Aims Diatoms are an important component of marine phytoplankton, and their photosynthetic production reaches more than 40% of the ocean primary productivity. The combined effects of enhanced solar UV radiation and seawater warming will affect the photosynthesis of diatoms, affecting their contribution to the primary production. In this study, we mainly explored the photosynthetic physiological regulation of diatoms in response to UVR radiation by warming, in order to further understand the effects of marine environmental changes on the photosynthesis of diatoms. Methods Thalassiosira weissflogii was cultured at 18oC and 24oC and exposed to high visible light (PAR, 400 to 700nm) and UV radiation (PAR+UVR, 280 to 700nm) to monitor changes in PSII function and other physiological responses. Important findings PAR and PAR+UVR inhibited the maximum photochemical efficiency (Fv/Fm) of PSII in Thalassiosira weissflogii. The photoinactivation rate constant (Kpi) of PSII increased significantly in the presence of UVR. The ratio of repair rate constant to phtotinactivation rate constant of PSII (Krec/Kpi) in UVR was similar to that under low temperature. Analysis of PSII subunit turnover showed that warming under visible light allowed cells to maintain a high PsbD pool, whereas warming under UVR synergistically promoted rapid clearance of damaged PsbA. In addition, the activities of SOD and CAT were higher in the cells under the increased temperature, and low level of NPQ was induced under all treatments. Our results showed that warming can promote the photosynthetic performance of the Thalassiosira weissflogii by adjusting its PSII repair cycle to counteract the inhibitory effect of UVR.

Aims Alpine shrublands are crucial for global carbon cycle due to their substantial soil carbon storage and sensitivity to global changes. Twig and leaf litter play a crucial role in terrestrial ecosystem carbon and nutrient cycling; however, comparative studies on their production and decomposition remain limited. This knowledge gap hinders accurate assessments of their contributions to soil carbon and nutrient cycling. Methods This study investigated the annual production, decomposition rates, and carbon and nitrogen retention of twig and leaf litter in an alpine shrubland ecosystem on the eastern margin of the Qinghai–Tibetan Plateau of China over a four-year period. Important findings Results found that: (1) Leaf litter production (138.94 g·m?2·a?1) was 4.41 times higher than twig litter production (31.48 g·m?2·a?1). Thus, leaf litter had a higher annual carbon and nitrogen inputs than twig litter. (2) Decomposition rate of twig litter (K = 0.356 a-1) was significantly slower than that of leaf litter (K = 0.522 a-1). The proportion of recalcitrant fraction of twig litter during decomposition was 4.86 times higher than that of leaf litter (0.287 vs. 0.059, respectively). (3) Nitrogen release patterns differed between twig and leaf litter: leaf litter exhibited a net nitrogen release, while twig litter followed a pattern of “enrichment—stabilization—release”. (4) After four years of decomposition, the estimated annual carbon retention of twig and leaf litter was similar (3.85 g?m-2?a-1 for twig litter and 3.72 g?m-2?a-1 for leaf litter). However, leaf litter retained significantly more nitrogen than twig litter (0.11 g?m-2?a-1 vs. 0.06 g?m-2?a-1). This study highlights the complementary roles of twig litter in promoting carbon accumulation in alpine shrubland due to its slower decomposition. In contrast, leaf litter plays a more crucial role in alleviating soil nitrogen limitation due to its faster nitrogen release and higher nitrogen return. Our results provide valuable foundation for accurately assessing the contributions of twig and leaf litter to soil carbon and nitrogen cycling.

Aims Plant sexual systems is an important reproductive role that affects plant mating, genetics, evolution, and species distribution. They are classified into three categories based on the floral organ's pistil and stamen arrangement: hermaphroditism, dioecy, and monoecy. Methods This article takes forest communities in Daiyun Mountain (elevation 900-1600 m) as the research object, analyzing changes in the quantitative characteristics of woody plant sexual systems and investigating their correlation with environmental factors via Mantel correlation analysis. Important findings The study area encompassed 85 woody plant species, with 49 hermaphroditic (57.6%), 26 dioecious (30.6%), and 10 monoecious (11.8%) species. Altitudinal increase led to a significant rise in the number of hermaphroditic and dioecious individuals, with no significant change in their species ratio, while monoecious individuals' number and species ratio significantly declined. The Shannon Wiener index and Pielou evenness index for sexual systems generally decreased with altitude, whereas the Simpson dominance index remained stable. Effective phosphorus and soil temperature were identified as the primary drivers of altitudinal changes in sexual systems characteristics. In conclusion, the quantitative characteristics of the sexual systems of woody plants on the altitudinal gradient of Daiyun Mountain showed significant differences, and the altitudinal distribution of the sexual systems was highly sensitive to environmental changes, indicating that plants adapt to environmental changes by regulating the composition of their reproductive systems, thereby ensuring the continuous survival and reproduction of their populations.

