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The soil organic carbon (SOC) pool of the Arctic region is currently protected by low temperatures, but is likely to decrease due to greater organic matter (OM) decomposition under a warmer climate. Negative feedback for climate warming can, however, be reversed by SOC accrual as climate warming leads to shifts in arctic vegetation (from grass to shrub) and soil faunal (introduction of macrofauna) communities affecting plant-soil C allocation. To decipher these contrasting effects, we performed a laboratory experiment with soils from dry tundra to test the interacting effects of plant litter quality (high-quality grass litter vs. the intermediate- and low-quality litter of shrubs) and soil fauna functional grouping (micro-, meso- and macrofauna [millipede]) on the processes of litter decomposition and OM stabilization. Our findings showed that macrofauna largely promoted decomposition of shrub litter, while soil micro- and mesofauna were mainly responsible for the decomposition of grass litter. Our study thus confirmed that, when introduced and established in a warmer Arctic, macrofauna may become an important agent in shrub litter decomposition. Our data also showed that with shrub litter, higher C content was stabilized as particulate OM (POM) in aggregates, whereas in grass litter and low-quality shrub litter, higher C content was stabilized as mineral-associated OM (MAOM). Both these effects were larger in the presence of macrofauna and with a higher abundance of fungi. This suggests that consequent shrub OM stabilization in occluded POM and MAOM fractions will be carried out jointly by macrofauna and fungi, which will probably lead to more efficient OM stabilization in Arctic soils than in the case of grass litter OM stabilization by micro- and mesofauna and bacteria. In conclusion, our study suggests that vegetation changes and the introduction of macrofauna in a warming climate will most probably lead to higher OM stabilization in Arctic soils. [Display omitted] • Macrofauna largely promoted decomposition of shrub litter. • Micro- and mesofauna decomposed mainly grass litter. • Higher C content was stabilized as particulate OM with shrub litter. • Higher C content was stabilized as mineral-associated OM with grass litter. • The effects were larger in the presence of macrofauna and fungi. [ABSTRACT FROM AUTHOR]

Abstract Factors shaping community structure of soil microbiota have been intensively studied; however, the pattern in community composition and structure of soil microbiota at large geographical scales and factors regulating its metabolic activity remains poorly understood. Here, we used a field transplantation experiments to investigate the effects of substrate and climatic conditions on basal soil respiration, microbial biomass C and diversity of soil microbiota by comparing local and transplanted soils along a latitudinal gradient. Soil samples collected in April 2008 at donor site (Sokolov, Czech Republic) in Central Europe were gamma-ray sterilized and transplanted to receptor sites in Europe and the USA in May and early June 2008. Soil samples were taken in June 2009 after one year of exposure and immediately prepared for laboratory analysis. Basal soil respiration in local soils increased from 22 to 42 mg CO 2 -C kg−1 h−1 with latitude while basal soil respiration in transplanted soils decreased with latitude from 32 to 19 mg CO 2 -C kg−1 h−1. The microbial biomass C in both transplanted and local soils decreased with latitude. Content of fungal and bacterial phospholipid fatty acids increased nearly twice with latitude in local soils. Shannon diversity index of fungal community decreased from 2.5 to 1.2 along the latitudinal gradient in transplanted soils while local soils increased from 0.9 to 2.4 with latitude. Based on our results, microbial activity is driven mainly by changes of the soil substrate along latitudinal and climatic gradients while microbial biomass is driven more by global climatic factors itself. The diversity of soil microbial communities is mostly affected by latitudinal and climatic factors while community structure is mostly shaped by substrate quality. Highlights • Basal soil respiration in local soils increased with latitude. • Basal soil respiration in transplanted soils decreased with latitude. • Fungal and bacterial PLFA increased with latitude in local soils. • Fungal diversity decreased with latitude in transplanted soils. • Fungal diversity increased with latitude in local soils. [ABSTRACT FROM AUTHOR]

