EFFECT OF REGULATING THE RED/FAR-RED LIGHT RATIOS BY SHADING ON SEEDLINGS OF MILICIA EXCELSA AND NAUCLEA DIDERRICHII
* ANJAH, G. M., *FOCHO D. A., *ANNIH M.G., ** KUM, C. K.
*Department of Plant Biology, Faculty of Science, University of Dschang. Dschang- Cameroon.
** Mathematics/Computer Science Department, Faculty of Science, University of Dschang. Dschang- Cameroon
abstract
Four week old seedlings of Milicia excelsa (A. CHEV) C.C BERG and Nauclea diderrichii (DE WILD and TH. DUR) were transferred from germination boxes to polypot bags to observe some growth parameters under varying red/far-red light ratios. These red/far-red light were regulated by shading the various replicate treatments. Three levels of shade were applied. The first lot were not shaded and registered a red/far-red light ratio of 0.99 lux/m2. the second lot were partially shaded and had a ratio of 0.61 while the third lot were totally shaded giving a ratio of – 1.325. Recording were done using a SKR instrument, in units of lux/m2.
The best results for both species were obtained for treatment with no shade. Seedlings were tallest but the least leaf number and leaf area under total shade for both species. M. excelsa seedling however had the highest survival percentage.
Analysis of variance confirmed that the differences between the species and light treatments was significant. This indicates that the species responded differently to the different treatments.
Key words: Red/Far-red, Complete shade, Partial shade, Total shade, Photoblastic, Canopy, Forest gap.
RESUME
Les jeunes plants de Milicia excelsa (A. CHEV). C.C BERG et Nauclea diderrichii (DE WILD and TH. DUR) ages de quatre semaines étaient transférré de la boite de germination au sac de polyplot pour observer quelques parameters de croissance sous des proportions rouge/rouge-lointain varies. Ces proportions rouge/rouge-lointain étaient obtenues par ombrage varié. A cet effet, trois niveau d’ombrage étaient retenus. Le premier lot n’était pas ombré, ce qui correspond à un ration de rouge/rouge-lointain de 0.99 lux/m2. Le second lot, partiellement ombré correspondait à un ratio de 0.631 lux/m2. Enfin, le troisième lot, totalement ombré donnait une proportion de –1.325 lux/m2.
Les meilleurs résultats pour les deux espèces furent obtenus avec le traitement sans ombrage. Les plantules de ce lot avaient une taille maximale
Les analyses de variance ont confirmé que les différences entre les espèces et les régimes de lumières étaient significatives et ont aussi montré que les interactions entre les espèces et les traitements de lumières étaient également significatives. Ce qui indique que les espèces répondaient différemment aux différents traitements.
Mots clés: Rouge/rouge-lointain, ombrage total, ombrage partiel
INTRODUCTION
Keay (1965) defined the forest as vegetation dominated by woody species in open or closed canopy from which grasses are virtually absent. The forest canopy is continually changing as trees grow up, die are replaced at the climax stage. Replacement is usually in the forest gaps. A forest gap here is a space in the above-ground canopy to or almost to ground level (Robert 1980). When the gap is created, many changes in the environment occur and the size of the gaps determines how extreme the changes can be. The changes include alteration on the light intensity and quality, temperature, competition of moisture, humidity and nutrient availability.
Evans (1960) termed the phenomenon of seeds responding to light as photoblastism. Seeds whose germination is stimulated by light are said to be positively photoblastic while those response is inhibited by light are negatively photoblastic. The visible spectrum of light ranges from wavelength of between 400 nm to 760 nm each of which reflects a different colour. Blue light has a wavelength of between 430 nm and 510 nm while that of red light is about 660 nm; yellow 600 nm and far-red 700 to 760 nm. These wavelengths play an important role in germination and seedling establishment in gaps. Plant remove the blue and the red lights and transmit the far-red light. Thus leaves exposed to sunlight will have a richer quantity of light than those in the dark.
Thus within the forest community, positively photoblastic seeds will be stimulated to germinate and establish successfully where a gap is created as a result of light which is richer in red light than the far-red light. When the seedlings are under the shade of other species especially under a green leafy canopy, the light which filters through this canopy becomes rather pour in red light and relatively richer in far-red light thus inhibiting seedling establisment.
The ration of red/far-red light at which most positively photoblastic seedlings establish under a closed forest canopy is however not known for more species.
A knowledge of this ratio for some pioneer photoblastic species like Milicia excelsa and Nauclea diderrichii would have a practical value in designing the degree of canopy opening to stimulate establishment of these seedlings.
