Biology subjects

Dulamsuren, C.

Publications and source records attributed to Dulamsuren, C..

4 recordsLinked to original sources

bioRxiv2026

T50 as a proxy of PS II heat tolerance: time dependence, differences in calculation methods and implications for its suitability to assess the heat tolerance of tree species

O_LIThe heat tolerance of tree species has recently received increased attention, as it is critical for the response of forest ecosystems to climate change. Most studies rely on laboratory experiments with detached leaves, where the thermostability of photosystem II (PS II) is analyzed using chlorophyll fluorescence analysis. The temperature at which the maximum quantum yield (Fv/Fm) of PS II is reduced by 50% (T50) is often used as key measure of heat tolerance despite of weak mechanistic corroboration and inconsistent definitions. We propose a new metric consisting of a critical temperature (TIP) and a corresponding fluorescence value (FIP). C_LIO_LIWe analyzed the effect of incubation time and temperature on different versions of T50. C_LIO_LIT50 was strongly dependent on the duration of heat exposure, decreasing exponentially with incubation time. T50 and TIP values derived from short-term treatments of different incubation times <1 h are not comparable, but stabilize after longer intervals of heat exposure. C_LIO_LIT50 of Fv/Fm specified without considering incubation time is a meaningless metric. Specifications derived from short-term heat treatments should be avoided, because the result is highly influenced by the experimental setup. Different calculation methods for T50 influence the result and elucidate different aspects of the heat response. C_LI

ecology↗

bioRxiv2026

Heat tolerance and canopy temperatures of Larix sibirica under highly continental climate in Mongolia's boreal forest

Compared to drought stress, direct heat damage has been considered secondary as a cause of climate change-induced tree mortality and productivity declines in forests. However, evidence from temperate, subtropical and tropical forests is accumulating that direct heat damage in photosystem II (PS II) is also a realistic scenario under climate change. We analyzed PS II heat tolerance in Larix sibirica, which represents a dominant boreal tree species in Siberia and northern Central Asia in cold environments with subzero or near-zero mean annual temperatures, but nevertheless warm summers. Thermal imaging was applied to relate heat thresholds found in the laboratory to canopy temperatures. Measurements were repeated in three months during the short growing season to test for the occurrence of heat acclimation. After 4 h of heat exposure, the temperature of the most rapid decline of the maximum fluorescence yield (Fv/Fm) due to heat (TIP), which is thought to indicate irreversible damage, was 41.2{+/-}0.0{degrees}C. The critical temperature (Tcrit) indicating initial reversible heat stress in PS II was 39.8{+/-}0.1{degrees}C. L. sibirica had large thermal safety margins, when TIP and Tcrit were compared to the canopy temperatures measured during the study period, but not compared to record heat maxima since 2000. The trees acclimated to heat over summer by increasing TIP and thus increasing the tolerance to severe heat stress. However, tolerance to moderate heat (indicated by Tcrit) was simultaneously weakened, suggesting the reallocation of resources during acclimation. In most summers, L. sibirica forests are not threatened by direct heat damage, but heat extremes as previously recorded from our study region in Mongolias boreal forest could increase mortality due to PS II damage. Heat can thus be seen as one out of several stressors that reduces the vitality and growth of southern boreal forests with L. sibirica under climate change.

ecology↗

bioRxiv2026

Low impact of internal stem decay on forest carbon stocks in fire-prone Pinus ponderosa forests

Large old trees are of eminent importance for organic carbon storage in forest ecosystems and thus play a role in mitigating climate change. Such trees also have an increased risk of internal stem decay and tree cavity formation, which promotes biodiversity, but complicates the prediction of their biomass and carbon stocks, which is usually done from stem diameter and tree height data applying allometric biomass functions. Since the extent of internal stem decay is known to vary widely between different forest ecosystems and data from moist temperate forests exhibited low significance of internal stem decay, we studied dry, frequently fire-exposed Pinus ponderosa forests in central Oregon to capture the other climatic extreme of temperate forests. We hypothesized high significance of internal stem decay for stand aboveground tree biomass, as we assumed widespread stem injury from fire. In addition, we tested the hypothesis that far more than the largest 1% of trees are necessary for 50% stand biomass, as this hypothesis is found in the literature, but has been challenged in other studies. We found low biomass loss due to internal stem decay by only ca. 1% suggesting that also for fire-prone temperate forests of western North America, biomass estimates based on allometric regression are reliable. The 1% largest trees-50% stand aboveground biomass hypothesis has to be rejection for our forests as long as only trees of a size are included that noteworthily contribute to stand biomass. This metrics strongly depends on regeneration density, which is not relevant for stand biomass.

ecology↗

bioRxiv2026

Heat tolerance and its seasonal acclimation in Fagus sylvatica compared to Fagus orientalis and Pseudotsuga menziesii

Heat tolerance determines the vitality of tree species under climate change independently of drought tolerance, but has been much less studied than tree water relations. We studied species-specific differences and the capacity for seasonal heat acclimation in Central Europes naturally most important tree species, Fagus sylvatica, in comparison with two exotic tree species (Fagus orientalis, Pseudotsuga menziesii) that are considered for silvicultural climate change adaptation in managed forests. Foliage of mature trees was incubated at temperatures from 35-50 {degrees}C for up to 4 h to simulate daily heat maxima during heat waves. The maximum quantum yield (Fv/Fm) of photosystem II (PS II) of dark-adapted leaves was measured, because the PS II is particularly sensitive to heat and its functionality can decide on plant survival under heat. Fagus sylvatica was much more tolerant to heat than Pseudotsuga menziesii, but weakly (albeit significantly) less tolerant than Fagus orientalis. Within its limits, Pseudotsuga menziesii showed high seasonal heat acclimation with constantly increasing tolerance during the growing season. Fagus orientalis, but practically not Fagus sylvatica, also acclimated to heat. This makes Fagus orientalis slightly superior over Fagus sylvatica in terms of heat tolerance, whereas the suitability of Pseudotsuga menziesii for silvicultural climate change adaptation is questionable. Strong heat acclimation, but also overall low heat tolerance, in Pseudotsuga menziesii might be the result of evergreenness, which requires the generation of both cold and heat tolerance during the year.

ecology↗