In this study, we discussed how temperature and other environmental factors affect the fruit growth and quality of Satsuma mandarin grown in a plastic house with heating. At 14 23°C, the average nighttime air temperature was positively correlated with the standardized fruit growth rate (GRFSt) in the young stage. In contrast, GRFSt was clearly depressed with a daytime air temperature at around 30°C, and the optimum air temperature for active fruit growth was 25°C. Moreover, in the middle and mature stages, the air temperature did not correlate with the GRFSt. These results indicate that, in the young stage, the air temperature should be controlled at around 25°C during the daytime and 20 23°C during the nighttime for active fruit growth. In the middle and mature stages, fruit growth might not require nighttime air temperatures that are as high as 20 23°C. The air temperatures did not correlate with the fruit soluble sugar content (SSC); in contrast, a close relationship was found between the predawn xylem water potential (Xy) and SSC. The day temperature, radiation and Xy were linearly correlated with the fruit titratable acidity (TA) in the young stage.

In order to control nighttime temperatures with energy saving, how different night temperature regimes affected on the fruit growth, quality and 13 C allocation from leaf to fruit were researched by both the partial heating and whole tree heating. One type, altering time of nighttime heating, the end of day (EOD) -heating, middle of night (MON) -heating, and predawn (Pd) -heating were applied. The EOD-heating temporally activated the fruit growth and accelerated the 13 C allocation from leaf to fruit through short term (hours) researches by the partial heating, however, comparing to the conventional heating as 20°C constant in nighttime by the whole tree heating during 60 90 days after full bloom (DAFB), no superiority was observed in both the fruit volume increase and fruit quality, and the MON-heating showed the depression of fruit growth. Another type of a regime determined by daily integrated solar radiation, comparing to the conventional heating as 17°C constant in nighttime during 78 120 DAFB, no superiority was observed in the fruit quality. Nighttime 13 C allocation from the leaf to fruit was detected at 90 DAFB, though was hardly detected at all at 120 DAFB regardless of night temperatures as high as 25°C at both days.

In order to clarify the effect of nighttime temperatures on fruit development of Satsuma mandarin, we examined the fruit water and carbon balances using the 13 C tracer method and the roles of phloem and xylem transports for fruit growth under moderate night temperatures (MN, set at 23°C) and low night temperatures (LN, set at 13°C). The average predawn xylem water potentials were 0.79 0.04 MPa under MN and 0.77 0.03 MPa under LN. Fruit growth used 86% of pedicel sap flux toward the fruit, while transpiratory water losses from the fruit surface were 14% of pedicel sap flux under both MN and LN. The daytime integrated xylem sap flux was negative, but it was positive in the nighttime. The integrated phloem sap flux (JPhlo) and the difference in JPhlo between MN and LN were only 6 10% and 4% of the total sap accumulated in the fruit, respectively. Integrated fruit photosynthesis and integrated CO2 efflux from the fruit surface were 7 8% and 22 23% of the total carbon supply toward the fruit, respectively. This indicates that carbon translocation from leaves to fruit via the phloem of the stem is the main source of carbon for the fruit.