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Contrasting effects of altered precipitation regimes on soil nitrogen cycling at the global scale

August 2022
Global Change Biology 28(22):6679-6695

August 2022
28(22):6679-6695

DOI:10.1111/gcb.16392

Authors:

Qiqian Wu

Zhejiang A&F University

Kai Yue

Fujian Normal University

Yuandan Ma

Zhejiang A&F University

Petr Heděnec

Universiti Malaysia Terengganu

Show all 10 authorsHide

Changes in precipitation regimes can strongly affect soil nitrogen (N) cycling in terrestrial ecosystems. However, whether altered precipitation regimes may differentially affect soil N cycling between arid and humid biomes at the global scale is unclear. We conducted a meta‐analysis using 1036 pairwise observations collected from 194 publications to assess the effects of increased and decreased precipitation on the input (N return from plants), storage (various forms of N in soil), and output (gaseous N emissions) of soil N in arid vs. humid biomes at the global scale. We found that (1) increased precipitation significantly increased N input (+12.1%) and output (+34.9%) but decreased N storage (‐13.7%), while decreased precipitation significantly decreased N input (‐10.7%) and output (‐34.8%) but increased N storage (+11.1%); (2) the sensitivity of soil N cycling to increased precipitation was higher in arid regions than in humid regions, while that to decreased precipitation was lower in arid regions than in humid regions; (3) the effect of altered precipitation regimes on soil N cycling was independent of precipitation type (i.e., rainfall vs. snowfall); and (4) the mean annual precipitation regulated soil N cycling in precipitation alteration experiments at the global scale. Overall, our results clearly show that the response of soil N cycling to increased vs. decreased precipitation differs between arid and humid regions, indicating the uneven effect of climate change on soil N cycling between these two contrasting climate regions. This implies that ecosystem models need to consider the differential responses of N cycling to altered precipitation regimes in different climatic conditions under future global change scenarios.

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Glob Change Biol. 2022;28:6679–6695. wileyonlinelibrary.com/journal/gcb

Received: 31 March 2022

Revised: 19 July 2022

Accepted: 11 August 2022

DOI : 10.1111/gcb .163 92

RESEARCH ARTICLE

Contrasting effects of altered precipitation regimes on soil

nitrogen cycling at the global scale

Jian Chen1 | Hui Zhang1 | Junjiong Shao1 | Scott X. Chang4 | Yan Li1

1State Key Laboratory of Subtropical Sil viculture, Zhejiang A&F Univer sity, Han gzhou , China

2Key Laborator y for Humid Subtropical Eco- Geographical Processes of t he Minis try of Education, School of Ge ographical Sciences, Fujian Normal Universi ty,

Fuzhou, China

3Instit ute of Tropica l Biodiversit y and Sus tainable Deve lopme nt, Universit y Malaysia Terengga nu, Kuala Nerus , Malaysia

4Depar tment of Renewab le Resources, University of Albert a, Edmo nton, Al bert a, Canada

Correspondence

Junjion g Shao, St ate Key Laboratory of

Subtropical Silviculture, Zhejiang A&F

University, Hang zhou 31130 0, China.

Email: jjshao@zafu.edu.cn

Funding information

Research and Deve lopme nt Fund

of Zhejiang A&F Universit y, Grant/

Award Number: 2021LFR010; Chi na

Postdoctoral Science Foundat ion,

Grant /Award Number: 2020 M671795

and 2020T130600; Natio nal Natu ral

Science Foundation of Chin a, Grant/

Award Number: 31800373, 31901294,

31922052 and 41730638; Open G rant

for Key Lab oratory of Sus taina ble Fore st

Ecosystem Management (Northeast

Forestry Universit y), Ministry of

Education, Gr ant/Award Number :

KFJJ2019YB04

Abstract

Changes in precipitation regimes can strongly affect soil nitrogen (N) cycling in terres-

trial ecosystems. However, whether altered precipitation regimes may differentially

affect soil N cycling between arid and humid biomes at the global scale is unclear.

We conducted a meta- analysis using 1036 pairwise obser vations collected from 194

publications to assess the effects of increased and decreased precipitation on the

input (N return from plants), storage (various forms of N in soil), and output (gaseous N

emissions) of soil N in arid versus humid biomes at the global scale. We found that (1)

increased precipitation significantly increased N input (+12.1%) and output (+34.9%)

but decreased N storage (−13.7%), while decreased precipitation significantly de-

creased N input (−10.7%) and output (−34.8%) but increased N storage (+11.1%); (2)

the sensitivity of soil N cycling to increased precipitation was higher in arid regions

than in humid regions, while that to decreased precipitation was lower in arid regions

than in humid regions; (3) the effect of altered precipitation regimes on soil N cycling

was independent of precipitation type (i.e., rainfall vs. snowfall); and (4) the mean an-

nual precipitation regulated soil N cycling in precipitation alteration experiments at

the global scale. Overall, our results clearly show that the response of soil N cycling

to increased versus decreased precipitation differs between arid and humid regions,

indicating the uneven effect of climate change on soil N cycling between these two

contrasting climate regions. This implies that ecosystem models need to consider the

differential responses of N cycling to altered precipitation regimes in different cli-

matic conditions under future global change scenarios.

KEYWORDS

altered precipitation, global climate change, mean annual precipitation, meta- analysis,

quantitative review, soil nitrogen cycling

13652486, 2022, 22, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/gcb.16392 by Zhejiang Agr & For University, Wiley Online Library on [17/10/2022]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

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1 | INTRODUC TION

Global climate change has resulted in altered precipitation re-

gimes, leading to increased occurrence of drought on the one hand

and flooding on the other hand (Piao et al., 2019; Smith, 2011).

Precipitation regimes can be extremely variable; precipitation may

increase or decrease depending on the time scale of concern and

the geographic location of the site (Allan et al., 2010; Thomas, 2011).

Changes in the precipitation regime, in turn, can significantly im-

pact the structure and function of ecosystems (Grimm et al., 2013;

Weltzin et al., 2003), especially material cycling and energy flow

(Cregger et al., 2 014; Nielsen & Ball, 2015). As a fundamental

element in supporting ecosystem function, nitrogen (N) and its

cycling can considerably affect soil chemistry, plant growth, litter

decomposition, greenhouse gas emissions, and other biological

processes, thereby potentially altering ecosystem structure and

function (Gruber & Galloway, 2008; Manning et al., 2008; Peñuelas

et al., 2013; Zhou et al., 2017). N cycling in terrestrial ecosystems has

been affected remarkably by multiple global change factors, such

as N deposition, warming, and altered precipitation regimes (Yue

et al., 2019). Although the effects of several global change factors

have been well studied, the effects of altered precipitation regimes

on soil N cycling, particularly between regions with contrasting cli-

matic regimes, are not fully understood. Thus, a better understand-

ing of the effects of altered precipitation regimes on soil N cycling

is important for providing a critical scientific basis to adapt to future

global climate change.

The effects of increased or decreased precipitation (Prec+

or Prec– , respectively) on N in plants and soils, as well as its gas-

eous emissions, have been reported in experimental studies. Prec+

may enhance plant N uptake and increase the plant N pool (Ren

et al., 2015), leading to a temporary decline in soil N availability

(Knapp et al., 2008; Stark & Firestone, 1995). Prec– has the opposite

effects by increasing water stress and decreasing plant transpiration

(Bista et al., 2018; Dijkstra et al., 2015) and demand for soil nutri-

ents, leading to soil N accumulation during drought periods (Weltzin

et al., 2003). Furthermore, large Prec+ events can lead to high run-

off and leaching rates and subsequently increase N losses and indi-

rectly decrease N retention (Yahdjian & Sala, 2010), while Prec– can

cause soil N accumulation due to the absence of runoff and leaching

(Cregger et al., 20 14). In addition, altered precipitation regimes will

affect the activities of microorganisms and enzymes involved in soil

N cycling (Fuchslueger et al., 2014). For exam ple, Pr ec– al te rs so il mi-

crobial compositions and enzyme activities, reducing soil N mineral-

ization and nitrification (Hartmann et al., 2013; Homyak et al., 2017;

Zhou et al., 2016). Nevertheless, the underlying mechanisms for the

effects of altered precipitation regimes on soil N cycling, including

input (N supplement from plants), storage (various forms of N in the

soil), and output (trace gaseous N emissions to the atmosphere), still

remain elusive.

