Soon after the Heskel et al. PNAS article was published, there was a push to use these findings to examine different its effect on modeling at different scales. I'm please to say that this week one of those papers is now online early; Liang et al. in Global Change Biology and the other paper was just accepted in Nature Communications, and will be available online soon.
Liyin Liang, Vic Arcus, and Louis Schipper, all representing the University of Waikato in New Zealand, contacted myself and the senior authors of the PNAS paper to examine this comprehensive dataset and test the Macromolecular Rate Theory (MMRT) to see if an arguably more theory-based approach to temperature modeling would yield the same results: that the temperature response of leaf respiration is invariant across biomes and plant functional types. This study found that indeed the conclusions hold, and that MMRT can be applied effectively to this dataset, and the derived parameters from this approach can be used as 'thermal traits' to describe these species.
The second modeling paper approaches respiration modeling at a much greater scale. Using the 'b,c' ("global polynomial equation" from the Heskel et al. PNAS paper), data-based, field collected estimates of R (from Atkin et al. 2015, New Phytologist), and also applying an acclimation effect, Chris Huntingford (Exeter, CEH in the UK) and a team of authors examined the impact of 'real' respiration and how it impacts global models of GPP, NPP, and other terrestrial global carbon parameters. This 'scaling up' can often reveal the large gaps in knowledge that have consequences for all aspects of the terrestrial carbon cycle when examined individually.
Working with modelers - both larger and smaller scale - has been illuminating, and allows for totally different perspectives on the application of these temperature response functions of respiration.
SES is a semester long intensive program where undergraduates take courses, have weekly day-long labs, and process and analyze collected data and present it for 9 weeks. After those nine weeks, student lead an independent project on their topic of choice in environmental science. For the third year in a row, I led the canopy scaling field and data activities. This year, the weather could not be nicer, though we dealt with some herbivory and temperature issues for getting optimal photosynthesis values - such is the challenge when measuring in September on Cape Cod!
Last year, I integrated a fluorescence element to the lab, and we used a WALZ PAM Jr to take light response curves of sun-adapted leaves and observe the response of non-photochemical quenching and yield of photosystem II at different light intensities in sun and shade leaves.
Students excelled at these tasks, despite a wonky LiCor 6400 (one was perfect, one gave us trouble) and hot temperatures. The rest of the week we went over scaling equations and discussed the different aspects of photosynthesis and how fluorescence and CO2 concentrations can be measured by different pieces of equipment to inform our ideas!
In May, I was asked to contribute a chapter for a book on pedagogy in Environmental Science undergraduate courses and the integration of EcoJustice. This task made me think deeply about values and how they can be not only taught, but modeled and explicitly discussed and practiced in science classrooms.
What do scientists value? How can we demonstrate those values in undergraduate courses?
To answer these questions, my chapter focuses on five 'scientific values' I identified through my experiences and through a informal survey of scientists at Ecosystems Center at MBL:
If scientists (especially scientists who are also teachers of undergraduates) place value on these aspects of their practice, how can this be demonstrated and discussed in the classroom? In this chapter, I promote the idea that they be integrated into the course design: assessments, activities, discussions, rubrics, etc. EcoJustice - a theme of the book - stands for inclusion of diverse ideas, equity, and sustainability. It was a personal challenge to weave these themes together, but the more I worked on it, the clearer it became in my mind.
How do you promote equity and inclusion in an Environmental Science classroom when you are talking about biogeochemistry of forests? Practice these values through collaboration and communication: discussions in the classroom can be arranged to ensure all student voices are promoted and listened to, ideas are constructively critiqued with different perspectives and goals in mind. Do not allow lazy classrooms where only the presenter is made to have an opinion. Keep students highly involved in the direction of the class.
As a teacher, with each year I realize more and more that I am an informed guide to learning, not a dictator on content and its presentation. Student learning requires individual agency. Students learn so much more through making mistakes, traveling down their own rabbit holes of inquiry, and being driven by their own interests within the sphere of a topic, than they do being lectured to for 3 hours a week. So my goal as an educator is to think of new ways (with the students - nothing behind the scenes!) to guide their learning.
