Estimating the effects of extreme drought on the photosynthetic rates (Pn) of dominant plant species is crucial for understanding the mechanisms driving the impacts of extreme drought on ecosystem functioning. Extreme drought may result from either reduced rainfall amount or decreased rainfall frequency, and the impacts of different patterns of extreme drought may vary greatly. In addition, different grasslands likely appear various sensitivity to different extreme drought patterns. However, there have been no reports on the effects of different extreme drought patterns on dominant species Pn in different grassland types. Here, we conducted multi-year extreme drought simulation experiments (reducing each rainfall event by 66% during the growing season, CHR vs. completely excluding rainfall during a shorter portion of the growing season, INT) in two different grasslands (desert grassland vs. typical grassland) from 2014. The Pn of two dominant species in each grassland was measured in July and August 2017. Both CHR and INT significantly decreased dominant species Pn, with INT causing more negative impacts on Pn regardless of grassland types. The response ratios of Pn in desert grassland were generally higher than that of typical grassland, especially for Leymus chinensis in CHR. These results demonstrated that decreased rainfall frequency had a more negative effect on Pn compared with reduced rainfall amount, with grassland types changing the magnitude, but not the direction, of the effects of extreme drought patterns. These findings highlight the importance of considering extreme drought patterns and grassland types in ecosystem management in the face of future extreme droughts.

Mongolian herder households maintain the health and condition of their livestock by adapting to the characteristics of the local vegetation distribution. Thus, predicting future vegetation changes is important for stable livestock grazing and sustainable rangeland use. We predicted the distributional extent of rangeland vegetation, specifically desert steppe, steppe and meadow steppe communities, for the period 2081-2100, based on vegetation data obtained from a previous study. Rangeland vegetation data collected in Mongolia (43-50° N, 87-119° E) between 2012 and 2016 (278 plots) were classified into community types. Species distribution modeling was conducted using a maximum entropy (MaxEnt) model. Distribution data for desert steppe, steppe and meadow steppe communities were used as objective variables, and bioclimatic data obtained from WorldClim were used as explanatory variables. CMIP6-downscaled future climate projections provided by WorldClim were used for future prediction. The area under the curve values for the desert steppe, steppe and meadow steppe models were 0.850, 0.847 and 0.873, respectively. Suitable habitat was projected to shrink under all scenarios and for all communities with climate change. The extent of reduction in potential suitable areas was greatest for meadow steppe communities. Our results indicate that meadow steppe communities will transition to steppe communities with future climate change.

A belowground bud bank is a collection of asexual propagules produced by the underground storage organs of geophytes. Renewal through belowground bud banks is the main reproductive strategy of geophytes. The belowground bud bank density reflects the potential renewal capacity of geophyte communities. However, the effects of different perturbation regimes and habitats on the belowground bud bank density of geophytes are not comprehensively understood. Moreover, whether different types of belowground bud banks respond differently to perturbations is still unclear. For this meta-analysis, relevant papers on the effects of environmental perturbations on the belowground bud bank density of geophytes were systematically collected. The cumulative effect size of different perturbation regimes and habitats on belowground bud banks among different bud types was analyzed. Overall, the effect of environmental perturbations on belowground bud bank density was small, which may result from opposite or fluctuating responses of bud banks to different perturbations. Drought negatively affected bud bank density. Environmental perturbations decreased rhizome bud density but increased tiller bud density. In wetlands, perturbations decreased belowground bud bank density. However, no significant effect was found for other habitat types. In general, belowground bud banks of geophytes are highly resistant and resilient. Changes in belowground bud bank density depend on the type of perturbations, the habitats in which plants are distributed and the type of bud banks.

Elevated CO₂ and warmer temperatures represent the future environmental conditions in the context of global change. A good understanding of plant response to their combined effects is, therefore, critically important for predicting future plant performance. This study investigated the photosynthetic acclimation of Amur linden (Tilia amurensis) seedlings (current year, about 60 cm tall), a shade-tolerant tree species in the temperate broadleaf deciduous forest, to the combination of current CO₂ concentration and temperature (CC) and the combination of the predicted future CO₂ concentration and temperature (FC). The results show that FC promoted aboveground growth, but reduced photosynthetic capacity (V_cmax: maximum rate of RuBP carboxylation and J_max: maximum photosynthetic electron transport rate). However, the photosynthetic rate measured under the corresponding growth CO₂ concentration was still higher under FC than under CC. FC depressed the photosynthetic limiting transition point (C_i-t, A_n-t) from Rubisco carboxylation to RuBP regeneration, i.e. A_n-t decreased without a change in C_i-t. FC did not change leaf N concentration but increased the total leaf N content per tree and photosynthetic nitrogen utilization efficiency. This suggests that N utilization, rather than photosynthetic capacity, may play an important role in the acclimation of the species to future climatic conditions. This study provides new insights into the photosynthetic acclimation of Amur linden and can be used to predict its possible performance under future climatic conditions.

