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Abstract Plant reproductive ecology is one of the research hotspots in ecology. With the increasing attention paid to the conservation of plant diversity, the research on reproductive characteristics and flowering biological characteristics of more species has attracted more attention. However, plant reproduction is affected by multiple interacting factors such as pollen limitation and resource availability. Vitex negundo var. heterophylla (Franch.) Rehder (Lamiaceae) is a significant species for water and soil conservation. Previous studies have revealed its mating system by the biological characteristics of flowering and SSR markers, but its reproductive strategies remain to be further studied. We evaluated reproductive success through artificial pollination to explore the reproductive characteristics of V. negundo var. heterophylla for the first time. From the results of fruit set, there is a mixed mating system dominated by outcrossing in V. negundo var. heterophylla accompanied by self‐compatibility, and it cannot carry out autonomous selfing. Our data show the pollinator‐mediated interaction in the success of reproduction, whereas the effect of anemophily is very weak. And the seed germination rate of inbred line progenies was lower than that of hybrid progenies, which is suspected to be caused by inbreeding depression. The research will provide scientific information for the protection and conservation of V. negundo var. heterophylla from the point of view of reproduction. In sum, the results are necessary to protect animal vectors in the background of insect decline.

. In the context of rapid urbanization, pollution and ecological degradation problems have frequently shown up and influenced environmental sustainability of rural China in the past decades. The rural residents have begun to pay attention to local environment protection, and researchers have been taking public perceptions into regional planning. However, comprehensive studies on the perceptions of villagers on rural environment development still remain less. This research carried out a face-to-face questionnaire investigation of 187 villages and ten residents from each village at a nationwide scale of China. The investigated village committee managers and residents were interviewed by asking the questions including the existing environmental problems, the targets of rural environment development, the ways to achieve these targets and the willingness to pay for pollution control. The results showed that household waste pollution, air pollution and pesticides pollution etc. are top concerned problems. A big proportion (65%) of the interviewed residents chose “environment with good quality for health” as their preferred living environment. While, more than half of the interviewed village managers took “green villages with sustainable agriculture” as their village development targets. And more than 50% of the interviewed residents advocated to increase the forest coverage rate to mitigate the degeneration of rural ecosystem services. As well, most residents strongly support rural green development and are willing to pay for pollution control. Our findings may provide new insights into rural environment development and rural revitalization in the context of rapid urbanization.

Climate varies along geographic gradients, causing spatial variations in the effects of energy and water on species richness and the explanatory power of different climatic factors. Species of the Quercus genus are important tree species in China with high ecological and socioeconomic value. To detect whether the effects of energy and water on species richness change along climatic gradients, this study built geographically weighted regression models based on species richness and climatic data. Variation partition analysis and hierarchical partitioning analysis were used to further explore the main climatic factors shaping the richness distribution pattern of Quercus in China. The results showed that Quercus species were mainly distributed in mountainous areas of southwestern China. Both energy and water were associated with species richness, with global slopes of 0.17 and 0.14, respectively. The effects of energy and water on species richness gradually increased as energy and water in the environment decreased. The interaction between energy and water altered the effect of energy, and in arid regions, the effects of energy and water were relatively stronger. Moreover, energy explained more variation in species richness in both the entire study area (11.5%) and different climate regions (up to 19.4%). The min temperature of coldest month was the main climatic variable forming the richness distribution pattern of Quercus in China. In conclusion, cold and drought are the critical climatic factors limiting the species richness of Quercus, and climate warming will have a greater impact in arid regions. These findings are important for understanding the biogeographic characteristics of Quercus and conserving biodiversity in China.

Sandstorm, as a disastrous weather phenomenon, seriously threatens the ecological environment and human health. In this study, the normalized brightness temperature dust index (NBTDI) data set of sandstorms in Yellow River Basin, China during 2000–2021 was constructed. Based on this, the temporal and spatial distribution pattern of sandstorms in the Yellow River Basin in the 21st century was analyzed. The variation trend of NBTDI in the past 22 years was discussed. The results showed that the interannual variation of sandstorms in the 21st century weakened first and then intensified. From the perspective of seasonal variation, sandstorm events occurred most frequently in spring (92.4%), followed by winter (5.6%), and occasionally in summer and autumn. In space, the distribution of sandstorms in the Yellow River Basin had obvious spatial heterogeneity. The central location of the sandstorm in the Yellow River Basin moved slightly to the north, but all of them were concentrated on desert areas. This was caused by the combination of unique geographical location and meteorological factors. The natural climate was closely related to the occurrence of sandstorms. The variation trend of long time-series NBTDI indicated that there were long memories between 22 years of sandstorms. NBTDI had an increasing trend in the long time series. In the future, sandstorms will become more frequent, in line with past trends. This study provides important data support for comprehensive understanding of extreme sandstorm weather, and has important significance for large-scale and long-term monitoring of sandstorm weather.

