ozone effects on the biomass, nodulation …...ozone effects on the biomass, nodulation and...
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OZONE EFFECTS ON THE BIOMASS, NODULATION AND NITROGENASE ACTIVITY OF CLOVER CULTIVARS
1,2HEWITT., D., 1MILLS, G., 1HAYES, F., 2WILKINSON, S. & 2DAVIES, W.
1 CENTRE FOR ECOLOGY AND HYDROLOGY 2 LANCASTER UNIVERSITY
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How do you make a cow? Amongst other things, 1kg of beef needs roughly: • 460 L drinking water • 43kg grain/hay • 46,000 L water to make the feed • 25g of N per kg of meat • 700kg cow ~ 17.5kg N This N must be obtained from the pasture forage
?+?= GOOGLE Images 2013
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A temperate pasture may require >100kg/ha-1 yr-1 of N input to meet the demands of grazing livestock.
• Some will be deposited (UK total N deposits <10kg - >21kg/ha yr-1) • Applied in fertilisers
• Obtained via clover (Trifolium spp.)
ROTAP, 2011
GOOGLE Images 2013
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• Bare symbioses with N-fixing rhizobia in organs called root nodules in N-limited conditions.
• Legumes are the primary source of protein for a substantial proportion of human population.
• Importance of legumes in agriculture known for millennia
White clover root nodules
Clovers are legumes (Fabaceae)
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• Ground level ozone most damaging air pollutant • Causes multi-billion $ losses annually in a range of important arable crops. • Further increases predicted during cause of this century
The Royal Society, 2008
GOOGLE Images 2013
Ozone concentrations have increased since pre-industrial era
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• Numerous studies show ozone may affect reductions in composition yield, & forage quality in temperate pasture
• Ozone shown to reduce nodulation/fixation in number of legumes • Modern cultivars of clover
Ozone effects on pasture
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Solardome study • Studies based at the CEH solardome facility (nr Bangor)
• Test of modern clover cultivars recommended for general use in grazed pasture (British Grassland Society, 2012).
• White clover (Trifolium repens cv. Crusader) • Red Clover (Trifolium pratense cv. Merviot)
Crusader Merviot
At start of experiment
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Broad aim to quantify physiological impacts on the cultivars.
• Plants exposed in to 7 ozone scenarios (with a unique scenario per dome).
• Scenarios based on a profile recorded at Aston Hill monitoring station (Flintshire, UK).
• 6 replicates per scenario; exposed for 12 weeks
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R² = 0.49 P=0.01
R² = 0.87 P<0.001
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R2 = 0.0004 P=0.54
R2 = 0.2108 P=0.09
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gs (m
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3 Month AOT40ppm h-1
Ozone injury
gs
● = Merviot ○ = Crusader
Ozone injury and stomatal conductance (gs)
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Shoot biomass Root biomass Root:shoot
Shoot and Root biomass
● = Merviot ○ = Crusader
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Nodules per pot Mass per nodule Nodule mass per pot
Nodule biomass
● = Merviot ○ = Crusader
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0.5 5.2 18.6
Nod
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AOT40 ppm h-1
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*
Crusader
Merviot
Nodules 0.7->1.5mm
Nodules <0.1mm-0.7mm
Nodule size
P<0.05
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In-situ nitrogenase activity (Acetylene reduction assays)
Low ozone High ozone
Week 10
Week 11
P<0.1
P<0.05
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What does this mean for the UK? Using 10 x 10km grid square and AOT40 values for pasture-growing areas of the UK*,
in a high ozone year (2006), there was potentially : April – June : a mean 12% reduction in nodule mass July – September: a mean 8% reduction in nodule mass
April-June July-Sept
* Data from Mhairi Coyle, in Mills et al., 2011, O3 and food security in the UK report for Defra
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Summary and conclusions
• Systemic reductions in below ground biomass and nodulation, and reduction in nitrogenase activity.
• Perhaps arising from a reduction in the translocation of assimilate.
• Continuing increases in the level of ozone may cause lasting declines in pasture fertility and productivity.
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• Mixed community of high sugar Ryegrass (‘AberMagic’) and Crusader
• 6 O3 treatments +/-Intermittent drought
• Sequential harvests and nitrogen fixation assays (= 220 pots!).
• Paper close to submission
This growing season……
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Special thanks to Aled Williams, Anni Gibeif, Steve Hughes, Harry Harmens, Chris Evans, Peter Wieland, Vicent Calatayud, Serena Wagg and Chiara Premoli for their advice and assistance. This is a NERC funded project (project code: NEC04456).
Acknowledgements
Thanks for your time!
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R² = 0.54 P=0.07
R² = 0.99 P=0.01
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R² = 0.17 P=0.43
R² = 0.95 P=0.01
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Nodules g-1 Nodule mass g-1