Does chronic nitrogen deposition have effects on grass physiology of natural habitats?

Abstract

Anthropogenic activities increase nitrogen deposition, which can have major consequences for biodiversity and ecosystem function. We experimentally investigated how a community of grass species would respond to three levels of nitrogen enrichment, considering their biomass and efficiency of photosynthesis. The experiments were conducted in an open savanna area with sparse trees (cerrado sensu stricto). Fifteen plots were divided considering high nitrogen supplementation, low nitrogen supplementation, and control (without nitrogen application) as treatments. The nitrogen dosages applied in each treatment were based on deposition estimates for 2050 in the Cerrado biome. Three native species had their photosynthetic metabolism evaluated 45 days after the last supplementation. Except for Echinolaena inflexa, all the 16 species found in the area expressed C4 metabolism. Echinolaena inflexa and Loudetiopsis chrysothrix showed an increase in leaf nitrogen with supplementation, with differences in chloroplastidic pigment contents. Differently from L. chrysothrix which increased its chlorophyll content, E. inflexa showed a decrease in chlorophyll and carotenoid contents under N supplementation. E. inflexa is a small species and its leaf expansion under higher contents of nitrogen suggests that this species was affected by shading caused by other community species that increased their biomass. Supplemental nitrogen did not affect the efficiency of photosynthesis of these species or severely change the grass community biomass. However, we noted only a tendency for higher biomass and biomass per tiller for Urochloa decumbens, which suggests a concern about exotic species' performance under conditions of greater availability of nitrogen.