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}