Showing papers by "Wenxuan Han published in 2013"

Enhanced nitrogen deposition over China

Abstract: Data on bulk nitrogen deposition, plant foliar nitrogen and crop nitrogen uptake in China between ad 1980 and ad 2010 show that the average annual bulk deposition of nitrogen increased by approximately 8 kilograms of nitrogen per hectare during that period and that nitrogen deposition rates in the industrialized and agriculturally intensified regions of China are as high as the peak levels of deposition in northwestern Europe in the 1980s. Atmospheric nitrogen emissions have increased substantially since the beginning of the industrial revolution, and the resulting deposition of nitrogen can have detrimental effects on human and ecosystem health. But little is known about the magnitude and environmental consequences of nitrogen deposition in today's fastest growing economy, China. This paper reports that average annual bulk deposition of nitrogen increased by 8 kg of nitrogen per hectare from the 1980s to the 2000s. Ammonium is the dominant form of nitrogen in bulk deposition, whereas the rate of increase is largest for nitrate deposition. Nitrogen deposition has also increased plant foliar nitrogen concentrations in semi-natural ecosystems and has elevated crop nitrogen uptake in long-term unfertilized croplands. China is experiencing intense air pollution caused in large part by anthropogenic emissions of reactive nitrogen1,2. These emissions result in the deposition of atmospheric nitrogen (N) in terrestrial and aquatic ecosystems, with implications for human and ecosystem health, greenhouse gas balances and biological diversity1,3,4,5. However, information on the magnitude and environmental impact of N deposition in China is limited. Here we use nationwide data sets on bulk N deposition, plant foliar N and crop N uptake (from long-term unfertilized soils) to evaluate N deposition dynamics and their effect on ecosystems across China between 1980 and 2010. We find that the average annual bulk deposition of N increased by approximately 8 kilograms of nitrogen per hectare (P < 0.001) between the 1980s (13.2 kilograms of nitrogen per hectare) and the 2000s (21.1 kilograms of nitrogen per hectare). Nitrogen deposition rates in the industrialized and agriculturally intensified regions of China are as high as the peak levels of deposition in northwestern Europe in the 1980s6, before the introduction of mitigation measures7,8. Nitrogen from ammonium (NH4+) is the dominant form of N in bulk deposition, but the rate of increase is largest for deposition of N from nitrate (NO3−), in agreement with decreased ratios of NH3 to NOx emissions since 1980. We also find that the impact of N deposition on Chinese ecosystems includes significantly increased plant foliar N concentrations in natural and semi-natural (that is, non-agricultural) ecosystems and increased crop N uptake from long-term-unfertilized croplands. China and other economies are facing a continuing challenge to reduce emissions of reactive nitrogen, N deposition and their negative effects on human health and the environment.

Leaf nitrogen and phosphorus concentrations of woody plants differ in responses to climate, soil and plant growth form

Abstract: Leaf chemistry is important in predicting the functioning and dynamics of ecosystems As two key traits, leaf nitrogen (N) and phosphorus (P) concentrations set the limits for plant growth, and leaf N:P ratios indicate the shift between N- and P-limitation To understand the responses of leaf chemistry to their potential drivers, we measured leaf N and P concentrations of 386 woody species at 14 forest sites across eastern China, and explored the eff ects of climate, soil, and plant growth form on leaf N, P and N:P ratios In general, leaf N and P were both negatively related to mean annual temperature and precipitation, and positively related to soil N and P concentrations Leaf N:P ratios showed opposite trends General linear models showed that variation in leaf N was mainly determined by a shift in plant growth form (from evergreen broadleaved to deciduous broadleaved to conifer species) along the latitudinal gradient, while variations in leaf P and N:P were driven by climate, plant growth form, and their interaction Th ese diff erences may refl ect diff erences in nutrient cycling and physiological regulations of P and N Our results should help understand the ecological patterns of leaf chemical traits and modeling ecosystem nutrient cycling

Relationship between the Relative Limitation and Resorption Efficiency of Nitrogen vs Phosphorus in Woody Plants

