西南喀斯特地区一年生构树苗木的光合特征

以一年生构树苗木为试验材料,利用光合作用测定系统监测其叶片光合生理生态特性及其环境因子日变化.结果表明,大气温度(T)和光合有效辐射(PAR)在13:00达到全天的最大值;构树幼苗的净光合速率(P_n)、蒸腾速率(T_r)和气孔导度(G_s)的日变化均呈双峰曲线,具有明显的光合"午休"现象;P_n在11:00左右出现第一次高峰,16:00左右出现第二次高峰;T_r在13:00和16:00分别出现两次高峰,在这两个时刻的值相差较为明显.与P_n相比,T_r在一天内的两个高峰值相对接近.胞间CO_2浓度(C_i)日变化与P_n呈负相关关系.P_n和T_r有比较明显的年变化,呈双峰型曲线,均在4月和8月出现,12月份相对较低,这与苗木年生长规律相一致,表明构树在长期的生长过程中形成了对季节变化的适应性.

The Photosynthesis Characteristics of Seedlings of Broussonetia papyrifera in the Southwest Karst Region

The eco-physiological photosynthetic characteristics of Broussonetia papyrifera leaves in one-vear-old seedlings and their environmental factors were measured using portable photosynthesis system.The results showed that atmospheric temperature (T) and photosynthetic active radiation (PAR) reached the maximum at 13:00.The diurnal change of net photosynthetic rate(P_n)presented a bimodal pattern,and had a clear midday depression.The diurnal variation pattems of leaf transpiration (T_r) and stomatal conductance (G_s)were also bimodal.The first peak of P_n was at 11 o'clock and the second peak was at 16 o'clock.In midday there was a photosynthetic depression..The two peaks of T_r was at 13 and 16 o'clock,the difference of values were distinct.Compared with the P_n,the two peaks values of T_r were relativeIv nearer.The diumal variations of between intercellular CO_2 concentration (C_i) and p_n were negative correlation.The yearly variation of average P_n and T_r were double peak curves,they present in April and August.Totally,from April to September,the P_n and T_r were much higher,but in November and December are relatively lower,which were accordant with the growth regularity of seedlings and it showed that Broussonetia papyrifera adapted to variety of seasons during growth.