Soil net nitrogen (N) mineralization (N ) is a pivotal process in the global N cycle regulating the N availability of plant growth. Understanding the spatial patterns of N its temperature sensitivity (Q ) and regulatory mechanisms is critical for improving the management of soil nutrients. In this study, we evaluated 379 peer-reviewed scientific papers to explore how N and the Q of N varied among different ecosystems and regions at the global scale. The results showed that N varied significantly among different ecosystems with a global average of 2.41 mg N soil kg day . Furthermore, N significantly decreased with increasing latitude and altitude. The Q varied significantly among different ecosystems with a global average of 2.21, ranging from the highest found in forest soils (2.43) and the lowest found for grassland soils (1.67) and significantly increased with increasing latitude. Path analyses indicated that N was primarily affected by the content of soil organic carbon (C), soil C:N ratio, and clay content, where Q was primarily influenced by the soil C:N ratio and soil pH. Furthermore, the activation energy (E ) of soil N mineralization was significantly and negative correlated with the substrate quality index among all ecosystems, indicating the applicability of the carbon quality temperature hypothesis to soil N mineralization at a global scale. These findings provided empirical evidence supporting that soil N availability, under global warming scenarios, is expected to increase stronger in colder regions as compared with that low-latitude regions due to the higher Q . This may alleviate the restriction of N supply for increased primary productivity at higher latitudes.

Abstract1. Bacteria are one of the most abundant and diverse groups of micro-organisms and mediate many critical terrestrial ecosystem processes. Despite the crucial ecological role of bacteria, our understanding of their large-scale biogeography patterns across forests, and the processes that determine these patterns lags significantly behind that of macroorganisms.2. Here, we evaluated the geographic distributions of bacterial diversity and their driving factors across nine latitudinal forests along a 3,700-km north-south transect in eastern China, using high-throughput 16S rRNA gene sequencing.3. Four of 32 phyla detected were dominant: Acidobacteria, Actinobacteria, Alphaproteobacteria and Chloroflexi (relative abundance > 5%). Significant increases in bacterial richness and phylogenetic diversity were observed for temperate forests compared with subtropical or tropical forests. The soil organic matter (SOM) mineralisation rate (SOM min , an index of SOM availability) explained the largest significant variations in bacterial richness. Variation partition analysis revealed that the bacterial community structure was closely correlated with environmental variables and geographic distance, which together explained 80.5% of community variation. Among all environmental factors, climatic features (MAT and MAP) were the best predictors of the bacterial community structure, whereas soil pH and SOM min emerged as the most important edaphic drivers of the bacterial community structure. Plant functional traits (community weighted means of litter N content) and diversity resulted in weak but significant correlations with the bacterial community structure.4. Our findings provide new evidence of bacterial biogeography patterns from tropical to cold temperate forests. Additionally, the results indicated a close linkage among soil bacterial diversity, climate and SOM decomposition, which is critical for

How to assess the temperature sensitivity (Q ) of soil organic matter (SOM) decomposition and its regional variation with high accuracy is one of the largest uncertainties in determining the intensity and direction of the global carbon (C) cycle in response to climate change. In this study, we collected a series of soils from 22 forest sites and 30 grassland sites across China to explore regional variation in Q and its underlying mechanisms. We conducted a novel incubation experiment with periodically changing temperature (5-30 °C), while continuously measuring soil microbial respiration rates. The results showed that Q varied significantly across different ecosystems, ranging from 1.16 to 3.19 (mean 1.63). Q was ordered as follows: alpine grasslands (2.01) > temperate grasslands (1.81) > tropical forests (1.59) > temperate forests (1.55) > subtropical forests (1.52). The Q of grasslands (1.90) was significantly higher than that of forests (1.54). Furthermore, Q significantly increased with increasing altitude and decreased with increasing longitude. Environmental variables and substrate properties together explained 52% of total variation in Q across all sites. Overall, pH and soil electrical conductivity primarily explained spatial variation in Q . The general negative relationships between Q and substrate quality among all ecosystem types supported the C quality temperature (CQT) hypothesis at a large scale, which indicated that soils with low quality should have higher temperature sensitivity. Furthermore, alpine grasslands, which had the highest Q , were predicted to be more sensitive to climate change under the scenario of global warming.