The purpose of this study was to determinate what requirements there should be on refilling material used as soil remediation based on the soil environment, i.e. soil processes and factors important to soil-dwelling organisms. The study was conducted by investigating which parameters that is important for the soil environment and by comparing them with each other. To exemplify how the parameters may change in different locations, data for total organic carbon, dry matter (i.e. water content), and pH were analyzed from different locations before and after soil remediation. Dry matter, organic matter, pH, compaction, grain size, porosity and soil composition were found to have a significant impact on various soil processes and soil organisms. Field investigations were made to examine dry- and organic matter and pH. The results were indicating that dry matter increased and that the organic matter decreased when the area was refilled with a coarse material. This study showed that there should be requirements on the characteristics of refilling material such as; organic matter content, good water holding capacity, a pH that is as neutral as possible and that the soil should not be too compact. A conclusion from this study was that crushed rock may not be the optimal refilling material after soil remediation.

Thesis (PhD (Biochemistry))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Antagonism of antimicrobial action represents an alternative survival strategy for cohabiting soil organisms. Under competitive conditions, our group previously showed that surfactin (Srf) produced by Bacillus subtilis acts antagonistically toward gramicidin S (GS) from a cohabiting bacillus, Aneurinibacillus migulanus, causing the loss the antimicrobial activity of GS. This antagonism appeared to be caused by inactive complex formation. This study aimed to elucidate whether the previously observed antagonism of GS activity by Srf is a general resistance mechanism that also extends to related peptides such as the tyrocidines (Trcs) and linear gramicidins (Grcs) from Bacillus aneurinolyticus. Molecular interaction between the antagonistic peptide pairs was investigated using biophysical analytical methods such as electrospray mass spectrometry (ESMS), circular dichroism (CD), fluorescence spectroscopy (FS) and nuclear magnetic resonance (NMR). Results from this study corroborated the previous findings, namely that Srf antagonised the activity of GS towards Gram positive bacteria. However, for Micrococcus luteus synergism of GS action was observed at low Srf concentrations, while antagonism only occurred at Srf concentrations above the critical micelle concentration (CMC) of Srf when the bacteria were pre-incubated with Srf. This result and an ultra-performance liquid chromatography massspectrometry (UPLC-MS) study indicated that Srf pre-absorbed to cells, as well as Srf micelles interacted with GS, preventing GS from reaching the membrane target. Antagonism of GS action by Srf was also observed towards the Srf producer B. subtilis ATCC21332 and B. subtilis OKB120, a non-producer. The Srf producer was less sensitive than the nonproducer towards GS, possibly due to Srf production. Pre-incubation of Srf at different concentrations caused a dose-dependent antagonism, from as low as 0.9 μM Srf of GS activity towards B. subtilis OKB120. This antagonism at the low Srf concentration may be related to the induction of more resistant biofilms by Srf in B. subtilis. It was also found that Srf significantly improved the survival of B. subtilis OKB120 above that of M luteus in a mixed culture. In addition, the Srf producer B. subtilis ATCC21332 grew in the inhibition zone of the GS producer A. migulanus ATCC9999 during co-culturing, while B. subtilis OKB120 growth was inhibited. Srf induced biofilm formation in B. subtilis may be important in protecting the bacteria in solution, but not on solid phase such as on or in agar plates. Also, the protection of various cell types (previous studies by our group) by Srf from GS indicated a directed antagonistic Srf mode of action. Srf formed complexes that are visible and stable under ESMS conditions with GS, with the peptide bonds in the Val-Orn-Leu-D-Phe moiety of GS and the Val-Asp- D-Leu-Leu moiety of Srf protected from fragmentation. 