Text by Lauri Laanisto
I felt like I was totally alone in an airport. Literally alone. It was half past one in the night. Tartu airport has just one arrival per day. Slightly after midnight from Helsinki. It had arrived, all the passengers came through the gate and left. Seemed like all the workers as well. Most lights had been shut off. Could not hear a single sound. And I was still waiting for Giacomo (I had to pick him up, because I had his keys – because of an ongoing urban ecology experiment). He was suppose to return from Bill Shipley´s trait course in Canada. His phone was off, I had been trying several times. If I hadn´t had a manuscript with me (which is still submitted to somewhere), that I could edit, I probably would have had already left, when finally some door in the darkness opened, and Giacomo came out. His luggage was lost, and he had been filling out the paperwork. And forgot to switch on the phone.
He started already in the airport. Triangle, he insisted, it´s always shaped like a triangle. I tried everything, he claimed, and it´s still triangular. My brain was already mostly asleep, it was way past my usual bedtime. And he had not been sleeping in the connecting flights. So it all felt a bit distant at that time.
Giacomo meant the interrelationships of different abiotic stress tolerance factors. Specifically drought, shade, watelogging and cold tolerance. These are the most omnipresent. (And have enough comparable data available as well.) Traditionally (e.g. Smith and Huston 1989 Vegetatio) it has been proposed that universal physiochemical constraints shape the polytolerance – capability of tolerating multiple stress factors at the same time. Of course, species tolerate a bit of everything, but according to the earlier stress models, a species can be adapted to either tolerate shade or drought, but not both at the same time. When it comes to conditions outside the moderate (a week without a rain is not yet drough, etc…). Physics does not allow it. However, some studies (e.g. Sack 2004 Oikos; Markesteijn et al. 2011 NewPhyt) found that there is seemingly no trade-off between, for example shade and drought (which is the most-studied stress-contrast in plants). And some studies (Laanisto & Niinemets 2015 GEB) have indicated that the supposed trade-off between shade and drought might be mitigated by other stress factors (cold and waterlogging), climatic conditions (length of vegetation season) or even adaptations (dormancy).
Couple of days later we´ll meet at work. And Giacomo continues with the triangle. Persistently. I finally start seeing it. I suggest that let´s just publish that. The triangle. It seems that it´s kind of a big deal – a significantly different approach to understanding the interrelationships of different stress factors. Plus, Giacomo´s triangle claims, among other things, that woody species´ shade and drought tolerance is actually independent from each other. Whether different life forms are analyzed separately, or leaf types, or evolutionary origins. Or even when random 100, 200, 300 etc. species are analyzed. The stress tolerance space is always triangular – drought versus waterlogging+cold tolerance on one PC axis, and shade on the other, alone (like me in the airport…).
But then we start thinking further – what is the types of trade-off that forms this stress tolerance space? Giacomo points out the recent review by Grubb. We add the third trade-off type – polytolerance (basically no boundaries in tolerating different types of abiotic stress). Then we ask Mike to join. He is supersceptical when we first describe it to him. He says he is too old for another spin-off of Grime and his stress triangle. We finally convince him that this is completly different stress triangle. And he comes on board as a third author. After all – it´s a triangle we´re trying to write…
Writing of the manuscript goes so quickly and smoothly (another shoutout to senior colleagues) that a few months later I do not remeber anything from the writing (might be from my own encroaching seniority…). It´s also quickly accepted in the first journal where it´s peer-reviewed. Well, that´s it…
Citation: Puglielli, G., Hutchings, M. J., & Laanisto, L. (2020). The triangular space of abiotic stress tolerance in woody species: a unified trade-off model. New Phytologist; https://doi.org/10.1111/nph.16952
- Tolerance of abiotic stress in woody plants is known to be constrained by biological trade‐offs between different forms of stress, especially shade and drought. However, there is still considerable uncertainty on the relationship between tolerances and the limits on tolerance combinations.
- Using the most extensive database available on shade, drought, waterlogging and cold tolerance for 799 northern hemisphere woody species, we determined the number of dimensions needed to summarise their tolerance combinations, and the best trade‐off model among those currently available, for description of the interdependence between tolerances.
- Two principal component analysis (PCA) dimensions summarised stress tolerance combinations. They defined a triangular stress tolerance space (STS). The first STS dimension reflected segregation between drought‐tolerant and waterlogging‐tolerant species. The second reflected shade tolerance, which is independent of the other tolerances. Cold tolerance scaled weakly with both dimensions. Tolerance combinations across the species in the database were limited by boundary‐line trade‐offs.
- The STS reconciles all major theories about trade‐offs between abiotic stress tolerances, providing a unified trade‐off model and a set of coordinates that can be used to examine how other aspects of plant biology, such as plant functional traits, change within the limits of abiotic stress tolerance.