Potential effects of a high CO2 future on leguminous species

Does the response of Rubisco and photosynthesis to elevated [CO2] change with unfavourable environmental conditions?

Climate change due to anthropogenic CO2 emissions affects plant performance globally. To improve crop resilience, we need to understand the effects of elevated CO2 concentration (e[CO2]) on CO2 assimilation and Rubisco biochemistry. However, the interactive effects of e[CO2] and abiotic stress are especially unclear. This study examined the CO2 effect on photosynthetic capacity under different water availability and temperature conditions in 42 different crop species, varying in functional group, photosynthetic pathway, and phenological stage. We analysed close to 3000 data points extracted from 120 published papers. For C3 species, e[CO2] increased net photosynthesis and intercellular [CO2], while reducing stomatal conductance and transpiration. Maximum carboxylation rate and Rubisco in vitro extractable maximal activity and content also decreased with e[CO2] in C3 species, while C4 crops are less responsive to e[CO2]. The interaction with drought and/or heat stress did not significantly alter these photosynthetic responses, indicating that the photosynthetic capacity of stressed plants responded to e[CO2]. Moreover, e[CO2] had a strong effect on the photosynthetic capacity of grasses mainly in the final stages of development. This study provides insight into the intricate interactions within the plant photosynthetic apparatus under the influence of climate change, enhancing the understanding of mechanisms governing plant responses to environmental parameters.

Photosynthetic Gains in Super-Nodulating Mutants of Medicago truncatula under Elevated Atmospheric CO2 Conditions

Legumes are generally considered to be more responsive to elevated CO2 (eCO2) conditions due to the benefits provided by symbiotic nitrogen fixation. In response to high carbohydrate demand from nodules, legumes display autoregulation of nodulation (AON) to restrict nodules to the minimum number necessary to sustain nitrogen supply under current photosynthetic levels. AON mutants super-nodulate and typically grow smaller than wild-type plants under ambient CO2. Here, we show that AON super-nodulating mutants have substantially higher biomass under eCO2 conditions, which is sustained through increased photosynthetic investment. We examined photosynthetic and physiological traits across super-nodulating rdn1-1 (Root Determined Nodulation) and sunn4 (Super Numeric Nodules) and non-nodulating nfp1 (Nod Factor Perception) Medicago truncatula mutants. Under eCO2 conditions, super-nodulating plants exhibited increased rates of carboxylation (Vcmax) and electron transport (J) relative to wild-type and non-nodulating counterparts. The substantially higher rate of CO2 assimilation in eCO2-grown sunn4 super-nodulating plants was sustained through increased production of key photosynthetic enzymes, including Rieske FeS. We hypothesize that AON mutants are carbon-limited and can perform better at eCO2 through improved photosynthesis. Nodulating legumes, especially those with higher nitrogen fixation capability, are likely to out-perform non-nodulating plants under future CO2 conditions and will be important tools for understanding carbon and nitrogen partitioning under eCO2 conditions and future crop improvements.

The Potential Impact of Climate Change on the Micronutrient-Rich Food Supply

Micronutrient deficiencies are a major cause of morbidity and mortality in low- and middle-income countries worldwide. Climate change, characterized by increasing global surface temperatures and alterations in rainfall, has the capacity to affect the quality and accessibility of micronutrient-rich foods. The goals of this review are to summarize the potential effects of climate change and its consequences on agricultural yield and micronutrient quality, primarily zinc, iron, and vitamin A, of plant foods and upon the availability of animal foods, to discuss the implications for micronutrient deficiencies in the future, and to present possible mitigation and adaptive strategies. In general, the combination of increasing atmospheric carbon dioxide and rising temperature is predicted to reduce the overall yield of major staple crops, fruits, vegetables, and nuts, more than altering their micronutrient content. Crop yield is also reduced by elevated ground-level ozone and increased extreme weather events. Pollinator loss is expected to reduce the yield of many pollinator-dependent crops such as fruits, vegetables, and nuts. Sea-level rise resulting from melting of ice sheets and glaciers is predicted to result in coastal inundation, salt intrusion, and loss of coral reefs and mangrove forests, with an adverse impact upon coastal rice production and coastal fisheries. Global ocean fisheries catch is predicted to decline because of ocean warming and declining oxygen. Freshwater warming is also expected to alter ecosystems and reduce inland fisheries catch. In addition to limiting greenhouse gas production, adaptive strategies include postharvest fortification of foods; micronutrient supplementation; biofortification of staple crops with zinc and iron; plant breeding or genetic approaches to increase zinc, iron, and provitamin A carotenoid content of plant foods; and developing staple crops that are tolerant of abiotic stressors such as elevated carbon dioxide, elevated temperature, and increased soil salinity.