It is well known that aboveground productivity usually increases with precipitation. However, how belowground carbon (C) processes respond to changes in precipitation remains elusive, although belowground net primary productivity (BNPP) represents more than one-half of NPP and soil stores the largest terrestrial C in the biosphere. This paper reviews the patterns of belowground C processes (BNPP and soil C) in response to changes in precipitation from transect studies, manipulative experiments, modeling and data integration and synthesis. The results suggest the possible existence of nonlinear patterns of BNPP and soil C in response to changes in precipitation, which is largely different from linear response for aboveground productivity. C allocation, root turnover time and species composition may be three key processes underlying mechanisms of the nonlinear responses to changes in precipitation for belowground C processes. In addition, microbial community structure and long-term ecosystem processes (e.g. mineral assemblage, soil texture, aggregate stability) may also affect patterns of belowground C processes in response to changes in precipitation. At last, we discuss implications and future perspectives for potential nonlinear responses of belowground C processes to changes in precipitation.

Variations in plant traits are indicative of plant adaptations to forest environments, and studying their relationships with tree growth provides valuable insights into forest regeneration. The spatial arrangement of plant seeds within the forest litter or soil critically influences the variations of root-leaf traits, thereby affecting the adaptive strategies of emerging seedlings. However, our current understanding of the impacts of individual root-leaf traits on seedling growth in different relative position, and whether these traits together affect growth, remains limited. This study focuses on the dominant tree species, Castanopsis kawakamii, within the Sanming C. kawakamii Nature Reserve of China. The present experiment aimed to examine the variations in root-leaf traits of seedling, focus on the relative positions of seeds within different layers: beneath or above the litter layer, or within the bare soil layer (without litter). Our findings provided evidence supporting a coordinated relationship between root and leaf traits, wherein leaf traits varied in conjunction with root traits in the relative positions of seeds. Specifically, we observed that seedlings exhibited higher values for specific leaf area and average root diameter, while displaying lower root tissue density. The mixed model explained 86.1% of the variation in root-leaf traits, surpassing the variation explained by the relative positions. Furthermore, soil nitrogen acted as a mediator, regulating the relationship between seedling growth and root-leaf traits, specifically leaf dry matter content and root tissue density. Therefore, future studies should consider artificially manipulating tree species diversity based on root-leaf traits characteristics to promote forest recovery.

The tree height-diameter at breast height (H-DBH) and crown radius-DBH (CR-DBH) relationships are key for forest carbon/biomass estimation, parameterization in vegetation models and vegetation-atmosphere interactions. Although the H-DBH relationship has been widely investigated on site or regional scales, and a few of studies have involved CR-DBH relationships based on plot-level data, few studies have quantitatively verified the universality of these two relationships on a global scale. This study evaluated the ability of 29 functions to fit the H-DBH and CR-DBH relationships for six different plant functional types (PFTs) on a global scale, based on a global plant trait database. Results showed that most functions were able to capture the H-DBH relationship for tropical PFTs and boreal needleleaf trees relatively accurately, but slightly less for temperate PFTs and boreal broadleaf trees (BB). For boreal PFTs, the S-shaped Logistic function fitted the H-DBH relationship best, while for temperate PFTs the Chapman-Richards function performed well. For tropical needleleaf trees, the fractional function of DBH satisfactorily captured the H-DBH relationship, while for tropical broadleaf trees, the Weibull function and a composite function of fractions were the best choices. For CR-DBH, the fitting capabilities of all the functions were comparable for all PFTs except BB. The Logistic function performed best for two boreal PFTs and temperate broadleaf trees, but for temperate needleleaf trees and two tropical PFTs, some exponential functions demonstrated higher skill. This work provides valuable information for parameterization improvements in vegetation models and forest field investigations.

