Response Of Growth And Chlorophyll Fluorescence Characteristics Of Cotton Seedlings To Coupling Of Water,Nitrogen And Phosphorus

Root system is very important to plants for absorbing water and mineral nutrition from soil.Photosynthesis is the only way for plants to convert light energy into chemical energy.Chlorophyll fluorescence parameters can be used as an important indicator to reflect plant adaptation to soil water and nutrient changes.Cotton(CV: BM5)seedlings were cultured with Hoagland nutrient solution,supplying with two nitrogen levels(normal nitrogen N1,17 mmol/ L and high nitrogen N2,85 mmol/ L)and two phosphorus levels(low phosphorus P1,0.2 mmol/ L and the normal phosphorus P2,2 mmol/ L)separately or combined each other.Polyethylene glycol(PEG-6000)was used to simulate drought stress.The aims were to study the response to water,nitrogen and phosphorus coupling in the growth(plant height,stem diameter,biomass,and leaf temperature),root morphological characteristics(total root length,and root surface area),chlorophyll fluorescence traits(fluorescence content,and chlorophyll fluorescence parameters)et al.in cotton seedlings.The results were:1.Drought stress significantly reduced the plant height,stem diameter,underground and aboveground biomass,weakened variable fluorescence(Fv),PSII potential photochemical efficiency(Fv/Fo),maximal quantum yield of PSII(Fv/Fm),electron transport rate(ETR),and the photochemical quenching coefficient(qP),and increased the ratio of root to shoot,total root length,root surface area,non-photochemical quenching coefficient(q N),and leaf temperature in cotton seedlings.Low phosphorus did similar impact with drought stress(except for plant height and the ratio of root to shoot),but with weaker effect than drought stress.High nitrogen significantly increased the underground and aboveground biomass,plant height,root length,root surface area,and chlorophyll content in cotton seedling and enhanced Fv,Fv/Fo,Fv/Fm,ETR,and q P,but decreased the leaf temperature,qN,and the ratio of root to shoot.2.Compared with the well water and nitrogen coupling,the coupling of drought stress and high nitrogen decreased plant height,underground and aboveground biomass,chlorophyll content,Fv,Fv/Fo,Fv/Fm,ETR,and qP,while increased leaf temperature,total root length,root surface area,and qN in cotton seedling,but with lower change amplitude than that of drought stress.Compared with well water and phosphorus,the coupling of drought stress and low phosphorus decreased stem diameter,underground andaboveground biomass,chlorophyll content,Fv,Fv/Fo,Fv/Fm,ETR,and qP,increased leaf temperature,total root length,root surface area,and qN,but with stronger variation than single drought stress or low phosphorus stress.Compared with coulping of normal nitrogen and phosphorus,the coupling of high nitrogen and low phosphorus decreased leaf temperature,aboveground biomass,and qN,while rised underground biomass,total root length,root surface area,chlorophyll content,Fv,Fv/Fo,Fv/Fm,qP,and ETR in cotton seedling,but their change rate was lower than that of single low phosphorus stress.Compared with coulpling of well water,nitrogen and phosphorus,the coupling of drought stress,high nitrogen and low phosphorus decreased plant height,stem diameter,aboveground and underground biomass,chlorophyll content,Fv,Fv/Fo,Fv/Fm,ETR,q P,and ETR in cotton seedlings,while increased leaf temperature,total root length,root surface area,and qN.In summary,single drought or low phosphorus stress inhibited the growth of cotton seedlings,but high nitrogen can promote the growth of cotton seedlings.Significantly,each treatment factor all increased the root total root length and root surface area.Higher nitrogen can effectively reduce the inhibition on plant growth(especially on root growth)and the PSII reaction center light energy conversion efficiency induced by drought stress.Higher nitrogen can also decrease adverse effects on light utilization and the electron transport induced by drought stress by affecting chlorophyll content and the leaf temperature,and can enhance the ability to heat dissipation and root morphology adaptability.Low phosphorus can increase the inhibition of drought stress on biomass accumulation and light energy use,with enhancing heat dissipation.Increased nitrogen can not completely inhibite low phosphorus effect on biomass accumulation,but can improve accumulation of root biomass and the formation of root morphological adaptability under low phosphorus.Increasing nitrogen fertilizer can effectively reduce the growth inhibition caused by phosphorus deficiency under drought conditions.While decreasing phosphorus was obviously weakened nitrogen effect on growth and utilization of light energy.The proportion of nitrogen and phosphorus fertilizer should be rationally arranged when cotton was planted.