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Responses of stomatal features and photosynthesis to porewater N enrichment and elevated atmospheric CO2 in Phragmites australis, the common reed
Date: 2021-04-01
Creator: Julian R. Garrison, Joshua S. Caplan, Vladimir Douhovnikoff, Thomas J. Mozdzer, Barry A. Logan
Access: Open access
- PREMISE: Biological invasions increasingly threaten native biodiversity and ecosystem services. One notable example is the common reed, Phragmites australis, which aggressively invades North American salt marshes. Elevated atmospheric CO2 and nitrogen pollution enhance its growth and facilitate invasion because P. australis responds more strongly to these enrichments than do native species. We investigated how modifications to stomatal features contribute to strong photosynthetic responses to CO2 and nitrogen enrichment in P. australis by evaluating stomatal shifts under experimental conditions and relating them to maximal stomatal conductance (gwmax) and photosynthetic rates. METHODS: Plants were grown in situ in open-top chambers under ambient and elevated atmospheric CO2 (eCO2) and porewater nitrogen (Nenr) in a Chesapeake Bay tidal marsh. We measured light-saturated carbon assimilation rates (Asat) and stomatal characteristics, from which we calculated gwmax and determined whether CO2 and Nenr altered the relationship between gwmax and Asat. RESULTS: eCO2 and Nenr enhanced both gwmax and Asat, but to differing degrees; gwmax was more strongly influenced by Nenr through increases in stomatal density while Asat was more strongly stimulated by eCO2. There was a positive relationship between gwmax and Asat that was not modified by eCO2 or Nenr, individually or in combination. CONCLUSIONS: Changes in stomatal features co-occur with previously described responses of P. australis to eCO2 and Nenr. Complementary responses of stomatal length and density to these global change factors may facilitate greater stomatal conductance and carbon gain, contributing to the invasiveness of the introduced lineage.
Seasonal acclimatization of antioxidants and photosynthesis in Chondrus crispus and Mastocarpus stellatus, two co-occurring red algae with differing stress tolerances
Date: 2004-01-01
Creator: Nissa L. Lohrmann, Barry A. Logan, Amy S. Johnson
Access: Open access
- Mastocarpus stellatus and Chondrus crispus are red macroalgae that co-dominate the lower rocky intertidal zones of the northern Atlantic coast. M. stellatus is more tolerant than C. crispus of environmental stresses, particularly those experienced during winter. This difference in tolerance has been attributed, in part, to greater contents or activities of certain antioxidants in M. stellatus. We compared the photosynthetic capacities and activities of three antioxidant enzymes - superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR) - as well as the contents of ascorbate from fronds of M. stellatus and C. crispus collected over a year. Photosynthetic capacity increased in winter, but did not differ between species in any season. The activities of the three antioxidant enzymes and the contents of ascorbate were significantly greater in tissues collected during months with mean air and water temperatures below 7.5°C ("cold" months; December, February, March, April) than in months with mean air temperatures above 11°C ("warm" months; June, July, August, October). Overall, C. crispus had significantly greater SOD and APX activities, while M. stellatus had higher ascorbate contents. Species-specific differences in GR activity depended upon mean monthly temperatures at the time of tissue collection; C. crispus had higher activities during cold months, whereas M. stellatus had higher activities during warm months. Taken together, these data indicate that increased ROS scavenging capacity is a part of winter acclimatization; however, only trends in ascorbate content support the hypothesis that greater levels of antioxidants underlie the relatively greater winter tolerance of M. stellatus in comparison to C. crispus.