Root exudates play an important role in soil carbon balance, acting as an important medium for material and energy exchange and information transfer between plant roots and soil, and also the crucial forms for plant response to environmental changes. Frequent extreme drought events accompanied with global climate change have imposed a profound impact on both above- and below-ground plant growth processes. However, significant limitation exists in understanding the responses of root exudates and their mediated rhizosphere priming effect to drought due to the complexity of root-soil interface interactions and the limitation in devices and methods for collecting root exudates. This paper reviews the effects of drought on the quantity and quality of plant root exudates, with emphasis on the rhizosphere priming effect mediated by root exudates under drought stress. The future research focuses on root exudates was also discussed. This study will provide suggestion for soil carbon sink assessment under the future climate change.

Aims Rhizosphere microorganisms play an important role in plant nutrient acquisition and carbon and nitrogen cycling, and plant fine roots (including absorptive roots and transport roots) are closely related to rhizosphere microbial communities. Elucidating the relationship between changes in fine root traits of pioneer tree species and rhizosphere microbial communities during post-fire forest restoration can provide theoretical support for post-fire vegetation restoration management based on fine roots and rhizosphere microbial dynamics.
Methods The pioneer tree species Betula platyphylla was used as the research object in the 30-year time series of the burned area of Da Hinggan Mountains. The 16S rRNA high-throughput sequencing technology was used to analyze the relationship between rhizosphere bacterial community structure and soil properties and fine root traits of B. platyphylla during post-fire recovery.
Important findings The results showed that post-fire recovery time significantly affected soil pH, absorptive root traits, and rhizosphere bacterial α diversity. With increasing time after fire, soil pH tended to increase, then decrease, and then increase again. The specific root length and specific root area of absorptive roots showed a trend of first increasing and then decreasing. Nine years after the fire was the turning point when the rhizosphere bacterial α diversity of B. platyphylla gradually recovered. Proteobacteria, Actinobacteriota, and Acidobacteriota were the main dominant phyla in the rhizosphere bacterial community at different post-fire recovery times, and Bradyrhizobium was the main dominant genus. Dominant genera such as Roseiarcus, Acidipila and Mycobacterium were significantly different at different post-fire recovery times. The α diversity of rhizosphere bacteria was mainly affected by soil pH and specific root length of absorptive roots, and the change of bacterial community structure was affected by carbon and nitrogen contents of fine roots and phosphorus content of transport roots. In conclusion, the interaction between fine roots, soil, and microorganisms jointly affects the community structure and diversity of B. platyphylla rhizosphere bacteria, thereby shaping the rhizosphere environment and promoting ecosystem recovery after fire.

Aims The ex situ decomposition of litter caused by tidal fluctuations is the most common decomposition approach in estuarine marshes. Exploring the effects of environmental variation on litter decomposition and nutrient release is of great significance for understanding nutrient cycling in estuaries.
Methods From March to December 2021, the natural environmental gradient in Spartina alterniflora distribution area in the Minjiang estuary was applied to simulate changes in decomposition environment. Three decomposition sub-zones including S. alterniflora marsh (M7, litter was denoted by L7) after seaward invasion for seven years, S. alterniflora marsh (M1, litter was denoted by L1) after seaward invasion for one year, and bare flat (BF) before invasion were laid in a seaward direction; and the potential effects of simulated environmental variation on the decomposition and phosphorus (P) release of S. alterniflora litter (L7 and L1) with different invasion years were investigated by using the litter bag method.
Important findings The change in environment could significantly affect the decomposition rate of S. alterniflora litter. The L7 in the M1 and BF environments decomposed faster than that in its original environment (M7), while the L1 in the M7 and BF environments decomposed slower than that in its original environment (M1). The variation in decomposition rate of L7 or L1 with the changing decomposition environments not only depended on the variations in the key environmental factors (temperature and pH) but also rested on the great alterations in litter quality (carbon/nitrogen and nitrogen/phosphorus ratios). Compared to the original decomposition environment, changes in the decomposition environment increased the concentration of total phosphorus (TP) in L7 generally increased while those in L1 decreased as a whole. It should be noted that the TP concentrations in L7 and L1 reached the highest values in the M1. The remaining dry mass was the common factor affecting the variations of TP in litter under different decomposition environments, while the alterations of the key environmental factor (electrical conductivity) and litter quality associated with decomposition environment changes were the primary drivers in inducing the differences of TP concentrations in different decomposition sub-zones. Stocks of P in decaying litter in different sub-zones generally showed the transfer from litter to the surroundings. This study found that both the decomposition rate and the amounts of P released from L7 and L1 were much higher in the M1, indicating that the P return rate in the M1 might be faster and this was favorable for elevating the P availability for the newly invaded S. alterniflora.

