A meta‐analysis of climate change effects on forage quality in grasslands: specificities of mountain and Mediterranean areas

Abstract

Atmospheric carbon dioxide (CO2), global mean temperature and interannual variability in temperature and rainfall are expected to increase significantly by the end of the 21st century. To review the effects of these factors on forage quality, we carried out a meta‐analysis of climate manipulation experiments. The first notable result was a lack of effect of elevated CO2 on structural carbohydrates and digestibility. Elevated CO2 increased the total non‐structural carbohydrates of forage tissues by an average of 25% and decreased forage nitrogen (N) content by 8%. Increased legume abundance in multispecies swards can, however, maintain N concentration in the harvested biomass. There were no consistent effects of warming on contents of N, water‐soluble and structural carbohydrates, or on digestibility. We highlight the continuum in the effect of water availability, from drought to irrigation, with a curvilinear increase of forage N as water availability decreased. Digestibility increased, on average, by 7% with drought, but with strong experimental variations. The review places special emphasis on discussion of the specificities of mountain and Mediterranean grasslands, the former being limited by low temperature, the latter by drought and heat. Elevated CO2 decreased forage N content in mountain areas and in temperate plains alike. It increased N content by an average of 3% in Mediterranean areas; this could be due to shifts in vegetation communities under elevated CO2 or to a greater concentration of N in plant tissues under drought conditions. Further experiments are needed to investigate the effects of combined factors, including extreme climatic events.

Predicted Yield and Nutritive Value of an Alfalfa–Timothy Mixture under Climate Change and Elevated Atmospheric Carbon Dioxide

“…The well-documented decrease in grass protein concentration due to elevated atmospheric [CO 2 ] (Milchunas et al, 2005;Soussana and Lüscher 2007;Irigoyen et al, 2014;Dumont et al, 2015) and elevated temperature (Wan et al, 2005) was probably offset by the increased percentage of alfalfa in the mixture in the present study. The beneficial effect of high legume abundance in this context has been described in a literature review (Soussana and Lüscher, 2007) and a recent meta-analysis (Dumont et al, 2015). In QE, however, annual CP concentration increased slightly in future scenarios; the increase was greater with the adaptation strategy than without it (+15 vs. +8 g kg -1 DM), and the largest increase was found in scenario DF8.5 with adaptation (+20 g kg -1 DM compared to the reference period).…”

“…Increased temperature was shown to reduce forage or pasture nutritive value (Thorvaldsson, 1992;Wan et al, 2005;Thorvaldsson et al, 2007;Lee et al, 2013), and specifically to reduce the in vitro neutral detergent fiber (NDF) digestibility in timothy (Bertrand et al, 2008;Jing et al, 2013b) and in vitro dry matter digestibility in alfalfa (Sanz-Sáez et al, 2012). Elevated atmospheric [CO 2 ] has been found to decrease the crude protein (CP) concentration of several species (Milchunas et al, 2005;Soussana and Lüscher 2007;Sanz-Sáez et al, 2012;Baslam et al, 2014;Irigoyen et al, 2014;Dumont et al, 2015), including alfalfa (Bertrand et al, 2007b), and to reduce the digestibility of grasses (Morgan et al, 2004a) but not that of alfalfa (Irigoyen et al, 2014).…”

“…Nonetheless, this increase in NDF concentration was smaller than for simulations without adaptation. Recent results from a meta-analysis of the effects of climate change on the nutritive value of pure forage stands showed that elevated [CO 2 ] and temperature will not affect forage structural carbohydrate concentrations (NDF, acid detergent fiber, and acid detergent lignin) or DM digestibility, provided that farmers harvest their crops earlier under climate change (Dumont et al, 2015).…”

How can forage production in Nordic and Mediterranean Europe adapt to the challenges and opportunities arising from climate change?

“…Elevated CO 2 tends to increase the competitive ability of legumes in legume-grass mixtures, if the legumes are not limited by minerals such as phosphorous (reviewed by Lüscher et al, 2004;Soussana and Lüscher, 2007;Soussana et al, 2010). This may compensate for the slight decrease in protein content of grasses at elevated CO 2 (Soussana and Lüscher, 2007;Dumont et al, 2015). Dumont et al (2015), in their meta-study of climate change effects on forage quality, found that elevated CO 2 did not affect digestibility, but increased the total non-structural carbohydrate content by an average of 25% and decreased N content by 8%, reflecting the shift in the C:N-ratio of the environment.…”

“…This may compensate for the slight decrease in protein content of grasses at elevated CO 2 (Soussana and Lüscher, 2007;Dumont et al, 2015). Dumont et al (2015), in their meta-study of climate change effects on forage quality, found that elevated CO 2 did not affect digestibility, but increased the total non-structural carbohydrate content by an average of 25% and decreased N content by 8%, reflecting the shift in the C:N-ratio of the environment. N content increased with increasing drought level, and unlike other sites, a decrease in herbage N concentration in response to elevated CO 2 was not found at Mediterranean sites.…”