Mixed Litter Research Articles

Litter decomposition and microbial communities alters depending on litter type and overstory species in revegetated agricultural land

Acacia and Eucalyptus species are commonly used for revegetation in Australia and other parts of the world, yet little is known regarding how their litter might differentially impact decomposition rates and extracellular enzyme activities. To investigate this, a litter decomposition experiment was established using a reciprocal design (litter type x dominant overstory genus) in Acacia and Eucalyptus revegetation shelterbelts on a common soil to assess rates of decomposition and C degradation associated with differences in enzyme activities and microbial communities. Litter bags with two mesh sizes were used to either exclude (<2 mm) or allow access (>2 mm) by soil macrofauna. Bags were filled with either Eucalyptus, Acacia or an equal mix of Acacia and Eucalyptus litter. Decomposition, enzyme activities and bacterial and fungal community profiles were determined following recovery of surface-placed bags at 40, 96, 187, 307 days and 395 days and a buried control at day 395. Our findings did not support that mixed litter and litter under the same overstory genus would decay at a faster rate than that under a different overstory, in our study litter decomposition was greatest in Acacia litter irrespective of overstory genus. The abundance and structure of bacterial and fungal communities were assessed by terminal restriction fragment length polymorphism (T-RFLP) of 16S rRNA genes and quantified by qPCR. We were able to demonstrate that distinct fungal and bacterial communities occupied each litter type and these also differed between dominant overstory genus. However, we still lack a predictive framework for understanding more generally the impact of different plant species mixes on revegetation outcomes, including rates of return of contribution to ecosystem function.

Pinus sylvestris L. and Fagus sylvatica L. effects on soil and root properties and their interactions in a mixed forest on the Southwestern Pyrenees

Tree species alter soil properties, potentially modifying forest nutrients cycling. In the current management context in which mixed species forests are favoured over monocultures due to their biodiversity and productivity-related advantages, the assessment of species effects on soils, as well as their interactions with other species, gains increasing relevance. In this study, the effects of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) on soil properties were evaluated. Fine roots were paid special attention, measuring their biomass, functional traits (specific root length, root tissue density) and vertical distribution in order to discern the direction of these species interaction, either complementary or competitive. The research was carried out in the Southwestern Pyrenees (northern Spain), in an originally Scots pine stand transformed nowadays into a mixed forest by European beech natural regeneration. Soil and root samples were taken close to pine trees surrounded by other pines in areas that remain similar to pine monospecific stands, and close to pine and beech trees surrounded by both species in mixed areas. A lower C/N ratio was found in the soil close to beech stems. This suggests better quality in mixed litter in comparison to pine litter, leading to higher decomposition rates. Higher fine root biomass was found in the mixed areas mainly due to beech fine roots great abundance, which correlated positively with microbial biomass. Fine roots functional traits such as specific root length and diameter did not vary depending on their proximity to different tree species, though Scots pine fine root biomass decreased sharply when close to beech trees. This reduction, together with the already more abundant fine root biomass of beech, with higher specific root length and root tissue density than pine, lead to a competitive interaction in which European beech tends to dominate the soil at all depths. In this case, no complementarity effect at belowground level, strong enough to allow Scots pines to cope with beech soil colonization, was found under natural conditions.

Effects of exogenous nitrogen addition on litter decomposition and nutrient release in a temperate desert

A litterbag decomposition experiment was carried out in southern Gurbantunggut Desert, with four nitrogen treatments: N0(0 g N·m-2·a-1), N5(5 g N·m-2·a-1), N10(10 g N·m-2·a-1) and N20(20 g N·m-2·a-1). The aims were to examine the effects of exogenous nitrogen addition on decomposition rate and nutrient release of Tamarix ramosissima, Salicornia europaea and their mixture. Results showed that decomposition rates were significantly different among litter types. After 345 days, the decomposition rates of T. ramosissima, S. europaea and their mixture under different treatments were 0.64-0.70, 0.84-0.99 and 0.71-0.81 kg·kg-1·a-1, respectively. Both mono- and mixed-litters exhibited nutrient release during decomposition process, with the release rates being 60.6%-67.4%, 56.7%-62.6%, 57.4%-62.3%, 46.8%-63.0% for N, and 51.9%-77.9%, 59.9%-74.7%, 53.0%-79.9%, 52.3%-76.4% for P, respectively for the N0, N5, N10 and N20 treatments. Nitrogen addition did not affect litter decomposition rate. The dynamics of N and P during decomposition of different litter types showed different responses to nitrogen addition. Nitrogen addition inhibited N and P releases of S. europaea litter and P release of the mixed litter, but did not affect the nutrient release of T. ramosissima. The results suggested that nitrogen input would not promote litter decomposition in temperate desert ecosystems, but might retard the nutrient returning to soil system.

