Physiological and Biochemical Responses of Mulberry (Morus alba L.) to Elevated CO₂ and Temperature and their Consequences on Silkworm (Bombyx mori L.) Performance

Abstract

Rising atmospheric carbon dioxide concentration and temperature are key components of ongoing climate change and are expected to exert significant influences on mulberry-based sericulture systems. Mulberry (Morus alba L.), a C₃ plant and the sole food source for the silkworm (Bombyx mori L.), responds strongly to elevated CO₂ through enhanced photosynthesis, increased leaf area development, and higher leaf biomass production. However, these quantitative gains are often accompanied by qualitative changes in leaf biochemistry, particularly under combined elevated CO₂ and temperature conditions. Open Top Chamber (OTC) studies conducted under tropical environments, including the Raichur experiment, demonstrate that elevated CO₂ and CO₂ + temperature treatments increase leaf sugars, total carbohydrates, phenols, and tannins, while reducing leaf nitrogen and protein content and increasing the C:N ratio. These biochemical shifts indicate a dilution of nutritional quality despite increased leaf yield. Such changes have important consequences for silkworm nutrition and physiology, as silk protein synthesis depends critically on dietary nitrogen and balanced amino acid supply. Reduced leaf protein and increased secondary metabolites are biologically expected to lower nutritional efficiency, constrain silk gland protein deposition, and induce digestive or oxidative stress, even when larval growth appears unaffected. Warming further intensifies these effects by imposing direct physiological stress on silkworms and indirectly degrading leaf functional quality. Overall, the combined effects of elevated CO₂ and temperature reveal a growing decoupling between mulberry leaf quantity and quality, highlighting the need for integrated evaluation of mulberry–silkworm interactions and adaptive management strategies to sustain sericulture productivity under future climate scenarios.