1H-NMR titration studies strongly indicated that the molecular interaction of Srf and GS involved the re-orientation of the DPhe4,9 and Orn2,7 residues in GS. From CD spectra it was observed that Srf induced a concentration dependent decrease in the β-turn component and increase in β-sheet structures of the GS-Srf mixture. Diffusion orientated NMR (DOSY) indicated that Srf and GS formed homo-oligomers with the Srf-GS mixture having a slightly higher diffusion coefficient indicating the formation of smaller homo-oligomers or more compact hetero-oligomers. These hetero-oligomers involve intermolecular interaction at <5Å between the Orn2,7 residue of GS with Asp residue of Srf, as observed with ROESY-NMR. These results strongly indicate that inactive complex formation between Srf and GS is part of the antagonistic mechanism of action of Srf towards GS. Two high performance liquid chromatography (HPLC) methods was developed to purify peptides from the tyrothricin complex, namely the Trcs (contains one GS Val-Orn-Leu-DPhe- Pro moiety) and Grcs. These peptides were used to assess if Srf has an antagonistic activity beyond that of GS. Srf indeed showed antagonistic action against the antimicrobial activity of Trcs towards B. subtilis ATCC21332 and OKB120, with the tyrocidine C (TrcC) being more sensitive to antagonism than tyrocidine B (TrcB). Srf had an ambiguous effect on the linear gramicidin A (GA) that is co-produced with Trcs in tyrothricin. GA acted synergistically with Srf at low GA concentrations, but slight antagonism was observed at high GA concentrations. In contrast, GA showed pronounced synergism with TrcB towards the M. luteus. However, Srf at 30 μM, antagonised the synergistic action of a lethal mixture of 25 μM GA and TrcB. The Srf producer was also able to withstand and grow in the presence of the tyrothricin producer B. aneurinolyticus ATCC10068, indicating that antagonism of peptide action may allow different organisms to cohabit. Basic NMR and ESMS studies failed to show complex formation between Srf and the Trcs. However, CD presented clear evidence of Srf induced changes in secondary structures and/or higher order self-assembled structures of the Trcs-Srf mixture. FS also provided evidence of the reorientation/exposure of the Trp6 residue of the Trcs in the presence of Srf. These results corroborated the previous findings that complexation between Srf and GS or peptides analogous to GS may be part of the mechanism of Srf antagonistic action. In conclusion, this study showed that the antagonism of GS activity by Srf, conferred in part by inactive complex formation, is a putative resistance mechanism that also extends to other peptides containing the Val-Orn-Leu-D-Phe-Pro moiety such as the Trcs from B. aneurinolyticus. / AFRIKAANSE OPSOMMING: Antagonisme van antimikrobiese aksie verteenwoordig ʼn alternatiewe oorlewingstrategie vir grondorganismes wat in dieselfde habitat gevestig is. Ons groep het gewys dat surfaktien (Srf), geproduseer deur Bacillus subtilis, antagonistiese werking teenoor gramisidien S (GS) vanaf die bacillus Aneurinibacillus migulanus, onder kompeterende kondisies, toon. Die antagonistiese werking, wat moontlik veroorsaak word deur vorming van onaktiewe