Forest size structure (the diameter distribution of trees in a forest) is a comprehensive indicator of forest demographic processes. It is the basis for determining forest successional stage and the state of forest health, estimating forest biomass and predicting forest carbon sink potential. Studies of forest size structure began with statistical descriptions before progressing to theoretical and mathematical deduction. In early statistical studies of forestry, many common probability distribution functions were used to fit plot-scale variations in size structure, but most of these functions were not derived from biological processes and therefore lack clear biological meaning. With the development of macroecology, the principle of maximum entropy and the central limit theorem have been used to explain the relatively consistent forest size structure at large spatial scales. Such models mainly focus on probabilistic statistics rather than ecological processes. Reports of a power-law size structure in natural mature forests in the early 2000s spawned a series of theoretical studies, including metabolic scaling theory and the theory of gap succession, among others. These theories have proposed that the observed power-law size structure results from the relationship between tree size and resource use on the individual scale and tree competition for resources on the community scale. Demographic equilibrium theory provides a general framework for analyzing the relationship between the steady state forest size structure and tree growth and mortality. Under this equilibrium framework, the hypothesis of demographic optimality further provides a new perspective for the analysis of forest size structure. Mathematical models including transition matrices, integral projections, and partial differential equations are powerful tools for analyzing forest size structure dynamics. However, due to the difficulty of identifying time-varying solutions to the mathematical models, most studies have been confined to the framework of forest demographic equilibrium. To understand dynamic variations of forest size structure and predict forest carbon sink potential in a rapidly changing climate, it is essential both to find general time-varying solutions to the mathematical models and to tighten empirical constraints on the effects of climatic factors on forest growth and mortality rates.

Aims Non-structural carbohydrates (NSCs) include starch and soluble sugars, the transformation of which enhances plant resistance to environmental stresses. Tropical rainforests play an important role in the carbon (C) pool of terrestrial ecosystems and in mitigating climate change, and they are also hotspots for atmospheric nitrogen (N) and phosphorus (P) deposition. To date, the response of leaf NSCs of dominant plants in primary and secondary forests to long-term N and P inputs is unclear.

Methods We investigated the effects of long-term N and P inputs on leaf NSCs of eight species from each of the primary and secondary forests based on a 10-year N and P addition experiment in Jianfengling, Hainan, and analyzed the relationships of NSCs with each of the leaf traits, photosynthesis parameters, and soil nutrients.

Important findings Dominant plant leaves in the secondary forest had higher soluble sugar and NSCs contents than that in the primary forest. Low N addition significantly reduced the content of starch, P addition significantly increased the content of soluble sugar, and combined N and P additions enhanced the ratio of soluble sugar and starch in dominant plant leaves of primary forest; whereas N and P additions did not impact the NSCs content of dominant plant leaves of secondary forest. In the two forests, leaf NSCs content of eight species were negatively correlated with leaf pH and specific leaf area, while positively correlated with leaf C content, photosynthesis rate, and photosynthetic N use efficiency. There was significant positive relationship between leaf NSCs and each of soil available N, total P contents in secondary forest. These results suggest that leaf NSCs of dominant plants is jointly impacted by leaf traits and soil nutrients in tropical rainforests. From the perspective of the leaf C economy, our study demonstrates that dominant plants are more sensitive to atmospheric N and P deposition in primary than in secondary forests, thereby highlighting the importance of protecting tropical primary rainforests.

Aims Despite grazing being a significant driving factor for grassland ecosystems, it remains uncertain whether the responses of grassland plant communities and functional groups to soil variables remain consistent across grazing intensity gradients.

Methods This study conducted field plant community surveys in the middle part of the northern slope of Tianshan Mountains, and lab soil analysis. It aimed to analyze the impact of grazing on plant communities and functional groups, as well as reveal differences in their responses to soil factors under grazing intensity.

