关键词: 植物氮库, 土壤氮库, 生物固氮, 少花蒺藜草

Abstract: Since the 1950s, the shortwaved solar radiation that the earth received has been reduced by 2.7% every decade, and this phenomenon is called “global dimming”, which may impact plants and their inhabitant ecosystems. However, no consensus concerning such impacts has been reached. In this paper, different degrees (0, 30%, 50% and 70%) of shading were installed to simulate the global dimming effect to study the population density, morphological features (shoot height, leaf area, and heading rate), and photosynthetic physiology (stomatal conductance, photosynthetic rate, and transpiration rate) of Leymus chinensis in response to shading. Shading decreased the shoot density somewhat, but increased the shoot height obviously, enlarged the leaf area significantly, and promoted the heading rate. Shading also significantly reduced the PAR that L. chinensis received. Under 0, 30%, and 50% shading, the afternoon depression in stomatal conductance, photosynthetic rate, and transpiration rate occurred. Under 70% shading, the stomatal conductance, photosynthetic rate, and transpiration rate at 11:00-16:00 were higher than those in other shading treatments, and the afternoon depression of photosynthetic rate and transpiration rate did not occur. The absence of the afternoon depression of photosynthetic rate and transpiration rate under 70% shading could be one of the main reasons of the increased productivity of some vegetation types after being shaded or being exposed to global dimming. To more precisely predict the responses of various ecosystems to global dimming, it would be necessary to conduct more empirical studies about the responses of plants to shading in more regions, with more habitat types and more plant functional types, and at more growth stages, and do more model studies and meta-analyses to incorporate the empirical data.

Key words: Cenchrus spinifex, soil nitrogen pool, biological nitrogen fixation., plant nitrogen pool