Mixing of plant litters strengthens their remediation effects on crude oil-contaminated soil.

To investigate the effects of the mixing of litters on their remediation efficiency in petroleum-contaminated soil, litters from two common plants in the petroleum-contaminated region of Northern Shaanxi, China, Bothriochloa ischaemum (L.) Keng and Sophora davidii Kom. ex Pavol., and their mixture were mixed with 45g/kg petroleum-contaminated soil. Based on these, a 150-day simulated remediation experiment was conducted at 25°C and consistent moisture conditions. The effects on the degradation of petroleum components and the restoration of nutrient contents, pH, and enzymatic activity in the disturbed soil were detected. The effects of the litter treatments on the community structure and carbon source utilization characteristics of soil microorganisms were also studied. The results indicated that all litter treatments significantly accelerated the degradation of petroleum components, while the mixing of litter exhibited significant synergistic effects, leading to significantly higher degradation rates of saturated hydrocarbons, aromatic hydrocarbons, and nonhydrocarbon substances than the observed rates in the single-litter treatments and the predicted rates based on the single-litter treatments. Litter treatment significantly increased the N and P contents and enzymatic activity of contaminated soil. The effects of mixed litter on soil chemical and biological properties fell between the effects of the 2 types of single-litter treatments. However, the mixing of litters exhibited significant synergistic effects in supplementing available P and increasing sucrase, dehydrogenase, lignin peroxidase, and laccase activity, while it exhibited significant antagonistic effects in supplementing nitrate nitrogen and increasing urease, phosphatase, polyphenol oxidase, and manganese peroxidase activity. Litter treatment significantly altered the community structure of soil microorganisms. The relative abundances of some petroleum-degrading microbial phyla or genera in mixed litter-treated soil were significantly different from those in single litter-treated soils, which might contribute to the strengthened remediation effects of mixed litter treatment. The results might provide a theoretical basis for the more effect utilization of biomass resources in the remediation of petroleum-contaminated soil.

Phenology and litter production in the mangrove genus Xylocarpus along rainfall and temperature gradients in tropical Australia

We investigated how variation in climate influences the timing and intensity of phenological events in two species of the mangrove genus Xylocarpus. Leaf fall in Xylocarpus granatum was continuous in high rainfall sites but was seasonal at sites with long dry seasons. Xylocarpus moluccensis is deciduous, and leaf shedding occurred over 1–2 months at different times in dry season months. Budding and flowering were tightly coupled in X. granatum and occurred in the wet season. At the highest rainfall site, flower fall in X. moluccensis occurred in the mid-wet season, but occurred 9 months later at other sites with protracted dry seasons. For X. moluccensis, the quantities of leaves, buds, flowers and total litter fall were negatively related to annual rainfall, whereas bud fall was negatively related to air temperature. Variations in the quantity of litter produced by X. granatum were not explained by the environmental variables considered. Mean litter production was significantly greater for X. moluccensis than X. granatum (5.16 v. 3.37Mgh–1 year–1 respectively). Mixed forest litter production was greater in forests containing X. moluccensis than X. granatum (7.86 v. 5.95Mgh–1 year–1 respectively). X. granatum has a more plastic response to environmental drivers of canopy production than X. moluccensis.

High fungal substrate specificity limits the utility of environmental DNA to detect fungal diversity in bogs

Fungi are a highly diverse group of organisms and play a significant role in decomposition and carbon cycling in boreal ecosystems. To determine how fungal communities are structured in peat bogs and how to obtain representative samples for monitoring fungal community changes, we separately sampled and sequenced (ITS2, Illumina MiSeq) peat, mixed litter and litter from individual dominant plant species in five permanent plots in raised bogs in the Jizerské Hory Mountains (Czech Republic). In total, we detected 68–103 OTUs per plot. The fungal assemblages were mostly influenced by substrate identity, whereas the effect of the site was minimal. Only a few identified OTUs behave like generalists. The most specific fungi were found in dead parts of Calluna vulgaris, Trichophorum cespitosum and Drosera rotundifolia. The high substrate heterogeneity means that sequencing soil core samples does not provide an exhaustive inventory of the fungal diversity in bogs. Poor correspondence was observed between the recorded OTUs and either visually inspected fruitbodies or literature reports on the fungal taxa associated with the analysed substrates.

