Articles
Diurnal patterns in sap flow through maize stems suggest a role for capacitance tissues in maintaining the transpiration stream
Article number
1419_8
Pages
59 – 66
Language
English
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.
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.
Publication
Authors
L.H. Comas, J.A. Wenz, D.M. Barnard
Keywords
heat ratio method sap flow, stem water storage, plant capacitance tissues, hydraulic resistance, sap flux, plant hydraulics
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