INTRODUCTION
Forest and forest
products play a very important role in the development of any nation. The
utilization of forest resources range from the provision of raw materials for
the ever increasing industry to yielding poles and firewood for domestic
consumption, regulation of water regime and climate, protection from
desertification and satisfaction of recreational needs. Increase in population
and attendant increase in demand for forest and forest products have made
plantation forestry attractive to tropical foresters.
The significant
contribution of Mycorrhiza to plant is the symbiosis, which are characterized by bi-directional
movement of nutrients where carbon flows to the fungus and in-organic nutrients
move to the plant, thereby providing a critical linkage between the plant root
and soil (Garbaye, 1994). In infertile soils,
nutrients taken up by the mycorrhiza fungi can lead
to improved plant growth and reproduction, as a result mycorrhiza
plants are often more competitive and better able to tolerate environmental
stresses than non- mycorrhiza plants.
Arbuscular mycorrhiza fungi belong to the order Glomales
and form highly branched structures called arbuscules,
within root cortical cells of many herbaceous and woody plant species. Arbuscular mycorrhiza fungi (AMF)
can be found in almost all habitat and climates (Bareaet al., 1997) and at different depth of soil (Michelsen
and Rosendahl, 1990).Although the occurrence and
efficiency of AMF have been widely examined in most valuable undomesticated
fruit trees (Mathur and Vyas,
2000), little is known of the mycorrhizal status and
responsiveness of inherently slow growing indigenous timber tree species such
as Mansonia altissima
However, in tropical
agriculture systems where most soils are fragile with low fertility, a major
beneficial effect of AMF is their role in maintenance and improvement of soil
structure by their external hyphae and the production of a special protein
called the glomalin (Diedhiouet al 2003). The mechanisms involved are as follows, the growth of
external hyphae into the soil to create a skeletal structure that holds soil
particles together and the formation of a ‘sticky’ string bag of hyphae by the glomalin, which contributes to soil aggregate stabilization
(Elsenet al 2003).
It is therefore
necessary to carry out studies on the effect of drought stress and inoculation
of arbuscular mycorrhiza
and nutrient application on the seedling performance of Mansonia altissima in order to know its growth behaviour and ascertain the best way to establish them in
plantations, extensively both as mixed and single species stands. This will restore its pride of place in both
local and international markets.
MATERIALS
AND METHOD
Seeds of Mansonia altissima were
sown directly into poly pots filled with top soil collected from Forestry
Research Institute of Nigeria arboretum. The mycorrhiza
used was supplied by Agronomy Department, University of Ibadan. The
inoculations were carried out according to the method of Carling et al., 1978, Fagbola et al., 2005and Kareem et al., 2012. Also N:P:K fertilizer were added. Three (3) seeds each were sown
directly into the poly pot and were arranged in screen house of Forestry
Research Institute of Nigeria. After germination, thinning was carried out to
reduce the number of seedlings to one plant per poly pot. A 3 X 3 X 3factorial
experiment was used for the study. The treatments were replicated five times.
The factors were mycorrhiza, N:P:K
fertilizer and water supply. While N:P:K fertilizer and water supply had three
levels(N:P:K 0g, 1g, and 2g and the water supply was once in a week, twice in a
week and every day(1/7, 4/7 and 7/7 respectively), mycorrhiza
also had three levels (myco 0g,10g and 20g (Glomus deserticola).
The seedlings were watered regularly for six weeks to allow proper
establishment before the drought stress treatment commenced.
Data
were collected at two weeks intervals and the whole experiment terminated after
24 weeks. During the growth period, measurements of plant height and collar
diameter were taken while leaf number was counted.
RESULT AND
DISCUSSION
Effect of mycorrhiza on seedlings growth of M.altissima
The
mean seedlings height for mycorrhiza ranged between
15.51cm and 17.22cm.Seedlings without mycorrhiza (M1)
had the highest and seedlings inoculated with 20g of mycorrhiza
(M3) had the least value (Table 1). There were no significant differences in
seedlings height between M2 and M3 with 15.86cmand 15.51cm respectively (Table
1).
