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Principal component analysis of soil, plant community and root characteristics along the successional gradient. Principal component analysis joint plot ordination of the successional stages studied: Herbs ( Δ ); Shrub (+); STree (o); TTree(ø): plant communities, located in gully beds, dominated by herbs, shrubs, small tress (<2 m) and tall trees (>2 m) respectively. Forest ( • ): plant communities located on forested slopes
Source publication
Background and aims
Our objectives were to evaluate changes in soil aggregate stability along a successional gradient, located in severely eroded Mediterranean gully bed ecosystems and to identify predictors of soil aggregate stability variations among several soil, root traits and plant community characteristics.
Methods
We selected 75 plots in gu...
Contexts in source publication
Context 1
... component analysis (PCA) was used to investigate the relationships between soil, root and plant community characteristics across successional stages ( Fig. 3). The first and second principal components explained respectively 33 and 15 % of the total variance. Axis 1 was positively correlated with soil aggregate stability, SOC concentration, percentage of fine sand, root mass density, species richness and diversity as well as root diameter and diversity. In contrast, axis 1 was negatively related to silt percentage and the specific root length. The projection of plant communities on PCA clearly discriminated early successional communities, namely Herbs and Shrub ones, from communities dominated by trees (Fig. 3). Late successional communities, namely TTree and Forest, are almost exclusively found on the right hand side and were characterized by high soil aggregate stability, SOC and fine sand percentage, coupled with a high species richness and diversity, together with high root diameter and root diameter diversity. The STree plots were equally distributed along the first axis (Fig. 3). Two Forest communities were at the extreme upper right part of the PCA, showing particular high species richness and root diameter diversity. At the opposite, early successional communities, namely Herbs and Shrub occupied the left part of the first axis and were characterized by high silt percentage, high specific root length and low soil aggregate stability. Axis 2 of the PCA was positively associated with clay percentage and negatively with CaCO 3 concentration, root length density and percentage of fine roots. Axis 2 poorly discriminated the various plant community types, except for the two forest communities on the upper right part of the PCA, with particularly high plant richness (Fig. ...
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... component analysis (PCA) was used to investigate the relationships between soil, root and plant community characteristics across successional stages ( Fig. 3). The first and second principal components explained respectively 33 and 15 % of the total variance. Axis 1 was positively correlated with soil aggregate stability, SOC concentration, percentage of fine sand, root mass density, species richness and diversity as well as root diameter and diversity. In contrast, axis 1 was negatively related to silt percentage and the specific root length. The projection of plant communities on PCA clearly discriminated early successional communities, namely Herbs and Shrub ones, from communities dominated by trees (Fig. 3). Late successional communities, namely TTree and Forest, are almost exclusively found on the right hand side and were characterized by high soil aggregate stability, SOC and fine sand percentage, coupled with a high species richness and diversity, together with high root diameter and root diameter diversity. The STree plots were equally distributed along the first axis (Fig. 3). Two Forest communities were at the extreme upper right part of the PCA, showing particular high species richness and root diameter diversity. At the opposite, early successional communities, namely Herbs and Shrub occupied the left part of the first axis and were characterized by high silt percentage, high specific root length and low soil aggregate stability. Axis 2 of the PCA was positively associated with clay percentage and negatively with CaCO 3 concentration, root length density and percentage of fine roots. Axis 2 poorly discriminated the various plant community types, except for the two forest communities on the upper right part of the PCA, with particularly high plant richness (Fig. ...
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... component analysis (PCA) was used to investigate the relationships between soil, root and plant community characteristics across successional stages ( Fig. 3). The first and second principal components explained respectively 33 and 15 % of the total variance. Axis 1 was positively correlated with soil aggregate stability, SOC concentration, percentage of fine sand, root mass density, species richness and diversity as well as root diameter and diversity. In contrast, axis 1 was negatively related to silt percentage and the specific root length. The projection of plant communities on PCA clearly discriminated early successional communities, namely Herbs and Shrub ones, from communities dominated by trees (Fig. 3). Late successional communities, namely TTree and Forest, are almost exclusively found on the right hand side and were characterized by high soil aggregate stability, SOC and fine sand percentage, coupled with a high species richness and diversity, together with high root diameter and root diameter diversity. The STree plots were equally distributed along the first axis (Fig. 3). Two Forest communities were at the extreme upper right part of the PCA, showing particular high species richness and root diameter diversity. At the opposite, early successional communities, namely Herbs and Shrub occupied the left part of the first axis and were characterized by high silt percentage, high specific root length and low soil aggregate stability. Axis 2 of the PCA was positively associated with clay percentage and negatively with CaCO 3 concentration, root length density and percentage of fine roots. Axis 2 poorly discriminated the various plant community types, except for the two forest communities on the upper right part of the PCA, with particularly high plant richness (Fig. ...
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... component analysis (PCA) was used to investigate the relationships between soil, root and plant community characteristics across successional stages ( Fig. 3). The first and second principal components explained respectively 33 and 15 % of the total variance. Axis 1 was positively correlated with soil aggregate stability, SOC concentration, percentage of fine sand, root mass density, species richness and diversity as well as root diameter and diversity. In contrast, axis 1 was negatively related to silt percentage and the specific root length. The projection of plant communities on PCA clearly discriminated early successional communities, namely Herbs and Shrub ones, from communities dominated by trees (Fig. 3). Late successional communities, namely TTree and Forest, are almost exclusively found on the right hand side and were characterized by high soil aggregate stability, SOC and fine sand percentage, coupled with a high species richness and diversity, together with high root diameter and root diameter diversity. The STree plots were equally distributed along the first axis (Fig. 3). Two Forest communities were at the extreme upper right part of the PCA, showing particular high species richness and root diameter diversity. At the opposite, early successional communities, namely Herbs and Shrub occupied the left part of the first axis and were characterized by high silt percentage, high specific root length and low soil aggregate stability. Axis 2 of the PCA was positively associated with clay percentage and negatively with CaCO 3 concentration, root length density and percentage of fine roots. Axis 2 poorly discriminated the various plant community types, except for the two forest communities on the upper right part of the PCA, with particularly high plant richness (Fig. ...
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... related to root thinness, such as the specific root length and percentage of very fine roots (<0.2 mm) were negatively linked to soil aggregate stability ( Fig. 3, Table 2). In the present case, the SRL and proportion of very fine roots decreased with the succession stage, as already observed by Zangaro et al. (2008). This is probably associated to the concomitant decrease in the proportion of grass and herbs species, which are dominant in early successional stages (Herbs communities) showing lowest SOC concentration, together with the lowest soil aggregate stability. In addition, Miller and Jastrow (1990) showed that the effect of very fine roots on soil aggregate stability was mainly indirect through associations with mycorrhizal fungi. The percentage of fine roots was positively, even though weakly, related to the stability of soil aggregates throughout the entire successional gradient (Fig. 3, Table 2) and ANCOVA analyses showed that the effect of the percentage of fine roots on soil aggregate stability was significant in plant communities showing low SOC concentration (<12 g.kg − 1 ), corresponding to early successional stages (Fig. 4). ANCOVA analyses thus reveal that the weak relation between the percentage of fine roots and soil aggregate stability throughout the entire gradient of succession does not question the role of fine roots in stabilizing aggregates but restricts its importance to poorly-organic soils. The positive impact of fine roots on the formation of stable aggregates has already been shown several times (Miller and Jastrow 1990; Gyssels et al. 2005), through the production of exudates, acting as binding agents, and the formation of a mesh entangling soil particles (Degens et al. 1994; Hütsch et al. 2002; Six et al. 2004). In addition, the percentage of fine roots was here positively correlated to the root mass density (Fig. 3; Appendix S3), indicating that the plots with a high proportion of fine roots have higher root biomass, which is known to positively impact soil aggregate stability (Miller and Jastrow 1990; Pérès et al. 2013). Indirect mechanisms can also explain the effect of fine roots which fuel the soil with organic compounds via the production of exudate or root decomposition, stimulating soil microbial communities stabilizing soil aggregates (Jastrow et al. 1998; Eisenhauer et al. 2010). Fine roots are also the docking stations for mycorrhizal fungi that themselves are able to stabilize soil aggregates directly by mechanical and chemical pathways as well as indirectly by promoting root growth and root branching (Rillig and Mummey 2006). The stronger effect of the percentage of fine roots on soil aggregate stability in early successional stages confirms the observations of Pohl et al. (2009), who suggested that vegetation characteristics are of particular importance to form stable aggregates in disturbed sites, generally poor in organic matter. It also supports the results of Le Bissonnais et al. (2007), who found that in poor organic soils (below around 12.5 g.kg − 1 ), SOC concentration is not the main driver of soil aggregate stability. Finally, mean root diameter and root diameter diversity were positively related to soil aggregate stability (Fig. 3, Table 2). In the present study, plant communities showing high mean root diameter and root diameter diversity were dominated by tree species, especially tall ones (TTree and Forest; Fig. 3), generally showing coarse and woody roots. These communities also showed highest SOC concentrations (Fig. 3) which made it difficult to identify the specific role of root diameter and diversity on soil aggregate stability. Nev- ertheless, root diversity tends to favor root exploration (Körner and Spehn 2002), potentially favoring soil aggregate stability. A high diversity in root diameter, related to diverse tissue chemistry and decomposition rate, can also offer a higher variety of niches for root-fed microorganisms which stabilize soil aggregates by their activity (Abiven et al. 2007). For example, fresh organic residue, most probably released by the decomposition or exudation of thin and lower order roots, stimulates the production of polysaccharides by bacteria and fungi acting as B glue ^ and increasing inter-particle cohesion (Chenu and Guerif 1991). Whereas more recalcitrant material, most probably released by the decomposition of coarse higher order roots, favor mainly fungal growth, with hyphae entangling soil particles and hydrophobic exuded substances decreasing aggregates wettability (Capriel et al. 1990). Several interlocking and complementary mechanisms can thus explain the stabilizing role of root diameter diversity on soil aggregates, suggested by the in situ correlation found here. The present study shows that soil aggregate stability increases significantly along the Mediterranean successional gradient in severely eroded gully bed ecosystems, showing the efficiency of plant dynamics to stabilize the soils of these ecosystems. Along the gradient, SOC accumulation, related to increased carbon input due to vegetation dynamics, was the main driver of soil aggregates stabilization. Our results also suggested that the diversity of plants and roots are likely to play an important role in the stabilization of soil aggregates along the successional gradient, through indirect diversity-driven SOC accumulation. In early successional stages characterized by low SOC concentration, we showed that fine sand, silt content and the percentage of fine roots were important co- drivers of soil aggregate ...
