Aims Solar radiation is the energy source of terrestrial ecosystem carbon and water cycles. Observation shows that solar radiation has experienced noticeable variations in recent decades and significantly impacted on plant photosynthesis. Our objective was to investigate the impacts of changes in solar radiation on gross primary production (GPP) at the Qianyanzhou eddy tower site in subtropical forest in China.
Methods We first established the relationship between diffuse radiation fraction and clearness index based on the observed solar radiation and diffuse radiation data. Then, a two-leaf ecological process model, the Boreal Ecosystem Productivity Simulator (BEPS), was used to simulate the impacts of different changes in solar radiation on shaded GPP, sunlit GPP, and canopy GPP in the typical subtropical evergreen needle-leaf plantations.
Important findings Results showed that the effects of changes in solar radiation on shaded leaves predominantly determined the changes in the canopy photosynthesis as the shaded leaves contributed 67% to the total GPP. The impacts of changes in solar radiation on GPP varied inter-annually due to variations in the intensity and distribution of solar radiation from year to year. The GPP during 2003-2005 reached maximum when the solar radiation changed by -5.44%, -1.83%, and 6.26% in each year, respectively. Increased solar radiation enhanced the GPP during May and June, but reduced the GPP from July through September. The shaded leaves responded to changes in radiation differently in different seasons, and the sunlit and shaded leaves had different responses in the same season. Consequently, there were patterns of apparent offset in the total GPP and reduced sensitivity to changes in solar radiation on an annual basis. The changes in solar radiation had the smallest impact on GPP when the clearness index was at 0.43.

Aims Our purpose was to characterize the effects of nitrogen (N) addition on plant carbon (C), N, phosphorus (P), and C:N:P ecological stoichiometric characteristics in six dominant plant species, including Kobresia myosuroides, Elymus nutans, Anemone rivularis, Pedicularis kansuensis, Potentilla fragarioides and Oxytropis ochrocephala, of alpine meadow on the Qinghai-Xizang Plateau, China.
Methods N was added at four levels. Concentrations of C, N and P were measured, and C:N:P was estimated in the six plant species following the N addition treatments.
Important findings Significant differences in leaf N and P concentrations existed among the six species under natural conditions. The N and P concentrations were highest in O. ochrocephala, at 24.5 and 2.51 g·kg^-1, respectively. The leaf N concentration was significantly lower and leaf P concentration was significantly higher in O. ochrocephala than in legume plants of other grasslands in China. Leaf N and P concentrations in the other five species were in the ranges of 11.5-18.1 and 1.49-1.72 g·kg ^-1, respectively. Kokresia myosuroides had the lowest N concentrations and E. nutans had the lowest P concentrations; they were significantly lower than the non-legume plants in other grasslands in China (p < 0.001). P and C concentrations did not respond to N addition in all the six plant species, but N concentration significantly increased with N addition in five species other than O. ochrocephala, which did not respond to N addition. Values of the N:P varied in the range of 7.3-11.2 in treatment without N addition, indicating that the plant growth was limited by N in the alpine meadow. Values of the N:P increased and were greater than 16 with N addition in five species other than O. ochrocephala, indicating that N addition induced P deficiency in these five species. Our results point to very low leaf N concentration and limitation of N on plant growth in alpine meadow on the Qinghai-Xizang Plateau, China, but different species had different responses to N addition. The legume plant O. ochrocephala was not susceptible to N addition, but leaf N concentration in other five plant species was increased by N addition. Findings in this study highlight the importance for fertilization and management of alpine meadow.

