Recent advances in stable isotope techniques, in-situ monitoring devices, and soil water extraction methods have increasingly supported the ecohydrological separation phenomenon: plants and streams appear to use water from different soil reservoirs and return it to the hydrosphere. This review summarizes the evolution of the “Two water worlds” (TWW) hypothesis since its initial proposal and discusses the latest research progress, particularly in small-scale field experiments, cross-scale analyses, and cross-ecosystem comparisons. We systematically review the mechanisms and spatiotemporal dynamics underlying the separation of bound water and mobile water in the soil. We also discuss the connectivity between these water pools under various environmental conditions. Key issues, including identifying plant water source, standardizing soil water sampling methods, and addressing model uncertainty, are examined. Future research should focus on investigating plant water uptake mechanisms, improving water stable isotope monitoring techniques, integrating ecohydrological separation processes into hydrological models, and conducting cross-regional comparative studies. This study seeks to improve the accuracy of assessing the coupling between vegetation water use and runoff formation, offering a process-interpretable basis for ecological restoration and watershed management.

Aims Plant root exudates have received increasing attention as a key link in plant-soil-microbe interactions in recent years. However, studies on the impact of climate warming on the root exudation rates of grassland plants remain relatively limited.
Methods In this study, we conducted a laboratory controlled experiment with 10 dominant plant species in alpine meadows of the Qingzang Plateau. We collected root exudates in situ to quantitatively analyze the changes in root carbon exudation rates of the dominant species under experimental warming (+4 °C) and identified the factors influencing these changes.
Important findings Our results showed that: (1) Warming significantly increased the root carbon exudation rate of most dominant species, with an overall increase of (83.48 ± 6.00) μg·g^-1·h^-1 (81.71%), but it decreased the root exudation rate in leguminous plants (11.15%); (2) The changes in root exudation rates induced by warming were closely related to plant nutrient traits and morphological traits, with root nitrogen content explaining the highest variation. These findings suggest that climate warming will enhance the root exudation rates of dominant species in alpine meadows and highlight the critical role of functional traits in regulating root exudation responses to warming. This study contributes to the understanding rhizosphere carbon dynamics in the context of climate change and provides scientific evidence for predicting changes in the soil carbon on the Qingzang Plateau.

Aims As a key component of terrestrial ecosystem carbon pools, soil carbon storage in grasslands, encompassing both soil organic carbon (SOC) and soil inorganic carbon (SIC) pools, plays a crucial role in terrestrial carbon cycling and climate feedback. However, current research has primarily focused on SOC dynamic, while the regulatory mechanisms governing the storage of both SOC and SIC remain poorly understood. The comprehensive understanding of soil carbon storage, including its composition and spatial distribution across different grassland types, is still lacking.
Methods Here, we conducted a field survey in temperate grasslands of Nei Mongol, selecting two grassland types: typical steppe and meadow steppe. We measured soil physicochemical properties, plant biomass and chemical traits, as well as microbial biomass carbon and community composition. Based on these data, we applied boosted regression trees and structural equation modeling to investigate the relative importance of the four explanatory factors—climatic, edaphic, vegetational, and microbial variables, in shaping total soil carbon storage and its organic and inorganic components. Additionally, we explored the mechanisms underlying their influence.
Important findings This study found that the SIC stock in the 0-60 cm soil layer of typical steppe ((2.75 ± 0.15) kg C·m^-2) was significantly higher than that in meadow ((0.45 ± 0.03) kg C·m^-2), while there was no significant difference in soil organic carbon storage ((8.61 ± 0.19) kg C·m^-2 for typical steppe and (8.32 ± 0.17) kg C·m^-2 for meadow), resulting in a significantly higher total soil carbon storage in typical grasslands compared to meadow grasslands. The SOC content of both grassland types decreased with soil depth. However, the SIC content in typical steppe exhibited pronounced accumulation in deeper soil layers, a pattern that was absent in meadow. Biotic and abiotic factors, including vegetation characteristics, climate, and soil properties, jointly influenced total soil carbon and its SOC and SIC components, with distinct regulatory mechanisms between grassland types. In typical steppe with strong water limitations, soil carbon storage was primarily regulated by climate factors, whereas in meadow steppe with relatively higher moisture availability, soil properties played a more prominent role. These findings provide a scientific basis for accurately assessing the soil carbon storage in temperate grasslands and enhance our understanding of the distribution mechanisms of soil carbon under multi-factor interactions.

