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Empirical evidence that soil carbon formation from plant inputs is positively related to microbial growth. Bradford BGC 2013


By sharg - Posted on 24 April 2013

http://bradfordlab.files.wordpress.com/2013/01/bradford-et-al-biogeochem...

Abstract Plant-carbon inputs to soils in the form of
dissolved sugars, organic acids and amino acids fuel
much of heterotrophic microbial activity belowground. Initial residence times of these compounds
in the soil solution are on the order of hours, with
microbial uptake a primary removal mechanism.
Through microbial biosynthesis, the dissolved compounds become dominant precursors for formation of
stable soil organic carbon. How the chemical class
(e.g. sugar) of a dissolved compound influences
stabilization in field soils is unknown and predictions
from our understanding of microbial metabolism,
turnover and identity are contradictory. We show that
soil carbon formation, from chronic amendments of
dissolved compounds to fertilized and unfertilized
grasslands, is 2.4-times greater from a sugar than an
amino acid. Formation rates are negatively correlated
with respiration rates of the compounds, and positively
correlated with their recovery in microbial biomass.
These relationships suggest that the efficiency of
microbial growth on a compound is positively related
to formation rates of soil organic carbon. Fertilization
does not alter these findings, but together nitrogen and
phosphorus additions reduce soil carbon formation.
Our results highlight the need to consider both nutrient
enrichment and global-change induced shifts in the
form of dissolved root inputs to soils to predict future
soil carbon stocks and hence phenomena such as
climate warming and food security to which these
stock sizes are intimately tied.

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