The soil C capture capacity and organic matter turnover rate vary according to photosynthetic pathways; therefore the evaluation of C at sites suffering changes from C3 to C4 vegetation and vice versa, is important to identify impacts of land use change on C cycle. This study aims to evaluate C storage under different land uses, and soil C dynamics using the 13C technique to identify the origin of soil C. In the Municipality of Alcala, Department of Valle del Cauca, Colombia, the natural abundance of δ13C was estimated, and data on land use history were gathered to calculate the organic matter turnover rate. The contribution of each type of vegetation to total percentage organic C and to storage at 0.30 m was estimated at sites suffering changes from C3 to C4 vegetation and vice versa. Average δ13C ranged between -25.79 and -20.72% at the three depths evaluated. Over a period of 13 yr, mature fallow lands replaced more than 70% of the C fixed by pastures over a period of 60 yr, whereas paddocks, over a period of 17 yr, only managed to replace 37.9% of the C fixed by associated coffee plantations during a period of 50-100 years. We conclude that the use of 13C avoided that C storage would have been attributed to current land uses when they are actually fixed by previous vegetation; and that C deposit from C3 vegetation is recalcitrant, while that corresponding to C4 vegetation has a relatively fast turnover rate.

Three new species of RighiodrilusZicsi, 1995 from Amazonia were described: R. andake sp. n., R. inga sp. n. y R. muinanei sp. n. With these new additions the genus now contains 26 species. A key for species is provided and some remarks related to characteristics and presence of Righiodrilusland uses are furnished.

Se describieron tres nuevas especies de Righiodrilus Zicsi, 1995 para la Amazonía: R. andake sp. n., R. inga sp. n. y R. muinanei. Con las nuevas adiciones el género suma 26 especies. Se presenta una clave para las especies y algunos comentarios relacionados con las características y presencia en usos del terreno de Righiodrilus.

In the Andean Mountains some agroecosystems are adequate environments for biodiversity conservation or for the readaptation, recolonization and natural recovery of species. To evaluate this phenomenon, soil macroinvertebrate communities were studied in different land uses of the Otún watershed in Colombia. Nineteen orders were found, with richness ranging from 12 to 16 groups per land use system; the forest had the highest while the plantations had the lowest diversity. Earthworms were the dominant group in terms of abundance (620 individuals m-2) and biomass (134.1 g.f.w. m-2). Highest diversity, frequency and homogeneity of distribution of the soil macrofauna were observed in the forest, together with a high percentage dominance and mixed dominance for certain epigeic groups such as millipedes, isopods and arachnids, considered indicators of more preserved ecosystems. The factorial correspondence analysis for macroinvertebrate abundance significantly separated (p < 0.01) the systems according to land use gradient and intervention level, with the first two components explaining 51% of the total variability.

En los sistemas montañosos andinos algunos agrosistemas son ambientes propicios para la conservación de la biodiversidad o para la readaptación, recolonización y multiplicación natural de las especies. Para evaluar este fenómeno, en la cuenca del río Otún, Colombia se caracterizó la comunidad de macroinvertebrados edáficos en diferentes sistemas de uso del terreno. Se identificaron 19 órdenes con riqueza media estimada entre 12 y 16 grupos; el relicto de selva tuvo mayor y las plantaciones menor riqueza. Las lombrices de tierra fueron el grupo dominante en abundancia (620 ind. m-2) y biomasa (134,1 g.p.f. m-2). Se encontró los valores más altos de diversidad y una distribución más homogénea y frecuente de los macroinvertebrados en el relicto de selva, así como alto porcentaje de dominancia y porcentaje de dominancia combinada (PDC) para determinados grupos epígeos como diplópodos, isópodos y arácnidos, que se consideraron indicadores de ecosistemas más conservados. El Análisis Factorial de Correspondencia para abundancia de macroinvertebrados separó significativamente (p < 0.01) los sistemas de acuerdo al gradiente de uso y el nivel de intervención, y los dos primeros componentes explicaron el 51% de la variabilidad total.

The relationship between changes in land use and soil carbon and nitrogen was assessed in Alcalá (Colombian coffee growing region), between 900 and 1600 m. Soils are Argiudolls and Melanudands and sampling units were defined according to the altitudinal gradient. Carbon and nitrogen content, C:N ratio, bulk density and 13C and 15N abundances were measured. Significant differences (p < 0.05) were found due to altitude effect, differentiating the high zone by high C (37.06 -42.88 t ha-1), N (3.12-3.86 t ha-1) and C: N (11.17-11.97), low bulk density (0.56-0.65 g cm-3) and 15N abundance (4.59-5.15 %o). Fallow and monocultures stored more carbon in deeper layers of the soil, while most preserved sites showed low C, N contents. The 13C in land uses ranged between -25.18%o and -21.17 %o, indicating that carbon was fixed mainly by C3 plants. It was concluded that land use changes affect C stocks, due to practices like chemical fertilization; and Alcalá soils have high potential for ecosystem services related with edaphic carbon capture.

Se estudió la relación de cambios en el uso del terreno con el C y N edáficos, en el municipio de Alcalá (región cafetera colombiana), entre 900 y 1600 m de elevación. Los suelos son Argiudolls y Melanudands y las unidades de muestreo fueron definidas según el gradiente altitudinal. Se midieron contenidos de C y N, relación C:N, densidad aparente y abundancias de 13C y 15N. Se encontraron diferencias significativas (p < 0,05) por el efecto de la altura. La zona alta mostró mayores contenidos de C (37,06-42,88 t ha-1) y N (3,12 - 3,86 t ha-1), mayor relación C:N (11,17 - 11,97), menor densidad aparente (0.56 - 0.65 g cm"³) y abundancia de 15N (4,59 - 5,15%o). Barbechos y monocultivos almacenaron más carbono en la parte subterránea del suelo; mientras que en sitios más conservados los contenidos de C y N fueron bajos. El 13C según los usos, fluctuó entre -25,18 y -21,27%o indicando que la mayoría del C fue fijado por plantas C3. Se concluyó que los cambios en el uso afectan el almacenamiento de C, principalmente por prácticas como fertilización con productos de síntesis química; y que los suelos de Alcalá tienen alto potencial para la prestación de servicios ecosistémicos relacionados con la captura de carbono edáfico.