Aims Grassland plant roots and mycorrhizal fungi are the main sources of soil organic carbon, which play an important role in the formation and turnover of soil organic carbon and its components, and they also affect the soil nitrogen pool. Under the scenario of climate change, global drought events are frequent. How drought affects the role of roots and mycorrhizal fungi on soil carbon and nitrogen pools of different components is still unclear.
Methods In this study, Cleistogenes squarrosa was planted in indoor pots and subjected to control and drought treatments. Root bags and mycorrhizal bags were set up to distinguish the effects of plant roots and mycorrhizal fungi on the carbon and nitrogen content of soil organic matter and its components during plant growth. After 64 days of plant growth, the plants were harvested. The soil inorganic nitrogen content, plant biomass, plant leaf carbon and nitrogen content, carbon and nitrogen content of soil organic matter and its components in root bags and mycorrhizal bags, and microbial community composition were measured.
Important findings The results showed that compared with mycorrhizal bags without root participation, the soil organic carbon and particulate organic carbon content in the root bags enhanced by 17.5% and 55.8%, and the mineral-associated organic nitrogen content increased by 10.1%. Drought treatment increased soil inorganic nitrogen content, reduced plant biomass, had no significant effect on the carbon and nitrogen content of soil organic matter and its components in the root bag, but significantly reduced the content of particulate organic carbon in the mycorrhizal bag. Drought treatment did not significantly change the microbial biomass in the root bag, but increased the microbial biomass in the mycorrhizal bag. The particulate organic carbon content in the mycorrhizal bags was negatively correlated with the amount of mycorrhizal fungi and the total microbial biomass. The results showed that during plant growth, the roots mainly affected the content of particulate organic carbon in the soil, and mycorrhizal fungi mainly affected the content of mineral-associated organic nitrogen. Short-term drought reduced the content of particulate organic carbon in the soil where mycorrhizal fungi were present. Future research should pay more attention to how global change affects the relative contributions of grassland plant roots and mycorrhizal fungi to soil organic matter and its components and their potential impact on soil organic carbon and nitrogen on a long-term scale.

Aims Alpine grassland ecosystems store vast amounts of organic carbon while are fragile. Understanding the responses of the ecosystem carbon storage to the synchronous atmospheric nitrogen deposition and changing precipitation regimes is critical to project the fate of ecosystem carbon budgets under the context of global change.
Methods Based on a manipulation field experiment of nitrogen addition (10 g·m^-2·a^-1) and precipitation change (precipitation reduction by 50% and increase by 50%) in an alpine meadow on the northeastern Qing-zang Plateau in 2017, the plant biomass, soil organic carbon content (SOCC) and its fractions were observed from 2022 to 2023, in order to explore the response of ecosystem carbon storage to the changes in nitrogen and precipitation.
Important findings The results showed that there were little interaction effects of nitrogen addition and precipitation change on vegetation aboveground biomass (AGB). The response of vegetation AGB to the changes in nitrogen and precipitation was functional group-dependent. Nitrogen addition treatment increased the AGB of graminoid and sedge. Decreased precipitation treatment reduced AGB by 27% while increased precipitation treatment impacted AGB insignificantly. Except for sedge, the proportion of functional group AGB against community AGB changed undetectably. The responses of 0-40 cm belowground biomass (BGB) and SOCC to the changes in nitrogen and precipitation were weak and depth- and year-dependent. The root/shoot ratio reduced by 31% in nitrogen addition treatment and increased by 83% in decreased precipitation treatment, respectively. Nitrogen addition treatment increased soil surface (0-10 cm) mineral-associated organic carbon (MAOC) content by 31%. The response ratio (RR) of vegetation AGB was positively related to graminoid. The RR of 0-40 cm BGB was determined by soil surface and deep (20-40 cm) BGB positively. The RR of 0-40 cm SOCC was equivalently regulated by each layer SOCC. Soil surface BGB directly impacted the surface particulate organic carbon (POC) content positively and indirectly impacted the surface MAOC content via POC content negatively. The vegetation AGB affected the deep MAOC content positively and the deep POC content negatively. The main effects, rather than the interaction effects of the changes in nitrogen and precipitation, affect AGB significantly while BGB and SOCC undetectably. The differential effects of plant biomass on soil organic carbon fractions are depth-dependent.

