Aims Kobresia pygmaea is a perennial cushion herb from the Cyperaceae family with a height of 1-3 cm and small linear leaves about 1 mm wide. It is mainly distributed on the low slopes of the high mountains ranging from 3 000 m to 5 960 m on the Qingzang Plateau. Its habitat is harsh, and extreme climate conditions such as low temperature, strong wind, and high sunlight intensity are the main abiotic stresses during plants growing season. The objectives of this study were to analyze the photochemical and non-photochemical energy distribution of the photosystem II (PSII) reaction center in K. pygmaea leaves, and their quenching protection mechanism after nocturnal low-temperature (NLT) treatment.

Methods Kobresia pygmaea meadow turfs (30 cm × 15 cm) were collected from the Alpine Grassland Ecosystem Research Station of the Resource of Three Rivers. The turf blocks were separated into two groups, one group was kept in a culture room with a temperature of 24/18 °C (day/night) as a control treatment, and another was kept in an artificial climate chamber with 0 °C in the evening as an NLT treatment. During the daytime, the NLT group was moved back to the culture room and irradiated together with the control group. On day 0, day 1, day 3, and day 5 after NLT treatment, the chlorophyll fluorescence of K. pygmaea leaves including, the light-response curve, PSII photochemical efficiency at 400 and 1 500 μmol·m⁻²·s⁻¹ steady-state light intensities, and dark relaxation were monitored using CF imager. Then, based on the “Lake Model”, the variation of the PSII actual photochemical efficiency (Φ_PSII), the quantum yield of non-regulated energy dissipation (Φ_NO) and regulated energy dissipation (Φ_NPQ) were explored. Additionally, the fast and slow relaxation components of PSII non-photochemical quenching were determined.

Important findings Nocturnal low temperature had limited effects on the rapid light-response curves of PSII relative electron transfer rate through PSII (rETR), the fraction of open PSII centers (q_L), and PSII non-photochemical quenching coefficient (q_NP). The comparison of chlorophyll fluorescence between 400 and 1 500 μmol·m⁻²·s⁻¹ steady-state light intensities confirmed that NLT treatment did not affect the activity of the PSII reaction center and the process of non-photochemical quenching of K. pygmaea. On the third day after NLT treatment, under high light intensity, the ratios of Φ_PSII:Φ_NO:Φ_NPQ were 36:19:45 and 38:19:43 in the control and NLT groups, respectively; while under lower light intensity, they were 66:22:12 and 66:23:11, respectively. The fast relaxation component (NPQ_f) was the main component in non-photochemical quenching (NPQ); the proportion of the slow relaxation component in non-photochemical quenching was 11% and 10% on day 1 and day 3 in control group, and 13% and 12% in NLT group, respectively. Our results indicated that the probability of photoinhibition of the PSII reaction center in K. pygmaeawas increased after NLT treatment; low light intensity and NLT led to the prolongation of photosynthetic induction time. Overall, the NLT treatment did not increase the tendency of excess excitation energy to be difficult to regulate and dissipate in K. pygmaea leaves, since PSII photochemical energy dissipation and protective regulation mechanism still effectively distributed the absorbed light energy.

Aims The anatomical structure of plant leaves could be a direct reflection of the plant’s mechanism of response and adaptation to climate change. The distribution of alpine steppe has increased due to climatic warming over the Qingzang Plateau.Stipa purpurea is the dominant species of alpine steppe. However, few studies have been conducted on the adaptation mechanisms of alpine steppe plants. In this study, we analyzed the characteristics of leaf anatomical structure among different populations of S. purpurea and the relationship between these characteristics and climatic factors over the Qingzang Plateau. The ultimate aim was to identify the mechanism by which S. purpurea acclimatizes to alpine environments.
Methods Leaves of S. purpurea were collected from eight sites on the Qingzang Plateau and fixed using FAA fixative solution. Then, the leaves were paraffin wax sectioned and double-stained. Samples were then observed with a microscope and photographed with a digital camera. The area and thickness of leaf anatomical structure were measured with the soft (Image-pro plus 6.0).
Important findings Leaves of S. purpurea generally had thick cuticles, which were able to reduce water loss and radiation exposure. From the results of one-way analysis of variance, there were significant differences among the eight populations in collenchymatous cell thickness, vessel diameter, bundle catheter cavity area/bundle of the main vascular area, and vascular area/leaf cross-sectional area, which were beneficial characteristics for S. purpurea in adapting to the local environment. The characteristics of leaf anatomical structure were significantly correlated with environmental factors via Pearson’s analysis and cluster analysis. The results from principal component analysis and redundancy analysis showed that the anatomical structures in arid regions were mainly affected by annual evaporation, and those in semi-humid regions were mainly affected by the average precipitation humidity index and annual precipitation/annual evaporation during the growing season. In conclusion, to adapt to the alpine and arid environment,S. purpurea has reduced water loss by simultaneously increasing its collenchymatous cell thickness and water-conducting tissue area (vessel diameter, bundle catheter cavity area/bundle of main vascular area, and vascular bundle area/leaf cross-sectional area).

