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. 2011 Mar;155(3):1051-9.
doi: 10.1104/pp.110.170704. Epub 2011 Jan 14.

Mechanisms linking drought, hydraulics, carbon metabolism, and vegetation mortality

Nathan G McDowell  1
Affiliations

Mechanisms linking drought, hydraulics, carbon metabolism, and vegetation mortality

Nathan G McDowell. Plant Physiol. 2011 Mar.
No abstract available

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Figures

Figure 1.
Figure 1.
Simulated effects of prolonged drought on total NSC content, photosynthesis, growth, and respiration of a generic tree. The model summarizes the general relationships among these carbon pools and fluxes; it is not intended to mimic any particular circumstance. Arrow 1, Based on experimental observations that growth is most sensitive to water stress, followed by photosynthesis, and finally respiration, the carbohydrate pool initially increases. Only after photosynthesis declines to a rate slower than respiration do carbohydrates decline. Arrow 2, Growth respiration becomes minimal and hence respiration is only for maintenance. If maintenance respiration increases with drought and high temperatures, the size of the carbohydrate pool might decline more rapidly (Supplemental Fig. S2). Arrow 3, The simulated NSC pool implicitly includes noncarbohydrate organic compounds such as Pro that can accumulate during drought but does not account for NSC utilization for osmotic adjustment or maintenance of phloem transport. A linear increase in carbohydrate (CHO) consumption is shown for demonstrative purposes (asterisk). The intercept point of NSC with the NSC required to maintain turgor is a hypothetical mortality threshold in the absence of attack by biotic agents. See Supplemental Data for a fuller description of the model.
Figure 2.
Figure 2.
Observations of whole-plant starch (A) and sugar (B) during shading in Douglas-fir (Pseugostuga menziesii) seedlings. Seedlings received zero light for the duration of the experiment and were maintained at three different temperatures (30°C, 20°C, and 10°C), with lower temperatures resulting in longer survival times. All seedlings were dead at the end of the experiment (J.D. Marshall, personal communication). Control plants received full sunlight, and both starch and sugar contents stayed above the values observed for shaded plants. Whole-plant (shoot, coarse root, new and old fine roots) carbohydrates were calculated from table 3 and figures 2 to 4 in Marshall and Waring (1985).
Figure 3.
Figure 3.
Observations of predawn water potential (A), loss of hydraulic conductivity of the root system (B), and net photosynthesis (C) of relatively isohydric and anisohydric species (piñon pine and one-seed juniper, respectively) during drought. Predawn water potential measurements are from Breshears et al. (2009). Root conductivity loss due to cavitation and net photosynthesis are shown for both species during this period using published species-specific equations for percentage loss of root hydraulic conductivity and net photosynthesis (McDowell et al., 2008; Willson et al., 2008; B and C). Roots were used rather than stems for B because they are more vulnerable and thus better represent the whole-plant connection to soil water availability and also because predawn water potentials (A) are expected to represent soil water availability. These estimates assume that refilling is possible when soil water potential is more positive than minimum predawn plant water potential, but they are conservative because the net photosynthesis model is for foliage only and does not include carbon losses to respiration of nonphotosynthetic tissues.
Figure 4.
Figure 4.
Hypothetical relationships of whole-plant hydraulic conductivity and carbohydrate availability during drought. Carbohydrate availability is plotted using the simulation from Figure 1, and hydraulic conductivity follows a typical pattern from Brodribb and Cochard (2009). The threats of hydraulic failure, biotic attack, or outright carbon starvation are enhanced by the interdependent feedbacks between conductivity and carbohydrates. The abundance of biotic agents that kill their hosts varies with species, climate, and region, so a flat line is used to indicate their general presence rather than a specific attack agent. If these agents are present, their attack is more likely to result in mortality after the threshold is exceeded.
See this image and copyright information in PMC

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