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Background: Microbial residues are significant contributors to stable soil organic carbon (SOC). Soil aggregates effectively protect microbial residues against decomposition; thus, microbial residue accumulation and distribution among soil aggregates determine long-term SOC stability. However, how tree species influence accumulation and distribution of soil microbial residues remains largely unknown, hindering the chances to develop policies for SOC management. Here, we investigated microbial residue accumulation and distribution in soil aggregates under four subtropical tree species (Cunninghamia lanceolata, Pinus massoniana, Michelia macclurei, and Schima superba) after 29 years of afforestation. Results: Accumulation of microbial residues in the 0–10 cm soil layer was 13.8–26.7% higher under S. superba than that under the other tree species. A structural equation model revealed that tree species affected the accumulation of microbial residues directly by altering fungal biomass. Additionally, tree species significantly affected microbial residue distribution and contribution to SOC in the top 20 cm soil. In particular, microbial residue distribution was 17.2–33.4% lower in large macro-aggregates (LMA) but 60.1–140.7% higher in micro-aggregates (MA) under S. superba than that under the other species in the 0–10 cm soil layer, and 14.3–19.0% lower in LMA but 43–52.1% higher in MA under S. superba than that under C. lanceolata and M. macclurei in the 10–20 cm soil layer. Moreover, the contribution of microbial residues to SOC was 44.4–47.5% higher under S. superba than under the other tree species. These findings suggest a higher stability of microbial residues under S. superba than that under the other studied tree species. Conclusions: Our results demonstrate that tree species influence long-term microbial persistence in forest soils by affecting accumulation and stabilization of microbial residues. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) decomposition, a key process controlling the carbon (C) loss from terrestrial soils to the atmosphere, varies with soil aggregate size and is influenced by increasing nitrogen (N) and phosphorus (P) inputs from anthropogenic activities. However, how increasing N and P affects SOC decomposition and its temperature sensitivity (Q10) in soil aggregates remains unclear. Thus, we collected soils from a subtropical Cunninghamia lanceolata forest receiving N and P addition for 8 years to explore the interactive effects of N and P fertilization on SOC decomposition and its Q10 in mega-aggregates (>2 mm, MeA), macroaggregates (0.25–2.0 mm, MaA), and microaggregates (<0.25 mm, MiA). Results showed that aggregate size has a huge influence on SOC decomposition and its Q10. Specifically, SOC decomposition in MiA is 49.2% and 26.0% higher than MeA and MaA, respectively. Moreover, the averaged Q10 values were 2.29, 2.26 and 1.83 in MeA, MaA and MiA. SOC decomposition significantly increased by 39.4% in MaA and 23.7% in MiA with N fertilization, but P fertilization had less impact. However, P fertilization increased Q10 by 46.7% in MeA and 46.6% in MaA. Furthermore, we found P fertilization changed the influences of N fertilization on SOC decomposition in MaA and MiA but had no effect on responses of Q10 to N fertilization. Overall, our findings suggested that there were differences in SOC decomposition and Q10 among aggregates, and fertilization treatment had an impact on them. Our results highlighted the significance of considering differences in SOC decomposition and its response to climate warming and nutrient input among different aggregates in the prediction of SOC dynamics and its feedback to environmental changes in terrestrial ecosystems under climate warming scenarios. [ABSTRACT FROM AUTHOR]

The replenishment and priming effect (PE) are two decisive processes that determine the carbon (C) sequestration potential of biochar. However, how increased nitrogen (N) availability affect these two processes and the consequent net C balance remains poorly understood. By collecting soils from three forest ecosystems (deciduous broad-leaf forest (DBF), evergreen coniferous forest (ECF), and evergreen broad-leaf forest (EBF)), we conducted a 365-day incubation experiment by adding 13C-labelled biochar plus five rates of inorganic N (0 to 15% N of soil total N). The -results showed that N addition significantly stimulated the early period (0–48 days) but did not affect the late period (49–365 days) of biochar decomposition. The effect of N addition on PE varied largely with the forest type and decomposition period; N addition significantly enhanced the negative PE -in both periods in DBF and at the late period in EBF, whereas it stimulated positive PE in the early period in EBF and ECF. At the end of incubation, the addition of biochar caused net C accumulation across all treatments due to the huge proportion of biochar (98.1%–98.9% of added biochar) retained in soils and the negative or neutral cumulative PE (−11.25–0.35 g C kg−1 SOC), and the magnitude of net C balance increased linearly with the N addition rate in DBF and EBF. Collectively, the results of this study indicate that biochar input can contribute to soil C sequestration and that N addition can enhance the C sequestration potential of biochar. [ABSTRACT FROM AUTHOR]