More importantly, the effects of altered precipitation re-

gimes on soil N cycling may vary between arid and humid regions

(Thomas, 2011) due to the differences in climatic conditions, soil

proper ties, water use strategies and drought tolerance of plants

and microorganisms (Quiroga et al., 2013; Schimel et al., 20 07;

Wallenstein & Hall, 2012). For example, soil microbes in arid re-

gions have greater tolerance to drought and more rapidly respond

to changes in precipitation than those in humid regions (Schimel

et al., 2007; Xiang et al., 2008). As a result, soil microbes in arid

regions can still mineralize N under Prec– conditions (Homyak

et al., 2016), although N uptake by plants is reduced due to a lack

of water (Kreuzwieser & Gessler, 2010). Moreover, the absence of

major N consumers in arid regions increases the availability of soil

N, which may be washed away in runoff events or denitrified into

gaseous N during rainfall events (Sher et al., 2012). However, sim-

ilar results are rarely found in humid regions. Although individual

studies have examined how soil N cycling responds to altered pre-

cipitation regimes, the results are divergent (e.g., Li et al., 2020; Shi

et al., 2021), and it is difficult to draw robust conclusions. These un-

certainties hinder our understanding of the global responses of soil

N cycling to altered precipitation regimes.

Recently, several meta- analyses have examined soil N cycling

under altered precipitation regimes. For example, Yue et al. (2019)

re po r ted positi ve ef fec t s of Prec+ on th e pla nt N po ol an d at tribu te d

those ef fects to the elimination of water limitation for plant grow th

and N uptake. Li et al. (2020) demonstrated that on a global scale,

Prec+ increased N2O emissions by 55%, while Prec– suppressed it

by 31%, regardless of the biome type, treatment method or sea-

son. Moreover, the impeded mineralization caused by drought may

increase soil mineral and dissolved organic N concentrations but

reduce N mineralization and nitrification rates (Deng et al., 2021).

Existing reviews and syntheses are limited in scope due to the lim-

ited availabilit y of data, a narrow focus on individual aspec ts of soil

N cycling (e.g., only input, storage, or output of N was studied), or

neglected differences between arid and humid regions. Therefore,

understanding the effects of altered precipitation regimes on soil N

cycling between arid and humid regions would significantly improve

our understanding of the effects of ongoing global climate change.

Here, we compiled 1036 pair wise observations from 194 pub-

lished articles to determine the responses of soil N input (from plant

foliar and root), storage (soil dissolved organic N, inorganic N, etc.),

output (soil N2O and NO emissions), and the relevant fac tors (soil

moisture availability, pH, enzymatic activities, and abundance of

functional genes related to N cycling) to altered precipitation re-

gimes, including increased and decreased precipitation. The main

objectives of this study were to (a) identify the global patterns of soil

N input, storage, and output that arise in response to increased or

decreased precipitation; (b) relate the variabilities in the responses

among studies to different precipitation types (rainfall vs. snowfall),

ecosystem types (forest, grassland, or others), climate regions (arid

vs. humid region), experimental durations and magnitudes of precip-

itation change, especially bet ween arid and humid regions; (c) exam-

ine the underlying biotic mechanisms responsible for the changed

soil N cycl in g in re spo nse to al ter ed prec ipi tat io n reg ime s; an d (d) an -

alyze the potential problems and limitations of the current research

and discuss directions for future research.

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2 | METHODS

2.1 | Data collection

Peer- reviewed journal papers published before September 2021

were identified by searching the Web of Science, Google Scholar and

China Knowledge Resource Integrated Database (CNKI). Our search

used the following keywords and their combinations: (“increased

precipitation” OR “decreased precipitation” OR “precipitation addi-

tion” OR “precipitation removal” OR “increased rain*” OR “decreased

rain*” OR “rain* addition” OR rain* removal” OR “increased snow*”

OR “decreased snow*” OR “snow* addition” OR “snow* removal”

OR irrigation OR drought OR “climate change”) AND (nitrogen OR

nutrient).

The criteria for inclusion in our database were as follows: (1)

precipitation manipulation experiments were conducted in the field

and included paired control and precipitation manipulation treat-

ments within the same ecosystem under the same environmental

conditions; (2) multiple obser vations included in a single study (i.e.,

observations from different locations, ecosystems or microclimates)

were considered separately; (3) at least one of the response vari-

ables utilized to reflect soil N cycling was measured simultaneously

in the control and precipitation manipulation treatments; (4) if mul-

tiple factors were studied, only the control and precipitation ma-

nipulation treatments were selected; (5) the experimental duration

was longer than 1 month; (6) data were obtained from surface soil

samples with a maximum depth of 30 cm; (7) for experiments with

repeated measurements, the last measurement was used to ensure

independence among observations; and (8) the means, sample sizes,

and standard deviations or standard errors were provided directly (in

the text or tables) or could be calculated or extracted from figures.

2.2 | Data compilation

For each paper, we screened the following variables reflecting soil

N cycling: atmospheric N deposition, plant foliar and root N pools,

soil dissolved organic N (DON), inorganic N (IN), microbial biomass

N (MBN), ammonium N

(

−N

)

, nitrate N

(

−

−N

)

, N leaching,

and N2O, NO, N2, and NH3 emission rates. Due to the small sample

si ze s of at mos p her ic N de p osi t ion , soil N le a chi n g, N2 and NH 3 em is-

sion rates in precipitation alteration experiments (sample sizes <20;

Table S1), their responses to altered precipitation regimes were not

represented. The remaining nine variables were categorized into

three groups: (1) N input, including the input of exogenous N into

the soil from plant foliar and root; (2) N storage, including the key

N species in soil: DON, IN, MBN,

NH+

−

and

NO−

3−N

; and (3) N

output, including N2O and NO emissions from th e soil to the atm os-

phere. Considering the difficulty in measuring the actual amount of

exogenous N in soils in most studies, we used the plant foliar and

root N (specific for each site) to calculate the total N input into the

soils. A total of 1036 observations (214 for N input, 401 for N stor-

age, 130 for N output and 291 for relevant factors) were derived

from 194 papers (Figure 1; Table S1; Appendix S1). Furthermore,

FIGURE 1 Global distribution of paired observations (blue circles) of the responses of soil nitrogen (N) cycling to altered precipitation

regimes. The data were collected from 196 peer- reviewed journal papers. The color scale indicates the long- term mean annual precipitation

(MAP) derived from WorldClim (https://www.world clim.org). [Color figure can be viewed at wileyonlinelibrary.com]

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WU et a l.

variables related to the soil N transformation rate were collected

as a supplement, although their sample sizes were relatively small

(mineralization, n = 22; nitrification, n = 26; and denitrification,

n = 5; Table S1).

In addition to the response variables reflecting soil N cycling de-

scribed above, we also collected data on site characteristics such

as latitude, longitude, mean annual temperature (MAT) and precip-

itation (MAP), plant characteristics, soil physicochemical proper ties

(soil moisture availability, pH, enzymatic activities, and abundance

of functional genes), and information regarding experimental setup

(precipitation type, ecosystem type, climate region, experimental

duration, and magnitude of precipitation change). Latitude, longi-

tude, MAT and MAP were ex tracted from the papers directly. When

the MAT or MAP data were not available, we retrieved the data from

WorldClim (https://www.world clim.org). If figures were provided

in the original paper, the data were extracted using the Engauge

Digitizer (Free Software Foundation, Inc.).

2.3 | Moderator variables

To explore fac tors that regulate the effects of altered precipitation

regimes on soil N cycling, the data corresponding to each observa-

tion were subdivided into six moderator groups: the precipitation

type (rainfall or snowfall), ecosystem type (cropland, deser t, for-

est, grassland, shrubland, tundra, or wetland), climate region (arid

or humid regions), experimental duration (shor t term, <12 months;

medium- term, 12– 24 months; or long term, >24 months), and ma gni-

tude of precipitation change (small, <25% change in MAP; moderate,

25%– 75%; or large, >75%; Wang et al., 2021; Wu et al., 2020). The

identities, levels and descriptions of the moderator variables used in

this meta- analysis are listed in Table S2.

2.4 | Statistical analyses

We quantified the effect sizes of altered precipitation regimes by

weighting the natural log of the response ratio (lnRR) according to

Hedges et al. (1999):

where Xe and Xc are the mean values derived in the altered precipi-

tation and control treatments, respectively. The variance (VlnRR) was

calculated as follows:

where ne and nc are the sample sizes of the altered precipitation

and control treatments, respectively, and SDe and SDc are the stan-

dard deviations in the altered precipitation and control treatments,

respectively (Borenstein et al., 2011). If the standard error (SE) rather

than the SD was reported, we converted the SE into SD in accordance

with the process outlined in Lajeunesse (2013). If neither SD nor SE

was reported, the missing SD values were approximated by multiplying

the reported mean by the average coefficient of variance (CV) in our

complete dat aset (van Groenigen et al., 2011).

