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Thinning is an important forest management practice to mitigate the adverse effects of increased drought on tree growth and productivity. However, the responses of the soil microbial community and its functions to thinning and drought have received little attention in planted forests. In this study, we assessed the combined effects of thinning (30% and 45% of trees removed) and precipitation reduction (− 30%) on soil fungal and bacterial communities and the multifunctionality associated with carbon, nitrogen, and phosphorus cycling during one growing season (from April to September) in a 16-year-old larch plantation. We found that 45% thinning, but not 30%, significantly increased soil multifunctionality during the growing season (except for April and May) and fungal diversity in June. In contrast, precipitation reduction significantly decreased soil multifunctionality during the growing season and fungal diversity in June. Thinning also considerably suppressed the relative abundance of ectomycorrhizal (ECM) fungi during the growing season, whereas precipitation reduction significantly increased the relative abundance of ECM fungi in June and July. Furthermore, soil multifunctionality was more related to ECM and saprotrophic fungal communities than to bacterial communities. Our results suggest that a high thinning level can mitigate the negative effect of precipitation reduction on soil multifunctionality and fungal diversity, and this effect depends on the sampling month. Therefore, thinning is recommended as a tool to mitigate the impact of precipitation reduction on soil multifunctionality and the microbial community in larch plantations.

1. Optimal resource partitioning theory predicts that plants should increase the ratio between water absorbing and transpiring surfaces under short water supply. An increase in fine root mass and surface area relative to leaf area has frequently been found in herbaceous plants, but supporting evidence from mature trees is scarce and several results are contradictory. 2. In 12 mature Fagus sylvatica forests across a precipitation gradient (820-540 mm yr⁻¹), we tested several predictions of the theory by analysing the dependence of standing fine root biomass, fine root production and fine root morphology on mean annual precipitation (MAP), the precipitation of the study year, and stand structural and edaphic variables. The water storage capacity of the soil (WSC) was included as a covariable by comparing pairs of stands on sandy (lower WSC) and loam-richer soils (higher WSC). 3. Fine root biomass, total fine root surface area, fine root production and the fine root : leaf biomass production ratio markedly increased with reduced MAP and precipitation in the study year, while WSC was only a secondary factor and stand structure had no effect. 4. The precipitation effect on fine root biomass and production was more pronounced in stands on sandy soil with lower WSC, which had, at equal precipitation, a higher fine root biomass and productivity than stands on loam-richer soil. 5. The high degree of allocational plasticity in mature F. sylvatica trees contrasts with a low morphological plasticity of the fine roots. On the more extreme sandy soils, a significant decrease in mean fine root diameter and increase in specific root area with decreasing precipitation were found; a similar effect was absent on the loam-richer soils. 6. Synthesis. In support of optimal partitioning theory, mature Fagus sylvatica trees showed a remarkable allocational plasticity as a long-term response to significant precipitation reduction with a large increase in the size and productivity of the fine root system, while only minor adaptive modifications occurred in root morphology. More severe summer droughts in a future warmer climate may substantially alter the above-/below-ground C partitioning of this tree species with major implications for the forest C cycle.

Changes in precipitation frequency and intensity are predicted to be more intense and frequent accompanying climate change and may have immediate or potentially prolonged effects on soil CO₂ and CH₄ fluxes. However, how soil CO₂ and CH₄ fluxes respond to change in precipitation patterns remains poorly understood, especially under nitrogen (N) addition. In this study, we investigated the fluxes of soil CO₂ and CH₄ during a two-year field experiment and the effects of long-time precipitation reduction (– 30% of through-fall), short-term precipitation pulse and change of snow thickness on their response to simulated N deposition (50 kg N hm⁻² y⁻¹). Soil CO₂ flux was greater enhanced by N addition in the relatively wet growing season (2016) than in the relatively dry growing season (2017), whereas soil CH₄ flux was more inhibited by N addition in the relatively wet growing season 2016 than in the relatively dry growing season 2017. However, reduced precipitation decreased the positive effect of N addition on soil CO₂ flux in the relatively wet growing season 2016, while changing the direction of N addition effect in the relatively dry growing season 2017. These results suggested that the precipitation patterns in the growing season may affect soil CO₂ and CH₄ fluxes response to N addition. Furthermore, we found that short-term extreme precipitation and thickness of snow cover had a significantly positive effect on soil CH₄ flux but had a significantly negative effect on soil CO₂ flux. The extreme precipitation, that is, very heavy precipitation, reduced the response magnitudes of soil CO₂ and CH₄ fluxes to reduced precipitation within 3 days, compared to wet precipitation and heavy precipitation. Our results indicated the significant effects of precipitation pattern changes on responses of soil C flux to N deposition, which should be incorporated into the global-C-cycling models to improve the prediction and reduce the uncertainty of C-climate feedbacks.

