DOI: 10.5061/dryad.qrfj6q5jr
title: Trait functional diversity explains mixture effects on litter decomposition at the arid end of a climate gradient

description: Litter decomposition is controlled by climate, litter quality and
 decomposer communities. Because the decomposition of specific litter types
 is also influenced by the properties of adjacent types, mixing litter
 types may result in non-additive effects on overall decomposition rates.
 The strength of these effects seems to depend on the litter functional
 diversity. However, it is unclear which functional traits or combination
 of traits explain litter mixture effects and if these depend on the range
 of trait values and the ecosystems involved. These uncertainties hamper
 our ability to predict decomposition in plant communities. We aimed at
 understanding whether and how functional diversity (measured as functional
 dispersion, FDis) influences litter decomposition, and how this influence
 varies among different climates and across decomposition stages. We
 calculated FDis based on litter traits related to nutrient concentrations
 or to litter recalcitrance, and tested whether these diversity measures
 and climatic parameters (soil moisture and temperature) explained litter
 mixture effects on decomposition. Additive mixture effects (i.e.
 decomposition of mixtures equalling the mean decomposition of the single
 litter types) were common in most of the evaluated climates. Non-additive,
 negative effects were mainly restricted to the driest and warmest sites,
 and decreased with time. Non-additive effects increased in magnitude with
 the mixtures’ FDis, with positive effects being related to FDis in
 nutrient traits and negative effects being related to FDis in
 recalcitrance traits. Synthesis: Litter mixing did not have strong effects
 on decomposition rates across the studied climatic gradient overall, and
 the direction and intensity of the mixture effects were context-dependent.
 The effects were stronger and more negative in the dryer ecosystems. Where
 effects were found, functional diversity calculated from selected groups
 of traits (related to nutrients or litter recalcitrance) predicted mixture
 effects, especially where trait ranges were broad, though much of the
 variation remains unexplained. We propose that functional diversity
 metrics based on litter traits that are mechanistically relevant, applied
 to diverse site-specific litter mixtures in different climates, can help
 to better understand under which conditions and in which direction litter
 diversity affects decomposition.
description: The dataset represents litter decomposition (i.e. mass loss, %)
 of 52 plant species, decomposing both individually as well as in litter
 mixtures (of 2, 4 or 6 litter species combined) in six different study
 sites along a climate gradient in Chile (arid, arid with fog influence,
 semi-arid, mediterranean, temperate-highland and temperate-lowland).
 Litterbags were set to decompose in the field for 6, 12 and 20 months. For
 each litterbag, the percentage of litter mass loss was calculated as (Mf
  - Mi) / Mi * 100, where Mf is the final dry mass after decomposition and
 Mi is the initial dry mass. The litter mixture effect
 (%), i.e. the percent difference in the observed mass loss of a mixture
 (Mo) relative to the mean of single-species mass loss of all the species
 that constituted a mixture (Mp), was calculated as (Mo – Mp) / Mp *100 for
 each mixture. Non-additive mixture effects occurred when the observed
 mixture mass loss was significantly different from the predicted mixture
 mass loss. These non-additive effects were positive or negative when the
 observed mixture mass loss was higher or lower than the predicted mass
 loss, respectively. Associated with these decomposition
 data, the file contains data on plant functional traits for each of the
 decomposing species. For 30 species, functional traits were retrieved from
 Canessa et al. (2021) and the associated dataset. For other species not
 present in that study, data were measured following the same methodology
 used in Canessa et al. (2021). Based on the plant
 functional traits data, functional dispersion values (FDis,
 <em>sensu</em> Laliberté & Legendre, 2010) for each of
 the litter mixtures were calculated using two different sets of traits
 that correlate with litter decomposition generally and that relate to the
 mechanisms responsible of litter mixture effects. The two calculated
 indices are (1) “nutrients FDis”, based on a distance matrix using traits
 that are potentially related to nutrient transfer among litter and thus,
 may mostly cause positive mixture effects (C/N, Mg, K and Ca); and (2)
 “recalcitrance FDis”, based on a distance matrix using traits that
 generally inhibit decomposition, and thus, are expected to produce
 negative mixture effects (tannins, total phenolics, lignin and
 Fp). Additionally, the file contains microclimatic data
 measured at the six study locations for the different decomposition
 periods (overall, between June 2017-January 2019). The evaluated
 parameters include mean soil temperature (MST) and mean soil moisture
 (MSM). For more details on the
 methodology, please refer to the methods section of the manuscript
 associated with this dataset.