Latitudinal pattern and the driving factors of leaf functional traits in 185 shrub species across eastern China

Aims To explore the pattern of the leaf functional traits of shrub species along a latitudinal gradient in eastern China and determine the driving factors of leaf trait variation at a large scale. Methods We investigated the leaf thickness (LT), leaf area (LA), specific leaf area (SLA) and leaf dry mass content (LDMC) of 185 shrub species from 13 sites across eastern China. The trends of these four-leaf traits were analyzed with respect to latitude, and the differences between different life forms (e.g., evergreen and deciduous) and habitats (e.g., understory and typical) were compared. We quantified the effects of the plant life forms and environmental factors on the leaf traits via mixed-model analyses. Important Findings The LT and LA decreased, whilst and the LDMC increased, as the latitude increased, and significant differences in these traits were observed between the different plant life forms. The LT and LA were smaller, whereas the SLA and LDMC were larger in deciduous shrubs than in evergreen shrubs. Among the different habitats, the LA and SLA were larger, while the LDMC was smaller in understory shrubs than in typical shrub species. These results indicate that typical shrub species are better adapted to drier environments, as indicated by a reduced LT and increased LDMC. Furthermore, general linear models showed that variations in the four-leaf traits with respect to latitude were mainly caused by a shift in plant life forms

Divergent changes in diversity and network complexity across different trophic-level organisms drive soil multifunctionality of fire-impacted subtropical forests

Widespread forest fires pose significant challenges to the diverse communities of soil-dwelling organisms and the multiple ecosystem functions they support. However, whether the biodiversity and interactions of various taxonomic groups respond to fire consistently in terms of direction and extent, and their relative role in regulating post-fire soil functioning, remains largely unexplored. In this study, we investigated whether the diversity and co-occurrence networks of soil organisms across various trophic levels (including bacteria, fungi, protists, and invertebrates) in subtropical forests exhibit consistent responses to fire. Furthermore, we investigated their contribution to regulating soil multifunctionality, which is measured by a range of soil extracellular enzyme activities, available nutrients and reduced potential fungal plant pathogens. Our findings revealed that fire led to a decline in the richness of fungi, protists, and invertebrates, without significantly impacting bacterial richness. Fire also simplified the microbial co-occurrence networks while complexifying the invertebrate networks. Interestingly, soil multifunctionality tended to decrease with the richness of lower-trophic communities (i.e., bacteria), whereas it increased with that of high-trophic communities (i.e., protists and invertebrates). Moreover, fire indirectly influenced soil multifunctionality by altering biodiversity and network complexity, particularly pronounced in high-trophic communities. Overall, our results underscored the divergent vulnerability of biodiversity and networks to fires across taxa groups, highlighting the crucial role of biodiversity and interactions of higher trophic taxa groups in shaping the recovery and functionality of fire-affected soils

No significant changes in topsoil carbon in the grasslands of northern China between the 1980s and 2000s

The grasslands of northern China store a large amount of soil organic carbon (SOC), and the small changes in SOC stock could significantly affect the regional C cycle. However, recent estimates of SOC changes in this region are highly controversial. In this study, we examined the changes in the SOC density (SOCD) in the upper 30 cm of the grasslands of northern China between the 1980s and 2000s, using an improved approach that integrates field-based measurements into machine learning algorithms (artificial neural network (ANN) and random forest (RF)). The RF-generated SOCD averaged 5.55 kg C m(-2) in the 19805 and 5.53 kg C m(-2) in the 2000s, and the change ranged from -0.17 to 022 kg C m(-2) at the 95% confidence level, suggesting that the overall SOCD did not vary significantly during the study period. However, the change in SOLD exhibited large regional variability: the topsoil of the Inner Mongolian grasslands experienced significant C loss (4.86 vs. 4.33 kg C m(-2)), while that of the Xinjiang grasslands exhibited an accumulation of C (5.55 vs. 6.46 kg C m(-2)). Furthermore, the topsoil C in the Tibetan alpine grasslands remained relatively stable (6.12 vs. 6.06 kg C m(-2)). A comparison of the different grassland types indicated that SOCD significantly decreased in typical steppe, whereas it increased in mountain meadow, and remained stable in the other grasslands (alpine meadow, alpine steppe, mountain steppe and desert steppe). Climate change could partly explain the changes in the SOCD of the different grassland types. Increases in precipitation could lead to SOC accumulation in temperate grasslands and SOC loss in alpine grasslands, while climate warming is likely to cause SOC loss in temperate grasslands. Overall, our study suggests that the grasslands of northern China remained a neutral SOC sink between the 1980s and 2000s. (C) 2017 Elsevier B.V. All rights reserved