IntroductionAs precipitation patterns are predicted to become increasingly erratic, the functional maintenance of warm-temperate forests constitutes a key challenge for forest managers. In this study, 2-year-old Quercus acutissima seedlings were selected to elucidate the mechanisms whereby they respond to soil water fluctuations and the drought hardening effects on plant carbohydrate dynamics.MethodsSeedlings were trained under different soil water conditions for 2 months: drought (D), well-watered (W), 1-month drought and then 1-month well-watered (D-W), and 1-month well-watered and then 1-month drought (W-D). The functional traits involved in water- and carbon-use strategies were explored at the end of the hardening period. Compared with seedlings in group W, seedlings in groups D, D-W, and W-D had increased potential for carbon uptake (i.e., light saturated point, maximum ribulose-1,5-bisphosphate (RuBP) saturated rate, and electron transport rate) and water uptake (i.e., fine root–to–coarse root ratio) and downregulated growth and mitochondrial respiration to decrease carbon consumption. After water fluctuation hardening, we performed a successional dry-down experiment for 1 month to detect carbohydrate dynamics and explore the acclimation caused by prior hardening.Results and discussionOur results revealed that there were more soluble sugars allocated in the leaves and more starch allocated in the stems and roots of seedlings hardened in the D, W-D, and D-W treatments than that of seedlings hardened in the W treatment. No significant changes in total non-structural carbohydrates were found. In addition, we found near-zero (seedlings trained by D and D-W treatments) or negative (seedlings trained by W-D treatment) growth of structural biomass at the end of the dry-down experiment, which was significantly lower than that of W-hardened seedlings. This suggests that there was a shift in allocation patterns between carbon storage and growth under recurrent soil drought, which can be strengthened by drought memory. We conclude that Q. acutissima seedlings adjusted water- and carbon-use strategies in response to water fluctuations, whereas stress memory can enhance their overall performance in reoccurring drought. Therefore, taking advantage of stress memory is a promising management strategy in forest nurseries, and drought-trained seedlings might be more suitable for afforestation practices in sites characterized by fluctuating soil water content, considering the ongoing global climatic changes.

The increase of nitrogen (N) deposition and the diversity of its components lead to significant changes in the structure and function of temperate meadow steppe, which could affect plant nutrient uptake, nutrient resorption and litter decomposition, thus affecting the biogeochemical cycle process. The distribution and metabolism of nitrogen and phosphorus in plants determine the growth process and productivity of plants. Plant nutrient uptake, nutrient resorption and litter decomposition play an important role in the nutrient cycling process of ecosystem. This study closely combined these three processes to carry out experiments with different nitrogen dosages and types, and systematically explored the response of nitrogen and phosphorus nutrient cycling to nitrogen deposition. The results showed that nitrogen deposition can greatly affect ecosystem nutrient cycle of nitrogen and phosphorus. Firstly, Nitrogen deposition has significant effect on plant nutrient uptake. Nitrogen uptake of stems and leaves increased with the increase of nitrogen addition dosage, while phosphorus uptake of stems and leaves showed a downward trend or no significant effect. Besides, nitrogen addition type had a significant effect on nitrogen and phosphorus content of stems. Secondly, Nitrogen addition dosage had a significant effect on plant nutrient resorption, while nitrogen addition type had no significant effect on it. Thirdly, nitrogen deposition has significant effect on litter decomposition. With the increase of nitrogen addition dosage, the initial nitrogen content of litters increased and the decomposition rate of litters accelerated. Nitrogen application type had significant effect on stem litter decomposition. These results indicated that nitrogen deposition significantly affects plant nutrient cycling, and thus affects the structure and function of grassland ecosystem.

IntroductionIt is of great significance to understand the characteristics and influencing factors of vegetation coverage variation in the warm temperate zone. As a typical region of the warm temperate zone in eastern China, the mountainous and hilly region in central-south Shandong Province has fragile ecological environment and soil erosion problem. Studying on vegetation dynamics and its influencing factors in this region will help to better understand the relationship between climate change and vegetation cover change in the warm temperate zone of eastern China, and the influence of human activities on vegetation cover dynamics.MethodsBased on dendrochronology, a standard tree-ring width chronology was established in the mountainous and hilly region of central-south Shandong Province, and the vegetation coverage from 1905 to 2020 was reconstructed to reveal the dynamic change characteristics of vegetation cover in this region. Secondly, the influence of climate factors and human activities on the dynamic change of vegetation cover was discussed through correlation analysis and residual analysis.Results and discussionIn the reconstructed sequence, 23 years had high vegetation coverage and 15 years had low vegetation coverage. After low-pass filtering, the vegetation coverage of 1911–1913, 1945–1951, 1958–1962, 1994–1996, and 2007–2011 was relatively high, while the vegetation coverage of 1925–1927, 1936–1942, 2001–2003, and 2019–2020 was relatively low. Although precipitation determined the variation of vegetation coverage in this study area, the impacts of human activities on the change of vegetation coverage in the past decades cannot be ignored. With the development of social economy and the acceleration of urbanization, the vegetation coverage declined. Since the beginning of the 21st century, ecological projects such as Grain-for-Green have increased the vegetation coverage.

