ABSTRACT
: The objective of this study was to assess the magnitudes of the leaf allelopathy of Ulex europaeus in two different habitats, and discuss the driver of the differences, including rhizobia. The magnitudes of leaf allelopathy of the samples collected in two different habitats were assessed by comparing the hypocotyl and radicle lengths of the lettuce seeds tested on the samples. One habitat was in and adjacent to an Acasia koa forest, while the other was more than 50 m away. A. koa is indigenous to Hawaii and known to have a close symbiotic relationship with Bradyrhizobium for nitrogen-fixing. Within the past three years, U. europaeus has newly invaded both sampling sites, whereas the A. koa forest has been there for several decades. The combined result of both hypocotyl and radicle lengths of the lettuce seeds tested on both sites by linear model and multicomparison analyses showed no significant difference. But the radicle lengths of the lettuce seeds tested on U. europaeus sampled in and adjacent to the A. koa forest were significantly longer than those of the samples more than 50 m away, as measured by t-test (p = 0.05). This result suggested that the magnitude of the leaf allelopathy of U. europaeus depended on the distance of the habitat from the A. koa forest.
ABSTRACT
Bacterial communities play an important role in nutrient cycles and plant development. Their distribution and activity may depend on location and environmental heterogeneity. This study characterized soil bacterial communities in cassava fields of Eastern (Andom) and Southern (Bityili) Cameroon using molecular tools. In both sites, two improved varieties (TMS-96/1414; TMS-92/0326) and a local variety (Local) were grown in a randomized block design. Composite bulk soils were collected at 10months after planting from cassava plots. The 16S rDNA region was amplified, MiSeq was performed and sequence data analyzed. The same 17 bacterial phyla were present in both Andom and Bityili, while Chlorobi and Deinococcus-Thermus were only specific to Andom. The phyla Proteobacteria, Planctomycetes, Actinobacteria and Acidobacteria were dominant. Although both sites shared similar phyla, the principal coordinate analysis revealed significant variations in their composition, suggesting that the functions of the bacteria in nutrients cycling are likely to differ between Andom and Bityili. Cassava yields were generally higher in Andom which also displayed a higher diversity of bacterial communities. This study provides useful information on the composition of bacterial communities in cassava fields in two agro-ecologies of Cameroon. It constitutes to our knowledge the first report describing soil bacterial communities in association with cassava growth in the country, using molecular tools.
