Yerba mate (Ilex paraguariensis) agroforestry systems: intraspecific differences in water relations and hydraulic architecture

Abstract

Intensive farming systems benefit from the additional ecosystem services provided by tree integration, which generate different growing conditions for the main crop. We studied yerba mate (Ilex paraguariensis) responses to growing conditions in monoculture (the conventional cropping system of yerba mate) and in three agroforestry systems: (1) yerba mate + Balfourodendron riedelianum; (2) yerba mate + Peltophorum dubium; and (3) yerba mate + Toona ciliata. Mainly, we focused on water relations and the hydraulic architecture of yerba mate. Agroforestry cropping systems provided a shade cover of around 34-45% and yielded as high as the conventional system. The shade cover influenced the allocation pattern to enhance leaf light capture, incrementing the leaf area to the sapwood area at the branch level. We also found a higher specific hydraulic conductivity in stems of yerba mate plants in consortium with T. ciliata than in the conventional cropping system, as well as higher resistance to water deficits due to lower vulnerability to embolism in the stems. During a severe drought, yerba mate plants had a similar stem and leaf water potential in both agricultural systems. Still, plants in monoculture had lower hydraulic safety margins and higher signs of leaf damage and mortality. This indicates that integrating trees into the yerba mate cultivation increases water stress resistance which would be beneficial to avoid restrictions on crop productivity under severe droughts induced by climate change.