青海高原小麦叶片净光合速率日变化的中午降低现象对环境中生态因素的响应

以土培盆栽和大田栽培小麦（Ｔｒｉｔｉｃｕｍａｅｓｔｉｖｕｍ）为研究材料，探讨了青海高原小麦在正常生长的自然条件下，出现的土壤水分含量（ＳＷＣ）的变化所引起的植物叶片相对含水量（ＲＷＣ）和叶水势（ｗｌ）的变化以及自然强光（ＰＦＤ；Ｑ）导致的高温（Ｔａ）所产生较低的空气相对温度（ＲＨ）对小麦叶片净光合速率（Ｐｎ）日变化的中午降低现象的影响。结果表明，在大田小麦正常生长的自然条件下，当ＳＷＣ等于或低干３０％时，小麦叶片的ＲＷＣ和ｗｌ下降，气孔导度（Ｇｓ）变小，气孔阻力增大，ＣＯ＿２的供给受到了限制，从而也引起了小麦叶肉细胞进行光合作用的能力下降，Ｐｎ日变化就出现了明显的中午降低现象。当ＳＷＣ在８０％左右时，小麦叶片的ＲＷＣ和ｗｌ升高，Ｇｓ增大，气孔阻力变小，ＣＯ＿２供应充分，小麦叶肉细胞进行光合作用的能力增强，Ｐｎ日变化就没有出现中午降低现象（图１），而青海高原偶然出现的自然强光（ＰＦＤ）导致较高的Ｔａ所产生较低的ＲＨ％和较低的ＳＷＣ一样也是晴天中午，小麦叶片Ｐｎ日变化产生中午降低现象的直接原因。所以说，晴天中午，青海高原大田ＳＷＣ的高低和ＲＨ％的大小是引起小麦叶片Ｐｎ日变化出现中午降低现象轻重与否的主要生态因素

THE RESPONSE OF MIDDAY DEPRESSION OF DIURNAL VARIATION OF NET PHOTOSYNTHETIC RATE OF WHEAT LEAVES ON ECOLOGICAL FACTORS IN THE FIELD ENVIRONMENT OF QINGHAI PLATEAU

The goal of this study was to explore the effects of water content of soil,relative water con-tent and water potential of wheat leaves and high air temperature,low air relative humidity understrong light in the field to the midday depression of diurnal variation of net photosynthetic rate ofwheat leaves in Qinghai Plateau, The experimental results showed that the midday depression ofdiurnal variation of net photosynthetic rate of wheat leaves in lack water was rnore significantthan abundance of water. That was to say,when water content of soil was equal or lower 30%,since the relative water content and water potential of wheat leaves was reduced,so the stomatalconductance was decrease and supplies of CO_2 was limited. Hence,the midday depression of diur-nal variation of net photosynthetic rate of wheat leaves were emerged. But when water content ofsoil was equal or over 80%,since the relative water content and water potential of wheat leaveswas rised,so the stomatal conductance was increase and supplies of CO_2 was full. Hence,the mid-day depression of diurnal varia tion of net photosynthetic rate of wheat leaves were not arised(Fig.1). However,the high air temperature,low air relative humidity under strong light in Qing-hai Plateau and the lack of water supply in soil to effect of every plant were the same of all. Thediurnal variation of net photosynthetic rate of wheat leaves in the lack of water conditions of soiland wheat had double peak curve , but the diurnal variation of net photosynthetic rate of wheatleaves in the ampleness of water conditions of soil and wheat had typical single peak curve. There-fore,the midday depression of diurnal variation of net photosynthetic rate of wheat leaves in thefield after irrigation,heavy rain,and increased air relative humidity were quite unclear.