Effects Of Litter Mixing Research Articles

The influence of plant litter diversity on decomposer abundance and diversity

Although there has been much recent interest in the effect of litter mixing on decomposition processes, much remains unknown about how litter mixing and diversity affects the abundance and diversity of decomposer organisms. We conducted a litter mixing experiment using litterbags in a New Zealand rainforest, in which treatments consisted of litter monocultures of each of 8 forest canopy and understory plant species, as well as mixtures of 2, 4 and 8 species. We found litter mixing to have little effect on net decomposition rates after either 279 or 658 days, and for each species decomposition rates in mixture treatments were the same as in monoculture. Litter species identity had important effects on litter microfauna, mesofauna and macrofauna, with different litter types promoting different subsets of the fauna. Litter mixing had few effects on densities of mesofauna and macrofauna, but did have some important effects on components of the microfauna, notably microbe-feeding and predatory nematodes. At day 279, litter mixing also consistently reduced the ratio of bacterial-feeding to microbe-feeding (bacterial-feeding+fungal-feeding) nematodes, pointing to mixing causing a significant switch from the bacterial-based to the fungal-based energy channel. Litter mixing sometimes influenced the community composition and diversity of nematodes and macrofauna, but effects of litter mixing on diversity were not necessarily positive, and were much weaker than effects of litter species identity on diversity. We conclude that litter mixing effects on the abundance and diversity of decomposer biota, when they occur, are likely to be of secondary and generally minor significance when compared to the effects of litter species identity and composition.

The impact of hemiparasitic plant litter on decomposition: direct, seasonal and litter mixing effects

Summary Nutrient‐rich litter of hemiparasites (and N‐fixers) has the potential to influence ecosystem‐level decomposition and nutrient cycling, which may be important in ecosystems where productivity is nutrient limited. This influence may be both direct, and indirect via impacts on the decomposition of other species’ litters in mixed‐species litter layers. We investigate the importance of these direct and indirect effects of sub‐arctic hemiparasite litter in a litterbed study and a field litterbag experiment, and compare these data with those from a microcosm study also involving litter mixtures. Field‐placed litterbags demonstrate for the first time the direct importance of hemiparasite litter on decomposition and nutrient cycling in a field setting: litter of the hemiparasite Bartsia alpina lost 18 times more N over 2 years than Betula nana litter. The majority of this N was released during the growing season, strongly supporting the proposal that hemiparasites can have a substantial direct impact on nutrient availability to other plants. The short spring and autumn periods were important for litter mass and N dynamics, with consequences for predicting effects of environmental change. However, hemiparasite litter did not indirectly affect the decomposition rate or nutrient release from litter mixtures in field‐placed litterbags. Furthermore, the direction and magnitude of litter mixing effects on mass loss varied strongly between methods; interactions were absent or negative in the litterbed, non‐significant in field litterbags and positive in microcosms. We thereby demonstrate the importance of the decomposition environment, rather than species‐specific litter quality, in determining litter‐mixing interactions, with implications for evaluating the impact of particular species on ecosystem carbon and nutrient fluxes via litter mixing We conclude that hemiparasites have a particular functional role in sub‐arctic heath systems: in effect they ‘short circuit’ generally slow nutrient cycles, with potential impacts on resource patchiness and local scale biodiversity.

Do invertebrate decomposers affect the disappearance rate of litter mixtures?

We designed an experiment using litter bags with fine and coarse mesh size to analyse interacting effects between invertebrate decomposers and the number of litter species on litter disappearance rates. We used litter of nine broad-leaved tree species to compare disappearance rates of litter from single species with mixtures of two to six species. Species composition of litter and invertebrates interacted strongly in their effects on litter disappearance rate. Contribution of invertebrates to litter disappearance increased with time mainly for litter which disappeared slower in the absence of invertebrates. Disappearance rates were positively correlated with initial N content and negatively correlated to initial C content of litter. These relationships were stronger in the presence of invertebrates, suggesting that their activity is positively related to initial litter chemistry. Number of component litter species, however, had no effect on disappearance rate irrespective of the activity of invertebrates. Using individual rates of disappearance for single species, we calculated the expected rates of disappearance for each of the experimental mixtures of leaf litters. We found that mixtures of several species of leaf litter resulted in significant deviations from the expected values. These deviations showed a significant effect of the number of component litter species. However, this result was caused by a strong negative deviation of one single mixture of six species. The presence of invertebrates resulted in even greater deviations from the expected values, suggesting an important contribution of invertebrates to the effects of litter mixing on litter disappearance rates. Hence, our results underline the importance of idiosyncratic effects of species traits in mixtures. Our results suggest that the influence of invertebrate decomposers interacts with litter chemistry during decomposition, but is not affected by litter species richness per se.

