2 results
Nutrient cycling and plant–soil feedbacks along a precipitation gradient in lowland Panama
- Louis S. Santiago, Edward A. G. Schuur, Katia Silvera
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- Journal:
- Journal of Tropical Ecology / Volume 21 / Issue 4 / July 2005
- Published online by Cambridge University Press:
- 27 June 2005, pp. 461-470
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This study addresses patterns of nutrient dynamics on a precipitation gradient (1800–3500 mm y−1) in lowland tropical forest with heterogeneous soil parent material, high plant species diversity and large changes in species composition. Mean foliar concentrations of phosphorus, potassium, calcium and magnesium decreased with increasing precipitation, whereas foliar carbon:nitrogen increased with increasing precipitation. Mean foliar nitrogen:phosphorus varied from 16.4–23.8 suggesting that plant productivity at these sites is limited by phosphorus. Total soil nitrogen increased as a function of foliar litter lignin:nitrogen, whereas net nitrogen mineralization rates decreased with increasing lignin:N indicating that as litter quality decreases, more soil nitrogen is held in soil organic matter and the mineralization of that nitrogen is slower. Extractable phosphorus in soil was negatively correlated with foliar litter lignin:phosphorus, illustrating effects of litter quality on soil phosphorus availability. Overall, the results suggest that variation in plant community composition along this precipitation gradient is tightly coupled with soil nutrient cycling. Much of our understanding of effects of precipitation on nutrient cycling in tropical forest is based on precipitation gradients across montane forest in Hawaii, where species composition and soil parent material are constant. Our results suggest that variation in parent material or species composition may confound predictions developed in model island systems.
Resumen: Este estudio trata sobre los patrones de dinámica de nutrientes en un gradiente de precipitación (1800–3500 mm y−1) en un bosque tropical de tierras bajas con material parental heterogéneo, alta diversidad de especies de plantas, y un gran cambio en la composición de especies. Las concentraciones promedio de fósforo, potasio, calcio y magnesio disminuyen con un aumento en la precipitación, mientras que la proporción carbono:nitrógeno aumenta con un aumento en la precipitación. La proporción promedio de nitrógeno foliar:fósforo varía de 16.4 a 23.8, lo cual sugiere que estos sitios tienen limitaciones de fósforo. El nitrógeno total del suelo aumenta como una función de la proporción de lignina foliar de la hojarasca:nitrógeno, mientras que la tasa de mineralización del nitrógeno neto disminuye con un aumento de la proporción de lignina:nitrógeno, lo cual indica que mientras la calidad de la hojarasca disminuye, más nitrógeno del suelo es retenido en la materia orgánica y la mineralización de ese nitrógeno es más lenta. El fósforo extraíble está correlacionado negativamente con la proporción de lignina foliar de la hojarasca:fósforo, lo cual ilustra el efecto de la calidad de hojarasca en la disponibilidad de fósforo del suelo. En resumen, estos resultados sugieren que la variación en la composición de plantas de una comunidad a lo largo de este gradiente de precipitación tiene un efecto considerable en la retroalimentación de los ciclos nutricionales del suelo. Gran parte de nuestros conocimientos sobre el efecto de los gradientes de lluvia en ciclos nutricionales del suelo han sido basados en estudios de gradientes de precipitación de bosques de montaña en Hawaii, en donde tanto la composición de especies y el material parental del suelo son constantes. Nuestros resultados sugieren que la variación del material parental del suelo y la composición de especies pueden confundir las predicciones desarrolladas en sistemas modelos de islas.
Seed germination, seedling growth and habitat partitioning in two morphotypes of the tropical pioneer tree Trema micrantha in a seasonal forest in Panama
- Katia Silvera, John B. Skillman, J. W. Dalling
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- Journal:
- Journal of Tropical Ecology / Volume 19 / Issue 1 / January 2003
- Published online by Cambridge University Press:
- 10 January 2003, pp. 27-34
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We examined the distribution, germination, growth and photosynthetic characteristics of two co-existing morphotypes of the pioneer tree Trema micrantha at the Barro Colorado Nature Monument (BCNM), Panama. Morphotypes differed significantly in distribution and in seed characteristics. A ‘large’-seeded morphotype (endocarp mass=3.83 mg) was associated with treefall gaps in the forest interior, whereas a ‘small’-seeded morphotype (endocarp mass=1.38 mg) was found predominantly on landslides on the margins of Lake Gatun. Seeds of the small-seeded morphotype germinated faster than seeds of the large-seeded morphotype, with seedlings of the small-seeded morphotype showing both a higher Unit Leaf Rate (ULR) and a lower Specific Leaf Area (SLA). Differences in photosynthetic rates reflected differences in SLA; the small-seeded morphotype had a higher rate on a leaf area basis, while the large-seeded morphotype had a higher rate on a leaf mass basis. Although allocation patterns between morphotypes varied in a way consistent with known interspecific differences between ‘sun’ and ‘shade’ plants, relative growth rates (RGR) of the morphotypes were similar across different light conditions suggesting that factors other than light, such as water uptake efficiency, soil nutrient requirements, and perhaps seed dispersal characters may explain the habitat partitioning of morphotypes.