Aims Global warming is expected to be the strongest in high altitude mountainous areas, which are more ecologically fragile and economically marginalized. The Qinghai-Xizang Plateau is among such areas most vulnerable to global warming, and more than 80% of its population depends on subsistence agriculture. The aim of this study is to understand the impacts of warming on indigenous crop production, which can help to devise better strategies for crop adaptation and food security in this area.Methods A field warming experiment using a facility of free air temperature increase was conducted to simulate the predicted warming level in Caigongtang town, Lhasa City, China. The experiment consisting of two treatments (warmed and non-warmed) was performed using a completely random design with three replicates. An infrared heater (180 cm in length and 20 cm in width) of 1 500 W was suspended 1.5 m above the ground in each warmed plot. In each non-warmed plot, a ‘dummy’ heater of same dimensions was also suspended to mimic the shading effects. The warming treatment was performed from the sown date to the harvest date. We measured dry matter and nitrogen accumulation, partition and translocation of winter wheat (Triticum aestivum) using ‘Shandong 6’ under warming and control treatments.Important findings Results showed that, with 1.1 °C increase in daily mean air temperature during winter wheat growing season, the dry matter accumulation rate at population level from sowing to anthesis stage, grain dry matter partition ratio and contribution of dry matter translocation amount to grain after anthesis were 27.5%, 5.6% and 68.6% higher, respectively, in the warmed plots than those in the non-warmed plots. Meanwhile, warming increased nitrogen accumulation rate at population level of winter wheat. Nitrogen distribution proportions in grain and nitrogen translocation efficiency from vegetative organs to grain after anthesis in the warmed treatment were 6.0% and 5.5% higher than those in the non-warmed treatment, respectively. Compared with non-warmed treatment, warming decreased harvest index by 3.1%, though the difference was not statistically significant. Grain yield, nitrogen uptake efficiency, nitrogen partial factor productivity and nitrogen harvest index were 8.1%, 20.8%, 8.1% and 6.0% higher, respectively, in the warmed plots than those in the non-warmed plots. In conclusion, an increase in daily mean air temperature of about 1.1 °C can enhance plant growth during the pre-anthesis phase by mitigating the low temperature limitation, and accelerate dry matter and nitrogen partition and translocation to the grain after anthesis in winter wheat. These results suggest that warming may benefit winter wheat production through increasing nitrogen use efficiency in high altitude areas.

AimsGlobal warming could have profound effects on ecosystem carbon (C) fluxes in alpine ecosystems. The aim of our study is to examine the effects of gradient warming on net ecosystem carbon exchange (NEE).MethodsIn the Northern Tibetan Grassland Ecosystem Research Station (Nagqu station), Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, we conducted various levels of temperature increasing experiments (i.e., 2 °C and 4 °C increments). The warming was achieved using open-top chambers (OTCs). In total, there were three levels of temperature treatments (control, 2 °C and 4 °C increment), and four replicates for each treatment. The ecosystem NEE was monitored every five days during the growing season in 2015.Important findings Our findings highlight the importance of soil moisture in mediating the responses of NEE to climatic warming in alpine meadow ecosystem. The 4 °C warming significantly stimulated NEE,except for July measurements. The 2 °C warming had no effects on NEE during the growing season. Compared to the 2 °C warming, the 4 °C warming significantly stimulated NEE. The results showed that our targeted ecosystem acts as a carbon sink under 2 °C warming, whereas will act as a net carbon source under 4 °C warming in the future. This study provides basic data and theoretical basis for evaluating the alpine ecosystem’s responses to climate change.

AimsElymus nutans is one of the dominant plant species in alpine meadow. Purpose of this research was to study the effects of nitrogen and silicon application on leaf nitrogen content and net photosynthetic rate in this species to provide scientific basis for fertilization practice in alpine meadow.MethodFour levels nitrogen combined with four levels silicon was applied to E. nutans plants in the alpine meadow. Leaf nitrogen content and net photosynthetic rate of E. nutans were measured.Important findings The results showed that there was a significant improvement in leaf nitrogen content and net photosynthetic rate of the E. nutans with nitrogen or silicon application alone; However, there was a significant interaction between nitrogen and silicon treatments on leaf nitrogen content and net photosynthetic rate; Combining with the three different levels nitrogen, low level silicon (Si₁) application did not increase leaf nitrogen content and net photosynthetic rate, but middle level silicon (Si₂) could significantly increase the leaf nitrogen content; Combining with the low (N₁) or middle (N₂) level nitrogen, middle level silicon (Si₂) application could significantly increase the net photosynthetic rate; Compared with that control without fertilization, the middle level nitrogen combined with the same level silicon treatment had the highest average of leaf nitrogen content and net photosynthetic rate, which increased by 119.99% and 85.70%, respectively. This study indicated application of nitrogen combined with silicon application enhanced leaf nitrogen content and net photosynthetic rate of E. nutans, and 8 g·m^-2silicon application had the best result among other treatments.

Trait-based approaches are often widely used in ecological research to predict or explain the complex ecological processes at both individual and ecosystem levels. Leaf function with morphological and physiological traits can play important roles in plan growth, survival, reproduction in natural environments. The aim of this study is 1) to determine the differences of leaf traits between both the species and the functional groups in a swamp meadow; 2) to explore the relationship between different leaf morphological traits and physiological traits.

Gas exchanges of 51 species (in 14 families) were measured on six fully expand health leaves (from different individual plants) using a portable photosynthesis system in the field during the peak of growing season. The leaf morphological traits was measured based on 6 single leaves form different individuals, include the net photosynthesis rate (P_n), transpiration rate (T_r), specific leaf area (SLA), relative leaf water content (LWC), leaf area (LA) and the water use efficiency (WUE = P_n/T_r).

Result showed that there were significant interspecific differences in the investigated traits as described in above methods. Among the traits, the LWC (coefficient of variation, CV = 0.11) was ranged from 58.12% to 81.83%, 0.0088-0.0278 m²·g^-1 for the SLA (CV = 0.27), and 0.51 cm² to 100.90 cm² for the LA (CV = 1.73), while the range of 4.25-19.23 μmol CO₂·m^-2·s^-1, 2.89-12.81 mmol H₂O·m^-2·s^-1 and 0.56-3.76 μmol CO₂·mmol^-1 H₂O for P_n (CV = 0.33), T_r (CV = 0.33), and WUE (CV = 0.36), respectively. There were also significant differences between the functional groups (sedge, grass and forbs) for these traits. Forbs have larger LA and higher LWC than sedge and grass; Grass have higher WUE and SLA than those of others; while Sedge have higher P_n. Our result also showed there were high correlation between P_n and SLA, WUE and LWC, indicated the strong impacts of leaf morphology on the gas exchange physiology. The SLA was also related to gas exchange traits both among species and functional groups, while the LWC was only among species and LA among functional groups. In conclusion, significant differences in these functional traits among species suggest that these species could vary in resource use and growth form in their community ecosystem. Also the difference among the functional groups in these traits indicates the resource use of the community would be largely influenced by its species composition, especially the differences of functional groups. The research finding will help to better understanding of the ecosystem function in alpine swamp meadow with related management implication.

