Presentation_1.PDF

<p>Phosphorus (P) is an important nutrient, whose plant-available form phosphate is often low in natural forest ecosystems. Mycorrhizal fungi mine the soil for P and supply their host with this resource. It is unknown how ectomycorrhizal communities respond to changes in P availability. Here, we used young beech (Fagus sylvatica L.) trees in natural forest soil from a P-rich and P-poor site to investigate the impact of P amendment on soil microbes, mycorrhizas, beech P nutrition, and photosynthesis. We hypothesized that addition of P to forest soil increased P availability, thereby, leading to enhanced microbial biomass and mycorrhizal diversity in P-poor but not in P-rich soil. We expected that P amendment resulted in increased plant P uptake and enhanced photosynthesis in both soil types. Young beech trees with intact soil cores from a P-rich and a P-poor forest were kept in a common garden experiment and supplied once in fall with triple superphosphate. In the following summer, labile P in the organic layer, but not in the mineral top soil, was significantly increased in response to fertilizer treatment. P-rich soil contained higher microbial biomass than P-poor soil. P treatment had no effect on microbial biomass but influenced the mycorrhizal communities in P-poor soil and shifted their composition toward higher similarities to those in P-rich soil. Plant uptake efficiency was negatively correlated with the diversity of mycorrhizal communities and highest for trees in P-poor soil and lowest for fertilized trees. In both soil types, radioactive P tracing (H₃³³PO₄) revealed preferential aboveground allocation of new P in fertilized trees, resulting in increased bound P in xylem tissue and enhanced soluble P in bark, indicating increased storage and transport. Fertilized beeches from P-poor soil showed a strong increase in leaf P concentrations from deficient to luxurious conditions along with increased photosynthesis. Based on the divergent behavior of beech in P-poor and P-rich forest soil, we conclude that acclimation of beech to low P stocks involves dedicated mycorrhizal community structures, low P reserves in storage tissues and photosynthetic inhibition, while storage and aboveground allocation of additional P occurs regardless of the P nutritional status.</p

Occurrence of the bacterial-feeding taxa <i>Cephalobus</i>, <i>Eucephalobus</i>, <i>Acrobeloides</i> and <i>Alaimus</i> in soil cropped with maize (plant), amended with maize shoot litter (litter) or bare soil.

<p>Abundance (individuals 100 g^-1 dry weight soil ± SD) is given in topsoil (0–10 cm), rooted zone (40–40 cm), and root free zone (60–70 cm) in the years 2012 and 2013. Values within a sampling date with the same or no letters are not significantly different according to Tukey´s HSD test at <i>P</i> < 0.05.</p

Disentangling the root- and detritus-based food chain in the micro-food web of an arable soil by plant removal

<div><p>Soil food web structure and function is primarily determined by the major basal resources, which are living plant tissue, root exudates and dead organic matter. A field experiment was performed to disentangle the interlinkage of the root-and detritus-based soil food chains. An arable site was cropped either with maize, amended with maize shoot litter or remained bare soil, representing food webs depending on roots, aboveground litter and soil organic matter as predominant resource, respectively. The soil micro-food web, i.e. microorganisms and nematodes, was investigated in two successive years along a depth transect. The community composition of nematodes was used as model to determine the changes in the rhizosphere, detritusphere and bulk soil food web. In the first growing season the impact of treatments on the soil micro-food web was minor. In the second year plant-feeding nematodes increased under maize, whereas after harvest the Channel Index assigned promotion of the detritivore food chain, reflecting decomposition of root residues. The amendment with litter did not foster microorganisms, instead biomass of Gram-positive and Gram-negative bacteria as well as that of fungi declined in the rooted zone. Likely higher grazing pressure by nematodes reduced microbial standing crop as bacterial and fungal feeders increased. However, populations at higher trophic levels were not promoted, indicating limited flux of litter resources along the food chain. After two years of bare soil microbial biomass and nematode density remained stable, pointing to soil organic matter-based resources that allow bridging periods with deprivation. Nematode communities were dominated by opportunistic taxa that are competitive at moderate resource supply. In sum, removal of plants from the system had less severe effects than expected, suggesting considerable food web resilience to the disruption of both the root and detrital carbon channel, pointing to a legacy of organic matter resources in arable soils.</p></div

Occurrence of the root-feeding <i>Malenchus</i>, the bacteria and unicellular eukaryote feeding <i>Eumonhystera</i>, and the fungal-feeding <i>Aphelenchus</i> and <i>Aphelenchoides</i> in soil cropped with maize (plant), amended with maize shoot litter (litter) or bare soil.

<p>Abundance (individuals 100 g^-1 dry weight soil ± SD) is given in topsoil (0–10 cm), rooted zone (40–50 cm), and root free zone (60–70 cm) in the years 2012 and 2013. Values within a sampling date with the same or no letters are not significantly different according to Tukey’s HSD test at <i>P</i> < 0.05.</p

Nematode food web conditions (Community Indices ± SD) at plots cropped with maize (plant), amended with maize shoot litter (litter) or bare soil, in topsoil (0–10 cm), rooted zone (40–50 cm) and root free zone (60–70 cm) after two vegetation periods.

<p>Nematode food web conditions (Community Indices ± SD) at plots cropped with maize (plant), amended with maize shoot litter (litter) or bare soil, in topsoil (0–10 cm), rooted zone (40–50 cm) and root free zone (60–70 cm) after two vegetation periods.</p

Micro-Food Web of an Arable Soil affected by Plant Removal

An arable site was cropped either with maize, amended with maize litter or remained bare soil. The microbial and nematode communities were investigated in two successive years along a depth transect.<br>The data shown are the raw data set of the publication "Disentangling the root- and detritus-based food chain in the micro-food web of an arable soil by plant removal in PLOS ONE<br

Proportion of nematode trophic groups (% ± SD) in soil cropped with maize (plant), amended with maize shoot litter (litter) or bare soil in topsoil (0–10 cm) in the years 2012 and 2013.

<p>ANOVA with the factors season (S) and treatment (T), significant effects are indicated by *, **, *** at <i>P</i> < 0.05, 0.01, 0.001.</p

Biomass of microbial groups determined as soil phospholipid fatty acids (PLFAs in nmol g^-1 dry weight soil ± SD) in soil cropped with maize (plant), amended with maize shoot litter (litter) or bare soil, in topsoil (0–10 cm), rooted zone (30–40 cm), and root free zone (60–70 cm) in the years 2012 and 2013.

<p>Given is the biomass for total microbial assemblages (PLFA_total), Gram-positive bacteria (PLFA_GR+), Gram-negative bacteria (PLFA_GR-) and fungi (PLFA_fungi). Values within a sampling date with the same or no letters are not significantly different according to Tukey´s HSD test at <i>P</i> < 0.05.</p

Occurrence of the bacterial-feeding taxa <i>Cephalobus</i>, <i>Eucephalobus</i>, <i>Acrobeloides</i> and <i>Alaimus</i> in soil cropped with maize (plant), amended with maize shoot litter (litter) or bare soil.

<p>Abundance (individuals 100 g^-1 dry weight soil ± SD) is given in topsoil (0–10 cm), rooted zone (40–40 cm), and root free zone (60–70 cm) in the years 2012 and 2013. Values within a sampling date with the same or no letters are not significantly different according to Tukey´s HSD test at <i>P</i> < 0.05.</p

Statistical analysis.

*<p>significant at a level <0.05.</p