Fine Root Dynamics in a Tropical Rain Forest is Influenced by Rainfall

Abstract

Quantifying patterns of fine root dynamics is crucial to the understanding of ecosystem structure and function, and in predicting how ecosystems respond to disturbance. Part of this understanding involves consideration of the carbon lost through root turnover. In the context of the rainfall pattern in the tropics, it was hypothesised that rainfall would strongly influence fine root biomass and longevity. A field study was conducted to determine root biomass, elemental composition and the influence of rainfall on longevity of fine roots in a tropical lowland evergreen rainforest at Danum Valley, Sabah, Malaysia. A combination of root coring, elemental analysis and rhizotron observation methods were used. Fine (less than 2 mm diameter) root biomass was relatively low (1700 kg ha −1 ) compared with previously described rainforest data. Standing root biomass was positively correlated with preceding rainfall, and the low fine root biomass in the dry season contained higher concentrations of N and lower concentrations of P and K than at other times. Observations on rhizotrons demonstrated that the decrease in fine root biomass in the dry season was a product of both a decrease in fine root length appearance and an increase in fine root length disappearance. Fitting an overall model to root survival time showed significant effects of rainfall preceding root disappearance, with the hazard of root disappearance decreasing by 8% for each 1 mm increase in the average daily (30 day) rainfall preceding root disappearance. While it is acknowledged that other factors have a part to play, this work demonstrates the importance of rainfall and soil moisture in influencing root biomass and root disappearance in this tropical rainforest.

Fine root dynamics along a 2,000-m elevation transect in South Ecuadorian mountain rainforests

“…This indicates that, as a whole, root growth of the mountain forest trees is stimulated by a higher water availability which seems to act as a second controlling factor besides temperature. This is in accordance with results from tropical lowland forests in Malaysia and Panama, where root growth was higher in moist than in dry seasons (Green et al 2005;Yavitt and Wright 2001). An exception was the lowermost stand at 1,050 m, which showed a positive effect of the VPD of the preceding month on fine root birth rate.…”

“…In contrast, studies on fine root turnover in tropical forests are still scarce and were mostly conducted in lowland forests (e.g. Jordan and Escalante 1980;Cuevas and Medina 1988;Green et al 2005;Silver et al 2005;Trumbore et al 2006). Even less is known about fine root dynamics in tropical montane forests despite their acknowledged importance in carbon cycling.…”

Root elongation in tropical Eucalyptus plantations: effect of soil water content

“…In addition, a decrease or even a halt in root elongation has been observed during the summer (Hendrick and Pregitzer, 1996;Joslin et al, 2001). A similar pattern has also been reported in tropical ecosystems exposed to a dry season, with higher elongation rates during the rainy season than during the dry season (Castellanos et al, 2001;Delitti et al, 2001;Green et al, 2005).…”

“…Care was taken to select trees with straight boles in a clean area with no dead trees in their immediate vicinity. Fine root dynamics were monitored using rhizotrons (Jourdan and Rey, 1997;Green et al, 2005;Metcalfe et al, 2007;Sword, 1998). Square panes of glass (0.9 × 0.9 m) were set up at a distance of about 1.5 m from the tree.…”

“…These methods are less labour intensive, but they come up against the problem of sample numbers, sampling periods and distinguishing between living and dead roots. The other family of techniques relies on direct observation of root elongation on large panes of glass (rhizotrons; Jourdan and Rey, 1997;Green et al, 2005;Sword, 1998) or on small-diameter transparent tubes inserted into the soil (minirhizotron, Hendrick and Pregitzer, 1993;Majdi et al, 2005). These visual methods enable quantitative and qualitative measurements of the root system (Vogt et al, 1998).…”