2010 ue sg mencuccini

Nitrogen deposition, elevated CO2 and forests: why pollutants are good for the trees but bad for the planet

M. Mencuccini

School of GeoSciences University of Edinburgh (UK)

OUTLINE  Global

change  Forest nitrogen (N) cycle and N deposition  Relationships between N deposition, carbon b (C) cycle l and d other th greenhouse h gases (GHG)  Implications for global change

N-deposition, year 2000

A BRIEF REVIEW ON N CYCLE 



 

Denitrifying: y g NO3- → NO2- → NO → N2O → N2



Probably most important nutrient (with P) Ultimately derived from the atmosphere by lightning g g strikes or biological N fixation N fixation by freefree-living or symbiotic bacteria Fundamental role of microbes i b iin N cycle l Forests very good at keeping hold of NO3-

Impacts of N deposition on terrestrial ecosystems REDUCED N (NH3)

OXIDISED N (NO, (NO NO2, HNO3)

Nitrogen sources Globally 72%

of fixed N is anthropogenic Electricity generation

35%

37%

Traffic

Industry

Aber et al al., 2003

Nitrous Oxide (N2O)

Atmospheric N2 fixed to reactive nitrogen (NR)

GHG balance Particulate Matter

Nitrogen oxides ((NOx)

NR Fertilizer manufacture

Ammonium nitrate in rain ((NH4NO3)

Ammonia (NH3)

NR

Further emission of NOx & N2O carrying i on the cascade

Crops for food & animal feed

The Nitrogen cascade in agriculture

Livestock farming

Leached Nitrate (NO3-)

Terrestrial Eutrophication & Soil Acidification Natural ecosystems Aquatic Eutrophication

Nitrate in Streamwaters

Concerns about forest decline in the 1980s

ďƒ˜ Reductions

in sulphur emissions ďƒ˜ Other reasons?

Boreal forests are N N--limited as judged from these simple, early demonstrations from Sweden

(Hogberg 2007) courtesy Sune Linder, Umea Univ

Growth trends of European forests

 Sparse S

d data t for f Mediterranean M dit  Impact p of drought g S i k 1988 Water, Spiecker W t Air Ai & Soil Pollution

The e te terrestrial est a ‘missing ss g s sink’

28-30% of emissions stay 28in terrestrial biosphere

  

Partly tropical Partly temperate Partly boreal

Canadell et al al, 2007

Hypotheses to explain the increase (the anthropogenic effect paradox)

CO

2

fertilization

Warming Management N-deposition

Probable all 4 are important

    POP-FACE



CO2 forcing

Young stands in temperate zone [CO2] = 550 ppm → 2050 Soil metabolism ↑ NPP ↑ Response dependent on nutrition

Norby et al al, 2005

Effects of N deposition on the global C cycle

Debate: 1) how responsive are forests to N deposition?

2) how long will the response last?

3) does the sensitivity to Ndep explain the terrestrial sink?

Magnani et al, 2007; De Vries et al, 2008; Reich et al 2008; De Schriver et al, 2008; Sutton et al 2008; Magnani et al, 2008

Complete accounting for GH effects +

Atmospheric ozone

+

Aerosol, CH4 turnover

–

N use and emissions

+ + N leaching leaching, water quality Biodiversit y acidificatio n Other environmental effects

N deposition on natural ecosystems

N 2O

+

?

Climate change g

+

+ Ecosystem C sink

_ –

40 vs 200 kg C / kg N

Climate forcing

Radiative forcing (IPCC) The change in net irradiance at the top of the troposphere relative to "unperturbed" values (1750).

Positive forcing (more incoming energy) Warming effect Negative forcing (more outgoing energy) Cooling effect.

For how long will the positive effect continue?

Saturation around here Aber et al (1998) Bioscience

OVERALL CONCLUSIONS Elevated CO2 and N deposition are speeding up the th C cycle l and d iincrease sequestration t ti  Elevated CO2 and N deposition p are NOT helping to moderate global change  Hence the title: ‘good good for trees, bad for the planet’  The biosphere is helping us; but WE need to solve our own problems 

Acknowledgements F. Magnani, M. Borghetti, D. Stevenson, T. van Noije, S. Raddi, J. Grace