Causal hypotheses accounting for correlations between decomposition rates of different mass fractions of leaf litter.

Whole-leaf decomposition rates are the sum of the decomposition rates of each chemical fraction (water-soluble, cellulose, hemicellulose, lignin), but the decomposition rates of each fraction show complicated patterns of covariation. What explains these patterns of covariation? After measuring the k values of each fraction in 42 different mixtures of tree leaf litters from five species, we tested three alternative causal hypotheses that have been proposed in the literature concerning these mixture interactions using structura equations modeling. All three hypotheses were rejected by the data.

Differences in elemental composition of tailings, soils, and plant tissues following five decades of native plant colonization on a gold mine site in Northwestern Québec.

Mining activities have significant environmental impacts, such as the production of acid mine drainage and the typical absence of vegetation on mine tailings whose absence can facilitate the migration of metals to adjacent ecosystems. We investigated the metal and metalloid composition of plants and substrates on, and near a former gold mine site to understand elemental dynamics in such environments. A mine tailings deposit rich in Mo and As in Northwestern Québec was studied following the natural colonization of the deposit by boreal plant species.

Can the biomass-ratio hypothesis predict mixed-species litter decomposition along a climatic gradient?

Background And Aims: The biomass-ratio hypothesis states that ecosystem properties are driven by the characteristics of dominant species in the community. In this study, the hypothesis was operationalized as community-weighted means (CWMs) of monoculture values and tested for predicting the decomposition of multispecies litter mixtures along an abiotic gradient in the field.

Methods: Decomposition rates (mg g(-1) d(-1)) of litter from four herb species were measured using litter-bed experiments with the same soil at three sites in central France along a correlated climatic gradient of temperature and precipitation.

Using the biomass-ratio and idiosyncratic hypotheses to predict mixed-species litter decomposition.

Background And Aims: A test is made of the acceptability of the biomass-ratio hypothesis (BMRH), operationalized as community-weighted means (CWMs), and of a new hypothesis (idiosyncratic annulment), for predicting the decomposition of multispecies litter mixtures. Specifically, (1) does the BMRH based on monoculture decomposition rates introduce systematic over- or underestimation of rates in mixtures? and (2) does the degree of variability of these rates decrease with increasing species richness (SR) beyond that expected from purely mathematical causes?

Methods: Decomposition rates (mg g(-1) d(-1)) of litter from six tree species in microcosms were measured under controlled conditions during 18 weeks of incubation, alone and in all possible combinations of two, three, five and six species. Observed mixture decomposition rates were compared with those predicted by the BMRH using CWMs calculated from the monoculture rates, and the variability of the differences were compared with the SR of the mixture.