Volatile organic compounds from leaf litter decomposition alter soil microbial communities and carbon dynamics.

Investigations into the transfer of carbon from plant litter to underlying soil horizons have primarily focused on the leaching of soluble carbon from litter belowground or the mixing of litter directly into soil. However, previous work has largely ignored the role of volatile organic compounds (VOCs) released during litter decomposition. Unlike most leaf carbon, these litter-derived VOCs are able to diffuse directly into the soil matrix. Here, we used a 99-d microcosm experiment to track VOCs produced during microbial decomposition of 13 C-labeled leaf litter into soil carbon fractions where the decomposing litters were only sharing headspace with the soil samples, thus preventing direct contact and aqueous movement of litter carbon. We also determined the effects of these litter-derived VOCs on soil microbial community structure. We demonstrated that the litter VOCs contributed to all measured soil carbon pools. Specifically, VOC-derived carbon accounted for 2.0, 0.61, 0.18, and 0.08% of carbon in the microbial biomass, dissolved organic matter, mineral-associated organic matter, and particulate organic matter pools, respectively. We also show that litter-derived VOCs can affect soil bacterial and fungal community diversity and composition. These findings highlight the importance of an underappreciated pathway where VOCs alter soil microbial communities and carbon dynamics.

Characteristics of liquid smoke from several kinds of waste

Research into making liquid smoke has been carried out using a 3 in 1 model furnace. The material used is waste consisting of wide leaf litter, a mixture of small leaf litter and mahogany bark. The results showed that the pH ranged from 3.82 to 4.69; specific gravity of 0.99. The content of phenol and acetic acid, liquid smoke, mahogany peel 0.34%, 0.62% and 0.86%, leaf litter mixture width 0.01% and 3.74% and small leaf litter mixture 0.06% and 0.88 %. From the results of the GCMS pyrolysis test, it was known that the acid derivatives, phenols and other components. The highest acid derived compound was obtained from liquid smoke of mixed litter of 66.53% relative and the lowest from liquid smoke of mixed leaf litter which was 8.78% relative. The highest phenol derivative content is from liquid smoke of mahogany bark of 29.45% relative and the lowest of liquid smoke of mixed litter is 4.92% relative. Liquid smoke obtained can be used as a trigger for plant growth and prevention of disease pests inplants.

Mixture of plant functional groups inhibits the release of multiple metallic elements during litter decomposition in alpine timberline ecotone

Mixed litter decomposition is a common phenomenon in nature and is very important for the circulation of material through an ecosystem. Different plant functional groups (PFGs) are likely to interact during decomposition. It is unclear how mixed decomposition influences the release of multiple metallic elements, and the biogeochemical circulation mechanism in the alpine ecosystem remains elusive. In this study, a two-year experiment on decomposition of mixed litter from six dominant PFGs was conducted at two elevations in an alpine timberline ecotone using the litterbag method. First, the results suggested that PFG identity had greater impacts on the release of all metallic elements than elevation. The release rates of potassium (K), calcium (Ca), magnesium (Mg) and copper (Cu) in graminoid, deciduous shrub and forb litter were significantly higher than those in evergreen conifer, evergreen shrub and mixed litter. Second, the release of metallic elements showed non-additive effects during mixed litter decomposition. K, Ca, Mg, sodium (Na), Cu, and aluminium (Al) exhibited antagonistic effects, while Fe exhibited a synergistic effect. The antagonistic effects on Na, K, Ca and Cu release increased with increasing elevation, while the antagonistic effects on Mg, Al and Mn release decreased with increasing elevation. Third, Al and Fe showed high levels of accumulation. The K release rate decreased while Al and Fe accumulation increased with plant litter upward shift. In conclusion, mixtures of PFGs inhibits the release of multiple metallic elements during litter decomposition in the alpine timberline ecotone. We speculate that an upward shift in PFGs in response to climate warming will slow the release of K and accelerate the enrichment of Fe and Al in alpine timberline ecotones.

