A importância da disponibilidade de nutrientes para a dinâmica de carbono abaixo do solo na Amazônia Central

Abstract

The availability of nutrients is related to primary production in tropical forests and observational evidence demonstrates a range of responses to soil nutrient availability highlighting the need to better understand how soil nutrients determine ecosystem processes. Theory suggests a limitation of tropical forest growth related to low phosphorus availability or even low cation? availability, raising new questions about how nutrient limitation arises and its various effects on different compartments of carbon cycling. One ecosystem process related to carbon and nutrient cycling that is rarely examined is fine root dynamics. The characteristics of the fine roots, including abundance, functional traits and mycorrhizal symbionts, can be highly sensitive to soil nutritional changes. Therefore, quantifying the responses of the fine roots and their symbionts to the alleviation of nutrient limitation can improve our understanding of the effect of low nutrient availability on the belowground ecosystem processes. In this research, we documented the response of fine roots, arbuscular mycorrhizal fungi (AMF) and total soil CO2 flux, to the availability of phosphorus, nitrogen and cations (potassium, magnesium and calcium) during six months of fertilization in a complete factorial design in one forest land firm in Central Amazonia. We observed that the addition of nutrients increased both the biomass and the yield of fine roots in the superficial layers of the soil, where the interaction between phosphorus and cations caused an increase in the biomass of thin roots in the layer of 10-30 cm, while the increase of productivity of fine roots in the 0-10 cm layer was caused only by the addition of cations. The morphological characteristics of the roots did not respond to the addition of the nutrients during the six months of collection. However, the addition of phosphorus strongly increased the total soil carbon flux as well as potentially increased the colonization of fine roots by arbuscular mycorrhizal fungi. Although there was an increase in the yield of fine roots and total soil carbon flux, there was not a significant relationship between these two factors, suggesting that the increase in the mycorrhizal community, together with the increase in microbial activity, may have strongly influenced the increase of the total soil CO2 flux. Together, this research experimentally shows that phosphorus and cations are the main co-limiting nutrients of belowground ecosystem processes in this Central Amazonian tropical forest, suggesting that further research is necessary to understand the role cations and their interactions with other major plant nutrients across tropical forests.