and phosphorus cycle in wetland watershed.
Numerous urban wetland parks have been established, yet the understanding of microbial interactions in response to tourism development is still limited. This study aims to elucidate the impact of tourism development on the complexity and stability of molecular ecological networks within the microbial communities of wetland sediments. Through an analysis of sediments properties, microorganism intra- and inter-domain co-occurrence characteristics in three different wetland functional areas (conservation, landscaping, and recreation areas), we found that tourism development influenced sediment physicochemical properties. These changes regulated the diversity and ecological networks of archaeal and bacterial communities. Specifically, areas with landscaping (LA) exhibited reduced network connectivity and robustness, suggesting that macrophyte coverage diminishes the complexity and stability of microbial communities in wetland parks. Notably, the transition from conservation areas (CA) to LA strengthened the correlations between microbial network modules and sediment total nitrogen (TN) and total phosphorus (TP), potentially enhancing the nitrogen and phosphorus cycles in wetlands. Structural equation modeling analysis revealed that both abiotic factors (TC, TP, TN, K, Mg, pH) and biotic factors (archaeal and bacterial α-diversity) can influence interdomain network complexity, accounting for 42% of the variation. Among these factors, sediment TN exerted the largest positive effect on network complexity (37.9%), while Mg had the most negative impact (59.8%). This study provides valuable insights for ecological assessments of urban wetlands and can inform strategies for effective wetland ecosystem management.
Microbial extracellular polymeric substances (EPS) are an important component in sediment ecology. However, most research is highly skewed towards the northern hemisphere and in more permanent systems. This paper investigates EPS (i.e., carbohydrates and proteins) dynamics in arid Austral zone temporary pans sediments. Colorimetric methods and sequence–based metagenomics techniques were employed in a series of small temporary pan ecosystems characterised by alternating wet and dry hydroperiods. Microbial community patterns of distribution were evaluated between seasons (hot–wet and cool–dry) and across depths (and inferred inundation period) based on estimated elevation. Carbohydrates generally occurred in relatively higher proportions than proteins; the carbohydrate:protein ratio was 2.8:1 and 1.6:1 for the dry and wet season respectively, suggesting that EPS found in these systems was largely diatom produced. The wet– hydroperiods Carbohydrate mean 102 μg/g; Protein mean 65 μg/g supported more EPS production as compared to the dry– hydroperiods (Carbohydrate mean 73 μg/g; Protein mean 26 μg/g). A total of 15,042 Unique Amplicon Sequence Variants (ASVs) were allocated to 51 bacterial phyla and 1127 genera. The most abundant genera had commonality in high temperature tolerance, with Firmicutes, Actinobacteria and Proteobacteria in high abundances. Microbial communities were more distinct between seasons compared to within seasons which further suggested that the observed metagenome functions could be seasonally driven. This study's findings implied that there were high levels of denitrification by mostly nitric oxide reductase and nitrite reductase enzymes. EPS production was high in the hot–wet season as compared to relatively lower rates of nitrification in the cool–dry season by ammonia monooxygenases. Both EPS quantities and metagenome functions were highly associated with availability of water, with high rates being mainly associated with wet– hydroperiods compared to dry– hydroperiods. These data suggest that extended dry periods threaten microbially mediated processes in temporary wetlands, with implications to loss of biodiversity by desiccation.
Afforestation is beneficial to improving soil carbon pools. However, due to the lack of deep databases, the variations in soil carbon and the combined effects of multiple factors after afforestation have yet to be adequately explored in >1 m deep soils, especially in areas with deep-rooted plants and thick vadose zones. This study examined the multivariate controls of soil organic carbon (SOC) and inorganic carbon (SIC) in 0–18 m deep under farmland, grassland, willow, and poplar in loess deposits. The novelty of this study is that the factors concurrently affecting deep soil carbon were investigated by multiwavelet coherence and structural equation models. On average, the SOC density (53.1 ± 5.0 kg m−2) was only 12% of SIC density (425.4 ± 13.8 kg m−2), with depth-dependent variations under different land use types. In the soil profiles, the variations in SOC were more obvious in the 0–6 m layer, while SIC variations were mainly observed in the 6–12 m layer. Compared with farmland (SOC: 17.0 kg m−2; SIC: 122.9 kg m−2), the plantation of deciduous poplar (SOC: 28.5 kg m−2; SIC: 144.2 kg m−2) increased the SOC and SIC density within the 0–6 m layer (p < 0.05), but grassland and evergreen willow impacted SOC and SIC density insignificantly. The wavelet coherence analysis showed that, at the large scale (>4 m), SOC and SIC intensities were affected by total nitrogen-magnetic susceptibility and magnetic susceptibility-water content, respectively. The structural equation model further identified that SOC density was directly controlled by total nitrogen (path coefficient = 0.64) and indirectly affected by magnetic susceptibility (path coefficient = 0.36). Further, SOC stimulated the SIC deposition by improving water conservation and electrical conductivity. This study provides new insights into afforestation-induced deep carbon cycles, which have crucial implications for forest management and enhancing ecosystem sustainability in arid regions.
Plastic waste discarded into aquatic environments gradually degrades into smaller fragments, known as microplastics (MPs), which range in size from 0.05 to 5 mm. The ubiquity of MPs poses a significant threat to aquatic ecosystems and, by extension, human health, as these particles are ingested by various marine organisms including zooplankton, crustaceans, and fish, eventually entering the human food chain. This contamination threatens the entire ecological balance, encompassing food safety and the health of aquatic systems. Consequently, developing effective MP removal technologies has emerged as a critical area of research. Here, we summarize the mechanisms and recently reported strategies for removing MPs from aquatic ecosystems. Strategies combining physical and chemical pretreatments with microbial degradation have shown promise in decomposing MPs. Microorganisms such as bacteria, fungi, algae, and specific enzymes are being leveraged in MP remediation efforts. Recent advancements have focused on innovative methods such as membrane bioreactors, synthetic biology, organosilane-based techniques, biofilm-mediated remediation, and nanomaterial-enabled strategies, with nano-enabled technologies demonstrating substantial potential to enhance MP removal efficiency. This review aims to stimulate further innovation in effective MP removal methods, promoting environmental and social well-being.
Carbon flows into and out of the soil are important processes that contribute to controlling the global climate. The relationship between soil organisms and the climate is interdependent since the organisms that contribute to carbon and greenhouse gas fluxes are simultaneously affected by climate change and soil management. Temperature, soil moisture, pH, nutrient level, redox potential and organic matter quality are key elements affecting the microorganisms involved in organic carbon flows in the soil. Climate, topography (slope and position in the landscape), soil texture, soil mineralogy and land-use regulate those key elements and, thus, the C fluxes in the pedosphere. Soil microbes can increase carbon influx and storage by promoting plant growth, mycorrhizal establishment, and particle aggregation. Conversely, microorganisms contribute to carbon efflux from the soil via methanogenesis, rhizospheric activity, and organic carbon mineralization. Nevertheless, strategies and management practices could be used to balance out carbon emissions to the atmosphere. For example, carbon influx and storage in the soil can be stimulated by plant growth promoting microorganisms, greater plant diversity via crop rotation and cover crops, cultivating mycotrophic plants, avoiding or reducing the use of fungicides and adopting organic farming, no-tillage crop systems and conservative soil management strategies. Therefore, this review aimed to shed light on how soil microorganisms can contribute to increase C influxes to the soil, and its significance for climate change. Then, we also seek to gather the practical actions proposed in the scientific literature to improve carbon sequestration and storage in the soil. In summary, the review provides a comprehensive basis on soil microorganisms as key to carbon fluxes and helpers to lessen climate change by increasing carbon fixation and storage in agroecosystems via stimulation or application of beneficial microorganisms.
Keywords
carbon cycle; soil microorganisms; climate change; soil organic carbon; carbon sequestration
Pengunaan bahan organik memiliki peranan penting untuk memperbaiki sifat fisik, biologi, maupun kimia tanah yang akan mempengaruhi pertumbuhan tanaman mentimun. Penelitian ini bertujuan untuk mengkaji dan mengungkap pengaruh aplikasi beberapa jenis bahan organik terhadap pertumbuhan dan hasil tanaman mentimun. Penelitian ini menggunakan metode pot yang disusun menggunakan Rancangan Acak Kelompok Lengkap (RKLT) dengan faktor tunggal. Jenis bahan organik digunakan sebagai faktor dalam penelitian ini yang terdiri atas kontrol-tanpa bahan organik, kompos jerami padi, kompos sekam bakar, kompos seresah daun, dan kompos kotoran sapi. Aplikasi masing-masing jenis bahan organik menggunakan dosis yang sama yakni 3 ton/ha. Pengulangan yang digunakan pada penelitian ini yaitu sebanyak empat kali dengan sampel pada masing-masing perlakuan sebanyak lima tanaman. Berdasarkan hasil penelitian menunjukkan bahwa aplikasi bahan organik menyebabkan tanaman mengalami pertumbuhan panjang dan jumlah daun pada setiap minggunya. Lebih lanjut, aplikasi bahan organik juga berpengaruh nyata terhadap panjang akar saat 2 MST dan bobot buah per tanaman. Aplikasi kompos jerami padi dan kompos kotoran sapi menghasilkan akar terpanjang saat tanaman berumur 2 MST dan bobot buah per tanaman tertinggi, sedangkan kontrol dan aplikasi kompos seresah daun menghasilkan akar terpendek saat 2 MST dan bobot buah per tanaman terendah.
