Effect of thinning and reshaping on the canopy structure and leaf quality at late growth stage in dense apple orchard in Loess Plateau of eastern Gansu, China.

Abstract

In order to examine the effects of thinning and reshaping on canopy structure, leaf physio-logical property at late growth stage, characteristic of nutrient accumulation and distribution in leaf, and the spatial and temporal distribution of soil moisture, 18 year-old 'Fuji' apple trees in dense apple orchards were used to measure the canopy size, types and numbers of branches, leaf area index before and after the thinning and reshaping practices. The results showed that before pruning, the photosynthesis was limited by non-stomatal factors, with a reduction in Fv/Fm, Fv/Fo PIabs by 1.2%, 11.5%, 13.9%, respectively. However, the thinning and reshaping practices reduced leaf area index and canopy coverage, increased light interception up to 79% and improved tree construction. The total number of shoots decreased to 1100400 per hectare, while the individual shoot numbers were increased by 5.0% and the ratio of spur increased up to 73%. Due to the improvement of canopy lighting distribution, the average leaf area, specific leaf quality, hundred leaf mass and chlorophyll content were increased. With the increases of photosynthesis, the accumulation of photosynthate such as starch was increased by 143.5%. There was a close correlation between leaf development and light interception. Our results indicated that tree structure and canopy light interception could be improved by thinning and reshaping the dense trees, which resulted in higher leaf growth, development and photosynthetic capability but less water loss. Thinning and reshaping should be recommended to the renewal of the dense apple orchards in Loess Plateau of eastern Gansu.