Soil heterotrophic respiration (Rh) is an important pathway of carbon (C) dioxide release from terrestrial soils to the atmosphere. It is often measured using sieved soil in a laboratory, but the uncertainty of how it is influenced by soil sieving persists, which limits the accuracy of predicting soil organic C dynamics in C models. To address how soil sieving during laboratory incubation affects Rh and its response to increased carbon availability, we investigated Rh in sieved and intact soil cores and its response to 13C-glucose addition. This was conducted through a 27-day laboratory incubation in four forests, including two ectomycorrhizal-dominated (ECM) forests and two arbuscular mycorrhizal-dominated forests. The significant influence of soil sieving on Rh in all forests was not observed during incubation when glucose was not added. After adding glucose, the Rh in the sieved soils on the 5th day of incubation was averaged 27.2% lower than that in intact soils in ECM forests. On the 27th day it was 22.1% lower in the Pinus massoniana forest, but 78.0% higher in the Castanea mollissima forest. Strong relationships were detected between Rh in sieved and intact soils (r2 = 0.888), and in soils both with and without the addition of glucose (r2 = 0.827). The measured soil variables explained 74.7% and 49.7% of the variation in Rh on the 5th and 27th day of incubation, and the role of soil nutrients and microbial PLFA groups in regulating Rh varied temporally. Our findings suggest that plant mycorrhizal types influenced the role of increased C availability to microbes in regulating the response of Rh to sieving in forest ecosystems. [ABSTRACT FROM AUTHOR]

The mineralization of soil organic carbon (SOC) is generally stimulated under global warming, known as temperature sensitivity (Q10), which is critical for predicting terrestrial C-climate feedback. However, how Q10 varies in different elevations, particularly with litter input, constraining the establishment of accurate models remains poorly understood. Here, the soil samples of three elevations (750, 950, and 1150 m) were collected from the transition zone of subtropical and warm temperate forests in China for incubation. Soils were incubated with and without 13C-labeled Cunninghamia lanceolata litter at 15 °C and 17.4 °C for 97 days. Incubation process was divided into two stages (0–37 days and 38–97 days) according to the dynamics of CO2 emission. The results showed that Q10 did not change significantly with elevation in the first stage, but Q10 at 950 m was significantly higher than that at 1150 m in the second stage. The variations in Q10 with elevation were regulated by pH in the first stage, while soil C/N was the primary factors that regulated Q10 in the second stage. Q10 showed no response to litter input at 750 m, while it decreased at 950 m in both stages. Following litter input, Q10 at 1150 m increased in the first stage but kept stable in the second stage. The change in Q10 with litter input was mainly affected by the restriction of soil P availability. Overall, our findings emphasized the importance of vertical spatial heterogeneity of Q10 of SOC mineralization in order to improve the prediction accuracy of C dynamics in terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

• The priming effect was strengthened by low nitrogen deposition whereas inhibited by high nitrogen deposition, with a threshold of 50 kg ha−1 yr−1 in temperate forests. • No nitrogen deposition effect on the priming effect was found in subtropical forests. • The alterations in priming effect under N deposition were separately controlled by recalcitrant organic carbon content and the ratio of fungal to bacterial PLFA in temperate and subtropical forests. • A stronger role of fungi in priming soil organic carbon decomposition was revealed in subtropical forests. The priming effect (PE) of soil organic carbon (SOC) decomposition has been widely demonstrated to be affected by elevated nitrogen (N) deposition, yet the response of the PE to N deposition in diverse climatic regions remains elusive. This study aimed at exploring the effects of N deposition on the PE and their controlling factors in temperate and subtropical forest ecosystems. We conducted an incubation experiment with temperate and subtropical forest soils that had been experimentally exposed to varying levels of N deposition. A global meta -analysis of the responses of the PE to N deposition in forest ecosystems was also conducted. We found that the response of the PE to increasing N deposition depended on the climatic region. In temperate forests, the PE was strengthened by low N deposition whereas inhibited by high N deposition, with an approximate threshold of 50 kg N ha−1 yr−1. Contrastingly, no pronounced impact was observed in subtropical forests regardless of N levels. These findings generally align with our meta -analysis of global forest studies, except for low N treatment in temperate forests. In N-limited temperate forests, the alterations in PE under N deposition were primarily controlled by soil recalcitrant organic carbon content. Conversely, in P-limited subtropical forests, the lack of N impacts on PE was attributed to the persistent ratio of fungal to bacterial PLFA. Correspondingly, the microbial mechanisms underlying the process of priming also varied in diverse climatic regions, particularly emphasizing the stronger role of fungi in subtropical forests. These results highlight the noteworthy alteration of SOC dynamics in temperate forests under increasing N deposition, and suggest that previous findings might have overestimated the effect of N deposition on the PE in subtropical forests. [ABSTRACT FROM AUTHOR]

