贝加尔针茅不同枝条叶片蒸腾特性与水分利用效率对瞬时CO_2和光照变化的响应

Responses in the transpiration properties and water use efficiency of leaves from different shoots of Stipa bacailensis to instantaneous changes in the CO_2 concentrations and photosynthetic radiation

利用人工光源测量了不同 CO2 浓度条件下贝加尔针茅 (Stipa bacailensis)营养枝条与生殖枝条叶片的净光合速率 (PN)、蒸腾速率 (E)、气孔导度 (gs)、胞间 CO2 浓度 (Ci)及叶面饱和蒸气压亏缺 (VPD)。营养枝与生殖枝 PN 及 E均随 CO2 浓度升高而增大 ,但 PN 增加幅度较大 ,E增加幅度较小。在高 CO2 浓度 (14 0 0 μmol/m ol)条件下 ,营养枝叶片最大 PN(2 7.2 3μmol CO2 /(m2 · s) )大于生殖枝 (17.13μm ol CO2 /(m2 · s) )。营养枝与生殖枝之间 E呈极显著差异。营养枝与生殖枝水分利用效率 (WUE= PN/E)均随 CO2 浓度升高而增大 ,生殖枝 WUE略高于营养枝 ,但差异未达到显著水平。光合速率的显著增加是贝加尔针茅水分利用效率随 CO2 浓度升高而增加的主要影响因素。CO2 浓度相对稳定条件下 (35 0 μmol/mol) ,生殖枝与营养枝 PN 与 E均随模拟光辐射 (SPR)强度增加而增大 ,但增幅逐渐趋缓 ,营养枝最大 PN 及 E均大于生殖枝。当 SPR强度从 0增加到 4 0 0 μmol/(m2 · s)过程中 ,营养枝与生殖枝叶片水分利用效率均呈陡然增大趋势 ,随着 SPR的进一步增强 ,WUE缓慢增大并在较高值附近达到波动平衡。贝加尔针茅营养枝与生殖枝之间的 gs差异是 PN 与 E差异的主要影响因素 ,也决定了 WUE对 CO2

Net photosynthetic rate (P_N), transpiration rate (E), stomatal conductance (g_s), intercellular CO_2 concerntration (C_i), vapor pressure deficit at the leaf surface (VPD) and water use efficiency (WUE=P_N/E) of Stipa bacailensis leaves were compared between the vegetative and reproductive shoots under a series of CO_2 concentrations and photosynthetic radiation levels. For the vegetative and reproductive shoots, both P_N and E increased with the increase in CO_2 concentration, but the increase in P_N was larger than that in E. The maximal P_N of the vegetative shoots (27.2μmol CO_2/(m^2·s)) was larger than that of the reproductive shoots (17.1μmol CO_2/(m^2·s)) at elevated CO_2 concentration of 1400μmol/mol. The increment of E of the vegetative shoots in response to the increase in CO_2 enrichment was significantly higher than the reproductive shoots. Significant difference of E between the vegetative and reproductive shoots was found under a series of CO_2 concentrations. Under elevated CO_2 concentrations, WUE values for the two types of shoots were both increased. The increase in WUE was primarily due to an increase in P_N and not to a decrease in E. P_N and E of the vegetative and reproductive shoots both increased with the level of simulated photosynthetic radiation (SPR) under ambient CO_2 concentration (350μmol/mol). As SPR increased from 0 to 400μmol/(m^2·s), WUE of both types of shoots increased sharply. Then, WUE showed little increase with further increase in SPR. The differences in g_s between the vegetative and reproductive shoots was the main factor determining the differences of P_N and E, and the responses of WUE to simulated CO_2 concentrations and photosynthetic radiation. These results indicate that there are significant differences in P_N and E between the vegetative and reproductive shoots and their responses to changes in both CO_2 enrichment and SPR level. However, there are only slight differences in WUE between the two types of shoots.