## 5 Conclusions  
The main take-home messages of this study exploring the potential of blending different datasets together for monitoring grassland ecosystems are:optical inputs to a simple empirical LUE model closely track seasonal carbon fluxes and provide a simple proxy to fill gaps in the eddy covariance datasets;
* the three NDVI methods give slightly different results depending on different band formulations, footprints and temporal sampling periods; however, low cost sensor (proxy NDVI) can be adopted for monitoring CO\({}_{2}\) fluxes;
* proper temporal aggregation improves model accuracy, and further analyses are needed to evaluate the quantitative impact of each aggregation method and period for different sites;
* due to hysteresis and possible stress in the late season, the hypothesis of a constant \(\varepsilon\) for our ecosystem seems violated over the entire season (May-October), but holds for half season periods;
* greening and senescence phases of the growing season are best captured using separate model fits and give the most accurate carbon flux estimates (model based on APAR\({}_{\text{green}}\); \(R^{2}\) = 0.69 for whole season, \(R^{2}\) = 0.79 for green-up phase and \(R^{2}\) = 0.77 for senescence phase);
* this approach is able to distinguish different levels of productivity in the two landscapes sampled, demonstrating the ability to distinguish different levels of carbon uptake.  
The following are available online at [[http://www.mdpi.com/2072-4292/8/3/260/s1](http://www.mdpi.com/2072-4292/8/3/260/s1)]([http://www.mdpi.com/2072-4292/8/3/260/s1](http://www.mdpi.com/2072-4292/8/3/260/s1)), Table S1: \(R^{2}\) and equations for fits between net CO\({}_{2}\) flux and different midday averaging period of proxy NDVI calculated both for the full season and for the first and second halves (green-up and senescence). The average intervals considered were 5-h, 3-h and 1-h around midday (approximately 13:30 local daylight savings time). In all cases, proxy NDVI was filtered with the method explained in the text.  
This study was financially supported by grants from the Rangeland Research University (University of Alberta), NSERC, and iCORE/AITF to [PERSON]. The collaboration between the Italian National Research Council (CNR) and University of Alberta was possible thanks to the COST Action ESO903: \"Spectral Sampling Tools for Vegetation Biophysical Parameters and Flux Measurements in Europe\" and to the MIUR-CNR Nextdata project. We wish to thank [PERSON] for field data collection and preliminary data processing, [PERSON] for assistance in MODIS NDVI products and provision of sensor bandpass data, [PERSON] for information on the vegetation of the sites, [PERSON] for set up and maintenance of eddy covariance, and [PERSON] and [PERSON] for providing the University of Alberta with the Mattheis Ranch to support long-term research.  
[PERSON] was the primary author and all authors contributed to the final paper [PERSON] conceived and designed the experiment. [PERSON], [PERSON] and [PERSON] collected field data. [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] conducted data analysis.  
The authors declare no conflict of interest.