CO₂ Enrichment on Biomass Accumulation and Nitrogen Nutrition of Spring Wheat Under Different Soil Nitrogen and Water Status

Abstract

Atmospheric CO₂ increase may bring unexpected consequences on field crops with less nitrogen (N) and water supply. This study investigated biomass accumulation and N nutrition of spring wheat (Triticum aestivum L.) grown under two atmospheric CO₂ concentrations (350 and 700 µmol mol⁻¹), two soil moisture treatments (well‐watered and droughted) and five N fertilizer treatments (0, 50, 100, 150, 200 mg kg⁻¹). Results showed that the effects of elevated [CO₂] on shoot and total biomass accumulation depended largely on the soil N levels. Shoot and total biomass increased significantly in responding to CO₂ enrichment only in moderate to high N treatments. With either the droughted or the well‐watered treatments, CO₂ enrichment didn't show any significant enhancement in biomass accumulation. Thus, elevated CO₂ concentrations did not relieve any adverse effects of droughted and N stress on the dry matter accumulation. Enriched [CO₂] levels reduced the shoot N contents, shoot and total N uptake significantly but only slightly decreased the root N content and uptake. Shoot critical N concentrations were lower for spring wheat grown at 700 µmol mol⁻¹ than at 350 µmol mol⁻¹ CO₂ concentration in both well‐watered and droughted treatments. The critical N concentrations were 1.6% and 2.1% for the well‐watered and droughted treatment at enriched [CO₂], and 1.9% and 2.6% at ambient [CO₂], respectively. Our results showed that CO₂ enrichment increased both the water use efficiency (WUE) and nitrogen use efficiency (NUE), possibly due to the reduced mass flow to the roots and thus reduced shoot and root N concentrations. The decrease in N uptake by spring wheat due to enriched [CO₂] could not be explained in this experiment.

Keywords:

• CO₂ enrichment
• Soil moisture status
• Nitrogen fertilizer
• Biomass accumulation
• N nutrition
• Nitrogen uptake

Acknowledgments

We are grateful for the grant support from Chinese National Science Fund (No. 49725102 and G1999011708) and from RGC of Hong Kong University Grants Council (HKBU2041/01M). And we also would like to thank the staffs of the Key Laboratory of Agricultural Soil and Water Engineering in the Arid and Semiarid Areas, Ministry of Education, P.R. China for their technical assistance.