Litter Mixture Interactions at the Level of Plant Functional Types are Additive

Abstract

It is very difficult to estimate litter decomposition rates in natural ecosystems because litters of many species are mixed and idiosyncratic interactions occur among those litters. A way to tackle this problem is to investigate litter mixing effects not at the species level but at the level of Plant Functional Types (PFTs). We tested the hypothesis that at the PFT level positive and negative interactions balance each other, causing an overall additive effect (no significant interactions among PFTs). Thereto, we used litter of four PFTs from a temperate peatland in which random draws were taken from the litter species pool of each PFT for every combination of 2, 3, and 4 PFTs. Decomposition rates clearly differed among the 4 PFTs (Sphagnum spp. < graminoids = N-fixing tree < forbs) and showed little variation within the PFTs (notably for the Sphagnum mosses and the graminoids). Significant positive interactions (4 out of 11) in the PFT mixtures were only found after 20 weeks and in all these combinations Sphagnum was involved. After 36 and 56 weeks of incubation interactions were not significantly different from zero. However, standard deviations were larger than the means, indicating that positive and negative interactions balanced each other. Thus, when litter mixture interactions are considered at the PFT level the interactions are additive. From this we conclude that for estimating litter decomposition rates at the ecosystem level, it is sufficient to use the weighted (by litter production) average decomposition rates of the contributing PFTs.

The effects of leaf litter evenness on decomposition depend on which plant functional group is dominant

“…When we only considered even and uneven (pooled CP-dominant uneven and T-dominant uneven together) mixtures, species evenness had no significant effects on decomposition rates (P 00.31, Table 3). This may be because the positive and negative effects among PFGs balance each other (Hoorens et al 2010). As a result, we could not detect significant roles when we chose species evenness per se as a main factor in our analysis.…”

“…The expected remaining mass of litter mixtures was estimated based on the remaining mass in the single-species litterbags of the component species decomposing in the same plot. This was calculated as follows (Hoorens et al 2010):…”

Control of climate and litter quality on leaf litter decomposition in different climatic zones

“…Although the litterbag method had some limitations, including burial of surface bags by falling litter through time, microclimatic effects, and potential exclusion of soil fauna (De Santo et al 1993;Kurz-Besson et al 2005), it remained the best method available for generating a large decomposition database (Kurz-Besson et al 2005). Studies on the decomposition of mixed litter were excluded due to the fact that decomposition rates were often more variablein mixtures than those expected from single litter (Meier and Bowman 2008;Hoorens et al 2010;Hättenschwiler and Jøgensen 2010). Beyond that, the studies on decomposition designed for special purposes (e.g., fire, fertilization, clear-cut and etc.)…”

A new model of Holocene peatland net primary production, decomposition, water balance, and peat accumulation

“…HPM does not consider interactions between litter types, so the long-term decomposition rate of litter from a particular PFT depends on that PFT's m i /m i,o , but not on values for any other PFTs (Hoorens et al, 2010). Loss of litter/peat structural integrity due to decomposition, coupled with accumulating mass above a decay cohort, leads to a collapse/compression of the peat (Clymo, 1991).…”