Root-zone salt dynamics, water use, and water redistribution in Atriplex spp. in saline lands

The greatest challenge for agriculture in the future lies in the fact production environments are unstable and degrading. Salinization has been identified as a major threat to agriculture and natural ecosystems because of its degrading effects on landscapes.

Salt-affected lands in Australia are estimated to be approximately 32 million ha in arable and permanent cropland . Of this total area around 2.5 million ha is subject to secondary dryland salinity. Secondary dryland salinity refers to human induced salinity in non-irrigated lands, and in Australia, is related to the clearing of land for agriculture

Drastic changes in dryland systems are needed to manage saline lands in a sustainable and productive way. Sustainability in these lands lies in restoring the previous water use, thus reducing the rise of watertables. One solution, which has received increasing attention in the past decades, is the revegetation of the salt affected lands with salt tolerant perennial plants (trees and fodder shrubs).

Research

The research in this PhD investigation focuses on the growth of saltbushes (Atriplex species). The work will address the following questions critical in evaluating the long-term sustainability of saltland pastures:

• Does plant morphology affect plant survival, moisture and salt concentration in the root zone?
• Are plant survival and growth affected by spatial and seasonal variations in soil salt concentrations?
• Does the plant change source of water in response to spatial and seasonal variation in moisture and salt concentrations?
• Are saltbushes a suitable component for long-term sustainable saltland pasture?

Aim

The aim of the project is to study the key processes in water redistribution and the effects of root zone salt and water dynamics in Atriplex spp. (saltbushes). This will permit me to evaluate factors influencing productivity (i.e. growth) and also determine whether saltbushes are a suitable component of saltland pastures in the long term. The specific aims are to assess the following processes:

1. Stemflow and its role in concentrating and distributing water in the soil profile. I will also assess how plant morphology (angles of stems and leaves) affects stemflow.
2. Water redistribution in the soil profile. I will assess whether hydraulic redistribution occurs in the root zone either driven by soil osmotic or matric potential gradients.
3. Seasonal water uptake and the plants ability to extract water from various zones in the soil profile, according to different soil water potentials
4. Plant growth and survival. I will estimate the influence of the above processes on plant functioning and growth in saline lands.

Methods

Glasshouse and Field studies will be used to consider

1. Rainfall redistribution, stemflow and root channelization
2. Seasonal and spatial dynamics of water and N uptake in Atriplex spp. in saline lands
3. Water redistribution in soil profile by plants roots

Coastal Saltbush (from Florabase, http://florabase.dec.wa.gov.au/)

Split-root experiment carried out to determine water use, water relations and growth of old man saltbush (Atriplex nummularia, ‘Eyres Green’) when roots are subject simultaneously to different salt concentrations in the root-zone.