Determine Decomposition Rates Research Articles

Wood nutrients: Underexplored traits with functional and biogeochemical consequences.

Resource storage is a critical component of plant life history. While the storage of nonstructural carbohydrates in wood has been studied extensively, the multiple functions of mineral nutrient storage have received much less attention. Here, we highlight the size of wood nutrient pools, a primary determinant of whole-plant nutrient use efficiency, and a substantial fraction of ecosystem nutrient budgets, particularly tropical forests. Wood nutrient concentrations also show exceptional interspecific variation, even among co-occurring plant species, yet how they align with other plant functional traits and fit into existing trait economic spectra is unclear. We review the chemical forms and location of nutrient pools in bark and sapwood, and the evidence that nutrient remobilization from sapwood is associated with mast reproduction, seasonal leaf flush, and the capacity to resprout following damage. We also emphasize the role wood nutrients are likely to play in determining decomposition rates. Given the magnitude of wood nutrient stocks, and the importance of tissue stoichiometry to forest productivity, a key unresolved question is whether investment in wood nutrients is a relatively fixed trait, or conversely whether under global change plants will adjust nutrient allocation to wood depending on carbon gain and nutrient supply.

Shifts in the Abundances of Saprotrophic and Ectomycorrhizal Fungi With Altered Leaf Litter Inputs.

Ectomycorrhizal (EcM) and saprotrophic fungi interact in the breakdown of organic matter, but the mechanisms underlying the EcM role on organic matter decomposition are not totally clear. We hypothesized that the ecological relations between EcM and saprotroph fungi are modulated by resources availability and accessibility, determining decomposition rates. We manipulated the amount of leaf litter inputs (No-Litter, Control Litter, Doubled Litter) on Trenched (root exclusion) and Non-Trenched plots (with roots) in a temperate deciduous forest of EcM-associated trees. Resultant shifts in soil fungal communities were determined by phospholipid fatty acids and DNA sequencing after 3 years, and CO2 fluxes were measured throughout this period. Different levels of leaf litter inputs generated a gradient of organic substrate availability and accessibility, altering the composition and ecological relations between EcM and saprotroph fungal communities. EcM fungi dominated at low levels of fresh organic substrates and lower organic matter quality, where short-distances exploration types seem to be better competitors, whereas saprotrophs and longer exploration types of EcM fungi tended to dominate at high levels of leaf litter inputs, where labile organic substrates were easily accessible. We were, however, not able to detect unequivocal signs of competition between these fungal groups for common resources. These results point to the relevance of substrate quality and availability as key factors determining the role of EcM and saprotroph fungi on litter and soil organic matter decay and represent a path forward on the capacity of organic matter decomposition of different exploration types of EcM fungi.

Can additional air supply enhance decomposition processes in sludge treatment reed beds?

This work was designed to investigate the influence of artificial aeration on the sludge decomposition process in mesocosm sludge treatment reed beds (STRBs). In addition to the typical STRB design, where ventilation is mainly provided by a drainage pipe, passive aeration via a "chimney" and active aeration via a blower were introduced. During the entire observation period of 1.5 years, O2 concentrations in the upper part of the filter were significantly higher in the artificially aerated beds. To determine decomposition rates, a study with decomposition bags, measurements of CO2 emissions from the STRB and isotopic partitioning of CO2 emissions were performed. The results indicate an accelerated sludge degradation process in both active and passive beds. However, this effect was limited to part of the season and could not be demonstrated by episodic measurements of CO2 efflux. The CO2 efflux showed a seasonal pattern. Average CO2 efflux was below 3.0 μmol m−2 s−1 in the winter months and reached 43 μmol m−2 s−1 in the warmer months. The low sludge load and drought period in summer 2018 resulted in an extremely low CO2 efflux in August 2018. Isotopic analyses revealed changes in decomposition dynamics for certain parts of the season, differences in contributions of sludge and plant derived CO2 to total CO2 emissions from differently aerated beds. Overall, passive aeration proved to be similarly efficient as active aeration and could therefore be considered for application in a full-scale system.

Influence of fungi and bag mesh size on litter decomposition and water quality.

