Agriculture Reference
In-Depth Information
Milewski, 2007). Germination of many legume seeds is stimulated by compounds in
smoke.
Because it is an ancient ecosystem, parts of which have only recently been converted
to agriculture (unlike the Mediterranean Basin), it has been suggested that the SWAFR
is an ideal place to study the impacts of agriculture. Webster et al. (2007) investigated
possible exchange of pathogens between native and introduced legumes and found,
for example, that the native species
Hardenbergia comptonia
house a potyvirus that can
damage
Lupinus angustifolius
, a recently introduced crop plant. Conversely, strains of
bean yellow mosaic virus, found in various introduced species, can damage the local
legume
Kennedia prostrata
. Knowledge of such exchange of pathogens is critical for the
management of both native and introduced plants.
Although the nutrient contents of SWAFR and Mediterranean Basin soils are dif-
ferent, they have other features in common, in particular soil acidity. This, coupled
with the similar climates has meant that the Australians have mined the Mediter-
ranean Basin and other areas are for legumes and rhizobia that have potential use in
Australian agriculture, which still relies heavily on fixed nitrogen. This is an ongoing
process - for example the search for new pasture legumes (Loi et al., 2005). Recently,
workers in Western Australia have also looked at South African legumes, for example
the pasture species
Lotononis angolensis
(Yates et al., 2007), uncovering in the process
some new nodulating bacteria (see Chapters 1 and 4).
The Cape Floristic Region
The Cape Floristic Region (CFR) has even more endemic legumes than the SWAFR
(Goldblatt & Manning, 2002, chapter 1), but with little work done until recently on
their nodulation and nitrogen fixation. Of the four predominantly African tribes of
Papilionoideae (Crotalarieae, Hypocalytpeae, Indigofereae and Podalyrieae), Hypoca-
lytpeae is exclusively endemic to CFR as are all but
Calpurnia
in the Podalyrieae. There
are also many species of other legume tribes with high levels of endemism. This may be
linked to the many different niches arising from the varied topography and soil types
(Manning, 2007). Like SWAFR, CFR is also subject to fire, which is an important factor
determining floristic composition and its changes with time between fire events (Man-
ning, 2007). All legumes in the CFR (with the exception of
Schotia afra
) and SWAFR
appear to be potentially nodulated. One genus,
Cyclopia
, has several species whose
leaves are used for the production of honeybush tea (Plate 2.10). At present production
is largely on a local scale, harvesting from natural populations, but is beginning to be
developed on a farm scale.
Aspalathus linearis
is endemic to this area, but is now grown
on a large scale for an international market in rooibos (red bush) tea (Plate 2.11).
A.
linearis
grows on soils with very low concentrations of nutrients, whose uptake is aided
by the profuse production of cluster roots. Both of these teas are tannin free, a feature
used strongly in their marketing (see Section 6.4 in Chapter 6).
2.5.2 Temperate, boreal and high altitude legumes
The majority of legumes occur in temperate latitudes. Although Houlton et al. (2008)
concluded that temperature limits nitrogen fixation in higher latitudes, all legumes
