Global climate change is expected to alter seasonal patterns of temperature and precipitation across much of North America impacting ecosystems such as northern temperate forests. Although large scale changes in potential climate have been well studied, finer grain effects of local weather patterns are still poorly understood. Fine scale effects of climate change are important because they can effect soil organisms such as soil fungi that play important roles in nutrient cycling. Yet, we know relatively little about how annual environmental variability affects fungal communities. In this study we collected soil cores from 6 long-term monitoring plots established in an old growth hardwood forest over the course of 5 years. Samples were collected every month and divided into three depths (2-, 6-, and 10-cm); soil was used to monitor chemistry and DNA fragment analysis and next generation sequencing were used to describe fungal communities. Our analysis includes examination of chemistry and fungal communities from 1080 samples collected across seasons, depth and year. We predicted that 1) fungal communities could respond consistently to seasonal changes in plant phenology, 2) fungal communities could respond strongly to microsite environmental conditions and 3) inter-annual variation in soil moisture and temperature could alter the communities.
Soil depth, plot location, season and year all had significant effects on fungal communities and there was a significant season by year interaction. This suggests that fungal communities are highly variable in space and time, but seasonally distinct communities were not apparent over the five years of our study (e.g. winter or summer communities). Rather, fungal communities responded significantly to microsite environmental conditions within and between years. Soil moisture, available phosphorus and total carbon and nitrogen were correlated with communities at all sample depths. Surprisingly, soil and air temperature were not significantly correlated with fungal communities; however, temperature variance was significantly correlated with communities at the deeper soil depths, indicating that temperature fluctuations could alter fungal communities. Continuous monitoring of soil temperature (15-min readings for 5 years) indicated that soil temperature rarely fell below 0 degrees Celsius, possibly due to regular snow cover (2.5-35.0 cm during winter months). Our data suggest that fungal community composition does not vary in a predictable seasonal fashion, but rather reflects temporal variation in microsite environmental conditions especially soil moisture. In addition, if future snow cover is lower, current responses of the community to winter weather might not reflect future responses to changing climate.