The influence of depth-to-groundwater on structure and productivity of Eucalyptus woodlands

Abstract

Although it is well documented that access to groundwater can help plants survive drought in arid and semiarid areas, there have been few studies in mesic environments that have evaluated variation of vegetation characteristics across a naturally occurring gradient in depth-to-groundwater (DGW). The aim of this study was to determine whether differences in groundwater depth influence structural attributes and productivity of remnant woodlands in south-eastern Australia. The study area was located in the Kangaloon bore-field area of New South Wales, where DGW varies from 2.4 m to 37.5 m and rainfall is plentiful. We examined structural (leaf-area index, basal area, stem density, tree height, Huber value (HV) and aboveground biomass) and functional (aboveground net primary productivity (ANPP)) attributes of seven woodland sites differing in DGW. We also used ∂13C analysis of sapwood across six sites, along with observed non-linear changes in structural attributes, to infer groundwater use by trees. Significant differences in structural attributes and ANPP were observed across sites. The three shallowest sites with 2.4 m, 4.3 m and 5.5 m DWG had significantly larger aboveground biomass and ANPP than did the four deepest sites (DGW ≥9.8 m). Across all attributes (except HV in the summer, where the mean values were significantly larger at sites where DGW was 5.5 m or less and across the four deeper sites (DGW ≥9.8 m), there were no differences in these three structural traits, nor in ANPP. Despite finding no significant differences in HV across sites in the summer, in winter, the two deepest sites had a significantly larger HV than did the two shallowest sites. Significant increases in ∂13C of sapwood occurred across five of the six sites, consistent with increasing water-use efficiency as DGW increased, reflecting the declining availability of groundwater with increasing DGW. This study has demonstrated that even in a mesic environment, putative access to groundwater can have important impacts on structural and functional traits of trees and, consequently, on woodland productivity.

Embolism recovery strategies and nocturnal water loss across species influenced by biogeographic origin

“…Ray parenchyma starch and nonstructural carbohydrates (NSCs) were collected during wet, drought, and rewatered periods. Plant characteristics including leaf area, tree height, and leaf temperature were measured using standard procedures (Palmer et al, ; Zolfaghar et al, ). Samples were collected during three periods: “Wet,” “Drought,” and “Re‐watered.” During the drought and rewatering treatments, plants received minimal water for 5–18 days until predawn leaf water potentials indicated plants were sufficiently stressed, and then, plants were rewatered to field capacity overnight.…”

“…Well‐watered leaf samples for each species were collected for plants before the drought was imposed and dried at 70°C for 72 hr. Three to four fully expanded, replicate leaves per species were ground and analyzed for the ratio of stable carbon 13 isotopes with Picarro G2101‐ i CO 2 analyser and Costech Combustion module (Picarro Inc.) Previously described methods were used (Zolfaghar et al, ).…”

Impact of groundwater depth on leaf hydraulic properties and drought vulnerability of Populus euphratica in the Northwest of China

“…Groundwater is the only available water resource for the vegetation's survival at the extremely arid zone in the northwest of China (Gries et al 2003). The previous studies found that the growth, distribution, and succession of riparian trees are closely related to the changes of groundwater depth (Aishan et al 2013;Gries et al 2003;Lammerts et al 2001;Zolfaghar et al 2014Zolfaghar et al , 2015. Researchers attach differences in groundwater depth to drought stress to study the physiological and morphological responses of riparian plants to investigate the adaptive traits (Chen et al 2003b(Chen et al , 2012Li et al 2013;Rzepecki et al 2011).…”

Variation in bulk‐leaf 13C discrimination, leaf traits and water‐use efficiency–trait relationships along a continental‐scale climate gradient in Australia

“…Functional and structural attributes of vegetation often change in a predictable manner along gradients of water availability. For example, across sites with varying depth-to-groundwater, aboveground biomass and net primary productivity increased and water-use efficiency decreased as water availability increased (Zolfaghar et al, 2014). Water availability significantly influences rates of sap flow and annual rates of water use of trees (Dragoni, Caylor, & Schmid, 2009;Rossatto, Silva, Villalobos-Vega, Sternberg, & Franco, 2012;Whitley et al, 2013;Zeppel et al, 2008).…”