Responses Of Leaf Photosynthesis,Stem Hydraulic Traits And Seed Production In Salix Psammophila And Caragana Korshinskii To Manipulated Precipitation Variation

Water is a key factor of limiting vegetation restoration and rehabilitation on the Loess Plateau of China,and precipitation variation plays an important role in shaping the structure and function of local ecosystem.In this paper,we selected Salix psammophila and Caragana korshinskii growing in water-wind erosion crisscross region of northern Shaanxi as the objects,and explored the effects of manipulated precipitation variation(control:normal precipitation;water addition:water was increased by 45%,drought:water was removed by 50%)on leaf photosynthesis,stem hydraulic structure and seed production.The major objectives were to reveal the physio-ecological mechanisms of the two shrubs adapting to the dry sandy environment,and to provide better understanding of the distribution and management of these two shrubs as well as the sustainability of ecosystems in the future.The main results were as the follows:(1)Most leaf morphology traits of two shrubs showed no response to manipulated precipitation variation.However,the leaf water potential,gas exchange,light response curve and CO2 response curve parameters showed obvious responses to rainfall variation.The main results were as the follows:a)Predawn leaf water potential(?pd)showed no significant difference among different treatments of 5.psammophila,while midday leaf water potential(?md)expressed significant difference in dry season;there was no significant difference in?pdand ?md among different treatmentsof C.korshinskii in dry season,but in wet season,drought significantly reduced ?pd and ?md.b)The leaf gas exchange parameters(net photosynthetic rate?stomatal conductance and transpiration rate)of both shrubs responded to irrigation in both dry and wet seasons,the response of leaf gas exchange parametrs to drought occurred in dry season for S.psammophila,and in wet season for C.korshinskii.c)The responses of light response and CO2 response curve parameters varied for species and seasons.(2)Stem hydraulic traits of S.psammophila and C.korshinskii had different responses to simulated rainfall changes.Midday leaf water potential and stem water transport efficiency of S.psammophila showed significant responses to irrigation rather than to drought.The cavitation resistance and native midday embolism showed no significant differences among different treatments of S.psammophila.For C.korshinskii,leaf water potential and water transport efficiency responded significantly to drought rather than irrigation.Drought increased native midday embolism significantly.The adaptive changes of leaf area index were helpful to maintain the water transport efficiency of the two shrubs and to reduce the degree of embolism.(3)Rainfall variation affected seed production and vigor of C.korshinskii.The number of pods per branch length and the pod-bearing rate of C.korshinskii were significantly affected by rainfall changes,and they were significantly higher under irrigation than those under drought.Drought significantly reduced the seed yield per branch length,and the number of seeds and the quality of single seed of irrigation treatment were significantly higher than those of drought.Drought reduced seed vigor,yet the effect of irrigation on the seed vigor was relatively small.