3种荒漠灌木的用水策略及相关的叶片生理表现

以新疆古尔班通古特沙漠南缘原始盐生旱生荒漠的3种建群灌木多枝柽柳(Ｔamarix ramosissima)、梭梭(Ｈaloxylon ammodendron)和琵琶柴(Reaumuria soongorica)为对象，跟踪自然降雨过程，利用LI-6400光合作用系统和Model 3005植物水分压力审测定光合作用和叶水势的变化，以研究浅层土壤水分条件改变对荒漠灌木主要叶片生理特征的影响；并在原始生境中将植株根系完整地深挖取出，进行根系形态结构调查，以确定此3种灌木根系功能型与用水策略。当浅层土壤分别处在水分充足及匮缺的条件下时．测定3种灌木的光合作用响应曲线和日过程曲线．以及黎明前和止午叶水势，结果表明：浅层土壤水分状况变化时，3种灌木的光合能力均没有显著改变；多枝柽柳的叶水势亦没有明显波动；而梭梭和琵琶柴的叶水势却表现出显著差异。在两种功能型根中，多枝柽柳为深根型，生存和乍理活动的维持主要依赖于地下水；而梭梭和琵琶柴为非深根型植物，主要水源是降水形成的浅层土壤水，其用水策略是根据水分条件行效调节根系和冠层生长，从而维持正常的光合作用。即荒漠灌木在长期适应的过样中．已形成不同的根系功能型和用水策略；叶水势对浅层土壤水分状况变化的种间差异性响应在一定程度上反映了这一点。同时．此3种荒漠灌小通过不同的个体适应策略都能够实现水分平衡和碳收支的有效调节，这主要体现为浅层土壤水分条件变化时光合响应的种间一致性。

Water Use Strategies and Corresponding Leaf Physiological Performance of Three Desert Shrubs

Tamarix ramosissima Ledeb., Haloxylon ammodendron (C.A.Mey) and Teaumuria soongorica (Pall.) Maxim.,three primitive and xeric desert shrubs growing and dominating in the southern boundary of the Garbantunggut desert,were tracked with The LI-6400 system by the LI-COR,Inc and Model 3005 plant water pressure chamber.To study the effects of changed water conditions on the photosynthesis performance of the desert shrubs and investigate functional types and water uses patterns of the root systems of desert shrubs.The response curves and daily CO_2 response curves of the three shrubs were respectively evolved when surface water was sufficient or deficient.The results showed that the change of surface water did not significantly affect the photosynthetic capacities of the three desert shrubs; Tamarix ramosissima Ledeb.belonged to a deep root type and its survival depended on underground water; Haloxylon ammodendron (C.A.Mey) and Teaumuria soongorica (Pall.) Maxim.belonged to other root types instead of deep root types and thus depended on water in shallow upper soil but could effectively adjusted the growth of their roots and canopies;different functional types of the root systems of desert shrubs had consistent influence on the photosynthetic responses under different water conditions in shallow soil and this implied that the functional types had formed different mechanisms to effectively adjust their own water balance in the development of their adaptations so as to maintain regular carbon uptake where water shortage occurred in shallow soil. With the rainfall increasing in the region under study year by year,different functional types of the root systems of desert shrubs might physiologically differ and thus dramatic change in rainfall interfered with competitive relations and species compositions of the communities of desert shrubs.