komplekse, lei tot die verlies van die antimikrobiese aktiwiteit van GS. Hierdie studie se doel was die ontrafeling van die moontlikheid dat die antagonisme van GS aktiwiteit deur Srf, soos deur vorige studies uitgewys, ʼn algemene weerstandsmeganisme is wat moontlik ook verwante peptiede soos die tirosidiene (Trcs) en lineêre gramisidiene (Grcs), afkomstig vanaf Bacillus aneurinolyticus, insluit. In hierdie studie is die molekulêre interaksie tussen antagonistiese peptiedpare ondersoek met biofisiese analitiese metodes wat elektrosproeimassaspektroskopie (ESMS), sirkulêre dichroïsme (SD), fluoressensie-spektroskopie (FS) en kernmagnetiese resonansspektroskopie (KMR) insluit. Die resultate wat tydens hierdie studie verkry is, het gewys dat Srf die werking van GS teenoor Gram-positiewe bakterie teenwerk, en het die vorige waarnemings ondersteun. Daar is egter sinergisme tussen Srf en GS werking by lae Srf-konsentrasies teenoor Micrococcus luteus waargeneem, terwyl antagonisme slegs waargeneem is by Srf-konsentrasies hoër as die kritiese miselêre Srf konsentrasie wanneer bakterieë vooraf met Srf met inkubeer is. Hierdie resultaat, tesame met ʼn ultra-hoë verrigting vloeistofchromatografie gekoppelde massaspektroskopie (UPLC-MS) studie, het daarop gedui dat Srf wat voorheen op selle geabsorbeer het, sowel as Srf-miselle in die media, met GS interaksie het en sodanig kan voorkom dat GS die membraanteiken bereik. Antagonisme deur Srf op die GS aktiwiteit is ook waargeneem teenoor die Srf-produseerder B. subtilis ATCC21332 en B. subtilis OKB120, ʼn nie-produseerder. Hierdie tipe antagonisme by ʼn lae konsentrasie van Srf mag verwant wees aan die induksie van meer weerstandige biofilms deur Srf in B. subtilis. Dit is ook gevind dat Srf die oorlewing van B. subtilis OKB120 aansienlik verhoog teenoor dié van M luteus in ʼn gemengde kultuur. Daar is verder bevind dat die Srf-produseerder, B. subtilis ATCC21332, in die inhibisiesone van die GS-produseerder, A. migulanus ATCC9999, gegroei het tydens kokultivering, terwyl die groei van B. subtilis OKB120 geïnhibeer is. Srf induseer biofilm-vorming in B. subtilis wat moontlik belangrik kan wees om die bakterieë in suspensie te beskerm, maar nie op soliede fase soos byvoorbeeld agar plate nie. Verder dui die beskerming van ʼn verskeidenheid sel-tipes (vorige studies deur ons groep) deur Srf teen GS, ʼn direkte antagonistiese aksie van Srf. Sigbare en stabiele komplekse tussen Srf en GS is waargeneem onder ESMS kondisies, waar die peptiedbindings in die Val-Orn-Leu-D-Phe-Pro eenheid van GS en die Val-Asp-Leu-D-Leu eenheid van Srf beskerm is teen fragmentering in die komplese. 1H-KMR titrasiestudies het duidelik aangetoon dat die molekulêre interaksie van Srf en GS die D-Phe4,9 en Om2, 7 residue in GS heroriënteer. SD-spektra van GS-Srf mengsels het daarop gedui dat Srf ʼn konsentrasieafhanklike vermindering in die β-draai komponente van die mengsel veroorsaak, maar dat β- plaat komponent van die mengsel vermeerder. Diffusie-georiënteerde KMR spektrometrie (DOSY) toon dat Srf en GS homo-oligomere vorm, maar ʼn hoër diffusie koeffisiënt vir die mengsel het aangedui dat die Srf-GS mengsel kleiner of meer kompakte hetero-oligomere. ROESY-KMR toon dat hierdie oligomere intermolekulêre interaksie(s) van <5Å tussen die Om2, 7 residue van GS en die Asp residu van Srf het. Die resultate gee ʼn sterk aanduiding dat die onaktiewe kompleks-vorming tussen Srf en GS deelneem in die antagonistiese werking van Srf teenoor GS. Twee hoë verrigting vloeistofchromatografie metodes is ontwikkel om peptiede uit die tirotrisienkompleks, naamlik die Trcs (bevat een GS Val-Om-Leu-D-Phe-Pro eenheid) en die gramisidiene (Grcs), te suiwer. Hierdie peptiede is gebruik om te bepaal of Srf antagonistiese aktiwiteit het