Tree-grass interactions for N in Nothofagus antarctica silvopastoral systems: Evidence of facilitation from trees to underneath grasses.

GARGAGLIONE V; ; P L PERI, ; G RUBIO

AGROFORESTRY SYSTEMS

SPRINGER

Lugar: Berlin; Año: 2014 vol. 88 p. 779 - 790

0167-4366

Questions: Do trees compete for N with grasses in N. antarctica silvopastoral systems in South Patagonia? Or in contrast, do trees facilitate N absorption to underneath grasses? Which process predominates? Location: Patagonia, South Argentine. Method: An experiment with 15N labeled fertilizer was carried out to compare N absorption by grasses growing under trees (silvopastoral system) vs. an open site. 15NH4 15NO3 solution at 10 % atom excess was added in spring in both sites. 15N pathway was measured in herbage, soil and trees every 30 days during the growing season. Results: Soil was the component that accounted with higher N amounts and 15N recovery. Significant differences were found in N and 15N concentrations in aerial components of grasses, being higher at the silvopastoral system. Instead, grasses in open sites showed higher total N (kg N ha-1), associated to higher biomass accumulation. Grasses growing in the silvopastoral system absorbed almost double of the 15N than grasses in open site (32.4 kg 15N ha-1). Root were also an important fate for 15N absorbed, since around 50 and 63% of total 15N recovered was in grass roots of open site and silvopastoral, respectively. Trees absorbed 69% less 15N than grasses in silvopastoral system and it was derived mainly to small branches, sapwood and fine roots. Overall, 15N recovery was 65% higher in silvopastoral system (tree + grasses) than in open site (grasses). Conclusions: Silvopastoral system had a more efficient use of the 15N added. The results indicated that N. antarctica trees in this silvopastoral system did not strongly compete for N with grasses. Conversely, trees may ?facilitate? grasses N absorption by improving environmental conditions like lower water stress (by protection of strong winds) or by reducing competence for inorganic N between soil microorganisms and grasses.