INTRODUCTION

In 1903, the explorer Robert Scott was one of the first humans ever to see the dry valleys of Antarctica. He called them ‘valley(s) of the dead’ in which ‘we have seen no sign of life, … not even a moss or lichen’. A century later, we know that the soils and rocks are home to many microscopic organisms that Scott could not have seen.

The dry valleys are part of the small percentage of the land surface of the Antarctic continent that is ice-free, amounting to about 4000 km2, and thus have rock and soil surfaces that can be colonized by terrestrial organisms. They are an ancient polar desert, perhaps as much as 2 million years old, located in Victoria Land between about 77 and 79° south (Fig. 1). The valleys are in a precipitation shadow caused by the Transantarctic Mountains, which rise over 4000 m. The Antarctic dry valleys are now recognized as one of the harshest terrestrial environments on Earth, characterized by summer maximum temperatures that rarely exceed 0 °C and only a few tens of millimetres of precipitation, most of which falls as snow and is ablated by strong winds carrying dry air from the polar plateau - potential evaporation far exceeds precipitation (Fig. 1).

SUMMARY

1. In many ecological studies, soil carbon is regarded as a barely differentiated whole with little attention paid to its underlying characteristics.

2. Although it is widely appreciated that decomposer organisms are nearly infallible as degraders of organic molecules, there are marked differences in the utilisation of different components of organic matter by organisms depending on chemical and physical characteristics, location and availability in time in soil.

3. We discuss the characteristics of soil carbon as a substrate and emphasise a ‘soil metabolomic’ approach for characterising the range of molecules in complex, composite substrates, and the potential that stable isotope probing offers for linking organisms to their substrates via enrichment of their biomolecules as they exploit isotopically enriched substrates.

4. Using selected examples, we examine the influence of the chemical characteristics/quality, quantity, location and timing of supply of organic matter on the amount, activity and, where possible, the diversity of soil organisms.

5. We are some way from unifying relationships between the quality, quantity, location and timing of delivery or availability of soil carbon on the size, activity and diversity of soil organisms. However, we point ways forward in which the information on the physics, chemistry and management are linked to the biology of soils.

Introduction

Currency of soil carbon

Humans view soil carbon in various physical (e.g. aggregates, density fractions), chemical (e.g. carbohydrates, aromatic compounds), biological (e.g. microbial biomass) and even economic (e.g. dollars per tonne or carbon credits) ways which are not usually ecological.