Access mats partially mitigate direct traffic impacts on soil microbial communities in temperate grasslands

Abstract

Significant areas of the mixedgrass prairie (MGP) in Alberta have experienced heavy equipment traffic due to industrial infrastructure development, which may change edaphic conditions that influence soil microbial communities. Direct wheeled traffic effects may be alleviated by using access mats that spread traffic impacts over a larger area; however, no scientific assessments of access mat efficacy have been conducted on soil microbial responses. Our objectives were to assess soil properties and the diversity, community structure, and size of soil microbial communities, as impacted by wheeled traffic occurring with and without access mat use on grassland. Two representative sites with differing soil texture (sandy versus loamy) were selected from a set of MGP sites established at the University of Alberta Mattheis Research Ranch in SE Alberta, Canada. Treatments at each site included non-disturbed vegetation controls, areas affected by direct traffic, and grassland with access mats placed for 12 weeks with traffic applied. Soil was sampled in July 2015 (immediately after access mat/traffic treatments ended) and in 2016 (12 months after access mat/traffic treatments) from both sites. Soil DNA was extracted and used to target N-cycling genes via qPCR and for next-generation sequencing (Illumina Miseq) of bacterial, archaeal, and fungal communities. Direct wheeled traffic without access matting increased the size of the N2O-reducing community in the sandy soil and conversely deceased the size of this community in the loamy soil. Non-metric multidimensional scaling, perMANOVA, and indicator species analyses indicated a large effect of traffic without access mat use on fungal community structure, as well as distinct bacterial and fungal indicator OTUs associated with disturbed soils compared to control soils. Fungal community structure remained affected by traffic impacts 12 months later, highlighting the extended impacts of traffic on fungal communities. Access matting mitigated some of the impacts direct traffic had on fungal community structure, but in the loamy site increased soil N and decreased the size of the N2O-reducing bacterial community. The latter indicates that ecosystem functioning of these grasslands may not only be impacted by direct wheeled traffic but also by using matting as a mitigation technique.