Niklaus Pascal A, Spinnler D, Körner C
Institute of Botany, University of Basel, Schönbeinstrasse 6, CH-4056 Basel, Switzerland (e-mail:
Oecologia. 1998 Nov;117(1-2):201-208. doi: 10.1007/s004420050649.
Water relations of nutrient-poor calcareous grassland under long-term CO enrichment were investigated. Understanding CO effects on soil moisture is critical because productivity in these grasslands is water limited. In general, leaf conductance was reduced at elevated CO, but responses strongly depended on date and species. Evapotranspiration (measured as HO gas exchange) revealed only small, non-significant reductions at elevated CO, indicating that leaf conductance effects were strongly buffered by leaf boundary layer and canopy conductance (leaf area index was not or only marginally increased under elevated CO). However, these minute and non-significant responses of water vapour loss accumulated over time and resulted in significantly higher soil moisture in CO-enriched plots (gravimetric spot measurements and continuous readings using a network of time-domain reflectometry probes). Differences strongly depended on date, with the smallest effects when soil moisture was very high (after heavy precipitation) and effects were largest at intermediate soil moisture. Elevated CO also affected diurnal soil moisture courses and rewetting of soils after precipitation. We conclude that ecosystem-level controls of the water balance (including soil feedbacks) overshadow by far the physiological effects observed at the leaf level. Indirect effects of CO enrichment mediated by trends in soil moisture will have far-ranging consequences on plant species composition, soil bacterial and faunal activity as well as on soil physical structure and may indirectly also affect hydrology and trace gas emissions and atmospheric chemistry.
研究了长期二氧化碳浓度升高条件下养分贫瘠的钙质草原的水分关系。了解二氧化碳对土壤湿度的影响至关重要，因为这些草原的生产力受水分限制。一般来说，二氧化碳浓度升高时叶片导度会降低，但响应强烈依赖于日期和物种。蒸散（以水汽交换测量）显示在二氧化碳浓度升高时仅略有降低且不显著，这表明叶片导度的影响被叶边界层和冠层导度强烈缓冲（在二氧化碳浓度升高时叶面积指数未增加或仅略有增加）。然而，这些水汽损失的微小且不显著的响应随时间累积，导致二氧化碳浓度升高地块的土壤湿度显著更高（重量法现场测量以及使用时域反射仪探头网络的连续读数）。差异强烈依赖于日期，当土壤湿度非常高（大雨后）时影响最小，而在中等土壤湿度时影响最大。二氧化碳浓度升高还影响了土壤湿度的日变化过程以及降雨后土壤的再湿润。我们得出结论，生态系统水平的水分平衡控制（包括土壤反馈）远远超过了在叶片水平观察到的生理效应。由土壤湿度趋势介导的二氧化碳浓度升高的间接影响将对植物物种组成、土壤细菌和动物活动以及土壤物理结构产生广泛影响，并且可能间接影响水文、微量气体排放和大气化学。
