Aims Our objective was to reveal the pattern of variations in seed morphology in Quercus variabilis across temperate-subtropical China and to determine how they respond to climate change.
Methods Seed samples were collected from 20 natural Q. variabilis populations across eastern China in autumn 2011. Seed width (SW) and seed length (SL) were used as measures for seed size, and the ratio of width and length (SW/SL) for seed shape.
Important findings The SW and SL ranged from 1.21 to 2.18 cm and from 1.20 to 2.96 cm, respectively, and the SW/SL ratio ranged from 0.57 to 1.10. There were significant differences among the populations (p < 0.001). There was also a significant linear relationship between SW and SL. Seed length increased significantly with mean temperature of warmest month (MTW), decreased with precipitation of wettest quarter (PWQ), and displayed negative linear and humped-shape relationships with equivalent latitude (ELAT) and longitude (LON), respectively. Seed width had a significant positive correlation with MTW and negative correlation with PWQ. The SW/SL was almost constant along the latitude and climate gradients. These results have important implications for understanding how the morphology of seeds responds to climate change.

Aims The water-carbon coupling model has become a major approach of eco-hydrology study under the complicated situation of climate changes. Our objective was to explore the applicability of the WaSSI-C model for the humid region in southwestern China.
Methods We focused on a large watershed, the upper Zagunao River watershed, situated in the upper reach of the Minjiang River, Yangtze River Basin. Applicability of the WaSSI-C model was assessed by evaluating the modeling results with two indexes: determination coefficient (R²) and Nash-Sutcliffe efficiency coefficient (NS). In order to make it better suited for the study area, two main improvements were introduced regarding to the snowmelt and evapotranspiration (ET) calculation. The calibration period was set as 1988-1996, and the validation period was set as 1997-2006. We validated the model using observed runoff and gross ecosystem productivity (GEP) and ET production of moderate resolution imaging spectroradiometer (MODIS) in the calibration and validation periods, respectively.
Important findings There was a good performance of our application of the WaSSI-C model in the study area. The R²of calibration period and NS for the total runoff of the study watershed were 0.86 and 0.82, respectively, and 0.78 and 0.67, respectively, for the validation period. Moreover, the R² of the GEP and ET were 0.89 and 0.78, respectively. We discussed the modeling process and results, and the future direction of improvements of the ET calculation in the end.

Aims Wetland ecosystems are an obvious carbon sink, but with constant land reclamation, many wetlands disappeared and degenerated, and reclamation also influences the carbon-cycle between wetland ecosystems and the atmosphere. Cropland is a dominant use of reed (Phragmites australis) wetland in the Yellow River Delta, but the CO₂ flux of wetland ecosystems under escalating human influences remains unclear. Our objective was to investigate the impact of wetland reclamation on net ecosystem CO₂ exchange (NEE) dynamics and quantify CO₂ exchange of the two ecosystems’ response to environmental and biological factors.
Methods Based on eddy covariance technique, we measured CO₂ fluxes over the reed wetland and cropland ecosystems and monitored environmental and biological factors in 2011.
Important findings The averaged diurnal variation of NEE showed the U-type curve in different months of the growing season over wetland and cropland ecosystems. In the non-growing season, NEE lacked a diurnal pattern and the range of NEE was very small as the result of soil microbial activity. Analyses of NEE showed that the wetland was a net sink for each month from April to September 2011 and a source of CO₂ to the atmosphere for the fall and winter months of November to March. In contrast, the cropland was calculated to be a significant net sink for CO₂ in the growing season (May to October), while significant net losses of CO₂ occurred in the non-growing season (November to April). During the growing season, the maximum daily CO₂ uptake and release rates were 16.04 (August 17) and 14.95 (August 9) g CO₂·m^-2·d^-1 and 18.99 (August 22) and 12.23 (July 29) g CO₂·m^-2·d^-1over wetland and cropland, respectively. Daytime NEE values were strongly correlated with photosynthetic active radiation (PAR) in the growing season. The CO₂ flux was mainly affected by temperature of soil (T_s) in the non-growing season. Soil water content (SWC) and T_s were the main factors that influenced nighttime NEE in the growing season. The two ecosystem respiration quotient (Q₁₀) were 2.30 (wetland) and 3.78 (cropland) during the growing season. The wetland and cropland ecosystems were both carbon sinks during the growing season as they absorbed 780.95 and 647.35 g CO₂·m^-2, respectively, which means wetland reclamation can reduce its carbon sequestration ability. During the non-growing season, the two ecosystems were carbon sources, releasing 181.90 (wetland ecosystem) and 111.55 (cropland ecosystem) g CO₂·m^-2. Over all of 2011, the wetland and cropland ecosystems both were obvious carbon sinks with absorption of 599.05 and 535.80 g CO₂·m^-2, respectively.