An understanding of the annual variations in the phytoplankton community in freshwater lakes, and of the drivers responsible for these variations, is essential for lake management. In this study we collected and analyzed seasonal samples of phytoplankton and assessed environmental variables in Nansi Lake from 2011 to 2015, in order to identify the seasonal dynamics of the phytoplankton community and the main drivers in each phylum. The results showed that phytoplankton diversity in Nansi Lake followed annual cycles, which were interrupted by a water diversion in 2013. The disruption of equilibrium was clearly demonstrated by the Shannon–Wiener diversity index, Pielou’s evenness index, and Simpson’s dominance index, whereas the species richness and abundance showed resilience, maintaining regular annual cycles. The dominant species were frequently Synedra acus Kütz (Bacillariophyta), Closterium gracile Bréb (Chlorophyta), and Scenedesmus quadricauda Bréb (Chlorophyta) in summer and autumn. Non-metric multidimensional scaling (NMDS) analysis suggested that the phytoplankton was most widely distributed in summer, when conditions were more conducive to phytoplankton growth and reproduction. Redundancy analysis (RDA) indicated that the main drivers for the phytoplankton community varied in different taxonomic units. Specifically, the NP ratio and permanganate index (CODMn) had significant effects on Chlorophyta, whereas pH, dissolved oxygen (DO), and transparency significantly influenced Bacillariophyta. This study highlights the importance of seasonal phytoplankton succession and the need for identification of the main drivers in each phylum in order to achieve more effective control of phytoplankton blooms in freshwater lakes.

Cultural Ecosystem Services (CES) play an important role in socio-natural ecosystems. Assessment of CES in rural areas is crucial for development planning and decision-making. However, assessment of CES at the local scale and, in particular, rural areas remain under-researched. In order to reveal the importance of different kinds of CES and the related land uses perceived by the rural residents, a simplified tick-scoring method was developed and tested in a case study of four villages in Shandong Province, China. This method poses CES questions and seeks answers about corresponding land use types in a questionnaire form that is accessible and useful to village residents. Furthermore, the important categories of CES and related land use types were identified and ranked based on the questionnaire. The results showed that ecological culture and aesthetic services ranked in the top two of twelve CES categories, while scenic spots/mountains, forests, and lakes/rivers/reservoirs scored for multiple CES and attained higher than average CES scores. Overall, the simplified method is practical to understand the perspectives of rural residents on the important CES and related landscapes. The established approach shed lights on CES assessment and management improvement at local scale of rural areas under different socio-environmental contexts in China and elsewhere.

It has widely been documented that nitrogen (N) enrichment stimulates plant growth and modifies plant functional traits in the terrestrial ecosystem. However, it remains unclear whether there are critical transitions or tipping points for the response of plant growth or traits to N enrichment, and how these responses differ to different N forms. We chose the native, perennial clonal grass, Leymus chinensis in Inner Mongolia steppe, and conducted a field experiment, in which six N addition rates (0, 2, 5, 10, 20, and 50 g N m–2 year–1) and five N compound types [NH4NO3, (NH4)2SO4, NH4HCO3, CO(NH2)2, slow-release CO(NH2)2] are considered. Here, we found that the different N compound types had no significant effect on the growth of L. chinensis. N addition rate significantly increased plant aboveground biomass and leaf nitrogen concentration, whereas decreased leaf dry matter content. The tipping point for N-induced aboveground biomass increase was at 10 g N m–2 year–1, and the changes in functional traits were at N addition rates of 20 g N m–2 year–1. Our findings suggested that the responses of aboveground biomass and functional traits to N addition were asymmetric, in which responses in aboveground biomass were more sensitive than that in functional traits. The differential sensitivity of aboveground biomass and functional traits of L. chinensis occurred to N deposition highlights the importance of functional traits in mediating ecosystem functioning in the face of N deposition, regardless of which chemical forms dominate in the deposited N.

Abstract Ziziphus jujuba var. spinosa has been used as a windbreak and for soil conservation and water retention. Previous studies focused on pharmacological effects and extraction of chemical components in this species, and very few explored the breeding system. The present study combined the analysis of floral morphology, behavior of flower visitors, and artificial pollination to reveal reproductive characteristics of the species. Its flowers are characterized by dichogamy, herkogamy, and stamen movement, which are evolutionary adaptations to its breeding system. There were more than 40 species of visiting insects, mainly Hymenoptera and Diptera, and the characteristics of dichogamous and herkogamous flower adapted to the visiting insects. The breeding system is outcrossing, partially self-compatible, and demand for pollinators. The fruit setting rate after natural pollination was 2%. Geitonogamy and xenogamy did not significantly increase the fruit setting rate, indicating that the low fruit setting rate was not due to pollen limitation by likely caused by resource limitation or fruit consumption. The fruit setting rate of zero in emasculated and in naturally and hand self-pollinated individuals suggested the absence of apomixis and spontaneous self-pollination. The above results can be utilized in studies on evolution and cultivation of Z. jujuba var. spinosa.

