Latitudinal variation in sugar maple fine root respiration

A changing global climate may impact the respiration of fine roots. While many models adjust fine root respiration as temperature increases, the influence of soil nutrient availability and the possibility that root respiration may be adapted to local climate are often not addressed. Rates of fine root respiration were measured in four sugar maple (Acer saccharum Marsh.) forests located along a latitudinal gradient in Michigan. Root respiration was measured as O2 consumption at temperatures ranging from 6 to 24 degrees C on excised fine root samples in early September, October, and November of 1994. Root respiration increased exponentially with temperature with an average Q10 of 2.7; there were no differences in Q10 among sites. However, there were differences among sites in mean respiration rate at a given temperature. This site effect did not indicate ecotypic adaptation to local climate, but rather reflected fine root N concentration. Respiration at a given temperature was consistently higher in roots with higher N concentrations, and higher root N concentrations always occurred at sites having greater N mineralization rates. Results suggest increases in soil temperature could significantly alter root respiration C flux at these sites, as could changes in site N availability associated with chronic N deposition or altered N mineralization resulting from global climate change.