Invasion Alters Plant and Mycorrhizal Communities in an Alpine Tussock Grassland

Abstract

Abstract Plant invasions now impact even the world’s most remote ecosystems, including alpine zones, altering key mutualisms that affect ecosystem functions. Plant-mycorrhizal associations can be sensitive to invasion, but previous studies have been limited in the types of mycorrhizas examined, favouring invaders that host arbuscular mycorrhizas or are non-mycorrhizal. Consequently, little is known about how invaders that host other types of mycorrhizas may affect community and ecosystem properties. 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. By exploring invasion of a plant with an atypical mycorrhizal type, our study expands knowledge of the ecosystem consequences of biological invasions.