Abstract Vegetation community complexity is a critical factor influencing terrestrial ecosystem stability. China, the country leading the world in vegetation greening resulting from human activities, has experienced dramatic changes in vegetation community composition during the past 30 years. However, how China's vegetation community complexity varies spatially and temporally remains unclear. Here, we examined the spatial pattern of China's vegetation community complexity and its temporal changes from the 1980s to 2015 using two vegetation maps of China as well as more than half a million field samples. Spatially, China's vegetation community complexity distribution is primarily dominated by elevation, although temperature and precipitation can be locally more influential than elevation when they become the factors limiting plant growth. Temporally, China's vegetation community complexity shows a significant decreasing trend during the past 30 years, despite the observed vegetation greening trend. Prevailing climate warming across China exhibits a significant negative correlation with the decrease in vegetation community complexity, but this correlation varies with biogeographical regions. The intensity of human activities have an overall negative influence on vegetation community complexity, but vegetation conservation and restoration efforts can have a positive effect on maintaining vegetation composition complexity, informing the critical role of vegetation management policies in achieving the sustainable development goal.

As nitrogen deposition intensifies under global climate change, understanding the responses of arbuscular mycorrhizal (AM) fungi to nitrogen deposition and the associated mechanisms are critical for terrestrial ecosystems. In this study, the effects of nitrogen addition and mowing on AM fungal communities in soil and mixed roots were investigated in an Inner Mongolia grassland. The results showed that nitrogen addition reduced the α-diversity of AM fungi in soil rather than that of root. Besides, nitrogen addition altered the composition of AM fungal community in soil. Soil pH and inorganic nitrogen content were the main causes of changes in AM fungal communities affected by nitrogen addition. Mowing and the interaction of nitrogen addition and mowing had no significant effect on AM fungal community diversity. In contrast, while mowing may reduce the negative effects of nitrogen addition on the richness and diversity of plants by alleviating light limitation, it could not do so with the negative effects on AM fungal communities. Furthermore, AM fungal communities clustered phylogenetically in all treatments in both soil and roots, indicating that environmental filtering was the main driving force for AM fungal community assembly. Our results highlight the different responses of AM fungi in the soil and roots of a grassland ecosystem to nitrogen addition and mowing. The study will improve our understanding of the effects of nitrogen deposition on the function of ecosystem.

Abstract Vitex negundo L. var. heterophylla (Franch.) Rehder (Lamiaceae) is an important tree species for soil and water conservation, yet the reproductive ecology of this species remains to be elucidated. To investigate the reproductive traits of V. negundo var. heterophylla, the phenology, morphological characteristics (a suite of characters was assessed: floral morphology, nectar production, pollen viability, and stigma receptivity) and mating system of this species were systematically revealed for the first time in this study. Phenological observations, morphological measurements, and nectar production analysis were conducted during anthesis. Pollen viability and stigma receptivity at different flowering stages were measured by biochemical methods. Finally, genetic analysis based on SSR markers was used to reveal the mating system; outcrossing index and pollen‐ovule ratio were also calculated to help analysis. V. negundo var. heterophylla showed several obvious characteristics of outcrossing, such as abundant and attractive flowers, secreting nectar, and emitting scent. In addition, mechanisms such as homogamy and a short anther‐stigma distance that can promote self‐fertilization were also identified in this species. The coexistence of selfing and outcrossing characteristics demonstrates a predominantly outcrossed mixed mating system (outcrossing rate, t = 95%). The scientific information provided by this study may contribute to conservation of V. negundo var. heterophylla from a reproductive perspective.

Plasticity of plant functional traits plays an important role in plant growth and survival under changing climate. However, knowledge about how leaf functional traits respond to the multi-level N addition rates, multiple N compound and duration of N application remains lacking. This study investigated the effects of 2-year and 7-year N addition on the leaf functional traits of Leymus chinensis and Thermopsis lanceolata in a meadow grassland. The results showed that the type of N compounds had no significant effect on leaf functional traits regardless of duration of N application. N addition significantly increased the leaf total N content (LN) and specific leaf area (SLA), and decreased the leaf total P content (LP) and leaf dry matter content (LDMC) of the two species. Compared with short-term N addition, long-term N addition increased LN, LP, SLA, and plant height, but decreased the LDMC. In addition, the traits of the two species were differentially responsive to N addition, LN and LP of T. lanceolata were consistently higher than those of L. chinensis. N addition would make L. chinensis and T. lanceolata tend to “quick investment-return” strategy. Our results provide more robust and comprehensive predictions of the effects of N deposition on leaf traits.

Seedlings in regenerating layer are frequently attacked by herbivorous insects, while the combined effects of defoliation and shading are not fully understood. In the present study, two Leguminosae species (Robinia pseudoacacia and Amorpha fruticosa) were selected to study their responses to combined light and defoliation treatments. In a greenhouse experiment, light treatments (L+, 88% vs L−, 8% full sunlight) and defoliation treatments (CK, without defoliation vs DE, defoliation 50% of the upper crown) were applied at the same time. The seedlings’ physiological and growth traits were determined at 1, 10, 30, and 70 days after the combined treatment. Our results showed that the effects of defoliation on growth and carbon allocation under high light treatments in both species were mainly concentrated in the early stage (days 1–10). R. pseudoacacia can achieve growth recovery within 10 days after defoliation, while A. fruticosa needs 30 days. Seedlings increased SLA and total chlorophyll concentration to improve light capture efficiency under low light treatments in both species, at the expense of reduced leaf thickness and leaf lignin concentration. The negative effects of defoliation treatment on plant growth and non-structural carbohydrates (NSCs) concentration in low light treatment were significantly higher than that in high light treatment after recovery for 70 days in R. pseudoacacia, suggesting sufficient production of carbohydrate would be crucial for seedling growth after defoliation. Plant growth was more sensitive to defoliation and low light stress than photosynthesis, resulting in NSCs accumulating during the early period of treatment. These results illustrated that although seedlings could adjust their resource allocation strategy and carbon dynamics in response to combined defoliation and light treatments, individuals grown in low light conditions will be more suppressed by defoliation. Our results indicate that we should pay more attention to understory seedlings’ regeneration under the pressure of herbivorous insects.

