Impact of elevated carbon dioxide and ozone on arbuscular mycorrhizal fungal communities in an aspen forest

Background/Question/Methods

The effects of increased tropospheric carbon dioxide and ozone have recently been the focus of many above-ground experimental studies. However, little is known on the impact of these gases on many below-ground components, particularly arbuscular mycorrhizal fungi (AMF). In many ecosystems, AMF have been shown to greatly improve plant growth and reproduction, and they may impact plant diversity. Understanding how plants and their associated AMF respond to anthropogenic inputs such as carbon dioxide and ozone is important to predicting ecosystem functioning in the future. We examined the AMF spore community at the Aspen Free-air CO₂ and O₃ Enrichment (AspenFACE) site in Oneida County, WI. Open air rings, pumping CO₂ (1.5 x ambient) and ozone (1.5 x ambient), were constructed in 1996. Sectors within the rings were planted with quaking aspen clones (Populus tremuloides) or aspen + sugar maple (Acer saccharum) in 1997. The treatments (plus control) were arranged in a factorial design, with three replicates. We collected replicate soil cores from the rings in 2007 (10 years after initial treatment), from both the aspen and aspen+maple sectors. Spores of AMF were indentified to species and enumerated.
Results/Conclusions

Within the aspen only sectors, total spore number was unexpectedly low (approximately 30 spores 100 ml^-1 for most samples). Even with the low sporulation, MANOVA revealed significant treatment effects of CO₂ and O₃ (Wilks’ lambda, F = 2.406, p = 0.019, and F = 2.691, p = 0.009, for CO₂ and O₃, respectively) on the fungal community. Carbon dioxide significantly increased AMF species richness in the aspen sectors. Sporulation of Glomus claroideum and G. constrictum was higher in CO₂ rings (relative to the untreated control). Sporulation of G. claroideum was higher in O₃ rings, compared with control rings. In the aspen+maple sectors, the AMF community was significantly affected by both CO₂ and O₃ (Wilks’ lambda, F = 2.355 and p = 0.017, and F = 3.972, p = 0.001, respectively). Richness of AMF in the aspen+maple sector was decreased in the O₃ rings. Glomus intraradices was the most abundant species in all treatments of aspen-maple quadrants. Spore number of several species was significantly lower in elevated CO₂ rings and O₃ rings, when compared with the control. It seems apparent that these treatments are affecting sporulation of the AMF community. However, it remains unclear if the CO₂ and O₃ have direct impacts on the fungi, or if their effects are mediated through the plant community.