Geoff Squire

Feral and volunteer crop populations in the arable environment

Not all the seed from crop plants is harvested; many seeds are lost, either falling to the ground within the field or dispersed by machinery, birds, etc. to end up beyond the field margins. In some cases the seeds survive in the seedbank giving rise to volunteer populations within subsequent crops or feral populations outside of the cropped area.  The persistence and spread of volunteer and feral populations can lead to significant weed problems while providing a bridge for the dispersal and escape of traits present in cultivated populations.

Volunteer oilseed rape

In the cultivation of oilseed rape (Brassica napus L.), large numbers of seed are shed and fall to the ground before and during harvest. Given the right environmental conditions a proportion of these seeds will become dormant and enter the seedbank, emerging later if subjected to appropriate germination triggers. This has led to the presence of volunteer weed populations within arable fields and to persistent seed bank populations.

Wild arable plants - diversity and function

The ecology and biology of wild arable plants are poorly understood. Of the more than 250 plant species to be found on arable farmland, typically five to 10, among which are wild oat, blackgrass, barren brome and cleavers, constitute the main weed burden of arable cropping. Many of the rest, particularly the broadleaf (dicotyledonous) species, support an arable food web that includes insect groups, mammals and birds. Despite the economic, ecological and aesthetic importance of wild arable plants, embarrassingly little is known about their ecology and genetic diversity.

Our first research paper in this new topic demonstrated the lack of basic information for even the common species (Hawes et al., 2005). If arable cropping systems are to be sustainable, then co-existence between crops and weeds must be managed with minimum or no herbicide application. To achieve this, fundamental and strategic research is necessary into the way wild arable plants respond to crops, weather and field management.

The persistence and spread of novel genes

A transgenic, that is genetically modified, oilseed rape (Brassica napus) provides the model system with which we have investigated the dynamics of novel genes in local populations. A stochastic, spatially explicit individual based model (IBM) was developed to simulate the dynamics of the transgene introduced into a non-transgenic population. The model combines life-history and management processes with environmental drivers to examine the effect of these on the spread and persistence of the transgene and the conferred trait.

The model has been used to explore a number of features of this system:

Gene flow patch diagramSpread and persistence in patchy populations - Plant populations, including arable weeds, typically exhibit spatial heterogeneity, that is patchiness, in their distribution. Together with the localised nature of plant to plant interactions this has the potential to affect the dynamics of a population and the spread and persistence of the genes they posses. Model simulations have shown that small scale spatial heterogeneity in the distribution of transgenic plants combined with localised pollen dispersal reduces mixing between populations and acts to limit the spread of the gene through the population.

The seedbank

Seeds from the arable seedbank - photograph by Gladys Wright/Stewart MaleckiBuried living seed - the seedbank - is central to the composition and succession of disturbed vegetation, allowing regeneration after agricultural or natural clearing of the existing plant cover. In arable-grass systems, the seedbank is the source of both the weed burden and the vegetation that supports the arable food web. Of around 250 species typically found in arable regions, only five to 10 are economically important as competitors to crops. Few of the poisonous species that were once a concern now remain in fields. Most of the other seedbank species have been reduced, in particular the broadleaf or dicotyledonous species that provide food and habitat for detritus feeders, herbivores, parasitoids, predators and pollinators. Knowing the seedbank is therefore essential for balancing the weed burden and biodiversity.

Plant population and community modelling

The objective of plant population and community modelling in the Agroecology group is to understand, and where necessary anticipate, the effects on arable vegetation of technical innovations and global change, and thereby to understand the role of the vegetation in the sustainability of the arable system as a whole.  System-level responses, such as primary production, nutrient retention and biodiversity, emerge over time, often unpredictably, from complex ecological and evolutionary processes. By developing models of plant populations and communities, we are able to assess the response of arable vegetation in a way that can't be addressed by experiment or observation alone.

Our current focus is the influence of the genetic and functional characteristics (life-history traits or their physiological determinants) of plants on system-level properties. A common thread is the definition of populations and communities in terms of the genetic and functional variation of individuals. Using the individual enables intra- and inter-specific variation to be presented on a common scale and both ecological and evolutionary processes to be combined in a single model framework.

Sustainable Systems

The biological mechanisms that drive primary production and other ecological functions should not be compromised: a balance must be kept between what is removed from the field for subsistence and profit and what is left to support the system’s essential life forms. We are attempting to define the bounds and conditions in which these life forms can operate so as to ensure the system’s long term health and resilience.   

.. a habit of mind in harmony with reason and the order of nature ..

Cicero, MT. De Inventione

Trait characterisation in crops

Photograph of growing-tubes in SCRI glasshousesCrop productivity has increased dramatically in recent decades through a combination of improved arable management and breeding of higher yielding crop genotypes.

Further increases in productivity are needed to cope with growing demands for food. The price, availability and high energy costs (carbon footprint) of inorganic fertiliser mean that food production will need to be achieved with fewer chemical inputs and with greater emphasis on a sustainable approach to arable cropping. 

New crop genotypes that require less chemical fertiliser and pesticide for a given level of yield could be developed by characterising plant traits associated with reduced nutrient requirements and high pest tolerance.

Contact: Alison Karley

Multi-Trophic Interactions

Photograph of a beetle on chicory flowerMulti-trophic Interactions is a new major research topic in Agroecology that combines existing lines of study at both SCRI and the University of Dundee. Trophic (or feeding) interactions drive the cycling of energy and nutrients in farmland. Insects and other invertebrates feed on plants and in turn are fed on by other insects, spiders, various symbionts, pathogens and vertebrates. A very small proportion of the total species in trophic interactions are pests of agriculture. Most mediate processes that are essential to the cropping cycle, such as the breakdown of dead organisms (crops, weeds, wood, animals), the regulation of pests and the pollination of flowers. These trophic interactions are exceedingly complex and are studied using advanced concepts and methods in organism biology, molecular biology and mathematical modelling.  Through gaining basic knowledge, the topic aims to provide a scientific basis for future management of invertebrate populations in farmland.

Plants and plant communities

Photograph of happy field workers sampling plantsResearch in Plants and Plant Communities aims to define those properties of crops and arable plants that would maintain yield and the purity of yield while reducing the environmental footprint of cropping. The work includes basic studies of plant processes such as germination, flowering and nutrition, genetic and physiological variation in model crops and arable plants, the ecology of plant (seedbank) communities, plants as the base of the arable food web and models of geneflow, selection and evolution. The practical output will be combinations of plant traits that can be targeted in crop improvement or encouraged by agronomy. Disciplines and methods include plant physiology, genetics, statistics, modelling, microscopy and field survey.

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