Wood ants maintain a stable, high temperature in their nests from spring to autumn. Much of the heat is generated by the nest's microbial community, which might be differently affected by the addition of available carbon (C) sources in spring, when the nest temperature increases, than in summer, when the nest temperature is maintained at a high level. We used an incubation experiment to examine the effects of honeydew and resin on microbial activity and biomarkers' contents in ant nest and forest floor substrates. The effects of resin lasted longer than those of honeydew. Microbial activity was higher in the ant nest substrate than in the forest floor substrate, indicating that the microorganisms in the ant nest substrate were better adapted to utilize both C sources. Although bacteria were expected to be dominant after honeydew addition, this was not the case probably because the available C from honeydew had been depleted by the end of the incubation. Fungal biomarkers dominated at 10 °C with both C sources probably because fungi are better able than bacteria to remain active at low temperatures. [ABSTRACT FROM AUTHOR]

Trees growing in nutrient-limited temperate forest soils can gain nutrients by root proliferation into nutrient-rich hotspots and/or by forming mycorrhizal symbioses. In this study we investigated the effects of nutrient-rich hotspots (inhabited wood ant nests) on Norway spruce root biomass and occurrence of ectomycorrhizal (EcM) exploration types. Substrates were collected from the mineral soil layer in a temperate middle-European spruce forest (Nationalpark Harz, Germany) from four micro-regions within each of the five wood ant nests sampled, i.e. 1) centre of the belowground part of a nest, 2) nest's rim, 3) nest's run-off zone (ca. 20 cm from nest's rim), and 4) from the surrounding forest soil (>10 m from nest's rim). Root biomass, EcM exploration types, moisture and nutrient contents were determined in all substrates. Although naturally enriched, wood ant nests had neither root biomass nor occurrence of EcM exploration types higher compared to the surrounding forest soil. The probable main reasons were high phosphorus content and low moisture maintained inside inhabited nests, although the effect was not significant. Apparently, other substrate properties not determined in our study also affect the occurrence of exploration types in wood ant nest substrates. Inhabited wood ant nests thus seem unfavourable for root proliferation and their subsequent EcM colonization. However, roots can gain nutrients from the run-off zone around nests where low moisture is not maintained and nutrient contents are higher due to leaching from the nest substrate. [ABSTRACT FROM AUTHOR]

Nutrient addition to soil can strongly affect interactions at the root-soil interface, which play a central role in terrestrial ecosystem functions. Controversies, however, remain on whether or not soils sequester more carbon (C) with nutrient addition (for example in the context of increasing atmospheric CO 2 concentrations), and what is the role of plant traits and growth strategies in these impacts. In this study, we conducted a laboratory manipulation experiment focused on the effects of a grass (Lolium perenne L.) species, a legume (Lotus corniculatus L.) species, and their mixture with or without nutrient addition on plant biomass, root-derived respiration, soil organic matter (SOM) decomposition, and microbial community structure. L. perenne biomass and root-derived respiration were more responsive than L. corniculatus biomass and root-derived respiration to nutrient addition. The decomposition of SOM decreased, and the priming effect (PE) was negative, both with and without nutrient addition, in both plant species. Nutrient addition, however, impacted the magnitude of PE to a lesser extent in L. corniculatus than in L. perenne and in monocultures than in the mixture. With nutrient addition, fungi were more abundant and utilized a greater proportion of root-derived C than bacteria. In conclusion, the current study suggests that nutrient addition may promote a positive soil C-balance through reduced SOM decomposition, and that plant species mixtures with increased root-derived C-flow (representing root and rhizomicrobial respiration) suppressed SOM decomposition to a greater extent. • Grass biomass and root-derived respiration were more responsive than legume to nutrient addition. • The PE was negative, both with and without nutrient addition, in both plant species. • Nutrient addition impacted the magnitude of PE to a lesser extent in legume than in grass. • Nutrient addition impacted the magnitude of PE to a lesser extent in monocultures than in the mixture. [ABSTRACT FROM AUTHOR]

