Aims The objective of this study was to estimate the carbon storage and its allocation in the Betula platyphylla forests of three different ages (25, 40, 61-year-old) in the cold temperate zone, NE China. Methods Through analyzing the field data, we estimated the carbon storage and sequestration rates of tree, understory layer (shrub layer, herb layer, litter layer) and soil layer (0-100 cm) of the 25, 40 and 61-year-old Betula platyphylla ecosystems in the north section of the Da Hinggan Ling Mountains. Important findings The results showed that the carbon content of each organ in the tree layer of the forests ranged from 440.7 to 506.7 g·kg^-1, that decreased as the forest age increases. Carbon content in the shrub and herb layers decreased first and then increased as the forest aged, while that in the litter layer decreased with the increase of forest age. The carbon content in soil layer (0-100 cm) increased significantly with the forest age (p < 0.05), and decreased as soil drought intensified. The carbon storage of B. platyphylla ecosystem at all levels increased significantly with the increase of forest age. The carbon storage of tree layer in the forests of 25, 40 and 61-year-old were 11.9, 19.1 and 34.2 t·hm^-2, respectively. The carbon storage of the organs follow the order of: trunk > root > branch > leaf, and the allocation ratio of trunk carbon increased as the forest aged. The carbon storage in the Betula platyphylla forest ecosystems of 25, 40 and 61-year-old were 77.4, 180.9 and 271.4 t·hm ^-2, respectively. Soil layer, the main carbon pool of the ecosystems, accounted for 81.6%, 87.7% and 85.9% of the total carbon storage. The annual net productivity (2.0-4.4 t·hm ^-2·a ^-1) and annual net carbon sequestration (1.0-2.1 t·hm ^-2·a ^-1) of the forests increased with the age increase of the forest, and the old-growth B. platyphylla forests hold a strong carbon sequestration capacity.

Aims Climate change and grazing activities have important effects on species diversity and productivity of grassland ecosystems. The aim of this study is to reveal the differences in responses of species diversity and productivity to warming, grazing and their interactions in an alpine meadow ecosystem. Methods Warming experiment was established in 2011. In 2016, the grazing experiment and the combination of warming and grazing experiment were added. A two-year continuous field experiment was conducted (from 2016 to 2017) and plant community structure, community composition, productivity and species diversity were monitored. Twelve sites were sampled, and were divided into four treatments: control, warming, grazing and the combination of warming and grazing. All sampled species were classified into three functional groups: sedges, grasses and forbs. The species diversity and productivity were sampled in three different treatments. Important findings Results showed that warming and grazing had significant interaction on vegetation height and net primary productivity in alpine grassland. Under grazing treatment, warming had no significant effect on plant height, while warming significantly increased plant height without grazing. Under grazing treatment, the warming effect on net primary productivity significantly differed between 2016 and 2017. In 2016, warming had no significant effect on net primary productivity, while in 2017, warming significantly decreased net primary productivity. Warming and grazing had no significant interaction on species richness, coverage, species important value and species diversity in the alpine meadow. Under the treatments of warming and grazing, the total vegetation coverage decreased, and the proportion of forbs significantly increased. However, no significant effect of warming or grazing was found on species diversity. This study showed that warming and grazing significantly changed the community structure of alpine grassland. Therefore, with the projected climate change in the future, the intensification of grazing activities may lead to the decrease of alpine meadow productivity.

Aims Leaf trait-environment relationships are critical for predicting the effects of climate change on plants. Our objective was to reveal the response of leaf traits of common broad-leaved woody plants to environmental factors on the eastern Qinghai-Xizang Plateau. Methods We measured 15 leaf traits of 332 species from 666 populations collected at 47 sites on the eastern Qinghai-Xizang Plateau. We investigated the extent of leaf trait variation in this area, and explored the response and adaptation strategies of leaf traits to environment at intra- and inter-species levels. Important findings Traits related to leaf size exhibited relatively high variation, and the leaf area was the most variant trait. Most leaf traits were significantly associated with elevation, except stomatal density. Climatic factors were important drivers of leaf trait variation because they explained 3.3%-29.5% of leaf trait variation. Meantime, temperature had the highest interpretation degree of leaf trait variation, and sunshine hours could explain the variation of most leaf traits. However, the interpretation degree of precipitation was relatively weak. In addition, the significant relationships between leaf traits and environmental (altitude and climatic) factors at intra-species level were far less than at inter-species levels. The reason for the result may be the coordinated variation and trade-off between plant traits, which make the variation of intra-species traits relatively small, and thus weaken the correlation between intra-plant leaf traits and environmental factors. Overall, leaf traits were closely related to woody plant adaptation strategies to the environment, and small, thick leaves and short petioles were selected for high-altitude plants to adapt to harsh environments such as strong winds and low temperature.

