Responses Of Natural Nitraria Tansutorum Shrubs To Simulated Rainfall

In order to reveal the adaptive strategies of desert ecosystems to the future spatiotemporal variability of rainfall, and to explore physiological and ecological characteristicsof desert plants in rain increased scenario, Nitraria tangutorum Bobr. shrub which isone of the typical desert plants was used to the research object in Minqin County, Gansu Province. Taking the five kinds of open artificial simulated rainfall(increased0%,25%,50%,75%and100%of mean annual precipitation, respectively), responses of the spatiotemporal dynamics of soil moisture, branches and leaves morphological characteristics and their physiological ecology indicators to different increased rainfall were analyzed in this paper, to reveal the relationship between leaf longevity and others leaf traits and their response to different increased rainfall, The main results of the study is as fllows.(1) The impact of different increased rainfall on soil moisture of N. tangutorum shrub had the different change over time. On the basis of of Minqin natural precipitation,10cm of soil moisture conditions of N. tangutorum shrub were significantly improved in the increased75%and100%treatments. In May and July of2011, soil moistures of30cm on the first day after rainfall and50cm layer on the third day of rainfall in the100%rainfall treatment were significantly greater than that in the0%rainfall treatment.(2) In June-September of2010and2011, the branches and leaves growth of N. tangutorum in the100%increased rainfall treatment were significantly promoted, but thebranches and leaves growth of N. tangutorum in the75%rainfall treatment were significantly promoted in2011. The significant differences of threshold of above five morphological indicators of branches leaves growth in the75%and100%rainfall treatment in2011were significantly lower than that of2010.(3) The100%increased rainfall significantly promoted the use of range of N. tang utorum leaves to photosynthetically active radiation, and enhanced the light absorption,conversion and use capacity. Among them, with increasing rainfall, the leaves light response parameters of maximum net photosynthetic rate (Amax), apparent quantum requirement (AQY), light saturation point (LSP) were increased, but light compensation point (LCP), stomatal limitation value (Ls) was gradually decreased. Apparent quantum requirement (AQY) in the increased100%rainfall treatment were significantly greater than thatof the increased0%rainfall treatment.Theirs values difference were70.00%The physiological metabolic activity of N. tangutorum leaves in the100%rainfalltreatment was promoted. During the growing season, leaf water potential, transpiration rate of N. tangutorum were increased with increasing rainfall, but water use efficiency(WUE) was gradually decreased with increasing rainfall. During July to September, theabove indexes in the100%rainfall treatment were significantly different. the relationship between net photosynthetic rate and water use efficiency (leaf water potential) were different in different months.(4) Leaf structure traits of N. tangutorum in response to different increased rainfallwere differences. During July to September, specific leaf area(SLA, leaf area per mass), photosynthetic nitrogen use efficiency(PNUE) were increased with increasing rainfall,but leaf dry matter content, area-based leaf nitrogen(Narea), mean leaf longevity was decreased with increasing rainfall.Mean leaf longevity were significantly shorten in different increased rainfall treatments. Mean leaf longevity in the25%,50%,75%and100%increased rainfall treatments were shorten the2.00d,2.25d,5.00d,7.75d than thatof the0%treatment. The relationship between mean leaf longevity and leaf dry mattercontent, Nmass, Narea were positively correlated, but mean leaf longevity and SLA were negatively correlated.(5) Leaf structure traits and functional traits have a good relationship, which characterized by the convergence of adaptation strategies of N. tangutorum on the environment. During July to September, mean leaf longevity and Pn, PNUE was significantly negatively correlated, while mean leaf longevity and WUE was significantly positively corr elated. while mean leaf longevity and WUE was significantly positively correlated (P <0.05). However, mean leaf longevity and length of flowering branches, length of vegetation branches, diameter of flowering branches, diameter of vegetation branches, dry matter weight of flowering branches, dry matter weight of vegetation branches was significantly negatively correlated, mean leaf longevity and soil moisture of10cm layer was significantly negatively correlated. To establish multiple linear regression equation of mean leaf longevity of N. tangutorum and Pn, WUE, SLA, leaf dry matter content, Nmass,Narea, PNUE, the total increased rainfall during growing season were well fitted. Amongthem, the impact of Narea on mean leaf longevity of N. tangutorum was the greatest,while PNUE was minimal impact.