| The enhancement of grain zinc (Zn) concentration of staple food crops, especially rice and wheat is crucial to resolve the problem of human zinc deficiency. In 2014 and 2015, a series of experiments were conducted to study the effect of foliar Zn application on Zn nutrition of rice and wheat under different growth conditions. This study was accomplished by the following five experiments.1 Four Zn compounds were applied as foliar spray to three rice varieties at flowering and 1 week after flowering under field conditions.2 Using FACE (Free Air CO2 Enrichment) platform, Y liangyou 2 hao were grown under two levels of CO2 concentration (Ambient and 50% higher than ambient) and foliar application of Zn, N, P and their combination (Zn, P, N, Zn+P, Zn+N, N+P, Zn+N+P,5N1Zn,5N6Zn) was performed after flowering.3 Under field conditions, as tested material, the ZnSO4 solution was sprayed on the conventional wheat Yangmai 15 and Zn-rich wheat Qingzi 1 hao at different growth stages, stem elongation and booting, booting and one week after flowering,1 and 2 weeks after flowering.4 Under field conditions, The liquid Zn fertilizer 5N6Zn or ZnSO4 solution was sprayed on Yangmai 15 and Qingzi 1 hao at 1 and 2 weeks after flowering.5 Using solar-illuminated gas fumigation platform, Qingzi 1 hao were grown under two levels of O3 concentration (clean air and 100 nL L-1 O3) and foliar application of ZnSO4 was conducted after flowering. Except liquid fertilizer, The Zn2+concentration of Zn-containing solution sprayed in rice was 0.2%, while that in wheat was 0.1%, P and N solutions were 0.2%K2H2PO4 and 1% urea.5N1Zn and 5N6Zn referred to liquid fertilizer WUXAL(?) Microplant and WUXAL(?) Zinc respectively. For all foliar application treatments, water was used as the control.1 The results from experiment one showed that Zn concentration of brown rice of grains from different parts of a panicle varied significantly, with Zn concentration of grains from upper part of a panicle being higher than that of middle or lower part. In contrast, phytic acid or the molar ratio of phytic acid to Zn (PA/Zn) showed the opposite trend. Compared with CK (water spray), foliar application of ZnSO4, Zn-citrate, Zn-gluconate and Zn-EDTA increased Zn concentration of brown rice by 33%,31%,26% and 27%, respectively. The grains at upper or middle part of a panicle were affected much more than that at lower part. Nipponbare showed greater response to Zn application than other genotypes. Zinc treatment had little effect on the concentration of phytic acid, but had great impact on PA/Zn. Averaged across all genotypes, PA/Zn in brown rice was reduced by 25%, 24%,22% and 18% by foliar application of ZnSO4, Zn-Citrate, Zn-Gluconate and Zn-EDTA, respectively. The reduction was greater in the grains from upper or middle part than lower part of a panicle. The reduction in Nipponbare or L71 was greater than that in L81. In most cases, significant interactions between Zn treatment and genotype or panicle position were detected.2 The experiment two revealed that grain Zn concentration, phytic acid concentration and PA/Zn of brown rice were higher than that of milled rice. High CO2 concentration decreased Zn concentration of milled rice and brown rice by 3% and 4%, respectively. Foliar fertilization increased the zinc concentration of milled rice and brown rice by 12% and 19%, with the largest increase occurred in Zn+N+P treatment by 26.1% and 37.4%. High CO2 concentration increased phytic acid concentration of milled rice by 5%. Foliar fertilization had no effect on the concentration of phytic acid in milled and brown rice. High CO2 concentration increased PA/Zn in milled rice by 8%, while foliar fertilization decreased PA/Zn by 11% and 14% in milled and brown rice, respectively. Among all foliar fertilizer treatments, the biggest decrease occurred in Zn+N treatment, with 26% in milled rice and 30% in brown rice. There were significant interactions between Zn treatment and CO2 or grain portion.3 Grain Zn concentration, Zn distribution, phytic acid concentration and PA/Zn in flour, shorts and bran all followed the trend of flour<shorts<bran. Compared with CK, foliar application treatments increased Zn concentration in wheat grains by 41% in average, S&B, B&1 and 1&2 treatments increased gran Zn concentration by 21%,41% and 61%, respectively. Zinc treatments decreased Zn accumulation in flour and shorts, but increased Zn accumulation in bran. Zinc treatment had no effect on the phytic acid concentration, but significantly decreased PA/Znby 26% in average, S&B, B&1 and 1&2 treatment decreased PA/Zn by 16%,27% and 36%, respectively. In most cases, significant interactions between Zn treatment and variety or grain part were detected.4 Compared with CK, Zinc foliar application increased Zn concentration in wheat grains by 59% in average,5N6Zn increased Zn concentration by 47% and ZnSO4 increased by 71%. Foliar application of Zn decreased PA/Zn by 34% in average,5N6Zn decreased PA/Zn by 30% and ZnSO4 by 39%.5 Ozone stress and foliar Zn application increased zinc concentration in different portions of wheat grains by 39% and 21% respectively, but decreased PA/Zn by 9% and 15% respectively. Ozone stress decreased Zn accumulation in flour, relative to whole grain by 18%, but Zn distribution pattern was not changed by foliar Zn application. Grain phytic acid concentration increased 26% by ozone stress, but was not affected by foliar Zn application. In most cases, significant interactions between ozone or Zn treatment and grain portion were detected.In summary, foliar Zn application had no effect on grain yield, but increased grain Zn concentration and Zn bioavailability of rice and wheat under different grown conditions. The increases varied with the varieties, Zn compounds, growth stages, panicle positions or grain portions. |
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