The role of seedbank composition and biotic function in vulnerable erosive agroecosystems 1,2
2
2
3
Ashley Gorman , Cathy Hawes , Blair M. McKenzie , John S. Rowan 1
Centre for Environmental Change and Human Resilience, University of Dundee, Nethergate, Dundee DD1 4HN, Scotland UK 2 The James Hutton Institute, Invergowrie, Dundee DD2 5DA, Scotland UK 3 School of Social Sciences, University of Dundee, Nethergate, Dundee DD1 4HN, Scotland UK Email: ashley.gorman@hutton.ac.uk
Objectives
Overview Arable weeds provide important ecosystem services within simplified agroecosystems (Lewis et al. 2013).
Weed seedbanks are influenced by cultivation practices with a trend towards reduced biodiversity and associated ecosystem services e.g. declining crop yield, soil water retention, and resource provision for higher trophic groups.
Accelerated soil erosion degrades physical and biogeochemical functioning of arable soils, threatening sustainable food production.
The expected increase in frequency of extreme storm events resulting from climate change will intensify the severity of soil erosion.
Quantify the significance of erosion and sedimentation to redistribute arable weed seeds and to influence seedbank diversity and function within agroecosystems. Investigate the role of seedbanks to influence physico-biogeochemical behaviour of agricultural soils. 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.
However, the impacts of soil erosion on the state and vitality of the arable seedbanks is largely overlooked. A
C
Source: Deng (2012)
D1
B D2
D3
Fig.3 Staining seeds with ruthenium red staining indicates the pectin component of mucilage, confirming myxospermy ability. (A) Capsella bursapastoris, i: inner layer; o: outer layer. 1 mm. (B) Arabidopsis thanalia, 0.6 mm. (C) Plantago major, 1-2 mm. (D1, D2, D3) Euphorbia helioscopia, 2-3 mm.
Ecological functions of myxospermy and morphology
Tillage Practices and Seedbank Composition: 10 Year Barley Field Trial
Building on a long term field trial at an experimental site (James Hutton Institute, Invergowrie (56.454871, -3.082004)), we investigated the effects of 3 tillage practices (no-till, conventional and deep plough) in spring and winter barley on seedbank distribution and composition over 4 depth intervals. Species abundance was recorded following the identification of emerging weeds under glasshouse conditions (Fig.1). Species were categorised into 16 functional groups determined by ecological and physiological characteristics. Data from year 1 show a management impact on species composition and a change in the balance of individuals across functional groups (Fig.2). Year 2 data collection is ongoing but we predict a change in species and functional group composition and abundance following conversion of no-till plots to conventional plough.
Selective erosion of seeds by detachment, transport and deposition depends on seed size, shape, appendages and the ability to secrete mucilage.
Fig.1 Species Rank-Abundance Shannon-Weaver diversity (H), evenness (E) and richness (R) scores found management with crop type (H = P-0.0027; E = P-0.002; R = P-0.006), and management with depth (H = P-0.007; E = P-0.015) to impact species composition and distribution.
Abundance (Log)
Differential mobility, and consequently mortality risk, therefore depends on seed morphology. The potential functions and ecological roles of myxospermous seeds have been reviewed recently (Yang et al. 2012), however quantitative studies are rare and limited to a single or a few model species. Physical alterations to soil could occur due to the adhesive nature of mucilage, stabilising soil structure and enhancing water retention. We will investigate the extent to which specific species and community assemblages are capable of preventing removal following erosion events and whether there is an existence of a mucilage threshold beyond which soil properties are altered.
Acknowledgements This PhD studentship is funded by CECHR (UoD) and The James Hutton Institute.
Canonical variance analysis of year 1 data shows tillage to significantly control the presence and distribution of species, leading to a change in representation of individuals across functional groups in the community.
No. of Species
Future Work
References Deng, (2012) Experimental and numerical analysis of behaviour of the myxospermous seeds of Capsella bursa-pastoris (L.) Medik. (shepherd’s purse) in soil. (PhD Thesis). Lewis et al. (2013) ‘Assessing the significance of soil erosion for arable weed seedbank diversity in agroecosystems’ Progress in Physical Geography, 37:622-641 Yang et al. (2012) ‘More than just a coating: Ecological importance, taxonomic occurrence and phylogenetic relationships of seed coat mucilage’ Perspectives in Plant Ecology, Evolution and Systematics 14:434– 442
Fig.2 Seedbank Composition and Tillage Management
We will test the adhesive powers of communities of myxospermic species and resulting biogeochemical changes to soil properties. This work will improve knowledge of seed fate to inform sustainable arable weed seedbank management. A 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.