Restoration of mining soils is important to the vegetation and environment. This study aimed to explore the variations in soil nutrient contents, microbial abundance, and biomass under different gradients of substrate amendments in mining soils to select effective measures. Soil samples were collected from the Bayan Obo mining region in Inner Mongolia Autonomous Region, China. Contents of soil organic matter (SOM), available nitrogen (AN), available phosphorus (AP), available potassium (AK), microbial biomass carbon/microbial biomass nitrogen (MBC/MBN) ratio, biomass, and bacteria, fungi, and actinomycetes abundance were assessed in Agropyron cristatum L. Gaertn., Elymus dahuricus Turcz., and Medicago sativa L. soils with artificial zeolite (AZ) and microbial fertilizer (MF) applied at T0 (0 g/kg), T1 (5 g/kg), T2 (10 g/kg), and T3 (20 g/kg). Redundancy analysis (RDA) and technique for order preference by similarity to ideal solution (TOPSIS) were used to identify the main factors controlling the variation of biomass. Results showed that chemical indices and microbial content of restored soils were far greater than those of control. The application of AZ significantly increases SOM, AN, and AP by 20.27%, 23.61%, and 40.43%, respectively. AZ significantly increased bacteria, fungi, and actinomycetes abundance by 0.63, 3.12, and 1.93 times of control, respectively. RDA indicated that AN, MBC/MBN ratio, and SOM were dominant predictors for biomass across samples with AZ application, explaining 87.6% of the biomass variance. SOM, MBC/MBN ratio, and AK were dominant predictors with MF application, explaining 82.9% of the biomass variance. TOPSIS indicated that T2 was the best dosage and the three plant species could all be used to repair mining soils. AZ and MF application at T2 concentration in the mining soils with M. sativa was found to be the most appropriate measure.
Globally, rejuvenation of soil health is a major concern due to the continuous loss of soil fertility and productivity. Soil degradation decreases crop yields and threatens global food security. Improper use of chemical fertilizers coupled with intensive cultivation further reduces both soil health and crop yields. Plants require several nutrients in varying ratios that are essential for the plant to complete a healthy growth and development cycle. Soil, water, and air are the sources of these essential macro- and micro-nutrients needed to complete plant vegetative and reproductive cycles. Among the essential macro-nutrients, nitrogen (N) plays a significant in non-legume species and without sufficient plant access to N lower yields result. While silicon (Si) is the 2nd most abundant element in the Earth’s crust and is the backbone of soil silicate minerals, it is an essential micro-nutrient for some plants. Silicon is just beginning to be recognized as an important micronutrient to some plant species and, while it is quite abundant, Si is often not readily available for plant uptake. The manufacturing cost of synthetic silica-based fertilizers is high, while absorption of silica is quite slow in soil for many plants. Rhizosphere biological weathering processes includes microbial solubilization processes that increase the dissolution of minerals and increases Si availability for plant uptake. Therefore, an important strategy to improve plant silicon uptake could be field application of Si-solubilizing bacteria. In this review, we evaluate the role of Si in seed germination, growth, and morphological development and crop yield under various biotic and abiotic stresses, different pools and fluxes of silicon (Si) in soil, and the bacterial genera of the silicon solubilizing microorganisms. We also elaborate on the detailed mechanisms of Si-solubilizing/mobilizing bacteria involved in silicate dissolution and uptake by a plant in soil. Last, we discuss the potential of silicon and silicon solubilizing/mobilizing to achieve environmentally friendly and sustainable crop production.
Endophytic bacteria have great potential for improving the growth and productivity of crop plants. However, individual or combined endophytic bacterial strains (consortia) and their application method had a significant impact on their efficacy in improving crop growth and productivity. In this regard, the present study was conducted to explore the potential of the plant growth-promoting endophytic bacterial strains (PsJN, MN17, and MW4C) to improve the growth, yield, and physiological and biochemical attributes of flaxseed through seed and foliar inoculation methods. The inoculated and un-inoculated (control) seeds of the flaxseed cultivar were sown in pots under controlled conditions. The bacterial inoculum was applied to the potting seeds and plants, while the control was treated with 10% tryptic soy broth. The study findings revealed that the MW4C strain alone and in consortium performed better under the seed application method. The consortium significantly increased fresh shoot-root biomass (1.82 g and 0.84 g) and yield-seed weight (3.32 g) as compared to the control. Likewise, the consortium enhanced the biochemical attributes, i.e., protein, flavonoids, and phenolic concentrations to approximately 78.16, 174.04, and 21.66 mg kg −1 FW, respectively, under the seed inoculation method. However, our results suggest that the selected bacterial strains improved the growth, yield, and physiological and biochemical index of flaxseed. Inoculation of endophytic bacteria significantly improved the growth, yield, and physiological and biochemical properties of flaxseed. The consortium applied through the seed inoculation method could be considered a potential biofertilizer technology for improved growth and productivity of flaxseed.
Tomato is an important field crop, and nutritional imbalances frequently reduce its yield. Diagnosis and Recommendation Integrated System (DRIS), uses ratios for nutrient deficiency diagnosis instead of absolute concentration in plant tests. In this study, local DRIS norms for the field tomatoes were established and the nutrient(s) limiting tomatoes yield were determined. Tomato leaves were analyzed for nutrients, to identify nutritional status using the DRIS approach. One hundred tomatoes fields were selected from Chatter Plain Khyber Pakhtunkhwa and the Sheikupura Punjab Pakistan. The first fully matured leaf was sampled, rinsed, dried and ground for analyzing P, K, Ca, Mg, Cu, Fe, Mn and Zn using an Inductively Coupled Plasma Atomic Emission Spectrophotometer (ICP AES). Plant tissue N and S were measured by the combustion method. The tomatoes yields were recorded at each location. The data were divided into high-yielding (≥3.79 kg/10 plant) and low-yielding (<3.79 kg/10 plant) populations and norms were computed using standard DRIS procedures. High-yielding plant population had a statistically greater mean S and Fe than the low-yielding population. The average balance index, the sum of functions, for S and Fe were −11.04 and −5.17 which reflected deficiency of S and Fe. Plant nutrients norms established may optimize plant nutrition in field tomatoes for high yield.
Several studies have suggested the pivotal roles of eutrophic lakes in carbon (C) cycling at regional and global scales. However, how the co-metabolism effect on lake sediment organic carbon (OC) mineralization changes in response to integrated inputs of labile OC and nutrients is poorly understood. This knowledge gap hinders our ability to predict the carbon sequestration potential in eutrophic lakes. Therefore, a 45-day microcosm experiment was conducted to examine the dominant mechanisms that underpin the co-metabolism response to the inputs of labile C and nutrients in lacustrine sediments. Results indicate that the labile C addition caused a rapid increase in the positive co-metabolism effect during the initial stage of incubation, and the co-metabolism effect was positively correlated with the C input level. The positive co-metabolism effect was consistently higher under high C input, which was 152% higher than that under low C input. The higher β-glucosidase activity after nutrient addition, which, in turn, promoted the OC mineralization in sediments. In addition, different impacts of nutrients on the co-metabolism effect under different C inputs were observed. Compared with the low nutrient treatments, the largest co-metabolism effect under high C with high nutrient treatment was observed by the end of the incubation. In the high C treatment, the intensity of the co-metabolism effect (CE) under high nitrogen treatment was 1.88 times higher than that under low nitrogen condition. However, in the low C treatment, the amount of nitrogen had limited impact on co-metabolism effect. Our study thus proved that the microorganisms obviously regulate sediment OC turnover via stoichiometric flexibility to maintain a balance between resources and microbial requirements, which is meaningful for evaluating the OC budget and lake eutrophication management in lacustrine sediments.
Article Info Excessive use of chemical fertilizers causing a serious threat to the agro-ecological system, developing resistance to pest and declining food safety. Under current scenario, the application of bio-organic nutrients sources become imperative to sustain the productivity of arable farming. Thus to study the possible use of bio-organic sources of nutrients in soil fertility, crop quality and saving the application cost of chemical fertilizer, a pot experiment was conducted in greenhouse at Land Resources Research Institute, NARC Islamabad. Integrated effects of bio-organic fertilizers such as phosphate solubilizing bacteria (PSB), vermicompost (VC) along with chemical fertilizer was investigated on soil-plant nutrients contents, growth and yield of tomato. Post-harvest results showed that the integrated use of bio-organic fertilizers with chemical fertilizer significantly increased the agronomic yield (Plant height and chlorophyll content) and fruit yield (Number of fruits, fruit weight, fruit diameter and yield) in tomato. The maximum plant height (161.24cm), chlorophyll contents (61.2), number of fruits (19), fruit weight (55g), fruit diameter (45.6a) and fruit yield (1.39 Kg/plant) were recorded in the treatment T5 where VC+PSB+75%RD were applied and minimum in treatment T1 (control). Treatment T5 has increased 117% fruit yield over control. The highest N (2.05% and 2.89%), P (0.33% and 0.50%) and K (2.32% and 6.67%) concentration in shoot and fruit of tomato respectively were found in treatment T5 (VC+PSB+75%RD). Similarly, in soil the highest N (4 mg Kg-1), P (0.66mg Kg-1) and K (3.53mg Kg-1) was recorded in treatment T6 (VC+PSB+100RD). Thus, study results recommend that the integrated use of bio-organic sources with appropriate proportion of chemical/synthetic fertilizers is best option of fertilizer savings and to achieve maximum benefits regarding quality and yield.
