Ecophysiology of root suckering of two temperate rainforest tree species with contrasting shade tolerance

Abstract

In this thesis, we addressed to determine the ecological role of root suckering through the ontogeny in tree species as a functional mechanism that shapes the regeneration light niche and allows them to share resources among ramets in a temperate rainforest understory. We evaluated changes and differences of the light regeneration niche, physiological responses to light, functional traits at leaf, stem and crown levels, and their relationships with individual performance of root suckers and saplings using two tree species of differing shade-tolerance that combines vegetative and sexual reproduction mechanisms (hereafter suckers and saplings, respectively): Embothrium coccineum (light-demanding) and Eucryphia cordifolia (shade-tolerant). Light availability above young recruit-types of each species and understorey were determined to evaluate niche selection and both interespecific and intraspecific (between recruit types) differentiation. Biomass allocation was used to calculate functional traits related to light capture and carbon balance (architectonic, leaf and whole plant traits) and water supply (i.e. stem trai) to infer performance of recruits. Both recruit-types of Eucryphia from similar light environment were digitized for crown carbon balance estimations. Recruit-types of both species were measured during one year period and harvested for allometric calculations and dual carbon-nitrogen content and isotopic composition analyses. Leaf carbon and nitrogen concentration and isotope composition were also analyzed along the light gradient. Pulse labeling with carbon (13CO2) was performed in the field to quantify resource transferring between young interconnected suckers of Embothrium. Our results were conclusive in that i) saplings showed functional traits that allow them to minimize water loss by maximizing carbon gains in shaded microsites, whereas opposite trends were displayed by suckers; ii) although suckers and saplings differed in the functional responses during the early stages of ontogeny for both species, root suckering extends the regeneration niche towards open and illuminated microenvironments regardless of their shade-tolerance; iii) root suckers of both species are water and nitrogen subsidized along the light gradient, but light-demanding ramets gain carbon for their own in the shaded-advanced forest succession when the parent tree is in senescent stage. Our results stress that suckers contribute to both the regeneration and persistence of the species in the evergreen temperate forest understorey, likely promoting the coexistence-by-persistence of early and later tree species. To what proportion suckers are subsidized with water, nitrogen and carbon along environmental gradients are still poorly clear, thereby more studies are needed to statement parental support.