The contribution of root respiration to soil respiration under different crop rotations and managements

It is important and difficult for quantifying the contribution of root respiration to soil respiration when study soil carbon balance. The root-and no root-zone respiration from the conventional and optimized winter wheat-summer maize double-cropping system( Con.W /M,Opt.W /M),optimized winter wheat-summer maize or summer soybean-spring maize three harvests over two years( W /M-M,W /S-M) and single spring maize system per year( M)were measured by combining soil CO2 fluxes system( LI-8100) with the method of root exclusion on the North China Plain,and the difference between root- and no root-zone respiration was calculated as the contribution of root respiration to soil respiration. The results showed that root- and no root-zone respiration had an obviously seasonal variation and had significant correlation each other. No root-zone respiration explained for 65% and 87% of root-zone respiration in winter wheat season in treatments Con.W /M and Opt.W /M,respectively,and they were 48% and 65% in summer maize season. No rootzone respiration explained 68%,76% and 58% of root-zone respiration in spring maize season in treatments W /M-M,W /S-M and M,respectively. The contributions of root respiration to soil respiration were 25.0% and 29.6% for winter wheat and summer maize in Con.W /M,respectively,and they were31.1% and 35.0% in Opt.W /M. The ratio of root respiration to soil respiration in spring maize season was not significantly affected by cropping rotations and managements,and they were 23.7%,24.8% and 24.9% for W /M-M,W /S-M and M,respectively. The root-and no root-zone soil respiration showed positive correlation with 5 cm depth soil temperature,and the root respiration significantly increased this kind of relationship.