Effects of Arbuscular Mycorrhizal Fungi on the Vegetative Vigor of Ailanthus altissima (Mill.) Swingle Seedlings under Sustained Pot Limitation

In order to invade new ecosystems, invasive alien plants need to cope with different microbial communities. Whilst the ability to avoid antagonists is well recognized, the opportunity to establish mutualistic associations is less known, even in widespread invasive species such as Ailanthus altissima (Mill.) Swingle. We sought to evaluate whether the beneficial effects of arbuscular mycorrhizal fungi (AMF) on Ailanthus seedlings are maintained over time, under prolonged pot limitation. We compared three-month-, three-year- and four-year-old mycorrhizal seedlings grown in natural forest soil (NT) with seedlings grown in sterilized (ST) and non-mycorrhizal (NM) soils, in pots of 3.4 L (22 x 15 cm). Growth parameters and leaf traits were assessed, including carbon (C-13) and nitrogen (N-15) stable isotope compositions. NT seedlings showed relatively higher vigor in the early stage but, subsequently, the benefits provided by AMF were lost. Interestingly, mycorrhizal seedlings consistently showed about 2 parts per thousand C-13 enrichment, relatively to the other treatments. Negative linear relationships between leaf C-13 and N content were found. Higher photosynthesis rates and WUE are the likely causes of the early enhanced growth in mycorrhizal seedlings. The symbiotic relationship between AMF and Ailanthus could be driven by resource availability. Greater insights into such aspects could provide an improved perspective on the ecological limits of Ailanthus.