Alien plant invasion has become a major global environmental issue, causing severe economic and ecological damages. Severe invasions have been reported in some regions of China. However, most studies have been conducted at local and provincial levels, and the overall degree of invasion in natural forests across China remains unclear. Here, we explored the biogeographic patterns and their environmental and socioeconomic controls of the invaded alien woody plants in natural forests across the country.

We compiled the data of 3573 natural forest plots across the mainland China and mapped spatial distribution of alien woody plant invasion. We also used logistic regression models to identify the key socioeconomic and environmental factors that were associated with the observed invasion patterns.

We found that only 271 plots among 3573 natural forest plots were invaded by alien woody plants, accounting for 7.58% of all plots. Among all 2825 woody plant species across all plots surveyed, only 5 alien species (0.177%) were found. Both human activities and climate factors were related to the observed invasion patterns. Since China’s natural forests are mostly located in remote mountainous areas with limited human disturbance, alien woody plant invasions are less than those reported in North America and Europe. However, with the development of transportation and increased economic activities in mountainous areas, more invasions by alien plants may be expected in the future. Therefore, proactive management and policy making are desired to prevent or slow down the invasion processes.

Long-term determination of root biomass production upon land-use conversion to biofuel crops is rare. To assess land-use legacy influences on belowground biomass accumulation, we converted 22-year-old Conservation Reserve Program (CRP) grasslands and 50+-year-old agricultural (AGR) lands to corn (C), switchgrass (Sw) and restored prairie (Pr) biofuel crops. We maintained one CRP grassland as a reference (Ref). We hypothesized that land-use history and crop type have significant effects on root density, with perennial crops on CRP grasslands having a higher root biomass productivity, while corn grown on former agricultural lands produce the lowest root biomass.

The ingrowth core method was used to determine in situ ingrowth root biomass, alongside measurements of aboveground net primary productivity (ANPP). Ancillary measurements, including air temperature, growing season length and precipitation were used to examine their influences on root biomass production.

Root biomass productivity was the highest in unconverted CRP grassland (1716 g m−2 yr−1) and lowest in corn fields (526 g m−2 yr−1). All perennial sites converted from CRP and AGR lands had lower root biomass and ANPP in the first year of planting but peaked in 2011 for switchgrass and a year later for restored prairies. Ecosystem stability was higher in restored prairies (AGR-Pr: 4.3 ± 0.11; CRP-Pr: 4.1 ± 0.10), with all monocultures exhibiting a lower stability. Root biomass production was positively related to ANPP (R2 = 0.40). Overall, attention should be given to root biomass accumulation in large-scale biofuel production as it is a major source of carbon sequestration.

The limitations of classical Lotka–Volterra models for analyzing and interpreting competitive interactions among plant species have become increasingly clear in recent years. Three of the problems that have been identified are (i) the absence of frequency-dependence, which is important for long-term coexistence of species, (ii) the need to take unmeasured (often unmeasurable) variables influencing individual performance into account (e.g. spatial variation in soil nutrients or pathogens) and (iii) the need to separate measurement error from biological variation.

We modified the classical Lotka–Volterra competition models to address these limitations. We fitted eight alternative models to pin-point cover data on Festuca ovina and Agrostis capillaris over 3 years in an herbaceous plant community in Denmark. A Bayesian modeling framework was used to ascertain whether the model amendments improve the performance of the models and increase their ability to predict community dynamics and to test hypotheses.

Inclusion of frequency-dependence and measurement error, but not unmeasured variables, improved model performance greatly. Our results emphasize the importance of comparing alternative models in quantitative studies of plant community dynamics. Only by considering possible alternative models can we identify the forces driving community assembly and change, and improve our ability to predict the behavior of plant communities.

The effects of biocrusts on vascular plants are rarely evaluated in coastal saline lands. Our aim was to examine whether and how a mosaic of biocrusts affect seed germination of two typical herbaceous plants in a coastal saline land of the Yellow River Delta, to enhance our understanding by which substrate heterogeneity influences plant community dynamics.