A weighted random- effec t model was used in this meta- analysis

to determine the overall effect of altered precipitation regimes on

soil N cycling (Gurevitch & Hedges, 2001; Yue et al., 2017). The

weighted mean effect size (lnRR++) was calculated as follows:

where m is the number of groups (precipitation type, ecosystem type,

etc.), k represents the number of observations in the ith group, w is

the weighting factor of each observation; and w was calculated by

taking the inverse of VlnRR. If the 95% CI of lnRR++ did not overlap 0,

the overall effect of the altered precipitation regime in the group was

significant (Koricheva et al., 2013). To test this approach, we assessed

whether the bias- corrected 95% bootstrap CI of lnRR++ overlapped

with 0 within 999 iterations (Rosenberg et al., 2000). The effects of

altered precipitation regimes on soil N cycling were also measured by

the mean percentage change (P) as follows:

The ef fect s were consi dered signif ic ant at p < .05 when the 95% CI did

not overlap 0.

The effects of the moderator variables on the magnitudes and

directions of the responses of soil N cycling to altered precipit a-

tion regimes were evaluated according to the moderator type and

the sample size. The total heterogeneity (Qtotal) among the differ-

ent moderator variable levels was divided into within- group het-

erogeneity (Qwithin) and between- group heterogeneity (Qbetween).

To evaluate the significance of each categorical moderator, a cat-

egorical random meta- analysis model was used to compare Qwithin

with Qbet ween (Borenstein et al., 2011). All of the meta- analyses and

lnRR++ calculations were conduc ted with MetaWin 2.1 (Rosenberg

et al., 2000). Finally, we used a linear mixed model implemented in

spss 20.0 (spss Inc.) to test how the precipitation change (%) affected

lnRRs and whether that effect was dependent on the MAP of the

experimental location.

2.5 | Sensitivity analysis to assess publication bias

As some correlative studies were present in our complete database,

the omission of potentially dependent observations might result

in publication bias; therefore, we conduc ted a sensitivity analysis

by removing these observations and repeating the analysis (Yue

et al., 2017). Additionally, we also assessed the publication bias in

the complete database related to the effects of altered precipitation

(1)

lnRR

−ln

(

c),

(2)

lnRR =SD

+SD

(3)

lnRR

++ =∑

i=1∑

j=1wijlnRRij

∑

1∑

wij

(4)

(

lnRR

++ −1

)

×100 %

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WU et al.

regimes on soil N cycling using funnel plots obtained through

Spearman's rank order and Kendall's tau.

3 | RESULTS

3.1 | Mean effect size of altered precipitation

regimes on soil N cycling

Across all ecosystem types, Prec+ increased soil N input and output

by 12.1% and 34.9%, respectively but decreased soil N storage by

13.7% (Figure 2a). In contrast, Prec– decreased soil N input and out-

put by 10.7% and 34.8% , respectively, but increased soil N storage

by 11.1% (Figure 2b). Prec+ also significantly increased plant foliar

and root N, MBN and N2O emissions but decreased DON, IN and

NO−

3−N

(Figure 2a). Moreover, Prec– resulted in opposite impacts

on those response variables except plant root N (Figure 2b). Prec+

and Prec– also significantly affected the related enzymatic activities,

functional genes of microorganisms, soil pH and moisture content.

However, the effect s of altered precipitation regimes on N deposi-

tion, N leaching and NH3 volatilization could not be explored due to

a lack of data. Based on the available data, the possible processes

underlying the changes in soil N cycling and the different drivers

involved are described in Figure 3.

The removal of correlative observations from the complete da-

tabase did not alter the trends or interpretations of the soil N input,

storage and output ( Tables S3– S8) Furthermore, the funnel plot was

symmetrical (Figure S1), indicating the absence of publication bias.

FIGURE 2 Responses of soil N cycling

(input, storage, and output) to overall

effect of increased (a) and decreased

(b) precipitation as a percentage change

relative to control (%). The effec ts of

increased and decreased precipitation

are significant when the 95% CI does not

overlap with 0. Red solid dots indicate

the significant positive effects, and blue

solid dots indicate the significant negative

effects. Values next to colorful solid lines

indicate the means and the numbers of

observations are shown in brackets. DON,

soil dissolved organic N; IN, soil inorganic

N; MBN, soil microbial biomass N;

−NH

soil ammonium N;

−

NO−

, soil nitrate N;

N2O, soil N2O emission and NO soil NO

emission. Input = plant foliar N + plant

root N; storage = DON + IN + MBN +

NH+

−N+NO

−

; output = N2O + NO

(if data available) [Color figure can be

viewed at wileyonlinelibrary.com]

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WU et a l.

3.2 | Responses of soil N input to altered

precipitation regimes

In our study, Prec+ resulted in a significant increase of only 14.6% in

soil N input in the rainfall experiments (Figure 4a). The responses of

soil N input to Prec+ in cropland (+33.7%), desert (+21.7%) and gr ass-

land (+33.5%) ecosystems were significant (Qbetween = 35.83, df = 4,

p < .001; Table 1). The ef fect s of Prec+ on N input were greater in ar id

regions (+23.7%) than in humid regions, and the dif ference bet ween

these two types of regions was significant (Qbetween = 16.61, df = 1,

p < .001; Table 1). In addition, the positive effects of short- and medium-

term studie s on soil N input were significant (Qbetween = 23.22, df = 2,

p < .001; Table 1). Finally, the small and moderate Prec+ treatments

significantly increased soil N input (Figure 4a).

Negative effects of Prec– were found in both the rainfall

(−10.9%) and snowfall (−6.8%) experiments (Figure 4b). Prec– de-

creased soil N input in crop land, grass land and t undra ecosy stems

by 30.0%, 20.8% and 7.7%, respectively, and significant differ-

ences were found among ecosystem types (Qbetween = 14.8 0,

df = 4, p = .005; Table 1). Prec– significantly decreased soil N

input in humid regions (−9.3%) but not in arid regions. Similarly,

Prec– decreased soil N input in both the short- (−11.4%) and

long- term (−13.1%) studies. Moreover, ≥25% decreases in pre-

cipitation significantly reduced soil N input. Additionally, the ef-

fect sizes (lnRRs) on soil N input had steeper linear relationships

with the magnitude of precipitation change in arid areas than in

humid areas (slopes: 0.0039 and 0.0022, respectively, p < .001;

Figure 5a,b).

FIGURE 3 Responses of terrestrial soil

N cycling to altered precipitation regimes.

The effects of altered precipitation

regimes on soil N input (green

background), storage (yellow background)

and output (blue background), related

enzymatic activities and func tional

genes of microorganisms (dashed boxes)

and soil pH and moisture are shown

in red (increased precipitation) or blue

(decreased precipitation), without enough

studies; ns, not significant; ON, organic N;

DON, dissolved organic N; MBN, microbial

biomass N. Biogeochemical N cycling

are attributed to N fixation, nitrification,

denitrification, ammonification, anaerobic

ammonium oxidation (anammox),

assimilation, and dissimilatory nitrate

reduction to ammonium process (DNR A).

In the soil N storage, microorganisms

carry enzymes that perform redox

reactions involving eight key inorganic N

species of different oxidation states. The

reactions involve reduction (red circle),

oxidation (blue circle), disproportionation

and comproportionation (green circle).

The following enzymes (purple) and the

functional genes of microorganisms (pink),

including but not limited to, are involved

in the N transformations: leucine amino

peptidase (LAP), N- acetyl- glucosaminidase

(NAG), urease, nirK, nirS, nosZ, archaeal

ammonia oxidation gene (Archaeal amoA),

and bacteria ammonia oxidation gene

(Bacterial amoA). This figure is modified

from Kuypers et al. (2018). [Color figure

can be viewed at wileyonlinelibrary.com]

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WU et al.

3.3 | Responses of soil N storage to altered

precipitation regimes

Increased rainfall decreased soil N storage by 16.3% (Figure 6a).

Prec+ decreased soil N storage in the forest (−20.5%) and grassland

(−13.7%) ecosystems and only in arid regions (−19.1%; Qbetween = 4. 89,

df = 1, p = .027; Table 1). Although the effects of Prec+ on soil N stor-

age did not change with experimental duration, the decrease caused

by Prec+ did not always occur in short- term studies. Additionally,

our result s in dicate that whe n th e ma gnitude of change in Prec+ wa s

moderate, Prec+ significantly decreased soil N storage (−17.3%).