Important findings The results indicated that perennial grasses and sedges were the main dominant functional groups in light grazing and no grazing sites. However, heavy grazing sites had poisonous grasses as dominant functional groups, with Achnatherum inebrians being the dominant species. Light grazing significantly increased above-ground biomass for functional groups such as perennial grasses, legumes, sedges, and forbs while notably decreased for poison grasses compared to heavy grazing along the gradient. In terms of functional group diversity, Shannon-Wiener index, Margalef index, and Pielou index were significantly higher under light grazing than heavy grazing; however, Simpson index did not show significant differences between different levels of grazing intensity. Results from redundancy analysis, Mantel test, and structural equation models demonstrated significant correlations between plant community characteristics (including functional groups), community diversity indices (Shannon-Wiener index), and various soil factors such as organic carbon content, available nitrogen content, available potassium content, total phosphorus content, total potassium content, soil density, soil water content. Grazing directly exerted a significant negative impact on grassland height, coverage, density, aboveground biomass, diversity within both plant communities and functional groups. The soil density increase and soil nutrient reduction caused by grazing can also impact community height, coverage, density, above-ground biomass, as well as the diversity of plant community and functional groups. In summary, soil factors played a pivotal role in maintaining the stable growth of grassland plant communities amidst grazing disturbance in middle part of northern slope of Tianshan Mountains. The findings provide a scientific foundation for the rational utilization of grassland plant resources in Xinjiang.

Aims The trait-based approach has been extensively utilized to evaluate the influence of neighborhood competition on seedling survival. However, previous studies used species average traits, ignoring intraspecific trait variation.

Methods Based on the monitoring of 150 seedling plots in a needleleaf and broadleaf mixed forest in Jiaohe, Jilin, we used a generalized linear mixed effect model of binomial distribution to compare the effects of intraspecific trait variation and species average traits on seedling survival rate, and explore how functional traits mediate seedling responses to neighborhood competition and abiotic environmental factors.

Important findings The intraspecific trait variation model and the species average trait model had inconsistent predictive abilities for seedling survival rate. Specifically, intraspecific variability model of specific leaf area (SLA) exhibited a smaller Akaike information criterion value and Bayesian information criterion value, a larger explanatory variance and a better fit. While species average trait model of leaf area (LA), leaf carbon content (LCC), and leaf nitrogen content (LNC) performed better. In addition, traits mediate the effects of neighborhood competition and soil nutrients on seedling survival. Seedlings with smaller LA have higher survival rates under the same density dependence. Higher LCC increases seedling survival rate in the absence of soil nutrients, while seedling survival rate decreases under fertile soil conditions. The ability of intraspecific trait variation in predicting individual survival of seedlings may not be stronger than species average trait, which may be related to forest stands and environmental factors. In addition, the presence of neighborhood competition and environmental variables can enhance the relationships between traits and seedling survival. Although intraspecific trait variation may not improve the prediction of seedling survival rate, this individual-based approach provides a new perspective for predicting seedling dynamics.

Aims Leaf traits are affected not only by plant sizes, but also by different canopy conditions where mature trees and saplings grow. Thus, these trees choose various survival strategies to adapt to different canopy conditions by adjusting their leaf traits. The aim of this study is to investigate the changes of leaf traits of three Acer trees along with the changes of plant size and canopy condition.

Methods In this study, three species (Acer ukurunduense, A. tegmentosumand A. pictumsubsp. mono) in broadleaf Pinus korainesis forest in Xiao Hinggan Mountains of Northeast China were selected. Six leaf economics spectrum traits, specific leaf area (SLA), leaf dry matter content (LDMC), leaf thickness (LT), chlorophyll (Chl) content, net photosynthetic rate per area (A_area) and non-structural carbohydrates (NSC) content, together with two defensive traits, total phenolics (TP) content and flavonoids (FLA) content of adult trees and saplings in gaps and saplings in understory were measured. Whether leaf traits and their relationships varied with plant sizes and canopy conditions was further analyzed to illustrate how gaps influence forest regeneration by altering leaf traits, and to explore the differentiation of survival strategies for plant individuals growing under various habitats.

