Chapter Five - Revisiting nutrient cycling by litterfall-Insights from 15 years of litter manipulation in old-growth lowland tropical forest
Sayer, E. J., . 2020.
Abstract
The crucial role of tropical forests in the global carbon balance is underpinned by their
extraordinarily high biomass and productivity, even though the majority of tropical for-
ests grow on nutrient-poor soils. Nutrient cycling by litterfall has long been considered
essential for maintaining high primary productivity in lowland tropical forests but few
studies have tested this assumption experimentally. We review and synthesise findings
from the Gigante Litter Manipulation Project (GLiMP), a long-term experiment in low-
land tropical forest in Panama, Central America, in which litter has been removed from
or added to large-scale plots for 15 years. We assessed changes in soil and litter nutrient
concentrations in response to the experimental treatments and estimated nutrient
return and nutrient use efficiency to indicate changes in nutrient cycling. The soil con-
centrations of most nutrients increased with litter addition and declined with litter
removal. Litter removal altered nitrogen, potassium, manganese and zinc cycling, dem-
onstrating the importance of litter inputs for maintaining the availability of these ele-
ments to plants. By contrast, litter addition only altered nitrogen cycling and, despite
low concentrations of available soil phosphorus, the effects of litter manipulation on
phosphorus cycling were inconsistent. We discuss potential mechanisms underlying
the observed changes, and we emphasise the importance of decomposition processes
in the forest floor for retaining nutrient elements, which partially decouples nutrient
cycling from the mineral soil. Finally, by synthesising GLiMP studies conducted during
15 years of litter manipulation, we highlight key knowledge gaps and avenues for future
research into tropical forest nutrient cycling.
