Responses of two desert shrubs to simulated rainfall pulses in an arid environment, northwestern China

Background and aimsDesert environments are characterized by limited and highly variable rainfall, which is an intermittent source of water critical to the evolution of the structure and functioning of desert ecosystems. The present study was the first to assess the effects of different amounts of rainfall received through discrete rainfall events and of their seasonality on two little-studied desert shrubs, namely Reaumurica soongorica and Nitria sphaerocarpa, in an arid inland river basin in north-western China.Materials and methodsPulse rainfall events were simulated at the following magnitudes (amount of water in millimeters per rainfall event): 0, 5, 10, 15, 25, and 40mm on two days in 2016, 24th June (early growing season) and 4th August (middle growing season), respectively. The rainfall effects were measured in terms of the following parameters: plant uptake of rainwater by plants as assessed by O-18 in the water within plant tissue, pre-dawn plant water potential, and the rates of photosynthesis and stomatal conductance.ResultsN. sphaerocarpa shows faster response to simulated pulse rainfall events than R. soongorica, and the response of both species was quicker in the middle- than in early- growing season. Water uptake increased non-linearly with the amounts of rainfall, reaching a plateau at about 25mm in R. soongorica and 20mm in N. sphaerocarpa. The accumulative carbon gain relative to the controlled experiment increased with the amounts of rainfall, the increase being greater in the middle growing season.ConclusionOur results clearly show that both the seasonality and the amounts of rainfall in discrete rainfall events took great impacts on response of plant ecophysiological activities and such responses are species dependent. The challenge ahead is to understand the consequences of long-term variability in rainfall for the physiology of desert plants and species dynamics in desert ecosystems.