Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 4/23/1996
Publication Date: N/A
Interpretive Summary: The rise in atmospheric CO2, due mainly to fossil fuel combustion and land use change, is an undisputed fact. This ongoing CO2 increase has important implications for vegetation. Plant growth is typically enhanced by elevated CO2. Carbon dioxide is the substrate of photosynthesis and, when elevated, water use efficiency goes up. Stimulation of root system development associated with increased growth may lead to potential changes in microbiology of both rhizosphere and soil. Microbes mediate carbon and nutrient flows within the soil. More rooting also implies the possibility of more water and nutrient capture. Enhanced plant growth further suggests greater delivery of carbon to soil, and thus potentially greater soil carbon storage. Soil is a vital reservoir in the global carbon cycle. Sequestration of soil carbon is closely linked to nutrient cycling.
Technical Abstract: Plant tissue nutrient concentration is largely determined by plant roots, the primary means of extraction of nutrients from the soil profile. Therefore, effects of atmospheric CO2 on roots, and other belowground processes, will affect plant nutrition. Whole plant nutrient uptake is often increased under elevated CO2 but the concentration (nutrients per unit weight of tissue) is diminished. Elevated CO2 usually increases plant size, resulting in greater total amounts of nutrients, but these nutrients are distributed throughout larger plants and thus, concentration per unit weight is diluted. Nutrient utilization efficiency generally rises under elevated CO2, while nutrient uptake efficiency often declines. Plants under high CO2 produce more biomass with available nutrients; however, their large root systems appear unable to gather proportionally more nutrients. Results on nutrient uptake and concentration are variable due to differences in nutrient application during the experiment. For example, when plants are grown under nutrient levels considered adequate or poor for ambient conditions, high CO2 results in large plants with lower tissue nutrient concentrations. On the other hand, if plants growing under high CO2 are supplied with higher levels of nutrients, concentration of nutrients in tissues and nutrient uptake efficiency are generally not affected by CO2 level. Overall, nutrients supplies are critical to plant systems and attenuate the dynamic flows of essential materials (e.g., carbon and water) through them. The key role of nutrients in our changing global C cycle must be elucidated to predict how this change will impact ecosystem function.