6. The research achievements in the past 5 years Since foundation of the Lhasa Plateau Ecological Research Station, we undertook more than 20 items of projects from National Key Project for Basic Research on Tibetan Plateau, China Natural Science Foundation, Chinese Academy of Sciences, Scientific Committee of Tibet Autonomous Region, and Logistic Department of Tibet Army. The main achievements are as follows. 1) Basic Research ① Solar radiation and energy balance in agricultural ecosystem in Tibet Plateau Tibet plateau is characterized by high elevation and intense solar radiation. Since the foundation of Lhasa Agro-ecological experimental Station, solar radiation and its transformation in farmland ecosystem has been listed as the emphasis for study. Radiation input, energy interception and utilization in the canopy of farmland were studied. We measured spectra of solar radiation and analyzed the temporal and spatial distribution of different spectra. Photosynthetically active radiation (PAR) coefficient, i.e. ratio of PAR in gross solar radiation, was calculated through measured data. Results indicate that PAR coefficient is lower although total solar radiation is much higher than lowland of other part of China. The climatic model of PAR and conversion coefficient between energy of PAR and light photon were proposed in Tibet Plateau. It is important for calculating and modelling of productive potential, photosynthesis and mechanisms of high production. We also analyzed the characteristics of energy budget of solar radiation through measuring gross radiation, reflex, long-wave radiation and atmospheric converse radiation. The radiation budget is linearly correlated with gross solar radiation. Therefore we can calculate energy budget from solar radiation. ② Photosynthesis and its response to CO2 enrichment The Tibet Plateau is characterized by high elevation, lower atmospheric pressure. The density of carbon dioxide in the air is only two thirds of lowland in North China Plain. So the characteristic of photosynthesis in the plateau is quite different from lowland. Especially the photosynthesis of plant is sensitive to CO2 elevation and global warming. In 1995 and 1996, we measured photosynthesis of winter wheat flag leave by CID 301 portable photosynthesis system. We found that initial light utilization efficiency in the plateau is lower than that of lowland. In 2001, Lhasa ecological station, in collaboration with Hokkaido University, Japan implemented a project on the response of winter wheat photosynthesis to CO2 enrichment by method of open top chamber. The result showed that apparent quantum yields of photosynthesis are 0.04870 ± 0.003 and 0.04796 ± 0.0024 mmol CO2 /mmol photons in 25°C and 30°C. Apparent quantum yield is negatively correlative with air temperature. In comparison with the lowland area in North China Plain, the quantum yield, varying from 0.043 to 0.0570, is 76~87% of those in lowland (0.050~0.075). CO2 enrichment can apparently increase the light utilization efficiency, quantum yield increase 16.8 ~ 26.2 % in contrast with the controls. ③ Solar energy transmission and mass production In 1994，Bowen ratio microclimate method and eddy covariance was used to measure CO2 flux, transpiration, apparent and potential heat, net solar radiation and soil heat flux in winter wheat ecosystem in Lhasa. The result indicates that canopy net photosynthesis rate is linearly correlative to radiation budget, and is higher than that of lowland in North China Plain. ④ Crop production modelling We established models to simulate LAI dynamics, light interception and dry matter accumulation of winter wheat in Lhasa. Through modelling production process of winter wheat, we analyzed that the main cause of high yield is longer growing period due to cool climate. 15 t. hm-2 is the maximum production of winter wheat. We also simulated the winter wheat production under the CO2 doubling, and 3 °C temperatures increase. The result indicated that in the future climate change scenario, the production will increase but the growing period will be reduced. There is little production increase in contrast the lowland in the same climate change scenario because reduction of growing season. This will counteract the production increase effect. ⑤ Greenhouse gas release and ecosystem carbon budget Soil respiration of different land use, i.e. winter wheat farmland, barley farmland and control naked land, was measured by method of infrared gas exchange. It indicated that the soil respiration is positively correlative to soil temperature of 5 cm depth. 5 cm soil temperature can be used to evaluate carbon flux. We estimated that the root respiration accounts 34~44 per cent of soil respiration. Soil respiration also was measured in Lhasa winter wheat ecosystem and Bange steppe ecosystem by closed chamber. The annual emission of CO2, N2O and CH4 from soil are 20.30 t .hm-2, 0.98 kg.hm-2 and -2.15 kg.hm-2, in Lhasa winter wheat cropland and 2.66 t.hm-2, 0.23 kg.hm-2 and -2.11 kg.hm-2 in Bange steppe. 2) R & D projects In this field, Lhasa ecological station carried out projects from Ministry of Agriculture, Tibetan Committee of Science and Technology, “Western Light” of personnel training, and Agricultural Development Office of Chinese Academy of Sciences. In addition, we also trained 400 persons for Tibetan Army and Tibet Agriculture and Livestock School. The main achievements are as follows: ① Demonstration and extension of crop varieties We introduced 135 varieties of crop since establishment of Lhasa Ecological Station. More than 10 varieties of high yield, high quality were selected and demonstrated in the station and in Tibet. Among others, winter wheat Bussyd, spring wheat 602, Northeast Agriculture maize series, oilseed rape series have prominent performance in the valleys of the Yalungzangbo River, Lhasa River and Nianchu River. Especially Bussyd winter wheat and 602 spring wheat was extended more than 15000 hm2. The Northeast-Agriculture sweet maize is also very popular in the Lhasa River Valley. ② species screening of forage and artificial grassland construction 145 species or varieties of forage were introduced into experimental site in Lhasa station. More than 10 species, such as紫花苜蓿、Vicina sp.、红豆草、Festuca arandinacea、Tall Festuca、Lolium perenne, 牧冰草、新麦草、青海老芒麦、Trifolium pratense等, These species was extended to North Tibet for demonstration and experiment. In the Lhasa River valley, branchy maize and Rumex are good species for fodder production. Their yield can reach 12000 kg.mu-1. ③ Vegetable cultivation in greenhouse Non-soil substrate vegetation in greenhouse has been successful in recent 3 years. From 2000 on, we constructed 500 m2 of plastic greenhouse and 340 m2 of glass greenhouse to research and demonstrate vegetable cultivation techniques. A series of vegetable such as cucumber, tomato, chili, eggplant, beans are cultivated. The production of cucumber and tomato can reach 9620 kg and 1280 kg per mu. Non soil substrate cultivation has he advantage of water and fertilizer saving and resistant to diseases and pests. This project was disseminated and demonstrated in Lhasa suburb and production base of the Logistics departments of the Tibet Army.