Litter decomposition is a complex process that is influenced by many different physical, chemical, and biological processes. Environmental variables and leaf litter quality (e.g., nutrient content) are important factors that play a significant role in regulating litter decomposition. In this study, the effects of adding fungi and using different mesh size litter bags on litter (Populus tomentosa Carr. and Salix matsudana Koidz.) decomposition rates and water quality were investigated, and investigate the combination of these factors influences leaf litter decomposition. Dissolved oxygen (DO), chemical oxygen demand (COD), total phosphorus (TP), and ammonia-nitrogen (NH3-N) were measured during the 112-day experiment. The salix leaf litter (k= 0.045) displayed faster decomposition rates than those of populous leaf litter (k= 0.026). Litter decomposition was initially slow and then accelerated; and by the end of the experiment, the decomposition rate was significantly higher (p= 0.012, p< 0.05) when fungi were added to the treatment process compared to the blank, and litter bags with different mesh sizes did not influence the decomposition rate. The variations in the decomposition rates and nutrient content were influenced by litter quality and a number of environmental factors. The decomposition rate was most influenced by internal factors related to litter quality, including the N/P and C/P ratios of the litter. By quantifying the interact effect of environment and litter nutrient dynamic, to figure out the revetment plant litter decomposition process in a wetland system in biological physical and chemical aspects, which can help us in making the variables that determine decomposition rates important for assessing wetland function.

Litter Quality Modulates Effects of Dissolved Nitrogen on Leaf Decomposition by Stream Microbial Communities.

Rates of leaf litter decomposition in streams are strongly influenced both by inorganic nutrients dissolved in stream water and by litter traits such as lignin, nitrogen (N) and phosphorus (P) concentrations. As a result, decomposition rates of different leaf species can show contrasting responses to stream nutrient enrichment resulting from human activities. It is unclear, however, whether the root cause of such discrepancies in field observations is the interspecific variation in either litter nutrient or litter lignin concentrations. To address this question, we conducted a controlled laboratory experiment with a known fungal community to determine decomposition rates of 38 leaf species exhibiting contrasting litter traits (N, P and lignin concentrations), which were exposed to 8 levels of dissolved N concentrations representative of field conditions across European streams (0.07 to 8.96mgNL-1). The effect of N enrichment on decomposition rate was modelled using Monod kinetics to quantify N effects across litter species. Lignin concentration was the most important litter trait determining decomposition rates and their response to N enrichment. In particular, increasing dissolved N supply from 0.1 to 3.0mgNL-1 accelerated the decomposition of lignin-poor litter (e.g. < 10% of lignin, 2.9× increase ± 1.4 SD, n = 14) more strongly than that of litter rich in lignin (e.g. > 15% of lignin, 1.4× increase ± 0.2 SD, n = 9). Litter nutrient concentrations were less important, with a slight positive effect of P on decomposition rates and no effect of litter N. These results indicate that shifts in riparian vegetation towards species characterized by high litter lignin concentrations could alleviate the stimulation of C turnover by stream nutrient enrichment.

Litter decomposition variation across a degradation gradient and two seasons in a critically endangered vegetation type within the Fynbos biome, South Africa

Litter decomposition is an ecosystem function essential for nutrient cycling; however until very recently it was considered of minor importance within the fire-prone Fynbos Biome. To investigate decomposition rate and litter nutrient dynamics, litterbags containing materials from three plant species from different functional types were placed in sites across a degradation gradient and over two seasons. Litterbags were removed after three and six months for both seasons to determine decomposition rates and change in nutrient concentration. Decomposition varied greatly among the species and was strongly correlated to initial nutrient values of the litter. The most nutrient rich litter type, the alien herbaceous Medicago spp., lost 65% of its original mass after six months while the most nutrient poor, the indigenous grass Pentameris eriostoma, lost 18%. Litter from Dicerothamnus rhinocerotis, an indigenous shrub, lost 27% of its original mass. For all litter types, the majority of the loss occurred during the first three months of the experiment. Season was found to significantly affect litter decomposition; however the exact mechanism behind this is unclear. Degradation level, at least defined by the metrics of this study, did not significantly affect litter decomposition rate. The faster decomposition rate shown in Medicago spp. suggests that in degraded areas where significant proportions of the species invade, nutrient cycling will be accelerated in comparison to pristine land; however broadening the species of study to include additional plant functional types, such as indigenous annuals, would help give insight into this hypothesis. This study affirms the notion that litter decomposition is an important ecosystem function within the Fynbos Biome with litter type acting as a strong controlling variable.

