Comunidad ectomicorrícica en una cronosecuencia de Pinus radiata (Pinophyta: Pinaceae) de la zona de transición climática mediterráneo-templada de Chile central The ectomycorrhizal community in a chronosequence of Pinus radiata (Pinophyta: Pinaceae) of the transitional Mediterranean-temperate climatic zone of central Chile

En ecosistemas naturales y plantaciones, las coníferas establecen asociaciones mutualistas con una comunidad diversa de hongos micorrícicos. El estudio de este tema en Sudamérica es aún incipiente, y no existen antecedentes sobre la dinámica temporal de esta comunidad, y menos de sus potenciales causas, a pesar de su importancia para un país forestal como Chile. En el presente trabajo se evaluó la dinámica de la comunidad ectomicorrícica, identificando y cuantificando los hongos formadores de esta asociación en raíces finas de Pinus radiata en plantaciones de 3, 10 y 20 años. Los resultados confirman que la comunidad ectomicorrícica de P. radiata cambia con la edad de los árboles, la cual difiere más bien en el patrón de dominancia que en la riqueza de especies, separándose un primer grupo de árboles de 3 y 10 años de un segundo grupo de 20 años. Un total de once morfotipos de micorrizas fueron diferenciados. Cuatro de ellos, identificados como Hebeloma crustuliniforme, Inocybe sp., Russula sardonia y Pinirhiza spinulosa, fueron los más abundantes (77, 29, 78 y 8 % respectivamente), mientras las otras se encontraron colonizando menos de 100 puntas de raíz (In natural forest ecosystems and plantations, most trees live in mutualistic association with mycorrhizal fungi. Studies of this association in South America are still scarce, especially when referring to the causes of temporal dynamics of this symbiotic community, despite its importance in countries with a thriving forestry industry like Chile. This study evaluates the dynamics of the ectomycorrhizal community of Pinus radiata stands of 3, 10 and 20 years of age, identifying and quantifying the most common fungal colonizers of fine roots in each age class. The results confirm that the mycobiont community changes with host tree age but that age classes differ in dominance patterns rather than in species richness, with the three- and ten-year-old tree cohorts forming a group separate from the 20-year-old trees. A total of eleven ectomycorrhizal root morphotypes could be distinguished. Four of them which were identified as Hebeloma crustuliniforme, Inocybe sp., Russula sardonia and Pinirhiza spinulosa, were the most abundant (77, 29, 78 and 8 % respectively) and were found in more than one root sample whereas the remaining morphotypes accounted for less than 100 (< 7 %) root tips and showed a patchy distribution. Inocybe sp. was only found on root tips of three-year-old trees, characterizing as an early-stage mycobiont. H! crustuliniforme appeared as a multi-stage colonizer in all three age classes but was clearly dominant on roots of three- and ten-year-old trees, whereas R! sardonia was mainly found on roots of 20-year-old trees, classifying as a late-stage species together with the unidentified morphotype Pinirhiza spinulosa which is reported for the first time from Chile. Our results suggest that the observed changes in the ectomycorrhizal community are not induced by the site per se, but are rather an effect of the interaction between the trees and their environment

Cell size, photosynthesis and the package effect: an artificial selection approach

Cell size correlates with most traits among phytoplankton species. Theory predicts that larger cells should show poorer photosynthetic performance, perhaps due to reduced intracellular self‐shading (i.e. package effect). Yet current theory relies heavily on interspecific correlational approaches and causal relationships between size and photosynthetic machinery have remained untested. As a more direct test, we applied 250 generations of artificial selection (c. 20 months) to evolve the green microalga Dunaliella teriolecta (Chlorophyta) toward different mean cell sizes, while monitoring all major photosynthetic parameters. Evolving larger sizes (> 1500% difference in volume) resulted in reduced oxygen production per chlorophyll molecule – as predicted by the package effect. However, large‐evolved cells showed substantially higher rates of oxygen production – a finding unanticipated by current theory. In addition, volume‐specific photosynthetic pigments increased with size (Chla+b), while photo‐protectant pigments decreased (β‐carotene). Finally, larger cells displayed higher growth performances and Fv/Fm, steeper slopes of rapid light curves (α) and smaller light‐harvesting antennae (σPSII) with higher connectivity (ρ). Overall, evolving a common ancestor into different sizes showed that the photosynthetic characteristics of a species coevolves with cell volume. Moreover, our experiment revealed a trade‐off between chlorophyll‐specific (decreasing with size) and volume‐specific (increasing with size) oxygen production in a cell

Data, codes and microscopy photos for Malerba et al. 2018 New Phytologist

Data, codes and microscopy photos for the article Malerba et al. 2018 New Phytology. The data include physiological measurements of photosynthetic characteristics of cells of Dunaliella tertiolecta as we were evolving their cell volumes toward smaller or larger sizes, using artificial selection. Also in the data, scanning electron microscopy photos and optical microscopy photos of the size-evolved cells. Please refer to the "READ ME_Instructions" file for more information

Photosynthetic characterization of two Nannochloropsis species and its relevance to outdoor cultivation

Despite the increased interest in exploring the potential of algal biomass production for food stock and renewable energy, very little work has been done in developing reliable screening protocols to enable the identification of species that are best suited to mass cultivation outdoors. Nannochloropsis is an algal genus identified as a potential source of lipids due to its ability to accumulate large quantities of these compounds, especially under nutrient-limiting conditions. The objective of the current work was to use two species of this genus, Nannochloropsis oceanica and N. oculata, as model organisms to develop a protocol that will allow the evaluation of their capacity to yield high biomass productivity under outdoor conditions. Growing the alga under different light intensities and measuring growth rate as well as a range of photosynthetic parameters based on light response curves and variable fluorescence highlighted significant differences between the two species. Our data show that N. oceanica cells have a better capacity to respond to higher light intensities, as reflected by growth measurements, photosynthetic electron transport rates, and oxygen evolution as well as their response to the very high photon flux densities expected in outdoor culture. On the other hand, N. oculata showed a higher tolerance to oxidative stress as reflected in its resistance to the reactive oxygen species generating compounds Rose Bengal (RB) and methyl viologen (MV). Based on the above evidence, we suggest that N. oceanica may perform better than N. oculata when grown under high light conditions typically found outdoors in summer, while N. oculata may perform better than N. oceanica under oxidative stress conditions usually found in outdoor cultures exposed to a combination of high light and low temperature commonly occurring in winter time.European Commission/[727874]/EU/Unión EuropeaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y Limnología (CIMAR