GPP and maximum light use efficiency estimates using different approaches over a rotating biodiesel crop

• Published in: Agricultural and forest meteorology Vol. 214-215; pp. 444 - 455
• Main Authors: Sánchez, M.L., Pardo, N., Pérez, I.A., García, M.A.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15-12-2015
• Subjects: Biofuel crops; Crops; Estimates; GPP; LUE models; Mathematical models; MODIS; MODIS GPP calibration; Peas; Rapeseed; Rapeseed rotation crops; Rye; Triticum aestivum; Wheat; MODIS GPP calibration; Biofuel crops; Rapeseed rotation crops; LUE models; GPP
• ISSN: 0168-1923; 1873-2240
• DOI: 10.1016/j.agrformet.2015.09.012

•GPP annuals in a biodiesel rotating crop showed a great inter-annual variability.•A LUE model applied to rapeseed, wheat, peas and rye, provided satisfactory results.•Optimal light use efficiency of each crop type was determined.•GPP and light efficiency were influenced by climate conditions and crop features.•GPP 8-d MODIS were calibrated overall and for each crop type.
This paper presents: (a) results of gross primary production (GPP) 8-d estimated values using a light use efficiency model (LUE) in a non-irrigated rotating rapeseed crop in the upper Spanish plateau, and (b) inter-comparison results of observed GPP with those concurrently retrieved by MODIS. The rotation scheme over the four-year study comprised rapeseed, wheat, peas and rye. Rapeseed, peas and, in part, rye grew under well-watered conditions whereas wheat was dominated by drought.
Input data for the LUE model were the fraction of PAR absorbed (FPAR) 8-d products supplied by MODIS (FPARMODIS), in situ photosynthetic active radiation (PAR) measurements and a scalar f varying between 0 and 1, to take into account the reduction of the maximum PAR conversion efficiency (ɛ0LUE) under limiting environmental conditions. In this study, f values were assumed to be dependent on air temperature (T) and the evaporative fraction which was considered a proxy of water availability. ɛ0LUE, a key parameter in LUE models, which varied according to land use, was derived through the results of a linear regression fit between observed GPP and concurrent GAPAR estimates defined as the product of PAR, FPARMODIS and f. Overall, the LUE model provided satisfactory results, R2=86.3%, significantly improving GPP MODIS estimates (GPPMODIS), R2=71.8%. GPPMODIS uncertainties have primarily been attributed to differences in the f stress factor involved in its formulation (fMODIS) depending on vapour pressure deficit and T which did not fully describe the environmental stress conditions at the measuring site.
Overall, ɛ0LUE yielded 3.33±0.10gCMJ−1 although this varied depending on crop architecture, phenology and prevailing meteorological conditions. Crop-to-crop ɛ0LUE ranged from 2.74±0.17 to 3.95±0.19gCMJ−1 for peas and rye, respectively, yielding intermediate values for rapeseed and wheat, 2.92±0.18 and 2.86±0.23gCMJ−1, respectively. ɛ0MODIS, derived from the linear fit of GPP versus GPPMODIS estimates, yielded 2.13±0.10gCMJ−1 and crop-to-crop ranged from 1.28±0.17 to 2.41±0.12gCMJ−1 for wheat and rapeseed, respectively. The best linear fits corresponded to crops growing under well-watered conditions, rapeseed and peas, and the worst fits were for wheat, affected by drought. GPP annuals were 1680, 710, 730 and 1410gCm−2 for rapeseed, wheat, peas and rye, respectively.