以渭北地区刺槐为研究对象,采用LI-6400便携式光合作用系统,于2009年6月和8月分别在晴天和阴天条件下,测定刺槐光合作用的日进程及光合光响应曲线。结果表明: 无论在6月还是8月,晴天刺槐的净光合速率(Pn)和气孔导度(Gs)在10:00以前高于阴天,而在午间12:00和14:00低于阴天。刺槐的胞间CO2浓度(Ci)、空气CO2浓度(Ca)、空气相对湿度(RH)、光能利用率(LUE)在晴天的绝大多数时间显著低于阴天,而蒸腾速率(Tr)、水汽压亏缺(VPD)、光合有效辐射(PAR)、空气温度(Ta)在晴天的全天都显著高于阴天。在晴天条件下,虽然刺槐的Gs,Ci,Ca,RH,LUE的日均值比阴天低,但Pn,Tr,VPD,PAR,Ta的日均值比阴天高,从而能够积累更多的日均光合固碳量。在阴天条件下,刺槐的最大光合速率(Pmax)高于晴天,且暗呼吸速率(Rd)和光补偿点(LCP)显著低于晴天,表现出很强的光合适应能力。
Diurnal course and light response curves of photosynthesis in the Black locust Robinia pseudoacocia in Weibei region were measured using a LI-6400 portable photosynthesis system under sunny and cloudy days in June and August 2009. Regardless in June or in August, the net photosynthetic rate (Pn) and stomatal conductance (Gs) of Black locust under the sunny days were higher than those under the cloudy days before 10:00, while both of them were lower between 12:00 and 14:00. The intercellular CO2 concentration (Ci), ambient CO2 concentration (Ca), relative humidity (RH), light use efficiency (LUE) across most times of the day were significantly lower under the sunny days than those under the cloudy days. In contrast, the transpiration rate (Tr), vapor pressure deficit (VPD), photosynthetic active radiation (PAR), air temperature (Ta) in the whole day were markedly higher under the sunny days compared to those under the cloudy days. Under the sunny day conditions, although Black locusts had lower daily mean values of Gs, Ci, Ca, RH, LUE, they showed higher daily mean values of Pn, Tr, VPD, Ta and could in turn accumulate more average daily photosynthetic carbon fixation amounts. Under the cloudy day conditions, Black Locusts presented a greater maximum photosynthetic rate (Pmax) and a pronouncedly lower dark respiration rate (Rd) and light compensation point (LCP), which indicated that Black locust had a strong photosynthetic acclimation capacity. This study would have great implications for the evaluation of stand productivities and for the production and management of Black locust plantations in Weibei region.