ROOT SURFACE PHOSPHATASE-ACTIVITIES AND UPTAKE OF P-32 LABELED INOSITOL PHOSPHATE IN FIELD-COLLECTED GRAY BIRCH AND RED MAPLE ROOTS

This study examined select, naturally-occurring tree mycorrhizae for d ifferences related to efficiency of organic phosphorus hydrolysis in f orest 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 be ech 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-nitrop henyl phosphate and phytic acid and thus the potential to mineralize m onoester 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 phospha te by gray birch and red maple roots suggested that phosphomonoesteras e activity was linked to P uptake from this source. Differences betwee n species in oxygen consumption rates were less pronounced than those observed for enzymatic activities, suggesting similar short-term energ y demands by the root types examined. The quantitative differences obs erved between plants growing on a common soil potentially relate to di fferences in host demand or reflect differences in basic morphology an d/or physiology of associated mycobionts. Further study is necessary t o understand the importance of these enzymes in the functional ecology of mycorrhizal fungi.