Search

Background Forest soils are considered sinks for atmospheric C. Many studies revealed that tree species and their mycorrhizal association affect forest floor and topsoil organic C (OC) and total N, while the knowledge of their effect on subsoil OC and N is still scarce. Aims We aimed to identify (1) tree species and mycorrhizal association effects on forest floor, topsoil (0–30 cm) and subsoil (30–80 cm) OC and N stocks and vertical distribution and (2) drivers for soil OC and N distribution. Methods We sampled forest floor, topsoil and subsoil under Fagus sylvatica L., Quercus robur L., Acer pseudoplatanus L. and Fraxinus excelsior L. in four Danish common garden experiments along a gradient in soil texture and determined OC and N stocks. Results Total N (forest floor + soil) was higher under oak than beech, while total OC was unaffected by species. Forest floor C and N were higher under oak and beech, both ectomycorrhizal species (ECM), compared to under maple and ash, which are both arbuscular mycorrhizal species (AM). Relatively more OC and N were transferred to the topsoil under AM than ECM species, and this could be explained by greater endogeic earthworm biomass in AM species. In contrast, a higher proportion of OC was stored under ECM than AM species in the subsoil, and here OC correlated negatively with anecic earthworms. Subsoil N was highest under oak. Conclusions Tree species and in particular their mycorrhizal association affected the vertical distribution of soil OC and N. Tree species differences in topsoil OC and N were not mirrored in the subsoil, and this highlights the need to address the subsoil in future studies on AM- versus ECM-mediated soil OC and N stocks.

Soil fauna is one of the key drivers of the litter decomposition at both local and global scales, yet the role of tree species in mediating the effects of soil fauna on litter decomposition remains elusive. We conducted a field experiment using litterbags with three different mesh sizes that allowed access of microfauna (0.1 mm), micro- and mesofauna (2 mm), and total soil fauna (5 mm) to evaluate the decomposition of foliar litter of two tree species associated with arbuscular mycorrhizal (AM) fungi and three tree species associated with ectomycorrhizal (ECM) fungi in six Danish common garden sites. We also assessed how differences in initial litter quality, soil properties, and microbial community composition among the tree species may affect litter decomposition as well as soil fauna effects on litter decomposition. Results showed that (1) litter mass loss varied significantly among different mesh sizes and tree species, with litter decomposition rates (k) ranging from 0.273 to 3.482; (2) the access of mesofauna significantly increased litter k of 0.658 for AM and 0.396 for ECM tree species with no access of soil fauna 255 and 92%, respectively, while the access of both meso- and macrofauna increased k by 265 and 108% for AM and ECM trees, respectively; (3) tree species identity, mycorrhizal association, initial litter quality, soil properties, microbial community composition, and ambient soil fauna biomass were all significantly influencing factors on litter decomposition, but tree species identity was the dominant factor regardless of litterbag mesh size; and (4) the effects of mesofauna on litter decomposition were predominantly controlled by tree species identity, initial litter Mg concentration and lignin:N ratio, while the small additional impact of macrofauna access was not well explained by any of the assessed factors. Overall, our results suggest that tree species affect litter decomposition via different stimulation of soil fauna functioning, and that A

The restoration of Nardus grasslands is often hampered by high bioavailability of soil phosphorus and disturbed soil communities. In order to better understand these bottlenecks, we studied Nardus grassland species grown together in communities with fast-growing species in 50-liter pots along a gradient of bioavailable phosphorus with or without inoculated soil biota. These mesocosms allowed the plants to freely interact, including competition for light and nutrients. We investigated changes in the plant community composition along the phosphorus gradient using Threshold Indicator Taxa Analysis (TITAN). We found a negative threshold of 11.5 mg POlsen kg−1 with six significant indicator plant species. Above the threshold, a small increase in phosphorus resulted in a disproportionally large drop in biomass for the indicator species, including four typical Nardus grassland species. The decline in these ‘oligotrophic indicator species’ was also linked to increasing plant community biomass, so we suggest the oligotrophic indicator species to be outcompeted for light by fast-growing plant species. We did not find an effect of the soil biota treatment on the biomass of the oligotrophic indicator species, but did observe a positive effect of inoculation with soil biota on the total biomass of the plant community. Interestingly, the threshold for the plant communities in the mesocosm experiment was comparable to the upper bioavailable phosphorus concentrations in remnant Nardus grasslands in northern Belgium. For the restoration of Nardus grasslands, such phosphorus-poor soil conditions appear to be essential, because the plant species that typically occur in these grasslands are able to handle nutrient limitation, but not light limitation.

Earthworms are key organisms in forest ecosystems because they incorporate organic material into the soil and affect the activity of other soil organisms. Here, we investigated how tree species affect earthworm communities via litter and soil characteristics. In a 36-year old common garden experiment, replicated six times over Denmark, six tree species were planted in blocks: sycamore maple (Acer pseudoplatanus), beech (Fagus sylvatica), ash (Fraxinus excelsior), Norway spruce (Picea abies), pedunculate oak (Quercus robur) and lime (Tilia cordata). We studied the chemical characteristics of soil and foliar litter, and determined the forest floor turnover rate and the density and biomass of the earthworm species occurring in the stands. Tree species significantly affected earthworm communities via leaf litter and/or soil characteristics. Anecic earthworms were abundant under Fraxinus, Acer and Tilia, which is related to calcium-rich litter and low soil acidification. Epigeic earthworms were indifferent to calcium content in leaf litter and were shown to be mainly related to soil moisture content and litter C:P ratios. Almost no earthworms were found in Picea stands, likely because of the combined effects of recalcitrant litter, low pH and low soil moisture content

A change in land use from agriculture to forest generally increases soil acidity. However, it remains unclear to what extent plant traits can enhance or mitigate soil acidification caused by atmospheric deposition. Soil acidification is detrimental for the survival of many species. An in-depth understanding of tree species-specific effects on soil acidification is therefore crucial, particularly in view of the predicted global increases in acidifying nitrogen (N) deposition. Here, we report soil acidification rates in a chronosequence of broadleaved deciduous forests planted on former arable land in Belgium. This region receives one of the highest loads of potentially acidifying atmospheric deposition in Europe, which allowed us to study a ‘worst case scenario’. We show that less than four decades of forest development caused significant soil acidification. Atmospheric deposition undoubtedly and unequivocally drives postagricultural forests towards more acidic conditions, but the rate of soil acidification is also determined by the tree species-specific leaf litter quality and litter decomposition rates. We propose that the intrinsic differences in leaf litter quality among tree species create fundamentally different nutrient cycles within the ecosystem, both directly through the chemical composition of the litter and indirectly through its effects on the size and composition of earthworm communities. Poor leaf litter quality contributes to the absence of a burrowing earthworm community, which retards leaf litter decomposition and, consequently, results in forest-floor build-up and soil acidification. Also nutrient uptake and N2 fixation are causing soil acidification, but were found to be less important. Our results highlight the fact that tree species-specific traits significantly influence the magnitude of human pollution-induced soil acidification.