Seasonal Dynamics of SPAC (Soil-Plant-Atmosphere Continuum)

摘要

Seasonal changes in the resistances to water movement along the soil-plant-atmosphere continuum (SPAC) were studied for spring wheat in the southern Australian wheatbelt. A mechanistically-based model, PROSPER, was expanded to include functional relationships between the SPAC resistances, the environment, and crop morphology. Resistances included: surface and aerodynamic in the vapor phase and stem, radial and axial root, soil/root, soil bulk and surface resistances in the liquid phase. Initially the model was tuned to fit measured monthly evapotranspiration (E/sub t/) using the first of two years' data (1971) from the well-documented Rutherglen experiment. Based on the 1971 data the model was tested against 1972 data, a drier year. The model was then used to study the effect of modifying crop morphological development on E/sub t/ by introduction of a uniculm habit, which fixes shoot density throughout the season. The effect of this on SPAC resistances arises from the delay in development of leaf area index (LAI), larger stems, and an increase in number of seminal roots. Estimates of E/sub t/ for October 1972 agreed poorly with measured values and this was attributed to the altered root/shoot ratios due to the drier conditions in 1972. Estimates of E/sub t/ for the simulated uniculm crop showed that E/sub t/ was lower during winter because of higher surface and stem resistances, but rose in spring due to better water availability resulting from greater storage and lower root resistance. The study emphasizes the strong biological control of the physical process of evapotranspiration. (ERA citation 08:047417)