Changing precipitation patterns have aggravated the existing uneven water distribution, leading to the alternation of drought and rewatering. Based on this variation, we studied species, namely, Robinia pseudoacacia and Quercus acutissima, with different root forms and water regulation strategy to determine physiological responses to repeated drought-rewatering under different planting methods. Growth, physiological, and hydraulic traits were measured using pure and mixed planting seedlings that were subjected to drought, repeated drought-rewatering (i.e., treatments), and well-irrigated seedlings (i.e., control). Drought had negative effects on plant functional traits, such as significantly decreased xylem water potential (Ψmd), net photosynthetic rate (AP), and then height and basal diameter growth were slowed down, while plant species could form stress imprint and adopt compensatory mechanism after repeated drought-rewatering. Mixed planting of the two tree species prolonged the desiccation time during drought, slowed down Ψmd and AP decreasing, and after rewatering, plant functional traits could recover faster than pure planting. Our results demonstrate that repeated drought-rewatering could make plant species form stress imprint and adopt compensatory mechanism, while mixed planting could weaken the inhibition of drought and finally improve the overall drought resistance; this mechanism may provide a theoretical basis for afforestation and vegetation restoration in the warm temperate zone under rising uneven spatiotemporal water distribution.

In recent decades, great changes have taken place in residents’ lifestyle and consumption structure. Urban household consumption plays an increasingly significant role in promoting energy use and related carbon emissions. Communities are regarded as the basic part of city, and also units and cases where management methods and policies are most likely to be operated and implemented. In this paper, questionnaire surveys were administered to investigate the consumption characteristics of urban households at the community scale in Zengcheng. Based on statistical analysis, we assessed the consumption differences among the five selected communities. Meanwhile, the carbon emissions caused by household energy consumption (CEs-HE) were evaluated and the influencing factors were studied. The results showed that respondents from different communities had significant differences in their residential consumption, housing conditions, daily travel distance, public transport charge, household durable goods service life, monthly staple food consumption, and monthly energy consumption, respectively. The average CEs-HE of each household were 410.6 ​kg CO2 per month. The Household demographic information, main expenditure items, housing conditions, daily travelling, family life habits and residents’ environmental awareness all had significant impacts on CEs-HE. The results supplied in this study could provide some valuable information for decision-makers to explore the road of urban sustainable development.

Plant size influences plant responses to combined environmental factors under climate change. However, their roles in plant ecophysiological responses are not fully understood. Two rapidly growing Leguminosae species (Robinia pseudoacacia and Amorpha fruticosa) were used to examine plant responses to combined drought and defoliation treatments (two levels of both treatments). Both 1.5 month-old seedlings and 3 month-old seedlings were grown in a greenhouse, and seedling growth, leaf gas exchanges, stem hydraulics, and concentrations of non-structural carbohydrates were determined after 60 days of treatment. Our results indicated defoliation had no significant effect on plant height, basal diameter, and total biomass whatever plant sizes and species. Under the low water availability treatment, the defoliated seedlings significantly increased by 24% in stem water potential compared with non-defoliated seedlings in large R. pseudoacacia. Compared with the high water availability in large non-defoliated R. pseudoacacia seedlings, the low water availability significantly reduced by 26% in stem starch concentration to maintain the stem soluble sugar concentration stable, but not in small R. pseudoacacia seedlings. We also found a negative correlation between leaf and root soluble sugar concentration under low water availability in A. fruticosa. The results demonstrate defoliation could relieve the effect of low water availability in large seedlings. Large seedlings had more compensatory mechanisms in response to defoliation and drought treatments than small seedlings, thus species with large carbon reserves are more recommended for vegetation restoration under combined drought and defoliation conditions. Future studies with more species are crucial for obtaining more rigorous conclusions.

Precise and accurate estimation of key hydraulic points of plants is conducive to mastering the hydraulic status of plants under drought stress. This is crucial to grasping the hydraulic status before the dieback period to predict and prevent forest mortality. We tested three key points and compared the experimental results to the calculated results by applying two methods. Saplings (n = 180) of Robinia pseudoacacia L. were separated into nine treatments according to the duration of the drought and rewatering. We established the hydraulic vulnerability curve and measured the stem water potential and loss of conductivity to determine the key points. We then compared the differences between the calculated [differential method (DM) and traditional method (TM)] and experimental results to identify the validity of the calculation method. From the drought-rewatering experiment, the calculated results from the DM can be an accurate estimation of the experimental results, whereas the TM overestimated them. Our results defined the hydraulic status of each period of plants. By combining the experimental and calculated results, we divided the hydraulic vulnerability curve into four parts. This will generate more comprehensive and accurate methods for future research.

