Effects of CO₂ enrichment，nitrogen and soil moisture on growth and dry matter ccumulation of spring wheat

Spring wheat(Triticum aestivum L．CV．Dingxi No．8654)is treated with the concentrations of 350umol／mol and 700umaol／mol of atmospheric C0₂ at two levels of soil moisture(wet and drought)and five levels of nitrogen fertilizer(0mg/kg_soil，50mg／kg_soil，100mg／kg _soil，150mg／kg_soil and 200mg／kg_soil)．The study shows that C0₂ concentration enrichment does not increase the tillers of spring wheat，while in low N treatment，tillers are reduced significantly．The results indicate that tillering of spring wheat needs enough N nutrition under atmospheric CO₂ concentration enrichment．At 55 days after sowing，the elevated C0₂ increases the leaf width and leaf area index(LAf)with N-added treatment but does not show any increase of those without N-added treatment． Adequate N and water can hasten the leaf growth and increase the leaf area and tiller．The effects of enriched 0 concentration on shoot dry mass depend on soil nitrogen leve1．In the medium N and high N trea tments，shoot dry mass increases significa ntly，but does not increase sign ificantly in the low N trea tment．CO₂ concentration enrichment does not increase more shoot dry mass in drought treatment than in wet treatment．Thus，the elevated C0₂ does not ameliorate the depressive effects of drought and nitrogen stres．In addition，the elevated C0₂ concentration does not increase root dry mas and root／shoot ratio，on the other hand，root dry mas decreases slightly and root／shoot ratio decreases significantly owing to CO₂ enrichment without N-added treatment under wet condition．