No isotopic evidence for a differential mineralization of old soil organic matter in sandy, nutrient-poor, tropical soils under eucalypts and acacias
Abstract
An increase in soil N availability by Acacia mangium in pure or mixed-species stands may reduce soil organic matter (SOM) mineralization compared to eucalypt stands. We measured the isotope composition (delta C-13) of coarse particulate organic matter (cPOM, 4-0.25 mm), of fine POM (fPOM, 0.25-0.05 mm) and of the remaining organo-mineral fraction (OMF, <0.05 mm), and of the forest floor in plantations established on a tropical C4-grass savannah. In contrast to our hypothesis, the presence of acacia either alone or in mixture did not impact delta C-13 of the most stable SOM fractions derived from the previous savannah vegetation, which suggests similar rates of native SOM mineralization under acacia and eucalypt trees.