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... related to root thinness, such as the specific root length and percentage of very fine roots (<0.2 mm) were negatively linked to soil aggregate stability ( Fig. 3, Table 2). In the present case, the SRL and proportion of very fine roots decreased with the succession stage, as already observed by Zangaro et al. (2008). This is probably associated to the concomitant decrease in the proportion of grass and herbs species, which are dominant in early successional stages (Herbs communities) showing lowest SOC concentration, together with the lowest soil aggregate stability. In addition, Miller and Jastrow (1990) showed that the effect of very fine roots on soil aggregate stability was mainly indirect through associations with mycorrhizal fungi. The percentage of fine roots was positively, even though weakly, related to the stability of soil aggregates throughout the entire successional gradient (Fig. 3, Table 2) and ANCOVA analyses showed that the effect of the percentage of fine roots on soil aggregate stability was significant in plant communities showing low SOC concentration (<12 g.kg − 1 ), corresponding to early successional stages (Fig. 4). ANCOVA analyses thus reveal that the weak relation between the percentage of fine roots and soil aggregate stability throughout the entire gradient of succession does not question the role of fine roots in stabilizing aggregates but restricts its importance to poorly-organic soils. The positive impact of fine roots on the formation of stable aggregates has already been shown several times (Miller and Jastrow 1990; Gyssels et al. 2005), through the production of exudates, acting as binding agents, and the formation of a mesh entangling soil particles (Degens et al. 1994; Hütsch et al. 2002; Six et al. 2004). In addition, the percentage of fine roots was here positively correlated to the root mass density (Fig. 3; Appendix S3), indicating that the plots with a high proportion of fine roots have higher root biomass, which is known to positively impact soil aggregate stability (Miller and Jastrow 1990; Pérès et al. 2013). Indirect mechanisms can also explain the effect of fine roots which fuel the soil with organic compounds via the production of exudate or root decomposition, stimulating soil microbial communities stabilizing soil aggregates (Jastrow et al. 1998; Eisenhauer et al. 2010). Fine roots are also the docking stations for mycorrhizal fungi that themselves are able to stabilize soil aggregates directly by mechanical and chemical pathways as well as indirectly by promoting root growth and root branching (Rillig and Mummey 2006). The stronger effect of the percentage of fine roots on soil aggregate stability in early successional stages confirms the observations of Pohl et al. (2009), who suggested that vegetation characteristics are of particular importance to form stable aggregates in disturbed sites, generally poor in organic matter. It also supports the results of Le Bissonnais et al. (2007), who found that in poor organic soils (below around 12.5 g.kg − 1 ), SOC concentration is not the main driver of soil aggregate stability. Finally, mean root diameter and root diameter diversity were positively related to soil aggregate stability (Fig. 3, Table 2). In the present study, plant communities showing high mean root diameter and root diameter diversity were dominated by tree species, especially tall ones (TTree and Forest; Fig. 3), generally showing coarse and woody roots. These communities also showed highest SOC concentrations (Fig. 3) which made it difficult to identify the specific role of root diameter and diversity on soil aggregate stability. Nev- ertheless, root diversity tends to favor root exploration (Körner and Spehn 2002), potentially favoring soil aggregate stability. A high diversity in root diameter, related to diverse tissue chemistry and decomposition rate, can also offer a higher variety of niches for root-fed microorganisms which stabilize soil aggregates by their activity (Abiven et al. 2007). For example, fresh organic residue, most probably released by the decomposition or exudation of thin and lower order roots, stimulates the production of polysaccharides by bacteria and fungi acting as B glue ^ and increasing inter-particle cohesion (Chenu and Guerif 1991). Whereas more recalcitrant material, most probably released by the decomposition of coarse higher order roots, favor mainly fungal growth, with hyphae entangling soil particles and hydrophobic exuded substances decreasing aggregates wettability (Capriel et al. 1990). Several interlocking and complementary mechanisms can thus explain the stabilizing role of root diameter diversity on soil aggregates, suggested by the in situ correlation found here. The present study shows that soil aggregate stability increases significantly along the Mediterranean successional gradient in severely eroded gully bed ecosystems, showing the efficiency of plant dynamics to stabilize the soils of these ecosystems. Along the gradient, SOC accumulation, related to increased carbon input due to vegetation dynamics, was the main driver of soil aggregates stabilization. Our results also suggested that the diversity of plants and roots are likely to play an important role in the stabilization of soil aggregates along the successional gradient, through indirect diversity-driven SOC accumulation. In early successional stages characterized by low SOC concentration, we showed that fine sand, silt content and the percentage of fine roots were important co- drivers of soil aggregate ...