The priming effect (PE) is a key mechanism contributing to the carbon balance of the soil ecosystem. Almost 100 years of research since its discovery in 1926 have led to a rich body of scientific publications to identify the drivers and mechanisms involved. A few review articles have summarised the acquired knowledge; the last major one was published in 2010. Since then, knowledge on the soil microbial communities involved in PE and in PE + C sequestration mechanisms has been considerably renewed.
This article reviews current knowledge on soil PE to state to what extent new insights may improve our ability to understand and predict the evolution of soil C stocks. We propose a framework to unify the different concepts and terms that have emerged from the international scientific community on this topic, report recent discoveries and identify key research needs.
Seventy per cent of the studies on the soil PE were published in the last 10 years, illustrating a renewed interest for PE, probably linked to the increased concern about the importance of soil carbon for climate change and food security issues. Among all the drivers and mechanisms proposed along with the different studies to explain PE, some are named differently but actually refer to the same object. This overall introduces ‘artificial’ complexity for the mechanistic understanding of PE, and we propose a common, shared terminology. Despite the remaining knowledge gaps, consistent progress has been achieved to decipher the abiotic mechanisms underlying PE, together with the role of enzymes and the identity of the microbial actors involved. However, including PE into mechanistic models of SOM dynamics remains challenging as long as the mechanisms are not fully understood. In the meantime, empirical alternatives are available that reproduce observations accurately when calibration is robust.
Based on the current state of knowledge, we propose different scenarios depicting to what extent PE may impact ecosystem services under climate change conditions.
Read the free Plain Language Summary for this article on the Journal blog.
Conceptual and empirical advances in soil biogeochemistry have challenged long-held assumptions about the role of soil micro-organisms in soil organic carbon (SOC) dynamics; yet, rigorous tests of emerging concepts remain sparse. Recent hypotheses suggest that microbial necromass production links plant inputs to SOC accumulation, with high-quality (i.e., rapidly decomposing) plant litter promoting microbial carbon use efficiency, growth, and turnover leading to more mineral stabilization of necromass. We test this hypothesis experimentally and with observations across six eastern US forests, using stable isotopes to measure microbial traits and SOC dynamics. Here we show, in both studies, that microbial growth, efficiency, and turnover are negatively (not positively) related to mineral-associated SOC. In the experiment, stimulation of microbial growth by high-quality litter enhances SOC decomposition, offsetting the positive effect of litter quality on SOC stabilization. We suggest that microbial necromass production is not the primary driver of SOC persistence in temperate forests. Factors such as microbial necromass origin, alternative SOC formation pathways, priming effects, and soil abiotic properties can strongly decouple microbial growth, efficiency, and turnover from mineral-associated SOC.
Soil enzymes are included in the process of decomposition of the organic matter. The essential virtue of using enzyme assays for soil is that they are comparatively simple and mostly available analytical methods. However, since enzyme analysis results vary with the biological chemical, physical properties of soils, analytical methods may not reflect the true results. With the developing technology, the enzyme analysis methods used in soil enzyme analysis should be updated with new methods. The purpose of this section is to procure information regarding current methods that can be determined with new technologies in soil enzyme analysis.
Unraveling the biogeographic pattern of soil fungal decomposers along temperature gradients – in a smooth linearity or an abrupt jump – can help us connect the global carbon cycle to global warming. Through a standardized global field survey, we identify the existence of temperature thresholds that control the global distribution of soil fungal decomposers, leading to abrupt reductions in their proportion (i.e. the relative abundance in fungal community) immediately after crossing particular air and soil temperature thresholds. For example, small increases over the mean annual temperature threshold of ~9ºC result in abrupt reductions in their proportion, paralleling a similar temperature threshold for soil carbon content. We further find that the proportion of soil fungal decomposers is more sensitive to temperature increases under arid conditions. Given the positive correlation between the global distributions of fungal decomposers and soil heterotrophic respiration, the reported temperature-driven abrupt reductions in fungal decomposers could further suppress their driven soil decomposition processes and reduce carbon fluxes from soils to the atmosphere with implications for climate change feedback. This work not only advances the current knowledge on the global distribution of soil fungal decomposers, but also highlights that small changes in temperature around certain thresholds can lead to potential unexpected consequences in global carbon cycling under projected climate change.
Background
It is well known that litter releases dissolved organic carbon (DOC), which would impact the role of litter in soil nitrogen (N) transformation. Thus, this study aimed to explore the effect of litters decomposed at different levels on soil N dynamics in the presence of labile carbon.
Methods
An incubation experiment was carried out with fresh litter (SF), partially decomposed litter (SP) or the combined addition of glucose and alanine in soils for 210 days. The influence of litter addition on soil was investigated by changes of soil soluble organic N, NH 4 ⁺ ‐N, NO 3 ⁻ ‐N and microbial biomass N (MBN).
Results
There was higher soil NH 4 ⁺ ‐N and NO 3 ⁻ ‐N in SF, nonetheless lower in SP than control. Litter addition decreased soil dissolved organic N (DON), but increased DOC compared to control. These results suggested that the effects of litter on soil N might change with the varying status of decomposed litter. Alanine addition increased each soil N form, which was more of DON and less of MBN in SP than SF. After adding amino acids, the priming amount of DON was computed positive at 0.5 day with the highest soil MBN, simultaneously. Moreover, the net N transformation rate preceded the gross rate. Glucose addition also improved soil NH 4 ⁺ ‐N and DON more in SP than SF, while lessened MBN in SF than SP. These results indicated that the differential effect of labile C sources, alanine and glucose, on soil N might be related to the chemistry of the differently decomposed litter. As a labile C source, glucose had a lesser effect on soil N than alanine.
Conclusions
Our findings highlighted the coexistence of litters at varied decomposition status and C sources released from litters, which are contributed to the N dynamics in soil and are critical for the ecological functioning of the degraded litter.
Aims
Traditional tillage represents a serious threat to the stability of soil ecosystems. Understanding the response mechanisms of soil microbial community assembly to different tillage practices is a major topic of soil ecological research.
Methods
Here, we investigated the bacterial community structures and assembly in bulk and rhizosphere soils of soybeans grown under traditional tillage (moldboard plow, MP) and two conservation tillage practices, namely, no-tillage (NT) and ridge tillage (RT), using high-throughput sequencing methods.
Results
Compared with MP, NT and RT increased the relative abundances of nitrifying bacteria of Nitrosospira sp. and the nitrogen-fixing bacteria of Mesorhizobium sp., Bradyrhizobium sp. and Burkholderia sp., but decreased the abundance of carbon-degrading bacteria, especially Blastococcus sp., Streptomyces sp. and Sphingomonas sp. The altered functional bacteria were mostly affiliated with biomarkers and keystone taxa in the NT and RT networks. For the results of network properties and assembly processes, we found that NT and RT habited a more stable bacterial network structure and a lower homogenizing dispersal value. Soil pH was the primary factor regulating both the bacterial community structures and assembly processes under the three tillage practices.
Conclusions
The soil bacterial community structures and assembly processes were profoundly altered by tillage practices. The changes in functional bacteria indicated that conservation tillage might contribute to soil carbon sequestration, while stimulating nitrogen fixation and nitrification.
A growing body of research has established that the microbiome can mediate the dynamics and functional capacities of diverse biological systems. Yet, we understand little about what governs the response of these microbial communities to host or environmental changes. Most efforts to model microbiomes focus on defining the relationships between the microbiome, host, and environmental features within a specified study system and therefore fail to capture those that may be evident across multiple systems. In parallel with these developments in microbiome research, computer scientists have developed a variety of machine learning tools that can identify subtle, but informative, patterns from complex data. Here, we recommend using deep transfer learning to resolve microbiome patterns that transcend study systems. By leveraging diverse public data sets in an unsupervised way, such models can learn contextual relationships between features and build on those patterns to perform subsequent tasks (e.g., classification) within specific biological contexts.
Sixty percent of the population of Pakistan is directly or indirectly reliant upon rain-fed agriculture that depends on predictable weather patterns. Global climatic change affects our agriculture and its impacts seem to increase daily. Pakistan produces wheat, rice, cotton, sugarcane, and maize and these crops are affected by climate change. Incessant escalation in earth temperatures globally is changing precipitation patterns including a shift in our monsoon season. These conditions affect agricultural production, farm livelihoods and agribusiness infrastructure that is leading to food insecurity and malnutrition among the farming communities. The aim of this review is to highlight the climate change impacts on Pakistan's agricultural sector, current risks, and mitigation potential to insure resilient agricultural practices that provide household food security.
Short-rotation coppice (SRC) Salix plantations have the potential to provide fast-growing biomass feedstock with significant soil and climate mitigation benefits. Salix varieties exhibit significant variation in their physiological traits, growth patterns and soil ecology-but the effects of these variations have rarely been studied from a systems perspective. This study analyses the influence of variety on soil organic carbon (SOC) dynamics and climate impacts from Salix cultivation for heat production for a Swedish site with specific conditions. Soil carbon modelling was combined with a life cycle assessment (LCA) approach to quantify SOC sequestration and climate impacts over a 50-year period. The analysis used data from a Swedish field trial of six Salix varieties grown under fertilized and unfertilized treatments on Vertic Cambisols during 2001-2018. The Salix systems were compared with a reference case where heat is produced from natural gas and green fallow was the land use alternative. Climate impacts were determined using time-dependent LCA methodology-on a land-use (per hectare) and delivered energy unit (per MJheat) basis. All Salix varieties and treatments increased SOC, but the magnitude depended on the variety. Fertilization led to lower carbon sequestration than the equivalent unfertilized case. There was no clear relationship between bio-mass yield and SOC increase. In comparison with reference cases, all Salix varieties had significant potential for climate change mitigation. From a land-use perspective, high yield was the most important determining factor, followed by SOC sequestration, therefore high-yielding fertilized varieties such as 'Tordis', 'Tora' and 'Björn' performed best. On an energy-delivered basis, SOC seques-tration potential was the determining factor for the climate change mitigation effect, with unferti-lized 'Jorr' and 'Loden' outperforming the other varieties. These results show that Salix variety has a strong influence on SOC sequestration potential, biomass yield, growth pattern, response to fertilization and, ultimately, climate impact.
