The significance of phloem transport for the speed with which canopy photosynthesis and belowground respiration are linked
Article first published online: 13 OCT 2009
© The Authors (2009). Journal compilation © New Phytologist (2009)
Volume 185, Issue 1, pages 189–203, January 2010
How to Cite
Mencuccini, M. and Hölttä, T. (2010), The significance of phloem transport for the speed with which canopy photosynthesis and belowground respiration are linked. New Phytologist, 185: 189–203. doi: 10.1111/j.1469-8137.2009.03050.x
- Issue published online: 1 DEC 2009
- Article first published online: 13 OCT 2009
- Received: 18 May 2009, Accepted: 24 August 2009
- canopy photosynthesis;
- carbon isotope discrimination;
- phloem transport;
- phloem water relations;
- soil respiration;
- speed of link
- •Ecosystem respiration is known to vary following changes in canopy photosynthesis. However, the timing of this coupling is not well understood.
- •Here, we summarize the literature on soil and ecosystem respiration where the speed of transfer of photosynthetic sugars from the plant canopy via the phloem to the roots was determined. Estimates of the transfer speed can be grouped according to whether the study employed isotopic or canopy/soil flux-based techniques. These two groups should provide different estimates of transfer times because transport of sucrose molecules, and pressure-concentration waves, in phloem differ. A steady-state and a dynamic photosynthesis/phloem-transport/soil gas diffusion model were employed to interpret our results.
- •Starch storage and partly soil gas diffusion affected transfer times, but phloem path-length strongly controlled molecule transfer times. Successful modelling required substantially different phloem properties (higher specific conductivity and turgor pressure difference) in tall compared with small plants, which is significant for our understanding of tall trees’ physiology.
- •Finally, we compared isotopic and flux-based approaches for the determination of the link between canopy photosynthesis and ecosystem respiration. We conclude that isotopic approaches are not well suited to document whether changes in photosynthesis of tall trees can rapidly affect soil respiration.