Effects of UV-B radiation on pollen germination and tube growth: A global meta-analysis.

Despite widespread recognition of pollen's potential sensitivity to ultraviolet-B (UV-B) radiation (280-315 nm), there remains ongoing debate surrounding the extent and mechanisms of this effect. In this study, using published data on pollen germination and tube growth including 377 pair-wise comparisons from 77 species in 30 families, we present the first global quantification of the effects of UV-B radiation on pollen germination and tube growth, along with its underlying mechanisms. Our results showed a substantial reduction in both pollen germination and tube growth in response to UV-B radiation, affecting 90.9 % and 84.2 % of species, respectively. Notably, these reductions exhibited phylogenetic constraints, highlighting the role of evolutionary history in shaping the sensitivity of pollen germination and tube growth to UV-B radiation. A negative correlation between elevation and the sensitivity of pollen tube growth was detected, suggesting that pollens from plants at higher elevations exhibit greater resistance to UV-B radiation. Our investigation also revealed that the effects of UV-B radiation on pollen germination and tube growth were influenced by a range of abiotic and biotic factors. Nevertheless, the intensity and duration of UV-B radiation exposure exhibited the highest explanatory power for the effects on both pollen germination and tube growth. This suggests that the responses of pollens to UV-B radiation are profoundly influenced by its dose, a critical consideration within the context of global change. In conclusion, our study provides valuable insights into the diverse responses of pollen germination and tube growth to UV-B radiation, highlighting the environment and species-dependent nature of pollen's susceptibility to UV-B radiation, with substantial implications for our understanding of the ecological and agricultural consequences of ongoing changes in UV-B radiation.

Degeneration of foundation cushion species induced by ecological constraints can cause massive changes in alpine plant communities.

Foundational cushion plants can re-organize community structures and sustain a prominent proportion of alpine biodiversity, but they are sensitive to climate change. The loss of cushion species can have broad consequences for associated biota. The potential plant community changes with the population dynamics of cushion plants remain, however, unclear. Using eight plant communities along a climatic and community successional gradient, we assessed cushion population dynamics, the underlying ecological constraints and hence associated plant community changes in alpine communities dominated by the foundational cushion plant Arenaria polytrichoides. The population dynamics of Arenaria are attributed to ecological constraints at a series of life history stages. Reproductive functions are constrained by increasing associated beneficiary plants; subsequent seedling establishment is constrained by temperature, water and light availability, extreme climate events, and interspecific competition; strong competitive exclusion may accelerate mortality and degeneration of cushion populations. Along with cushion dynamics, species composition, abundance and community structure gradually change. Once cushion plants completely degenerate, previously cushion-dominated communities shift to relatively stable communities that are overwhelmingly dominated by sedges. Climate warming may accelerate the degeneration process of A. polytrichoides. Degeneration of this foundational cushion plant will possibly induce massive changes in alpine plant communities and hence ecosystem functions in alpine ecosystems. The assessment of the population dynamics of foundation species is critical for an effective conservation of alpine biodiversity.

Diversity patterns of cushion plants on the Qinghai-Tibet Plateau: A basic study for future conservation efforts on alpine ecosystems.

The Qinghai-Tibet Plateau (QTP) is an important cushion plant hotspot. However, the distribution of cushion plants on the QTP is unknown, as are the factors that drive cushion plant distribution, limiting our understanding of the evolution of cushion species in the region. In this study, we assessed spatial patterns of total cushion plant diversity (including taxonomic and phylogenetic) over the entire QTP and compared patterns of diversity of cushion plants with different typologies (i.e., compact vs. loose). We also examined how these patterns were related to climatic features. Our results indicate that the southern QTP hosts the highest total cushion plant richness, especially in the south-central Hengduan Mountains subregion. The total number of cushion species declines from south to north and from southeast to northwest. Compact cushion plants exhibit similar patterns as the total cushion plant richness, whereas loose cushion plants show random distribution. Cushion plant phylogenetic diversity showed a similar pattern as that of the total cushion plant richness. In addition, cushion plant phylogenetic community structure was clustered in the eastern and southwestern QTP, whereas random or overdispersed in other areas. Climatic features represented by annual energy and water trends, seasonality and extreme environmental factors, had significant effects on cushion plant diversity patterns but limited effects on the phylogenetic community structure, suggesting that climatic features indeed promote the formation of cushion plants. Because cushion plants play vital roles in alpine ecosystems, our findings not only promote our understanding of the evolution and formation of alpine cushion plant diversity but also provide an indispensable foundation for future studies on cushion plant functions and thus alpine ecosystem sustainability in the entire QTP region.

