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Plant-soil-water interactions

Work Package Crop and grassland production and disease control

Research Deliverable 
Plant-soil-water interactions

Introduction

Plants form the base of the terrestrial food chain and plant roots, which acquire the water and essential mineral elements required for crop production, are key to food security. Indeed, they are considered a necessary focus of the next “Green Revolution”. Many Scottish soils exhibit non-optimal water relations for root growth, for example periodic waterlogging or soil drying, or lack sufficient mineral elements, such as nitrogen (N), phosphorus (P) and potassium (K), for optimal crop production. This results in a need for soil water and fertility management, which incurs financial costs. In addition, resources for fertiliser production are finite and geopolitically insecure, and the inappropriate use of fertilisers can have negative environmental consequences. In the interests of sustainability, it is important to optimise the use of water and fertilisers in agriculture.

Rhizosheath: the rhizosheath is defined as the soil that adheres to the roots by help of root hairs and mucilage. It maintains the contact between roots and the soil, improving water and nutrient uptake.

Aim of Research

Plant, Soil, Water Interactions: To identify the interactions between plants and soils that can be exploited to achieve food security and sustainable production of sufficient, safe and nutritious food. Crop yield and quality, biodiversity, and soil health are largely determined by the interactions between plant roots and the soil. The focus is on understanding, and modelling, the physical, chemical and biological interactions between plant roots, soil and water, which could improve crop and grassland production efficiency and sustainability.

Progress

2018 / 2019
2018 / 2019

Databases for root architectural traits, exudate composition and rhizosheath characteristics were compiled for various lines of barley, brassica and potato. The rhizosheath is defined as the soil that adheres to the roots by help of root hairs and mucilage. It maintains the contact between roots and the soil, improving water and nutrient uptake. A selection of different genetic lines was used to study the interactions between roots and rhizosphere properties. Data is being used to develop quantitative models of the impact of root and rhizosphere types on crop production. Similarly, a database of the rhizosheath properties of flowering plants was compiled, showing the potential to enhance this trait in a range of crops.

Field trials have suggested that a vigorous young root system alone does not improve resource acquisition and yield of potatoes subject to reduced phosphate fertiliser and drought. Studies on barley indicated associations between its genetics, soil processes and rhizosheath formation, but not between carbon inputs to soil and rhizosheath formation. Fungal and bacterial associations have been shown to differ between barley landraces (locally adapted, traditional varieties) and newer varieties, with specific bacteria promoting enhanced micronutrient efficiency in landraces. Studies of belowground food webs have shown that bacterial communities are impacted by grazing protists (microscopic organisms), but their effects differ in barley and tomatoes.

A technique for imaging root hair growth along the axis of barley roots was developed, which complements previous research to characterise root system architecture. Root elongation rates were obtained for 20 cereal varieties in response to two levels of soil compaction and will be used to inform field studies.

Information on root traits, interactions between plants, soil properties and soil biota and consequences of these for field crops are being incorporated into quantitative models. A model describing how root architecture, including root hairs, affects water uptake and phosphorus extraction at field scale is being developed. Simulations will explore the effects of different climate rainfall scenarios on phosphorus uptake by barley phenotypes with and without root hairs.

Highlights:

  • The importance of root/soil/biota interactions in crop production was raised with farmers and the public at an Open Farm Sunday event. Information was provided on a grassland plot experiment into soil stabilisation and varietal differences in root contributions to soil stability and links to research on greenhouse gas emissions from grasslands, which has been shown to differ dependent on grass variety grown, was highlighted. 
  • A Root-Rhizosphere Interactions Workshop was held together with the ISRR Medal Lecture given by Professor Liam Dolan, who spoke about using fossils and genes to understand the development and evolution of plant rooting systems. The audience of forty researchers and students was informed of progress on root phenotyping and root-microbe interactions, whilst an informal poster session allowed networking opportunities.
  • An experimental setup for imaging root hair growth along the barley root axis was developed and results from physical (hydraulic and mechanical) testing of rhizosphere soils as affected by both root and seed exudates were published.
  • An important paper was published showing that greater juvenile root vigour of potato varieties accelerated phosphorus (P) acquisition and canopy development and, thereby, increased tuber yields. Juvenile root vigour is a heritable trait and can be selected to improve P-fertiliser use efficiency of potato. Genes associated with the trait are being identified in collaboration with an EU-funded project called_SolACE.
2017 / 2018
2017 / 2018

A database for root architectures was constructed and root architectures of potato varieties were quantified. Nitrogen emissions from barley varieties were quantified and relationships with root exudates are being explored. Interactions between roots, soil structure and symbiotic fungi were investigated. Quantitative models describing the effects of root traits on acquisition of water and nutrients are being developed and field experiments are planned to test hypotheses from this work.

