Environmental Engineering Using Seed Mimics to Support Increased Crop Water Use Efficiency

Background: Lack of water availability seriously impacts the productivity of crops in many regions of the world (including Australia, Sub-Saharan Africa, India). This lack of water can affect plants at several stages of development, including limiting seed germination and root elongation, through high soil strength and via matric suction where the limited water available is stored in small pores such that roots have to work hard to extract it. This latter mechanism can impact on early and late biomass development and/or on seed-filling in grain crops. The water holding capacity of the soil matrix is an important part of the relationship between the water use efficiency of the plant in terms of crop yield per unit volume (commonly termed, “crop-per-drop”). For example, in free-flowing soils such as very sandy soils, precipitation in the form of rain can be only available to plants for a very short period of time, before either draining from soil due to gravity and lack of small pores (which act as capillaries for water storage) or water loss due to evaporation. There are potential natural solutions, however, to maintain water in soil for later exploitation. These may have utility in plant cropping systems in arid climates, therefore providing new, environmentally friendly technologies.
Interestingly, the incidence of seed myxospermy (myxospermy is the ability of a seed to produce and expand mucilage on hydration) is significantly higher in plants that occupy environments characterised by water deficit and particularly sandy rooting mediums. Seed mucilage has high water holding capacity that is thought to protect against desiccation stress and improve the success of germination. However, the ecological significance of myxospermy is not yet being fully understood. Recent research by Valentine and Iannetta has identified specific myxospermous seed-bank densities which allow seedlings to develop normally (based on root elongation rates) in sand rooting medium with 5x less water compared to no-seedbank controls. Thus, there is the potential that the mucilage could act as a protectant to the seedling during germination and root emergence. Here we further hypothesis that the mucilage could be utilized to support plant growth and development later in plant development and aim to establish the optimum technology for delivery.

Aim: Develop and test techniques for delivering mucilage via seed mimics into sandy arid environments enabling maximal plant and root growth under reduced water supply.

Methods / Approach: This project aims to develop myxospermous seed mimics to deliver sand pore space management to maintain and improve plant growth with reduced irrigation, while still supporting cropping, or restoration efforts, to ensure high productivity. This will require the student to initially develop the bioassay to test the level of mucilage / seed mimics required (plant growth assay), assess a range of mucilage / seed mimics in terms of chemical and physical properties and then combine and test combinations. The student will be expected to develop the understanding of why combinations work, and not just which ones work. One important aspect will be to investigate longevity of the seed mimics/mucilage and the effect of breakdown products on soil water relations, as breakdown compounds may increase soil hydrophobicity rather than increase it It is envisaged that the initial plant growth experiments will use forage (legume) crops for the supported crop (for biomass), in contrast to the previous work that utilized barley at the seedling stage only. This will enable faster cycling to latter growth stages for experimental purposes. Water status of the growth material will be monitored using, for example: mass changes, water sensors and / or tensiometers, with wetting properties assessed with a small-scale infiltrometer. Plant growth and underlying stress will be monitored using, manual plant growth measurements and imaging using 2D and 3D imaging (for plant size) and hyperspectral imaging (for plant stress status). In addition, the student will undertake research into potentially useful mucilage options through literature sources, utilizing previous research of supervisors and utilizing methodologies (confocal microscopy, µCT, tension tables water release analysis, and chemical analysis) to assess mucilage properties.