Aims Grazing is the primary human disturbance in grassland ecosystems and serves as a key external filtering factor in the grassland community assembly. However, the specific mechanisms about the influence of grazing intensity on community assembly in grasslands, particularly the relative roles of intraspecific and interspecific trait variation, remain unclear. This study systematically analyzed the responses of aboveground (shoots and leaves) and belowground (roots) plant traits to grazing, and examined the filtering effect of grazing intensity by considering intraspecific and interspecific trait variation at two spatial scales: from the auger coring to plot scale, and from the plot to site scale.
Methods In this study, we conducted field investigation based on a long-term grazing manipulation experiment in a typical steppe in Nei Mongol, China. Samples of plant aboveground parts and root systems were acquired at the individual plant level using the auger coring method. The filtering effects of grazing intensity were assessed at both the auger coring and plot scales. Furthermore, we explored the regulatory mechanisms of soil moisture and nutrients on grazing filtration.
Important findings (1) Intraspecific and interspecific variations in most aboveground traits tended to increase with higher grazing intensity, they were opposite in root traits. (2) At the auger coring scale, the filtering intensity of grazing based on intraspecific variation and interspecific variation of aboveground traits initially increased, peaked at moderate grazing intensity, and then decreased. However, the filtering intensity based on intraspecific and interspecific variations of root traits consistently increased. At the plot scale, the filtering intensity of grazing based on intraspecific and interspecific variations of aboveground traits linearly decreased; the grazing filtration intensity based on intraspecific variation of roots traits increased, while the grazing filtration intensity based on interspecific differences weakened. (3) As the spatial scale increased, the influence of grazing intensity on grassland community assembly shifted from filtering based on interspecific trait variation to filtering based on intraspecific trait variation. This shift was regulated by soil moisture and nutrient availability. These findings provide new insights into the regulatory mechanisms of grazing on grassland community assembly and provide important bases for understanding vegetation landscape heterogeneity and assessing scale effects resulting from long-term grazing. There were certain limitations in this study, where leaf and root traits mainly focused on structural characteristics. we could integrate chemical traits, such as leaf and root carbon and nitrogen contents, to comprehensively exploring the regulatory mechanisms of grazing on the variation of aboveground and belowground plant traits in future studies.

Aims The ecological stoichiometric characteristics and variation of plant leaves can reflect the response of plants to their environment, serving as a key to understanding the interaction between plants and the environment. The unique Tiankeng environment creates favorable conditions for plant growth. By exploring the nutrient utilization characteristics and environmental adaptability differences of Tiankeng plants, this study aims to reveal the adaptive mechanism of Tiankeng forest plants, and basic data can be provided for nutrient cycling and community construction in Tiankeng forest.
Methods Our study compared the chemical stoichiometry of carbon (C), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) nutrients in the leaves of plants inside and outside the Tiankeng Complex in Dashiwei, Guangxi. Statistical methods such as correlation analysis and redundancy analysis were used to explore the intrinsic relationship between chemical stoichiometry and the influence of environment on these characteristics.
Important findings (1) The leaves of 64 plant species from 36 families and 55 genera in the study area have lower C content, higher N, P, K, Ca, Mg contents, and lower C:N, C:P compared to plants in other karst and terrestrial plants in China. This indicates that the plants in Tiankeng Complex are characterized by low C sequestration, high nutrient accumulation, high growth rate, and low nutrient utilization efficiency. (2) The N:P mean value of the plant leaves in the Dashiwei Tiankeng Complex was 16.65, the N:K mean value was 1.50, and the K:P mean value was 10.10, indicating that the Tiankeng plants generally have an abundance of K content but are limited by N and P contents. (3) There were significant differences in the nutrient content and stoichiometric ratios of plants in different locations and functional groups. Different environments and plant types adopt distinct nutrient absorption strategies. (4) Correlation analysis showed that there were significant correlations between most of the nutrient contents and stoichiometric ratios of plant leaves, indicating that the nutrient uptake by plant leaves had a certain proportional composition and coordinated relationship. (5) Redundancy analysis showed that soil is a key environmental factor influencing leaf nutrients. The results of our study revealed the characteristics of plant nutrient utilization, habitat nutrient differences, and plant adaptability to the environment in the Dashiwei Tiankeng Complex, providing basic data for exploring the nutrient cycling and community construction mechanism of Tiankeng forest ecosystems.

