Aims Competition for different limiting resources among plant species is the main factor that influences plant community composition, diversity and productivity. Our objective was to investigate the effects of different levels of nitrogen addition on species richness and aboveground productivity of alpine meadow of the Qinghai-Tibetan Plateau, China.

Methods We added nitrogen in a completely randomized block design and measured plant aboveground biomass, species composition, vegetation light penetration and soil pH and NO₃^--N content in each plot. Regression and analysis of variance were used to analyze the responses of these measures to different levels of nitrogen addition.

Important findings Nitrogen addition changed the soil physical and chemical properties, enhancing the content of NO₃^--N available resources in the soil, increasing plant cover and reducing vegetation light penetration. With increasing N addition, species richness decreased sharply (p < 0.001). N addition changed aboveground productivity significantly (p < 0.05). With increasing N addition, aboveground productivity increased first then decreased, and grass biomass increased while forb and legume biomasses decreased. There was a significant linear positive relationship between species richness and vegetation light penetration (p < 0.05) and also between aboveground productivity and soil NO₃^--N content (p < 0.05). The relationship between aboveground productivity and species richness was negative. We suggested that the short term effects of nitrogen addition on community composition and aboveground productivity were determined by the changed soil NO₃^--N content.

Aims Overgrazing is a key factor driving grassland degradation in arid and semiarid regions. In this study, we explored how spatial and temporal patterns of grassland degradation were linked to vegetation sensitivity and socioeconomic drivers in the Xilin River Basin, Inner Mongolia, China.

Methods We categorized grassland degradation by species composition and community characteristics by comparing a 1980’s vegetation map with data from field surveys done in 1984 and 2004 across the Xilin River Basin. Five types of grasslands were distinguished: non-degraded, slightly degraded, moderately degraded, heavily degraded, and extremely degraded. We also classified two additional types of grasslands based on their conditions 20 years ago: salinized and restored grasslands.

Important findings The distribution of degraded grasslands exhibited an obvious spatial pattern across the Xilin River Basin. In general, the degree of grassland degradation increased from upstream in the southeast to downstream in the northwest of the basin. Moderately degraded grasslands were distributed mostly in the southeast, and heavily degraded and salinized grasslands were located in areas close to the river and over much of the Hunshandak sandland. Extremely degraded grasslands were distributed throughout the northern part of the basin where ecosystems were more vulnerable to over grazing. Non-degraded and slightly degraded grasslands were scattered patchily across the basin. In contrast, some abandoned farmlands and fenced pastures rested from grazing showed restoration over the past two decades. Grassland degradation in the basin also showed vegetation-type specific characteristics. About 43% of the shrubland was slightly degraded. More than 50% of Festuca ovina and Ulmus pumila dominated grasslands were moderately degraded, and half of the Stipa baicalensis and Bromus inermis dominated grasslands were heavily degraded. For both Stipa krylovii and Caragana microphylla dominated grasslands, more than 50% of the total areas were extremely degraded. For Leymus chinensis grassland, only small part of the total area had been degraded. Based on our analysis, overgrazing is the most important socioeconomic factor driving grassland degradation in the Xilin River Basin. The grassland degradation was positively correlated with increasing stocking rate from the 1970’s to 2004. Other factors, such as shifts in the density of villages and network of roads, were also attributed to the widespread grassland degradation in the Xilin River Basin.

Aims Our major objective was to reveal the distribution pattern of plant species diversity in the mountainous region of Ili River Valley, Xinjiang, China and explore how environmental gradients influenced the pattern.

Methods Based on a survey of 94 sample plots in the study area, DCCA was performed to analyze the relationships between diversity indices and environmental gradients and GAM was employed to model the response curve of diversity indices to elevation.

Important findings We recorded 259 plant species, including 235 herbaceous species; the species of woody plants were very limited. Communities with complex vertical structure had higher values of diversity. The distribution pattern of species diversity on the northern slope was affected by elevation, slope aspect, slope gradient, total nitrogen, total potassium, soil water content, organic matter, etc., and that on the southern slope was mainly affected by slope gradient, elevation, available phosphorus, soil water content, etc. On the northern slope, Patrick index and Shannon-Wiener index had a bimodal pattern with elevation and Simpson index and Pielou index showed a partially unimodal pattern. On the southern slope all the distribution pattern of species diversity indices showed two peaks, though that of the Patrick index was not obvious. These patterns were formed by the synthetic action of a variety of environmental factors in which elevation played an important role.

