Yunqi Wang

Quantifying components of soil respiration and their response to abiotic factors in two typical subtropical forest stands, southwest China.

Separating the components of soil respiration and understanding the roles of abiotic factors at a temporal scale among different forest types are critical issues in forest ecosystem carbon cycling. This study quantified the proportions of autotrophic (R A) and heterotrophic (R H) in total soil (R T) respiration using trenching and litter removal. Field studies were conducted in two typical subtropical forest stands (broadleaf and needle leaf mixed forest; bamboo forest) at Jinyun Mountain, near the Three Georges Reservoir in southwest China, during the growing season (Apr.–Sep.) from 2010 to 2012. The effects of air temperature (AT), soil temperature (ST) and soil moisture (SM) at 6cm depth, solar radiation (SR), pH on components of soil respiration were analyzed. Results show that: 1) SR, AT, and ST exhibited a similar temporal trend. The observed abiotic factors showed slight interannual variability for the two forest stands. 2) The contributions of R H and R A to R T for broadleaf and needle leaf mixed forest were 73.25% and 26.75%, respectively, while those for bamboo forest were 89.02% and 10.98%, respectively; soil respiration peaked from June to July. In both stands, CO2 released from the decomposition of soil organic matter (SOM), the strongest contributor to R T, accounted for over 63% of R H. 3) AT and ST were significantly positively correlated with R T and its components (p<0.05), and were major factors affecting soil respiration. 4) Components of soil respiration were significantly different between two forest stands (p<0.05), indicating that vegetation types played a role in soil respiration and its components.

Quantitative comparison of semi- and fully-distributed hydrologic models in simulating flood hydrographs on a mountain watershed in southwest China

To investigate the performance of fully- and semi-distributed hydrologic models in simulating the process of transformation from rainfall to runoff in mountain areas, the fully-distributed models Basin Pollution Calculation Center (BPCC) and HECHMS are calibrated for the Zhenjiangguan watershed located in the upper stream of Minjiang River Southwest China using streamflow observations at the basin outlet. Semi-automatical optimization method is implemented to both models to improve simulated results by removing artificial errors. Based on the consistency of the simulated hydrographs with the observed ones, the statistical coefficients such as the relative error, the probability distribution and the correlation coefficient, are further introduced to evaluate quantitatively the performance of the two models. Analyses indicate that the hydrographs simulated by the BPCC are relatively closer to the observed ones than those simulated by the HEC-HMS in view of the spatial heterogeneity in terrain, soil texture, land cover and meteorological conditions in mountain areas.

Effects of root spatial distribution on the elastic-plastic properties of soil-root blocks

Plant roots significantly influence soil properties, especially in soil beyond the limited area surrounding the main root stem. Some bias results may be generated if plastic properties of soil are merely used in evaluating slope stability without considering the effects of plant roots. In this research, effects of root spatial distribution on the elastic-plastic characteristics of soil-root blocks were examined. Triaxial tests and the Duncan-Chang model were used to analyze the correlation between root spatial characteristics and soil elastic-plastic properties. Safety factors of vegetated slopes were calculated to investigate the effect of roots on slope stability. The limit stress of remoulded soil was 103.52% to 231.61% greater than undisturbed soil in shallow soil layers. Increased root quantity led to an increased the failure ratio of soil bulk and the initial tangent modulus increased with root diameter. When calculating the safety factor of vegetated slopes, soil indexes for soil beyond the small cylinder surrounding the main stem should be properly considered to avoid safety factor overestimation.

Exploitation of wild Chinese herbs leads to environmental degradation and possible loss of the resource.

B the typical herbs that are used as a source of traditional Chinese medicines are an important substitute for more costly synthetic drugs, they are an important natural resource. Unfortunately, they are mainly distributed in fragile landscapes where it is difficult to harvest the herbs sustainably. Therefore, concealed by the prosperity of the Chinese medicinal herb industry is a huge social and ecological problem that has resulted from the industry’s rapid expansion (Figure 1).