Background: Inputs of above- and belowground litter into forest soils are changing at an unprecedented rate due to continuing human disturbances and climate change. Microorganisms drive the soil carbon (C) cycle, but the roles of above- and belowground litter in regulating the soil microbial community have not been evaluated at a global scale. Methods: Here, we conducted a meta-analysis based on 68 aboveground litter removal and root exclusion studies across forest ecosystems to quantify the roles of above- and belowground litter on soil microbial community and compare their relative importance. Results: Aboveground litter removal significantly declined soil microbial biomass by 4.9% but root exclusion inhibited it stronger, up to 11.7%. Moreover, the aboveground litter removal significantly raised fungi by 10.1% without altering bacteria, leading to a 46.7% increase in the fungi-to-bacteria (F/B) ratio. Differently, root exclusion significantly decreased the fungi by 26.2% but increased the bacteria by 5.7%, causing a 13.3% decrease in the F/B ratio. Specifically, root exclusion significantly inhibited arbuscular mycorrhizal fungi, ectomycorrhizal fungi, and actinomycetes by 22.9%, 43.8%, and 7.9%, respectively. The negative effects of aboveground litter removal on microbial biomass increased with mean annual temperature and precipitation, whereas that of root exclusion on microbial biomass did not change with climatic factors but amplified with treatment duration. More importantly, greater effects of root exclusion on microbial biomass than aboveground litter removal were consistent across diverse forest biomes (expect boreal forests) and durations. Conclusions: These data provide a global evidence that root litter inputs exert a larger control on microbial biomass than aboveground litter inputs in forest ecosystems. Our study also highlights that changes in above- and belowground litter inputs could alter soil C stability differently by shifting the microbial community structure in the opposite direction. These findings are useful for predicting microbe-mediated C processes in response to changes in forest management or climate. [ABSTRACT FROM AUTHOR]

Optimal methods for incorporating soil microbial mechanisms of carbon (C) cycling into Earth system models (ESMs) are still under debate. Specifically, whether soil microbial physiology parameters and residual materials are important to soil organic C (SOC) content is still unclear. Here, we explored the effects of biotic and abiotic factors on SOC content based on a survey of soils from 16 locations along a ~4000 km forest transect in eastern China, spanning a wide range of climate, soil conditions, and microbial communities. We found that SOC was highly correlated with soil microbial biomass C (MBC) and amino sugar (AS) concentration, an index of microbial necromass. Microbial C use efficiency (CUE) was significantly related to the variations in SOC along this national‐scale transect. Furthermore, the effect of climatic and edaphic factors on SOC was mainly via their regulation on microbial physiological properties (CUE and MBC). We also found that regression models on explanation of SOC variations with microbial physiological parameters and AS performed better than the models without them. Our results provide the empirical linkages among climate, microbial characteristics, and SOC content at large scale and confirm the necessity of incorporating microbial biomass and necromass pools in ESMs under global change scenarios. [ABSTRACT FROM AUTHOR]