Aims Atmospheric nitrogen deposition derived from fossil-fuel combustion, fertilization, land clearing and biomass burning is occurring over almost the entire world. As an important ecosystem, wetland in industrialized regions has experienced greater rates of nitrogen deposition in recent decades. Our objectives were to determine the effect of increased nitrogen deposition on the diurnal and seasonal variation of soil respiration in a reed (Phragmites australis) wetland and to relate the variation to environmental and biological factors.
Methods From June to October 2012, we conducted a simulated nitrogen deposition field experiment in a reed wetland in the Yellow River Delta, China. The levels of nitrogen deposition were control (CK), low nitrogen (LN) and high nitrogen (HN) with 0, 50 and 100 kg N·hm^-2·a^-1, respectively. Soil respiration was measured during the growing season by using a LI-8100 soil CO₂ efflux system.
Important findings Nitrogen deposition promoted soil respiration in the reed wetland during the entire growing season. Compared with CK, the LN and HN treatments increased the average rates of soil respiration by 19% and 58%, respectively. Surface ponding had a significant effect on the diurnal variation patterns of soil respiration. When there was no surface ponding, the diurnal variation of soil respiration in different treatments all showed “a unimodal” pattern. When surface ponding occurred, the diurnal variation of soil respiration did not show a unimodal pattern or the peak value of soil respiration rate was delayed. In addition, response of soil respiration to air temperature was affected by surface ponding. When there was no surface ponding, soil respiration exhibited a significantly positive exponential relationship with air temperature, which explained 69.9%, 64.5% and 59.9% of the seasonal variation of soil respiration in CK, LN and HN, respectively. However, there was no significant relationship between soil respiration and air temperature when surface ponding occurred. The Q₁₀ (temperature sensitivity coefficients of soil respiration) of CK, LN and HN were 1.68, 1.75 and 1.68, respectively, suggesting that low nitrogen deposition increases the temperature sensitivity of soil respiration and high nitrogen deposition has no significant influence on it.

Aims Our objective was to evaluate (a) the impact of livestock grazing disturbance on physiological traits of Stipa baicalensis and (b) the adaptive mechanisms that S. baicalensis employed.
Methods We investigated the diurnal variations of photosynthetic characteristics, water relations, light energy utilization, photosynthetic apparatus activity and osmotic regulation of S. baicalensis growing in both grazing and enclosed grassland of Hulun Buir, Inner Mongolia.
Important findings Both ribulose-1,5-bisphosphate carboxylase (RUBPCase) and chlorophyll content increased and the direction of electronic chain was altered with grazing, which is beneficial for S. baicalensis to cope with the impact of grazing disturbance by accumulating more assimilates. The midday depression of photosynthesis of S. baicalensis in the enclosed grassland resulted from the decline of RUBPCase carboxylation capacity, which is due to the absence of P. The photochemical quenching (q_P) of S. baicalensis in the grazed grassland is higher, which reflects that it tended to use more absorbed solar energy to improve photosynthetic capacity, which was adaptive to the effects of grazing. Lower leaf water content of S. baicalensis in the grazed field led to the increase of osmotic regulating substances for obtaining sufficient water from the soil. In addition, grazing disturbance promoted the absorption and utilization of N by S. baicalensis. Negative correlation of leaf mass per area (LAM) with photosynthetic nitrogen-use efficiency (PNUE) and photosynthetic phosphorus-use efficiency (PPNE) was observed in the S. baicalensis in both grasslands. Our research demonstrated that various ecophysiological mechanisms were employed by S. baicalensis as adaptive to grazing.