Litter Decomposition in Yellowstone Grasslands: The Roles of Large Herbivores, Litter Quality, and Climate

Plant litter decomposition is a key process that influences carbon and nutrient cycling in terrestrial ecosystems. Litter decomposition is controlled by a number of factors such as temperature, moisture, litter quality, and the composition of soil microbial communities. Large herbivores can affect litter decomposition by modifying each of these factors. The goal of this study was to examine the contribution of herbivores in determining decomposition rates across an ecosystem with a steep climatic gradient. We examined the effect of migratory grazing ungulates (primarily elk) on litter decomposition by comparing rates of mass loss over 1.5 years inside and outside fenced exclosures at 10 grassland sites that spanned gradients of temperature, precipitation, plant community composition, and grazing intensity in Yellowstone National Park (YNP). Based on previous studies indicating positive feedbacks of herbivory on soil carbon and nutrient processes in grazed YNP grasslands, we predicted that YNP grazers should also improve litter quality and stimulate litter decomposition. Instead, we found that variation in precipitation was the predominant driver of litter decomposition across the ecosystem. Grazing decreased litter lignin:nitrogen ratio (improved quality), but did not affect decomposition rates. Our results suggest that while grazers can influence the quality of litter, climate is a more important driver of litter decomposition across the YNP ecosystem.

Decomposition rates and nutrient dynamics of Picea abies needles, twigs and fine roots after stem-only harvesting in eastern and western Norway

Decomposition of the finest harvest residues is important for the carbon and nutrient cycle in forest ecosystems both before and after tree felling. We assumed that decomposition is dependent on harvest residue fraction and chemistry, soil temperature and moisture, and aimed at determining decomposition rates and nutrient dynamics of needles, twigs and fine roots from newly felled Picea abies trees in two sites with different climate and topography. Decomposition of needles, twigs and fine roots in mesh bags was followed for up to six years and four years in harvesting sites in eastern and western Norway, respectively. The western site had a more humid climate and a steeper terrain than the eastern site. The mass loss after two years was significantly higher for needles (49–59%) than for twigs and fine roots (29–38%). Between sites, there was no significant difference between mass loss for neither needles nor twigs. Nitrogen accumulated in needles during the first year, but 35% of initial needle N had been released after three years. The initial needle and twig decomposition rate was dependent on soil moisture and topographic aspect. During the first three years, needle lignin concentrations retarded whereas P concentrations stimulated needle mass loss. For twigs, P concentrations stimulated mass loss, whereas higher soil temperatures reduced it. Lignin and P concentrations of plant parts and soil temperature were the most important factors for the first three-year mass loss. The slow release of nutrients shows the importance of remaining needles, twigs and fine roots as a long-time nutrient source in the ecosystems under study.

Interactions among temperature, moisture, and oxygen concentrations in controlling decomposition rates in a boreal forest soil

Abstract. Determining environmental controls on soil organic matter decomposition is of importance for developing models that predict the effects of environmental change on global soil carbon stocks. There is uncertainty about the environmental controls on decomposition rates at temperature and moisture extremes, particularly at high water content levels and high temperatures. It is uncertain whether observed declines in decomposition rates at high temperatures are due to declines in the heat capacity of extracellular enzymes as predicted by thermodynamic theory, or due to simultaneous declines in soil moisture. It is also uncertain whether oxygen limits decomposition rates at high water contents. Here we present the results of a full factorial experiment using organic soils from a boreal forest incubated at high temperatures (25 and 35 °C), a wide range of water-filled pore space (WFPS; 15, 30, 60, 90 %), and contrasting oxygen concentrations (1 and 20 %). We found support for the hypothesis that decomposition rates are high at high temperatures, provided that enough moisture and oxygen are available for decomposition. Furthermore, we found that decomposition rates are mostly limited by oxygen concentrations at high moisture levels; even at 90 % WFPS, decomposition proceeded at high rates in the presence of oxygen. Our results suggest an important degree of interaction among temperature, moisture, and oxygen in determining decomposition rates at the soil core scale.