Background and aims: Priming effect (PE) of soil organic carbon (SOC) decomposition induced by exogenous organic C is an important ecological process in regulating the soil C cycle. The objective of this study was to evaluate how the PE varied among different ecosystems at the global scale and explore factors that drive the direction and magnitude of the PE. Methods: Using 2048 experimental comparisons compiled from 94 incubation studies with stable (13C) or radioactive (14C) carbon isotopic techniques, we performed a meta-analysis on the effect of exogenous organic C input on native SOC decomposition (i.e., PE) across multiple terrestrial ecosystems. In particular, the linear mixed-effect model was used to examine the relationship between the PE and potential influencing factors. Results: The addition of exogenous organic C significantly enhanced native SOC decomposition by 47.5% (i.e., positive PE), with the highest value in cropland soils (60.9%) and the lowest value in forest soils (26.2%). The intensity of the PE decreased with increasing SOC content, soil total nitrogen content, soil C/N, incubation duration, and incubation temperature, but increased with increasing exogenous organic C addition rate and soil pH. Soil PE was not affected by the complexity of exogenous organic C. Conclusions: Our results indicate that positive PE is a widespread phenomenon in terrestrial ecosystems, and that the magnitude is closely related to soil properties and experimental conditions. These findings may be useful for understanding soil C priming and the effect on soil C balance under climate change scenarios. [ABSTRACT FROM AUTHOR]

Increasing nitrogen (N) deposition may alter soil organic carbon (SOC) decomposition, thereby strongly affecting SOC storage in terrestrial ecosystems. Its specific influence may depend on the different types of N deposition and soil nematodes. However, little is known about how N deposition and soil nematodes affect the SOC cycle process. To address this issue, we evaluated the effects of different types of N deposition on SOC decomposition under the conditions of applying nematocide or not in a temperate forest. Soils collected from the simulated N deposition forest for 5 years were incubated in the presence and absence of soil nematocide at 15 °C for 150 days. N deposition suppressed soil C cycle processes, such as SOC decomposition and soil enzyme activities, and caused the accumulation of labile SOC, which depended on N types. A mixture of inorganic and organic N (MN) deposition had the highest suppression of SOC decomposition at 31.5%, followed by organic N (ON) deposition (24.4%) and inorganic N (IN) deposition (19.8%), thereby suggesting that inhibition effects of N deposition on SOC decomposition based on a single IN or ON source are underestimated. Nematocide application stimulated SOC decomposition, with the highest in MN (19.5%), followed by IN (13.5%), ON (11.2%), and control treatment (4.6%). The stimulation effect of SOC decomposition by soil nematode exclusion also depended on N types. N deposition and soil nematode exclusion had no interactive effect on SOC decomposition. These results imply that atmospheric N deposition favors the increase of C stocks in soil by reducing the SOC loss, and that N types should be considered during assessment of N deposition effects on soil C cycle processes. [ABSTRACT FROM AUTHOR]

• Root exclusion had higher effects on microbial residues than leaf-litter exclusion. • Fungal residues had larger responses to litter exclusion than bacterial residues. • Higher effects of litter exclusion on microbial residues were in microaggregates than large macroaggregate. • Proportions of fungal residues to SOC were more strongly related to live microbial biomass and nutrients than bacterial residues. • Changes in soil microbial residue-carbon accumulation coefficient caused by litter exclusion differently responded in aggregates. Microbial residues as the key component of the stable soil organic carbon (SOC) play a critical role in stabilizing SOC, and their accumulation is influenced by plant litter. However, how the accumulation of microbial residues in different aggregate fractions of forest soils responds to changes in the inputs of leaf and root litter remains poorly understood. Here, we test the hypothesis that root exclusion has greater effects on microbial residues than leaf-litter exclusion among soil aggregate fractions based on a litter-input manipulation experiment in a subtropical coniferous forest. The concentrations of bacterial, fungal, and total microbial residues were higher in large macroaggregates (> 2000 μm) but lower in small macroaggregates (250–2000 μm). Root exclusion decreased the concentrations of bacterial, fungal, and total microbial residues in microaggregates (< 250 μm), and leaf-litter exclusion decreased fungal residues in microaggregates. Fungal residues had higher proportions to SOC (20.7–34.9%) than bacterial residues (10.8–18.6%) in soil aggregate fractions, and their proportions were higher in large macroaggregates than other aggregate fractions. Root exclusion reduced the higher proportions of bacterial, fungal, and total microbial residues to SOC in microaggregates (14.5%, 15.7%, and 15.3%, respectively), compared to the reduction observed in large macroaggregates (10.8%, 7.1%, and 8.4%, respectively). And leaf-litter exclusion reduced the proportions of fungal and total microbial residues to SOC in microaggregates. Soil microbial residue-carbon accumulation coefficient was higher in large macroaggregates and lower in small macroaggregates. The coefficient was increased by root exclusion in macroaggregates but decreased in microaggregates, and it was also decreased by leaf-litter exclusion in large macroaggregates and microaggregates. Proportions of fungal residues to SOC were more strongly related to the live microbial biomass and nutrients than those of bacterial residues. Our results suggest that root exclusion exerts stronger effects on soil microbial residues than leaf-litter exclusion but these effects vary among soil aggregate sizes. [ABSTRACT FROM AUTHOR]

