Some hot topics in plant physioecology research have recently made regular appearances in a number of important international journals (Science, Nature, etc. ). These describe the responses of plant physioecology and growth to factors such as: increasing CO2 concentration, ultraviolet radiation enhancement, changes in temperature, sunlight irradiation and the enlargement of salty habitats. All of these factors are closely associated with the processes of global climate change. Some of the research, however, aims to investigate the response of plants to existing environmental stresses in specialised environmental habitats. Among the intensive studies, the carbon budget of terrestrial ecosystems is one of the hottest topics, research conducted recently, including: the emission of greenhouse gasses, sink and source dynamics of carbon at regional and global scales and the function of the terrestrial and oceanic ecosystems. Although the responses of C3 and C4 species to elevated CO2 are still the main topics in most journals, there has been much progress in study of CAM functional types. Progress in the application of new technologies such as stable isotope methods, free air CO2 enrichment (FACE) facilities, and chlorophyll fluorescence technology have helped greatly in understanding these general problems.

Photosynthetic capabilities of 12 different genotypes of Triticum aestivum L. were studied, including 2 cultivars from Beijing area. The results showed that net photosynthetic rate (Pn) of cultivars Xiaoyan 22,Shanmai897 and 8901-11-5 exceeded 20 μmol CO2·m-2·s-1,and were higher than the other cultivars studied. The overall photochemical quantum yield of PSII (Yield),the coefficient of photochemical fluorescence quenching (qP) and the water use efficiency (WUE) of these three cultivars were also higher. While their dark respiration rates (Rd) and coefficients of non-photochemical fluorescence quenching (qN) were lower. The results illustrated that the photosynthetic and physiological functions of three cultivars mentioned above were by far the best among the 12 tested cultivars ,and that these parameters had a pattern of chain interrelations. It is suggested that if winter wheat cultivars from other parts of the country are to be introduced into Beijing area as field-grown cultivars or as parent material for hybrid breeding, the above three cultivars should take top-priority of among 10 cultivars we studied.

Net assimilation rate, transpiration rate and water use efficiency of endophyte-infected (EI) and endophyte-free (EF) populations of Lolium perenne were determined under drought stress so as to investigate the effect of endophyte infection on the host plant. The physiological characteristics of L. perenne populations depended much on drought stress levels, and the effects of endophyte infection were significant under prolonged severe stress. 1) At the late stage of severe drought stress, the EI populations assimilated CO2 at a significantly higher rate than the EF populations. After rewatering, however, there were no significant differences between the two populations 2)Transpiration rate of the populations was more affected by drought stress than endophyte infection. 3) Only at the later stage of severe drought stress, was the water use efficiency of the EI populations higher than that of the EF populations.

The effects of simulated acid rain on important N-metabolism enzymes and correlated substances were studied by treating spring and summer leaves of Eucommia ulmoides to simulated rain with varying pH levels. In both seasons it was found that below a threshold value of pH the activities of nitrate reductase (NR), glutamine synthetase (GS), glutamate dehydrogenase (GDH) and glutamic-pyruvic transaminase (GPT) declined with decreasing pH, though the rate of decrease of these enzymes were higher in the summer. It was also found that soluble protein and total nitrogen content decreased with decreasing pH of acid rain. Total free amino acid content was negatively correlated with pH in both seasons. We conclude from these results that simulated acid rain had significant effects on N-metabolism of Eucommia ulmoides leaves.

Research on the restoration and reconstruction of disturbed wetland vegetation has increased since the 1990s. From this now copious literature, we summarize the objectives, techniques for prioritization of sites, strategies, theories, methods, long-term monitoring, and evaluation of wetland restoration. The restoration techniques of bog and fen peatlands are particularly emphasized. Repairing and rebuilding were the two main strategies for wetland restoration, and the key theories of secondary succession, self-design and invasion guided the restoration practice. The main techniques for restoring disturbed peatland vegetation were the sowing of seed, spreading of Sphagnum fragments, transplanting of higher plants and blocks, etc. The seed (or propagule) bank also played an important role in vegetation restoration. Nurturing and management at the early stages of restoration were clearly necessary. Two problems in wetland restoration that need urgent attention are highlighted in the discussion.

