Abstract
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.
Highlights
Global livestock production has increased rapidly and substantially in recent decades as a result of world population growth and a shift towards diets with a higher animal protein content in many countries (Tilman and Clark, 2014)
There was a significant effect of CO2–extreme climatic event (ECE) interaction during the period preceding the November cut (Table 1, p = 0.014), reflecting a higher soil water content (SWC) for the control at 520 ppm CO2 compared to the other treatments
This study shows that different drivers of climate change, i.e. elevated atmospheric CO2 concentration and ECEs, have contrastive impacts on forage quality through their effects on plant characteristics
Summary
Global livestock production has increased rapidly and substantially in recent decades as a result of world population growth and a shift towards diets with a higher animal protein content in many countries (Tilman and Clark, 2014). The livestock sector is singled out as a significant contributor to global human-induced greenhouse gas (GHG) emissions (Gerber et al, 2013), through energy and protein losses in the form of enteric methane (CH4) and ammonia (NH3), urea, and nitrous oxide (N2O) released during ruminant digestion. Using 100-year-timescale global warming potentials of 34 for CH4 and 298 for N2O (compared to CO2) (IPCC, 2013), the livestock supply chains emit an estimated total of 7.1 Gt CO2 eq yr−1, with ruminants by far the largest contributors (Gerber et al, 2013). Reducing GHG emissions is a crucial challenge for Earth system governance, and there is significant potential for mitigation in the ruminant sector (Herrero et al, 2016)
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