Aims Revealing the regional variation of functional traits and adaptation strategies of eurybiont is of great significance for predicting the adaptation potential of plants under climate change. Methods Here, Setaria viridis was studied with 18 water-carbon related functional traits of stem and leaf organs measured and 9 study sites were selected along the precipitation gradient from southeast to northwest China. The methods of trait network and principal component analysis were used to quantify the regional differentiation of traits, and to clarify their habitat adaptation strategies. Important findings The results showed that: (1) In humid regions, Setaria viridis exhibited the largest vessel diameter and specific leaf mass; in the semiarid/humid region, Setaria viridis exhibited the highest maximum net photosynthetic rate per unit leaf area, anatomical maximum stomatal conductance and stomatal area fraction; in arid regions, Setaria viridis exhibited the highest thickness-to-span ratio of vessel and maximum net photosynthetic rate per unit leaf mass. These various reflected the Setaria viridis’ adaptation strategies in different regions. (2) With the decrease of precipitation, the correlation between traits decreased, the connectivity of the network decreased, and the complexity increased. The proportion of positive correlation between traits of the network reached the maximum in the semiarid/humid regions, showing the best cooperative relationship between plant traits, which may be related to the balanced allocation of water and light resources in this region. (3) The results of the trait network of 9 sites indicating that the adaptation of Setaria viridis along the precipitation gradient was mainly regulated by stomatal traits. This study has great significance for predicting the potential mechanisms of plant’/vegetation’ adaptation under the background of climate change.

Aims The Shenzhen Bay Mangrove Nature Reserve is the only national nature reserve in China located within an urban area. Studying the potential biodiversity of urban mangrove wetlands, which are significantly impacted by human disturbance, can provide a pathway for the sustainable management of mangrove ecosystems. Methods This study conducted an ecological survey of different areas (core/non-core) in the Shenzhen Bay Mangrove National Nature Reserve. Species co-occurrence and distribution probability was assessed using the hy-pergeometric method, and the vegetation characteristics of the area were analyzed based on the survey data. Important findings (1) A total of nine mangrove species were distributed in the Shenzhen Bay Mangrove Nature Reserve, with Kandelia obovata being the dominant species. In the core area, K. obovata had the highest importance value (IV) (mean = 96.4%), while its importance value in the non-core area was significantly lower (p < 0.05), where Sonneratia apetala and S. caseolaris appeared. (2) In the Shenzhen Bay mangrove ecosystem, S. caseolaris and S. apetala exhibited a strong coexistence tendency, with a z-score value of 2.82. Meanwhile, S. apetala and K. obovata displayed competitive exclusion, with a z-score value of -2.41. Z-score values reflect non-random species co-occurrence patterns. (3) A significant positive correlation was found between the existing species diversity and the community integrity index in the Shenzhen Bay mangroves. The higher the community integrity, the higher the existing species diversity. Some non-core area plots are at risk of S. apetala spreading, and ecosystem management and protection should be strengthened. The distribution probability of K. obovata in the core area (0.51 ± 0.09) is significantly higher than that in the non-core area (0.41 ± 0.15). However, in certain plots of the core area, such as the plots in the mid-tide zones of transects 8, community completeness is relatively low. It is recommended to appro-priately replant native mangroves to enhance species diversity.

Potaninia mongolica is an important constructive species and ancient endemic species in the Alxa Desert, and it is a national secondary key protected plants in China. Investigating the characteristics of the natural communities of Potaninia mongolia and studying its community classification and the relationship between diversity and environmental factors can provide data support for the conservation and long-term monitoring of this species. In this study, the representative communities of Potaninia mongolia was selected in eastern Alxa, the community characteristics were studied by sample method, and the relationship between community species diversity and environmental factors was discussed by redundancy analysis (RDA). The results showed that: (1) A total of 48 plants species were recorded in the investigated communes, belonging to 38 genera of 14 families, dominated by Gramineae, Chenopodiaceae, Compositae and Leguminosae; The life form was dominated by annual (or biennial) herbaceous species, accounting for 33.33% of the total species, perennial herbs (25.00%), shrubs (20.83%) and half-shrubs (20.83%) had similar proportions, but the shrubs was the dominant synusia of the community; The water ecological type was mainly composed of xerophytes, accounting for 79.17% of the total species, of which strong xerophytes accounted for 35.42%, reflecting the strongly arid climatic characteristics. The floristic geographic element was dominated by Gobi species and Gobi-Mongolia species, accounting for 29.16% and 22.92%, respectively, reflecting the floristic characteristics of desert vegetation. (2)According to the life form and dominance degree, Potaninia mongolica desert in eastern Alxa was divided into three association groups: Potaninia mongolica-herbs desert association group, Potaninia mongolica+shrubs-herbs desert association group, Potaninia mongolica+shrubs desert association group, which were further divided into 13 associations. (3) Results of the RDA analysis showed that temperature and precipitation were the main factors influencing the species diversity of the community.

