Interweaving Monitoring Activities and Model Development towards Enhancing Knowledge of the Soil-Plant-Atmosphere Continuum

Abstract

The study of water pathways from the soil to the atmosphere through plants-the so-called soil-plant-atmosphere con nuum (SPAC)-has 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 ac vies and model development related to SPAC in clima c, ecological, and applica ons other than the tradi onal agrohydrological, and it is therefore mely to review the current status of this topic and outline future direc ons of research. The ini a ve for the special sec on of Vadose Zone Journal on SPAC emanated from several sessions we recently organized in interna onal conferences and mee ngs. With a view to the specifi c research ques ons covered in this special sec on, this ar cle introduces and reviews SPAC underlying issues and then provides a brief overview of the invited contribu ons. We have grouped together the 15 contribu ons under three main sec ons related to the local, fi eld, and landscape spaal scales of interests. Within these sec ons, the papers present their innova ve results using diff erent measuring techniques (from classic tensiometers and TDR sensors to more advanced and sophis cated equipment based on tomography and geophysics) and different modeling tools (from mechanis c models based on the Richards equa on to more parametrically parsimonious hydrologic balance models). They provide a snapshot of the current state of the art while emphasizing the signifi cant progress a ained in this fi eld of research. New technological developments and applica ons are also highlighted.Abbrevia ons: SPAC, soil-plant-atmosphere con nuum Soil is a key component of the earth's biosphere linking surface water and groundwater and the atmosphere. Most soil hydrological processes take place over vegetated land areas, and therefore the plant rooting system becomes the most active zone for transfer of water (and dissolved nutrients) between soil and atmosphere through the plants.Parallel to early attempts at quantitative and mechanistic description of water fl ow in soil (Buckingham, 1907;Gardner et al., 1922;Richards, 1931) and in the absence of methods for measurement of energy state of water in the soil-plant system, Veihmeyer and Hendrickson (1927) proposed a simple concept for estimating available water for plant growth based on soil water content values at fi eld capacity and permanent wilting (Romano and Santini, 2002). Th is simple conceptual model was originally developed for irrigation scheduling and water management, but soon was adopted by hydrologists for modeling of rainfall-runoff processes and other soil hydrological processes (Horton, 1933).Realistic fl ows of water in the soil and concurrent plant root water uptake are highly dynamic phenomena that are far more complex than simplifi ed by the fi eld capacity concept, involving cycles of soil wetting and drying. Th ese cycles are essentially driven by infi ltration and redistribution processes, and re...

Technical Note: Monitoring streamflow generation processes at Cape Fear

“…As discussed for Table 1, larger differences among the WRFs occur close to full saturation mainly due to the local and unpredictably different degrees of compaction and aggregation of the primary soil particles. Interestingly, the WRF pertaining to the soil core tested through the evaporation experiment shows a certain bimodal behavior, whose description through a bimodal relation leads to a much better prediction of K (as discussed in (Romano et al, 2012)), see the right panel In Figure 3, points obtained by processing measured data with a modified Wind's method match very well analytical findings obtained through the evaporation inverse method developed by (Romano and Santini, 2002). Importantly, HCFs of the soil cores collected at positions from P02 to P05 are simply predicted from WRFs parameters and from measured K sat values.…”

Critical Zone Research and Observatories: Current Status and Future Perspectives

“…The special section titled “Soil–Plant–Atmosphere Continuum” in Vadose Zone Journal in 2012 reported advances in the measurement and understanding of soil–water, soil–plant, and plant–atmosphere interfacial processes. A series of interdisciplinary studies were included in this special section that linked aboveground and belowground processes, including the new methods of quantifying and modeling soil–plant interactions from a single plant to the field scale (e.g., Zarebanadkouki et al, 2012; Assouline et al, 2012), the impact of canopy interception and root uptake on the variability of soil moisture in space and time (e.g., Moradi et al, 2012; Guswa, 2012), modeling water flux through the SPAC (e.g., Romano et al, 2012; Schröder et al, 2012), and the improved assessment of soil moisture and land–atmosphere interactions (e.g., Scanlon and Kustas, 2012). Although the synthesis of knowledge from various compartments of the SPAC into a holistic view remains challenging, these studies brought a new perspective that the whole CZ could function as a complex system.…”

“Cape Fear”—A Hybrid Hillslope Plot for Monitoring Hydrological Processes

“…As discussed for Table 1, larger differences among the WRFs occurred close to full saturation mainly due to the local and unpredictably different degrees of compaction and aggregation of the primary soil particles. Interestingly, the WRF of the soil core tested through the evaporation experiment showed a certain bimodal behavior, whose description through a bimodal relation leads to a much better prediction of K (as discussed in [52]), see the right panel of Figure 3.…”