Comparation and Analysis of Leaf Photosynthetic Potentials in Thinned and Densely-planted Apple Orchards ( I ) The vertical distribution characteristics of photosynthetic active radiation and photosynthetic rate

摘要

At present, the fruiting or aging apple orchards of main apple production districts in China, which were mostly densely-planted with vigorous rootstocks during 80 years of the last century, have not accorded with modern orchard administration. So transforming the densely-planted orchards has been turning to one of central tasks. Thinning has been one of main technical measurements to transform the densely-planted orchards. It was studied that leaf photosynthetic potentials and photosynthetic active radiation (PAR) vertically distributed and their characteristics was analyzed at various levels of canopies by means of comparing the densely-planted with the thinned orchards. The main aim was to provide theoretical basis for further studying the effect of the transformation on the use efficiency of PAR, fruit quality and yield. The results showed that the thinning obviously improved the radiation environment in the tree canopy, and PAR distribution within the canopy in the thinned was more wellpropartioned than that in the densely-planted. The invalid space under 30% of relative photosynthetic active radiation (PAR,) was nearly null in the thinned; but in the densely-planted, mini PAR,, was 17%, and the space under 0.3 of relative canopy hight was invalid for photosynthesis. The leaf photosynthetic efficiency in the thinned was evidently improved. Compared with the densely-planted photosynthetic rates (Pn) at the middle and bottom of the canopy respectively increased by 7.8% and 10.2% in the thinned.