Aims Providing indispensably theoretical evidence for establishing indices of evaluation on drought tolerance in shrubs, and screening for tree species that are drought tolerant for afforestation in arid regions or for matching their characteristics with suitable habitat conditions are the key to vegetation restoration in the Qinghai-Xizang Plateau. However, these issues are not adequately addressed in recent research due to lack of systematic methods. Therefore, our objective was to make a comprehensive evaluation on drought tolerance in 20 shrub species collected from different areas in Qinghai-Xizang Plateau, and to study their underlying mechanisms in drought tolerance.
Methods We made measurements on variables depicting root characteristics, including the root length (TRL), surface area (TRSA), volume (TRV), and tips number (TRTN) of all roots, the root length (FRL), surface area (FRSA), volume (FRV), and tips number (FRTN) of fine roots (d≤2 mm), and derived plant characteristic indices including thickness of cuticle (CT), thickness of palisade tissue (TPT), thickness of spongy tissue (TST), TPT/TST, thickness of leaf (LT), palisable tissue cell density, and tissue structural tense ratio (CTR = TPT/LT × 100%) and spongy tissue loosened ratio (SR = TST/LT × 100%) of leaf anatomical structure, root to shoot ratio (RSR), leaf transpiration rate (T_r), instantaneous water use efficiency (WUE_i), and carbon isotopic composition (δ¹³C) of the 20 shrub species through field experiments. Correlation analysis and principal component analysis were performed on the 19 variables and indices.
Important findings Different shrubs had different mechanisms of drought tolerance. In this study, the character- istics of drought tolerance were mainly categorized into 6 types, involving modifications of (1) root systems, (2) leaf anatomical structure, (3) leaf pattern, and (4) biomass allocation, or via (5) low water-consumption and (6) high WUE_i. Different genera or different tree species within the same genus clearly differed in drought tolerance. The species of the genus Hippophae were relatively poorly tolerant to drought, whereas several shrubs including Potentilla fruticosa, Berberis julianae, Caragana arborescens, Spiraea salicifolia and Hippophae rhamnoides ssp. mongolica occurred to be more drought tolerant than other shrub species investigated in this study. On the other hand, there were highly significant correlations among the characteristics of root systems and among characteristics of leaf anatomical structure. The results of principal component analysis on 19 variables and indices showed that TRL, TRSA, TRV, TRTN, FRL, FRSA, FRV, FRTN, CT, TPT, TST and WUE_i could be effective indicators of drought tolerance of shrubs in the Qinghai-Xizang Plateau. In addition, the drought tolerance of shrubs had a close connection with their origin of collections; the shrubs collected from Xining prefecture in Qinghai Province were more drought tolerant than those from Tianshui Prefecture in Gansu and Lasa Prefecture in Xizang.

Aims Several local varieties of wheat (Triticum aestivum) developed by Northwest Institute of Plateau Biology, Chinese Academy of Sciences, are widely cultivated in the agricultural regions in Qinghai-Xizang Plateau. These varieties are well adapted to multiple environmental stresses such as low temperature, strong solar radiation, and drought. The objective of this study was to determine the responses of PSII photochemical efficiency to high solar irradiance in leaves of four wheat varieties. We examined whether photo-inhibition was appeared in wheat varieties and analysed variations of quantum yield of quenching due to light-induced and non-light-induced.
Methods Field experiments were conducted on the farmland of Xiangride, which is located in the eastern side of Caidamu Basin, Qinghai Province. Four local wheat varieties were used during the heading stage in 2013. Measurements of photochemical efficiency and quantum yield were made on the abaxial surface of flag leaves facing the Sun by using a FMS-2 fluorometer, and the content of photosynthetic pigments and specific leaf weight (SLW) were concurrently determined. Pulse-modulated in-vivo chlorophyll fluorescence technique was used to obtain rapid information on photosynthetic processes. The maximum quantum efficiency of PSII photochemistry (F_v/F_m) was determined at 8:30, 12:00 and 16:30 on clear days after allowing for 20 min dark adaptation with leaf clips. The PSII maximal and actual photochemical efficiency (F_v′/F_m′ and Φ_PSII), the PSII photochemical and non-photochemical quenching coefficient (q_P and NPQ) were analyzed between morning and afternoon using inner actinic light with photosynthetically active photon flux density at 1120 μmol photons∙m^-2∙s^-1. Furthermore, along with analysis of the fraction of PSII reaction centers that are opened (q_L), the quantum yield of quenching due to light-induced processes (Φ_NPQ) and non-light-induced processes (Φ_NO) were explored.
Important findings There were significant differences in the content of photosynthetic pigments and SLW among the four wheat varieties. Under conditions of clear days, the flag leaves exhibited marked depressions in F_v/F_m at three typical times when determined after 20 min dark adaptation. At a given light intensity, the values of F_v′/F_m′ were significantly reduced in the afternoon due to influences by long-lasting high-light irradiation, and Φ_PSII showed little differences among the four wheat varieties and no difference between morning and afternoon. There were almost similar variations in q_P and NPQ among the four wheat varieties, suggesting that q_P and NPQ belong to instinct property and are influenced by the accumulative stresses of high-light intensity. The fractions of Φ_NPQ were higher than that of Φ_NO in the four wheat varieties and the up-regulatory of Φ_NPQ in the afternoon indicated that the photosynthetic apparatus in these wheat varieties had already acclimated to strong solar irradiation in agricultural regions of Qinghai-Xizang Plateau.