• Fungal-bacterial network complexity is related to soil pH. • Lower network stability and integration is found at neutral pH soil. • Microbial keystone taxa decrease towards higher pH. • pH is the strongest predictor of soil microbial network structure. Patterns in the network structure of microbial communities may give indications of their degree of interaction and interdependence, and their resilience to environmental disturbance. Geographical differences in network patterns of forest communities may reflect broad-scale differences in ecosystem structure and responses to environmental change. We analyzed a large dataset of 144 samples of soil bacterial and fungal communities characterized by 16S and ITS amplicon sequencing from forests in eastern China, along a 4,100 km latitudinal transect. This showed that fungal-bacterial network complexity was most closely related to soil pH. Results showed that pH was the strongest predictor of variation in community network structure across the forest soils of eastern China. Lower network complexity and stability were found around neutral pH, which was the strongest environmental predictor. This may be due to the optimal conditions that neutral soils provide for microorganism survival, reducing the necessity for physiological interdependence, consequently leading to fewer positive connections. Additionally, neutral soils provide more generalized niches, resulting in less specific niche exclusion, showing up as fewer negative connections. Unlike the trend for overall connectivity, the richness and relative abundances of keystone taxa were significantly and negatively correlated with pH. Overall, both connectivity and numbers of keystones were consistent in suggesting that network complexity was greatest overall at acidic pH. It appears that at the broad scale studied here, pH plays a more significant role in shaping microbial community integration than such factors as ecosystem productivity or climate. [ABSTRACT FROM AUTHOR]

Forests are critical for supporting multiple ecosystem services such as climate change mitigation. Microbial diversity in soil provides important functions to maintain and regenerate forest ecosystems, and yet a critical knowledge gap remains in identifying the linkage between attributes of regenerated woody plant (RWP) communities and the diversity patterns of soil microbial communities in subtropical plantations. Here, we investigated the changes in soil microbial communities and plant traits in a nine hectare Chinese fir (Cunninghamia lanceolata ; CF) plantation to assess how non-planted RWP communities regulate soil bacterial and fungal diversity, and further explore the potential mechanisms that structure their interaction. Our study revealed that soil bacterial richness was positively associated with RWP richness, whereas soil fungal richness was negatively associated with RWP basal area. Meanwhile, RWP richness was positively correlated with ectomycorrhizal (ECM) fungal richness but negatively correlated with the richness of both pathogenic and saprotrophic fungi, suggesting that the RWP-fungal richness relationship was trophic guild-specific. Soil microbial community beta diversity (i.e., dissimilarity in community composition) was strongly coupled with both RWP beta diversity and the heterogeneity of RWP basal area. Our study highlights the importance of community-level RWP plant attributes for the regulation of microbial biodiversity in plantation systems, which should be considered in forest management programs in the future. • Soil bacterial richness was positively associated with regenerated woody plant (RWP) richness. • Soil fungal richness was negatively associated with RWP basal area. • RWP-fungal richness relationship was trophic guild-specific. • Soil microbial community beta diversity was strongly coupled with RWP beta diversity. [ABSTRACT FROM AUTHOR]

• Different patterns whereas similar controls of PE and N inhibition effect at regional and global scales was revealed. • Soil pH and N availability separately controlled the pattern of PE and N inhibition of PE. • The general N inhibition of PE supports the N mining theory at a large scale. • The PE and N inhibition effect in coniferous forests were more sensitive to latitude than those in broadleaved forests. Although the priming effect (PE) of soil organic matter mineralization and its response to nitrogen (N) amendment are widely studied in terrestrial ecosystems, great uncertainties in their geographic patterns constrain the establishment of advanced climate-carbon (C) model. By combining a laboratory experiment incubating soils from nine temperate forests in China with a meta-analysis of 32 publications across global forests, we tested the PEs and their response to N addition to explore their geographic patterns and the potential determinants. We found a weak dependence of the PE on latitude and mean annual temperature (MAT) in temperate forests in China, but a significant dependence of the PE on MAT across global forests after controlling for the exogenous C quantity. Soil pH was evidenced to control the geographic patterns of the PE. Consistent with meta-analysis, a general inhibition impact of mineral N addition on PE was detected in the laboratory experiment, ranging from −5.50 to 228.41%. In contrast with an inapparent dependence on MAT at the global scale, N inhibition effect in incubation experiment was experimentally detected to negatively correlate with MAT. Increase in soil N availability basically attenuated the response of PE to N addition. Across the globe, the PE and N inhibition effect in coniferous forests were more sensitive to latitude than those in broadleaved forests. Overall, our results uncovered distinct patterns but consistent controls of PE and N inhibition effect between the regional and global scales, and emphasized the importance of considering forest type in predicting soil C dynamics in response to global change. [ABSTRACT FROM AUTHOR]