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... related to root thinness, such as the specific root length and percentage of very fine roots (<0.2 mm) were negatively linked to soil aggregate stability ( Fig. 3, Table 2). In the present case, the SRL and proportion of very fine roots decreased with the succession stage, as already observed by Zangaro et al. (2008). This is probably associated to the concomitant decrease in the proportion of grass and herbs species, which are dominant in early successional stages (Herbs communities) showing lowest SOC concentration, together with the lowest soil aggregate stability. In addition, Miller and Jastrow (1990) showed that the effect of very fine roots on soil aggregate stability was mainly indirect through associations with mycorrhizal fungi. The percentage of fine roots was positively, even though weakly, related to the stability of soil aggregates throughout the entire successional gradient (Fig. 3, Table 2) and ANCOVA analyses showed that the effect of the percentage of fine roots on soil aggregate stability was significant in plant communities showing low SOC concentration (<12 g.kg − 1 ), corresponding to early successional stages (Fig. 4). ANCOVA analyses thus reveal that the weak relation between the percentage of fine roots and soil aggregate stability throughout the entire gradient of succession does not question the role of fine roots in stabilizing aggregates but restricts its importance to poorly-organic soils. The positive impact of fine roots on the formation of stable aggregates has already been shown several times (Miller and Jastrow 1990; Gyssels et al. 2005), through the production of exudates, acting as binding agents, and the formation of a mesh entangling soil particles (Degens et al. 1994; Hütsch et al. 2002; Six et al. 2004). In addition, the percentage of fine roots was here positively correlated to the root mass density (Fig. 3; Appendix S3), indicating that the plots with a high proportion of fine roots have higher root biomass, which is known to positively impact soil aggregate stability (Miller and Jastrow 1990; Pérès et al. 2013). Indirect mechanisms can also explain the effect of fine roots which fuel the soil with organic compounds via the production of exudate or root decomposition, stimulating soil microbial communities stabilizing soil aggregates (Jastrow et al. 1998; Eisenhauer et al. 2010). Fine roots are also the docking stations for mycorrhizal fungi that themselves are able to stabilize soil aggregates directly by mechanical and chemical pathways as well as indirectly by promoting root growth and root branching (Rillig and Mummey 2006). The stronger effect of the percentage of fine roots on soil aggregate stability in early successional stages confirms the observations of Pohl et al. (2009), who suggested that vegetation characteristics are of particular importance to form stable aggregates in disturbed sites, generally poor in organic matter. It also supports the results of Le Bissonnais et al. (2007), who found that in poor organic soils (below around 12.5 g.kg − 1 ), SOC concentration is not the main driver of soil aggregate stability. Finally, mean root diameter and root diameter diversity were positively related to soil aggregate stability (Fig. 3, Table 2). In the present study, plant communities showing high mean root diameter and root diameter diversity were dominated by tree species, especially tall ones (TTree and Forest; Fig. 3), generally showing coarse and woody roots. These communities also showed highest SOC concentrations (Fig. 3) which made it difficult to identify the specific role of root diameter and diversity on soil aggregate stability. Nev- ertheless, root diversity tends to favor root exploration (Körner and Spehn 2002), potentially favoring soil aggregate stability. A high diversity in root diameter, related to diverse tissue chemistry and decomposition rate, can also offer a higher variety of niches for root-fed microorganisms which stabilize soil aggregates by their activity (Abiven et al. 2007). For example, fresh organic residue, most probably released by the decomposition or exudation of thin and lower order roots, stimulates the production of polysaccharides by bacteria and fungi acting as B glue ^ and increasing inter-particle cohesion (Chenu and Guerif 1991). Whereas more recalcitrant material, most probably released by the decomposition of coarse higher order roots, favor mainly fungal growth, with hyphae entangling soil particles and hydrophobic exuded substances decreasing aggregates wettability (Capriel et al. 1990). Several interlocking and complementary mechanisms can thus explain the stabilizing role of root diameter diversity on soil aggregates, suggested by the in situ correlation found here. The present study shows that soil aggregate stability increases significantly along the Mediterranean successional gradient in severely eroded gully bed ecosystems, showing the efficiency of plant dynamics to stabilize the soils of these ecosystems. Along the gradient, SOC accumulation, related to increased carbon input due to vegetation dynamics, was the main driver of soil aggregates stabilization. Our results also suggested that the diversity of plants and roots are likely to play an important role in the stabilization of soil aggregates along the successional gradient, through indirect diversity-driven SOC accumulation. In early successional stages characterized by low SOC concentration, we showed that fine sand, silt content and the percentage of fine roots were important co- drivers of soil aggregate ...
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... related to root thinness, such as the specific root length and percentage of very fine roots (<0.2 mm) were negatively linked to soil aggregate stability ( Fig. 3, Table 2). In the present case, the SRL and proportion of very fine roots decreased with the succession stage, as already observed by Zangaro et al. (2008). This is probably associated to the concomitant decrease in the proportion of grass and herbs species, which are dominant in early successional stages (Herbs communities) showing lowest SOC concentration, together with the lowest soil aggregate stability. In addition, Miller and Jastrow (1990) showed that the effect of very fine roots on soil aggregate stability was mainly indirect through associations with mycorrhizal fungi. The percentage of fine roots was positively, even though weakly, related to the stability of soil aggregates throughout the entire successional gradient (Fig. 3, Table 2) and ANCOVA analyses showed that the effect of the percentage of fine roots on soil aggregate stability was significant in plant communities showing low SOC concentration (<12 g.kg − 1 ), corresponding to early successional stages (Fig. 4). ANCOVA analyses thus reveal that the weak relation between the percentage of fine roots and soil aggregate stability throughout the entire gradient of succession does not question the role of fine roots in stabilizing aggregates but restricts its importance to poorly-organic soils. The positive impact of fine roots on the formation of stable aggregates has already been shown several times (Miller and Jastrow 1990; Gyssels et al. 2005), through the production of exudates, acting as binding agents, and the formation of a mesh entangling soil particles (Degens et al. 1994; Hütsch et al. 2002; Six et al. 2004). In addition, the percentage of fine roots was here positively correlated to the root mass density (Fig. 3; Appendix S3), indicating that the plots with a high proportion of fine roots have higher root biomass, which is known to positively impact soil aggregate stability (Miller and Jastrow 1990; Pérès et al. 2013). Indirect mechanisms can also explain the effect of fine roots which fuel the soil with organic compounds via the production of exudate or root decomposition, stimulating soil microbial communities stabilizing soil aggregates (Jastrow et al. 1998; Eisenhauer et al. 2010). Fine roots are also the docking stations for mycorrhizal fungi that themselves are able to stabilize soil aggregates directly by mechanical and chemical pathways as well as indirectly by promoting root growth and root branching (Rillig and Mummey 2006). The stronger effect of the percentage of fine roots on soil aggregate stability in early successional stages confirms the observations of Pohl et al. (2009), who suggested that vegetation characteristics are of particular importance to form stable aggregates in disturbed sites, generally poor in organic matter. It also supports the results of Le Bissonnais et al. (2007), who found that in poor organic soils (below around 12.5 g.kg − 1 ), SOC concentration is not the main driver of soil aggregate stability. Finally, mean root diameter and root diameter diversity were positively related to soil aggregate stability (Fig. 3, Table 2). In the present study, plant communities showing high mean root diameter and root diameter diversity were dominated by tree species, especially tall ones (TTree and Forest; Fig. 3), generally showing coarse and woody roots. These communities also showed highest SOC concentrations (Fig. 3) which made it difficult to identify the specific role of root diameter and diversity on soil aggregate stability. Nev- ertheless, root diversity tends to favor root exploration (Körner and Spehn 2002), potentially favoring soil aggregate stability. A high diversity in root diameter, related to diverse tissue chemistry and decomposition rate, can also offer a higher variety of niches for root-fed microorganisms which stabilize soil aggregates by their activity (Abiven et al. 2007). For example, fresh organic residue, most probably released by the decomposition or exudation of thin and lower order roots, stimulates the production of polysaccharides by bacteria and fungi acting as B glue ^ and increasing inter-particle cohesion (Chenu and Guerif 1991). Whereas more recalcitrant material, most probably released by the decomposition of coarse higher order roots, favor mainly fungal growth, with hyphae entangling soil particles and hydrophobic exuded substances decreasing aggregates wettability (Capriel et al. 1990). Several interlocking and complementary mechanisms can thus explain the stabilizing role of root diameter diversity on soil aggregates, suggested by the in situ correlation found here. The present study shows that soil aggregate stability increases significantly along the Mediterranean successional gradient in severely eroded gully bed ecosystems, showing the efficiency of plant dynamics to stabilize the soils of these ecosystems. Along the gradient, SOC accumulation, related to increased carbon input due to vegetation dynamics, was the main driver of soil aggregates stabilization. Our results also suggested that the diversity of plants and roots are likely to play an important role in the stabilization of soil aggregates along the successional gradient, through indirect diversity-driven SOC accumulation. In early successional stages characterized by low SOC concentration, we showed that fine sand, silt content and the percentage of fine roots were important co- drivers of soil aggregate ...
