水分胁迫对柑桔光合作用的影响

Photosynthesis of citrus under water stress.

柑桔植株在土壤失水时,叶片相对含水量(LWC)和叶片水势(ψ_1)随土壤含水量(SWC)的减少而下降,前两者与SWC成对数关系.在SWC大于50％田间持水量时,LWC和ψ_1下降较小.SWC大于55％时植株蒸腾变化不明显.水分胁迫导致柑桔叶片光合(Pn)下降有一ψ_1阈值为-1.70MPa,当ψ_1低于此值时,Pn陡降.与这一ψ_1对应的SWC为42.5％田间持水量.柑桔叶片的叶肉阻力(r_m)比气孔阻力(r_s)大得多,在水分胁迫时更为明显.结果表明柑桔在水分胁迫条件下光合受抑主要来自非气孔性的限制.

The experiment was carried out with 3-year-old satsuma mandarins (Citrus unshiu Marc. cv. Yonezawa unshiu) trees on Poncirus trifoliata (L. ) Raf. rootstocks to study the changes in plant water status and photosynthesis under water stress imposed by soil drying. The results were as follows; the leaf relative water content (LWC) and water potential (ψ1) were found to be logarithemically related to water content of the soil in which the plants were grown, hut lagged considerably behind as the soil water was depleted through plant transpiration. Appreciable decline in LWC and ψ1 occurred only when the soil water content (SWC) was reduced below 50% of field capacity. Transpiration rate (Tr) of the plants was essentially constant as long as SWC was above 55% field capacity. Hence, it was concluded that the availability of soil water did not change significantly when SWC was within the range between field capacity and 55% of it. A dramatic decline of Pn took place when a threshold of ψ1 was overpassed, which was - 1, 70 MPa and cor-responded to the SWC of 42. 5% of field capacity. Mesophyll resistance (rm) of citrus leaves was much higher than stomatal resistance (rm), especially when plants were under water stress. The results presented showed that the non-stomatal component was more important than the stomatal component in limiting leaf photosynthesis under water stress.