Limitations of microbial activity in different soil microsites in the Patagonian steppe, Argentina.

GONZALEZ-POLO, M.; AUSTIN, A. T.

Milwaukee, Wisconsin

Congreso; Annual meeting of the Ecological Society of America; 2008

Ecological Society of America

Background/Question/Methods In arid and semiarid ecosystems, an indirect effect oflow rainfall for microorganisms is the small amount of organic matter entering the soil.As soil microorganisms obtain C and energy from plant debris by enzymaticdegradation, these reactions could be limited by substrate or enzyme, and regulated byenvironmental conditions. We conducted a laboratory experiment with soils from theshrub-grass steppe in Patagonia, Argentina, examining the effects of the vegetationpatches on the cellulose enzymatic degradation. Under optimal assays conditions andwith an excess of either substrate or enzyme, it is possible to disentangle the relativeimportance of these two factors on enzymatic activity. We collected soils from belowthe 2 dominant species of shrubs (Mulinum spinosum and Adesmia volckmannii) andsoils from microsites experimentally created by either the removal of these shrubs or theaddition of a dead shrub to a bare soil area. We determined the comparative response ofsoil amendments in these soils with: 1) buffer+carboximethyl-cellulose (CMC) 2)buffer+cellulase (Sigma- Trichoderma viridae) and 3) buffer (control).Results/Conclusions We found that the addition of available substrate (CMC), but notenzymes alone, significantly increased cellulase activity, and the magnitude of theincrease depended on the microsite. For instance, soil under Adesmia increased theiractivity 800% with respect to control, but soil from bare soil microsites did not respondto CMC additions. Soils from beneath the Adesmia removal demonstrated significantlyincreased activity but not in soils from Mulinum removal microsites. These resultssuggest that cellulase activity in these semiarid soils are primarily limited by Cavailability rather than enzyme concentration in soil under shrubs. On the contrary, inbare soil microsites, cellulase activity appears to be limited by both C and enzymeavailability. Results from the generated microsite suggests that the Mulinum‘footrprint’ was erased 3 years after removal, being more similar to bare soil, but thelegacy of the Adesmia microsite still remained