Wood ant nests are hotspots of nutrients and microbial activity in nutrient-limited coniferous forest ecosystems, as ants accumulate honeydew and nutrients in their nests due to foraging and building activities. In this study we carried out a microcosm experiment focussing on the role of bacteria and protozoa on carbon and nitrogen turnover in nutrient-rich and nutrient-poor litter materials. Two types of litter material, (i) ant nest material or (ii) surrounding forest floor material were sterilized and inoculated either with bacteria alone (B treatment) or with bacteria and protozoa in combination (BP treatment). The litter materials were subsequently incubated in laboratory microcosms for 21 days. Respiration of the microcosms was measured during the whole incubation period and leachates were sampled every week and analysed for ammonium and nitrate. Our results showed lower ammonium leaching and increased respiration in the BP treatment, which could be explained by higher microbial biomass in this treatment. The negative effect of protozoa on ammonium leaching was independent of the type of litter material suggesting that available carbon in nest material supported fixation of nitrogen in the bacterial biomass. Our data show that protozoan grazing can play a critical role in retaining nitrogen in ant nests by increasing microbial activity and biomass, and thereby preventing nitrogen leaching. [ABSTRACT FROM AUTHOR]

Wood ants build large, long-lasting nests and maintain stable high temperatures in nest centers from April to September to support brood development. Similar nest temperatures have been recorded regardless of latitude and altitude, suggesting that nests from colder environments produce more heat than nests from warmer environments. We measured changes in temperature and in situ respiration in nests from 700 and 1000 m a.s.l. We also sampled ants and nest materials from the same nests and measured their respiration at 10 and 20 °C in the laboratory. Both ant and microbial respiration increased greatly as temperature increased in spring, especially at 1000 m, resulting in the increase in nest temperature in spring. Metabolic activity greatly increased for ants in March and for nest microorganisms in April when nutrient contents also increased because of input of plant material and food. Nests from 1000 m maintained similar temperatures as nests from 700 m in summer but were colder in winter. Ants were responsible for the maintenance of high temperatures during summer but metabolic activity did not differ between the two altitudes, suggesting that the increased respiration and heat production in summer by ants at the higher altitude resulted from an increase in numbers of ants per colony. [ABSTRACT FROM AUTHOR]

We investigated the seasonal fluxes of CH 4 and CO 2 in wood ant ( Formica aquilonia ) nest mounds and in the surrounding temperate forest soil because temperate forest soils are important sinks of CH 4 and sources of CO 2 . Gas fluxes were measured eight times (at 1- to 2-month intervals) from July 2013 to May 2014 using a static chamber method in a spruce forest in the Czech Republic. Nest and air temperatures were recorded using dataloggers. Averaged across the 11-month sampling period, CH 4 flux was less negative in ant nest mounds (−16 ± 19 μg CH 4 m −2 h −1 ) than in the forest soil (−44 ± 18 μg CH 4 m −2 h −1 ). CH 4 flux did not show a strong seasonal pattern and was negative in ant nest mounds and forest soil, even in winter when the surfaces of ant nest mounds and forest soil were frozen. The only exception occurred in ant nest mounds in summer, when CH 4 fluxes tended to be less negative. Averaged across the 11-month sampling period, CO 2 flux was higher in ant nest mounds (189 ± 204 μg CO 2 m −2 h −1 ) than in the forest soil (105 ± 80 μg CO 2 m −2 h −1 ). The biggest difference in CO 2 flux occurred in July when it was almost six times higher in the ant nest mounds than in the forest soil. CO 2 flux was greater in summer than in winter in both ant nest mounds and the forest soil. In conclusion, ant nest mounds oxidize less CH 4 and produce more CO 2 than the surrounding forest soil. [ABSTRACT FROM AUTHOR]

