Study of soil respiration and fruit quality of table grape (Vitis vinifera L.) in response to different soil water content in a greenhouse

To understand the response of grape (Hutai No.8) quality and soil respiration (R-s) to different soil relative water contents (SRWCs), this study was designed with three soil moisture levels (A: 80-95%, B: 60-75%, and C: 40-55% of SRWC) for grape cultivation. Meanwhile, environmental factors, including air temperature (T-a), air relative humidity, and light intensity, were also recorded. The results showed the following: (1) Through the comprehensive analysis of fruit quality by the method of subordinate function, we concluded that the optimum soil moisture treatment was 60-75% SRWC, and the soluble sugars, proanthocyanidin, and resveratrol were most abundant. In addition, vitamin C (Vc) content was the largest under C treatment. (2) Photosynthetic characteristic under high soil moisture was better than those under low soil moisture condition during grape coloring periods, and it was largest under A treatment in 2015. R-s rate was in accordance with the trend of grape photosynthesis. High soil moisture could accelerate the photosynthetic rate of grape leaves and increase R-s. (3) Correlation analysis showed that higher soil moisture and air humidity and lower soil temperature (T-s) and T-a could promote the accumulation of more nutrients in grape berries; it also could increase photosynthetic rate and R-s during grape coloring periods. In conclusion, 60-75% SRWC was the optimum soil moisture condition, which could improve the nutrient contents and accumulate more bioactive substances. Of course, keeping a lower T-s and T-a, as well as higher air humidity, was also necessary. Abbreviations: SRWC: soil relative water content; A, 90-95% SRWC; B, 70-75% SRWC; C, 40-55% SRWC; Rs: soil respiration; Ta: air temperature; Ts: soil temperature; OPC: proanthocyanidin; TSS: total soluble solids.