Dynamics of non-structural carbohydrates in terrestrial plants: a global synthesis
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Jordi Martínez-Vilalta
, Anna Sala
, Dolores Asensio
, Lucía Galiano
, Günter Hoch
, Sara Palacio
, Frida I. Piper
and Francisco Lloret
Abstract
high NSC sign for oversupply or necessary for survivial or inaccessible?
NSC about 10% dry plant biomass, higesht in leaves, lowest in stem
strong depletion during growing season
high in conifers with relatively high seasonal minimum
starch as future reservoir, soluble sugars for immediate functions (osmoregulation)
Introduction
non-structural carbon compounds (NCC)
NSC: starch, soluble sugars, fructants (in some herbs)
neutral lipids (in some taxa)
role as storage: support night metabolism, support in stressful periods
starch might be depleted, soluble sugars need to be above a certain threshold for everyday functions like phloem transport, turgor stability, …
size of soluble sugars threshold unknown
NSC lower in stems because of more lignins and non-living tissue
Methods
Results
NSC(leaves) > NSC(belowground) > NSC(stem)
NSC varies with plant functional type
seasonal NSC oscillations
minimum NSC between 30% and 50% of seasonal maximum
Discussion
imbalance between photosynthesis and C demands not only reason for NSC seasonal patterns
soluble sugars seldom depleted suggesting that it serves important immediate physiological functions
neutral lipids (not measured) can comprise almost half of total NSC in some species
Conclusion
dual function of NSC as storage (starch) and performing immediate physiological functions (soluble sugars)
plants exhibit relatively high NSC thresholds, mortality should occur when NSC falls below these thresholds, even in non-stressed plants
dual function with soluble sugar to starch conversion would have to be explicitly modeled
My remarks
in ACGCA NSC to biomass ratio is constant for fine roots and leaves and cannot be used for regrowth, so we assume it is needed for metabolism somehow
in stem, NSC lever is supposed to be lower, nevertheless, some threshold should not be undershot- let’s say half of the leaves-fine root average is the normal stem NSC average, then say half of it is needed as soluble sugars:
\begin{equation}
\nonumber
\min\delta_S = \frac{1}{4}\,\frac{\delta_L+\rho_{RL}\,\delta_R}{1+\rho_{RL}} \approx 0.02
\end{equation}