Soil lichens and their sphere of influence underground
Lichens are drivers of ecosystem patterns where there are few other producers in a landscape; lichens in desert soil crusts and in the Antarctic are crucial for plant and animal community development there. Our work addresses the less well understood role of soil lichens in forests, when they are in direct contact with the soils but represent a small portion of total productivity. The NJ Pinelands is a good place to carry out these investigations because the lichens are abundant, their communities are well characterized, and the soils have low nutrient availability so any lichen-induced effects will be important for the whole forest. Our study asked whether the lichens altered soil nutrient cycling patterns, and whether the lichens have top-down influence on soil micro-arthropod communities. To compare the influence of lichens with that of other ground covers, we made a transplant grid with different aboveground material (lichens, pine needles, oak leaves, and bare ground) on two sites in the Pinelands in January 2013; we present data from these sites that were monitored seasonally for 2 years, and show analyses of trends in soil moisture, soil chemistry, soil microbial community activity, and soil arthropod presence.
We found that the influence of lichens on soils varies with soil conditions and with climate conditions. In summer, when soils have low water content (< 10% water), lichens help them retain significantly more moisture, and when soils have higher inorganic phosphorus availability (> 3ug/g PO4-P), lichens significantly reduce extractable phosphorus concentrations. In our study the lichens did not have significant effects on soil ammonium or nitrate levels. The microbial community activity did not respond dramatically to lichens, increasing acid phosphatase activity slightly under the lichens when inorganic soil P was less available. Although lichens are known to leach phenolic compounds into the soil, lichens did not promote increased production of any enzymes affiliated with recalcitrant carbon compounds like phenol-oxidase or peroxidase. Lichens did, however, decrease decomposition rates of leaves in litterbags, a phenomenon that may be mediated by low temperatures underneath lichens. Lichens also promoted higher densities of collembolans in the summer; this may be due to lichen influence on soil moisture content as these organisms are more sensitive to desiccation than more waterproof cryptostigmatid mites.