Interweaving monitoring activities and model development towards enhancing knowledge of soil-plant-atmosphere continuum.

The study of water pathways from the soil to the atmosphere through plants (the so-called soil-plant-atmosphere continuum, SPAC) have always been central to agronomy, hydrology, plant physiology and other disciplines using a wide range of approaches and tools. In recent years, we have been witnessing a rapid expansion of interweaving monitoring activities and model development related to SPAC in climatic, ecological and applications other than the traditional agro-hydrological and it is therefore timely to review the current status of this topic and outline future directions of research. The initiative for the special section of Vadose Zone Journal on SPAC emanated from several sessions we recently organized in international conferences and meetings. With a view to the specific research questions covered in this special section, this article introduces and reviews SPAC underlying issues and then provides a brief overview of the invited contributions. We have grouped together the 15 contributions under three main sections related to the local, field, and landscape spatial scales of interests. Within these sections, the papers present their innovative results using different measuring techniques (from classic tensiometers and TDR sensors to more advanced and sophisticated equipment based on tomography and geophysics) and different modeling tools (from mechanistic models based on the Richards equation to more parametrically parsimonious hydrologic balance models). They provide a snapshot of the current state of the art while emphasizing the significant progress attained in this field of research. New technological developments and applications are also highlighted.