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Effects of elevated CO2 and extreme climatic events on forage quality and in vitro rumen fermentation in permanent grassland

Abstract. The aim of this study was to analyze changes in botanical and chemical
composition, as well as in vitro rumen fermentation characteristics of an upland
grassland exposed to climate changes in controlled CO2
concentration, air temperature and precipitation conditions. Grassland was
exposed to a future climate scenario coupled with CO2 treatments (390
and 520 ppm) from the beginning of spring. During summer, an extreme
climatic event (ECE; 2 weeks of a +6 ∘C increase in temperature,
together with severe drought) was applied and then followed by a recovery
period. Three cutting dates were considered, i.e. in April, June and
November. The results indicate that increases in greenness, nitrogen (N)
content and changes in water-soluble carbohydrate profile in association with
botanical composition changes for the November cut lead to higher in vitro
dry matter degradability (IVDMD) in the rumen. The neutral detergent
fiber : nitrogen (NDF:N) ratio appeared to be a key driver of forage
quality, which was affected in opposite ways by elevated CO2 and
ECE, with a strong impact on rumen fermentation. Atmospheric CO2
concentration in interaction with ECE tended to affect IVDMD, indicating that
the effects of elevated CO2 and ECE may partly offset each
other. Our findings indicate that the various factors of climate change need
to be considered together in order to properly characterize their effects on
forage quality and use by ruminants.
