Life in the Soil - Soil: Reflections on the Basis of our Existence - page 59

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Diversity above and below ground. Mention high biodiversity and many would think of the
Amazonian rainforest and its thousands of tree species, hundreds of bird species and countless insect
species. A single leaf in the rainforest can host lichens, algae and all sorts of bugs. Scandinavian conif-
erous forests, on the other hand, are poor in species, with few plants, animals and fungi above ground.
Here, the odd birch is visible among the spruce trees, while lingonberry bushes and moss dominate on
the ground. But it is in the humus-rich soils of this type that the greatest biodiversity is to be found,
even though we have not yet managed to identify more than a fraction of all the species present
Advances in molecular biology have improved insight and understanding of this diversity.
Soil microbiologists have acquired tools to study the most prevalent species in the soil—not
only those that can be cultivated in a petri dish. The spruce forest in the photo contains around
one hundred species of mycorrhizal fungi. Boletes and brittlegills appear as mushrooms in the
autumn but live for many years as mycelia underground

The lecture insights were still with me when the Swedish Royal Academy of
Sciences in Stockholm invited me to give a lecture of my own on biodiversity in
Swedish spruce forests.
Thus I found myself standing in front of an assortment of scientific luminaries
seated in comfortable armchairs. I began by showing images from the Amazonian
rainforest, a familiar environment and home to hundreds and thousands of bird and
insect species respectively. Then I asked the audience to don a pair of special glasses
and join me on a trip below ground to explore diversity on another, much less famil-
iar, scale. Interest visibly grew as the academy members watched my images of
the rainforest's thin topsoil and near-sterile red earth lying directly beneath the fine
upper roots of the trees and their sparse covering of leaf litter. The leaves were suf-
fused with fungi, which along with bacteria decomposed the leaves and created a
supply of nutrients for the trees. Few other organisms were present in the thin soil.
We then shifted to a Swedish spruce forest, where thick blueberry scrub and a
lush layer of stair-step moss covered the ground. Amid the spruce stood a few
birches and aspens but nothing like the diverse array of tree species—thousands in
a single hectare—found in the Amazon. By contrast, the thick soil is home to a host
of fungi and bacteria—a diversity that the barren rainforest earth cannot come close
to matching. Carefully pull up the turf surrounding a boulder and you will find a
complex network of roots and hyphae. The hyphae belong to mycorrhizal fungi that
live in symbiosis with the trees. They extend the surface area of the tree roots many
times over, absorbing and transporting water and minerals to the roots in return for
access to carbohydrates synthesised by the tree. This symbiosis is different from
the mycorrhizae that developed with the first terrestrial plants, as described in the
“How is soil formed?” chapter. A far greater number of mycorrhizal species exist
in symbiosis with trees. Indeed, most of the fungi we see on a typical walk through
the forest—milk caps, boletes and chanterelles, to name some of the commoner
groups—coexist closely with trees. Some, like the birch bolete, are restricted to a
specific species; others, like the golden chanterelle, can form mycorrhizal partner-
ships with different trees. A single forest can host hundreds of different species.
Worldwide there are several thousand species of fungi that form mycorrhizal
partnerships with plants, but the number pales in comparison to microfauna like
nematodes, of which there are more than thirty thousand species, and unicellular