Physiological responses of Haloxylon ammodendron to rainfall pulses in temperate desert regions, Northwestern China

Physiological characteristics except WUE of H. ammodendron have obvious response to rainfall pulses of 6-12 mm, and rainfall in this range at least is "effective" precipitation for H. ammodendron. In water-limited ecosystems, pulses of rainfall can trigger a cascade of plant physiological responses. Small precipitation events account for a large proportion of the precipitation received in arid regions. Their potential ecological importance, however, has previously been ignored. Here the responses of the physiological characteristics of Haloxylon ammodendron (H. ammodendron) to rainfall were evaluated by rainfall manipulative experiments during the growing season of 2012 in the desert region of Northwestern China. Net Photosynthesis rate (P (n)), transpiration (Tr), water use efficiency (WUE), stomatal conductance (G (s)), internal concentration of CO2 (C (i)), sap flow, leaf water potential (I), and soil volumetric water content (SVWC) were monitored throughout the experimental period. The results showed that the water status of H. ammodendron is highly sensitive to rainfall pulses. P (n), Tr, and G (s) increased with rainfall and then decreased gradually after rainfall. WUE decreases after rainfall and increases in times of increasing drought, although within a narrow range. H. ammodendron has a special buffering ability induced by harsh environmental conditions, particularly the rainfall patterns. Collectively, a 6-mm or greater rainfall amount is "effective" precipitation for H. ammodendron from the perspective of plant physiology. This study result is essential to the theories and practice of combating desertification.