Abstract: Most previous studies have ascribed variations in the resorption of a certain plant nutrient to its corresponding environmental availability or level in tissues, regardless of the other nutrients' status. However, given that plant growth relies on both sufficient and balanced nutrient supply, the nutrient resorption process should not only be related to the absolute nutrient status, but also be regulated by the relative limitation of the nutrient. Here, based on a global woody-plants dataset from literature, we test the hypothesis that plants resorb proportionately more nitrogen (or phosphorus) when they are nitrogen (or phosphorus) limited, or similar proportions of nitrogen (N) and phosphorus (P) when co-limited by both nutrients (the relative resorption hypothesis). Using the N:P ratio in green foliage as an indicator of nutrient limitation, we found an inverse relationship between the difference in the proportionate resorption of N vs P and this foliar N:P ratio, consistent across species, growth-forms, and vegetation-types globally. Moreover, according to the relative resorption hypothesis, communities with higher/lower foliar N:P (more likely P/N limited) tend to produce litter with disproportionately higher/lower N:P, causing a worsening status of P/N availability; this positive feedback may somehow be counteracted by several negative-feedback mechanisms. Compared to N, P generally shows higher variability in resorption efficiency (proportion resorbed), and higher resorption sensitivity to nutrient availability, implying that the resorption of P seems more important for plant nutrient conservation and N:P stoichiometry. Our findings elucidate the nutrient limitation effects on resorption efficiency in woody plants at the global scale, and thus can improve the understanding of nutrient resorption process in plants. This study also suggests the importance of the foliar N:P ratio as a key parameter for biogeochemical modeling, and the relative resorption hypothesis used to deduce the critical (optimal) N:P ratio for a specific plant community.

Resorption proficiency and efficiency of leaf nutrients in woody plants in eastern China

Abstract: Aims (i) t o explore variations in nutrient resorption of woody plants and their relationship with nutrient limitation and ( ii) to identify the fac- tors that control these variations in forests of eastern china. Methods We measured nitrogen (N) and phosphorus (P) concentrations in both green and senesced leaves of 172 woody species at 10 for - est sites across eastern china. We compared the nutrient resorption proficiency (Nu r P) and efficiency (Nu r E) of N and P in plant leaves for different functional groups ; we further investigated the latitudi - nal and altitudinal variations in Nu r P and Nu r E and the impacts of climate, soil and plant types on leaf nutrient resorptions. Important Findings

Species richness patterns and water-energy dynamics in the drylands of Northwest China.

Abstract: Dryland ecosystems are highly vulnerable to climatic and land-use changes, while the mechanisms underlying patterns of dryland species richness are still elusive. With distributions of 3637 native vascular plants, 154 mammals, and 425 birds in Xinjiang, China, we tested the water-energy dynamics hypothesis for species richness patterns in Central Asian drylands. Our results supported the water-energy dynamics hypothesis. We found that species richness of all three groups was a hump-shaped function of energy availability, but a linear function of water availability. We further found that water availability had stronger effects on plant richness, but weaker effects on vertebrate richness than energy availability. We conducted piecewise linear regressions to detect the breakpoints in the relationship between species richness and potential evapotranspiration which divided Xinjiang into low and high energy regions. The concordance between mammal and plant richness was stronger in high than in low energy regions, which was opposite to that between birds and plants. Plant richness had stronger effects than climate on mammal richness regardless of energy levels, but on bird richness only in high energy regions. The changes in the concordance between vertebrate and plant richness along the climatic gradient suggest that cautions are needed when using concordance between taxa in conservation planning.

Effects of nitrogen and phosphorus fertilization on leaf carbon, nitrogen and phosphorus stoichiometry of Arabidopsis thaliana

Abstract: 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. Methods Based on a pot experiment in a phytotron with N and P fertilizer additions, we measured the leaf car- bon (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 ele- ments 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 sig- nificant 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.

Response of carbon dioxide emissions to sheep grazing and nitrogen application in an alpine grassland

Abstract: Introduction Conclusions References