Fire decreases soil respiration and its components in terrestrial ecosystems

The impact of fire on aboveground biomass has significant consequences on soil carbon (C) dynamics, which is essential in predicting the global C budget during the Anthropocene. However, there is considerable spatiotemporal variability in the directions and magnitudes of fire effects on soil respiration, and the drivers associated with these effects are not well understood. Here, we conducted a global meta-analysis of 1327 individual observations from 170 studies to determine the extent to which fire influenced soil total respiration (Rs), heterotrophic respiration (Rh), and autotrophic respiration (Ra). We found fires reduced Rs, Rh, and Ra, with an average effect of -11.0%, -17.5%, and -40.6%, compared to unburnt sites. Specifically, wildfires significantly reduced Rsand Rh (-20.4% and -25.0%, respectively), and prescribed fire significantly decreased Ra (-74.8%). The influences of fire on Rs and its components were moderated by fire severity, season, type, climate zones, and biomes. After several years from the time of the fire, the negative effects of fire on Rs diminished and then recovered to a state not significantly different from unburnt sites; Rh exhibited a similar but decayed temporal response. Similarly, the negative effects on Ra disappeared after 3 years following the latest fire. The magnitude of the effect on Rs was strongly associated with soil temperature, cation exchange capacity, total nitrogen (N) content, and N-acquiring enzyme activity. In contrast, the magnitude of the effect on Rh significantly changed with pH, bulk density, texture, soil C and nutrient contents, and C- acquiring enzyme activity. Our findings advance the understanding of the inhibition and associated mechanisms of fire on Rs and its components, highlighting the need for new research efforts to predict the spatial-temporal shifts in underground C cycling induced by fire.Funding provided by: National Natural Science Foundation of ChinaCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100001809Award Number: 41930756Funding provided by: National Natural Science Foundation of ChinaCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100001809Award Number: 32201528Funding provided by: Natural Science Foundation of Fujian ProvinceCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100003392Award Number: 2021J05040We extracted data directly from text, tables, figures, and appendices from the primary articles using the Getdata 2.2.5 software. In cases where site coordinates were not provided, we estimated them by referring to site descriptions and cited sources. Additionally, for unavailable climate data, we used a global database (http://www.worldclim.org/) and used spatial coordinates to fill in the missing climate data

Soil extracellular enzyme activity and stoichiometry in China's forests

Ecoenzymatic stoichiometry links microbial decomposition with nutrient mineralization and improves our understanding of nutrient cycling in terrestrial ecosystems. Microbial C:N:P acquisition in the topsoil converged at a ratio of 1:1:1 in global ecosystems. However, whether the ratio of microbial acquisition is stable in forest soils, and is applicable among different soil depths remain unknown. Based on large-scale soil sampling in China's forests, we examined the patterns and environmental drivers of the eight most-widely measured enzyme activities and the relevant stoichiometry. We found that the ratio of C:N:P acquisition significantly deviated from 1:1:1. The specific enzyme activities (normalized by SOC) did not change significantly with latitude except those for xylosidase and acid phosphatase. Similarly, only the C:P acquisition ratio increased with latitude. Vertically, the specific activities of C-acquiring enzymes mainly increased, N-acquiring enzymes decreased and P-acquiring enzymes did not change with soil depth. Moreover, all ratios of microbial acquisition decreased, and the percentage of recalcitrant C increased significantly with increasing depth. Our study also showed that temperature and soil C:N ratio were the important factors in explaining the variations in specific enzyme activities and microbial nutrient acquisition, respectively. Our results indicated that no constant microbial C:N:P acquisition ratio can be widely recognized, and that SOC quality changed from labile to recalcitrant with depth. We highlight that depth-dependent enzymatic processes should be considered in future SOC dynamic models. A free Plain Language Summary can be found within the Supporting Information of this article

