Search

Slash-and-burn cultivation in the humid tropics can cause changes in the composition of topsoil, depending on the duration of the fallow. We studied differences between practices, using the small-volume micromorphological method, to quantify the distribution of solid components in the topsoil, concentrating on plant organs and biogenic structures created by soil animals. We compared samples of topsoil from five plots, two at Maripasoula, an Aluku village along the Maroni river (French Guiana), with short fallow (= 8 years), and the other three at Elahe, a Wayana village along the same river, with long fallow (= 25 years). At both sites structures created by arthropods other than ants gave way to ones formed by ants and annelids under the influence of fire and cultivation. This change was more abrupt under long fallow, because of the time needed to restore the arthropod community. Charcoal and charred plant material were incorporated by earthworms into the mineral soil, forming dark grey to black aggregates. Charcoal became mixed with the mineral soil faster at Elahe than at Maripasoula, where it accumulated in the topsoil. The reason seems to be an imbalance between charcoal inputs (from repeated fires) and the capacity of burrowing animals (earthworms, ants) to mix it with the mineral soil. [ABSTRACT FROM AUTHOR]

Abstract: In the humid tropics, slash-and-burn cultivation causes changes in the composition of soil biota communities. We investigated the soil macroinvertebrates (body length mm) in five sites, two at Maripasoula, an Aluku village along the Maroni river (French Guiana), with short fallow ( years), and the other three at Elahe, a Wayana village along the same river, with long fallow ( years). We report observed species richness, the corresponding estimates by bootstrap and its associated standard deviation. At both sites the cultivation led to impoverished communities. The overall observed species richness i.e. diversity was ca. twice as larger in Elahe than in Maripasoula. The landscape at Maripasoula was dominated by highly disturbed areas with the direct consequence that local species richness relied on colonization from an impoverished regional species pool. On the contrary, in Elahe, crops formed small patches scattered across a landscape essentially constituted of rich undisturbed or slightly disturbed forests hence higher diversity. The proportion of rare species ranged from 44% to 54%. We found 6 indicator species amongst which 5 were associated to the old secondary forest in Elahe and one, the earthworm Pontoscolex corethrurus was associated to crop fields in Maripasoula (short fallow system). Results are discussed in a landscape context in terms of conservation and management of soil macrofaunal diversity in agro-ecosystems. [Copyright &y& Elsevier]

Inselbergs are hills rising abruptly from the surrounding plains where cyanobacteria are the only living organisms under conditions of intense solar radiation. A survival mechanism to prevent UV-damage has been associated with synthesis of the ultraviolet-screening, photostable sheath pigment scytonemin. The organic extract of Scytonema sp., collected on the Mitaraka inselberg, French Guyana, yielded three new pigments, tetramethoxyscytonemin (1), dimethoxyscytonemin (2), and scytonine (3), derived from the scytoneman skeleton of scytonemin. These structures were assigned mainly on the basis of (1)H and (13)C NMR and MS experiments.