Aims Stipa grandis is a dominant species of Inner Mongolia typical grassland. Our objective is to explore the responses of S. grandis seedlings to changed precipitation patterns to provide insight into responses of Inner Mongolia grassland to future global climate change.

Methods A simulated experiment was conducted in 2009 to examine the effects of precipitation quantity and interval on S. grandis seedlings in open-top chambers at the Inner Mongolia Grassland Ecosystem Research Station of the Chinese Academy of Sciences.

Important findings At final harvest, aboveground biomass of S. grandis seedlings was significantly increased by an average of 23% (p < 0.05) by increased precipitation quantity (+50%) and by an average of 48.8% (p < 0.001) by extending the precipitation interval from 5 to 15 days. Precipitation quantity had no significant effect on belowground biomass. When compared with that under regular precipitation interval with same precipitation quantity, belowground biomass was significantly increased 56.2% (p < 0.001) with extended precipitation interval under low precipitation quantity, but was not significantly affected by extended precipitation interval under high precipitation quantity. The effect of precipitation quantity and interval on root/shoot ratio depended greatly on each other. Root/shoot ratio was significantly decreased by 28.4% (p < 0.05) by increased precipitation quantity only under the extended precipitation interval level and significantly decreased by 28.8% (p < 0.05) by extended precipitation interval only under increased precipitation quantity. During the whole treatment period, differences in aboveground, belowground and total biomass of seedlings between treatments for seedlings treated for 30 days and 45 days were determined by total precipitation quantity, and biomass differences for seedlings treated for 75 days were determined by precipitation interval. Therefore, precipitation interval could be as important as precipitation quantity on growth of S. grandis seedlings. Effects of precipitation patterns could be complex since the effects of precipitation quantity and precipitation interval interacted greatly and changed with seedling growth period.

Aims Changes in permafrost wetland plant communities were indicators of the retreat of permafrost in the Da Hinggan Mountains in China. Our objective was to understand the changes in species diversity and ecological characteristics of permafrost wetland plant communities along environmental gradients as the keys to predict changes in permafrost and permafrost wetlands in response to global warming.

Methods We analyzed the distribution of 24 permafrost wetland plant communities in the Da Hinggan Mountains using detrended canonical correspondence analysis (DCCA). Species diversity, life forms and hydro- ecotypes of permafrost wetland plant communities were compared in three types of permafrost using multiple comparisons in ANOVA.

Important findings The 24 permafrost wetland plant communities were classified into three groups according to three types of permafrost. From the predominantly continuous permafrost to the sparsely island permafrost to the predominantly continuous and island permafrost, shrub diversity decreased (p < 0.05), herbaceous diversity increased (p < 0.05), the percentage of mesophytes was 38.5%, 55.9% and 64.4%, respectively, the importance value decreased for helophytes (p < 0.05) and increased for mesophytes and xerophiles (p < 0.05), suggesting that the soil moisture tended to a moderate amount of moisture, and even drought. Hemicryptophytes were dominant and phanerophytes and geophytes were subdominant in the three types of permafrost, suggesting short summers and long, cold, wet winters in the areas. The species diversity and ecological characteristics of permafrost wetland plant communities in the predominantly continuous and island permafrost were similar to that in the sparsely island permafrost.

Aims Quercus mongolica is the main secondary forest species in northeastern China. Study of the responses of its organic carbon accumulation and storage capacity to climate changes may provide a scientific basis for predicting community regeneration and growth. Our aim was to determine responses of non-structural carbohydrate (NSC) of Q. mongolica seedlings to the combined effects of elevated CO₂ concentration, temperature and soil nitrogen.

Methods We used three artificial climate chambers whose environmental conditions were 1) CO₂ concentration elevated to 700 μmol·mol^-1 and temperature elevated 4 °C (HCHT), 2) temperature elevated 4 °C and CO₂ concentration unaltered (HT) and 3) temperature and CO₂ concentration unaltered. Three different soil nitrogen concentrations were used to determine effects on the dynamics of NSC in one-year old seedlings during the growing season: N2 (15 mmol·L^-1), N1 (7.5 mmol·L^-1, i.e., the normal nitrogen supply) and N0 (no nitrogen).