Vegetation coverage, the ratio of vegetation occupying a unit area, is a very important parameter in the development of climate and ecological models. On-ground fieldwork surveys of vegetation coverage are time consuming and expensive and produce low-precision results. Estimation of vegetation coverage from remote sensing data may be a more efficient approach. This study explores the potential of deriving vegetation coverage from normalized difference vegetation index (NDVI) using remotely sensed data. As each pixel of a TM image represents a mosaic of structures on the ground, sub-pixel models for vegetation coverage estimation are proposed. The utility of different sub-pixel models for vegetation coverage estimation based on land cover classification is also described. The accuracy of vegetation fraction estimation using this model is high. Vegetation coverage of Haidian district in 1975, 1991 and 1997 were modelled using this method in Beijing. The spatio-temporal patterns of change in vegetation coverage and its driving processes during this period are also discussed in this paper.

About 7.0 Pg (1 Pg=109 t) of carbon is annually released to the atmosphere from fossil fuel combustion and the buring and clearance of tropical forests, of which 3-3.4 PgC of the carbon adds to the atmospheric carbon pool and about 2.0 PgC is uptaken by oceans. The terrestrial biosphere is considered to hold its carbon dynamic in balance with approximately equal rates of sequestration and emission. Therefore 1.6 to 2.0 PgC per year is unattributed and this is known as the ’missing sink’. Many studies, including the monitoring of atmospheric components, analysis of forest inventories, CO2 flux measurements and modeling simulations, have suggested that the mid- and high latitude terrestrial ecosystems of the Northern Hemisphere are functioning as a significant carbon sink, though with a large uncertainty and considerablly spatio-temporal heterogeneity. Global warming, CO2 fertilization, increasing nitrogen and phosphorus deposition, and the expansion and re-growth of forests are major factors impacting the size and distribution of these carbon sinks. Study on the role of soils in the carbon cycles-as well as long-term monitoring and improvement of existing carbon model simulations is a critical step required to reduce uncertainty in the size of this sink.

A simulation model of canopy radiation was developed for the calculation of within-and between-tree shading. The model accounts for the canopy structure of an even-aged plantation on a sloping site and heterogeneity of leaf area density within tree crowns. It can be used to simulate instantaneous radiation at any point within crowns, the direct, diffuse and scattered fractions as well as daily radiation within 1 hour time steps. Canopy photosynthetic productivity can also be simulated with the radiation model

Soil seed banks of different ecosystems subject to different disturbances were studied in a dry valley prone to debris flow in Northern Yunnan. It was found that variation in the type of disturbance had a strong effect on the density and composition of the soil seed bank. Restoration with a Leucaena glauca plantation(with over 6 years free of disturbance from humans or domestic animals) increased the seed bank density and the dominant species changed from aridity-tolerant to shade-tolerant species. Seed bank density and the variety of species was reduced in an annually cut Coriaria sinica plantation, though the composition of the seed bank remained constant. Landslides and soil erosion had a negative effect on seed bank density and species types as many seeds were removed from the soil. Debris flow created the greatest disturbance as it destroying both the soil surface and seed bank.

Although ecologists have made great efforts and produced a large number of hypotheses and models attempting to explain species coexistence and the mechanisms of species diversity maintenance in plant communities, this problem remains unresolved. We investigate relationships between species diversity and the patterns of realized niche distribution of species along five soil resource gradients (C, N, P, K and H2O) in a species-rich Leymus chinensis herb meadow community, on the Songnen Plain of Northeast China. The results showed that despite niche differentiation between species, the degree of niche overlap between species was high. We present a mechanism for coexistence deriving from small-scale pattern competition. However, we must conclude that niche differentiation cannot solely account for maintenance of species diversity in this grassland community, and that greater attention should be paid to the longterm co-evolution of species biological properties.