Applying ‘drought’ to potted plants by maintaining suboptimal soil moisture improves plant water relations
We investigated the hypothesis that continuous water application allows favorable and steady water content and hydraulic conductivity in the root zone, thus enabling higher water potential in the soil–root interface (ψroot). Elevated ψroot increases transpiration (T) and prevents yield loss due to stomatal closure or to low root osmotic potential that develops in response to low ψroot. We assume further, that the advantage of continuous water application is more pronounced for young plants, where water uptake per root length and competition on resources in the root system is higher. We investigated this hypothesis by examining the average water content of the root zone and T as a function of time for sunflowers grown under varied irrigation frequencies experimentally and in a modeled simulations, and by solving for the necessary effective root length and ψroot for each case. High frequency water application was shown to positively affect root water uptake efficiency and yield, especially when plants were young. Irrigation frequency affected growth through the water content in the bulk soil (θsoil) which in turn affects ψroot. A low θsoil and coupled low hydraulic conductivity decreased T and yield. Moreover, a decreased θsoil caused low ψroot, inefficient allocation of energy and carbohydrates and eventual yield loss. It was likely that these phenomena were more pronounced with young plants due to higher water uptake per root length.