Long-term water use efficiency and non-structural carbohydrates of dominant tree species in response to nitrogen and water additions in a warm temperate forest

Nitrogen (N) deposition tends to accompany precipitation in temperate forests, and vegetation productivity is mostly controlled by water and N availability. Many studies showed that tree species response to precipitation or N deposition alone influences, while the N deposition and precipitation interactive effects on the traits of tree physiology, especially in non-structural carbohydrates (NSCs) and long-term water use efficiency (WUE), are still unclear. In this study, we measured carbon stable isotope (delta C-13), total soluble sugar and starch content, total phenols, and other physiological traits (e.g., leaf C:N:P stoichiometry, lignin, and cellulose content) of two dominant tree species (Quercus variabilis Blume and Liquidambar formosana Hance) under canopy-simulated N deposition and precipitation addition to analyze the changes of long-term WUE and NSC contents and to explain the response strategies of dominant trees to abiotic environmental changes. This study showed that N deposition decreased the root NSC concentrations of L. formosana and the leaf lignin content of Q. variabilis. The increased precipitation showed a negative effect on specific leaf area (SLA) and a positive effect on leaf WUE of Q. variabilis, while it increased the leaf C and N content and decreased the leaf cellulose content of L. formosana. The nitrogen-water interaction reduced the leaf lignin and total phenol content of Q. variabilis and decreased the leaf total phenol content of L. formosana, but it increased the leaf C and N content of L. formosana. Moreover, the response of L. formosana to the nitrogen-water interaction was greater than that of Q. variabilis, highlighting the differences between the two dominant tree species. The results showed that N deposition and precipitation obviously affected the tree growth strategies by affecting the NSC contents and long-term WUE. Canopy-simulated N deposition and precipitation provide a new insight into the effect of the nitrogen-water interaction on tree growth traits in a temperate forest ecosystem, enabling a better prediction of the response of dominant tree species to global change

Mixture of tree species enhances stability of soil bacterial community through phylogenetic diversity

The composition of tree species might influence microbial diversity considerably, yet investigation of the consequences of changes in diversity on stability of the microbial community is still in its early stages. Understanding how diversity governs community stability is vital for predicting the response of an ecosystem to environmental changes. Phylogenetic diversity (PD) describes the distinct evolution of species in a community, and might be useful for estimating the effects of biodiversity on ecosystem function and stability. High‐throughput 16S rRNA gene sequencing was used to examine soil bacterial phylogenetic distances, phylogenetic diversity and interactions between individuals in five single‐species plantations and three mixed‐species plantations. The plantations were established on the same initial substrate, and sampling was at 68 relatively spatially independent sites. Our results showed that mixed tree species enhanced soil bacterial phylogenetic diversity and community stability, and that phylogenetic diversity had a positive effect on stability of the soil microbial community. We also found evidence that microbial communities characterized by distantly related species with weak interactions were more stable in mixed plantations than communities with strong interactions in single‐species plantations. These results may be explained by the ‘insurance hypothesis’, that large phylogenetic diversity of microbial communities which share different ecological niches insures them against decline in their stability. This is because, even if some microbial species fail to deal with environmental change, others might not necessarily be affected similarly. Our findings demonstrate that phylogenetic diversity is the main controlling factor of the variation in stability across sites and requires more attention in sustainable forest management

Influences of Canopy Nitrogen and Water Addition on AM Fungal Biodiversity and Community Composition in a Mixed Deciduous Forest of China

Nitrogen (N) deposition and precipitation could profoundly influence the structure and function of forest ecosystems. However, conventional studies with understory additions of nitrogen and water largely ignored canopy-associated ecological processes and may have not accurately reflected the natural situations. Additionally, most studies only made sampling at one time point, overlooked temporal dynamics of ecosystem response to environmental changes. Here we carried out a field trial in a mixed deciduous forest of China with canopy addition of N and water for 4 years to investigate the effects of increased N deposition and precipitation on the diversity and community composition of arbuscular mycorrhizal (AM) fungi, the ubiquitous symbiotic fungi for the majority of terrestrial plants. We found that (1) in the 1st year, N addition, water addition and their interactions all exhibited significant influences on AM fungal community composition; (2) in the 2nd year, only water addition significantly reduced AM fungal alpha-diversity (richness and Shannon index); (3) in the next 2 years, both N addition and water addition showed no significant effect on AM fungal community composition or alpha-diversity, with an exception that water addition significantly changed AM fungal community composition in the 4th year; (4) the increment of N or water tended to decrease the abundance and richness of the dominant genus Glomus and favored other AM fungi. (5) soil pH was marginally positively related with AM fungal community composition dissimilarity, soil NH4+-N and N/P showed significant/marginal positive correlation with AM fungal alpha-diversity. We concluded that the effect of increased N deposition and precipitation on AM fungal community composition was time-dependent, mediated by soil factors, and possibly related to the sensitivity and resilience of forest ecosystem to environmental changes