Aims Community assembly processes based on the ecological niche theory and neutral theory is crucial to the biodiversity maintenance mechanism, which is one of the hotspots in forest ecology research. Mountainous areas are rich in biodiversity, yet relatively few studies have explored the patterns of functional diversity and community assembly of mycorrhizal plants along altitudinal gradients.
Methods In this study, based on eight 1 hm² dynamic monitoring plots established at an altitude of 600-2 100 m in Fanjing Mountain National Nature Reserve, we divided 261 woody plants with diameter at breast height (DBH) of ≥1 cm into three functional groups: arbuscular mycorrhizal (AM) plants, ectomycorrhizal (EcM) plants, and ericoid mycorrhizal (ErM) plants. The change patterns of their community assembly process and functional diversity along the altitude gradients were analyzed, and the potential role of the assembly process in maintaining functional diversity was revealed.
Important findings The study showed that the functional diversity of the different mycorrhizal plants varied significantly with altitude, among which, the functional richness and functional dispersion of AM and EcM plants showed a significant decreasing trend with altitude, the community weighted means of leaf area and specific leaf area of AM and EcM plants showed a decreasing trend with altitude. The leaf dry matter content, leaf nitrogen and phosphorus content of EcM plants showed an increasing trend with altitude, while the leaf area, leaf dry matter and phosphorus content of ErM plants showed an increasing trend with altitude. The community assembly of three mycorrhizal plants were dominated by stochastic processes, in which the drift of ErM plants contributed more to community assembly than AM and EcM. The βNTI (beta nearest taxon index) of AM plants had no significant effect on the functional diversity, whereas it had a significant effect on the community weighted mean of functional traits of EcM and ErM plants. The βNTI had a significant positive effect on functional diversity of EcM and ErM plants, which maintained their functional diversity. In addition, soil nutrients (soil organic carbon, total nitrogen and hydrolysable nitrogen) content had a significant positive effect on the functional diversity of AM and EcM plants, but had a significant negative effect on the functional diversity of ErM plants. Altitude had a significant negative effect on AM and ErM plants, and a significant positive effect on EcM plants. The results of the study provide scientific basis for revealing the mechanism of biodiversity maintenance in the southwestern mountain ecosystems, which is of great significance for the protection and restoration of natural forests in the central subtropics.