Aims In the context of global climate change, drought-induced xylem embolism is considered as the main factor driving tree death. Therefore, analyzing the intrinsic anatomical determinants of xylem embolism resistance (water potential at 50% loss of xylem conductivity, P₅₀) is of great significance for understanding the mechanism between its structure and function, and provides a theoretical basis for the selection of tree species for vegetation restoration in the context of climate change.
Methods We measured the xylem vessel diameter, vessel grouping index, fractions of xylem tissues, pit morphology, pit membrane ultrastructure and water storage capacity (such as wood density and saturated water content), and explored the relationships between xylem embolism resistance and their anatomical structure and structural characteristics of 12 main evergreen tree species in Nonggang karst forest of Guangxi.
Important findings We found that: (1) P₅₀ had no significant correlation with vessel diameter, density, vessel grouping index and fraction of xylem tissues; (2) The correlations between P₅₀ and pit morphology, thickness of pit membrane and depth of pit chamber were not significant; (3) P₅₀ was negatively correlated with wood density and marginally positively correlated with saturated water content. Tree species with high wood density and low saturated water content had strong embolism resistance. The results indicated that using a single anatomical structure trait could not give out comprehensive evaluation on drought-induced embolic resistance. In addition, there was a trade-off between xylem water capacity and embolism resistance. This result was of great ecological significance for deeply understanding the internal structural mechanism of drought tolerance and diversified water use strategies of karst plants.

Aims Investigating the adaptive regulation of stem anatomy in desert plants under different precipitation scenarios will lead to a better understanding of the coordination mechanisms between water and carbon transport in desert plants under future precipitation patterns.
Methods In this study, a two-factor completely randomized experiment was conducted to determine the axial and radial variation in the xylem and phloem anatomy of Artemisia ordosica stems under different precipitation conditions by manipulating precipitation in the field in a semi-arid climate zone, with three precipitation treatments in amounts (30% precipitation reduction, natural precipitation and 30% precipitation increase) and two precipitation intervals (5 d precipitation interval and 15 d precipitation interval).
Important findings The results indicate: 1) Under altered precipitation, A. ordosica did not develop more conductive axial xylem structures and more conductive axial phloem structures to adapt to the changes; 2) Precipitation changes affected the radial anatomical traits of xylem and phloem of A. ordosica by altering the moisture content of the 40-60 cm soil layer. Under low moisture habitats, A. ordosica reduced the conduit diameter and increased the conduit wall thickness to ensure the safety of water transport, and maintained the phloem conductivity by increasing the lumen area of phloem sieve cells to ensure the effective transport of carbon, thus ensuring the normal physiological activities of A. ordosica; 3) The xylem conduit and phloem lumen of A. ordosica had an equal scaling axial scaling pattern, and the two were synergistically related to each other to maintain the hydraulic function, and this correlation was not affected by changes in precipitation. This study showed that A. ordosica adapted to changes in precipitation by altering the radial stem structure rather than the axial. This study is a valuable addition to the anatomical knowledge of the hydraulic structure of desert shrubs and provides a theoretical basis for future management of vegetation stability maintenance under changing precipitation patterns in semi-arid desert areas.

Aims As a plant gets taller, the distance of water flow becomes longer and hydraulic resistance becomes bigger. Dicotyledons have evolved special xylem structure to compensate for the increase of hydraulic resistance to water transport with height growth by widening conduits downwards. However, monocots have no secondary growth and thus will limit the maintenance of xylem hydraulic efficiency during ontogeny. Therefore, it is important to figure out the axial changes of the hydraulic architecture of monocots, and investigate the maintenance mechanism of water transport efficiency of these plants and the reason for their wide distribution in nature.
Methods The vessel lumen size, vessel number, stem diameter, hydraulically weighted mean vessel diameter (D_h), mean vessel area, vessel density, vessel area/vessel density parameters at different heights along the stem of two arborescent bamboos, Phyllostachys violascens ‘Prevernalis’ and Bambusa textilis from Jinhua, Zhejiang Province were studied. Standardized major axis estimation (SMA) was used to analyze the changes of traits along the axis of stem, and the covariant relationship among the traits.
Important findings In both species, hydraulic diameter increased, vessel density decreased, and the ratio of vessel area to vessel density increased accordingly from the stem apex to the base. There was a significantly negative correlation between vessel density and vessel size. These results indicated that the size of vessels in bamboo gradually widens from the stem apex to the base, and the number of vessels in the unit cross sectional area of xylem gradually decreases. It is characterized by trade-off between changes in the size and number of vessels within stem. The results show insight on the growth adaptation strategies of monocotyledonous plants.