Characteristics of fungal community structure during the decomposition of mixed foliage litter from Pinus massoniana and broadleaved tree species in southwestern China

AbstractAimsThe conifer litter is fairly recalcitrant and nutrient poor, and broadleaved litter promotes coniferous litter decomposition by increasing degradable nutrients and promoting microbial metabolism. Mixing Pinus massoniana litter and three broadleaved litters may increase the diversity and abundance of fungal decomposers compared with those in P. massoniana litter and vary depending on the number and proportion of broadleaved species included.MethodsWe analysed the composition and diversity of fungal communities during mixed litter decomposition in southwestern China with 35 treatments (P. massoniana, Toona sinensis, Cinnamomum camphora and Sassafras tzumu litter) using Illumina high-throughput sequencing.Important FindingsThe mixed litters increased fungal diversity and richness compared with those in the single-species litter, except in the following treatments: P. massoniana litter accounting for 70%–80% in the P. massoniana + T. sinensis, P. massoniana + S. tzumu + T. sinensis and P. massoniana + S. tzumu + C. camphora combinations, and P. massoniana + S. tzumu + C. camphora + T. sinensis combination with small proportion of T. sinensis litter. The diversity and richness of the 7:1:2 combination of P. massoniana + C. camphora + T. sinensis were significantly higher than those in the other treatments. Ascomycota and Basidiomycota were the dominant phyla, and Aspergillus was the most abundant genus. The decomposition of litters from one needleleaf and one broadleaved species (6:4) and one needleleaf species and two broadleaved species (broadleaved litter accounting for 30%–40%) exhibited synergistic interactions throughout the decomposition process, and the relative abundance of fungi that decompose refractory substances increased. The P. massoniana + C. camphora + T. sinensis combination and a 30%–40% broadleaf litter proportion increased fungal diversity and accelerated the decomposition of recalcitrant coniferous litter. Therefore, C. camphora and T. sinensis are a potential candidate species for mixed planting with P. massoniana.

Drought conditions alter litter decomposition and nutrient release of litter types in an agroforestry system of China.

Evaluating how decomposition rates and litter nutrient release of different litter types respond to changes in water conditions is crucial for understanding global carbon and nutrient cycling. However, it is unclear how decreasing water affects litter mixture interactions for the maize–poplar system in arid regions. Here, the responses of the litter decomposition process and litter mixture interactions in the agroforestry system to changes in water conditions (control, light drought, and moderate drought) were tested. Moderate drought significantly decreased the decomposition rate for poplar leaf and mixed litters, and decomposition rate was significantly reduced for maize straw litter in light and moderate drought stress. The mass loss rates of maize straw and mixed litters were significantly higher than that of the poplar leaf litter under drought conditions, but there was no significant difference among the three litter types in the control. There was no interaction between mass loss of the mixed litter in the control and light drought conditions, and the litter mixture interaction showed nonadditive synergistic interactions under moderate drought. In terms of nutrient release, there was also no interaction between litter mixture with nitrogen and carbon, but there was antagonistic interaction with potassium release under the light drought condition. Our results demonstrate that drought conditions can lead to decreasing decomposition rate and strong changes in the litter mixture interactions from additive effects to nonadditive synergistic effects in moderate drought. Moreover, light drought changed the mixture interaction from an additive effect to an antagonistic interaction for potassium release.

Influences of litter diversity and soil moisture on soil microbial communities in decomposing mixed litter of alpine steppe species

Many studies have examined the effects of plant diversity and soil water availability on litter decomposition, but little is known about how these two factors interactively influence soil microbial communities, especially in alpine ecosystems. Therefore, the objective of this work was to investigate how litter diversity influences soil microbial communities under different moisture conditions in an alpine steppe ecosystem in Northern Tibet. We collected litter of four abundant plant species (Stipa purpurea, Sp; Carex moorcroftii, Cm; Leontopodium pusillum, Lp; and Artemisia nanschanica, An), and used phospholipid fatty acid (PLFA) analysis to measure soil microbial biomass and community structure. A fully factorial litter mixing experiment under different soil moisture conditions (i.e., 20%, 30% and 40% water holding capacity) was employed. The results showed that litter composition, rather than species richness, significantly affected soil microbial biomass and community composition. The presence of Sp, Cm and An exerted positive or negative effects on soil microbial communities. Litter quality (i.e., C:N ratio) could explain the effects of litter composition on soil microbial communities. High soil moisture facilitated the growth of gram-negative bacteria, while gram-positive bacteria and fungi were more abundant in lower moisture soil. We did not detect any interactive effects of litter species richness and soil moisture on the microbial communities. However, the effects of litter composition on soil microbial communities were dependent on soil moisture condition. These findings indicate that litter composition, rather than species richness, shows interactive effects with soil moisture on soil microbes, and both factors are important in regulating ecosystem functions.

