PARENT SESSION
Oral Session # 56: Plant Ecology IV: Plant - Water Relations II.
Presiding: D Rosenthal
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 200.

Association of root morphology and gas exchange with northern temperate tree species landform affinity.

Kunkle, Justin^*,1, Walters, Michael¹, Kobe, Richard, ¹ Michigan State University, East Lansing, Michigan, USA

ABSTRACT- Greater use efficiency and access to water may be two general adaptive mechanisms to low soil water availability. Contrasting glacial landforms with differences in water holding capacity (outwash-low, ice contact-moderate, moraine-high), and dominant vegetation, in Northwestern Lower Michigan provide an ideal system to develop a mechanistic understanding of the association between plant traits and plant performance. First-year seedlings of eight tree species (in order of increasing site moisture affinity, (Quercus velutina, Quercus alba, Quercus rubra, Prunus serotina, Acer rubrum, Acer saccharum, Fraxinus Americana, Betula alleghaniensis) were transplanted across these landforms. In their third year, leaf gas exchange and soil moisture were measured monthly, and seedlings were completely excavated early-summer and fall to obtain growth, size and morphological characteristics. 2002 had a dry growing season with July-September precipitation of 113 mm vs. a 30-year average of 318 mm. Soil moisture decreased from moraine to outwash sites and all sites were lowest in July. Maximum seedling rooting depth differed among species (p < 0.0001) and was highest for drought tolerant oaks, and lowest for black cherry and red maple. Rooting depth varied among sites (p < 0.0001) with outwash seedlings deepest rooted, however, contrary to expectations, outwash seedlings had the lowest root depth extension between summer and fall harvests. Photosynthesis estimated at common transpiration rates of 0.25 mmol H₂O/m²/s (Aw) differed among sites (p < 0.01) with outwash seedlings generally having higher values for all species. Aw also differed among species (P< 0.001) but not in the order expected with drought tolerant oaks having lower values, and thus lower water use efficiency than the other species. Aw was negatively related to rooting depth on ice contact and moraine sites indicating lower water use efficiency for more deeply rooted species, however, there was no clear relationship for outwash sites.

Key words: plant-water relations, northeastern temperate tree seedlings, gas exchange, drought