Does the 13C of foliage-respired CO2 and biochemical pools reflect the 13C of recently assimilated carbon?

Abstract

Isotopic labelling experiments were conducted to assess relationships among 13C of recently assimilated carbon (δCA), foliage respiration (δCF), soluble carbohydrate (δC SC), leaf waxes (δCLW) and bulk organic matter (δCOM). Slash pine, sweetgum and maize were grown under 13C depleted CO2 to label biomass and then placed under ambient conditions to monitor the loss of label. In pine and sweetgum, δCF of labelled plants (∼-44 and -35‰, respectively) rapidly approached control values but remained depleted by ∼4-6‰ after 3-4 months. For these tree species, no or minimal label was lost from δCSC, δCLW and δCOM during the observation periods. δCF and δCSC of labelled maize plants rapidly changed and were indistinguishable from controls after 1 month, while δCLW and δCOM more slowly approached control values and remained depleted by 2-6‰. Changes in δCF in slash pine and sweetgum fit a two-pool exponential model, with the fast turnover metabolic pool (∼3-4 d half-life) constituting only 1-2% of the total. In maize, change in δCF fits a single pool model with a half-life of 6.4 d. The 13C of foliage respiration and biochemical pools reflect temporally integrated values of δC A, with change in isotopic composition dampened by the size of metabolic carbon reserves and turnover rates. © 2009 Blackwell Publishing Ltd.