Leaf chlorophyll constraint on model simulated gross primaryproductivity in agricultural systems

tLeaf chlorophyll content (Chll) may serve as an observational proxy for the maximum rate of carboxylation(Vmax), which describes leaf photosynthetic capacity and represents the single most important controlon modeled leaf photosynthesis within most Terrestrial Biosphere Models (TBMs). The parameterizationof Vmaxis associated with great uncertainty as it can vary significantly between plants and in responseto changes in leaf nitrogen (N) availability, plant phenology and environmental conditions. outlined asemi-mechanistic relationship between V25max(Vmaxnormalized to 25◦C) and Chllbased on inter-linkagesbetween V25max, Rubisco enzyme kinetics, N and Chll. Here, these relationships are parameterized for awider range of important agricultural crops and embedded within the leaf photosynthesis-conductancescheme of the Community Land Model (CLM), bypassing the questionable use of temporally invariant andbroadly defined plant functional type (PFT) specific V25maxvalues. In this study, the new Chllconstrainedversion of CLM is refined with an updated parameterization scheme for specific application to soybeanand maize.The benefit of using in-situ measured and satellite retrieved Chllfor constraining model simulationsof Gross Primary Productivity (GPP) is evaluated over fields in central Nebraska, U.S.A between 2001 and2005. Landsat-based Chlltime-series records derived from the Regularized Canopy Reflectance model(REGFLEC) are used as forcing to the CLM. Validation of simulated GPP against 15 site-years of fluxtower observations demonstrate the utility of Chllas a model constraint, with the coefficient of effi-ciency increasing from 0.91 to 0.94 and from 0.87 to 0.91 for maize and soybean, respectively. Modelperformances particularly improve during the late reproductive and senescence stage, where the largesttemporal variations in Chll(averaging 35–55 g cm−2for maize and 20–35 g cm−2for soybean) areobserved. While prolonged periods of vegetation stress did not occur over the studied fields, given theusefulness of Chllas an indicator of plant health, enhanced GPP predictabilities should be expected infields exposed to longer periods of moisture and nutrient stress. While the results support the use of Chllas an observational proxy for V25max, future work needs to be directed towards improving the Chllretrievalaccuracy from space observations and developing consistent and physically realistic modeling schemesthat can be parameterized with acceptable accuracy over spatial and temporal domains

HOUBORG Rasmus;  MCCABE Matthew F;  CESCATTI Alessandro;  GITELSON Anatoly; 

2018-01-16

ELSEVIER SCIENCE BV

JRC99981

0303-2434,   

http://www.sciencedirect.com/science/article/pii/S0303243415000707?via%3Dihub,    https://publications.jrc.ec.europa.eu/repository/handle/JRC99981,   

10.1016/j.jag.2015.03.016,