Increasing drought caused by the ongoing climate change, and forest management by thinning that aims at mitigating its impact, may modify the current relationships between forest functions and drought intensity and preclude our ability to forecast future ecosystem responses. We used 15 yr of data from an experimental rainfall exclusion (−27% of rainfall) combined with thinning (−30% stand basal area) to investigate differences in the drought–function relationships for each component of above-ground net primary productivity (ANPP) and stand transpiration in a Mediterranean Quercus ilex stand. Rainfall exclusion reduced stand ANPP by 10%, mainly because of lowered leaf and acorn production, whereas wood production remained unaffected. These responses were consistent with the temporal sensitivity to drought among tree organs but revealed an increased allocation to wood. Thinning increased wood and acorn production and reduced the sensitivity of standing wood biomass change to drought. Rainfall exclusion and thinning lowered the intercept of the transpiration–drought relationship as a result of the structural constraints exerted by lower leaf and sapwood area. The results suggest that historical drought–function relationships can be used to infer future drought impacts on stand ANPP but not on water fluxes. Thinning can mitigate drought effects and reduce forest sensitivity to drought.

The decreasing precipitation with global climate warming is the main climatic condition in some sandy grassland ecosystems. The understanding of physiological responses of psammophytes in relation to warming and precipitation is a possible way to estimate the response of plant community stability to climate change. We selected Lespedeza davurica , Artemisia scoparia , and Cleistogenes squarrosa in sandy grassland to examine the effect of a combination of climate warming and decreasing precipitation on relative water content (RWC), chlorophyll, proline, and antioxidant enzyme activities. We found that all experimental treatments have influenced RWC, chlorophyll, proline, and antioxidant enzyme activities of three psammophytes. L. davurica has the highest leaf RWC among the three psammophytes. With the intensification of precipitation reduction, the decreasing amplitude of chlorophyll from three psammophytes was L. davurica > C. squarrosa > A. scoparia . At the natural temperature, the malondialdehyde (MDA) content of the three psammophytes under severe drought treatment was much higher than other treatments, and their increasing degree was as follows: A. scoparia > C. squarrosa > L. davurica . At the same precipitation gradient, the proline of three psammophytes under warming was higher than the natural temperature. The differences in superoxide dismutase (SOD) among the three psammophytes were A. scoparia > L. davurica > C. squarrosa. Moreover, at natural temperature, more than 40% of precipitation reduction was most significant. Regardless of warming or not, the catalase (CAT) activity of A. scoparia under reduced precipitation treatments was higher than natural temperature, while the response of L. davurica was opposite. Correlation analyses evidenced that warming (T) was significant in L. davurica and precipitation (W) was significant in A. scoparia and C. squarrosa according to the Monte-Carlo permutation test ( p = 0.002, 0.004, and 0.004). The study is important in predicting how local plants will respond to future climate change and assessing the possible effects of climate change on sandy grassland ecosystems.

Agroforestry could be a major strategy to adapt agriculture to climate change, thanks to the microclimate effects of trees and improved infiltration. However, the experimental validation of these claims is scarce. In this methodological review, we discuss options for the experimental simulation of drought conditions in agroforestry field experiments, comparing it with strategies adopted in natural, agricultural, or forestry ecosystems. We classify rainout shelters used in field experiments according to mobility, completeness of rain interception and height of rainout shelter. We show that specificities of agroforestry systems create constraints and require compromises in the design and operation of rainout shelters. We conclude that large rainout shelters, which induce drought for both the trees and the crops while limiting artifacts and biases, would be most relevant for studying the resistance of agroforestry systems to drought. Unfortunately, the review of rainout shelters already used in agroforestry systems reveals a lack of rainout shelters capable of intercepting rain on both trees and crops, achieving total rain interception, while being relatively low-cost and manageable by a small team. Therefore, we benchmark three novel rainout shelter designs that we tested in a mature agroforestry system under Mediterranean climatic conditions. We discuss their advantages and disadvantages in terms of both scientific and operational aspects. While compromises had to be done between experimental design, risks of artifact/bias, effectiveness, ease of installation, operation and maintenance, and agricultural management, these prototypes are starting points for achieving well-performing rainout shelters and testing the effects of drought in agroforestry experiments.

Soil microorganisms critically affect the ecosystem carbon (C) balance and C‐climate feedback by directly controlling organic C decomposition and indirectly regulating nutrient availability for plant C fixation. However, the effects of climate change drivers such as warming, precipitation change on soil microbial communities, and C dynamics remain poorly understood. Using a long‐term field warming and precipitation manipulation in a semi‐arid grassland on the Loess Plateau and a complementary incubation experiment, here we show that warming and rainfall reduction differentially affect the abundance and composition of bacteria and fungi, and soil C efflux. Warming significantly reduced the abundance of fungi but not bacteria, increasing the relative dominance of bacteria in the soil microbial community. In particular, warming shifted the community composition of abundant fungi in favor of oligotrophic Capnodiales and Hypocreales over potential saprotroph Archaeorhizomycetales. Also, precipitation reduction increased soil total microbial biomass but did not significantly affect the abundance or diversity of bacteria. Furthermore, the community composition of abundant, but not rare, soil fungi was significantly correlated with soil CO2 efflux. Our findings suggest that alterations in the fungal community composition, in response to changes in soil C and moisture, dominate the microbial responses to climate change and thus control soil C dynamics in semi‐arid grasslands. Impact statement Semi‐arid grasslands play a critical role in the global carbon (C) cycle and C‐climate feedback. Understanding the responses of soil microorganisms to warming and rainfall change is key to evaluating and predicting soil C dynamics in semi‐arid grasslands under future climate change scenarios. Our study showed that warming induced a shift in the abundant fungal community, favoring oligotrophic fungi (i.e., Capnodiales and Hypocreales) over the potential saprotrophic Archaeorhizomycetales, and reduced C efflux. These findings advance our understanding of soil microbial and C responses to climate change drivers and may help predict and possibly manage soil C sequestration in semi‐arid grasslands.

