Sala O E, Lauenroth W K, Parton W J, Trlica M J
Natural Resource Ecology Laboratory and Range Science Deparment, Colorado State University, 80523, Fort Collins, CO, USA.
Oecologia. 1981 Mar;48(3):327-331. doi: 10.1007/BF00346489.
In an attempt to describe some major relationships between soil and plant compartments in a shortgrass steppe, the process of water loss from the system and plant water relations throughout a drying cycle were studied. The water supply was manipulated and some soil and plant variables monitored throughout a drying cycle. Leaf conductance and leaf water potential of blue grama (Bouteloua gracilis) were measured periodically at predawn and noon. Soil water content and water potential of different layers were also monitored.Three different periods were distinguished in the water loss process throughout a drying cycle. These distinctions were made taking into account the relative contribution of different soil layers. Leaf conductance and water potential at noon slowly declined throughout the first 50 days of plant growth. After that, they rapidly decreased, reaching values of 0.29 mm s and-5.0 MPa, respectively. The predawn leaf water potential remained unchanged around-0.5 MPa during the first 45 days, then rapidly decreased. This occurred when soil water of the wettest soil layer was near depletion.Predawn leaf water potentials were highly correlated with water potentials of the wettest layer. Leaf conductance and water potential at noon were correlated with effective soil water potential (soil water potential weighted by the root distribution in the profile). We concluded that root surface area limited the water flow through an important part of the day in this semiarid ecosystem. Axial root resistance did not appear important in determining the equilibrium status between leaves and the wettest soil layer.
为了描述矮草草原中土壤与植物各部分之间的一些主要关系，研究了整个干旱周期内系统的水分流失过程和植物水分关系。在整个干旱周期内，对供水进行了调控，并监测了一些土壤和植物变量。定期在黎明前和中午测量蓝格兰马草（Bouteloua gracilis）的叶片导度和叶片水势。还监测了不同土层的土壤含水量和水势。
在整个干旱周期的水分流失过程中区分出三个不同阶段。这些区分是考虑到不同土层的相对贡献做出的。在植物生长的前50天里，中午的叶片导度和水势缓慢下降。此后，它们迅速降低，分别达到0.29毫米/秒和-5.0兆帕的值。黎明前叶片水势在最初45天里保持在-0.5兆帕左右不变，然后迅速下降。这发生在最湿润土层的土壤水分接近耗尽时。黎明前叶片水势与最湿润土层的水势高度相关。中午的叶片导度和水势与有效土壤水势（根据根系在土壤剖面中的分布加权的土壤水势）相关。我们得出结论，在这个半干旱生态系统中，根系表面积在一天中的重要时段限制了水分流动。轴向根系阻力在决定叶片与最湿润土层之间的平衡状态方面似乎并不重要。
