Transpiration and plant water relations of evergreen woody vegetation on a recently constructed artificial ecosystem under seasonally dry conditions in Western Australia

Abstract

Abstract:Understanding transpiration and plant physiological responses to environmental conditions is crucial for the design and management of vegetated engineered covers. Engineered covers rely on sustained transpiration to reduce the risk of deep drainage into potentially hazardous wastes, thereby minimizing contamination of water resources. This study quantified temporal trends of plant water potential (c p ), stomatal conductance (g s ), and transpiration in a 4-year-old evergreen woody vegetation growing on an artificial sandy substrate at a mine waste disposal facility. Transpiration averaged 0.7 mm day À1 in winter, when rainfall was frequent, but declined to 0.2 mm day À1 in the dry summer, when the plants were quite stressed. In winter, the mean c p was À0.6 MPa at predawn and À1.5 MPa at midday, which were much higher than the corresponding summer values of À2.0 MPa and À4.8 MPa, respectively. The g s was also higher in winter (72.1-95.0 mmol m À2 s À1) than in summer (<30 mmol m À2 s À1 ), and negatively correlated with c p (p < 0.05, r 2 = 0.71-0.75), indicating strong stomatal control of transpiration in response to moisture stress. Total annual transpiration (147.2 mm) accounted for only 22% of the annual rainfall (673 mm), compared with 77% to 99% for woody vegetation in Western Australia. The low annual transpiration was attributed to the collective effects of a sparse and young vegetation, low moisture retention of the sandy substrate, and a superficial root system constrained by high subsoil pH. Amending the substrate with fine-textured materials should improve water storage of the substrate and enhance canopy growth and deep rooting, while further reducing the risk of deep drainage during the early stages of vegetation establishment and in the long term. Overall, this study highlights the need to understand substrate properties, vegetation characteristics, and rainfall patterns when designing artificial ecosystems to achieve specific hydrological functions.

Hydrological Impacts of Urbanization and Urban Roof Water Harvesting in Water-limited Catchments: A Review

“…Water-limited environments are characterized by annual potential evapotranspiration exceeding annual precipitation (Gwenzi et al 2012;2013). Hydrological processes, such as infiltration, runoff and groundwater recharge, are highly seasonal and episodic, and exhibit non-linear and threshold-like behaviour (Gwenzi 2010;Gallo et al 2013).…”

“…This urban heat island effect induces the development of convective air masses, and consequently thunderstorms, and could potentially increase vapour pressure deficit or atmospheric water demand. Vapour pressure deficit controls water vapour fluxes, especially when moisture is non-limiting (Gwenzi et al 2012(Gwenzi et al , 2013. Overall, the increase in catchment runoff coefficient, thermal regimes and diversion of roof runoff are the key mechanisms accounting for the impacts of urbanization and urban roof water harvesting systems on rainfall partitioning and the hydrological behaviour.…”

“…Soil moisture availability and vapour pressure deficit are the key drivers of evapotranspiration (Gwenzi et al 2012(Gwenzi et al , 2013. Compared to other hydrological processes, such as runoff, the effect of urbanization on evapotranspiration is still poorly understood.…”

“…Water-limited catchments experience highly episodic rainfall (Gwenzi 2010;Gwenzi et al 2012;2013) resulting in high temporal and spatial variability of surface water resources. For example, sub-Saharan Africa (SSA) is prone to frequent hydroclimatic risks such as droughts, dry spells and floods (Ngigi et al 2005(Ngigi et al , 2007, making the provision of water to sustaining livelihoods, food security and public health in SSA a challenge.…”

Non-invasive monitoring of electrical parameters of Schefflera arboricola leaf

“…The water potential quantifies the amount of work needed to move 1 mole of water from one point to other and has a unit of pressure (Pa). The capacitance and resistance or the complex permittivity that were measure in our experiments can be directly related to the water potential variations that also determines the plant transpiration [5]. A simple electrical model of water potential was shown by Zhuang et alwhere the plant can be seen as an electrical circuit with a potential Ψ s at the soil and Ψ l at the leaf.…”