狗尾草蒸腾特性与水分利用效率对模拟光辐射增强和CO2浓度升高的响应

 在人工控制光照强度和CO2浓度条件下，测量了禾本科C4植物狗尾草（Setaria viridis）的光合速率（Pn），蒸腾速率（Tr），胞间CO2浓度（Ci），气孔导度（Gs）和叶面饱和水汽压亏缺（Vpdl）对不同模拟光辐射（SPR）强度与CO2浓度的响应。结果表明：Pn, Tr 及Gs均随SPR的升高而增大，增幅趋缓，最终趋于动态平衡。SPR增强的起始阶段，水分利用率（WUE）逐渐增大，在SPR为1200 μmol·m-2·s-1时达到最大值，然后逐渐降低。Ci与Vpdl则随SPR的增强而减小，SPR高于600 μmol·m-2·s-1之后，两者均达到平衡状态。CO2浓度从300增至600 μmol·mol-1的过程中，狗尾草Pn逐渐增大，从600增至1 000 μmol·mol-1过程中，其Pn逐渐降低。Ci、Vpdl和WUE随CO2浓度的升高而增大，Gs和Tr则随CO2浓度的升高而减小。即禾本科一年生C4植物的光合作用对CO2浓度升高响应不敏感，水分蒸腾消耗的减少和WUE的提高对CO2浓度升高的响应极显著。可见，CO2浓度升高对C4植物光合作用的直接促进作用有限，但是却能从提高现有水分利用效率途径促进植物的第一性生产。

RESPONSE OF TRANSPIRATION CHARACTERISTICS AND WATER USE EFFICIENCY OF SETARIA VIRIDIS TO THE ENHANCEMENT OF SIMULATED PHOTOSYNTHETIC RADIATION AND CO2 ENRICHMENT

To determine how transpiration characteristics and water use efficiency of annual C4 plants respond to simulated photosynthetic radiation enhancement and CO2 enrichment, we used LI-6400 Portable Photosynthesis System to examine photosynthesis rate (Pn), transpiration rate (Tr), intercellular CO2 concentration (Ci), stomatal conductance (Gs) and vapor deficit at the leaf surface (Vpdl) of Setaria viridis under simulated photosynthetic radiation (SPR) intensities from 0 to 2400μmol·m-2·s-1 and CO2 concentration from 300 to 1000μmol·mol-1. Pn, Tr and Gs increased with enhanced SPR intensity. The increase in Pn, Tr and Gs with each unit SPR added was reduced as SPR intensity increased. At last, these physiological parameters tend to dynamic balance. Water use efficiency (WUE) increased with enhanced SPR, then plateaued as SPR intensity exceeded 1200μmol·m-2·s-1. For photosynthesis process demands CO2, so Ci intensity enhancement. Vpdl also decreased with SPR intensity increase, then reached dynamic balance as SPR intensity exceeded 600μmol·m-2·s-1. Pn increased with CO2 concentration between 300 and 600μmol·mol-1, and then decreased as CO2 concentration increased from 600 to 1000μmol·mol-1. Ci, Vpdl and WUE of Setaria viridis rose with the elevation of CO2 concentration. Both Gs and Tr dropped as the CO2 concentration was elevated. We conclude that Pn of annual C4 plants was not sensitive to CO2 concentration variation. The response of Tr and WUE to CO2 enrichment was most significant. It is obvious that the function of instantaneous simulated CO2 enrichment to increased photosynthesis rate was gradually diminished. However, it could enhance primary production by improving the use efficiency of existing water.