Aims Little study has been conducted to quantify plant water sources for Myricaria squamosa, which is a dominant alpine riparian shrub in the Qinghai Lake basin and plays a key role in maintaining riverine wetland system. The objective of this study was to quantify water sources for M. squamosa growing under different hydrological conditions.
Methods We collected the water samples from the xylem of M. squamosa, groundwater, river, and soils in the Qinghai Lake basin from June through September, and analyzed the seasonal variation of hydrogen stable isotope ratio (δD) in the xylem and potential water sources using stable hydrogen isotope tracer method. We then compared the differences in water sources for M. squamosa growing under two contrasting hydrological conditions.
Important findings Myricaria squamosa plants growing on the river bank mainly used groundwater and water from the river stream in June and July, with groundwater contributing up to 89% of water use in June and 55% in July and river stream contributing up to 86% in June and 65% in July, respectively; whilst in August, they used water mainly from the 0-20 cm soil layer; the water source in September was identifiable. In contrast, Myricaria squamosa plants growing approximately about 100 m away from the river bank mainly accessed the groundwater and river water in June (91% and 70%, respectively), and used water from the 0-60 cm soil layer during the rainy months July, August and September. Results suggest that M. squamosa plants on the river bank use mainly groundwater and river water; soil water was more important for those far away from the river bank. These are resulted from the responses of this shrub species to specific water conditions when growing under contrasting water regimes.

Aims The study aimed to: 1) investigate the accuracy of thermal time model in predicating seed germination response to temperature for different legume species after dormancy release; 2) compare temperature requirements for seed germination of different legume species from the Qingzang Gaoyuan.
Methods The seeds of four Vicia species were germinated over the constant temperature range of 5-30 °C at 5 °C interval. The effects of temperature on seed germination were summarized in terms of the thermal time model for germination.
Important findings The base temperature (T_b) did not differ significantly within each sub-population by regressing germination rate on sub-optimal temperatures. In contrast with T_b, the ceiling temperature (T_c) differed significantly within each sub-population by regressing germination rate on supra-optimal temperature in all species except Vicia sativa. These imply the base temperature for all individual seeds in the populations were relative constant, but the ceiling temperatures may vary within the sub-populations. T_b value estimated by repeated probit analysis was quite close to the value estimated by regressing germination rate within sub-optimal temperatures; however, T_c value estimated by this method was close to the value estimated with T₅₀. Compared to two perennial legume species, annual legume species had lower T_b and T_c. The thermal model was accurate to predict the germination time course under different temperatures.

Aims Native alpine plants that have grown and evolved on the Qinghai-Tibetan Plateau of China for a long time have developed a strong adaptation capacity for harsh environmental factors, such as low temperature, low air pressure, strong sunlight and solar UV-B radiation. The objective of this study was to determine the response of PSII photochemistry efficiency to short-term enhanced solar UV-B intensity in alpine plants. We examined whether UV-B-absorbing compounds were sufficiently efficient to protect the photosynthetic apparatus from UV-B photo-inactivation or photo-damage and evaluated the influence of UV-B radiation on photosynthetic pigments.
Methods Field experiments were conducted during the 2008 and 2009 growing seasons in alpine Kobresia humilis meadow near Haibei Alpine Meadow Ecosystem Research Station (37°29°-37°45° N, 101°12°-101°33° E; alt. 3 200 m) using the native alpine plant Saussurea superba. Short-term UV-B-supplementation studies were performed over 5 days using UV-B-313 fluorescence lamps, which were filtered with a cellulose diacetate film to get increased UV-B treatment and a Mylar film as a control. Pulse-modulated in-vivo chlorophyll fluorescence was used to obtain rapid information of UV-B on photosynthetic processes. The 3-min dark-adapted maximum quantum efficiency of PSII photochemistry, F_(v)/F_(m), and PSII photochemistry efficiency were measured under natural sunlight. The contents of photosynthetic pigments and UV-B-absorbing compounds were analyzed based on leaf area unit.
Important findings Although there was no significant difference, F_(v)/F_(m) showed a decreasing trend after short-term exposure to enhanced UV-B radiation in all measurements throughout the growing season. The reduction of the actual photochemical quantum efficiency and photochemical quenching as well as the increase of non-photochemical quenching in UV-B supplemented treatment, when compared to the control, indicated there was a decrease in PSII photochemistry efficiency and an increase in non-photochemical quenching. These phenomena indicated photo-inactivation or photo-damage of photosynthesis occurred in the PSII reaction center. The photosynthetic pigments showed a small decrease in the UV-B supplemented treatment, which may be related to the enhancement of photo-oxidation, a reduction of pigment synthesis and small variation of leaf thickness. The UV-B-absorbing compounds were not influenced by short-term enhancement of UV-B radiation when analyzed based on leaf area unit. This demonstrated that higher contents of UV-B-absorbing compounds in the epidermal layer of alpine plant S. superba were efficient for defense against UV-B radiation and stabilized for further enhancement of UV-B radiation

Aims Strong solar UV-B radiation accompanied with strong solar visible radiation is a characteristic of the environment of China’s Qinghai-Tibet Plateau. Previous study confirmed that current ambient UV-B intensity has a small negative influence on the physiological response of the photosynthetic apparatus of the alpine plant Saussurea superba. Our objectives were to further analysis the influence of ambient UV-B intensity on PSII photochemistry efficiency under different weather conditions.
Methods Short-term field experiments of UV-B were conducted during the luxuriant growing season in Kobresia humilis meadow in the Haibei Alpine Meadow Ecosystem Research Station. We used the pulse-modulated in vivo chlorophyll fluorescence technique to obtain rapid information on the effects of UV-B intensities on photosynthetic performances in the native alpine plant S. superba. The maximum quantum efficiency of PSII photochemistry (F_(v)/F_(m)) was measured after 3 minutes of dark radiation. The PSII photochemistry efficiency and non-photochemical quenching parameters were also measured. All chlorophyll fluorescence parameters were statistically analyzed with SPSS 11.0 software according to sunny, cloudy and shady weather states. Two-way ANOVA and least significant difference method (LSD) were used to compare differences among UV-B treatments and weather states.
Important findings There were significant increases of F_(v)/F_(m) in both ambient UV-B and low UV-B treatments when the weather changed from clear days to overcast days. Although there were no significant differences, F_(v)/F_(m) showed an increased trend in low UV-B when compared with ambient UV-B in all three weather states. This suggests that ambient UV-B intensity can delay the recovery of optimal photochemistry efficiency in S. superba. There were (a) increased tendency in actual photochemical efficiency of PSII (Φ_PSII) and photochemical quenching (q_P) and (b) small decreased tendency in non-photochemical quenching (NPQ) in low UV-B treatment in comparison with ambient UV-B; however, all those fluorescence parameters were significantly changed among the three weather states. The variation of these PSII photochemistry efficiency parameters demonstrated that natural UV-B component can limit the photosynthetic performance. Further analysis confirmed that significant difference (p < 0.05 on sunny days and p < 0.01 on shady days) existed in relative limitation of quantum efficiency (L_(PFD)) and fraction of opened PSII centers (q_L). Although its effects were not always significant when compared with the influence of photosynthetically active radiation (PAR), UV-B radiation can influence primary quinine electron acceptor of PSII (Q_A) and there were negative effects on photosynthetic organization in S. superba.