Phenological research is engaged in monitoring the influence of climate change on the natural environment. The International Phenological Gardens (IPG) network provides a valuable dataset of standardized tree phenology records dating back to the mid-20th century. To make best use of this actively growing record, it is important to investigate how network data can be applied to predict the timing of phenological events in natural populations. This study compared clonally propagated IPG downy birch (Betula pubescens Ehrh.) and hazel (Corylus avellana L.) specimens of central European provenance to nearby wild populations at the western-most margin of the IPG network, in the south-west of Ireland. In addition to monitoring by trained scientists, observations by citizen scientists were included. The order of the timing of phenological events among sites was consistent across 2 years, confirming reproducibility of the results. IPG trees had the earliest B. pubescens leaf unfolding and C. avellana flowering dates of the sites studied. In addition, leaf unfolding occurred later in the wild populations than expected from the temperature responses of the B. pubescens and C. avellana IPG clones. Natural variation in phenology also exceeded the historical change observed at the IPG site, suggesting a potential genetic basis for climate adaptation. Trunk circumference, reflecting the age-dependent increase in tree size, was found to influence C. avellana phenology, with earlier timing of phenological events in larger trees. This finding highlights tree size as an important consideration in the management of phenological gardens and tree phenology research in general.

Although characterization of plant interactions has become a research hotspot to assess the adaptability of endangered plants, the underlying molecular basis remains elusive. Dove tree (Davidia involucrata) seedlings were watered with distilled water (CK), leaf water extract (0.025 g mL^-1) and branch water extract (0.1 g mL^-1) from Cornus controversa, respectively. Subsequently, the morphology, biomass and gene expression levels of DiSOC1-b and DiCCoAOMT1 were analyzed. The results showed that morphological traits and biomass accumulation of D. involucrata seedlings were decreased by the addition of leaf water extracts, and increased by branch water extracts. Moreover, the gene expression level of DiSOC1-b was significantly down-regulated, while the gene expression level of DiCCoAOMT1 was significantly up-regulated in the stems and roots of D. involucrata upon treatment with leaf water extracts of C. controversa. In contrast, the gene expression level of DiSOC1-b was significantly up-regulated in the leaves and stems, while the gene expression level of DiCCoAOMT1 was significantly down-regulated in the roots of D. involucrata upon treatment with branch water extracts of C. controversa. In addition, the expression level of DiSOC1-b was positively correlated with most of morphological traits and total biomass (Pβ<β0.05), while DiCCoAOMT1 was negatively correlated with the majority of morphological traits in D. involucrata seedlings (Pβ<β0.05). Taken together, these results suggest that water extracts from the leaves and branches of the C. controversa exhibit opposite allelopathic effects and affect the expression levels of genes related to growth (DiSOC1-b) and environmental adaptability (DiCCoAOMT1) in D. involucrata seedlings.

Arbuscular mycorrhizal fungi (AMF) enhance plant tolerance to abiotic stresses like salinity and improve crop yield. However, their effects are variable, and the underlying cause of such variation remains largely unknown. This study aimed to assess how drought modified the effect of AMF on plant resistance to high calcium-saline stress. A pot experiment was performed to examine how AMF inoculation affects the growth, photosynthetic activity, nutrient uptake and carbon (C), nitrogen (N) and phosphorus (P) stoichiometric ratio (C:N:P) of maize under high calcium stress and contrasting water conditions. The results showed that high calcium stress significantly reduced mycorrhizal colonization, biomass accumulation, C assimilation rate and C:N stoichiometric ratio in plant tissues. Besides, the adverse effects of calcium stress on photosynthesis were exacerbated under drought. AMF inoculation profoundly alleviated such reductions under drought and saline stress. However, it barely affected maize performance when subjected to calcium stress under well-watered conditions. Moreover, watering changed AMF impact on nutrient allocation in plant tissues. Under well-watered conditions, AMF stimulated P accumulation in roots and plant growth, but did not induce leaf P accumulation proportional to C and N, resulting in increased leaf C:P and N:P ratios under high calcium stress. In contrast, AMF decreased N content and the N:P ratio in leaves under drought. Overall, AMF inoculation improved maize resistance to calcium-salt stress through enhanced photosynthesis and modulation of nutrient stoichiometry, particularly under water deficit conditions. These results highlighted the regulatory role of AMF in carbon assimilation and nutrient homeostasis under compound stresses, and provide significant guidance on the improvement of crop yield in saline and arid regions.

