蜡梅光合与蒸腾速率日变化的初步研究

摘要

对野生蜡梅在不同天气中的净光合速率(Pn)和蒸腾速率(Tr)日变化及其与环境因子的关系进行了初步研究,结果如下:(1)蜡梅在晴天和阴天的Pn日进程均呈一双峰型曲线.但晴天的两个峰值比在阴天出现要早,Pn的总体水平要高于阴天,且在午后发生明显的光合"午休"现象.(2)Tr在晴天的日变化呈单峰型曲线,在午后强光和高温条件下,Tr可高达10 mmol H2O m-2s-1以上.在阴天,Tr日进程波动很小,且蒸腾作用微弱,全天大多保持在0.8 mmol H2O m-2s-1以下的水平.(3)在光合有效辐射(PAR)为800～900 μmol m-2s-1、大气温度(TA)28 ℃左右、相对湿度(RH)约75%的条件下,野生蜡梅的Pn可高达23.6 μmol CO2 m-2s-1.但蜡梅的光饱和点与光补偿点均较低,分别约为900 μmol m-2s-1和20 μmol m-2s-1.(4)PAR和TA是影响蜡梅光合与蒸腾速率日进程的主导生态因子.蜡梅对强光和高温反应敏感,在超过光饱和点且气温高达42 ℃以上时,其蒸腾作用强烈,能量转换与水分利用效率(WUE)大大降低,光合能力减弱,导致Pn急剧下降.%Abstract:The measurement of the net photosynthetic rate (Pn) and transpiration rate (Tr) for Chimonanthus praecox (L.) Link. under the natural conditions on sunny and cloudy days was carried out. The influences of environmental factors on diurnal variation of Pn and Tr for C. praecox were also analyzed in this paper. The present experimental results show: (1) The diurnal courses of the Pn for C. praecox on sunny and cloudy days were both double-ridged curves. On sunny days the two peak values of Pn appeared earlier and the general Pn value was higher than that on cloudy days. The phenomenon of midday depression of photosynthesis was obviously observed on sunny days. (2) The diurnal course of Tr for C. praecox on sunny days was of a single-ridged-form. The peak value of Tr reached beyond 10 mmol H2O m-2s-1 under the condition of intense light and high temperature in the afternoon. On cloudy days, the Tr curve was smooth. The transpiration was weak, below 0.8 mmol H2O m-2s-1 during a whole day. (3) The Pn of the wild C. praecox reached as high as 23.6 μmol CO2 m-2s-1 when the photosynthetic active radiation (PAR) was 800～900 μmolm-2s-1, air temperature (Ta) 28 ℃, relative humidity (Rh) 75%. The light saturation point and light compensation point of C. praecox were quite low, about 900 μmolm-2s-1 and 20 μmolm-2s-1 respectively. (4) PAR and Ta were dominant ecological factors limiting the diurnal variation of Pn and Tr for C. praecox. This plant was sensitive to high temperature and intense light. When PAR exceeded the light saturation point and Ta surpassed 42 ℃, the transpiration increased rapidly while the energy transformation and water use efficiency (WUE) decreased remarkably, the photosynthetic capacity was much weakened, all these above lead to the sharp descend of Pn.