Tropical rain forest trees often experience several episodes of different light environments during their growth from seedlings into canopy trees, such as in canopy gaps with high irradiance and in forest understorey with very low irradiance. Shade tolerant trees usually have low photosynthetic capacities and low plasticity in photosynthetic acclimation to different light environments. They may suffer from excess light when growing in high light environment, resulting in photoinhibition and photoxidation. Also, when forest understorey plants are suddenly exposed to high irradiance such as canopy gap creation, they may suffer severe photodamage. Plants have two major mechanisms to prevent photodamage, i.e., thermal dissipation through the development of an increased transthylakoid pH gradient and xanthophyll cycle, and antioxidant system to scavenge oxygen free radicals resulting from excess light energy. When growing in high light, plants may increase photosynthetic energy utilization or increase photoprotection capacities or both. This study investigated the effect of growth light level on the capacities of photosynthesis, heat dissipation and antioxidation in seedlings of two tropical rainforest tree species, Pometia tomentosa (Sapindaceae), an important canopy species, and Horsfieldia tetratepala (Myristicaceae), a subcanopy species. The seedlings were cultivated under shading nets with three different light levels, i.e. 100%, 25% and 8% daylight, respectively. The maximum photosynthetic rate (Pmax) of P. tomentosa increased with the growth light level. In contrast, Pmax of H. tetratepala grown in 100% daylight was smaller than that in 25% daylight. Under either 100% or 8% daylight, P. tomentosa had larger Pmax values than H. tetratepala. The values of both photosynthetic light saturation point and chlorophyll content per unit mass increased with growth light level for both species, and under the same light levels, P. tomentosa had greater values than H. tetratepala. Chlorophyll a/Chlorophyll b ratios were not significantly different for both species under the three different light levels; however, P. tomentosa had significantly larger values than H. tetratepala. Compared to the shaded situations, in the fully open site, the maximum photochemical efficiency of photosystem II (Fv/Fm) of both species were reduced, indicating that sustained photoinhibition occurred in the seedlings grown under full sun. When the shaded seedlings were transferred to full sun, on the first day, photoinhibition (as indicated by the decrease of ΔF/Fm′) accelerated from dawn to noon, and the recovery from photoinhibition occurred gradually in the afternoon but was not completed until sunset in P. tomentosa seedlings from the 8% daylight site and in H. tetratepala seedlings from both 8% and 25% daylight sites. The light response curves of non-photochemical quenching showed that heat dissipation capacity of H. tetratepala increased with growth light level. Whereas, P. tomentosa had lower heat dissipation capacity in the fully open site compared to in shaded sites. In the fully open site and in 25% daylight site, P. tomentosa had lower heat dissipation capacity than H. tetratepala. The contents of O-[]·2, H2O2 and activities of SOD and CAT in the seedlings in the open site were the greatest for both species, and these were higher in P. tomentosa than in H. tetratepala under the same light levels. With the pooled data from both species under all light levels, there were significantly correlations among O-[]·2, H2O2 content, and SOD and CAT activities. This indicated that oxygen free radicals in seedlings were scavenged through the enhancement of activities of antioxidative enzymes. The present study shows that the canopy species P. tomentosa has higher photosynthetic plasticity but lower thermal dissipation capacity compared to the subcanopy species H. tetratepala. Under photoinhibitory conditions, the photoprotection of P. tomentosa was more dependent on the enhancement of activities of antioxidative enzymes, while H. tetratepala was more dependent on the non_radiative heat dissipation. H. tetratepala showed poor acclimation to grow in fully open sites.

