首页|Thirsty trees: even with continuous river flow, riparian cottonwoods are constrained by water availability
Thirsty trees: even with continuous river flow, riparian cottonwoods are constrained by water availability
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NSTL
Springer Nature
Key message Despite the abundant alluvial groundwater below the floodplain, riparian cottonwoods are limited by water availability during warm and dry periods, as revealed with substantially increased sap flow following flood irrigation. In dry ecoregions trees are generally restricted to floodplains along perennial streams, where river water recharges the alluvial groundwater, supplementing the sparse local precipitation. Precipitation and river flow often decline through the warm and dry summer and we hypothesized that water availability would become limiting. To test this, we measured sap flow in narrowleaf cottonwoods (Populus angustifolia) along the Oldman River in the semi-arid prairie region of western Canada. After slight rain and river recession through July and August, we provided a flood irrigation treatment to four of eight study trees, which doubled the shallow soil moisture (theta(g)). There were slight increases in dawn (psi(d)) and mid-day (psi(md)) leaf water potentials although only temporary differences between the irrigated and non-irrigated trees in psi(d) (- 0.4 vs. - 0.6 MPa), psi(md) (- 1.5 vs. - 1.7 MPa) or their difference, increment psi. The daily sap flux density (F-d) was increased by 26% over a 12-day interval after irrigation, revealing increased water use and an upward shift in the association between canopy stomatal conductance (G(S)) vs. vapour pressure deficit (D). In contrast, F-d in non-irrigated trees declined 15% with the shortening days and aging leaves. The sap flow response contrasts with prior studies, probably due to differences in irrigation volume and timing. Thus, even with abundant groundwater from river infiltration, cottonwood transpiration was limited by water availability in the dry interval of late summer. For the underlying mechanism, we introduce the River Riparian Tree Atmosphere Continuum (RRTAC), which coordinates the system hydrology and water relations.
FloodplainsGroundwaterPopulusRiver riparian tree atmosphere continuumSap flowWater relationsPOPULUS-FREMONTIIVAPOR-PRESSUREGAS-EXCHANGEOLDMAN RIVERSAP FLOWRESPONSESIRRIGATIONTRANSPIRATIONSOUTHERNFEMALE
Phelan, Colleen A.、Pearce, David W.、Rood, Stewart B.
NSTL
Springer Nature