Aims Due to concurrent variations of multiple factors influencing soil heterotrophic respiration (Rh), it is difficult to determine the responses of Rh to changes in individual factors and their interactive effects under field conditions. In this study, we conducted a laboratory incubation experiment with controlled temperature and water levels to determine the responses of Rh to changes in soil temperature and moisture using soil samples collected from an Stipa krylovii (Stipa sareptana var. krylovii) grassland in Nei Mongol.
Methods The incubation experiment consisted of five temperature treatments (9, 14, 22, 30, and 40 °C) and five water treatments (20%, 40%, 60%, 80%, and 100% of water holding capacity (WHC)), with a full factorial arrangement. We measured Rh at an interval varying from every two days to once a week, and soil dissolved organic carbon (DOC) and microbial biomass carbon (MBC) at an 18-day interval during the 71 days of incubation period.
Important findings The results showed that Rh differed significantly among different temperature treatments (p < 0.001) and was positively related to temperature (p = 0.001); the temperature sensitivity of Rh (Q₁₀) also increased with increasing moisture level. The relationship between Rh and water was best fitted using quadratic equations, and the optimal moisture condition increased when temperature rose. There existed significant interactions between soil temperature and moisture (p < 0.001) and their interactions could be best fitted using the function lnRh = 0.914 + 0.098T + 0.046M + 0.001TM - 0.002T² - 0.001M², it suggested that the models in additive form could explain the Rh response better than those in multiple form. Our results also showed that the relationship between Rh and MBC varied during incubation, and DOC was not significantly related to Rh (except for the 20th incubation day), suggesting that microbial turnover and community transformation could lead to the changes of gross microbial activity.

Aims Specific information on geographic distribution of a species is important for its conservation. This study was conducted to determine the potential geographic distribution of Sinopodophyllum hexandrum, which is an endangered plant used in traditional Tibetan medicine, and to predict how climate change would affect its geographic range.
Methods The potential geographic distribution of S. hexandrum under the current conditions in western China was simulated with MaxEnt software based on species presence data at 136 locations and 21 climatic variables. The future distributions of S. hexandrum were also projected for the periods 2020s, 2050s and 2080s under the climate change scenarios of A1B, A2 and B1 described in the Special Report on Emissions Scenarios (SRES) of IPCC (Intergovernmental Panel on Climate Change).
Important findings Results showed that mean temperature of the warmest quarter, annual precipitation, temperature seasonality, and isothermally were the four dominant climatic factors influencing the geographic distribution of Sinopodophyllum hexandrum. For the entire region of the seven provinces in western China, 11.71% of the areas were identified as suitable habitats, 15.86% as marginally suitable habitats, and 72.43% as, unsuitable habitats. The suitable habitats are mainly located in Sichuan, Gansu, Qinghai in the eastern edge of Qinghai-Xizang Plateau, and in areas with rich secondary vegetation and complex terrain in high altitudes. The model simulations indicated that the marginally suitable habitats would have a relatively small change under the climate change scenarios of SRES-A1B, SRES-A2 and SRES-B; whereas the suitable habitats would initially decrease by 2020s, followed by a trend of moderate increased thereafter. The average elevation of suitable habitats would be increased, and both the distributional range and the center of distribution would shift northward first, and then move west to the higher altitudes in mountainous areas of Qinghai-Xizang Plateau.

Aims Our objective was to simulate and predict the impact of climate change on potential distribution in the relic and endangered Amygdalus mongolica, hence providing scientific basis for understanding the evolution and protection of this species.
Methods Maximum entropy (MAXENT) model was employed to simulate, forecast, compare, analyze, and reveal the changes in the distribution range and spatial pattern in the relic and endangered A. mongolica at the Last Glacial Maximum (based on Community Climate System Model and the Model for Interdisciplinary Research on Climate), and under the historical (1961-1990) and future climate conditions (2020, 2050 and 2080, all based on the Intergovernmental Panel on Climate Change (IPCC) and Special Report on Emissions Scenarios A2A). The accuracy evaluation of repeat models of A. mongolica, and the average probability of occurrence and standard deviation based on repeat models were analyzed with the spatial analysis methods in the ArcGIS10.0.
Important findings The potential distribution of A. mongolica under the historical climate conditions centered in Ömnögovǐ and Dornogovǐ of Mongolia, Bayannur City, Alxa Zuoqi, Ordos City, and western Xilin Gol Meng of Nei Mongol, the central and eastern regions of Hexi Corridor, the northern Ningxia and Shaanxi, and part of the northern Heibei. Furthermore, the distribution of A. mongolica at the Last Glacial Maximum based on Community Climate System Model climate scenario experienced the widely southward shift and range retraction. Last but not the least, under the future A2A climate scenario of IPCC, the potential distribution of A. mongolica would be significantly increased by 2020, and then decreased by 2050, with a slightly increasing trend until 2080. The distribution patterns of A. mongolica showed a large spread and shift to eastern Hebei and the eastern Nei Mongol of China, and to the eastern, northern, and western Mongolia.