In the 1970s’, by exploiting the poorly understood phenomenon called heterosis (first generation of hybrid plants is typically more vigorous and productive than either parent) in rice, China had improved the yield of rice in F1 hybrid 20%-30% more than either parent and has since then played the leading role in hybrid rice research and production. In order to further improve rice yield to feed the increasing population, China had carried out the “super high-yield rice project” since 1996. Tremendous progress was made during the “ninth five-year plan” and several new varieties of the rice hybrids with “super-high” yield released. Liang-youpeijiu (Pei-ai64S × 9311) and Hua-an3 (X07S × Zihui100) were two of such varieties, both with a yield of more than 10 500 kg·hm-2, compared with the traditional rice hybrid Shanyou63 (Zhenshan97A × Minghui63) with a yield of about 7 500-8 250 kg·hm-2. The two super high-yield rice hybrids had a 20%-30% higher yield. The photosynthetic characters, pigments content, net photosynthesis rate and water use efficiency of the different developmental stages of Liangyoupeijiu and Hua-an3, and the traditional hybrid rice Shanyou63 were studied. The results showed that at the seedling stage, no significant difference in the content of chlorophyll per leaf area was observed among the three rice hybrids, while the carotenoid content of Shanyou63 was the highest. The chlorophyll content and carotenoid of the two super high-yield rice hybrids were higher than that of Shanyou63 at the tillering stage, especially in the flag leaves of the heading stage. The net photosynthesis rate (Pn) of the two super high-yield rice hybrids were higher than that of Shanyou63 from seedling stage to heading stage, especially under the midday strong sunlight of the seedling stage and under the twilight of tillering and heading stages. The water use efficiency of the Shanyou63 was slightly higher than that of the super high-yield rice hybrids at seedling stage, but was lower at tillering and heading stages. The physiological basis of their higher yield in the super high-yield rice hybrids could be attributed to the fact that they had a higher net photosynthesis rate, higher resistance to photoinhibition, and also used the dim sunlight effectively, as seen in our results. The higher water use efficiency of the super high-yield rice hybrids at tillering and heading stages indicates economical use of water.

The atmospheric CO2 concentration is predicted to double to 700 μl·L-1 during this century. The effect of doubled atmospheric CO2 on higher plants has been studied extensively, but little is known for aquatic plants, especially freshwater bloom-algae. In order to study the impacts of elevated atmospheric CO2 concentration on freshwater bloom-algae, Anabena flos-aquae was cultured with doubled CO2 concentration (700 μl·L-1) and its growth, photosynthesis and chlorophyll and fluorescence were investigated. Atmospheric CO2 enrichment increased the biomass by 50% at the end of culture in comparison with the ambient CO2 concentration (350 μl·L-1). Light-saturated photosynthetic rate, photosynthetic efficiency and photochemical efficiency of PSⅡ (Fv/Fm) of Anabena flos-aquae also increased by CO2 enrichment. However, elevated atmospheric CO2 concentration had no significant effect on the dark respiration and light-saturated points. The photosynthetic affinity for Dissolved Inorganic Carbon (DIC) reduced when the cells were grown in CO2 enriched conditions, which implies that HCO-3 utilization was depressed. It was concluded that elevated atmospheric CO2 concentration resulted in the increasing biomass, which is due to the elevated photosynthetic rate.

A network of ion channels, which controls stomatal movements, has been well characterized in the plasma and vacuolar membranes of guard cells. However, it is still not clear how water flows through the membranes to regulate guard cell volumes. Water channels, which can specifically and quickly promote the transportation of water, have been found in the plasma and vacuolar membranes of guard cells. It is suggested that water may flow through water channels during stomatal movements and water channels may be involved in stomatal movements with ion channels. Broad bean (Vicia faba L.) was grown in pots and watered every three days to keep the soil moisture level at 80%±5% soil water capacity. Three-week-old fully expanded leaves were harvested. The abaxial epidermis was peeled off and soaked in the MES/KOH buffer containing different salts in different concentrations. Stomatal movements and states were observed and open stomata/total stomata ratios recorded from randomly selected fields under the microscope. Stomatal movements appeared to be inhibited by the addition of HgCl2 at 0.8 mmol·L-1 concentration, while LaCl3 (at 0.5 mmol·L-1) or TEACl (at 5 mmol·L-1) (Tetraethylammonium chloride) had little effect. The effect of HgCl2 could beneutralized by 5 mmol·L-1 β-mercaptoethanl (ME). Stomatal movements were almost completely inhibited under HgCl2+LaCl3, HgCl2+TEACl, or HgCl2+LaCl3+TEACl treatments LaCl3, as Ca2+ channel blocker, could affect stomatal movements by the inhibition of the changes of guard cell cytosolic Ca2+ concentration or the blockage of Ca2+ signal transduction pathway. TEACl, as K+ channel blocker, inhibited the changes of guard cell cytosolic K+ concentration to affect stomatal movements. HgCl2 affected stomatal movements by the inhibition of water channels. All of them were involved in the regulations of water fluxes between guard cells and mesophyll cells directly or indirectly and affected stomatal movements significantly. Data appeared that they affected stomatal movements by HgCl2>>LaCl3>TEACl. Above results suggested that the environmental factors might affect stomatal movements in two ways: i) water channels activities were regulated and water flowed quickly across the membranes to control guard cell volumes. Some special stomatal movements, such as stomatal oscillation, could happen in this way; ii) ion channels activities were regulated and ions flowed across the membranes to change the osmotic or water potentials. Here water flows were transported with ion fluxes by co-transport or anti-transport. Previous studies have proposed pathways for regulating stomatal movements from the point of view of ions. However, from our study, it is evident that water channels may play an important part in regulating stomatal movements.

