In silico assessment of environmental factors affecting the spectral signature of C4 plants in the visible domain

Monocotyledonous (C-4) plants, such as maize and sugarcane, have a central role in the economy and ecology of our planet. In many regions, the main food sources are based on C-4 crops. These crops are also major suppliers of raw materials used in the production of biofuel. Due to their increasing global demand, it becomes essential not only to monitor and analyse the effects of abiotic stress factors, such as limited water and nutrient supplies, on their productivity, but also to determine their ecological impact (e. g. related to their irrigation needs). Computer simulations, or in silico experiments, are being routinely employed in remote-sensing investigations aimed at these goals. Besides these applications, in silico experiments paired with measured data can also contribute to expand the existing knowledge about the biophysical mechanisms responsible for the remarkable tolerance of C-4 plants to adverse environmental conditions. In this article, we evaluate the applicability of a computer model (ABM-U) to the assessment of biophysical responses of C-4 plants in the visible (photosynthetic) domain when subjected to abiotic stress factors. Initially, we verify the accuracy of model readings obtained in this spectral domain. This verification is performed through quantitative and qualitative comparisons of modelled results with measured data. We then proceed to investigate apparently conflicting reflectance profiles resulting from experiments involving maize specimens under moderate water stress, which is usually associated with unfavourable climate changes. The results of our simulations indicate that ABM-U can reliably predict spectral signature variations caused by abiotic stress factors affecting the photosynthetic apparatus of these plants, which, in turn, have a direct impact on their agricultural yield. Furthermore, our in silico experiments suggest that the decrease in the amount of light reflected by (in vivo) water-stressed specimens may result from changes in the internal arrangement of the main components of their photosynthetic apparatus, namely the chloroplasts. We close the article with a discussion of putative physiological processes responsible for such changes.