Literature review: Impact of Chilean needle grass ... - Weeds Australia

Like vascular plant diversity, community richness appears to be highly dependent on past management. Morgan (2004) found
that sites burnt at 1-2 yr intervals had lower diversity in the bryophyte mat than those burnt at 4-20+ year intervals, apparently
due to loss of mosses. The liverworts Fossombronia intestinalis Taylor and Lethocolea pansa (Taylor) G.A.M.Scott and
K.Beckmann, and the moss Rosulabryum billardieri (Schwaegr.) Spence occurred at all sites and were considered to be adapted
to fire at all frequencies. Morgan (2004) found a strongly significant positive correlation between the cover of T. triandra and the
species richness of the bryophyte mat, but no correlation with vascular plant species richness.
Based on observations of ungrazed and grazed native grassland reserves and experimental studies by other workers Scarlett
(1994 p. 127) determined that the cryptogam crust in T. triandra grasslands “delays the establishment of some alien weeds and
minimises their cover/abundance when they are already established”. In south-eastern Australia, invasions of Holcus lanatus,
Briza maxima, Bromus hordeaceus and Vulpia spp. are facilitated by crust damage. Soil crusts dominated by brypophytes have
been found to delay or inhibit germination of some plants by affecting the penetration of light and its spectral characteristics, and
through leachates, and the crusts also maintain a more humid environment at ground level. They increase the time a seed spends
above ground, increasing its probability of predation, dessication or destruction by fire, although awned seeds, including those of
N. neesiana, are less affected. They also could be expected to restrict root growth of any seedlings that do germinate (Scarlett
1994). Davies (1997) noted that seeds of native plants are generally better adapted to penetrating cryptogam crusts than those of
many grassland weeds.
The commonest components of the soil crust in Victorian volcanic plains grasslands include the prostrate leafy and thallose
liverworts Riccia spp., F. intestinalis, F. pusilla and L. pansa, the mosses R. billardieri, Fissidens spp., Tortella calycina, and the
squamulose lichen Cladia sp. (Scarlett 1994, Morgan and Rollason 1995, Morgan 2004). Large mosses including Bruetelia
affinis, Triquetrella papilata and Campylopus clavatus occur mainly around the bases of T. triandra tussocks and create denser
cover, while Polytrichum juniperinum and various liverworts occur on stony rises. The basalt rocks are occupied by thallose and
crustose lichens. Drier sites tend to have a crust dominated by crustose lichens and algae (Scarlett 1994). Thick moss mats are
relatively rare and there is relatively little variation in composition of the crust over the 500-600 mm rainfall zone (Scarlett
1994). Non-vascular plants accounted for 25% of plant diversity at Evans St., Sunbury (Morgan and Rollason 1995), 28% at six
sites surveyed by Morgan (2004) and 13.5% for the Victorian basalt plains flora as a whole (Willis 1964).
The non-lichenised fungi constitute another diverse element of the biota but little specific information related to Australian
native grasslands appears to be on record. Fuhrer (1993) noted that some species are restricted to grasslands and recorded
Lycoperdon spp. and Xerula australis (H. Dorfelt) R.H. Peterson from grasslands. Slime moulds (Protocista: Myxomycota) are
similarly poorly known. Most fungi species are very small, a high proportion are undescribed and identification is difficult. Öster
(2008) concluded from a study of semi-natural grasslands in Sweden that there was probably low congruence bewteen vascular
plants and grassland fungi and that some grasslands with low plant richness can have high macrofungi richness. Many plant
pathogenic fungi occur on grassland plants, notably on grasses, which are infected by a range of smuts, rusts and endophytic
fungi.
Endophytic grass fungi
Grass endophytes, Neotyphodim spp., have not been found in 13 genera of Australian native grasses investigated, including T.
triandra, Microlaena stipoides, Austrodanthonia spp., Chloris spp., Poa spp. and Bothriochloa macra, except for an unknown
species in Echinopogon ovatus (G. Forst.) P. Beauv. and Neotyphodium-like hyphae in herbarium species of other Echinopogon
species (Aldous et al. 1999).
A Tilletiopsis Derx. fungus, related to smut fungi, has been isolated from seeds of Austrodanthonia pilosa (R.Br.) H.P. Linder;
an Acrodontium De Hoog. sp. from seeds of Chloris ventricosa R.Br., a species similar to Neotyphodium from seed of
Austrodanthonia racomosa (R.Br.) H.P. Linder, and the seed-transmitted Atkinonella hypoxylon (Peck) Dell is common on a
range of Austrodanthonia spp. (Aldous et al. 1999).
Soil microflora
The soil microflora of the temperate native grasslands of south-eastern Australia also appears to have been little investigated.
Such floras consist mainly of bacteria and fungi that decompose organic matter and those that form symbiotic relationships with
plants (Keane 1994). The vast majority of plants form sysmbioses with soil fungi via their roots, known as mycorrhizae. Many
grasses and herbs form vesicular-arbuscular mycorrhizae with zygomycetes, that are characterised by “little bush-like growths
inside the root cells and large, swollen vesicles within the roots”(Keane 1994 p. 132). The fungi have never been grown in pure
culture and they benefit by gaining sugars from the plant while assisting plant P uptake. Orchids form more complicated
symbioses with Rhizoctonia fungi. Legumes form associations with Rhizobium bacteria that are important N fixers. Some herbs
and liverworts form associations with cyanobacteria that are capable of fixing atmospheric N (Keane 1994). The soil also
contains parasitic microbes which can cause new plant disease problems when the soil is disturbed. Manipulation of the soil
microflora is widely practiced in agriculture, but has been little investigated in Australian native vegetation, except in regard to
orchids (Keane 1994). Exotic soil microbes may be important in south-eastern grasslands, but the best known species in
Australia Phytophthora cinnamomi does not appear to cause problems.
Exotic plant components
The criterion of