Traditional singletree water consumption acquired by means of the scaling-up method from leaflet transpiration measurement, caused serious deviation to the very value. The whole tree water consumption by crown transpiration is closely approximated to the same of sap flow rate in the trunk sapwood which was measured by thermal dissipation probe (TDP) implanted in the trunk. The forest community water consumption can be acquired by scaling-up of singletree water consumption. Spatial-and-temporal sap flow velocity (SFV) fluctuation in the sapwood at lower and upper trunk position of Quercus variabilis and Pinus tabulaeformis, and other meteorological factors, such as solar radiation intensity, air humidity, air temperature, wind speed and soil temperature were measured in a 48 year-old mixed stand at an east hill slope, in the Forest Research Station of Beijing Forestry University in the West Mountains of Beijing (N 39°54′, E 116°28′) in May, 2001. The main elements of sap flow ascending force were transpiration pulling tension (which was determined by crown transpiration) and capillary tension (which was determined by the capillary diameter). Patterns of daily and diurnal SFV fluctuation of the two tree species were quite different. Diurnal SFV fluctuation of Q. variabilis appeared “ascend promptly in the morning (5:30 -10:00 am) and get the peak in the afternoon （13:00-16:00）, then descend slowly and reach the valley during the night”. SFV in upper trunk of Q. variabilis was much higher than that in the lower trunk, and the peak and valley appearing time in the upper trunk were much more early than that in the lower trunk, too. SFV and its rhythm of P. tabulaeformis were different to that of Q. varaibilis during the measuring season with the daily crest appeared in the early morning (4:20-8:00) and went down to the valley in the mid-day (11:00-14: 20). Daily SFV peak height of P. tabulaeformis was only one fourth of Q. variabilis. Fluctuation of solar radiation intensity, air temperature, and air humidity appeared a similar rhythm to the SFV of Q. variabilis, and indicated that there was a close relation between SFV and the meteorological factors. Problems existed in the SFV measurements were discussed in this paper.

Biomass allocation, resources use and competitive pattern, the main contents in plant inter-and intra-specific competition research provide insight into the mechanism driving natural vegetation change and therefore, for better silviculture practices. In this study, we chose Amur linden (Tilia amuransis Rupr.), a dominant canopy species of the Pinus koraiensis coniferous-broadleaved forest and a commercially valuable species to address the following issues: (1) the aboveground and underground biomass allocation of Amur linden under different planting distance; (2) quantifying the effect of below-and above-ground biomass on the total biomass of the seedling; (3) to compare the allocation (or consumption) of aboveground and belowground resource in the inter-and intra-specific competition of Amur linden and Larix spp.; (4) analyzing the resource use and the competition pattern of the seedling.Experiments were designed for cultivated Amur linden juvenile pure and its mixture with Larix spp. Respectively on a sand groundmass (10 m (length), 20 m (width)， 1 m (depth)) under different planting distance (including 10, 20, 30, 40 cm) in May 1997 at Mao’ershan experiment station of Northeast Forestry University, Heilongjiang province, China. The seedlings were watered and fertilized regularly to maintain growth under limited resources. At the end of September 1999, the seedling leaves, stems and roots were harvested and weighed separately to obtain the wet and dry biomass. Path analysis was applied to quantify the effect of below-and above-ground biomass on the total biomass of the seedlings, to determine the resource use and the competition pattern of the seedlings. Path analysis is a linear regression where the regression coefficient is standardized to decrease the correlativity among independents. Hence it may be applied to quantify the direct and indirect influence from the related belowground and aboveground growth to the total growth of Amur linden, and compare the relative importance of the two dependents to the independent.The biomass of root, stem, and leaf of the Tilia increased with growth space increase, with the exception of the 10 cm planting distance. Through path analysis, the contribution of belowground roots to the total growth is 0.236 1-0.286 9, that of stem and leaf is 0.732 5-0.775 8, which is 2.95 times of the former. The biomass between Tilia amurensis and Larix spp. differed significantly. The biomass of roots, stems and leaves of Larix spp. was approximately 2, 5, 4 times greater than those of the mixed Tilia amurensis. Through comparison of the direct path coefficient between mono-culture and mixed-culture experiment, we found that the competition ability of Tilia amurensis for underground water and nutrients was decreased by 36.84% and that for light and space was increased by 11.63% after mixed with Larix spp. The influence of the Larix spp. on Tilia amurensis increased with decrease in growth space. The influence from the intra-specific competition of Larix spp. on Tilia amurensis was not notable in terms of root growth while the growth of stem and leaf was influenced significantly only within the limited growth space in our experiment. The intra-specific competition of Tilia amurensis and Larix spp. is the interaction of two species which belong to different grade for resource utilization respectively. Although Larix spp. has a larger root system, Tilia amurensis still can acquire underground water and nutrients proportional to its size and can equally possess underground space through symmetric competition, so there is less underground competition from Larix spp. In aboveground competition, Larix spp. with its spatial advantage for aboveground growth, can asymmetrically compete the aboveground resource, by interception and capture more light from Tilia amurensis, which affects the growth of Tilia amurensis in limited spatial range.

