Drought changes litter quantity and quality, and soil microbial activities to affect soil nutrients in moso bamboo forest

Protists and fungi: Reinforcing urban soil ecological functions against flash droughts

Rising instances of flash droughts are contributing to notable variability in soil moisture across terrestrial ecosystems. These phenomena challenge urban ecosystem services, yet the reaction of soil ecological functions (SEFs) to such events is poorly understood. This study investigates the responses of SEFs (about nutrient metabolism capacity and potential) and the microbiome under two specific scenarios: a flooding-drought sequence and a direct drought condition. Using quantitative microbial element cycling analysis, high-throughput sequencing, and enzyme activity measurements, we found that unlike in forests, the microbial composition in urban soils remained unchanged during flash drought conditions. However, SEFs were affected in both settings. Correlation analysis and Mantel test showed that forest soils exhibited more complex interactions among soil moisture, properties, and microbial communities. Positive linear correlation revealed that bacteria were the sole drivers of SEFs. Interestingly, while multi-threshold results suggested bacterial α diversity impeded the maximization of SEFs in urban soils, fungi and protists had a beneficial impact. Cross-domain network of urban soils had higher number of nodes and edges, but lower average degree and robustness than forest soils. Mantel test revealed that fungi and protist had significant correlations with bacterial composition in forest soils, but not in urban soils. In the urban network, the degree and eigenvector centrality of bacterial, fungal and protistan ASVs were significantly lower compared to those in the forest. These results suggest that the lower robustness of the microbial network in urban soils is attributed to limited interactions among fungi, consumer protists, and bacteria, contributing to the failure of microbial-driven ecological functions. Overall, our findings emphasize the critical role of fungi and protists in shielding urban soils from drought-induced disturbances and in enhancing the resistance of urban ecological functions amidst environmental changes.

Photosynthetic and biochemical responses of four subtropical tree seedlings to reduced dry season and increased wet season precipitation and variable N deposition

Interspecific variations in phenotypic plasticity of trees that are affected by climate change may alter the ecosystem function of forests. Seedlings of four common tree species (Castanopsis fissa, Michelia macclurei, Dalbergia odorifera and Ormosia pinnata) in subtropical plantations of southern China were grown in the field under rainout shelters and subjected to changing precipitation (48 L of water every 4 days in the dry season, 83 L of water every 1 day in the wet season; 4 g m-2 year-1 of nitrogen (N)), low N deposition (48 L of water every 2 days in the dry season, 71 L of water every 1 day in the wet season; 8 g m-2 year-1 N), high N deposition (48 L of water every 2 days in the dry season, 71 L of water every 1 day in the wet season; 10 g m-2 year-1 N) and their interactive effects. We found that the changes in seasonal precipitation reduced the light-saturated photosynthetic rate (Asat) for C. fissa due to declining area-based foliar N concentrations (Na). However, we also found that the interactive effects of changing precipitation and N deposition enhanced Asat for C. fissa by increasing foliar Na concentrations, suggesting that N deposition could alleviate N limitations associated with changing precipitation. Altered precipitation and high N deposition reduced Asat for D. odorifera by decreasing the maximum electron transport rate for RuBP regeneration (Jmax) and maximum rate of carboxylation of Rubisco (Vcmax). Ormosia pinnata under high N deposition exhibited increasing Asat due to higher stomatal conductance and Vcmax. The growth of D. odorifera might be inhibited by changes in seasonal precipitation and N deposition, while O. pinnata may benefit from increasing N deposition in future climates. Our study provides an important insight into the selection of tree species with high capacity to tolerate changing precipitation and N deposition in subtropical plantations.

Differential responses of soil extracellular enzyme activity and stoichiometry to precipitation changes in a poplar plantation

Changes in precipitation patterns can significantly affect belowground processes. Although soil extracellular enzymes play a vital role in several biogeochemical processes, our knowledge of how precipitation changes affect soil extracellular enzyme activity (EEA) and stoichiometry remains insufficient. In this study, we investigated the activities of C-acquiring enzyme (β-1,4-glucosidase), N-acquiring enzymes (β-N-acetylglucosaminidase and leucine aminopeptidase), and P-acquiring enzyme (acid phosphatase) under different precipitation scenarios [ambient precipitation (CK), 30% decrease in precipitation (moderate DPT), 50% decrease in precipitation (extreme DPT), 30% increase in precipitation (moderate IPT), and 50% increase in precipitation (extreme IPT)] in a poplar plantation. We found soil EEA exhibited more pronounced increases to moderate IPT compared to moderate DPT (positive asymmetry), the opposite trend (negative asymmetry) was observed under extreme precipitation; whereas soil EEA C:N:P stoichiometry exhibited negative asymmetry at moderate precipitation changes, and exhibited positive asymmetry at extreme precipitation changes. Under moderate precipitation changes, the asymmetry of soil EEA was mainly regulated by asymmetries of respective microbial biomass and litter mass; the asymmetry of soil EEA stoichiometry was mainly regulated by asymmetries of respective soil stoichiometric ratios and litter mass. Furthermore, under extreme precipitation changes, the asymmetries of soil EEA and stoichiometry were best explained by the asymmetry of soil moisture. Our results provide the first evidence of double asymmetric responses of soil EEA and stoichiometry to precipitation changes and highlight the need to consider this asymmetry when modeling the dynamics of biogeochemical cycling in forest ecosystems.