Abstract: As ecosystem engineers, wood ants (Formica s. str.) influence many processes in forest ecosystems. Their nests are “hot spots” for CO2 production, and some nests are relatively wet (>35% moisture content) while others are dry (<20% moisture content). In this study, we compared CO2 production, the contribution of ant and nest material respiration to the overall CO2 production, and the rate of decomposition in dry vs. wet nests of wood ants (Formica polyctena). We also determined whether ants increase microbial respiration in nest material. Respiration in ant nests was higher than in the surrounding soil and was higher in wet nests than in dry nests. Ant contribution to the overall respiration was significantly higher than that of nest material respiration: the average ratio of the contributions (ants:nest material) was 75:25%. Litter mass loss (determined with litter bags buried in the nests) was significantly higher in wet nests than in dry nests. In a laboratory experiment, respiration was significantly higher with the combination of nest material and ants (provided with honey) than with the sum of respiration with nest material and ants (provided with honey) kept separately. This indicates that ants stimulate microbial respiration, most likely because they incorporate honey solution into the nest material. [Copyright &y& Elsevier]

Abstract: Soil biota were studied at four post-mining areas along a climatic gradient in the USA. The natural climax vegetation was hardwood forest (TN, IN), tallgrass prairie (IL), or shortgrass prairie (WY). Two chronosequences were used in each state, each contained young (2–5 y) and old (15–20 y) post-mining and a site with the area's climax vegetation. All sites were sampled in spring 2008 and 2011. Microbial biomass, microbial respiration, ergosterol, composition of microbial community (using phospholipid fatty acids), community composition of soil nematodes and macrofauna, soil chemistry, and soil microstructure (using thin soil sections) were studied. Total carbon and nitrogen content increased with successional age, while total phosphorus was often greater in young post-mining sites than in climax sites. Microbial biomass in forest chronosequences increased with age, actinobacteria were associated with prairie sites, and fungi were associated with forest sites. Root-feeding nematodes and macroflora were dominant in the shortgrass prairie sites. Earthworms were absent in such shortgrass sites but were present in the wetter, eastern sites. In forest chronosequences, other saprophages, litter transformers, and microphagous groups were also abundant. Absence of saprophagous groups, and especially earthworms, resulted in the absence of bioturbation in shortgrass prairie sites while worm casts and other biogenic structures formed an important part of the soil profile in other chronosequences. Both young and old restoration sites were much closer to the climax condition in shortgrass prairie than in the other sites. The shortgrass prairie soil community contained abundant root-feeding organisms, which may establish quicker than the more saprophagous soil biota that were abundant at the other sites. In chronosequences other than the one in shortgrass prairie, bioturbation played an important role in topsoil formation, which result to complex soil profile development compare to shortgrass prairie which may contribute to faster recovery communities in shortgrass prairie in comparison with tallgrass prairie and forest. [Copyright &y& Elsevier]

Organic soil amendments benefit agricultural soils depleted in soil organic matter because they improve soil chemical and biological properties. Biochar and compost, used as organic amendments, differ in their contents of total vs. available nutrients and may therefore differ in their effects on soil properties. The effects of these amendments have seldom been assessed in coarse-textured temperate soils and in no-tillage agriculture. In this study, we conducted a 6-month laboratory experiment with a coarse-textured temperate soil with a history of conventional farming to determine the effects of biochar, compost, and their combination, which were spread evenly on the soil surface, on microbial activity and biomass, and nutrient release and leaching. Both biochar and compost increased microbial activity and nutrient release compared to the no-addition treatment, but compost effects were relatively short term (six months). Biochar and compost had additive effects on all properties when added in combination. Biochar addition to soil increased soil pH, microbial biomass, and the abundance of fungi, G+ bacteria, and actinobacteria after 6 months of incubation compared to the compost treatment and the no-addition treatment. Although biochar was expected to reduce loss of nutrients through leaching, the short exposure time and disturbance of the soil probably hindered its capacity to adsorb nutrients and to thereby limit leaching; as a consequence, the biochar acted only as a slow-release nutrient fertilizer during the 6-month incubation. [Display omitted] • Compost increased microbial activity and nutrient release during the short term. • Biochar increased microbial activity and nutrient release during the long term. • Biochar increased microbial biomass, abundance of fungi and bacteria, and soil pH. • Biochar did not reduce loss of nutrients through leaching. [ABSTRACT FROM AUTHOR]