Aims Alpine grasslands, a critical component of global ecosystems, are highly sensitive to climate change and human activities. The carbon and nitrogen pools of plants and soil microbes constitute essential parts of the carbon and nitrogen pools in these ecosystems. Grazing, one of the primary land-use practices in alpine grasslands, directly shapes the allocation, storage, and utilization of carbon and nitrogen resources by both plants and soil microbes.
Methods To investigate the effects of different grazing regimes on alpine grassland carbon and nitrogen pools, a field experiment was conducted in Xihai Town, Haibei Prefecture, Qinghai Province. The experiment included six treatments: only yak grazing (YG), only Tibetan sheep grazing (SG), mixed grazing of yak and Tibetan sheep at ratios of 1:2 (MG1:2), 1:4 (MG1:4), and 1:6 (MG1:6), as well as a no-grazing control (CK).
Important findings The results revealed that under no-grazing conditions, the plant community carbon pool and microbial biomass carbon pool were 930.81 and 58.43 g·m^-2, respectively. Yak grazing significantly reduced the plant community carbon pool, but had no effect on microbial biomass carbon pool. Similarly, mixed grazing treatments decreased the plant community carbon pool, but notably increased microbial biomass carbon pool. Regarding nitrogen pools, the no-grazing treatment had plant community nitrogen and microbial biomass nitrogen pools of 20.50 and 11.87 g·m^-2, respectively. Both yak and Tibetan sheep grazing did not alter plant community nitrogen pools, yet significantly increased microbial biomass nitrogen pool. In contrast, mixed grazing significantly reduced plant community nitrogen pools, but leaved microbial biomass nitrogen unchanged. The above results indicate that even under moderate grazing intensities, different grazing regimes exert divergent effects on the plant community and microbial carbon and nitrogen pools in alpine grasslands.

Aims Dendrobium huoshanense (Orchidaceae) is a nationally protected and endangered medicinal plant with dual-purpose (medicinal and edible) value in China. While facility and understory cultivation dominate its artificial propagation, the linkages between aboveground biomass and substrate/soil microbial communities remain unclear, hindering the understanding of aboveground-belowground association.
Methods Hence, we conducted field experiments with randomized sampling at a D. huoshanense cultivation base in the Dabie Mountains, Anhui, to investigate nutrient-regulated plant-microbe association under facility vs understory modes.
Important findings Facility substrates and understory soil showed significant differences in microbial biomass, diversity, and community composition. Specifically, facility substrates had higher microbial biomass carbon (MBC) and nitrogen (MBN) contents than understory soil, along with enriched bacterial diversity and ectomycorrhizal fungi (ECM). While understory cultivation significantly altered soil microbial composition, facility substrates maintained stable microbial communities. The biomass of D. huoshanense in the facility substrate was significantly higher than that in the understory soil. Further, structural equation modeling results revealed that nutrient content in substrate/soil and the composition of microbial communities exhibit significant regulatory associations with the biomass of D. huoshanense plants, with distinct patterns emerging under varying cultivation regimes. Specifically, ECM fungi under nutrient-rich facility conditions directly promoted aboveground biomass, whereas pathogen proliferation in nutrient-limited understory soils might suppress aboveground growth. These findings clarify the associations between aboveground biomass and microbial communities in the facility and understory cultivation modes of D. huoshanense, providing actionable insights for developing microbial inoculants to enhance cultivation efficiency and conserve this endangered species.

Aims Phragmites australis, a typical perennial rhizomatic wetland plant, is an important species in marsh wetland ecosystems. However, with the global climate change and the gradual drying of wetlands, the growth of P. australis is often limited by soil moisture. Understanding the response of P. australis to changes in soil moisture can provide a theoretical basis for the protection and dynamic prediction of its community, as well as for research on the response mechanisms of wetland plants in heterogeneous habitats.
Methods In this study, P. australis communities in three typical marsh wetlands in northern China, i.e., Daihai Wetland, Horqin Wetland and Qingtongxia Reservoir, were studied, and the effects of low and high soil moisture, and other environmental factors on the aboveground traits, belowground traits and their relationships of P. australis were analyzed.
Important findings Compared with low soil moisture, high soil moisture significantly increased the aboveground biomass and specific leaf area, and significantly reduced the root to shoot ratio of P. australis. High soil moisture significantly reduced the contents of non-structural carbohydrates in leaves, and nitrogen and phosphorus in stems. High soil moisture significantly increased the root biomass, root surface area and root volume, and significantly decreased the root diameter of P. australis. Soil moisture did not affect the positive correlation between root biomass and stem non-structural carbohydrates content. However, the decrease of soil moisture reversed the negative correlation between root diameter and leaf nitrogen content under high soil moisture, as well as the positive correlations between root diameter and leaf non-structural carbohydrates content, and between root diameter and stem non-structural carbohydrates content. In high soil moisture areas, total soil nitrogen and total soil phosphorus were important factors that affected the aboveground and belowground traits of P. australis; in low soil moisture areas, temperature and precipitation were also important factors. Our results indicate that soil moisture may indirectly affect total soil nitrogen and total soil phosphorus and temperature to change the correlations between some aboveground and belowground traits. In summary, high soil moisture was beneficial to the growth of aerial parts and roots of P. australis, but it reduced the contents of nitrogen and phosphorus in stems and the content of non-structural carbohydrates in leaves. soil moisture influences the aboveground and belowground traits and their relationships in P. australis, by indirectly affecting soil nitrogen and phosphorus contents, as well as temperature.

