Assessing the significance of soil erosion to arable weed seedbank composition and biotic function 1,2
2
2
1
Ashley Gorman , Cathy Hawes , Blair M. McKenzie , John S. Rowan 1
Centre for Environmental Change and Human Resilience, University of Dundee, Nethergate, Dundee DD14HN, Scotland UK The James Hutton Institute, Invergowrie, Dundee DD2 5DA, Scotland UK Email: ashley.gorman@hutton.ac.uk 2
Overview
Objectives
Arable weeds provide important ecosystem services within simplified agroecosystems (Lewis et al., 2013). Seed dispersal plays a central role in shaping the composition and functioning of plant assemblages. However, the potential for erosion and deposition to redistribute seeds and effect their fate has largely been overlooked. Weed seedbanks are influenced by cultivation practices with a trend towards reduced biodiversity and associated ecosystem services e.g. declining crop yield, water retention, and habitat provision for higher trophic groups.
The key aims of this project are to: Quantify the significance of erosion and sedimentation to redistribute arable weed seeds and to influence seedbank diversity and function within agroecosystems.
Climate change predicts increased frequency and intensity of soil erosion but the risks to seedbank composition through altered species recruitment, dispersal, germination and seedling survival rates is under researched.
Better understanding of the biophysical linkages between seedbank composition, soil properties and land management will contribute to the policy drivers of sustainable intensification and increased food security.
Undertake quantitative analysis of seed inputs (seed rain, deposition) and loss (germination, mortality, dispersal) to create a seed fate budget over a variety of physical and temporal scales. Investigate the role of weed seedbank to influence physico-chemical behaviour of agricultural soils. Use an improved knowledge of seed fate to inform sustainable arable weed seedbank management.
EPIZOOCHORY
FECUNDITY
SEED TRAITS
SECONDARY DISPERSAL
PRIMARY DISPERSAL
SIZE PARENT SURVIVAL
Machinery, Tyres, Clothing etc.
SURFACE SEED
APPENDAGES MUCILAGE SECRETION
BURIAL
ACTIVE SEEDBANK
WATER AGRO MANAGEMENT
Disturbance, Application of Herbicides, Tillage
OTHER
PREDATION
PHYSICAL DAMAGE
DISEASE
Acknowledgements This PhD studentship is funded by CECHR (UoD) and The James Hutton Institute. References
Bochet, E. (2015) ‘The fate of seeds in the soil: a review of the influence of overland flow on seed removal and its consequences for the vegetation of arid and semiarid patchy ecosystems’ SOIL, 1:131-146 Lewis et al. (2013) ‘Assessing the significance of soil erosion for arable weed seedbank diversity in agro-ecosystems’ Progress in Physical Geography, 37:622-641
MORTALITY
TEMPERATURE
SECONDARY DORMANCY
SUN
HYDROCHORY
A Conceptual Framework for Quantifying Seed Fate
FATAL GERMINATION
ANEMOCHORY
Method Development
EMERGENCE
GERMINATION
DEPOSITION
ABIOTIC
ANTHROPOCHORY
SHAPE
BIOTIC
DEPTH
PHYSIOLOGY
GAS
DORMANT SEEDBANK
Tests are on-going to compare the relative merits of physical seed extraction versus seedling emergence protocols to determine seedbank density, composition and richness.
The seedbank is regenerated through primary dispersal via the parent plant, as well as secondary dispersal. Dormancy allows for the seedbank to persist for long periods of time until germination is stimulated.
Seed Emergence:
To date quantification of seed fate has focused on the biological controls on mortality, germination and some stages of secondary dispersal.
Though described in drylands (Bochet, 2015), erosive redistribution is under-investigated in agroecosystems.
This project will use multiple experiments (laboratory, field and modelling) to evaluate the significance of physical processes on weed seedbank function.
Seed Input Process Seed Loss Process
Influences on Seed Input Influences on Seed Loss
Determines germinability under glasshouse conditions by counting emerging seedlings. Can underestimate seedbank density due to variations in dormancy.
Seed Extraction:
Seed Flow Management (Site Specific)
Key Questions
Requires sieving, followed by floatation in a salt solution and microscope identification. Detects greater seed densities but ineffective for small seeded species and is time consuming.
Assessing the Importance of Tillage Practices on Seedbank Composition: 10 Year Barley Field Trial This study builds on a long term field trial at the Mid Pilmore experimental site at the James Hutton Institute, Invergowrie (56.454871, -3.082004) which examines the effects of three tillage practices (no till, conventional and deep plough) on winter and spring barely crop yield, soil structure, water retention and carbon dynamics. Here we are investigating the effects of long term tillage practices on seedbank distribution, composition and viability, over four depth intervals to a maximum of 32 cm. We will assess how the seedbank assemblage has altered after 10 years of continuous barely cropping using two seedbank assessment methods. Results thus far are restricted to a first flush of emergence observations, from which we have obtained 16 preliminary functional groups determined by six categories (cotyledons, annuality, germination and flowering timing, potential height and seed size).
Canonical Variance 2
EROSION
SECONDARY DISPERSAL
ENDOZOOCHORY
No Till Conventional Deep Plough Canonical Variance 1 Figure 1. Following the first flush of emergence experiments, canonical variance analysis shows management practice to influence the functional groups present within the seedbank and therefore altering species composition.