Effects of urban environmental conditions on the symbiosis between vesicular-arbuscular mycorrhizal fungi and silver maple (Acer saccharinum L.)

Roots of silver maple (Acer saccharinum L.) trees from downtown Montreal and the municipal nursery in Terrebonne were sampled to determine their vesicular-arbuscular mycorrhizal (VAM) colonization levels. Soil was analyzed to determine the concentration of various soil nutrients, pH, and bulk density. It was found that trees from downtown Montreal grow in soils with lower phosphorus and magnesium, and higher copper, zinc, sodium, pH and bulk density than nursery trees. Downtown tree health, in terms of % dieback, was positively correlated with soil phosphorus, potassium, calcium, the phosphorus:copper ratio and negatively correlated with soil copper, zinc, bulk density and tree age. It is suggested that tree health and survival are associated with tree location. Older and healthier trees grow on streets that provide larger soil volumes. Downtown trees had significantly higher VAM colonization levels (44.9%) than those from the nursery (36.1%). The colonization level in downtown trees was positively correlated with the phosphorus:copper ratio and tree age, and negatively correlated with soil potassium. It is hypothesized that downtown trees living under the most stress will be those with the highest VAM colonization. Under controlled conditions 81.5% of the variability of % VAM infection of silver maple seedlings could be explained by soil zinc, phosphorus, copper, sodium, and potassium. Zinc, phosphorus and copper negatively affected VAM colonization, while a slight positive effect of sodium and potassium was found. This suggests that VAM colonization in downtown trees may be affected by soil factors, but the effects may be masked by other conditions, such as water stress, light, or size of root systems