wat verder strek as net dié van GS. Dit was inderdaad die geval en daar is gevind dat Srf antagonisties is teenoor die antimikrobiese aktiwiteit van Trcs met B. subtilis ATCC21332 en OKB120 as teikens, met tirosidien C (TrcC) wat meer sensitief vir antagonistiese werking van Srf was as tyrosidien B (TrcB). Srf het ʼn gemengde effek getoon teenoor lineêre gramisidien A (GA) wat saam met die Trcs in tirotrisien gekoproduseer word. GA het sinergisties met Srf gewerk by lae GA konsentrasies, maar milde antagonistiese werking getoon by hoë GA konsentrasies. Daarteenoor het GA en TrcB uitgesproke sinergisme getoon teenoor M. luteus. In teenstelling het Srf by 30 μM die sinergistiese aksie van die dodelike mengsel van 25 μM GA en TrcB elk geantagoniseer. Die Srf produseerder was ook bestand en kon in die teenwoordigheid van die tirotrisien produseerder B. aneurinolyticus ATCC10068 groei wat aangedui het dat die antagonisme van antibiotiese peptiedaktiwiteit die kohabitasie van organismes toelaat. Basiese KMR en ESMS studies kon nie kompleksvorming tussen Srf en die Trcs aantoon nie, terwyl SD duidelike bewyse gelewer het dat Srf verandering geïnduseer het in die sekondêre strukture en/of hoër orde/self-geassosieerde strukture van die Trc-Srf mengsel. FS het ook bewyse gelewer van die reoriëntasie/blootstelling van die Trp6 residu in die Trcs in die teenwoordigheid van Srf. Hierdie resultate ondersteun die vorige bevindinge dat kompleksvorming tussen Srf en GS of GS-peptiedanaloë deel van die meganisme van Srf se antagonistiese aksie uitmaak. Samevattend het hierdie studie getoon dat die antagonisme van GS aktiwiteit deur Srf deels toegeken kan word aan onaktiewe kompleksvorming tussen die twee peptiede en dat die voorgestelde weerstandsmeganisme ook ander peptiede wat die Val-Orn-Leu-D-Phe-Pro eenheid, soos die Trcs van B. aneurinolyticus, insluit.

Thesis (PhD (Botany and Zoology))—University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Metal pollution is a problem of increasing global concern. It could arise from industrial activities, as well as pesticide use in agriculture, among other sources. For adequate protection of the soil ecosystem from metal toxicity, the bioavailability of metals must be properly evaluated. A plethora of soil factors affect the bioavailability of metals to soil organisms. These include pH, clay and organic matter contents, salinity among others. While much is known about the influence of some of these parameters, little is known on how clay content and salinity modify the bioavailability of metals to soil organisms. This study investigated the influence of clay content and salinity on partitioning, uptake and toxicity of two essential metals (Cu and Zn) to the earthworm Eisenia fetida in separate laboratory trials. Partitioning of the metals was evaluated with 0.01 M CaCl2, DTPA (di-ethylene-triamine-penta acetic acid), and nitric acid extractions. The metal content of worms was determined by acid digestion, while growth, cocoon production, and mortality were used as endpoints showing toxicity to metals and/or salinity. To test the validity of some of the laboratory results, a field study was undertaken, using the earthworm Aporrectodea caliginosa. Further, the study assessed the effect of salinity, using a battery of laboratory tests (acute, chronic and avoidance tests) with natural and/or artificial soils on four species of organisms (a collembolan Folsomia candida, a potworm Enchytraeus doerjesi and two earthworm species E. fetida and A. caliginosa), representing different feeding patterns and ecological roles in soil. Results showed that with increased clay content, there was increased availability of Cu in the substrate, and increased toxicity to E. fetida as shown by data for mortality