Effect Of Boron On The Utilization And Distribution Of C And N In Apple Trees

To investigate the changes of different boron forms in apple trees, the protective enzymeactivity of leaves, photosynthetic characteristics, as well as the characteristics of distribution,utilization of¹³C and¹⁵N in different organs,2year old grafted Red Fuji/Malus. hupehensisRehd and15year old ‘Starkrimson’ apple trees were used as materials in the experiment. Themain results were as follows:The sand culture experiment proved that the content of water soluble boron andsemi-bound boron in leaves increased significantly with the increasing content of boron.Moreover, leaf water soluble boron is sensitive to the content of boron. Application of boroncould increase the activity of protective enzymes such as superoxide disumtase（SOD）,catalase（CAT）, but the activity of peroxidase（POD） decreased; The photosynthetic rate,transpiration rate and stomatal conductance firstly increased and then decreased with theincrease of boron concentration, however, the change of intercellular CO2concentration wason the contrary; The¹³C and¹⁵N distribution ratio of roots was the highest, then followed byleaves, xylem, and phloem respectively; but boron application greatly affected the distributionrate and utilization rate of¹³C and¹⁵N. The¹³C distribution rate of leaves firstly decreasedthen increased with the increasing of boron concentration, but in the roots they firstlyincreased and then decreased with the increasing of boron concentration, the results showedthat application of boron could contribute the¹³C transports from leaves to roots; The Ndffvalue of each organ firstly increased and then decreased with the increasing of boronconcentration, and in roots it was the highest, while in leaves it was the lowest. The¹⁵Ndistribution rate of leaves firstly increased then decreased with the increase of boroncongcentration, and it reached the highest at the treatment of B2; In the roots, the¹⁵Ndistribution rate increased with the increase of boron concentration; Boron deficiency resultedin the utilization rate of¹⁵N was significantly lower than that of control, and the¹⁵Nutilization rate in tree was the lowest and just36.17%at the B0treatment, but at the B2treatment, it was51.80%and1.43times than that of B0treatment. In a word, application ofboron fertilizer could affect the utilization and distribution of¹³C and¹⁵N in apple trees.Under filed condition,the content of different boron forms in fruits and water soluble boron and semi-bound boron in leaves could be improved by different applications of boronfertilization, meanwhile apple fruits sprayed with boron fertilization had higher soluble sugar,fruit acidity and soluble solids than those of soil application,and the treatment of T4has thebest effect. So foliar boron was a more effective way than soil boron application according tothe results in the current year.