Aims Plant growth is influenced by a combination of their own characteristics and soil microbial communities. However, it remains unclear how plant resource acquisition strategies affect their own biomass through the diversity of rhizosphere soil fungi in natural communities.
Methods In this study, we selected 12 dominant and common plant species from the meadow steppe of Saihanba in Hebei Province, and performed high-throughput sequencing on their rhizosphere soil fungi, and simultaneously measured the functional traits of these plants’ leaves and roots, as well as aboveground biomass. The aim was to delve into the relationship between rhizosphere soil fungal diversity and aboveground biomass under different resource acquisition strategies.
Important findings The study found that: 1) in terms of resources acquisition strategies, leguminous plants belonged to the “fast-growing” strategy species, while Cyperaceae and Poaceae plants belonged to “slow-growing” strategy species. Cyperaceae plants exhibited a “do-it-yourself” strategy, and most non-leguminous forbs tended to be “outsourcing” strategy. 2) Plants with “slow-growing” and “do-it-yourself” strategies increased the overall rhizosphere fungal and saprotrophic fungal diversity, and the above-ground biomass of plants with these strategies dominated the community. 3) Rhizosphere soil fungal diversity was positively correlated with plant above-ground biomass, with the diversity of saprotrophic and pathogenic fungi playing particularly crucial roles. 4) The differences in above-ground biomass within the community were mainly directly influenced by the “fast-slow” economic spectrum of plants. These findings not only reveal the regulatory effect of plant resource acquisition strategies on rhizosphere soil fungal communities, but also highlight the key role of the “fast-slow” economic spectrum and rhizosphere soil fungal diversity in driving above-ground biomass accumulation. This study provides a theoretical basis for understanding the impact of plant-microbe interactions on the functions of grassland ecosystems.

Aims Pinus sylvestris var. mongolica, an evergreen coniferous tree species, plays a pivotal role in ecological restoration efforts in the deserts of northern China. This study aimed to elucidate the community assembly of belowground fungi and the intricate relationships between P. sylvestris var. mongolica and fungi in P. sylvestris var. mongolica plantations. The findings would provide the novel microbial perspectives for sustainable management strategies of P. sylvestris var. mongolica plantations.
Methods Pinus sylvestris var. mongolica plantations of different stand ages (26, 37, and 46 a) in the Hulun Buir Sandy Land were selected to examine the diversity, composition and assembly pattern of root-associated fungi (RAF), rhizosphere soil fungi (RhSF) and non-rhizosphere soil fungi (NRhSF).
Important findings (1) Stand ages and niches significantly influenced fungal diversity. The fungal community richness and diversity indices ranked as follows: 46 a > 26 a > 37 a, and the dissimilarity gradually increased with the increase of the stand age. Among the different niches, the richness, diversity indexes, and dissimilarity were the highest in NRhSF, the middle in RhSF and the lowest in RAF. (2) The belowground fungi were assigned to 14 phyla and 592 genera. The belowground fungal communities of 26, 37, and 46 a plantations had 3, 1, and 5 abundant genera respectively, and they had symbiotic capability of endophytic or ectomycorrhizal fungi. RAF, RhSF, and NRhSF had 3, 8, and 5 abundant genera, respectively, and the proportions of Mortierellomycota and saprotrophic fungi increased from root to soil. (3) The primary assembly processes of belowground fungal communities were the dispersal limitation (63.54%), drift (22.06%) and homogeneous selection (12.90%). Stand age significantly correlated with structure of belowground fungi. Soil total phosphorus content, soil total nitrogen and phosphorus contents, and soil organic matter content were the main factors influencing RAF, RhSF, and NRhSF, respectively. This study highlights temporal and spatial heterogeneity of fungal community diversity and composition in P. sylvestris var. mongolica plantations. Stochastic processes mainly were dispersal limitations, shaping these communities, while the deterministic processes were influenced by host selection and environmental filtering.

