Xiankun Li

This study investigates drought resistance-growth trade-offs in dominant tree species across elevationally stratified habitats (depression, middle slope, hilltop) of Nonggang karst seasonal rainforest in southwestern China. Analysis of 38 species along a 190-meter aridity gradient reveals drought resistance enhancement through foliar modifications: 56.79% increase in cuticle thickness, 56.42% denser palisade mesophyll thickness, and 36.48% expansion in spongy mesophyll thickness, accompanied by 45.67% growth reduction. Structural equation modeling confirms a significant drought resistance-growth trade-off (β = − 0.504), indicating carbon allocation constraints. Hilltop species employ an anisohydric strategy combining stomatal optimization (4.45% shorter length, 27.17% wider apertures achieving 33.10% increased opening) with 15.52% reduced upper epidermis cell width and cuticle thickening, enhancing hydraulic efficiency despite 111.63% elevated dark respiration rates. This high-resistance/low-growth strategy contrasts with depression-adapted species showing superior low-light performance: 30.35% higher quantum yield and 63.44% lower light compensation points compared to hilltop counterparts. Environmental driver analysis identifies soil moisture (β = − 0.706) and bedrock exposure (β = − 0.594) as key factors shaping trait divergence. Drought suppresses growth through dual pathways: direct resource limitation (β = − 0.667) and indirect metabolic costs of resistance traits (β = − 0.469). Coordinated leaf trait evolution reduces niche overlap via drought-growth trade-offs, establishing habitat filtration-mediated biodiversity maintenance in karst ecosystems. These results provide a multidimensional framework for balancing stress resistance and productivity in tropical karst vegetation restoration.

Forest biomass accumulation is fundamental to ecosystem stability, material cycling, and energy flow, and pit lays a crucial role in the carbon cycle. Understanding the factors influencing aboveground biomass (AGB) is essential for exploring ecosystem functioning mechanisms, restoring degraded forests, and estimating carbon balance in forest communities. Tropical karst seasonal rainforests are species-rich and heterogeneous, yet the impact mechanisms of biotic and abiotic factors on AGB remain incompletely understood. Based on the survey data of a 15 ha monitoring plot in a karst seasonal rainforest in Southern China, this study explores the distribution characteristics of AGB and its intrinsic correlation with different influencing factors. The results show that the average AGB of the plot is 125.7 Mg/ha, with notable variations among habitats, peaking in hillside habitats. Trees with medium and large diameters at breast height (DBH ≥ 10 cm) account for 83.94% of the aboveground biomass (AGB) and are its primary contributors; dominant tree species exhibit higher AGB values. Both biotic and abiotic elements substantially influence AGB, with biotic factors exhibiting the largest influence. Among abiotic factors, topographic factors have a strong direct or indirect influence on AGB, while soil physicochemical properties have the smallest indirect impact. This research provides a comprehensive understanding of AGB distribution and its influencing factors in tropical karst forests (KFs), contributing to the management of carbon sinks in these ecosystems.

In a community, due to the different characteristics of each species, their contributions to community beta diversity may vary. Quantifying the contribution of each species to overall beta diversity (SCBD) is essential for explaining the patterns of beta diversity. However, there is currently limited research linking SCBD with species functional traits, and how species functional traits influence SCBD remains unclear. This study is based on tree census data, species functional traits, and environmental variables from a 15 ha permanent monitoring plot in a tropical karst rainforest in south China. By calculating species-specific SCBD based on abundance and presence–absence data, as well as functional distinctiveness and species ecological niche characteristics (niche position and niche width), we applied structural equation modeling (SEM) to analyze how functional traits, distinctiveness, and niche characteristics jointly influence SCBD. The results revealed that SCBD based on abundance is positively correlated with occupancy and abundance, whereas SCBD based on presence–absence data exhibits a hump-shaped relationship with occupancy and abundance. Species ecological niche characteristics directly influence SCBD, with species occupying central ecological niches having a negative effect on SCBD and niche width having a positive effect. Functional traits and functional distinctiveness indirectly impact SCBD through their influence on species ecological niche characteristics. SEM models based on the presence–absence data provide higher explanatory power. In summary, in the seasonal rainforest communities of northern tropical karst regions in China, the combined effects of species’ functional traits, functional distinctiveness, and ecological niche characteristics determine SCBD. This not only contributes to a deeper understanding of how species traits influence β-diversity, making SCBD a more applicable tool for biodiversity conservation, but also allows for the development of more effective biodiversity protection strategies by elucidating the link between SCBD and ecosystem multifunctionality.