Application of a coupled model of photosynthesis and stomatal conductance for estimating plant physiological response to pollution by fine particulate matter (PM 2.5 )

Fine particulate matter (PM2.5) is a current environmental issue that has an impact on the global ecology. Vegetation is a known sink for PM2.5 deposition but the effects of these particles on plant growth, and specifically on plant photosynthesis by changing their leaf water potential, are still not well understood. This study aimed to determine and characterize possible relationships between PM2.5 and plant photosynthesis under different PM2.5 concentrations. Both indoor and outdoor measurements were carried out to evaluate the variation dynamics of net photosynthetic rate and stomatal conductance of four plant species with different leaf characteristics under different PM2.5 levels. A calibrated coupled model of photosynthesis and stomatal conductance was developed to estimate the relationship between plant photosynthesis and PM2.5 reliably. Net photosynthetic rate and stomatal conductance declined over time at elevated PM2.5, with large variations with PM2.5 concentrations. Using a calibrated model of photosynthesis coupled to stomatal conductance, we show that PM2.5 can influence plant photosynthesis that primarily occurs through the stomata on leaves. Although the effect of particles on plant photosynthesis was not as high as that of photosynthetically active radiation, temperature, and CO2 concentration around the leaf, the effect from PM2.5 can be significant, in particular, in highly polluted atmospheres.

Variation characteristics of nitrogen concentrations through forest hydrologic subcycles in various forests across mainland China

Increased anthropogenic nitrogen emissions and more severe environmental issues (e.g. air pollution, soil acidification, and plant nutrient imbalances) are striking forest ecosystems. Data on concentrations in throughfall and stemflow were collected to estimate variation characteristics of nitrogen concentrations through forest hydrological processes across China. A typical study was carried out in the three forest types in the Jinyun Mountain region of Chongqing, from May to October 2012. Nitrogen concentrations in throughfall and stemflow are higher than those in atmospheric precipitation. DIN concentrations in atmospheric precipitation, throughfall, and stemflow, across China and in the Jinyun Mountain region, were 2.18 and 1.51, 3.19 and 3.88, and 5.14 and 3.92 mg N L−1, respectively. concentration was higher than concentration, suggesting is the dominant nitrogen component in China. Additionally, across China, a linear relationship existed between DIN and , and between DIN and in atmospheric precipitation. DIN concentrations in throughfall and stemflow changed with the observed changes in precipitation, and DIN concentrations in precipitation positively correlated with those in throughfall and in stemflow were also observed. Moreover, average DIN concentrations in throughfall and stemflow varied in different forest types, resulting from differences in forest canopy structures and tree species characteristics. In the Jinyun Mountain region, both throughfall and stemflow DIN concentrations were the highest in the mixed broadleaved/coniferous forest, followed by evergreen broadleaved forest, and the lowest in moso bamboo forest. Monthly variations of concentrations, in throughfall and stemflow, were observed in the Jinyun Mountain region.

Evaluation of Critical Sulfur Loads based on Weathering Rate Modeling in Three Gorges Reservoir Area, China.

This study developed a new empirical model to reduce the number of parameters required to assess the weathering rate and to facilitate its accurate calculation. The critical loads of sulfur were assessed based on the weathering rate calculated using the empirical model. Seven types of soil were studied in five districts of the Three Gorges Reservoir Area, i.e., yellow soil, rice soil, purple soil, yellow brown soil, yellow rendzina, brown soil, and yellow-red soil. A PROFILE model combined the soil properties to perform a regression analysis and filter appropriate parameters for establishing the empirical model. Finally, the silt and pH levels were selected. The weathering rates varied from 0.27 to 2.21 keq ha1 yr−1 in the empirical model. The coefficient of determination was relatively high (R2 = 0.653) for the weathering rates obtained using the empirical model and the PROFILE model test. Thus, the empirical model could predict the weathering rates better in the study area. The critical loads of sulfur were relatively high and ranged from 2.35 to 4.83 keq ha−1 yr−1 based on the weathering rates calculated using the empirical model. Compared with other acid rain areas, the risk of soil acidification is relatively low in this region. However, we should remain aware of the harmful effects of acidic substances.