Differences in soil texture (which helps inform us about water holding capacity) and soil pH (which tells us something about nutrient availability) are two key ways in which soils might differ from Point A to Point B. So, plants that require free-drainage (like many Banksia in southern Australia that are found primarily on deep, acidic sands) probably won't do very well when they try to establish on poorly-draining clays.
But soils don't just provide nutrients and water. They are also the reservoir of soil biota that includes important groups such as mycorrhizal fungi.
Mycorrhizas are associations between fungi and plant roots that can be beneficial to both the plant and the fungi. The fungi link the plant with soil by acting as agents of nutrient exchange. The fungi receive carbohydrates as energy from the host plant root whilst nutrients such as phosphorus and zinc are passed back into the plant roots from the soil. Mycorrhizal associations may also reduce attack from root pathogens and increase the tolerance of the plant to adverse conditions such as heavy metals, drought, and salinity. In general, mycorrhizas play an important role in plant productivity.
It got me to thinking. How important are mycorrhizal associations when plant disperse to new soils? Could their absence (from the new soil types) inhibit colonisation potential of species trying to track their climate envelope shift?
While we know that mycorrhizal associations are important in plant communities (work in ecological restoration, for instance, has shown that some species are incredibly hard to re-establish if mycorrhizae are missing from the rehab site), it is hard to find much evidence for their existence in the plants I work with in southern Australia. In particular, what about the importance of mycorrhizal fungi for short-lived plants like annuals.
|Hyalosperma praecox - one of the annual species|
I work with in grassy woodlands.
The starting place to even begin to answer this question has to be: do annual plants form mycorrhizal associations in soils in the short-time that they are active? Using some old fashioned techniques (germinating annuals in their 'native' soil, then extracting them 4 weeks later, preparing roots by staining and using a microscope), we've recently found that many annual plants do indeed form mycorrhizal associations. This is the first study of its kind on grassland annuals in Australia, so rather exciting news.
|Vesicles and hyphae, shown here by the staining, in a root |
of the annual daisy Triptilodiscus pygmaeus
(Photo: Rohan Ball)
Of the eight species we surveyed (all in the Asteraceae), we can confidently say that the roots of six species were colonised by VAM within 4 weeks of germination. You can see VAM in the photos as dark, stained areas - both vesicles and hyphae stain here quite clearly. We are not yet sure what growth advantage this gives these developing plants, but we think it points to an interesting set of experiments. For instance, would VAM form in plant roots grown on 'non-native' soils (i.e. soils that are very different to those the species currently occur on)? If we remove VAM from the 'native' soil, does this affect growth and reproduction? Such questions are important because they have an applied outcome: are VAM necessary for annuals to recolonise agricultural lands? Will the lack of VAM affect colonisation potential of native species that disperse to new areas?