As a main method of forest regeneration, stump sprouting plays a crucial role in forest community succession and vegetation restoration. We aimed to investigate the response of stump sprouting capacity to stubble height, unveil its nutrient-accumulation and allocation strategies and determine the appropriate stubble height most favorable for stump sprouting of Hippophae rhamnoides ssp. sinensis. Fifteen-year plants with signs of premature aging were coppiced at 0, 10 and 20 cm from the ground level. With the increase in stubble height, the number of stump sprouts increased linearly, and the survival rate decreased linearly. The height, diameter and cluster width of stump sprouts first increased, reached the highest level at a stubble height of 10 cm and then decreased. The contents and reserves of N, P, K, Ca and Mg showed a similar trend as the growth, positively correlating with each other. Compared with the control (no coppicing), the coppicing increased the nutrient element allocation of leaves, vertical roots and horizontal roots. Magnesium plays an important role in stump sprouting. The findings suggest that coppicing changed the accumulation ability and allocation pattern of nutrient elements, and further affected the sprouting ability of stumps. The best stubble height for stump sprouting and nutrient accumulation potential was 11.0-14.0 cm estimated by the regression.

An important challenge in ecology is to link functional traits to plant survival for generalizable predictions of plant demographical dynamics. However, whether root and leaf traits are consistently associated with tree survival remains uncertain because of the limited representation of root traits. Moreover, the relationships between plant traits and survival are rarely linear and are likely to vary with tree size. We analyzed demographic data from 17 901 trees of 32 subtropical tree species under 3-year-old monocultures to test whether root and leaf traits have consistent relationships with tree survival and how the relationships between traits and tree survival vary with tree diameter. We discovered that leaf and root traits have inconsistent effects on tree survival. Specifically, while specific leaf area (SLA; an acquisition strategy) showed a marginally significant negative impact on survival, root diameter (RD; a conservative trait within the one-dimensional root economic spectrum) also demonstrated a significant negative effect on survival. Furthermore, we found size-dependent relationships between traits and tree survival. The effect of SLA, leaf phosphorus concentration and specific root length, on survival shifted from negative to positive with increasing tree size. However, species with high leaf thickness and RD were positively linked to survival only for small trees. The results highlight that to accurately predict the relationships between traits and tree survival, it is essential to consider both above- and belowground traits, as well as the size-dependent relationships between traits and tree survival.

Global climate change is expected to have a significant impact on ecosystems worldwide, especially for alpine meadows which are considered as one of the most vulnerable components. However, the effects of global warming on the plant nitrogen-phosphorus stoichiometry and resorption in alpine meadows remain unclear. Therefore, to investigate the plant nitrogen-phosphorus stoichiometry and resorption in alpine meadows on the Qinghai-Tibet Plateau, we conducted an artificial warming study using open-top chambers (OTCs) over the 3 years of warming period. We selected three dominant species, four height types of OTCs (0.4, 0.6, 0.8 and 1 m) and four warming methods (year-round warming, winter warming, summer-autumn-winter warming and spring- summer-autumn warming in the experiment) in this experiment. In our study, soil temperature significantly increased with increasing the height of OCTs under the different warming methods. Kobresia pygmaea presented an increase in nitrogen (N) limitation and Kobresia humilis presented an increase in phosphorus (P) limitation with increasing temperature, while Potentilla saundersiana was insensitive to temperature changes in terms of nitrogen and phosphorus limitations. Both nitrogen resorption efficiency:phosphorus resorption efficiency and N:P trends in response to rising temperatures were in the same direction. The differential responses of the chemical stoichiometry of the three species to warming were observed, reflecting that the responses of nitrogen and phosphorus limitations to warming are multifaceted, and the grassland ecosystems may exhibit a certain degree of self-regulatory capability. Our results show that using chemical dosage indicators of a single dominant species to represent the nitrogen and phosphorus limitations of the entire ecosystem is inaccurate, and using N:P to reflect the nutritional limitations might have been somewhat misjudged in the context of global warming.

