Document: AND-3-68-40

Effects of fire and simulated grazing on fine root dynamics and soil respiration in a mixed-grass prairie.

HUBBARD, J.A.* ¹, S.R.ARCHER ¹, T.BOUTTON ¹ and R.J.ANSLEY ^1,2

Texas A&M University, College Station, TX 77843-2126 USA ¹
Texas A&M Research and Extension Center, Vernon, TX 76348 USA ²

Abstract:
Fire and grazing characterize many prairie ecosystems, yet their effects are seldom considered concurrently. To investigate the role of fire (spring burn, control), simulated grazing (mow repeatedly, control), and their interaction on root dynamics and soil respiration, we conducted one year field experiments replicated in time (1998 and 1999) on plots which had not been burned or grazed in ca. 27 years. The 1998 experiment was conducted under conditions of severe drought; the 1999 experiment received above-normal annual rainfall. Control plots were dominated by C₃ grasses, primarily annual brome (Bromus japonicus). All treatments (mowing [M], burning [B] and B+M) caused a species composition shift to domination by C₄ grasses in both years. Above- and belowground biomass and soil respiration (SR) were highest (2-3X) in the wet year, regardless of treatments. In each year, aboveground production was stimulated on B and M plots, but was unaffected on B+M plots. Treatment impacts on belowground variables (biomass, root length density and root diameter) were pronounced in the wet year, but were non-significant during the dry year. Under above-normal rainfall, B and M independently stimulated root biomass and root length density by a factor of 3 relative to controls, but suppressed SR. In contrast, B+M treatments had no impact on root production, but elicited a decrease in SR. In this system, grazing and burning effects on belowground structure and function thus appears to be manifested indirectly via their effects on species composition. Grazing and/or spring burning promoted a rapid shift from domination by annual and C₃ perennial grasses to C₄ perennial grasses. Attendant changes in soil respiration, root biomass and root length density were highly contingent on annual rainfall.

Keywords: root dynamics, soil respiration, fire, grazing, grasslands

This abstract is being presented at: 3:30 PM in session:
ROOT PROCESSES