小麦和大豆叶片的气孔不均匀关闭现象

用14CO2放射自显影的方法研究了田间小麦和大豆叶片在水分胁迫下的气孔关闭状况。正常浇水的小麦和大豆叶片呈现出对14CO2的均匀吸收。在小麦与大豆"片水势分别降至-1．75和-1．32MPa的土壤干旱条件下，两种作物叶片都发生气孔不均匀关闭。离休叶片在空气中快速脱水易引起气孔不均匀关闭。正常供水小麦叶片在晴天中午明显的光合午休时，无CO2的不均匀吸收。某些晴天中午，在大豆光合午休低谷时段观察到较明显的气孔不均匀关闭，用气体交换资料计算出的细胞间隙CO2浓度并不随气孔年度的降低而下降，反而略有回升。

Nonuniform Stomatal Closure in Leaves of Wheat and Soybean

The occurrence of "patchy" pattern of CO2 uptake across the surface of leaves was exanhned in wheat and soybean under field conditions by14 CO2 autoradiography. Well-watered leaves had uniform distribution of photosynthesis.Plant water deficits causing a leaf water potential depression to - 1. 75 MPa in wheat (Fig. 2B) and -1. 32 MPa in soybean (Fig. 1B) resulted in nonuniform CO2 assidrilation patterns. The leaf water potential at which nonuniform stomatal closure occurred in soybean was not as low as that in wheat.Nonuniform stomatal closure occurred when a leaf was subjected to a rapid dehydration in air for a few minutes(Fig.2C). An increase in the calculated value of intercellular CO2 concentration was often observed. The increase probably resulted from an erroneous calculation due to "patchy " stomatal closure, but alight also be caused by an enhanced photorespiration or respiration rates.When the photosynthetlc rate of wheat flag leaves showed thedday depression under field conditions on clear days,nonuniform stomatal closure was not observed (Fig. 2E). Soybean leaves, on the other hand, sometimes Showed nonuniform stornatal closure when midday depression occurred with an increase of Ci (Fig. 1C). ugher VPDduring midday period was probably the main factor causing nonuniform stomatal closure of soybean leaves. It is not certain whether the observed increase of intercellular CO2 concentration in soybean leaves was due to nonstomatal limitalion or an overestimahon due to "patchy" stomatal closure, or bath. It is suggested that, whenever nonuniform stornatal closure takes place, one should not infer the occurrence of nonstornatal limitation of photosynthesis from an increase of Ci.