Effects And Mechanism Of CO₂ Enrichment On Vegetables As Well As Regulation Techniques Of CO₂ Environment In Solar Greenhouse

Solar greenhouse is the main form of protected cultivation in spring and winter in northern China, it has been showed that CO2 deficiency in solar greenhouse becomes crucial limiting factor for vegetable yield , however, basic studies on principles of CO2 regulation are weak. Based on the productive practice of solar greenhouse , the law of space-time changes of the CO2 environment and the physiological and biochemical mechanisms of vegetable photosynthesis and growth promoted by CO2 enrichment were studied, and the properties of different CO2 sources were evaluated in this paper. The main results were as follows: 1 .The CO2 environment in conventional greenhouse was surveyed, the results indicated that: Diurnal change curve of CO2 concentration appeared 揢?shape, the maximum of CO2 concentration was observed before the unveiling of straw mat every morning, and the minimum happened at about12:OOAM拁?14:OOPM; Sometimes, two valleys were found on the curve, which appeared respectively before ventilation at noon and at 15:OOPM棐16:3OPM. In the process of cross-winter cultivation, the daily maximum concentration of CO2 in solar greenhouse decreased gradually, at the other hand, the daily minimum concentration and daytime average conce- ntration dropped first, then went up: At the same time, the CO2 deficient time prolonged day by day, from December to March of next year, the deficiency of CO2 happened from 2 ?-3 hours to 0.5 lhour after the straw mat was unveiled in the morning. In the daytime, both during and after ventilation, solar greenhouse always showed the deficiency of CO2. The time length of CO2 deficiency in a day was 4? hours ,so CO2 enrichment in solar greenhouse is extremely necessary.Comparing the CO2 concentration at different sites inside greenhouse, it was found that, in the morning and in the evening, the front>the middle>the behind, the lower>the middle>the upper~ but at noon ,the front tbe upper>the middle; In the daytime, the site with the lowest CO2 concentration was at the front part of the greenhouse and the height of plant canopy. Photo flux density was the most important of the environment factors affecting CO2 concentration. 2.Canopy photosynthesis, soil respiration and air exchange between inside and outside the greenhouse were measured at tomato seedling stage and fruiting stage. The results by a path analysis showed that, air exchange affected the CO2 concentration mostly at seedling stage, when CO2 enrichment was not necessary because of higher CO2 concentration in greenhouse; But at fruiting stage, canopy photosynthesis and air exchange both became important factors, it was necessary to avoid CO2 deficienc~. Ventilation neither prevent CO2 from diffusing out of the greenhouse, nor avoid CO2 deficiency in greenhouse. 87 8~i~I.E CO2 ~-~flt~ CO~4~I~ 3.Expaiments of CO2 enrichment were carried out respectively at seedling stage of cucumber and tomato, and fruiting stage of cucumber. It indicated that:C02 enrichment promoted the growth of vegetable seedlings and was beneficial to raising vigorous transplants, the chilling tolerance of C02-enriched plants was also strengthened; CO2 enrichment at 700 ?100 ~i I .1?and 1100 ?100 ~?I 憀?for three hours every morning at cucumber seedling stage increased fruit yield by 8.31% and 13.11%, for tomato,21.93% and 8.47% respectively; CO2 enrichment at around 1000 ii I {?at fruitin8 stage increased total yield of cucumber by 2 7.06%; Both at seedling and at fruitin...