Our group examined the differences between root biomass at different depths within the forest and the pasture.

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Introduction

• Our group examined the differences between root
  biomass at different depths within the forest and
  the pasture.
• Roots are an important part of the soil because
  they store large amounts of carbon. According to
  the IPCC, 45 of the dry biomass of any plant
  material is composed of pure carbon.
• Some scientists hypothesize that tropical
  pastures can act as important carbon sinks.

Procedure

• We used a post-digger to dig a cylindrical
  volume, with a diameter of 13cm. We then
  collected soil samples at intervals of 10cm.
• We separated the roots from the soil, washed and
  dried them, and then weighed the roots.
• We attempted to distinguish different root
  morphotypes among our samples.

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Module 6 Roots, Biomass, and Carbon Mass

• SEE-U Brazil 2001

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Total Dry Biomass and Carbon Mass (g/m2)
0-10cm 10-20cm 20-30cm
Forest
Biomass 226.02 75.34 113.01
Carbon 101.71 33.90 50.85
Pasture
Biomass 188.35 188.35 N/a
Carbon 84.76 84.76 N/a
Carbon mass calculated using carbon
sequestration index provided by the International
Panel on Climate Change Based on extrapolated
values for dry root biomass
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Survey of Root Morphotype Diversity
Forest Coarse Forest Fine Pasture Coarse Pasture Fine
0-10 cm 2 types 9 types 1 type 5 types
10-14 cm n/a n/a none 5 types (all old)
10-20 cm none 7 types (5 old, 2 new) n/a n/a
20-30 1 type (old) 4 types (all old) n/a n/a
Total types 2 11 1 5
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Summary of Data

• Our graphs illustrate the abundance of coarse and
  fine roots in the soil of the pasture and the
  forest.
• In general, we found more fine roots than coarse
  roots, and we found the majority of the coarse
  roots in the first ten centimeters of the soil.
• In the pasture we were only able to dig to the
  depth of 14cm because we encountered large rocks
  that impeded our excavation. Thus, we used the
  obtained data from the 10-14cm layer of the soil
  in order to extrapolate the expected biomass of
  the roots for a 10-20cm layer of soil.
• Our table shows the calculated values for the
  expected biomass of the roots per meter squared.
  Using the IPCC carbon sequestration index, we
  calculated the approximate amounts of carbon per
  square meter.

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• Though we only were able to reach a depth of 14cm
  in the pasture, our extrapolated value for total
  biomass from 0-20cm in the pasture was greater
  than our obtained value for total biomass from
  0-20cm in the forest.
• We estimate that 16.7 more carbon is sequestered
  in the first 10 cm of forest soil than in the
  corresponding amount of pasture soil.
• We found a larger quantity of coarse roots in the
  forest soil.
• A greater number of root morphotypes were found
  in forest soil (13 types) than in pasture soil (6
  types).
• Root morphotype diversity decreased with soil
  depth.

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Conclusions

• Had we been able to reach further depths in the
  pasture, we may have had more significant data
  demonstrating differences between root content of
  the forest and the pasture.
• The only conclusive difference we found between
  our two sample sites was a larger number of
  coarse roots that extended to greater depths in
  the forest soil. These coarse roots accounted for
  the slightly larger amount of dry biomass in the
  forest sample.
• Though more carbon is sequestered in forest root
  systems, well-managed pastures may be useful as
  carbon sinks where forest conservation is not
  possible.