Lianas are a crucial component of karst seasonal rainforests, yet research on them has predominantly focused on non-karst regions. Consequently, their abundance and species richness remain relatively understudied within karst ecosystems. We aimed to document the abundance and species richness of lianas and investigate their relationships with abiotic and biotic factors, based on data from a fully mapped 15 ha plot in a karst seasonal rainforest of Nonggang (SW China). Structural equation models (SEMs) were employed to estimate the path coefficients and variation of dependent variables, enabling a comprehensive analysis of the factors affecting the abundance and species richness of liana. Within the 15 ha plot, a total of 23,819 lianas were identified, encompassing 113 species from 34 families. These lianas constituted 24.16% of the total woody plant density and 33.44% of the species present, but only 4.32% of the total woody plant basal area. Lianas are primarily influenced by abiotic factors, especially elevation and phosphorus (P), with less impact from biotic factors. Our findings reveal that lianas, despite constituting a relatively small percentage of the total woody plant basal area, significantly contribute to the density and diversity of the forest. Notably, abiotic factors such as elevation and phosphorus availability predominantly shape the distribution and richness of lianas, highlighting the importance of these environmental variables. The findings offer valuable insights for future liana studies and the preservation of karst forests’ biodiversity.

望天树是我国热带季节性雨林的标识性树种，其原生境热带森林群落是我国植物热带性最强烈、种类组成最复杂、雨林特征最浓厚的植被类型，但现存分布区域狭窄。近期广西弄岗热带喀斯特峰丛洼地森林发现高72.4米的望天树，打破了我国喀斯特区域和华南地区的最高树记录，刷新了以往对热带喀斯特森林植被特征的认知。该文基于弄岗望天树原生境森林群落调查样方，展示了其群落的林层结构、物种组成及生态特征，与我国其他望天树群落对比分析探讨了其植被生态学意义。结果表明：（1）该群落有高50米以上望天树巨树散生乔木冠层之上；连续乔灌层可分为四层，平均高度分别为36.9 m、25.6 m、9.5 m和2.7m；在2400 m2样方内乔、灌、藤、草、附生植物分别有64种、24种、31种、26种、8种；（2）林冠上层优势种有望天树、人面子等典型热带区系树种，蚬木、肥牛树等喀斯特专性树种，岭南酸枣、白头树等落叶树种；（3）在乔木层的物种中，热带亚洲（印度-马来）分布型占65.6%，大高位芽植物占15.6%，常绿植物占85.9%，复叶植物占39.1%，革质叶片占60.9%，典型喀斯特植物占28.1%；（4）该区域群落乔木层优势属与我国其他望天树群落的相似性从高到低依次为，广西那坡县、云南马关和勐腊县、广西巴马、田阳和大化县；群落结构组成差异与气候环境条件显著相关。综上，广西弄岗望天树原生境群落是在热带喀斯特峰丛洼地的局域封闭生境条件下发育形成的巨树散生、林层复杂的热带季节性雨林植被，孕育着丰富的耐旱型的典型喀斯特植物。

Rhizosphere microbes have an extremely close relationship with plants and the study on the relationship between rhizosphere microorganisms and their influencing factors is conducive to the protection of vegetation and the maintenance of biodiversity. Here we investigated how plant species, slope positions and soil types affect the rhizosphere microbial community. Slope positions and soil types were collected from northern tropical karst and non-karst seasonal rainforests. The results indicated that soil types played a predominant role in the development of rhizosphere microbial communities (28.3% of separate contribution rate), more than plant species identity (10.9% of separate contribution rate) and slope position (3.5% of separate contribution rate). Notably, environmental factors closely related to soil properties were the major influence factors that controlling the rhizosphere bacterial community structure in the northern tropical seasonal rainforest, especially pH. Additionally, plant species also influenced the rhizosphere bacterial community. In low nitrogen content soil environments, rhizosphere biomarkers of dominant plant species were often nitrogen-fixing strains. It suggested that plants might have a selective adaptation mechanism to rhizosphere microorganisms to obtain the advantages of nutrient supply. Overall, soil types exerted the biggest influence on rhizosphere microbial community structure, followed by plant species and finally slope positions.