Climatic warming has advanced the spring phenology of plants and disrupted the alignment of phenology with weather patterns. Such misalignments can cause problems as extreme weather events become more frequent and thus impact the survival, growth and reproduction of plants. To prevent freezing within their cells during the growing season, plants adopt a supercooling strategy. However, the weather event severity and seasonal timing may impact the plant’s recovery after a freezing event. We conducted experiments to investigate how extreme freezing events of four different severities impacted the supercooling points and senescence of two dominant alpine plant species, Potentilla saundersiana (mid-summer flowering) and Gentiana parvula (late-summer flowering) on the Qinghai-Tibet Plateau (QTP). We also explored how the phenological stage impacted P. saundersiana’s response to freezing events. We found that both species exhibited supercooling upon exposed to frost damage. However, the average supercooling point for P. saundersiana was -6.9°C and was influenced by minimum temperature, duration and phenological stage. Whereas, the average supercooling point for G. parvula was -4.8°C, and neither minimum temperature nor duration had an effect on the supercooling point. In addition, the minimum temperature treatment of -10°C caused death in both plants when held constant for 4 h. Our study provides the first experimental dataset exploring the supercooling points of alpine plants on the QTP. Given the increasing probability of alpine plants encounters frost events, these results are of great significance for understanding the growth and survival strategies of alpine plants to cope with the adverse effects of extreme climate.

Coastal wetland ecosystems are increasingly threatened by escalating salinity levels, subjecting plants to salinity stress coupled with interactions in the community. Abiotic factors can disrupt the balance between competition and facilitation among plant species. Investigating the effects of different neighboring species and trait plasticity could extend the stress gradient hypothesis and enhance understanding of vegetation distribution and diversity in salt marshes. We conducted a greenhouse experiment and investigated the plastic response of wetland grass Phragmites australis to seven neighboring plants of three functional types (conspecifics, graminoids and forbs) under soil salinity (0 and 10 g/L). Plant height, base diameter, density, leaf thickness, specific leaf area and total and part biomasses were measured. Additionally, the relative interaction index (based on biomass) and the relative distance plasticity index (RDPI) were calculated. Salinity significantly reduced the biomass, height, density and diameter of P. australis. The functional types of neighboring plants also significantly affected these growth parameters. The influence of graminoids on P. australis was negative under 0 g/L, but this negative effect shifted to positive facilitation under 10 g/L. The facilitation effect of forbs was amplified under salinity, both supporting the stress gradient hypothesis. The growth traits of P. australis had a plastic response to salinity and competition, such as increasing belowground biomass to obtain more water and resources. The RDPI was higher under salt conditions than in competitive conditions. The plant-plant interaction response to stress varies with plant functional types and trait plasticity.

Asymmetric seasonal warming, characterized by more pronounced temperature increases in winter than in summer, has become a critical feature of global warming, especially in cold and high-altitude regions. Previous studies have primarily focused on year-round warming, while comparatively less attention was paid to winter warming. However, a significant knowledge gap exists regarding the impacts of winter warming on ecosystem functions. To address this, we conducted an 8-year manipulated warming experiment in an alpine grassland on the Tibetan Plateau, employing three treatments: no warming, year-round warming and winter warming. We found that neither year-round warming nor winter warming significantly alters species richness at the community level. Notably, community biomass stability was maintained via species asynchrony. However, warming exerted significant effects on the plant abundance groups (dominant, common and rare species). Specifically, winter warming enhanced the stability of dominant species by increasing species asynchrony of dominant species, as the compensatory dynamics occurred between the grass and forbs. In contrast, year-round warming reduced the stability of common species, correlated with an increase in species richness and a decline in asynchrony among common species. Thus, our study underscores the capacity of alpine grassland to maintain community biomass stability via asynchrony dynamics of species under different warming conditions, although the stability of different abundance groups would be changed. Importantly, our results provide valuable insights for understanding the alpine grassland ecosystem on the Tibetan Plateau.

