Effects of nitrogen reduction on photosynthetic characteristics and photo-synthetic nitrogen use efficiency of soybean under no-tillage conditions in black soil region
In order to investigate the effects of nitrogen reduction on the photosynthetic performance and photosynthetic nitrogen use efficiency of soybean in the black soil region,a control treatment involving conventional nitrogen application under traditional tillage was employed.Five treatments were established:conventional nitrogen application under no-tillage,15%nitrogen reduction under no-tillage,30%nitrogen reduction under no-tillage,and no-tillage without nitrogen application.These treatments aimed to examine and analyze their effects on soybean leaf area index,photo-synthetic characteristics,photosynthetic lightresponse curve,and photosynthetic nitrogen use effi-ciency.Additionally,the study sought to elucidate the mechanism underlying photosynthetic nitrogen use efficiency.The results indicated that the net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs),maximum net photosynthetic rate(Pnmax),dark respiration rate(Rd),apparent quantum rate(α),chlorophyll content(SPAD),and leaf area index(LAI)initially increased and then decreased with reduced nitrogen application.With the reduction of nitrogen application,the intercellular CO2 concentration(Ci)initially decreased and then increased.Compared with the control treatment,the no-tillage 15%treatment during each growth stage significantly reduced soybean Ci by 8.03%-11.16%and improved soybean SPAD,LAI,Pn,Tr,and Gs by 3.21%-6.52%,9.60%-35.00%,14.13%-42.20%,12.93%-38.66%,and 18.62%-40.87%,respectively.The photosynthesis-light response curve and photosynthetic response parameters of soybean leaves showed significantly improved changes when treated with a 15%nitrogen reduction under no-tillage,compared to other treatments.Additionally,the photo-synthetic nitrogen use efficiency of soybean leaves initially increased and then decreased as the nitrogen application decreased under different treatments.These results indicated the potential benefits of reducing nitrogen application in improving the photosynthetic performance of soybean leaves in a no-tillage system.Compared with the control treatment,the photosynthetic nitrogen use efficiency of soybean leaves increased by 13.29%-25.43%under no-tillage conditions,with the greatest effect observed.Furthermore,there was a significant positive correlation between the photosynthetic nitrogen use efficiency of soybean leaves and LAI as well as SPAD.
black soil regionnitrogen reductionsoybean photosyntheticphotosynthetic nitrogen efficiencyno-tillage
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