Study On Tomato Water-saving And Fruit-quality Modulation And Stomatal Conductance Simulation At Elevated Carbon Dioxide Concentration Under Alternative Partial Root-zone Irrigation

In order to further elucidate the water-saving and fruit quality-regulating mechanism under alternate partial root-zone irrigation(PRI),and further in elevated carbon dioxide concentration(e[CO2])environment,the indication of stable carbon isotope on water use efficiency(WUE)was introduced,field plot associated with climate-controlled greenhouse pot experiments were presented in the current study,the objective were to investigate the mechanism and response of combined effects of PRI strategy and two[CO2]concentration environment on WUE and nitrogen use efficiency(NUE),stomatal conductance simulation and fruit comprehensive quality of tomato plant.This findings were anticipated to provide valuable knowledge and reasonable guide on achieving crop high-quality and efficient irrigation for adapting to the future water-limited and[CO2]-enriched environment.The main results were outlined as follows:(1)Tomato fruit fresh yield(Y)and WUE at fresh yield scale(WUEY)could be a perfect representative of dry yield(DY)and WUE at dry yield scale(WUEFY),the WUEY of PRI usually indicated an improvement on 19.6%over that of conventional irrigation(CI)with no significant difference in yield,but a 33.3%of irrigation water was saved.PRI was a more efficient irrigation method for regulating leaf photosynthetic process,accommodating stomatal aperture close to an optimum,and decreasing Ci/Ca,thereby,inducing a lower carbon isotope discrimination(?13C)of leaf and fruit and a greater WUE from leaf to field scale than CI,especially under drip irrigation.Consequently,the ?13C of tomato tissues in fruit ripening period could be adopted as an appropriate and quick way for phenotyping and optimizing WUE of tomato plant at some extent.(2)Plants harvested from adequate nitrogen(N)supply associated with e[CO2]environment possessed the greatest photosynthetic rate,and lowest stomatal conductance and transpiration rate,resulting in the highest WUE at stomatal and leaf levels.Especially PRI strategy coupled with e[CO2]had the potential to synergistically reduce stomatal conductance and transpiration rate while sustain photosynthetic rate and leaf water status,and further improve tomato leaf WUE.e[CO2]combined with sufficient N fertilizer enhanced the biomass,carbon(C)accumulation and N uptake of plants under PRI regime;Disregarding[CO2]environment,yet the WUE and NUE at whole plant scale were affected solely by the N supply being greater in low N fertilization.(3)The slope of Ball-Berry stomatal conductance model(BB-model)was significantly improved at e[CO2],indicating that stomatal conductance was independently acclimated to e[CO2]from photosynthetic rate.The soil matric potential in both root-zone was considered to modify the BB-model.The modified BB-model was capable of predicting stomatal conductance and WUE of tomato leaves in various irrigation regimes,especially for PRI strategy at both[CO2]environments.A greater WUE could be seen in plants grown under e[CO2]associated with PRI regime.(4)At the ripening stage,the fruit quality attributes as exemplified by firmness,total soluble solid,vitamin C,organic acid and soluble sugar content of tomato plants grown in the field were significantly improved and mediated by the water stress under PRI regime.The most sensitive period of single fruit quality response to water deficit was normally at fruit veraison stage under different irrigation methods,especially for PRI strategy with 1/3 irrigation quota saved,indicating that PRI regime could more effectively modulate the formation,accumulation and distribution process of tomato fruit quality during the critical fruit growth period.(5)Lower N supply reduced fruit number and yield,whereas it enhanced some of the quality attributes of fruit as indicated by greater firmness,higher concentrations of sugars and organic acids across irrigation and[CO2]treatments.e[CO2]environment attenuated the negative influence of reduced irrigation(deficit irrigation(DI)and PRI)on fruit yield.Combinatorial assess revealed that the reduced irrigation regimes,especially PRI,in combination with e[CO2]could synergistically promote the accumulation and conversion of photosynthesis to fruits and improve the comprehensive quality of mineral and favour concentration in tomato fruits at high N supply.