Interactions between two plant species can be influenced by the presence of other plant species and such an effect may change as the diversity of the other species increases. To test these hypotheses, we first constructed aquatic communities consisting of 1, 2 and 4 emergent plant species and then grew ramets of Lemna minor only, ramets of Spirodela polyrhiza only or ramets of both L. minor and S. polyrhiza within these aquatic communities. We also included controls with ramets of L. minor, S. polyrhiza or both but without any emergent plants. Biomass and number of ramets of L. minor and S. polyrhiza were significantly smaller with than without the emergent plants, but they did not differ among the three richness levels. The presence of S. polyrhiza did not significantly affect the growth of L. minor, and such an effect was not dependent on the richness of the emergent plant species. Without the emergent plant species, the presence of L. minor markedly reduced biomass (-92%) and number of ramets (-88%) of S. polyrhiza. However, such a competitive effect of L. minor on S. polyrhiza became much weaker in the presence of one emergent plant species (-46% biomass and -39% number of ramets) and completely disappeared in the presence of two or four emergent plant species. Therefore, both the presence and richness of emergent plant species can alter competitive interactions between the two duckweed species. These findings highlight the importance of species diversity in regulating plant-plant interactions.

Soil nematodes as the most diverse metazoan taxa, serve a diversity of functions in soil food webs and thus can regulate microbial community composition and affect organic matter decomposition and nutrient turnover rates. Because nematodes depend on water films to access food resources, drought can negatively affect nematode-microbial food webs, yet the impacts of drought on nematode diversity and abundance and how these changes may influence food web members and their functions are seldom explored. Here, we coupled research along a drought gradient in arid and semiarid grasslands with a detailed intact plant-soil microcosm experiment to explore the patterns and mechanisms of how drought impacts nematode abundance and carbon footprint, microbial phospholipid fatty acid and heterotrophic soil respiration. Over all in the field and in the microcosm experiment, we found that nematode abundance, carbon footprint and diversity, microbial phospholipid fatty acid and heterotrophic respiration all declined under drier conditions. In addition, drought altered nematode and microbial community composition, through reducing the nematode channel ratio and increasing the relative fungivorous nematode abundance and the fungal to bacterial ratio. In response to drought, the soil decomposition channel shifted from a bacterial to a fungal pathway, indicating decelerated heterotrophic respiration under drought. The study highlights the important contribution of soil nematodes and their associated microbial food web to soil carbon cycling. Our results underscore the need to incorporate key soil fauna into terrestrial ecosystem model evaluation.

Allelopathy plays an important role in the interaction between invasive and resident plants. Atmospheric nitrogen (N) deposition has become a global problem, but it is unclear whether N enrichment affects the interaction between invasive and resident plants by affecting their allelopathy. Thus, we performed a greenhouse experiment in which the resident plant community was grown under two levels of invasion by S. canadensis (invasion vs. no invasion) and fully crossed with two levels of allelopathy (with or without adding activated carbon) and two levels of N addition (with or without). The resident plant communities were constructed with eight herbaceous species that often co-occur with S. canadensis. The results showed that both allelopathy of S. canadensis and the resident plants had obvious positive effects on their own growth. Nitrogen addition had more obvious positive effects on the resident plants under invasion than those that were not invaded. Moreover, N addition also altered the allelopathy of resident plants. Specifically, N addition improved the allelopathy of resident plants when they were invaded but decreased the allelopathy of resident plants when they grew alone. Although nitrogen addition had no obvious effect on S. canadensis, it reduced the allelopathy of S. canadensis. These results suggest that N addition could improve the resistance of resident plants to invasion by improving the allelopathy of resident plants and reducing the allelopathy of S. canadensis. These findings provide a scientific basis to manage and control the S. canadensis invasion.

