IFEVA   02662
INSTITUTO DE INVESTIGACIONES FISIOLOGICAS Y ECOLOGICAS VINCULADAS A LA AGRICULTURA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Direct and indirect effects of photodegradation on carbon and nutrient turnover in species from temperate South America
Autor/es:
AUSTIN, A.T.; BALLARÉ, C.L.
Lugar:
Foz de Iguacu
Reunión:
Congreso; America American Geophysical Union Meeting of the Americas; 2010
Institución organizadora:
American Geophysical Union
Resumen:
The importance of litter quality as a major control on litter decomposition has been explored extensively in mesic and humid terrestrial ecosystems; lignin and lignin:nutrient ratios have been identified as key characteristics determining the rate of organic matter turnover. Recent experimental evidence has shown that, in semiarid ecosystems, photodegradation can be important in controlling litter decomposition; however, correlations with litter characteristics and decomposition and nutrient release are much less obvious. Our objective in this study was to evaluate the susceptibility to photochemical mineralization in a range of temperate species in order to quantify the importance of abiotic photodegradation on mass loss and subsequent biotic decomposition. We harvested litter from 25 native and introduced species growing in temperate ecosystems in Argentina ranging from mesic forests to semiarid steppe of Patagonia and natural grasslands and agroecosystems of the Pampa region. Initial samples of all species were analyzed for water and ash content, lignin, cellulose and nutrient content and specific leaf area. In a factorial experiment, we subjected litter of the twenty-five species in transparent plastic cups to three light treatments: 1) Control (>95% solar radiation transmission): 2) ultraviolet block (attenuation of radiation <400 nm [UV-B and UV-A]) and 3) UV and shortwave visible block (attenuation of radiation <600 nm). There was a highly significant effect of both litter type (P<0.001) and light treatment (P<0.0001) on abiotic mass loss. While direct photodegradative losses were relatively small overall, the magnitude of the effect with attenuation of UV and visible light was 12% and 65% respectively. Both lignin content and specific leaf area were positively correlated to abiotic mass loss, while nutrient content and C:N ratios demonstrated no relationship with photodegradation. When these litter samples were then placed on the soil surface for biotic incubation, we observed a strong and consistent (P<0.0001) photofacilitation effect, with litter previously exposed to full solar radiation decomposing up to 120% more quickly. These results suggest that a wide variety of plant litter types could be susceptible to photodegradation, and that both direct and indirect effects of photodegradation could play an important role on carbon loss and nutrient release in a range of terrestrial ecosystems.