Author?& Address

題目：

Soil microbial responses to large changes in precipitation with nitrogen deposition in an arid ecosystem

通訊作者：

Zhenzhu Xu

地址：

State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093 China

Abstract

Climatic change severely affects terrestrial ecosystem functioning by modifying?soil microbial communities, especially in arid ecosystems.?

However, how precipitation patterns affect soil microbes and the underlying mechanisms remain largely unclear, particularly under long-term dry–wet cycling and vice versa in field settings.?

In this study, a field experiment was conducted to quantify soil microbial responses and resilience to precipitation changes with nitrogen addition.?

We?established five levels of precipitation?with?nitrogen addition?over the first 3?years and then balanced this with compensatory precipitation in the fourth year (i.e., reversed the precipitation treatments), to recover to the levels expected over 4?years in a desert steppe ecosystem.?

Soil?microbial community biomass?increased with increasing precipitation, and the reversed precipitation reversed these responses. The?soil microbial response ratiowas constrained by the initial reduction in precipitation, whereas the resilience and limitation/promotion index of most microbial groups tended to increase.?Nitrogen addition?reduced the response rates of most microbial groups, depending on the soil depth. The soil microbial response and limitation/promotion index could be distinguished by antecedent soil features.?The precipitation regime can regulate the responses of soil microbial communities to climatic change via two potential mechanisms:

(1)?concurrent nitrogen deposition?and

(2)?soil chemical and biological mediation.

Soil microbial behaviors and their associations with soil properties should be considered when assessing the responses of terrestrial ecosystems to climatic change.

Result

FIGURE 1

Soil moisture (a) and temperature (b) under precipitation treatments in 2018 (the last year of the initial precipitation treatments) and 2019 (the year of reversed precipitation treatments). The five precipitation regimes were 50% reduction, 25% reduction, ambient precipitation (CK), 25% addition, and 50% addition in 2016–2018, followed by a reversal of each to 50% addition, 25% addition, ambient precipitation, 25% reduction, and 50% reduction (reversed treatments) in 2019, respectively. Meanwhile, there were two levels of N treatments (ambient N, N elevated by 10?g?N?m?2?year?1). Thex-axis is labeled by precipitation treatments of the first 3?years (2016–2018). Different uppercase (2018) and lowercase (2019) letters represent significant differences at?p?<?0.05 among five precipitation treatments during the 2?years.

FIGURE 2

ffects of precipitation and N addition treatments on soil ammonium-nitrogen (NH4+-N, a–d) and nitrate-nitrogen (NO3?-N, e–h) content at 0–10 (a, b, e, f) and 10–20?cm (c, d, g, h) soil layers before (2018, a, c, e, g) and after (2019, b, d, f, h) reversing precipitation regimes. N0, ambient N; N10, N elevated by 10?g?N?m?2?year?1. Note different scales ony-axes during the 2?years (mean?±?SE,?n?=?4).

FIGURE 3Soil microbial response ratio to precipitation alterations and N addition. The?x-axis is labeled by precipitation treatments of the first 3?years (2016–2018). Act, actinomycetes; AMF, arbuscular mycorrhizal fungi; F/B, ratio of fungi to bacteria; GN, Gram-negative bacteria; GP, Gram-positive bacteria; GP/GN, ratio of GP to GN. N0, ambient N; N10, N elevated by 10?g?N?m?2?year?1. *, ** and *** indicate significant effects of precipitation treatment (P), N addition (N), depth (D) and their interactions at?p?<?0.05,?p?<?0.01, and?p?<?0.001, respectively. Different lower case letters indicate differences between precipitation treatments across N and soil depth treatments (mean?±?SE,?n?=?4).

FIGURE 4

Soil microbial resilience to precipitation alterations and N addition. Thex-axis is labeled by precipitation treatments of the first 3?years (2016–2018). Act, actinomycetes; AMF, arbuscular mycorrhizal fungi; F/B, ratio of fungi to bacteria; GN, Gram-negative bacteria; GP, Gram-positive bacteria; GP/GN, ratio of GP to GN. N0, ambient N; N10, N elevated by 10?g?N?m?2?year?1. *, ** and *** indicate significant effects of precipitation treatment (P), N addition (N), depth (D), and their interactions at?p?<?0.05,?p?<?0.01, and?p?<?0.001, respectively. Different lower case letters indicate differences between precipitation treatments across N and soil depth treatments (mean?±?SE,?n?=?4).

FIGURE 5

Soil microbial limitation/promotion index (LPI) under precipitation alterations and N addition. Thex-axis is labeled by precipitation treatments of the first 3?years (2016–2018). Act, actinomycetes; AMF, arbuscular mycorrhizal fungi; F/B, ratio of fungi to bacteria; GN, Gram-negative bacteria; GP, Gram-positive bacteria; GP/GN, ratio of Gram-positive bacteria to Gram-negative bacteria. N0, ambient N; N10, N elevated by 10?g?N?m?2?year?1. *, ** and *** indicate significant effects of precipitation treatment (P), N addition (N), depth (D) and their interactions at?p?<?0.05,?p?<?0.01, and?p?<?0.001, respectively. Different lowercase letters indicate above SE bars significant differences between precipitation treatments across N and soil depth treatments (mean?±?SE,?n?=?4).

FIGURE 6

Correlations of soil microbial response ratio, resilience, and limitation/promotion index (LPI) with soil chemical and biological features in the last year (2018) of initial precipitation treatments (a, response ratio; b, resilience; c, LPI) and in the year (2019) of reversed precipitation treatments (d, response ratio; e, resilience; f, LPI). Act, actinomycetes; AMF, arbuscular mycorrhizal fungi; Bac, bacteria; BGB, belowground biomass; Fun, fungi; GN, Gram-negative bacteria; GP, Gram-positive bacteria; MBC, soil microbial biomass carbon; MBN, soil microbial biomass nitrogen; NH4, ammonium-nitrogen; NO3, nitrate-nitrogen; pH, soil pH; Pro, protozoa; SOC, soil organic carbon; SWC, soil water content; TC, soil total carbon. Each soil microbial group name represent their response ratios (a, d), resilience (b, e), and LPI (c, f). The circle area sizes represent the correlation coefficients. The colors of the circles indicate positive or negative correlation. * and ** denote significance at 0.05 and 0.01 levels, respectively (n?=?64–80).

Conclusion

The soil microbial community can be enhanced/constrained with increased/decreased precipitation, and the responses can be largely reversed by reversing these precipitation treatments. The response ratio of the soil microbial groups to the measurements was higher under the increased precipitation treatments than under the decreased precipitation treatments, with no systematic effect on resilience. A high LPI occurred under regimes with initially reduced precipitation followed by increased precipitation. Nitrogen addition reduced the response and resilience of most of the microbial groups. The response ratio and LPI of the soil microbial groups were closely associated with belowground abiotic and biotic characteristics before the reversal treatment. The current results highlight that the responses of soil microbes in desert steppe ecosystems to large precipitation variability (ranging from extremely dry to extremely wet conditions and followed by reversal of the treatment) can be driven by two potential mechanisms: concurrent nitrogen deposition and soil chemical and biological involvement. These findings shed light on the potential responses of soil microbial communities to future climate change, particularly in vulnerable arid ecosystems.

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