Aims While the phenomena that environmental stresses induce growth differentiations between male and female seedlings are confirmed by many controlled experiments in recent years, the potential impacts on adult trees of dioecious plants caused by climate change have not yet attracted much attention. In order to further reveal the differential effects of climate warming on the dendrological characteristics of female and male trees, a typical dioecious plant, Populus cathayana, was selected as a test material in the study.
Methods Wood samples were taken from 40 adult trees of P. cathayana (including 20 female and 20 male individuals, respectively). We employed the dendroclimatological approach to analyze the gender-specific differences in seven tree-ring variables (i.e. maximum ring density, latewood mean density, earlywood mean density, minimum ring density, annual ring width, earlywood width, and latewood width), and their differential responses to climate factors (monthly mean, minimum and maximum air temperature and precipitation) in Xiaowutai Mountains of China.
Important findings Firstly, with an increase in the local air temperature during the past 30 years (1982-2011), the male and female P. cathayana trees exhibited the similar trend in radial growth but with apparent differences in the pattern of density growth. Compared with the males, the female trees displayed significantly (p < 0.05) higher maximum ring density and latewood mean density. Secondly, there was a similar pattern of variations in the residual chronologies between the male and female trees, but the male trees showed much higher magnitude of variations than the female trees. Thirdly, based on the residual chronologies, it was found that the response months are quite different between the two sexes. For the female trees, maximum ring density had a significant positive correlation with the maximum air temperature in current August. However, the maximum ring density was significantly and negatively correlated with the air temperature in current January and April for the male trees. Fourthly, for trees of both sexes, climate change prior to growing season limited the radial growth while maximum air temperature in current June obviously restricted the growth of earlywood. These results indicate that there are different tree-ring growth strategies between trees of different sexes in response to global warming in dioecious plants, and that the female trees invest more in density growth than the male trees.

Aims Trade-off is the basis of life history strategy theory. Elucidation of the trade-off between plant height and branch numbers is important for understanding the phenotypic plasticity of plants under different habitat conditions. Our objective was to examine how Stellara chamaejasme would adapt to changes in slope aspect through trade-off between height and branch numbers.
Methods In a degraded alpine grassland on the northern slope of the Qilian Mountains, Gansu Province, China, 80 plots were set up on sites of four different aspects at intervals of 10 m vertically from the foot of an isolated hill moving upward. Handheld GPS was used to record latitude, longitude and altitude of each plot. Community traits were investigated and five S. chamaejasme plants were harvested randomly on each plot for measuring the plant height, brunch numbers, leaf area, and above-ground biomass. ArcGIS was used to construct the digital elevation model (DEM) and to extract data on elevation, aspect, slope, slope of slope, and slope of aspect for the study sites. The 80 plots were categorized into groups of north, east, south, and east aspects. Generalized additive model (GAM) was used to select the most effective terrain factors, and partial correlation analysis method was used to examine the trade-off between plant height and brunch numbers on sites of different aspects.
Important findings With a change of the aspect from north to east, south and west, the above-ground biomass and cover of the grassland community displayed a pattern of decline―increase―decline; whereas the average height of the community displayed a pattern of increase―decline. Aspect was the predominant terrain factor affecting spatial variations of the height and branch numbers in S. chamaejasme. When the aspect changed from north and east to west and south, the average height of S. chamaejasme populations declined and the branch numbers increased, resulting in a trade-off in the form of an inversed relationship between the height and branch numbers; whilst the specific leaf area increased first and then decreased. The trade-off between height and branch numbers with changes in slope aspect of the habitat reflected the mechanism of biomass allocation under conditions of multiple competitions for resources in diverse habitats and the regeneration strategy for enhanced adaptation in S. chamaejasme populations.