Global climate change, characterized by nitrogen (N) deposition and precipitation reduction, can disrupt soil microbial stoichiometry and soil nutrient availability, subsequently affecting soil nutrient cycles. However, the effects of N deposition and precipitation reduction on microbial stoichiometry and the soil nutrient status in temperate forests remain poorly understood. This study addresses this gap through a 10-year field trial conducted in a Korean pine mixed forest in northeastern China where three treatments were applied: precipitation reduction (PREC), nitrogen addition (N50), and a combination of nitrogen addition with precipitation reduction (PREC-N50). The results showed that N50 and PREC significantly increased carbon-to-phosphorus (C/P) and nitrogen-to-phosphorus (N/P) imbalances, thereby exacerbating microbial P limitation, while PREC-N50 did not alter the nutrient imbalances. PREC decreased soil water availability, impairing microbial nutrient acquisition. Both N50 and PREC influenced soil enzyme stoichiometry, leading to increasing the ACP production. The results of redundancy analysis indicated that microbial nutrient status, enzymatic activity, and composition contributed to the variations in nutrient imbalances, suggesting the adaption of microorganisms to P limitation. These results highlight that N addition and precipitation reduction enhanced microbial P limitation, boosting the shifts of microbial elemental composition, enzyme production, and community composition, and subsequently impacting on forest nutrient cycles.

Soil extracellular enzymes can regulate the decomposition processes of soil organic carbon (SOC). Thus, understanding how extracellular enzyme activity (EEA) and ecoenzymatic stoichiometry respond to altered nitrogen (N) deposition and precipitation patterns may establish a link between changes in soil organic matter and microbial responses in the context of climate change. The long-term field simulation experiments including the control, N deposition (N50, 50 kg·ha −1 ·yr −1 ), throughfall reduction (TR, − 30%), and their interactions (TR + N50) were built in a temperate forest in 2009. N50 significantly increased all EEAs except leucine aminopeptidase (LAP) and acid phosphatase (ACP). In addition, TR significantly reduced other EEAs except for ACP and polyphenol oxidase (PPO). N50 mainly promotes EEAs by influenced pH, increased SOC, and microbial biomass carbon (MBC). TR inhibited EEAs mainly by reducing soil moisture content (SMC), SOC, and MBC. Furthermore, the positive effects of N50 on EEAs were offset by the negative effects of TR under the interactive of N deposition and penetration reduction. In the control, C acquisition enzyme (C-acq):N acquisition enzyme (N-acq):P acquisition enzyme (P-acq) ≈ 1:1:1, N50, and TR resulted in alterations in the ecoenzymatic stoichiometric equilibrium. Wherein, N50 reduced BG: NAG + LAP but increased BG:ACP and NAG + LAP:ACP. The effect of TR on the ecoenzymatic stoichiometric ratio showed completely opposite to N50. TR + N50 reduced all ecoenzymatic stoichiometric ratios. Our study suggests that pH, SMC, substrate quality, and microbial biomass may be the main drivers for changes in EEAs. Our results elucidate the response mechanism of extracellular enzyme activity to N deposition and precipitation reduction, providing insights into the dynamics of SOC pools in the context of global change. In addition, this study proves that N limitation rather than phosphorus limitation exists in northeast temperate forests, providing a theoretical basis for future forest management.

Aims We examine how root system demography and morphology are affected by air warming and multiple, simultaneous climate change drivers. Methods Using minirhizotrons, we studied root growth, morphology, median longevity, risk of mortality and standing root pool in the upper soil horizon of a temperate grassland ecosystem for 3 years. Grassland monoliths were subjected to four climate treatments in a replicated additive design: control (C); elevated temperature (T); combined T and summer precipitation reduction (TD); combined TD and elevated atmospheric CO₂ (TDCO₂). Results Air warming (C vs T) and the combined climate change treatment (C vs TDCO₂) had a positive effect on root growth rate and standing root pool. However, root responses to climate treatment varied depending on diameter size class. For fine roots (≤ 0.1 mm), new root length and mortality increased under warming but decreased in response to elevated CO₂ (TD vs TDCO₂); for coarse roots (> 0.2 mm), length and mortality increased under both elevated CO₂ and combined climate change drivers. Conclusions Our data suggest that the standing roots pool in our grassland system may increase under future climatic conditions. Contrasted behaviour of fine and coarse roots may correspond to differential root activity of these extreme diameter classes in future climate.