Transpiration inQuercus subertrees under shallow water table conditions: the role of soil and groundwater

Abstract

Abstract:Water is one of the major environmental factors limiting plant growth and survival in the Mediterranean region. Quercus suber L. woodlands occupy vast areas in the Iberian Peninsula, frequently under shallow water table conditions. The relative magnitude of soil and groundwater uptake to supply transpiration is not easy to evaluate under these circumstances. We recently developed a conceptual framework for the functioning of the root system in Q. suber that simulates well tree transpiration, based on two types of root behaviour: shallow connected and deep connected. Although this significantly improved knowledge on the functional traits of Mediterranean Q. suber, the approach has the limitation of requiring root sap flow data, which are seldom available. In this work, we present alternative methodologies to assess if trees are connected to groundwater and to estimate the soil and groundwater contributions to tree transpiration. We provide evidence on the tree unrestricted access to groundwater solely based on meteorological, stem sap flow and leaf water potential data. Using a soil mass balance approach, we estimated the yearly soil and groundwater contributions to tree transpiration: 69.7% and 30.3%, respectively. Groundwater uptake became dominant in the dry summer: 73.2% of tree transpiration. Results reproduce extremely well those derived from root modelling. Because of its simplicity both in formulation and data requirements, our approach is potentially liable to be adapted to other groundwaterdependent Mediterranean oak sites, where interactions between land use and water resources may be relevant.

Responses of shelterbelt stand transpiration to drought and groundwater variations in an arid inland river basin of Northwest China

“…Gou and Miller (2014) found that the water source for transpiration in a blue oak stand (Q. douglasii) in a California savanna turned from soil water in the wet season to groundwater in the dry season. Similar results had been found in a Scots pine stand (P. sylvestris) in a sandy soil with shallow water table that the contribution of groundwater to transpiration from May to November reached 61%, while the groundwater contributed to 98.5% during the drought period in June (Vincke and Thiry, 2008), and in a cork oak woodland (Quercus suber) in the Mediterranean region where the yearly groundwater contribution to tree transpiration occupied by 30.3%, while groundwater uptake accounted for 72.3% in dry summer (Pinto et al, 2014). The critical role of groundwater is especially significant for shelterbelt under dry conditions.…”

Fine root distributions of shelterbelt trees and their water sources in an oasis of arid northwestern China

“…Their results indicated that the groundwater uptake accounted for 19% of tree transpiration during the growing season of 2013 in the same area as our study. Pinto et al (2013) estimated the yearly groundwater contribution to the transpiration of Quercus suber to be 30.3%, whereas groundwater uptake became dominant in the dry summer to account for 73.2% of the transpiration. The contribution of groundwater to tree transpiration varied with rainfall conditions.…”

Water and forests in the Mediterranean hot climate zone: a review based on a hydraulic interpretation of tree functioning

“…For this particular purpose, both spatial surveys and modelling are important. Several models are available to estimate the dynamics of groundwater use by tree transpiration (Gou & Miller, 2014;Orellana et al, 2014;Pinto et al, 2014). The large-scale mapping of zones where roots might have or not access to groundwater (groundwater dependent ecosystems) has been most frequently done indirectly, through remote sensing techniques coupled with geographic information systems (Howard & Merrifield, 2010;Gou et al, 2015;Yin et al, 2015).…”