IMPACTS OF CLIMATE CHANGE ON SOIL MICROORGANISMS IN NORTHERN HARDWOOD FORESTS

As global climate continues to change, it becomes more important to understand possible feedbacks from soils to the climate system. This dissertation focuses on soil microbial community responses to climate change factors in northern hardwood forests. Two soil warming experiments at Harvard Forest in Massachusetts, and a climate change manipulation experiment with both elevated temperature and increased moisture inputs in Michigan were sampled. The hyphal in-growth bag method was to understand how soil fungal biomass and respiration respond to climate change factors. Our results from phospholipid fatty acid (PLFA) analyses suggest that the hyphal in-growth bag method allows relatively pure samples of fungal hyphae to be partitioned from bacteria in the soil. The contribution of fungal hyphal respiration to soil respiration was examined in climate change manipulation experiments in Massachusetts and Michigan. The Harvard Forest soil warming experiments in Massachusetts are long-term studies with 8 and 18 years of +5 °C warming treatment. Hyphal respiration and biomass production tended to decrease with soil warming at Harvard Forest. This suggests that fungal hyphae adjust to higher temperatures by decreasing the amount of carbon respired and the amount of carbon stored in biomass. The Ford Forestry Center experiment in Michigan has a 2 x 2 fully factorial design with warming (+4-5 °C) and moisture addition (+30% average ambient growing season precipitation). This experiment was used to examine hyphal growth and respiration of arbuscular mycorrhizal fungi (AMF), soil enzymatic capacity, microbial biomass and microbial community structure in the soil over two years of experimental treatment. Results from the hyphal in-growth bag study indicate that AMF hyphal growth and respiration respond negatively to drought. Soil enzyme activities tend to be higher in heated versus unheated soils. There were significant temporal variations in enzyme activity and microbial biomass estimates. When microbial biomass was estimated using chloroform fumigation extractions there were no differences between experimental treatments and the control. When PLFA analyses were used to estimate microbial biomass we found that biomass responds negatively to higher temperatures and positively to moisture addition. This pattern was present for both bacteria and fungi. More information on the quality and composition of the organic matter and nutrients in soils from climate change manipulation experiments will allow us to gain a more thorough understanding of the mechanisms driving the patterns reported here. The information presented here will improve current soil carbon and nitrogen cycling models.

THE ROLE OF ECTOMYCORRHIZAL FUNGI ON FERTILIZED AND UNFERTILIZED NURSERY GROWN WHITE SPRUCE

Nursery grown seedlings are an essential part of the forestry industry. These seedlings are grown under high nutrient conditions caused by fertilization. Though grown in a controlled environment, symbionts such as ectomycorrhizal fungi (EcMF) are often found in these conditions. To examine the effects of EcMF in these conditions, colonized Picea glauca seedlings were collected from Toumey Nursery in Watersmeet, MI. After collection, the EcMF present were morphotyped, and seedlings with different morphotypes were divided equally into two treatment types- fertilized and unfertilized. Seedlings received treatment for one growing season. After that time, seedlings were collected, ectomycorrhizas identified using morphotyping and DNA sequencing, and seedlings were analyzed for differences in leaf nutrient concentration, content, root to shoot ratio, total biomass, and EcMF community structure. DNA sequencing identified 5 unique species groups- Amphinema sp. 1, Amphinema sp. 5, Thelephora terrestris, Sphaerosporella brunnea, and Boletus variipes. In the unfertilized treatment it was found that Amphinema sp. 1 strongly negatively impacted foliar N concentration. In fertilized seedlings, Thelephora terrestris had a strong negative impact on foliar phosphorus concentration, while Amphinema sp. 1 positively impacted foliar boron, magnesium, manganese, and phosphorus concentration. In terms of content, Amphinema sp. 1 led to significantly higher content of manganese and boron in fertilized treatments, as well as elevated phosphorus in unfertilized seedlings. Amphinema sp. 5 had a significant negative effect on phosphorus content. When examining root to shoot ratio and biomass, those seedlings with more non-mycorrhizal tips had a higher root to shoot ratio. Findings from the study shed light on the interactions of the species. Amphinema sp. 5 shows very different functionality than Amphinema sp. 1. Amphinema sp. 1 appears to have the highest positive effect on seedling nutrition when in both fertilized and unfertilized environments. Amphinema sp. 5 and T. terrestris appear to behave parasitically in both fertilized and unfertilized conditions.