AimsShrublands is an indispensable part of estimating carbon density in terrestrial ecosystems, and the expansion of shrublands is considered as one of the key reasons leading to the increase of carbon density in terrestrial ecosystems in China, and yet there are great uncertainties in the carbon sink capacities of shrublands. Our objectives were to estimate the carbon density and distribution characteristics of common shrublands in North China. Methods The carbon density and distribution characteristics of two typical shrublands (Caragana jubata and Carpinus turczaninowii) in Dongling Mountain, Beijing, were measured based on the field investigation data and by employing allometric approaches. Important findings The results showed that the carbon density (427.59 t?hm-2) of C. jubatashrubland was significantly higher than that (178.19 t?hm-2) of the C. turczaninowii shrubland, in which the carbon storage of soil layer was the most (98.53%and 81.31%), and the carbon storage were 421.29 t?hm-2 and 144.89 t?hm-2, respectively. Soil organic carbon was enriched in the 0–50 cm soil layer, and showed a decreasing trend with increasing soil depth. The organic carbon density in different soil layers of the C. jubata shrubland is higher than that of the C. turczaninowii shrubland, mainly due to the lower temperature and smaller slope in the distribution area of the former, which is conducive to the accumulation of organic matter. The contribution of the shrub layer and the arbor-shrub layer to the carbon density of the entire ecosystem were relatively small (1.27% and 17.77%), with values of 5.44 and 31.69 t?hm-2, respectively. The carbon density of different organs in the arbor layer was in the order of trunk > root > branch > leaf, while the order of carbon density in the shrub layer was branch > root > leaf in both shrublands. Moreover, the carbon density of each organ in the shrub layer of C. jubata shrubland was significantly lower than that in the C. turczaninowii shrubland.The herbaceous layer and litter layer contributed the least to the total carbon density of C. jubata and C. turczaninowii shrublands (0.20% and 0.91%), with values of 0.86 and 1.62t?hm-2, respectively. The carbon density of the herbaceous layer(0.55 t?hm-2) in C. jubata shrubland was significantly higher than that (0.35 t?hm-2) in C. turczaninowii shrublands. Moreover, carbon density of the aboveground and underground parts of the herbaceous layer in C. jubata shrubland was similar, while in C. turczaninowii shrubland, the aboveground carbon density was significantly lower than that of the underground part. The carbon density of the litter layer (1.27 t?hm-2) in C. turczaninowii shrubland was significantly higher than that (0.31 t?hm-2) in C. jubata shrubland.

Aims Nitrogen (N) addition significantly affected the aboveground net primary productivity (ANPP) and belowground net primary productivity (BNPP) of grassland ecosystems. However, the different responses of plant ANPP and BNPP to N addition and their saturation response thresholds at different levels of N addition are not clear. Methods Therefore, eight N addition levels (0, 1, 2, 4, 8, 16, 24, 32 g N m-2 year-1) were set up in the Leymus secalinus grassland in northern Shanxi Province, and the changes of plant ANPP, BNPP and total net primary productivity (NPP) were monitored for five years from 2017 to 2021. The temporal stability, N saturation threshold and N response efficiency of plant productivity were also calculated. Important findings The results showed that: (1) ANPP and NPP were increased nonlinearly with the increase of N addition level. The saturation response thresholds of ANPP and NPP across five years (2017-2021) were 25.7 g N m-2year-1 and 21.3 g N m-2year-1, respectively. (2) ANPP and BNPP had different sensitivities to N addition, and the sensitivity of ANPP was higher than that of BNPP. The change in NPP was mainly caused by changes in ANPP, suggesting that plant productivity distribution to the ground increased as the level of N addition increased. (3) NREANPP showed an exponential downward trend with the increase of N addition levels, while the NREBNPP and NRENPP showed a linear downward trend with the increase of N addition level. (4) Structural equation model analysis showed that soil NO3--N and pH regulated the effects of N addition and years on plant ANPP and BNPP. There was different regulatory mechanisms of ANPP and BNPP under low N and high N addition treatments. Both ANPP and BNPP were directly affected by N addition under low N addition treatments, while the soil inorganic N indirectly regulated the response of ANPP and BNPP to N addition under high N addition treatments. This study showed that plant productivity in grassland ecosystem responded nonlinearly with N addition level, which provided data support for improving the ecosystem service function of Leymus secalinus grassland in northern Shanxi Province under the background of N deposition.

