Document: JOS-3-33-5

Beyond Weaver: The relationship between the structure of root systems and resource utilization

CRAINE, J.M.* ¹, D.A.WEDIN ², F.S.CHAPINIII ³, P.B.REICH ⁴ and ⁵

University of California, Berkeley, Berkeley, CA, USA ¹
University of Nebraska, Lincoln, Lincoln, NE, USA ²
University of Alaska, Fairbanks, Fairbanks, AK, USA ³
University of Minnesota, St. Paul, MN, USA ⁴

Abstract:
Understanding the consequences of changing resource availability on ecosystems and species composition requires understanding the relationship between root system structure and ecosystem processes and how species differ in root system structure. Despite the extensive work on root systems by John Weaver and his contemporaries and over four decades of subsequent research, our understanding of the belowground systems of grasslands remains rudimentary. We measured a series of traits associated with root system structure and resource utilization on eleven species of grassland species of Cedar Creek Natural History Area, MN. Species were grown in monoculture in mesocosms in the field and harvested in their third growing season. Among the species we measured, it was clear that there were differences the patterns of root system structure and resource utilization among 1) warm-season legumes, 2) rhizomatous C₃ grasses and a C₃ forb, and 3) a separate gradient of differentiation from tallgrass (C₄ grass and C₃ forb) to mixed grass (C₄ grass) to shortgrass species (C₄ grass and C₃ grass). It is clear that a commonly used functional classifications (C₃ grasses, C₄ grasses, forbs, legumes) may not be the most robust classification with regard to productivity and resource utilization. The grassland species differed in their construction, production, and placement of fine and coarse biomass in the soil profile. This led to consistent patterns in aboveground production, nitrogen and water utilization, and ecosystem nitrogen retention. Across all species and depths examined, there were strong relationships between the amount of fine root biomass present in a unit of volume of soil and the amount of water or nitrogen available, but no relationship for coarse root biomass. As such, separation of coarse and fine root biomass is as important as separating stems and leaves. In general there were few differences among these species in the total biomass N and differences in biomass were due to dilution of N, not to higher acquisition.

Keywords: root systems, plant functional classifications, NPP, nitrogen, water, grasslands

This abstract is being presented at: 4:15 PM in session:
Oral Session #12: Roots.