Aims The accumulation of granite spoils destroys soil structure and increases carbon emissions. Even after ecological restoration, these soils still suffer from low stability of carbon pools. As a key interface of plant-soil-microorganism interactions, root system, particularly its architecture characteristics, significantly affect the transformation of soil organic carbon. However, the effect of root architecture on the transformation of organic carbon in granite spoil dump soils is not clear yet.
Methods In this paper, we compared the organic carbon fraction contents between rhizosphere and bulk soils of the taproot system Medicago sativa (MR and MNR) and the fibrous-root system Elymus dahuricus (PR and PNR) to reveal the effects of root architecture on organic carbon fraction contents in a granite spoil dump. Furthermore, we analyzed soil physicochemical properties, enzyme activities, and bacterial community characteristics to reveal their underlying drivers.
Important findings Our results showed that: (1) total organic carbon (TOC), dissolved organic carbon (DOC) and particulate organic carbon (POC) content were significantly increased by plants in both systems; (2) the rhizosphere effects on TOC and DOC were significantly higher in Elymus dahuricus (50.36% and 78.60%) than that in Medicago sativa (13.38% and -7.10%), suggesting a stronger effect on carbon enhancement in the fibrous-root system relative to the taproot system; (3) Compared to MR, PR was more effective at significantly increasing soil fast-acting nutrient content, enhancing cellulase activity, and enriching the Proteobacteria (relative abundance 41.09%), and thus creating a more suitable microenvironment for carbon accumulation; (4) correlation analysis showed that ammonium nitrogen, effective phosphorus and cellulase activity were significantly and positively correlated with TOC, DOC and POC contents. In summary, the driving effect of the fibrous-rooted Elymus dahuricus was more effective for organic carbon accumulation in granite spoil reconfigured soils compared to the taproot system Medicago sativa. This study provides theoretical support for the stabilization of organic carbon pools in granite dumps, and the screening and community allocation of ecological restoration plants.

Aims Understanding the multidimensional traits of plant biomass dynamics and root system architecture is essential for optimizing the use of building space to enhance urban green volume, improve ecological service quality and promote overall building performance. This study provides theoretical support for rational urban greening construction.
Methods Two commonly used lianas with well-developed root systems, Vinca major ‘Variegata’ (cascading type) and Trachelospermum jasminoides ‘Variegatum’ (climbing type), were selected from urban greening landscapes in East China. The study compared their three-year growth dynamics, root architecture, and biomass changes across different substrates and predicted their longevity under these conditions.
Important findings (1) Plant biomass and root architecture followed a unimodal growth pattern in the traditional mixed substrate, with a rapid increase followed by a decline, whereas in the novel medium, they exhibited a steady, linear growth trend. (2) Correlation and principal component analyses of plant biomass and root architecture across different substrate types revealed significant variations in root length, number of root tips, root forks, root surface area, and root volume. These traits were identified as key indicators for modeling plant longevity, each serving distinct functions: root surface area and root volume were stable, systematic assessment parameters, while root length and number of root tips were highly sensitive evaluation parameters. (3) Growth curves modeling of plants cultivated in the novel container medium predicted peak growth periods of 6.99 and 10.77 a, respectively, substantially longer than the 2-3 a observed in the traditional mixed substrate. The optimal compaction and nutrient content of the novel medium enhanced root vitality and turnover, thereby extending plant lifespan and the duration of ecological services. By revealing and quantifying the complex structure and function of the root system of urban greening vines, this study helps to build a more stable and efficient plant community, which can improve the level of urban biodiversity. Additionally, it provides experimental and theoretical support for iterative greening camping techniques for special habitats such as green roofs and vertical green walls.

