Abstract:

Plants play an important role in ecosystem processes. Functional meaning of trait variation in wide environmental gradients is well known but is scarcely known across narrow gradients. We analyze the variation of morphological, physical and chemical traits of dominant plant species and the potential rates of dry mass loss and N release/immobilization during senesced leaf decomposition of these species across a narrow aridity gradient, and to identify indicative traits useful to set species functional groups sharing decomposition patterns.

We analyzed the variation of morphological, physical and chemical traits (specific leaf area, seed mass, N and soluble phenols in green and senesced leaves, plant height) in dominant plant species at 12 sites across an aridity gradient in northern Patagonia, Argentina. We collected senesced leaves of each plant species at each site and used them to estimate the potential rates of dry mass loss and N release/immobilization from decomposing senesced leaves in a microcosm experiment. We analyzed the variation of plant traits and decomposition rates across the aridity gradient. We grouped plants species according to growth forms (perennial grasses, deciduous shrubs, evergreen shrubs) and different combinations of morpho-physical and chemical traits of green and senesced leaves and compared the potential rates of dry mass loss and N release/immobilization during leaf decomposition among these groups delimited by each grouping criteria.

Plant traits did not vary across the aridity gradient. The potential rate of dry mass loss was positively related to aridity, while the potential rate of N release/immobilization did not vary across the gradient. Grouping species by separately morpho-physical and chemical traits resulted in a large overlapping in mean values of decomposition rates among groups. In contrast, plant groupings based on growth forms and those including all morpho-physical and chemical traits of green or senesced leaves yielded groups with differentiated rates of decomposition processes. The two latter groupings clustered species from more than one growth form indicating some overlapping in the rates of decomposition processes among species of different growth forms. Among traits, N concentration in senesced leaves and plant height explained the highest variation in decomposition rates being positively related to potential rates of dry mass loss and N release/immobilization. We concluded that plant groupings based on morpho-physical and chemical traits of either green or senesced leaves may be more powerful to differentiate functional species groups sharing decomposition patterns than the growth form grouping. Moreover, plant height and N concentration in senesced leaves may be considered relevant synthetic functional traits in relation to decomposition processes in narrow aridity gradients.

Key words: mass loss, morpho-physical and chemical plant traits, N release/immobilization rate, plant growth forms