Studies On Nitrogen Sensitivity And Its Mechanism Of Epiphytic Lichens Foraged By Rhinopithecus Roxellanae In Shennongjia Nature Reserve

In the backgrounds of increasing global nitrogen deposition, more and more ecosystem accidents happened such as ecosystems degenerated, biodiversity decreased and rare species endangered and so on. In order to protect growth and reproduce of the population of Rhinopithecus roxellanae, 7 kinds of lichen eaten by these monkeys were selected as research subjects in Shennongjia, Sichuan. Nitrogen sensitivity and its action mechanism of these kinds of lichens treated by different concentrations and forms of nitrogen were studied by determining Chlorophyll fluorescence characteristics, chlorophyll degradation(OD₄₃₅/OD₄₁₅), cell membrane integrity, nitrogen absorption characteristics and nitrogen metabolism enzyme activity. All results could reveal the mechanism of action of nitrogen deposition on staple lichen eaten by R. roxellanae in shennongjia. The main results were presented as following:1) The maximum photosynthetic efficiency, chlorophyll degradation and cell membrane integrity of 7 kinds of lichen were significantly affected by some or one certain nitrogen treatment, showed that they had nitrogen sensitivity. Different lichen has its own nitrogen sensitivity to different forms of nitrogen, as well as its mechanism.2) Based on growth and survival index, it reflected the health condition and nitrogen sensitivity of the lichen. The influence of different concentration of nitrogen on lichen growth showed that the lower the concentration of nitrogen was, the poorer the growth of lichen was. But, if nitrogen concentration is too high, which would lead to the decrease of the growth and even death.3) Absorption characteristics of ammonium nitrogen and nitrate nitrogen of 7 kinds of lichen accorded with Michaelis-Menten enzyme kinetics equation model through the analysis of the kinetic parameters. Treated with different concentrations of ammonium nitrogen as a single source of nitrogen, the absorption rates to NH₄⁺?Usnea dasopoga, U. betulina, Lobaria pulmonaria and L. orientalis? tended to first decrease, then increase, while the absorption rate to NH₄⁺?U. longissima, U. luridorufa and Ramalina calicaris var. japonica? tended to increase with the increase of the concentration of NH₄⁺.4) When treated with different concentrations of nitrate nitrogen as a single source of nitrogen, at low concentration nitrate solution, except U. betulina other 6 kinds of lichen can released NO₃^-. The absorption rate to NO₃^-?U. luridorufa, R. calicaris var. japonica, U. betulina and L. orientalis? showed a tendency to increase with the increase of the concentration of nitrate nitrogen. The absorption rates to NO₃^-?U. dasopoga and L. pulmonaria? tended to first increase, then decrease and eventually increase. U. longissima tended to first decrease, and then increase.5) Nitrate reductase activities of 7 kinds of lichen had a certain and different threshold value when treated to nitrate nitrogen. Within a certain range of concentrations of nitrate-nitrogen, the nitrate reductase activities of lichens were always increasing with the increase of the concentration of nitrate-nitrogen. But, these enzyme activities were inhibited if the concentration of substrate is too high.6) When treated with different concentrations of nitrate nitrogen as a single source of nitrogen, the glutamine synthetase activity?U. longissima, U. luridorufa, R. calicaris var. japonica, U. dasopoga and U. betulina? showed unimodal curve change trend along with the increase of the concentration of nitrate-nitrogen; For L. orientalis, it tended to first increase, then decrease and eventually increase, while for L. pulmonaria, showed a tendency to decrease.7)The above results showed that the influence of different concentrations and forms of nitrogen on 7 kinds of licen caused the changes of F_v/F_m, OD₄₃₅/OD₄₁₅ and RE values, affecting the growth and survival of lichen.