Is there a trade‐off between the plant's growth response to elevated CO2 and subsequent litter decomposability?

Abstract

Under elevated levels of atmospheric CO2, leaf N concentration usually decreases due to dilution of N by excess carbon. Thus, the larger the growth response to elevated CO2, the larger the decrease in leaf N concentration should be. This should, in turn, lead to a proportional decline in litter N concentration and litter decomposition rate. Thus, we hypothesize a trade‐off between a plant's growth response to elevated CO2 and subsequent litter decomposability. We tested this hypothesis by measuring the growth response, green leaf and leaf litter chemistry and litter respiration of six plant species grown under ambient and elevated atmospheric CO2 concentrations in the greenhouse.Growth response increased in the order Calluna vulgaris<Sphagnum cf. recurvum<Carex rostrata<Calamagrostis epigejos<Molinia caerulea<Vicia lathyroides. We did not consistently find the hypothesized patterns (between growth response and green leaf N concentration, green leaf and litter N concentration and between litter N concentration and litter respiration) in our six‐species dataset. To be able to draw more robust conclusions, we supplemented our six‐species dataset with data from the literature. Regression analyses on this larger dataset did reveal the hypothesized positive correlations between green leaf and litter N concentration and between litter N concentration and litter decomposition response ratios. However, there was no significant negative correlation between growth response and green leaf N concentration response ratios. As a result, also in the large dataset there was no trade‐off between growth response to elevated CO2 and litter decomposability. This implies that the productivity response of plant species to elevated CO2 is, in general, uncoupled from the decomposition response.