The study of biodiversity has tended to focus primarily on relatively information-poor measures of species diversity. Recently, many studies of local diversity (alpha diversity) have begun to use ...measures of functional and phylogenetic alpha diversity. Investigations into the phylogenetic and functional dissimilarity (beta diversity) of communities have been far less numerous, but these dissimilarity measures have the potential to infer the mechanisms underlying community assembly and dynamics. Here, we relate levels of phylogenetic and functional alpha diversity to levels of phylogenetic and functional beta diversity to infer the mechanism or mechanisms responsible for the assembly of tree communities in six forests located in tropical and temperate latitudes. The results show that abiotic filtering plays a role in structuring local assemblages and governing spatial turnover in community composition and that phylogenetic measures of alpha and beta diversity are not strong predictors of functional alpha and beta diversity in the forests studied.
1. Plant ecologists have been rather slow to appreciate the existence and the effects of imperfect detection probability in plants. Sources of heterogeneous detectability include differences in ...morphology or life-form, patch size, observers and survey effort. Understanding the relationship between such factors and detectability is crucial for the efficient design of new plant distribution studies and for the interpretation of existing ones. 2. We have studied the factors affecting detectability in a large permanent plot (24 ha) in East China where the true distribution of six shrub and tree species was known from a detailed earlier inventory. Two observers independently resurveyed and recorded detection and non-detection of each species in each 20 x 20 m sampling quadrat. A total of 288 quadrats were resurveyed (218 by observer A, 211 by observer B and 141 by both). We used generalized linear mixed modelling to study the relationships between detection and species, observer, survey effort and patch size. 3. Detectability of an occupied quadrat was remarkably low and ranged from 0.09 to 0.34 on average for the six shrub and tree species. Differences of detection among species were mainly as a result of distinctive morphology rather than life-form. There was no significant difference of overall detection probability between the two observers. Detectability increased to 0.95 as the survey path approached 20% area of the sampling quadrat and as a plant patch covered c. 19% of the area of the sampling quadrat. 4. Synthesis. Our results suggest that imperfect detection is much more widespread than currently acknowledged by most plant ecologists. We identify several sources of heterogeneity in detectability (species, survey effort and patch size) that ought to be considered when studying and modelling the distribution of plant species. Detectability should be accounted for in plant distribution studies to avoid spurious inferences.
Nitrogen (N) addition has been well documented to decrease plant biodiversity across various terrestrial ecosystems. However, such generalizations about the impacts of N addition on soil microbial ...communities are lacking. This study was conducted to examine the impacts of N addition (urea-N fertilizer) on soil microbial communities in a semi-arid temperate steppe in northern China. Soil microbial biomass carbon (C), biomass N (MBN), net N mineralization and nitrification, and bacterial and fungal community level physiological profiles (CLPP) along an N addition gradient (0-64 g N m⁻² year⁻¹) were measured. Three years of N addition caused gradual or step increases in soil NH₄-N, NO₃-N, net N mineralization and nitrification in the early growing season. The reductions in microbial biomass under high N addition levels (32 and 64 g N m⁻² year⁻¹) are partly attributed to the deleterious effects of soil pH. An N optimum between 16 and 32 g N m⁻² year⁻¹ in microbial biomass and functional diversity exists in the temperate steppe in northern China. Similar N loading thresholds may also occur in other ecosystems, which help to interpret the contrasting observations of microbial responses to N addition.
AIM: The phylogenetic constraint hypothesis of flowering phenology states that closely related species flower at similar times of the year. We test this hypothesis for the Chinese angiosperm flora ...and assess additional effects of growth form, deciduousness, pollination mode and fruit type. We further examine whether the phylogenetic conservatism of flowering phenology tends to increase from tropical to temperate latitudes. LOCATION: China. METHODS: The midpoint of flowering time for 19,631 angiosperm species present in China was compiled. The phylogenetic signal for flowering time was evaluated for the whole country using the Blomberg K‐value (adjusted for circular data). We then regressed the phylogenetic signal for 28 provinces as a function of their latitude. An analysis of variance for circular data was conducted to test the differences among growth forms. Watson–Williams tests for circular flowering data were used to compare flowering dates between deciduous and evergreen species, animal‐pollinated and wind‐pollinated species, and fleshy and non‐fleshy fruits. RESULTS: The results support the phylogenetic constraint hypothesis. The phylogenetic signal at the whole country scale was lower than that at the province scale. Phylogenetic signal was also lower at tropical latitudes than at temperate latitudes. Flowering dates were associated with biological traits, with growth form having the largest effect. MAIN CONCLUSIONS: Flowering phenology was constrained by phylogeny, and so one should account for phylogeny when studying the underlying drivers of phenology. The strength of phylogenetic conservatism appears weaker at larger scales and becomes stronger towards temperate regions. Flowering phenology also varies predictably according to biological traits such as growth form, suggesting that both phylogeny and traits could be used to inform the flowering times of species for which no phenology data are available. It remains to be tested whether the phylogenetic signal for other functional traits putatively related with flowering time also increases with latitude.