Aims By investigating aboveground and belowground nutrient allocation strategies of dominant tree species (i.e., Juniperus saltuaria and Rhododendron nivale) under different interaction intensities at the alpine treeline of Sygera Mountains, we aim to provide theoretical basis and support for ecological protection and restoration for alpine zone.
Methods This study focuses on the J. saltuaria community (Canopy coverage of the arbor layer: 60%), the J. saltuaria dominated community (Canopy coverage of the arbor layer: 20%), the R. nivale dominated community (Coverage of the shrub layer: 56%), and the R. nivale community (Coverage of the shrub layer: 75%) at the alpine treeline of Sygera Mountains. In August 2022, leaves, roots, and soil within the canopy range of dominant species in these four plant communities were collected. The nutrient element content of the samples was measured, and the aboveground and belowground nutrient and other stoichiometric characteristics of J. saltuaria and R. nivale under different interaction intensities were analyzed using ecological stoichiometry and Partial Least Squares Path Model (PLS-PM). We aimed to clarify the differences in nutrient strategies of the two dominant tree and shrub species under varying interaction intensities at the alpine treeline of Sygera Mountains.
Important findings The results showed that (1) leaf carbon (C) content in the J. saltuaria community was higher than that in the J. saltuaria dominated community, while nitrogen (N), phosphorus (P), and potassium (K) contents were opposite; root C content in the J. saltuaria community was lower than that in the J. saltuaria dominated community, while N, P, and K contents were higher. In the R. nivale dominated community, leaf C and K contents were higher than those in the R. nivale community, whereas N and P contents were lower; root C and N contents were higher in the R. nivale dominated community, while P and K contents were lower. In all four plant communities, leaf C, N, P, and K contents were significantly higher than in roots. (2) Compared to the J. saltuaria community, the J. saltuaria dominated community preferred to allocate more nutrients to leaves, representing an aggressive nutrient strategy. In contrast, the R. nivale dominated community transported more nutrients to roots compared to the R. nivale community, reflecting a more conservative nutrient strategy. Additionally, a positive feedback mechanism exists between plant communities and soil nutrients in the study area.

Aims Drought effects on the carbon (C) balance are considered the major factor of tree mortality and are assumed to be regulated by soil nutrient (e.g., nitrogen (N)) availability. However, the effects of nitrogen addition on trees’ carbon and nitrogen distribution between aboveground and belowground and the coupling between carbon and nitrogen relations in various organs in response to drought are still unclear in trees.
Methods A two-year full factorial microcosm experiment was set up with sessile oak (Quercus petraea). Nitrogen addition was performed in the first year, and a drought treatment was conducted in the second year. Isotope ¹⁵N and ¹³C labelling were carried out before drought and during drought, respectively. Three consecutive samplings were conducted after the dual labelling with ¹³C and ¹⁵N in the second year, and the effects of nitrogen addition on carbon and nitrogen allocation dynamics during progressive drought were tested.
Important findings Our results showed that previous nitrogen addition promoted photosynthetic carbon fixation and nitrogen allocation, increased root nitrogen uptake, reduced the non-structural carbohydrates (NSC) contents in all organs and changed the relationships of carbon and nitrogen in aboveground and belowground organs. In contrast, drought had minor effects on nitrogen and carbon allocation between aboveground and belowground and the relationship of carbon with nitrogen in all organs (represented by the ratio of ¹³C to ¹⁵N in all organs). Drought only significantly reduced the content of NSC. During drought (from day 40 to 73), previous nitrogen addition led sessile oak to prioritise belowground carbon and nitrogen allocation. Our results indicate that sessile oak can change its carbon and nitrogen allocation strategies to adapt to drought, while previous nitrogen addition may increase its drought sensitivity.

