| In the southern regions of China, it is very hot and relative humidity is high during summer. Similar conditions also prevail inside the greenhouse. The use of cooling systems evidently increases production costs, though the results are not always satisfactory. In this experiment, it was observed that when roof ventilations were closed at noon, the greenhouse temperature could rise as high as 50℃. This resulted in serious plant injury and in certain cases, death of plants. The primary objective of protected cropping is to provide sufficient control of the aerial and root environments so as, to enable production of high quality of crops at greater economic benefit to the producer compared to open field production.In addition, utilization of soilless cultivation is widely implemented by modern growers and in precision agriculture. It consists of using other growing medium rather than soil. Depending on the appropriate growing medium selected, the results are usually more satisfactory than in soil cultivation.Generally, plant responses to environmental factors are non linear and responses which involve two or more environmental stimuli are usually not additive. We observed that the effects of previous environmental conditions can be persistent under certain circumstances and the plants themselves could influence the environment around them.The aim of our research was to study the effects of high temperature regimes on cherry tomato plants cultivated in different cultivation systems at different growth stages. Our objective was to assess the critical temperature at a precise growth stage, and thereafter propose an appropriate cultivation system which can mitigate the thermal stress during summer.In this study, after a brief presentation on cherry tomato and its requirements^ heat stress and its effects on plant physiology are also discussed. The investigation is a comparative study of heat stress on cherry tomato cultivated in different substrate systems: soil, peat moss, peat/perlite(3/2), perlite and a NFT (Nutrient Film Technique) during summer time. The study was undertaken in a glasshouse from June to September 2002. 35 days after sowing (DAS) in a plant nursery, the cherry tomato seedlings were transplanted in three different rooms (1, 2, 3) with different temperature regimes: 25/20C, 35/25C, and >35/>25C day/night temperatures respectively. The interaction of environmental gas exchanges was studied. There was a negative linear relationship between temperature and RH (Regression coefficient: 0.894-0.972), and also between temperature and CO2 in all the rooms (Regression coefficient: 0.668-0.786). The growth and development were assessed. The growth rate (based on stem elongation) was decreasingly slower with plant development. The stem elongation was specifically related to the growing media. The internode's length was somehow affected by temperature regimes. Temperature and growing medium affected independently but strongly the leaf expansion. The critical effect of temperature was noted particularly during the flowering stage. Not only were flower initiation and multiplication delayed by higher temperature, but fruit set was also seriously compromised.The plant water status was evaluated using the leaf water potential measurements, leaf relative water content, leaf chlorophyll content and air /leaf temperature gradient. The analysis of variance shows a significant effect on the interaction of heat stress and growing media on leaf water potential when the treatment is applied only at midday. Highly significant differences in water potential caused independently by temperature and growing medium (at dawn or at midday) were noticed in our study. Leaf relative water content was not significantly affected either by temperature or by growing medium. At midday, we noted a strong effect of temperature on air/leaf temperature gradient. Significant differences in leaf chlorophyll B content, caused by the interaction of temperature and growing media, were detected. In addition, root zone area environ... |
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