Annual variation in delta(13)C values of maize and wheat: Effect on estimates of decadal scale soil carbon turnover

作者：Christensen Bent T; Olesen Jorgen E; Hansen Elly M; Thomsen Ingrid K^*

来源：Soil Biology and Biochemistry, 2011, 43(9): 1961-1967.

DOI：10.1016/j.soilbio.2011.06.008

• delta(13)C variability
• C3-/C4-plants
• Soil C turnover
• Maize
• Wheat
• Climate

On sites where C4-plants have replaced C3-plants, changes in soil delta(13)C allow the turnover of C3- and C4-derived C to be separated. Studies of decadal scale turnover of soil C following conversion to C4-plants generally lack delta(13)C values for previous C4-residue inputs and assume that estimates of C4-derived soil C to be based on a fixed delta(13)C value. Further assumptions are that changes in the initial (time-zero) soil delta(13)C values are insignificant following conversion to C4-plants. We tested these assumptions by measuring: 1) the delta(13)C of annual samples of silage maize biomass (C4-plant) and winter wheat grains (C3-plant) grown during 1988 to 2006, and 2) the delta(13)C of soil kept under bare fallow during 1956 to 1983. The delta(13)C of plants was related to climate variables, and the impact of maize delta(13)C was based on estimates of maize-derived soil C using different approaches to establish the delta(13)C in maize inputs. The delta(13)C of both maize and wheat decreased with time, but the rate of change and annual variations were considerably larger for wheat than for maize. Maize as well as wheat delta(13)C was best related to year (probably reflecting a decrease in atmospheric delta(13)C) and the water balance during the active growth period. Using the smallest (-12.44 parts per thousand) and the largest (-11.26%) delta(13)C measured during 1988 and 2006, estimates of maize-derived C in soil after 18 years ranged from 13.2% to 14.2% of the soil total C. Despite a loss of 31% of the soil C pool under bare fallow, the increase in soil delta(13)C was significant only at P < 0.10. We conclude that annual variations in maize delta(13)C values and changes in the delta(13)C of the soil C fraction derived from the preconversion C3-vegetation have only little impact on estimates of maize-derived soil C that cover a few decades. For estimates covering several decades to centuries, the subtle but consistent changes in plant and soil delta(13)C need to be accounted for. The variability in delta(13)C in wheat grains suggest that the use of any fixed delta(13)C value for C3-residues in estimates of C turnover in soils on which C4-plants have been replaced by C3-plants can be associated with considerable uncertainty.

• 出版日期2011-9