Intrinsic effects of species on leaf litter and root decomposition: a comparison of temperate grasses from North and South America.

Plant species affect natural ecosystems through interactions between environmental and genetic factors. The importance of plant species in controlling decomposition is now well-established through its influence on litter quality, which affects mass loss and nutrient release. At the same time, direct species effects are often confounded with indirect site effects due to the ecophysiological responses of plants to environmental variability. We evaluated the intrinsic effects of species on litter quality and decomposition, comparing 14 native perennial grass species from three different grassland ecosystems in North and South America. Plants were grown under controlled greenhouse conditions to eliminate any indirect effects of climate on litter quality, and senescent material of leaf litter and roots were collected. The initial litter nutrient quality and the carbon quality were assessed, and decomposition was determined over a period of one year by placing litterbags in a common grassland site. In spite of constant growth conditions, species' litter showed broad and significant differences in N, P and lignin concentration, as well as C:N ratio, with the greatest differences occurring between C(3) and C(4) species and leaf litter and root material. In addition, decomposition was significantly different among species and between leaf litter and roots within species, with constants (k) ranging from 1.50 to 3.65 year(-1) for leaf litter, and 0.51-1.82 year(-1) for roots. These results highlight the fact that, independent of climate or edaphic changes due to human activity, changes in plant species or in allocation patterns among plant organs in grassland ecosystems could have a large effect on carbon turnover. At the same time, the way in which intrinsic species characteristics affect decomposition demonstrates a large degree of functional convergence among species from grasslands of North and South America.