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Rakesh Tiwari

@shimogarakesh.bsky.social

168 followers 441 following 10 posts

Postdoc at Uppsala University | studies heat sensitivity of photosynthesis

Posts Replies Media

Reposted by Rakesh Tiwari

bioRxiv Physiology @biorxiv-physio.bsky.social · 13/06/2026

Decoupled phenology and PSII thermal plasticity in seasonally dry tropical forest trees www.biorxiv.org/content/10.64898/20…

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Rakesh Tiwari @shimogarakesh.bsky.social · 21/05/2026

New #review: we look at how #photorespiration may act as a #heat “safety valve” in #trees, why this matters for #forest #carbon and #energy #fluxes, & which field measurements are needed to test it across biomes dx.doi.org/10.1002/gcb4... @bobmuscarella.bsky.social @svs-plant-geog.bsky.social

Conceptual framework linking leaf-level photorespiratory biochemistry to global-scale uncertainty in carbon cycle modelling. Rubisco acts as a temperature-sensitive biochemical switch: at optimal temperatures (~25°C) carboxylation dominates and drives biomass accumulation, whereas heat stress (>35°C) favours oxygenation and initiates photorespiration (Left). Under combined heat and high-light stress, photorespiration serves as a 'safety valve', dissipating excess ATP and NADPH, and protecting photosystem II, at the cost of 30-50% additional energy expenditure (Centre). A key knowledge gap remains at ecosystem scale: the stoichiometric constant λ = 0.5, which parameterises photorespiratory CO2 release in terrestrial biosphere models, is unvalidated for woody species (Right). Resolving this uncertainty will require multi-site measurements, tree isotope profiling, CO2 enrichment experiments, and in situ warming manipulations.

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Rakesh Tiwari @shimogarakesh.bsky.social · 30/03/2026

@bobmuscarella.bsky.social @svs-plant-geog.bsky.social @jxbotany.bsky.social

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Rakesh Tiwari @shimogarakesh.bsky.social · 30/03/2026

We took advantage of the microclimate gradient & measured photosynthetic temperature response & PSII thermal tolerance. We find a significant negative relationship. This could suggest a trade-off between investing resources to achieve higher Topt & maintaining PSII heat stability 3/3

Relationship between PSII chlorophyll fluorescence thermal thresholds (T5 ) against thermal optima of CO2 assimilation rate (Topt,anet) measured during the warm summer period on tree species in a central Western Ghats forest in India. Relationships show linear mixed-effects models with species as random effect, P-values are for the parameters fitted, and R2 are pseudo R2 for the fits. Dotted lines indicate 95% confidence intervals for the fit. Standard major axis regression R² = 0.16, P = 0.022.

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Rakesh Tiwari @shimogarakesh.bsky.social · 30/03/2026

We studied 11 trees spp. across hilltop–slope–valley #thermal gradients (summer peaks: 46.1°C, 40.1°C, 31.8°C) measuring photosynthetic temperature responses and #photosystemII (PSII) T5 (5% impairment) at peak summer. 2/3

Schematic depicting the distribution of the tree species studied in the Western Ghats, India. Rectangles on the left indicate the relative change in irradiance level, water availability, tree density, and soil depth from hilltops to valley areas. Codes for the species are as follows: Terminalia paniculata (TP), Terminalia chebula (TC), Careya arborea (CA), Psydrax dicoccos (PD), Tetrapilus dioicus (TD), Memecylon umbellatum (MU), Symplocos racemosa var. racemosa (SR), Hopea ponga var. ponga (HP), Knema attenuata (KA), Garcinia cambogioides var. cambogioides (GC), and Garcinia gummi-gutta (GG).

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Rakesh Tiwari @shimogarakesh.bsky.social · 30/03/2026

#Tropical #trees can't simultaneously raise photosynthetic heat optima AND PSII stability: resource trade-off! Inverse Topt, Anet-T5 link in #WesternGhats warns of #warming limits #PlantPhys #Climate #Photosynthesis #TropForRes doi.org/10.1093/jxb/... 1/3

Schematic illustrating contrasting resource allocation strategies between CO2 assimilation and PSII heat tolerance. (A) CO2 assimilation is prioritized over PSII heat stability and (B) PSII heat stability is prioritized over CO2 assimilation. (C) Temperature response curves for CO2 assimilation and PSII quantum yield for two species exhibiting contrasting responses, as presented in Fig. 4C. The schematic highlights shifts in ATP and NADPH investment between PSII maintenance and Rubisco activation energy. The large curved arrow indicates the direction of resource allocation involving ATP, NADPH, and the energetic costs of D1 and turnover of other proteins. Red colour represents higher temperatures, whereas blue indicates lower temperatures

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Reposted by Rakesh Tiwari

bioRxiv Plant Bio @biorxiv-plants.bsky.social · 26/11/2025

Large differences in photorespiration and its temperature response among temperate trees www.biorxiv.org/content/10.1101/202…

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Rakesh Tiwari @shimogarakesh.bsky.social · 19/08/2025

Thanks to @pplplantarum.bsky.social & @florianabusch.bsky.social, we have full length versions in #Kannada and #Sanskrit #language s See the supplementary section: doi.org/10.1111/ppl.... #sciencecommunication #India #WesternGhats #forest

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Rakesh Tiwari @shimogarakesh.bsky.social · 19/08/2025

Some trees thrive in heat. Our #WesternGhats #Tropical #forest #India study shows evergreen trees 🌳🌳 on hill slopes increase #photosynthesis in the dry, hot season, not the wet - indicating heat preference 🌡️🌡️ doi.org/10.1111/ppl.... @pplplantarum.bsky.social @bobmuscarella.bsky.social

Photosynthesis rate at thermal optima measured in situ during two time periods in a forest site in the Central Western Ghats region show distinct dry and wet period differences.

- Hilltop deciduous trees: Max out photosynthesis in the wet season, conserve water in dry spells—just as expected!

- Valley evergreens: Keep photosynthesis steady during wet and dry periods.

- evergreens on hill slopes: Surprisingly ramp up photosynthesis during the dry period - hinting at a taste for warmth!

Our findings show that coexisting tropical trees have different heat sensitivities.

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Rakesh Tiwari @shimogarakesh.bsky.social · 04/05/2025

Big thanks to SVS for support, and to SWIFT Balachandra Hegde & IDSG College for organizing. Excited that some students are now part of our photorespiration field campaign! 🌱🔬 @bobmuscarella.bsky.social

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Rakesh Tiwari @shimogarakesh.bsky.social · 04/05/2025

Had a fantastic four-day workshop with masters & doctoral students from across India! Trained them on photosynthesis basics, heat sensitivity, and hands-on leaf trait measurements as part of the @svs-plant-geog.bsky.social -funded field campaign #Photosynthesis #ScienceWorkshop #SVS #FieldCampaign

Balachandra Hegde providing the overview of the forest landscape at Sayimane

Rakesh Tiwari demonstrating field photosynthesis measurements

Discussion on interpreting photosynthesis response curves

Students taking fluorescence measurement

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Rakesh Tiwari @shimogarakesh.bsky.social · 25/03/2025

Very proud and my first post here!

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