Natural Regeneration Following Partial and Clear-Cut Harvesting in Mature Aspen-Jack Pine Stands in Eastern Canada

Over the last three decades, the ecological basis for the generalized use of even-aged silviculture in boreal forests has been increasingly challenged. In boreal mixed-wood landscapes, the diminishing proportion of conifers, to the benefit of intolerant hardwoods, has been a primary concern, coupled with the general rarefication of old-growth conifer-dominated stands. In this context, partial cutting, extended rotations and forest renewal techniques that eliminate or reduce regenerating hardwoods have been proposed as means of regaining greater conifer cover. As a result, experimentation and industrial application of various forms of both variable retention and partial harvesting are occurring across the commercial Canadian boreal forest. In this study, we compared the effects of two harvesting intensities, clearcutting and low-intensity partial cutting (removal of 25–31% of tree basal area), on hardwood and conifer regeneration levels 7–19 years following treatments in aspen (Populus tremuloides)-dominated stands and verified whether regeneration differences existed between micro-sites on and off machinery trails. The abundance of aspen regeneration increased with percent basal area removal and was positively correlated to the abundance of mature aspen prior to harvesting. The abundance of fir (Abies balsamea) regeneration after partial cutting was similar to controls and higher than after clear-cutting and was positively correlated with ground cover of mixed litter (i.e., mixture of needles and leaves) and negatively correlated with ground cover of broadleaf litter. These results suggest that it is possible in boreal mixed-woods to control aspen abundance and promote or maintain conifer regeneration through silvicultural treatments that limit canopy opening and promote mixed forest floor litter.

Effect of monospecific and mixed litters on bacterial communities' structure and functions under contrasting Mediterranean climate conditions

Global climate change is expected to contribute to intense droughts and heatwaves in the Mediterranean basin, motivating ecological research to explore the responses of litter microbial communities to more drastic climatic conditions. Here, we investigated how the functioning of microbial decomposition systems may be affected by litter source and mixing in two contrasting Mediterranean climate contexts: a sub-humid climate in France vs a semi-arid climate in Algeria. Studies included in situ incubation of litter bags of monospecific litters (Pinus halepensis, Pistacia lentiscus, and Quercus ilex) and binary mixtures (Pinus/Pistacia; Pinus/Quercus) of litters in France and Algeria. Following a 12-month incubation, the remaining litter was chemically characterised using elemental analyses and solid-state 13C NMR spectroscopy. Microbial properties evaluated included basal respiration (BR), active microbial biomass (MB), community-level physiological profiling (CLPP), and molecular fingerprinting (T-RFLP). In both countries, negative correlations were observed between MB and ratios of C/N and (aromatics+phenols)/N. Basal respiration was also negatively correlated to both ratios in France; however, the opposite trend was found in Algeria. The effect of litter mixing on MB, BR, and microbial functional diversity (catabolic diversity index ECO H′) also differed between climates. The mixture of Pinus and Quercus litter led to limited heterotrophic CO2 release in the Algerian arid context i.e. a synergistic effect on MB associated with an antagonistic effect on BR. Higher bacterial genetic diversity (Terminal Restriction Fragment TRF richness and evenness) was found in Algeria whereas higher functional diversity (catabolic diversity index ECO H′) was found in France, suggesting that the higher genetic diversity potential in the arid climate context did not lead to functionally diverse bacterial communities. Our findings on the differing effect of litter chemical properties- (aromatics+phenols)/N and C/N- on microbial functioning (BR and MB) in sub-humid and semi-arid climates indicate that the impact of litter chemistry (litter source; litter admixtures) on C cycling is climate-dependent.