Milicia excelsa (A. Chev.) C.C. Berg is a member of the Moraceae family. It is a large sometimes deciduous high forest tree. It measures up to 60 m in height and is about 2.5 m in diameter. It is a straight cylindrical bole of about 30 m. the bark, the leaves and oozing latex all have uses in local medicine (FAO 1986). The yellowish brown wood is durable and fairly resistant to fire and decay (Burkill 1985). Nauclea diderrichii De Wild and Th. Dur. is a lowland forest species measuring about 40 m tall with girth of 2.2 m. Branches are often horizontal and whorled. The bole clears up to 30 m. It is a member of Rubiaceae family (Gills 1988, Burkill 1988).
Materials and Methods
The experimental site was the green house of the Department of Forest Resources Management, University of Ibadan. A SKR instrument with number SKR100-06903194 calibrated for sensor was used for recording daily red/far-red light ratios.
Black polipot bags were filled with forest soil collected from the Gambary forest reserve. They were 18 in number and 2 for each replicate under each treatment. They were perforated at the base and sides to allow free respiration.
The first level of treatment and its replicate in the green house were not shaded; the second were partially shaded using three layers of green plastic netting combined with a layer of white plastic polythene bags while the third and its replicates were totally shaded with black polythene plastic bags.
Three seedlings each of about 4 weeks were transplanted from germination boxes into one polypot bag for each treatment and the following growth parameters observed on a weekly basis:
· Shoot height (cm)
· Leaf area (cm2)
· Number of leaves
A meter rule was used to measure the heights of seedlings. The leaf area was measured by tracing the entire number of all the leaves on one seedling on graph paper, counting the number of squares and then calculating the mean of all the leaves. Leaf number was determined by counting the number of leaves of each seedling.
DESIGN
We used a 2-factor factorial design. The effects of species and red/far-red ratios of light were monitored on the early establishment of seedlings.
RESULTS
SHOOT HEIGHT
It was observed that for both two species, there a gradual increase in seedling height from week one to week six. Seedlings under no shade or control showed a slower rate of increase in shoot height while those under partial shade and complete shade showed a faster rate. However, shoots under the control treatment were sturdier, more healthy and erect compared to those under partial shade which were weaker, frail and tended to wilt. Most seedlings under complete shade died off in just about a week after transplanting.
These results are summarized in table I and figures I and II are histograms for the average shoot height of M. excelsa and N; diderrichii per week respectively. The histograms show that the peak for Milicia is recorded under complete shade during the third week and this height remains constant for the rest of the weeks. The peak for Nauclea is recorded during the sixth week under partial shade while seedlings under complete shade maintain a constant peak of 0.92 cm from week 2.
Leaf area
Seedlings of M. excelsa and N. diderrichii growing under no shade had the highest leaf areas for all the six weeks.
The leaf areas for the two species for this period under three treatments are shown in table II.
Leaf number
There a gradual increase in leaf number off Milicia from week 1 to week 4 under no shade and under partial shade. Ther was no increase under complete shade were seedlings wilted off after the first week of growth. Changes in leaf number for the two species are presented in table III.
The histograms III and IV show that the increase in leaf number depends on the light ratio for Milicia while no shade and partial shade do not effect much change in leaf number for Nauclea.
