HR: 17:50h
AN: B34A-07    [Abstracts]
TI: Effects of litter position on mass loss and nitrogen release in the semiarid Patagonian steppe
AU: * Austin, A T
EM: austin@ifeva.edu.ar
AF: University of Buenos Aires, Faculty of Agronomy, IFEVA-CONICET Av. San Martin 4453, Buenos Aires, CAP C1417DSE, Argentina
AB: The patchy distribution of vegetation in arid and semiarid ecosystems results in a mosaic of microsites of soil properties and variable abiotic conditions, including the well-documented "islands of fertility", low nutrient conditions in exposed bare soil and large amounts of standing dead material. I evaluated the relative importance of litter position on mass loss and nutrient release in a variety of realistic litter positions both in vegetated, unvegetated, aerial and buried microsites in a natural semiarid steppe in Patagonia, Argentina. Position demonstrated a highly significant effect on mass loss for all litter types (P<0.0001), but surprisingly, the fastest decomposition occurred in litter that was suspended in aerial positions or buried (k=0.25 and 0.32 year^-1, respectively), intermediate values for mass loss of litter in bare soil and in shrub removal patches (k=0.21 and 0.24 year^-1, respectively), and markedly slowest decomposition occurring under shrub patches (k = 0.018 year^-1). In contrast, nutrient release showed a very different pattern with nutrient immobilization occurring only in shrub and buried microsites while all other positions demonstrated a gradual decrease in nitrogen over time. These results support the idea that abiotic photodegradation may be an important driver affecting carbon losses in litter in positions exposed to solar radiation, while nutrient dynamics appear to be largely biotically mediated and concentrated in photoprotected areas where biotic activity dominates. Global change may differentially affect carbon and nutrient turnover due to the relative importance of abiotic and biotic factors affecting litter decomposition in semiarid ecosystems.
DE: 0428 Carbon cycling (4806)
DE: 0469 Nitrogen cycling
DE: 0476 Plant ecology (1851)
SC: Biogeosciences [B]
MN: 2007 Joint Assembly