| Apple (Malus domestica L.) is a major commercial fruit tree which occupies the largest cultivated area and production in northern China. However, during the fruit quality has decreased, in part, due to greater emphadiameter on increasing the fruit yield. Most of the previous studies on improving fruit quality have failed to address the interactions between foliar-applied nitrogen and girdling on the status of nutrients in the tree and fruit quality, especially on aroma components. In this study, factorial combination of four rates of foliar urea without girdling (0,0.2,0.5and0.8%; i.e. N0, N1, N2and N3, respectively) or with girdling (girdling+0, girdling+0.2%, girdling+0.5%and girdling+0.8%; i.e. HB+N0, HB+N1, HB+N2and HB+N3, respectively) were evaluated on’Fuji’apple leaf nutrition, fruit quality parameters, aroma components and activities of two key enzymes in aroma metabolism. In a parallel experiment, effects of four different foliar-applied organic nitrogen compounds without girdling (Leucine, Isoleucine, Valine, Alanine; i.e. Leu, Ile, Val and Ala, respectively) or with girdling (girdling+Leu, girdling+Ile, girdling+Val and girdling+Ala; i.e. HB+Leu, HB+Ile, HB+Val and HB+Ala, respectively) were evaluated on’Fuji’apple aroma components and activities of two key enzymes in aroma metabolism. The results are beneficial for increasing yield and quality of fruit. The main conclusions are as follows:1. From young fruit period to later expanding period, the content of nitrogen (N) in leaves decreased first, then increased, and finally reached an optima; phosphorus (P) content increased at first, then decreased, finally increased; potassium (K) increased at first, then decreased, and finally reached a stable level. The contents of N, P and K decreased by girdling, while improved by foliar-applied urea. Furthermore, N showed an obvious increase among three elements. N, P and K contents under N0treatment were reasonably high, i.e., about19.47%,10.37%and5.6%higher than those at N0. Combination of girdling and urea application, HB+N2treatment had a similar effect as that from N0.2. During fruit expansion to ripening stage, fruit weight, diameter and soluble sugar content gradually increased, while vitamin C and titratable acid content decreased, soluble protein content increased followed by a decrease, amino acid content decreased and remained steady. Girdling treatment increased fruit weight, diameter, soluble sugar, vitamin C and amino acid content, while fruit soluble protein and titratable acid content decreased. Foliar urea increased fruit weight, diameter, titratable acid, soluble protein and vitamin C content. Vitamin C content was the highest in N1treatment. However, all other response parameters attained the peak in N2treatment. Soluble sugar content decreased with increase in concentration of foliar urea. Girdling treatment at a given rate of foliar-applied urea, fruit single weight, diameter and amino acid to be maximized under HB+N2treatment, higher11.26%,16.2%and18.4%than No treatment, respectively. Vitamin C content higher12.7%than No treatment.3. We also detected41aroma substances in the fruits, including seventeen esters, seven alcohol derivities, four ketones and eight other substances. The following aroma components, i.e. isobutyl alcohol,2-caproaldehyde, hexen-2-al,1-hexyl alcohol,3-Nonanone, farnesene, acetic acid,2-methyl butyl ester, butanoic acid,2-methyl-, hexyl ester, butanoic acid,2-methyl-, butyl ester, butanoic acid and2-methyl-ethyl ester, were94.6%of the total aroma components. Foliar urea without girdling increased the above aroma and ester components, while girdling decreased these components. The aroma content of N2treatment was greater by22.3%as compared to that of the N0treatment. The ester content of the fruit was greater in the trees with foliar application of Val as compared to those of the other treatments regardless of girdling. In addition, the contents of acetic acid,2-methyl butyl ester and butanoic acid,2-methyl-, ethyl ester were the highest of all esters. The content of acetic acid,2-methyl butyl ester under Ile was lower than Leu, Ala and Val78.9%,54.7%and73.8%, respectively.2-methyl-, ethyl ester content under Leu was lower than Ile, Ala and Val treatments about8.4%,11.1%and19.9%, respectively.4. Acyltransferase (AAT) and alcohol dehydrogenase (ADH) activity of fruit were decreased by girdling. Foliar urea without girdling increased AAT and ADH activities, but no significant difference across different N rates. In the case of girdles treatment, AAT activity was significantly greater at N2rates of foliar urea as compared to that in N0or N1treatments. However, no significant difference was evident in ADH activity across different N rates. Among the foliar amino acid treatments without girdling, the AAT activity was greater in Val treatment than that in the other treatments. ADH activity was greater in Val and Ala treatments than that in other treatments.5. The rate of foliar urea was positively correlated with either fruit diameter, amino acid content, ADH activity, titratable acid content or AAT activity, while negatively correlated with vitamin C and soluble sugar content. The magnitudes of F values across the above parameters were in the order:girdling>foliar urea. The foliar urea×girdling interaction was significant only on for the fruit weight.This article initial revealed the synergistic effect of girdling and foliar-applied nitrogen on leaf nutrition and apple fruit quality, through the effect by N, P, K and key enzyme in aroma metabolism on fruit quality and aroma. Along with the phenophase, leaf nutrition and fruit quality showed different dynamic change trend, and coordinated control by girdling and foliar-applied nitrogen. Girdling and foliar-applied nitrogen influenced aroma content and types by influencing key enzymes. The interactive effects among the above treatments were not mostly significant for all variables except foliar urea×girdling for weight. This study demonstrated that combined application of girdling and foliar spray of nitrogen improved most of fruit quality parameters and aroma content. |
