| Rubber-tea community was planted in large areas of Xishuangbanna. Studying the response of its structure and function to changing elevation was instructive for the practice of rubber planting. This research was conducted at two elevations in Xishuangbanna (Menglun Alt. 570 m, Guanping Alt. 870 m). Quantitative characteristics, growth, biomass, litterfall and productivity of rubber-tea community and rubber monoculture from the two elevations were investigated. Photosynthesis of tea leaves from rubber-tea community and tea monoculture at the two elevations were also measured. Basing on the observation data, the effect of rubber-tea intercropping on the growth, biomass and productivity of rubber tree at the two elevations was analyzed. The results were as following:1) The average height, crown width and stem girth of rubber-tea community and rubber monoculture from the high altitude were significantly lower than those from the low altitude. The annual increments of stem girth of rubber trees at the low altitude were 2.52%, 2.38% in rubber-tea community and pure rubber plantation, respectively. Annual stem growth increment of rubber trees at the high altitude was found to be 38% lower compared to the rubber trees at the low altitude. The stem girth increment occurred mainly in rainy-season, and was significantly higher in rubber-tea community than in rubber monoculture.2) The LAI of rubber tree canopy decreased significantly during January and February. The canopy LAI of the low altitude fluctuated around 3.38 and 3.70 after March in rubber-tea community and rubber monoculture respectively, and around 2.63 and 3.00 for the high altitude. The LAI of the rubber canopy at the high altitude was significantly lower than that from the low altitude.3) The litterfall of rubber tree from the high altitude was 50.46% lower than that from the low altitude in the rubber-tea community, and 46.91% lower was found in the rubber monoculture. Leaves were the dominant part of total litterfall, and accounted for 70% in rubber plantations at the low altitude. The annual variation of total litterfall showed a two peaks'pattern at the low altitude. The first peak appeared in February, while the second appeared in September. There was only one peak at the high altitude, which occurred during January and February.4) ANPP from rubber-tea community and rubber monoculture was 15.28 Mg hm-2yr-1 and 16.03 Mg hm-2 yr-1 at the low altitude. And it was 8.61 Mg hm-2 yr-1, 8.35 Mg hm-2 yr-1 respectively at the high altitude. The ANPP, biomass increment and litterfall from the low altitude were significantly higher than those from the high altitude. The yield of solid latex, biomass increment and net primary productivity of rubber tree in rubber-tea community were lower than those in rubber monoculture at the low altitude, but the result at high altitude showed the reverse.5) The annual tea yield in the rubber-tea community from the low altitude was significant higher than that from the high altitude. The yield was 0.14 Mg hm-2 and 0.24 Mg hm-2 at the low and high altitude, respectively. Intensive fluctuations and a peak during February and March occurred at the low altitude, while weak fluctuations around certain yield during all picking time were found at the high altitude.6) The diurnal variations of net photosynthetic rate (Pn) in tea leaves of rubber-tea community at the two altitudes showed a single peak. Photo flux density (PFD), Pn , transpiration rate (Tr) and stomatal conductance (Gs) in tea leaves of high elevation were significantly higher than those of low elevation. The correlation analysis demonstrated that PFD was the main controlling factor causing photosynthetic differences between tea leaves in rubber-tea community.7) The maximum net photosynthetic rate (Pmax), dark respiration rate (Rd), light compensation point (LCP) and light saturation point (LSP) of tea leaves in the rubber-tea community were significantly lower than those of pure tea plantation. Photosynthetic capacity of tea leaves were inhibited by canopy covering in the rubber-tea community.It is concluded that lower temperature at higher altitude slowed rubber tree growth, decreased LAI and crown coverage, improved light condition and tea yield in the understory of community. Moreover, rubber-tea community as a planting mode improved rubber growth, which made biomass and ANPP of rubber tree in the community higher than those of the rubber monoculture at the high elevation. With altitude increasing, establishing rubber-tea community may increase economic benefit totally. |
