Taylor MillsZachary Davies

GEOG 4401/5401 Soils GeographyFall 2007 – Univ of Colorado, Boulder

STUDY SITESMcMurdo Dry

Valleys, AntarcticaArctic, Brooks

Range, Alaska

MCMURDO FACTSLocated at 77°30'S

163°00'E Largest ice free area

of AntarcticaHarshest ecosystem

on earthLowest species

diversity on earth Primarily dominated

by Nematodes and algae

GLOBAL COOLING…?

Mcmurdo dry valleys have been cooling over the past 50 years

Cooler temperatures lead to dryer soilLess melt water = fewer streamsSoil water consistently frozen

PRESERVING SOIL HYDROLOGY FOR FUTURE GENERATIONSPast climate

influences current soil characteristicsColder drier = less

PP = less organic matter deposits

Organic matter is energy source for current soil organisms

PRESERVING SOIL HYDROLOGY FOR FUTURE GENERATIONS Cycle of lake

expansion and desiccation recharges soil OMLittle to no PP in the

soil itselfDeposition of

organic matter is either aeolian or lake deposits

SUMMARY OF COOLING EFFECT ON MCMURDO DRY LAKES

Reduces amount of liquid waterLowers soil moisturePrevents formation of lakes and pondsGreatly reduces inputs of organic matter into

the soilDecreases soil organism diversity and richness

Implications of Global Warming on the Tussock tundra

North Slope of the Brooks range in Alaska

Why Study Tundra Ecosystem?Global warming is predicted to be most pronounced at high

LatitudesOne-third of the global soil carbon pool is stored in northern

latitudesChanges in carbon storage in these areas could have a large

effect on global warming

Effects of Global Warming on Arctic Terrestrial EcosystemIncrease plant litter and SOMChange in soil Carbon storageLoss of MycorrhizalChange in Soil AcidityPositive feedback on Global Warming?

Plant LitterTemperatures are expected to increase 1-4 degrees in Arctic

ecosystemsBio mass Production

-increase of plant litter and SOM

-increased C stored aboveground by stimulating plant productivity and by shifting species composition from slow-growing species to more productive shrubs that accumulate C in long-lived woody biomass

Figure 1 Effect of fertilization on vascular plant aboveground net primary production (ANPP) in tundra. Fertilized plots in moist acidic tundra near Toolik Lake, Alaska, havereceived 10 g Nm22 yr21 and 5 g Pm22 yr21 since 1981.

-litter from shrubs decomposes more slowly than the graminoid litter they replace, so conversion to shrub tundra was thought to slow decomposition and increase ecosystem C accumulation

DecompositionIncreased nutrient availability stimulated the decomposition of

old litter in deep soil layers, leading to loss via mineralization and leaching of dissolved organic C

The rate of decomposition was greater than the increase in production

Net loss of 2,000g C m-2 from

the ecosystem

Control Fertlilizer

Increased nutrients in upper soil HorizonsArctic ecosystem extremely nutrient limitedMost Vascular plant species are mycorrhizalIncrease of nutrients = decrease mycorrhizas

Fig. 1 Percentage of ectomycorrhizal colonization of Betula rootsin the tussock tundra, Alaska, under different treatments: control(C), fertilizer addition (F), Ledum removal (LR), Ledum removal+fertilizer addition (LR+F). Error bars indicate +1 SE (n=6blocks). Bars with the same letters are not significantly different[Tukey’s honestly significant difference (HSD) test, P <0.05]

Soil AcidityArctic region dominated by Moist Arctic Tundra including

permafrostHigh soil moisture leaches cations resulting in high soil acidityThe increase of organic matter will lead to greater soil acidity

-OM forms soluble complexes with non-acid nutrient cations which can than be leached

- OM source of H+ ions as OM contains numerous acid functional groups from which these Ions can dissociate

Further reduction of Cation Exchange Capacity

SummaryGlobal Warming Effects

-Increase in Biomass and SOM

-Greater increase in decomposition than production leading to decrease Carbon in soil

- Loss of Symbiotic relationship between mycorrhizal fungi and vascular plant roots

- Increase of acidity

Hmmmmm?Will loss of Carbon stores further global warming creating a

positive feedback mechanism?

What will happen to terrestrial vegetation with the loss of mycorrhizal fungi and increasing soil acidity?

Sources Urcelay C, Bret-Harte MS, Diaz S, et al.

Mycorrhizal colonization mediated by species interactions in arctic tundra OECOLOGIA 137 (3): 399-404 NOV 2003

Mack MC, Schuur EAG, Bret-Harte MS, et al.Ecosystem carbon storage in arctic tundra reduced by long-term nutrient fertilization NATURE 431 (7007): 440-443 SEP 23 2004

Adams G. A. and Wall D. H. (2000) Biodiversity above and below the surface of soils and sediments: linkages and implications for global change, Bioscience, 50: 1043-1048.

Wolters V., Silver W. L., Bignell D. E., Coleman D. C., Lavelle P., van der Putten W., deRuiter P. C., Rusek J., Wall D. H., Wardle D. A., Brussaard L., Dangerfield J.M., Brown V. K., Giller K. E., Hooper D. U., Sala O. E., Tiedje J. M., and vanVeen J. A. (2000) Global change effects on above and below ground biodiversity in terrestrial ecosystems: interactions and implications for ecosystem functioning , Bioscience, 50: 1089-1099.

Burkins, M.B., R.A. Virginia, C.P. Chamberlain and D.H. Wall (2000) The Origin of Soil Organic Matter in Taylor Valley, Antarctica: A Legacy of Climate Change, Ecology, 81: 2377-2391.