Regional and seasonal patterns of litterfall in tropical South America

[摘要] The production of aboveground soft tissue represents an important share oftotal net primary production in tropical rain forests. Here we draw from alarge number of published and unpublished datasets (n=81 sites) to assessthe determinants of litterfall variation across South American tropicalforests. We show that across old-growth tropical rainforests, litterfallaverages 8.61±1.91 Mg ha⁻¹ yr⁻¹ (mean ± standarddeviation, in dry mass units). Secondary forests have a lower annuallitterfall than old-growth tropical forests with a mean of 8.01±3.41 Mg ha⁻¹ yr⁻¹. Annual litterfall shows no significantvariation with total annual rainfall, either globally or within forest types.It does not vary consistently with soil type, except in the poorest soils(white sand soils), where litterfall is significantly lower than in othersoil types (5.42±1.91 Mg ha⁻¹ yr⁻¹). We also study thedeterminants of litterfall seasonality, and find that it does not depend onannual rainfall or on soil type. However, litterfall seasonality issignificantly positively correlated with rainfall seasonality. Finally, weassess how much carbon is stored in reproductive organs relative tophotosynthetic organs. Mean leaf fall is 5.74±1.83 Mg ha⁻¹ yr⁻¹ (71% of total litterfall). Mean allocationinto reproductive organs is 0.69±0.40 Mg ha⁻¹ yr⁻¹ (9%of total litterfall). The investment into reproductive organs divided by leaflitterfall increases with soil fertility, suggesting that on poor soils, theallocation to photosynthetic organs is prioritized over that to reproduction.Finally, we discuss the ecological and biogeochemical implications of theseresults.

[学科分类] 地球化学与岩石