Aim Temperature is an important environmental factor influencing seed germination. Our objective was to research the seed germination response of 12 Compositae species from the eastern Qinghai-Tibet Plateau of China to different temperatures using the accumulated temperature model.
Methods All 12 species belong to four genera of Compositae. Seeds of each species were germinated at five constant temperatures (5, 10, 15, 20 and 25 °C), and germination was recorded once per day. We combined the logistic function and the accumulated temperature equation and used non-linear regression to estimate the base temperature and accumulated temperature for seed germination of each species.
Important findings The average base temperature and accumulated temperature of the 12 species were 0 °C and 94.5 °C·d, respectively. The base temperature was lower and the accumulated temperature was higher than reported by previous researchers. These are the result of long-term adaptation to the temperature environment of the Qinghai-Tibet Plateau. There was a significant negative correlation between base temperature and accumulated temperature (p = 0.04). Therefore, species with lower base temperature would avoid the risk of seeds germinating earlier in an environment with changeable temperature. A significant positive correlation existed between seed mass and accumulated temperature (p = 0.01). Under relatively constant base temperature, small-seeded species germinated faster than large-seeded ones, giving them priority of germination in early succession.

Aims Stipa purpurea is a dominant species of alpine grassland in northern Tibet, a region sensitive to climate change. Environmental variations in temperature, water and atmospheric carbon dioxide (CO₂) concentration caused by regional climate change should affect the photosynthetic physiology of plants. Our objective was to investigate the response of S. purpurea to environmental variation.
Methods We irrigated natural alpine grassland to imitate rainfall increasing soil moisture and then used a portable gas exchange system (LI-6400) to measure photosynthesis parameters at the irrigated field (H) and a natural field (CK). During measurement, we set three levels of leaf temperature (15, 20 and 25 °C) and gradually elevated CO₂ concentration from 50 to 1 500 μmol·mol^-1.
Important findings CO₂, temperature and soil moisture affected photosynthesis parameters of S. purpurea significantly, and interactions were apparent among these three factors. Rising CO₂ gradually increased net photosynthetic rate (P_n) until it decreased at extremely high CO₂. Higher temperature caused P_n to decrease, but sufficient water supply partially alleviated the negative effect. Sufficient water supply increased P_n. With rising CO₂, intercellular CO₂ concentration (C_i) increased, transpiration rate (T_r) decreased, water use efficiency (WUE) increased and stomatal conductance (G_s) decreased; higher temperature caused G_s to decrease faster. The photosynthesis parameters above were also impacted by the combined actions of humidity and temperature. G_s was maximized at 20 °C, and sufficient water supply increased G_s further. C_i increased with increased temperature, and this response was more pronounced with sufficient water. T_r was positively correlated with temperature and soil water. Vapor pressure deficit (VPD) was directly proportional to temperature and decreased with sufficient water. Increased temperature and increased water supply made WUE decline. Therefore, increased soil water had compensatory effects on the relationship between high temperature and photosynthetic parameters.

Aims In the Qinghai-Tibet area, high levels of UV-B radiation reach the earth’s surface as part of strong solar radiation. It is therefore important to examine the response and adaptation of native alpine plants to strong UV-B radiation. Our objective was to determine the physiological response of the photosynthetic apparatus to current ambient UV-B intensity.
Methods UV-B-exclusion experiments were conducted on a field site with UV-B-excluding and UV-B-transmitting filters. The two filters transmitted similar levels of photosynthetically active radiation, and there were no differences in air temperature and relative humidity under these metal-frame suspended plastic filters. The experiments were performed in alpine Kobresia humilis meadow with the native alpine species Saussurea superba. Pulse-modulated in vivo chlorophyll fluorescence was mainly used to obtain rapid information on UV-B effects on photosynthetic processes. The trials lasted 15 or 16 days during the growing season of July and August in 2008 and 2009. We measured the 3-min dark-adapted quantum efficiency of PSII photochemistry (F_(v)/F_(m)), PSII photochemistry efficiency and photosynthetic gas exchange parameters under natural sunlight. The contents of photosynthetic pigments and UV-B-absorbing compounds were analyzed in terms of both leaf area and leaf fresh weight units.
Important findings Net photosynthetic rate, significantly increased after removal of UV-B components from natural sunlight. Although there was no significant difference, the F_(v)/F_(m) was increased in low UV-B treatment compared with the ambient UV-B control. Both the coefficient of photochemical quenching and actual photo- chemical efficiency of PSII in the light were higher in low UV-B treatment compared to ambient UV-B during the 16 days of continuous measurement during clear days. Variation of PSII maximum efficiency in the light and nonphotochemical quenching further confirmed that the decrease in PSII photochemistry efficiency and increase in nonphotochemical quenching were the results of a strong solar UV-B component in natural sunlight. There was only a slight increase in photosynthetic pigments based both on leaf area and fresh weight after removing UV-B radiation, and these phenomena indicated that strong solar UV-B radiation could photo-oxidize photosynthetic pigments and further accelerate the maturity and senescence of plant cells. UV-B-absorbing compounds were not altered after removal of UV-B radiation, which suggested that high levels of UV-B-absorbing compounds in the epidermal cell layer could protect photosynthetic function from UV-B.

Aims The subalpine coniferous forests in eastern Qinghai-Tibet Plateau provide a natural laboratory for studying effects of climate warming on terrestrial ecosystems. Research on differences between tree species in their responses to experimental warming can provide insights into their regeneration behavior and community composition under a future warmer climate.

