|Acosta Mercado, Dimaris|
Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/23/2007
Publication Date: 3/1/2008
Citation: Acosta Martinez, V., Acosta Mercado, D., Sotomayor, D., Cruz, L. 2008. Microbial communities and enzymatic activities under different management in semiarid soils. Applied Soil Ecology. 38(3):249-260. Interpretive Summary: Still in 2005, little is known about the microbial population size, composition, and function in many arid and semiarid regions of the world. This study evaluated several properties of four representative semiarid soils from Puerto Rico as affected by different land use or management. Soil organic C (12.1 to 46.5 mg C kg-1 soil) at 0-5 cm depth was decreased (24%) by tillage compared to no-tillage practices in agricultural soils and it was decreased even more when compared to pasture. The C from the microbial biomass was up to 2.4 times lower in agricultural sites under tillage compared to no-tillage sites and > 2.4 times higher under pasture at 0-5 cm depth. Different microbial community was developed under tilled agricultural soils compared to pasture at 0-5 and 5-15 cm depths, and trends indicated that tillage can differentiate the microbial community compared to no-tillage practices in agricultural soils. The soil microbial community contained more abundance of fungi than bacteria populations, and lack protozoa in the four semiarid soils studied. Enzyme activities of C, N, P, and S cycling also demonstrated differentiation in soil biochemical processes in agricultural sites under tillage compared to no-tillage, and even more in agricultural soils compared to pasture. An assessment of the distribution of arylsulfatase in these soils, an important enzyme to S cycling, revealed that the released enzymes from microbial cells represented 47% of the total enzyme activity of soil. Because the soil microbial community size and composition determine soil functioning, our findings should be considered in decisions for land use transformations on these semiarid soils.
Technical Abstract: Still in 2005, knowledge about the size, composition, and ecological function of the soil microbial community in many semiarid regions of the world remains unknown. This study evaluated several properties of four representative semiarid soils from Puerto Rico as affected by different land use or management. Organic C (12.1 to 46.5 mg C kg-1 soil) was decreased by tillage compared to no-tillage (>24%) in agricultural soils and compared to pasture (>47%) at 0-5 cm. Total N was not affected by tillage. Microbial biomass (Cmic=167 to 1401 mg C g-1 soil) was up to 2.4 fold higher in agricultural sites under no-tillage and > 2.4 times higher in pasture compared to the tilled sites at 0-5 cm, and at 5-15 cm for one of the pasture sites. Similar trends showed Nmic (23 to 194 mg N g-1 soil). Principal Component Analyses of fatty acids methyl ester profiles clearly separated the microbial community of the two tilled agricultural soils from pasture, and one of the tilled agricultural soil compared to the no-tilled counterpart. The microbial community of these soils was predominantly composed of fungi compared to bacteria, and generally lacked protozoa. Enzyme activities, including different pools of arylsulfatase, were also differentiated (lower) in tilled agricultural soils compared to no-tillage, and to pasture. For these semiarid soils, arylsulfatase activity in chloroform fumigated minus non-fumigated soils was 47% of the total activity, which is considered to represent the released intracellular microbial enzymes. Since soil function is linked to microbial diversity and enzyme-mediated biochemical processes, our results indicate that caution should be taken into the effects of land use transformations for these soils. Keywords: Intracellular arylsulfatase; Enzyme activities; Cropping systems; Soil management; FAME; Tillage