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EFFECTS OF CLIMATE CHANGE ON LABILE AND STRUCTURAL CARBON IN DOUGLAS-FIR NEEDLES AS ESTIMATED BY DELTA 13C AND C AREA MEASUREMENTS
Citation:
Hobbie, E. A., J W. Gregg, D M. Olszyk, P T. Rygiewicz, AND D T. Tingey. EFFECTS OF CLIMATE CHANGE ON LABILE AND STRUCTURAL CARBON IN DOUGLAS-FIR NEEDLES AS ESTIMATED BY DELTA 13C AND C AREA MEASUREMENTS. GLOBAL CHANGE BIOLOGY. Blackwell Science, Inc., Malden, MA, 8:1072-1084, (2002).
Description:
Isotopic measurements may provide new insights into levels in leaves of labile and structural carbon (C) under climate change. In a 4-year climate change experiment using Pseudotsuga menziesii (Douglas-fir) seedlings and a 2x2 factorial design in enclosed chambers (n=3), atmospheric CO2 levels were maintained at ambient or 179 ppm above ambient by injecting 13C-depleted CO2, and temperatures were maintained at ambient or 3.5*C above ambient. Two open plots were maintained as chamberless controls. We measured %C and isotopic composition (*13C) in needles of different age classes over a 4-year period (1993-1997) and needle sugar levels in 1997. Foliar %C varied by treatment, with elevated CO2 producing lower %C and elevated temperatures producing higher %C. In contrast, sugar levels were higher under elevated CO2 and lower under elevated temperature treatments relative to ambient. No interactive effects of temperature and CO2 on foliar %C or sugar levels were observed. Changes in *13C values were used to track recently fixed C in needles. Needle cohorts generally declined in *13C as they aged, indicating turnover of labile C. At final harvest, current-year needles from open plots, ambient CO2 chambers, and elevated CO2 chambers averaged -29?, -34?, and -39?, respectively. Declines in *13C over time in ambient and elevated CO2 treatments reflected inputs of two isotopically depleted sources, tank CO2 (*13C = -36?) and litter- and soil-respired CO2 (*13C = -26?). Relative amounts of labile C in second- and third-year nis one component, will increase the usefulness of stable isotope ratios in understanding N-cycling and, hopefully, help draw greater attention to the critical ecosystem roles played by fungi.