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Purpose: Anthropogenic activities have increased the nitrogen (N) inputs in terrestrial ecosystems, thereby altering both the carbon (C) and phosphorus (P) availability along with resource stoichiometry. Stoichiometric deviations between microbial biomass and resources availablity cause stoichiometric imbalances and nutrient limitations for microbial activity. However, whether N deposition will further aggravate the existing P limitation is unknown. Furthermore, how soil microbes respond to these conditions, along with the biogeochemical cycles they mediate, still remains unclear. Methods: To answer these questions, a 7-year N addition experiment (+0, +50, +150 kg N ha−1 yr−1; CK, LN, HN) has been conducted in a subtropical evergreen-broadleaved forest in the Rainy Area of West China, where received the highest background N deposition in the world and the highest precipitation in inland China. Soil-available nutrients, microbial biomass, C-, N-, and P-acquiring enzyme activities, microbial community composition and diversity were measured. Results: With increasing N addition, the soil DOC:AP and AN:AP ratios increased significantly, whereas microbial biomass C:P and N:P ratios decreased significantly, resulting in increased C:P and N:P imbalances between the soil microbes and resources, thereby aggravating the existing P limitation of microorganisms in this subtropical N-saturated forest. Microbial communities maintained stoichiometric homeostasis by increasing ACP enzyme activity (by 8.99% to 19.28% under N treatment) and threshold elements ratio (TER) at P-limited levels. The aggravated imbalance of C:P and N:P caused by N addition decreased the bacterial and fungal community alpha-diversity. Interestingly, changes in the beta-diversity of the bacterial rather than the fungal community responded more strongly to stoichiometric imbalance. Bacterial communities transitioned from coprophilous (Proteobacteria-dominated) to oligotrophic (Actinobacteriota-dominated) under N addition treatment. Conclusions: This study not only highlights the importance of stoichiometric imbalances in regulating the soil microbial community structure and enzymatic activity, but also may help in understanding how global N deposition-induced resource stoichiometry changes affect the terrestrial C and nutrient flows. [ABSTRACT FROM AUTHOR]

Common walnut Juglans regia L. suffered devastating damage from the white‐striped longhorn beetle Batocera horsfieldi (Hope) in southwest China, which resulted in a dramatic decrease of local walnut production. However, the control of this wood‐boring pest with traditional methods is difficult as a result of its cryptic feeding habit.We proposed that developing host‐plant resistance is a more effective way of controlling this insect with long‐term benefits. One way of improving host‐plant resistance is to identify plant traits related to host‐plant preference of targeted insects.In the present study, we investigated the differences in feeding and oviposition preferences of B. horsfieldi on four J. regia cultivars in the field and tested whether such preferences are associated with structural and chemical traits in plant branches.The results obtained showed that the host‐plant resistance of J. regia cultivars to B. horsfieldi was related to increased wood density, higher amounts of cellulose and lignin, and higher contents of tannins, total flavonoids and total phenolics, whereas the susceptible cultivars were characterized by thicker bark, higher contents of water, sugar and soluble protein.The identified traits involved in host‐plant preference can subsequently contribute to the selection and breeding of resistant J. regia cultivars to B. horsfieldi. [ABSTRACT FROM AUTHOR]

How stoichiometry in different ecosystem components responds to long-term nitrogen (N) addition is crucial for understanding within-ecosystem biogeochemistry cycling processes in the context of global change. To explore the effects of long-term N addition on nutrient stoichiometry in soil and plant components in forest ecosystem, a 10-year N addition experiment using ammonium nitrate (NH 4 NO 3 ) was conducted in a bamboo forest in the Rainy Zone of West China, where the background N deposition is the highest in the world. Four N treatment levels (+0, +50, +150, +300 kg N ha -1 yr -1 ) (CK, LN, MN, HN) were applied monthly since November 2007, and then, the C:N:P stoichiometry of soil, microbial biomass, and enzymes in rhizosphere soil and bulk soil, and plant organs were measured. N addition decreased the stoichiometry of C:N:P of soil, microbial biomass, and enzymes. Soil C:N:P change under N addition treatments was stronger in bulk soil, while C:N:P changes for microbial biomass and enzyme activity were significant in rhizosphere soil. N addition significantly decreased TOC in bulk soil. Changes in MBC:MBN:MBP in rhizosphere and bulk soil were mainly caused by MBN and MBP, and MBP performance was consistent with that of AP. The main variable leading to the change of enzyme C:N:P in rhizosphere soil was BG and AP, and in bulk soil was LAP + NAG activity. Plant root C:P and N:P increased with N addition, while those for leaves and twigs did not. N addition significantly reduced the pH of both rhizosphere and bulk soils. These results suggest that the stoichiometry responses of rhizosphere and bulk soils were different due to the influence of plant roots. Soil acidification, enhanced aluminum toxicity potential, decreased root biomass and enhanced microbial P limitation caused by N addition were the important mechanisms that promoted stoichiometry changes in this ecosystem. Under the chronic input of N deposition, the stoichiometry between plant and soil evolved in different directions, which may lead to the decoupling of plants from soils., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)