Writing about these topics was surprisingly fun, and really brought me back to teaching high school. It is heartening to read about how undergraduate biology programs are being restructured to be more student-driven and inclusive and creative. While that was not my undergraduate experience, I can only assume it will draw more students who may be timid about biology (and science in general) to take the plunge and learn about the natural world in college.
In the past 6 months, two papers have been published discussing nuances of the "Kok method", which uses measurements of high resolution low-light curves to detect the degree of inhibition of respiration by light. I have worked extensively with this method for my graduate research in the Arctic, and more recently in deciduous hardwood canopy species at Harvard Forest.
The first paper, by Farquhar and Busch approaches the method with concern that the acceleration of the quantum yield at very low lights is controlled by the change in chloroplastic CO2 concentration, and not a signal of a relaxation of inhibition at low light.
In response to these claims, a paper by Buckley, Vice, and Adams, applied the Kok method in young and old leaves under two measurement O2 concentrations, and used this data for evidence to oppose the claims made by Farquhar and Busch. Primarily, Buckley, Vice, and Adams show that the breakpoint and the acceleration of quantum yield at low light cannot be explained fully by just changes in chloroplastic CO2 concentrations, but rather is tied to respiration. However, the note the importance of accounting for cc when using this method, and voice concern about it's broad application.
These papers follow a vigorous discussion about respiration in the light that has resulted in two more recent publications led by Guillaume Tcherkez in New Phytologist: one describing the workshop last summer in Angers, France (that I am grateful to have attended), and another that reviews the state of respiration in the light using multiple approaches.
This active (and all polite and open-minded!) exchange of ideas in New Phytologist promotes the ongoing challenge of how to deal with respiration in the light in leaves, and also in whole canopies. The application of the inhibition in models can have large consequences for how we think about carbon exchange at different scales.
For the past 3 years or so, I have been an online scientist mentor for the Planting Science program. This is a great way to reach out to students at the middle and high school levels on a weekly (and more often usually) basis and discuss plant biology, experimental design, data analysis, and presenting ideas - especially when somewhat cloistered away from students at a non-teaching institute. The Planting Science program connects scientists with high school and middle school teachers and classrooms, and assigns scientists to groups of 2-4 students during a ~6 week module on a topic in plant biology. Students brainstorm and design experiments with feedback from the scientist mentor and their teacher, and we connect through email messaging and the occasional class skype session. For the past few years I've mentored 2 teams each semester, and had a blast guiding them through their experiment via open questions and answering their queries on "scientist life" as well as basic concepts.
I am proud to announce that I applied and was selected to be a "Digging Deeper" Fellow with PlantingScience. This fellowships includes traveling to a workshop to collaborate with high school and middle school teachers in Colorado Springs this summer, and work on improving a few of the modules for classrooms, and then being the lead scientist mentor for two classrooms in the fall. My experiences with Planting Science have been great so far, and I think it's an excellent way for teenagers to learn not only about plants, but also that scientists are real (mostly) normal people, and doing science is a job that is not as removed from their lives as they might think based on media depictions. Very excited to head to CO this summer and continue working with this great organization!
Much to report on my end in the last few months - it has been a productive (and reproductive) few weeks/months on my end. Foremost, Will and I welcomed our daughter into the world in mid-February! She is robust and healthy and wonderful - though quite a lot of work to keep her fed! I'm off on maternity leave for the next couple of months to enjoy, practice and learn to be a mother.
In other news, this has been a productive winter for publications. I have been part of many projects and writing teams - ranging from my old research stomping grounds in Arctic Alaska (Prager et al), to the excellent New Phytologist meeting on the Kok Effect that took place in Angers, France last July (Tcherkez et al.), to local phenology projects at Harvard Forest (Yang et al.), to stoichometry in a tropical forest (Mo et al.), to the application of revised acclimation and temperature response equations in global vegetation models (Huntingford et al). The wide range of these projects, and being a part of them in different capacities (data collection, writing, analysis, meeting participation, etc), really makes me happy to be where I am today - part of many diverse groups pushing for new approaches and understanding of how plants are impacted by the environment, and how to capture this variability quantitatively.
Okay - I hear someone is hungry... Full citations of accepted publications below. Others listed above are in revision - hopefully accepted soon!