Pre c– signif ic antly increase d soil N sto ra ge (10.6%) only in the rain-

fall experiments (Figure 6b). Prec– significantly increased soil N stor-

age in grassland (+19.3%). Soil N storage did not significantly change in

arid regions but was significantly increased in humid regions (+12.0%).

Prec– also significantly increased soil N storage in long- term studies

FIGURE 4 Responses of soil N

input to increased (a) and decreased (b)

precipitation as a percentage change

relative to control (%). The effec ts of

increased and decreased precipitation

are significant when the 95% CI does not

overlap with 0. Red solid dots indicate

the significant positive effects, and

blue solid dots indicate the signific ant

negative effects. Values next to colorful

solid lines indicate the means and the

numbers of observations are shown in

brackets. [Color figure can be viewed at

wileyonlinelibrary.com]

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WU et a l.

(+20.9%). When the reduction in precipitation was 25%– 75%, the soil

N storage increased significantly. Moreover, none of the moderator

variables influenced the effect of Prec– on soil N storage (Table 1).

Similarly, steeper linear relationships between the lnRRs of soil N

storage and the magnitude of precipitation change were also found

in areas with lower MAP values, with slopes of −0.0049 versus

−0.00 45 in arid and humid areas, respec tively (p < .0 01; Figure 5c,d).

3.4 | Responses of soil N output to altered

precipitation regimes

Prec+ increased soil N output only in the rainfall experiments, with

an increase of 36.8% (Figure 7a). Prec+ increased N output in the

forest (+76.8%) and grassland (+36.3%) ecosystems. Additionally,

Prec+ signific antly increased soil N output only in arid regions

(+36.5%). Due to the lack of long- term studies, significant Prec+ ef-

fects were observed only in the short- (+43.1%) and medium- term

(+37.4%) studies. The effects of Prec+ were significantly positive in

both small (+33.0%) and medium size (+50.6%) studies. Ultimately,

none of the moderator variables significantly altered the effect of

Prec+ on soil N output (Table 1).

The soil N output showed negative responses to Prec– only in

the rainfall experiments (−37.2%; Figure 7b). Additionally, Prec– sig-

nificantly decreased soil N output in the forest (−33.4%), grassland

(−57.3%), and shrubland (−36.3%) ecosystems. Furthermore, the ef-

fect of Prec– on soil N output was significant only in humid regions

(−37.0%). Soil N output exhibited significant negative responses to

Prec– in the short- (−21.3%) and long- term (−69.5%) studies. The

magnitude of precipitation change significantly and analogously in-

fluenced the effects of Prec− on soil N output (Figure 7b). In sum-

mary, significant differences in soil N output were found among the

TAB LE 1 Between- group heterogeneity (Qbetween) and probability (p) of altered precipitation regimes ef fects on soil N c ycling

Variable Moderator Qbetween df p

N input under increased precipit ation Precipitation type 1.96 1.161

Ecosystem type 35.83 4<.0 01

Climate region 16. 61 1<.001

Experimental duration 23.22 2<.0 01

Precipitation change magnitude 1.08 2.582

N input under decreased precipit ation Precipitation type 0.16 1.693

Ecosystem type 14. 80 4.005

Climate region 1.59 1.208

Experimental duration 1.68 2.431

Precipitation change magnitude 0.17 2.920

N storage under increased precipitation Precipitation type 1.55 1.212

Ecosystem type 2.61 5.759

Climate region 4.89 1.027

Experimental duration 1.96 2.375

Precipitation change magnitude 0.90 2.640

N storage under decreased precipitation Precipitation type 0.09 1.76 4

Ecosystem type 2.21 3.530

Climate region 0.20 1.654

Experimental duration 2.61 2.271

Precipitation change magnitude 0.42 2.810

N output under increased precipitation Precipitation type 0.68 1.409

Ecosystem type 2.50 1.114

Climate region 0.37 1.5 42

Experimental duration 0.05 1.823

Precipitation change magnitude 1.71 2.426

N output under decreased precipitation Precipitation type 1.25 1.263

Ecosystem type 23.79 3<.001

Climate region 2.60 1.107

Experimental duration 32.17 2<.0 01

Precipitation change magnitude 7. 3 4 2.026

Note: Bold values represent significant differences.

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FIGURE 5 Responses of soil N input (a, b), storage (c, d) and output (e, f) to precipitation change magnitude in arid (a, c, e) and humid (b,

d, f) regions. Data points represent the effect sizes (lnRRs) of N input, storage, and output to altered precipitation regimes; yellow indicates

arid region, and blue indicates humid region. The linear regressions (means and 95% CIs) are based on predicted values of the simplest linear

mixed effect model, including precipitation change magnitude. [Color figure can be viewed at wileyonlinelibrary.com]

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studied ecosystem types, experimental durations and magnitudes of

precipitation change (Table 1).

4 | DISCUSSION

To better understand the entire soil N cycling process under the

stress of altered precipitation regimes, we integrated soil N input,

storage, and output into the same framework to gain a comprehen-

sive perspective, rather than considering each factor separately as in

previous studies (e.g., Li et al., 2020; Shi et al., 2021; Yue et al., 2019).

Considering the complexity of soil N cycling, we first assessed the

whole process (Figures 2 and 3) and then emphasized the respective

effects of altered precipitation on soil N input, storage, and output.

We demonstrated that Prec+ increased both soil N input and N out-

put but caused a significant reduction in N storage. However, the

opposite results were obser ved under the Prec– treatment. We also

found that soil N cycling showed a higher sensitivity to Prec+ in arid

regions, while soil N cycling in humid regions was more sensitive to

Prec– . The significant dif ference in the responses of soil N cycling

FIGURE 6 Responses of soil N

storage to increased (a) and decreased

(b) precipitation as a percentage change

relative to control (%). The effec ts of

increased and decreased precipitation

are significant when the 95% CI does not

overlap with 0. Red solid dots indicate

the significant positive effects, and

blue solid dots indicate the signific ant

negative effects. Values next to colorful

solid lines indicate the means and the

numbers of observations are shown in

brackets. [Color figure can be viewed at

wileyonlinelibrary.com]

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between arid and humid regions to similar precipitation regime

alterations was reflected in the derived variabilities in soil N input,

storage, and output.

4.1 | Effects of altered precipitation regimes on soil

N input

The positive effects of Prec+ and the negative effects of Prec- on

soil N inpu t (Figure 2) ar e co nsist en t wit h Pre c+ and Prec– increas-

ing and decreasing plant N, respectively, as observed in previous

meta- analyses (He & Dijkstra, 2014; Yue et al., 2019). The decreased

in plant N due to Prec– was most likely due to the red uced plant N

uptake caused by (1) Prec– reducing th e N mi ner alization and t hus

N supply (Sanaullah et al., 2012); (2) Prec– reducing N diffusion

and mass flow in the soil (Lambers et al., 2008); and (3) Prec– af-

fecting the kinetics of N uptake by roots (Bassirirad, 2000). Thus,

the migr at ion of N from soi l to plant s is severely li mited in parched

soils (da Silva et al., 2011). In contrast, when water stress is re-

lieved by Prec+, plants ab sorb more N to sup po rt their growth (Liu

et al., 2018). Therefore, it is not surprising that high and low plant

N occurs under Pr ec+ and Prec– , res pec ti ve ly. Howev er, an exce p-

tion was observed in which Prec– did not significantly decrease

root N (Figure 2b). This was likely a consequence of the dif ferent

FIGURE 7 Responses of soil N

output to increased (a) and decreased

(b) precipitation as a percentage change

relative to control (%). The effec ts of

increased and decreased precipitation

are significant when the 95% CI does not

overlap with 0. Red solid dots indicate

the significant positive effects, and

blue solid dots indicate the signific ant

negative effects. Values next to colorful

solid lines indicate the means and the

numbers of observations are shown in

brackets. [Color figure can be viewed at

wileyonlinelibrary.com]

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nutrient allocation strategies under water shortage or enrichment

conditions. In other words, species that allocate more water, bio-

mass C or N to their aboveground parts increase litter production

under enriched water conditions, while more sucrose is available

for trans port to belowgrou nd pla nt p ar ts to resist wat er short ag es

under drought conditions (Wang et al., 2018; Zhao et al., 2020);

these mechanisms can explain the non- significant response of

root N to Prec– in our study. Hence, we expect that root N may

respond to Prec+ in arid regions and to Prec– in humid regions,

although we do not have sufficient data to substantiate this

hypothesis in this study.

