PARENT SESSION
Oral Session #43: Soil Ecology: Mycorrhizae and Roots. Presiding: W. Stock.
Wednesday, August 8, 2001. 8:00 AM to 12:15 PM. Hall of Ideas F.

Effects of climate and soil on root systems of grasses.

Schenk, H. Jochen¹, Jackson, Robert¹, ¹

ABSTRACT- Grasslands span one fifth of the Earth's surface and occur under a large range of climates. Predictions about responses of grasslands to global climatic change require an understanding of the relationships between grass rooting depths and environmental factors. As part of a project at the National Center for Ecological Analysis and Synthesis, we collected records of the maximum rooting depths of individual grass plants and of grassland root profiles globally, and analyzed their relationships with aboveground plant sizes, growth forms (cespitose, rhizomatous, or stoloniferous), and photosynthetic types in generalized linear models, which included soil texture, precipitation, and potential evapotranspiration (PET) as further independent variables. Grasses in arid and semi-arid grasslands had a median rooting depth of 1 m, increased with mean annual precipitation and PET, and reached maximum depths of 4 to 6 m in semi-deserts and dry savannas. Rooting depths in mesic grasslands had a median of 0.6 m and rarely exceeded 1.8 m. Growing in the same climate, grasses were more deeply rooted in fine-textured soils than in medium to coarse textured ones, and cespitose grasses were more shallowly rooted than rhizomatous or stoloniferous ones. Root profiles contained 95% of root mass in ~0.4 m depth in humid meadows, ~0.9 m in prairie, ~1.2 m in semi-arid steppe, and ~1.4 m in dry savannas. The results suggest that rooting depths of grasses vary greatly and predictably with environmental conditions. Vegetation models could use such data to improve simulations of water, carbon, and nutrient cycles.

KEY WORDS: roots, grasslands, climate, soil