Warming Reduces Net Carbon Gain and Productivity in Medicago sativa L. and Festuca arundinacea

Abstract

High temperature stress imposes constraints on the productivity of agricultural systems, such as pastures, and predicted increases in global temperatures are set to exacerbate these limitations. Here, we sought to understand the impact of warmer growth temperature on gas exchange and net primary productivity for two widely cultivated pasture species. We grew a C3 legume, Medicago sativa (lucerne), and a C3 grass, Festuca arundinacea Schreb (tall fescue), in a climate-controlled facility exposed to two temperature treatments (ambient: 26 °C, aT; elevated: 30 °C, eT). Soil water was maintained at non-limiting conditions in both temperature treatments to control for the confounding effects of warming on soil moisture. We found that warming reduced photosynthetic capacity and increased leaf dark respiration (Rdark) in lucerne, while tall fescue showed little physiological change at the leaf level, but increased ecosystem respiration (Reco). Growth temperature had no significant impact on the thermal optimum of photosynthesis (Topt) or water use efficiency in either species. Both species exhibited significant reductions in productivity with warming; lucerne had greater reductions in shoot biomass, while tall fescue had greater reductions in root biomass. Our results highlight the potential for significant declines in pasture productivity associated with even modest increases in average temperature and highlights the need for suitable management strategies and implementation of more heat-resistant cultivars. Improvements in photosynthetic performance for greater heat tolerance in lucerne, and traits associated with biomass allocation and root performance at higher temperatures in tall fescue, should be the focus for improving high temperature resistance in these plant species.

Drought and warming alter gross primary production allocation and reduce productivity in a widespread pasture grass

“…At the leaf-level, we found no significant change in A leaf in plants grown at elevated relative to ambient, temperature, suggesting that temperatures in this study were at or near optimum. This is supported by a reported temperature optimum of 28-29°C for net leaf photosynthesis in F. arundiancea (Jacob et al, 2020). Furthermore, increased plant respiration in a warmer climate is predicted to drive many ecosystems from being C sinks to sources (Feng et al, 2018;Luo, 2007), although this response was not observed for dark R leaf in our study.…”

“…The leaf physiological responses to the combined drought and warming treatment, such as an increase in the dark R leaf and reduction in Ψ MD and A leaf , were mainly driven by drought. Negative effects of temperature on leaf physiology were not apparent in our study, potentially because it was at or near the thermal optimum for growth and productivity (Hill et al, 1985; Jacob et al, 2020). Garcia‐Forner et al (2016) also found that the effect of combined drought and heat treatment on hydraulics and gas exchange in trees was not synergistic.…”

“…However, in our experiment, the moisture content in the combined treatment pots was higher than the drought only treatment, which effects of temperature on leaf physiology were not apparent in our study, potentially because it was at or near the thermal optimum for growth and productivity (Hill et al, 1985;Jacob et al, 2020). Garcia- 4.4 | Do drought and warming limit regrowth following harvest?…”

Pastures and Climate Extremes: Impacts of Cool Season Warming and Drought on the Productivity of Key Pasture Species in a Field Experiment

“…Festuca and Medicago are widely planted across Europe, North and South America, Australasia and Africa ( Gibson and Newman, 2001 ; Ghaleb et al, 2021 ), contributing to the pasture feed-base that underpins global livestock production. These temperate species have optimum temperatures for photosynthesis in the region of 20–29 o C ( Festuca; Sasaki et al, 2002 ; Sinclair et al, 2007 ; Jacob et al, 2020 and 15–30 o C ( Medicago; Al-hamdani and Todd, 1990 ; Jacob et al, 2020 ). Whilst winter warming is, therefore, likely to stimulate gross photosynthetic rates, spring temperatures were regularly above these thresholds, especially in the later part of the season where daily maxima of over 45 o C were recorded in warmed plots.…”

Pastures and Climate Extremes: Impacts of cool season warming and drought on the productivity of key pasture species in a field experiment

“…Festuca and Medicago are widely planted across Europe, North and South America, Australasia and Africa (Gibson and Newman, 2001;Ghaleb et al, 2021), contributing to the pasture feed-base that underpins global livestock production. These temperate species have optimum temperatures for photosynthesis in the region of 20-29 o C (Festuca; (Sasaki et al, 2002;Sinclair et al, 2007;Jacob et al, 2020) and 15-30 o C (Medicago;Al-hamdani and Todd, 1990;Jacob et al, 2020). Whilst winter warming is, therefore, likely to stimulate gross photosynthetic rates, spring temperatures were regularly above these thresholds, especially in the later part of the season where daily maxima of over 45 o C were recorded in warmed plots.…”