Root functioning, tree water use and hydraulic redistribution in Quercus suber trees: A modeling approach based on root sap flow

Abstract

Mediterranean evergreen oaks have to survive a long summer drought. Roots may play a relevant role under these conditions. We studied their structure and function in a mature Quercus suber L. tree in central Portugal. The root system was mapped till the lowest water table level (4.5 m depth). Xylem anatomy was analyzed in a vertical profile belowground. Sap flow was continuously monitored for 1.5 yrs in the stem and roots of this intensively studied tree (heat field deformation method) and in the stem of four trees (Granier method), in relation to environmental variables and predawn leaf water potential. The sources of water uptake were assessed by stable isotope analyses in summer. Results showed a dimorphic root system with a network of superficial roots linked to sinker roots, and a taproot diverting into tangles of deep fine roots submerged for long periods, with parenchyma aerenchyma. Transpiration was not restricted in summer due to root access to groundwater. The isotopic d 18 O signature of twig xylem water was similar to that of groundwater in the dry season. Two functional types of superficial roots were identified: shallow connected and deep connected roots. A modeling approach was built considering that each superficial root was linked to a sinker, with part of the root deep connected (between the stem and the sinker) and part shallow connected (between the sinker and topsoil). This conceptual framework simulated tree stem sap flow from root sap flow with a high efficiency (R 2 = 0.85) in four plot trees. On an annual basis, soil water and groundwater contributions were 69.5% and 30.5% of stem flow, respectively. Annual hydraulic lift and hydraulic descent were 0.9% and 37.0% of stem flow, respectively. The trees maximize the exploitation of the environmental resources by using the topsoil water during most of the year, and groundwater together with hydraulic lift (nutrient supply) in the dry summer. This study shows that a dimorphic root system, with roots reaching groundwater, is an efficient strategy of Q. suber trees to cope with seasonal drought. Knowledge of the functional behavior of Q. suber trees under shallow water table conditions may contribute to the definition of better adapted management practices and to anticipate their responses to climate change.

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

“…This strategy is particularly important for evergreen trees that must survive a dry season. Several studies confirmed that Mediterranean oaks (Quercus suber and Quercus ilex in the Iberian Peninsula and Quercus douglasii in California) use this deep rooting strategy to tap water from groundwater reservoirs, whenever the superficial soil is dry and the water table is within the reach of the deep roots (David et al, 2004(David et al, , 2007(David et al, , 2013Lubczynski & Gurwin, 2005;Miller et al, 2010;Barbeta et al, 2015). This drought avoidance trait has also been observed in Australia (Zencich et al, 2002;O'Grady et al, 2006), South Africa (Le Maitre et al, 1999), China (Yin et al, 2015) and even in temperate forests during occasional droughts (Dolman, 1988).…”

“…This is particularly relevant in evergreen oaks in dehesas and montados, where a low density tree stratum coexists with pasture or crops in the open spaces. Ploughing, which has a damaging effect on tree root systems (superficial roots are connected to sinkers, see Figure 4), should be avoided as well as soil compaction promoted by heavy machinery or livestock overpressure (Hillel, 1982;Nadezhdina et al, 2012;David et al, 2013). Ploughing activities and livestock browsing have also been found to affect negatively cork oak natural regeneration (Pausas et al, 2009;Arosa et al, 2015), and may contribute to the spread of diseases and modify the physical properties of soils (Bugalho et al, 2009).…”

“…Ploughing activities and livestock browsing have also been found to affect negatively cork oak natural regeneration (Pausas et al, 2009;Arosa et al, 2015), and may contribute to the spread of diseases and modify the physical properties of soils (Bugalho et al, 2009). Therefore, minimum tillage techniques are recommended (David et al, 2013). Furthermore, soil conservation practices capable of improving soil surface infiltration and of maintaining high soil water holding capacities are of paramount relevance, particularly in the Mediterranean agroforestry systems where soils are usually shallow and poor in organic matter (Grant et al, 2013).…”

Open field-applicable instrumental methods for structural and functional assessment of whole trees and stands

“…40) depends on the water potential gradients. Changes in the direction of flow therefore depend on the local soil water supply, which can differ significantly in soil layers at different depths , 2012b, David et al 2013 or if water storage is highly asymmetrical around the tree ). Deep soil layers can supply water to shallow soil layers via tap or sinker roots under drought if they contain more water.…”

PERAN HYDRAULIC LIFT JA MBU METE PADA PEMELIHARAAN LENGAS TANAH DAN STATUS AIR JAGUNG SAAT KEKERINGAN / The Role of Cashew Hydraulic Lift in Maintaining Soil Moisture and Water Status of Maize under Drought Condition

“…Hasil penelitian sebelumnya di tingkat lapangan dan skala pot ditemukan adanya fenomena hydraulic lift (HL) pada tanaman jambu mete, karena setiap terjadi kehilangan lengas tanah di lapisan atas akibat proses evapotranspirasi yang tinggi pada siang hari selalu diikuti oleh proses pemulihan peningkatan lengas tanah pada periode setelahnya (Pitono et al 2016a;Pitono et al 2016b). Fenomena tersebut melengkapi temuan-temuan sebelumnya yang menyatakan bahwa lebih dari 30 spesies tanaman hutan dan gurun telah teridentifikasi memiliki kemampuan HL (Caldwell et al 1998;Bleby et al 2010;Prieto et al 2011;David et al 2013;Rocha et al 2014;Evaristo et al 2015).…”