15N uptake and distribution in grasses growing under Nothofagus antarctica vs. grasses in an open site.

GARGAGLIONE, VERONICA; BAHAMONDE, HECTOR; PERI, PABLO LUIS

Congreso; XVIII International Plant Nutrition Colloquium,; 2017

In Patagonia, Argentine, there is an extensive area from 36º 30´ to56º 00´SL where Nothofagus antarctica (ñire) native forest is distributed in a narrow strip being the main use assilvopastoral system. In these systems, understory vegetation (composed mainlyby grasses) is grazed mainly for cattle and sheep. Next to the N. antarctica forest, inthe ecotone zone, there are grasslands also used for extensive sheep or cattleproduction with many grass species in common with understory forest species. Likewise,as nitrogen is usually a limiting nutrient in most of the ecosystems, we aimedto know how grasses utilize and distribute the available N when they aregrowing in open areas or accompaniedd with trees. We hipotethized that in these austral ecosystems, when water may belimiting owing to strong winds in summer, grasses under trees could uptake anduse better the available N than grasses growing without trees. 15N atom excess was detectedin all components of grasses: leaves, tillers and roots, although the aerial components had the highest concentrations. In general, grasses growing under trees usually had double 15N atom excess in leaves and tillers compared with grasses growing in the open grassland. This would indicate that grasses growing under trees exploited better the fertilizer added than grasses in the open site. In these sites where water deficit iscommon owing to the low precipitations and the high wind speed, it is probably that grasses protected by trees took advantage and absorbed more thefertilizer applied. Roots also were a destinationfor the 15N added and this could be destinated to plant reserves.