Search

Temperate coniferous forest soils are considered important sinks of soil organic carbon (C). Fresh C inputs may, however, affect soil microbial activity, leading to increased organic matter decomposition and carbon dioxide production. Litter consists of labile and recalcitrant fractions which are thought to be utilized by distinct microbial communities and at different rates during the growing season. In this study, we incubated the whole litter (LC + RC), the labile (LC) and the recalcitrant (RC) fractions with the coniferous soil at two temperatures representing spring/autumn (10 °C) and summer (20 °C) for one month. Soil respiration and microbial community composition were regularly determined using phospholipid fatty acids as biomarkers. The LC fraction greatly increased soil respiration at the beginning of the incubation period but this effect was rather short-term. The effect of the RC fraction persisted longer and, together with the LC + RC fraction, respiration increased during the whole incubation period. Decomposition of the RC fraction was more strongly affected by higher temperatures than decomposition of the more labile fractions (LC and LC + RC). However, when we consider the relative increase in soil respiration compared to the dH2O treatment, respiration increased more at a lower temperature, suggesting that available C is more important for microbial metabolism at lower temperatures. Although C was added only once in our study, no changes in microbial community composition were detected, possibly because the microbial community is adapted to relatively low amounts of additional C such as the amounts naturally found in litter. [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]

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]