Elevational patterns of functional diversity and trait of Delphinium (Ranunculaceae) in Hengduan Mountains, China.

Elevational patterns of trait occurrence and functional diversity provide an important perspective for understanding biodiversity. However, previous studies have mostly examined functional diversity at the community scale. Here, we examined large-scale patterns of trait occurrence and functional diversity in Delphinium along an elevational gradient from 1000 to 5700 m in the Hengduan Mountains, SW China. Elevational distribution and trait data of 102 Delphinium species were compiled to evaluate the patterns of interspecific traits, species richness, and functional diversity. We found that the distribution of species richness showed a unimodal curve that peaked between 3500 and 4000 m; functional diversity and traits showed different patterns along an elevational gradient. The functional diversity increased at a lower rate along an elevation gradient, whereas species richness continued to increase. Species with large ranges and non-endemic species were most affected by geometric constraints. Richness of species endemic to the Hengduan Mountains peaked at higher elevations, likely due to increased speciation and restricted dispersion under alpine conditions. We conclude that the middle elevation region is not only the functionally richest but also the most functionally stable region for Delphinium, which could be insurance against environmental change. Extreme conditions and strong environmental filters in an alpine environment may cause the convergence of species traits, which could relate to reducing nutrient trait investment and increasing reproductive trait investment. We conclude that large-scale studies are consistent with previous studies at the community scale. This may indicate that the relationship between functional diversity and species richness across different scales is the same.

Pulvinatusia (Brassicaceae), a new cushion genus from China and its systematic position.

The new genus and species Pulvinatusiaxuegulaensis (Brassicaceae) are described and illustrated. The species is a cushion plant collected from Xuegu La, Xizang, China. Its vegetative parts are most similar to those of Arenariabryophylla (Caryophyllaceae) co-occurring in the same region, while its leaves and fruits closely resemble those of Xerodrabapatagonica (Brassicaceae) from Patagonian Argentina and Chile. Family-level phylogenetic analyses based on both nuclear ITS and plastome revealed that it is a member of the tribe Crucihimalayeae, but the infra-/intergeneric relationships within the tribe are yet to be resolved.

Alpine community recruitment potential is determined by habitat attributes in the alpine ecosystems of the Himalaya-Hengduan Mountains, SW China.

The fragility and sensitivity to climate change of alpine ecosystems make it difficult to maintain the stability of their plant communities. Thus, it is important to determine which plant propagules are stored in the soils in order to understand community recruitment potential, especially under different environmental conditions. Based on a soil seed germination and seedling cultivation experiment, we aimed to identify differences in the soil seed attributes between three typical habitat types in the alpine subnival ecosystems of the Himalaya-Hengduan Mountains and hence to predict the community recruitment potential of each of these different communities. We found that the seed assemblages in the soils differed between habitats. The most abundant taxa were from the genera Saxifraga, Kobresia, Arenaria, Polygonum, Draba, and Viola, while the taxa with lowest abundance were Apiaceae, Campanulaceae, Circaea, Crassulaceae, and Gentiana. Different habitats exhibited variable soil seed richness, diversity, and density. However, the patterns differed between study sites. Specifically, at Baima (BM) and Shika (SK) snow mountains, soil seed richness, diversity, and density were generally highest in grassland, followed by rock bed and bare ground. In contrast, on Jiaozi (JZ) snow mountain, the rock bed supported the highest soil seed richness and density, followed by grassland and bare ground. These results suggest that the attributes of habitats and communities can both affect the accumulation of soil seeds. Bare ground supports the lowest seed diversity and density but also harbors the most empty niches. We, therefore, predict that, once the thermal conditions become suitable as a result of global warming, this habitat has the potential to see greater changes than grassland and rock bed in terms of community recruitment.

Spatial phylogenetics of two topographic extremes of the Hengduan Mountains in southwestern China and its implications for biodiversity conservation.

