Acid Rain Impacts on Calcium Nutrition and Forest Health

Transcription

1 Acid Rain Impacts on Calcium Nutrition and Forest Health D E H A Y E S E T A L J A N A M I H A L I C F E B R U A R Y 1 7,

2 Outline Background Study Design Findings Implications

3 Red Spruce Picea rubens Native to eastern North America Perennial Coniferous Live for years phyta_nonfloweringseedplants/pinaceae.htm

4 Background Acid deposition Global phenomenon Although sulfate concentrations are down acidic deposition persists especially in eastern North America Acid deposition has led to a 50% Ca reduction in soil over past 45 years No evidence of widespread forest decline due to acidic deposition HOWEVER acidic deposition implicated in red spruce decline NAPAP 1992

5 Stressors leading to Red Spruce decline Perturbation of Ca nutrition Al mobilization reduces Ca storage in soil thereby reducing root uptake availability Diseases Insect pests Freezing stress Increase dark respiration Decrease in photosynthesis

6 What DeHayes hopes to explain How acid deposition alters the foliar Ca pool Plasma membrane-cell wall Provide evidence that altered foliar Ca causes freezing injury Discuss broad implications of foliar Ca alterations

7 Current Year (CY) vs Year Old (YO) Needles Year Old Current Year phyta_nonfloweringseedplants/pinaceae.htm

8 Freezing injury to Red Spruce Caused by subfreezing temperatures Almost always limited to current year needles 10⁰C less tolerant than 1 year old needles Any environmental disturbance that might reduce cold tolerance a few degrees would result in dramatic increase of freezing injury

9 Figure 1

10 Acid rain and cold tolerance Both simulated and ambient exposure to acidic cloud water reduces cold tolerance in CY needles Reduces freezing tolerance by 3-10⁰C

11 Potential involvement of foliar calcium Red spruce decline firmly linked to inputs of acid deposition Red spruce with low foliar Ca levels are less cold tolerant Acid mist induces foliar Ca leaching

12 Figure 2

13 Figure 3

14 Acid-induced foliar leaching and cold tolerance reductions Exposed red spruce trees to ph 3 and ph 5 acid mists ph 3 Ca concentration in leachate 2-10 times higher 60 times more H + than ph 5 treated needles Most (~85%) of leached Ca from needles CY foliage had ~ 50% more leached Ca than YO needles Acid-mist induced Ca loss accompanied by membrane disruption Indicates a direct negative impact on membrane stability

15 Figure 4

16 Importance of membrane-associated calcium Most Ca in conifer needles is insoluble and extracellular with little physiologic importance Physiologic important Ca is in equilibrium within the plasma membrane (mca) mca influences the response of cells to changing environmental conditions Subtle mca concentrations may be masked by the immobile insoluble total Ca pool Cold weather may trigger mca transport into the cytoplasm

17 Figure 6

18 How plasma membranes work Mediate cold acclimation and help resist freezing injury Influence solution movement across membrane Resist dehydration Resist extracellular ice damage Possibly resist intracellular freezing during cold acclimation

19 Seasonal changes in mca mca pools in CY but not YO needles Needles are responsive to temporal environmental changes mca very important in cold tolerance If reduced thru acid leaching membrane function may be impaired Low-temp signal transduction Freezing injury susceptibility

20 Figure 8

21 Perturbations to mca vs total foliar Ca pools Method developed for measuring mca in woody plant tissue DeHayes study

22 DeHayes study objectives Examined Freezing tolerance mca Total foliar Ca Foliar Ca leaching Sand/perlite soil

23 Experimental Design

24 Results Soil Treatments Soil Ca addition Increased respiration Enhanced total foliar Ca Soil Al addition Inhibited Ca incorporation Altered foliar gas exchange Reduced growth Direct and independent of foliar Ca nutrition [I]mplies that belowground manipulations of soil and foliar calcium pools may not have important physiological consequences for the red spruce trees.

25 Results Acid Mist ph 3.0 mist application in summer and early autumn Foliar Ca leaching Reductions in late fall and winter freezing tolerance Reduction of mca in CY needles mca changes Enhanced Ca leaching Membrane instability Disruption of Ca environmental transduction

26 Table 2

27 Figure 5

28 Table 3

29 Influence of ph and Al treatment on foliar nutrition Reductions in cation concentration associated with Al were greater for ph 5 than ph 3 Interactions of ph and Al did not mask overall acid-reduced mca concentrations [O]ne of the most physiologically meaningful findings was the conspicuous lack of interaction among other treatment combinations.

30 Nature of Ca leaching and cold tolerance perturbations Ca leaching could follow H + displacement of Ca 2+ on exchange sites Removal of Ca 2+ by SO 4 2- at the cell wall membrane SO 4 2- directly toxic to red spruce independent of freezing stress Reduction of cold tolerance seen independent of acid mists with SO 4 2- [A]cid mist induced calcium leaching and cold tolerance reductions are not SO 4 2- driven but are most likely the result of cation exchange driven by differential H + exposure.

31 Nature of Ca leaching and cold tolerance perturbations Acid deposition on needles unique environmental stress Preferentially removes mca leading to deficiency mca is not replaced in autumn mca deficiency may by not be detected if simply examining total foliar Ca pools Better/more sensitive analytical techniques are needed

32 Figure 7

33 Proposed mechanism Direct acidic deposition displaces Ca ions specifically associated with plasma membranes of mesophyll cells Leads to secondary symptoms freezing injury One explanation into the decline of Red Spruce in eastern North America Consistent with H + displacing Ca 2+ not just SO 4 2-

34 Figure 9

35 Broad forest health implications Acid deposition affects foliar base cations directly independent of belowground processes Direct acid induced disruption overrides soil Ca influences Physiological impairment of trees exhibiting foliar Ca deficiency also have reduced mca Phenomenon is not limited to Red Spruce but exacerbated by freezing injury If soil Ca depletion affects mca and membrane stability then Ca mediated predisposition to stress induced injury could have huge influence on forest health

36 Food for thought How can H+ be further reduced Other ways to increase mca?