Marine phytoplankton generate half of global primary production, making them essential to ecosystem functioning and biogeochemical cycling. Though phytoplankton are phylogenetically diverse, studies rarely designate unique thermal traits to different taxa, resulting in coarse representations of phytoplankton thermal responses. Here we assessed phytoplankton functional responses to temperature using empirically derived thermal growth rates from four principal contributors to marine productivity: diatoms, dinoflagellates, cyanobacteria, and coccolithophores. Using modeled sea surface temperatures for 1950–1970 and 2080–2100, we explored potential alterations to each group’s growth rates and geographical distribution under a future climate change scenario. Contrary to the commonly applied Eppley formulation, our data suggest phytoplankton functional types may be characterized by different temperature coefficients (Q10), growth maxima thermal dependencies, and thermal ranges which would drive dissimilar responses to each degree of temperature change. These differences, when applied in response to global simulations of future temperature, result in taxon-specific projections of growth and geographic distribution, with low-latitude coccolithophores facing considerable decreases and cyanobacteria substantial increases in growth rates. These results suggest that the singular effect of changing temperature may alter phytoplankton global community structure, owing to the significant variability in thermal response between phytoplankton functional types. Phytoplankton communities are important players in biogeochemical processes, but are sensitive to global warming. Here, a meta-analysis shows how the varied responses of phytoplankton to rising temperatures could potentially alter growth dynamics and community structure in a future ocean.
Sewage sludge is an unpreventable by-product of the wastewater treatment system due to its increasing volume, and the impacts related to its disposal is making it a key issue for many countries. Management and recycling of sewage sludge are the best options, but it requires a high level of characterization
because it contains many harmful compounds, which are disturbing the ecosystem, such as heavy metals and organic pollutants. It is considered as an alternative valuable raw material for the production of agricultural fertilizers due to the composition of high nutrient and organic matter. The use of sewage sludge as a means of fertilization in the agricultural system seems to be the best possible way for its proper disposal. Due to the blind jump in need for food and feed, a risk exists for a shortage supply of fertilizer, and that impact on the economy has increased manyfold. The research established the methods of utilization of sewage sludge for fertilizer materials manufacturing. The application of sewage sludge in agriculture is attractive from environmental as well as economic points of view. However, the presence of toxic material constrains the use of sewage sludge which may represent a significant hazardous impact on the groundwater, environment, and human health due to the presence of hydrophilic compounds. This chapter will describe the natural method of attenuation for detoxification of sewage slug to reduce its toxicity and use as fertilizer to achieve fertilizer security for potential agriculture production.
Many plant species simultaneously interact with multiple symbionts, which can, but do not always, generate synergistic benefits for their host. We ask if plant life history (i.e. annual vs perennial) can play an important role in the outcomes of the tripartite symbiosis of legumes, arbuscular mycorrhizal fungi (AMF), and rhizobia.
We performed a meta‐analysis of 88 studies examining outcomes of legume–AMF–rhizobia interactions on plant and microbial growth.
Perennial legumes associating with AMF and rhizobia grew larger than expected based on their response to either symbiont alone (i.e. their response to co‐inoculation was synergistic). By contrast, annual legume growth with co‐inoculation did not differ from additive expectations. AMF and rhizobia differentially increased phosphorus (P) and nitrogen (N) tissue concentration. Rhizobium nodulation increased with mycorrhizal fungi inoculation, but mycorrhizal fungi colonization did not increase with rhizobium inoculation. Microbial responses to co‐infection were significantly correlated with synergisms in plant growth.
Our work supports a balanced plant stoichiometry mechanism for synergistic benefits. We find that synergisms are in part driven by reinvestment in complementary symbionts, and that time‐lags in realizing benefits of reinvestment may limit synergisms in annuals. Optimization of microbiome composition to maximize synergisms may be critical to productivity, particularly for perennial legumes.
Mycorrhiza is a symbiotic association between the roots of plants with fungi. Among the various types of mycorrhizal fungi, arbuscular mycorrhizal fungi (AMF) are the most prominent as they are obligate symbionts with a wide host range, and they play a major role in shaping ecosystems and associated productivity. Approximately 71% of vascular plant species are able to form symbiotic association with AMF. AMF primarily rely on the host for photosynthates but give much more in return for the well-being of the host plant. Most importantly they are able to improve tolerance of host plants against various biotic stresses, such as—bacterial, fungal, viral, nematode phytopathogens and herbivores. The underlying mechanism includes—competition for nutrients, space, and host photosynthates, rhizosphere alteration and host defense induction. The effectiveness of an AM association in conferring biotic stress tolerance is context dependent, affected by various biotic and abiotic factors. This review describes various mechanisms involved in AMF mediated biotic stress tolerance in plant and the biotic and abiotic factors which influences the performance of AM association.
Agricultural intensification has substantially reduced soil biodiversity as well as agroecosystem functions and services. Sustainable agroecosystems that increase crop diversity through rotation may promote soil biodiversity and above-belowground interactions. Studying ecological networks, soil communities, and abiotic impacts simultaneously increases our understanding of complex C cycling encompassing all components of a given system. Higher rotational diversity enhances primary productivity by increasing the photosynthetic intensity of crops in rotation relative to systems where a given crop is grown continuously. In addition, greater temporal crop diversity stimulates above-belowground interactions, which affects carbon allocation, rhizodeposition, and the growth of rhizobiomes. Stronger above-belowground interactions will intensify ecological connections between microbial and faunal networks among roots, rhizosphere, and bulk soil. This further strengthens soil functions and interactions between networks of biotic elements (plant inputs and soil food web functioning) and abiotic factors (soil matrix and microenvironments), providing positive feedback loops on soil organic C accrual. This review describes how interactions between rotational and biological diversity drive biodiversity-function relationships. By increasing the quantity, quality, and chemical diversity of C inputs, crop rotations with higher functional diversity foster soil communities and enhance biotic-abiotic interactions, with positive impacts on the formation and storage of soil organic matter.
AimsIn this study, we examine the rhizosphere processes influencing organic P (Po) utilization in soil with low inorganic P (Pi) availability and how they change with plant development. Interactions between plants and the rhizosphere microbial community triggered by P deficiency may provide insights into the role of P availability on degradation of soil organic matter (SOM).Methods
Maize (Zea mays) plants were grown in low P containing soil. Soil pH, potential acid phosphatase activities, soil C and P pools, microbial biomass C and P, microbial community structure, and plant P content were analyzed at different vegetative growth stages (VGS).ResultsAt early VGS, the plants were P deficient which correlated with greater rhizosphere potential acid phosphatase activity, degradation of SOM and a reduction in the Po pool. At late VGS, the plants appeared to recover which correlated with a decrease in Meh (III) extractable P, an increase in microbial biomass C and P, change in microbial community structure, and greater total P (TP) in the plant biomass.Conclusions
The mineralization of organic C and Po are coupled in low P soil where N is not limited. The overall findings from this study advance our understanding of the coupled biogeochemical rhizosphere processes controlling P cycling at different plant growth stages and notably the importance of Po to the overall P needs of plants in soil with low Pi availability.
Biological nitrogen fixation (BNF) varies in different soils and is impacted by rice planting. This study was conducted to investigate the extent of BNF in acidic soil planted with rice and to explore if the light and flood layer thickness affected the BNF. Soil and rice together were incubated in a 15N2-labeled closed chamber for whole growth period, and light and water depth effects were measured by labeling aboveground parts of rice plants in a plastic bag and labeling air in bottle without rice plants, respectively. The results showed that the total N fixation of soil and plant was 11.65 kg ha−1; nevertheless, it was only 2.11 kg ha−1 under fallow soil. In planted soil, plants and soil accounted for 25.1% and 74.9% of total 15N fixed, correspondingly. Soil NH4+-N concentration decreased due to uptake by the rice plants. There was higher available iron (Fe2+) in soil with rice plantings than in the fallow soil which was beneficial for BNF. Furthermore, 15N atom% in the roots was found higher than in the aboveground plant parts or leaves whether from experiment with whole rice-soil labeled in 15N2-enriched closed chamber or from that only rice aboveground parts labeled by 15N2, whereas water depth above the soil surface insignificantly influenced BNF without rice planting. Rice planting may significantly increase the amount of N fixation in acidic paddy soils. Further work regarding the role of rice plant and thickness of the water layer in BNF is highly important to gain an improved understanding of the N cycle in the rice ecosystem.
