A test of the relationships between climate, net primary productivity and biomass quality at the regional scale.

ENRICO, L.; DÍAZ, S. M.; PÉREZ-HARGUINDEGUY, N.

Tartu

Simposio; 56th Symposium of the International Association for Vegetation Science; 2013

International Association for Vegetation Science

Despite numerous studies, it is not clear that the amount and the quality of biomass production across regional environmental gradients are linked in a consistent way across regions and ecosystem types. Considering the effect of climatic variables structuring ANPP of ecosystems, and its influence as a filter for the establishment of plant species with certain leaf attributes, we analysed how ANPP and plant quality vary along a climatic (mostly precipitation) gradient of Central-western Argentina. We predicted an increase in ANPP as precipitation increases along the gradient, as well as a replacement from conservative (lower leaf quality) to acquisitive (higher quality) dominant plant species from ecosystem with lower ANPP to those with higher ANPP. We sampled 9 ecosystems, including arid shrublands, grasslands, dry forests and savannas. Within each ecosystem we established 20 plots, in which we selected the 10 most abundant plant species, estimated their relative cover, and measured 7 leaf traits on them, as indicators of biomass quality: content of carbon (C), nitrogen (N), and phosphorous (P), C:N and N:P ratios, leaf tensile strength (LTS) and specific leaf area (SLA) to calculate weighted means for each trait. We estimated ANPP based on MODIS satellite imagery. In agreement to our prediction, N (in woody ecosystems only), P and SLA increased from low to high ANPP ecosystems. Grasslands showed a significantly lower value of N than woody ecosystems. On the other hand, C:N ratio decreased with PPNA only for woody ecosystems. LTS showed no clear trend. The dominant plant growth forms (graminoids, forbs, shrubs and trees) strongly determined the prevalence of certain attributes at the different sites, as reflected in the comparison between grassland and woody ecosystems. The dominance of certain functional attributes, and therefore green biomass quality, was determined in a nested way by both precipitation and the associated ANPP, as well as by the dominant plant functional types.