Plant community composition, soil nutrients, tussock morphometrics, C. rubra root colonisation, soil microbial PLFA and NLFA in 75 plots that vary in invasive Calluna vulgaris density, Tongariro National Park, New Zealand

We studied invasion by an ericoid mycorrhizal host plant (Calluna vulgaris L., heather) in alpine tussock grasslands in New Zealand. We investigate the effects of increasing C. vulgaris density on the plant and soil microbial community and on mycorrhization in the dominant native species (Chionochloa rubra Z., red tussock), an arbuscular mycorrhizal host. We show that variation in plant community composition among sites was driven by C. vulgaris density. Higher densities of C. vulgaris were associated with a reduced diameter of C. rubra plants and lower densities of neighbouring plant species, especially woody shrubs. Belowground, we show that higher densities of C. vulgaris were associated with lower rates of mycorrhization in native C. rubra and higher abundances of the fungal fatty acid methyl ester (FAME) biomarker but had little effect on the total microbial community biomass, suggesting that increased ericoid mycorrhizal fungal biomass increased the ratio of fungi relative to bacteria in high C. vulgaris density stands.