Methods We used open-top chamber (OTC) to determine short-term effects of two levels of air temperature (ambient and warmed) and light (full light and ca. 10% of full light regimes) on the early growth and physiology of Betula albo-sinensis and Abies faxonianaseedlings.

Important findings The OTC manipulation increased mean air temperature and soil surface temperature by 0.51 ℃ and 0.33 ℃, respectively, under the 60-year plantation and 0.69 ℃ and 0.41 ℃, respectively, under the forest opening. Warming generally increased the growth, biomass accumulation and advanced physiological processes for seedlings of both species. In response to warming, both species allocated relatively more biomass to foliage and had significantly decreased root/shoot ratios (R/S), which might provide tree species an adaptive advantage when other environmental factors are not limiting. Warming may enhance photosynthesis in the two seedlings by increasing efficiency of PSⅡ in terms of increase inF_v/F_m, photosynthetic pigment concentrations and apparent quantum yield (Φ). However, the effects of warming on seedling growth and physiological performance varied by light conditions and species. For B. albo-sinensis seedlings, the effects of warming were pronounced only under full-light conditions, while the growth and physiological responses of A. faxoniana seedlings to warming were found only under low-light conditions. Competitive and adaptive relationships between the two species may be altered as a result of response differences to warming manipulation. The short-term beneficial impact of warming on the early growth and development of the two species suggests that global warming may lead to changes in regeneration dynamics and species composition in subalpine coniferous forest ecosystems.

Aims Mosses constitute major ground cover of the subalpine forests in the eastern Tibetan Plateau. Moss leaves have one layer of cells and are highly sensitive to environment changes. This attribute of mosses can be used to monitor environment conditions and guide restoration. However, moss growth and especially variables affecting moss growth in subalpine forest ecosystems are poorly known. Even worldwide, the growth rate of mosses has been rarely studied because of time-consuming, inaccurate measuring methods.
Methods Two plots, one in old-growth spruce forest and the other in nearby clear-cut land in subalpine western Sichuan, were selected. We labeled and measured mosses on May 7, 2001 and remeasured on August 7, 2001 and simultaneously recorded microclimate measurements.
Important findings The growth rate of mosses varied among species and habitats. Hylocomium splendens had the highest growth rate, while Dicranum assamicum had the lowest. The growth of H. splendens, D. assamicum, and Thuidium lepidoziaceum was faster in forest than in clear-cut land, where it was inversely correlated with distance to forest. Actinothuidium hookeri and Rhytidiadelphus triquetrus had moderate growth rates nearly independent of habitat. From May to July, the forest almost always had lower radiation level and vapor pressure deficit (VPD) favorable for moss growth. For habitat-insensitive species, microtopographic factors might have offset the effect of habitat. Moss growth rate and habitat VPD were strongly negatively correlated. Moss growth rate can be used to suggest favorable habitat.