Novel approaches to recording observable characteristics of plants are being developed. Data were collected on the composition of root exudates and nitrogen emissions from a range of barley varieties. It was observed that barley varieties differed in both root exudates composition and nitrogen emissions.

Several studies of the interactions between roots and the rhizosphere have been completed. These indicate that both root hairs and exudates influence soil structure and stability, potentially offsetting the harmful effects of intensive agriculture on soil properties. Experiments investigating selection pressures on arbuscular mycorrhizal fungi in agricultural systems were completed. A paper showing that plant type affects the influence of arbuscular mycorrhizal fungi on plant growth has been published.

To characterise food webs in the rhizosphere, rhizosphere soils from barley varieties in which amoeba feeding on bacteria were present or absent have been sampled and the resulting bacterial communities are being profiled by DNA sequencing. Experiments to study the effects of plant biodiversity on bacterial communities in the rhizosphere have been planned. Interactions between plant roots and nematodes have been studied using innovative live-screening techniques. Field experiments to study the influence of root system architecture on tolerance to water stress and low phosphorus availability have been designed.

Information on root architectures and exudates, root-rhizosphere interactions and the consequences for these for resource acquisition are being integrated into quantitative models describing the effects of root system architecture, root exudation, rhizosheath properties and microbial communities on nutrient and water acquisition by plants.

Highlights:

  • An overview of how plant roots can help develop a fertile soil was published in Trends in Plant Science. This article illustrated the interactions between roots, soils and microbes that facilitate water and nutrient acquisition by crops, which might inspire breeding for root traits appropriate to soil conditions.
  • A Root-Rhizosphere Interactions Workshop was held with the ISRR Medal Lecture by Professor Michelle Watt. The audience was informed of state-of-the-art research on root phenotyping and root-soil interactions, whilst informal poster-networking opportunities at the workshop enabled future collaborations to develop across and between attendees. 
  • The root characteristics database is being developed to allow cross experimental analysis of the impact of root type on productivity (either measured in field or in glasshouse experiments).  Many root traits can only be measured in the laboratory and at scales not practical in field / larger i.e. mature plant experimental systems. 
2016 / 2017
2016 / 2017

Root architectural traits and exudate profiles have been quantified in different genetic lines (genotypes) of cereals and brassicas. The effects of these on rhizosphere physical characteristics, resource capture and nitrogen emissions are being quantified. Genetic factors associated with the rhizosheath have been identified. Methods to observe the effects of soil structure on root architecture have been developed. Progress has been made in understanding environmental factors influencing microbial activities and their effects on the acquisition of soil resources by crops.

A database of images of root systems was constructed and architectural traits used to construct models were quantified. Root exudates from barley and brassica genotypes were analysed, a technique to assay phosphatase activity in the rhizosphere was developed, and images of the rhizosphere were collected. Exudate profiles differed between types and could underlie differences in nitrogen emissions and nutrient acquisition.

Fungal endophytes (organisms that live between living plant cells) were isolated and some inhibited the cereal pathogen Fusarium avenaceum. Three isolates were suitable for field testing. Amoeba-bacteria-root growth interactions were examined. Barley was not as responsive to the rhizosphere microbial loop as other plants, such as tomato. The effects of agricultural selection pressures on interactions between roots and arbuscular mycorrhizal (AM) fungi were studied.

Data have been obtained that can be integrated into quantitative models describing the effects of root system architecture, rhizosheaths, microbial communities and soil structure on nutrient and water acquisition by plants. Progress has been made towards developing the structure of these models.

Highlights:

  • A new method to screen species for the presence/absence and strength of rhizosheath (a measure of stress tolerance) shows the potential to enhance the trait in a range of crop species and contribute to future agricultural sustainability.
  • The importance and functionality of our soils was demonstrated at The Royal Highland Show, Edinburgh at an event titled "Science Matters for Future Farming" attended by the cabinet secretary, other Scottish Government representatives, industry and scientists. Outputs highlighted the importance of the government-funded research programme and the benefits through joined up research for tackling both national and international challenges. The main topics included working towards sustainable intensification, remediation of degraded soils and the development of tools to inform and develop policies in the future.
  • A one-day meeting was held with a focus on root-soil interactions, including a session on soil stabilisation. Ten spoken presentations, plus the 'ISRR Medal Lecture' from Professor PJ Gregory on rooting depth and 8 posters were presented to sixty attendees (researchers plus industry representatives).
  • Protocols for assessing the characteristics of root architectures using 2D imaging systems have been developed. These give information on root growth rates, branching rates and branching angles that can be used to construct models of root architecture and exploitation of the soil volume. This work was presented at the "New Frontiers in Crop Research" Conference in October 2016.

Future Activities

This research programme has been re-organised. Some aspects will be discontinued and others will continue within other parts of the wider programme