Determinants of litter mixing effects in a Swedish boreal forest

When the litter of a given species decomposes, it will often break down in the proximity of litters from other species. We investigated the effects of litters of 10 different species in a boreal forest of northern Sweden on each others' decomposition and N release rates; this was done through the use of litterbags containing two compartments separated by single mesh partition. Different litters could be placed on opposite sides of this mesh so that they were in contact with each other. Treatments consisted of all the possible pairwise combinations of the 10 species, with members of each pair placed in different compartments of the same litterbag. Litterbags were harvested after 1, 2 and 4 years in the field. Species differed significantly in their effects on decomposition and N loss rates of associated litters. Generally, litters from feather mosses and lichens showed the greatest promotion of decomposition on associated litters, while some vascular plant species, notably Empetrum hermaphroditum, showed the least. At year four, feather mosses also had the greatest positive effects on N loss from the litters of associated species. There were several instances in which litter of a given species decomposed at different rate when litter from its own species, rather than that of a different species, was placed in the adjacent litterbag compartment. This was particularly apparent in the second year, when across the entire data set, litters decomposed fastest when associated with their own litters. Generally, slowly decomposing litters had the greatest positive effects on decomposition of associated litters. It is proposed that in boreal forests slow decomposing litters (particularly those of feather mosses) may contribute to enhancing moisture attention in the litter layer, which in turn promotes the decomposition and N release of associated litters. Further, while litter mixing effects were clearly demonstrated in our study, they were also shown to be of secondary importance to the effects of species identity on decomposition.

Decomposition of broadleaf and needle litter in forests of British Columbia: influences of litter type, forest type, and litter mixtures

We measured rates of decomposition at three sites representing the major mixedwood forest types of British Columbia: (i) boreal forests of white spruce (Picea glauca (Moench) Voss) and trembling aspen (Populus tremuloides Michx.); (ii) coastal forests of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and red alder (Alnus rubra Bong.); and (iii) a wet interior forest of Douglas-fir, paper birch (Betula papyrifera Marsh.), and lodgepole pine (Pinus contorta Doug. ex Loud.). Mass loss of litter of each species (both pure and in combination with the other species) was measured for 2-5 years in forests of each species to determine (i) if broadleaf litter decomposed faster than needle litter, (ii) if litter decomposed faster in broadleaf or mixedwood forests than in coniferous forests, and (iii) if mixing with broadleaf hastened decomposition of needle litter. The broadleaf litters decomposed faster than needles during the first year but, thereafter, decomposed more slowly, so differences were small after 3 years. Litter tended to decompose faster in the broadleaf forests than in the coniferous forests. There was either no effect or a slight suppression of decomposition when litters were mixed; thus, there was no evidence that addition of broadleaf litter hastened decomposition of needle litter. The results clearly indicate that the mixing of needle litter with broadleaf litter is unlikely to hasten decomposition in mixedwood forests of British Columbia. The main influence of broadleaves was more rapid decomposition in broadleaf or mixedwood forest floors, which does not appear to be simply an effect of litter quality or litter mixing.

Consequences of the reduction of plant diversity for litter decomposition: effects through litter quality and microenvironment

Decomposition of plant litter is a key process for the flow of energy and nutrients in ecosystems that may be sensitive to the loss of biodiversity. Two hypothetical mechanisms by which changes in plant diversity could affect litter decomposition are (1) through changes in litter species composition, and (2) by altering the decomposition microenvironment. We tested these ideas in relation to the short‐term decomposition of herbaceous plant litter in experimental plant assemblages that differed in the numbers and types of plant species and functional groups that they contained to simulate loss of plant diversity. We used different litterbag experiments to separate the two potential pathways through which diversity could have an effect on decomposition. Our two litterbag trials showed that altering plant diversity affected litter breakdown differently through changes in decomposition microenvironment than through changes in litter composition. In the decomposition microenvironment experiment there was a significant but weak decline in decomposition rate in relation to decreasing plant diversity but no significant effect of plant composition. The litter composition experiment showed no effect of richness but significant effects of composition, including large differences between plant species and functional groups in litter chemistry and decomposition rate. However, for a nested subset of our litter mixtures decomposition was not accurately predicted from single‐species bags; there were positive, non‐additive effects of litter mixing which enhanced decomposition. We critically assess the strengths and limitations of our short‐term litterbag trials in predicting the longer‐term effects of changes in plant diversity on litter decomposition rates.

