Physiological Adaptation To Water And Fertilizer Interaction And Nutrient Utilization Of Three Native Grass On Qinghai-Tibet Plateau

In this paper,Poa crymophila,Festuca coelestis and Stipa purpurea,three native plants on the Qinghai-Tibet Plateau,were selected as the research objects,and three water gradients were set by pot experiment.Soil field water capacity of low water(35%),medium water(55%),high water(75%)and four fertilizer amounts CK(0g/kg),low fertilizer(0.11g/kg),medium fertilizer(0.33g/kg),high fertilizer(0.45g/kg).The physiological characteristics and nutrient cycling response of water and fertilizer coupling to Poa crymophila,Festuca coelestis and Stipa purpurea were studied.The results are as follows:1.Under drought stress,the net photosynthetic rate of tested plants showed a downward trend,and proper fertilization could offset part of the negative photosynthetic effect by adjusting stomatal conductance by changing stomatal size.The daily average net photosynthetic rate of Poa crymophila and Festuca coelestis was the highest under high water and fertilizer,while Stipa purpurea showed the highest under high water and low fertilizer,which were significantly increased by 71.2%,108.4% and25.4% compared with CK,respectively.Drought affected the water consumption of Poa crymophila and Festuca coelestis,and water use efficiency decreased,while Stipa purpurea was on the contrary.2.The proline content of Poa crymophila and Festuca coelestis increased with the increase of water stress and fertility,and the maximum value appeared in low water and high fertility,which were significantly increased by 56.8% and 39.6% compared with CK,respectively.Water stress increased the accumulation of soluble sugars,starch and nonstructural carbohydrates,but decreased gradually with the addition of nitrogen.The interaction of water and fertilizer had little effect on Stipa purpurea.The accumulation of proline,soluble sugar,starch and nonstructural carbohydrate under water and low fertilizer was beneficial,and the contents of the latter two under water and low fertilizer were similar to that under water and control.In general,Stipa purpurea had higher osmotic stress adaptability than Poa crymophila and Festuca coelestis.Poa crymophila and Festuca coelestis adapted to the dry environment by increasing osmotic regulatory substances.Nitrogen application promoted the accumulation of proline,but inhibited the increase of soluble sugars,starch and non-structural carbohydrates.3.Under drought stress,rhizosphere and non-rhizosphere environments of the three plants were affected,and the contents of alkali-hydrolyzed nitrogen and available phosphorus in soil decreased,while low fertilizer compensated for the loss of phosphorus to some extent.Under high fertilizer,soil nitrogen content of Poa crymophila and Stipa purpurea increased,but soil alkali-hydrolyzed nitrogen content of Festuca coelestis decreased.4.The growth of root surface area,root length and root volume of the three plants were inhibited to varying degrees with the increase of drought.In low water,high fertilizer restricted the growth and development of Festuca coelestis root surface area,root length and root volume,while Poa crymophila and Stipa purpurea were less affected.In middle water,the addition of height and fertilizer of Festuca coelestis,Stipa purpurea and Poa crymophila significantly promoted the growth and development of root system.In high water level,Poa crymophila and Festuca coelestis needed medium fertilizer,and Stipa purpurea needed low fertilizer.Meanwhile,the average root diameter of the three plants was not significantly affected by water and fertilizer.5.Above-ground biomass and N use efficiency of the three species decreased with the increase of water stress and fertility.The underground biomass and N use efficiency were different under different water and fertilizer treatments.The underground biomass of Poa crymophila and Festuca coelestis increased with the increase of fertility,but N use efficiency had no significant change.In middle water,the underground biomass and N use efficiency of Poa crymophila decreased with the increase of fertility,but the opposite was true for Festuca coelestis.In high water and middle water,the underground biomass was less affected by fertility,and N use efficiency showed a downward trend with the increase of fertility.On the whole,the biomass and N use efficiency of the three species decreased with the increase of water stress,the biomass increased first and then decreased with the increase of fertility,and the N use efficiency decreased gradually.In order to adapt to the extreme environment in alpine region,herbaceous plants have different requirements for water and fertilizer and have different survival adaptation strategies.The comprehensive analysis showed that water was the key limiting factor for successful supplementary sowing of the three plants.The optimal water and fertilizer ratio of Poa crymophila and Festuca coelestis was high water and high fertilizer,while Stipa purpurea was high water and high fertilizer.This study provides a theoretical basis for the re-seeding of native plants on the Qinghai-Tibet Plateau,and provides important information for reducing the risk of ecological restoration failure in similar areas...