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1. Microbial biomass in forest soils under altered moisture conditions: A review

   https://doi.org/10.1002/saj2.20344  

   Ni, Xiangyin; Liao, Shu; Wu, Fuzhong; Groffman, Peter_M (January 2022, Soil Science Society of America Journal)

   Abstract Microbial biomass is known to decrease with soil drying and to increase after rewetting due to physiological assimilation and substrate limitation under fluctuating moisture conditions, but how the effects of changing moisture conditions vary between dry and wet environments is unclear. Here, we conducted a meta‐analysis to assess the effects of elevated and reduced soil moisture on microbial biomass C (MBC) and microbial biomass N (MBN) across a broad range of forest sites between dry and wet regions. We found that the influence of both elevated and reduced soil moisture on MBC and MBN concentrations in forest soils was greater in dry than in wet regions. The influence of altered soil moisture on MBC and MBN concentrations increased significantly with the manipulation intensity but decreased with the length of experimental period, with a dramatic increase observed under a very short‐term precipitation pulse. Moisture effect did not differ between coarse‐textured and fine‐textured soils. Precipitation intensity, experimental duration, and site standardized precipitation index (dry or wet climate) were more important than edaphic factors (i.e., initial water content, bulk density, and clay content) in determining microbial biomass in response to altered moisture in forest soils. Different responses of microbial biomass in forest soils between dry and wet regions should be incorporated into models to evaluate how changes in the amount, timing, and intensity of precipitation affect soil biogeochemical processes. 

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2. Effects of precipitation changes on soil heterotrophic respiration and microbial activities in a switchgrass mesocosm experiment

   https://doi.org/10.1016/j.ejsobi.2024.103602  

   Dai, Wei; Parajuli, Madhav; Jian, Siyang; Hui, Dafeng; Fay, Philip; Li, Jianwei (March 2024, European Journal of Soil Biology)

   Precipitation changes altered soil heterotrophic respiration, but the underlying microbial mechanisms remain rarely studied. This study conducted three-year switchgrass (Panicum virgatum L.) mesocosm experiment to investigate soil heterotrophic respiratory responses to altered precipitation. Five treatments were considered, including ambient precipitation (P0), two wet treatments (P+33 and P+50: 33% and 50% enhancement relative to P0), and two drought treatments (P-33 and P-50: 33% and 50% reduction relative to P0). The plant’s aboveground biomass (AGB), soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon (MBC), heterotrophic respiration (Rs), biomass-specific respiration (Rss: respiration per unit of microbial biomass as a reciprocal index of microbial growth efficiency), and extracellular enzymes activities (EEAs) were quantified in soil samples (0–15 cm). Despite significantly different soil moisture contents among treatments, results showed no impact of precipitation treatments on SOC and TN. Increasing precipitation had no effect, but decreasing precipitation significantly reduced plant AGB. Relative to P0, P+33 significantly increased Rs by more than 3-fold and caused no changes in MBC, leading to significantly higher Rss (P < 0.05). P+33 also significantly increased hydrolytic enzyme activities associated with labile carbon acquisition (Cacq) by 115%. The only significant effect of drought treatments was the decreased β-D-cellobiosidase (CBH) and peroxidase (PEO) under P-33. Nonparametric analyses corroborated the strong influences of moisture and CBH on the enhanced precipitation, which stimulated soil respiratory carbon loss, likely driven by both elevated hydrolase activities and reduced microbial growth efficiency. However, the less sensitive drought effects suggested potential microbial tolerance to water deficiency despite depressed plant growth. This study informs the likely decoupled impacts of microbes and plants on soil heterotrophic respiration under changing precipitation in the switchgrass mesocosm experiment. 

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3. Determination of carbon and microbial biomass amounts in neglected urban pavement crevice soils

   https://doi.org/10.1016/j.scitotenv.2025.180921  

   Manu, Matthew; Gamage, Lahiru; Pandey, Aviyan; Li, Jianwei (December 2025, Science of The Total Environment)

   Urbanization is causing soil sealing and ecosystem fragmentation, affecting soil health, biodiversity, and carbon storage potential. While green infrastructure is being promoted to address these challenges, small-scale habitats such as urban crevice soils (UCSs), referred to as soils in the gaps between concrete and asphalt surfaces in heavily urbanized areas, remain overlooked. The aim of this study was to determine whether UCSs are advantageous ecological units that sustain microbiological life and perform ecosystem services. This study quantified soil heterotrophic respiration, microbial biomass carbon (MBC) and nitrogen (MBN), soil organic carbon (SOC) and inorganic carbon (SIC), and total nitrogen (TN) in UCSs (with and without plants), nearby roadside soils, and soils from a switchgrass cropland in an urban farm within the Nashville metropolitan area in Tennessee, USA. On average, UCSs exhibited up to 436.2 %, 59.4 %, 217.6 %, and 266.9 % higher SOC, MBC, MBN, and C/N ratio compared to roadside and switchgrass soils, respectively. UCSs with plants have the highest microbial biomass, highlighting the synergistic role of plant presence in enhancing microbial function. These findings challenge the belief that urban soils are universally degraded and biologically inert, and regard UCSs as dispersed, small-scale contributors to urban ecosystem services. UCSs could serve as scalable, low-cost nature-based solutions that support resilient and sustainable cities amid rapid urbanization and environmental stress. Future studies should evaluate the ecological potential of UCSs as microhabitats for microbial biodiversity conservation, carbon storage, and ecosystem service delivery across various cities of different scales. 

