Can the biomass-ratio hypothesis predict mixed-species litter decomposition along a climatic gradient?
OBJECTIVE
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. All possible combinations from one to four species mixtures were tested over 28 weeks of incubation. Observed mixture decomposition rates were compared with those predicted by the biomass-ratio hypothesis. Variability of the prediction errors was compared with the species richness of the mixtures, across sites, and within sites over time.


RESULTS
Both positive and negative prediction errors occurred. Despite this, the biomass-ratio hypothesis was true as an average claim for all sites (r = 0·91) and for each site separately, except for the climatically intermediate site, which showed mainly synergistic deviations. Variability decreased with increasing species richness and in less favourable climatic conditions for decomposition.


CONCLUSIONS
Community-weighted mean values provided good predictions of mixed-species litter decomposition, converging to the predicted values with increasing species richness and in climates less favourable to decomposition. Under a context of climate change, abiotic variability would be important to take into account when predicting ecosystem processes.
Département de Biologie, Université de Sherbrooke, Sherbrooke, QC, J1K 2R1, Canada.
Antoine
A
Tardif
Bill
B
Shipley
Juliette M G
JM
Bloor
Jean-François
JF
Soussana
D000531:Altitude; D044822:Biodiversity; D018533:Biomass; D002980:Climate; D057231:Climate Change; D017753:Ecosystem; D005602:France; D008954:Models, Biological; D012987:Soil / Q000737:chemistry*
D012987:Soil
BMRH; Biomass-ratio hypothesis; Festuca rubra; Lolium perenne; Taraxacum officinale; Trifolium repens; climatic gradient; community-aggregated traits; community-weighted means; litter decomposition