Complementary responses of morphology and physiology enhance the stand‐scale production of a model invasive species under elevated CO₂ and nitrogen

Abstract

Elevated atmospheric carbon dioxide (eCO2) concentrations and nitrogen (N) enrichment are known to enhance plant productivity and invasion. However, the implications of their interactive effects for plant productivity are not well understood, especially at the stand scale, presumably because morphological and physiological responses to these global change factors are rarely studied together in the field or assessed at the stand level. We first determined how leaf‐level morphological and physiological traits responded to factorial combinations of ambient and elevated CO2 and N. We collected trait data from the model invasive species Phragmites australis (common reed) that were measured over 3 years in a long‐term global change field experiment. We then combined the trait data and additional descriptions of P. australis canopies in a simulation model of carbon assimilation to determine how morphology and physiology contribute to P. australis’ stand‐scale productivity. At the leaf level, we found that light‐saturated rates of photosynthesis were strongly stimulated by eCO2 (37%) and that this effect was enhanced by increasing salinity. N had a smaller effect (17% stimulation) on physiological responses than eCO2, but leaf morphological traits responded primarily to N; plant height increased by 27% and leaf area increased by 47%. Stand‐scale simulations demonstrated that that morphological and physiological adjustments induced approximately additive responses when P. australis experienced both eCO2 and N enrichment. The simulations also indicated that morphological changes (which were primarily associated with canopy size) influenced stand‐scale carbon assimilation more than physiological changes. Moreover, 97% of the N response was due to changes in morphology, whereas 62% of the eCO2 response was caused by physiological shifts. Our analysis indicates that morphological and physiological trait responses to elevated CO2 and nitrogen are likely to enhance the productivity of P. australis in complementary ways, potentially accelerating its invasion in North America. Furthermore, our data suggest that changes in morphological traits may have a greater influence on carbon gain than leaf‐level physiology under near‐future environmental conditions. Our study also highlights the importance of accounting for both morphological and physiological responses when attempting to infer global change responses from leaf‐level data. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13106/suppinfo is available for this article.

Responses of stomatal features and photosynthesis to porewater N enrichment and elevated atmospheric CO2inPhragmites australis, the common reed

“…We did not expect eCO 2 to alter stomatal length, as this has not been observed in other studies (e.g., Haworth et al, 2013), except for those encompassing evolutionary to geologic timescales (Franks et al, 2009). We expected eCO 2 and N enr to have an additive effect on photosynthetic CO 2 assimilation, as previously demonstrated (e.g., Mozdzer and Caplan, 2018). Finally, under the assumption that changes to stomatal morphology underlie P. australis ’ growth responses to global change, we expected eCO 2 and N enr to have similarly additive effects on relationships between stomatal characteristics, maximal stomatal conductance, and photosynthesis.…”

“…Despite the key role of stomata in mediating gas exchange, prior studies have not connected stomatal morphology of P. australis directly to its strong physiological response to eCO 2 and N enr . For example, Mozdzer and Caplan (2018) reported eCO 2 and N enr effects on stomatal characteristics and rates of photosynthesis but did not examine the relationship between them.…”

Fine‐root traits are linked to species dynamics in a successional plant community

“…, van Kleunen et al. , Mozdzer and Caplan ), but the strong aboveground bias has meant that inferences do not necessarily encompass the full range of trait‐mediated dynamics. Investigations focusing on root traits explicitly could therefore yield additional insight into the means by which belowground foraging strategies influence species dynamics.…”

Toward “Rules” for Studying Biological Invasions

“…However, several or even most impacts are likely mediated through physiological mechanisms such as stress responses to perceived predation threats by invasive predators (Preisser and Bolnick ), reductions in food resources in the presence of invasive competitors (Lennox et al. ), and changes in energetic demands triggered by invasion‐mediated alterations of an organism's physical environment (increased shade, denser vegetation, increasing salinity; e.g., Funk , Mozdzer and Caplan ). These stress responses precede population declines in many instances, potentially providing a way to assess the impacts of invasive species mechanistically across multiple spatial and biological scales, and such responses may also provide an opportunity for managers to preemptively intervene and avoid negative impacts.…”