soilplantatmosphere

The soil–plant–atmosphere continuum (SPAC) is the integrated system that links soil water and nutrients, plant water uptake and transpiration, and atmospheric demand at the land surface. It emphasizes hydraulic and mass transfer across three compartments—soil, vegetation, and air—and the feedbacks that govern water, energy, and carbon fluxes in terrestrial ecosystems.

In the soil, water moves under gradients of matric potential and is stored in pores; roots access water and nutrients and transmit them to the shoot via the plant’s vascular system. The canopy loses water by transpiration, driven by atmospheric demand and regulated by stomatal conductance. Leaves exchange CO2 and moisture with the atmosphere, shaped by radiation, humidity, wind, and temperature.

The continuum is critical for understanding plant and ecosystem responses to drought, irrigation, and climate variability, as soil moisture status, rooting depth, and stomatal behavior determine transpiration and carbon uptake.

Measurement and modeling approaches include soil moisture sensing, sap flow or trunk measurements to quantify plant water transport, eddy covariance for evapotranspiration and CO2 fluxes, and process-based models of soil and plant hydraulics and canopy gas exchange that link hydrology with plant physiology and atmospheric physics.