Ecology and biology of Hydrozetes paulista (Acari: Oribatida) in the benthic zone of a temporary lake in Brazil

Oribatid mites are mainly terrestrial animals, but some are aquatic, including all species of the genus Hydrozetes (Hydrozetidae). They have often been recorded in abundance on the water’s surface, while their presence in the benthic zone is poorly documented. A litterbag experiment was carried out in Coutos Lake, a shallow temporary lake in Southeast Brazil, in order to study the ecology and biology of Hydrozetes paulista. This mite species greatly dominated the benthic invertebrate community (82%), and at the end of the experiment it reached a density (652 individuals per 1 g of dry substrate) higher than that ever previously reported before for any Hydrozetes species. This density was correlated with some water parameters, stronger with conductivity, and less with temperature. The adults dominated in the stage structure (constituting over 80% of sample population), but the participation of the juveniles increased with the time. Larvae were first noticed on 25th day of experiment and after that were present for the rest of the season. During the course of this experiment, mite fecundity and body size decreased. This species is known as bisexual, but we observed only females in the 5354 adults we collected.

Response of Organic Matter Decomposition to No-Tillage Adoption Evaluated by the Tea Bag Technique

Organic matter (OM) decomposition is a fundamental ecosystem service in conservation agriculture, but the response of this process to the conversion from conventional tillage (CT) to no-tillage (NT) systems is not fully understood, especially during the transition period. Here, using a litterbag experiment (tea bag technique), we studied OM decomposition in a chronosequence of NT fields of different ages since conversion from CT (1 to 7 years) around Beauvais (northern France). We found that, in contrast with physico-chemical soil properties, the decomposition of both high quality (green tea) and low quality (rooibos tea) organic matter was significantly correlated with the NT age. Irrespective of the OM quality, the OM mass losses linearly increased with the time span since conversion from CT to NT. Taken together, our results suggest that adopting NT practices provides more favorable habitats for microorganisms involved in OM decomposition.

FOREST LITTER DECOMPOSITION AS AFFECTED BY EUCALYPTUS STAND AGE AND TOPOGRAPHY IN SOUTH-EASTERN BRAZIL1

Forest litter decomposition is a major process in returning nutrients to soils and thus promoting wood productivity in the humid tropic. This study aimed to assess decomposition of eucalypt litter in the Rio Doce region, Brazil. Leaf litter was sampled under clonal eucalypt stands aged 2, 4 and 6 years on hillslopes and footslopes. Soil and soil+litter samples were incubated at two levels of soil moisture, temperature and fertilization. C-CO2 emissions from soil measured during 106 days were higher at 32 °C than at 23°C, mainly for the 2-yr-old stand on footslope. When leaf litter was added on soils, C-CO2 emissions were eight times higher, mainly on footslopes, with no effect of stand age. Leaf decomposition in situ, assessed with a litterbag experiment showed a mean weight loss of at least 50% during 365 days, reaching 74% for 2 yr-old stands on footslopes. In comparison with data from the native forest and the literature, no apparent restrictions were found in eucalypt litter decomposition. Differences between in vitro and in situ results, and between eucalypt and native forest, were most likely related to the response of diverse decomposer communities and to substrate quality.

The responses of early foliar litter humification to reduced snow cover during winter in an alpine forest

Ni, X., Yang, W., Li, H., Xu, L., He, J., Tan, B. and Wu, F. 2014. The responses of early foliar litter humification to reduced snow cover during winter in an alpine forest. Can. J. Soil Sci. 94: 453–461. Snow cover can be reduced by ongoing winter warming in alpine biomes, affecting foliar litter humification, but few reports are available. To quantitatively clarify how early foliar litter humification responds to reduced snow cover in winter, a field litterbag experiment was conducted in an alpine forest in southwestern China. Mass losses, ΔlogK, E4/E6, degrees of humification and humification rates of six typical local foliar litters were investigated at the snow formation, snow cover and snow melt stage under snowpack levels differing in depth (deep snowpack, medium snowpack, thin snowpack, no snowpack) from November 2012 to April 2013. The results indicated that 14–15% of willow (Salix paraplesia), 8–9% of fir (Abies faxoniana), 6–7% of birch (Betula albo-sinensis), 5–8% of cypress (Sabina saltuaria), larch (Larix mastersiana) and azalea (Rhododendron lapponicum) foliar litter was humified, which was about 50% of what decomposed during the first winter. Moreover, the early humification of foliar litter (except for fir and birch) responded positively to the reduced snow cover, but mass loss exhibited negative responses. Such results suggest that reduced snow cover in winter would increase soil carbon or other material sequestration in the scenario of climate change.

Test of validity of a dynamic soil carbon model using data from leaf litter decomposition in a West African tropical forest

We evaluated the applicability of the dynamic soil carbon model Yasso07 in tropical conditions in West Africa by simulating the litter decomposition process using as required input into the model litter mass, litter quality, temperature and precipitation collected during a litterbag experiment. The experiment was conducted over a six-month period on leaf litter of five dominant tree species, namely Afzelia africana, Anogeissus leiocarpa, Ceiba pentandra, Dialium guineense and Diospyros mespiliformis in a semi-deciduous vertisol forest in Southern Benin. Since the predictions of Yasso07 were not consistent with the observations on mass loss and chemical composition of litter, Yasso07 was fitted to the dataset composed of global data and the new experimental data from Benin. The re-parameterized versions of Yasso07 had a good predictive ability and refined the applicability of the model in Benin to estimate soil carbon stocks, its changes and CO2 emissions from heterotrophic respiration as main outputs of the model. The findings of this research support the hypothesis that the high variation of litter quality observed in the tropics is a major driver of the decomposition and needs to be accounted in the model parameterization.

Changes of tannin and nutrients during decomposition of branchlets of Casuarina equisetifolia plantation in subtropical coastal areas of China

A litterbag experiment was conducted to investigate the changes of tannins and nutrients in branchlets at different decomposition stages of Casuarina equisetifolia in southern subtropical coastal zone, China, using the colorimetric assays. The time required for the loss of half of the initial dry weight (t₅₀) was 9.13 months. Total phenolics (TP), extractable condensed tannins (ECT), protein-bound condensed tannins (PBCT), total condensed tannins (TCT) and protein precipitation capacity (PPC) of branchlets litter decreased rapidly, while fibre-bound condensed tannins (FBCT) increased during decomposition. Nitrogen and phosphorus concentration of the branchlet litter both increased gradually during decay. Negative correlations between TP and nitrogen or phosphorus, as well as TCT and nitrogen or phosphorus were found. These chemical changes enhanced the current knowledge on the potential ecological role of nutrient transformation in tannins in C. equisetifolia plantations.