Introduction Procedure 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.

Module 6 – Roots, Biomass, and Carbon Mass SEE-U Brazil 2001

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 188.35 188.35† N/a 84.76 84.76 † * Carbon mass calculated using carbon sequestration index provided by the International Panel on Climate Change † Based on extrapolated values for dry root biomass

Survey of Root Morphotype Diversity Forest Coarse Fine Pasture Coarse Pasture Fine 0-10 cm 2 types 9 types 1 type 5 types 10-14 cm n/a none (all old) 10-20 cm 7 types (5 old, 2 new) 20-30 (old) 4 types Total types 2 11 1 5

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.

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.

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.