The direction of the responses of soil N input did not differ be-

tween rainfall and snowfall even though only the rainfall experiments

had significant effects under both the increased and decreased

precipitation treatments (Figure 4). This was most likely because

plants need more water to support active growth and physiologi-

cal activities in the growing season than in the non- growing season.

Therefore, although the effects of snowfall may continue until the

following growing season (Walker et al., 1999), th e ab un da nce or de-

ficienc y of rainfall has a more significant impact. However, currently,

there is limited experimental evidence on how the prolonged effects

of altered snowfall regimes affect ecological processes such as soil

N input, and more research is needed to fill this knowledge gap in

the future.

Here, we observed significant effects of altered precipitation

regimes (both Prec+ and Prec– ) on soil N input in both the cropland

and grassland ecosystems. One possible explanation for this finding

is that croplands are highly dependent on human inputs. The com-

mon herbaceous plants in grasslands prefer to use water that is ex-

tracted from the uppermost soil layers and are thus more sensitive

to altered precipitation regimes; conversely, woody plants in forests

generally have deep root s and are less af fected by water deficit in

the surface soil (Dodd et al., 1998 ).

Interestingly, the soil N input was more sensitive to Prec+ in

arid regions and to Prec– in humid regions. The sensitivity of eco-

systems to Prec+ is likely dependent on the local MAP (Knapp

et al., 2017; Liu et al., 2018); Prec+ significantly increased soil N

in p ut, es p eci a lly in ar id re g ion s , whil e Prec– ha d th e opp osite ef f ect,

particularly in humid regions. The results of the linear- mixed mod-

els also supported this point (Figure 5a,b). In addition, the negative

effects of Prec– on soil N input were most significant in long- term

(>24 months) and large (>75% change in MAP) experiment s, and

this trend was opposite to that observed for Prec+. This was most

likely due to the ability of plants to cope with drought, which re-

sulted in only large and long- term decreases in precipitation having

a significant negative effect on plants, consistent with a previous

study (Wang et al., 2021). In co ntrast, large and long- term incr eases

in precipitation may have minimal effects when the ambient water

availability is high enough for plant growth. Therefore, the positive

effects of the large and long- term increases in precipitation on soil

N input from plants were not significant, which reflected the eco-

logical roles of precipitation intensity and duration (Fay et al., 2008;

Yan et al., 2018).

4.2 | Effects of altered precipitation regimes on

soil N storage

We found that Prec+ decreased soil N storage (−13.7%), whereas

Prec– treatments increased that correspondingly (+11.1%), which

was consistent with the results of other studies (Cregger et al., 2014;

Deng et al., 2021). These trends could be attributed to the follow-

ing processes in the soil. First, Prec+ may directly increase soil

N losses through

NO−

3−N

leaching (Dirnböck et al., 2016; Jabloun

et al., 2015), thus decreasing N storage (Mudge et al., 2017; Yahdjian

& Sala, 2010). Second, mineralized N under Prec– treatments may

not be fully absorbed by water- stressed plants due to reduced soil

moisture availabilit y (Dijkstra et al., 2015; Weltzin et al., 2003), re-

sulting in the observed increases in soil N storage (Bista et al., 2018).

Similarly, when precipitation increases, N uptake by plants and mi-

crobes also increases, leading to declining soil N storage (Cregger

et al., 2014). This asynchrony between the N supply and demand

was also reflected in the response of MBN to altered precipit ation

regimes (Figure 2), indicating the critical role of water in support-

ing microbial life. Consistent with other studies, we found increased

amounts of IN associated with Prec– (Evans & Burke, 2013; Yahdjian

et al., 2006). IN and

NO−

3−N

were increased by Prec– but were de-

creased by Prec+, which might be explained by the negative relation-

ship between IN and soil moisture content (Song et al., 2020). Except

for the decreased plant and microbial N uptake mentioned above,

this negative relationship may also be driven by decreased litter and

root production under Prec– (Deng et al., 2021; Wang et al., 2021).

Interestingly, we did not find any effects of altered precipitation

regimes on

NH+

−

, which may have been due to the different

ammonia- oxidation processes dominated by ammonia- oxidizing ar-

chaea and bacteria. Prec+ causes increased leaching of base cati-

ons and therefore lowers the soil pH (McCauley et al., 2009); the

resulting acidic environment is conducive to the growth of ammonia-

oxidizing archaea. In contrast, ammonia- oxidizing bacteria prefer the

higher soil pH caused by Prec– (Hu et al., 2014; Zhang et al., 2012).

Hence, regardless of whether Prec+ or Prec– occurs, the ammonia-

oxidation process does not shift, and

NH+

−

is continuously

consumed. Additionally, changes in the activities of enzymes asso-

ciated with N mineralization (such as leucine amino peptidase and

N- acetyl- glucosaminidase) related to altered precipitation regimes

can also strongly affect

NH+

−

oxidation (Hartmann et al., 2013;

Xiao et al., 2018). Our results for soil pH, extracellular enzyme

activity and functional genes supported the points listed above

(Figure S2). Finally, the dieback of microbes due to the water stress

caused by Prec– can directly release DON into soils (Borken &

Matzner, 2009; Schaeffer et al., 2017 ), which explains the dynamics

of DON observed in response to altered precipitation regimes.

Here , the dir ect io n of infl ue nce of alte re d sno wfa ll on soi l N st or-

age was consistent with that of altered rainfall; however, the effect

magnitudes associated with altered snowfall were not as significant

as those associated with altered rainfall (Figure 6). Although our re-

sults were similar to those found in a prior assessment on snow ma-

nipulation, indicating no significant effects of altered snowfall on soil

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DON, IN, or

NO−

3−N

(Li et al., 2016), we can still infer that alteration

of the snowfall regime has and will continue to affect soil N pool size

(Jones, 1999). Snowpack keeps the microenvironment warmer and

moister, thus promoting microbial and enzyme activities and favor-

ing the release of N from litter (Freppaz et al., 2008; Mackelprang

et al., 2011) and thereby indirectly changing the dynamics of soil N

storage. As we expected, grassland ecosystems were sensitive to

both Prec+ and Prec– . Given the relatively simple structure, shallow

root system and low plasticit y of root traits in grassland ecosystems,

it is conceivable that herbaceous species have low resistance to al-

tered precipitation regimes, although they may have evolved various

water use strategies to address conditions with abundant or defi-

cient water supply (Zhou et al., 2021). Moreover, we found that soil

N storage in arid regions tended to be more responsive to Prec+

than that in humid regions, while a correspondingly high sensitiv-

ity to Prec– was evident in humid regions. The mechanisms under-

lying these differences may involve different water use strategies

of microbes related to N transformation. Namely, soil microbes in

arid, water- stressed regions may show stronger drought resistance

(Zhou et al., 2018) since these communities are adapted to low water

availability. Therefore, Prec– does not significantly impact the activ-

ities or relevant N transformations of these ecosystems. However,

as Prec+ alleviates water stress, microbial activities, and relevant

N transformation processes in these ecosystems can be improved,

and this process is conducive to the accumulation of N in soil. The

soil moisture in arid regions was more likely to be significantly in-

creased by Prec+, while the soil moisture was significantly decreased

by Prec– in humid regions (Figure S2); these changes may have af-

fected microbial N transformation. Furthermore, we also found that

the effect sizes of altered precipitation regimes had steeper negative

relationships with the magnitude of precipitation change in arid re-

gio ns than in humid regions (Figure 5c,d), thus verifying the different

influences of altered precipitation regimes in arid and humid regions.

4.3 | Effects of altered precipitation regimes on

soil N output

Th e inc rea s e d soil N ou tpu t (+34.9%) in response to Prec+ (Figure 2a)

is generally comparable to the results of a recent study that re-

ported increased N2O emissions (+55%) in response to Prec+ (Li

et al., 2020). In contrast, Prec– significantly suppressed soil N out-

put (Figure 2b), in agreement with most previous studies (Hartmann

& Niklaus, 2012; Homyak et al., 20 17; Hu et al., 2019). Most soil N

output was caused by soil N2O emissions, together with soil N2O

being mainly produced by denitrification and nitrification; the varia-

tions in soil moisture related to Prec+ and Prec– were likely the key

factor influencing these processes. Generally, the declining micro-

bial activities and abundances and nitrification rates were caused

by decreased soil water availability in the Prec– treatment (Auyeung

et al., 2015; Deng et al., 2021). Prec+, in turn, had the opposite ef-

fect, which was also due to the increased nirK abundance (Figure S2;

Shi et al., 2021). In contrast to N2O, NO showed a positive response

to Pr ec– (Figure 2b). Du e to the small sample size (n = 5), we can only

infer that this result may be attributed to the following processes

asso ciated with Prec– : the reduced soil water- filled porosit y reduces

NO diffusion, and the accumulation of

NO−

provides sufficient sub-

strate for NO production (Homyak et al., 2016). In theory, sufficient

inp ut of N an d so il moi st ur e may lead to ac ti ve nit ri fi cati on and deni-

trification and thereby result in high N2O emissions (Ji et al., 2013).

