Agriculture Reference
In-Depth Information
native to these regions are potentially nodulated (Chapter 1). Many have been used
in agriculture for centuries and thus have been well studied. Indeed, nitrogen fixation
research had its origins in these areas well over a century ago (Nutman, 1987). In spite
of this, beyond the recording of nodulation and development of inoculants for a few
species, very little is known about how much nitrogen is fixed or with which bacteria.
In the Southern Hemisphere, New Zealand has very few native legumes, but quite
a few nodulated actinorhizal plants; islands such as the Falklands (Malvinas) have
neither. Temperate Australia has a wealth of legumes, mainly acacias and endemic
papilionoid species. Both nodulation and rhizobia have been well studied in acacias,
generally with a view to their being used for land reclamation and farm forestry,
reviewed by Brockwell et al. (2005). As indicated above, there are relatively few studies
on native papilionoid legumes, although there is now an increasing interest. To date,
all endophytes have been classified as
-rhizobia, both fast and slow-growing (Lafay
& Burdon, 1998).
In the Northern Hemisphere, there is interest in North American genera that can
fix nitrogen in boreal areas. Both hosts and their rhizobia are well adapted to their
environment For example, Poinsot et al. (2001) found that a strain of
Mesorhizobium
nodulating
Oxytropis arctobia
in Northern Canada had a modification to its Nod factor
(see Chapter 5) giving cold tolerance.
Oxytropis
is one of a number of papilionoid genera
with species near or within the Arctic circle (Sprent, 2001), They are all perennial herbs,
frequently rhizomatous and rapidly generate new growth in spring. In Europe, grain
legumes are widely grown, usually nodulating effectively with local rhizobia, but there
has been little work on their nodulation since the topic edited by Jones &Davies (1983).
There is some renewed interest in pasture species for sustainable agriculture, especially
in Scandinavia where forage legumes are important for cattle, but again the number of
species covered is very limited, mainly
Trifolium repens, T. pratense
and
Medicago sativa
,
and, to a lesser extent
T. hybridum
and
Lotus corniculatus
(Frankow-Lindberg et al.,
2005). However, the total number of native legumes in Great Britain and Northern
Europe is relatively low, consisting of about 24 genera (133 spp.) from 6 papilionoid
tribes (Table 2.5)
In Asia there is now interest in some harsh areas, notably in mainland China, where
studies of native legumes on the Qinghai-Tibet Plateau and elsewhere are being carried
out (Plate 2.12). Many of these areas have a long history of agriculture and have become
degraded as a result of grazing pressure.
Vi c ia faba
has been grown in China for over
4000 years and now accounts for nearly half the world's production of this crop (Tian
et al., 2007). Different rhizobia nodulate the crop in different ecological regions. In the
Qinghai-Tibet plateau, where faba beans have been grown for only 2000 years, it is
nodulated by
Rhizobium leguminosarum
, which was also found to nodulate species of
Oxytropis
and
Medicago archiducis-nicolai
(Kan et al., 2007). These workers also looked at
nodulation in 21 legume species from the area and the nearby Loess Plateau and found
a range of rhizobia in them, These plateaux are 4000 to 6000 metres above sea level,
having low oxygen levels, high irradiation, low temperature and often also salinity.
Some of the strains isolated were tolerant of high pH and salinity. In other parts of
central Asia, there are numerous genera with species growing at altitude, but apart
from registering their occurrence, little is known about them. Table 2.6 lists some of the
genera recorded in
Legumes of Northern Eurasia
(Yakovlev et al., 1996).
