Friut Quality And Photosynthetic Characteristics Of Nectarine Under Protected Culture

The interactive effects of nitrogen and calcium on fruit quality and photosynthet-ic characteristics in protected cultivation were studied by using3-years-old nectarine(Prunus persica var．nectariana cv．Zhongyou5) trees which were watered by mixedsolution of nitrogen and calcium at different levels.The main results were presented as follows:1. Under different nitrogen levels, different levels of calcium all promoted thegrowth of new shoot, the leaf quality and the development of fruit, increased leaf area,the weight of dry leaf and fresh leaf, specific leaf weight. Under the low nitrogenlevel(5mmol/L) and the high nitrogen level(25mmol/L), the most suitable calciumconcentrations were4mmol/L and8mmol/L, respectively. Under these twocombinations, interactive effects of nitrogen and calcium had the the best effect forthe growth and development of new shoot and fruit, the quality of leaf. Under thesame calcium levels, the influence of nitrogen on all the indicators above performanc-ed that: high nitrogen performanced better than low nitrogen.2. Under different nitrogen levels, different levels of calcium all improved thefruit quality: increased the fruit weight, vertical diameter, horizontal diameter andfirmness; increased the contents of soluble solids, soluble sugar, sugar-acid ratio,ascorbic acid, soluble solids and free amino-acids; reduced the contents of titratableacid. Under low nitrogen level and high nitrogen leve, friut quality were improvedfirstly and then decreased with the increasing of calcium levels, and reached best at4mmol/L and8mmol/L, respectively, which significantly differenced from ohertreetments (P＜0.05). Under the same calcium level, the influence of nitrogen onfruit quality performanced that: high nitrogen performanced better than low nitrogen.3. Under different nitrogen levels, the contents of Chla, Chlb and Chl（a+b）, netphotosynthetic rates (Pn)，transpiration rates (Tr)，stomatal conductances (Gs)，intercellular CO2concentrations(Ci), maximal photochemical efficiencies ofPS Ⅱ(Fv/Fm)， electron transfer rate (ETR), quantum yields of PS Ⅱelectrontransport(ΦPSⅡ), and photochemical quenching coefficients (qP) increased firstlyand then decreased with the increase of calcium levels，while the initial fluorescence (Fo) and non-photochemical quenching coefficients (NPQ) decreased firstly and thenincreased．Under the low nitrogen level(5mmol/L) the interactive effects of nitrogenand calcium on photosynthesis are the best with4mmol/L calcium level，whichsignificantly differenced from oher treetments (P＜0.05). Under the high nitrogenlevel (25mmol/L), the interactive effects of nitrogen and calcium on photosynthesisare the best with8mmol/L calcium level，which significantly differenced from othertreetments (P＜0.05)．The most suitale proportions of calcium and nitrogen aboutphotosynthetic characteristic were same with growth and development of new shootand fruit and fruit quality.4. The diurnal variations of Pn of nectarine leaves under the protected cultureunder different treetments were all presented as “double-peak curve”. Trough and thesecond peak appeared at the same time, they were13:00、16:00; calcium and nocalcium treetments, the first peak appeared at differen time, they were9:00and8:00,correspondly. Compared with no calcium treetments, interactive effects of nitrogenand calcium had higher diurnal variations of Pn and higer diurnally accumulatedphotosynthetic products.5. Compared with no calcium treetment, the interactive effects of nitrogen andcalcium had higher light energy utilization and CO2utilization and Maximumphotosynthetic potential. The characteristic parameters changed as belows: maximumnet photosynthetic rate(Pmax), apparent quantum efficiency(φc), light compensationpoint(LCP), light saturation point(LSP), carboxylation efficiency(CE), lightrespiration rate(Rp) were all increased.6. Calcium up-regulated the chlorophyll biosynthesis pathway: under lownitrogen level, by improving the activity of UROS, up-regulated the transformationfrom PBG to Urogen Ⅲ, and then up-regulated chlorophyll intermediate products andchlorophyll biosynthesis and accumulation; under high nitrogen level, by improvingthe activities of ALAD and UROS, up-regulated the transformation from ALA toPBG and PBG to Urogen Ⅲ, and then up-regulated chlorophyll intermediate productsand chlorophyll biosynthesis and accumulation. The most suitable proportions ofcalcium and nitrogen were low nitrogen level (5mmol/L),4mmol/L calcium leveland high nitrogen level (25mmol/L),8mmol/L calcium level, which were same withgrowth and development of new shoot and fruit, fruit quality and photosyntheticcharacteristic. The regulation of interactive effects of nitrogen and calcium was "lownitrogen-low calcium, high nitrogen-high calcium".