Development of an Air-Curtain Roof Chamber to Assess Climate Change Effects on Crop Plants: A Study with Rice

Recent years have brought unsettled, especially hot weather. These bouts of heat are aparently one result of global warming, induced to a considerable degree by human activities such as gigantic-scale fossil-fuel combustion and deforestation (Rosenzweig and Hillel, 1998; Brönninmann, 2015). Projected temperature rises are 2.6― 4.8°C (higher scenario) to 0.5―1.7°C (lower scenario) for 2081―2100 relative to 1986―2005. The observed increase in global carbon emissions over the past 15―20 years has been consistent with the higher scenario (Hayhoe et al., 2017). Higher temperatures than those of normal seasons affect crop growth and yields depending on their intensity level and duration. Observed typical effects are hastening of leaf appearance, flowering, and maturity, increased sterility, and decreased grain weight and quality (Stone, 2001; Menzel and Sparks, 2006). Unless these human-triggered changes terminate, adaptation to them will be necessary by the breeding of tolerant crop species and varieties against these changes, or shifting of the season and location in crop cultivation (Rosenzweig and Hillel, 1998; Lafarge et al., 2011; Redden et al., 2014). In Japan, the planting time of rice crop has advanced to a considerable degree, concurrent with the dissemination of early season culture. Therefore, grain filling often occurs during high temperatures of summertime, which degrades grain weight and quality (e.g. imperfect rice kernels including chalky grain; Nagato et al., 1960; Nagato and Ebata, 1965; Tashiro and Wardlaw, 1991). Hightemperature-induced deterioration of rice production is occurring worldwide concomitantly with recent global warming (Jagadish et al., 2007; Oh-e et al., 2007; Kobata et al., 2011). As a countermeasure to this, the breeding of new rice cultivars tolerant to high temperatures which includes metabolic changes, is progressing but it is not satisfactory at present (Ishimaru et al., 2016; Morita et al., 2016; Tayade et al., 2018; Fahad et al., 2019). To forecast crop behavior in response to global environmental changes, a series of experiments corresponding to such changes using environmental control facilities is expected to be beneficial. At present, facilities of various types such as the greenhouses and phytotrons (Went, 1957; Downs, 1980), temperature gradient chamber (TGC; Mihara, 1971; Oh-e et al., 2007), open-top chamber (OTC; Heagle et al., 1973; Drake et al., 1989), and free-air carbon dioxide enrichment (FACE; Allen et al., 1992; McLeod and Long, 1999) with natural or artificial light sources are adopted in response to experimental needs from basic to applied situations of crop performance under environmental changes (Hashimoto, 1987). In addition to these facilities, we have developed a new growth chamber, the “air-curtain roof chamber (ACRC),” with appearance that does not differ largely from that of OTC. A great difference from existing OTC is use of the ‘air-curtain’ shed roof, which functions as the ceiling without intercepting sunlight or rain. Air from the curtain source circulates