The mean seedling
diameter ranged from 3.26mm to 3.63mmwith the highest mean observed for
seedlings under 0g mycorrhiza (M1) while the least
collar diameter was observed from M2 which is 10g (Table 1)
The
leaf production increased with increase in age of the seedlings, mean leaf
production in seedlings inoculated with mycorrhiza
was 8 which indicates that there were no significant differences among the
three levels of mycorrhiza used (p>0.05) (Table 1
).
Arbuscular mycorrhiza are
obligate biotrophs and the symbiosis formed between
the host plant and fungal partner is normally mutualistic (Smith and Read,
2008). However, evidences suggest that the symbiosis can range from parasitic
to mutualistic depending on the host plant and Arbuscular
Mycorrhiza (A.M) fungal species involved (Kilronmos, 2003); soil physical, chemical and other
associated characteristics as well as environmental conditions (Diop et al.,
1994, Loth 1996, Weber and Claus 2000). Hence, an attempt to specifically
understand the contribution of introduced AMF in a controlled environment
before the prevailing conditions in the field is important. Mycorrhiza
inoculation can have positive effect (Michelsen and Rosendahl 1990, Osonubi et al., 1991, Noydet al., 1995, Fagbola et al., 2005 and Kareem et
al., 2012); negative effect (Hetricket al., 1990,
Taylor and Harrier ( 2000) or
non-significant (Manjunath and Habte,
1988) effects on the growth of plants.
In
this study, inoculation of M. altissima with G.
deserticola had no significant effect on the
growth variables assessed, which is in line with findings of (Manjunath and Habte, 1990), this
contradiction maybe due to lower physiological compatibility of G. deserticola with
Mansonia altissima since
variability in compatibility has been reported for various A.M symbiosis (Krishma et al.,
1985, Rajapakse and Miller 1987, Raoet al., 1990 and Mercy et al.,1990).
The
application of N.P.K fertilizer significantly increased the plant height,
collar diameter and number of leaves in seedlings of Mansonia altissima. This might be due to the fact
that Nitrogen is a major nutritional element required for tissue
differentiation and its role in increasing plant growth and development which
are well documented by various researchers (Shedeed et al., 1986, Aziz, 2007). Like
Nitrogen, Phosphorus is an essential constituent of the genetic material and
augments cell division (Aziz, 2007). The study clearly demonstrates the
nutritional importance of N.P.K supply to M.
altissima seedlings for better growth and
development and the results revealed application of N.P.K 1g/seedling to be
beneficial and therefore enhanced seedlings performance under tropical agroclimatic condition. The optimum level of fertilizer
requirement for a tree species like M. altissima is dynamic and changes with the age of plant.
Therefore, the fertilizer requirement studies need further long term evaluation
for different agro-ecological regions.
Water
is a significant factor in tree growth and development in the tropics (Awodola and Nwoboshi, 1993).
Water is required by plants to manufacture carbohydrate and as a means for
transportation of food and mineral elements. Various vital processes in plants
such as cell division, cell elongation stem as well as leaf enlargement and chlorophyII formation depends on plant water availability
(Price et al., 1986). The knowledge
of the response of the seedling under conditions of restricted moisture may
provide an indication of its response to increased water stress. Also, the
evaluation of the morphological and physiological growth of plants at period of
restricted moisture is useful for the isolation of plants with seedling
characteristics acceptable for afforestation in drought prone environments.
The
finding from this study revealed that watering regimes applied to the seedlings
of M. altissima
had significant effect on the seedling height, collar diameter and leaf production.
The highest value for seedling height,
collar diameter and leaf production were observed in seedlings watered everyday to pot capacity. This is in agreement with the
previous studies (Akinyele, 2007 and Ogunwande, 2014).The interaction effect of fertilizer and
watering regimes had significant effect on the growth parameters assessed.
CONCLUSION
Interaction between mycorrhiza,
fertilizer and moisture supply resulted in enhancement of growth and
development of Mansonia altissima
seedlings indicating that arbuscular mycorrhiza was not parasitic, However fertilizer was found
to exert more influence than mycorrhizain respect of
morphological characteristics of M. altissima seedlings.
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