Soil environment and spectra properties coregulate tomato growth, fruit quality, and yield in different colored biodegradable paper mulching during the summer season

Plastic film (PF) is the primary material applied for soil mulching, but it may also cause heat and drought stresses to crops in the summer season. In a previous study, we revealed that biodegradable paper (BP) was a potential mulching material for summer crop production, because it could not only decrease soil temperature, but also increase soil moisture during the summer season. However, it is still unclear whether different colored BPs have various efficiencies in improving soil environment, when used as soil mulching materials. Therefore, in this study, gray PF and different colors (red, dark, blue and yellow) of BPs were used as soil mulching materials to explore their influences on soil temperature and moisture, spectral and photosynthetic characteristics, plant growth, and fruit quality and yield of tomato in the summer season. The non-mulching (NM) served as control. In general, PF exhibited the highest illuminance and photosynthetic irradiance, and thereby led to the highest soil temperature. However, soil temperature decreased on average of 5.73% and 20.28% in BPs as compared to NM and PF, respectively. Soil moisture increased on average of 8.15%, 5.41%, and 10.98% in dark, red, and blue BPs, respectively, as compared to NM. The ratio of blue-violet to red-orange irradiance were 1:2, 2:3, 1:4, 1:3, and 1:1 in NM, PF, yellow BP, red BP, and blue BP, respectively. The red and blue BPs generally enhanced root growth, and thereby increased total fruit yield by 36.56% and 41.64% on average, respectively, as compared to PF. In addition, an overall improvement in fruit quality (vitamin C, soluble sugar, and sugar-acid ratio) was observed in red and blue BPs as compared to PF and other colored BPs. Our results demonstrated that red and blue BPs can be applied to improve soil environment and spectral characteristics, and thereby enhance fruit yield and quality, during the summer crop production.