Table I: Shoot height (cm)
WeekSpecies / Treatment / Red/far-red / 0 / 1 / 2 / 3 / 4 / 5 / 6
M. excelssa
/ No shade / +0.99 / 0 / 2.4 / 2.64 / 2.9 / 3.16 / 3.4 / 3.64Partial shade / +0.631 / 0 / 2.79 / 3.15 / 3.56 / 4.06 / 4.5 / 4.85
Complete shade / -1.325 / 0 / 4.1 / 4.9 / 5.0 / 5.0 / 5.0 / 5.0
N. diderrichii
/ No shade / +0.99 / 0 / 3.9 / 0.43 / 0.46 / 0.48 / 0.52 / 0.55Partial shade / +0.631 / 0 / 0.71 / 0.78 / 0.86 / 0.93 / 0.99 / 1.062
Complete shade / -1.325 / 0 / 0.92 / 0.95 / 0.95 / 0.95 / 0.95 / 0.95
Table II: Leaf area (cm2)
WeekSpecies / Treatment / Red/far-red / 0 / 1 / 2 / 3 / 4 / 5 / 6
M. excelssa
/ No shade / +0.99 / 0 / 0.7 / 1.12 / 1.61 / 2.08 / 2.48 / 2.98Partial shade / +0.631 / 0 / 0.3 / 0.67 / 1.00 / 1.31 / 1.59 / 1.94
Complete shade / -1.325 / 0 / 0.15 / 0.15 / 0.16 / 0.16 / 0.16 / 0.16
N. diderrichii
/ No shade / +0.99 / 0 / 0.14 / 0.17 / 0.21 / 0.24 / 0.27 / 0.31Partial shade / +0.631 / 0 / 0.15 / 0.16 / 0.18 / 0.21 / 0.23 / 0.25
Complete shade / -1.325 / 0 / 0.17 / 0.07 / 0.07 / 0.07 / 0.07 / 0.07
Table III: Leaf number
WeekSpecies / Treatment / Red/far-red / 0 / 1 / 2 / 3 / 4 / 5 / 6
M. excelssa
/ No shade / +0.99 / 0 / 5 / 6 / 7 / 7 / 8 / 9Partial shade / +0.631 / 0 / 4 / 4 / 5 / 6 / 7 / 8
Complete shade / -1.325 / 0 / 2 / 2 / 2 / 2 / 2 / 2
N. diderrichii
/ No shade / +0.99 / 0 / 2 / 4 / 4 / 6 / 6 / 6Partial shade / +0.631 / 0 / 2 / 4 / 4 / 6 / 6 / 6
Complete shade / -1.325 / 0 / 2 / 2 / 2 / 2 / 2 / 2
ANALYSIS OF VARIANCE RESULTS
Table IV: Shoot height
Source of variation / d.f / Sum of squares / Mean sum of squares / FcalBetween species / 1 / 87.9156268 / 87.9156268 / 518.0218*
Between treatments / 2 / 7.832274667 / 3.916137334 / 23.0749*
Interaction between species and treatments / 2 / 2.840950233 / 1.420475117 / 8.3698*
Error / 30 / 5.09142370 / 0.169714123
Total / 35 / 103.6802754
Table V: Leaf area
Source of variation / d.f / Sum of squares / Mean sum of squares / FcalBetween species / 1 / 6.9169 / 6.9169 / 37.8508*
Between treatments / 2 / 4.865716667 / 2.432858334 / 13.3131*
Interaction between species and treatments / 2 / 9.67940003 / 1.839725002 / 10.0674*
Error / 30 / 5.482223333 / 0.182741111
Total / 35 / 103.6802754
Table VI: Leaf number
Source of variation / d.f / Sum of squares / Mean sum of squares / FcalBetween species / 1 / 11.11111111 / 11.11111111 / 6.66667*
Between treatments / 2 / 100.66666670 / 50.33333335 / 30.2000*
Interaction between species and treatments / 2 / 8.22222219 / 4.111111095 / 2.4667**
Error / 30 / 50.000 / 1.666666667
Total / 35 / 170.000000
· = significant at 1%
** = not significant at 1%
INTERPRETATION OF RESULTS
At the 1% level of significance, the variation in growth height between species and between light regimes (treatments) were both significant. The variation due to interaction between species and light regimes was also significant (Table IV).
The variation in leaf area between species, light regimes and due to the interaction effect between species and light regimes were all significant (Table V).
In case of leaf number, only the variation between treatments was significant (Table VI).
DISCUSSION AND CONCLUSION
Milicia excelsa and Nauclea diderrichii are both indigenous fast growing species (Keay R. W, Onochi C.F. 1965). In the forest these species appear more or less isolated or in clumps of few trees. Nauclea seeds all year round. The fruits are usually green when not mature and then change to orange at maturity.
Light is required by plants because it provides energy during photosynthesis for the manufacture of food. This energy storing process involves the conversion of light energy to the chemical energy stored in carbohydrate from which it can be released in the form useful for vital activities of living things. In the absence of light, sufficient energy is not available, then the seedlings growing under such conditions are usually devoid of enrgy. Consequently they lack sufficient food to sustain them and therefore etiolate (Kiew 1982).
Seedlings of Milicia and Nauclea growing under a red/far-red treatment of 0.99 were studier, erect and hard. They had shorter lengths but with more uniform shoots. With constant watering, they grew and established more firmly in the soil. Seedlings of treatment 0.631 were taller but looked very frail and tiny. This is because the amount of red light was not sufficient to produce an adequate food supply (Hess 1975). Improper watering caused the seedlings to be uprooted indicating weak establishment in the soil. Seedlings under treatment –1.325 died off after one week.