Light condition is a fundamental environmental factor for high-quality plant production. In this paper, we discuss how light condition affects fruit development in the long and short term, and attempt to clarify management methods for active fruit development under conditions of low solar radiation, by using quantitative research on fruit water and carbon balance during greenhouse cultivation of Satsuma mandarin (Citrus unshiu Marc.). A significant decrease in yield due to shading was not detected, but we confirmed that shading treatment affected the dry weights of source-sink units, fruit volume, increase in volume of the fruits, and fruit quality parameters, such as sugar accumulation, acid content, and rind color. Qualitatively, the carbon balance of Satsuma mandarin fruit is comparable to that of tomato fruit or rice panicle, but quantitatively, the carbon balance of Satsuma mandarin fruit may differ, as shown by low sink relative growth rate. In addition, fruit growth parameters such as translocation rate for a fruit and fruit relative growth rate showed significant positive correlations with dark respiration, despite the shading treatment. The fruit carbon demand may be simply described by fruit dark respiration as the sum of new photosynthetic carbon and stored carbon translocation for a fruit.

To establish cultural practice based on a consecutive growth model for potted 1-year-old seedlings of Satsuma mandarin (Citrus unshiu Marc.), growth analysis by classical and functional approaches was conducted under different light conditions and air temperatures over 2.5 years, and the active growth of potted seedlings in the greenhouse was investigated. Under the classical approach, the general change patterns of relative growth rate (RGR) and net assimilation rate (NAR) were hard to determine because of irregularities including quiescence of vegetative growth. Under the functional approach, plant mass modeled using linear, exponential, power-law, monomolecular, three-parameter logistic, four-parameter logistic (4L), and Gompertz functions showed significant correlations with the observed plant mass. 4L was the best model because it showed the highest r, and the lowest root mean square error and Akaike Information Criterion, so RGR and NAR were estimated by 4L. Analysis of the RGR components showed significant positive correlations between RGR and NAR. Analysis of covariance indicated the NAR costs for increasing RGR were lower in the greenhouse than in open culture; this was explained by differences in specific leaf area (SLA). Therefore, in greenhouse culture, growth was primarily enhanced by NAR as net photosynthesis and underpinned by SLA as a morphological trait improvement for the relatively low light intensity compared with open culture. A multiple regression model for NAR using the pooled data (n = 60) suggested solar radiation had a positive effect (P < 0.0001) and air temperature had a negative effect (P < 0.01) on NAR.

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.

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