Alpine treelines are considered ecological monitors recording the impacts of climate change on trees and forests. To date, most treeline research has focused on how climate change drives treeline dynamics. However, little is known about how biotic interactions mediate treeline shifts, particularly in the case of tree recruitment, a bottleneck of treeline dynamics. We hypothesized that inter- and intraspecific facilitation determined the establishment and survival of tree seedlings at alpine treelines. To test this hypothesis, 630 Abies georgei var. smithii seedlings with different ages (4-6, 7-9 and 10-15 years old) were transplanted into three growth habitats (canopy-in, canopy-out and meadow) across the alpine treeline ecotone (4300-4500 m) in the Sygera Mountains, on the southeastern Qinghai-Tibetan Plateau. Microclimate, height growth, mortality rates and leaf functional traits of transplanted seedlings were measured over 3 years. We found that the variations in leaf functional traits were driven by microclimate. After the transplantation, the leaf concentrations of soluble sugars and starch and C:P ratio increased, whereas leaf size decreased. The resource use of seedlings gradually shifted to a more conservative strategy as indicated by changes in non-structural carbohydrates and nutrient concentrations. Radiation, temperature and moisture conditions, mediated by plant interactions, influenced seedling mortality and annual growth by affecting leaf morphological traits. Our findings illustrate how facilitation plays a crucial role in altering solar radiation and leaf trait functioning, determining seedling survival and growth at alpine treelines. We provide new insights into the underlying mechanisms for tree establishment and alpine treeline shifts in response to climate change.

Extreme drought and insect herbivores can affect plant community non-independently, and their interaction may be influenced by drought pattern. However, few studies have explored the interaction on plant community structure, and no study has investigated whether the interaction is affected by drought pattern. We explored the interaction of different extreme drought patterns and insect herbivores with a manipulated experiment in a semiarid grassland. There were three treatments for drought: control—ambient precipitation; chronic drought—66% precipitation reduction in the growing season (May-August); intense drought—completely exclusion of rain events from June to July. Herbivores removal and present treatments were imposed within each drought treatment. We found that although herbivores had no significant effects on the impacts of droughts on total species richness, it alleviated the impacts of chronic drought on total cover, and the alleviating role decreased under intense drought. Comparing with intense drought, more increasing of grass cover led to more alleviation under chronic drought associated with the decrease of forb which has low leaf carbon and dry matter content, along with high starch, calcium, magnesium and manganese concentration. These results indicate that the interaction of drought and herbivores is affected by drought pattern, and the changes in leaf traits that reduce herbivores feeding in grass might alleviate the impact of drought on grassland.

Belowground parameters, e.g. root production and dynamics, play a pivotal role in evaluating the restoration degree of degraded grasslands. However, it remains unclear how roots respond to the combined restoration measures. To investigate root responses to different restoration treatments, a field experiment was conducted in a degraded Songnen meadow from 2013 to 2014. The treatments included: free grazing (FG), no ploughing (NP), only ploughing (OP), ploughing and fertilizer (PF), ploughing and mulching (PM), ploughing with fertilizer and mulching (PFM). Our results showed the seasonal dynamics pattern of roots was a unimodal pattern, which mainly was influenced by precipitation rather than restoration measures. The impacts of different restoration measures on root production were dependent on precipitation. In 2013, compared with FG, only PFM significantly increased root production by 242.34% (0-10 cm) and 90.8% (10-20 cm), which was mainly attributed to the increase of aboveground net primary production, soil moisture and root numbers. However, restoration measures had minor effects on root production in 2014. Root turnover ranged from 0.47 to 0.78 yr-1 and was not significantly changed by different restored measures. This is because the dominant annual species, Chloris virgata, exhibited relatively small changes in root turnover across different plots. Moreover, PFM improved soil conditions, leading to increased root lifespan and survival rate. Our results suggest that the combined measures are an effective way to accelerate belowground restoration in the degraded Songnen meadow.

Leaf trichomes are derived from epidermal cells and serve an important function in regulating leaf heat balance and gas exchange. Variation in leaf functional traits is critical for predicting how plants will react to global climate change. In this study, we aimed to investigate how leaf trichome densities vary along large geographic gradients and how they interact with stomata in response to environmental change. We investigated the leaf trichome densities of 44 Quercus variabilis populations in Eastern Asia (24°-51.8° N, 99°-137° E) and their correlation with climatic factors and stomatal traits. In addition, 15 populations were grown in a common garden to study their adaptive variation and coordination with stomata. The mean value of trichome density in situ conditions was 459.78 trichome mm-2 with a range of 325.79-552.38 trichome mm-2. Trichome density increased with latitude and decreased with longitude. Both temperature and precipitation reduced the trichome density. Moreover, trichome density was positively correlated with stomatal density whether in situ or in the common garden, and both increased with drought. Our results suggested that leaf trichomes possess highly adaptive variation and are in close coordination with stomata in response to climate change. Our findings provide new insights toward elucidating the interactions between leaf traits and the adaptive strategies of plants under climate change.