Responses to precipitation treatment for Haloxylon ammodendron growing on contrasting textured soils

The responses to precipitation of Haloxylon ammodendron (C.A. Mey.) Bunge (Chenopodiaceae), a small xerophilous tree growing on contrasting textured soils, were evaluated under no, natural, and double precipitation treatments during the entire growing season of 2006. The contrasting textured soils are sandy and heavy textured, and both are the original habitat of H. ammodendron at the south edge of Gubantonggute Desert, Central Asia. Photosynthesis, leaf water potential, transpiration, water use efficiency and leaf biomass production were monitored throughout the growing season. Root distribution of H. ammodendron was evaluated at the end of the experiment. Overall, this small tree did not show significant response to a large summer precipitation pulse or precipitation treatments, in terms of photosynthetic carbon assimilation on either soil. The leaf water potential, transpiration, and water use efficiency appeared to be highly sensitive to a large precipitation pulse and precipitation treatments in sandy soil; and leaf biomass production was also much higher for plants in sandy than that of heavy‐textured soil. In sandy soil, defoliation occurred when pre‐dawn leaf water potential dropped below −3.0 MPa, while in heavy‐textured soil, defoliation occurred when pre‐dawn leaf water potential dropped below −3.75 MPa. For similar above‐ground parts, the small trees at the sandy site developed much deeper root systems and had nearly double the surface area of feeder roots compared to those at the heavy‐textured site. Partially owning to the deeper and larger root system, H. ammodendron growing at coarse‐textured site was in better water conditions than those at heavy‐textured site under the same climatic conditions.