Effects Of Nitrogen Forms And Drought Stress On Pea Growth And Its Ability Of Symbiotic Nitrogen Fixation

Drought stress and nitrogen (N) forms affect not only the growth of leguminouscrops, but also nodulation and N fixation. Pea is the main rotation crop in arid andsemiarid regions. Study the effects of different N forms under drought stress ongrowth, nodulation and N fixation of pea has an important guiding significance for Nresources management of leguminous rotation cropping systems in arid area. Potexperiment was used to study the effects of drought stress and N forms on pea growth,yield formation, nodulation and N fixation. Stress of50%relative water content wasexerted in three ways, i.e.budding stage—flowering and podding stage—maturationperiod (W2), branching stage—budding stage+flowering and poddingstage—maturation period (W3), branching stage—budding stage—flowering andpodding stage (W4), while75%relative water content was maintained in wholegrowth stage (W1) as contrast (CK). Two kinds of N fertilizer were ammonium andnitrate. Eight treatments were designed in the trail. The main results were as follows:1. Drought stress accelerated the growth process of pea, but rewatering afterdrought stress prolonged the growth stage. Drought stress of W2, W3and W4shortened the growth duration for10,8and10days respectively compared with W1.Adequate water supply in budding—podding stage significantly prolonged thegrowth period, while N forms had litter effect on growth duration. Under the droughtstress conditions, nitrate extended the reproductive growth period than ammonium.Drought stress affected the organs formation of pea. Compared with W3, W4significantly improved the plant height, main root length and main stem leaf numberin flowering and podding stage. Rewatering after drought stress had significantcompensation effect on plant elongation growth and main stem leaf number increases.Nitrogen forms didn’t affect the occurrence of organ, but nitrate promoted peaelongation growth than ammonium when adequate water supply was provided.2. Drought stress significantly reduced the accumulation of biomass and yield, sodid the the dry weight in branching stage, flowering and podding stage and maturationperiod, and the inhibition of dry matter accumulation were the highest when drought stress occurred in budding—flowering and podding stage. Biomass of W3increasedby30%than that of W4in flowering and podding stage, and W3had significantgrowth compensation. Nitrate was beneficial to improving pea dry matteraccumulation significantly than ammonium. The increases were10.48%and9.65%respectively in branching and maturity stage. In the same water conditions, the impactof N forms on plant growth was not significant. Drought stress significantly reducedpea grain yield, grains per pods and pods per plant, and W3had the smallest declinethan the others drought stress. W3significantly increased the grain yield than W2andW4. Sufficient soil moisture in budding stage—flowering and podding stage was animportant guarantee to improve grain yield. The effects of N forms, and theinteraction between water and N forms on yield components were not significant.3. Drought stress significantly reduced the total nodule number, effective nodulenumber, total nodule fresh weight and the effective nodule fresh weight in branchingstage, flowering and podding stage and maturation period. Nodule number and nodulefresh weight of W3were significantly increased than that of W4in flowering andpodding stage. Rewatering after drought stress had significant compensation onnodule formation and its growth. Nitrate was conducive to the formation of nodulebefore budding stage and nodule growth after budding than applying same amount ofammonium. Nitrate was beneficial to the formation and growth of effective nodule inthe nutritional growth period, but ammonium improved effective nodulation in thereproductive growth stage. The interaction between W3and ammonium increased theeffective nodules number after budding, and the interaction between W2andammonium increased the rate of effective nodule growth after budding.4. Drought stress significantly reduced the nodule nitrogenase activity. W3significantly improved nodule nitrogenase activity than W4, but the improvementcould not reach the level of W1. The interaction between W3and ammoniumpromoted nitrogenase activity significantly in budding stage, flowering and poddingstage. N fixation efficiency and N fixiation amount decreased significantly underdrought stress. N fixation efficiency and N fixation amount, N fixation efficiency andbiomass, biomass and N fixation amount showed a significant positive correlation, the correlation coefficient (R2) were0.9738,0.8764and0.710.