Nitrous oxide (N2O), like carbon dioxide, is a long-lived greenhouse gas that accumulates in the atmosphere. Over the past 150 years, increasing atmospheric N2O concentrations have contributed to stratospheric ozone depletion¹ and climate change², with the current rate of increase estimated at 2 per cent per decade. Existing national inventories do not provide a full picture of N2O emissions, owing to their omission of natural sources and limitations in methodology for attributing anthropogenic sources. Here we present a global N2O inventory that incorporates both natural and anthropogenic sources and accounts for the interaction between nitrogen additions and the biochemical processes that control N2O emissions. We use bottom-up (inventory, statistical extrapolation of flux measurements, process-based land and ocean modelling) and top-down (atmospheric inversion) approaches to provide a comprehensive quantification of global N2O sources and sinks resulting from 21 natural and human sectors between 1980 and 2016. Global N2O emissions were 17.0 (minimum–maximum estimates: 12.2–23.5) teragrams of nitrogen per year (bottom-up) and 16.9 (15.9–17.7) teragrams of nitrogen per year (top-down) between 2007 and 2016. Global human-induced emissions, which are dominated by nitrogen additions to croplands, increased by 30% over the past four decades to 7.3 (4.2–11.4) teragrams of nitrogen per year. This increase was mainly responsible for the growth in the atmospheric burden. Our findings point to growing N2O emissions in emerging economies—particularly Brazil, China and India. Analysis of process-based model estimates reveals an emerging N2O–climate feedback resulting from interactions between nitrogen additions and climate change. The recent growth in N2O emissions exceeds some of the highest projected emission scenarios3,4, underscoring the urgency to mitigate N2O emissions.
It is well known that the hydrolysable tannin (tannin acid) and condensed tannins in a plant can influence the availability of soil nitrogen (N) through the formation of tannin–organic N complexes. However, the lack of research on the effect of tannin acid–organic N complexes on soil N hinders our understanding of the subsequent role of these complexes. In this line, an incubation experiment was carried out with the addition of tannin acid-arginine and tannin-bovine serum albumin (BSA) complexes, where tannin acid was represented as the hydrolysable tannin. For the necessary comparisons, tannin acid, arginine, or BSA was added to the soil samples. The results showed that tannic acid addition quickly decreased protein contents at the beginning of incubation and decreased soluble organic N (SON) after 3 days to produce the inorganic N in the soil as compared to control. Tannin-arginine complexes increased NH4+–N compared with control and this increased degree was found lower than arginine treatment. Moreover, the addition of tannin–BSA complexes did not significantly increase soil NH4+–N as BSA alone treatment did. NO3−–N and N2O emission increased in each treatment compared with control indicating nitrification was not limited. The increase of NH4+–N was mainly attributed to the decrease of SON after 3 days of incubation. These results suggested that tannin acid quickly formed the complexes with protein to impact soil N. While, the effects of tannin-arginine and tannin–BSA complexes on soil N transformation were quite dissimilar. Thus, this study highlighted the subsequent role of tannin–organic N complexes under the influence of tannin. Tannin and tannin–organic N complexes naturally coexist in the ecosystem to impact soil N dynamics and may interact with each other as well.
In the forest ecosystems, litterfall is an important component of the nutrient cycle that regulates the accumulation of soil organic matter (SOM), the input and output of the nutrients, nutrient replenishment, biodiversity conservation, and other ecosystem functions. Therefore, a profound understanding of the major processes (litterfall production and its decomposition rate) in the cycle is vital for sustainable forest management (SFM). Despite these facts, there is still a limited knowledge in tropical forest ecosystems, and further researches are highly needed. This shortfall of research-based knowledge, especially in tropical forest ecosystems, may be a contributing factor to the lack of understanding of the role of plant litter in the forest ecosystem function for sustainable forest management, particularly in the tropical forest landscapes. Therefore, in this paper, I review the role of plant litter in tropical forest ecosystems with the aims of assessing the importance of plant litter in forest ecosystems for the biogeochemical cycle. Then, the major factors that affect the plant litter production and decomposition were identified, which could direct and contribute to future research. The small set of studies reviewed in this paper demonstrated the potential of plant litter to improve the biogeochemical cycle and nutrients in the forest ecosystems. However, further researches are needed particularly on the effect of species, forest structures, seasons, and climate factors on the plant litter production and decomposition in various types of forest ecosystems.
Net ecosystem exchange of CO2 (NEE) measurement was carried out in tropical lowland paddy at ICAR-National Rice Research Institute, Cuttack, Odisha, India, in 2015 using eddy covariance technique with the objective to assess the variation of NEE of CO2 in lowland paddy and to find out the most suitable model for better partitioning of net ecosystem exchange of CO2 in tropical lowland paddy. Paddy is grown twice (dry and wet season) a year in this region in the lowland, and the field is kept fallow during the remainder of the year. Two different flux partitioning models (FPMs)—the rectangular hyperbola (RH) and the Q10, were evaluated to assess NEE of CO2, and its partitioning components—gross primary production (GPP) and ecosystem respiration (RE), and the resulting flux estimates were compared. The RH method assessed the effects of photosynthetically active radiation on the NEE, whereas the Q10 method utilized the relationship between ecosystem respiration and temperature in lowland paddy. The average NEE during the dry season and wet season was − 1.62 and − 1.83 g C m−2 d−1, respectively, whereas it varied from − 5.71 to 2.29 g C m−2 d−1 during the observation period covering both the cropping seasons and the fallow period. The mean difference between modeled GPP and RE from two FPMs was found significant in both the seasons. The maximum correlation for GPP estimation was found between two FPMs at the panicle initiation stage during both the dry season (R2 = 0.767) and wet season (R2 = 0.321). It was evident from the study that the Q10 method reliably produced the most realistic carbon flux estimates over the RH method, for the lowland paddy. The Q10 model which used nighttime flux and temperature data to estimate RE produced estimates that had lower prediction error (RMSE) as compared to the RH model. It can be concluded that in lowland paddy, the Q10 predicted better estimates of RE and GPP values than the RH method, suggesting that the Q10 model can be used for partitioning of NEE in tropical lowland paddy.
Soil stores more carbon (C) than all vegetation and the atmosphere combined. Soil C stocks are broadly shaped by temperature, moisture, soil physical characteristics, vegetation, and microbial-mediated metabolic processes. The efficiency with which microorganisms use soil C regulates the balance between C storage in soil and the atmosphere. In this review, we discuss how microbial physiology and community assembly processes determine microbial growth rate and efficiency and, in turn, soil organic C cycling through the lens of community ecology. We introduce a conceptual framework cataloging life history (i.e., growth rate, resource acquisition, and stress tolerance) and assembly traits (i.e., competition, facilitation, and dispersal) that correspond with different growth efficiencies. We also compare how dominant mycorrhizal fungal type affects growth efficiency. We propose that further development and inclusion of specific community parameters in microbial-explicit Earth system models are needed for accurately predicting soil organic C responses to global change.
There is a need to quantify agriculture’s potential to sequester carbon (C) to inform global approaches aimed at mitigating climate change effects. Many factors including climate, crop, soil management practices, and soil type can influence the contribution of agriculture to the global carbon cycle. The objective of this study was to investigate the C sequestration potential of conservation agriculture (CA) (defined by minimal soil disturbance, maintaining permanent soil cover, and crop rotations). This study used micrometeorological methods to measure carbon dioxide (CO2) flux from several alternative CA practices in Harare, central Zimbabwe. Micrometeorological methods can detect differences in total CO2 emissions of agricultural management practices; our results show that CA practices produce less CO2 emissions. Over three years of measurement, the mean and standard error (SE) of CO2 emissions for the plot with the most consistent CA practices was 0.564 ± 0.0122 g CO2 m⁻² h⁻¹, significantly less than 0.928 ± 0.00859 g CO2 m⁻² h⁻¹ for the conventional tillage practice. Overall CA practices of no-till with the use of cover crops produced fewer CO2 emissions than conventional tillage and fallow.
Purpose
This long-term study used a lysimeter platform to monitor the changes of organic matter and total nitrogen content in deep soils of various fertilization treatments of wheat-maize in the Huanghuaihai area, with the goal to improve the soil environment and increase the quantity and diversity of soil microbes, and then provide a theoretical basis for synergetic improvement of production and resource utilization efficiency.
Materials and methods
The experiment included a no-N-fertilizer treatment as a control (CK) to study the following three fertilizer treatments: the exclusive application of urea (U), the exclusive application of cattle manure (M), and the combined application of organic and inorganic fertilizers (UM).
Results and discussion
These results showed that fertilization significantly increased the soil organic matter content. Compared with CK, the average soil organic matter content of each soil layer treated with M, UM, and U was increased by 25.00%, 22.81%, and 8.96% in wheat growing season, respectively. The average soil organic matter content of each soil layer in the 2-year average M, UM, and U treatments increased by 148.70%, 16.81%, and − 7.18% maize growing season, respectively. In the 2-year wheat field, in the 0–20 cm soil layer, the effects of each treatment on the total nitrogen content of the soil were significant, and compared with the CK treatment, the UM, M, and U treatments increased by 105.72%, 75.07%, and 47.13%. For maize field, compared with the CK treatment, the total nitrogen content of M, UM, and U increased by 83.34%, 50.27%, and 7.10%. The addition of organic fertilizer can increase the number and diversity of bacteria and fungi in the soil, and the application of urea significantly reduced the quantities and diversities of bacteria. The combined application of organic and inorganic fertilizers can increase the number and diversity of soil actinomycetes. The combined application of organic and inorganic fertilizers could significantly increase the number of maize roots. Compared with CK treatment, the number of roots increased by 66.67%. After long-term experimental treatment, the yields of wheat and maize were all expressed as UM > U > M > CK.