Mixing litter from Larix kaempferi (lamb.) Carr. and broad-leaved trees enhances decomposition by different mechanisms in temperate and subtropical alpine regions of China

Larix kaempferi planting with broad-leaved trees can increase production and alleviate soil degradation; however, the mechanism is unclear, especially on large scales and in different climate regions. This paper attempts to explain the underlying mechanism in a temperate region and northern subtropical alpine region of China. Litter decomposition rates, nutrient release, enzyme activity and microbial community composition were determined in conifer litter, broad-leaved litter and mixed litter by the litterbag method during about 500 days in the two regions. Decomposition rate was increased by 4.00% in temperate region and 3.38% in the subtropical region after litter mixing and the synergistic effect increased with decomposition progress. However, nutrients release was not always enhanced, and enzyme activities were enhanced at the most of decomposition time and higher in the subtropical region. After litter mixing, a few new dominant taxa emerged, and the microbial gene quantities were increased in the temperate region, but not in the subtropical region. The dominant bacterial taxa were similar, while most of the dominant fungal taxa shifted with decomposition. In addition, the dominant fungi completely differed between the two regions. The environmental variables with greater influence on microbial community were similar in the two regions, including C:N, C:P and pH. After mixing with broad-leaved litter, the decomposition of Larix kaempferi was enhanced by increasing enzyme activities and microbial quantities in the temperate region, but the mechanisms were not clear in the subtropical region.

Nonadditive effects of decomposing mixed foliar litter on the release of several metallic elements in a Pinus massoniana Lamb. forest

The mixture of decomposing litter from three predominant tree species in a Masson pine ( Pinus massoniana Lamb.) forest showed advantages in elemental cycling, and the species component identities were found to be an important driver for the release of several metallic elements. Although mixed forests have long been considered essential to sustainable forestry management, little information is available regarding the effects of the mixed planting of predominant afforestation species on several metallic elements during litter decomposition in the Three Gorges Reservoir region, China. The objectives of this study were to investigate the potential nonadditive effects on element loss from decomposing litter and to estimate the relationship between the mixing effect and the change in litter quality with environmental hydrothermal dynamics. Treatments with one, two, or three species of pine, oak (Quercus variabilis Bl.) and cypress (Cupressus funebris Endl.) based on equal litter mass proportions were used in a field litter bag experiment, and the release of potassium, calcium, magnesium, manganese, iron, copper, zinc, and sodium was measured. Over the 360-day incubation period, most elements decayed faster in oak litter than in the other single-species treatments. A comparison of the litter mixtures revealed that most elements displayed their slowest decay in the pine+cypress combination, whereas the decay values obtained with the cypress+oak or pine+oak combinations were generally greater than those obtained with the pine+cypress+oak combination. Increases in the nonadditive effect on the release of metallic elements, with the exception of calcium, magnesium, and copper, were found in the different phases compared with the incubation time. Changes in elemental traits and environmental hydrothermal dynamics can regulate mixing effects on elemental decay in litter mixtures. The mixing of the studied tree species can alter elemental cycling in plantations, and mixed planting with oak appears to strengthen the cycling process.

Effects of mixed coniferous and broad-leaved litter on bacterial and fungal nitrogen metabolism pathway during litter decomposition

Litter decomposition and nitrogen metabolism are the key determinants of nutrient cycling in forest ecosystems. However, how processes and functional groups are affected by mixed litter decomposition is poorly understood. The aim of this research is to determine how the microbial functional pathways involved in nitrogen cycling varied according to the changes in the microbial community composition induced by mixing of litter. The fallen leaf litters were collected on days 60, 150, 270, and 360 in Larix, Sassafras, and Larix/Sassafras plantations. The nitrogen properties, enzyme activities, microbial communities, and nitrogen metabolism pathways were evaluated during decomposition of three litter types. The pH, nitrate content, and organic nitrogen degradative enzyme activities of mixed litter were higher than those of Larix litter. Mixed litter promoted the abundances and potential nitrogen metabolism functions of Sphingomonas, and Janthinobacterium versus Larix litter during decomposition. The abundances of genes associated with microbial organic nitrogen degradation and assimilatory nitrate reduction differed significantly according to litter types. The abundance of microbial functional genes related to the production of ammonium was significantly higher in mixed litter than in Larix litter. Co-occurrence network analyses showed that mixed litter had a less complex but more stable microbial co-occurrence pattern versus monospecific litter. The difference of litter pH and nitrate content between mixed litter and Larix litter are determinants of changes in microbial functional potentials of nitrogen metabolism. Mixing Sassafras/Larix litter would selectively modulate nitrogen metabolism related bacterial groups, together with functional pathways of organic nitrogen degradation and assimilatory nitrate reduction processes. These changes were mainly driven by litter pH and nitrate content.

Shifts in plant functional community composition under hydrological stress strongly decelerate litter decomposition.

