Effects of vapor-permeable reflective film mulching on citrus tree microenvironment, shoot growth and fruit development

Abstract:【Objective】The study is to explore the effects of vapor-permeable reflective film mulching on canopy microenvironment, shoot growth and fruit quality of Satsuma mandarin (Citrus unshiu Marc.), and provide a new reference model for citrus cultivation.【Methods】The experimental material was 32-yearold Satsuma mandarin (C. unshiu Marc.) trees. Plants with consistent vigor in the open field were selected and white vapor-permeable reflective film mulching was carried out in the late July 2015. Internal and ex⁃ternal fruit qualities, canopy light characteristics and light quality, soil physical and chemical properties, and tree growth were measured. For fruit quality evaluation, fruit vertical and horizontal diameters, fruit color, peel pigments, TSS, and contents of titratable acids, sugars and vitamin C were determined. For can⁃opy light characterization, reflected light intensity and quality were analyzed, and for determinations of soil physical and chemical properties, rhizosphere soil microbes and water content were measured.【Results】The growth of shoots during the fruit development was less affected by mulching with vapor -perme⁃able reflective film. The treatment significantly improved photosynthetic rate, which was constantly higher than in the control. Vapor-permeable reflective film mulching also significantly increased the reflected light intensity by 2-7 times at ground level, canopy bottom and the middle of the crown, and the absolute radiation of visible light at the three positions was also significantly improved. The treatment significantly reduced the soil moisture at three depths, 10 cm, 30 cm and 40 cm in the open field, where soil moisture declined by 7.55%, 2% and 6%, respectively. At the depth of 20 cm, the water content in mulching treat⁃ment was significantly higher at 0 day. However, it gradually reduced to a level similar to that in the control at harvested. Meanwhile, mulching saw a greater number of bacteria and fungi, which increased by 77% and 233%, respectively, while the quantity of actinomycetes had no significant change. Mulching had the biggest influence on the number of fungi. Many nutritional elements in citrus leaves increased. At 60 days of mulching, N, P, Ca and Mg had increased to some extent while K decreased. Trace elements Zn and B increased as well. Fruit vertical and horizontal diameters were decreased by 13% and 10% by mulching, respectiveluy. Vapor-permeable reflective film mulching significantly improved the fruit color,luminance value (L) and the red-green value (a*) of the fruit, with L and a* values increased by 10% and 18%, respectively, while blue-yellow value (b*) displayed a slight increase. The content of peel chloro⁃phyll a also decreased significantly by nearly 17% and total carotenoids increased by 36%. Mulching sig⁃nificantly increased fruit TSS content by nearly 3%, while decreased titratable acids by 0.2% with signifi⁃cant difference. Glucose and fructose were both increased by about 30%, sucrose by 20% and total sugar by 26%. In the open field, vitamin C content in mulching treatment at harvest was 29.55 mg·100 g^-1,which was 22% higher than the control.【Conclusion】It turned out that mulching with vapor-permeable reflective film significantly improved the tree microenvironment, including light  environment and rhizo⁃sphere environment, which is favorable for fruit development. At the same time, mulching improved the photosynthesis while inhibited shoot growth. All of the above changes finally contributed to the improve⁃ment of fruit quality.