Decomposition of broadleaf and needle litter in forests of British Columbia: influences of litter type, forest type, and litter mixtures

We measured rates of decomposition at three sites representing the major mixedwood forest types of British Columbia: (i) boreal forests of white spruce (Picea glauca (Moench) Voss) and trembling aspen (Populus tremuloides Michx.); (ii) coastal forests of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and red alder (Alnus rubra Bong.); and (iii) a wet interior forest of Douglas-fir, paper birch (Betula papyrifera Marsh.), and lodgepole pine (Pinus contorta Doug. ex Loud.). Mass loss of litter of each species (both pure and in combination with the other species) was measured for 2-5 years in forests of each species to determine (i) if broadleaf litter decomposed faster than needle litter, (ii) if litter decomposed faster in broadleaf or mixedwood forests than in coniferous forests, and (iii) if mixing with broadleaf hastened decomposition of needle litter. The broadleaf litters decomposed faster than needles during the first year but, thereafter, decomposed more slowly, so differences were small after 3 years. Litter tended to decompose faster in the broadleaf forests than in the coniferous forests. There was either no effect or a slight suppression of decomposition when litters were mixed; thus, there was no evidence that addition of broadleaf litter hastened decomposition of needle litter. The results clearly indicate that the mixing of needle litter with broadleaf litter is unlikely to hasten decomposition in mixedwood forests of British Columbia. The main influence of broadleaves was more rapid decomposition in broadleaf or mixedwood forest floors, which does not appear to be simply an effect of litter quality or litter mixing.

Effects of Plant Litter Species Composition and Diversity on the Boreal Forest Plant-Soil System

Although most plant products eventually enter the below-ground subsystem as plant litter, relatively little is known about the effects of plant litter diversity or composition on ecosystem processes and no study has considered the responses of plant growth to these factors. We conducted an experiment in which humus substrate was collected from three field sites in the boreal forest of northern Sweden. Litter was then placed on the humus surface, and the litter used consisted of monocultures of Empetrum hermaphroditum (dwarf shrub), Betula pendula (tree), and Pleurozium schreberi (feather moss), as well as mixtures containing all the possible (two-way and three-way) combinations of these species: the experiment was maintained in out-door conditions. Although decomposition rates of this surface-placed litter differed between species few effects of litter mixing on litter mass loss were apparent. Added litter of Pinus sylvestris litter broke down most slowly when placed in E. hermaphrodnum litter but sometimes showed elevated decomposition rates when placed in some of the multiple species litter mixes. Soil microbial biomass and activity was lowest when plant litter was absent, but as long as plant litter was present on the humus surface the species composition and diversity of the litter was irrelevant. There were few effects of litter treatments on growth of seedlings of either B. pendula or P. sylvestris planted into the humus. However, for one site there were significant effects of mixing litter of P. sclueberi and E. hermaphroditum in reducing growth of both seedling species. Litter treatments generally did not alter the competitive balance between B. pendula and P. sylvestris seedlings when grown together but for all sites litter treatments had significant effects on the overall intensity of competition, and mixing of litter of B. pendula and P. sehreheri had significant non-additive effects on competition intensity for two of the three sites. The abundance of mycorrhizae on seedlings was only weakly related to litter treatment but there were some positive effects of litter mixing on one of the most abundant mycorrhizal morphotypes on both species of seedlings for one of the sites. Our results suggest that litter presence was important in influencing a range of above ground and below ground properties and processes. In some instances individual species effects and litter mixing effects were also important but few general patterns emerged, and the nature of significant effects tended to be idiosyneratic. Ultimately our results show that plant litter has important afterlife effects which need to be considered in order to develop a more complete understanding of how biodiversity affects ecosystems.