Document: GLE-3-63-5

The impacts of soil moisture and temperature on longleaf pine (Pinus palustris) fine root dynamics.

STEVENS, G.N.* ¹, R.H.JONES ¹, R.J.MITCHELL ², S.L.HURST ² and S.D.PECOT ²

Virginia Tech, Blacksburg, VA 24060, U.S.A. ¹
Joseph W. Jones Ecological Research Center, Newton, GA, U.S.A. ²

Abstract:
Soil moisture and temperature are thought to play a major role in fine root dynamics in forest systems. However, few field experiments have been conducted to determine the specific impacts of these environmental variables. In an attempt to provide such direct evidence, we conducted an experiment to measure pine fine root dynamics across a range of canopy conditions (open to dense) in a Pinus palustris savanna in southern Georgia. We installed minirhizotrons in January 1998 to measure pine fine root dynamics on a weekly basis for a full year (July 1998 to July 1999) and made concomitant measurements of soil temperature and moisture at 10 cm depth increments to 40 cm. Fine root standing crop was low at the beginning of sampling possibly due to the early summer drought in 1998. Total fine root length increased greatly (> 350%) from July to November, a period of 'typical' rainfall levels. Fine root length standing crop per minirhizotron tube in November 1998 was significantly (p<0.05) but negatively correlated with soil moisture levels; i.e. higher production occurred on drier sites. Fine root mortality patterns seem also to be correlated with moisture: an episode of rapid decline in fine root length (20% reduction in standing crop) occurred in April 1999, this decline appears closely correlated with low rainfall levels (< 8 mm total) for the same month. Temperature was not significantly correlated with moisture or with fine root production, suggesting that temperature plays a fairly minor role in this warm temperate system. Overall, it appears that soil moisture levels control patterns of Pinus palustris fine root production and mortality. Extreme moisture values, both high and low, are associated with low fine root standing crop. However, the mechanisms by which moisture controls root mass, i.e. reduced production or increased mortality, remain unclear.

Keywords: fine roots, minirhizotron, longleaf, Pinus palustris

This abstract is being presented at: 2:00 PM in session:
Oral Session #12: Roots.