Effects Of Nitrogen Deposition And Drought Stress On Growth And Nitrogen Metabolism Of Phyllostachys Edulis Seedlings

With the rapid development of industry and agriculture,nitrogen deposition has also shown a rapid increase.Phyllostachys edulis is an important ecological bamboo species in China.Water and nitrogen have important effects on its growth.In this study,the Phyllostachys edulis seedlings were subjected to a completely random design with two levels of water condition(water,W 75 ± 5% field capacity;drought,D 35 ± 5% field capacity)and four levels of nitrogen deposition(control,CK 0 kg·ha-1a-1;low N,LN 30 kg·ha-1a-1;medium N,MN 60 kg·ha-1a-1;high N,HN 90 kg·ha-1a-1).The aim of our study was exploring the combined effects of nitrogen deposition and drought on the growth,photosynthetic characteristics,nitrogen metabolism and substrate of Phyllostachys edulis seedlings.These results could be conducive to provide a scientific basis for the study of the physiological and biochemical characteristics of plants under global environmental change,and to provide theoretical guidance for the management and production practice of Phyllostachys edulis seedlings.Results showed that:(1)The nitrogen deposition increased the content of salkali-hydrolyzable nitrogen and reduced the p H value and available phosphorus contents of the substrate of Phyllostachys edulis seedlings.The drought stress reduced the available phosphorus content and had no significant effect on the available nitrogen content and p H value.(2)The total biomass,aboveground biomass and belowground biomass of Phyllostachys edulis seedlings increased with nitrogen application rate increment,but there was no significant difference in root/shoot ratio.Under drought stress,the aboveground biomass of CK,LN,MN and HN treatments reduced by 47.17%,25.99%,22.27% and 54.98% respectively compared to normal water treatment.The root/shoot ratio of CK and HN treatments increased significantly.In the late drought stress period(30 days),drought treatment significantly reduced the activities of superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)and significantly increased the content of proline(Pro),the content of malondialdehyde(MDA)and the relative electrical conductivity(REC)in the leaves of Phyllostachys edulis seedlings under HN and CK levels;The drought stress significantly increased POD activity and slowed down the increase the malondialdehyde content and relative conductivity of LN and MN treatments.(3)Photosynthetic pigment content and photosynthetic rate of Phyllostachys edulis seedlings increased with the increase of nitrogen deposition.The drought stress significantly reduced the net photosynthetic rate(Pn)of CK,LN,MN and HN treatments by 49.47%,42.41%,29.27% and 84.91%respectively.Under drought stress,the maximum photochemical efficiency(Fv/Fm),photochemical quenching coefficient(q P),apparent electron transport rate(ETR)and starch content of LN and MN treatments were significantly higher than those of CK;Under HN treatment,the Fv/Fm and ETR were lower than CK level,and the non-photochemical quenching coefficient(q N)was the opposite.(4)Nitrogen deposition could significantly increase nitrogen metabolism-related enzyme activities and different forms of nitrogen contents in leaves of Phyllostachys edulis seedlings.The descending order of nitrite reductase(Ni R),nitrate reductase(NR),glutamine synthetase(GS)and glutamate synthetase(GOGAT)activities and soluble protein content caused by drought stress were HN> CK>LN> MN;Drought stress significantly increased glutamate dehydrogenase(GDH)activity which reached maximum under HN treatment.The results indicate that nitrogen deposition could significantly increase the content of salkali-hydrolyzable nitrogen in the substrate,restrict the supply of available phosphorus and make the substrate acidified;The drought stress further aggravated the limitation of the available phosphorus in the substrate.LN and MN treatments could help to alleviate the limitations of drought on the growth of Phyllostachys edulis seedlings,mainly by enhancing the antioxidant enzyme system and nitrogen metabolism related enzyme activities of the leaves,reducing the degree of membrane lipid peroxidation to maintain a relatively stable cell membrane structure and function,maintaining more stable photocontracting capabilities.And the effect is better under the treatment of 60 kg·ha-1a-1.Drought stress significantly limited the aboveground growth of HN treatment,which was related to the increase of active oxygen free radical metabolism and osmotic adjustment disorders,the change of the ammonia assimilation pathway to reduce the nitrogen use efficiency and the reduce of light energy of the photochemical electron transport,causing the hindrance of the photosynthetic electron transport chain,increasing the dissipation of non-radiative energy,and thus reducing the photosynthetic capacity.