The soil in rainforests stores much of the carbon of tropical regions in the form of soil organic matter (SOM). Conversion of natural forest to plantations severely affects the quality and quantity of SOM and thereby its ecological functions.
Previous studies have shown that the conversion of tropical forest to rubber plantation changed soil carbon (C) and nitrogen (N) storage. However, the underlying mechanisms are yet to be fully understood.
In a study published in Catena, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) tried to elucidate the effect on SOM dynamics of tropical rainforest conversion to rubber plantation.
The researchers quantitatively determined the changes in SOM fractions of different aggregate- and density-size and measured soil C and N and their respective isotopic abundances of δ13C and δ15N in bulk soil.
They found that both aggregate- and density-size fractionations significantly aided the separation of functional SOM fractions which could be employed as good early indicators of SOM stability after the land use change. Individual aggregate- and density-size fractions provided better insight than bulk soil into the physical and chemical shifts in response to land use change.
Furthermore, the mean weight diameter, geometric mean diameter, and water stable aggregates proportion was greater in tropical rainforest soil compared with those in rubber plantation.
Land use change significantly decreased C and N in bulk soil, aggregate-size, and density fractions and the overall stability of SOM. The losses in soil organic carbon and nitrogen from the bulk soil following land use change were mainly driven by the loss of proportion of macroaggregates (HF and LF).
Overall, conversion of tropical rainforest to monoculture rubber plantation enriched δ13C but depleted δ15N.
"A simple way to restore SOM quality and quantity could be planting intercrops within monoculture RP," said Dr. ZHOU Wenjun, correspondence author of the study.
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