1. Reduced Growth and Biomass:
- Cd exposure, even at low concentrations, can inhibit plant growth and reduce biomass production.
- Low CO2 levels further exacerbate this effect, as CO2 is essential for photosynthesis and plant growth.
- The combined stress of Cd and low CO2 leads to reduced photosynthetic rates, impaired nutrient uptake, and overall stunted growth.
2. Alterations in Photosynthesis:
- Cd can disrupt the photosynthetic process by damaging chloroplasts, reducing chlorophyll content, and inhibiting the activity of key photosynthetic enzymes.
- Low CO2 levels limit the availability of the primary carbon source for photosynthesis.
- The combination of Cd and low CO2 severely impairs photosynthetic efficiency, leading to reduced carbon assimilation and energy production.
3. Oxidative Stress:
- Cd exposure generates reactive oxygen species (ROS) that can cause oxidative stress in plants.
- Low CO2 levels can also induce oxidative stress by disrupting redox balance and reducing antioxidant defenses.
- The combined effect of Cd and low CO2 intensifies oxidative stress, leading to lipid peroxidation, protein damage, and DNA damage, ultimately affecting plant health and survival.
4. Nutrient Imbalances:
- Cd interferes with nutrient uptake and translocation within plants, affecting the balance of essential elements.
- Low CO2 levels can alter nutrient availability in the water column, further exacerbating nutrient imbalances.
- The combined effects of Cd and low CO2 can lead to deficiencies or toxicities of specific nutrients, disrupting metabolic processes and plant growth.
5. Changes in Plant Morphology and Anatomy:
- Cd and low CO2 can induce morphological changes in aquatic plants, such as reduced root and shoot growth, leaf curling or wilting, and altered root architecture.
- Anatomical changes may include reduced xylem vessel size, altered chloroplast structure, and increased cell wall thickening, affecting water transport, photosynthesis, and overall plant function.
6. Impact on Aquatic Ecosystems:
- The decline in aquatic plant growth and productivity due to combined Cd and low CO2 stress can have cascading effects on the entire aquatic ecosystem.
- Reduced plant biomass affects the food chain, alters habitat structure, and disrupts nutrient cycling, impacting the survival and abundance of other organisms.
Understanding these responses is crucial for managing aquatic environments and mitigating the adverse effects of Cd and low CO2 on aquatic plant communities and ecosystem health.
