Ongoing global climate change is increasing the risk of drought stress in some areas, which may compromise forest health. Such drought events also increase outbreaks of insect herbivores, resulting in plant defoliation. Interactions between drought and defoliation are poorly understood. In a greenhouse experiment, we selected a native species, Quercus acutissima, and an alien species, Quercus rubra, to explore their physiological responses to drought and defoliation treatments. After the treatments, we determined the seedlings’ physiological responses on days 10 and 60. Our results showed that the defoliation treatment accelerated the carbon reserve consumption of plants under drought stress and inhibited the growth of both seedling types. Under the drought condition, Q. rubra maintained normal stem-specific hydraulic conductivity and normal growth parameters during the early stage of stress, while Q. acutissima used less water and grew more slowly during the experiment. Sixty days after defoliation treatment, the stem starch concentration of Q. acutissima was higher than that of the control group, but the stem biomass was lower. This indicates that Q. acutissima adopted a ‘slow strategy’ after stress, and more resources were used for storage rather than growth, which was conducive to the ability of these seedlings to resist recurrent biotic attack. Thus, Q. acutissima may be more tolerant to drought and defoliation than Q. rubra. The resource acquisition strategies of Quercus in this study suggest that the native Quercus species may be more successful at a long-term resource-poor site than the alien Quercus species.

Phytoplankton community characterized by strong vitality response to environmental change in freshwater ecosystems. This study aims to evaluate the effectiveness of using phytoplankton diversity as a water quality indicator in wetlands, and find out the main environmental variables affecting the distribution of phytoplankton. From 2020 to 2021, we examined phytoplankton assemblages and water environmental variables in spring, summer, and autumn at eight sampling sites from Hulanhe Wetland, Northeast (NE) China. The results showed that Bacillariophyta was the dominant species. Phytoplankton composition and abundance differed among sampling sites in each season; the abundance in summer (613.71 × 10⁴ ind. L^–1) was higher than that in autumn and spring. The water quality assessment of the trophic state index (TSI) based on the four physicochemical indicators was compared with phytoplankton diversity indices, which indicated that the phytoplankton community was stable, and these two indices were significantly lower in summer than in spring and autumn. According to redundancy analysis (RDA), total phosphorus (TP) and nitrogen (TN) were the main environmental variables affecting the distribution of phytoplankton. Temperature and dissolved oxygen (DO) changes also played a role, and their impact on the community was discussed. This work can provide relevant scientific references on the usefulness of phytoplankton diversity structure in assessing water quality in cold regions, in which the succession can be significantly affected by nutrients and temperatures.

Understanding the vegetation greenness dynamics in the forest–steppe transition zone is essential for ecosystem management, and in order to study ecological changes in the region. This study provides a valuable record of the vegetation greenness dynamics in the western Greater Khingan Range over the past 193 years (1826–2018) based on tree-ring data represented by the normalized difference vegetation index (NDVI). The reconstructed vegetation greenness dynamics record contains a total of 32 years of high vegetation greenness and 37 years of low vegetation greenness, together occupying 35.8% of the entire reconstructed period (193 years). Climate (precipitation) is the main influence on the vegetation greenness dynamics at this site, but human activities have also had a significant impact over the last few decades. The magnitude, frequency, and duration of extreme changes in vegetation greenness dynamics have increased significantly, with progressively shorter intervals. Analyses targeting human behavior have shown that the density of livestock, agricultural land area, and total population have gradually increased, encroaching on forests and grasslands and reducing the inter-annual variability. After 2002, the government implemented projects to return farmland to its original ecosystems, and for the implementation of new land management practices (which are more ecologically related); as such, the vegetation conditions began to improve. These findings will help us to understand the relationship between climate change and inter- and intra- annual dynamics in northeastern China, and to better understand the impact of human activities on vegetation greenness dynamics.

Research on plant functional traits have advanced our understanding of plant investment acquisition strategies. However, it is still unknown how a plant investment acquisition strategy varies or how the relative position of plants on the leaf economic spectrum changes across different habitats. Therefore, we conducted the field experiments at two long‐term ecological research sites in Shandong and Xinjiang, China, in August 2023. Twenty‐two common species in both sites and four endemics in each site were selected for leaf gas exchange traits, leaf growth traits, and leaf nutrient trait measurements. We used two different methods to quantify the leaf economic spectrum, PCA quantification and functional area quantification. We found that the 22 common species had a significantly faster investment acquisition strategy than local endemics on the leaf economic spectrum. Besides, the plasticity of the 22 common species was not coupled with the plasticity of their investment acquisition strategy. According to our results, we quantified and constructed the leaf economic spectrum of the 30 woody plant species in Shandong and Xinjiang and discussed that high plasticity and fast investment acquisition strategy may be an ecological adaptation and distribution strategy for widely distributed species.

Under the background of global climate change, climate warming has led to an increase in insect herbivory, which significantly affects the growth, survival, and regeneration of forest plants in the warm temperate zone of China. Plants can adopt defense responses to adapt to insect defoliation. Therefore, field experiments were conducted on five common warm temperate species, Quercus acutissima, Quercus serrata, Quercus aliena, Quercus dentata, and Robinia pseudoacacia. We measured the leaf traits of healthy trees and insect defoliated trees, to explore the response strategies of common species in warm temperate zones to insect defoliation. Our results showed that native species stored more carbon in extreme environments for survival rather than growth, while the alien species R. pseudoacacia tended to adopt active resource acquisition strategies and were more inclined towards growth. The content of tannins and flavonoids in the alien species R. pseudoacacia did not significantly increase after leaf damage, while the content of secondary metabolites such as tannins, flavonoids, and total phenols in the native species Q. acutissima, Q. serrata, Q. aliena, Q. dentata increased significantly after leaf damage. This indicated that compared to alien species, native species invested more resources in defense, which might reduce resource allocation for growth. Thus, the native Quercus species have stronger resistance than the alien species R. pseudoacacia after insect defoliation.