Plant Functional Types Differ in Their Long-term Nutrient Response to eCO2 in an Extensive Grassland

Increasing atmospheric CO2 enhances plant biomass production and may thereby change nutrient concentrations in plant tissues. The objective of this study was to identify the effect of elevated atmospheric CO2 concentrations on nutrient concentrations of grassland biomass that have been grown for 16 years (1998-2013). The grassland biomass grown at the extensively managed Giessen FACE experiment, fumigated with ambient and elevated CO2 (aCO(2); eCO(2); +20%) was harvested twice annually. Concentrations of C, N, P, K, Ca, Mg, Mn, Fe, Cu and Zn were determined separately for grasses, forbs and legumes. Under eCO(2), the concentration of N was reduced in grasses, Ca was reduced in grasses and forbs, P was reduced in grasses but increased in legumes, Mg concentration was reduced in grasses, forbs and legumes and K was reduced in grasses but increased in forbs. The nutrient yield (in g nutrient yield of an element per m(-2)) of most elements indicated negative yield responses at a zero biomass response to eCO(2) for grasses. K and Zn nutrient yields responded positively to eCO(2) in forbs and Mn and Fe responded positively in forbs and legumes. The results suggest that under eCO(2) the nutrient concentrations were not diluted by the CO2 fertilization effect. Rather, altered plant nutrient acquisitions via changed physiological mechanisms prevail for increased C assimilation under eCO(2). Furthermore, other factors such as water or nutrient availability affected plant nutrient concentrations under eCO(2).

Automated summary

The study found that increasing atmospheric CO2 concentrations have both positive and negative impacts on nutrient concentrations in grassland biomass. While some nutrients decreased under elevated CO2 levels, others showed an increase, indicating a complex response of plants to changing environmental conditions.