Modeling whole-tree carbon assimilation rate using observed transpiration rates and needle sugar carbon isotope ratios

Authors

Jia Hu, University of ColoradoFollow
David J. P. Moore, King’s College London
Diego Andrés Riveros-Iregui, University of Nebraska - LincolnFollow
Sean P. Burns, National Center for Atmospheric ResearchFollow
Russell K. Monson, University of Colorado,

Document Type

Article

Date of this Version

2010

Comments

Published in New Phytologist (2010) 185: 1000–1015 www.newphytologist.org

Abstract

• Understanding controls over plant–atmosphere CO₂ exchange is important for quantifying carbon budgets across a range of spatial and temporal scales. In this study, we used a simple approach to estimate whole-tree CO₂ assimilation rate (A_Tree) in a subalpine forest ecosystem.
• We analysed the carbon isotope ratio (δ¹³C) of extracted needle sugars and combined it with the daytime leaf-to-air vapor pressure deficit to estimate tree water-use efficiency (WUE). The estimated WUE was then combined with observations of tree transpiration rate (E) using sap flow techniques to estimate A_Tree. Estimates of A_Tree for the three dominant tree species in the forest were combined with species distribution and tree size to estimate and gross primary productivity (GPP) using an ecosystem process model.
• A sensitivity analysis showed that estimates of ATree were more sensitive to dynamics in E than δ¹³C. At the ecosystem scale, the abundance of lodgepole pine trees influenced seasonal dynamics in GPP considerably more than Engelmann spruce and subalpine fir because of its greater sensitivity of E to seasonal climate variation.
• The results provide the framework for a nondestructive method for estimating whole-tree carbon assimilation rate and ecosystem GPP over daily-to weekly time scales.