Rainer Schultze-Kraft

Phytoremediation in the Tropics—The Effect of Crude Oil on the Growth of Tropical Plants

ABSTRACT Phytoremediation is a nondestructive, cost-effective in-situ technology to clean up contaminated soils. In the case of contamination with petroleum hydrocarbons, plants enhance microbial degradation of the contaminant in the rhizosphere. The potential of this technology for the tropics should be high due to prevailing climatic conditions favoring plant growth and stimulating microbial activity. Investigations of the potential of tropical plants for phytoremediation, however, are scarce. The present work studied two grasses and six legumes from the eastern savannah of Venezuela on their reaction to crude oil contamination in soil. Results shall help to identify plants with a potential for phytoremediation and subsequent studies. Seedling emergence and biomass production were determined for plants growing in soil contaminated with 0%, 3%, and 5% heavy crude oil. Contamination had, in general, a tendential but not significant negative influence on seedling emergence. Dry matter production was reduced by only a few percent to up to 85%. Furthermore, in some legumes inhibition of nodulation was observed. The grass Brachiaria brizantha and the legumes Centrosema brasilianum and Calopogonium mucunoides are promising for phytoremediation because in contaminated soil they combined high seedling emergence with least affected biomass production. Since they are cultivated forage/soil cover species also in other regions of the tropics, their potential for phytoremediation of petroleum contaminated soils extends beyond Venezuela.

Potential of vetiver (Vetiveria zizanioides (L.) Nash) for phytoremediation of petroleum hydrocarbon-contaminated soils in Venezuela

Venezuela is one of the largest oil producers in the world. For the rehabilitation of oil-contaminated sites, phytoremediation represents a promising technology whereby plants are used to enhance biodegradation processes in soil. A greenhouse study was conducted to determine the tolerance of vetiver (Vetiveria zizanioides (L.) Nash) to a Venezuelan heavy crude oil in soil. Additionally, the plants potential for stimulating the biodegradation processes of petroleum hydrocarbons was tested under the application of two fertilizer levels. In the presence of contaminants, biomass and plant height were significantly reduced. As for fertilization, the lower fertilizer level led to higher biomass production. The specific root surface area was reduced under the effects of petroleum. However, vetiver was found to tolerate crude-oil contamination in a concentration of 5% (w/w). Concerning total oil and grease content in soil, no significant decrease under the influence of vetiver was detected when compared to the unplanted control. Thus, there was no evidence of vetiver enhancing the biodegradation of crude oil in soil under the conditions of this trial. However, uses of vetiver grass in relation to petroleum-contaminated soils are promising for amelioration of slightly polluted sites, to allow other species to get established and for erosion control.

Influence of fertilizer levels on phytoremediation of crude oil-contaminated soils with the tropical pasture grass Brachiaria brizantha (Hochst. ex A. Rich.) Stapf

Determination of fertilizer levels in phytoremediation of petroleum hydrocarbons is a complex issue, since nutrient demands of the plant and of degrading microorganisms in the rhizosphere have to be considered. In the present work, three fertilizer levels were tested in a greenhouse experiment with the aim of optimizing growth of the tropical pasture grass Brachiaria brizantha and enhance microbial degradation of heavy crude oil in soil. Fertilizer was applied twice in a concentration of 200, 300, and 400 mg each of N, P, and K per kg soil before and after the first sampling (14 wk). The medium fertilizer concentration resulted in best root growth and highest absolute oil dissipation (18.4%) after 22 wk. The highest concentration produced best shoot growth and highest relative oil dissipation after 14 wk (10.5% less than unplanted control). In general, degradation of total oil and grease was higher in planted than in unplanted soil, but differences diminished toward the end of the experiment. Next to fertilizer quantity, its composition is an important factor to be further studied, including the form of available nitrogen (N-NO 3 − vs. N-NH 4 +). Field trials are considered indispensable for further phytoremediation studies, since greenhouse experiments produce particular water and nutrient conditions.

Land Degradation on Barren Hills: A Case Study in Northeast Vietnam

The term “barren hills” has been a keyword for land degradation in the uplands of Vietnam for over a decade. Nevertheless, the “barren” land is still not adequately ecologically characterized. In this work, we analyze land use-induced changes in vegetation and soil properties along a sequence of barren hills types formed on one physiotope. The study is undertaken in the Bac Kan province, one of the poorest upland regions where livestock plays an important role. A transition from an old-growth laurel forest to a sparse manmade grassland is characterized by a total of 177 species, rapid species turnover, and discrete dominants, and an overwhelming effect of disturbance history on both soil and vegetation patterning. Land degradation is most apparent in land use-induced maintenance of arrested successions, and the regeneration course is shifted towards drier formations. We hypothesize a conceptual model as an aid to understanding the process of early fallow differentiation in response to the patterned, fine-scale disturbances. The larger-scale implications of the observed trends in regeneration potentials deviation, and, in particular, the effect of water buffaloes in halting fallow successions, are discussed.

