Effects Of Ammonium And Nitrate On The Stress Resistance Of Stoloniferous Herb Glechoma Longituba Suffering From Heterogeneous Cd Stress

Heavy metal pollution,especially cadmium（Cd）pollution,is serious in china.Long pollution cycle,high toxicity and difficult to degrade are the most obvious characteristics of soil Cd pollution.Therefore,the food security in our country is seriously affected by soil Cd pollution.Nitrogen（N）can improve plant tolerance to Cd stress and alleviate Cd stress damage to some extent.Ammonium（NH₄⁺）and nitrate（NO₃^-）ions are the two major forms of nitrogen taken up by plants.Both ammonium and nitrate play important roles in alleviating Cd stress for plants,but their alleviated effects are different.How ammonium and nitrate affect the alleviated effects still remains poorly understood.The most striking feature of clonal plants is their capacity for physiological integration,which enables the inter-connected ramets to share water,carbohydrates,minerals and nutrients.Thus,clonal plants in heterogeneous environment（environment with uneven distribution of resources）can obtain resource from the ramets which grow in resource-rich patches.In this study,a pot experiment was conducted using Glechoma longituba clonal fragments.Each clonal fragment consisted of one parent ramet and one connected offspring.To avoiding the interference of nitrogen form on Cd absorption by roots,nitrogen（ammonium or nitrate）and Cd（0.1 or 2.0 mmol?L-1）were respectively added to parent ramet and its connected offspring.Offspring ramet can obtain nitrogen from its parent by physiological integration.By this experimental design,the effects of ammonium and nitrate on the stress resistance of clonal plants suffering from heterogeneous Cd stress were studied,which provided more accurate evidences for exploring the differences between ammonium and nitrate in alleviating Cd stress.The resoults of this study could be used as an important reference for the rational nitrogen application in agricultural production.In addition,this paper could provide important theoretical basis for nitrogen nutrient management strengthening phytoremediation.The main contents and results are as follows:（1）In this papper,the different effects between ammonium and nitrate supplied to parent ramets of Glechoma longituba on alleviating Cd stress for offspring were studied.The results showed that the addition of nitrogen,especially ammonium,to parent ramets was beneficial for offspring ramets to decrease oxidative damage（malondialdehyde（MDA）content was decreased）,improve antioxidant capacity（glutathione（GSH）content,proline（Pro）content,superoxide dismutase（SOD）activity,peroxidase（POD）activity and catalase（CAT）activity were increased）and photosynthetic capacity（maximum quantum yield of PSII（Fv/Fm）,effective quantum yield of PSII（ΦPSII）and chlorophyll content were increased）,promote plant growth and enhance plant adaptability to stressful environments（biomass was increased）.（2）In order to prove the important role of nitrogen nutrient management in strengthening phytoremediation,the different effects between ammonium and nitrate supplied to parent ramets of Glechoma longituba on Cd accumulation in offspring ramets were investigated.The results demonstrated that the addition of ammonium to parent ramets could reduce the Cd content（Cd accumulation in per unit mass of tissue）in offspring ramets,while nitrate could significantly improve the Cd content in offspring ramets.With the increases of the concentration and time of Cd treatment,the Cd content in offspring ramets increased gradually.And the content of Cd in root was higher than that in stem and leaf of offspring ramets.In addition,the application of nitrogen,especially nitrate,could enhance Cd accumulation ability（Cd accumulation in per plant）of offspring ramets,which indicated that nitrogen,especially nitrate,was effective on strengthening phytoremediation.