Utility of clinical metagenomics in diagnosing malignancies in a cohort of patients with Epstein-Barr virus positivity

BackgroundsDifferentiation between benign and malignant diseases in EBV-positive patients poses a significant challenge due to the lack of efficient diagnostic tools. Metagenomic Next-Generation Sequencing (mNGS) is commonly used to identify pathogens of patients with fevers of unknown-origin (FUO). Recent studies have extended the application of Next-Generation Sequencing (NGS) in identifying tumors in body fluids and cerebrospinal fluids. In light of these, we conducted this study to develop and apply metagenomic methods to validate their role in identifying EBV-associated malignant disease.MethodsWe enrolled 29 patients with positive EBV results in the cohort of FUO in the Department of Infectious Diseases of Huashan Hospital affiliated with Fudan University from 2018 to 2019. Upon enrollment, these patients were grouped for benign diseases, CAEBV, and malignant diseases according to their final diagnosis, and CNV analysis was retrospectively performed in 2022 using samples from 2018 to 2019.ResultsAmong the 29 patients. 16 of them were diagnosed with benign diseases, 3 patients were diagnosed with CAEBV and 10 patients were with malignant diseases. 29 blood samples from 29 patients were tested for mNGS. Among all 10 patients with malignant diagnosis, CNV analysis suggested neoplasms in 9 patients. Of all 19 patients with benign or CAEBV diagnosis, 2 patients showed abnormal CNV results. The sensitivity and specificity of CNV analysis for the identification for tumors were 90% and 89.5%, separately.ConclusionsThe application of mNGS could assist in the identification of microbial infection and malignancies in EBV-related diseases. Our results demonstrate that CNV detection through mNGS is faster compared to conventional oncology tests. Moreover, the convenient collection of peripheral blood samples adds to the advantages of this approach

Legume Plants Enhance the Resistance of Soil to Ecosystem Disturbance

Cultivation of legume plants is well known to improve soil N level and net primary productivity; besides, it may deliver other ecosystem benefits such as increasing soil carbon sequestration and soil food web complexity. However, little is known about whether legumes can improve the resistance of soils to ecosystem disturbances. In the present study, we compared the resistance of soils to an ecosystem disturbance (understory removal) in the presence or absence of a legume species (Cassia alata) in mixed tree species plantations in southern China. Soil physico-chemical and biotic properties were employed to quantify the resistance of soils to understory removal. Our results showed that the resistance indices of soil water content, omnivorous-predacious nematode abundance and nematode channel index to understory removal were greater in the presence of legumes than those without legumes in wet season. The resistance indices of fungal to bacterial ratio, fungivorous nematode abundance and total arthropod abundance were greater in the presence of legume than those without legume species in dry season. Our results indicate that legumes may enhance the resistances of soil physico-chemical and biological properties to the ecosystem disturbance. Our findings could provide a better understanding of the myriad ways in which legumes can positively affect ecosystem functioning

Stoichiometric flexibility and soil bacterial communities respond to nitrogen fertilization and neighbor competition at the early stage of primary succession

At the early stage of primary succession, there are deficient nutrient resources as well as competition stress among neighboring plants. Our aims were to elucidate the flexibility of tree seedlings' stoichiometric relationships and their effects on soil microbial communities, and to determine the driving forces of species turnover during primary succession through the evaluation of carbon (C) : nitrogen (N) : phosphorus (P) stoichiometric relationships. We conducted an experiment testing N addition effect on two species from the early stage of primary succession, under intra- and interspecific competition conditions. Our results showed that higher values of delta N-15-NO(3)(-)and delta C-13 were observed inPopulus purdomiiindividuals than inSalix rehderianaafter N application, which indicated a more efficient N uptake and water-use efficiency inP. purdomiiplants. Furthermore, under N addition, the intraspecific competition ofP. purdomiipresented a higher urease activity, microbial biomass C (MBC), microbial N:P ratio (MBN:MBP), and phylogenetic diversity compared to the intraspecific competition ofS. rehderiana. The results showed thatP. purdomiiseedlings influenced soil properties in a way that led to a positive feedback on their performance with an increasing N availability. In contrast,S. rehderianaseedlings influenced soil properties in a way that caused a negative feedback on their performance with increasing N. Such events can promote species turnover fromSalixtoPopulusduring succession. Additionally, DNA sequencing of soil bacterial communities showed differences in the composition of microbial communities in response to N fertilization and different competition patterns. Altogether, our results showed that plant, soil, and microbial community responses to N fertilization in a subalpine glacier forefield differed among tree species and competition patterns. This study brings new insight into mechanisms that drive species replacement and biogeochemical cycling during primary succession.Peer reviewe