Our study shows that soil N input (Figure 2) and moisture availabil-

ity (Figure S2) in arid regions were more sensitive to Prec+, while

these fac tors were more likely to respond to Prec– in humid regions.

However, to date, limited attention has been given to the differential

effects of altered precipitation regimes on soil N output between

arid and humid regions. Moreover, although the sample size for a

certain magnitude of precipitation change was small in Prec+ experi-

ments (e.g., n = 8 for moderate size and n = 4 for large size), the eco-

logical roles of rainfall intensity and duration on soil N output were

also obser ved in Prec+ and Prec– experiments and were similar to

the response of soil N input . Overall, this lack of research limits our

understanding of the feedback mechanisms between soil N output

and ongoing climate change on a global scale.

4.4 | Future research perspective

Based on this meta- analysis, we recommend the following for future

research: (1) Coordinated distributed precipitation manipulation ex-

periments should be established (Sternberg & Yakir, 2015) to spe ci fi -

cally study the question of how altered precipitation influences soil

N cycling. Although a large number of experiments have focused on

the impact of altered precipitation regimes on soil N cycling, most

of these studies have been limited to forest and grassland ecosys-

tems in the middle or high latitudes in the Northern Hemisphere

(Figure 1). For example, the small sample size for certain ecosystems

(i.e., cropland ecosystems) affects our ability to draw a more robust

conclusion. (2) The effect of not only the magnitude of precipita-

tion change but also the changes in precipitation frequency, inten-

sity, duration, seasonal distribution, and physical form etc. on soil

N cycling should be studied (Dore, 2005; Trenberth, 2011). Small

sample sizes for some variables may lead to non- significant or even

biased results (Loladze, 2014). For instance, due to the lack of pair-

wise snowfall observations, the impact of altered snowfall on soil N

cycling in arid and humid regions is still unknown. Therefore, more

data from specialized precipitation experiments with a full factorial

design are needed to draw more robust conclusions. (3) More em-

phasis should be placed on uncovering the underlying mechanisms

of changes in N cycling. Although altered precipitation regimes

have been shown to have far- reaching impacts on soil N cycling, the

detailed mechanisms responsible for the differences observed be-

tween arid and humid regions or among dif ferent ecosystems are

still unclear. For example, combining routine analytical methods with

cutting- edge “omics” techniques provides a useful platform to inves-

tigate functional genes and microbial communities associated with

N cycling (Hathaway et al., 2 014; Nelson et al., 2015). Although our

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database included many factors that are potentially related to these

change mechanisms, such as site, plant, and soil physicochemical

characteristics, further research is needed to better understand the

mechanisms involved. (4) Research focusing on the effects of altered

precipitation regimes on specific soil N cycling processes is sparse,

which limits our abilit y to conduct a meaningful global analysis.

Specifically, N deposition, leaching and NH3 volatilization are also

critical components of soil N cycling. In addition to the input, storage

and output of N, soil N cycling also includes many transformation

processes. However, there is less research focused on the dynamics

of these processes under altered precipitation regimes (sample sizes

<20; Table S1; Figure 3), and the lack of data reduced the breadth of

our analysis. We recommend that future studies pay more attention

to the complete soil N cycling process

5 | CONCLUSIONS

Our meta- analysis revealed that (1) increased precipitation had

significantly positive effects on N input and output and a negative

effect on N storage, more so in arid regions while decreased pre-

cipitation produced the opposite results, more so in humid regions;

(2) the effects of altered precipitation regimes on soil N cycling did

not depend on the precipitation form, although the effect of altered

snowfall was not as significant as that of altered rainfall; and (3)

MAP regulated the responses of soil N cycling to altered precipita-

tion regimes at the global scale: arid regions tended to be more re-

sponsive than humid regions to increased precipitation, while soil

N cycling was more responsive to decreased precipitation in humid

regions than in arid regions. These findings should be taken into ac-

count when predicting the responses of ecosystem- scale N cycling

to global climate change.

AUTHOR CONTRIBUTIONS

Yan Li and Qiqian Wu planned the study; Hui Zhang, Yuandan Ma

and Jian Chen collected the data; Qiqian Wu and Yuandan Ma per-

formed all data analyses; Qiqian Wu, Kai Yue and Junjiong Shao

wrote the first draft of the manuscript, and all authors contributed

to revisions.

ACKNOWLEDGMENTS

We thank the authors of all referenced papers included in this

analysis for their data as well as the anonymous reviewers for their

comments and suggestions. We are also grateful to Dr. Xinqi Wang

for the constructive comments on the early draft. This work was

financially supported by the National Natural Science Foundation

of China (41730638, 31901294, 31922052 and 3180 0373),

China Postdoctoral Science Foundation (2020M671795 and

2020T13060 0), the Research and Development Fund of Zhejiang A&F

University (2021LFR010), and the Open Grant for Key Laborator y

of Sustainable Forest Ecosystem Management (Nor theast Forestr y

University), Ministry of Education (KFJJ2019YB04).

CONFLICT OF INTEREST

There are no conflicts of interest.

DATA AVA ILAB ILITY STATE MEN T

The data that support the findings of this study are openly avail-

able in Figshare digital data repository at https://doi.org/10.6084/

m9.figsh are.20327754.

ORCID

Qiqian Wu https://orcid.org/0000-0002-4371-6303

Kai Yue https://orcid.org/0000-0002-7709-8523

Yuandan Ma https://orcid.org/0000-0002-9747-0804

Petr Heděnec https://orcid.org/0000-0002-9425-8525

Yanjiang Cai https://orcid.org/0000-0002-5376-7884

Jian Chen https://orcid.org/0000-0001-8289-5685

Hui Zhang https://orcid.org/0000-0002-6355-5404

Junjiong Shao https://orcid.org/0000-0002-2412-2892

Scott X. Chang https://orcid.org/0000-0002-7624-439X

Yan Li https://orcid.org/0000-0002-1503-0515

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SUPPORTING INFORMATION

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How to cite this article: Wu, Q., Yue, K., Ma, Y., Heděnec, P.,

Cai, Y., Chen, J., Zhang, H., Shao, J., Chang, S. X., & Li, Y.

(2022). Contrasting effec ts of altered precipitation regimes

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Jun 2024
WATER RES

Aridity threshold for alpine soil nitrogen isotope signature and ecosystem nitrogen cycling

Article

Jun 2024
GLOBAL CHANGE BIOL

Determination of tipping points in nitrogen (N) isotope (δ ¹⁵ N) natural abundance, especially soil δ ¹⁵ N, with increasing aridity, is critical for estimating N‐cycling dynamics and N limitation in terrestrial ecosystems. However, whether there are linear or nonlinear responses of soil δ ¹⁵ N to increases in aridity and if these responses correspond well with soil N cycling remains largely unknown. In this study, we investigated soil δ ¹⁵ N and soil N‐cycling characteristics in both topsoil and subsoil layers along a drought gradient across a 3000‐km transect of drylands on the Qinghai–Tibetan Plateau. We found that the effect of increasing aridity on soil δ ¹⁵ N values shifted from negative to positive with thresholds at aridity index (AI) = 0.27 and 0.29 for the topsoil and subsoil, respectively, although soil N pools and N transformation rates linearly decreased with increasing aridity in both soil layers. Furthermore, we identified markedly different correlations between soil δ ¹⁵ N and soil N‐cycling traits above and below the AI thresholds (0.27 and 0.29 for topsoil and subsoil, respectively). Specifically, in wetter regions, soil δ ¹⁵ N positively correlated with most soil N‐cycling traits, suggesting that high soil δ ¹⁵ N may result from the “openness” of soil N cycling. Conversely, in drier regions, soil δ ¹⁵ N showed insignificant relationships with soil N‐cycling traits and correlated well with factors, such as soil‐available phosphorus and foliage δ ¹⁵ N, demonstrating that pathways other than typical soil N cycling may dominate soil δ ¹⁵ N under drier conditions. Overall, these results highlight that different ecosystem N‐cycling processes may drive soil δ ¹⁵ N along the aridity gradient, broadening our understanding of N cycling as indicated by soil δ ¹⁵ N under changing drought regimes. The aridity threshold of soil δ ¹⁵ N should be considered in terrestrial N‐cycling models when incorporating ¹⁵ N isotope signals to predict N cycling and availability under climatic dryness.