Phenological, agronomic and forage quality diversity among germplasm accessions of the tropical legume shrub Cratylia argentea

SUMMARYCratylia argentea (Desv.) O. Kuntze is a drought-tolerant tropical shrub legume that can helpto ensure continuity of forage supply in smallholder systems either through direct grazing or as acut-and-carry plant for fresh foliage or silage. A collection of 38 accessions was characterized agro-nomically and nutritionally. High diversity was detected between accessions. Time to floweringranged from 217–329 days after transplanting seedlings to the field and from 129–202 days aftercutting. Flowering is probably induced by reduction of day length. Seed production was high butvariable. Dry matter production ranged from 190–382 g/plant in the rainy and from 124–262 g/plantin the dry season, content of in vitro digestible dry matter from 589–690 g/kg, crude protein contentfrom184–237g/kgandfibrecontentfrom403–528 g/kg(neutraldetergent fibre,NDF),240–335 g/kg(acid detergent fibre, ADF), and 9–13 g/kg (acid detergent fibre-bound nitrogen, N-ADF).Accessions CIAT 18674 and CIAT 22406 were identified as promising for further study. They weresuperior to the commercial cultivar in terms of dry matter (DM) production, particularly in the dryseason. Further research is required to determine the prevailing reproduction strategy of C. argenteaand to quantify outcrossing-rates. Multilocational trials with a selected set of accessions should beconducted under different environmental conditions.INTRODUCTIONLivestock productivity in the tropics is severelyaffected in the dry season by low availability andquality of fodder (NAS 1979; Ranjhan 1986;Enri´quez et al. 2003). High-protein legumes, in par-ticular shrub species, can contribute to improvedproductivity of livestock during dry seasons and atthe same time maintain and even restore soil fertility(Brewbaker 1986; Schultze-Kraft & Peters 1997;Peters et al. 2001; Shelton 2001). Cratylia argentea(Desv.) O. Kuntze (syn. C. floribunda Benth., Diocleaargentea Desv.) is a shrub legume which was selectedas promising for dry-season supplementation, par-ticularly in regions with acid soils and extended dryseasons(Argel MArgelLPeters & Schultze-Kraft 2002).Cratylia argentea belongs to the familyLeguminosae, subfamily Papilionoideae, and is themostwidely distributed ofthe fivespecies in the genus(de Queiroz & Coradin 1996; Pizarro et al. 1997). Theleafy shrub usually reaches 1.5–3 m, but there aretrees up to 10 m tall. It is found in a broad range ofhabitats from Western Peru to the state of Ceara´ inBrazil, and is well adapted to acid soils of low tomedium fertility and altitudes up to 1200 m asl(Xavieretal.1995;Maass1996;Schultze-Kraft1996;Peters & Schultze-Kraft 2002). Its nutritive value ishigher than thatof most other shrublegumes adaptedto acid soils. Plants contain only trace amounts oftannins(Lascano1996;Shelton2001).Ithasexcellentregrowthcapacityaftercuttingandcanbeusedassoilcover, mulch and green manure. The species is verydrought tolerant and remains green and productive

RAPD variation among North Vietnamese Flemingia macrophylla (Willd.) Kuntze ex Merr. accessions

Flemingia macrophylla (Willd.) Kuntze ex Merr., a multi-purpose legume with potential as dry-season forage crop, mainly occurs in subhumid to humid environments of tropical and subtropical Asia. Despite increasing interest in conservation of germplasm suitable for low-input production systems information on the genetic diversity of F. macrophylla is extremely scarce. The creation of baseline data is supposed to contribute to more efficient conservation management and to identify collecting strategies of novel germplasm. Random amplified polymorphic (RAPD) markers were used to investigate the genetic variation among 37 F. macrophylla accessions. Germplasm analysed in this study originated from Bac Kan province, Northeast Vietnam. Eight primers generated a total of 47 amplified RAPD loci of which 38 were polymorphic. Jaccard’s similarity coefficients among accessions ranged from 0.069 to 1 with a mean of 0.67. The UPGMA dendrogram revealed three clusters along with three outliers. No correspondence between geographic and genetic distance was found (Mantel test: Rxa0=xa00.21; Pxa0=xa00.016). Analysis of molecular variance (AMOVA) revealed significant (Pxa0<xa00.001) differentiation between accessions collected in lowland and upland regions. Results of UPGMA clustering were confirmed by the pattern of principle coordinates analysis (PCO) plotting. Future collecting strategies should target populations at large distances and along the altitudinal range. Ex situ conservation should encompass those accessions that showed genetic divergence. In situ conservation may consist of establishing a system of interconnected population fragments to guarantee continuing genetic exchange via corridors and of rehabilitating degraded habitats.

Extent and structure of genetic diversity in a collection of the tropical multipurpose shrub legume Cratylia argentea (Desv.) O. Kuntze as revealed by RAPD markers

The tropical multipurpose shrub legume Cratylia argentea is well adapted to acid soils of low to medium fertility and has excellent drought-tolerance. Due to its high nutritive value it is particularly suited as forage for dry-season supplementation. A collection of 47 C. argentea accessions in a collection, derived from seed replicating of original accessions with differing geographic origin and morphological and agronomic characteristics was investigated using molecular markers (RAPD (random amplified polymorphic DNA)). Genetic diversity ( H T = 0.145) in the collection was low, with 30% of differentiation among groups and high genetic similarity among accessions ( GS = 0.805). Within-accession variability was high. One taxonomic mismatch and five possible duplicate accessions were identified. Our results suggest that the genetic diversity in the C. argentea accessions studied is relatively homogeneously distributed, indicating the likelihood of extensive outcrossing. The genetic diversity of original accessions should be assessed to determine if outcrossing has occurred during or before ex situ storage. This might also support any decision on whether accessions should be bulked rather than maintaining them individually.