Abstract: Several previous studies reported on how the chemistry of the wood ant nest differs from the chemistry of the surrounding soil. There is enhanced amount of nutrients and cations in the ant nest and pH also differs from the nest surroundings. In this contribution, we focused on changes in soil chemistry with distance from the nest. Samples of mineral soil 0–5cm deep were taken in grid pattern at 1–19m from six Formica polyctena nests in a spruce forest in the Czech Republic. Soil pH decreased with distance; pH decreased rapidly between 1 to about 8m and then decreased more slowly. The decrease in pH corresponded with the increase in organic matter content with distance from the nest. Organic matter content was significantly and positively correlated with available Ca and K, i.e., available Ca and K increased with distance from the nest. The changes in organic matter content, pH, and available Ca were caused by ants collecting and using needles as building material. Wood ants can affect soil properties by rearranging organic matter, in nest surroundings. [ABSTRACT FROM AUTHOR]

The rate of litter and soil organic matter decomposition depends on temperature and on leaf carbon content and its availability to decomposers. The effects of these variables on decomposition in temperate forest soils are incompletely understood although future increases are predicted for temperature, the ratio of litter fractions, and the ratio of deciduous to coniferous forests. In this study, a 14-month laboratory incubation experiment of adding deciduous (beech) and coniferous (spruce) litter to soil (Cambisol) was carried out to test the effects of litter fraction, tree species, and temperature on soil respiration (as indicated by CO 2 release). The addition of the soluble and insoluble litter fractions as well as the whole tissue caused an increase in soil respiration (relative to the no-addition treatment). The effect of the soluble fraction, however, was less persistent than the effects of whole tissue or insoluble fractions, which suggests generally greater long-term effects of the latter fractions on soil respiration. Fractions derived from the beech litter increased soil respiration more than those derived from the spruce litter. This trend was especially apparent with the soluble litter fraction. A temperature increase of 3 °C caused no difference in soil respiration after the addition of beech litter fractions and even reduced soil respiration after the addition of spruce litter fractions. These results suggest that a future increase in the soluble fraction coupled with a shift in tree species composition from coniferous to deciduous might lead to an increase in soil respiration and thus to an increase in CO 2 release from the forest floor. The results, however, also suggest that a 3 °C increase in temperature will not lead to increases in CO 2 release from the forest floor, even if deciduous trees become more abundant. Unlabelled Image • Soluble litter fraction affected microbial activity for <30 days. • Whole tissue and insoluble fraction affected microbial activity for at least 409 days. • Beech litter increased soil microbial activity more than spruce litter. • The effect of temperature increase on microbial activity differed with tree species. [ABSTRACT FROM AUTHOR]

How litter at various stages of decomposition reacts to C and N additions is unclear. Here we used five substrates (litter, fermentation [Oe] layer, bulk soil, and the light fraction [LF] and heavy fraction [HF] of SOM) obtained from sites supporting five plant monocultures (Alnus glutinosa , Quercus robur , Salix caprea , Calamagrostis epigejos , or Picea omorica) with foliage C:N ratios ranging from 17 to 48. These plant-specific communities were experimentally planted on a post-mining heap and had affected the substrates used in this study for 40 years. Soils and other environmental factors were similar among the sites. Substrates were incubated for 3 weeks without nutrient addition or with C (glucose) or N (ammonium nitrate) addition, and microbial respiration was determined weekly. Substrate C:N ratios were determined at the start of the incubation and were highest for litter followed by Oe layer > LF > bulk soil and HF. Foliage C:N ratio was a better indicator of microbial respiration than the substrate C:N ratio, suggesting that the foliage C:N ratio reflected unmeasured leaf properties that determined microbial respiration. Respiration was highest in the litter followed by Oe layer > bulk soil > LF > HF. C addition increased respiration of the bulk soil (+39%), LF (+48%), and HF (+72%). Priming of SOM respiration was therefore higher in substrates with less available C. N significantly increased respiration of litter (+19%) but decreased respiration of bulk soil (−18%). The difference in respiration of HF vs. bulk soil following N addition suggested that, in addition to the stage of decomposition, environmental properties present in bulk soil but absent in HF may cause the reduction in respiration after N addition to bulk soil. Overall, the results indicate that differences in the contents of SOM fractions among soils will affect the responses of those soils to C and N additions. • Initial foliage C:N was a better indicator of microbial respiration than substrate C:N. • C addition increased respiration of the more-decomposed organic matter. • N addition increased respiration of litter but decreased respiration of bulk soil. • Different responses to N addition may be caused by interactions with the soil matrix. [ABSTRACT FROM AUTHOR]