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... related to root thinness, such as the specific root length and percentage of very fine roots (<0.2 mm) were negatively linked to soil aggregate stability ( Fig. 3, Table 2). In the present case, the SRL and proportion of very fine roots decreased with the succession stage, as already observed by Zangaro et al. (2008). This is probably associated to the concomitant decrease in the proportion of grass and herbs species, which are dominant in early successional stages (Herbs communities) showing lowest SOC concentration, together with the lowest soil aggregate stability. In addition, Miller and Jastrow (1990) showed that the effect of very fine roots on soil aggregate stability was mainly indirect through associations with mycorrhizal fungi. The percentage of fine roots was positively, even though weakly, related to the stability of soil aggregates throughout the entire successional gradient (Fig. 3, Table 2) and ANCOVA analyses showed that the effect of the percentage of fine roots on soil aggregate stability was significant in plant communities showing low SOC concentration (<12 g.kg − 1 ), corresponding to early successional stages (Fig. 4). ANCOVA analyses thus reveal that the weak relation between the percentage of fine roots and soil aggregate stability throughout the entire gradient of succession does not question the role of fine roots in stabilizing aggregates but restricts its importance to poorly-organic soils. The positive impact of fine roots on the formation of stable aggregates has already been shown several times (Miller and Jastrow 1990; Gyssels et al. 2005), through the production of exudates, acting as binding agents, and the formation of a mesh entangling soil particles (Degens et al. 1994; Hütsch et al. 2002; Six et al. 2004). In addition, the percentage of fine roots was here positively correlated to the root mass density (Fig. 3; Appendix S3), indicating that the plots with a high proportion of fine roots have higher root biomass, which is known to positively impact soil aggregate stability (Miller and Jastrow 1990; Pérès et al. 2013). Indirect mechanisms can also explain the effect of fine roots which fuel the soil with organic compounds via the production of exudate or root decomposition, stimulating soil microbial communities stabilizing soil aggregates (Jastrow et al. 1998; Eisenhauer et al. 2010). Fine roots are also the docking stations for mycorrhizal fungi that themselves are able to stabilize soil aggregates directly by mechanical and chemical pathways as well as indirectly by promoting root growth and root branching (Rillig and Mummey 2006). The stronger effect of the percentage of fine roots on soil aggregate stability in early successional stages confirms the observations of Pohl et al. (2009), who suggested that vegetation characteristics are of particular importance to form stable aggregates in disturbed sites, generally poor in organic matter. It also supports the results of Le Bissonnais et al. (2007), who found that in poor organic soils (below around 12.5 g.kg − 1 ), SOC concentration is not the main driver of soil aggregate stability. Finally, mean root diameter and root diameter diversity were positively related to soil aggregate stability (Fig. 3, Table 2). In the present study, plant communities showing high mean root diameter and root diameter diversity were dominated by tree species, especially tall ones (TTree and Forest; Fig. 3), generally showing coarse and woody roots. These communities also showed highest SOC concentrations (Fig. 3) which made it difficult to identify the specific role of root diameter and diversity on soil aggregate stability. Nev- ertheless, root diversity tends to favor root exploration (Körner and Spehn 2002), potentially favoring soil aggregate stability. A high diversity in root diameter, related to diverse tissue chemistry and decomposition rate, can also offer a higher variety of niches for root-fed microorganisms which stabilize soil aggregates by their activity (Abiven et al. 2007). For example, fresh organic residue, most probably released by the decomposition or exudation of thin and lower order roots, stimulates the production of polysaccharides by bacteria and fungi acting as B glue ^ and increasing inter-particle cohesion (Chenu and Guerif 1991). Whereas more recalcitrant material, most probably released by the decomposition of coarse higher order roots, favor mainly fungal growth, with hyphae entangling soil particles and hydrophobic exuded substances decreasing aggregates wettability (Capriel et al. 1990). Several interlocking and complementary mechanisms can thus explain the stabilizing role of root diameter diversity on soil aggregates, suggested by the in situ correlation found here. The present study shows that soil aggregate stability increases significantly along the Mediterranean successional gradient in severely eroded gully bed ecosystems, showing the efficiency of plant dynamics to stabilize the soils of these ecosystems. Along the gradient, SOC accumulation, related to increased carbon input due to vegetation dynamics, was the main driver of soil aggregates stabilization. Our results also suggested that the diversity of plants and roots are likely to play an important role in the stabilization of soil aggregates along the successional gradient, through indirect diversity-driven SOC accumulation. In early successional stages characterized by low SOC concentration, we showed that fine sand, silt content and the percentage of fine roots were important co- drivers of soil aggregate ...
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... related to root thinness, such as the specific root length and percentage of very fine roots (<0.2 mm) were negatively linked to soil aggregate stability ( Fig. 3, Table 2). In the present case, the SRL and proportion of very fine roots decreased with the succession stage, as already observed by Zangaro et al. (2008). This is probably associated to the concomitant decrease in the proportion of grass and herbs species, which are dominant in early successional stages (Herbs communities) showing lowest SOC concentration, together with the lowest soil aggregate stability. In addition, Miller and Jastrow (1990) showed that the effect of very fine roots on soil aggregate stability was mainly indirect through associations with mycorrhizal fungi. The percentage of fine roots was positively, even though weakly, related to the stability of soil aggregates throughout the entire successional gradient (Fig. 3, Table 2) and ANCOVA analyses showed that the effect of the percentage of fine roots on soil aggregate stability was significant in plant communities showing low SOC concentration (<12 g.kg − 1 ), corresponding to early successional stages (Fig. 4). ANCOVA analyses thus reveal that the weak relation between the percentage of fine roots and soil aggregate stability throughout the entire gradient of succession does not question the role of fine roots in stabilizing aggregates but restricts its importance to poorly-organic soils. The positive impact of fine roots on the formation of stable aggregates has already been shown several times (Miller and Jastrow 1990; Gyssels et al. 2005), through the production of exudates, acting as binding agents, and the formation of a mesh entangling soil particles (Degens et al. 1994; Hütsch et al. 2002; Six et al. 2004). In addition, the percentage of fine roots was here positively correlated to the root mass density (Fig. 3; Appendix S3), indicating that the plots with a high proportion of fine roots have higher root biomass, which is known to positively impact soil aggregate stability (Miller and Jastrow 1990; Pérès et al. 2013). Indirect mechanisms can also explain the effect of fine roots which fuel the soil with organic compounds via the production of exudate or root decomposition, stimulating soil microbial communities stabilizing soil aggregates (Jastrow et al. 1998; Eisenhauer et al. 2010). Fine roots are also the docking stations for mycorrhizal fungi that themselves are able to stabilize soil aggregates directly by mechanical and chemical pathways as well as indirectly by promoting root growth and root branching (Rillig and Mummey 2006). The stronger effect of the percentage of fine roots on soil aggregate stability in early successional stages confirms the observations of Pohl et al. (2009), who suggested that vegetation characteristics are of particular importance to form stable aggregates in disturbed sites, generally poor in organic matter. It also supports the results of Le Bissonnais et al. (2007), who found that in poor organic soils (below around 12.5 g.kg − 1 ), SOC concentration is not the main driver of soil aggregate stability. Finally, mean root diameter and root diameter diversity were positively related to soil aggregate stability (Fig. 3, Table 2). In the present study, plant communities showing high mean root diameter and root diameter diversity were dominated by tree species, especially tall ones (TTree and Forest; Fig. 3), generally showing coarse and woody roots. These communities also showed highest SOC concentrations (Fig. 3) which made it difficult to identify the specific role of root diameter and diversity on soil aggregate stability. Nev- ertheless, root diversity tends to favor root exploration (Körner and Spehn 2002), potentially favoring soil aggregate stability. A high diversity in root diameter, related to diverse tissue chemistry and decomposition rate, can also offer a higher variety of niches for root-fed microorganisms which stabilize soil aggregates by their activity (Abiven et al. 2007). For example, fresh organic residue, most probably released by the decomposition or exudation of thin and lower order roots, stimulates the production of polysaccharides by bacteria and fungi acting as B glue ^ and increasing inter-particle cohesion (Chenu and Guerif 1991). Whereas more recalcitrant material, most probably released by the decomposition of coarse higher order roots, favor mainly fungal growth, with hyphae entangling soil particles and hydrophobic exuded substances decreasing aggregates wettability (Capriel et al. 1990). Several interlocking and complementary mechanisms can thus explain the stabilizing role of root diameter diversity on soil aggregates, suggested by the in situ correlation found here. The present study shows that soil aggregate stability increases significantly along the Mediterranean successional gradient in severely eroded gully bed ecosystems, showing the efficiency of plant dynamics to stabilize the soils of these ecosystems. Along the gradient, SOC accumulation, related to increased carbon input due to vegetation dynamics, was the main driver of soil aggregates stabilization. Our results also suggested that the diversity of plants and roots are likely to play an important role in the stabilization of soil aggregates along the successional gradient, through indirect diversity-driven SOC accumulation. In early successional stages characterized by low SOC concentration, we showed that fine sand, silt content and the percentage of fine roots were important co- drivers of soil aggregate ...
