Alpine grassland soils accumulate massive stocks of organic carbon and function as important carbon sinks on the Qinghai-Tibetan Plateau. Substantial uncertainties prevent a full understanding of ecosystems’ carbon pools and their responses to environmental factors, mainly because of limited observations and inconsistent up-scaling algorithms. This study compiled data since 2000 for 422 alpine grassland sites in Qinghai Province, China, to investigate vegetation and organic carbon densities in the topsoil (at 0–30 cm depth) and their spatial variations. The site-averaged below-ground biomass carbon density (BOD) and topsoil organic carbon density (SOD) were both highest in alpine meadows with values of 0.43 ± 0.34 (Mean ± S.D.) and 12.52 ± 5.74 kg C/m2, respectively. They are about five times the lowest corresponding values of alpine desert steppes. The above-ground biomass carbon density (AOD) is not significantly different between alpine steppes and alpine desert steppes, and averaged 32.66 ± 22.02 g C/m2, around twice that for alpine meadows. Boosted regression tree models and a structural equation model consistently show that mean annual precipitation, rather than mean annual air temperature, was the predominant factor influencing the spatial variability of site-level AOD, BOD, and SOD across the alpine grasslands. The boosted regression tree models, integrated with spatial datasets of topographic attributes, mean annual air temperature and precipitation, and mean annual maximal normalized difference vegetation index, yielded area-averaged AOD, BOD, and SOD values of 22.67 ± 4.48 g C/m2, 0.37 ± 0.074 kg C/m2, and 9.53 ± 4.48 kg C/m2, respectively. Modeling results indicate that ecosystem carbon densities increase from northwest to southeast, mainly following the spatial patterns of vegetation greenness and precipitation. The size of the total terrestrial ecosystem carbon pool in Qinghai province is estimated to be 3.65 Pg C, of which 96.02

Land-use changes have widespread impacts on terrestrial ecosystems. However, few studies have focused on the responses of soil environmental factors, soil microbial properties, and links between primary productivity, soil microbes, and soil multifunctionality during land-use change in the ecologically sensitive alpine areas on the Qinghai-Tibetan Plateau. In this study, we evaluated the effects of land-use changes from alpine grassland to farmland to shrubland on soil factors and soil microbial characteristics and investigated the associations between aboveground biomass, soil microbial diversity, network complexity, and soil multifunctionality in the Qinghai Lake Basin. The results showed that soil environmental factors and microbial community composition exhibited patterns of gradual recovery toward natural grassland along with the conversion of farmland to shrubland, and soil phosphorus content played a regulatory role in soil microbial restoration along with the conversion of landuse. Furthermore, we found that the recovery of soil microbial co-occurrence network complexity would require a longer time than that of microbial community composition and functional taxa after the conversion of farmland to shrubland. Importantly, we showed that network complexity is an important microbial property mediating the association between primary productivity and soil multifunctionality during land-use changes. These findings address the gap in our understanding of farmland during land-use change surrounding saltwater lake habitats, with great significance for broadening our understanding of land-use change and promoting the development of restoration decisions for alpine ecosystems worldwide.

Changes in soil microorganisms caused by enclosure have long been an important topic in grassland ecology. However, few studies have described the responses of the soil microbial community composition, functional groups, and co-occurrence networks at different growth stages to long-term grazing exclusion or compared the indicative abilities of diversity and network parameters on soil ecosystem functions after grazing exclusion. In this study, we conducted a field experiment to evaluate the response of soil microbes to long-term grazing exclusion in an alpine steppe on the Qinghai-Tibetan Plateau. Our results showed that both soil fungal and bacterial community compositions at different growth stages showed significant differences. However, the enclosure only altered the fungal community composition. Differences in soil microbial functional groups between fungi and bacteria were also detected. The leading group in soil fungi was governed by grazing exclusion, and most bacterial functional groups showed significant differences between the growth stages. The co-occurrence network patterns of the fungi and bacteria differed significantly. Unexpectedly, the enclosure did not significantly alter the fungal or bacterial co-occurrence networks. Network parameters had a stronger ability to indicate soil ecosystem functions than the diversity index, displaying better relationships between network parameters and soil organic carbon and nitrate. These findings suggest that elucidating the responses of soil microbes at different growth stages is necessary to comprehensively understand soil ecosystems after long-term grazing exclusion in the alpine steppe.

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 N-15 pool dilution method and MR using a dynamic CO2 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 (R-2 = 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.

Recent studies have demonstrated that the presence of belowground neighbours induces varied morphological and biochemical responses in plants. Plant allelopathic activity is elicited by the presence of competitor seedlings or competitor root exudates. However, it is unknown whether allelopathy also influences root recognition behaviour in weed–crop interaction. To assess barnyardgrass response to the presence of allelopathic rice roots, we conducted a greenhouse experiment of barnyardgrass–rice mixed culture, including barnyardgrass monoculture, barnyardgrass mixed with the allelopathic rice line PI312777 and barnyardgrass mixed with the nonallelopathic rice cultivar Liaojing-9. Our results showed that the presence of allelopathic rice roots enhanced root allocation and tissue density (RTD) of barnyardgrass, whereas it decreased root biomass, total root length, specific root length (SRL) and topological index (TI), compared to barnyardgrass grown in monoculture; moreover, there was a significant correlation of topological index with root foraging precision and competition. Therefore, the presence of allelopathic rice roots affected the barnyardgrass root morphology, nutrient foraging and competition, suggesting that allelopathy plays a key role in root recognition behaviour of barnyardgrass–rice competitive interaction.