Aims Clonal plants are physiologically integrated, allowing translocation of photosynthates, water, nutrients and other substances between connected ramets within a clone. This suggests that the sizes of ramets of different ages may be correlated. So far, however, little is known about the effects of fertilization on the size relationships between ramets of different ages. In this study, we aim to examine how fertilization affects the relations of diameter at breast height (DBH) between ramets of different ages in the giant clonal bamboo Phyllostachys edulis.
Methods We established 112 20 m × 30 m plots of P. edulis in Longquan City, Zhejiang Province, China. Among them, 46 plots were fertilized only in 2008, 49 fertilized in five consecutive years from 2004 to 2008, and 17 unfertilized (the control). We measured DBH of ramets of one, three and five years old in each plot in 2009. The relations of DBH between ramets of different ages in different fertilization treatments were examined using allometric scaling by the standardized major axis (SMA) analysis, and that were also analyzed by multiple linear regression.
Important findings The DBH of the 1-year-old ramets was significantly greater than that of the 5-year-old ones in the 5-year fertilization plots, while no significant difference was found in the 1-year fertilization plots. Under different fertilization treatments, the slopes of SMA (0.88-1.10) for the relations of DBH between ramets of one, three and five years old were not significantly different from 1.00 (p > 0.05), suggesting isomeric growth relationships. Compared to the control (unfertilization), fertilization in one or five years did not change the slope of SMA. However, fertilization in five years increased the intercept of SMA, indicating that continuous fertilization could result in greater DBH increment in the 1-year-old ramets. The multiple linear stepwise regression analysis indicated that 3-year-old ramets could greatly influence DBH of the newly produced ramets, and that the effect of DBH of the 5-year-old ramets on that of the 1-year-old ramets increased after five years of continuous fertilization.

Root exudates have specialized roles in nutrient cycling and signal transduction between a root system and soil, as well as in plant response to environmental stresses. They are the key regulators in rhizosphere communication, and can modify the biological and physical interactions between roots and soil organisms. Root exudates play important roles in biogeochemical cycle, regulation of rhizospheric ecological processes, and plant growth and development, and so on. Root exudates also serve roles in the plant-plant, plant-microbe, and microbe-microbe interactions. Plant allelopathy, intercropping system, bioremediation, and biological invasion are all the focal subjects in the field of contemporary agricultural ecology. They all involve the complex biological processes in rhizosphere. There are increasing evidences that various positive and negative plant-plant interactions within or among plant populations, such as allelopathy, consecutive monoculture problem, and interspecific facilitation in intercropping system, are all the results of the integrative effect of plant-microbe interactions mediated by root exudates. Recently, with the development of biotechnology, the methods and technologies relating to soil ecological research have achieved a remarkable progress. In particular, the breakthroughs of meta-omics technologies, including environmental metagenomics, metatranscriptomics, metaproteomics, and metabonomics, have largely enriched our knowledge of the soil biological world and the biodiversity and function diversity belowground. Research on plant-soil-microbe interactions mediated by root exudates has important implications for elucidating the functions of rhizosphere microecology and for providing practical guidelines. The concept and components of root exudates as well as the functions are reviewed in this paper. An overview on the root-bacteria, root-fungi, and root-fauna interactions is presented in detail. Methods to study root exudates and microbial communities are reviewed and the aspects needed to be further studied are also suggested.