The Responses Of Tamarix Ramosissima Seedlings On Nitrogen Distribution And Utilization And Growth Under Drought Stress

Tamarix ramosissima Ledeb.is a dominant species in the lower reaches of the Tarim River,and plant survival and growth is suffered from water and nutrient double coercion in the process of ecological restoration of the lower reaches.Four soil watering regimes?D₁-20%,D₂-35%,D₃-50%and D₄-75%of relative field capacity?and two types of N addition(¹⁵N-KNO₃ and ¹⁵N-NH₄Cl)were provided in order to explore the changes in T.ramosissima growth,photosynthetic physiological traits and the distribution and utilisation of nitrogen in seedlings under drought stress and nitrogen.The studies can provide the theoretical basis for ecological restoration in the lower reaches of Tarim River.The test result indicated that:Water is the main factor of apparent growth of T.ramosissima seedlings,and we found an increase in plant height with the enhancement of N supply.At D₁,ammonium nitrogen significantly affected on plant height,but nitrate nitrogen is more significant at the D₄.Ammonium nitrogen is more easy to be absorbed by the root for total biomass accumulation,and nitrate nitrogen affect the total biomass of seedlings more significant only when the soil water content is D₄.With the enhancement of N supply,the specific root length decreased more significant indicating more distribution on the ground when the soil water content is D₂ and D₃.When water is scarce,significantly increased the root-shoot ratio of nitrate nitrogen,nitrogen are uptake for growing seedling roots.Only at water fitness?D₃?,ammonium nitrogen affects root-shoot ratio significantly decreased,and is used for crown diameter.When seedlings were subjected to water stress,the photosynthetic system of T.ramosissima seedlings was inhibited?The value of Fv/Fo decreased significantly?,two types of nitrogen on chlorophyll a content has a significant affection.In addition to the soil moisture for D₄,chlorophyll b was more sensitive to ammonium nitrogen supply than chlorophyll a.With the enhancement of N supply,we found an increase in photosynthetic efficiency(?_PS???-quantum yield of PS II linear electron and ETR-estimated electron transport rate).At D₁ and D₃ the affection of ammonium nitrogen is more significant,but at D₂ the affection of nitrate is more significant.The capacity for nitrogen absorption was diminished for seedlings under D₁ and D₄.The nitrogen absorption capacity of the seedlings presented the trend of first increasing and then decreasing with the increase in soil moisture.The distribution of¹⁵N-KNO₃ to seedlings was higher as opposed to ¹⁵N-NH₄Cl,but the utilisation of¹⁵N-NH₄Cl was higher.Under drought stress?D1?,the roots of seedlings occupied the higher distribution to two nitrogen.As the level of drought stress reduced,nitrate nitrogen in the aerial parts of plants increased with distribution but ammonium nitrogen in the roots occupied more.In addition,seedlings showed higher utilisation of nitrate nitrogen only at D4.Meanwhile,underground showed high utilisation of seedlings for nitrogen under drought stress.With the water increased,the aerial part showed high utilisation of nitrogen gradually.Therefore,water is the key factors of T.ramosissima seedlings,and when seedlings absorbs nitrogen,the coupling effect of water and nitrogen can be conducive to seedlings change their growth and physiological effects to adapt the undesirable surroundings.