Plants may maintain long-term xylem function via efficiency-safety tradeoff and segmentation. Most studies focus on the growing season and community level. We studied species with different efficiency-safety tradeoff strategies, Quercus acutissima, Robinia pseudoacacia, Vitex negundo var. heterophylla, and Rhus typhina, to determine the seasonality of this mechanism. We separated their branches into perennial shoots and terminal twigs and monitored their midday water potential (Ψmd), relative water content (RWC), stem-specific hydraulic conductivity (Ks), loss of 12, 50, and 88% of maximum efficiency (i.e., P12, P50, P88) for 2 years. There were no correlations between water relations (Ψmd, RWC, Ks) and embolism resistance traits (P12, P50, P88) but they significantly differed between the perennial shoots and terminal twigs. All species had weak annual hydraulic efficiency-safety tradeoff but strong segmentation between the perennial shoots and the terminal twigs. R. pseudoacacia used a high-efficiency, low-safety strategy, whereas R. typhina used a high-safety, low-efficiency strategy. Q. acutissima and V. negundo var. heterophylla alternated these strategies. This mechanism provides a potential basis for habitat partitioning and niche divergence in the changing warm temperate zone environment.

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.

Abstract Wetlands are an important carbon reservoir pool in terrestrial ecosystems. Light fraction organic carbon (LFOC), heavy fraction organic carbon (HFOC), and dissolved organic carbon (DOC) were fractionated in sediment samples from the four wetlands (ZR: Zhaoniu River; ZRCW: Zhaoniu River Constructed Wetland; XR: Xinxue River; XRCW: Xinxue River Constructed Wetland). Organic carbon (OC) from rivers and coasts of China were retrieved and statistically analyzed. At regional scale, HFOC stably dominates the deposition of OC (95.4%), whereas DOC and LFOC in ZR is significantly higher than in ZRCW. Concentration of DOC is significantly higher in XRCW (30.37 mg/l) than that in XR (13.59 mg/l). DOC and HFOC notably distinguish between two sampling campaigns, and the deposition of carbon fractions are limited by low nitrogen input. At the national scale, OC attains the maximum of 2.29% at precipitation of 800 mm. OC has no significant difference among the three climate zones but significantly higher in river sediments than in coasts. Coastal OC increases from Bohai Sea (0.52%) to South Sea (0.70%) with a decrease in latitude. This study summarizes the factors affecting organic carbon storage in regional and national scale, and have constructive implications for carbon assessment, modelling, and management.

The relative importance of bottom-up versus top-down effects in aquatic ecosystems remains a longstanding and ongoing controversy. To investigate these effects on phytoplankton communities in freshwater lakes, phytoplankton and zooplankton were sampled, and physical-chemical variables were measured during spring and summer in two important freshwater lakes in northern China: Nansi Lake and Dongping Lake. The redundancy analysis results showed that phytoplankton density and biomass were regulated by physical-chemical variables (bottom-up effects) and predation (top-down effects) together, and the former was more prominent in both lakes. However, the correlation analysis indicated that the top-down effects of zooplankton on phytoplankton were not significant in spring and summer in both lakes, while the bottom-up regulation of physical-chemical variables on phytoplankton had different patterns in the two lakes. In Nansi Lake, the bottom-up effects of physical-chemical variables on phytoplankton were weaker in summer than that in spring due to the abundant nutrients in summer. In Dongping Lake, the bottom-up effects of physical-chemical on phytoplankton were significant both in spring and summer, and the dominant bottom-up control factor shifted from total nitrogen in spring to total phosphorus in summer, with an increased ratio of nitrogen to phosphorus due to changes in limiting factors. In the two studied lakes, with fish culture, the bottom-up effects of phytoplankton on zooplankton were more important than the top-down effects of zooplankton on phytoplankton. These results demonstrate the interactions between phytoplankton and zooplankton and highlight the importance of phytoplankton regulation in freshwater lakes, which has implications for the effective management of freshwater lake ecosystems.

The influence of Alternanthera philoxeroide (alligator weed) invasion on wetland organic matter (OM) accumulation and bacterial changes is rarely studied, but is possibly an important step for revealing the invasion mechanism. Thus, the distribution characteristics of light fraction organic carbon and nitrogen (LFOC and LFON), and heavy fractions organic carbon and nitrogen (HFOC and HFON) were analyzed. Sampling was done on two sediment depths (0–15 cm and 15–25 cm) of invaded and normal habitats of two natural wetlands and two constructed wetlands, and bacterial taxa and composition in surface sediments were also analyzed by high-throughput sequencing. In the surface sediments, the LFOC and LFON contents were significantly higher in the constructed wetlands (0.791 and 0.043 g·kg−1) than in the natural wetlands (0.500 and 0.022 g·kg−1), and the contents of the C and N fractions were also prominently higher in the invaded areas than in normal wetland habitats. The OM storage was relatively stable. Proteobacteria (55.94%), Bacteroidetes (5.74%), Acidobacteria (6.66%), and Chloroflexi (4.67%) were the dominant bacterial phyla in the wetlands. The abundance of Acidobacteria, Actinobacteria, and Gemmatimonadetes were significantly higher in the invaded areas than in the normal habitats. The relative high abundance-based coverage estimator (ACE) index in the constructed wetlands and invaded areas suggested the corresponding high bacterial diversity. The significant and positive relationship between Acidobacteria and organic nitrogen concentrations suggested their potential and positive interrelationships. This study demonstrated that the alligator weed invasion could significantly change the compositions of sediment organic matterand bacteria, thus further changing the nutrition cycle and wetland microhabitat.