Aims The frequency and intensity of exceptional climatic events such as warm spring have increased significantly over the past few decades and exerted a significant impact on the spring phenophases of plants. However, the influence of exceptional climatic events on the thermal requirements of spring phenophases is still unclear, which limits the predictive accuracy of the future phenological changes. Here we aim to demonstrate how the first leaf dates of woody plants and their associated thermal requirements change under exceptional climatic conditions and how exceptional climatic conditions affect the ability of the growing degree model to predict leaf unfolding date. Methods Using data on the first leaf date of 39 woody species at Xi’an Botanical Garden from 1963 to 2018 and the corresponding meteorological data, this study firstly classified each year into the cold year, normal year and warm year. Subsequently, we analyzed the phenological change in the years with abnormal climate compared to the years with normal climate. Second, three kinds of algorithms were used to calculate the thermal requirements of the first leaf date for each plant, and the difference in the thermal requirements between years with abnormal climate and normal climate was compared. Finally, the error of the traditional growing degree day model in the simulation of the first leaf date in exceptional climatic conditions was assessed. Important findings For all plant species, the first leaf date was earlier in warm years than that in normal years with a mean advance of 8.6 days, and it was later in cold years with a mean delay of 8.2 days. In warm years, the thermal requirement of the first leaf date (257.5 degree days on average) was significantly higher than that in normal years (195.1 degree days on average, p < 0.05) for most species. However, in cold years, the thermal requirement (168.0 degree days on average) was lower than in normal years (not statistically significant) for most species. In cold years, the ancient group delayed by more in first leaf date and showed smaller changes in thermal requirement than the young group, but there was no significant difference in warm years.There were no significant differences in changes of first leaf date and thermal requirement among different life forms. The high temperature in the previous winter caused plants to receive less chilling, and thus reduced the thermal requirement in the following year. The first leaf date of woody plants simulated by the growing degree day model was 4.1 days earlier than the observed date in warm years, and was 3.0 days later than the observed date in cold years. Therefore, when predicting the future phenological changes, it is necessary to consider changes in the thermal requirement under exceptional climatic conditions; otherwise, it will overestimate the promotion effects of climate warming on the leaf unfolding date.

Aims This study is to examine the relative changes in resource use efficiencies and their responses to the environmental variables of a typical desert plant Artemisia ordosica in the semi-arid area of Northwest China. Methods We measured the net photosynthetic rate (P_n), transpiration rate (E), leaf surface photosynthetically active radiation (PAR_l), leaf surface temperature (T_l), leaf surface relative humidity (RH_l) of Artemisia ordosica from May to October, 2018 using a portable photosynthesis analyzer. We also analyzed nitrogen per leaf area (N_area) in the lab. We related nitrogen use efficiency (NUE), water use efficiency (WUE), light use efficiency (LUE) of the plant and their relative changes to the environmental variables. Important findings Temperature mainly affected the P_n of Artemisia ordosica under sufficient and stable light intensity. There was a significantly negative correlation between NUE, WUE and VPD₁, T_l. NUE, WUE and LUE was positively correlated. The maximum NUE, WUE and LUE occurred in May, July and September, respectively, being 9.43 μmol CO₂·g^-1·s^-1, 3.86 mmol·mol^-1, and 0.04 mol·mol^-1. The changes in resource use efficiencies were mainly affected by P_n. The results indicate that temperature affects resource use efficiencies by affecting the distribution of plant N and changes in P_n. WUE was significantly and positively correlated with LUE. These results may contribute to development of the energy exchange process model for the desert ecosystems.