Previous attempts to elucidate the drivers of speciation mechanisms and spatial distribution patterns of biodiversity in mountain regions have treated different floras within a single geological region as one flora, ignoring the potential contributions of high habitat/ecosystem heterogeneity. Furthermore, current conservation strategies largely focus on forest ecosystems and/or specific flagship species, ignoring marginal ecosystems, leaving species in these ecosystems at risk. Here, we compared the spatial patterns of biodiversity and the potential drivers of these patterns in the river valley and subnival ecosystems of the Hengduan Mountains region (HDM) in southwestern China. Specifically, we compared spatial patterns of diversity, endemism, and threatened species in these ecosystems based on both traditional measurements and recent phylogenetic approaches. We then examined how those patterns were related to environmental factors and human activity in these same regions. We found that the middle-southern HDM supports the highest diversity and endemism for the river valley and subnival ecosystems; however, the distribution patterns of neo- and paleo-endemism in these two ecosystems differ. Regression models indicate that habitat diversity and paleo-climatic fluctuation are important drivers of diversity and endemism for these two ecosystems. Temperature and precipitation, however, showed different influences on the spatial patterns in different ecosystems. Categorical analysis of neo- and paleo-endemism (CANAPE) indicated that most endemism centers are not covered by current nature reserves. Moreover, the intensity of human activity is highest in the southern and southeastern HDM, which coincides with the distribution patterns of diversity, mixed-endemism and high-priority (and threatened) species. These findings suggest that different floras within a single geographic/floristic region respond differently to environmental factors and show different spatial phylogenetic patterns. We, therefore, recommend that future research into the drivers of biodiversity consider the contributions of various ecosystem types within a single geological region. This study also provides a theoretical basis for protecting habitat diversity. Our work confirms that current conservation efforts are insufficient to protect ecosystem diversity in the river valley and subnival ecosystems of the Hengduan Mountains. Therefore, we recommend the establishment of nature reserves in the regions identified in this study; furthermore, we strongly recommend improving current and establishing new management policies for biodiversity conservation in this region.

Plant diversity in Yunnan: Current status and future directions.

Yunnan, located in southwestern China, harbors more than 19,000 higher plants, which represents the highest plant diversity in the country. However, plant diversity in Yunnan faces enormous threats today, including habitat destruction and fragmentation, environmental pollution, and over-exploitation of natural resources. Despite recent efforts to protect biodiversity, there are still thousands of threatened species, some of which have become extinct. We analyzed available data to gain a greater understanding of plant diversity and the status of plant conservation in Yunnan. We found that southern, southeastern, and northwestern Yunnan are hotspots of total species, endemic species, specimens, new species and threatened species, whereas southeastern Yunnan is a hotspot for plant species with extremely small populations. Moreover, we found that there are still conservation gaps and poorly protected areas in central, eastern, and northeastern Yunnan. We conclude that conservation of plant diversity in Yunnan requires modern field investigation, systematic research, the development of comprehensive databases, and government support. We recommend that conservationists pay more attention to building and improving functional protection systems and popularizing science.

Current progress and future prospects in phylofloristics.

The species composition of regional plant assemblages can in large part be explained by a long history of biogeographical and evolutionary events. Traditional attempts of floristic studies typically focus on the analyses of taxonomic composition, often ignoring the rich context that evolutionary history can provide. In 2014, Swenson and Umaña introduced the term 'phylofloristics' to define a phylogenetically enabled analysis of the species composition of regional floras. Integrating phylogenetic information into traditional floristic analysis can provide a promising way to explore the ecological, biogeographic, and evolutionary processes that drive plant assemblies at multiple spatial scales. In this review, we summarize the current progress on the phylogenetic structure, spatial phylogenetic pattern, origin and diversification, phylogenetic regionalization of floristic assemblages, and application of phylogenetic information in biodiversity conservation. These summaries highlight the importance of incorporating phylogenetic information to improve our understanding of floristic assembly from an evolutionary perspective. The review ends with a brief outlook on future challenges for phylofloristic studies, including generating a highly resolved species-level phylogenetic tree, compiling detailed and refined information regarding the geographic distribution of all plant life, extracting trait information from publications and herbarium specimens, and developing technological and methodological approaches for big data analysis.