ECOPHYSIOLOGICAL ATTRIBUTES OF THE NATIVE ACER-SACCHARUM AND THE EXOTIC ACER-PLATANOIDES IN URBAN OAK FORESTS IN PENNSYLVANIA, USA

When the exotic Acer platanoides L. (Norway maple) and the native A. s accharum Marsh. (sugar maple) grow together in the understories of urb an Quercus forests in the eastern USA, average annual height growth in crements are nearly twice as large in A. platanoides as in A. saccharu m, 19.26 +/- 3.22 versus 10.01 +/- 1.69 cm. We examined several ecophy siological mechanisms that might be associated with the superior invas ive ability and growth of A. platanoides in two urban oak forests in P ennsylvania. Leaf longevity was 12 days greater in AI platanoides than in A, saccharum. In addition, leaf mass/leaf area ratio was greater i n A. platanoides than in A. saccharum (2.67 +/- 0.03 versus 2.32 +/- 0 .02 mg cm(-2)); however, leaf thickness was significantly lower in A. platanoides than in A. saccharum suggesting that A. platanoides contai ns more dense palisade and mesophyll cell layers than A. saccharum. Fi eld net photosynthesis (mass basis) and photosynthetic light response curves (area basis) indicated significantly greater carbon assimilatio n, and nitrogen and phosphorus use efficiencies in A. platanoides than in A. saccharum. Acer platanoides also exhibited higher water use eff iciency than A. saccharum (0.88 +/- 0.12 versus 0.32 +/- 0.09 mmol CO2 mol(-1) H2O). Acer platanoides exhibited significantly lower osmotic potentials than A. saccharum, but a similar relative water content at zero turgor. We conclude that A. platanoides utilizes light, water and nutrients more efficiently than A. saccharum.