Alpha and beta diversity of functional traits in subtropical evergreen broad-leaved secondary forest communities.

Introduction: Intra-speciic variation is the main source of functional trait diversity and has similar ecological effects as inter-speciic variation. Methods: We studied 79 species and 3546 individuals from 50 ixed monitoring plots in subtropical evergreen broad - leaved secondary forests in Zhejiang Province, China. Using trait gradient analysis, we examined nine traits (speciic leaf area, leaf dry matter content, wood density, leaf area, chlorophyll content, leaf nitrogen content, leaf phosphorus content, leaf potassium content, and nitrogen-phosphorus ratio) by decomposing species functional traits into alpha (within-community) and beta (among-communities) measure the impact of environmental gradients and the presence of other species on the variation of traits. Result: All nine functional traits showed some degree of differentiation in the forest communities, with a greater range of variation in alpha values than in beta values . Correlations were signiicantly different between the trait differences in the communities. The alpha values of each trait showed a higher correlation with other components than the beta values. The factors affecting intra-speciic trait variation were relatively complex. The alpha component had a more signiicant and stronger effect on intra-speciic trait variation compared to the beta component. Abiotic factors, such as soil nutrient content, soil nitrogen-phosphorus content, directly affected the beta component. In contrast, biotic factors, such as tree height variation, had a direct and stronger effect on the alpha component. Discussion: Our results demonstrate that alpha and beta components, as independent differentiation axes among coexisting species, have different sensitivities to different environmental factors and traits in different ecological strategies and spatial scales. Trait gradient analysis can more clearly reveal the variation patterns of species traits in communities, which will help to understand the scale effects and potential mechanisms of trait relationships.

Thinning alters nitrogen transformation processes in subtropical forest soil: Key roles of physicochemical properties.

Thinning-a widely used forest management practice-can significantly influence soil nitrogen (N) cycling processes in subtropical forests. However, the effects of different thinning intensities on nitrification, denitrification, and their relationships with soil properties and microbial communities remain poorly understood. Here, we conducted a study in a subtropical forest in China and applied three thinning treatments, i.e., no thinning (0 %), intermediate thinning (10-15 %), and heavy thinning (20-25 %), and investigated the effects of thinning intensity on the potential nitrification rate (PNR), potential denitrification rate (PDR), and microbial communities. Moreover, we explored the relationships among soil physicochemical properties, microbial community structure, and nitrogen transformation rates under different thinning intensities. Our results showed that intermediate and heavy thinning significantly increased the PNR by 87 % and 61 % and decreased the PDR by 31 % and 50 % compared to that of the control, respectively. Although the bacterial community structure was markedly influenced by thinning, the fungal community structure remained stable. Importantly, changes in microbial community composition and diversity had minimal impacts on the nitrogen transformation processes, whereas soil physicochemical properties, such as pH, organic carbon content, and nitrogen forms, were identified as the primary drivers. These findings highlight the critical role of managing soil physicochemical properties to regulate nitrogen transformations in forest soils. Effective forest management should focus on precisely adjusting the thinning intensity to enhance the soil physicochemical conditions, thereby promoting more efficient nitrogen cycling and improving forest ecosystem health in subtropical regions.

Environmental Filtering and Dispersal Limitations Driving the Beta Diversity Patterns at Different Scales of Secondary Evergreen Broadleaved Forests in the Suburbs of Hangzhou.

Subtropical suburban secondary evergreen broadleaved forests are essential in regulating the ecological environment's quality and promoting urban sustainable development. In the suburbs of Hangzhou City, well-preserved secondary evergreen broadleaved forest communities were selected to establish a 6 ha forest dynamic monitoring plot. Community surveys and environmental factor measurements were conducted in this area. This study investigated the beta diversity patterns at different scales by considering the environmental and spatial factors to explore the driving beta diversity. Using a similar paired-site beta diversity decomposition method, the study aimed to investigate the differences in species composition and the mechanisms of multiple species coexistence within the secondary evergreen broadleaved forest communities. The results showed that the beta diversity of the suburban secondary evergreen broadleaved forest communities decreased with the increasing spatial scale. Both the dispersal limitation and the environmental filtering were found to drive the formation of beta diversity patterns in these subtropical suburban forests. At relatively smaller scales (<100 m), species turnover was found to determine the beta diversity patterns of the suburban secondary evergreen broadleaved forests. Dispersal limitation had a dominant influence at more minor scales, while the effect of environmental filtering gradually increased with scale, and the impact of the dispersal limitation decreased. The partitioning of the beta diversity in subtropical secondary evergreen broadleaved forests in China provides critical scientific insights into the spatial distribution patterns and changes in biodiversity. It offers valuable knowledge for the conservation and understanding of biodiversity maintenance in the region.

Citrus Huanglongbing correlated with incidence of Diaphorina citri carrying Candidatus Liberibacter asiaticus and citrus phyllosphere microbiome.

In China, citrus Huanglongbing (HLB) disease is caused by the Candidatus Liberibacter asiaticus bacterium, which is carried by the Asian citrus psyllid Diaphorina citri Kuwayama. It was hypothesized that the epidemic of the HLB may related with the rate of bacterium presence in the insect vector and bacterium content in plant tissues, as well as the phyllosphere microbe communities changes. This study systematically analyzed the presence or absence of Ca. L. asiaticus in citrus tree leaves and in the insect vector D. citri over a 6-year period using real-time PCR. In addition, changes in the number of bacteria carried by D. citri over 12 months were quantified, as well as the relationship between the proportion of D. citri carrying Ca. L. asiaticus and the proportion of plants infected with Ca. L. asiaticus were analyzed. Results showed that the proportion of D. citri carrying bacteria was stable and relatively low from January to September. The bacteria in citrus leaves relatively low in spring and summer, then peaked in December. The proportion of D. citri carrying bacteria gradually declined from 2014 to 2019. The proportion of D. citri carrying Ca. L. asiaticus showed a significant positive correlation with the proportion of diseased citrus. The phyllosphere bacterial and fungal communities on the healthy citrus leaf were significantly different with the disease leaf in April and December. Pathogenic invasions change the citrus phyllosphere microbial community structure. It could be summarized that citrus Huanglongbing correlated with incidence of Diaphorina citri carrying Candidatus Liberibacter asiaticus and citrus phyllosphere microbiome.