Efeito do clima e solos na produção de serapilheira em florestas de terra firme na Amazônia central

Abstract

Tropical forests account for about one-third of global net primary productivity (NPP), of which approximately 34% (4.8 ± 0.3 Mg C ha−1 yr−1) is quantified through litter biomass. Litter consists of the layer of organic matter deposited beneath the soil surface and represents the main pathway for nutrient transfer from vegetation to soil through organic matter cycling. This deposition and cycling process is crucial for maintaining the fertility of highly weathered soils in central Amazonia, ensuring the preservation of vital ecosystem services provided by the forest. The influence of climate, soil and vegetation characteristics strongly affects litter deposition and cycling patterns. Increasingly frequent extreme weather events also impact litter deposition patterns, thereby altering nutrient cycling processes. To understand how climate and soil characteristics affect litter productivity in different areas, this study aimed to determine total litter production and its components (leaves, woody materials, flowers, fruits, and residues) over time, relating them to local climatic variables (precipitation, maximum temperature, radiation, cumulative water deficit – CWD, and wind speed), global indices (El Niño Southern Oscillation - ENSO and Tropical Atlantic Index - NTA), and soil fertility (Exchangeable Cations and Phosphorus Concentration - P). We investigated spatial and temporal patterns using a long series of up to 10 years of litter production, collected biweekly in 150 traps of 0.25 m² in 6 plots located in 3 different upland forest areas in central Amazonia. The average annual litter production was 7.2 ± 0.8 Mg ha-1yr-1. Production followed a seasonal pattern, with peaks in productivity during the drier months (0.8 ± 0.1 Mg ha-1 month-1 from June to October), while production in the wetter months was nearly half (on average 0.4 ± 0.1 Mg ha-1 month-1 from November to May). Most of the litter consisted of leaves (74%), followed by fine wood (15%), flowers (3%), fruits (4%), and residues (3%). Maximum temperature, radiation, MCWD, precipitation, and average wind speed were the climatic factors that most influenced total litter production. Among global variables, El Niño 3.4 and NTA influenced total production. At this spatial scale, P concentration also influenced total litter production; however, there was higher flower production in areas with lower P concentration. These results highlight the effects of climate and soil on litter productivity, serving as a basis for improving vegetation models and understanding the impact of climate change on Amazonian forest productivity.