Cover stories: Volume 109 Issue 11

The cover image for our November issue features a fall sunset over a New England salt marsh dominated by Spartina alterniflora (smooth cordgrass). This image relates to the research article: Short- and long-term effects of nutrient enrichment on salt marsh plant production and microbial community structure, by Hanley, Bowen, Kearns and Hughes.

Here the author Torrance Hanley tells us the story behind the image.

A fall sunset over a New England salt marsh dominated by Spartina alterniflora (smooth cordgrass). Sweeney Creek in Rowley, Massachusetts, USA is located within the Plum Island Ecosystems LTER and an experimental site in the TIDE project – a long-term, wholeecosystem, nutrient-enrichment study examining the cumulative effects of moderate eutrophication on salt marsh ecosystems. Photograph by Randall Hughes. 

The first time I really experienced and appreciated a salt marsh was September 2013, when I made the jump from freshwater to saltwater and landed squarely up to my hip in marsh mud in Sweeney Creek, a beautiful site within the Plum Island Ecosystems LTER (PIE LTER) and part of the TIDE project – a long-term, whole-ecosystem, nutrient-enrichment study examining the effects of moderate eutrophication on salt marsh ecosystems. I was fairly mortified, as this was my first day in the field with my postdoctoral advisor, Dr. Randall Hughes, who had somehow navigated the creek crossing with grace and skill, while I had become decidedly stuck…

I not so gracefully extracted myself and went on to collect the plants that would ultimately be used for the study featured on the cover of the November 2021 issue of Journal of Ecology. We collected plugs of short-form Spartina alterniflora (smooth cordgrass) from the field and planted individual stems in the greenhouse at the Northeastern University Marine Science Center.

Spartina alterniflora growing in the greenhouse at the Northeastern University Marine Science Center in Nahant, MA. Photograph: Torrance Hanley

It’s common to see tall-form Spartina alterniflora growing along the creek bank in the low marsh because this area gets flooded almost daily with the high tides, but short-form Spartina dominates the high marsh, which only experiences inundation ~30% of the time, meaning there are fewer opportunities for nutrient delivery in the high marsh than in the low marsh.

West Creek in Rowley, MA – one of the unenriched reference sites in the TIDE project and the location of two of the four gardens in the reciprocal transplant experiment in this study. Photograph: Torrance Hanley

The TIDE project and the welcoming community of researchers at PIE LTER provided a unique opportunity to test the effects of long-term nutrient-enrichment on the performance of short-form Spartina and the structure of its associated microbial community. For this study, we combined a greenhouse common garden propagating Spartina genotypes from Sweeney Creek (an enriched creek that had received elevated nutrient inputs for 10 years; cover image) and West Creek (an unenriched reference creek) with a field reciprocal transplant to examine how a history of long-term enrichment may affect the capacity of this foundation species to respond to subsequent changes in nutrient availability, as well as microbial community structure and plant-microbe interactions.

Spartina alterniflora genotypes planted in bottomless pots lined with window screen were measured monthly during the growing season; plants in early spring (L) and late summer (R). Photograph: Torrance Hanley

In this study, we found strong effects of nutrient enrichment on both Spartina performance and microbial community structure in the short-term (i.e., the duration of the two-year reciprocal transplant experiment). Importantly, we also found strong effects of plant population history, with plants from the enriched site having decreased above- and below-ground production compared to plants from the unenriched site, most notably in unenriched gardens. Our results suggest that nutrient enrichment can have long-lasting effects on plant populations and associated microbial communities that potentially compromise their ability to respond to changing resource conditions in the future.

This project was a wonderful collaboration with Dr. Randall Hughes, Dr. Jennifer Bowen, and Dr. Patrick Kearns, made possible by Dr. Linda Deegan and the wonderful team of scientists in the TIDE project. I now look forward to every opportunity to get stuck in the mud and learn more about ecologically-important and economically-valuable salt marsh ecosystems!

Torrance Hanley, Marine Science Center, Northeastern University, USA.

You can read the full research article here: Short- and long-term effects of nutrient enrichment on salt marsh plant production and microbial community structure

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