PARENT SESSION
Oral Session # 19: Biogeochemistry II: Grasslands.
Presiding: JT Lennon
Tuesday, August 5. 8:00 AM to 11:30 AM, SITCC Meeting Room 105.
Abiotic and biotic controls on litter decomposition in the semiarid Patagonian steppe.
Austin, Amy*,1, Vivanco, Lucía1, 1 Faculty of Agronomy and IFEVA-CONICET, Buenos Aires, austin@ifeva.edu.ar, ARGENTINA
ABSTRACT- Controls on decomposition and nutrient turnover in water-limited ecosystems are elusive, as many studies of litter decomposition have shown contradictory results and little correlation with annual precipitation. We carried out two different factorial experiments designed to disentangle the abiotic and biotic controls on litter decomposition in water-limited ecosystems. In the first experiment, we decomposed litter of mixed native grasses under different light regimes (full sunlight, reduced ultraviolet-B (UV-B) radiation, and blocked total radiation), in combination with a treatment of soil sterilization. In the second experiment, we decomposed litter of mixed native grasses treating underlying soils with additions of labile carbon and inorganic nitrogen. After one year of decomposition in the field, photodegradation was the dominant control on mass loss (P<0.001) with a 50% and 250% reduction in litter mass loss in the reduced UV-B and blocked total radiation treatments, respectively. Soil sterilization had no effect on mass loss. In the substrate addition experiment, increased inorganic nitrogen accelarated litter mass loss by 15% (P=0.05), while carbon or combined carbon and nitrogen additions did not affect decomposition. Nutrient release in early stages of decomposition, however, was significantly affected by soil substrate availability, with increased nitrogen immobilization in litter from carbon addition plots (P<0.01). We conclude that photodegradation is the dominant control on litter mass loss in this ecosystem, and that surprisingly, UV-B radiation may account for a large fraction of these abiotic losses. Biotic controls are secondary to photodegradation for litter mass loss, but may become critical for soil organic matter turnover and nutrient cycling.
Key words: photodegradation, nitrogen release, litter decomposition, semiarid ecosystems