Estimating forest soil organic carbon content using vis-NIR spectroscopy: Implications for large-scale soil carbon spectroscopic assessment

Large-scale soil organic carbon (SOC) stock assessment is expensive as a large number of samples must be collected and then their time-consuming measurements must be made in the laboratory. Previous studies have shown that visible-near-infrared reflectance (vis-NIR) spectroscopy can quickly predict SOC content at a low cost. However, the application of this method at the large scale remains challenging due to the high spatial heterogeneity of SOC and the spatially dependent relationships of soil spectra and SOC content. Here, we conducted large-scale soil sampling across China's forests and established the Chinese forest soil spectral library (CFSSL) by measuring SOC content and scanning the vis-NIR reflectance of 11, 213 soil samples. Compared with the traditional global partial least squares regression (PLSR) modeling method (R-2 = 0.75, RPIQ = 1.95), the clustering by fast research and find of density peak in combination with the Cubist model significantly improved the prediction ability of SOC content (R-2 = 0.96, RPIQ = 5.83). This study provided a cost-efficient spectroscopic methodology, including measurement and prediction modeling, for large-scale SOC estimation

Estimation of plot-level soil carbon stocks in China's forests using intensive soil sampling

Forest soil is a large carbon (C) pool and plays a pivotal role in the global C cycle. The accurate estimation of soil organic carbon (SOC) stocks in forests is the cornerstone of studying the C budget; however, current assessments of forest SOC stocks are highly uncertain. One of the key reasons for this uncertainty is that most previous studies only used a few soil profiles for their estimation, whereas SOC stocks are highly spatially heterogeneous. To accurately evaluate the plot-level SOC stocks of China's forests, we conducted intensive soil sampling (100 soil cores within a plot) in 33 plots across 11 forest sites from south to north China. The average SOC density (SOCD) of these forest sites was 137.4 +/- 12.1 Mg C ha(-1) (0-100 cm), with significant geographic variations. The highest SOCD (306.8 +/- 7.6 Mg C ha(-1)) was observed in deciduous needleleaf forest (boreal forest) in northeast China, while the lowest one (64.8 +/- 0.9 Mg C ha(-1)) was found in subtropical evergreen broadleaf forest in south China. We also showed that the error of the SOCD estimates obtained from the intensive soil sampling was significantly smaller than that of estimates obtained from the traditional sampling method (5.3 +/- 1.3% vs. 24.2 +/- 5.6%, with a confidence level of 0.95). Our results suggest that intensive sampling can significantly reduce the uncertainty in forest SOC stock estimation by guarding against the effects of spatial heterogeneity, and provide an important methodological reference for accurately evaluating forest SOC stocks and C budgets in other regions

Ecological consequences of shrub encroachment in the grasslands of northern China

ContextShrub encroachment is a critical environmental issue in arid and semi-arid landscapes. However, due to the complicated effects of shrub characteristics and environmental variables, ecological consequences of shrub encroachment significantly differ in different regions. As a result, although the phenomenon of shrub encroachment is widespread in the grasslands of northern China, its ecological consequences and associated drivers have not been well documented at the regional scale.ObjectivesWe explored the effects of shrub encroachment on ecosystem structures (herb richness and abundance) and functioning (above- and belowground biomass, and soil carbon and nitrogen content) and evaluated the relative importance of climatic variables (temperature and precipitation) and shrub characteristics (cover, area, and height) as drivers of these effects.MethodsBased on field data from 53 sites that stretch across approximately 3000km in northern China, we conducted the relative interaction intensity (RII) of the response variables between shrub patches and grassy matrix, and then used the structural equation modeling (SEM) to assess the relative importance of chosen drivers on the ecological consequences.ResultsShrub encroachment increased the landscape heterogeneity by decreasing the richness, abundance and aboveground biomass of herbs, while by increasing the soil carbon and nitrogen content. The SEM explained 25-43% of the variation in shrub characteristics and 5-34% of the variation in the effects of shrub encroachment. Shrub height had greater effects on the RII of herb richness, soil carbon and soil nitrogen content, and the standardized total effects were 0.48, 0.25 and 0.18, respectively. Precipitation and temperature positively affected the impacts of shrub encroachment on herb richness, abundance, biomass, and multi-indexes. However, the direct effects of climate could be partially mediated by indirect effects via shrub characteristics.ConclusionsThe height, size and cover of shrub patches significantly influenced the community structures and functioning of grassland ecosystems. The increasing aridity could potentially exacerbate the negative consequences of shrub encroachment in arid regions. Our results also demonstrated that the effects of climate variables on grassland ecosystems could be mediated by shrub management