Conclusions
The combination of organic and inorganic N fertilizers increased the soil organic matter content, improved the soil environment, increased the quantity and diversity of soil microbes, promoted the growth and development of crop roots, and increased the yield of wheat and maize. It was a reasonable fertilization method to synergistically improve the production and resource utilization efficiency.
The rapid anthropogenic climate change that is being experienced in the early twenty-first century is intimately entwined with the health and functioning of the biosphere. Climate change is impacting ecosystems through changes in mean conditions and in climate variability, coupled with other associated changes such as increased ocean acidification and atmospheric carbon dioxide concentrations. It also interacts with other pressures on ecosystems, including degradation, defaunation and fragmentation. There is a need to understand the ecological dynamics of these climate impacts, to identify hotspots of vulnerability and resilience and to identify management interventions that may assist biosphere resilience to climate change. At the same time, ecosystems can also assist in the mitigation of, and adaptation to, climate change. The mechanisms, potential and limits of such nature-based solutions to climate change need to be explored and quantified. This paper introduces a thematic issue dedicated to the interaction between climate change and the biosphere. It explores novel perspectives on how ecosystems respond to climate change, how ecosystem resilience can be enhanced and how ecosystems can assist in addressing the challenge of a changing climate. It draws on a Royal Society-National Academy of Sciences Forum held in Washington DC in November 2018, where these themes and issues were discussed. We conclude by identifying some priorities for academic research and practical implementation, in order to maximize the potential for maintaining a diverse, resilient and well-functioning biosphere under the challenging conditions of the twenty-first century.
This article is part of the theme issue ‘Climate change and ecosystems: threats, opportunities and solutions’.
Conservation agriculture is a well-established method for promoting carbon sequestration and reducing greenhouse gas emissions, but little is known about how it affects subtropical dryland farming systems. The goal of this study was to evaluate the potential of conservation agriculture in Pakistan's subtropical dryland to reduce atmospheric CO 2 enrichment and alter soil organic carbon fractions. In a field experiment, fallow-wheat (farmers' practice) and the conservation tillage methods minimum tillage (MT), reduced tillage (RT), and zero tillage (ZT) were compared to conventional tillage (CT) in the main plots and the cropping systems sorghum-wheat (S-W) and mungbean-wheat (M-W) to fallow-wheat (F-W) in the sub-plots. Multiple assessments taken over a two-year period revealed that CT plots lacked greater soil organic carbon and its fractions than ZT and RT plots. In comparison to CT, ZT, and RT exhibited higher average total organic carbon (TOC), microbial biomass carbon (MBC), particulate organic carbon (POC), and mineral-associated organic carbon (MOC) concentrations, respectively, of 1.43% and 1.31%, 4.61% and 2.83%, 2.42% and 1.97%, and 1.66% and 1.76%. In comparison to the S-W cropping system, the F-W and M-W cropping systems showed increased MBC and MOC, but POC and TOC were little impacted. The maximum TOC (0.589% and 0.589%), MBC (0.021% and 0.021%), POC (0.195% and 0.192%), and MOC (0.489% and 0.485%) were found in the combinations of ZT with F-W and M-W. Regardless of the cropping systems, cumulative CO 2 flow was lowest in ZT plots compared to the other tillage techniques. The CENTURY model confirmed that the use of continuous tillage is a major threat to both soil fertility and production. The study, therefore, concludes that ZT and RT systems in particular are potential possibilities for carbon sequestration in subtropical dryland soils for CO 2 reduction.
The rhizosphere is one of the most dynamic interfaces on the Earth. Understanding the magnitudes of rhizosphere effect (RE, difference in bio-physicochemical properties between rhizosphere and bulk soils) on soil microbial communities and their moderators are important for study on below-ground carbon (C) cycling. A comprehensive meta-analysis was conducted to quantify the REs on soil microbial biomass, community structure, respiration, and C-degrading enzymes. We found that REs on soil C and nutrients, total microbial biomass, the abundance of specific microbial groups, fungi to bacteria ratio, respiration, and C-degrading enzymes were positive, but the magnitudes were varied with biomes, plant functional types, and mycorrhizal types. REs on microbial biomass, respiration, and C-degrading enzymes increased with the increase of mean annual temperature and mean annual precipitation, but decreased with the increase of soil clay, C, nitrogen (N), and phosphorus (P) contents. The REs on microbial biomass and respiration also increased as the REs on soil C:N:P increased. Compared with bulk soil, per unit rhizosphere soil C supported more microbial biomass, per unit of which respired more C, leading to faster C decomposition in rhizosphere. Our findings indicate that increase in microbial biomass, co-metabolism induced by labile and energy-rich organic C of root exudates, and overflow respiration induced by stoichiometric imbalance together contribute to the enhanced C decomposition in rhizosphere. The global pattern of REs on soil microbial communities are critical to revealing the plant-microbe-soil interactions in terrestrial ecosystems.
Soil microbial biomass and microbial stoichiometric ratios are important for understanding carbon and nutrient cycling in terrestrial ecosystems. Here, we compiled data from 8862 observations of soil microbial biomass from 1626 published studies to map global patterns of microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP), and their stoichiometry using a random forest model. Concentrations of MBC, MBN, and MBP were most closely linked to soil organic carbon (SOC), while climatic factors were most important for stoichiometry in microbial biomass ratios. Modeled seasonal MBC concentrations peaked in summer in tundra and in boreal forests, but in autumn in subtropical and in tropical biomes. The global mean MBC/MBN, MBC/MBP, and MBN/MBP ratios were estimated to be 10, 48, and 6.7, respectively, at 0–30 cm soil depth. The highest concentrations, stocks, and microbial C/N/P ratios were found at high latitudes in tundra and boreal forests, probably due to the higher soil organic matter content, greater fungal abundance, and lower nutrient availability in colder than in warmer biomes. At 30–100 cm soil depth, concentrations of MBC, MBN, and MBP were highest in temperate forests. The MBC/MBP ratio showed greater flexibility at the global scale than did the MBC/MBN ratio, possibly reflecting physiological adaptations and microbial community shifts with latitude. The results of this study are important for understanding C, N, and P cycling at the global scale, as well as for developing soil C‐cycling models including soil microbial C, N, and P as important parameters.
In the current era of global warming, the Himalayan forests are under tremendous pressure due to intensified anthropogenic activity, resulting in the loss of forest diversity. However, the potential of carbon (C) sinks by increasing carbon storage and/or sequestration is still uncertain. Therefore, the present study was undertaken to examine the C-sequestration and mitigation potential of eight different tree plantations, namely Pinus roxburghii, Quercus leucotrichophora, Acacia mollissima, Acacia catechu, Alnus nitida, Albizia procera, Ulmus villosa, and Eucalyptus tereticornis in the mid-hill of Indian Himalayas. The soil samples were also drawn (humus, 0-20, 20-40, and 40-100 cm) to determine the soil and ecosystem C density. The analysis revealed that the maximum tree biomass (300.19 Mg ha-1), vegetation biomass (305.43 Mg ha-1), vegetation carbon (153.59 Mg ha-1), and total ecosystem C density (369.93 Mg ha-1) were recorded under U. villosa plantation. Similarly, P. roxburghii plantations had the maximum detritus C density (7.25 Mg ha-1) whereas A. nitida (224.71 Mg ha-1) had the maximum soil C density. The highest C-sequestration was also recorded in U. villosa (183.0 Mg ha-1). A significantly higher and lower rate of C-sequestration and CO2 mitigation was observed in Ulmus villosa (5.9 & 21.64 Mg ha-1 yr-1) and Eucalyptus tereticornis (3.9 & 14.3 Mg ha-1 yr-1). The findings of the study concluded that indigenous tree species such as U. villosa, A. procera, A. nitida, and Q. leucotrichophora should be encouraged for afforestation on degraded lands to support climate change mitigation strategies in the sub-temperate forest ecosystem.
Traditional methods of weeds management have caused serious environmental and health concerns. Therefore, development of alternate strategies for effective management of weeds is becoming indispensable for sustainable agriculture. In this study, the comparative effectiveness of chemical and bio-herbicides for the management of weeds in wheat has been assessed under laboratory and field conditions. Two effective allelopathic rhizobacteria (6K and 6) were selected from initial screening experiment which had abilities to suppress the growth of selective weeds as well as had potential to improve the growth of wheat. Based on 16S ribosomal RNA (16S rRNA) gene sequencing, the selected allelopathic rhizobacteria were identified as Pseudomonas fluorescens strain 6K and Bacillus sp. strain 6. Further, sorghum allelopathic water extract was also used in combination with selected allelopathic rhizobacteria as a bio-herbicide. Five treatments used for the laboratory and field experiments were control (T1: without herbicide), chemical herbicide (T2: mesosulfuron methyl + idosulfuron methyl; Atlantis® 6WG), sorghum allelopathic extract (T3), consortium of two different allelopathic rhizobacteria (T4) and combined application of allelopathic extract of sorghum and consortium of two allelopathic rhizobacteria (T5= T3 + T4). Results of laboratory experiment showed that T5 significantly suppressed the seed germination percentage of four selected weeds i.e., Anagallis arvensis L., Phalaris minor Retz., Cynodon dactylon L. and Melilotus indicus L. and the same treatment (T5) also significantly improved seed germination of wheat as compared to all other treatments. Further evaluation under field condition showed that T5 significantly decreased the weed density and total weed biomass at 15, 30 and 45 days after sowing (DAS) of all weeds as compared to T1 (control). Field trial results also indicated that T5 significantly increased the wheat growth traits including the biological yield (73%) and grain yield (53%) as compared to T1. Likewise, the economic analysis revealed that T5 improved the net benefits with a higher marginal rate of return than all other treatments. Our findings indicated that combined application of allelopathic rhizobacterial consortium and allelopathic extract of sorghum remained more effective for controlling weeds and improving the growth and yield traits of wheat as compared to their sole application. Therefore, co-application of allelopathic rhizobacterial consortium and sorghum allelopathic water extract could offer an economically viable lever for the biological management of weeds of wheat for sustainable production.
