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Title: Aboveground sink strength in forests controls the allocation of carbon below ground and its [CO₂]-induced enhancement

Author: Palmroth, Sari; Oren, Ram; McCarthy, Heather R.; Johnsen, Kurt H.; Finzi, Adrien C.; Butnor, John R.; Ryan, Michael G.; Schlesinger, William H.

Date: 2006

Source: Proceedings of the National Academy of Sciences. 103(51): 19362-19367

Description: The partitioning among carbon (C) pools of the extra C captured under elevated atmospheric CO₂ concentration ([CO₂]) determines the enhancement in C sequestration, yet no clear partitioning rules exist. Here, we used first principles and published data from four free-air CO₂ enrichment (FACE) experiments on forest tree species to conceptualize the total allocation of to below ground (TBCA) under current [CO₂] and to predict the likely effect of elevated [CO₂]. We show that at a FACE site where leaf area index (L) of Pinus taeda L. was altered through nitrogen fertilization, ice-storm damage, and droughts, changes in L, reflecting the aboveground sink for net primary productivity, were accompanied by opposite changes in TBCA. A similar pattern emerged when data were combined from the four FACE experiments, using leaf area duration (L_D) to account for differences in growing-season length. Moreover, elevated [CO₂]-induced enhancement of TBCA in the combined data decreased from [approximately] 50% 700 g(Cm^-2y^-1) at the lowest L_D to [approximately] 30%(200 gCm^-2y^-1) at the highest L_D. The consistency of the trend in TBCA with L and its response to [CO₂] across the sites provides a norm for predictions of ecosystem C cycling, and is particularly useful for models that use L to estimate components of the terrestrial C balance.

Key Words: forests, carbon, CO₂, free-air CO₂ enrichment (FACE), TBCA

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Palmroth, Sari; Oren, Ram; McCarthy, Heather R.; Johnsen, Kurt H.; Finzi, Adrien C.; Butnor, John R.; Ryan, Michael G.; Schlesinger, William H.  2006.  Aboveground sink strength in forests controls the allocation of carbon below ground and its [CO₂]-induced enhancement  Proceedings of the National Academy of Sciences. 103(51): 19362-19367.