Species richness and composition of shrub-encroached grasslands in relation to environmental factors in northern China

Aims Shrub encroachment has taken place in many of China's northern grasslands. This study attempts to answer the following questions: which plant communities are present in these shrub-encroached grasslands (SEGs)? What are the species richness and composition of these communities? Which environmental factors determine the spatial distribution thereof? Methods We investigated the community characteristics of 255 SEG plots with a size of 20 m x 20 m at 69 locations across grasslands in northern China. In each plot, paired 1-m(2) quadrats were established within shrub patches and the neighbouring grassy matrix to record herb species composition. The quantitative characteristics (abundance, coverage and height) of herbs were measured in 0.25-m(2) subquadrats, and soil samples were collected in the quadrats. Two-way indicator species analysis (TWINSPAN), detrended canonical analysis (DCA) and canonical correspondence analysis (CCA) were used for community clustering and ordination. Important Findings The DCA and TWINSPAN results suggested that the SEGs in northern China can be divided into six community types: Potentilla fruticosa + Carex atrofusca, Spiraea hypericifolia + Festuca ovina, Caragana acanthophylla + Stipa sareptana, Caragana microphylla + Leymus chinensis, Caragana microphylla + Stipa klemenzii and Caragana tibetica + Cleistogenes songorica. At a regional scale, climate and soil nutrients controlled the spatial patterns of species richness and community composition of the SEGs in northern China. Temperature exerted a negative impact, whereas precipitation and nutrients had positive effects on species richness. Among the environmental factors used, climate was the major controller of the variations in community structure. These results provide new insights into the community composition of SEGs in China and enrich the global dataset of SEGs

Biogeography of soil protistan consumer and parasite is contrasting and linked to microbial nutrient mineralization in forest soils at a wide-scale

Despite their essential role in soil microbiome and the global ecological processes, large-scale biogeographical patterns and predictors of protists are poorly characterized. Investigating the diversity and distribution of protists is crucial for understanding their biogeographic patterns and underlying the drivers across phylogenetic, ecological, and functional scales. Here, we explored a wide-scale pattern of protistan communities, and linked it with soil functions, in 107 soil samples from nine forest sites along a large climatic gradient. Our results showed that the biogeography of protistan communities in forest soils generally fitted the temperature diversity gradients (TDG), metabolic niche theory (MNT) and distance-decay relationships (DDR). Strikingly, the dominant protistan phyla, Cercozoa (consumer) and Apicomplexa (parasite), followed highly different/contrasting biogeographic patterns along the climatic gradient, as a result of environmental selection and stochastic processes. Cercozoa were relatively more abundant in cold arid soils while Apicomplexa thrived in tropical wet sites. Homogenizing dispersal had a stronger effect on the distribution of the Cercozoa, while ecological drift controlled the distribution of the Apicomplexa. In addition, we found that protist network modularization explained 57.5% of the variation in soil nutrient mineralization, suggesting the critical roles of Cercozoa and Apicomplexa in nutrient cycling. Collectively, we showed the general applicability of TDG, MNT and DDR to the soil protistan communities and revealed contrasting biogeographic patterns of protistan consumer and parasite along climatic gradients. Our study highlights the crucial contribution of protistan communities to nutrient mineralization in forest soils