We conducted growth chamber experiments to investigate the effects of biocrusts and uncrusted soil from bare patch-, Phragmites australis-, Suaeda glauca- and Tamarix chinensis-dominated habitats on seed germination percentage and mean germination time of two herbaceous plants: the perennial P. australis and the annual S. glauca. We also explored the mechanisms underlying the effects of substrate on seed germination.

Compared with uncrusted soil, biocrusts increased water content, nutrient accumulation and concentration of most salt ions, but they reduced soil pH value. Biocrusts with mosses directly decreased soil pH value and concentration of Mg2+, resulting in an indirect increase in seed germination percentage of S. glaucas. The low soil pH value also resulted in an indirect decrease in seed germination speed of P. australis in their own habitats. Bare patch directly increased accumulation of Cl−, resulting in an indirect decrease in seed germination speed of P. australis. These results suggest that biocrusts with mosses in P. australis habitats offer a window of opportunity for germination of S. glaucas. Biocrusts combined with habitat type have the potential to influence plant community structure through an effect on seed germination and establishment.

Sorghum halepense is a perennial invasive weed causing great harm worldwide, including some regions on Hainan island. In this study, we compared the performance between plants from outbreaking (dense stands covering large areas) and those from non-outbreaking (less dense stands covering smaller areas) populations. We also tested the hypothesis that plants with greater intraspecific competitive ability will have a lower stand biomass when grown under high-density conditions.

We grew plants of S. halepense individually, with an intraspecific competitor, with two interspecific competitors and with three or six plants from the same population per pot, and tested whether outbreaking and non-outbreaking populations differed in their performance. We also tested whether stand biomass (i.e. total biomass when three or six plants were grown together) was related to total biomass of individuals grown alone, and intra- or interspecific competitive ability.

Outbreaking and non-outbreaking populations of S. halepense differed in their biomass when individuals were grown alone, but not when grown in competition or when three or six plants from the same population were grown together. Across populations, biomass of individuals grown alone was negatively correlated with intra- and interspecific competitive ability, indicating that there is a trade-off between individual growth and competitive ability. Stand-level biomass was not related to total biomass of individuals grown alone, and intra- or interspecific competitive ability, indicating that low biomass when grown alone and high competitive ability may not reduce the performance of S. halepense when grown in dense monocultural stands.

Environmental heterogeneity affects the performance of clonal aquatic plants. Few researchers integrated two aspects of heterogeneity into the study of clonal plant ecology. The aims of the present study are to (i) test whether different substrate heterogeneity and submergence exert similar effects on plant performance and (ii) explore the foraging behaviour.

In this study, Scirpus yagara was subjected to multiple levels of substrate heterogeneity and submergence. Substrate treatments included one homogeneous substrate and three heterogeneous substrates (two-patch, four-patch and eight-patch). Water level treatments included 0, 10 and 30 cm. Traits including ramet number, generation number, leaf number, bulb number, ramet height, culm length, rhizome length, clonal radius, spacer length, spacer thickness, total biomass, biomass of bulbs and biomass per bulb were measured.

Deeper water levels significantly reduced variables associated with growth such as ramet number, generation number, leaf number and bulb number, while substrate patchiness induced significant variations in traits such as spacer length and spacer thickness. Significant interactive effects of the two factors were found for ramet number, leaf number and spacer length. Scirpus yagara showed colonization towards the lake sediment patch in two-patch and four-patch substrates, and more structures were placed in the lake sediment patch. Especially for the two-patch substrate, all structures occupied the lake sediment patch. Two-sided intrusion was observed in the eight-patch substrate, which induced an even allocation of structures in different patches. The foraging behaviour was correlated with the patch size.

Water and nitrogen (N) are two key resources in dryland ecosystems, but they may have complex interactive effects on the community structure and ecosystem functions. How future precipitation (rainfall vs snowfall) change will impact aboveground net primary production (ANPP) is far from clear, especially when combined with increasing N availability.

