The Physiological And Ecological Response Of Jatropha Curcas Seedlings To Drought Stress And Nitrogen Application

The constant increasing deficiency of water and nutrition in arid and semi-arid systems would badly restrict plant growth and vegetation regeneration. How to alleviate this trend of inhibition and gradually improve the deteriorated environment had been the key problems that managers of arid system is facing in present and future. Understanding the response mechanism of adaptable plants in arid system to climate change scenarios has important strategic meaning to regulating drought environment and improve vegetation condition in arid system. This research selected the Jatropha curcas which is an important woody oil specie, starting at growth, physiology and resource utilization, according to water and nitrogen control experiment in greenhouse, seting four water treatments (80%FC,60% FC,40%FC and 20%FC) and four nitrogen application rates (No 0 kg N·hm-2, NL 96 kg N·hm-2, NM 288 kg N·hm-2, NH 480 kg N·hm-2), the physiological and ecological response of J. curcas to drought stress and nitrogen application were systematically studied to reveal the drought resistance mechanism of J. curcas, and try to explore that whether nitrogen application could increase the drought adaptability of J. curcas and promote the seedling establishment under drought condition. It viewed to provide theoretical reference for the water and fertilizer management of cultivation and management technology of J. curcas.(1) The response of growth, biomass accumulation and distribution of J. curcas seedlings to drought stress and nitrogen application.The height, basal diameter, leaf number, leaf area and biomass of J. curcas decreased with the enhancement of drought stress degree, while root length increased. The effect of nitrogen application on growth was dependent on drought intensity and nitrogen application rate. On water conditions of 80%FC and 60%FC, the seedlings of each nitrogen application treatment all exhibited relatively high leaf number, leaf area, height, basal diameter, root length and biomass compared with No, and the promotion effect of NM was most strong. While on water conditions of 40%FC and 20%FC, NL had the best promotion effect, NM and NH weakened the effect or made it negative. Fine root biomass distribution proportion on drought condition was higher than 80%FC, leaf and coarse root distribution proportion were relatively high on water conditions of 80%FC and 60%FC, but stem distribution proportion increased under water conditions of 40%FC and 20%FC. Under water conditions of 80%FC and 60%FC, nitrogen application increased the leaf and fine root distribution proportion, but decreased coarse root and stem distribution proportion. Nitrogen application increased stem distribution proportion under water conditions of 40%FC and 20%FC, while decreased leaf distribution proportion, and NL treatment significantly increased root distribution proportion.(2) The response of water status of J. curcas seedlings to drought stress and nitrogen application.The leaf and root water content of J. curcas seedlings began to significantly decrease under water condition of 40%FC, stem water content significantly increased under water condition of 60%FC and 40%FC, and severe drought stress (20%FC) did not cause significantly decreasing compared with 80%FC. Nitrogen application under 60% FC could significantly increase the water content of all components, and that of NM were highest. NL and NM treatment under 40%FC could improve leaf and stem water status to a certain degree. While nitrogen application under 20%FC had no obvious effect to water status of seedlings, and NL and NM treatment even deteriorated water status.(3) The response of photosynthetic and physiological characteristics of J. curcas seedlings to drought stress and nitrogen application.The leaf photosynthetic efficiency of J. curcas seedlings significantly decreased with the enhancement of drought stress degree, while photosynthetic pigments increased on water conditions of 60%FC and 40%FC. Under mild and moderate drought conditions, stomatal limitation might be the main cause of decreasing of photosynthetic rate, while under severe drought condition, non-stomatal limitation might be the main cause. Rational nitrogen application under drought conditions had obvious compensation effect on the decreasing of photosynthetic efficiency caused by water deficiency. But NM and NH treatment only had significant promotion effect under water conditions of 80%FC and 60%FC, the promotion effect of NM and NH weakened or made it negative under 40%FC and 20%FC, and NL had the best promotion effect under thsis water condition.(4) The response of osmotic adjustment of J. curcas seedlings to drought stress and nitrogen application.The soluble sugar, soluble protein and free proline in the stem and root of seedlings accumulated quickly under drought stress. The free proline content in leaf also jumped sharply with the enhancement of drought stress, the soluble protein content in leaf increased progressively under moderate drought (40%FC), while soluble sugar content in leaf decreased significantly under severe drought (20%FC). The Na+, Ca2+ and Mg2+ accumulated highly in each component of seedlings under drought stress, but the K+ only accumulated highly in the stem, the K+ content in the leaf and root increased very slowly. The effects of nitrogen application on the osmotic adjustment were dependent on drought intensity and nitrogen application rate. Specially, increasing nitrogen application level could promote the accumulation of each soluble substance in different components of J. curcas seedlings obviously under mild drought (60%FC), the promotion effect of NH decreased under moderate drought, and NL had the best promotion effect while NM and NH weakened the effect or made it negative under severe drought stress (20%FC).(5) The response of antioxidant metabolism of J. curcas seedlings to drought stress and nitrogen application.The SOD, POD and CAT activity of leaf and root, the SOD and POD activity of stem increased under drought conditions, the CAT activity of stem decreased, while under severe drought condition the leaf SOD and CAT activity decreased to control level. Increasing nitrogen application rate under 60%FC could significantly increase the SOD, POD and CAT activity of all components, and decreased the MDA content. Under water condition of 40%FC, NL and NM seedlings exhibited high enzymatic activity and low MDA content, while NH had no obvious effect. Under severe drought stress (20%FC), although NM and NH treatment increased the POD and CAT activity of stem, but significantly inhibited the protective enzyme activity of leaf and root, and increased MDA content of all components, NL had the best promotion effect under this water condition.(6) The response of nutrient uptake and use efficiency of J. curcas seedlings to drought stress and nitrogen application.The C, N and P accumulation amount, N and P uptake efficiency of J. curcas seedlings decreased with the enhancement of drought stress degree, while N and P use efficiency increased. When soil water was between 80%FC and 40%FC, nitrogen application could increase the C, N and P accumulation amount, and NM seedlings exhibited the highest nutrient accumulation amount. While under water condition of 20%FC, NL had the best promotion effect. Under the same water condition, increasing nitrogen application rate significantly decreased the N use efficiency and increased P uptake efficiency. NL and NM treatment under drought stress decreased P use efficiency, but increased P uptake efficiency. In addition, drought stress decreased the distribution proportion of C, N and P in leaf, while increased C, N and P distribution proportion in stem, and increasing nitrogen application rate could improve C, N and P accumulation in stem.Comprehensive analysis showed as follows. Drought stress caused water deficiency of J. curcas seedlings, decreased photosynthetic and nutrient uptake efficiency, therefore inhibited the growth, biomass accumulation, C, N and P accumulation of seedlings. But the plant could resist drought environment by self-adaptive protection mechanism and changing resources distribution pattern, so as to maintained life activity long time under extreme drought environment. Rational nitrogen application under drought condition could improve the plant water status by osmotic adjustment, increased photosynthetic efficiency and biomass accumulation by increasing photosynthetic pigments and protective enzyme activity, so as to alleviate the negative effect of J. curcas seedlings caused by drought stress. But excessive nitrogen application under severe drought condition had no significantly effect and even aggravated the drought injury to plant.