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Abstract:
Fine roots are the most dynamic portion of a
plant’s root system and a major source of soil organic matter.
By altering plant species diversity and composition, soil
conditions and nutrient availability, and consequently belowground
allocation and dynamics of root carbon (C) inputs,
land-use and management changes may influence organic C
storage in terrestrial ecosystems. In three German regions,
we measured fine root radiocarbon (14C) content to estimate
the mean time since C in root tissues was fixed from
the atmosphere in 54 grassland and forest plots with different
management and soil conditions. Although root biomass
was on average greater in grasslands 5.1±0.8 g (mean±SE,
n=27) than in forests 3.1±0.5 g (n=27) (p <0.05), the
mean age of C in fine roots in forests averaged 11.3±1.8 yr
and was older and more variable compared to grasslands
1.7±0.4 yr (p <0.001). We further found that management
affects the mean age of fine root C in temperate grasslands
mediated by changes in plant species diversity and composition.
Fine root mean C age is positively correlated with
plant diversity (r =0.65) and with the number of perennial
species (r =0.77). Fine root mean C age in grasslands was
also affected by study region with averages of 0.7±0.1 yr
(n=9) on mostly organic soils in northern Germany and
of 1.8±0.3 yr (n=9) and 2.6±0.3 (n=9) in central and
southern Germany (p <0.05). This was probably due to differences
in soil nutrient contents and soil moisture conditions
between study regions, which affected plant species diversity
and the presence of perennial species. Our results indicate
more long-lived roots or internal redistribution of C in
perennial species and suggest linkages between fine root C
age and management in grasslands. These findings improve our ability to predict and model belowground C fluxes across
broader spatial scales.