In this study, we investigated changes in community productivity, abundance and aboveground biomass of two dominant plant functional groups (PFGs), i.e. perennial rhizome grasses (PR) and perennial bunchgrasses (PB) under the impacts of increased precipitation (rainfall vs snowfall) combined with N addition in a semiarid temperate steppe.

Summer rainfall augmentation marginally increased community ANPP, whereas it significantly increased the abundance and aboveground biomass of PR, but not those of PB. Summer rainfall addition increased the fraction of PR biomass (f_PR) while decreased that of PB (f_PB). Spring snow addition had no effect on aboveground biomass of either compositional PFG although it marginally increased community ANPP. Nitrogen addition significantly increased community ANPP with greater increase in PR under summer rainfall addition, indicating strong interactive effects on community ANPP largely by enhancing PR biomass. We also found a nonlinear increase in the positive effect of nitrogen addition on productivity with the increased precipitation amount. These findings indicate an amplified impact of precipitation increase on grassland productivity under the accelerated atmospheric N deposition in the future.

Rapid warming at high altitudes may lead to a higher sensitivity in tree growth to temperature. The key factors constraining tree radial growth and to what extent regional tree growth has suffered from climatic changes are unclear.

Tree-ring width data were collected from 73 sites across the Hindu Kush Himalaya (HKH), including three dominant genera (Abies, Juniperus and Picea) at high altitudes over 3000 m. Dynamic time warping was introduced to develop subregional chronologies by considering the synchrony of annual tree growth among different sites. We quantified the contribution of the climate variables, and analyzed the spatiotemporal variation of the growth–climate relationship.

The site chronologies were grouped into three clusters, corresponding to the three distinct bioclimatic zones, i.e. the western HKH, central-eastern HKH and southeastern Tibetan Plateau (TP). Tree growth was positively correlated to winter and spring precipitation in the drier western HKH, and to winter temperature and spring precipitation in the humid southeastern TP. Tree growth was markedly constrained by the minimum temperature, especially in winter, with its importance increasing from the west toward the east. As shown by moving correlation analysis, the signal of winter temperature in tree growth was weakened in the western and central-eastern HKH, while it was enhanced in the southeastern TP following rapid warming since the 1980s. Our results highlight that continuous warming may cause forest recession due to warming-induced moisture deficit in the western HKH, but forest expansion in the southeastern TP.

Recent warmer and wetter climate in northern China remains a hot topic in recent years, yet its effect on vegetation growth has not been fully understood. This study investigated the temporal change of vegetation cover and its correlations with climatic variables from 1982 to 2018 for grasslands in northern China. Our aim is to clarify whether the warmer and wetter climate in recent years drives the greening of the vegetation in this region.

We investigated the temporal dynamic of vegetation normalized difference vegetation index (NDVI) and its driving forces based on long time-series data. Piecewise regression was used to examine whether there was a turning point of the trend of NDVI and climatic variables. Pearson correlation analyses were conducted to quantify the relationship between NDVI and climatic factors. Stepwise multivariable regression was used to quantify the contributions of climate variables to the temporal variations in NDVI.

We found a turning point of NDVI trend in 2008, with GIMMS NDVI indicating a slight increase of 0.00022 yr⁻¹ during 1982–2008 to an increase of 0.002 yr⁻¹ for GIMMS NDVI during 2008–2015 and 0.0018 yr⁻¹ for MODIS NDVI during 2008–2018. Precipitation was the predominant driver, and air temperature and vapor pressure deficit exerted a minor impact on the temporal dynamics of NDVI. Overall, our results suggest a turning point of NDVI trend, and that recent warmer and wetter climate has caused vegetation greening, which provides insights for better predicting the vegetation cover in this region under changing climate.

Although increases in precipitation variability in arid ecosystems are projected due to climate change, the response of desert shrub communities to precipitation change has not been fully elucidated. Such knowledge is important since drought-adapted plants exhibit varied mechanisms of survival that may contribute to species coexistence.

