Effects Of N And P Addition On Plant Tissue Nutrient Characteristics And Root Architecture Of Alhagi Sparsifolia And Achnatherum Splendens

Nutrient resorption is an important strategies for plants to adapt to arid environment and makes plants less dependent on the environment.It is vital to the individual life activities,composition and stability of plant community,and nutrient cycle of ecosystem.Nitrogen?N?and phosphorus?P?are essential for plant growth and play important roles in physiological regulation.Previous studies have focused on the effects of N or P addition on leaf nutrient contents and nutrient resorption,however,knowledge about the effects of different supply level of N,P and different N:P ratios on tissue nutrient traits,nutrient resorption and root architecture of plant is still limited,especially for eremophyte.Potted plant experiments were conducted to study the effects of different soil nutrient levels(1.5,4.5,13.5 g N m^-22 yr^-1)and different N:P ratios?5,15,25?on leaf morphological traits,nutrient resorption,nutrient contents and root architecture of Alhagi sparsifolia and Achnatherum splendens,which are two typical desert plants.The aims of this study are to provide theoretical supports for the improvement and management of salinization in arid areas.The main results are as follows:?1?The effects of different soil nutrient levels(1.5,4.5,13.5 g N m^-22 yr^-1)and different N:P ratios?5,15,25?on leaf morphological traits of the two plants were inconsistent.The increase of soil nutrition significantly increased the specific leaf area?SLA?of green leaves of A.sparsifolia,but decreased the leaf dry matter content?LDMC?of green leaves and SLA of senesced leaves of A.splendens.Increasing soil nutrient level significantly increased SLA of green leaves of A.sparsifolia,SLA and thickness of blade?TB?of senesced leaves of A.splendens under the same N:P condition.At the same nutrient level,variations in N:P ratios had no significant effects on LDMA,SLA and TB of senesced leaves of A.sparsifolia.The increase of N:P ratios significantly increased the SLA of green leaves of A.splendens at lower nutrient level,while decreased the LDMC of senesced leaves of A.splendens at moderate nutrient level.?2?The responses of nutrient contents of each tissue in the two plants to different soil nutrient levels(1.5,4.5,13.5 g N m^-22 yr^-1)and different soil N:P?5,15,25?were different.The increase of soil nutrient level significantly increased N,P contents in green leaves of the two plants,N contents in green stems of A.sparsifolia,and N,P contents in green roots of A.splendens,while the response of N contens in green roots to N:P ratios was nonlinear.However,the increase of soil N:P ratio significantly decreased P contents in green stems and senesced roots of A.sparsifolia,senesced leaves and green roots of both plants,while N contents in green leaves and P contents in senescence roots of A.splendens decreased initially,followed by an increase with increase of N:P ratio.Under the same soil N:P condition,the increase of soil nutrient level had effects on N and P contents in ground and subterranean tissues of A.sparsifolia,respectively.At the same nutrient level,the content of N,P in senesced leaves and green stems were mainly affected by soil N:P ratio.Nutrient contents in leaves and roots of A.splendens were affected by both soil nutrition level and N:P ratio.?3?The N and P nutrient resorption?NRE,PRE?of leaves of the two plants responded differently to different soil nutrient levels(1.5,4.5,13.5 g N m^-22 yr^-1)and different soil N:P?5,15,25?.The increase of soil nutrient level significantly increased NRE and PRE of A.splendens,while the increase of soil N:P ratio significantly decreased NRE and decreased PRE.No significant differences were observed in NRE and PRE of A.sparsifolia with the increase of soil nutrient level and N:P ratio.The increase of soil nutrient level significantly increased the NRE and PRE of A.sparsifolia at higher N:P ratio?25?,PRE of A.splendens at lower N:P ratio?5?,and NRE of A.splendens at moderate and higher N:P ratio?15,25?.The NRE of A.sparsifolia significantly decreased and increased at lower and higher level of soil nutrition with the increase of N:P ratio,respectively.The increase of soil N:P ratio significantly increased NRE of A.splendens at all soil nutrient levels.?4?Different soil nutrient levels(1.5,4.5,13.5 g N m^-22 yr^-1)and different soil N:P?5,15,25?had different effects on root architecture of the two plants.The increase of soil nutrient level significantly decreased the the mean diameter?MD?of green roots of A.splendens and projection area?PA?of green and senesced roots of A.sparsifolia,but increased the PA and FD of green roots of A.splendens.However,only PA of green roots of A.sparsifolia significantly decreased with the increase of soil N:P ratio.The increase of soil nutrient level significantly increased MD and FD of green roots of A.sparsifolia and A.splendens,respectively,but decreased PA of green leaves of A.sparsifolia and senesced leaves of A.splendens at lower and moderate N:P ratio?5,15?.At higher N:P ratio?25?,the increase of soil nutrient level significantly decreased FD,MD and PA of green roots of A.sparsifolia,but increased FD and MD of green roots of A.splendens.The MD and PA of green roots of A.sparsifolia significantly increased,while the MD of green roots of A.splendens significantly decreased with the increase of N:P ratio at lower and moderate level of soil nutrition.At higher level of soil nutrition,the increase of N:P ration significantly decreased MD and PA of green and senesced roots of A.sparsifolia,but significantly increased MD of green roots,FD and PA of senesced roots of A.splendens.In conclusion,the results of this study indicated that the responses of leaf morphological traits,nutrient characteristics,tissue nutrient contents and root architecture of legumes A.sparsifolia and grasses A.splendens to soil nutrient level and N:P were different,indicating that different tissues of typical desert plants had different adaptive strategies to the changes of soil nutrient,which also suggested that the adaptive strategy of legume A.sparsifolia is significantly better than that of A.splendens in desert ecosystem.