Aims This study aimed to investigate how the colonization numbers of nitrogen-fixing, phosphate-solubilizing, and potassium-solubilizing bacteria affect the physiological traits of Malus sieversii and to ascertain the abundance of rhizosphere microorganisms conducive to their thriving in Xinjiang, China.
Methods In this study, we utilized the rhizosphere soil of M. sieversii sourced from eight distinct natural populations in Xinjiang as our primary experimental materials. Our objectives included the isolation and quantification of nitrogen-fixing bacteria (NFB), organic phosphate-solubilizing bacteria (oPSB), inorganic phosphate-solubilizing bacteria (iPSB), and potassium-solubilizing bacteria (KSB). Additionally, we assessed the physiological characteristics of M. sieversii leaves, as well as determined the nitrogen, phosphorus, and potassium content in both the leaves and the soil.
Important findings (1) A statistically significant difference was observed in the total count of four functional bacterial strains colonizing the rhizosphere across eight distinct populations of M. sieversii. The population in Wild Fruit Forest, Xinyuan County exhibited the highest cumulative count of oPSB, iPSB, NFB, and the four functional strains, while the population in Nazi Work Team, Gongliu County, displayed the highest count of KSB. (2) Both the cumulative count of the four functional bacterial strains and the count of PSB exhibited a positive correlation with changes in catalase activity within the leaves. Simultaneously, the count of KSB demonstrated a positive correlation with peroxidase activity. These findings support the existence of a correlation between the population of rhizosphere bacteria activating nitrogen, phosphorus, and potassium in M. sieversii and its resistance to external factors. (3) Regarding nutrient uptake, the counts of oPSB corresponded to phosphorus and nitrogen levels in the leaves, while iPSB counts aligned with soil phosphorus content. Additionally, both oPSB and NFB counts correlated with soil nitrogen content, while KSB counts reflected the potassium content in both leaves and soil. (4) Optimal nutritional growth of M. sieversii occurred with bacterial colonization counts of 7.08 × 10⁴ CFU·g^-1 (NFB), 2.7 × 10⁷ CFU·g^-1 (PSB), and 4.98 × 10⁵ CFU·g^-1 (KSB), respectively, resulting in higher nitrogen, phosphorus, and potassium levels in both leaves and soil.

Aims Soil ecological stoichiometry is an important indicator of soil fertility and plant nutrient status. Investigating impacts of restoration approaches on forest soil ecological stoichiometry characteristics provides a theoretical foundation and data support for accurately assessing responses of the ecosystem material cycling processes to disturbance and restoration efforts.
Methods This study compared the forest soil stoichiometry from two forest restoration approaches, i.e., artificial (RG) and natural regenerations (TR) that included three coniferous or broadleaf mixed stands and four deciduous broadleaf stands, respectively, in eastern Northeast China. The carbon (C), nitrogen (N), and phosphorus (P) contents of both soil by horizons, litterfall and litter were determined, as well as the soil properties such as pH and bulk density.
Important findings The results showed that soil C, N, and P contents decreased with the soil depth in the RG and TR. The soil C, N and P contents of the O (organic) horizon varied from 53.78 to 90.59 g·kg^-1, 5.02 to 7.83 g·kg^-1, and 0.75 to 0.91 g·kg^-1 in all the stands, respectively. The soil C and N contents of the RG were significantly lower than those of the TR in the O horizon, while the soil C, N and P contents of the RG were higher than those of the TR in the A (humus) and B (illuvial) horizons. The soil C density of the O horizon in the RG was significantly lower than that in the TR. The C:N, C:P, and N:P varied from 10.08 to 12.53, 43.97 to 135.52, and 4.56 to 11.64 in all the stands, respectively. The C:N of the O horizon had no significant difference between RG and TR, but the C:P and N:P of the O and A horizons in the RG were significantly lower than those in the TR. There was a significant positive correlation between C and N contents in all soil horizons (R² ranged from 0.40 to 0.76). Except for C:N, restoration approaches, soil horizons and their interaction had significant effects on the content, density and stoichiometry of C, N and P in soil. Soil bulk density and litterfall C content significantly affected soil C, N and P contents. These findings suggest that increasing the proportion of coniferous species by reforestation reduced the content of C and N in the topsoil, which decreased the carbon sequestration accordingly. However, restoration approaches had no significant effect on the C:N, featuring a relatively stable carbon and nitrogen stoichiometry.