Effects Of Different Regulated Deficit Irrigation Schemes On Growth Yield And Quality Of Pepper In Greenhouse

Pepper is widely cultivated around the world.However,pepper is a shallow root plant,with thin and weak roots,high degree of cork,which lead it very sensitive to water changes.The traditional irrigation method is to irrigate crops in large quantities for the sole purpose of pursuing high yield.This not only wastes water resources,but also decrease the quality of pepper.How to increase the yield of pepper while ensuring its quality and improving economic benefits has become the focus of people’s attention.This study took pepper as the research object,with adequate water supply（75%-85%θ_f）for the whole growth period as control（CK）.And carried out greenhouse experiments of regulated deficit irrigation（RDI）in the Key Laboratory of Agricultural Soil and Water Engineering of Ministry of Education in Arid Regions in Northwest A&F University.Two kinds of deficit degree（mild RDI:65%-75%θ_f,severe RDI:55%-65%θ_f,θ_fis filed capacity）and two kinds of deficit duration（short RDI:deficit four days,long RDI:eight days）were set in three growth stages（seedling,flowering,and fruiting stage）.The effects of regulated deficit irrigation on growth and physiological,yield and quality indexes of pepper were studied.Achievements have been made in the following aspects:（1）The plant height,stem diameter,leaf area and dry matter of vegetative organ of pepper were inhibited by water deficit in different growth stages.Among them,water deficit at seedling stage inhibited the morphological indexes and dry matter of vegetative organ of pepper the most.However,the mild water deficit of different duration at seedling stage（MLS-4 and MLS-8）eventually promoted the dry matter of pepper reproductive organs.However,severe water deficit at seedling stage（MSS-4 and MSS-8）reduced the dry matter of reproductive organs in pepper.At flowering stage,the dry matter of reproductive organs significantly decreased under both mild and severe water deficit with different durations compared with CK except short-term mild deficit（HLS-4）.Pepper is sensitive to water deficit in fruiting period,water deficit with different intensity or duration would reduce chili dry matter of reproductive organ,therefore,the deficiency of water at fruiting stage was not conducive to the accumulation of dry matter in reproductive organs.However,MLS-4,MLS-8 and HLS-4 can effectively reduce the"redundant growth"of pepper,will help the photosynthesis production transfer to reproductive growth.（2）Under the same duration of deficit,net photosynthetic rate（P_n）,stomatal conductance（G_s）,transpiration rate（T_r）and intercellular carbon dioxide concentration（C_i）decreased with the increase of deficit degree in each growth period.Under mild water deficit,plants closed part of stomata to adapt to water deficit environment to reduce transpiration,so P_n,G_s,T_rand C_i decreased.Under severe water deficit,gas exchange parameters decreased more significantly.On the day of rehydration,all indexes recovered fast,but only part of treatments recovered to CK level.After 4 days of rehydration,the gas exchange parameters under MLS-4,HLS-4 and GLS-4 recovered to the level of CK,indicating that the short-term mild deficit did not cause irreversible damage to pepper,and the rehydration after moderate water deficit had a good compensation effect.（3）The chloroplast and starch grains expanded and moved to the cell center when the pepper was subjected to long-term severe deficit at all growth stages（MSS-8,HSS-8 and GSS-8）,especially when the pepper was subjected to water deficit at flowering stage,the chloroplast overlaps and the damage degree was the largest.After rehydration for 4 days,the chloroplasts under MSS-8,HSS-8 and GSS-8 treatments recovered to normal state,but they did not completely recover to normal level.As a result,the net photosynthetic rate under MSS-8,HSS-8 and GSS-8 treatments was still significantly different from CK after rehydration for 4 days,and only partial compensation was generated.（4）Photochemical quenching coefficient（qP）,maximum photochemical efficiency of PSII（F_v/F_m）were significantly positively correlated with P_n,while minimum fluorescence after dark adaptation（F₀）,non photochemical quenching coefficient（NPQ）were significantly negatively correlated with P_n.When water supply was sufficient,q P and F_v/F_m at flowering stage were the highest,indicating that plants had the strongest light conversion capacity and light energy utilization efficiency at flowering stage.Under water deficit,q P and F_v/F_mdecreased with the increase of water deficit and the extension of deficit duration,while NPQ and F₀ increased with the increase of water deficit,and leaves applied more energy to non-photochemical reactions.The rehydration effect was closely related to the degree and duration of deficit.F₀,NPQ,F_v/F_m and q P treated with short-term mild deficit at all growth stages could quickly recover to CK after 4 days of rehydration.This indicates that short-term mild deficit did not cause irreversible damage to photosynthesis.（5）The superoxide dismutase（SOD）activity,malondialdehyde（MDA）,soluble sugar（SS）and proline（Pro）contents of leaves at different growth stages increased with the increase of deficit degree and deficit duration,and showed a significant negative correlation with P_n.On the day of rehydration,SOD and MDA decreased sharply,but there was still significant difference with CK.However,the contents of Pro and SS recovered to CK level under MLS-4,HLS-4 and GLS-4（Pro under MLS-4 did not recover to CK）.After 4 days of rehydration,SOD activity and MDA content of MLS-4,HLS-4 and GLS-4 had nearly equal compensation effect.The contents of Pro and SS showed near equal compensation effect under short-term mild deficit,short-term severe deficit and long-term mild deficit（except the treatment of MLS-8 and GSS-4）,while long-term severe deficit had partial compensation effect.The results showed that after 4 days of rehydration,most of the treated plants could effectively remove reactive oxygen species,reduce membrane lipid peroxidation,improve osmotic potential and restore normal physiological metabolic function.（6）The period,degree and duration of water deficit had significant effect on yield per plant.In terms of RDI stage,water deficit with different intensity or duration significantly reduced the yield of pepper at fruiting stage,while at seedling stage and flowering stage,the yield could be improved by adjusting the deficit degree and duration.MLS-4,MLS-8 and HLS-4 could significantly improve pepper yield.In addition,water deficit at flowering and fruiting stage could improve fruit quality,VC content,fruit color index and capsaicin in pepper were significantly increased compared with CK.The results showed that the fruit quality could be improved by regulating the water supply at flowering and fruiting stage.After multi-objective comprehensive evaluation analysis,it was found that the score of HLS-4 was the highest,ranking first.Therefore,in consideration of the yield and quality of pepper,it is suggested to carry out short-term mild water deficit at flowering stage to improve the yield and quality of pepper in greenhouse.