Abstract
In order to define the effects of fruit crop load on the distribution and utilization of carbon and nitrogen in dwarf apple trees, we conducted three crop load levels (High-crop load, 6 fruits per trunk cross-sectional area (cm2, TCA)), Medium-crop load (4 fruits cm−2 TCA), Low-crop load (2 fruits cm−2 TCA)) in 2014 and 2015. The results indicated that the 15N derived from fertilizer (Ndff) values of fruits decreased with the reduction of crop load, but the Ndff values of annual branches, leaves and roots increased. The plant 15N-urea utilization rates on Medium and Low-crop load were 1.12–1.35 times higher than the High-crop load. With the reduction of crop load, the distribution rate of 13C and 15N in fruits was gradually reduced, but in contrast, the distribution of 13C and 15N gradually increased in annual branches, leaves and roots. Compared with High-crop load, the Medium and Low-crop load significantly improved fruit quality p < 0.05. Hence, controlling fruit load effectively regulated the distribution of carbon and nitrogen in plants, improved the nitrogen utilization rate and fruit quality. The appropriate crop load level for mature M.26 interstocks apple orchards was deemed to be 4.0 fruits cm−2 TCA.
Highlights
According to the characteristics of the output and input of plant photosynthetic products, the tissues and organs can be divided into two categories, namely “sink” and “source”
The leaf is the main organ of photosynthesis to produce the dry matter, and the chlorophyll is the main chemical compounds with nitrogen[38,39]
The leaf area on Medium and Low-crop load treatments were significantly higher than that of High-crop load treatment (Table 1), which was consistent with the above results, but the leaf chlorophyll content and photosynthetic rate reduced with the increase of fruit crop load (Table 1), which were contrary to the previous studies
Summary
According to the characteristics of the output and input of plant photosynthetic products, the tissues and organs can be divided into two categories, namely “sink” and “source”. High crop load reduced trees storage nutrition, which significantly affected the vegetative growth and flower bud differentiation in the second year[8]. Fruit thinning is effective in managing the relationship between vegetative and reproductive growth, which ensures high quality and yield in fruit trees by adjusting the relationship between “sink” and “source” and changing the transportation and distribution of photosynthate[9,10]. The reasonable crop load is a crucial factor of guaranteeing the tree’s growth to gain the high yield, stable production and good quality[16,17]. The tree’s growth and its yield are closely related to the nutrient distribution of carbon and nitrogen. Coordinating the reasonable distribution of carbon and nitrogen in plants is of great significance to improve their production
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