Litter decomposition is a key process of nutrient and carbon cycling in terrestrial ecosystems. The decomposition process will likely be altered under ongoing climate change, both through direct effects on decomposer activity and through indirect effects caused by changes in litter quality. We studied how hydrological change indirectly affects decomposition via plant functional community restructuring caused by changes in plant species’ relative abundances (community‐weighted mean (CWM) traits and functional diversity). We further assessed how those indirect litter quality effects compare to direct effects. We set up a mesocosm experiment, in which sown grassland communities and natural turf pieces were subjected to different hydrological conditions (dryness and waterlogging) for two growing seasons. Species‐level mean traits were obtained from trait databases and combined with species’ relative abundances to assess functional community restructuring. We studied decomposition of mixed litter from these communities in a common “litterbed.” These indirect effects were compared to effects of different hydrological conditions on soil respiration and on decomposition of standard litter (direct effects). Dryness reduced biomass production in sown communities and natural turf pieces, while waterlogging only reduced biomass in sown communities. Hydrological stress caused profound shifts in species’ abundances and consequently in plant functional community composition. Hydrologically stressed communities had higher CMW leaf dry matter content, lower CMW leaf nitrogen content, and lower functional diversity. Lower CWM leaf N content and functional diversity were strongly related to slower decomposition. These indirect effects paralleled direct effects, but were larger and longer‐lasting. Species mean traits from trait databases had therefore considerable predictive power for decomposition. Our results show that stressful soil moisture conditions, that are likely to occur more frequently in the future, quickly shift species’ abundances. The resulting functional community restructuring will decelerate decomposition under hydrological stress.

Macro-detritivores Assist Resolving the Dryland Decomposition Conundrum by Engineering an Underworld Heaven for Decomposers

Litter decomposition in most terrestrial ecosystems is regulated by moisture-dependent microorganism activity, among other things. Decomposition models typically underestimate rates of plant litter decomposition in drylands, suggesting the existence of additional drivers of decomposition. Attempts to reveal these drivers have predominantly focused on abiotic degradation agents, alternative moisture sources, and soil–litter mixing. The role of burrowing animals in promoting decomposition has received less attention despite greatly contributing to plant litter transfer from the harsh desert surface to the moister and nutrient-rich environment belowground. Our goal was to explore how macro-detritivore burrows affect plant litter mineralization dynamics. We introduced 13C-labeled litter belowground into (1) desert isopod (Hemilepistus reaumuri) burrows and (2) artificial burrows, and aboveground on top of (3) isopod fecal pellet mounds and (4) bare soil crust. We compared the litter mass loss between the four treatments and used cavity ring-down spectroscopy to reveal the in situ mineralization dynamics. No litter mineralization was evident during the dry summer months both above- and belowground. Following rain events, mineralization rates spiked in all four micro-environments, quickly diminishing aboveground while slowly waning belowground. Total litter mass loss was twofold higher below than aboveground and was significantly higher in isopod burrows compared to artificial burrows. Our findings demonstrate that burrowing macro-detritivores promote litter decomposition in deserts by transferring organic matter to their burrows where favorable climatic conditions and a nutrient-enriched environment foster microbial activity. Thus, attempts to resolve the dryland decomposition conundrum should not be limited to exploring factors that allow decomposition under harsh desert surface climatic conditions, but focus on the role that animals play in facilitating decomposer-friendly environments to which they translocate plant litter.

Synergistic effects: a common theme in mixed-species litter decomposition.

Litter decomposition plays a key role in nutrient cycling across ecosystems, yet to date, we lack a comprehensive understanding of the nonadditive decomposition effects in leaf litter mixing experiments. To fill that gap, we compiled 69 individual studies with the aim to perform two meta-analyses on nonadditive effects. We show that a significant synergistic effect (faster decomposition in mixtures than expected) occurs at a global scale, with an average increase of 3-5% in litter mixtures. In particular, low-quality litter in mixtures shows a significant synergistic effect, while additive effects are observed for high-quality species. Additionally, synergistic effects turn into antagonistic effects when soil fauna are absent or litter is in very late stages of decomposition (near-humus). In contrast to temperate and tropical areas, studies in boreal regions show significant antagonistic effects. Our two meta-analyses provide a systematic evaluation of nonadditive effects in mixed litter decomposition studies and show that litter quality alters the effects of litter mixing. Our results indicate that nutrient transfer, soil fauna and inhibitory secondary compounds can influence mixing effects. We also highlight that synergistic and antagonistic effects occur concurrently, and the final litter mixing effect results from the interplay between them.