Abstract
Understanding how tropical trees will respond to extreme temperatures and drought is essential to predict how future increases in the severity, frequency and duration of extreme climatic events will affect tropical systems. In this study, we investigated leaf thermotolerance by quantifying the temperatures that resulted in a 50 % decrease in photosystem II function (T50) in experimentally grown saplings of 12 tree species from a seasonally dry tropical forest. We examined the relationship of thermotolerance with leaf functional traits and photosynthetic rates. Additionally, we tested how water limitation altered thermotolerance within species, and examined the relationship between thermotolerance and drought tolerance among species. Thermotolerance ranged from 44.5 to 48.1 °C in the least and most thermotolerant species, respectively. The observed variation in thermotolerance indicates that the upper limits of leaf function are critically close to maximum temperatures in this region, and that these species will be vulnerable to, and differentially affected by, future warming. Drought increased temperature tolerance, and species that were more drought tolerant were also more thermotolerant. Importantly, thermotolerance was positively related to the key leaf functional trait-leaf mass per area (LMA), and congruent with this, negatively related to photosynthetic rates. These results indicate that more productive species with lower LMA and higher photosynthetic rates may be more vulnerable to heat and drought stress, and more likely to be negatively affected by future increases in extreme climatic events.
Highlights
Sastry et al – Thermotolerance, drought and leaf traits in dry tropical forest trees likely to be exacerbated by exposure to more severe and frequent drought (Allen et al 2017)
Our results show that more productive species with lower leaf mass per area (LMA) and higher photosynthesis are less thermotolerant, and likely to be more vulnerable to future global warming, and this may result in directional changes in future species composition favouring species with high LMA and lower photosynthesis
The upper limits of leaf thermotolerance in the saplings of the 12 study species were close to the maximum temperatures experienced in this region, and future increases in temperatures are likely to negatively impact most of these species
Summary
Plants will experience extreme temperatures more frequently (Meehl and Tebaldi 2004; Hansen et al 2012), and this will often be accompanied by reduced water availability and drought (Toomey et al 2011; Niu et al 2014; Allen et al 2015).Tropical species may be vulnerable to future warming as they are already living closer to their absolute thermal limits, have narrower thermal niche breadth and may be limited in their ability to acclimate to warmer temperatures (Deutsch et al 2008; Doughty and Goulden 2008; Cheesman and Winter 2013; O’Sullivan et al 2017). Sastry et al – Thermotolerance, drought and leaf traits in dry tropical forest trees likely to be exacerbated by exposure to more severe and frequent drought (Allen et al 2017) Such exposure to extreme climatic events will increase cellular stress and damage, which in turn will decrease photosynthesis and growth, and could result in mortality of individuals (Niu et al 2014; Teskey et al 2015). A recent study demonstrated that the upper thermal limits of leaf photosynthetic and respiratory function in over 200 tree species were inversely related to latitude (O’Sullivan et al 2017) This confirmed previous results that suggested higher thermotolerance in tropical plants compared to temperate and alpine plants (Lange and Lange 1959; Weng and Lai 2005; Cunningham and Read 2006). Variation in thermotolerance in coexisting species can range from 10 to 20 °C (Lösch 1980; Gauslaa 1984; Knight and Ackerly 2003; Weng and Lai 2005; Neuner and Buchner 2012)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