and growth. The situation with Zn was less significant at sub-lethal concentrations but much so at lethal concentrations. DTPA and CaCl2 extracted metals revealed changes in partitioning of Cu and Zn with changes in clay content, but this trend was not always consistent. Both DTPA and CaCl2 revealed increased availability of Zn in substrates with increased salinity. Salinity had an additive to synergistic effect with Zn in toxicity to E. fetida. When combined with Cu, salinity also increased the availability of Cu as shown by CaCl2 extracted fraction, and had additive effect on toxicity of Cu to the earthworm. The field study did not succeed in in iv confirming the results of the laboratory study due to confounding role of flooding after heavy rainfall and subsequent leaching of salts and Cu. The results of the experiment on acute and chronic toxicity tests for NaCl on E. fetida showed LC50 of 5436 mg/kg NaCl and EC50 for growth and cocoon production of 4985 and 2020 mg/kg NaCl. These values showed that earthworms might be negatively affected in many soils containing fairly moderate concentrations of salts. Similarly, A. caliginosa could not survive in natural soil containing relatively low salt concentrations (EC = 1.62 dS/m) while reproduction was severely affected at lower EC value of 0.52 dS/m. F. candida and E. doerjesi could survive in the highest salinity soil (EC = 1.62 dS/m) used in this study but their reproduction was severely affected from 1.03 dS/m. Overall, it appears that of all the taxa used, earthworm species were the most sensitive to saline stress and could proof useful in determining ‘safe levels’ of salt in contaminated soils. The results of the avoidance test showed that A. caliginosa avoided both natural and artificial saline soil containing concentrations lower than those avoided by E. fetida. The conclusion is that the influence of clay content and salinity on the bioavailability of Cu and Zn depends largely on the metal in question, but generally speaking, bioavailability and toxicity of the metals were reduced with increased clay content while the opposite was true for salinity. If the species used in this study can be seen as fairly representative of a wide range of soil organisms, the conclusion is that salinisation of soil will be detrimental to most soil organisms at relatively low saline concentrations. Given the role of beneficial soil organisms in several soil processes which in turn contribute to soil fertility and sustainable use of land, it is recommended that any farming practices that may lead to an increase in salt content of agricultural soils should be discouraged. / AFRIKAANSE OPSOMMING: Metaalbesoedeling is ‘n probleem wat toenemende globale kommer veroorsaak. Dit kan ontstaan as gevolg van industriële aktiwiteite sowel as van plaagmiddelgebruik in die landbou en ander bronne.Ten einde die grondekostelsel genoegsaam te beskerm, moet die biobeskikbaarheid van metale ge-evalueer word. ‘n Verskeidenheid van grondfaktore be-invloed die biobeskikbaarheid van metale vir grondorganismes Hulle sluit onder andere in pH, klei, organiese inhoud en soutgehalte. Hoewel heelwat bekend is oor die rol van sommige van hierdie parameters, is min bekend oor hoe klei en soutgehalte die biobeskikbaarheid van metale vir grondorganismes kan modifieer. Hierdie studie het die invloed van kleiinhoud and soutgehalte op die verdeling/partisie, opname en toksisiteit van twee essensiële metale (Cu en Zn) vir die erdwurm Eisenia fetida in afsonderlike laboratoriumproewe ondersoek. Kompartementele verdeling van die metale is geevalueer deur middel van ekstraksie-metodes met 0.01 M CaCl2, DTPA (di-etileentriamien- penta asysnsuur), en salpertersuur ekstraksies. Die metaalinhoud van wurms is bepaal deur