Aims Ants play important roles in material cycling and energy flow in subtropical forests. However, there remains a knowledge gap regarding how different canopy tree species regulate ant community structure by altering seasonal patterns of understory microclimate, soil surface environment, and litter properties. Methods From July 2023 to March 2024, ant community structure composition, taxonomic and functional group differences, diversity characteristics, as well as their seasonal dynamic changes were investigated in a common garden of Fujian Sanming Forest Ecosystem National Observation and Research Station. Six representative canopy tree species were selected to check the relationships between trees and ant community in the mid-subtropical evergreen broad-leaf forests. Important findings During the investigation, a total of 30 389 ants were collected, belonging to 19 genera and 30 species with the dominant species of Pheidole nodus and Crematogaster rogenhoferi. we found higher ant diversity in summer and fall but lower diversity in winter and spring. The tree species significantly influenced ant abundance, with the following order: Liquidambar formosana > Castanopsis carlesii > Sapindus saponaria > Cunninghamia lanceolata > Michelia macclurei > Pinus massoniana. Moreover, sampling season and its interaction with tree species also significantly affected the structure of ant functional groups. Among others, the abundance of Generalized Myrmicinae under Cunninghamia lanceolata in summer was significantly higher than them under other tree species, whereas Climate Specialists showed relatively higher abundance under Castanopsis carlesii in spring but lower abundance under Pinus massoniana. Canonical correspondence analysis revealed that soil temperature, soil organic matter content, aboveground biomass, and litter production could explain more than 50% of the variation in ant community structure. The results not only elucidated the relationships between tree species and ant community in mid-subtropical forests, but also provided primary data for knowledge on other similar soil fauna.

Aims Rhododendron xiaoxidongense is endemic, rare and endangered species in China, with a narrow distribution in the central part of the Luoxiao Mountains. The R. xiaoxidongense was once assessed as extinct (EX) because its habitat and individual numbers are so rare that it is difficult to find in the wild. However, as details on the resource status, population structure and dynamics of the species are lacking, the conservation of this species is severely constrained. This study aims to clarify the survival status and future development trend of the population, and key factors to affect population regeneration through to analyses structure and dynamics characteristics of the existing populations of R. xiaoxidongense, which will provide scientific basis for the conservation, management, and revitalization of wild populations. Methods Based on the investigated parameters, the age structure of the R. xiaoxidongense population was obtained by using a space-for-time substitution method. Subsequently, the dynamic index, static life table, survival curves and survival function curves of the population were determined to analyze the population structure characteristics and survival potential. The time series prediction model was employed to predict the future development trend of the population, and the aggregation degree index was used to determine the spatial distribution pattern of the population. Important findings (1) The age structure of the four populations of R. xiaoxidongense was incomplete, with an overall trend of more middle-aged and mature individuals and a severe lack of low-aged and old individuals, the age structure tended to be a decline type. (2) The dynamic index of adjacent age class (Vn) showed a fluctuating trend of “decline-growth-stability-decline” with increasing age class, the dynamic index without external interference (Vpi) > the dynamic index under external disturbance (V′pi) > 0, V′pi was closed to 0. The maximum risk probability in response to random disturbance (Pmax) under external environmental interference was 11.11%, indicating that the population was high risk probability to external disturbance and had a very weak resistance to disturbances. (3) The life expectancy (ex) was highest at age class I, and the population survival curve tended to be Deevey-II type. (4) The mortality rate (qx) and vanish rate (Kx) curves showed a dynamic change of “increase-decrease-increase”, which indicated the population was in an unstable state. (5) The survival function curve showed the trend of sharp decline in the early stages, relative stability in the middle stages, and slow decline in the later stages, and entered the decline phase at a relatively small age class (2.25 age class), which indicated that the population had weak viability. (6) In the future, after the 2, 4, 6, and 8 age classes, the population number of low and middle-aged individuals would decrease, in contrast, the number of adult and old individuals would increase, indicating that the population will face a risk of decline. (7) The overall spatial pattern of the population was clumped distribution, but the degree of aggregation decreased with increasing age class, transitioning to random distribution in age classes VII-VIII. Conclusion In summary, the small population size, narrow distribution range, low resistance to external disturbance, and difficulty in seedling regeneration are the likely factors contributing to the endangered status of the R. xiaoxidongense. We suggest strengthening the habitat protection and tending management of R. xiaoxidongense population, and achieving population conservation and revitalization through multiple approaches, including in situ and near situ conservation.