Important findings Adults in gaps had higher LDMC, Chl content, FLA content and NSC content compared with saplings in gaps, which meant adults had adequate photosynthetic accumulation and they were more capable to defend against herbivory. LDMC, LT, Chl content and A_area of gap saplings were significantly higher than saplings in understory, indicating that canopy condition was a vital source of leaf trait variations. The absolute slope of relationship between SLA and LDMC for adults was significantly higher than that for saplings in gaps, but the absolute slope of understory saplings was significantly lower than that of the gap saplings. The relationship between defensive traits remained stable among different plant sizes and canopy conditions. These evidences showed that, adults invested more in leaf construction such as leaf thickness and defensive substances, so they chose “conservative” strategy. Saplings in understory improved their ability to acquire light by increasing SLA, they therefore tended to choose “acquisitive” strategy. Saplings in gaps however, showed the transition strategy between “conservative” and “acquisitive” strategies. Results further indicated that, when saplings were not limited by light, their photosynthetic rate increased rapidly to be significantly higher than that of adults. In addition, forest gaps can promote the regeneration of forest stand by enhancing the abilities of photosynthesis and resistance to herbivory of saplings.

Aims Individual size reflects the radial growth of trees, while fine roots are highly sensitive to changes in the rhizosphere soil environment. Investigating the relationship between functional traits of fine root and the microenvironment of rhizosphere soil in trees at different sizes can contribute to elucidating interaction mechanisms within the forest subsurface ecosystem of trees at the individual level.

Methods In this study, fine roots and rhizosphere soil sampling were conducted based on Machilus pauhoi individuals of different sizes in an 11-year-old plantation. The aim is to analyze the relationship between fine root functional traits, rhizosphere soil nutrients content, microbial community structure, and enzyme activities of M. pauhoi individuals of different sizes.

Important findings The results indicate that: 1) There are differences in fine root functional traits and rhizosphere microenvironment among trees of different sizes. Significant differences were observed in traits such as fine root biomass, specific root length, root length density, root volume density, root tissue density, root nitrogen content and root phosphorus content. Except for the specific root area and root tissue density, other fine roots functional traits were highest in the medium-sized individuals, and rhizosphere soil carbon, nitrogen, and phosphorus contents were also highest in medium-sized M. pauhoi. 2) Variability coefficients of fine root traits such as specific root length, root volume density, fine root biomass, and rhizosphere soil fungal and actinomycete contents were relatively large among M. pauhoi individuals of different sizes, particularly pronounced in medium- sized individuals and relatively low in small-sized individuals. All individuals tend to adapt to environmental changes by adjusting traits such as root volume density, fine root biomass, rhizosphere soil fungal contents and nitrate nitrogen content. 3) The fine roots at different individual sizes adopted different resource utilization strategies. Medium-sized M. pauhoi exhibited larger specific root length, root nitrogen content, and root phosphorus content, indicating a resource acquisition strategy to optimize nutrient acquisition capacity. Small-sized individuals with larger root tissue density adopted a resource conservation strategy to enhance their ability to cope with environmental stress, while large individuals exhibited a balanced strategy between above-ground and below-ground growth. 4) Soil total carbon content, microbial biomass carbon content, actinomycete content, ammonium nitrogen content, acid phosphatase activity, and microbial biomass nitrogen content in the rhizosphere soil microenvironment were identified as the main factors influencing fine root functional traits of M. pauhoi. The relationship between fine root functional traits and rhizosphere microenvironment varied among individuals of different sizes. Fine roots of small-sized M. pauhoi individuals were mainly affected by rhizosphere soil nutrients, while those of medium-sized M. pauhoi individuals were primarily influenced by the content of actinomycete and acid phosphatase activity in the rhizosphere soil. Fine root traits of large-sized individuals were affected by both rhizosphere soil nutrients and soil microbial community structure, including bacteria and actinomycete content. The finding provide theoretical insights for implementing afforestation of M. pauhoi on a microtopographic scale, precisely developing artificial forest tending and thinning measures, and cultivating large-diameter timber plantations.

Aims Dioecious plants typically exhibit varying resource demands due to different reproductive costs. Gender disparities in the nutritional requirements of dioecious plants often result in sexual dimorphism during their life cycle. This study seeks to deepen our understanding of gender-related differences in plant resource needs by examining the performance patterns and characteristics of sexual dimorphism in dioecious plants across different reproductive costs and growth stages. We focus on Acer barbinerve, a dioecious plant native to the natural coniferous and broadleaf mixed forest in Jiaohe, Jilin, and assess the leaf elemental stoichiometric characteristics to measure sexual dimorphism among different sexes of A. barbinerve plants in this region. Our goal is to investigate sexual dimorphism in A. barbinerve across different growth stages and reproductive costs.