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•The potential synergistic effects of climate and land use change on 191 Chinese endemic Rhododendron species were studied.•A nearly equal number of species was projected to lose or ...gain their suitable habitat.•Low-elevation species are more vulnerable to climate and land use change than high-elevation species.•The species at lower altitudes need more conservation attention under climate and land use change.•Endemic Rhododendrons can be good indicators for the assessment of biodiversity conservation.
The combination of climate change and land use change may have profound effects on terrestrial biodiversity in more significant ways than either has separately. However, most studies focus largely on the climate change impacts, which hampers our ability to develop appropriate conservation strategies in a dramatically changing world. Here, we predict the distributions of 191 Chinese endemic Rhododendron species under future climate and land use change, combining two dispersal constraint scenarios by using a species distribution model. We then assess the vulnerability and extinction risk of these species and identify areas at risk of highest species loss. We find that 52% of the species are predicted to expand and shift their geographic ranges, typically to the northwest and north. The remaining 48% of species are predicted to contract in geographic ranges under the 'perfect-dispersal' scenario. And only 7% of Rhododendron are predicted to keep 'still', while the rest of species shrank with varying degree under the 'no-dispersal' scenario. Species lost particularly at lower elevations, and we also identify four regions at particularly high risk from the impacts of climate and land use change, namely the parallel ridge-and-valley areas of eastern Sichuan, southeastern Tibet, western and eastern Yunnan, southern Shaanxi, plus scattered areas in Guangdong, Hainan and Taiwan. We conclude that Chinese endemic Rhododendron species at lower elevations are highly vulnerable to climate and land use change, facing an elevated risk of extinction under varying scenarios. These species therefore call for more attention and protection. We highlight the critical role of endemic Rhododendron species as good indicators for measuring, evaluating and understanding the effectiveness of our biodiversity conservation efforts. Our work provides insight into the status, trends and threats regarding endemic Rhododendron species, identifying risks and prioritizing conservation in a rapidly changing world.
Depletion of stratospheric ozone has led to increased UV radiation reaching the surface of the Earth. This may damage plants. Using physiological, proteomic and quantitative real-time PCR (qPCR) ...methods, we systematically studied the response of 16-day-old rice seedlings to UV 0.67 W m(-2) biologically effective UVB (UVB(BE)) and 0.28 W m(-2) UVA exposure for 6, 12 and 24 h. UV exposure resulted in the appearance of light brown patches on leaves, a decrease in the net photosynthetic rate (Pn), lipid peroxidation, accumulation of UV-absorbing compounds (including flavonoids and other phenolic pigments) and differential expression of 22 proteins. Both physiological and molecular responses became stronger with increasing UV exposure time, indicating the effects of UV accumulation on plants. UV-induced responses included (i) phytohormone-regulative responses (up-regulation of proteins related to phytohormone synthesis such as IAA and ethylene); (ii) injurious responses (photosynthesis suppression, lipid peroxidation and visible injury); and (iii) protective responses (accumulation of UV-absorbing compounds and differential expression of proteins involved in detoxification/antioxidation, defense, protein processing, RNA processing, carbohydrate metabolism and secondary metabolism). The identification of UV-responsive proteins provided a better understanding of the molecular mechanism of plant responses to UV stress. Proteomic and qPCR analysis identified one up-regulated and two induced proteins with important functions: tryptophan synthase α chain (production of radical oxygen species), glyoxalase I (detoxification/antioxidation) and a Bet v I family protein (defense). These results will contribute to future research into their roles in UV stress responses in plants.
The subtropical forest biome occupies about 25% of China, with species diversity only next to tropical forests. Despite the recognized importance of subtropical forest in regional carbon storage and ...cycling, uncertainties remain regarding the carbon storage of subtropical forests, and few studies have quantified within-site variation of biomass, making it difficult to evaluate the role of these forests in the global and regional carbon cycles. Using data for a 24-ha census plot in east China, we quantify aboveground biomass, characterize its spatial variation among different habitats, and analyse species relative contribution to the total aboveground biomass of different habitats. The average aboveground biomass was 223.0 Mg ha(-1) (bootstrapped 95% confidence intervals 217.6, 228.5) and varied substantially among four topographically defined habitats, from 180.6 Mg ha(-1) (bootstrapped 95% CI 167.1, 195.0) in the upper ridge to 245.9 Mg ha(-1) (bootstrapped 95% CI 238.3, 253.8) in the lower ridge, with upper and lower valley intermediate. In consistent with our expectation, individual species contributed differently to the total aboveground biomass of different habitats, reflecting significant species habitat associations. Different species show differently in habitat preference in terms of biomass contribution. These patterns may be the consequences of ecological strategies difference among different species. Results from this study enhance our ability to evaluate the role of subtropical forests in the regional carbon cycle and provide valuable information to guide the protection and management of subtropical broad-leaved forest for carbon sequestration and carbon storage.