We tested the responses of eight drought-adapted plants, a mix of graminoids, shrubs and forbs to three summer precipitation scenarios (1.3, 2.6 and 3.9 cm per month) in a common garden experiment in the Great Basin (Owens Valley, California). Changes in mineral nutrient uptake (carbon, nitrogen, phosphorus, potassium, calcium, magnesium, manganese, copper, boron, zinc, iron and sodium) and gas exchange parameters (photosynthetic rate and stomatal conductance) were investigated in the studied species.

Two graminoids (Sporobolus airoides and Leymus triticoides) and one salt tolerant shrub species (Atriplex confertifolia) responded to increased water availability with increases in photosynthetic rate and/or stomatal conductance. There was a significant correlation between water availability and uptake of nutrients for five out of eight species. Artemisia tridentata, with higher rates of photosynthesis, contained greater amounts of potassium, copper and boron, while Juncus arcticus, with higher rates of photosynthesis, contained greater amounts of magnesium and iron, and less sodium. Juncus arcticus and three salt-adapted species (A. confertifolia, Distichlis spicata and S. airoides) exhibited correlations with stomatal conductance and concentrations of nutrients. Results indicate that differential physiological response mechanisms to increased moisture and associated nutrient uptake strategies in drought-adapted species may mediate coexistence under increased summer precipitation.

The aims of this study were to assess how functional diversity (FD) and functional redundancy respond to subalpine meadow ecosystem degradation under anthropogenic disturbance and how species contribute to functional redundancy along the disturbance gradient.

The study was carried out in the subalpine meadow in Mount Jade Dragon, which is located at the southeastern edge of the Tibetan Plateau. Four disturbance intensities [no disturbance (ND), weak disturbance (WD), moderate disturbance (MD) and severe disturbance (SD)] were identified. Species richness, soil properties and five key plant functional traits were assessed along the disturbance gradient. Simpson’s diversity index, FD based on the Rao algorithm, functional redundancy, community-weighted mean of each functional trait and species-level functional redundancy were determined.

Unimodal change pattern of FD and functional redundancy along the disturbance gradient were found in the present study, with their maximum in MD and WD, respectively. Species diversity showed a decreasing trend with increasing disturbance intensity. As disturbance intensified, species with traits related to conservative growth strategies, such as low specific leaf area (SLA) and high leaf dry matter content (LDMC), decreased, whereas species with resource acquisitive strategies, such as small plant, high SLA and low LDMC, increased in the community. At the species level, species showed species-specific roles in functional redundancy. Notably, some species were important in the community in terms of their unique function. For instance, Ligularia dictyoneura in ND and Potentilla delavayi in MD and SD.

The introduction of Robinia pseudoacacia (RP) has some effects on undergrowth herbaceous plants (UH), soil properties and their relationships, which may be related to the vegetation zone. However, few studies have tested effects of RP on UH and soil over a large-scale area of the Loess Plateau.

The study area consisted of three vegetation zones (the steppe, forest-steppe and forest zone). Two canopy plant types were selected: RP stands and adjacent native vegetation. We measured five leaf functional traits: leaf carbon content (LC), leaf nitrogen content (LN), leaf phosphorus content (LP), specific leaf area (SLA) and leaf tissue density (LTD). The functional diversity, species diversity and community-weighted mean (CWM) traits were calculated.

(i) CWM.LN, CWM.LP and CWM.SLA increased significantly, whereas CWM.LC and CWM.LTD decreased significantly in the three vegetation zones, compared with the native communities. (ii) Species diversity, functional diversity and community biomass decreased in the steppe zone, increased in the forest zone, and did not differ significantly in the forest-steppe zone. (iii) We found only soil organic carbon (P < 0.05) and soil total nitrogen (P < 0.05) in the forest zone decreased significantly compared with the native plots. (iv) The relationship between UH and soil properties was affected by RP and the vegetation zone. Overall, the effect of RP on UH and soil properties was associated with the vegetation zone. This result is of great significance to the planning of restoration and reconstruction of artificial forests in the Loess Plateau.