Aims Ecological stoichiometry has been recognized as a useful indicator of nutrient status and process regulation in ecosystems. Quantifying the effects of stand age on stoichiometric characteristics of carbon (C), nitrogen (N), phosphorus (P) and ecosystem C storage allocation patterns is critical for understanding the mechanisms of biogeochemical cycles and ecological functions in plantation ecosystems.
Methods This study compared the ecological stoichiometry and the C storage partitioning patterns among different stand ages in walnut (Juglans regia) plantations on the eastern of Taihang Mountains, North China. Plant and soil samples from four stand ages (4, 8, 12, and 16 a) were collected and analyzed.
Important findings 1) Mean C contents in organs (root, stem, branch, and leaf) were 437.17, 449.87, 448.16, and 441.39 g·kg^-1, respectively, showing no significant increasing trend with stand ages. N and P contents of different organs were 4.15-26.68 g·kg^-1 and 0.59-1.95 g·kg^-1, respectively, decreasing significantly with stand ages. C:N and C:P ratios increased significantly, while N:P remained stable. 2) Under anthropogenic management, soil C, N, and P contents exhibited an initial decline followed by an increase with stand ages, with significant variations among age classes. Trends in C:N, C:P and N:P ratios aligned with nutrient content changes. 3) Correlation analysis showed that soil C content was significantly positively correlated with soil N content. Leaf C content showed a negatively correlation with leaf N content, while leaf N content demonstrated a significantly positive correlation with leaf P content. Soil P content was significantly positively correlated to leaf N, branch P, stem P and N content. 4) Total ecosystem C storages for 4, 8, 12, and 16 a plantations were 167.59, 123.69, 136.03, and 202.37 Mg·hm^-2, respectively. The soil layer constituted the primary C pool, contributing 88.2%-99.7% of total ecosystem C storage. This study provides a scientific basis for systematically understanding nutrient cycling mechanisms and C sequestration functions in mountain economic plantation ecosystems.

Aims The interactions between soil fungal and bacterial communities are crucial for maintaining microhabitat balance. However, the key factors regulating their co-occurrence patterns remain poorly understood. The study aims to reveal the interactions between fungal and bacterial communities in Pinus sylvestris var. mongolica plantations in Horqin Desert. Soil samples were collected from plantations of different stand ages (half-mature, near-mature, and mature forest) with a reference sandy grassland as control.
Methods Based on the 16S rRNA high-throughput sequencing technology, molecular ecological network analysis was conducted to investigate the characteristics and driving factors of soil fungal-bacterial networks in Pinus sylvestris var. mongolica plantations.
Important findings The results revealed that: (1) as stand age increased, the complexity of soil fungal-bacterial network decreased. The half-mature forest exhibited the most intense fungal-bacterial interactions, with the highest stability and resistance to disturbance. In contrast, the sandy grassland displayed a more complex network overall. The synergistic relationships predominated among bacterial communities in both the plantation and sandy grassland, indicating a more intensive interaction within bacterial communities. (2) Key nodes of the soil fungal-bacterial network varied across different stand ages, with all identified key nodes being bacterial operational taxonomic units (OTUs). The half-mature forest exhibited the highest number of key nodes, with Proteobacteria representing the largest proportion. Acidobacteria were identified as key nodes in the co-occurrence networks of both the half-mature and near-mature forests. These results suggest that Proteobacteria and Acidobacteria play crucial roles in maintaining the stability of the fungal-bacterial network, while no key nodes were identified in the sandy grassland. (3) The complexity of soil fungal-bacterial network was primarily influenced by soil available phosphorus and water content, while the network’s stability was significantly correlated with soil organic matter and available phosphorus content. These findings enhance our understanding of the soil fungal-bacterial co-occurrence network and provide valuable insights for the sustainable management of P. sylvestris var. mongolica plantations.