Date Published:

2019 Aug 30

Abstract:

Carbon dynamics in canopy and roots influence whole tree carbon fluxes, but little is known about canopy regulation of tree-root activity. Here, we assess the patterns and dynamics of canopy-root carbon coupling in tropical trees. We used large aeroponics to directly study the root systems of Ceiba pentandra and Khaya anthotheca saplings at different light intensities. In Ceiba, root respiration (R ) co-varied with photosynthesis (A ) in large saplings (3-to-7-m canopy-root axis) at high-light, but showed no consistent pattern at low-light. At medium-light and in small saplings (c. 1-m axis), R tended to decrease transiently towards midday. Proximal roots had higher R and non-structural carbohydrate concentrations than distal roots, but canopy-root coupling was unaffected by root location. In medium-sized Khaya, no R pattern was observed, and in both species, R was unrelated to temperature. The early-afternoon increase in R suggests canopy-root coupling is based on mass flow of newly fixed carbon in the phloem, while the early-morning rise in R with A indicates an additional coupling signal that travels faster than the phloem sap. In large saplings and potentially also in higher trees, light and possibly additional environmental factors control the diurnal patterns of canopy-root coupling, irrespective of root location. This article is protected by copyright. All rights reserved.