Effects of pine afforestation on biodiversity and functioning of semiarid mountain grassland streams in Córdoba, Argentina: which is the role of biofilm?

CIBILS MARTINA, LUCIANA; PRINCIPE, ROMINA; GARI, NOEMÍ; MÁRQUEZ, JAVIER; ALBARIÑO, RICARDO

Girona

Workshop; 4th Biofilm Workshop: Basis and application of biofilms to assess the effects of environmental change in aquatic ecosystems; 2016

Instituto de Ecología acuática, Universitat de Girona; ICRA

The use of exotic species in plantations has spread over extensive areas of the Southern Hemisphere,with little knowledge on the pros and cons on biodiversity and provision of resources. In Córdoba,Argentina, more than 36000 ha of grasslands have been replaced by pine plantations, producing 50%reduction in annual water yield of headwater streams. As a general hypothesis we proposed thatafforestation modifies the energy input to fluvial systems, given that implanted trees reduce lightincidence and contribute with great amounts of coarse particulate organic matter. Our aim was toevaluate the effect of pine afforestation on the structure and functioning of grassland streams in theupper basin of the Ctalamochita river (Córdoba, Argentina). We conducted benthic invertebrate andperiphyton field samplings and in situ experiments in order to compare taxonomical and functionalstructure of communities and to compare leaf litter breakdown, primary production and herbivorybetween grassland and afforested streams. Afforestation changed composition, structure, andfunctional diversity of algae and invertebrates. Grazing reduced algal density and richness ingrassland streams, but had little importance in afforested streams, suggesting light limitation on algalgrowth. Pine leaf litter decay was similar between grassland and afforested streams, except when theeffect of temperature was removed, by measured decay rate in degree days. The lower temperature inafforested streams and the low decomposition rate of needles may reduce microbial activity and themineralization of organic matter. In further studies, we plan to evaluate the effect of pineafforestation on biofilms and to elucidate its role on carbon processing. In afforested streams weexpect a more heterotrophic biofilm, with lower structural complexity, that favor a detritus-basedfood web, where protozoa and meiofauna become important in the transference of energy and matterto higher trophic levels. Furthermore, needle accumulation can lead to changes in the quantity andquality of DOM, being more recalcitrant, consequently affecting the heterotrophic community andstream metabolism. Thus, due to changes in biofilm composition and structure, C processing will bedifferent between grassland and afforested streams.