Background and Aims The study area is located on the eastern Qinghai-Tibetan Plateau (101°-103° E, 34°-35°70' N). The altitude ranges from 2 900 m to 4 000 m, and the climate is cold and humid with an annual rainfall of 450-780 mm, which is mainly distributed in July, August and September. Mean annual air temperature is 1.8 ℃ with -10.7 ℃ in January and 11.7 ℃ in July, and average annual frost days are no less than 270 d. The grassland types include mainly alpine meadow (59.32%), brushy meadow (33.39%), woodland meadow (0.32%), saline meadow (0.15%), swampy meadow (5.61%) and upland grass (1.21%). The vegetation belongs to typical alpine meadows, and the species composition of the plant community is dominated by many monocotyledons and various dicotyledons. The capacity of seed germination and seedling establishment determines partially the regeneration of plant communities of the grassland. However, there is few germination data. Accordingly, we have undertaken a major study of the gramineous species of the alpine meadow. A comparison of the germination biology of many species will provide an ecological context for subsequent studies of field distribution.
Methods Seeds were collected from as many sources as possible to get an adequate representation of the whole community from July to October in 2003. Enveloped seeds were spread on tables at room temperatures(about 15 ℃)until dried and threshed by hand through screens. The experiment of germination started on March 3, 2004. For each species 50 seeds were placed in Petri-dishes on filter paper moistened with distilled water in a growth chamber with a 12-h day at 25 ℃ and a 12-h night at 5 ℃. This temperature regime has relevance to field conditions: it approximates the mean daily maximum and minimum temperature in 5 cm deep soil from May to August. The percentage of seeds germinated was recorded every day. Newly emerged seedlings were removed from the Petri-dishes and seeds were regularly watered with distilled water. A seed was considered germinated when the length of the emerged radicle was equal to the length of seed. Germination was judged to be complete when no further germination occurred for five successive days. The remaining ungerminated seeds were checked for viability by soaking in water at 30 ℃ for 2 h, removing the seed coats and sliting open the seeds, then soaking the embryos in 0.1% tetrazomium chloride for 4 h at 30 ℃. In viable seeds embryos were stained pink. The amount of germination was then calculated as a percentage of the total number of viable seeds and rate of seed germination as the number of seeds germinating each day expressed as a percentage of the final germination. In this study, we make use of 4 indices: percent germination, days to first germination, germination period and days to 50% germination.
Key Results Of the 54 species examined, the following 26 species exceeded 80% germination: Achnatherum inebrians, Agrostis alba, A. sp1., A. stolonifera, Aneurolepidium dasystachys, Arundinella anomala, Bromus tectorum, Deschampsia caespitosa, Deyeuxia scabrescens, D. sp., Elymus dahuricus, E. tangutorum, Festuca sinensis ,Helictotrichon leianthum, Mellica scabrosa , Orinus kokonorica, Poa schoenites, P. sinattenuata, P. botryoides, P. poophagorum, P. pratensis, Ptilagrostis dichotoma, P. mongholica, P. roshevitsiana, Roegneria nutans and R. stricta. The following 11 species had 60%-80% germination: Achnatherum sibiricum, A. splendens, Brachypodium sylvaticum, Bromus magnus, B. sinensis, Deyeuxia arundinacea, Gramineae sp., Helictotrichon tibeticum, Ptilagrostis junatovii, Stipa capillacea and S. przewalskyi. The following 8 species had 40%-60% germination: Agrostis hugoniana, Brachypodium sp., Festuca ovina, F. rubra, Helictotrichon sp2., Poa declinata, Roegneria kokonorica and Stipa aliena. The following 5 species had 20%-40%germination: Aristida triseta, Helictotrichon schellianum, H. sp1., Koeleria cristata and Oryzopsis munroi and the following 4 species had values of less than 20%: Stipa purpurea, Agrostis sp2., Stipa penicillata var. hirsuta and A. trinii; 14 species, Achnatherum inebrians, A. splendens, Agrostis alba, Aneurolepidium dasystachys, Arundinella anomala, Brachypodium sp., Bromus tectorum, Elymus dahuricus, E. tangutorum, Mellica scabrosa, Orinus kokonorica, Poa sinattenuata, Ptilagrostis mongholica and Roegneria nutansbegan, began to germinate within 3-5 days; 29 species, Poa schoenites, Achnatherum sibiricum, Agrostis sp2., A. stolonifera, Brachypodium sylvaticum, Bromus magnus, B. sinensis, Deschampsia caespitosa, Deyeuxia arundinacea, D. sp., Festuca ovina, F. rubra, F. sinensis, Gramineae sp., Helictotrichon sp2., H. tibeticum, Koeleria cristata, Oryzopsis munroi, Poa botryoides, P. declinata, P. poophagorum, P. pratensis, Ptilagrostis junatovii, P. roshevitsiana, Roegneria kokonorica, R. stricta, Stipa aliena, S. capillacea and Stipa penicillata var. hirsuta, began to germinate within 6-8 days; 10 species, Agrostis hugoniana, A. sp1., A. trinii, Aristida triseta, Deyeuxia scabrescens, Helictotrichon leianthum, H. schellianum, H. sp1., Ptilagrostis dichotoma and Stipa przewalskyi, began to germinate within 9-10 d; and only Stipa purpurea exceeded 10 d. For species such as Stipa purpurea, Achnatherum inebrians, Agrostis alba, A. sp1., A. sp2., A. stolonifera, Aneurolepidium dasystachys, Aristida triseta, Arundinella anomala, Elymus dahuricus, E. tangutorum, Helictotrichon schellianum, H. sp1., Mellica scabrosa, Poa poophagorum and P. sinattenuat (16 species), the germination period was short (1-7 d); 28 species, Poa schoenites, Achnatherum splendens, Agrostis hugoniana, A. trinii, Brachypodium sp., Bromus magnus, B. sinensis, B. tectorum, Deschampsia caespitosa, Deyeuxia arundinacea, D. scabrescens, D. sp., Festuca ovina, F. rubra, F. sinensis, Gramineae sp., Helictotrichon leianthum, H. tibeticum, Koeleria cristata, Orinus kokonorica, Oryzopsis munroi, Poa botryoides, P. declinata, P. pratensis, Roegneria kokonorica, R. nutans, Stipa capillacea and Stipa penicillata var. hirsuta, had the germination period of 8-14 d; and 10 species, Achnatherum sibiricum, Brachypodium sylvaticum, Helictotrichon sp2., Ptilagrostis dichotoma, P. junatovii, P. mongholica, P. roshevitsiana, Roegneria stricta, Stipa aliena and S. przewalskyi, germinated over a longer period (15-21 d);for species such as Poa sinattenuata, Achnatherum inebrians, Agrostis alba, Aneurolepidium dasystachys, Arundinella anomala, Brachypodium sp., Bromus tectorum, Elymus dahuricus, E. tangutorum, Mellica scabrosa and Roegneria nutans (11 species), germinated 50% within 1-7 d, while Poa schoenites, Achnatherum splendens, Agrostis hugoniana, A. sp1, A. stolonifera, Bromus magnus, B. sinensis, Deschampsia caespitosa, Deyeuxia arundinacea, D. scabrescens, D. sp., Festuca ovina, F. rubra, F. sinensis, Gramineae sp., Helictotrichon leianthum, H. tibeticum, Orinus kokonorica, Poa botryoides, P. declinata, P. poophagorum, P. pratensis, Ptilagrostis mongholica, P. roshevitsiana, Roegneria kokonorica, R. stricta and Stipa capillacea (27 species) germinated 50% within 8-14 d; and the time to 50% germination of Achnatherum sibiricum, Brachypodium sylvaticum, Ptilagrostis dichotoma, P. junatovii and Stipa przewalskyi exceeded 14 d, but 11 species, Agrostis sp2., A. trinii, Aristida triseta, Helictotrichon schellianum, H. sp1., H. sp2., Koeleria cristata, Oryzopsis munroi, Stipa aliena, S. purpurea and Stipa penicillata var. hirsuta, failed to germinate 50% after the experiment.
Conclusions These species showed four germination patterns: rapid (e.g. Achnatherum inebrians and Agrostis alba), slow (e.g. Achnatherum sibiricum and Stipa przewalskyi), intermediate (e.g. Deschampsia caespitosa and Orinus kokonorica) (percent germination >50%) and low germination (e.g. Oryzopsis munroi and Stipa purpurea) (percent germination <50%).The experiment illustrated that the gramineous species of the alpine meadow on the eastern Qinghai-Tibetan Plateau are heterogeneous in their germination characteristics. Nevertheless, knowledge of other factors (e.g. light, temperature and storage methods) influencing germination is needed before we can fully understand the relationships between germination characteristics and field distribution.