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4. Consistent microbial and nutrient resource island patterns during monsoon rain in a Chihuahuan Desert bajada shrubland

   https://doi.org/10.1002/ecs2.4475  

   Darrouzet‐Nardi, Anthony; Asaff, Isabel Siles; Mauritz, Marguerite; Roman, Kathleen; Keats, Eleanor; Tweedie, Craig E.; McLaren, Jennie R. (April 2023, Ecosphere)

   Abstract In dryland soils, spatiotemporal variation in surface soils (0–10 cm) plays an important role in the function of the “critical zone” that extends from canopy to groundwater. Understanding connections between soil microbes and biogeochemical cycling in surface soils requires repeated multivariate measurements of nutrients, microbial abundance, and microbial function. We examined these processes in resource islands and interspaces over a two‐month period at a Chihuahuan Desert bajada shrubland site. We collected soil inProsopis glandulosa(honey mesquite),Larrea tridentata(creosote bush), and unvegetated (interspace) areas to measure soil nutrient concentrations, microbial biomass, and potential soil enzyme activity. We monitored the dynamics of these belowground processes as soil conditions dried and then rewetted due to rainfall. Most measured variables, including inorganic nutrients, microbial biomass, and soil enzyme activities, were greater under shrubs during both wet and dry periods, with the highest magnitudes under mesquite followed by creosote bush and then interspace. One exception was nitrate, which was highly variable and did not show resource island patterns. Temporally, rainfall pulses were associated with substantial changes in soil nutrient concentrations, though resource island patterns remained consistent during all phases of the soil moisture pulse. Microbial biomass was more consistent than nutrients, decreasing only when soils were driest. Potential enzyme activities were even more consistent and did not decline in dry periods, potentially helping to stimulate observed pulses in CO₂efflux following rain events observed at a co‐located eddy flux tower. These results indicate a critical zone with organic matter cycling patterns consistently elevated in shrub resource islands (which varied by shrub species), high decomposition potential that limits soil organic matter accumulation across the landscape, and nitrate fluxes that are decoupled from the organic matter pathways. 

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5. Nitrogen Availability and Changes in Precipitation Alter Microbially Mediated NO and N₂O Emissions From a Pinyon–Juniper Dryland

   https://doi.org/10.1111/gcb.70159  

   Zhao, Sharon; Krichels, Alexander_H; Stephens, Elizah_Z; Calma, Anthony_D; Aronson, Emma_L; Jenerette, G_Darrel; Spasojevic, Marko_J; Schimel, Joshua_P; Hanan, Erin_J; Homyak, Peter_M (March 2025, Global Change Biology)

   ABSTRACT Climate change is altering precipitation regimes that control nitrogen (N) cycling in terrestrial ecosystems. In ecosystems exposed to frequent drought, N can accumulate in soils as they dry, stimulating the emission of both nitric oxide (NO; an air pollutant at high concentrations) and nitrous oxide (N₂O; a powerful greenhouse gas) when the dry soils wet up. Because changes in both N availability and soil moisture can alter the capacity of nitrifying organisms such as ammonia‐oxidizing bacteria (AOB) and archaea (AOA) to process N and emit N gases, predicting whether shifts in precipitation may alter NO and N₂O emissions requires understanding how both AOA and AOB may respond. Thus, we ask: How does altering summer and winter precipitation affect nitrifier‐derived N trace gas emissions in a dryland ecosystem? To answer this question, we manipulated summer and winter precipitation and measured AOA‐ and AOB‐derived N trace gas emissions, AOA and AOB abundance, and soil N concentrations. We found that excluding summer precipitation increased AOB‐derived NO emissions, consistent with the increase in soil N availability, and that increasing summer precipitation amount promoted AOB activity. Excluding precipitation in the winter (the most extreme water limitation we imposed) did not alter nitrifier‐derived NO emissions despite N accumulating in soils. Instead, nitrate that accumulated under drought correlated with high N₂O emission via denitrification upon wetting dry soils. Increases in the timing and intensity of precipitation that are forecasted under climate change may, therefore, influence the emission of N gases according to the magnitude and season during which the changes occur. 

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