AimsSupratidal zones of sandy coastlines are occasionally influenced by storm surges, and they contain distinctive plant communities and some unique species. Our objective was to solve the questions: 1) how sandy coast plants are grouped into plant communities and 2) how such anthropogenic disturbances as tourist trampling and pond fishery affect such communities.
Methods Three long sandy coasts were investigated for species composition and abundances, representing three typical states of human disturbances: nearly original state, tourist trampling and pond fishery. Each coast was investigated with 20 sampling lines of 50 m. Their species abundance patterns were compared and analyzed via four classic models of species abundance patterns: the neutral theoretical model, geometric series model, overlapping niche model and broken stick model.
Important findings The neutral theoretical and geometric series models fit the species abundance patterns of the coastal plant communities well, and the broken stick and overlapping niche models were not reliable. The disturbances could decrease vegetation cover and cause local extinction of some rare species. Some evidence suggests that plant species on sandy coasts are variable, thus that stochastic establishment of plant individuals may well play a major role in community assembling, as the neutral theory describes. However, these species have very small differences in their traits and resource capturing, and their integrative effects are supposed to take many years to accumulate for ultimately causing evident differences, which can be fitted via the geometric series model at times. Local governments ought to control anthropogenic disturbances, so as to conserve the rare plants.

Aims Arabidopsis thaliana, a widely used model organism in plant biology, is an ideal plant to test the growth rate hypothesis (GRH) and homeostasis theory about plant nutrition. Our objectives are to test i) whether GRH applies to this plant species, ii) how leaf nitrogen (N) and phosphorus (P) of A. thaliana follow the homeostasis theory and iii) whether the allometric relationship between leaf N and P content is consistent with the 3/4 power function (N-P^3/4) for individual plant species.
MethodsBased on a pot experiment in a phytotron with N and P fertilizer additions, we measured the leaf carbon (C), N and P content and leaf biomass of A. thaliana. Specific growth rate (mg·mg^-1·d^-1) was the leaf biomass increment divided by the initial biomass at planting, and by the days after planting. The homeostasis of plant elements is indicated by the exponent (reciprocal of the regulation coefficient) of the power function of leaf nutrient against soil nutrient concentrations.
Important findings P is the limiting nutrient of the culture substrate for A. thaliana, while N fertilization could cause toxic effects in cases of excessive N uptake. The growth of A. thaliana is consistent with GRH—the specific growth rate decreases with increasing leaf N:P or C:P. Leaf P content shows a significant regulation coefficient (3.51) (leaf-P-substrate-P^1/3.51), but leaf N content has no significant relationship with substrate N. There is a significant allometric relationship between leaf N and P content, which is inconsistent with the 3/4 power function (N-P^3/4). The power exponent (0.209) between leaf N content and leaf P content in the P fertilization treatments is significantly lower than the exponent (0.466) in the N fertilization treatments, suggesting that fertilization may affect the allometry between nutrients. Our findings can offer reference for future field studies on plant ecological stoichiometry at scales from species to community to ecosystem.

Impact of rising air temperature on structure and functions of forest ecosystems is potentially a large issue. This paper introduces a large experiment being carried out at Dinghushan Forest Ecosystem Research Station in southern China. We focus on the impact of rising temperature on model forest ecosystems in southern China. The experimental design, its uniqueness and the research contents are illustrated to benefit the design of other related experiments.

Plant-plant interactions play an important role in determining the population dynamics and community structures. Field experiments have highlighted the existence and importance of positive interactions (facilitation) in plant communities. To go beyond the limitations of empirical field studies, mathematical and simulation models have been increasingly used in the facilitation studies. In the present work, based on individual-based simulation models, we explored the effects of positive interactions on population dynamics and community structures. We reviewed the definitions and mechanisms of positive interactions in plant communities and the changes in plant-plant interactions along environmental gradients. Positive interactions are the relationships between plants that benefit at least one of the participants. Positive interactions occur when one plant makes the local environment more favorable for its neighbor either directly (such as by habitat amelioration or resource enrichment), or indirectly (such as by associational defense). The stress gradient hypothesis predicts that the strength or importance of facilitation should increase with the severity of environmental stress. However, a growing number of studies suggested that the stress gradient hypothesis might need further refinement. Using grid-based models and zone-of-influence models as examples, we reviewed individual-based approaches for modeling plant-plant interactions. Furthermore, we focused on the applications of these individual-based simulation models in this field, and summarized the studies on the effects of positive interactions among plants on population dynamics (e.g. biomass-density relationship), spatial pattern and community structures (e.g. community biomass-species richness relationship). We also presented future directions for facilitation research. Further research should focus on deeper understanding of the concepts and mechanisms of positive interactions, new models, new ecological questions of plant populations, communities and ecosystems, and conducting research in the context of global warming.

We discuss standards for the data analysis portion of the materials and methods section of ecology theses. We also comment on statistical questions frequently encountered in ecological theses, including: more effective statistical approaches, correlated dependent variables, heteroscedasticity, statistical significance vs. biology/ecology significance, and pseudo-replication.