Publication Date:
2016-12-15
Description:
Improving the accuracy of estimates of forest carbon exchange is a central priority for understanding ecosystem response to increased atmospheric CO 2 levels and improving carbon cycle modeling. However, the spatially-continuous parameterization of photosynthetic capacity (Vcmax) at global scales and appropriate temporal intervals within terrestrial biosphere models (TBMs) remains unresolved. This research investigates the use of biochemical parameters for modelling leaf photosynthetic capacity within a deciduous forest. Particular attention is given to the impacts of seasonality on both leaf biophysical variables and physiologic processes, and their inter-dependent relationships. Four deciduous tree species were sampled across three growing seasons (2013-2015), approximately every 10 days for leaf chlorophyll content (Chl Leaf ) and canopy structure. Leaf nitrogen (N A rea ) was also measured during 2014. Leaf photosynthesis was measured during 2014-15 using a Li-6400 gas-exchange system, with A-Ci curves to model Vcmax. Results showed that seasonality and variations between species resulted in weak relationships between Vcmax normalised to 25°C (Vcmax 25 ) and N A rea (R 2 = 0.62, p〈0.001), whereas Chl Leaf demonstrated a much stronger correlation with Vcmax 25 (R 2 = 0.78, p〈0.001). The relationship between Chl Leaf and N A rea was also weak (R 2 = 0.47, p〈0.001), possibly due to the dynamic partitioning of nitrogen, between and within photosynthetic and non-photosynthetic fractions. The spatial and temporal variability of Vcmax 25 was mapped using Landsat TM/ETM satellite data across the forest site, using physical models to derive Chl Leaf . TBMs largely treat photosynthetic parameters as either fixed constants, or varying according to leaf nitrogen content. This research challenges assumptions that simple N A rea -Vcmax 25 relationships can reliably be used to constrain photosynthetic capacity in TBMs, even within the same plant functional type. It is suggested that Chl Leaf provides a more accurate, direct proxy for Vcmax 25 and is also more easily retrievable from satellite data. These results have important implications for carbon modelling within deciduous ecosystems. This article is protected by copyright. All rights reserved.
Print ISSN:
1354-1013
Electronic ISSN:
1365-2486
Topics:
Biology
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Energy, Environment Protection, Nuclear Power Engineering
,
Geography
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