Important findings The HTHC treatment changed the proportion of NSC partitioned to different organs of the seedlings and increased the accumulation of sugar and starch by the seedlings. N2 supply increased the accumulation of NSC, but there was no promotion effect on the accumulation of total NSC of the seedlings. The HT treatment significantly affected the accumulation and allocation of NSC of the seedlings, promoted the accumulation of NSC of the seedlings and increased the proportion of allocation of NSC to taproots under N2 supply. The dynamics of the soluble sugar content were different among the three treatments in different organs of the seedlings. The starch content increased in taproots, but gradually decreased in fine roots. Added nitrogen may promote the growth of Q. mongolica seedlings with future climate warming, thereby increasing their carbon storage, ability to withstand adverse environmental conditions and potential natural regeneration.

Aims Sprouting is an efficient mechanism for forest regeneration to regain lost biomass after disturbances, and it is the main regeneration mechanism of some Quercus forests. Our objective was to study (a) root and sprout growth dynamics of Q. aquifoliodes shrubs after coppicing and (b) the supply of nutrients from the roots and the soil to the new sprouts.

Methods The sites selected were located on Zheduo Mountain of western Sichuan on the south-eastern fringe of the Tibetan Plateau. Post-fire, approximately 30-year Q. aquifoliodes shrubs were cut and sprouts and roots were sampled at 0, 30, 60, 90, 120, 150 and 180 days after coppicing. The roots were separated into fine roots (< 2.5 mm), medium roots (2.5-5.0 mm), coarse roots (> 5.0 mm), and taproot. Root biomass was investigated by excavating whole root systems and sprout biomass by harvesting. The concentrations of nutrient elements were determined by conventional methods. Nutrient supply to sprouts from the root and the soil was calculated based on change in nutrient content of the roots with time and accumulation of nutrients in the sprouts.

Important findings The mean aboveground and belowground biomass of Q. aquifoliodes shrubs was (11.25 ± 0.92) and (34.85 ± 2.02) t·hm^-2, respectively, giving a dry weight root: shoot ratio of 3.10. The biomass of sprouts linearly increased during the course of sprouting. Maximum biomasses of living fine and medium roots occurred in summer. No significant variation was observed for the stump and taproot biomasses. N and P concentrations in fine and medium roots increased in the first 60 days after harvesting; however, the stump, coarse roots and taproot decreased in N, K and Ca concentration. Of all nutrients, Mg showed the greatest variation in the root system. The root system stored much of the nutrient content. The soil, stump, coarse roots and taproots are the main nutrient sources for the initial growth of sprouts between harvesting and 120 days. All nutrients allocated to the sprouts, excluding K, were supplied by the soil between harvesting and 60 days. K was the nutrient most dependent on root reserves for the initial growth of sprouts. K, followed by Mg and Ca, is the nutrient most dependent on root reserves for sprout growth between 60 and 120 days, and the relative contribution of root to sprout P and Mg was very small in this period. Except for K, the soil is an important nutrient source between 120 and 180 days. The management of Q. aquifoliodes shrubs should focus on the protection of underground root systems.

Aims It is well documented that the increment of nitrogen application rates leads to the release of photosynthesis acclimation of C₃ plants under elevated atmospheric CO₂ concentration. However, current knowledge of the effects of nitrogen application rates on photosynthetic electron transport and distribution and its potential influence on photosynthesis acclimation is inadequate. The objective of our potted-experiment was to study the effect of nitrogen application rates on photosynthetic electronic transports and distribution in wheat leaves under elevated atmospheric CO₂ concentration.

Methods Using open-top chambers in simulating elevated atmospheric CO₂ concentration, we grew wheat (Triticum aestivum) under different nitrogen application rates and atmospheric CO₂ concentrations. We estimated the photosynthetic electron transport rate and its distribution by measurement of photosynthetic rate (P_n)-intercellular CO₂ concentration (C_i) curves and chlorophyll fluorescence parameters of wheat leaves in the heading stage.