Context 11
... found that SOC concentration had the highest ex- planatory power for soil aggregate stability variations along the successional gradient ( Table 2). The positive and central role of SOC concentration has already been shown several times (Tisdall and Oades 1982; Haynes and Swift 1990; Le Bissonnais and Arrouays 1997; Chenu et al. 2000; Six et al. 2004; Le Bissonnais et al. 2007; Abiven et al. 2009) and our results are thus consistent with previous literature. SOC is known to increase the stability of soil aggregates through several direct and indirect mechanisms (Abiven et al. 2009). First, SOC binds mineral particles (such as clay or quartz) which increase soil aggregate stability (Tisdall and Oades 1982; Chenu 1989; Haynes and Swift 1990). SOC is also known to protect soil against slaking and to reduce aggregate wettability (Le Bissonnais and Arrouays 1997; Chenu et al. 2000), favoring the formation of stable aggregates. More precisely, in the early stages of the successional gradient, when plant communities are dominated by herbs, it is most likely that SOC is mainly composed by easily decomposable components (Garnier et al. 2004; Freschet et al. 2013), known to stimulate microorganisms exuding hydrophil- ic polysaccharides, hence increasing inter-particle cohesion. Going further along the successional gradient, the higher proportion of tree species is probably linked to an increase in recalcitrant hydrophobic compounds in SOC (Abiven et al. 2009), known to decrease aggregate wettability and thus protect aggregates against slaking (Jouany 1991; Le Bissonnais et al. 2007). The domi- nance of recalcitrant materials in the soils of later stages of successional gradient could also enhance the growth of mycorrhizal fungal hyphae, which are known to increase soil aggregate stability by enmeshing soil particles and reducing mechanical breakdown (Abiven et al. 2007; Annabi et al. 2007). In the present study, we found that SOC accumulation along the successional gradient was associated with an increase in species richness and diversity (Simpson), as well as increased values in root mass density, mean root diameter, root diameter diversity and percentage of fine roots and decreased values in specific root length and in the percentage of very fine roots (Appendix S3). These correlations suggest that SOC accumulation is most probably due to a combination of an increase in root and aboveground biomass and a decrease in litter decomposition rate as succession proceeds, as fast growing species that produce high-quality litter are progressively replaced by slow-growing species producing more recalcitrant litter, as previously pointed by Garnier et al. (2004) in a similar context. Such correlations may thus reflect some legacy effect along the successional gradient with increased input of carbon into the soil resulting from increased biomass production. Even though not studied here, SOC is generally positively correlated with soil microbial biomass (Wardle 1992), which positively influences soil aggregate stability (Six et al. 2004). Soil particle size distribution was also related to soil aggregate stability. More precisely, ANCOVA analyses underlined that the influence of soil granulometry was significant only for plant communities with SOC concentration below 24 g. kg − 1 (Fig. 4). This result confirms previous observations underpinning the role of soil particle size distribution on soil aggregate stability (Lehrsch et al. 1991; Oades 1993; Kiem and Kandeler 1997; Six et al. 2004), especially for soils with low SOC concentration (<15 g.kg − 1 ; Le Bissonnais et al. 2007). In line with previous results, silt content was negatively related to soil aggregate stability (Le Bissonnais 1996; Cosentino et al. 2006). More surprisingly, fine sand content (50 μ m<fine sand<1 mm) was associated with more stable soil aggregates, and clay concentration was not related to soil aggregate stability. These results are in opposition with the dispersive role of sand and the cohesive role of clay usually observed (Tisdall and Oades 1982; Pohl et al. 2009). The lack of effect of clay in the present study may be related to the weak and non- significant variations of clay concentration in the plots considered (Table 1). The positive relation between fine sand and soil aggregate stability (Fig. 3) may be a side- effect of the development of vegetation in gully beds, acting as a filter retaining more efficiently coarse soil particles when overland flow occurred (Lee et al. 2000). This would explain that the fine sand particles are observed in higher proportions in late successional stages showing more stable and developed vegetation cover, associated with higher soil aggregate stability. The positive relation between fine sand content and soil aggregate stability observed for low organic soils (Fig. 5) may be related to the important role of root enmeshment observed in these poor organic soils (Fig. 5). In coarse- textured sandy soils, fine roots growing into pores and crosslinking sand particles is indeed known to be one of the major stabilizing mechanisms whereas SOC-related or abiotic drivers are marginal (Oades 1993; Degens and Sparling 1996). Moreover, badlands of the French Southern Alps are characterized by intense wetting and drying as well as freezing and thawing cycles (Descroix and Mathys 2003), known to disrupt soil aggregates, especially in clayed soils because of clay swelling and shrinking (Six et al. 2004). Sand particles, less sensible to such microclimate variability, may counterbalance these disrupting abiotic factors, explaining partly the higher stability of aggregates in soils with higher sand content compared to fine textured soils (Denef et al. 2001). Contrary to our expectations, carbonates and sodium concentrations were not related to soil aggregate stability. We suggest that this lack of relation is due to the lack of variation of these variables in our study plots. Relationships between plant community characteristics and soil aggregate stability Results showed that species richness and diversity (Simpson) were positively related to soil aggregate stability (Table 2; Fig. 3). These results agree with previous works, highlighting the positive role of species richness and diversity in soil aggregate stability in both annual and perennial grassland ecosystems (Tisdall and Oades 1979; Jastrow 1987; Rillig et al. 2002; Le Bissonnais et al. 2007; Pohl et al. 2009; Fattet et al. 2011; Pérès et al. 2013). In our case, the joint increase in species richness and diversity with the accumulation of SOC along the successional gradient suggest that the effect of plant diversity is mainly indirect, through legacy effect of diversity-driven accumulation of SOC. Such indirect effect of plant diversity confirms the results obtained in grassland plant diversity experiment (Pérès et al. 2013) where the positive effect of plant diversity on soil aggregate stability resulted from the increase in several drivers of aggregate stability such as SOC, root biomass, soil microbial biomass and earthworm biomass. In later stages of succession, the high standing biomass in diverse and species-rich plant communities may also play an important role in the protection of soil aggregates against disruptive forces. Plant communities showing high species richness and diversity generally produce more shoot biomass than species-poor plant communities (Hooper et al. 2005; Reich et al. 2012) and shoot biomass is known to protect soil against detachment by splash during rainfall events (Greenway 1987; Thornes 1990). In our case, the more diverse and species-rich plant communities contained trees and thus also show a multi-layer plant cover (Appendix S1), known to be more efficient to protect soil against splash effect and surface runoff (Greenway 1987; Thornes 1990), hence limiting disruptive forces to impact soil aggregates. Finally, more diverse plant communities generally lead to the production of litter of contrasted properties, able to feed diverse macro- and microorganisms (Wardle et al. 2004; Viketoft et al. 2009; Eisenhauer et al. 2010, 2011), which can influence soil aggregate stability through various mechanisms such as the production of microbial exudate acting as a B glue ^ or the enmeshment of soil particles by hyphae of mycorrhizal fungi (Six et al. 2004; Rillig and Mummey ...
