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Recently evolved satellite-based sun-induced fluorescence (SIF) spectroscopy is considered as a direct measure of photosynthetic activity of vegetation. We have used monthly averages of satellite-based SIF retrievals for three agricultural year cycles, i.e. May to April for each of the three years, viz. 2007-08, 2008-09 and 2009-10 to assess comparative performance of SIF and normalized difference vegetation index (NDVI) for predicting net primary productivity (NPP) over the Indo-Gangetic Plains, India. Results show that SIF values for C4 crop-dominated districts were higher than C3 crop-dominated districts during summer and low during winter for all three years. SIF explained more or less above 70% of variance in NPP. The variance explained by integrated NDVI ranged from 60% to 67%. Thus the present study has shown the potential of SIF data for improved modelling of agricultural productivity at a regional scale. [ABSTRACT FROM AUTHOR]

Studies on CO2 and water vapour exchange in natural and man-made vegetation are necessary for quantifying their role in landscape-level carbon budget. The present study investigated variations in carbon and water vapour fluxes and monthly net ecosystem exchange (NEE) over a 9-year-old mixed forest plantation (Holoptelea integrifolia, Dalbergia sissoo, Acacia catechu and Albizia procera) in Terai Central Forest Division of Nainital district, Uttarakhand using January to September 2013 eddy covariance data. During leafless period (i.e. January), the plantation acted as a net carbon source (i.e. positive NEE) with daily mean release of 0.35 g Cm-2 day-1, while from leaf onset to growing period (i.e. April to September), it acted as a sink (i.e. negative NEE) due to carbon uptake by an increasing number of leaves. The monthly mean daily NEE was noticed to be increasingly more negative in each subsequent month until September. The diurnal trend in NEE closely followed the variations in the intensity of photosynthetically active radiation. The diurnal NEE in all months was related to vapour pressure deficit with time-lag. Maximum daytime uptake (-29.5 μmol m-2 s-1) and night-time release of CO2 (8.2 μmol m-2 s-1) was observed in July. Monthly mean of daily NEE over plantation continuously increased from February and was highest (-5.74 g Cm-2 day-1) in September. Rectangular hyperbolic function provided reasonably good fit between NEE and PAR. Ecosystem parameters (α and Pmax) of the light response curve also followed the canopy development trend. [ABSTRACT FROM AUTHOR]