Important findings Compared with ambient atmospheric CO₂ concentration treatments, more light energy excited by antenna pigments was dissipated as heat in wheat leaves under elevated atmospheric CO₂ concentration, the photochemical rate was increased and heat dissipative rate was decreased significantly in high-N wheat leaves. The non-photochemical quenching was decreased in high-N leaves but increased in low-N leaves, photochemical quenching coefficient was not changed significantly in both high-N and low-N leaves and the opening ratio of PSII reaction center would be increased and heat dissipation would be decreased where N was sufficient under elevated atmospheric CO₂ concentration. The photosynthetic electron rate of PSII (J_F) was increased, noncyclic electron transport rate involved in photorespiration (J₀) in high-N wheat leaves was decreased by 88.40% and J_F-J₀ increased and J₀/J_F decreased significantly under elevated atmospheric CO₂ concentration. Therefore, photorespiration was inhibited and more photosynthetic electrons were transported to photochemical process in wheat leaves under elevated atmospheric CO₂ concentration and the P_n was increased by 46.47%. We concluded that although more excited light energy of wheat leaves would be dissipated as heat under elevated atmospheric CO₂ concentration, the opening ratio of PSII reaction center, photochemical rates and J_F increased, J₀ decreased where nitrogen was applied sufficiently and more photosynthetic energy was transported to photochemical process. This may be a reason why photosynthesis acclimation of C₃ plant is released in higher nitrogen content soil under elevated atmospheric CO₂ concentration.

Aims Our principal aim was to test the hypothesis that pima cotton (Gossypium barbadense) and upland cotton (G. hirsutum) have different photoinhibition and photoprotection strategies due to differences in light capturing and photosynthetic characteristics.

Methods We measured diurnal leaf movement, incident photon flux density (PFD) on leaves, leaf temperature, maximal photochemical efficiency of PSII (F_v/F_m), PSII photochemical efficiency (Φ_PSII), electron transport rate (ETR), photochemical quenching coefficient (q_P), non-photochemical quenching (NPQ), net photosynthetic rate (P_n), stomatal conductance (G_s) and photorespiration (P_r) in pima and upland cotton.

Important findings Upland cotton had higher P_n and G_s than pima cotton. Nevertheless, the ratio of photorespiration rate to gross photosynthetic rate was generally higher in pima cotton. Pima cotton and upland cotton had similar degrees of photoinhibition. Furthermore, pima cotton had generally higher thermal energy dissipation capacity than upland cotton. All results indicated that differences in leaf diaheliotropic movement and G_s in pima cotton and upland cotton resulted in differences of both incident PFD on leaves and leaf temperature. Upland cotton and pima cotton preferentially used electron transport flux and thermal energy dissipation, respectively, for light energy dissipation toward photoprotection to against photoinhibition. Nevertheless, more electron transport flux was distributed into the photorespiration pathway to prevent over-reduction of the photosynthetic electron transport chain and photoinhibition in pima cotton.

Aims Our objective was to investigate the saline-alkali tolerance mechanism of Nitratia tangutorum to provide the basis for its use in saline areas in Heilongjiang Province of China and contribute to the theoretical understanding of urban tree species.

Methods We treated seedlings of N. tangutorum to 20 kinds of mixed salt solutions with different salinities and alkalinities and examined saline-alkali stress on lipid peroxidation and enzyme activities.

Important findings Injury to the plasma membrane of leaves increased with increasing salinity and alkalinity. Cell membrane permeability and electrolyte leakage of leaves were enhanced under salinity of 300 mmol·L^-1. The selectivity of plasma membrane permeability was damaged. The variation of malondialdehyde lipid peroxidation as plasmalemma peroxide product was consistent with that of electrolyte leakage, which showed a significant positive correlation (r = 0.796). The activities of superoxide dismutase, peroxidase and catalase increased with both increased salinity and pH, which enhanced the ability of the active cell membrane system. Linear regression analysis showed that the significance order of four stress factors is salinity > pH > [HCO₃^-] > [CO₃^2-]. Nitratia tangutorum had a high tolerance to complex saline-alkali stress when the salinity was < 300 mmol·L^-1 and pH was < 10.59.

Aims The valuable ornamental plant Osmanthus fragrans var. thunbergii is grown in city gardens and on roadsides in the regions of the Yangtze River Basin, where often it has been contaminated with cadmium. Our objective was to characterize the effects of different cadmium stresses on (a) biomass production, (b) C, N and P accumulation and distribution patterns and (c) N and P use efficiency in O. fragrans var. thunbergii.

