A review of dipterocarps - Center for International Forestry Research

Root Symbiosis and Nutrition
in Sabah showed that increasing concentrations of
fertiliser resulted in increased growth rates but that
growth was reduced when 2000 mg of NH 4 NO 3 was
applied (Yap and Moura-Costa, in press). It will be
interesting to see the final outcome of this large-scale
field experiment.
Lee and Lim (1989) found that foliar P concentration
in naturally regenerated seedlings of Shorea curtisii and
S. leprosula growing in a logged over forest site with
low levels of available P (5.8 to 7.1 ppm) was significantly
correlated with the extent of ectomycorrhizal infection.
Lee and Alexander (1994) working with Hopea helferi
and H. odorata found positive growth responses to
mycorrhizal infection but variable responses to nutrient
treatments. They also reported the first direct
experimental evidence that ectomycorrhizal infection
improved P uptake and growth of a dipterocarp species,
H. odorata. Scleroderma dicstyosporum and S.
columnare were reported to increase levels of nitrogen,
phosphorus and potassium in seedlings of Shorea
mecistopteryx (Supriyanto et al. 1993b) but these results
may have been misinterpreted. Increased plant height
growth, diameter and dry weight as well as uptake of Fe,
Mn, Cu, Zn and Al by seedlings of Shorea compressa, S.
pinanga, S. stenoptera, H. odorata and Vatica
sumatrana inoculated with chopped fruit bodies of
Russula sp., Scleroderma sp. and Boletus sp. have been
reported in Indonesia (Santoso 1989, Santoso et al.
1989). However, it is not clear whether ectomycorrhizas
were formed by the test fungi or by contaminants.
In a study of site characteristics and distribution of
tree species in mixed dipterocarp forests in Sarawak,
Baillie and co-workers (1987) considered phosphorus
the most critical nutrient while magnesium was thought
to be important because of possible effects on the
efficiency of the dipterocarp mycorrhizal root systems.
Some species of dipterocarps, e.g. Shorea parvifolia
were consistently associated with sites of high P status
while others like S. quadrinervis were associated with
sites of low P status. Amir and Miller (1990) found
potassium to be the primary limiting nutrient in two
separate forest reserves in Peninsular Malaysia. Burslem
et al. (1994), however, are of the opinion that any of the
macronutrients and micronutrients can become
potentially limiting to plant growth when the primary
limitation by P is overcome. From a study of soils under
mixed dipterocarp forest in Brunei, Takahashi et al.
(1994) stated that logged over forests are suitable for
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enrichment planting with dipterocarps since loss of soil
nutrients and degradation of nutrient status would be small
because of nutrient accumulation in the deeper horizons.
It is known that different tree species have differing
site requirements reflecting their differing abilities to
take up nutrients from intractable soil sources due to
differences in root system architecture and in the
particular differences in the mycorrhizal relationships
between species (Miller 1991). Yasman (1995) found
that light demanding Shorea leprosula seedlings could
form many more ectomycorrhizal types than shade
tolerant Dipterocarpus confertus seedlings. Mineral
nutrition, plant light requirements and mycorrhizal
infection are very intimately related but it is only recently
that the importance of this relationship has begun to
receive recognition. Newton and Pigott (1991a) working
with oak and birch found that application of fertilisers
could reduce the number of mycorrhizal types and their
relative abundances. Lee and Alexander (1994) found that
full nutrient application prevented ectomycorrhizal
formation in Hopea odorata but not in H. helferi. This
may indirectly affect the drought tolerance of the host
plants and consequently have implications on forest
management. Burslem et al. (1994) suggested that
mycorrhizas play an important role in enabling
Melastoma to grow on very nutrient poor soils despite
being highly nutrient demanding. They suggested that for
mycorrhizal plants, limitation by the major cations may
prove more significant than limitation by P. In a more
recent study, Burslem et al. (1995) suggest that shade
tolerant seedlings of lowland tropical forest which
possess mycorrhizas are not limited by P supply because
the mycorrhizas effectively relieve them of P limitation
and/or because such plants have a low demand for
nutrients for growth at low irradiance.
It is clear that there is an urgent need for more
integrated studies on dipterocarp mineral nutrient
requirements and that such studies must take into
consideration the role of the dipterocarp mycorrhizal
association and the effect of different light regimes.
While such studies are more easily conducted in the
nursery with potted plants, there is also a need to test
the conclusions of such experiments in the field.
Research Priorities
The need for more research into the dipterocarp
mycorrhizal association is already well recognised and