6种草本植物对干旱胁迫和CO_2浓度升高交互作用的生长响应

Growth responses to the interaction of elevated CO_2 and drought stress in six annual species

以CO2浓度升高为主要标志的全球气候变化及由其引起的极端气候变化对陆地生态系统产生了重要的影响。利用步入式CO2生长室模拟研究了CO2浓度变化(400和700μL/L)和干旱胁迫(水分充足CK:100%FC(田间持水量);中度干旱MS:40%FC;重度干旱SS:20%FC)的交互作用对草本植物网果酸模(Rumex chalepensis)、野豌豆(Vicia sepium)、泥胡菜(Hemmistepta lyrata)、风轮菜(Clinopodium chinense)、藜(Chenopodium album)和玉米石(Sedum album)生长特性的影响。结果表明:CO2浓度升高总体上刺激了网果酸模、野豌豆、泥胡菜、风轮菜和藜这5种C3植物在任何水分条件下的生长,也刺激了玉米石在水分条件较好下的生长;干旱胁迫总体上抑制了所有6种植物的生长,但中度干旱胁迫有刺激CAM植物玉米石生长的趋势。CO2浓度升高能否缓解干旱的负面影响具有明显的种间差异:CO2浓度升高减缓了干旱胁迫对泥胡菜和风轮菜的负面影响,这种缓解作用在网果酸模和野豌豆中显著降低,对藜没有明显的促进作用,对干旱下的玉米石的生长却起到了抑制作用。CO2浓度升高总体上增加了根质量分数和干物质含量;干旱胁迫明显提高了6种草本植物的根生物量的分配比例,降低了干物质含量;但CO2浓度升高和干旱胁迫的交互作用可导致不同的物种产生不同的响应,说明植物能够通过调节生物量分配和植株本身的水分含量保持能力来适应CO2浓度和干旱胁迫的交互影响,这种调节能力取决于植物在碳的吸收和水分散失之间的平衡"trade-off"。研究结果有助于增进草本植物对未来气候变化的适应性理解,为评估和预测全球气候和水文变化对植物的生理生态影响提供理论依据。

Carbon dioxide （CO2） is the most important anthropogenic greenhouse gas. Global atmospheric CO2 may reach 700 μL/L by 2100 and increase at a high rate of 0.4% per year according to the Intergovernmental Panel on Climate Change. Elevation of atmospheric CO2 can have an indirect influence on global climate change through ＂the greenhouse effect＂ and a direct influence on plant growth, survival, and reproduction. Therefore, elevated COL will have a great effect upon structure and function of terrestrial ecosystems and on the distribution and productivity of global vegetation. Global warming has recently resulted in uneven precipitation and more frequent extreme droughts and shortages of available soil water in many areas of the world. In addition, plants have different sensitivities to elevated CO2 and drought stress, even when growing in the same environment. Thus it is essential to consider both elevated CO2 and different soil moisture conditions in order to assess the possible effect of global climate change on different species. In this paper, the six annual species, Rumex chalepensis , Vicia sepium , Sedum album, Hemmistepta lyrata , Clinopodium chinense and Chenopodium album, were treated with two levels of CO2 concentrations （400 μL/L and 700 μL/L） and three levels of drought stress （CK： 100% FC （field capacity）, MS： 40% FC and SS： 20% FC） in walk-in CO2 chambers to determine the responses of growth and biomass allocation to the interaction of elevated CO： and drought stress and to test whether elevated atmospheric CO2 ameliorates negative effects of drought by increasing water use efficiency. Results showed that V. sepium and S. album survived under all experimental conditions. However, there was some mortality in other species in drought treatments. Elevated CO2 stimulated the growth of the five C3 plants R. chalepensis, V. sepium, H. lyrata, C. chinense and C. album under three levels of drought stress, while it inhibited the growth of S. album under drought stress. Drought stress inhibited the growth of all six species, but the growth of the CAM plant S. album was fastest under drought stress. The interaction of elevated CO2 and drought stress showed significant interspecific variation： elevated CO2 concentration alleviated the negative impact of drought on H. lyrata and C. chinense but less so in R. chalepensis and V. sepium; elevated CO2 had no effect on the impact of drought on C. album; for S. album, elevated CO2 even inhibited its growth under drought stress. Overall, elevated CO2 increased the root mass fraction （RMF） and dry matter content （DMC） for most of the species; drought stress obviously increased RMF and decreased DMC in all six species. However, different species had different responses to the interaction of elevated CO2 and drought stress. This indicated that plants could adapt to the interactive effect of elevated CO2 and drought stress by regulating biomass allocation and moisture retention capacity, as dependent on the trade-off between carbon absorption and water loss. The results could help us to understand the adaptation of annual herbs to future climatic change and provide a basis for assessing and evaluating global climate change and its hydrological effect on plant physiological ecology.