The Growth Responses Of Three Legume Seedlings And Their Adaptation Strategies To Different Nitrogen And Phosphorus Addition Treatments

Previous studies have shown that the leguminous nitrogen-fixing plants have a more competitive advantage in low-nitrogen and high-phosphorus environments.In fact,the nitrogen-fixing leguminous trees are relatively rare in many nitrogen-deficient temperate zones and high-altitude forests,but more riched in nitrogen-rich tropical and low elevations.This paradox is largely due to the different nitrogen and phosphorus nutrient requirements and environmental adaptation strategies of legume.Therefore,it is necessary to explore the adaptability of different nitrogen-fixing leguminous species under different soil nitrogen and phosphorus conditions.Does the difference of nitrogen demand of different legume species correlate with nitrogen and phosphorus in the growing environment?Adopted with greenhouse potted control test method,at the elevation 820 m of Jianfengling,there were 5 nitrogen gradients(0?75?150?300?600 mg N·kg^-1)and 2phosphorus(0?50 mg P·kg^-1)gradients in the experiment.6 replicates were set for each treatment,and the growth period were 9-13 months.The experimental subject are Ormosia balansae Drake,with low nitrogen requirements;Ormosia semicastrata Hance f.litchifolia How,with medium nitrogen requirements and Archidendron clypearia?Jack?I.C,with high nitrogen requirements.The main experimental results are as follows:?1?Under the condition of nitrogen addition,with analysis of the seedling height,basal diameter,total leaf area,leaf number,total root length,root surface area and total biomass,three species all showed low nitrogen preference,and the sensitivity to medium and high nitrogen addition was O.balansae>A.clypearia>O.semicastrata f.litchifolia.Total leaf area and leaf number were the two most sensitive indexes to the N concentration change,followed by the total root length and root surface area.O.balansae and A clypearia seedlings showed a greater growth rate under low P addition than High P addition,reflecting low N and P demand of these two species.However,O.semicastrata f.litchifolia seedlings grew faster under low N and high P condition.?2?With the increase of nitrogen concentration,the N:P trend of roots and leaves of O.balansae,O.semicastrata and A.clypearia seedlings showed increasing first and then decreasing,increasing,and no obvious,and the minimum value>16,and phosphorus concentration was less than 1 mg g^-1,which was limited by phosphorus;the N:P value of the O.balansae and O.semicastrata was root>leaf,while that of A.clypearia was opposite.?3?From changes of N and P contents in rhizosphere and non-rhizosphere soil,with the increase of nitrogen gradients,the trend of O.balansae,O.semicastrata and A.clypearia rhizosphere and non-rhizosphere soil p H was decreasing,increasing and decreasing respectively;the change trend of available phosphorus content was not obvious;the content of ammonium nitrogen and nitrate nitrogen showed an increasing trend.?4?With the increase of nitrogen concentration,the root-canopy ratio of O.semicastrata seedlings increased significantly,but there was no significant difference between O.balansae and A.clypearia.The biomass allocation strategy of O.semicastrata seedlings could reflect its strong adaptability to medium and high concentration of nitrogen;the nitrogen and phosphorus utilization efficiency of three seedlings was not the adaptive strategy to medium and high concentration of nitrogen;from the enrichment efficiency,the three seedlings were all the same:soil acidification did not occur.Available phosphorus,ammonium nitrogen and nitrate nitrogen contents were rhizosphere<non-rhizosphere,and more nitrogen sources need to provid seedling growth from non-rhizosphere area.