Woody plants represent the ancestral growth form in angiosperms with herbs evolving repeatedly from them. While there are a number of hypotheses about drivers of the evolution of the herbaceous habit, the ability to avoid frost damage in winter by discarding their aboveground biomass has often been invoked as the main force in their evolution. We propose instead that any unpredictable disturbance might have been much more important than the seasonal frost, as herbs easily survive repeated disturbance.

We tested this hypothesis by comparing herbs and woody plants in their ability to deal with three types of simulated disturbances, more predictable winter freezing, less predictable spring freezing and herbivory. Comparison was made in an experimental common garden setup with 20 species differing in woodiness. We evaluated the effects of these disturbances on mortality and regrowth of plants.

Herbs did not have an advantage over woody plants in survival when exposed to winter freezing. In less predictable conditions of spring freezing herbs survived the treatment better than woody plants and this advantage was even larger in case of the simulated herbivory treatment. The advantage of herbs over woody plants in less predictable conditions suggests that herbaceous growth form might be an adaptation to unpredictable disturbance, which herbs are able to tolerate thanks to their ability to survive loss of aboveground biomass. Consequently, factors such as mammal herbivory or fire might have been the most likely factors in the transition from woody species to herbs.

Dioecious plants exhibit sexual dimorphism in both sexual features (reproductive organs) and secondary sex characteristics (vegetative traits). Sexual differences in secondary traits, including morphological, physiological and ecological characters, have been commonly associated with trade-offs between the cost of reproduction and other plant functions. Such trade-offs may be modified by environmental stressors, although there is evidence that sexually dimorphic responses to stress do not always exist in all plant species. When sexual dimorphism exists, sexually different responses appear to depend on the species and stress types. Yet, further studies on dioecious plant species are needed to allow the generalization of stress effects on males and females. Additionally, sexual dimorphism may influence the frequency and distribution of the sexes along environmental gradients, likely causing niche differentiation and spatial segregation of sexes. At the present, the causes and mechanisms governing sex ratio biases are poorly understood. This review aims to discuss sex-specific responses and sex ratio biases occurring under adverse conditions, which will advance our knowledge of sexually dimorphic responses to environmental stressors.

Identifying the potential role of vegetation context (defined as the density, species identity/diversity and height of co-occurring plants) in modifying selection on floral traits is a critical step for clarifying and predicting the floral evolutionary trajectory in complex co-flowering species competition environments. It is also helpful to understand the variation in pollinator-mediated selection.

We experimentally reduced vegetation height around individual plants of Spiranthes sinensis (a bumblebee-pollinated perennial orchid herb) and estimated how vegetation context modified selection on four floral traits (flowering start, plant height, corolla size and number of flowers) through female function and pollen removal over two continuous years. We randomly selected independent plants in each year.

We demonstrated that vegetation context modified selection for earlier flowering start and shorter plant height of S. sinensis. The strength of selection differed between years. In addition, selection was stronger through female function than through pollen removal. Our findings indicate the potential role of vegetation context in shaping the differentiation and diversification of flowers in angiosperms.

Interactions between plants and their soil biota, arbuscular mycorrhizal fungi (AMF) in particular, may play a vital role in the establishment and the range expansion of exotic plants in new environments. However, whether there are post-introduction shifts in dependence on AMF and how dependency interacts with competition remains poorly understood.

We conducted a common garden greenhouse experiment to examine how native (USA) and invasive (China) populations of the plant species Plantago virginica, respond to soil biota, and whether these responses change in the presence of a competitor.