Rubber plantations have increased significantly under unprecedented economic growth in tropical areas, which leads to soil degradation and thereby alters soil hydrological processes. However, our understanding of how forest conversion affects soil hydrological processes remains unclear. Here, we collected soil samples from secondary forests (SF) and rubber plantations (RP) to determine the soil hydrological characteristics. We found the topsoil (0-20 cm) water retention in SF was higher than that of RP but displayed the contrast pattern in a deeper soil layer (20-60 cm). Meanwhile, the soil infiltration rates among the two vegetation types decreased significantly with infiltration time, with higher stable soil infiltration rates in SF than those in RP. Moreover, soil properties were also impacted by the forest conversion, such as the topsoil capillary porosity (CP) and total porosity (TP) in SF were higher than those of RP but contrasted in a deep soil layer. In comparison, the topsoil bulk density (BD) in SF was lower than that of RP, but contrasted in the deep soil layer and reached a significant level in the 0-10 and 40-50 cm (P<0.05). Overall, the soil water retention was mainly determined by the CP, which could explain 31.56% of the total variance in soil water retention, followed by TP (26.57%) and soil BD (26.47%), whereas soil texture exerts a weak effect on soil water retention. Therefore, we can conclude that the conversion of tropical rainforest into rubber plantations may accelerate soil erosion owing to its lower topsoil water retention and soil infiltration rates.

Hemisphere photos are now widely applied to provide information about solar radiation dynamics, canopy structure and their contribution to biophysical processes, plant productivity and ecosystem properties. The present study aims to improve the original 'edge detection' method for binary classification between sky and canopy, which works not well for closed canopies. We supposed such inaccuracy probably is due to the influence of sky pixels on their neighbor canopy pixels. Here, we introduced a new term 'neighbor distance', defined as the distance between pixels participated in the calculation of contrast at the edges between classified canopy and sky, into the 'edge detection' method. We showed that choosing a suitable neighbor distance for a photo with a specific gap fraction can significantly improve the accuracy of the original 'edge detection' method. We developed an ND-IS (Neighbor Distance-Iteration Selection) method that can automatically determine the threshold values of hemisphere photos with high accuracy and reproductivity. It combines the modified 'edge detection' method and an iterative selection method, with the aid of an empirical power function for the relationship between neighbor distance and manually verified gap fraction. This procedure worked well throughout a broad range of gap fractions (0.019-0.945) with different canopy compositions and structures, in five forest biomes along a broad gradient of latitude and longitude across Eastern China. Our results highlight the necessity of integrating neighbor distance into the original 'edge detection' algorithm. The advantages and limitations of the method, and the application of the method in the field were also discussed.

When facilitating other species and sustaining plant community structures and biodiversity, alpine cushion plants simultaneously experience negative feedback effects from surrounding vegetation. However, the impact of surrounding vegetation on cushion dynamics remains poorly understood, particularly in terms of allelopathic potentials. To investigate the allelopathic potentials of surrounding vegetation on seedling establishment of the typical cushion plant Arenaria polytrichoides Edgew. along an elevational gradient, we extracted potential allelopathic compounds and tested their impacts on seed germination and seedling growth of A. polytrichoides. In addition, exclusion experiments using activated carbon were conducted to further elucidate these effects. Our results demonstrate that surrounding vegetation exhibits certain allelopathic potentials on A. polytrichoides seedling establishment, with variations observed based on elevation, source and concentration of allelopathy compounds, as well as growing season. Specifically, low-elevation vegetation exerts pronounced suppression on seedling establishment. Conversely, higher-elevation vegetation generally shows no effect on seed germination but stimulates seedling growth through allelopathy mechanisms. Moreover, aboveground vegetation predominantly inhibits both seed germination and seedling growth in low-elevation communities; however, the effects of belowground vegetation depend on elevation and extract concentration levels. The identified allelopathic potentials of surrounding vegetation significantly influence the population dynamics of cushion A. polytrichoides by potentially accelerating population degeneration in lower-elevation communities while ensuring consistent population recruitment and expansion in higher-elevation communities.