The biosphere and land vegetations are the material foundation on which human being live, and which provide us valued resources, such as food, medicinal materials, and original materials. Therefore, the net primary productivity　(NPP) is the main character

Xishuangbanna, located in southwest China, bounded by Laos and Myanmar on the upper Mekong River, is on the northernmost edge of tropical Asia. As a result, a mosaic distribution of tropical seasonal rain forest, which mainly appears in the wet valleys, usually with small streams or on the low hills and flats below 1000 m altitude exists in Xishuangbanna. The tropical seasonal rain forest in Xishuangbanna is rich in species and has a complex forest canopy and structure. In 1999, 119 species with DBH>10 cm were recorded in the 1 hm2 study plot. Based on the “small catchment” approach and input-output budgets, we studied on the nitrogen cycling in the seasonal rain forest. The nitrogen stock in the seasonal rain forest ecosystem (6 481.2 kg·hm-2) was higher than that of montane rain forest in Hainan of China (6 345 kg·hm-2), but lower than montane rain forest in New Guinea (20 190 kg·hm-2), lowland rain forest in Brazil (7 537 kg·hm-2), and lowland rain forest in Ghana (7 230 kg·hm-2). The distribution of the nitrogen stock in the seasonal rain forest ecosystem is as follows: 970.9 kg·hm-2 (15.0%) in the living biomass, 37.7 kg· hm-2 (0.6%) in the forest floor, and 5 481.2 kg·hm-2 (84.4%) in the soil (0-30 cm). We found that most of the nitrogen in the seasonal rain forest was stored in the soil, but not in the living biomass. Soil (0-10 cm) net nitrogen mineralization rate was 90.4 kg·hm-2·a-1. Soil played a very important role of stocking and providing N to plants. The nitrogen content in precipitation, throughfall, stemflow and stream flow were 0.565, 0.828, 0.983 and 1.042 mg·dm-3, respectively. The nitrogen input from precipitation, throughfall and stemflow were 8.89, 10.97 and 3.57 kg·hm-2·a-1, respectively. The nitrogen output in stream flow was 5.95 kg·hm-2·a-1. The nitrogen net increase in the seasonal rain forest was 2.94 kg·hm-2·a-1. In the nitrogen biological cycling, 149.86 kg·hm-2·a-1 was taken up by plants，69.30 kg·hm-2·a-1 stored in living biomass，and 80.56 kg·hm-2·a-1 returned to soil. This undisturbed seasonal rain forest had the nitrogen conservation mechanism and remained in the nitrogen accumulation state.

Arsenic contamination in soil is a severe environmental problem. Currently, there is economical and effective remediation technique for arsenic. The study of using tolerant and hyper-accumulating plants to remediate heavy metal contaminated soils, termed

