Increased Quantity and Quality of Coarse Soil Organic Matter Fraction at Elevated CO2 in a Grazed Grassland are a Consequence of Enhanced Root Growth Rate and Turnover |
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Authors: | V Allard PCD Newton M Lieffering J-F Soussana RA Carran C Matthew |
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Institution: | (1) Agresearch Grasslands, Private Bag 11008, Palmerston North, New Zealand;(2) INRA-Agronomie, 234 avenue du Brézet, 63100 Clermont-Ferrand, France;(3) lnstitute of Natural Resources, College of Sciences, Massey University, PO Box 11222, Palmerston North, New Zealand |
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Abstract: | The aims of this study were to determine whether elevated atmospheric CO2 concentration modifies plant organic matter (OM) fluxes to the soil and whether any change in the fluxes can modify soil
OM accumulation. Measurements were made in a grazed temperate grassland after almost 4 years exposure to elevated atmospheric
CO2 (475 μl l-1) using a Free Air CO2 Enrichment (FACE) facility located in the North Island of New Zealand. Aboveground herbage biomass and leaf litter production
were not altered by elevated CO2 but root growth rate, as measured with the ingrowth core method, and root turnover were strongly stimulated by elevated CO2 particularly at low soil moisture contents during summer. Consequently, significantly more plant material was returned to
the soil under elevated CO2 leading to an accumulation of coarse (> 1 mm) particulate organic matter (POM) but not of finer POM fractions. The accumulating
POM exhibited a lower C/N ratio, which was attributed to the higher proportion of legumes in the pasture under elevated CO2. Only small changes were detected in the size and activity of the soil microbial biomass in response to the POM accumulation,
suggesting that higher organic substrate availability did not stimulate microbial growth and activity despite the apparent
lower C/N ratio of accumulating POM. As a result, elevated CO2 may well lead to an accumulation of OM in grazed grassland soil in the long term. |
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Keywords: | C sequestration FACE ingrowth cores particulate organic matter root growth root turnover |
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