Abstract
Resource utilization by earthworms affects soil C and N dynamics and further colonization of invasive earthworms. By applying 13C-labeled Tabebuia heterophylla leaves and 15N-labeled Andropogon glomeratus grass, we investigated resource utilization by three earthworm species (invasive endogeic Pontoscolex corethrurus, native anecic Estherella sp, and native endogeic Onychochaeta borincana) and their effects on soil C and N dynamics in Puerto Rican soils in a 22-day laboratory experiment. Changes of 13C/C and 15N/N in soils, earthworms, and microbial populations were analyzed to evaluate resource utilization by earthworms and their influences on C and N dynamics. Estherella spp. utilized the 13C-labeled litter; however, its utilization on the 13C-labeled litter reduced when cultivated with P. corethrurus and O. borincana. Both P. corethrurus and O. borincana utilized the 13C-labeled litter and 15C-labeled grass roots and root exudates. Pontoscolex corethrurus facilitated soil respiration by stimulating 13C-labeled microbial activity; however, this effect was suppressed possibly due to the changes in the microbial activities or community when coexisting with O. borincana. Increased soil N mineralization by individual Estherella spp. and O. borincana was reduced in the mixed-species treatments. The rapid population growth of P. corethrurus may increase competition pressure on food resources on the local earthworm community. The relevance of resource availability to the population growth of P. corethrurus and its significance as an invasive species is a topic in need of future research.
Highlights
Invasive earthworms have caused significant effects on local biota and ecosystem processes in the invaded areas, e.g., European Lumbricids in North America [1,2,3].Population declines of native earthworms, in remote and non-fragmented forests, have contributed to a result of competitive exclusion by expanding invasive earthworm populations [2,4,5].Lachnicht et al [6] observed that invasive Pontoscolex corethrurus (Müller, 1856) earthworms, when incubated with native Estherella sp., utilized different N resources, possibly avoiding direct competition on food resource
Anecic Estherella spp. was observed to reduce its utilization on 13 C-labeled litter or microbial community when cultivated with P. corethrurus or both P. corethrurus and
The individual species effect on soil C and N dynamics was altered with mixed earthworm assemblages
Summary
Population declines of native earthworms, in remote and non-fragmented forests, have contributed to a result of competitive exclusion by expanding invasive earthworm populations [2,4,5]. Lachnicht et al [6] observed that invasive Pontoscolex corethrurus (Müller, 1856) earthworms, when incubated with native Estherella sp., utilized different N resources, possibly avoiding direct competition on food resource. Winsome et al [7] found that invasive Aporrectodea trapezoides (Dugès, 1828) lost its competition advantage when co-existing with native Argilophilus marmoratus (Eisen, 1893) in the resource-poor habitat of a Californian grassland. Interactions between native and invasive earthworms varied with resource utilization of earthworm species and resource availability [6,7]. Earthworms are Forests 2016, 7, 277; doi:10.3390/f7110277 www.mdpi.com/journal/forests
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