The effect of mixing prunings of two tropical shrub legumes (Calliandra houstoniana and Indigofera zollingeriana) with contrasting quality on N release in the soil and apparent N degradation in the rumen

Lack of synchronization between N released from prunings applied to the soil as green manures and crop uptake as well as optimization of protein digestibility for ruminants, remain major research objectives for the selection of multipurpose tree and shrub legumes (MPT) for mixed smallholder systems in the tropics. Prunings of the high tannin, low quality MPT Calliandra houstoniana CIAT 20400 (Calliandra) and the tannin free, high quality MPT Indigofera zollingeriana (Indigofera) were mixed in the proportions 100:0, 75:25, 50:50, 25:75, and 0:100 (w/w) in order to measure the aerobic rate and extent of N release in a leaching tube experiment, and the anaerobic extent of N degradation in an in vitro gas production experiment. Parameters measured in Calliandra:Indigofera mixtures were compared to theoretical values derived from single species plant material (i.e. 100:0 and 0:100). Aerobic N release and apparent anaerobic N degradation increased with increasing proportion of the high quality legume (Indigofera) in the mixture. While N release in the soil was lower than theoretical values in the mixture 50% Calliandra/50% Indigofera, this was not the case with apparent anaerobic N degradation with the same mixture. Aerobic N immobilization was more pronounced for the mixture 75% Calliandra/25% Indigofera than for 100% Calliandra and negative interaction was observed with apparent anaerobic N degradation in the mixture 75% Calliandra/25% Indigofera. Plant quality parameters that best correlated with aerobic N release and apparent anaerobic N degradation in the rumen were lignin + bound condensed tannins (r=−0.95 and −0.95 respectively, P<0.001). In addition, a positive correlation (r=0.89, P<0.001) was found between aerobic N release in the leaching tube experiment and apparent N degradation in the in vitro anaerobic gas production experiment. Results show that mixing prunings of MPT materials with contrasting quality is an effective way to modify aerobic N release pattern as well as apparent anaerobic N degradation and could possibly be applied to minimize N losses in the rumen and in the soil. In addition, apparent anaerobic N degradation was identified as good predictor of aerobic N release in the soil, which has resource saving implications when screening MTP to be used as green manures.

EARLY ADOPTION OF THE TROPICAL FORAGE LEGUME ARACHIS PINTOI IN HUETAR NORTE, COSTA RICA

SUMMARY The legume Arachis pintoi has a number of characteristics which enable it to make a valuable contribution to the development of sustainable and productive pastures in the tropics. It was introduced to Costa Rica for this reason, in 1987. The objective of this study was to analyse the adoption of A. pintoi as a forage legume in Huetar Norte, a region in the north of Costa Rica. The adoption process was analysed to identify the contributory factors and to make recommendations for measures which could be taken to promote the process. To collect the data, 115 randomly selected livestock holders and an additional 34 farmers known to have planted A. pintoi were interviewed. Farmers see improved pastures to be the most important technology to enhance forage and cattle production. It was confirmed that A. pintoi is a potential improved pasture alternative. Although A. pintoi was well known, the adoption rate was low. Lack of availability of seed, technical assistance and information about the use and management of A. pintoi hinder adoption. Difficulties in establishment and maintenance were also recorded.

Analysis of Genetic Variation Among Accessions of Pueraria montana (Lour.) Merr. var. lobata and Pueraria phaseoloides (Roxb.) Benth. based on RAPD Markers

Pueraria montana var. lobata and P. phaseoloides originating from tropical Asia and parts of Oceania are ecologically and economically important legumes that are used as green manure, cover crop or forage plants. Conservation and use of plant genetic resources require an understanding of the extent and distribution of genetic diversity in any given region. In this study, genetic variation of five P. montana var. lobata and 16 P. phaseoloides accessions was analysed developing a random amplified polymorphic DNA (RAPD) marker methodology for Pueraria species and thereby creating basic data for follow-up research and the development of conservation strategies. Seeds were collected from native populations in Bac Kan Province, a mountainous region in Northeast Vietnam. P. montana var. lobata presented a high level of variation with 54.3% of the detected markers being polymorphic, whereas P. phaseoloides exhibited an intermediate to high level of variation (45.5%). The P. montana var. lobata accessions clustered in congruence with their eco-geographical origin. For P. phaseoloides no correspondence between sampling sites and genetic differentiation was found. Inter-population differentiation was measured as Jaccards similarity coefficient (JSC). Mean JSC amounted to 0.35 in P. montana var. lobata and 0.52 in P. phaseoloides. Results are compared to other genetic studies of herbaceous legumes and conservation strategies are suggested.