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Trait functional diversity explains mixture effects on litter decomposition at the arid end of a climate gradient

Citation

Canessa, Rafaella et al. (2022), Trait functional diversity explains mixture effects on litter decomposition at the arid end of a climate gradient, Dryad, Dataset, https://doi.org/10.5061/dryad.qrfj6q5jr

Abstract

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.

Methods

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, sensu 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.

Funding

Deutsche Forschungsgemeinschaft, Award: BA 3843/6-1

Deutsche Forschungsgemeinschaft, Award: TI 338/14-1

Deutsche Forschungsgemeinschaft, Award: TI 338/14-2