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Title: The phenology of leaf quality and its within-canopy variation is essential for accurate modeling of photosynthesis in tropical evergreen forests

Leaf quantity (i.e., canopy leaf area index, LAI), quality (i.e., per-area photosynthetic capacity), and longevity all influence the photosynthetic seasonality of tropical evergreen forests. However, these components of tropical leaf phenology are poorly represented in most terrestrial biosphere models (TBMs). Here in this paper, we explored alternative options for the representation of leaf phenology effects in TBMs that employ the Farquahar, von Caemmerer & Berry (FvCB) representation of CO 2 assimilation. We developed a two-fraction leaf (sun and shade), two-layer canopy (upper and lower) photosynthesis model to evaluate different modeling approaches and assessed three components of phenological variations (i.e., leaf quantity, quality, and within-canopy variation in leaf longevity). Our model was driven by the prescribed seasonality of leaf quantity and quality derived from ground-based measurements within an Amazonian evergreen forest. Modeled photosynthetic seasonality was not sensitive to leaf quantity, but was highly sensitive to leaf quality and its vertical distribution within the canopy, with markedly more sensitivity to upper canopy leaf quality. This is because light absorption in tropical canopies is near maximal for the entire year, implying that seasonal changes in LAI have little impact on total canopy light absorption; and because leaf quality has a greater effect onmore » photosynthesis of sunlit leaves than light limited, shade leaves and sunlit foliage are more abundant in the upper canopy. Our two-fraction leaf, two-layer canopy model, which accounted for all three phenological components, was able to simulate photosynthetic seasonality, explaining ~90% of the average seasonal variation in eddy covariance-derived CO 2 assimilation. This work identifies a parsimonious approach for representing tropical evergreen forest photosynthetic seasonality in TBMs that utilize the FvCB model of CO 2 assimilation and highlights the importance of incorporating more realistic phenological mechanisms in models that seek to improve the projection of future carbon dynamics in tropical evergreen forests.« less
Authors:
ORCiD logo [1] ;  [1] ;  [2] ;  [3] ;  [4] ;  [1] ;  [3] ; ORCiD logo [1]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States). Dept. of Environmental & Climate Sciences
  2. Princeton Univ., NJ (United States). Dept. of Geosciences
  3. Univ. of Arizona, Tucson, AZ (United States). Dept. of Ecology and Evolutionary Biology
  4. Carnegie Inst. of Science, Stanford, CA (United States). Dept. of Global Ecology; Pacific Northwest National Lab. (PNNL), College Park, MD (United States). Joint Global Change Research Inst.
Publication Date:
Report Number(s):
BNL-114156-2017-JA
Journal ID: ISSN 1354-1013; R&D Project: 80888; YN1901000
Grant/Contract Number:
SC0012704
Type:
Accepted Manuscript
Journal Name:
Global Change Biology
Additional Journal Information:
Journal Volume: 23; Journal Issue: 11; Journal ID: ISSN 1354-1013
Publisher:
Wiley
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; big leaf; gross primary productivity; leaf age; leaf area index; light use efficiency; multilayer; photosynthetic capacity; sun/shade
OSTI Identifier:
1376177