Document: RIC-3-67-13

Patterns of below-ground microbial community development in primary succession: A study of recently deglaciated terrain in Alaska and New Zealand.

BARDGETT, R.D.* ¹, D.A.WARDLE ² and L.WALKER ³

Lancaster University, Lancaster LA1 4YQ United Kingdom ¹
Landcare Research, Lincoln 8152 New Zealand ²
University of Nevada, Las Vagas, NV 89154-4004 USA ³

Abstract:
Many studies have examined patterns and processes of primary succession and community development that occur above-ground. However, there is a dearth of information concerning patterns of primary succession that occur below-ground, and how these changes relate to those occurring above-ground. This study aimed to examine patterns of soil microbial community development, measured by phospholipid fatty acid anaysis (PLFA), in a range of soil chronosequences of different aged geological substrates. We will present data from two classic primary successions on recently deglaciated terrain which are characterized by severe nutrient stress in later stages of succession, namely: (1) the Franz Joseph Glacier in New Zealand which encompasses > 22, 000 years of primary succession, and; (2) the Muir Glacier at Glacier Bay in Alaska, which encompasses > 14,000 years of succession. Our data reveal that, in accordance with changes in above-ground plant biomass and soil organic matter status, total soil microbial biomass (total PLFA) in the surface soil increases by 3-4 fold during primary succession from bare gravel to climax forest (i.e. spruce-hemlock forest on terrain of 230 years old at Glacier Bay and rata-kamahi forest on terrain of 1,000-5000 years old at Franz Joseph). This change in total microbial biomass is attributed to an increase in the abundance of fatty acids synthesised by gram-positive bacteria (i15:0, a15:0 and i17:0) and fungi (18:26), and is associated with a shift, over time, in the composition of the soil microbial community towards increasing fungal dominance over bacteria. The abundance of the fungal fatty acid and the ratio of fungal:bacterial PLFAs was at its highest in soils of old-growth forest (> 10,000 years old), suggesting that these later stages of succession, which are characterised by severe nutrient stress, have a microbial community that is very much dominated by fungi. The eventual replacement of old-growth forest to low-diversity bog, which occurred after some 14,000 yrs at Glacier Bay and 22,000 years at Franz Joseph, was associated with dramatic declines in total microbial biomass (total PLFA), fungal biomass (18:26) and the ratio of fungal:bacterial PLFA.

Keywords: soil microorganisms, primary succession, phospholipid fatty acids, Glacier Bay, Franz Joseph

This abstract is being presented at: 11:15 AM in session:
Oral Session #23: Soil Ecology.