Suaeda salsa community is a vegetation type in saline-alkali areas. Weed invasion and colonization in S. salsa communities lead to fragmentationsof S. salsa communities. The colonization of invaded weeds in S. salsa communities is related to community succession of saline-alkali zones. The fragmented S. salsa community may be restored if the mechanism of invaded weed colonization in S. salsa communities is clearly elucidated. Thus, we studied the ecological stoichiometric characteristics of soils and plants in a salt marsh to explain the high colonization possibility of invaded weeds in S. salsa communities. In October 2014, soils and plants were collected from Dongfeng Salt Marsh, Jiaozhou Bay, Shandong Province, China. The ratio of Ex-N/Ex-P in soil was less than 13, which suggests a relative nitrogen limitation for the primary production in the zone. The minimum phosphorus content in plants was higher than 1 mg g-1, whereas the maximum nitrogen content in plants was less than 13 mg g-1. These results imply that phosphorus was abundant, whereas nitrogen was deficient in the area. The plants in the salt marsh may be limited by nitrogen. Given the relatively lower nitrogen contents in Cyperus glomeratus, Echinochloa crusgalli, and Aster subulatus than that in S. salsa, these three species exhibited higher competitiveness than S. salsa did when nitrogen was limited in primary production. These weed species may colonize highly in S. salsa communities. Moreover, nitrogen fertilization might be effective to maintain S. salsa community in Dongfeng Salt Marsh, whereas its effects on controlling weeds colonization in S. salsa communities need more studies to verify.

Temporal heterogeneity of a resource supply can have a profound effect on the interactions between alien and native plant species and their potential invasiveness. Precipitation patterns may be variable and result in a higher heterogeneity of water supply with global climate change. In this study, an alien shrub species, Rhus typhina, introduced to China from North America and a native shrub species, Vitex negundo var. heterophylla, were grown in monoculture and mixed culture under different water supply regimes, with four levels of water supply frequencies but with a constant level of total supplied water. After 60 days of treatments, the alien species was found to be the superior competitor in the mixed culture and was unaffected by changes in the water supply pattern. The dominance of R. typhina was mainly owing to its greater biomass and effective modulation of leaf physiology. However, in the mixed culture, V. negundo var. heterophylla exhibited both leaf- and whole-plant-level acclimations, including higher leaf length to petiole length and root to shoot biomass ratios, and lower specific leaf weight and leaf length to leaf width ratio. Plant height of V. negundo var. heterophylla was comparable to that of R. typhina in the mixed culture, which is a strategy to escape shading. Although water treatments had little effect on most traits in both species, the possible influence of water regimes should not be neglected. Compared with high-frequency water supply treatments, more individuals of V. negundo var. heterophylla died in low-water-frequency treatments when in competition with R. typhina, which may lead to species turnover in the field. The authors recommended that caution should be exercised when introducing R. typhina to non-native areas in the context of global climate change.

China has shown a rapid economic development in recent decades, and several drivers of this change are known to enhance biological invasions, a major cause of biodiversity loss. Here we review the current state of research on plant invasions in China by analyzing papers referenced in the ISI Web of Knowledge. Since 2001, the number of papers has increased exponentially, indicating that plant invasions in China are an emerging hot topic in invasion science. The analyzed papers cover a broad range of methodological approaches and research topics. While more that 250 invasive plant species with negative impacts have been reported from China, only a few species have been considered in more than a handful of papers (in order of decreasing number of references: Spartina alterniflora, Ageratina adenophora, Mikania micrantha, Alternanthera philoxeroides, Solidago canadensis, Eichhornia crassipes). Yet this selection might rather reflect the location of research teams than the most invasive plant species in China. Considering the previous achievements in China found in our analysis research in plant invasions could be expanded by (1) compiling comprehensive lists of non-native plant species at the provincial and national scales and to include species that are native to one part of China but non-native to others in these lists; (2) strengthening pathways studies (primary introduction to the country, secondary releases within the country) to enhance prevention and management; and (3) assessing impacts of invasive species at different spatial scales (habitats, regions) and in relation to conservation resources.

