Photosystem II Heat Tolerance in Tropical Trees Operates Independently of Leaf Phenology
A study of 27 co-occurring tree species in India's Western Ghats found that photosystem II heat tolerance increases seasonally in both evergreen and deciduous trees, with no meaningful difference between the two groups. The research measured three thermal damage thresholds across the wet and post-wet seasons in a seasonally dry tropical forest, a period preceding drought-induced leaf loss. The findings challenge the assumption that drought-avoidance leaf phenology predicts a tree's capacity to thermally acclimate its photosynthetic machinery.
Researchers tested whether seasonal changes in photosystem II (PSII) heat tolerance—the point at which a tree's photosynthetic apparatus begins to sustain heat damage—track with leaf phenology in tropical trees of the central Western Ghats, India. Across 27 co-occurring species, both the damage onset temperature (T5) and the damage midpoint temperature (T50) rose significantly from the wet to the post-wet season, by approximately 1.7°C and 0.9°C respectively, indicating broad seasonal acclimation. Contrary to predictions, this thermal plasticity was not structured by whether a species was evergreen or deciduous, nor by its successional status. Responses were instead species-specific, suggesting that species identity is the primary driver of PSII thermal plasticity rather than leaf habit. While thermal safety margins based on T50 appeared large for most species, the more sensitive T5 metric identified several late-successional evergreens—including Saraca asoca, Ficus spp., and Careya arborea—as potentially vulnerable. A trade-off between heat damage prevention and tolerance breadth was conserved across the community, though the two leaf-habit groups diverged in their positioning along this trade-off under post-wet conditions. The results indicate that PSII thermotolerance regulation is largely decoupled from drought-avoidance phenology in seasonally dry tropical forests.
What's missing
The study is a preprint posted to bioRxiv and has not yet undergone peer review, so findings should be treated as preliminary. The authors note that measurements were taken at a single site and during one seasonal transition, limiting generalizability across broader geographic or climatic gradients. It remains unclear whether the observed thermal acclimation translates to whole-plant fitness differences or altered carbon gain under field conditions. The study does not address how projected increases in ambient temperature under climate change scenarios might interact with the observed plasticity limits.
What different sources said
- bioRxivCenter
Decoupled phenology and PSII thermal plasticity in seasonally dry tropical forest trees
Related
Gut Bacteria Enzyme Found to Break Down Heat-Processed Food Compounds, Producing Novel Biogenic Amines
Researchers have discovered that an enzyme in common gut bacteria can degrade N-epsilon-carboxymethyllysine (CML), a compound formed during thermal food processing, producing previously unknown biogenic amines. The enzyme, ornithine decarboxylase SpeC from enterobacteria, acts on CML and related modified lysine derivatives through a low-level 'underground' catalytic activity. This finding suggests a previously unrecognized communication axis between thermally processed dietary compounds and gut microbial physiology, with potential implications for host health.
Full-Length Gene Sequencing Reveals Two Distinct Bacterial Communities in Black-Legged Ticks Expanding Into Canada
Researchers used Oxford Nanopore full-length 16S rRNA gene sequencing to characterize the microbiome of Ixodes scapularis black-legged ticks collected in Nova Scotia, Canada, distinguishing between tick-adapted bacteria and environmentally acquired bacteria. The study comes as I. scapularis — the primary vector of Lyme disease — is rapidly expanding northward into Canada due to climate change. The findings suggest that environmentally derived bacteria in tick microbiomes are not mere contamination, which has implications for how tick microbiome data is collected and interpreted across surveillance studies.
Study Identifies Metabolic Link Between Cell Envelope Stress and Biofilm Formation in Bacteria
Researchers have discovered that the metabolite acetyl-CoA directly inhibits enzymes that degrade the bacterial signaling molecule c-di-GMP, connecting cell envelope biosynthesis stress to biofilm formation in Pseudomonas aeruginosa. The study found that sub-inhibitory concentrations of antibiotics targeting early peptidoglycan biosynthesis — but not other antibiotic classes — elevate c-di-GMP levels by reducing phosphodiesterase activity, with acetyl-CoA competing for the enzyme active site. Because the relevant enzyme domain is broadly conserved across bacterial species, this checkpoint mechanism may be widespread and could have implications for understanding antibiotic-induced biofilm responses.