Diurnal patterns in sap flow through maize stems suggest a role for capacitance tissues in maintaining the transpiration stream

Authors: Comas, Louise; Wenz, Joshua; Barnard, David

Submitted to: Acta Horticulture Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/3/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Monitoring water movement through plants has suggested that there may be pools of water stored in shoots that allow plants to remain active at times when their roots are limited in taking up water. We examined three data sets for evidence of these stored water pools. We found that there were times when water was not entering plants from their roots, but they remained active, and times when water was entering from the roots, but plants were not actively using water. Plants also used more stored water when they had less water available from irrigation. These stored water supplies within plant shoots are important for plants to maintain functioning on days when the water supply is limited. Being able to identify genotypes with greater water storage capacity may allow us to improve crop productivity under short-term drought.

Technical Abstract: Lags in hydraulic time constants have been routinely observed across multiple species and sap flow sensor types. These lags have been construed as instances when water uptake through root systems was insufficient and stored water from plant capacitance tissues downstream of sap flow sensors was required to supplement transpiration. Rather than showing a diurnal lag with a similar offset in hydraulic time constants throughout the cycle, we routinely find lags in maize sap flow increasing through the morning when compared to continuous gravimetric transpiration measurements in young plants in pots in the greenhouse. In the field, we similarly found increasing lags between sap flow and solar radiation through the morning. Sap flow either continued or had secondary peaks after the sun went down, with a few exceptions. Days with heavy morning irrigation or low solar radiation lacked the increase of morning lags and presence of secondary nighttime peaks in sap flow. Treatments with deficit irrigation had similar daytime lags but reduced sap flow and had proportionally greater secondary nighttime compared to daytime peaks. These nuanced patterns are consistent with an interpretation of capacitance tissues compensating for limitations in root system hydraulic conductivity during periods of high plant water use and suggest that capacitance tissues are crucial for maintaining daily plant transpiration rates. Being able to identify genotypes with greater hydraulic capacitance tissues and breed for this trait could provide valuable new avenues for improving crop productivity.