Context 12
... found that SOC concentration had the highest ex- planatory power for soil aggregate stability variations along the successional gradient ( Table 2). The positive and central role of SOC concentration has already been shown several times (Tisdall and Oades 1982; Haynes and Swift 1990; Le Bissonnais and Arrouays 1997; Chenu et al. 2000; Six et al. 2004; Le Bissonnais et al. 2007; Abiven et al. 2009) and our results are thus consistent with previous literature. SOC is known to increase the stability of soil aggregates through several direct and indirect mechanisms (Abiven et al. 2009). First, SOC binds mineral particles (such as clay or quartz) which increase soil aggregate stability (Tisdall and Oades 1982; Chenu 1989; Haynes and Swift 1990). SOC is also known to protect soil against slaking and to reduce aggregate wettability (Le Bissonnais and Arrouays 1997; Chenu et al. 2000), favoring the formation of stable aggregates. More precisely, in the early stages of the successional gradient, when plant communities are dominated by herbs, it is most likely that SOC is mainly composed by easily decomposable components (Garnier et al. 2004; Freschet et al. 2013), known to stimulate microorganisms exuding hydrophil- ic polysaccharides, hence increasing inter-particle cohesion. Going further along the successional gradient, the higher proportion of tree species is probably linked to an increase in recalcitrant hydrophobic compounds in SOC (Abiven et al. 2009), known to decrease aggregate wettability and thus protect aggregates against slaking (Jouany 1991; Le Bissonnais et al. 2007). The domi- nance of recalcitrant materials in the soils of later stages of successional gradient could also enhance the growth of mycorrhizal fungal hyphae, which are known to increase soil aggregate stability by enmeshing soil particles and reducing mechanical breakdown (Abiven et al. 2007; Annabi et al. 2007). In the present study, we found that SOC accumulation along the successional gradient was associated with an increase in species richness and diversity (Simpson), as well as increased values in root mass density, mean root diameter, root diameter diversity and percentage of fine roots and decreased values in specific root length and in the percentage of very fine roots (Appendix S3). These correlations suggest that SOC accumulation is most probably due to a combination of an increase in root and aboveground biomass and a decrease in litter decomposition rate as succession proceeds, as fast growing species that produce high-quality litter are progressively replaced by slow-growing species producing more recalcitrant litter, as previously pointed by Garnier et al. (2004) in a similar context. Such correlations may thus reflect some legacy effect along the successional gradient with increased input of carbon into the soil resulting from increased biomass production. Even though not studied here, SOC is generally positively correlated with soil microbial biomass (Wardle 1992), which positively influences soil aggregate stability (Six et al. 2004). Soil particle size distribution was also related to soil aggregate stability. More precisely, ANCOVA analyses underlined that the influence of soil granulometry was significant only for plant communities with SOC concentration below 24 g. kg − 1 (Fig. 4). This result confirms previous observations underpinning the role of soil particle size distribution on soil aggregate stability (Lehrsch et al. 1991; Oades 1993; Kiem and Kandeler 1997; Six et al. 2004), especially for soils with low SOC concentration (<15 g.kg − 1 ; Le Bissonnais et al. 2007). In line with previous results, silt content was negatively related to soil aggregate stability (Le Bissonnais 1996; Cosentino et al. 2006). More surprisingly, fine sand content (50 μ m<fine sand<1 mm) was associated with more stable soil aggregates, and clay concentration was not related to soil aggregate stability. These results are in opposition with the dispersive role of sand and the cohesive role of clay usually observed (Tisdall and Oades 1982; Pohl et al. 2009). The lack of effect of clay in the present study may be related to the weak and non- significant variations of clay concentration in the plots considered (Table 1). The positive relation between fine sand and soil aggregate stability (Fig. 3) may be a side- effect of the development of vegetation in gully beds, acting as a filter retaining more efficiently coarse soil particles when overland flow occurred (Lee et al. 2000). This would explain that the fine sand particles are observed in higher proportions in late successional stages showing more stable and developed vegetation cover, associated with higher soil aggregate stability. The positive relation between fine sand content and soil aggregate stability observed for low organic soils (Fig. 5) may be related to the important role of root enmeshment observed in these poor organic soils (Fig. 5). In coarse- textured sandy soils, fine roots growing into pores and crosslinking sand particles is indeed known to be one of the major stabilizing mechanisms whereas SOC-related or abiotic drivers are marginal (Oades 1993; Degens and Sparling 1996). Moreover, badlands of the French Southern Alps are characterized by intense wetting and drying as well as freezing and thawing cycles (Descroix and Mathys 2003), known to disrupt soil aggregates, especially in clayed soils because of clay swelling and shrinking (Six et al. 2004). Sand particles, less sensible to such microclimate variability, may counterbalance these disrupting abiotic factors, explaining partly the higher stability of aggregates in soils with higher sand content compared to fine textured soils (Denef et al. 2001). Contrary to our expectations, carbonates and sodium concentrations were not related to soil aggregate stability. We suggest that this lack of relation is due to the lack of variation of these variables in our study plots. Relationships between plant community characteristics and soil aggregate stability Results showed that species richness and diversity (Simpson) were positively related to soil aggregate stability (Table 2; Fig. 3). These results agree with previous works, highlighting the positive role of species richness and diversity in soil aggregate stability in both annual and perennial grassland ecosystems (Tisdall and Oades 1979; Jastrow 1987; Rillig et al. 2002; Le Bissonnais et al. 2007; Pohl et al. 2009; Fattet et al. 2011; Pérès et al. 2013). In our case, the joint increase in species richness and diversity with the accumulation of SOC along the successional gradient suggest that the effect of plant diversity is mainly indirect, through legacy effect of diversity-driven accumulation of SOC. Such indirect effect of plant diversity confirms the results obtained in grassland plant diversity experiment (Pérès et al. 2013) where the positive effect of plant diversity on soil aggregate stability resulted from the increase in several drivers of aggregate stability such as SOC, root biomass, soil microbial biomass and earthworm biomass. In later stages of succession, the high standing biomass in diverse and species-rich plant communities may also play an important role in the protection of soil aggregates against disruptive forces. Plant communities showing high species richness and diversity generally produce more shoot biomass than species-poor plant communities (Hooper et al. 2005; Reich et al. 2012) and shoot biomass is known to protect soil against detachment by splash during rainfall events (Greenway 1987; Thornes 1990). In our case, the more diverse and species-rich plant communities contained trees and thus also show a multi-layer plant cover (Appendix S1), known to be more efficient to protect soil against splash effect and surface runoff (Greenway 1987; Thornes 1990), hence limiting disruptive forces to impact soil aggregates. Finally, more diverse plant communities generally lead to the production of litter of contrasted properties, able to feed diverse macro- and microorganisms (Wardle et al. 2004; Viketoft et al. 2009; Eisenhauer et al. 2010, 2011), which can influence soil aggregate stability through various mechanisms such as the production of microbial exudate acting as a B glue ^ or the enmeshment of soil particles by hyphae of mycorrhizal fungi (Six et al. 2004; Rillig and Mummey ...
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A soil depleted of its organic carbon content is typically destabilized, i.e., its capacity to maintain its microstructure intact under various stress conditions weakens, and consequently, landslides and mudflows can be triggered and propagated more easily. In a previous work, we showed with a rheological analysis that the removal of the sole water...
Citations
... This is unexpected because, in comparison to higher-order roots, lower-order roots have smaller diameters, and higher concentrations of N. Since, first-order roots have a shorter life span, so one essential factor for the soil's preservation of carbon is a slower rate of decomposition (Fan and Guo 2010;McCormack et al. 2015). Moreover, greater root length density can also boost soil organic carbon stabilization through occlusion inside microaggregates, even though it primarily affects soil macroaggregation (Erktan et al. 2016;Ontl et al. 2015;Poirier et al. 2017). Furthermore, with different soil organic C concentrations, the effect of fine roots on macroaggregation also differed. ...
... Furthermore, with different soil organic C concentrations, the effect of fine roots on macroaggregation also differed. Organic C-poor soils with more fine roots had higher macroaggregation, while soil organic C-rich soil with lesser fine roots had lower macroaggregation (Erktan et al. 2016). Therefore, the distribution of roots at different depths is a vital parameter to influence C stabilization and storage in the soil. ...
Soil carbon sequestration is a vital ecosystem function that mitigates climate change by absorbing atmospheric carbon dioxide (CO2). Root characteristics such as depth, diameter, length, and branching pattern affect soil carbon dynamics through root-soil interactions and organic matter breakdown. Here we review field surveys, laboratory analysis, and mathematical modeling to understand how root structures affect soil carbon storage. Further, certain root features increase soil carbon sequestration, suggesting that selective breeding and genetic engineering of plants could maximize this ecological benefit. However, more research is needed to understand the complex interactions between roots, soil biota, and soil organic matter under changing environmental conditions. In addition, the benefit of climate change mitigation methods and soil carbon models from the inclusion of root architecture was reviewed. Studies in the realm of root-soil interactions encompass a variety of academic fields, including agronomy, ecology, soil science, and plant physiology. Insights into how roots interact with their soil environment and the effects of these interactions on plant health, agricultural productivity, and environmental sustainability have been gained through this research.
... Existing studies show that dense root networks can enhance soil aggregate stability by anchoring and releasing the soluble carbon-rich compounds continuously uniformly into soil (Bissonnais et al., 2018;Rillig et al., 2015). In this context, increasing root length density is helpful to fortify soil aggregation via strengthening the physical links between soil particles and micro-aggregates (Erktan et al., 2016). Similarly, greater root surface area and root length density can offer a broader area of plant root contact with soil, which can promote plant-soil resource exchange and benefit soil aggregation (Bissonnais et al., 2018). ...
Plastic fragments are widely found in the soil profile of terrestrial ecosystems, forming plastic footprint and posing increasing threat to soil functionality and carbon (C) footprint. It is unclear how plastic footprint affects C cycling, and in particularly permanent C sequestration. Integrated field observations (including 13C labelling) were made using polyethylene and polylactic acid plastic fragments (low-, medium- and high-concentrations as intensifying footprint) landfilling in soil, to track C flow along soil-plant-atmosphere continuum (SPAC). The result indicated that increased plastic fragments substantially reduced photosynthetic C assimilation (p<0.05), regardless of fragment degradability. Besides reducing C sink strength, relative intensity of C emission increased significantly, displaying elevated C source. Moreover, root C fixation declined significantly from 21.95 to 19.2 mg m-2, and simultaneously root length density, root weight density, specific root length and root diameter and surface area were clearly reduced. Similar trends were observed in the two types of plastic fragments (p>0.05). Particularly, soil aggregate stability was significantly lowered as affected by plastic fragments, which accelerated the decomposition rate of newly sequestered C (p<0.05). More importantly, net C rhizodeposition declined averagely from 39.77 to 29.41 mg m-2, which directly led to significant decline of permanent C sequestration in soil. Therefore, increasing plastic footprint considerably worsened C footprint regardless of polythene and biodegradable fragments. The findings unveiled the serious effects of plastic residues on permanent C sequestration across SPAC, implying that current C assessment methods clearly overlook plastic footprint and their global impact effects.
