We resampled one of the earliest replicated experimental sites used to investigate the impacts of native tropical tree species on soil properties, to examine longer term effects to 1-m depth. The monodominant stands, established in abandoned pasture in 1988 at La Selva Biological Station, Costa Rica, contained six species, including one exotic, Pinus patula ssp. tecunumanii (Eguiluz & J.P. Perry) Styles, and five native species: Pentaclethra macroloba (Willd.) Ktze (N2-fixing); Hyeronima alchorneoides Allemao; Virola koschnyi Warb.; Vochysia ferruginea Mart.; and Vochysia guatemalensis J.D. Smith. Soil organic carbon (SOC) differed significantly among species in the surface (0–15-cm) layer, ranging from 44.5 to 55.1 g kg1, compared with 46.6 and 50.3 g kg1 in abandoned pasture and mature forest, respectively. The change in surface SOC over 15 yr ranged from 0.03 to 0.66 Mg C ha1 yr1. The species differed in the quantity and chemical composition of their detrital production. Soil organic C was significantly correlated with fine-root growth, but not with aboveground detrital inputs. Soil organic C increased with potential C mineralization on a grams of C basis, indicating that species influenced both the quality and quantity of SOC. Contrary to expectations, SOC declined with increasing fine-root lignin concentrations, indicating that ligninderived C did not dominate refractory SOC pools. We hypothesize that differences among species in the capacity to increase SOC stocks involved fine-root traits that promoted soil microbial turnover and, thus, greater production of recalcitrant, microbial-derived C fractions.
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