Over the past two decades, society has become increasingly aware of problems of forest degradation. The effects of forest degradation transcend individual countries and now impact global processes. Research on the restoration of degraded forests has become a key issue in global ecology. Of particular concern are the effects of human activities on forest productivity and site fertility, especially as the demands for fuel and timber from tropical forests increase. Removal and burning of biomass causes nutrient losses and changes to the soil’s physical and chemical characteristics. The amount of nutrient loss depends on the intensity of the activities, local environmental factors, and the type and successional state of the forest. If nutrient losses cannot be recovered during regrowth, forests often become degraded through time. Thus, it is important that the nutrient dynamics of human-impacted forests are well understood in order to develop plans for restoration of degraded forests and for sustainable forest management. Most of the primary tropical forests in southern China have been degraded by human activities during the past several hundred years. Factors leading to their degradation include: timber harvesting, unsustainable agriculture, overgrazing by domestic animals, and intensive harvesting for fuel. In extreme cases, the land has become completely denuded. Attempts to reverse this process of land degradation have been initiated in this region of southern China. Over the last few decades, large areas have been reforested with a native pine species, Pinus massoniana, to prevent further degradation to the landscape. Cutting of trees is now prohibited, but harvesting of the understory and collection of litter is still allowed to satisfy local fuel needs. Compared with whole-tree harvests, this practice removes less biomass from the forests; however, as the understory and litter are relatively nutrient-rich, this practice may slow or prevent the recovery of soil fertility and productivity of these forest ecosystems. The objective of this study was to determine the effects of harvesting understory plant species and litter on nutrient accumulation dynamics in a Pinus massoniana forest of subtropical China. The results are used to address the following questions: 1) How are nutrients distributed in plants of this pine forest; 2) What quantity of nutrients are removed annually from the ecosystem by the practice; 3) Is this harvesting practice sustainable or not; 4) What alternative management options are available for continued use to meet fuel needs while at the same time improving site fertility, productivity and regeneration processes; and, 5) How do stressed ecosystems respond when the stressors are removed, that is, how would the forest respond if the harvesting practice was stopped. In order to achieve the objectives above, an experiment was established in a MAB reserve of subtropical China in May 1990. The experiment was a paired-plot design with 20 replicates. Each pair consisted of a treatment (continued harvest) and control (no harvest) plot, 10 m×10 m in size and surrounded by a 10 m wide buffer strip. In the treatment plots, local people continued to harvest litter and understory plants according to local practice (about 2－3 times a year) from the beginning of the experiment in May 1990. The harvesting according to local practice occurred during the period of 1990 to 1995 and was stopped after this time. Control plots were protected from any harvesting. Each set of paired plots was similar in soil, slope, aspect, and elevation. In this paper we report only the results of nutrient dynamics and its responses to human impacts over a ten-year period from 1990 to 2000.

Seasonal and diurnal variations in zeaxanthin content of Kobresia humilis and Polygonum viviparum took the form of a monotonic curve, which was closely related to the seasonal and diurnal changes in solar radiation in Haibei Research Station.

Changes in fatty acid composition of roots of Elymus nutans, Poa sphyondylodes, and Bromus sinensis growing in alpine area were investigated over late fall and early winter. The results indicated that there were marked changes in the fatty acid composition in this period. The content of saturated palmitic acid (16:0) decreased by 40% while the content of unsaturated linolenic acid (18:3) increased by 112%, resulting in an increase in IUFA (index of unsaturated fatty acid) melting level. Membrane fluidities were low at the freezing-melting stage, but higher in the freezing stage. Ca2+, Mn2+ ATPase activities of plasma membranes increased, but Mg2+ ATPase activities decreased. The results suggested that increase in unsaturated fatty acid content of roots may be a very important physiological response to cold acclimation, which is directly associated with changes in the properties of plasma membranes, in maintaining membrane fluidity and controlling the activities of membrane integrated enzymes.

In this paper, the contents of protein, fat and starch were compared among Kobresia humilis plants grown at different altitude in Qinghai-Xizang plateau (Daban Mt, 4,000 m a.s.1; Jinyang Mt,3,800 m a.s.1;Haibei station, 3,200 m a.s.1;Xining,2,200 m a.s.1). The results show that some biochemical component in aboveground and belowground tissues of the plants tended to increase with increasing altitude. As compared with those plants in Jinyang Mountain, Haibei Station and Xining, on average, the plants grown at Daban Mountain had a higher protein content by 9.9% ,17.3% and 39.4%, a higher fat content by 7.5% ,77.8% and 106.8%, and a higher starch content by 2.4%, 21.6% and 32.7% ,respectively. It is clear that altitude had effects on the seasonal changes of the contents of some biochemical components.The results suggest that the stronger frost resistance of the plants located at a higher altitude are associated with their stronger synthesis of the protein, fat, starch and related substances.

The relation of distribution, density and diurnal changes of stomatal opening and closure in six plants of alpine Kobresia humilis meadow were studied during May–September in 1986. The results indicate that the leaf stomata of most plants are distributed in both the upper and lower epidermis, but with the K. humilis they are distributed in the lower epidermis, and with the Festuca ovina, they are all distributed in the upper epidermis. The leaf stomata open at 9 am until 3pm and then close gradually. Transpiration intensity of plants varies with the stomata’s opening and closure. The transpiration intensity of K. humilis achieved peak at about 11 am, but Elymus nutans and Saussurea superba at about 1 pm, after which it falls gradually until stops completely sunset. The changes of stomatal opening and closure as well as the transpiration intensity of plants are affected by both air temperture and the relative ambient humidity.

The present study in transpiration intensity of plants in alpine Kobresia humilis meadows was carried out at Haibei Research Station of Alpine Meadow Ecosystem during the growing season from May to September in 1986.The transpiration intensity of Kobresia humilis and plants of nine other species, the daily courses of transpiration intensity of Elymus nutans and plants of two other species as well as the evapotranspiration intensity of different ground covers in Kobresia humilis meadows were measured by method of cobalt paper. At the same time,meteorological data ewer also recorded.The study results are as follows:

1. The transpiration intensity of Kobresia humilis and plants of nine other species and their phenological phases, were lower during the early growth period and higher during the growth-development period. In general, the transpiration intensity of plants in alpine meadows is higher due to the special habitat conditions on the Qinghai-Xizang plateau.

2. The daily transpiration courses of Elymus nutans and plants of other species showed one peak curve at noon or afternoon, due to the longer time opening of the stoma to which is also one of the reasons of the higher transpiration intensity. But on the other hand, the transpiration coefficient is higher and the transpiration ratio is lower of the plants in Kobresia humilis meadows.

3. The evapotranspiration of different ground covers showed that evapotranspiration with ground cover is higher than that without ground cover (bare land).