Plant functional biodiversity and carbon storage: an empirical test in seasonally dry forest ecosystems

GEORGINA CONTI; SANDRA DÍAZ; PEDRO JAUREGUIBERRY; LUCIANA MESTRE; VERÓNICA SCHINQUEL

Portland, Oregon

Congreso; Portland ESA 2012. 97th Annual Meeting. Life on earth: Preserving, utilizing and sustaining our ecosystem; 2012

Ecological Society of America

Carbon storage in vegetation and soil is the ecosystem process underpinning the vital ecosystem service of climate regulation through carbon sequestration. Two models have been proposed to link carbon storage and plant functional diversity. According to the mass-ratio model, carbon storage should be most closely associated with the locally most abundant values (weighted mean) of key stem and leaf functional traits. In contrast, the niche complementarity model predicts an increase in carbon storage with an increasing range of functional trait values. We tested these models empirically by comparing four different local ecosystems. These ecosystems, which differed in their plant functional trait composition, were derived by different historical and present land -use regimes from initially the same vegetation, under the same climate and substrate conditions. In each ecosystem we measured six key leaf and stem traits in all vascular dominants plants following standard protocols. We also carried out detailed measures of carbon content of several aboveground and soil compartments. We then related carbon storage to different components of functional diversity: community-weighted mean (CWM), traits value distribution and abundance of particular species. Each functional component was tested individually and in combination to find the best predictive model. The CWM of stem traits (height and wood density) were strongly and positively linked to carbon storage; wider ranges of values of these two stem traits, in contrast, were negatively associated with carbon storage. Among leaf traits associated to plant resource use, none of the CWM showed a relationship with carbon storage, while only the functional divergence of leaf toughness and leaf nitrogen content were positive and significantly associated with carbon storage. However, leaf toughness was only significantly related to the soil carbon stock, and leaf nitrogen content showed very low divergence level across sites. Final step-wise models included as best predictor variables the CWM of stem traits, the range of stem traits and the presence of particular species. Only the divergence of leaf toughness was included as an important variable predicting soil organic carbon stock. Our findings give support to the mass-ratio model over the niche complementarity model: what matters the most to biological carbon storage in these semi-arid ecosystems is the abundance of plants with tall, dense stems, with a narrow range of variation around these values. However, consistent links with carbon storage were only found for stem traits, with no clear patterns for leaf traits normally associated with plant resource use strategy.