Contrasting Hydraulic Strategies during Dry Soil Conditions in Quercus rubra and Acer rubrum in a Sandy Site in Michigan

Julia Thomsen,Heidi Renninger,Ashley Matheny,Gil Bohrer,Valeriy Ivanov,Karina Schäfer,Lingli He

doi:10.3390/f4041106

Julia Thomsen, Heidi Renninger + Show 5 more

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https://doi.org/10.3390/f4041106

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Abstract

Correlation analyses were carried out for the dynamics of leaf water potential in two broad-leaf deciduous tree species in a sandy site under a range of air vapor pressure deficits and a relatively dry range of soil conditions. During nights when the soil is dry, the diffuse-porous, isohydric and shallow-rooted Acer rubrum does not recharge its xylem and leaf water storage to the same capacity that is observed during nights when the soil is moist. The ring-porous, deep-rooted Quercus rubra displays a more anisohydric behavior and appears to be capable of recharging to capacity at night-time even when soil moisture at the top 1 m is near wilting point, probably by accessing deeper soil layers than A. rubrum. Compared to A. rubrum, Q. rubra displays only a minimal level of down-regulation of stomatal conductance, which leads to a reduction of leaf water potential during times when vapor pressure deficit is high and soil moisture is limiting. We determine that the two species, despite typically being categorized by ecosystem models under the same plant functional type—mid-successional, temperate broadleaf—display different hydraulic strategies. These differences may lead to large differences between the species in water relations, transpiration and productivity under different precipitation and humidity regimes.

Highlights

In forest ecosystems, evaporative demands are projected to increase almost everywhere as a result of increasing global temperatures [1]
The overall direct effects of soil moisture or vapor pressure deficit (VPD) on minimum leaf water potential were not significant. This was not because soil moisture or VPD had no effect, but, as indicated by the significance of the interaction terms this was driven by the fact that there were significantly different response to soil moisture and VPD between the two species (Table 1, effects of Species × SM and Species × VPD)
By correlating pre-dawn water potentials with the soil moisture in each layer separately, we found that pre-dawn leaf water potential in A. rubrum were correlated with soil water potential in each depth up to 60 cm

Summary

Introduction

In forest ecosystems, evaporative demands are projected to increase almost everywhere as a result of increasing global temperatures [1]. Water use strategies differ between plants, and it is necessary to understand species-specific regulation of transpiration to determine the relative contribution of species to the ecosystem water budget This is especially true in mixed forest stands. Plants must maintain water potentials above a minimum threshold [5,6,7] This can be achieved through a combination of root uptake of soil water and stomatal regulation of transpiration water losses [3]. One mechanism to mitigate transpiration losses is through partial or complete stomatal closure during midday periods of high evaporative demand [8,9,10] This can prevent a large decrease in leaf water potential (ψL) and a loss of hydraulic conductance within the xylem [11]

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