Differences in water depth determine leaf-litter decomposition in streams: implications on impact assessment reliability

Leaf-litter decomposition is a widespread functional indicator to assess the stream ecosystem status. However, the spatial location of leaf-bags could distort the impact assessment since intrinsic features of a given site have an important role in the spatial distribution of macroinvertebrates, which could affect decomposition rate. A source of variability that can be easily controlled is the water depth at which bags are incubated in stream bed. Therefore, we tested if water depth within a same mesohabitat (riffles) can determine decomposition rates. Due to the seasonal variability of macroinvertebrate assemblages in temperate regions, the study was performed in autumn-winter and spring to test the consistency of the findings. In three streams from North of Spain 15 mesh bags with alder leaves were placed in riffles covering a gradient of depths. Depth had a positive effect on decomposition rates and biomass of associated total invertebrates and shredders in autumn-winter, fauna variables helping to explain the differences in rates. In spring, depth affected negatively rates, the observed variability being weakly explained by invertebrates, which did not show differences along depth. Despite the opposite trend between seasons, water depth influences the decomposition rates, which may reduce or increase differences among systems if the water depth distribution is greatly biased. Our study highlights the importance of covering a similar range of water depths in the different systems being compared.

In-stream litter decomposition along an altitudinal gradient: does substrate quality matter?

In temperate streams, water temperature and organic matter inputs from surrounding forest vary along the altitude. We tested if the different features of streams of similar size determined by an altitudinal gradient might differentially affect the processing rate of different quality leaves (alder, oak and beech). To distinguish the relative contribution of microbial decomposition from overall decomposition, fine- and coarse-mesh bags were used. We determined decomposition rates, leaf-N and -P concentration, microbial respiration (fine bags), invertebrate colonisation (coarse bags) and density and identity of benthic invertebrates in three second-order streams. Alder decomposed faster than the other species in all three streams and regardless of mesh size due to its lower values of C:N, C:P and N:P. Unexpectedly, microbial decomposition rate did not vary among streams for any of the leaf species. The total decomposition rate of alder and oak showed a negative trend along the altitudinal gradient, the magnitude of the change in decomposition rates being similar for both species. The density and structure of the invertebrate community differed along the altitudinal gradient, related to temperature and surrounding vegetation, determining the decomposition rate. Unexpectedly, sensitivity of decomposition rate of different quality leaves to temperature does not differ along the gradient.

Determination of Mannitol Decomposition Rate under Hydrothermal Pretreatment Condition

For utilization of kelp, which is produced abundantly in Japan, recovery of mannitol is important because mannitol is a main component of kelp. Mannitol can be recovered into liquid phase by hydrothermal pretreatment of kelp, but when treatment condition is too severe, decomposition of the product mannitol also takes place. To determine the optimum condition for hydrothermal pretreatment, determination of mannitol decomposition rate is indispensable. The purpose of this study is to determine decomposition rate parameters of mannitol under hydrothermal conditions for mannitol recovery from kelp without concomitant decomposition. The decomposition rate was successfully determined using a flow reactor, and the rate constant was expressed with a first-order Arrhenius rate equation with a pre-exponential factor of 3.23 s−1 and activation energy of 26.5 kJ/mol. The obtained reaction rate predicted the behavior of mannitol during hydrothermal pretreatment of kelp with average error of 4.6 %.

Moss and lichen decomposition in old-growth and harvested high-boreal forests estimated using the litterbag and minicontainer methods