Prager C, Naeem S, Boelman N, Eital J, Greaves H, Heskel MA, Magney T, Menge D, Vierling L, Griffin KL. (2017) A gradient of nutrient enrichment reveals non-linear impacts of fertilization on Arctic plant diversity and ecosystem function. Ecology & Evolution. Accepted.
Tcherkez G, Gauthier P, Buckley T, Busch F, Barbour MM, Bruhn D, Heskel MA, Gong XY, Crous
KY, Griffin KL, Way DA, Turnbull MH, Adams M, Atkin OK, Bender M, Farquhar GD, Cornic G.
(2017) Tracking the origins of the Kok effect, 70 years after its discovery. New Phytologist. Accepted.
Yang H, Yang X, Zhang Y, Heskel MA, Lu X, Munger W, Sun S, Tang J. Chlorophyll fluorescence
tracks seasonal variations of photosynthesis from leaf to canopy in a temperate forest. (2017) Global
Change Biology. Accepted. doi: 10.1111/gcb.13590
Temperature response of soil respiration largely unaltered by experimental warming - Carey et al. now out in PNAS
I'm proud to announce that Joanna Carey (my lab mate, house-mate in Woods Hole, good friend, and now co-author, had her massive meta-synthesis published in PNAS this week. This work is a large effort with over 20+ co-authors who all contributed either analytical and writing input and/or raw data from multiple field sites.
Collectively the data show that experimental warming experiments, regardless of the duration of the experiment or the type of experiment (infrared heating, passive warming, buried cables, etc), does not significantly alter the temperature response of soil respiration in many ecosystem types. This implies that under future, warmer climates, soil respiration will likely show a similar response to current ambient temperatures - neither acclimated or enhanced. While respiration still generally increases with temperature, the degree of increase is unchanged under experimental warming. This is a great contribution to the literature, and a huge team effort led by Joanna.
The paper can be found here:
After publishing on the new Global Polynomial Model of the short-term temperature response of respiration, based on 231 species' response curves measured at high resolution, we (the author team) received responses through email and more recently through a letter to PNAS on alternatives to our findings and conclusions. The response by Adams et al (http://www.pnas.org/content/early/2016/10/03/1608562113?trendmd-shared=0) used our open data on the model fit parameters and applied these to an alternative R-T response model based on an Arrhenius fit. The authors found similar convergence in the response across Biomes and PFTS - confirming our major finding that the response of respiration to temperature is conserved across diverse species and climates. The authors suggest an alternative, more 'mechanistic' approach to modeling this response in addition, or as an alternative to the model we presented.
We responded to this response (http://www.pnas.org/content/early/2016/10/03/1612904113?trendmd-shared=0) with an acknowledgement of their modeling approach, though a disagreement in what we view as mechanistic/process vs. phenomenological model. For instance, the use of a 'activation energy' does not necessarily make a model a process model (say, compared to the Farquhar equation), as there are so many overlapping processes involved in respiration, that this activation energy actually describes a suite of reactions. I was encouraged by the convergent finding, and the gracious and supportive discourse about models and how they are applied at different scales. This interaction was not competitive, ego-driven, or angry, as can be the case in science, but rather driven by ideas, competing hypotheses (not labs!) and used data to back up arguments. I appreciated the challenge, and the opportunity to reframe ideas to emphasize our main points in the first paper. Kudos to Adams et al for bringing alternatives to the party, and opening this discussion.
Joanna Carey, a fellow postdoc at Ecosystems Center at MBL and Woods Hole housemate, had her excellent manuscript on soil warming accepted by PNAS last Friday. This manuscript is novel in that it amassed a huge amount of real measurements of soil respiration taken in ambient and warmed experimental plots from sites around the world, and analyzed the fluxes and soil temperatures to determine that the temperature sensitivity of soil respiration was common in control and warmed plots. Thus, despite long term warming, the rate of response of soil R is conserved in control and warmed soils - simplifying modeling long-term warming effects.
This study was funded by a USGS Powell Center Working Group led by Jim Tang (MBL), Pam Templer (Boston University), and Kevin Kroeger (USGS). I participated in the first of the working group meetings, but had to miss the second due to field work schedules - it was a great experience, and I'm so pleased that this analysis is now accepted at PNAS. Congrats, Joanna!
Details on DOI, etc to come after it is formatted and published.