• Microbial respiration (MR) showed a hump-shaped latitudinal distribution. • Soil physicochemical variables primarily controlled MR. • Soil organic carbon was the best indicator of MR across the north-south transect. • The significance of soil organic carbon in regulating MR decreased in low-latitude region. Soil microbial respiration (MR) is a key process controlling the soil-atmosphere CO 2 flux, and is widely studied at individual sites. Yet its spatial variation and underlying mechanism at larger spatial scales are still poorly understood, limiting our estimates of the carbon cycle in terrestrial ecosystems and its feedbacks to climate change. Here, a novel incubation experiment based on the mean annual temperature of soil origin sites along a 4,200 km north–south forest transect of eastern China was conducted to investigate the spatial variations in MR. MR showed a hump-shaped relationship with latitude and peaked around 32° N, which coincided exactly with the ecotone of subtropical and temperate forests. Climate, soil physicochemical and microbial traits explained 56.1% of the total variations in MR across the transect, whereas explained 77.4% and 34.6% in tropical and subtropical versus temperate region, respectively. Soil physicochemical properties were consistently more important in controlling the MR's variation than other variables. Specifically, soil organic carbon was the most important factor in regulating the MR's variation across the transect, whereas its significance decreased when scaling down to tropical and subtropical regions. The mean annual temperature turned into the best indicator of MR in tropical and subtropical forests, whereas the combination of soil organic carbon with total nitrogen concentrations primarily regulated the variations in MR in temperate region. Collectively, our study showed a non-linear latitudinal pattern of soil MR and revealed the diverged controlling factors and mechanisms of MR in different climatic regions. These findings can potentially improve our capacity to predict the soil CO 2 flux in Earth system models and the feedbacks to climate change. [ABSTRACT FROM AUTHOR]

Nitrogen (N) mineralization in soils generally controls biological N availability in terrestrial ecosystems. As the pivotal first step in the overall N mineralization process, gross N mineralization (GNM, defined as the production of ammonium from microbial mineralization of organic N) is inherently coupled with microbial mineralization of soil organic carbon (C) which is commonly referred to as microbial respiration (MR), and that has often been used as a proxy of C availability. However, the pattern of GNM and its underlying mechanisms at a regional scale, and its linkage with MR remain unclear. By analyzing 100 soil samples collected across different forest types along a 3800 km long north-south transect in eastern China, we simultaneously measured the potential GNM using a 15N pool dilution method and MR using a dynamic CO 2 trapping technique. We conducted a structural equation model (SEM) to examine the interactive effects of climate, soil pH, microbial substrate availability, and microbial biomass on potential GNM along the forest transect. Furthermore, we conducted a non-linear regression analysis between potential GNM and MR. We found that both potential GNM and MR varied largely, from 0.55 to 16.14 mg N kg−1 soil d−1 and from 3.64 to 24.30 mg C kg−1 soil d−1, respectively, but were not significantly affected by forest type. The SEM analysis showed that 51% of the variation in potential GNM was explained, with microbial substrate availability being the most important influencing factor. There was a positive non-linear relationship between potential GNM and MR (R2 = 0.52, P < 0.0001). Notably, MR alone exerted a comparable role in explaining the variation in potential GNM compared to the interactive effects between multiple factors used in the SEM. Our findings confirm the dominant control of C availability to microbes on potential GNM, and necessitate the incorporation of MR for better modeling GNM in forest soils. [Display omitted] • Potential gross N mineralization (GNM) varied largely along a forest transect. • The pattern of microbial respiration (MR) was similar to that of potential GNM. • Microbial substrate availability was the most important factor for potential GNM. • There was a positive non-linear relationship between potential GNM and MR. [ABSTRACT FROM AUTHOR]