Dissertation (PhD (Bosb))--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: This study was conducted to evaluate and compare the water and nutrient relations of three
indigenous deciduous tree species, viz., Cordia africana Lam., Croton macrostachyus Del.,
Millettia ferruginea (Hochst.) Baker and two widely planted eucalypts, viz., Eucalyptus
camaldulensis Dehnh and Eucalyptus globulus Labill from Ethiopia. The study was organized as
glasshouse and field observations in Ethiopia. Owing to the lack of baseline studies on the water
and nutrient relations of the deciduous tree species, the glasshouse experiments involved a wide
range of water and nutrient applications. Seedlings were grown with the supply of various levels of
water and nutrients during which gas exchange, water potential, relative water content, tissue
nutrient content and biomass production were measured. The field observations were limited to the
study of surface root distribution and leaf nutrient composition of mature trees and their effects on
soil nutrient pool. The observations were made on isolated trees and mixed or pure stands of trees
in Badessa area, Eastern Ethiopia. The field site was selected because of the availability of the
study species and suitability of the trees for the study.
In the glasshouse, increased water deficit significantly reduced predawn leaf water
potential, relative water content, stomatal conductance, photosynthetic rate, whole plant water use
efficiency, plant height, diameter, leaf area and biomass production. Both of the eucalypts did not
grow faster than the deciduous species under well-watered conditions unlike under water stress
conditions. C. macrostachyus and C. africana had higher transpiration rates and tissue nutrient
accumulations than the other species. They also demonstrated higher biomass allocation to roots
than all the other species to support the intensive water and nutrient uptake rate. Due to the ability
to re-orient its leaves to avoid direct solar irradiance, M. ferruginea maintained higher tissue water
potential and relative water content than all the other species under water stress regimes.
The impact of imposed drought was quick and more damaging to the eucalypts compared
to the deciduous tree species indicating that the eucalypts may not survive extreme drought
conditions unlike the deciduous species that drop their leaves and may remain dormant for weeks.
The current study gave new experimental proof that E. globulus was more vulnerable to drought
than E. camaldulensis.
Soil N stress resulted in an overall reduction of tissue N concentration, N:P ratio,
photosynthetic rate, stomatal conductance and photosynthetic water use efficiency in all the species
studied. Pants with high foliar nitrogen concentration had higher photosynthetic capacities
indicating that N plays a key role in photosynthesis and growth of all the studied species. The
current study showed that for all the tree species, more attention has to be given to soil N than to P
as soil P had minor effects on the photosynthetic activities of plants of all species compared to N.The investigation on tissue nutrient composition confirmed that N:P ratio could be used to detect Plimitation
in plants. However, N:P ratio could not distinguish between N-limitation and combined
limitations of N and P.
The study of isolated C. africana and C. macrostachyus trees on soils in Badessa, Eastern
Ethiopia indicated improved soil N, P and K under tree canopies whereas no effects were observed
on the other soil nutrients studied. Similar to glasshouse conditions, C. macrostachyus and C.
africana produced extensive surface roots, interfering with crops grown in association. Due to their
high nutrient cycling potential the net effect on soil was positive. Comparison of E. camaldulensis
woodlot and a mixed stand composed of deciduous species indicated that the fine root biomass in
the surface soil under E. camaldulensis was about three times that under the mixed stand. The fine
root biomass of E. camaldulensis inside the stand and 10 meters away from the stand were
comparable in the surface soils showing the presence of root competition with adjacent crops.
Therefore, planting of E. camaldulensis in association or adjacent to croplands should be avoided.
Nutrient and carbon pool of soil inside the mixed stand was generally higher than that of E.
camaldulensis indicating that trees of the mixed stand recycled more nutrients to the soil. / AFRIKAANSE OPSOMMING: Die doel van hierdie studie was om die verskille tussen water- en voedingstofverhoudings van drie
inheemse blaarwisselemde boomsoorte te vergelyk, viz., Cordia africana Lam., Croton
macrostachyus Del., Millettia ferruginea (Hochst.) Baker en twee bekende eucalyptus spesies, viz.,
Eucalyptus camaldulensis Dehnh en Eucalyptus globulus Labil van Etiopië. Die studie het bestaan
uit kweekhuis- en veldobservasies in Etiopië. As gevolg van beperkte navorsing ten opsigte van
water- en voedingstofverhoudings in bladwisselende boomsoorte, het die kweekhuis-eksperimente
bestaan uit 'n wye verkeidenheid water- en voedingstoftoetse. Saailinge is gegroei deur
verskillende vlakke van water- en voedingstowwe by te voeg. Gaswisseling, waterpotensiaal,
relatiewe hoeveelheid water, hoeveelheid voedingstowwe en produksie van biomassa is gemeet.