... On the other hand, the increase in aboveground biomass after the conversion of sloping farmland to land covered with different vegetation increased organic matter, improved soil fertilities and promoted the formation of new and richer aggregates [56,57], which increased the stability of soil aggregates and thereby increased soil resistance to erosion. Therefore, improving the stability of soil aggregates and reducing soil susceptibility to erosion can be achieved through vegetation measures [58]. ...
The world’s natural wetlands, which have important ecological functions, are being lost at an alarming rate. The erosion and deposition of soil on wetlands is a major cause of wetland conversion to agriculture. An urgent problem to be solved is how to slow down the erosion and deposition of wetlands resulting from land use. Land use patterns affect soil properties, thereby affecting soil aggregate stability and erodibility. Evaluating the effects of land use patterns on soil aggregate stability and erodibility in small watersheds of wetland ecosystems of karst plateau is of great importance. Thus, we compared the soil properties, aggregate stability indicators and soil erodibility of shrubland, grassland, artificial forest land and sloping farmland for evaluating the impact of various land use patterns on soil aggregate stability and erodibility in typical karst plateau wetland ecosystems. Our results showed that the mass fraction of soil aggregates >0.25 mm was the main component in the four land uses, with greater variation in aggregates >5 mm; overall, MWD, GMD and WSA0.25 were higher in grassland and shrubland than in sloping farmland and artificial forest land, while K values, PAD and SCAI showed the opposite trend. Correlation analysis showed that effective soil nutrients had a positive effect on soil aggregate stability. In conclusion, the stability of soil aggregates and resistance to soil erosion were strongest under the influence of shrubland. Our study showed that shrubland can better improve soil aggregate stability and erosion resistance, which may provide a guide for protecting and restoring karst plateau wetland ecosystems.
... The high heterogeneity of soil affects the distribution and activity of microorganisms and enzymes [49,50], directly influencing the cycling and transformation of key nutrients such as carbon and nitrogen, thereby affecting the soil's ecological service functions in agricultural planting. Enhancing the stability of soil aggregates can effectively reduce soil erosion and compaction [51,52]. Microorganisms, especially fungi, arbuscular Mycorrhizal fungi, and actinomycetes, play a key role in forming stable soil aggregates by binding soil particles with their extracellular polysaccharides [53,54]. ...
Soil microorganisms play a crucial role in maintaining the structure and function of soil ecosystems. This study aims to explore the effects of microbial fertilizers on improving soil physicochemical properties and promoting plant growth. The results show that the application of microbial fertilizers significantly increases the richness of soil microorganisms, maintains soil microecological balance, and effectively improves the soil environment. Through various secondary metabolites, proteins, and mucilage secreted by the developing plant root system, microbial fertilizers recruit specific fungal microorganisms. These microorganisms, by binding soil particles with their extracellular polysaccharides and entwining them, fix the soil, enhance the stability of soil aggregates, and ameliorate soil compaction. Moreover, after the application of microbial fertilizers, the enriched soil microbial community not only promotes the plant’s absorption and utilization of key elements such as nitrogen (N), phosphorus (P), and potassium (K), thereby increasing fruit yield and quality, but also competes with pathogens and induces systemic resistance in plants, effectively warding off pathogenic invasions. This study highlights the potential and importance of microbial fertilizers in promoting sustainable agricultural development, offering new strategies and perspectives for future agricultural production.
... [41]. In contrast, plants significantly reduced soil macropore volume, likely due to roots improving soil structure and stability against crack formation through the production of exudates acting as binding agents or by root mechanical engagement with soil aggregates [69,70]. Our experiment also allows us to discuss the importance of nutrient availability for GHG emissions. ...
Earthworms can stimulate microbial activity and hence greenhouse gas (GHG) emissions from soils. However, the extent of this effect in the presence of plants and soil moisture fluctuations, which are influenced by earthworm burrowing activity, remains uncertain. Here, we report the effects of earthworms (without, anecic, endogeic, both) and plants (with, without) on GHG (CO 2 , N 2 O) emissions in a 3-month greenhouse mesocosm experiment simulating a simplified agricultural context. The mesocosms allowed for water drainage at the bottom to account for the earthworm engineering effect on water flow during two drying-wetting cycles. N 2 O cumulative emissions were 34.6% and 44.8% lower when both earthworm species and only endogeic species were present, respectively, and 19.8% lower in the presence of plants. The presence of the endogeic species alone or in combination with the anecic species slightly reduced CO 2 emissions by 5.9% and 11.4%, respectively, and the presence of plants increased emissions by 6%. Earthworms, plants and soil water content interactively affected weekly N 2 O emissions, an effect controlled by increased soil dryness due to drainage via earthworm burrows and mesocosm evapotranspiration. Soil macroporosity (measured by X-ray tomography) was affected by earthworm species-specific burrowing activity. Both GHG emissions decreased with topsoil macropore volume, presumably due to reduced moisture and microbial activity. N 2 O emissions decreased with macropore volume in the deepest layer, likely due to the presence of fewer anaerobic microsites. Our results indicate that, under experimental conditions allowing for plant and earthworm engineering effects on soil moisture, earthworms do not increase GHG emissions, and endogeic earthworms may even reduce N 2 O emissions.
... Certain studies have shown that diversity of aboveground plants can also promote stability of soil aggregates because the different chemical compositions of plant communities can affect the decomposition of their organic matter. Root sediment, root biomass, soil microbial biomass, and organic carbon increase with increasing plant diversity (Demenois et al. 2018;Abiven et al. 2009;Erktan et al. 2016). In the deep soil, soil aggregate stability and MWD were higher in T1 and T2 than in CK, possibly because the soil layer is less affected by human activities and extension and proliferation of the root system lead to more root exudates, which promotes the cementation of aggregates. ...
Aims
To demonstrate how intensive management practices affect the belowground productivity of Moso bamboo, we examined the spatial distribution of fine root traits under three stands with high-intensity (T1, tillage plus biennial fertilization), low-intensity (T2, tillage plus quadrennial fertilization), and extensive (CK, no-tillage plus no fertilization) management, and evaluated the relationships among root traits and soil properties, aggregate stability (MWD).
Methods
Bamboo fine root and soil samples were collected from three depths (0–10, 10–20, 20–30 cm) and three horizontal distances (20, 40, 60 cm) under three management strategies. Root biomass, root morphology, soil properties, and aggregate composition were determined.
Results
Compared with CK, T1 and T2 had higher fine root biomass (FRB), and the largest FRB in the 10–20 cm soil layer. T1 had significantly higher allocation proportion of D1–2 class FRB and root length density (RLD) and significantly lower specific root length (SRL) and specific surface area (SSA). Vertically, intensive management led to an increase in FRB in the 10–20-cm soil layer and MWD in the 20–30-cm soil layer. Horizontally, FRB was highest at a distance of 20 cm from bamboo culm. A strong positive correlation was identified among FRB, RLD, and TP in each soil layer as well as among MWD, TP, and RLD.
Conclusions
Intensive management promotes fine root growth with high length in response to more soil P content, and high-intensity management shifts the expression of root functional traits toward transport fine roots proportion and 10–20-cm soil layer, and facilitates aboveground productivity of Moso bamboo. TOC, TP, and RLD are the main three drivers correlated with soil aggregate stability.
... Many studies have investigated the mechanism of soil aggregate formation and stabilization, owing to the importance of aggregate stability [5]. However, most of these studies focused on different land-use types (such as farmland, orchard, grass, or forest) [6,7], tillage measures [8,9], and plant community levels [10,11] to determine the factors that affect aggregate stability but often ignored the plant-soil interactions of different tree species. Moreover, these focus areas cannot determine the effects of tree species or forest type on soil aggregates. ...
... Mycorrhizal fungi form a mutualistic relationship with plant roots, where the fungi help the plant acquire nutrients from the soil while receiving carbohydrates from the plant in return. This fungal network can enhance soil structure and stability in several ways [11]. Root exudates from fine roots can directly act as binding agents of soil particles, decompose SOM, enhance the nutrient supply, and stimulate the stability of soil aggregates through interactions with the soil microbial community [36,47]. ...