Temperate forest soils are important carbon (C) sinks, where the C-stock is largely determined by the balance of leaf inputs and losses through respiration. However, studies dealing with leaf inputs to coniferous forest soils are limited although coniferous forests are widespread through the Northern temperate zone. In this study, we focused on the effects of soluble, insoluble and whole-tissue coniferous needle fractions on soil organic matter (SOM) decomposition and C storage in soil fractions. In addition, the effect of future increased C input was tested by applying a doubled amount of the soluble fraction (whole-tissue + soluble fraction). 13C-labelled needles were produced from spruce seedlings in growth chambers and needle fractions were added to the coniferous forest soil in laboratory microcosms. CO 2 respired during incubation from the microcosms was partitioned into needle- and SOM-derived components. After seven months, soils were destructively harvested and analysed for C content in soil fractions and microbial community composition. The soluble, insoluble and whole-tissue fractions resulted in cumulative priming (increased SOM-derived CO 2 relative to unamended controls) of 25 ± 8%, 40 ± 1%, and 39 ± 7%, respectively. The doubled soluble-C addition caused a slightly lower priming (38 ± 2%) than the whole-tissue fraction alone. The addition of needle fractions did not significantly affect the C content of soil fractions. However, the soluble fraction retained in soil was mainly found adsorbed onto mineral particles, whereas the insoluble and whole-tissue fractions occurred mainly as free particulate organic matter or adsorbed onto mineral particles. The insoluble and whole-tissue fraction led to increased fungal abundance and decreased abundance of G+ bacteria and actinobacteria. All the fractions were primarily incorporated into fungal biomass after seven months suggesting that fungi were the main consumers of all needle fractions after the labile C had been depleted. When considering all the C gains and losses, the addition of all needle fractions resulted in net soil C increase. This suggests that, although the input of the coniferous needles leads to some C losses through the priming of SOM decomposition, these C losses are compensated by new C storage either in SOM fractions or microbial biomass. • Soluble, insoluble and whole-tissue needle fractions cause positive priming of SOM. • Addition of needle fractions did not affect the C content of soil fractions. • Carbon from needle fractions was incorporated into fungal rather than bacterial biomass. • Addition of all the needle fractions to soil resulted in net soil C increase. [ABSTRACT FROM AUTHOR]

