Forest soils are a sink for atmospheric methane (CH) and play an important role in modulating the global CH budget. However, whether CH uptake by forest soils is affected by global environmental change is unknown. We measured soil to atmosphere net CH fluxes in temperate forests at two long-term ecological research sites in the northeastern United States from the late 1990s to the mid-2010s. We found that annual soil CH uptake decreased by 62% and 53% in urban and rural forests in Baltimore, Maryland and by 74% and 89% in calcium-fertilized and reference forests at Hubbard Brook, New Hampshire over this period. This decrease occurred despite marked declines in nitrogen deposition and increases in atmospheric CH concentration and temperature, which should lead to increases in CH uptake. This decrease in soil CH uptake appears to be driven by increases in precipitation and soil hydrological flux. Furthermore, an analysis of CH uptake around the globe showed that CH uptake in forest soils has decreased by an average of 77% from 1988 to 2015, particularly in forests located from 0 to 60 °N latitude where precipitation has been increasing. We conclude that the soil CH sink may be declining and overestimated in several regions across the globe.

Spatiotemporal redistribution of incident rainfall in vegetated ecosystems results from the partitioning by plants into intercepted, stemflow, and throughfall fractions. However, variation in patterns and drivers of rainfall partitioning across global biomes remains poorly understood, which limited the ability of climate models to improve the predictions of biome hydrological cycle under global climate change scenario. Here, we synthesized and analyzed the partitioning of incident rainfall into interception, stemflow, and throughfall by trees and shrubs at the global scale using 2430 observations from 236 independent publications. We found that (1) globally, median levels of relative interception, stemflow, and throughfall accounted for 21.8%, 3.2%, and 73.0% of total incident rainfall, respectively; (2) rainfall partitioning varied among different biomes, due to variation in plant composition, canopy structure, and macroclimate; (3) relative stemflow tended to be driven by plant traits, such as crown height:width ratio, basal area, and height, while relative interception and throughfall tended to be driven by plant traits as well as meteorological variables. Our global assessment of patterns and drivers of rainfall partitioning underpins the role of meteorological factors and plant traits in biome‐specific ecohydrological cycles. We suggest to include these factors in climate models to improve the predictions of local hydrological cycles and associated biodiversity and function responses to changing climate conditions.

Aim Forest soils contain large amounts of terrestrial organic carbon (C), but the formation pathway of soil organic C (SOC) remains unclear. Recent evidence suggests that microbial necromass is a significant source of SOC, yet a global quantitative assessment across the whole soil profile is lacking. We aimed to assess the vertical distribution and control of microbial‐derived SOC in forest soils. Location Global forests. Time period 1996–2019. Major taxa studied Soil microbial necromass carbon. Methods We evaluated the proportions of fungal and bacterial necromass C in total SOC in the litter layer, O horizon soil, and various depths of mineral soil in forests using microbial biomarker (glucosamine and muramic acid) data. Results The total microbial necromass C increased significantly with soil depth, ranging from 30% of SOC in O horizon soil to 62% of SOC in mineral soils below 50 cm. However, only bacterial necromass C followed this increasing trend with soil depth; fungal necromass C showed little variation across the whole soil profile. Higher fungal and bacterial necromass C was observed in soils with lower C/N ratios and smaller aggregate sizes. Soil C/N ratio and microbial biomass C dominantly determined microbial necromass C in surface soil (above 20 cm), but soil clay content was the primary factor in subsoil (below 20 cm). Main conclusions Microbial necromass C accounted for high percentages of the total SOC in forest soils (particularly at depths >20 cm), but its long‐term stabilization may be governed by different mechanisms at different soil horizons. Substrate quality regulates microbial activity and then controls biomass turnover in surface soil, while aggregate occlusion facilitates mineral protection of microbial necromass C in subsoil. These differential controls of microbial‐derived organic C could be applied in Earth system studies for predicting soil organic C dynamics in forests.

Nitrogen (N) deposition has increased globally and has profoundly influenced the structure and function of grasslands. Previous studies have discussed how N addition affects aboveground biomass (AGB), but the effects of N addition on the AGB of different functional groups in grasslands remain unclear. We conducted a meta-analysis to identify the responses of AGB and the AGB of grasses (AGB grass ) and forbs (AGB forb ) to N addition across global grasslands. Our results showed that N addition significantly increased AGB and AGB grass by 31 and 79%, respectively, but had no significant effect on AGB forb . The effects of N addition on AGB and AGB grass increased with increasing N addition rates, but which on AGB forb decreased. Although study durations did not regulate the response ratio of N addition for AGB, which for AGB grass increased and for AGB forb decreased with increasing study durations. Furthermore, the N addition response ratios for AGB and AGB grass increased more strongly when the mean annual precipitation (MAP) was 300-600 mm but decreased with an increase in the mean annual temperature (MAT). AGB forb was only slightly affected by MAP and MAT. Our findings suggest that an acceleration of N deposition will increase grassland AGB by altering species composition.Nitrogen (N) deposition in terrestrial ecosystems is estimated to increase to 200 Tg N yr −1 by 2050 due to industrial and agricultural N fertilizer use 1 . Nitrogen enrichment will potentially influence species diversity, biomass production and soil conditions 2-6 . The effects of N addition on forest ecosystem biomass have been summarized and analysed in previous studies 7-9 . However, because grasslands are mainly controlled by water, the effects of changes in precipitation patterns on aboveground biomass (AGB) were emphasized in previous studies [10][11][12] , and the effects of N addition on grassland biomass remain unknown. Grasslands are a type of terrestrial ecosystem and cover approximately 25% of the land surface on Earth 13 . AGB is an important contributor to soil organic matter, which significantly impacts the global carbon cycle under the background of N deposition 14,15 . Therefore, analysing and summarizing the effects of N addition on grassland AGB are particularly important for estimating and predicting the carbon budget under climate change.Many case studies that have been conducted to understand how N addition (N deposition) affects grassland AGB have yielded significantly different results 2, 16-18 . For example, several studies have reported significant increases 2,18,19 and decreases 17 or insignificant changes in AGB 16,20 following N addition. The differences between these results may be attributed to the use of different N addition rates, study durations, plant functional types and climatic conditions (such as the mean annual precipitation (MAP) or the mean annual temperature (MAT)). For instance, some previous studies have demonstrated a threshold value for the positive effects of N addition on AGB 2,21 . If N appl...

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