Root surface phosphatase activities and uptake of P-32-labelled inositol phosphate in field-collected gray birch and red maple roots

This study examined select, naturally-occurring tree mycorrhizae for differences related to efficiency of organic phosphorus hydrolysis in forest soils. We investigated the activity of several phosphatases and root respiration in field-collected ectomycorrhizae of American beech and gray birch and VAM of red maple. Root materials were collected in the early and late growing season from a common soil type. American beech occurred in a late-successional stand, whereas gray birch and red maple grew in a mid-successional stand. All of the root types examined had phosphatase activities with p-nitrophenyl phosphate, bis-p-nitrophenyl phosphate and phytic acid and thus the potential to mineralize monoester and diester forms of organic phosphorus. Rates of hydrolysis at pH 5.0 were greatest with p-nitrophenyl phosphate. Although enzyme activity varied with season and ectomycorrhizal morphotype, VAM roots of red maple consistently had the lowest enzyme activities on a length and dry weight basis. Comparison of P-32 uptake from inositol phosphate by gray birch and red maple roots suggested that phosphomonoesterase activity was linked to P uptake from this source. Differences between species in oxygen consumption rates were less pronounced than those observed for enzymatic activities, suggesting similar short-term energy demands by the root types examined. The quantitative differences observed between plants growing on a common soil potentially relate to differences in host demand or reflect differences in basic morphology and/or physiology of associated mycobionts. Further study is necessary to understand the importance of these enzymes in the functional ecology of mycorrhizal fungi.