Fungal necromass is reduced by intensive drought in subsoil but not in topsoil

The frequency and intensity of droughts worldwide are challenging the conservation of soil organic carbon (SOC) pool. Microbial necromass is a key component of SOC, but how it responds to drought at specific soil depths remains largely unknown. Here, we conducted a 3-year field experiment in a forest plantation to investigate the impacts of drought intensities under three treatments (ambient control [CK], moderate drought [30% throughfall removal], and intensive drought [50% throughfall removal]) on soil microbial necromass pools (i.e., bacterial necromass carbon, fungal necromass carbon, and total microbial necromass carbon). We showed that the effects of drought on microbial necromass depended on microbial groups, soil depth, and drought intensity. While moderate drought increased total (+9.1% ± 3.3%) and fungal (+13.5% ± 4.9%) necromass carbon in the topsoil layer (0-15 cm), intensive drought reduced total (-31.6% ± 3.7%) and fungal (-43.6% ± 4.0%) necromass in the subsoil layer (15-30 cm). In contrast, both drought treatments significantly increased the BNC in the topsoil and subsoil. Our results suggested that the effects of drought on the microbial necromass of the subsoil were more pronounced than those of the topsoil. This study highlights the complex responses of microbial necromass to drought events depending on microbial community structure, drought intensity and soil depth with global implications when forecasting carbon cycling under climate change.

Impact of drought on soil microbial biomass and extracellular enzyme activity

Introduction

With the continuous changes in climate patterns due to global warming, drought has become an important limiting factor in the development of terrestrial ecosystems. However, a comprehensive understanding of the impact of drought on soil microbial activity at a global scale is lacking.

Methods

In this study, we aimed to examine the effects of drought on soil microbial biomass (carbon [MBC], nitrogen [MBN], and phosphorus [MBP]) and enzyme activity (β-1, 4-glucosidase [BG]; β-D-cellobiosidase [CBH]; β-1, 4-N-acetylglucosaminidase [NAG]; L-leucine aminopeptidase [LAP]; and acid phosphatase [AP]). Additionally, we conducted a meta-analysis to determine the degree to which these effects are regulated by vegetation type, drought intensity, drought duration, and mean annual temperature (MAT).

Result and discussion

Our results showed that drought significantly decreased the MBC, MBN, and MBP and the activity levels of BG and AP by 22.7%, 21.2%, 21.6%, 26.8%, and 16.1%, respectively. In terms of vegetation type, drought mainly affected the MBC and MBN in croplands and grasslands. Furthermore, the response ratio of BG, CBH, NAG, and LAP were negatively correlated with drought intensity, whereas MBN and MBP and the activity levels of BG and CBH were negatively correlated with drought duration. Additionally, the response ratio of BG and NAG were negatively correlated with MAT. In conclusion, drought significantly reduced soil microbial biomass and enzyme activity on a global scale. Our results highlight the strong impact of drought on soil microbial biomass and carbon- and phosphorus-acquiring enzyme activity.

Temporal Changes in Litterfall and Nutrient Cycling from 2005-2015 in an Evergreen Broad-Leaved Forest in the Ailao Mountains, China

The study of litter can provide an important reference for understanding patterns of forest nutrient cycling and sustainable management. Here, we measured litterfall (leaves, branches, etc.) from a wet, evergreen, broad-leaved forest in Ailao Mountains of southwestern China on a monthly basis for 11 years (2005-2015). We measured the total biomass of litter fall as well as its components, and estimated the amount of C, N, P, K, S, Ca, and Mg in the amount of litterfall. We found that: The total litter of evergreen, broadleaved forest in Ailao Mountains from 2005 to 2015 was 7.70-9.46 t/ha, and the output of litterfall differed between years. This provides a safeguard for the soil fertility and biodiversity of the area. The total amount of litterfall and its components showed obvious seasonal variation, with most showing a bimodal pattern (peak from March to May and October to November). The majority of litterfall came from leaves, and the total amount as well as its components were correlated with meteorological factors (wind speed, temperate and precipitation) as well as extreme weather events. We found that among years, the nutrient concentration was sorted as C > Ca > N > K > Mg > S > P. The nutrient concentration in the fallen litter and the amount of nutrients returned showed a decreasing trend, but the decreasing rate was slowed through time. Nutrient cycling was influenced by meteorological factors, such as temperature, precipitation, and wind speed, but the nutrient utilization efficiency is high, the circulation capacity is strong, and the turnover time is short. Our results showed that although there was nutrient loss in this evergreen, broad-leaved forest, the presence of forest litterfall can effectively curb potential ecological problems in the area.