The spatial patterns of biodiversity and their underlying mechanisms have been an active area of research for a long time. In this study, a total of 63 samples (20m × 30m) were systematically established along elevation gradients on Mount Tai and Mount Lao, China. We explored altitudinal patterns of plant diversity in the two mountain systems. In order to understand the mechanisms driving current diversity patterns, we used phylogenetic approaches to detect the spatial patterns of phylogenetic diversity and phylogenetic structure along two elevation gradients. We found that total species richness had a monotonically decreasing pattern and tree richness had a unimodal pattern along the elevation gradients in the two study areas. However, altitudinal patterns in shrub richness and herbs richness were not consistent on the two mountains. At low elevation, anthropogenic disturbances contributed to the increase of plant diversity, especially for shrubs and herbs in understory layers, which are more sensitive to changes in microenvironment. The phylogenetic structure of plant communities exhibited an inverted hump-shaped pattern along the elevation gradient on Mount Tai, which demonstrates that environmental filtering is the main driver of plant community assembly at high and low elevations and inter-specific competition may be the main driver of plant community assembly in the middle elevations. However, the phylogenetic structure of plant communities did not display a clear pattern on Mount Lao where the climate is milder. Phylogenetic beta diversity and species beta diversity consistently increased with increasing altitudinal divergence in the two study areas. However, the altitudinal patterns of species richness did not completely mirror phylogenetic diversity patterns. Conservation areas should be selected taking into consideration the preservation of high species richness, while maximizing phylogenetic diversity to improve the potential for diversification in the future.

Wetland ecosystems are represented as a significant reservoir of organic carbon and play an important role in mitigating the greenhouse effect. In order to compare the compositions and distribution of organic carbon in constructed and natural river wetlands, sediments from the Xinxue River Constructed Wetland and the Xinxue River, China, were sampled at two depths (0-15 cm and 15-25 cm) in both upstream and downstream locations. Three types of organic carbon were determined: light fraction organic carbon, heavy fraction organic carbon, and dissolved organic carbon. The results show that variations in light fraction organic carbon are significantly larger between upstream and downstream locations than they are between the two wetland types; however, the opposite trend is observed for the dissolved organic carbon. There are no significant differences in the distribution of heavy fraction organic carbon between the discrete variables (e.g., between the two depths, the two locations, or the two wetland types). However, there are significant cross-variable differences; for example, the distribution patterns of heavy fraction organic carbon between wetland types and depths, and between wetland types and locations. Correlation analysis reveals that light fraction organic carbon is positively associated with light fraction nitrogen in both wetlands, while heavy fraction organic carbon is associated with both heavy fraction nitrogen and the moisture content in the constructed wetland. The results of this study demonstrate that the constructed wetland, which has a relatively low background value of heavy fraction organic carbon, is gradually accumulating organic carbon of different types, with the level of accumulation dependent on the balance between carbon accumulation and carbon decomposition. In contrast, the river wetland has relatively stable levels of organic carbon.

Recurrent water level fluctuation and submergence of plants are common in riparian zones. Our study objectives were to test the independent and interactive effects of submergence level and fluctuation frequency on a globally important riparian invasive plant, Alternanthera philoxeroides. To this end, we conducted a greenhouse experiment, in which ramets of the plants, obtained from a wetland in China, were treated with four fluctuation frequencies (0, 3, 6, and 12 cycles over a 96-day experimental period) under three water levels (0, 10, and 30 cm). We found that effects of fluctuation frequency were non-significant, negative, and positive under water levels of 0, 10 and 30 cm, respectively. As fluctuation frequency increased, the effects of increasing water level decreased significantly. When water levels were high, A. philoxeroides allocated greater biomass to shoot production probably in order to elongate and escape from submergence. However, as fluctuation frequency increased, biomass investment in roots and leaves also increased, probably in order to maximize nutrient absorption and photosynthesis, respectively. These results suggest that water level fluctuation may alleviate the effects of submergence on A. philoxeroides. In addition, A. philoxeroides showed significant phenotypic plasticity, adjusting its functional traits, such as number of nodes and leaves per stem, as well as stem diameter and pith cavity diameter, according to recurrent water level fluctuation. We conclude that A. philoxeroides may perform better in shallow water zones under conditions of disturbance that include recurrent water level fluctuation. This ability to adapt to disturbance likely promotes its growth and invasion in disturbed habitats.

In order to explore the efficient utilization of plant resources from constructed wetlands, the potential anti-metastatic effects of flavonoids from Potamogeton crispus L. were investigated in human ovarian cancer cells (ES-2). Two major flavonoids, luteolin-3'-O-β-D-glucopyranoside and flavone-6-C-β-D-glucopyranoside, were isolated from P. crispus and identified. The effects of these flavonoids on cell proliferation, cell morphology, cell cycle, apoptosis, and cell migration and invasion were then investigated. Furthermore, reverse transcriptase polymerase chain reaction assays and western blotting analysis were conducted to examine the expression level of mRNA and protein. Results indicated that Luteolin-3'-O-β-D-glucopyranoside inhibited ES-2 cell migration and invasion and suppressed the expression of two matrix metalloproteinases (MMPs), MMP-2 and MMP-9, and Flavone-6-C-β-D-glucopyranoside had no significant inhibitory effects on ES-2 cells. Thus, this study demonstrated the potential anti-metastatic properties of a P. crispus flavonoid, and provided a scientific approach for the screening of promising natural resources from constructed wetlands to identify useful products for use in the pharmaceutical and healthcare industries.