Methods A controlled pot-experiment was arranged with different treatments of five cadmium concentrations (CK: 0, I: 25, II:50, III: 100, and IV: 200 mg·kg^-1). One-year old O. fragrans var. thunbergii was cultivated in the pots. Biomass production and concentrations of C, N and P in plant components were measured over one growing season. Biomass, distribution of C, N and P and N and P use efficiency were calculated.

Important findings Treatments with higher cadmium concentrations (II, III and IV) significantly decreased O. fragrans var. thunbergii biomass and C, N and P accumulation, as well as altered their distribution patterns, but the treatment with lower cadmium concentration (I) had no significant effects. Treatments with lower cadmium concentrations (I, II and III) increased N use efficiency but decreased P use efficiency, and both the lowest N and P use efficiencies were observed under the treatment with the highest cadmium concentration (IV). Results suggest that O. fragrans var. thunbergii could efficiently adapt to cadmium-contaminated environments by altering nutrient use strategy and biomass distribution pattern.

Aims Coal-fired flue gas desulfurated waste residue (abbreviated as desulfurated waste residue) may be a feasible approach to improving saline-alkali soil. Our objective was to explore the effects of desulfurated waste residue application on saline-alkali soil amelioration and growth of oil-sunflower (Helianthus annuus).

Methods Based on field and pot experiments, we studied soil properties (including pH and total salt content), and plant eco-physiological traits (root length and volume, leaf cell membrane permeability and oxidative protection enzyme systems) from 2006 to 2008. The field experiment was carried on alkali soil of Xidatan, Pingluo, Ningxia, and the desulfurated waste residue was added at ratios of 0, 11.25 × 10³, 22.50 × 10³, 33.75 × 10³ and 45.00 × 10³ kg·hm^-2.

Important findings The application of desulfurated waste residue to alkali soil decreased soil pH, total salt content, oil-sunflower leaf cell membrane permeability and superoxide dismutase (SOD) activity and increased oil-sunflower root length and volume. Therefore, application of desulfurated waste residue can improve saline-alkali soil markedly and enhance the growth of oil-sunflower on such soil. The amelioration effect increased with time during the 3-year experiment period. Considering economic factors, the 11.25 × 10³ kg·hm^-2 treatment achieved the best amelioration effect.

Aims Phytolacca americana is a serious invasive plant species, which has harmed biodiversity and arboreal regeneration in coastal protective forests in Shandong Province. Our objective was to reveal its mechanism of reproduction and dispersal in order to provide guidance for controlling its invasion.

Methods To study the spatial and temporal pattern of seed rain of P. americana, we conducted field surveys under Robinia pseudoacacia forest in Lingshan Bay National Forest Park from September to December 2008. We established five transects at 15 m intervals from forest edge to forest interior and within each transect set up 30 samples (1 m × 1 m) to survey seed densities. We also chose eight mother plants of P. americana at 10 m intervals in each transect and placed seed traps (30 cm × 30 cm × 10 cm) at 11 sample points at every 30 cm surrounding them. We collected fallen seeds one or two days. One-way ANOVA was used to test the diversity.

Important findings The quantities and densities of seed rain were 1 846-2 273 seeds and 621-1 382 seeds per square meter, respectively, and values decreased from forest edge to interior. In five transects, the average seed rain densities were 33.64%-60.80% of reproduction, and the total average seed rain density accounted for 49.52% of seed reproduction densities; the rest was removed by firewood collecting and seed predation by animals. Seed rain began in mid September and ended in late December, and it occurred on forest edges before forest interiors. There were two seed-rain peaks in late October and mid December, and maximum intensities were 32 and 59 seeds per square meter per day, respectively. The dispersal distance of seed rain decreased from forest edge to forest interior. The same pattern existed with increasing distance from mother plant. The maximal dispersal and weighted mean distances were 210-180 cm and 94.32-63.03 cm, respectively; the average weighted mean distance was 81.00 cm. Phytolacca americana seed rain had obvious spatio-temporal heterogeneity. Findings were important to predict the invasive potential of P. americana and the trend in community structure.