Nitrogen uptake and biomass resprouting show contrasting relationships with resource acquisitive and conservative plant traits
© 2019 International Association for Vegetation Science Questions: Disturbances can cause fluctuations in resource availability that influence plant performance. In systems with such dynamics, inter-specific differences in resource capture may promote co-existence by partitioning competition between periods of high or low resource availability. Such differences in resource use strategy have been described with the Plant Economics Spectrum, which hypothesizes that functions related to resource use and processing should co-vary and can be predicted from plant traits. In pyrogenic systems, fires are associated with short-term increases in soil nitrogen availability (“pulses”), and thus contribute to a fluctuating resource supply. In this study, we sought to understand whether plants differed in their capacity to capture a nitrogen pulse, and to what extent that ability influenced biomass recovery. Methods: In two consecutive greenhouse experiments, we tested whether two functions — nitrogen assimilation (Experiment 1) and biomass regrowth after disturbance (Experiment 2) — co-varied, and how each function corresponded to leaf and root functional traits. Results: In Experiment 1, four co-occurring shrubs differed in their temporal patterns of nitrogen uptake, and nitrogen uptake was positively correlated with resource-acquisitive leaf traits (leaf percent nitrogen). In Experiment 2, the biomass regrowth of a resource acquisitive and a resource conservative species was the same regardless of competitive environment (i.e., when grown in pots of mixed-species or same-species pairs). Rather than being associated with the capture of new nitrogen, biomass resprouting of both species was associated with the size of below-ground resource stores and specific root length. Conclusions: Our work suggests that resource acquisition and processing may be decoupled from each other after disturbance, and also highlights the need for explicit tests of the relationships between root traits and above-ground plant function.
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