Response Of Branches And Leaves Traits Of Nitraria Tangutorum To Environment And The Effect Of Wind Prevention And Sand Fixation

Nitraria tangutorum is one of the wind prevention and sand fixation plant which distributed in Northwest China.The effect of wind prevention and sand fixation is mainly decided by the plant cluster types and configuration mode.In this research,a large number of investigations were carried out in the natural distribution area of N.tangutorum.It was found that the plant cluster types of N.tangutorum in different environments were quite different.Taking the characteristics of branches and leaves as research objects,the response of plant cluster shape of N.tangutorum to slope direction,slope position,site type and sand burial environment were analyzed;according to these results,the response of branches and leaves traits and plant cluster shape of N.tangutorum to water conditions,saline alkali stress,sand burial environment and mechanical damage were discussed by control experiments.Wind tunnel simulation tests were carried out on the configuration forms of different plant cluster types;and the wind and sand prevention effects of different plant cluster types and configurations were compared and analyzed.This study would set a theoretical foundation to get the ideal plant cluster types by artificially inducing,so as to promote the ecological utilization value of N.tangutorum in the field of wind and sand prevention.The main conclusions are as follows:（1）Water is the main limiting factor for growth and development.The length of branches,branch angle,base diameter,branch ratio and other indicators of N.tangutorum reached the maximum when the rainfall increases by 15%,and the shape of plant clusters gradually transits from"upright"to"semi upright".When the precipitation is lower than the annual average precipitation,the growth of branches and leaves are adversely affected to a certain extent.However,it is conducive to the increase of the nods and new branches in lower water condition.When the rainfall decreases by 30%,the number of primary branches is the largest.The leaves length,width,thickness and length to width ratio of N.tangutorum reach the maximum when the rainfall increases by 30%,and the leaf length is21.46mm,the width is 4.69mm and the thickness is 0.47mm;When rainfall decreases by30%,the leaves appear"compound epidermis",and mucous cells appear in the mesophyll.（2）The saline alkali stress in the environment mainly acts on the plant through physiological drought.NaCl single salt and NaCl+Na₂SO₄neutral mixed salt with the concentration of 0.8%～1.6%can promote the elongation growth of N.tangutorum;The branching angle and branching ratio of branches are the largest with the concentration is 0.8%.Na₂CO₃+Na HCO₃ alkaline mixed salt with the concentration of 0.4%can promote the elongation growth of N.tangutorum;when the concentration is 1.2%,it can effectively improve the branch ratio.NaCl treatment had no significant effect on the plant cluster shapes of N.tangutorum.NaCl+Na₂SO₄ and Na₂CO₃+Na HCO₃ treatment could increase the branch angle of primary branches and induce the plant cluster shapes of N.tangutorum to be"semi erect"or"creeping".The leaves of N.tangutorum under various salt stress were generally smaller than those under normal environment;Compared with NaCl single salt and NaCl+Na₂SO₄ neutral mixed salt treatment,the leaves of N.tangutorum treated by Na₂CO₃+Na HCO₃ were smaller,with a length of 16.14～18.53mm,a width of 4.01～4.50mm and a thickness of 0.41～0.44mm.When the concentration was higher than 0.8%,the leaves showed was"compound epidermis",and mucus cells began to appear in the mesophyll.（3）Moderate sand burial has a beneficial effect on the growth of N.tangutorum branches.It can increase the branch angle and branch ratio,so as to change the plant cluster type from"erect"and"semi erect"to"creeping".The optimum sand burial depth of N.tangutorum branches is 4cm～6cm.（4）The optimum left height of N.tangutorum is 5cm～10cm while stubble.The primary growth,secondary growth and branching ability of branches can respond to the mechanical damage caused by flat stubble to the greatest extent;Most of N.tangutorum with left height of 0cm～10cm stubble are"creeping",and most of N.tangutorum with left height of 10cm～15cm stubble are"semi upright".（5）When the branch angle of N.tangutorum is less than 40°,the variation law of the air velocity field of the model is relatively close,and the shape of the plant cluster showed"upright";When the branch angle of N.tangutorum is btween 40°～70°,the variation law of the air velocity field of the model is relatively close,and the shape of the plant cluster showed"semi upright";When the branch angle of N.tangutorum is more than 70°,the variation law of the air velocity field of the model is relatively close,and the shape of the plant cluster showed"creeping".（6）Taking N.tangutorum as artificial afforestation materials,the configuration of different plant clusters are as follows:The windbreak effect of N.tangutorum with"single cluster"configuration is not effective,so it is not recommended in practice.The"single row"style configuration of N.tangutorum could do better in wind prevention,and the"creeping"plant clusters are more advantageous to reduce the leeward crosswind velocity.For"two rows"style,the"upright"and"semi upright"clumps are more effective than"creeping"clumps to windbreak on the windward side.In practice,the row spacing is recommended to be in the range of 5H～8H.Under the low wind speed,the row spacing can be increased to 8H～10H.