... Soil particle size distribution is also related to soil aggregate stability. We found that silt content was negatively correlated with aggregate stability, which was consistent with a previous report [11]. Although clay content was not correlated with aggregate stability, sand content was positively correlated. ...
In soils, high aggregate stability often represents higher quality and anti-erosion ability; however, few studies have systematically analyzed how different forest stands affect soil aggregate stability. We selected five typical mixed forest stands on Jinyun Mountain in Chongqing, China, as research sites to evaluate soil aggregate stability. Within these sites, we analyzed the factors influencing soil aggregate stability in different stands by measuring soil characteristics and root traits. Soil aggregation stability, plant root traits, and soil properties varied among the mixed forest stands. The broadleaf tree mixed forest improved soil aggregate stability by 57%–103% over that of the Pinus massoniana mixed forest. The soil organic carbon, cation exchange capacity, Fe-Al oxides, and fine root proportion were positively correlated with soil aggregate stability. The specific root length and very fine root proportion were negatively correlated with soil aggregate stability, whereas the fine root proportion was positively correlated with this property. Specifically, we found that arbuscular mycorrhizal fungi did not affect soil aggregate stability in acid rain areas. Structural equation modeling indicated that soil aggregate stability was closely related to soil physicochemical properties and plant root characteristics. Predictive factors accounted for 69% of the variation in mean weight diameter, and plant root traits influenced soil aggregate stability by affecting soil organic matter, texture, and Fe-Al oxides. This study elucidated the impact of soil physicochemical properties and plant root characteristics on soil aggregate stability in different forest stand types, which has crucial implications for optimizing the management of various forest types.
... Soil aggregates are considered the functional unit of soil structure which could affect the soil's physical and chemical characteristics (Zhang et al., 2023). Aggregate stability can be used as an indicator of vital soil functions during assessment of soil nutrient quality and protection (Erktan et al., 2016). Additionally, the size of aggregate fractions can impact P availability through their involvement in soil P sorption and desorption. ...
Background and aims
Soil organic phosphorus (Po) fractions were deemed as potentially significant reservoirs of plant-available phosphorus, profoundly influenced by the physiochemical and biological characteristics of soil. Here we clarify how soil Po fractions and transformation in topsoil aggregates after 15 years of introducing N2-fixing tree species into Eucalyptus plantation.
Methods
We measured different Po fractions and used phospholipid fatty acids (PLFAs) and four extracellular enzymes activities as bioindicators of soil microbiota and function, respectively. The research was carried out within a 15-years of monoculture Eucalyptus urophylla plantation (PP) and mixed plantation (MP) of Eucalyptus urophylla × Acacia mangium.
Results
The mean weight diameter (MWD) was 19.28% greater (P < 0.05) in MP than PP. Soil organic matter (SOM), total nitrogen (TN), NO3⁻-N, C:P and N:P ratios were notably increased but Po content decreased significantly in bulk soil and most of the aggregates in MP than those in PP. Furthermore, the PLFA contents of total microbes, bacteria, and fungi were more abundant in bulk and aggregate soils in MP than PP. Enzyme activities related to N and P cycles showed significant improvement in bulk and most aggregate soils in MP than PP.
Conclusions
Our findings extend the evidence that promoting soil Po transformation may be related to the increasing of N availability, SOC, pH, fungi, and AMF colonization. Taken together, our results highlighted the soil Po fractions response to long term N2-fixing tree species application which might be a suitable strategy through efficient management of P in subtropical Eucalyptus plantations.
... Soil and climate conditions are widely recognized as the main factors restricting plant diversity, directly affecting the composition and distribution of communities (Britton et al., 2021;Leff et al., 2018). Close mutual feedback relationship between plants and soil, in the process of plant growth, the necessary nutrients are provided by the soil, and plant growth and development also can improve the soil nutrient (Cindy, 2002;Mekonnen, 2020), Soil organic matter is an important source of soil nutrients, and the content of soil organic matter is directly related to plant diversity (Erktan et al., 2016). In addition, soil physical and chemical properties, such as soil water content and soil temperature, as the main driving factors of plant diversity change, affect plant growth and species composition (Gong et al., 2008). ...
The relationship between plants and the environment is the foundation of plant community composition. It is urgent to clarify the distribution pattern and influencing factors of community biodiversity, especially the driving patterns of environmental factors under the conditions of invasive alien species. In this study, we investigated the effects of various environmental factors, especially altitude and Ageratina adenophora invasion, on forest community differentiation in Pinus yunnanensis forest in Panxi region, providing a strong theoretical basis for forest management and natural resource protection in this area. Based on the field survey data of 40 sample sites, a total of 18 environmental factors, including climate, terrain, soil and biology are selected, which may affect Pinus yunnanensis community. The methods of Two-way indicator species analysis (TWINSPAN), Redundancy analysis and Locally weighted linear regression are adopted by quantitative ecology. The effects of environmental factors on forest community type, species distribution pattern and species diversity were discussed. The results show that: (1) The Pinus yunnanensis community was divided into 4 types by TWINSPAN. (2) Altitude, annual mean temperature, soil pH, soil total phosphorus, Ageratina adenophora invasion were significantly correlated with forest community types and species distribution. (3) With the increase in altitude, the species diversity of Pinus yunnanensis community decreased firstly and then increased, and reached its lowest point at about 1800–2000 m a.s.l. With the increase in Ageratina adenophora invasion, the species diversity index of the community showed a downward trend. (4) The species diversity index of the tree layer was negatively correlated with the altitude. The species diversity index of herbaceous layer was negatively correlated with the Ageratina adenophora invasion intensity. Environmental factors had little influence on the species diversity index of shrub layer. It is suggested that the next research focus should be on setting up experimental areas for the invasion area of Ageratina adenophora, exploring scientific and effective removal methods, strengthening the restoration research and demonstration construction of the invaded ecosystem. By simulating and reconstructing the historical distribution dynamics of Ageratina adenophora, analyzing its diffusion trend and environmental interpretation, predicting the suitable areas in China under the background of climate change. We will conduct long-term monitoring and risk assessment of invaded and potential spread areas, and formulate and implement prevention and control policies.
... As a crucial indicator in evaluating soil quality, soil aggregates exhibit a robust response to secondary succession. The process of secondary succession involves various factors, such as the refractory portion of litter [33,34], soil microorganisms [35,36], and plant roots [37,38], which are believed to play significant roles in regulating the composition of soil aggregates. These factors contribute to an increase in refractory carbon components within the soil and facilitate aggregate formation [39,40]. ...
... From the perspective of soil aggregate stability and population characteristics, most indicators of soil aggregate stability exhibit a negative correlation with tree species diversity but a positive correlation with tree litter production and tree biomass. This finding slightly deviates from the results reported by Pérès et al. [49] and Erktan et al. [37], which may be attributed to differences in the selected stands. During the succession process of the selected broad-leaved Korean pine secondary forest, maple birch and positive pioneer tree species dominated the stand initially. ...
The composition and stability of soil aggregates are important characteristics for evaluating soil health. The objective of this study was to explore the effects of different restoration modes and secondary succession sequences of Korean pine on the stability of forest soil aggregates after clear cutting and their causes. The stability and composition of soil aggregates in 0–10 cm, 10–20 cm, and 20–40 cm were analyzed in four natural forests in the secondary succession sequence and a Pinus koraiensis plantation in the clear-cutting area of Liangshui National Nature Reserve, and the effects of forest community characteristics and cementing materials on these aggregates were explored. With the advancement of succession, the large soil water-stable aggregates and mechanical aggregates increased, and the stability increased. From the pioneer community to the top community, the proportion of macroaggregates in the soil mechanical aggregates in the 20–40 cm soil layer increased by 36%, while that in the water-stable aggregates in the 10–20 cm soil layer increased by 19%. Compared with plantation, the stability of soil aggregates in natural forests with a similar age was stronger. Water-stable aggregates were negatively correlated with bulk density, density, and porosity, and positively correlated with organic-matter-related cement. The volume of the dominant tree, litter yield, tree species diversity, biomass of various tree species, and litter biomass in the undecomposed layer were the key indicators affecting the stability of aggregates. In terms of restoration measures, natural restoration is better than plantations with a single tree species. In addition, succession makes forest soil aggregates more stable. The change of dominant tree species leads to changes in soil aggregate stability, and the effect of organic-related cementing material was stronger than that of iron oxide.
