Fungal and Bacterial Communities Exhibit Consistent Responses to Reversal of Soil Acidification and Phosphorus Limitation over Time

Chronic acid deposition affects many temperate hardwood forests of the northeastern United States, reduces soil pH and phosphorus (P) availability, and can alter the structure and function of soil microbial communities. The strategies that microorganisms possess for survival in acidic, low P soil come at a carbon (C) cost. Thus, how microbial communities respond to soil acidification in forests may be influenced by plant phenological stage as C allocation belowground varies; however, this remains largely unexplored. In this study, we examined microbial communities in an ecosystem level manipulative experiment where pH and/or P availability were elevated in three separate forests in Northeastern Ohio. Tag-encoded pyrosequencing was used to examine bacterial and fungal community structure at five time points across one year corresponding to plant phenological stages. We found significant effects of pH treatment and time on fungal and bacterial communities in soil. However, we found no interaction between pH treatment and time of sampling for fungal communities and only a weak interaction between pH elevation and time for bacterial communities, suggesting that microbial community responses to soil pH are largely independent of plant phenological stage. In addition, fungal communities were structured largely by site, suggesting that fungi were responding to differences between the forests, such as plant community differences

Impact of Deer and Soil Chemistry on Plant Mutualists in Forest Soil

In temperate forests, understory herbaceous plants are often affected by the abundance of white tailed deer, both directly through herbivory and indirectly through soil compaction. Soil chemistry, particularly soil pH, also has a large effect on the soil microbial communities that influence plant growth and survival. The objective of this study was to study the interactive effects of deer herbivory and soil chemistry on plant mutualists in forest soil using Jack-in-the-Pulpit plants. Jack-in-the-Pulpit are common understory herbs in temperate forests that deer will eat but are not preferred. In Bole Woods at the Holden Arboretum, 760 Jack-in-the-Pulpit plants were planted into 19 plots (both deer exclosures and un-fenced controls), each containing 4 subplots, 3 where soil chemistry had been altered and a control. Soil samples were collected from each subplot to be used for DNA analysis. Using PCR-terminal restriction fragment length polymorphism, we determined community structure of the fungal and bacterial communities. Our results showed that across communities of general fungal, AM fungi and bacteria, there were taxonomic differences present with soil chemistry alteration. Subplots that were amended with limestone and calcium had similar communities compared to subplots that were amended with triple superphosphate or the control. These differences reflected changes in soil pH that we had seen previously.</p

Mycorrhizal Response to Experimental pH and P Manipulation in Acidic Hardwood Forests

<div><p>Many temperate forests of the Northeastern United States and Europe have received significant anthropogenic acid and nitrogen (N) deposition over the last century. Although temperate hardwood forests are generally thought to be N-limited, anthropogenic deposition increases the possibility of phosphorus (P) limiting productivity in these forest ecosystems. Moreover, inorganic P availability is largely controlled by soil pH and biogeochemical theory suggests that forests with acidic soils (i.e., </p></div

Rarefaction curves showing the expected number of species (97% OTUs) as a function of the number of EcM root tips from each treatment.

<p>Although the control appears to have lower diversity than the treatments, this visual difference is not statistically significant (95% confidence intervals not shown to improve figure clarity).</p

CCA ordinations showing the effect of location, treatment, pH, and P availability on the on AM (A) and EcM (B) communities.

<p>Region is denoted by shape: glaciated (triangles) and unglaciated (inverted triangles) and treatment is denoted with color: control (white), elevated pH (grey), elevated P (dotted grey), and elevated pH+P (black). Centroids and error bars represent the mean and standard errors of axes scores within a given treatment. Monte Carlo <i>P</i>-values for eigenvalues for the AM and EcM ordinations were 0.03 and <0.01, respectively. Joint-plot overlays were unable to detect any significant correlations between tree species and either the AM or EcM community composition.</p

The effect of region and treatments on soil pH and phosphorus with mean values and standard errors.

<p><i>P</i>-values for the effect of region and treatments from the LME model with forest blocks as the random effect (n = 9). Asterisks denote a significant difference, in comparison to controls, at <i>P</i><0.05 (**) and <i>P</i><0.10 (*).</p