thermal time constant

[teixeirak]

@NidhiVinod , we have a lot of notes on thermal time constant in the manuscript, but little content on how they relate to the vertical gradient, so at the moment, it contributes little. I'm moving content here, and if we can say something meaningful, we can re-instate to the manuscript:

Several of the morphological traits above influence a leaf's thermal time constant, defined as (quantifies heat flux in a leaf through incorporating heat stored versus heat exchanged with the environment, with relation to time) [@michaletzEnergeticCarbonEconomic2016]. It comprises of several underlying traits -- leaf area, LMA, leaf width, leaf dry matter content and stomatal conductance [@michaletzEnergeticCarbonEconomic2016]. Typically, at a steady state, larger leaves with greater leaf width experience longer leaf cooling time and thus increased thermal time constant compared to leaves with smaller leaf width. Dissections in leaves, such as lobes, decrease leaf width and thus thermal time constant [@leighInfluenceLeafSize2017]. Additionally, a leaf with a smaller time constant experiences variable leaf temperatures in relation to the environment and exhibits instantaneous carbon assimilation rate and stable photosynthesis enabled by greater LMA [@michaletzEnergeticCarbonEconomic2016] Guessing, sun exposed leaves have lower thermal time constant than shaded?

• Curtis et. al, 2018 – higher in more exposed leaves (heat up slower, cool slower)
• Michaeletz has used this in theoretical calculations (Michaeletz et al. 2016 and 2015?

Tserej & Feeley 2021 experimentally showed that the rate of leaf warming is negetively correlated with leaf water content per unit leaf area (Lawren mentioned in the meeting as well?)

[from @SlotMartijn : I have Michaletz's code to calculate the thermal time constant, so if there are data, or general tendencies for changes in leaf area, LMA, leaf width and leaf dry matter content we can determine how these trends would translate into changes in thermal time constant. In practice, an important driver seems to be leaf water content per unit area (I think Lawren might have mentioned this as well in our meeting), so if we can conclude that that is something that scales with the vertical gradient, then we can make an informed guess about how the thermal time constant will change]

[NidhiVinod]

@teixeirak, maybe the above content is a lot, but seems like thermal time constant is longer in the lower canopy and shaded tree (Fauset and Curtis)

[teixeirak]

Okay. Do you think it's mechanistically significant?

[NidhiVinod]

Okay. Do you think it's mechanistically significant?

It seems like thermal time constant is longer with greater leaf water content, which seems to be greater down the vertical gradient. So, it makes sense why thermal time constant would be longer, but I don't know of other studies that that have looked at thermal time constant at a vertical gradient

[teixeirak]

@NidhiVinod , I think we can close this.