Bryophytes and lichen are important components of many boreal forest ecosystems, making the quantification of moss and lichen decomposition rates critical to understanding the C cycle of these forests. Cryptogam decomposition has been predominantly studied in wetlands, while few studies exist for forest-habitat mosses and even fewer for foliose ground lichen. We used a) the litterbag and b) the minicontainer (MC) method to quantify the decomposition rates of i) feathermoss, ii) forest peatmoss, iii) foliose ground lichen, and iv) alder leaves (reference litter) in cool, wet high-boreal Labrador black spruce forests. A total of 1560 litter samples (360 litterbags, 1200 MCs) were incubated for two years in six forest stands of different disturbance origin: three old-growth stands of wildfire origin, and three recently clearcut stands. Litter samples were retrieved after 6.5, 13, 47, 57 and 109 weeks of field incubation, and analysed for mass loss, C, N, nutrient, and fibre content.While clearcut harvesting had no significant effect on litter decomposition at all, decomposition rates significantly differed between litter types, with residual mass increasing in the order alder ≤ lichen < feathermoss ≤ peatmoss. Compared to wetlands, forest moss litter was more labile in the studied forest types, with lichen producing especially fast-decomposing litter. Litter type was a better predictor of decomposition rates than individual chemical parameters, indicating that, even in extreme climates like in Labrador, substrate quality is more important in determining decomposition rates than environmental factors. For all litter types, decomposition models accounting for the seasonality of decay dynamics performed better than models assuming constant or continuously decreasing decay rates. Compared to the litter bag method, which yielded decomposition rates comparable to previous studies, the MC method overestimated decomposition rates for alder and lichen due to fragmentation artefacts. The small sample size of the MC method therefore outweighs its statistical advantages arising from ease of replication. In order to derive reliable estimates of litter decomposition, both the field incubation method and the applied decomposition model must therefore be selected to suit the studied litter types.

A new method to measure small peptides amended in seawater using high performance liquid chromatography coupled with mass spectrometry

Quantifying peptide decomposition rate is crucial in understanding marine carbon and nitrogen cycling, because proteins and peptides constitute a major fraction of labile organic matter. However, analytical techniques of detecting small peptides in nanomolar levels in seawater are limited. A new method was developed to measure low concentrations of small peptides amended in seawater, using high performance liquid chromatography coupled with mass spectrometry (HPLC–MS). This technique reduces the detection limit of small peptides by two orders of magnitude relative to the common ultraviolet (UV) detection. A 6-way valve was added before the MS and the valve was programmed to guide the salt peak to waste before the peptide peak was introduced to the MS. Therefore, peptides amended in seawater were injected directly to the HPLC–MS without desalting pretreatment. This new method can detect as low as 0.23pmol of tetrapeptide alanine–valine–phenylalanine–alanine (AVFA), a peptide fragment of Ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO), with less than 5% precision (relative standard deviation). This method was applied successfully to determine decomposition rates of two small peptides, AVFA and serine–tryptophan–glycine–alanine (SWGA), in coastal oceans, and first data of peptide hydrolysis rates using small plain peptides at lower than micromolar concentrations were obtained. Hydrolysis of AVFA and its fluorescent analog was also compared at such low concentration levels. This analytical method broadens our capability to examine the biogeochemical behavior of small peptides, including their hydrolysis, decomposition, and other possible transformation processes in aquatic environments.

Effects of differential grazing on decomposition rate and nitrogen availability in a productive mountain grassland

Background and aims Grazing may influence nutrient cycling in several ways. In productive mountain grasslands of central Argentina cattle grazing maintain a mosaic of different vegetation patches: lawns, grazed intensively and dominated by high quality palatable plants, and open and closed tussock grasslands dominated by less palatable species. We investigated if differencesin theresources deposited on soil (litter and faeces) were associated with litter decomposition rates and soil nitrogen (N) availability across these vegetation patches. Methods We compared the three vegetation patches in terms of litter and faeces quality and decomposability, annual litterfall and faeces deposition rate. We determined decomposition rates of litter and faces in situ and decomposability of the same substrates in a common garden using “litter bags”. We determined soil N availability (with resin bags) in the vegetation patches. Also, we performed a common plant substrates decomposition experiment to assess the effect of soil environment on decomposition process. This technique provides important insights about the soil environmental controls of decomposition (i.e. the sum of soil physicochemical and biological properties, and microclimate), excluding the substrate quality. Results The litter quality and faeces deposition rate were higher in grazing lawns, but the total amounts of carbon (C) and nitrogen (N) deposited on soil were higher in tussock grasslands, due to higher litterfall in these patches. The in situ decomposition rates of litter and faeces, and of the two common plant substrates were not clearly related to either grazing pressure, litterfall or litter quality (C, N, P, lignin, cellulose or hemicellulose content). In situ litter decomposition rate and soil ammoniumavailabilitywerecorrelatedwiththedecomposition rates of both common plant substrates. This may suggest that difference in local soil environment among patch types is a stronger driver of decomposition rate than quality or quantity of the resource that enter the soil. Conclusions Our results show that, although high grazing pressure improves litter quality and increases faeces input, the reduction in biomass caused by herbivores greatly reduces C and N input for the litter decomposition pathway. We did not find an accelerated decomposition rate in grazing lawns as proposed by general models. Our results point to soil environment as a potential important control that could mask the effect of litter quality on field decomposition rates at local scale.

