Efeito da temperatura no funcionamento de ecossistemas aquáticos ao longo de um gradiente húmico

Abstract

Freshwater ecosystems are the most vulnerable to the effects of climate change, especially alterations in temperature and precipitation patterns. Temperature increases impact the metabolic demands of organisms and may stimulate primary production (PP). Simultaneously, changes in precipitation can affect the input of allochthonous organic matter, consequently increasing the concentration of humic substances (HS) in ecosystems. HS reduce PP due to decreased light penetration in the water column and play a crucial role in structuring phyto and zooplankton communities. Zooplankton community structure may be altered in terms of richness, density, and biomass due to elevated HS concentrations in the water (linked to reduced primary production) and rising temperatures. In this study, we assessed the interactive effects of warming and water HS concentration on zooplankton community structure and PP. We conducted an experiment using a bifactorial design comprising two temperature scenarios combined with four HS levels. We observed that PP decreased along the HS gradient, likely due to a combination of light limitation and increased zooplankton grazing pressure on primary producers due to their higher metabolic demands. However, warming stimulated PP at high HS levels, attributed to temperature becoming a regulator of PP under conditions of increased light limitation. We also noted that zooplankton community richness, density, and biomass declined with rising HS, with no significant effect of temperature scenario or interaction between these factors. This indicates that HS concentration was a stronger environmental factor for zooplankton than temperature increase. We conclude that HS concentration could be a significant effect of climate change on planktonic community dynamics and aquatic ecosystem functioning. Additionally, although we did not observe a significant temperature effect on the zooplankton community, the reduction in PP associated with temperature increase affects zooplankton's food resource and the available energy to sustain the ecosystem.