sapwood and respiration

[ckoven]

The sapwood values we've been using are unrealistically small (default parameter values for fates_allom_latosa_int and fates_allom_latosa_slp). However, I've found that if I put in reasonable values, the respiratory costs become too high and the plants die off. I think this is because the plants are using fine root C:N for their sapwood respiration (under the assumption, like leaves and roots, that maintenance respiration scales with total N content). Code here: https://github.com/NGEET/fates/blob/master/biogeophys/FatesPlantRespPhotosynthMod.F90#L522

But the fine root C:N ratios are quite low (default value 42). There are published obs of this value that are much higher, e.g. here: https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/nph.12943 which report median sapwood C:N for tropical trees at 210 gC/gN. So I propose to add a new wood C:N ratio parameter and use this for the maintenance respiration rates for live stem and coarse roots.

[ckoven]

realizing this is partial overlap with #335

[rosiealice]

This totally sounds reasonable to me. 2018-06-01 12:00 GMT-06:00 Charlie Koven <[email protected]>:

…

realizing this is partial overlap with #335 <#335> — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#392 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AMWsQ-Um96I6-pJbmcJslGH5Z_zy1c-2ks5t4YFFgaJpZM4UXFD4> .

-- ----------------------------------------------------------------- Dr Rosie A. Fisher Staff Scientist Terrestrial Sciences Section Climate and Global Dynamics National Center for Atmospheric Research 1850 Table Mesa Drive Boulder, Colorado, 80305 USA. +1 303-497-1706 http://www.cgd.ucar.edu/staff/rfisher/

[ckoven]

ok, so I just did a first attempt at this, commit 4724747. I changed latosa to 0.5 and made woodcn 210. Interestingly, the trees still die, or at least the big ones do anyway. What appears to be going on is that, since sapwood cross-sectional area scales with LAI, it means that stem respiration per tree scales with LAI * height, whereas all other maintenance respiration scales with LAI. So the value of latosa and woodcn seem to define a maximum survivable height. which is kind of interesting if it is qualitatively correct behavior; but also suggests that maybe the hypothesis that wood N determines maintenance respiration isn't correct, if we are using realistic values of wood C:N and sapwood area parameters?

a possible solution is to further increase the value of wood C:N until we have reasonable stem respiration rates? we are going to need to sort this out for FATES-hydro if we are to have reasonable sapwood conductance...

[rosiealice]

Maybe it's to do with sapwood tapering? e.g. Fig 4 and 5 herein: Sapwood taper models and implied sapwood <https://www.researchgate.net/profile/Douglas_Maguire/publication/237866830_Sapwood_taper_models_and_implied_sapwood_volume_and_foliage_profiles_for_coastal_Douglas-fir/links/54ef4d030cf25f74d721e3ed/Sapwood-taper-models-and-implied-sapwood-volume-and-foliage-profiles-for-coastal-Douglas-fir.pdf> 2018-06-01 12:54 GMT-06:00 Charlie Koven <[email protected]>:

…

ok, so I just did a first attempt at this, commit 4724747 <4724747>. I changed latosa to 0.5 and made woodcn 210. Interestingly, the trees still die, or at least the big ones do anyway. What appears to be going on is that, since sapwood cross-sectional area scales with LAI, it means that stem respiration per tree scales with LAI * height, whereas all other maintenance respiration scales with LAI. So the value of latosa and woodcn seem to define a maximum survivable height. which is kind of interesting if it is qualitatively correct behavior; but also suggests that maybe the hypothesis that wood N determines maintenance respiration isn't correct, if we are using realistic values of wood C:N and sapwood area parameters? a possible solution is to further increase the value of wood C:N until we have reasonable stem respiration rates? we are going to need to sort this out for FATES-hydro if we are to have reasonable sapwood conductance... — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#392 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AMWsQzDd579YUVyJtf-xdqIJBfbDXLxoks5t4Y3XgaJpZM4UXFD4> .

-- ----------------------------------------------------------------- Dr Rosie A. Fisher Staff Scientist Terrestrial Sciences Section Climate and Global Dynamics National Center for Atmospheric Research 1850 Table Mesa Drive Boulder, Colorado, 80305 USA. +1 303-497-1706 http://www.cgd.ucar.edu/staff/rfisher/

[ckoven]

@rosiealice thanks for sending that. it does seem like we may need to include a sapwood taper term in order to have reasonable respiratory costs of sapwood. a couple questions we ought to discuss:

1. in the interest of minimizing new parameters, maybe we should go for a linear taper model (i.e. effectively just multiplying the volume by 0.5) rather than the more complex ones in that paper?
2. do you/anyone know of observations of sapwood area taper in tropical forest trees?
3. if we do this, should we include the sapwood area taper in the hydro code too (or is it already?) my reading of that code (here: https://github.com/NGEET/fates/blob/master/biogeophys/FatesPlantHydraulicsMod.F90#L379 ) says that it is assuming a cylindrical rather than a tapered sapwood model.

cc @bchristo @xuchongang

[rgknox]

One thing to note @ckoven , is that sapwood in our model extends below ground, so it it scaled not just by height, but by height/agb_frac.

Perhaps the we should scale the volume by 0.5 for just the above ground portion? I guess we have not had too many conversation on how how below-ground, non-fine, live-tissues really function (in terms of resource demands).

[bchristo]

The hydro code does not assume any sapwood taper, so yes, for consistency we should include whatever taper parameter there as well as here

I am not aware of any sapwood volume and/or taper studies, but htat doesn't mean there aren't some out there -- the main ones I'm familiar with are Calvo-Alvarado et al. 2003 and Ryan et al. 1994 Oecologia (respiration and sapwood volume, which was derived rather simply from sapwood depth).

[bchristo]

Just an observation regarding @ckoven 's observation that in the model sapwood scales with LAI*H

Of the five species in Calvo-Alvarado et al. 2008, four of them had increasing leaf area:sapwood area ratios with height. Depending on the value of that slope, it may partially cancel the effect of multiplying by height again to get the sapwood volume...