Soil organic carbon in an old-growth temperate forest: Spatial pattern, determinants and bias in its quantification

Although there exists a consensus regarding the spatial variation of Soil Organic Carbon (SOC) are important inputs in the models being used to understand the present and future C cycle and to predict the global climate change, neither the way to quantify the relative contribution of factors such as topography or canopy composition on SOC variation nor how soil sampling intensity affects the estimated fraction is completely clear. In this study, we propose the use of variation partitioning with environmental factors (topographic and soil variables), canopy composition and spatial structure, as a powerful tool for partitioning spatial variation in SOC. Furthermore, we address the importance of sampling density of observations that are required to characterize the spatial variations in SOC. Our results indicated that SOC variation was mainly determined by soil factors like moisture and pH, but the topography and canopy composition also contributed significantly. The spatial pattern of SOC was weaker along trajectories of sparser sampling density when compared with the reference data (n=967). SOC is spatially structured, partially due to the soil conditions that determine decomposition rates of the organic matter, but also due to the sink-source balance of the canopy structure and composition, and to the different conditions created by the topographic heterogeneity. Moreover, these factors are interrelated because topographic conditions can influence soil variations. The estimation of SOC variation is strongly dependent on sampling density, and, thus, to draw strong conclusions about local patterns, an exhaustive and intensive sampling effort is needed.

Fresh root decomposition pattern of two contrasting tree species from temperate agroforestry systems: effects of root diameter and nitrogen enrichment of soil

Fresh tree root decomposition induced by tillage is an important source of soil nutrients in agroforestry systems. Here we examined the effects of tree species, root size and soil N enrichment on fresh root decomposition under laboratory conditions. Fresh roots with two diameters (<2 and 2- 5m m) ofPopulus euramericana cv. 'N3016' (poplar) and Pinus tabu- laeformis (pine) collected from agroforestry systems in Northeast China were used in the experiment. For each root treatment, four N levels (0, 50, 100 and 150 μ gN g �1 soil) were added. We recognized N concentration and C/N ratio as the root quality variables, and determined decomposition rates as cumulative CO2 production and mass loss. Poplar roots had higher N concentration and lower C/N ratio and decomposed faster than pine roots, and smaller roots decomposed faster than the corresponding larger roots. The effect of N addition on root decomposition varied from positive to negligible to negative, and depended on root quality and N addition rates. Increased N availability did not accelerate and even suppressed poplar root decompo- sition, whereas generally stimulated pine root decom- position. Our results suggest that root quality should be incorporated into the design of agroforestry systems. Moreover, the differential responses of N addition on decomposition of fresh roots with different quality provide insights into soil nutrient management in agroforestry practices.

Red alder leaf decomposition and nutrient release in alder and conifer riparian patches in western Washington, USA

