Balancing trade-offs: Enhanced carbon assimilation and productivity with reduced nutritional value in a well-watered C4 pasture under a warmer CO2-enriched atmosphere.

The concentration of atmospheric CO2 and temperature are pivotal components of ecosystem productivity, carbon balance, and food security. In this study, we investigated the impacts of a warmer climate (+2 °C above ambient temperature) and an atmosphere enriched with CO2 (600 ppm) on gas exchange, antioxidant enzymatic system, growth, nutritive value, and digestibility of a well-watered, managed pasture of Megathyrsus maximus, a tropical C4 forage grass, under field conditions. Elevated [CO2] (eC) improved photosynthesis and reduced stomatal conductance, resulting in increased water use efficiency and plant C content. Under eC, stem biomass production increased without a corresponding increase in leaf biomass, leading to a smaller leaf/stem ratio. Additionally, eC had negative impacts on forage nutritive value and digestibility. Elevated temperature (eT) increased photosynthetic gains, as well as stem and leaf biomass production. However, it reduced P and K concentration, forage nutritive value, and digestibility. Under the combined conditions of eC and eT (eCeT), eT completely offset the effects of eC on the leaf/stem ratio. However, eT intensified the effects of eC on photosynthesis, leaf C concentration, biomass accumulation, and nutritive value. This resulted in a forage with 12% more acid detergent fiber content and 28% more lignin. Additionally, there was a decrease of 19% in crude protein leading to a 15% decrease in forage digestibility. These changes could potentially affect animal feeding efficiency and feedback climate change, as ruminants may experience an amplification in methane emissions. Our results highlight the critical significance of conducting multifactorial field studies when evaluating plant responses to climate change variables.

Silicon via fertigation with and without potassium application, improve physiological aspects of common beans cultivated under three water regimes in field.

Frequent droughts have led to an expansion of irrigated common bean (Phaseolus vulgaris L.) cultivation areas. An effective strategy to enhance water use efficiency and optimize crop growth is the application of silicon (Si) and potassium (K). However, the interaction between Si dosage, water regimes, and plant potassium status, as well as the underlying physiological mechanisms, remains unknown. This study aimed to assess the effects of Si doses applied via fertigation under various water regimes, in the presence and absence of potassium fertilization, on gas exchange, water use efficiency, and growth of Common beans in field conditions. Two experiments were conducted, one with and one without K supply, considering that the potassium content in the soil was 6.4 mmolc dm-3 in both experiments and a replacement dose of 50 kg ha was applied in the with K treatment, with the same treatments evaluated in both potassium conditions. The treatments comprised a 3 × 4 factorial design, encompassing three water regimes: 80% (no deficit), 60% (moderate water deficit), and 40% (severe water deficit) of soil water retention capacity, and four doses of Si supplied via fertigation: 0, 4, 8, and 12 kg ha-1. Where it was evaluated, content of photosynthetic pigments, fluorescence of photosynthesis, relative water content, leaf water potential and electrolyte extravasation, dry mass of leaves, stems and total. The optimal doses of Si for fertigation application, leading to increased Si absorption in plants, varied with decreasing soil water content. The respective values were 6.6, 7.0, and 7.1 kg ha-1 for the water regimes without deficit, with moderate water deficit, and with severe water deficit. Fertigation application of Si improved plant performance, particularly under severe water deficit, regardless of potassium status. This improvement was evident in relative water content, leaf water potential, and membrane resistance, directly impacting pigment content and gas exchange rates. The physiological effects resulted in enhanced photosynthesis in water-deficient plants, mitigating dry mass production losses. This research demonstrates, for the first time in common bean, the potential of Si to enhance irrigation efficiency in areas limited by low precipitation and water scarcity.