Metagenomic data highlight shifted nitrogen regime induced by wetland reclamation

Article

Full-text available

Apr 2024
BIOL FERT SOILS

Natural wetlands are mostly nitrogen-limited ecosystems, while reclamation stimulates the loss of nitrogen (N) in soils by shifting the N regime. To investigate the microbial mechanisms of the N regime shift, we first conducted a global meta-analysis to quantify the wetland reclamation impacts on soil mineral N pools and then a field campaign to sample 24 soil cores up to 100 cm depth in a natural wetland and a 23-year cultivated soybean field from the Sanjiang Plain in northeastern China. After wetland reclamation, the N regime was shifted to cause a potential risk of massive N loss in soils; their microbial mechanisms were revealed through metagenomic data. In cropland, the relative abundance of genes involved in nitrification and assimilatory nitrate reduction to ammonia (ANRA) were enriched while those in N fixation, mineralization, denitrification, and dissimilatory nitrate reduction to ammonia (DNRA) were diminished. Wetland reclamation substantially enhanced the relative abundance of genes involved in nitrification (except for genes for ammonia oxidation to NH2OH) and denitrification in surface (0–30 cm) soils but decreased them in subsurface (30–100 cm) soils. After wetland reclamation, the relative abundance of genes involved in denitrification and DNRA significantly reduced in spring and summer, but such patterns were not found in autumn and winter. This change enhanced potential microbial-driven N loss in spring and summer. The metagenomic data serve as surrogate data sources for quantifying soil roles on soil N cycles under land use change.

Elevated CO2 levels promote both carbon and nitrogen cycling in global forests

Article

Full-text available

Apr 2024
Nat. Clim. Change.

Forests provide vital ecosystem services, particularly as carbon sinks for nature-based climate solutions. However, the impact of elevated atmospheric carbon dioxide (CO2) levels on carbon and nitrogen interactions of forests remains poorly quantified. We integrate experimental observations and biogeochemical models to elucidate the synergies between enhanced nitrogen and carbon cycling in global forests under elevated CO2. Elevated CO2 alone increases net primary productivity (+27%; 95% CI: 23–31%) and leaf C/N ratio (+26%; 95% CI: 16–39%), while stimulating biological nitrogen fixation (+25%; 95% CI: 0–56%) and nitrogen use efficiency (+32%; 95% CI: 5–65%) according to a global meta-analysis. Under the elevated CO2 middle-road scenario for 2050, the forest carbon sink is projected to increase by 0.28 billion tonnes (PgC yr⁻¹), with reactive nitrogen loss decreasing by 8 Tg yr⁻¹ relative to the baseline. The monetary impact assessment of the elevated CO2 impact on forests represents a societal value of US$271 billion.

Continuous shallow groundwater decline and accidental extreme precipitation control the soil nitrate leaching of a well-irrigated area in the North China Plain

Article

Apr 2024

Global response of different types of grasslands to precipitation and grazing, especially belowground biomass

Article

Apr 2024
AGR ECOSYST ENVIRON

Differential effects of altered precipitation regimes on soil carbon cycles in arid vs . humid terrestrial ecosystems

Article

Full-text available

Sep 2021

Changes in precipitation regimes have significant effects on soil carbon (C) cycles; however, these effects may vary in arid vs. humid areas. Additionally, the corresponding details of soil C cycles in response to altered precipitation regimes have not been well documented. Here, a meta-analysis was performed using 845 pairwise observations (control vs. increased or decreased precipitation) from 214 published articles to quantify the responses of the input process of exogenous C, the contents of various forms of C in soil and the soil-atmosphere C fluxes relative to increased or decreased precipitation. The results showed that the effects of altered precipitation regimes did not differ between rainfall and snowfall. Increased precipitation significantly enhanced the soil C inputs, pools and outputs by 18.17, 18.50, and 21.04%, respectively, while decreased precipitation led to a significant decline in these soil C parameters by 10.18, 9.96, and 17.98%, respectively. The effects of increased precipitation on soil C cycles were more significant in arid areas (where mean annual precipitation, MAP < 500 mm), but the effects of decreased precipitation were more significant in humid areas (where MAP ≥ 500 mm), indicating that the original MAP partially determined the responses of the soil C cycles to altered precipitation regimes. This study implies that for the same of precipitation variation, soil C cycles respond at different magnitudes: not only should the direction (decrease vs. increase) be counted, but also the region (arid vs. humid) should be considered. These results deepened our understanding on regional differentiation in soil C cycles under climate change scenarios.

Responses of soil N2O emissions and their abiotic and biotic drivers to altered rainfall regimes and co‐occurring wet N deposition in a semi‐arid grassland

Article

Full-text available

Jul 2021

Global change factors such as changed rainfall regimes and nitrogen (N) deposition contribute to increases in the emission of the greenhouse gas nitrous oxide (N2O) from the soil. In previous research, N deposition has often been simulated by using a single or a series of N addition events over the course of a year, but wet N deposition actually co‐occurs with rainfall. How soil N2O emissions respond to altered rainfall amount and frequency, wet N deposition, and their interactions is still not fully understood. We designed a three‐factor fully factorial experiment with factors of rainfall amounts (ambient, −30%) rainfall frequency (ambient, ±50%) and wet N deposition (with/without) co‐occurring with rainfall in semi‐arid grassland mesocosms, and measured N2O emissions and their possible biotic and abiotic drivers. Across all treatments, reduced rainfall amount and N deposition increased soil N2O emissions by 35% and 28%, respectively. A significant interactive effect was observed between rainfall amount and N deposition, and to a lesser extent between rainfall frequency and N deposition. Without N deposition, reduced rainfall amount and altered rainfall frequency indirectly affected soil N2O emissions by changing the abundance of nirK and soil net N mineralization, and the changes in nirK abundance were indirectly driven by soil N availability rather than directly by soil moisture. With N deposition, both the abundance of nirK and the level of soil water filled pore space contributed to changes in N2O emissions in response to altered rainfall regimes, and the changes in the abundance of nirK were indirectly driven by plant N uptake and nitrifier (AOB) abundance. Our results imply that unlike wetter grassland ecosystems, reduced precipitation may increase N2O emissions and N deposition may only slightly increase N2O emissions in arid and semi‐arid N‐limited ecosystems that are dominated by grasses with high soil N uptake capacity.

Differential responses of litter decomposition to warming, elevated CO2 , and changed precipitation regime

Article

Full-text available

Oct 2020
PLANT SOIL

Background and aims Litter decomposition is a fundamental process of biogeochemical cycles and particularly sensitive to global change. However, the overall effects of warming, elevated carbon dioxide and changed precipitation regime on litter decomposition are not well studied. Methods To assess the effects of these three common global change factors on litter decomposition, we performed a meta-analysis using 366 pairwise observations from 103 published articles. We quantified the responses of litter decomposition rate to the effects of warming, elevated CO2 , and changed precipitation regime (increased and decreased). Results At the global scale, warming and precipitation addition significantly stimulated litter decomposition rate by an average of 4.20% and 11.72%, respectively. In contrast, elevated CO2 and precipitation removal showed significant negative effects on litter decomposition rate (-2.99% and -12.60%). In addition, study type, plant functional traits, and climate were consistent mod-erators. These results indicate that warming, elevated CO2 , and changed precipitation regime have significantly affected litter decomposition, but the direction and magnitude of the effects of different factors varied, and were also differently mediated by moderator variables. Conclusions Global cycles of carbon and nutrients via the litter decomposition process can be substantially affected by global change. However, the combined effects of these global change factors on litter decomposition and the different effects between the arid and humid areas cannot be addressed due to the lack of data, indicating the need of more focus on multi-factor ma-nipulative experiments in a wider range of study sites.

