The thermal tolerance of photosynthetic tissues: a global systematic review and agenda for future research

Abstract

Summary Understanding plant thermal tolerance is fundamental to predicting impacts of extreme temperature events that are increasing in frequency and intensity across the globe. Extremes, not averages, drive species evolution, determine survival and increase crop performance. To better prioritize agricultural and natural systems research, it is crucial to evaluate how researchers are assessing the capacity of plants to tolerate extreme events. We conducted a systematic review to determine how plant thermal tolerance research is distributed across wild and domesticated plants, growth forms and biomes, and to identify crucial knowledge gaps. Our review shows that most thermal tolerance research examines cold tolerance of cultivated species; c. 5% of articles consider both heat and cold tolerance. Plants of extreme environments are understudied, and techniques widely applied in cultivated systems are largely unused in natural systems. Lastly, we find that lack of standardized methods and metrics compromises the potential for mechanistic insight. Our review provides an entry point for those new to the methods used in plant thermal tolerance research and bridges often disparate ecological and agricultural perspectives for the more experienced. We present a considered agenda of thermal tolerance research priorities to stimulate efficient, reliable and repeatable research across the spectrum of plant thermal tolerance.

A high-throughput method for measuring critical thermal limits of leaves by chlorophyll imaging fluorescence

“…Many methods are used for measuring plant thermal tolerance limits, but such variation has potential consequences for generating reasonable interpretations and interspecific comparisons. Often, the rationale behind a published method is unclear and the impacts of small methodological differences are difficult to assess (Geange et al . 2021).…”

“…Then, one could investigate the correlation between CT and LT metrics and determine the extent and reversibility of damage. A more complete micro-scale understanding of thermal tolerance responses and species specificity would be enhanced by exploring tissue biochemistry, the regulation of heat shock proteins, and gene expression at thermal extremes (Geange et al . 2021).…”

“…Understanding both vulnerability and tolerance limits of plants to thermal extremes is a priority for plant biology research as the Earth’s climate continues to change, thereby exposing these sessile organisms to increased thermal stress (O’Sullivan et al . 2017; IPCC 2018; Geange et al . 2021).…”

“…Chlorophyll fluorimetry has become a widely used tool for assessing the thermal limits of photosynthesis for both cold and heat tolerance (Geange et al . 2021).…”

Leaf heat tolerance of 147 tropical forest species varies with elevation and leaf functional traits, but not with phylogeny

“…In 1935, Sapper (1935) wrote that since the pioneering work by Sachs (1864) various studies had been conducted to investigate plant heat tolerance, but that systematic comparisons are complicated by the alltoo-different methodologies used. This remains true 85 years later (Geange et al 2020). A recent study (Lancaster & Humpreys 2020) compiled heat tolerance data from across the plant kingdom, but combined metrics with fundamentally different meanings, such as T 50 of F v /F m as defined in the current study (using data from e.g., Slot et al .…”