Quercus liaotungensis is a special species in China as an oak forest tree species, as well as one of the dominant species in the deciduous broad-leaved forest in the warm temperate zone. Gomphidius viscidus and Russula foetens are the ectomycorrhizal fungi which can symbiose and form ectomycorrhizae with Q. liaotungensis in the field. The effects of these two kinds of ectomycorrhizae on the growth of seedlings of Q. liaotungensis were studied in this paper. The seeds of Q. liaotungensis were planted in pots and grown to seedlings in the greenhouse. Five different kinds of inoculation were carried out with G. viscidus and R. foetens to form ectomycorrhizae as follows: CK, non-inoculation; Gv, inoculation with G. viscidus; Rf, inoculation with R. foetens; G-R, inoculation with G. viscidus in one side of the pot and with R. foetens in the other side; G/R, inoculation with a mixture of G. viscidus and R. foetens. After 3 months of inoculation, the height, biomass, root/shoot ratio, net photosynthetic rate, transpiration rate and nitrogen and phosphorus content of the mycorrhizal seedlings and non-mycorrhizal seedlings were measured and compared. All of these results show that ectomycorrhizae can significantly promote the growth of Q. liaotungensis seedlings. The biomass, height, photosynthetic rate and water use efficiency of the mycorrhizal seedlings are higher, but the transpiration rate is lower, than those of non-mycorrhizal seedlings. Nitrogen and phosphorus content in mycorrhizal seedlings are significantly higher than non-mycorrhizal seedlings, being 1.7 and 2.2 times higher, respectively. Ectomycorrhizal formation also changes the allocation ratio of nitrogen and phosphorus to organs of seedlings. Compared with non-mycorrhizal seedlings, nitrogen and phosphorus ratio in the stem of mycorrhizal seedlings decreased, but phosphorus ratio in leaves of mycorrhizal seedlings increased. The acceleration is different among the four kinds of inoculation. Gv is similar to Rf, but Rf is a little higher. The biomass of G-R is significantly higher than Gv and Rf, and the biomass of G/R is higher than G-R. These results demonstrate that co-inoculation with G. viscidus and R. foetens significantly promotes the growth of seedlings, compared to inoculation with G. viscidus or R. foetens alone.

Utilizing the data of the intensive observation period (May-June 2000) in Dunhuang oasis of Dunhuang land-surface process field experiment that belongs to “Land-atmosphere Interactive Field Experiment over Arid Region of Northwest China”, the radiation budget, energy balance and microclimate at surface in Dunhuang oasis are analyzed systemically. It is found that, (a) the short-wave irradiance at surface in Dunhuang oasis is very high and can reach 1 038.1 w·m-2, (b) the surface net radiation can exceed 600 w·m-2, (c) the daily-integral values of sensible heat flux, latent heat flux and soil heat flux are in same order of magnitude, and (d) soil heat flux is larger than latent heat flux and is almost in same order of magnitude, in the partition of surface energy. The daily-integrated values of the short-wave irradiance, downward long-wave, upward long-wave and reflection radiation over Dunhuang oasis are 31.17, -36.15, 27.51 and -8.08 MJ·m-2·d-1, respectively. The daily integration of the net radiation is 14.53 MJ·m-2·d-1, and accounts for about 50% of that of the short-wave irradiance. The daily-integrated values of the sensible heat, the latent heat and the soil heat flux over Dunhuang oasis are respectively 4.04, 4.31 and 2.02 MJ·m-2·d-1 which account respectively for 27.7 %, 30.00% and 14.0 % of the net radiation. The residue of energy budget arrives at 28.7%. The surface albedo of oasis is always evidently bigger than that of Gobi desert except for noon when the surface albedo of oasis is evidently bigger than that of Gobi desert. The Bowen ratio over oasis is within 1-2, which is larger than that over desert (or Gobi). The considerable deficit of surface energy budget found in Dunhuang oasis, maybe the result of local thermodynamic circulation caused by surface thermodynamic differencce between oasis and desert nearby.

Mycorrhiza is defined as a mutualistic symbiosis between plants and fungi localized in roots or root_like structures in which energy moves primarily from plants to fungi and inorganic resources move from fungi to plants. Since most land plants in the world belong to families that are commonly mycorrhizal, mycorrhizal fungi may play important roles in nature. Findings of many researches, especially those of recent studies, are helpful in understanding the role of mycorrhizal fungi in the structure and functioning of ecosystems. In this paper, the following aspects of mycorrhizal fungi research were introduced: 1) As an important part of ecosystems, mycorrhizal fungi consume a great deal of photosynthate and are parts of food chains between autotrophic plants and fungivores; 2) Mycorrhizal fungi have a great effect on the biogeochemical cycling through taking part in the enzymatic decomposition of litter, promoting the absorption of inorganic ions or compounds, accelerating the weathering of miners, and contributing to the process of biological nitrogen fixation; 3) Mycorrhizal fungi affect the structure and functioning of the ecosystems in different ways. They have an interaction with microbes in the soil and thus may have an influence on the composition of soil microbes. They influence the inter-or intra-specific interactions of plants through having beneficial effects on host plants or connecting different plants with mycorrhizal networks. Mycorrhizal fungi play an important role in the maintenance of biodiversity and stability of plant communities, and they can also act as an indicator, participator and promoter of succession of plant communities; 4) The magnitude and species composition of mycorrhizal fungi may indicate the changes of an ecosystem, and mycorrhizal fungi can also be used in the conservation of natural ecosystems or restoration of damaged or desert ecosystems. The focuses of recent mycorrhizal fungi researches and a brief perspective was also discussed in this paper.