We found that while native populations consistently had a higher AMF colonization rate and benefited from AMF in both biomass and seed production, invasive populations received less benefit from AMF, and even showed reduced biomass with AMF in the presence of a competitor. This low mycorrhizal dependency in invasive populations correlated with greater suppression by an indigenous competitor for the invader. The different responses of the invasive and native populations to AMF suggest that alteration of mycorrhizal dependency has occurred during the invasion of P. virginica into China. Our findings suggest that this reduced dependency incurs a cost during interspecific competition.

Plant nutrient use efficiency, an important factor driving primary production, is sensitive to nitrogen (N) deposition. Because of strengthened regulations of N emissions, atmospheric N deposition is decreasing in many countries. It remains unknown whether historical N enrichment would alter plant nutrient use efficiency and whether such impacts would be mitigated by ecosystem management strategy.

We assessed the effects of historical N addition and mowing on plant N and phosphorus use efficiency (NUE and PUE) at both functional group and community levels in a temperate steppe after the cessation of 6-year N addition.

Historical N addition had negative legacy effects on plant NUE but not on PUE at the functional group level. There were negative legacy effects of N addition on community-level NUE and PUE, but only in the unmown plots. Mowing mitigated the negative legacy effects of N enrichment on community-level NUE and PUE by reducing the dominance of tall rhizomatous grass but enhancing that of tall bunchgrass. Our results highlight the importance of community composition variations caused by mowing in driving the legacy effects of N enrichment on community-level nutrient use efficiency. Given the slow recovery of community composition following cessation of N deposition, our findings suggest that the lower nutrient efficiency of plant community would be long-lasting.

Pulse effects of precipitation cause soil organic matter to rapidly decompose and release CO₂ in a short period. The pulse effects of precipitation are important for ecosystem C cycling and soil C balance, although their spatial variation in forest soils and the underlying mechanisms remain unclear.

Soil samples (0–10 cm) from 22 typical forest ecosystems in eastern China were used, to investigate the effects of simulated pulse precipitation on soil microbial respiration rates (R_s). We simulated pulsed precipitation to reach 65% water-holding capacity, the R_s was measured on a minute scale for 48 h.

Precipitation pulses can cause a rapid 1.70–38.12-fold increase in the rate of mineralized decomposing organic matter. Maximum R_s (R_s-soil-max), cumulative R_s (A_Rs-soil) and the time taken to arrive at the maximal R_s (T_Rs-soil-max) were significant differences among different soil samples. Furthermore, the pulse effects in different climate zones were significantly different. R_s-soil-max (11.701 µg C g−1soil h−1) and A_Rs-soil (300.712 µg C g−1 soil) were the highest in the mid-temperate zone. Soil chemical properties (total C and, N, pH and oxidation–reduction potential) and soil fractions were strongly correlated with the pulse effects in forest soils, but soil microbes contributed less. Our findings demonstrated that the pulse effects increase forest soil carbon emissions in the short term at a regional scale, and identified the factors with the greatest influence on this change. These findings help guide future studies on the C cycles of forest ecosystems and regulating ecosystem C cycles.

Functional traits are usually used to predict plant demographic rates without considering environmental contexts. However, previous studies have consistently found that traits have low explanatory power for plant demographic rates. We hypothesized that accounting for environmental contexts instead of focusing on traits alone could improve our understanding of how traits influence plant demographic rates.

We used generalized linear mixed-effect models to analyse the effects of functional traits (related to leaf, stem, seed and whole plant), environmental gradients (soil nutrients, water and elevation) and their interactions on the survival dynamics of 14 133 saplings and 3289 adults in a 9-ha old-growth temperate forest plot.

We found that environmental variables, neighbour crowding and traits alone (i.e. main effects) influenced plant survival. However, the effects of the latter two variables varied between saplings and adults. The trait–environment interactions influenced plant survival, such that resource conservative traits increased plant survival under harsh conditions but decreased survival under mild conditions. The elevational gradient was the most important environmental factor driving these effects in our plot. Our results support the hypothesis that functional traits influence plant survival depending on environmental contexts in local communities. These results also imply that one species with limited trait variation cannot occupy all environments, which can promote species diversity.