Effects Of Reduced Irrigation And Calcium Fertilization On Water And Nutrients Physiology And Fruit Quality Of Glasshouse Tomatoes

Shortage of freshwater resource is a major factor constrainting agricultural production.This is particularly true in some drought-prone regions in China. Therefore, how to uselimited irrigation water resource more efficiently, namely to ‘produce more crops per drop’, isessential for ensuring food security in China. In the present study, tomato plants （Solanumlycopersicum L.） were grown in split-root pots in a climate controlled glasshouse. Fromflowering to fruit maturity stages, the plants were exposed to partial root-zone drying （PRD）and deficit irrigation （DI） in combination with three Ca fertilization rates, viz.,0,100, and200mg Ca kg-1soil （denoted as Ca0, Ca1and Ca2, respectively）. The effects of thetreatments on stomatal conductance, plant water relations, leaf and root growth, N, P, Caccumulation and¹⁵N and¹³C natural isotope composition (¹⁵N and¹³C, respectively) inplant organs, plant N and P use efficiencies, incidence of blossom-end rot （BER）, K, Ca, andMg contents and partitioning in plant organs, and fruit quality attributes including fruitfirmness, dry matter content, fruit juice pH, total soluable solid （TSS）, reducing sugars andorganic acid, as well as mineral contents （P, K, Ca, and Mg） were investigated. The resultsshowed that:（1）Compared to DI, PRD tended to better maintain leaf water status. Across the twoirrigation regimes, Ca2plants had higher leaf osmotic potential but lower leaf turgor than didCa0and Ca1plants. Leaf elongation was enhanced by PRD compared to DI in Ca1and Ca2but not in Ca0. Root length and surface area were identical between PRD and DI, and thehighest for Ca1, intermediate for Ca2, and lowest for Ca0. The irrigation and Ca fertilizationtreatments did not affect dry weights of above ground organs; while that for root wassignificantly higher for Ca1and Ca2than for Ca0. N and P contents in plant organs wereunresponsive to the either irrigation or Ca fertilization treatments, only root P contentdecreased with increasing Ca fertilization rate. C content was higher for PRD than for DI inleaf, while the reverse was true in stem. Root and fruit C contents were unaffected byirrigation regime but were significantly affected by Ca fertilization rate. Basically, irrigationregimes did not affect¹⁵N in plant organs but with a trend that PRD plants had slightlyhigher¹⁵N in the stem and fruits. Across the two irrigation regimes, Ca fertilization rate had no effect on¹⁵N in the leaves and stem, but significantly affected it in the roots and fruits,namely root and fruit¹⁵N were significantly higher for Ca1and Ca2as compared with Ca0.In leaves,¹³C was significantly higher for PRD than for DI, whilst the reverse was the casein the fruits. Ca fertilization rate had no effect on¹³C in plant organs of tomato. In addition,neither irrigation nor Ca fertilization treatments affected N and P use efficiencies of tomatoplants. It was concluded that, compared to DI, PRD better maintained plant water status andleaf elongation growth; however, such effects did not bring about increases of plant drybiomass, N, P and C accumulation, and N and P use efficiencies.（2）In comparison with DI treatment, PRD significantly reduced BER incidence in tomatofruits. A greater xylem sap ABA concentration, a lower stomatal conductance, and higherplant water status in the PRD in relation to the DI plants might have contributed to theenhanced fruit Ca uptake, which could have reduced BER development in tomato fruits. Inaddition, besides fruit Ca content, the ratios of Mg to Ca and K to Ca in the fruits wereinvolved in inducing BER in tomatoes. Therefore, under conditions of limited freshwaterresources, application of PRD irrigation could be a promising approach for saving water andfor preventing BER development in tomatoes.（3） Both irrigation and Ca-fertilization treatments had no significant effect on fruit yield,plant water use, and water use efficiency （WUE）, fruit number and fruit size. However, PRDregime significantly increased the TSS, sugars （glucose and fructose）, organic acids （citric andmalate acids）, minerals including P, K, and Mg contents in the fruit juice as compared withthe DI treatment, particularly at high Ca-fertilization rate （i.e., Ca2）, the increase was morepronounced. Whereas Ca content in tomato juice was neither affected by irrigation norCa-fertilization treatments. Across the two irrigation regimes, Ca-fertilization significantlyincreased TSS, P, K, and Mg contents in the fruit juice being that the contents of thoseconstitutes were enhanced with increasing Ca fertilization rate. Collectively, our resultsindicated that even though PRD did not over perform DI in terms of improving fruit yield andWUE, the irrigation treatment significantly increased several fruit quality attributes, resultingin better flavour fruits than the DI practice.