Effects of carbon quality additions on soil enzymatic activity and litter decomposition in a mixed southern beech forest in Patagonia, Argentina

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

San Jose, California, USA

Congreso; Annual meeting of the Ecological Society of America; 2007

Ecological Society of America, USA

The quality of organic matter incorporated in the soil spans a diverse range in forestecosystems, from highly labile dissolved organic carbon to recalcitrant coarse woodydebris. At the same time, how variation in carbon quality, rather than quantity, affectsecosystem functioning has been little explored in natural ecosystems. Evidence fromlaboratory incubations suggest that the lability of carbon substrates can have importanteffects on soil biotic activity, but demonstrations in field conditions are lacking. Weconducted a manipulative experiment in a southern beech forest in Patagonia,Argentina, examining the effects of carbon additions of sugar (labile) and sawdust(recalcitrant) on soil enzymatic activity and litter decomposition. We hypothesized thatsoil C additions of would alter soil enzymatic activity with recalcitrant C additionsstimulating beta-glucosidase and phenol oxidase activity and labile C additions reducingenzyme activity. Forest floor plots of 1m2 were established in mid-summer with thefollowing treatments: 1) control (no addition); 2) sugar; 3) sawdust and 4)sugar+sawdust. In addition, we placed litterbags of Nothofagus pumilio and twigs in allplots. We collected soil samples in nine dates during one year, and collected litterbagsand twigs at three dates (4, 8, and 12 months). We found that C additions hadmarginally significant effects on beta-glucosidase and phenol oxidase activity in the fallsampling (P<0.1), with sawdust stimulating enzyme activity and sugar without asignificant effect. Litter decomposition was significantly different (P<0.05), but incontrasting ways: recalcitrant C additions stimulated decomposition of litter while labileC additions reduced mass loss of twigs. These results suggest that soil microbialcommunities were affected in both the short- and medium-term by modification ofdetritus quality, which could have altered their physiological capacities, and this effecthad an important consequence for carbon turnover in this forest ecosystem.