龙眼光合特性及其影响因子的研究

A Study on Photosynthesis of Longan ( Dimocarpus Longana Lour. ) and Its Influencial Factors

在田间和试验室条件下研究了龙眼叶片的光合作用特性。结果表明:龙眼叶片光合速率(Pn)的季节变化呈双峰曲线,最高峰在6月,次高峰在8月,5～9月Pn均维持在较高水平;春季(5月)Pn的日变化曲线为单峰型,高峰在正午,夏季(7月)Pn的日变化为双峰型,高峰在10时,16时有一小高峰;晴天Pn的日变化有明显的“午休”现象,多云天“午休”现象不明显,阴雨天pn较低,且无“午休”现象;Pn由负转正的叶龄为7～10天,30～40天叶龄叶片的Pn最高,60天后Pn缓慢下降;Pn的最适温度范围比较狭窄;环境温度为27℃和22℃时的光合最适温分别为28±2℃和25±2℃。龙眼的光合作用光补偿点和光饱和点分别为600～800μEm-2s-1和30～40μuEm-2s-1。最适土壤相对含水量为58％～84％。灌水临界期为土壤相对含水量38％～42％。

The photosynthetic characteristics of Longan leaves under field and laboratory conditions were studied. The results were as followed; The curve of annual variation of Longan leaf photosynthesis showed two peaks, the first was in June, and the second was in August. Pn remened higher level from May to September. The curve of diurnal variation of Pn in the spring ( May) demonstrated a single peak appearing at noon. The diurnal variation of Pn in summer ( July) demonstrated two peaks. The first peak appeared at 10 I 00 a. m. , the second and smaller peak appeared at 16 :00 p. m. . Under fair weather conditions, there was a typical two peak model with a so-called' midday slump'. In cloudy conditions however, the' midday slump' disappeared. Under overcast weather conditions, there was a single peak with low level of Pn. The leaf age when the net photosynthetic rate ( Pn) changed from negative to positive was 7- 10 days. At the age of of 30- 40 days, Longan leaf absorbed photosynthetically active radiation ( PAR) most efficiently, and showed a highest Pn. Pn began to fall slowly after the leaf age reached 60 days. The response curve of Pn to leaf temperature ( TL) was a typical paradola one, in which the scope of optimum TL for Pn was narrow. The optimum TL of photosynthesis was 28 ± 2℃ and 25±2℃ when ambient air temperature ( Ta) was 27℃ and 22℃ , respectively. Light compensation point of photosynthesis ( LCP) and light saturation point ( LSP) in Longan leaves were 20- 30μE·m-2 · S-1 and 600- 800μE ·m2 ·s-1 respectively. The optimum SRWC of Pn varied from 62% to 84%. The critical level of SRWC, at which the plant needs irrigation, was 38% - 42%.