Die veldobservasies was beperk tot oppervlak-wortelverspreiding en blaarvoedingstof hoeveelhede
van volwasse bome, sowel as die effek op grondvoedingstowwe. Observasies was beperk tot
geïsoleerde, gemengde en een spesie opstande, in die Badessa area, Oos Etiopië. Die studiearea was
gekies op grond van die voorkoms van die gekose boomsoorte, sowel as die toepaslikheid van die
bome vir die studie.
In die kweekhuis is gevind dat die verhoogte watertekort die pre-sonop
blaarwaterpotensiaal, relatiewe hoeveelheid water, stomatiese geleiding, fotosintetiese tempo,
heelplant water-gebruikseffektiwiteit, plant hoogte, diameter, blaararea en biomassa produksie
beduidend verminder het. Nie een van die eucalyptus spesies het vinniger as die bladwisselende
spesies onder voldoende hidrasie gegroei nie. Dit was egter nie die geval onder die waterbeperkte
toestande nie. C. macrostachyus en C. africana het ‘n hoër transpirasie tempo sowel as
weefselvoedingstof waardes gehad as die ander spesies. Hierdie boomsoorte se wortelbiomassa
was ook meer as die ander spesies, om vir die tempo van water- en voedingstofopname te
akkomodeer. As gevolg van die vermoë om blare te kan oriënteer om direkte sonlig te vookom,
het M. ferruginea ‘n hoër water-weefselpotensiaal en relatiewe waterinname gehad in vergelyking
met die ander boomsoorte in beperkte water toestande.
Die impak van gëinisieerde droogte het vinnig voorgekom en het meer skade aan die
eucalyptus aangerig in vergelyking met die bladwisselende boomsoorte. Dit dui aan dat die
eucalyptus-spesie nie ekstreme droogte kan oorleef nie, waar bladwisselende spesies hul blare laat
afval en vir weke aan een dormant kan bly. Hierdie studie gee eksperimentele bewyse dat E.
globulus minder bestand is teen droogte as E. camaldulensis.
Beperkte N in die grond het veroorsaak dat daar ‘n algemene vermindering van weefsel Nkonsentrasie,
N:P ratio, fotosintetiese tempo, stomatiese geleiding en fotosintetiese watergebruiks
effektiwiteit in al die bestudeerde spesies was. Plante wat oor hoër blaar-stikstofkonsentrasiesbeskik, het hoër fotosintetiese kapasiteite wat aandui dat N ‘n belangrike rol in fotosintese en die
groei van al die bestudeerde spesies speel. Die oorhoofse bevindings van die studie was, dat daar
meer aandag gegee moet word aan grond-N as P omdat grond-P net ‘n kleiner rol speel in die
fotosintetiese aktiwiteite van plante van al die spesies in vergelyking met N. Die ondersoek na
weefselvoedingstof hoeveelhede het bewys dat die N:P ratio gebruik kan word om P-tekorte in
plante aan te dui. Die N:P ratio kan egter nie die verskil in N-tekorte en gekombineerde tekorte van
N en P aandui nie.
Die studie van die geïsoleerde C. africana en C. macrostachyus bome op grondtipes in
Badessa, Oos Etiopië het verbeterde grond-N, P en K onder kroondak gebiede getoon, daar was
egter geen verskille in die ander grondvoedingstowwe wat bestudeer is nie. In toestande
gelykstaande aan die van die kweekhuis, het C. macrostachyus en C. africana meer
oppervlaksswortels ontwikkel. Die toename aan oppervlakswortels het ingedring op gewasse wat in
assosiasie gegroei is, dit het egter ‘n positiewe effek op die grond gehad as gevolg van die hoë
voedingstof-siklus-potensiaal. Die E. camaldulensis opstand is gevergelyk met ‘n gemengde
opstand van bladwisselende spesies waar daar gevind is dat die fynwortel biomassa in die
oppervlak grond onder die E. camaldulensis ongeveer drie keer soveel was as die van onder die
gemengde opstand. Kompetisie met aangrensende gewasse is aangeui deurdat die fynwortel
biomassa van E. camaldulensis binne die opstand en 10 meter weg van die opstand vergelykbaar
was in die oppervlakgronde. Dit dui dus aan dat die plant van E. camaldulensis in assosiasie of
aangrensend aan gewasse vermy moet word. Die teenwoordigheid van voedingstowwe en koolstof
in die grond van die gemengde opstand was oor die algemeen hoër as die van die E. camaldulensis.
Dit is ‘n aanduiding dat die bome van die gemengde opstand meer voedingstowwe aan die grond
verskaf.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16050 |
| Date | 12 1900 |
| Creators | Gindaba, Jiregna |
| Contributors | Rozanov, A., Negash, Legesse, University of Stellenbosch. Faculty of Agrisciences. Dept. of Forest and Wood Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | x, 180 leaves : ill. |
| Rights | University of Stellenbosch |
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