Abstract: The variation of CO₂ concentration in winter spring cultivated solar greenhouse in northern China was studied. The diurnal change of CO₂ concentration showed an irregular 'U' shape in most case, the maximum value appeared prior to unveiling straw mat in the morning, and the minimum between12:00 and 14:00 PM. Sometimes, an irregular 'W' shape curve with two valleys was also observed, with the first one appeared prior to the ventilation at noon, and the second occurred between15:00～16:30 PM. During the period of winter spring cultivation, the daily maximum concentration of CO₂ in solar greenhouse decreased gradually, while the daily minimum concentration and daytime average concentration dropped first, then went up. At the same time, the time of CO₂ depletion lasted longer and longer. In December, CO₂ depletion happened 2.1～3.1 hours after morning unveiling. In the next March, however, it moved up to 0.6～1.1 hours after unveiling in the morning. At daytime, both during and after ventilation, solar greenhouse often showed CO₂ depletion. The period of CO₂ depletion extended from 4～5.8 hours per day in December to 8～8.5 hours per day in March of next year. The spacial distribution of CO₂ concentrations within the greenhouse showed that in the morning and in the evening, the order was the front>the middle>the back, and the ground>the canopy>the upper, and at midday, the order was the front <the middle<the back, and the ground>the upper>the canopy. Photon flux density was the most important environmental factor affecting CO₂ concentration in greenhouse. Ventilation did not avoided CO₂ depletion. Canopy photosynthetic rate and soil respiratory rate were measured at different growth stages of tomato. At seedling stage, CO₂ concentration in greenhouse was higher than that outside, due to the vigorous soil respiration and lower canopy photosynthetic rate. But at fruiting stage, severe CO₂ depletion occurred because of stronger canopy photosynthesis and weak soil respiration.

Key words: Solar greenhouse, CO₂ concentration, Diurnal change, Seasonal change, Spacial distribution, cloning library, Daya Bay, high-throughput sequencing, Sanger sequencing, 18S rDNA.