Warming and precipitation are key global change factors driving soil carbon (C) dynamics in terrestrial ecosystems. However, the effects of warming and altered precipitation on soil microbial diversity and functional genes involved in soil C cycling remain largely unknown. We investigated the effects of warming and increased precipitation on soil C cycling in a temperate desert steppe of Inner Mongolia using metagenomic sequencing. We found that warming reduced plant richness, Shannon-Wiener and Simpson index. In contrast, increased precipitation significantly influenced Shannon-Wiener and Simpson index. Warming reduced soil microbial species by 5.4% while increased precipitation and warming combined with increased precipitation led to increases in soil microbial species by 23.3% and 2.7%, respectively. The relative abundance of Proteobacteria, which involve C cycling genes, was significantly increased by warming and increased precipitation. Warming significantly reduced the abundance of GAPDH (Calvin cycle) and celF (cellulose degradation) while it enhanced the abundance of glxR (lignin degradation). Increased precipitation significantly enhanced the abundance of pgk (Calvin cycle), coxL (carbon monoxide oxidation), malZ (starch degradation), and mttB (methane production). Moreover, a wide range of correlations among soil properties and C cycling functional genes was detected, suggesting the synergistic and/or antagonistic relationships under scenario of global change. These results may suggest that warming is beneficial to soil C storage while increased precipitation negatively affects soil C sequestration. These findings provide a new perspective for understanding the response of microbial communities to warming and increased precipitation in the temperate desert steppe.

Although the effects of arbuscular mycorrhizal fungi (AMF) on host plants have been well documented, whether the effects of AMF on parental generations affect offspring performance is not fully clear. We conducted a common garden experiment to determine whether AMF status of host plants (Medicago truncatula) affects phenotype and transcriptome expression of their offspring. Seeds from four type parental treatments (low-phosphorus (P) soil without AMF, low-P soil with AMF, high-P soil without AMF and high-P soil with AMF) were grown under low-P (LPS) and normal-P soil (OHS) conditions. The flowering pattern of LP offspring was similar to their parents, such that plants with AMF flowered earlier than those without AMF under OHS condition but were opposite under LPS condition. The transcriptome differential analysis showed that some differential transcripts (45 for parental plants growing under low-P condition and 3 for parental plants growing under high-P condition) expression patterns between offspring were comparable, and that only affected by parental AMF status regardless of the P environment that offspring was grown. Others (146 for parental plants growing under low-P condition and 2 for parental plants growing under high-P condition), however, were affected both by the parental AMF status and the offspring P environment. In addition, the number of differential transcripts between offspring whose parental plants grew under high-P condition was far less than under low-P condition. These results indicate that AMF may not only affect the current generation of host plants but also affect the offspring especially when their parents have experienced a stressful environment.

Although biotic and abiotic factors have been confirmed to be critical factors that affect community dynamics, their interactive effects have yet to be fully considered in grassland degradation. Herein, we tested how soil nutrients and microbes regulated plant-soil feedback (PSF) in a degraded alpine grassland. Our results indicated that soil total carbon (STC; from 17.66 to 12.55 g/kg) and total nitrogen (STN; from 3.16 to 2.74 g/kg) exhibited significant (P < 0.05) decrease from non-degraded (ND) to severely degraded (SD). Despite higher nutrients in ND soil generating significantly (P < 0.05) positive PSF (0.52) on monocots growth when the soil was sterilized, a high proportion of pathogens (36%) in ND non-sterilized soil resulted in a strong negative PSF on monocots. In contrast, the higher phenotypic plasticity of dicots coupled with a higher abundance of mutualists and saprophytes (70%) strongly promoted their survival and growth in SD with infertile soil. Our findings identified a novel mechanism that there was a functional group shift from monocots with higher vulnerability to soil pathogens in the ND fertile soil to dicots with higher dependence on nutritional mutualists in the degraded infertile soil. The emerging irreversible eco-evolutionary in PSF after degradation might cause a predicament for the restoration of degraded grassland.