Out of the huge quantity of agricultural wastes produced globally, rice straw is one of the most abundant ligno-cellulosic waste. For efficient utilization of these wastes, several cost-effective biological processes are available. The practice of field level in-situ or ex-situ decomposition of rice straw is having less degree of adoption due to its poor decomposition ability within a short time span between rice harvest and sowing of the next crop. Agricultural wastes including rice straw are in general utilized by using lignocellulose degrading microbes for industrial metabolite or compost production. However, bioconversion of crystalline cellulose and lignin present in the waste, into simple molecules is a challenging task. To resolve this issue, researchers have identified a novel new generation microbial enzyme i.e., lytic polysaccharide monooxygenases (LPMOs) and reported that the combination of LPMOs with other glycolytic enzymes are found efficient. This review explains the progress made in LPMOs and their role in lignocellulose bioconversion and the possibility of exploring LPMOs producers for rapid decomposition of agricultural wastes. Also, it provides insights to identify the knowledge gaps in improving the potential of the existing ligno-cellulolytic microbial consortium for efficient utilization of agricultural wastes at industrial and field levels.
Arbuscular mycorrhizal (AM) fungi lack efficient exoenzymes to access organic nutrients directly. Nevertheless, the fungi often obtain and further channel to their host plants a significant share of nitrogen (N) and/or phosphorus from such resources, presumably via cooperation with other soil microorganisms. Because it is challenging to disentangle individual microbial players and processes in complex soil, we took a synthetic approach here to study 15N-labelled chitin (an organic N source) recycling via microbial loop in AM fungal hyphosphere. To this end, we employed a compartmented in vitro cultivation system and monoxenic culture of Rhizophagus irregularis associated with Cichorium intybus roots, various soil bacteria, and the protist Polysphondylium pallidum. We showed that upon presence of Paenibacillus sp. in its hyphosphere, the AM fungus (and associated plant roots) obtained several-fold larger quantities of N from the chitin than it did with any other bacteria, whether chitinolytic or not. Moreover, we demonstrated that adding P. pallidum to the hyphosphere with Paenibacillus sp. further increased by at least 65% the gain of N from the chitin by the AM fungus compared to the hyphosphere without protists. We thus directly demonstrate microbial interplay possibly involved in efficient organic N utilisation by AM fungal hyphae.
Soil pollution with nickel (Ni) casts detrimental effects on the quality of crops. Low-cost amendments can restrict Ni mobility in soil and its uptake by the plants. In this pot experiment, the effects of pistachio husk biochar (PHB) and arbuscular mycorrhizal fungi (AMF) on the distribution of Ni in mung bean and its bioavailability in Ni-spiked soil were evaluated. Plant parameters like Ni plant height, root dry weight, shoot dry weight, grain yield, chlorophyll contents, oxidative stress, Ni distribution in the roots, shoot, and grain, as well as the nutritional potential of grains, were measured on plants grown on Ni-contaminated soil amended or not (control) with AMF, zeolite (ZE), PHB, ZE + AMF, and PHB + AMF. Moreover, DTPA (diethylenetriamine pentaacetate)-extractable Ni in the soil, microbial biomass carbon (MBC), total glomalin (TG), extractable glomalin (EG), mycorrhizal root colonization (MRC), and the activities of soil enzymes (i.e., urease, acid phosphatase, and catalase) were also assessed after the plant harvest. With few exceptions, all treatments had significant effects on plant and soil parameters. The PHB + AMF treatment showed the topmost significant increment in plant physical parameters while reducing the Ni distribution in plant parts and oxidative injury. Based on these findings, it is proposed that PHB + AMF treatment can reduce Ni distribution and oxidative stress in mung bean plants and improve the biochemical compounds in grain.
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Increased anthropogenic nitrogen (N) deposition is driving N-limited ecosystems towards phosphorus (P) limitation. Plants have evolved strategies to respond to P limitation which affect N cycling in plant‐soil systems. A comprehensive understanding of how plants with efficient P‐acquisition or ‐use strategies influence carbon (C) and N cycling remains elusive. We highlight how P‐acquisition/-use strategies, particularly the release of carboxylates into the rhizosphere, accelerate soil organic matter (SOM) decomposition and soil N mineralisation by destabilising aggregates and organic‐mineral associations. We advocate studying the effects of P-acquisition/-use strategies on SOM formation, directly or through microbial turnover.
The presence of Ni above the permissible limit in agriculture soils poses negative effects on soil health, crop quality, and crop productivity. Surprisingly, the usage of various organic and inorganic amendments can reduce Ni mobility in the soil and its distribution in the crops. A pot experiment was conducted to elucidate the effects of olive pulp biochar (BR), calcite (CAL), and wheat straw (WS), as sole amendments and their mixtures of 50:50 ratio, added to Ni polluted soil on Ni mobility in the soil, Ni immobilization index (Ni − IMi), soil enzymatic activities, Ni distribution in parts of chili plant, Ni translocation factor and bioaccumulation factor in fruit, plant growth parameters and oxidative stress encountered by the plants. Outcomes of this pot experiment revealed that amendments raised soil pH, improved soil enzymatic activities, values of Ni − IMi, while significantly reduced bioavailable Ni fraction in the post-harvest soil. However, the highest activities of acid phosphatase, urease, catalase, and dehydrogenase by 50, 70, 239, and 111%, respectively, improvement in Ni − IMi up to 60% while 60% reduction in the bioavailable Ni fraction was observed in BR + CAL treatment, compared to control was noted. Among all amendments, the top most reduction in Ni concentrations in shoots, roots, fruit, Translocation Factor (TF), and Bioaccumulation Factor (BAF) values of fruit by 72%, 36%, 86%, 72%, and 86%, in BR + CAL treatment, compared to control. Moreover, the plants growing on BR + CAL amended Ni contaminated soil showed the topmost improvement in plant phonological parameters while encountered the least oxidative stress. Such findings refer to the prospective usage of BR + CAL at 50:50 ratio than BR, CAL, WS alone, and BR + WS as well as WS + CAL for reducing Ni mobility in the soil, improving Ni − IMi, soil enzymatic activities, plant phonological and oxidative stress while reducing Ni distribution in plant parts.
Novelty statement
In this experiment, it was hypothesized that amending Ni polluted soil with olive pulp biochar (BR), CAL, and WS as alone soil amendments and their combinations at 50:50 ratios can reduce Ni bioavailability in soil, Ni distribution in chili plant and oxidative stress encountered by the plants. Moreover, these amendments may improve, soil enzymatic activities, Ni immobilization index, plant phenological traits. Therefore, it was aimed to undertake useful scientific planning and research, to restore and rehabilitate the dwellings, biological resources and to minimize the sufferings of the peoples in nutrient-poor Ni contaminated soils, by improving soil health and chili productivity.
The potential of a stepwise fusion of proximally sensed portable X-ray fluorescence (pXRF) spectra and electromagnetic induction (EMI) with remote Sentinel-2 bands and a digital elevation model (DEM) was investigated for predicting soil physicochemical properties in pedons and across a heterogeneous 80-ha crop field in Wisconsin, USA. We found that pXRF spectra with partial least squares regression (PLSR) models can predict sand, total nitrogen (TN), organic carbon (OC), silt contents, and clay with validation R² of 0.81, 0.74, 0.73, 0.68, and 0.64 at the pedon scale but performed less well for soil pH (R² = 0.51). A combination of EMI, Sentinel-2, and DEM data showed promise in mapping sand, silt contents, and TN at two depths and Ap horizon thickness and soil depth across the field. A clustering analysis using combinations of mapped soil properties or proximal and remote sensing data suggested that data fusion improved the characterization of field-scale variability of soil properties. The cost-benefit analysis showed that the most accurate management zones (MZs) for topsoil can be generated only using estimated soil property maps while it was the most costly as compared to other data sources. For an intermediate-high (for topsoil) and high (subsoil) accuracy and a moderate economic budget, the combination of sensors (proximal + remote sensing + DEM) might be a better approach for effective MZs generation than collecting soil samples for laboratory analysis while the latter produced the most accurate maps for topsoil. It can be concluded that pXRF spectra can be useful for predicting key soil properties (e.g., sand, TN, OC, silt, clay) at different soil depths, and a combination of proximal and remote sensing provides an effective way to delineate soil MZs that are useful for decision-making.
An experiment was conducted at the University of Agriculture, Sub-campus Burewala Vehari during spring 2018 to investigate the most effective growth media for the growth of kinnow Mandarin seedlings along with highest potential of root, shoots, branches and leaves growth. The growing media is crucial for better plant growth and development. Seeds of Kinnow Mandarin were sown in twelve (12) different composite media (made from different proportions of peat moss, coco coir, compost, baggase, and soil) in CRD with three repeats. Data regarding germination of kinnow seeds and seedling quality parameters (Fresh weight, dry weight, seedling length, root shoot ratio, dry matter contents) were recorded during the experiment. The results proved that the peat moss was the most efficient among all the other growing media for producing the maximum number of leaves, shoot length, root length and seedling length while, compost was found to be a most effective medium for maximum seed germination. The composition in 1:1 of baggase + peat moss was most prominent to produce leaves with larger surface areas. Therefore, peat moss is an effective growth media among other growing media for Kinnow production.
