草原植物根系起始吸水层深度测定方法及其在不同群落状态下的表现

Abstract

We studied water uptake by plant roots in two typical steppe communities,at the Inner Mongolia Grassland Ecosystem Research Station of the Chinese Academy of Sciences,Xilin Gol League,Inner Mongolia,China.Water uptake by roots forms the base of the Soil-Plant-Atmosphere Continuum.Previously,a model of root water uptake has been used,based on root distribution,but there has been no effective way to research water uptake of steppe plants directly.We used a new method to determine where the plant roots begin the uptake of water.First,we excavated to the subsoil and measured soil water seepage in the selected plots.By watering the plants and then measuring leaf water potential using a water potential system,we were able to use changes in water potential to indicate water uptake.The initial depth of water uptake by roots could thus be determined indirectly.We contrasted two different successional communities,a recovery plot enclosed since 1983,and an open,grazed,degraded plot.Second,we measured uptake by some major plants in different successional communities.We found that the initial depth of water uptake by roots could be measured using the soil excavation method described.In the degraded community,six species showed initial root water uptake at 0-5 cm beneath the surface,Agropyron michnoi,Artemisia frigida,Carex korshinskyi,Cleistogenes squarrosa,Leymus chinensis and Stipa grandis.In the restored community,different species exhibited deeper initial uptake of water.The initial depth of water uptake by roots of Carex korshinskyi,Cleistogenes squarrosa and Artemisia frigida was 0-5 cm below the surface.Here a spatial niche overlap exists in the exploitation of water.However,initial uptake depth of Leymus chinensis,Stipa grandis and Agropyron michnoi was 5-10 cm,these species also share a similar niche.Obviously,the former species uptake water more shallowly than the latter,providing evidence for some spatial separation of water utilization niches.In a different restored community,the initial depth of root water uptake of Carex korshinskyi,Cleistogenes squarrosa and Artemisia frigida did not change with a transition to overgrazing.However,Leymus chinensis,Stipa grandis and Agropyron michnoi began to take up water more shallowly following degradation.As plants miniaturized and root systems became shallower,the initial layer of water uptake also becomes increasingly shallow.This indicated that the steppe plant community was able to vary its use of water resources.In a typical steppe community,there was more substantial niche overlap and less niche separation among plant species.In general,taller plants showed a tendency towards deeper initial depth of water uptake than shorter plants.