Methods Sixty male and female A. barbinerve individuals were selected from the sample plot and divided into three groups. Group I received no treatment, Group II had all buds removed at an early flower bud stage, and Group III had all flowers removed at the end of the flowering period. Leaves were collected at both flowering and fruiting stages, and a two-way ANOVA was conducted to determine the significance of differences in leaf elemental characteristics between male and female A. barbinerve under various reproductive costs.

Important findings Sex had significant effects on the contents of carbon (C), phosphorus (P), potassium (K), magnesium (Mg) and sulfur (S) in leaves at the flowering stage, as well as the contents of C, nitrogen (N), P, K, calcium (Ca), Mg, and S in leaves at the fruiting stage. During the flowering stage, the leaf C content and C:N, C:P, N:P of male plants in Groups II and III was significantly higher than that of female plants. Additionally, the contents of P, K, Mg, S in female plants were significantly higher than those in male plants. In Group I, the leaf C content and C:N, C:P, N:P of female plants was significantly higher than that of male plants, while the leaf N, P, K, Ca, Mg and S contents of male plants, were significantly higher than those of female plants. These results indicate that the elemental stoichiometry of male and female A. barbinerve leaves exhibits sexual dimorphism. Changes in reproductive cost and growth stage affect the occurrence of sexual dimorphism in dioecious plant.

Aims Forest fire is an important driver of boreal forest regeneration, and commonly generates a series of products, which play an important role in promoting or inhibiting seed germination. While seed germination in soil seed banks following forest fire is the main pathway for renewal and recovery of seed plants, relatively limited research has been conducted in China on post-fire renewal and recovery of trees compared to herbaceous and shrub plants. In this paper, the seeds of Larix gmelinii on the Da Hinggan Mountains area were selected to investigate their germination response to fire disturbance, which could provide theoretical support for the rapid renewal and recovery of L. gmelinii after fire.

Methods The individual and joint effects of heat shock, fire ash, and light on the germination rate and germination potential of L. gmelinii seeds were examined with analysis of variance.

Important findings The germination rate of L. gmelinii seeds was highest under dry thermal stimulation at 90 °C for 5 min (61.11%), 21.11% higher than the control, and the seeds were inactivated under the wet thermal stimulation at 90 °C for 5 min and above. The quality of fire ash was positively correlated with the germination rate of L. gmelinii seeds, and the germination rate of L. gmelinii seeds under the addition of 1 g of fire ash was 71.1%, 30% higher than the control; the quality of light was negatively correlated with the germination rate of L. gmelinii seeds, and the germination rate of the seeds under 100% shading increased by 14.00%, while this rate under 0 shading decreased by 16.67% compared to the control. In terms of the interactions among heat stimulation, fire ash and light, the highest seed germination rate (57%) of L. gmelinii seeds (17% higher than the control) appeared under the 1 g fire ash + 100% shading. The contributions of multiple factors to seed germination followed the order, fire ash > dry heat shock > light > wet heat shock, each explaining 33.0%, 31.8%, 20.3%, and 14.9% of the variance. Ash was the most dominant abiotic driver, and factor importance was as follows: fire ash (1.00 g) > dry heat shock (60 °C 3 min) > light (0 shading) > wet heat shock (90 °C 3 min) > wet heat shock (60 °C 3 min) > light (100% shading) > fire ash (0.25 g) > dry heat shock (120 °C 3 min) at the 95% confidence interval.

Aims Fire is an important disturbance factor that limits plant growth and development, affects plant metabolism and even leads to plant mortality. Non-structural carbohydrates (NSC) mainly include soluble sugar (SS) and starch (ST), which play an important role in plant survival under disturbance. However, the response mechanism of plant NSC and its components to time since fire is unclear.

