Effects Of Drought Stress And Nitrogen Form On Traits Of Understory Components Of Hemarthria Altissima

The grassland ecosystem is the largest terrestrial ecosystem in China.The climate change is seriously affecting the grassland ecosystem in China.In arid and semi-arid regions,water and nitrogen,as two limiting factors of ecosystem and plant growth,have always been a hot issue.As the main accompanying grass species of Songnen grassland,Hemarthria altissima has obvious advantages of high nutritional value,good palatability and strong resistance.However,there are few studies on drought and nitrogen response of Hemarthria altissima,especially on nitrogen form.In this paper,the processing factors of drought stress and nitrogen form are simulated in the domain of Hemarthria altissima.Normal water content W1（70%-75%of field water capacity）,moderate drought stress W2（50%-55%of field water capacity）and severe drought stress W3（30%-35%of field water capacity）.The responses of biomass,structural characters and chemical characters to different drought stress and nitrogen form in the lower part of the grassland were investigated under CK（0 N）,N1（100%NH₄⁺-N）,N2（100%NO₃^--N）and N3（NO₃^--N and NH₄⁺-N 1:1 mixture）.The aim is to provide theoretical basis for the future scientific management of grassland.The main results and conclusions are as follows:（1）Nitrogen form and the interaction between drought stress and nitrogen form had no significant effect on the biomass of Hemarthria altissima.With the increase of drought stress,the aboveground biomass and total biomass of Hemarthria altissima decreased significantly.Under the condition of no nitrogen application,the biomass of moderate drought stress was significantly decreased by 30%compared with that of normal water content,and the biomass of severe drought stress was significantly decreased by 48%compared with that of normal water content.Under normal water content conditions,the aboveground biomass of the treatment of NO₃^--N and NH₄⁺-N1:1 mixture fertilization was about 20%higher than that of other treatments,which was more conducive to biomass accumulation and thus improved the yield of Hemarthria altissima.（2）Drought stress had a significant effect on root and rhizome morphological characters,while the root length,root surface area,root area,root volume,root volume,root tip number,bifurcation number and the relative growth rate of each trait were all decreased with the deepening of drought degree.Under moderate drought conditions,the relative growth rates of root length,root surface area,root volume and root tip number of plants treated with single nitrate nitrogen were significantly higher than those of other treatments.（3）With the increase of drought severity,N and P contents in roots and rhizome increased,but C content did not change significantly.Without nitrogen application,plant roots need to consume more energy to maintain root growth.Under the condition of severe drought stress,the rhizomes of CK preferred to expand to spatial environment,and the rhizomes of nitrogen treatment preferred to store nutrients.（4）Drought stress,nitrogen form,and coupling between drought stress and nitrogen form all had significant effects on soil C content.Nitrogen form significantly affected soil N content,soil C/N ratio and soil N/P ratio.In conclusion,drought stress had greater effect on the growth of Hemarthria altissima,and NO₃^--N and NH₄⁺-N 1:1 mixture fertilization could significantly increase aboveground biomass and total biomass of Hemarthria altissima.The application of nitrate nitrogen was more beneficial to the growth of the underground part of Hemarthria altissima under moderate drought.The results are of great significance for further understanding the effects of climate change on plant growth.