Soil organic matter (SOM) performs an essential function in soil fertility, biomass and crop productivity, environmental sustainability, and climate change mitigation. We examined how land use change from native forest to either pasture [sown buffel (Cenchrus ciliaris cv. Biloela)] or cropping [primarily wheat (Triticum aestivum L.) and sorghum (Sorghum bicolor L.)] affected total soil organic C (SOC) stocks as well as stocks of three SOC fractions, particulate organic C, humus organic C and resistant organic C. Furthermore, for the cropping system, we also examined whether the use of a ley pasture phase could reverse the loss of SOC. It was found that land use change from native forest to pasture decreased SOC stocks by 12.2 % and soil total N (STN) stocks by 24.6 % during the land development to pasture establishment (≤ 1.75 y), although there were no significant (P > 0.05) changes thereafter up to 33 y and final values were generally similar to initial values. Furthermore, stocks of the three SOC fractions did not change with time in this pasture system. In contrast to these modest changes following conversion to pasture, for land use change to cropping, SOC decreased by 48 % at 0−0.1 m and 38 % (from 54 to 33 Mg ha⁻¹) at 0−0.3 m, due mainly to insufficient C inputs to maintain SOM at steady state. Moreover, stocks of all three SOC fractions decreased with time, including the resistant organic C fraction, indicating that this fraction was not recalcitrant under cropping. The biomass C inputs by crops, mainly as root biomass, were not sufficient to reverse or slow down the rate of decrease of SOC in this soil. However, the introduction of pasture during the last 4 y indicated that the decreases in the stocks of SOC could be arrested by a ley pasture phase.
Microbial nitrogen (N) immobilization in soil can be enhanced by increasing carbon (C) bioavailability, yet the response of microbial N immobilization to the addition of organic matter is uncertain. In the present study, we investigated the effect of organic matter quality on microbial N immobilization. The response ratio (ln R), i.e., the ratio of microbial N immobilization in organic-C amended soil to that in control treatments, was calculated using data from 51 published studies. Overall, the addition of organic-C increased significantly microbial N immobilization by 105% relative to unamended soil. The type of organic-C affected the response of microbial N immobilization to organic-C addition. Glucose (classified as a labile compound) was more effective in stimulating microbial N immobilization than cellobiose and cellulose (classified as intermediately decomposable compounds). Tannin and oxalic acid (classified as recalcitrant compounds) did not significantly affect microbial N immobilization. The C/N ratio of organic materials did not affect the response of microbial N immobilization in the short-term (≤280 d); differences in the effect size (ln R+) were not significant among different C/N ratio groups. The effect of the form of inorganic-N (ammonium [NH4⁺] or nitrate [NO3⁻]) on the response of microbial N immobilization to organic-C addition was not significant, with a mean ln R+ of 0.838 (confidence interval [CI]: 0.590–1.099) for NH4⁺ and 1.642 (CI: 0.951–2.452) for NO3⁻. Moreover, the ln R of microbial NH4⁺ immobilization showed a significant positive relationship (P < 0.01) with that of microbial NO3⁻ immobilization. The ln R+ for the experimental period decreased in the order of <30 d, 60–120 d, ≥120 d, and 30–60 d. The chemical quality of organic-C defined by three C pools (i.e., labile, intermediate, and recalcitrant) rather than the C/N ratio is a critical factor regulating the response of microbial N immobilization to organic-C addition.
In the past two decades, more and more attentions have been paid to soil-derived greenhouse gases (GHGs) including carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) because there are signs that they have rising negative impacts on the sustainability of the earth surface system. Farmlands, particularly paddy soils, have been regarded as the most important emitter of GHGs (nearly 17%) due to a large influx of fertilization and the abundance in animals, plants and microorganisms. Geobacter, as an electroactive microorganism widely occurred in soil, has been well studied on electron transport mechanisms and the direct interspecies electron transfer. These studies on Geobacter illustrate that it has the ability to be involved in the pathways of soil GHG emissions through redox reactions under anaerobic conditions. In this review, production mechanisms of soil-derived GHGs and the amount of these GHGs produced had been first summarized. The cycling process of CH4 and N2O was described from the view of microorganisms and discussed the co-culture relationships between Geobacter and other microorganisms. Furthermore, the role of Geobacter in the production of soil-derived GHGs is defined by biogeochemical cycling. The complete view on the effect of Geobacter on the emission of soil-derived GHGs has been shed light on, and appeals further investigation.
Burning is the most common practice for rice straw disposal. Due to associated negative environmental and climatic effects, development of viable alternatives, preferably based on the natural functions of soil biota are needed. In the conditions of non-tropical rice-growing systems, where periods of flooding are very short, such an approach seems to be particularly promising. We carried out a mesocosm experiment to assess the possibility of using the model earthworm species Eisenia fetida (Savigny 1826) to decompose rice residues and control associated CO2 and CH4 emissions from paddy soils at different soil moisture levels. We filled 96 mesocosms with three types (32 each) of rice paddy soils collected in key regions of rice production in Russia: Krasnodarsky Krai (the Sea of Azov lowland, Calcic Phaeozems), the Republic of Kalmykia (the Volga river valley, Haplic Phaeozems) and Primorsky Krai (Khanka lake lowland, the Russian Far East, Umbric, Histic Fluvisols). We added 2.5 g dry rice straw in each mesocosm. The experiment had a full factorial design including three categorical factors: soil type (n = 3), soil moisture level (12, 25, 50 and 75% soil water holding capacity) and E. fetida earthworm addition (none and 4 individuals per mesocosm). The integral emission of CO2 across the observation period of 10 days significantly differed between moisture classes with the highest values at 25% (p < 0.05). Earthworm amendment had no effect on CO2 flux in all moisture treatments besides 75%, where it was positive. The detectable CH4 emissions were observed only at soil moisture levels of 50 and 75%. Earthworms strongly positively affected this parameter at 75% soil moisture level (p < 0.05). Carbon content after the experiment was significantly higher in the earthworm-inoculated microcosms only at the 25% moisture level. We conclude that E. fetida may positively contribute to carbon sequestration during rice straw degradation in the studied rice paddy soil types only under certain levels of substrate moisture (25% in our case). This highlights the importance of soil encountering abiotic conditions when developing climate-friendly systems for rice straw decomposition and carbon immobilization. It also suggests the potential of using E. fetida as a viable agent of biological rice straw recycling during the drained stages in non-tropical rice paddies or in artificial confinements.
Accurate digital soil maps of soil organic matter (SOM) are needed to evaluate soil fertility, to estimate stocks, and for ecological and environment modeling. We used 5982 soil profiles collected during the second national soil survey of China, along with 19 environment predictors, to derive a spatial model of SOM concentration in the topsoil (0-20 cm layer). The environmental predictors relate to the soil forming factors, climate, vegetation, relief and parent material. We developed the model using the Cubist machine-learning algorithm combined with a non-parametric bootstrap to derive estimates of model uncertainty. We optimized the Cubist model using a 10-fold cross-validation and the best model used 17 rules. The correlation coefficient between the observed and predicted values was 0.65, and the root mean squared error was 0.28 g/kg. We then applied the model over China and mapped the SOM distribution at a resolution of 90 x 90 m. Our predictions show that there is more SOM in the eastern Tibetan Plateau, northern Heilongjiang province, northeast Mongolia, and a small area of Tianshan Mountain in Xinjiang. There is less SOM in the Loess Plateau and most of the desert areas in northwest China. The average topsoil SOM content is 24.82 g/kg. The study provides a map that can be used for decision-making and contribute towards a baseline assessment for inventory and monitoring. The map could also aid the design of future soil surveys and help with the development of a SOM monitoring network in China.
Lead-contaminated soils are becoming an ecological risk to the environment because of producing low-quality food which is directly causing critical health issues in humans and animals. We hypothesized that incorporation of dicalcium phosphate (DCP), eggshell powder (ESP) and biochar (BH) at diverse rates into a Pb-affected soil can proficiently immobilize Pb and decline its bioavailability to spinach (Spinacia oleracea L.). A soil was artificially spiked with Pb concentration (at 600 mg kg-1) and further amended with DCP, ESP, and BH (as sole treatments at 2% and in concoctions at 1% each) for immobilization of Pb in the soil. The interlinked effects of applied treatments on Pb concentrations in shoots and roots, biomass, antioxidants, biochemistry, and nutrition of spinach were also investigated. Results depicted that the highest reduction in DTPA-extractable Pb and the concentrations of Pb in shoots and roots was achieved in DCP1%+BH1% treatment that was up to 58%, 66%, and 53%, respectively over control. Likewise, the DCP1%+BH1% treatment also showed the maximum shoot and root dry weight (DW), chlorophyll-a (Chl-a) and chlorophyll-b (Chl-b) contents and relative water content (RWC) in spinach up to 92%, 121%, 60%, 65%, and 30%, respectively, compared to control. Likewise, DCP1%+BH1% treatment noticeably improved antioxidant enzymes, biochemistry, and nutrition in the leaves. Moreover, the DCP1%+BH1% treatment depicted mostly enhanced activities of dehydrogenase, catalase, acid phosphatase, alkaline phosphatase, phosphomonoesterase, urease, protease and B-glucosidase in the post-harvested soil up to 118%, 345%, 55%, 92%, 288%, 107%, 53% and 252%, respectively over control.