1. Non-structural carbohydrates influence water relations in Pinus ponderosa Aurora Bayless The Sala lab of Plant Physiological Ecology Division of Biological Sciences University of Montana

2. Why study water relations in Ponderosa pine? Drought is predicted to increase with climate change Drought stress mortality is a major driving factor in forest ecology 2,562 matches Mainsfield search 123,000 articles google scholar Forests hold lots of carbon, and influence global cycles The specific mechanisms behind drought related mortality are still unknown Shinneman et al. 2016

4. Photosynthesis makes carbohydrates Sugars are hydrophilic Structural Carbohydrates (cellulose) Non-Structural Carbohydrates (NSC)

5. Making sugar requires water loss. Water loss increases xylem tension.

6. Xylem tension is dangerous! Plants must prevent water loss or the water column will break leading to catastrophic hydraulic failure

7. Plants can close stomata to prevent water loss However, closing stomata to prevent water loss prevents photosynthesis  carbon starvation

8. Two main hypotheses for the mechanisms of drought stress mortality: 1) hydraulic failure, mortality is caused by xylem cavitation We know this 2) Carbon starvation happens as a result of stomatal closure (McDowell, et al. 2008). We don’t know the threshold yet

9. NSC is not used as expected Palacio et al. 2008. Funct. Ecol. Galvez et al. 2011. Tree Physiol. Sala & Hoch 2009. PCE Drought does not deplete starch Wiley et al. 2015.Tree Physiol. drought control

10. Reservoir Metabolism Osmotic role NSC may help retain and move water Why so much NSC?

11. It is critical to know how NSC affects hydraulic function to predict mortality. First we need to know if there is a threshold for carbon starvation Then, we can ask how carbon starvation may drive the hydraulic failure to critical thresholds and vice versa

12. Research hypotheses: 1) Non-Structural Carbohydrates are related to hydraulic function. 2) NSC below a certain threshold causes mortality.

13. CONTROL TREATMENT 7

14. Non-Structural Carbohydrates decreased in the dark Stepwise NSC decline with dark exposure

15. Non Structural Carbohydrates decreased in the dark Stepwise NSC decline with dark exposure. Weeks 1-3 and weeks 4-6 have similar NSC

16. Hypothesis 1 Non-Structural Carbohydrates are related to hydraulic function.

17. Pre-Dawn Water potential

18. Water Potential (  Decreases with dark exposure despite irrigation Increasing water stress

19. High water stress despite irrigation is related to declining NSC C 1 2 3 4 5 6

20. Water stress occurs at about 40% NSC relative to controls C 1 2 3 4 5 6

21. Positive carbon assimilation occurs after one and four weeks of dark exposure Declining NSC after four weeks of dark exposure stimulates C assimilation. This could be a compensation mechanism to make up for lost carbohydrates, because of shade.

22. Higher water stress despite irrigation related to declining NSC Increasing water stress

23. Higher water stress despite irrigation related to declining NSC Increasing water stress NSC-depleted plants with low water stress tend to maintain positive photosynthesis. This indicates that Carbon is needed to retain water.

24. Hypothesis 2 2) NSC below a certain threshold causes mortality.

25. In well watered groups the first mortality occurs after three weeks of dark exposure

26. Below 40% NSC relative to controls plants are unable to maintain hydraulic function and mortality increases

27. What does this mean for the future? Drought is a major issue, and we need to model it to understand mortality and Carbon cycles. How is this research important for land managers, modelers, forest managers, et cetera? We need to start considering the interactions of hydraulic function and Non Structural Carbohydrates in order to model future tree mortality.

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29. Thank you! Sala Lab Physiological Plant Ecology Anna Sala (PI) Beth Roskilly (MS student) Sean Pinnell (MS Student) Gerard Sapés (PhD Student)

30. QUESTIONS?