Current management practices encourage conversion of red alder ( Alnus rubra) riparian forests to conifers in the Pacific Northwest U.S. Patches of young naturally regenerated conifers are commonly present in alder dominated riparian areas and an understanding of the soil processes in these patches will be helpful in guiding future riparian management. Study objectives were to: (1) determine decomposition rates of red alder leaves in riparian alder and conifer patches, (2) relate decomposition rates to environmental factors and litter chemistry, and (3) determine nutrient release from decomposing alder leaves in these patches. Study sites were riparian areas adjacent to Brown and Le Bar creeks in the Skokomish River basin, Olympic National Forest, Washington. Red alder leaves were placed in litterbags in red alder and conifer riparian patches along each stream in November 2000 and collected after 1 and 3 years. There was rapid mass loss of alder leaves in the first year in both patch types, but decomposition was significantly faster ( p < 0.05) in alder patches (43.2% mass remaining, k = 0.855 year −1) than in conifer patches (48.4% mass remaining, k = 0.734 year −1). There was little mass loss after the first year and no significant difference in decomposition rates. After 3 years mass remaining was 44.2% ( k = 0.283 year −1) and 47.8% ( k = 0.48 year −1) in alder and conifer patches, respectively. Decomposition rate differences were attributed more to the effects of the different litters in each patch and the influence on soil microbial and faunal communities than differences in soil temperature and moisture. The forest floor was deeper in conifer patches (3.7 cm) than alder (1.8 cm) patches. This was ascribed to slower decomposition rates in conifer patches, greater litterfall in conifer patches, and/or removal of alder surface litter by flooding. Alder patches were lower in elevation (0.8 m above bankfull width) than conifer patches (2.2 m). Forest floor and soil C and N concentrations and pHs were not significantly different in alder and conifer patches. Nutrient release from decomposing alder leaves was not significantly different in conifer and alder patches, although there was a trend for C, N, P, K, and Ca to be lost faster from leaves in alder patches than conifer patches in the first year. Red alder litter input to riparian conifer patches will initially decompose rapidly and provide nutrients, particularly N and P to conifers, as well as enhancing soil C since long-term decomposition rates are slow.

Plant controls on decomposition rates: the benefits of restoring abandoned agricultural lands with native prairie grasses

Plant species can both directly and indirectly affect soil processes in various ways, including through functional traits related to the quantity and chemistry of biomass produced. Understanding how functional traits affect soil processes may be particularly important in restorations that specifically select a target plant community. In this study, I examined how species differing in litter traits alter decomposition, both directly via chemistry and indirectly via influences on soil microclimate. Decomposition dynamics of two old-field grasses were compared with the native prairie grass, Andropogon gerardii, in two Michigan old-fields. Decomposition rates were strongly, negatively related to tissue chemistry, but showed little effect of microclimate differences. Soil bacterial community composition differed between species at one site, while extracellular enzyme activities differed between species at the other site. These findings suggest plant species may be altering microbial community function. Overall, litter chemistry was the dominant factor determining decomposition rates, suggesting that restoring native prairie grasses with recalcitrant litter into grass-dominated old-fields could slow litter decomposition and ultimately lead to changes in soil carbon and nitrogen cycling. Eventually, this could lead to soils that more closely resemble the more organic-rich soils of native prairies and ultimately increase prairie plant community restoration success.

Context dependency of litter‐mixing effects on decomposition and nutrient release across a long‐term chronosequence

Litter decomposition is an important driver of terrestrial systems, and factors that determine decomposition rate for individual litter species have been widely studied. Fewer studies have explored the factors that regulate how mixing litters of multiple species affects litter decomposition and nutrient dynamics, and only a handful of studies have investigated how litter‐mixing effects may differ among different habitats or ecosystems, or how they respond to environmental gradients. We used a well‐established retrogressive chronosequence involving thirty lake islands in northern Sweden in which time since fire disturbance increases with decreasing island size; smaller islands therefore have reduced rates of aboveground and belowground ecosystem processes. On each of these islands we utilized plots with and without the long‐term experimental removal of shrubs. Litters from the six most common plant species on the islands were prepared in single‐, three‐ and six‐species litterbags, and placed on both the shrub‐removal and non‐removal plots on each island to decompose for one year. We found significant non‐additive effects of litter mixing on litter decomposition rates, on final litter N and P concentrations, and on litter N loss, but these non‐additive effects varied both in direction and magnitude with changed number of species, and even among litter mixtures with the same number of species. Further, the magnitude of non‐additive effects of litter mixing on both litter decomposition and nutrient dynamics was significantly influenced by both island size and the interaction between island size and shrub‐removal treatment. When shrubs were present, there was a U‐shaped relationship between these non‐additive effects and island size, while the relationship was positive when shrubs were removed. Hence, our results support previous findings that litter mixing may produce non‐additive effects on litter decomposition and nutrient dynamics, and that these effects tend to be idiosyncratic due to the importance of effects of individual species in the mixture. Most importantly, our results show that non‐additive litter‐mixing effects change greatly across environmental gradients, meaning that the biotic and abiotic characteristics of an ecosystem can be a powerful driver of the magnitude and even the direction of litter‐mixing effects on ecosystem processes.