Root anatomical traits determined leaf‐level physiology and responses to precipitation change of herbaceous species in a temperate steppe

Article

Full-text available

Aug 2020
NEW PHYTOL

Root anatomy plays important roles in the control of leaf water relations. However, few studies have evaluated whether and how anatomical traits of absorptive roots influence leaf physiology of herbaceous species in a temperate grassland. We measured absorptive root anatomical traits and leaf physiological traits of 15 herbaceous species in a temperate steppe and monitored their responses to increased precipitation in a field stimulating experiment. Root anatomical and leaf physiological traits differed among monocotyledonous grasses, monocotyledonous liliaceous species and dicotyledonous forbs. The species with higher stele: root diameter, lower root diameter and cortex thickness exhibited higher transpiration rates and stomatal conductance, but lower intrinsic water‐use efficiency. Increased precipitation enhanced transpiration and stomatal conductance of forbs and lilies, but it enhanced photosynthesis in lilies exclusively. The sensitive response of lilies to precipitation may be related to their large root diameter and cortex thickness. In summary, we observed distinct differences in anatomical traits of absorptive roots among plant groups in temperate steppes. These differences drove variations in leaf physiological traits and their diverse responses to precipitation change. These findings highlight the important roles of root anatomical traits in driving leaf‐level physiological processes in temperate grasslands.

Impacts of drought and nitrogen enrichment on leaf nutrient resorption and root nutrient allocation in four Tibetan plant species

Article

Full-text available

Mar 2020
SCI TOTAL ENVIRON

Plant nutrient resorption, a process by which plant withdraws nutrients from senescing structures to developing tissues, can significantly affect plant growth, litter decomposition and nutrient cycling. Global change factors, such as nitrogen (N) deposition and altered precipitation, may mediate plant nutrient resorption and allocation. The ongoing global change is accompanied with increased N inputs and drought frequency in many regions. However, the interactive effects of increased N availability and drought on plant nutrient-responses remain largely unclear. In a pot experiment, we examined the impacts of N enrichment and drought on leaf N and phosphorous (P) resorption and root nutrient allocation in four species from the Qinghai-Tibet Plateau, including two graminoid species (Kobresia capillifolia and Elymus nutans) and two forb species (Delphinium kamaonense and Aster diplostephioides). Our results showed divergent resorption patterns within the two functional groups. E. nutans and D. kamaonense showed stronger N resorption than K. capillifolia and A. diplostephioides. N addition did not alter their N resorption efficiencies, but decreased the N resorption proficiencies of the former two species. In contrast, drought did not affect N or P resorption proficiencies, but decreased N resorption efficiency of K. capillifolia. Besides, N addition facilitated P resorption in K. capillifolia and D. kamaonense, and drought did the same in A. diplostephioides, suggesting that P resorption plays an important role in nutrient conservation in these species. Moreover, species with stronger N resorption allocated more biomass C or N to aboveground and enhanced their litter quality under N enrichment, while species with weaker resorption allocated more biomass C and/or N to belowground part under drought. Together, these results show that the responses of nutrient resorption and allocation to N enrichment and drought are highly species-specific. Future studies should take these differential responses into consideration to better predict litter decomposition and ecosystem nutrient cycling.

Terrestrial N2O emissions and related functional genes under climate change: A global meta‐analysis

Article

Full-text available

Sep 2019

Nitrous oxide (N2O) emissions from soil contribute to global warming and are in turn substantially affected by climate change. However, climate change impacts on N2O production across terrestrial ecosystems remain poorly understood. Here, we synthesised 46 published studies of N2O fluxes and relevant soil functional genes (SFGs, i.e. archaeal amoA, bacterial amoA, nosZ, narG, nirK and nirS) to assess their responses to increased temperature, increased or decreased precipitation amounts, and prolonged drought (no change in total precipitation but increase in precipitation intervals) in terrestrial ecosystem (i.e. grasslands, forests, shrublands, tundra and croplands). Across the dataset, temperature increased N2O emissions by 33%. However, the effects were highly variable across biomes, with strongest temperature responses in shrublands, variable responses in forests and negative responses in tundra. The warming methods employed also influenced the effects of temperature on N2O emissions (most effectively induced by open‐top chambers). Whole‐day or whole‐year warming treatment significantly enhanced N2O emissions, but day‐time, night‐time or short‐season warming did not have significant effects. Regardless of biome, treatment method and season, increased precipitation promoted N2O emission by an average of 55%, while decreased precipitation suppressed N2O emission by 31%, predominantly driven by changes in soil moisture. The effect size of precipitation changes on nirS and nosZ showed a U‐shape relationship with soil moisture; further insight into biotic mechanisms underlying N2O emission response to climate change remain limited by data availability, underlying a need for studies that report SFG. Our findings indicate that climate change substantially affects N2O emission and highlight the urgent need to incorporate this strong feedback into most climate models for convincing projection of future climate change.

Introduction to Meta‐Analysis

Book

Jun 2021

Drought effects on soil carbon and nitrogen dynamics in global natural ecosystems

Article

Jan 2021
EARTH-SCI REV

Extreme droughts have serious impacts on the pools, fluxes and processes of terrestrial carbon (C) and nitrogen (N) cycles. A deep understanding is necessary to explore the impacts of this extreme climate change event. Here, to investigate how soil C and N pools and fluxes respond to drought and explore their mechanisms we conducted a meta-analysis synthesizing the responses of soil C and N cycles to drought (precipitation reduction experiment) in three main natural ecosystems: forests, shrubs and grasslands. Data were collected from 148 recent publications (1815 sampling data at 134 sites) with the drought experiment from 1 to 13 years across the globe. Drought reduced soil organic C content (-3.3%) mainly because of decreased plant litter input (-8.7%) and reduced litter decomposition (-13.0%) across all the three ecosystem types in the world. Meanwhile, drought increased mineral N concentration (+31%) but reduced N mineralization rate (-5.7%) and nitrification rate (-13.8%), and thus left total N unchanged. Drought increased the accumulation of dissolved organic C and N concentrations by +59% and +33%, respectively, compared with the normal precipitation conditions and the results reflected retarded mineralization and higher stability of dissolved organic matter. Among the three ecosystem types, forest soils strongly increased litter C (+64%, n=8) and N concentrations (+33%, n=6) as well as microbial CO2 (+16%, n=55), whereas total CO2 emission remains unaffected. Drought decreased soil CO2 emission (-15%, n=53) in shrubs due to reduction of microbial respiration and decreased root biomass. The 98% (n=39) increase of NH4⁺ concentration in forest soils corresponds to 11% (n=37) decrease of NO3⁻ and so, it reflected the increase of N mineralization rate, but the decrease of nitrification. For shrubs and grasslands, however, stabilized or decreased N mineralization and nitrification mean less N uptake by plants under drought. Overall, the effects of drought on soil C and N cycles were regulated by the ecosystem type, drought duration and intensity. Moreover, the drought effects appear to be stronger with high drought intensity and duration, especially on the total CO2 emission that decreased with drought duration and intensity. However, present studies mainly focused on the short-term drought effects, lack a comprehensive understanding of how drought effects in a long-term scale. So, future studies should strengthen drought frequency impacts on ecosystem C and N dynamics in the long-term sequence (> 10 years) in order to face the impacts of global change.

THE META-ANALYSIS OF RESPONSE RATIOS IN EXPERIMENTAL ECOLOGY

Article

Jun 1999

Rainfall amount and timing jointly regulate the responses of soil nitrogen transformation processes to rainfall increase in an arid desert ecosystem

Article

Apr 2020
GEODERMA

Climate models predict greater rainfall will occur in the arid and semiarid regions of Northwest China, where nitrogen (N) cycling is particularly sensitive to changes in rainfall regimes. Yet, how increasing rainfall regulates soil N transformation processes in these water-limited regions is still not well understood. We conducted a manipulative experiment in a desert ecosystem in Northwest China, whereby we simulated five different scenarios of future rain regimes (natural rains plus 0%, 25%, 50%, 75% and 100% of the local mean annual precipitation) each month from May to September in 2009. We examined in situ net N mineralization and soil N availability in both vegetated and bare soils, as well as leaf litter N release for the dominant shrub species Nitraria tangutorum monthly after each rain addition. We found that increased water availability via the simulated rain addition significantly decreased total net N mineralization rates over the growing season in both vegetated and bare soils. A larger amount of litter N was released after rain addition in vegetated soils, which could contribute to the higher concentrations of inorganic N in vegetated soils compared to bare soils. Furthermore, we found that the responses of soil N transformation processes to rain additions showed great seasonality, and thus both rainfall amount and timing jointly regulate the responses of soil N transformation processes to rainfall increase under future rainfall scenarios in this arid desert ecosystem. Over the growing season, rainfall addition reduced soil inorganic N concentrations but favored plant N uptake and microbial N immobilization. We suggest that the cycling of N will be greatly changed under future rainfall regimes, which may have consequences for ecosystem stability and functioning in this “N-conserving” desert ecosystem.

Contrasting effects of altered precipitation regimes on soil nitrogen cycling at the global scale

Abstract

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