suurverterings en spektrofotometriese analises te doen terwyl groei, kokonproduksie en mortaliteit van organismes gebruik is as gevoeligheidseindpunte om toksisiteit van metale en soutgehalte aan te toon. Om die geldigheid van somige van die laboratoriumresultate te toets, is ‘n veldstudie ook onderneem met die erdwurm Aporrectodea caliginosa. Die effek van soutgehalte is verder ondersoek deur ‘n battery van laboratoriumtoetse met vier spesies (‘n kollembool Folsomia candida,’n potwurm Enchytraeus doerjesi en twee erdwurmspesies E. fetida en A. caliginosa), wat verskillende voedingspatrone verteenwoordig. Die resultate het getoon dat met toenmende klei-inhoud was daar ‘n toename in die beskikbaarheid van Cu vir opname vanuit die substraat, asook ‘n toename in toksisiteit vir E. fetida soos deur die gegewens vir mortaliteit en groei uitgewys. Die situasie met Zn was minder betekenisvol by subletale konsentrasies en selfs baie minder so by letale konsentrasies. DTPA en CaCl2 ge-ekstraheerde metale het veranderinge in die partisie/verdeling van Cu en Zn uitgewys met verandering in klei-inhoud, maar die tendens was nie altyd konstant nie. Beide DTPA en CaCl2 ekstraksie het toenemende beskikbaarheid van Zn in substrate uitgewys met toenemende soutinhoud. Soutinhoud het ‘n additiewe/toegevoegde tot sinergistiese vi toksisiteitseffek saam met Zn vir E. fetida. In kombinasie met Cu het soutgehalte ook die geskatte biobeskikbaarheid van Cu verhoog soos uitgewys deur die CaCl2, geekstraheerde fraksie, en het ‘n additiewe effek gehad op die toksisitiet van Cu vir die erdwurm. Die veldstudie kon nie die resultate van die laboratoriumstudie bevestig nie weens die belemmerende rol van vloede na swaar reënneerslae en daaropvolgende uitloging van soute en Cu. Die resultate van die eksperimentele ondersoek na die akute en chroniese effekte van NaCl op E. fetida het ‘n LC50 van 5436 mg/kg NaCl en EC50 vir groei en kokonproduksie van 4985 en 2020 mg/kg NaCl opgelewer. Hierdie waardes het aangetoon dat erdwurms moontlik negatief beinvloed kan word in baie gronde wat ‘n redelike gemiddelde konsentrasie van soute bevat. Soortgelyk kon A. caliginosa nie oorleef in natuurllike grond wat relatief lae soutkonsentrasies bevat het (EC=1.62 dS/m) nie terwyl voortplanting sterk ge-affekteer is by ‘n lae EC waarde van 0.52 dS/m. F. candida en E. doerjesi kon oorleef in die grond met die hoogste soutgehalte (EC= 1.62 dS/m) maar hulle voortplanting is ernstig geknou vanaf 1.03 dS/m. In geheel blyk dit dat van allle taksa wat gebruik is, erdwurms die sensitiefste was vir die stres wat deur soutgehalte veroorsaak is. Die kennis kan nuttig wees in die bepaling van “veilige vlakke” van sout in gekontamineerde gronde. Die resultate van die vermydingstoetse het getoon dat A. caliginosa beide natuurlike en kunsmatig versoute gronde vermy het by konsentrasies wat heelwat laer was as dié wat deur E. fetida vermy is Die gevolgtrekking is dat die invloed van klei en soutgehalte op die biobeskikbaarheid van Cu en Zn grootliks afhanklik is van die metale wat betrokke is en dat biobeskikbaarheid en toksisiteit normaalweg verminder het met verhoogde klei-inhoud, met die teenoorgestelde wat waar was in die geval van soutgehalte. Indien die spesies wat in die studie gebruik is beskou kan word as redelik verteenwoordigend van ‘n wye reeks van grondorganismes, is die gevolgtrekking dat versouting van gronde nadelig sal wees vir meeste grondorganismes, selfs by relatief lae soutkonsentrasies. In die lig van die rol wat nuttige grondorganismes speel in verskeie grondprosesse wat bydraend is tot grondvrugbaarheid en volhoubare gebruik van gronde, word dit aanbeveel dat enige boerderypraktyk wat mag lei tot verhoging van die soutinhoud van landbougronde ontmoedig moet word.

