Responses of rice and winter wheat to free-air CO2 enrichment (China FACE) at rice/wheat rotation system
Free-air CO2 enrichment (FACE) system at a Chinese rice–wheat rotation field was constructed to investigate responses of rice and wheat crop growth to elevated CO2 and nitrogen fertilization. A factorial experiment design was set up with two levels of atmospheric CO2 concentration (350 and 550 μmol mol−1) and N application rates (LN: 150 kg N ha−1 for rice and 125 kg N ha−1 for wheat; HN: 250 kg N ha−1 for rice and wheat, respectively). Across the entire crop growing seasons, plant fractions (i.e. leaf, stem, ear and root) were differentiated at representative growth stages and analyzed using widely recognized parameters, relative growth rate (RGR) and allometric coefficient K a (RGR ratio of above ground to below ground plant biomass). The C/N ratio and phosphorus concentration of plant were also determined. Rice and wheat RGRs responded to elevated CO2 in different ways, i.e. wheat RGR was always stimulated by elevated CO2 while rice RGR seemed to be depressed between rice tillering to jointing stages. Elevated CO2 affected the plant fractions differentially. For example, rice leaf might be the most strongly affected organ by RGR analysis and by K a analysis it seems that elevated CO2 always led to higher below ground biomass (root) than above ground biomass. Besides, elevated CO2 usually resulted in a higher C/N ratio of plant due to its impact on N concentration instead of carbon. Regardless of CO2 treatment statistic analysis of rice and wheat RGR did not yield significant difference in plant growing patterns under LN and HN treatments, although LN always triggered a slightly higher C/N ratio of plant over the investigated period. Furthermore, it was generally observed that elevated CO2 could stimulate crop biomass to a greater extent under LN treatment than HN treatment. Phosphorus concentration of rice and wheat crop showed distinctive response to elevated CO2 and N constraint.
KeywordsElevated CO2 Relative growth rate (RGR) Carbon Nitrogen Phosphorus
The authors are greatly indebted to the staffs of Wuxi Experimental Station for running FACE system, the core platform of The Chinese Rice/Wheat FACE Project initiated by China–Japan Science and Technology Cooperation Agreement. This work was supported by the Natural Science Foundation of China (NSFC, 40231003, 40571157 and 40110817), the National Key Project on Basic Sciences (grant number 2002CB714003), the Knowledge Innovation Program of Chinese Academy of Sciences (KZCX3-SW-440, KZCX2-SW-133), and the 973 Project (CCDMCTE-2002CB412502) and the Jiangsu Provincial Science Foundation (BK2006252).
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