通过设置对照(0)、低氮(50 kg N/(hm^2·a))、中氮(100 kg N/(hm^2·a))和高氮(150 kg N/(hm^2·a))4种水平的氮添加实验,研究武夷山米槠(Castanopsis carlesii)径向生长的季节特征及其对模拟氮沉降的短期响应。结果表明,米槠的全年生长可分为水分恢复期、快速生长期和缓慢生长期3个阶段。不同生长阶段对施肥的响应不同,低氮和中氮处理对米槠的全年胸径相对生长速率有显著促进作用,这种影响主要在快速生长期(6—10月)产生,氮添加在缓慢生长期(11—4月)对米槠径向生长无显著影响。氮添加对不同径级树木生长的影响存在差异,低氮和中氮处理显著促进低径级(5 cm25 cm)米槠径向生长无显著响应。中氮处理显著提高研究区内米槠群落的生物量增长速率(p<0.05),其他处理的效果不显著。
In recent decades, there have been a number of debates on climate warming and its driving forces. Based on an extensive literature review, we suggest that （1） climate warming occurs with great uncertainty in the magnitude of the temperature increase; （2） both human activities and natural forces contribute to climate change, but their relative contributions are difficult to quan- tify; and （3） the dominant role of the increase in the atmospheric concentration of greenhouse gases （including CO2） in the global warming claimed by the Intergovernrnental Panel on Climate Change （IPCC） is questioned by the scientific communities because of large uncertainties in the mechanisms of natural factors and anthropogenic activities and in the sources of the increased atmospheric CO2 concentration. More efforts should be made in order to clarify these uncertainties.
Understanding the patterns of forage quantity and quality and investigating the factors influencing these patterns are essential for the development of animal husbandry.However,there is very little field evidence focused on these issues at a large spatial scale.In the current study,we analyzed forage quantity and quality at 177 sites distributed in all the major grassland types across China,and explored the relationship between forage quantity and quality based on consistent sampling protocols.We also investigated potential factors influencing forage quality patterns across China.Our study indicates the Tibetan grasslands had both higher quantity and quality forage than the Inner Mongolian grasslands,and alpine meadow had the best quantity and quality forage because of the meadow's high productivity and the crude protein and nitrogen free extract content of the meadow forage.For the main vegetation formations,Kobresia tibetica meadows and Achnatherum splendens steppes had the highest quantity,while Kobresia pygmaea meadows and Kobresia humilis meadows had the best quality.We also found that although environmental factors,such as temperature and soil fertility,could affect physiological processes and so influence forage quality,the large scale patterns of change were mainly a result of the differences in vegetation types.Finally,we reported a negative relationship between forage quantity and quality:higher forage quantity means more crude fiber but less ether extract and crude protein.These findings improve our understanding on the spatial patterns of forage quantity and quality,and provide solid evidence related to the future development of animal husbandry.
SHI YueMA YinLeiMA WenHongLIANG CunZhuZHAO XinQuanFANG JingYunHE JinSheng
Forests play a leading role in regional and global carbon (C) cycles. Detailed assessment of the temporal and spatial changes in C sinks/sources of China's forests is critical to the estimation of the national C budget and can help to constitute sustainable forest management policies for climate change. In this study, we explored the spatio-temporal changes in forest biomass C stocks in China between 1977 and 2008, using six periods of the national forest inventory data. According to the definition of the forest inventory, China's forest was categorized into three groups: forest stand, economic forest, and bamboo forest. We estimated forest biomass C stocks for each inventory period by using continuous biomass expansion factor (BEF) method for forest stands, and the mean biomass density method for economic and bamboo forests. As a result, China's forests have accumulated biomass C (i.e., biomass C sink) of 1896 Tg (1Tg=1012g) during the study period, with 1710, 108 and 78 Tg C in forest stands, and economic and bamboo forests, respectively. Annual forest biomass C sink was 70.2 Tg Ca-1 , offsetting 7.8% of the contemporary fossil CO2 emissions in the country. The results also showed that planted forests have functioned as a persistent C sink, sequestrating 818 Tg C and accounting for 47.8% of total C sink in forest stands, and that the old-, mid- and young-aged forests have sequestrated 930, 391 and 388 Tg C from 1977 to 2008. Our results suggest that China's forests have a big potential as biomass C sink in the future because of its large area of planted forests with young-aged growth and low C density.
Vegetation dynamics could lead to changes in the global carbon and hydrology cycle,as well as feedbacks to climate change.This paper reviews the response of forest dynamics to climate change.Based on palaeoecological studies,we summarized the features and modes of vegetation response to climate change and categorized the impacts of climate change on vegetation dynamics as three types:climate stress on vegetation,buffer effects by non-climatic factors,and perturbation of the vegetation distribution by stochastic events.Due to the openness of the vegetation system and the integrated effects of both climatic and non-climatic factors,the vegetation-climate relationship deviates far from its equilibrium.The vegetation distribution shows a non-linear response to climate change,which also makes it difficult to quantify the modern vegetation distribution in terms of specific climatic factors.Past analog,space-for-time-substitution and Dynamic Global Vegetation Models(DGVMs)are three approaches to predicting the future vegetation distribution,but they have all been established on the assumption of vegetation-climate equilibrium.We propose that improving DGVMs is a future task for studies of vegetation dynamics because these are process-based models incorporating both disturbance(e.g.fire)and the variability in Plant Functional Types(PFTs).However,palaeoecological results should be used to test the models,and issues like spatial and temporal scale,complexity of climate change,effects of non-climatic factors,vegetation-climate feedback,and human regulation on vegetation dynamics are suggested as topics for future studies.