Agricultural soils have lost enormous amounts of soil organic matter (SOM) as the result of conventional agriculture. Nowadays, returning plant biomass in the form of crop residues is used as an efficient strategy to increase the amount of SOM. In addition, earthworms help increase the SOM content by transforming OM into stable forms. There is, however, limited information on how earthworms transform and stabilize various forms of crop residues and what the potential feedbacks on soil quality are. In a five-month laboratory manipulation experiment, we added maize biomass and/or biochar to a temperate agricultural soil both in the presence and absence of earthworms and carried out physical fractionation to analyse the stabilization of OM either as aggregate-occluded particulate OM (oPOM) or mineral-associated OM (MAOM). We show that the combination of maize biomass, maize biochar and earthworms proved to be highly efficient in increasing the OM content in agricultural soils and that earthworms can simultaneously enhance both OM decomposition and stabilization. In the absence of earthworms, the OM was stabilized more in the oPOM fraction, suggesting that both maize substrates acted as aggregation agents. In the presence of earthworms, however, maize substrates were stabilized more in the MAOM fraction, either through direct sorption as plant-derived substrates or as microbial necromass, suggesting that earthworms facilitate stabilization of both more-available maize biomass and more-recalcitrant maize biochar on mineral particles. We provide evidence that plant-derived rather than microbial-derived MAOM is present in the earthworm-affected agricultural soil and is thus important in increasing the SOM content and stability. • Earthworms can simultaneously enhance both OM decomposition and stabilization. • In the absence of earthworms, the OM was stabilized more in the oPOM fraction. • In the presence of earthworms, the OM was stabilized more in the MAOM fraction. • Plant-rather than microbial-derived MAOM is present in the earthworm-affected soil. [ABSTRACT FROM AUTHOR]

Microbial necromass carbon (C) can substantially contribute to stabilized soil organic matter (SOM), and effective management of this C may help mitigate climate change. However, factors important to the formation of microbial necromass are only partly understood. While bioavailable plant inputs may induce necromass formation by boosting microbial growth and C use efficiency, other microbial traits, such as those related to secretion systems or adhesion and motility, may also be relevant. These traits may be independent of the bioavailability of plant inputs and modulated by environmental factors such as soil depth or site age. Such links, however, have hardly been studied. Here, we used replicated plots of European alder (more bioavailable inputs) and Scots pine (less bioavailable inputs) to investigate links among plant inputs, soil depth, site age, microbial community composition, and microbial necromass C in stabilized SOM, i.e., particulate organic matter occluded within aggregates (oPOM) and mineral-associated organic matter (MAOM). We did not find evidence that bioavailable plant inputs, nor soil depth and site age, were major drivers of microbial necromass formation. Instead, certain microbial taxa, and microbial diversity in particular, were most tightly related to microbial necromass C in MAOM. Microbial necromass C also substantially contributed to oPOM (up to ∼57% of the C stored in that fraction), a C pool considered to largely derive from plant biomolecules. Combined, however, microbial necromass C in oPOM and MAOM only accounted for ∼23% of bulk C contents. Our results imply that effective C-focused research and management have to consider constraints on microbial community composition and diversity, microbial necromass in pools other than MAOM, and formation of plant-derived SOM. • Bioavailability of plant inputs is widely unrelated to microbial necromass C. • Microbial diversity most tightly related to microbial necromass C in MAOM. • Fungal taxa with certain traits were coupled with necromass C in MAOM. • Necromass accounted for substantial proportion of C in oPOM (up to ∼50%). [ABSTRACT FROM AUTHOR]

The study addresses the role of microbial community and soil properties development on species replacement during succession. During succession, plants directly and indirectly affect microbial communities and soil properties. Such belowground changes then feedback on plants. Although of both substrate-plant and microflora–plant interactions have been studied, the joint interactions of all three remain underexplored. We studied the effects of the microbial community and substrate on plants in a full-factorial experiment. Substrates from 10- and 50-year-old post-mining sites were sterilized. Suspensions from the early and late substrate, each applied in two dilutions (high and low diversity), were used to inoculate each substrate. Substrates were sown with three early and three late successional plant species both with one grass and two herbs. Aboveground plant biomass was higher in the late than early successional substrate. Grasses were not stimulated by higher diversity of microbial community while herbs grew better with the more diverse microbial community. Late successional herbs grew better with the late successional microbial community but early successional herbs grew well with both early and late microbial community. Grasses were thus very responsive to substrate quality and were not stimulated by microbial diversity while herbs responded positively to microbial diversity. This may affect species replacement during succession, from early succession herbs not showing strong responses to microbial community composition to late succession herbs showing specific responses to microbial communities, with grasses responding to nutrient conditions. Also nutrient supply and reduction of microbial community is likely to support grasses over herbs. [ABSTRACT FROM AUTHOR]