Soil microbial biomass and soil respiration in Munessa Forest, Ethiopia: a comparison between natural and adjacent plantation forest

Abstract

Conversion of natural forests to monocrop plantations is a common forest management, yet its impact on ecosystem processes has rarely been evaluated and some earlier studies along the same line were inconsistent and contradictory. The present study compared the difference in soil microbial biomass and soil respiration between natural and adjacent Cupressus lusitanica plantation in Munessa forest. Weekly measurements of soil CO₂ efflux were carried out using LI-8100 infrared gas analyzer at 20 randomly selected locations from May 2009 to April 2010. On both forest stands, organic C, total N and microbial biomass declined significantly with increasing soil depth (p<0.05). There were no major differences in microbial composition and dominance between the two forest types. However, the total phospholipids fatty acid (PLFA) tended to be significantly larger in soils under the natural forest stand than adjacent plantation forest stand (p = 0.032). Mean soil CO₂ efflux rates was found to range from 2.23 and 7.22 μmol m^-2s^-1 versus 2.39 to 6.84 μmol m^-2s^-1 in the natural and plantation forest stand, respectively. Soil moisture appeared to be the major variable controlling soil CO₂ efflux rate. Unlike soil moisture, soil temperature had weak relation with soil CO₂ efflux and was better explained in the plantation forest stand using exponential function (r² = 0.12; p<0.01). The results indicate that the natural forest is better in sustaining soil microbial biomass and nutrients than monocrop plantation. We conclude that the natural forest played a significant role in the annual forest ecosystem carbon budget.

Keywords/phrases: PLFA, Soil CO₂, Soil moisture, Soil temperature