Les plantations d'Eucalyptus, au Congo (région de Pointe-Noire) comme au Maroc (forêt de la Maâmora), soulèvent des controverses quant à leurs effets sur des sols sableux pauvres en matière organique. Dans un enjeu de développement durable de tels écosystèmes anthropiques, les recherches sur le sujet se sont multipliées. Toutefois, les connaissances relatives au fonctionnement biologique des sols sous ces plantations méritent encore d'être approfondies. Principaux acteurs de ce fonctionnement biologique, les organismes vivant dans ces sols et leurs activités ne sont que trop peu décrites, et nécessitent en ce sens de se trouver au cœur des études sur le sujet. Notre travail de thèse s'inscrit dans ces problématiques. Ainsi, nous évaluons les conséquences du reboisement sur les communautés de la macrofaune et des microorganismes de ces sols, et également l'activité des enzymes clés liées aux principaux cycles biogéochimiques (C, N et P).Cette recherche présente la particularité de la prise en compte simultanée de deux facteurs peu souvent évoqués, que sont, l'« âge des plantations » et la « profondeur du sol ». Nous avons abordé ces questions par une étude multi-échelle.Ainsi, nous avons étudié les macroinvertébrés quant à leur diversité taxonomique et à leur composition verticale, selon une approche combinée (TSPF + carré anglais). Par la suite, les premières caractérisations de structure et de diversité des communautés microbiennes ont été réalisées. Ceci, par mesure de densité et par déterminations morphotypiques (cultures in vitro) et génétiques (DGGE), au niveau des communautés totales. Par mesure du potentiel métabolique pour ce qui est des communautés fonctionnelles (plaques Biolog). Enfin, l'activité biologique des sols a été évaluée en mesurant l'activité de huit enzymes et l'activité microbienne globale (hydrolyse FDA).Ainsi, par comparaison à la forêt naturelle adjacente, cette étude nous a permis de mettre en évidence que l'introduction d'eucalyptus sur savane (Congo) ou sur chêne-liège dégradé (Maroc), modifie la structure et la diversité des communautés de la macrofaune et des microorganismes du sol ainsi que le profil des activités enzymatiques. Aussi bien en fonction de l'âge des plantations que de la profondeur du sol, ceci est valable. C'est le fonctionnement biologique qui se trouve donc impacté.Les proportions et les conséquences de cet impact restent toutefois particulières à chaque cas. Il faut cependant noter exception pour les activités enzymatiques liées au cycle de l'azote, qui apparaissent influencées de façon comparable dans les deux cas à l'étude. Ces activités diminuent significativement avec l'âge du peuplement, confirmant le statut déficitaire en azote de ce type de plantation. / Eucalyptus plantations in Congo (Pointe-Noire region) and in Morocco (Mamora forest) raised certain controversies regarding their effects on the sandy poor soils. In such anthropogenic ecosystems, researches on the subject have multiplied in order to ensure their sustainable management. However, knowledge on the biological functioning of soils in these plantations still needs to be explored. Main actors of this biological functioning are soil organisms and their activities which have been described very little, and need to be more studied. Our thesis encompasses this problematic. Therefore, we evaluated the impact of reforestation on the communities of macrofauna and microorganisms of soil, and the activity of different key enzymes, as well, related to main biogeochemical cycles (C, N and P). This research presents, particularly, a simultaneous consideration of two factors rarely mentioned before: the "age of the plantations" and "soil depth". We addressed these issues by a multi-scale study. We studied macroinvertebrates by their taxonomic diversity and vertically composition by a combined approach (TSPF + English square). Subsequently, the characterization of structure and diversity of microbial communities was done by density measurements, morphotype-specific (in-vitro culture) and the genetic determinations (DGGE) and by measuring the metabolic potential in terms of functional communities (Biolog plates). Finally, soil biological activity was evaluated by determining the activity of eight different enzymes and the total microbial activity (FDA hydrolysis).Therefore, as compared to the adjacent natural forest soils, this study allowed us to demonstrate that the introduction of eucalyptus plantations, in savanna (Congo) or in degraded cork oak ecosystem (Morocco), alters the structure and diversity of macrofauna communities, soil microorganisms and the enzymatic activity profiles. Consequently, the biological functioning of the soils is impacted both in terms of the age of plantations and soil depth. However, the proportions and the consequences of this impact were very specific in each case, with the exception of enzymatic activities related to the nitrogen cycle, which influenced comparatively in both studies. These activities decreased significantly along with the stand age of eucalyptus plantations, confirming the deficient status of nitrogen in such plantations.

No description available.