A review of dipterocarps - Center for International Forestry Research

Root Symbiosis and Nutrition
However, no data on the nature or level of mycorrhizal
infection were presented. The report by Louis and Scott
(1987) of mycorrhizal synthesis in root organ cultures
of Shorea roxburghii can be discounted as their
illustrations and descriptions do not show
ectomycorrhizas but hyphal invasion into root cells.
Moreover the fungus they used, Rhodophyllus sp. was
from a genus not normally considered to be
ectomycorrhizal.
The effects of various environmental factors on
dipterocarp ectomycorrhizas and their subsequent
effects on plant growth have been the subject of some
recent studies. Smits (1994) suggested that the obligate
nature and temperature sensitivity of the dipterocarp
ectomycorrhizal relationship are the determining factors
for good dipterocarp seedling performance. Yasman
(1995) stated that light intensity influenced
ectomycorrhizal formation in dipterocarp seedlings but
that the effects varied between different host species.
The physiology of how light regulated ectomycorrhizal
formation was, however, not examined. According to
Yasman (1995), neither light nor soil conditions
represented the main factors for successful dipterocarp
regeneration under a closed canopy; dipterocarp seedling
survival was mainly related to the presence of
mycorrhizal inoculum and the support of the seedlings
by their ectomycorrhizal connections to roots from
mother trees that had well illuminated emergent crowns.
However, this may be an oversimplification as different
species of dipterocarps have different light requirements
(Mori 1980, Sasaki and Mori 1981). Lee et al. (in press)
found high levels of ectomycorrhizal infection (60%)
on seedlings of Hopea nervosa and Shorea leprosula
under heavy shade in undisturbed forest supporting
Yasman’s (1995) hypothesis, but also found that S.
leprosula which is a light demanding species had poor
survival compared to H. nervosa which is a shade
tolerant species.
Mineral Nutrition
It must be emphasised that very few studies have been
conducted on the very important aspect of mineral
nutrient requirements of dipterocarps. Fertiliser trials
have been conducted for several dipterocarp species but
the information presently available is far from
conclusive. Although a preliminary guide for the
diagnosis of nutrient deficiency of tropical forest trees
105
has been developed (Fassbender 1988), its applicability
and suitability for dipterocarps has to be tested more
extensively.
Sundralingam (1983) found that NP fertilisers
generally improved growth of potted Dryobalanops
aromatica and D. oblongifolia seedlings. In another
experiment, Sundralingam and her co-workers (1985)
found that nitrogen rather than phosphorus was the most
important fertiliser required for improved growth of
potted Shorea ovalis seedlings. Madius (1983) found
that potted Shorea bracteolata and S. parvifolia
seedlings had improved growth and increased nutrient
uptake at higher fertiliser levels, particularly when
moisture supply was abundant. Turner et al. (1993),
however, found that potted Shorea macroptera seedlings
did not respond to fertiliser application. However, they
found that the extent of mycorrhizal infection on S.
macroptera seedlings was correlated with seedling dry
mass in the unfertilised control. Similarly, Burslem et
al. (1995) working with potted Dipterocarpus kunstleri
seedlings, found no positive growth response to nutrient
additions although addition of P increased the
concentrations of K and Ca in the leaves. Burslem and
his co-workers (1995) caution that results of pot
bioassay experiments may be dependent on factors such
as pot size, irradiance and soil moisture conditions and
that conclusions drawn from such experiments need to
be tested by field fertilisation experiments.
Turner et al. (1993) also reported that naturally
regenerated seedlings of Shorea curtisii and Hopea
beccariana did not show any significant response to
fertiliser application in the field. They suggested that
addition of nutrients to promote higher growth rates in
regenerating seedlings in dipterocarp forests is unlikely
to be a silvicultural practice although ensuring adequate
infection could be beneficial. Aminah and Lokmal (1995)
reported that outplanted rooted, stem cuttings of H.
odorata showed a significant increase in stem diameter
and height only nine to 24 months after application of
granular compound fertiliser. No growth response was
recorded when plants were measured earlier. Nussbaum
et al. (1994) found that nutrient availability was the major
factor limiting the establishment of Dryobalanops
lanceolata and S. leprosula seedlings on degraded soils
in Sabah rather than low soil moisture or high soil
temperature. Preliminary results of the effects of NPK
fertilisers on the growth of D. lanceolata and S.
leprosula on a large-scale enrichment planting project