Potential effects of a high CO₂ future on leguminous species

Abstract

The Leguminosae family comprises approximately 800 genera and 20,000 species, and constitutes the third largest family of flowering plants (Stagnari et al., 2017). In terms of agronomically important crops, grain legumes (pulses), soybean, and certain forage species (e.g., alfalfa [Medicago sativa]) provide value as both food and feed due to their high levels of protein and health-promoting properties (Darmadi-Blackberry et al., 2004; Graham & Vance, 2003; Singh et al., 2017). In addition, their capacity to fix nitrogen through their symbiotic relationship with rhizobia allows approximately 50-70 Mt of nitrogen to be fixed annually in agricultural systems (Herridge, Peoples, & Boddey, 2008). This reduces the need for synthetic nitrogen fertilizers, which currently support 30%-50% of non-leguminous crop yields (Erisman et al., 2008), with more than 50% of applied fertilizer typically lost from cereal crops as runoff or to the

A global meta-analysis of woody plant responses to elevated CO2: implications on biomass, growth, leaf N content, photosynthesis and water relations

“…Similar findings where a leguminous plant attained more biomass than nonleguminous plant grown at eCO 2 were reported by Lee et al (2003). Moreover, Singer et al (2020) reported that leguminous species have a close relationship with arbuscular mycorrhizal fungi which promotes efficient uptake of P, in turn increasing biomass of leguminous trees. In addition, increase in nodule mass in legumes which is non-existent in non-leguminous trees could have contributed to the total biomass production of legumes.…”

“…Indeed, many short-term studies have reported an increase in C assimilation and a subsequent increase in photosynthesis under saturating light and elevated CO 2 (eCO 2 ), more so for C 3 species relative to their C 4 counterparts (Zhang et al 2021;Raubenheimer and Ripley 2022). This is driven mainly by the fact that C 3 photosynthesis does not saturate at current levels of CO 2 (Singer et al 2020). High CO 2 uptake not only increases shoot growth and biomass, but also root depth and biomass, which further promotes soil nutrient and water uptake, indirectly enhancing photosynthesis (Thompson et al 2017).…”

“…This phenomenon is the depletion of leaf N content as a result of higher accumulation of non-structural carbohydrates (NSCs) and biomass (Li et al 2019). Because a considerable proportion of leaf N is derived from Rubisco, a reduction in Rubisco content at eCO 2 also reduces leaf N (Singer et al 2020;Kitao et al 2021;Wang and Wang 2021b). Dilution effect and reduced Rubisco content at eCO 2 reduce herbivore diet quality, as the decline in leaf N and increased C:N ratio reduce foliage digestibility (Du et al 2020).…”

“…Inter and intraspecific variation among woody plants is due to differences in phenology, leaf types, nitrogen fixation capacity and photosynthetic pathways (Mathias and Thomas 2021;Wang and Wang 2021a, b). For instance, leguminous plants are highly likely to respond more positive due to their relationship with rhizobia which facilitates nodulation in legumes, thereby increasing C sink (Singer et al 2020). Moreover, legumes tend to establish a symbiotic relationship with arbuscular mycorrhizal fungi which in turn increases nutrient uptake, e.g.…”

“…Increase in NSCs and reduction in leaf N, rate of photosynthetic Rubisco carboxylation (V cmax ) and photosynthetic electron transport rate (J max ) over time are implicated as the main drivers of photosynthetic downregulation (Wang and Wang 2021a). The high capacity for ribulose bisphosphate (RuBP) regeneration relative to Rubisco has been reported as a cause of reduction in photosynthetic capacity, leading to eventual downregulation (Bhargava and Mishra 2021;Singer et al 2020). Ascertaining plant responses to eCO 2 requires thorough assessment of physiological processes inherent in photosynthesis as well as mechanisms underlying these processes across a wide range of CO 2 concentrations and plant traits on long-term basis (Poorter et al 2021).…”