生长在步人式植物生长箱中的小麦幼苗，当光子流密度(PFD)下降时，蒸腾速率发生了有规律的波动。波动周期与下降幅度有关，下降幅度越大，周期越长。在波动进行期间，当再次降低PFD(100μmol m-2s-1到30 μmol m-2S-1)后，波动频率和振幅都有所降低。通过外界压力使叶鞘部木质部变形，以导致在变形区的水流阻力增加，在稳态条件下也能导致蒸腾波动的产生，而一旦在水中将小麦幼苗的根系统切除后，无论是光暗转变还是暗光转变，蒸腾波动现象都没有出现。这些现象说明，水流阻力是蒸腾波动产生的重要前提条件，而蒸腾波动则可能是气孔开合波动的直接结果。%The transpiration oscillation phenomena of young wheat leaves were observed in a plant growth chamber. When photon flux density (PFD) decreased, transpiration oscillations occurred and its period was relative to the mount of decrease. During oscillation under 100 μmol m-2s-1 illumination, the frequency and amplitude decreased after PFD was decreased to 30 μmol m-2s-1. When an external pressure was applied to the leaf sheath xylem vessels near the leaf base of young wheat, a resistance to water flow at the deformation site was achieved and transpiration oscillation was induced under steady environment. After the root system of young wheat was cut below the water surface, no oscillation was observed when changed the light intensity. All the phenomena show: water flow resistance is the important prerequisite to cause transpiration fluctuation, and the latter can be the result of stomatal oscillation.
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