Exotic earthworms accelerate plant litter decomposition in a Puerto Rican pasture and a wet forest

Liu ZG, Zou XM

ECOLOGICAL APPLICATIONS
12 (5): 1406-1417 OCT 2002

Abstract:
Tropical land-use changes can have profound influence on earthworms that play important roles in regulating soil processes. Converting tropical forests to pastures often drastically increases the abundance of exotic earthworm populations such as Pontoscolex corethrurus. We initiated this study to examine the influence of exotic earthworms on the decomposition of plant leaves and roots in a tropical pasture and a wet forest of Puerto Rico. We employed two treatments: control with natural earthworm population, and earthworm reduction using an electroshocking technique. Decomposition rates of plant leaves on the ground surface and root materials within the surface mineral soil were estimated using a litterbag technique. To understand the role that exotic earthworms play in altering plant litter decomposition, we also compared soil CO2 evolution rates, soil microbial biomass, and physical and chemical soil properties between the controls and earthworm-reduced plots during a one-year period. Earthworm populations in the electroshocked enclosures were reduced by 85% and 87% as compared with pasture and forest controls by the end of the experiment. Earthworm reduction significantly decreased the annual decay rates of plant leaves but had no effects on those of plant roots in both pasture and forest sites. Although the control plots had less mass remaining on every litterbag collecting date, significant treatment effects on leaf decomposition occurred only after 240 d in both sites. The decay rates were greater when organic materials had low carbon to nitrogen or phosphorus ratios. Soil respiration was also decreased in the earthworm-reduced plots. In contrast, soil microbial biomass C was not affected by earthworm reduction. Furthermore, there were no significant differences between the two treatments in soil bulk density, moisture content, pH, or temperature at either site. Our results suggest that exotic earthworms may accelerate leaf litter decomposition by elevating rates of litter consumption/digestion or microbial activity, rather than by improving soil physical/chemical conditions or altering microbial biomass.

Author Keywords:
Amynthas rodericensis, Caribbean National Forest, Puerto Rico, decomposition, earthworm, microbial biomass, Pontoscolex corethrurus, soil respiration, tropical forest

KeyWords Plus:
PONTOSCOLEX-CORETHRURUS GLOSSOSCOLECIDAE, SCOTS PINE FOREST, ORGANIC-MATTER, ADAPTIVE STRATEGIES, COMMUNITY STRUCTURE, LIGNIN CONTROL, HUMID TROPICS, SOIL, DYNAMICS, NITROGEN

Addresses:
Zou XM, Univ Puerto Rico, Inst Trop Ecosyst Studies, POB 23341, San Juan, PR 00931 USA
Univ Puerto Rico, Inst Trop Ecosyst Studies, San Juan, PR 00931 USA

Publisher:
ECOLOGICAL SOC AMER, 1707 H ST NW, STE 400, WASHINGTON, DC 20006-3915 USA

IDS Number:
614PM

ISSN:
1051-0761