Abstract
In order to compare the differences of gas exchange between sun-tolerant and shadetolerant plants,diurnal variations in photosynthetic and transpiration indices were measured using LI-6400 portable photosynthesis system in two endangered species,Ostrya rehderiana Chun(sun-tolerance)and Acer yangjuechi Fang et P.L.Chiu(shade-tolerance).Our results showed that O.rehderiana was a bimodal curve in diurnal change of photosynthesis rate(Pn),while A.yangjuechi was a unimodal curve.A.yangjuechi had a higher light use efficiency(RUE)than O.rehderianaunder a relatively weak light(p0.05),suggesting A.yangjuechi had an increased net photosynthesis rate(Pn)in weaker light conditions,e.g.under a long-term shade circumstance.The water use efficiency(WUE)was also higher in A.yangjuechi than in O.rehderiana(p0.05).This indicated A.yangjuechi had a lower transpiration in shaded conditions.
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