Rural agricultural activity generates cropland, secondary vegetation and straggling primary forest and can modify the soil seed bank (SSB), potentially impacting the restoration of preferred species. The interaction between vegetation and seed banks during the recovery process is dependent on management practices and recovery pathways. This study was carried out in Guilin of southwest China to assess the variation in plant diversity and species composition of both aboveground and soil seed banks across three typical vegetation types with different human interventions: orchard, bamboo shrub and primary forest. The results show that there were significant differences in the species composition and diversity of aboveground vegetation and SSB, as well as in soil properties among three typical vegetation types. The primary forest had the highest aboveground species diversity, while the orchard had the highest species diversity and seed density of SSB. In addition, principal component analysis (PCA) and canonical correspondence analyses (CCAs) showed that the species composition and plant life forms of the three typical vegetation types were significantly influenced by soil properties. Based on these findings, the characteristics of aboveground vegetation and the soil seed bank and their correlations with soil properties are expected to drastically change with human intervention. These results imply that unsustainable land use has greatly impacted soil properties, and consequently, the aboveground vegetation and SSB. Nevertheless, vegetation will recover quickly after farming is abandoned. The successful restoration of fragmented ecosystems requires the addition of seeds and seedlings of target species, especially perennial woody plants from the relevant natural ecosystems, to accelerate succession from bamboo shrub to forest.

: Foundation species play important roles in structuring forest communities and ecosystems. Foundation species are difficult to identify without long-term observations or experiments and their foundational roles rarely are identified before they are declining or threatened. We used new statistical criteria based on size-frequency distributions, species diversity, and spatial codispersion among woody plants to identify potential (“candidate”) foundation species in 12 large forest dynamics plots spanning 26 degrees of latitude in China. We used these data to identify a suite of candidate foundation species in Chinese forests; test the hypothesis that foundation woody plant species are more frequent in the temperate zone than in the tropics; and compare these results with comparable data from the Americas to suggest candidate foundation genera in Northern Hemisphere forests. We identified more candidate foundation species in temperate plots than in subtropical or tropical plots, and this relationship was independent of the latitudinal gradient in overall species richness. Two species of Acer , the canopy tree Acer ukurunduense and the shrubby treelet Acer barbinerve were the only two species that met both criteria in full to be considered as candidate foundation species. When we relaxed the diversity criteria, Acer, Tilia , and Juglans spp., and Corlyus mandshurica were frequently identified as candidate foundation species. In tropical plots, the tree Mezzettiopsis creaghii and the shrubs or treelets Aporusa yunnanensis and Ficus hispida had some characteristics associated with foundation species. Species diversity of co-occurring woody species was negatively associated with basal area of candidate foundation species more frequently at 5- and 10-m spatial grains (scale) than at a 20-m grain. Conversely, Bray-Curtis dissimilarity was positively associated with basal area of candidate foundation species more frequently at 5-m than at 10- or 20-m grains. Our data support the hypothesis that foundation species should be more common in temperate than in tropical or boreal forests, and suggest that in the Northern Hemisphere that Acer be investigated further as a foundation tree genus.

Both deterministic and stochastic processes have been linked to forest community assembly; however, their contribution to beta diversity has not been properly explored, and no studies to date have investigated their impacts on sparse depleted soils in forests that contain widespread exposed limestone karst. We found that the pairwise differences in species composition between quadrates was determined by a balanced variation in abundance, whereby the individuals of some species at one site were substituted by an equivalent number of individuals of different species at another site. Both the total beta diversity and its balanced variation in abundance declined with increasing sampling grain size. Our research indicated that environmental differences exert a strong influence on beta diversity, particularly total beta diversity and its balanced abundance variation in larger grain sizes. It was evident that deterministic and stochastic processes worked together, and that deterministic processes were more important than stochastic processes in the regulation of beta diversity in this heterogeneous tropical karst seasonal rainforest of Southern China. However, in future research a functional trait based approach will be required to tease out the relative degree of deterministic and stochastic processes toward an assessment of the temporal changes in species composition.