Aims Seed emergence is a key stage of plant life history and thus of important impacts on interspecific relationships and community composition. Increasing evidence has shown that seed mass determines (or strongly affects) seed emergence within a species, but it has seldom been tested across species at different depths of soil burial. Accordingly, the purpose of this study was to examine the influence of soil burial depths on the relationship between seed mass and seed emergence. Methods We performed a full-factorial experiment. Two factors included plant species (i.e. Achillea millefolium, Achnatherum sibiricum, Chenopodium glaucum, Centaurea maculosa, Medicago falcata, Poa pratensis, P. secunda, Solidago canadensis, Stipa bungeana and Vulpia octoflora) and soil burial depth (i.e. 0, 1, 2, 4 and 8 cm). Each combination was replicated five times, totaling 250 pots (10 species × 5 burial depths × 5 replicates). For each species, seed mass was determined prior to sowing at a given soil burial depth. We watered the pots and recorded seed emergence every day for 30 days. We determined the first date of seed emergence, and calculated the overall seed emergence, the tolerance to soil burial, and T₅₀ (i.e. the number of days in the presence of 50% emergence). Seed mass and seed emergence were analyzed using an analysis of variance, and the relationships between two variables were tested using correlation analyses. Important findings We found that: (1) The optimum soil burial depth for seed emergence varied among the species, and for most of tested species this optimum depth ranged from 0 to 2 cm (i.e. shallow soil); six species had the maximum seed emergence at 1 cm soil burial depth, and no species had the maximum seed emergence at 4 or 8 cm. (2) There was a positive correlation between seed mass and the tolerance to soil burial across the 10 tested species, specifically, the tolerance to soil burial and the optimum depths increased with seed mass. (3) At deeper soil burial depths (i.e. 4 or 8 cm), there were significantly positive correlations among seed mass, seed emergence, and T₅₀; in contrast, such correlations did not occur at shallower burial depths (i.e. 0, 1 or 2 cm).

Aims The study about the effects of different calcium concentrations on the growth and physiology of Paspalum wettsteinii seedlings is very important to reveal the adaptive mechanism of Paspalum wettsteinii to the environment with different calcium concentrations. Methods Potted sand culture was used to study the effects of different calcium concentrations (0, 5, 25, 50, 100 and 200 mmol·L^-1 CaCl₂) and different treatment times (7, 14, 21 and 28 d) on the growth, osmotic regulator content, antioxidant enzyme activity, chlorophyll content and photosynthetic parameters of Paspalum wettsteinii seedlings. Important findings Results showed that, with the increase of the CaCl₂ concentration and the extension of treatment time, the morphological indexes, biomass, osmotic regulators content, antioxidant enzyme activity, chlorophyll content and photosynthetic parameters of Paspalum wettsteinii seedlings displayed a similar trend of first increasing and then decreasing. Under the low calcium concentrations (5-50 mmol·L^-1), plant height, leaf length, leaf width, root length and biomass all increased. The contents of proline, soluble protein, soluble sugar and the activities of peroxidase, catalase, superoxide dismutase, chlorophyll content, net photosynthetic rate, transpiration rate and stomatal conductance increased as well, but, malondialdehyde content and intercellular CO₂ concentration decreased. Under the high calcium concentrations (200 mmol·L^-1), the contents of proline, soluble protein, soluble sugar and the activities of peroxidase, catalase and superoxide dismutase decreased. Malondialdehyde content and intercellular CO₂ concentration increased as well, but chlorophyll content, net photosynthetic rate, transpiration rate and stomatal conductance decreased. Combined with the membership function analysis, the treatment of low calcium concentrations (5-50 mmol·L^-1) had no inhibitory effect on the seedlings of Paspalum wettsteinii, indicating that Paspalum wettsteinii had certain tolerance to low calcium salt stress. Under the treatment of high calcium concentration (200 mmol·L^-1), Paspalum wettsteinii seedlings could rapidly regulate the physiological and metabolic functions of plants by increasing the content of organic osmotic regulating substances, enhancing enzyme activity, chlorophyll content and photosynthesis, so as to adapt to high calcium concentration environment.

The Beishan Mountain of Jinhua is located in the northern part of the mid-subtropical region. In vegetation division, this region belongs to the northern sub-zone of mid-subtropical evergreen broad-leaved forest vegetation belt. The vegetation in this mountain is a secondary forest restored from a severe deforestation. It is currently in a rapid process of positive succession. Thus, this region is suitable for studying the dynamics and succession mechanisms of plant communities and the restoration of degraded ecosystems. To further understand the community characteristics of the main vegetation types in Beishan Mountain, we surveyed the main plant communities on its southern slope with a fixed plot method (the plot area is 30 m × 30 m for forests and 20 m × 10 m, 30 m × 10 m for shrubs) based on the internationally accepted forest survey approach used in the survey of dynamic forest plots. The species composition, quantitative characteristics and habitat information of all plant communities were investigated and recorded. The importance values of trees and shrubs were calculated. The community types and their characteristics were analyzed. The spatial distribution maps of the major trees and shrubs in each plot were also drawn. In the present study, detailed community data for 24 sampled plots representing 11 formations were presented (consisting of 21 forest plots and 3 shrub plots).