A better understanding of soil microbial ecology is critical to gaining an understanding of terrestrial carbon (C) cycle–climate change feedbacks. However, current knowledge limits our ability to ...predict microbial community dynamics in the face of multiple global change drivers and their implications for respiratory loss of soil carbon. Whether microorganisms will acclimate to climate warming and ameliorate predicted respiratory C losses is still debated. It also remains unclear how precipitation, another important climate change driver, will interact with warming to affect microorganisms and their regulation of respiratory C loss. We explore the dynamics of microorganisms and their contributions to respiratory C loss using a 4-year (2006—2009) field experiment in a semi-arid grassland with increased temperature and precipitation in a full factorial design. We found no response of mass-specific (per unit microbial biomass C) heterotrophic respiration to warming, suggesting that respiratory C loss is directly from microbial growth rather than total physiological respiratory responses to warming. Increased precipitation did stimulate both microbial biomass and mass-specific respiration, both of which make large contributions to respiratory loss of soil carbon. Taken together, these results suggest that, in semi-arid grasslands, soil moisture and related substrate availability may inhibit physiological respiratory responses to warming (where soil moisture was significantly lower), while they are not inhibited under elevated precipitation. Although we found no total physiological response to warming, warming increased bacterial C utilization (measured by BIOLOG EcoPlates) and increased bacterial oxidation of carbohydrates and phenols. Non-metric multidimensional scaling analysis as well as ANOVA testing showed that warming or increased precipitation did not change microbial community structure, which could suggest that microbial communities in semiarid grasslands are already adapted to fluctuating climatic conditions. In summary, our results support the idea that microbial responses to climate change are multifaceted and, even with no large shifts in community structure, microbial mediation of soil carbon loss could still occur under future climate scenarios.
Biodiversity is and always has been an important issue in ecological research. Biodiversity can reflect niche partitioning among species at several spatial and temporal scales and is generally ...highest in the tropics. One theory to explain it is that low-latitude tropical ecosystems are dominated by species that are generally only distributed over a narrow area. This principle is known as Rapoport's rule. One previously unconsidered extension of Rapoport's rule may be reproductive phenology, where variation in flowering and fruiting length may reflect a temporal range. Herein, we collected reproductive phenology data for more than 20,000 species covering almost all angiosperm species in China. We used a random forest model to quantify the relative role of seven environmental factors on the duration of reproductive phenology. Our results showed that the duration of reproductive phenology decreased with latitude, although there was no obvious change across longitudes. Latitude explained more of the variation in the duration of flowering and fruiting phases in woody plants than in herbaceous plants. Mean annual temperature and the length of the growing season strongly influenced the phenology of herbaceous plants, and average winter temperature and temperature seasonality were important drivers of woody plant phenology. Our result suggests the flowering period of woody plants is sensitive to temperature seasonality, while it does not influence herbaceous plants. By extending Rapoport's rule to consider the distribution of species in time as well as space, we have provided a novel insight into the mechanisms of maintaining high levels of diversity in low-latitude forests.
Studying the distribution of samara species is of ecological and economic significance. This information helps us with understanding species dispersal mechanisms, evaluating the risk of invasive ...species, and the management of ecological forests. However, limited research has explored, on a large scale, the geographic distribution of samara species and their influential abiotic factors. Here, we use the distribution data of 835 vascular samara species and growth form data to explore their geographic patterns in China and the environmental determinants. We divided China into 984 grid cells and examined the relationship between the proportion of samara species and climate variables using both ordinary and spatial linear regressions for each grid cell. Total samara species richness is higher in southern China in low altitude regions and the proportion of woody samara species is significantly higher than that of herbaceous samara species. The proportion of woody samara species is higher in the northeast regions where precipitation is sufficient, winters are dry and mild, and temperature seasonality and land surface relief degree values are high. Annual precipitation and temperature seasonality are the most important climatic drivers for the distribution of woody samara species. In contrast, herbaceous samara species prefer to distribute to the areas where climate is warm and dry but have higher temperature seasonality. Temperature related variables (mean annual temperature, mean diurnal range, and temperature seasonality) are the most important drivers for the distribution of herbaceous samara species. Samara species can better adapt to climatic regions with large temperature fluctuations and dry winters. The present distribution patterns of samara species are formed by the combined adaptation of fruit traits and growth form to climate. This work contributes to predictions of the global distribution of samara species under future climate change scenarios and conservation and management for the samara species.
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