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.
Our new Global Change Biology paper is garnering media attention in Australia, where many of the species we measured for high temperature physiology occur. This study, led by Odhran O'Sullivan, covers the response of fluorescence and respiration at high temperatures in more than 200 plant species across a wide range of ecosystems and climates, and data for this study was collected at over a dozen field sites. Analysis revealed the plants existing in more temperate regions may be at an even greater risk than tropical systems based on physiological measurements and predicted future climate. Some of the articles are linked below:
Sydney Morning Herald:
Owen Atkin interviewed by the ABC:
http://www.abc.net.au/news/2016-09-14/study-warns-of-tipping-point-for-inland-plants/7843326This week, I've been guiding the canopy photosynthesis lab for the Semester of Environmental Science at The Ecosystems Center
This week also marked my second year of leading the photosynthesis lab for the Semester of Environmental Sciences at The Ecosystems Center at the Marine Biological Laboratory. For this week long lab, we went to the field on Monday and measured gas exchange using my old friends the 6400s and fluorescence using a brand new WALZ PAM Jr. The fluorescence aspect of the lab is brand new, and after some background in lecture from Zoe Cardon, I think the students were able to grasp the proportional variation of NPQ, ETR, and quantum yield by measuring a rapid light response curve. On Tuesday, Wednesday, and Thursday, the students will work up their data from the IRGA and PAM measurements, and develop a modeled canopy, where photosynthesis is driven by PAR through the day at two canopy heights. Many of the students are still beginners when organizing and applying data, so this lab helps build concepts of modeling, using error minimization to optimize your model, and applying data they collected to a idealized system. Next week, groups will present their findings. Always a good day when you get to teach about photosynthesis.
Good news from the weekend: a paper I am co-authoring with Odhran O'Sullivan, Owen Atkin, and others recently got accepted to Global Change Biology.
The paper covers a large dataset of high temperature thresholds of respiration and chlorophyll fluorescence in species measured in arctic to tropical ecosystems. More later when it is out in pre-print edition!
So much time has passed since I last posted - guilt (and procrastination) have finally kicked in to a motivating degree!
Also, so much has happened since late March...a brief bulleted recap list below. I will attempt to go into more detail about each item in the next month.
More detailed updates soon!
Chris Neill and Kelly Holzworth graciously put together a blog post for the study that is now posted on the Ecosystems Center homepage. The Arctic LTER site that is managed by scientists at Ecosystems Center was the only arctic tundra site used in the study, included ~20 species of C3 herbs, evergreen shrubs, and deciduous shrubs, which fleshed out many PFT categories for the study. The Arctic plants had the highest rates of respiration per area when measured at the same temperature, which is to be expected.
More here: http://www.mbl.edu/ecosystems/global-study-of-tundra-to-desert-plants-shows-leaves-respond-to-warming-in-remarkably-similar-ways/
Very excited to announce that my paper on the temperature response of respiration in leaves is now out in PNAS
In brief, high-resolution temperature response curves (over 750 total) were measured in 231 dominant and common plant species from around the globe. We assessed which competing temperature response model best represented how respiration fluxes respond to warming, and found a second order polynomial was the most representative across a wide temperature range. Following that, we grouped species by biome and plant functional type, and found across these groupings, which are often applied in terrestrial biosphere models to estimate carbon fluxes, there were no significant differences in the shape parameters of the curve. In short, all these plants respond to short-term warming in a similar way across biomes and PFTs. We then applied this new model, our "global polynomial model" to the JULES terrestrial biosphere model to assess how it impacted how plant R was modeled compared to the traditional Q10=2 framework. Our model showed decreased leaf R in cold sites and in temperate sites at cold times of year.
The paper is receiving attention from the press as well. Some clippings below:
Also got some unexpected reddit coverage!
The author team is comprised of 19 authors (10 different nationalities) representing 12 institutions located in 6 countries; fieldwork occurred in 18 sites in Australia, Peru, Sweden, US, French Guiana, and Costa Rica, and was funded by US, Australian, UK govts. Proud to be part of this diverse team, work with excellent, supportive scientists, and analyze and present data that can hopefully simplify/improve how carbon fluxes are modeled in different ecosystems around the world.
Over multiple growing seasons, the B4Warmed experiment in Minnesota has warmed seedlings of evergreen and deciduous plants representing the northern-edge of southern-ranged species and the southern-edge of northern-ranged species. I was fortunate to work with the B4Warmed team for two summers in 2014 and 2013 taking measurements on the high-resolution short-term temperature response of dark respiration in leaves of these species (in ambient and warmed conditions). This week in Nature, Reich et al. describe their observations of acclimation in boreal and temperate forest species that are grown under this long-term elevated temperatures, and translate this acclimation impact into reduced carbon loss from respiration. They measured an incredible amount of R-T response curves, and found consistent patterns of acclimation - hopefully given much needed multi-species long-term support for including acclimation of R into larger-scale models.
I briefly discussed this paper and it's impact with a journalist, and the article was published in Science News: http://www.sciencemag.org/news/2016/03/some-trees-could-help-fight-climate-change
I was very nervous to talk to the press, since each experiment has it's own objective, and scaling beyond those objectives and context can be difficult. For instance, I am unfamiliar with how many DGVM models are run - the specific equations can vary and have their own set of parameters, to which acclimation may or may not be a large factor in how carbon is accounted. Recent articles by Slot et al. and Vanderwel et al. show consistent acclimation across a broad range of plant functional types and groups, using a range of datasets. Identifying these trends of acclimation within `10 species, very definitively as in Reich et al. or across many studies and published values (as in the Slot and Vanderwel papers) - are both highly useful, but these studies do not directly address the impact of acclimation on future land surface temperatures via model tests. Lombardozzi et al. recently aimed to incorporate acclimation into such models, and based on these new papers, and others, hopefully we can hone in on how to best quantitatively capture this response. And in the meantime, I'll still be nervous speaking to press about 'conclusions' since, in science, everything is a work in progress by definition.
After a year of submissions, revisions, rejections, additional very-cool modeling, resubmissions, and a lot of waiting anxiously, my manuscript on the global convergence of leaf respiration temperature response was finally accepted today at PNAS! I'm incredibly happy and relieved. Taking the night off :)