Methods In this study, five severely burned plots in Huzhong area of Da Hinggan Mountains with different postburn time and one adjacent unburned plot were selected for space-for-time substitution approach. Leaf, fine root and rhizosphere soil samples of Betula platyphylla were collected. The content of NSC and its components, the traits of leaf and fine root, and rhizosphere soil properties were measured.

Important findings The content of ST and NSC in B. platyphylla leaves decreased significantly, while the content of ST and NSC in fine roots increased significantly with increasing time since fire. The content of NSC in leaves and fine roots tend to be stable at 30 and 17 years after fire, respectively, and not differ from the unburned plot, indicating that the NSC of fine roots recovered faster from severe fire disturbance. Postburn time directly affect the NSC content of B. platyphylla leaves, and also has an indirect effect on the NSC content of leaves by affecting the specific leaf area. The effect of postburn time on NSC content in B. platyphylla fine roots is mediated by affecting soil pH and specific leaf area. In conclusion, the effect of postburn time on NSC content in plants differs among organs. This result contributes scientific data and theoretical basis to the study of vegetation restoration in burned areas.

Aims As a typical water-related physiological parameter, the stem water content of living standing trees has always been one of the most effective characterization parameters of the life state of living standing trees, which plays an important role in maintaining the water balance of the whole tree, and has been highly valued by researchers and forest tender. However, the method of obtaining stem water content sequence of living standing trees has been affected by factors such as cumbersome operation, expensive cost, poor real-time performance, low accuracy and damage to the life of living standing trees, which limits its in-depth research and application. We innovatively adopted a stem water content sensor with independent intellectual property rights to obtain the stem water content of standing trees in real time and non-destructively, and conducted a thorough investigation of the stem water content sequence and its influencing factors.

Methods A common virescence tree species Acer pictumsubsp. mono was chosen as the research object. The stem water content sensors based on the standing wave rate principle independently developed by our team were used to achieve in-situ and non-destructive monitoring of stem water content in the growing season. Meanwhile, meteorological parameters were simultaneously measured. The sequence characteristics of stem water content and its response to meteorological factors at different stages of growing season were analyzed.

Important findings (1) In spring (April) and mid-late autumn (from September to October), the stem water content presented the rhythm of “rising in the day and falling in the night”, while from summer to middle autumn (from May to August) presented a rhythm of “falling in the day and rising in the night”; the daily range and maximum of stem water content would be inhabited under the cloudy day, while rainy days led the stem water content surge to a large value, and dry days dropped the stem water content. (2) During the germination stage, the main meteorological factors that had direct effects on the variation of stem water content were air temperature and vapor pressure deficit. During the growth period, the main meteorological factors directly affecting stem water content were vapor pressure deficit and soil temperature. During the defoliation stage, the main meteorological factors that had direct effects on stem water content were air temperature and vapor pressure deficit, and the Pearson correlation coefficients between stem water content and these two factors were higher. A stepwise regression analysis method was used to model the relationship between stem water content and various meteorological factors in these three periods, the meteorological factors entering the regression model at different periods were different. In conclusion, this study revealed that stem water content exhibited different sequence characteristics and influencing factors under the synergistic effects of different meteorological factors, which could provide some insights into the internal water transport capacity and environmental adaptation mechanism of plant stems.

Aims The aim of this study was to isolate the harmful strain and analyze the effects of its metabolites on Rehmannia glutinosa, which provided theoretical support for solving R. glutinosa continuous cropping obstacles.

Methods The fungi were isolated from continuous cropping soil. The fungal fermentation liquid metabolites were separated using different polarity gradient extraction and silica gel column chromatography. Metabolites were determined by high performance liquid chromatography and liquid chromatography-mass spectrometry.

Important findings A strain of Penicillium oxalicum C11 was isolated from continuous cropping soil. The toxic metabolite of P. oxalicum C11 was identified as cyclo (L-Arg-L-Leu) dipeptide (molecular weight: 269.347, molecular formula: C₁₂H₂₃N₅O₂). Results indicated P. oxalicum C11 inhibited R. glutinosa yield by 41.5%, suggesting that the toxic metabolite L-Arg-L-Leu could be vital for R. glutinosacontinuous cropping obstacles.