Interactions between ozone and drought stress in plants: mechanisms and implications. Sally Wilkinson and William J. Davies, Lancaster University

Transcription

1 Interactions between ozone and drought stress in plants: mechanisms and implications Sally Wilkinson and William J. Davies, Lancaster University

2 STOMATA: At the leaf surface water is lost to the atmosphere via transpiration through stomatal pores bounded by a pair of guard cells. When these pores are open, ozone flux to the leaf When these pores are open, ozone flux to the leaf interior also occurs.

3 HOW IS STOMATAL CONTROL ACHIEVED: Stomatal closure Decreased soil water availability ABA ABA ABA ABA ABA ABA Increased ABA synthesis and upwardly directed transport ABA (abscisic acid) is a chemical signal alerting the shoot of a soil water deficit, that induces adaptive change. Soil drying closes stomata via ABA: the plant retains water

4 It has become generally accepted that: a) ozone damages stomata (or s photosynthetic CO 2 fixation, thus ing substomatal [CO 2 ]) so that apertures are reduced in many genotypes (= d biomass). b) when drought closes stomata, t fortuitously, ozone flux is also thought to be reduced, and this has sometimes been associated with reduced d injury.

5 However, some data in the literature suggested that this was not the full story: Stomata in stressed plants of some genotypes close much less readily than normal they respond sluggishly We have been investigating how this occurs, its implications, and how widespread the phenomenon might be.

6 We exposed plants +/- 70 ppb ozone in 1.0 m 2 climate chambers c (p pb ) O3 con Ozone concentration in Snowdonia, M ay 1 Ju ne 1 Ju ly 1 A ug Gina Mills and Felicity Hays CEH, Bangor, UK

7 Leontodon hispidus Intact plants +/ soil drying and +/ foliar Intact plants +/- soil drying, and +/- foliar sprays of ABA.

8 OZONE = STOMATA CLOSE LESS SENSITIVELY TO SOIL DRYING: IMPLICATIONS: OZONE UPTAKE INTO LEAVES IS REINFORCED, PLANTS LOSE MORE WATER atal condu uctance (% ww cont trol) WW control WW + ozone DD control 120 DD + ozone Stom (am) 1(pm) 2 3 Time from start of soil drying treatment (days)

9 Spraying intact plants with or without ABA (the drought hormone ): STOMATA CLOSE LESS SENSITIVELY ctrl ctrl + ABA + ozone + ozone+aba ) (mmol m -2 s * * * gs DARK 100 * * Duration of ozone treatment (days)

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11 Effect of ozone concentration on stomatal conductance (gs). From Mills et al. 2009, GCB.

12 IMPLICATIONS Ozone can interfere with stomatal responses to ANY stress that produces ABA: high VPD, high light, salinity stress (literature) Water loss may be too high to support full turgor: secondary reductions in growth, high susceptibility to subsequent stress, reduced yields death (current)? High gs will deplete soil moisture (forest) Ozone flux is maintained closer to the high prestress level, injury levels remain high (current)? This response may be the cause of some of the genetic variability in ozone sensitivity (link to gs already shown e.g. Biswas et al. 2008). Need to revisit flux-response relationships? Anomalies?

13 Sensitive white clover (NCS) has more open stomata than the resistant genotype (NCR), particularly under drought. 120 Sensitive 1 ) ol m -2 s -1 st omatal conductan nce (mm Resistant 100 Sensitive + ozone Resistant + ozone Weeks from start of ozone/drought treatment

14 McLaughlin et al. 2007: Measured and modelled streamflow: Walker Branch Watershed, S. Appalachian forest, USA. Reduced ozone increased streamflow. Authors conclusion: ozone-induced d increases in whole-tree canopy conductance caused subsequent depletions in soil water content.

15 Sluggish species (LU, CEH): Leontodon hispidus (forb) Dactylis glomerata (grass) Anthoxanthum odoratum (grass) Beech (tree) Phaseolus (pod crop) Wheat (grain crop - under study) Clover (forb) Poa (grass)

16 Ozone stimulates ethylene production (GC) Effect of 9 days exposure +/- 80ppb 24h ozone on ethylene generation by Leontodon leaves sprayed +/- 3x10-6 M ABA once daily over the preceding 3 days. 1.2 Ethyle ene generatio on (nl gfw hr) ozone + ozone ctrl Treatment 3x10-6 M ABA Wilkinson & Davies 2009 PCE 16

17 Ethylene prevents ABA from closing stomata, but stomata close as normal when ethylene perception is inibited with 1-MCP. l g FW h -1 ) Ethylen ne evolution (nl 10 b a ab a gs (% contro ol) a b - 1-MCP + 1-MCP b a b ctrl ACC concentration (mmol m -2 ) ctrl +ABA +ABA+ACC Treatment

18 1-MCP restores the stomatal closure response to ABA despite the continued presence of ACC. This shows that the effect of ACC is mediated through ethylene, as 1-MCP is an ethylene perception inhibitor. 100 a a - 1-MCP + 1-MCP 1MCP a gs (% con ntrol) 80 b b b ctrl 1 +ABA 2 +ABA+ACC 3 Treatment

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20 A OZONE B H 2 O H 2 O Ethylene H 2 O H 2 O ABA ABA H 2 O H 2 O DRYING SOIL DRYING SOIL ABA closes stomata, leaf retains water Ethylene prevents ABA from closing stomata

21 Relationships between grain-filling rate and concentrations of ABA (a), ethylene (b), and the ratio of ABA to ACC (c) in superior (closed symbols) and inferior (open symbols) grains of wheat t( (cvs Yangmai i6 and dyangmai i11)d during linear grain growth. Treatments were wellwatered (WW), moderately soil-dried (MD) and severely soil-dried (SD). From Yang et al. (2006).

22 CONCLUSIONS Ozone closing stomata t is NOT the full story: ozone can open them, particularly under stress. This is not limited to a few spp: search literature for genotypes that increase ethylene in response to ozone = likely to exhibit this response this includes many crops besides bean and wheat. Implications for water use, yields and food security, health of natural vegetation eg. Injury rates. Mitigation: 1-MCP (Invinsa), rhizobacterial soil additions, screening for genotypes that close stomata as normal under stress, legislation for REDUCED PRECURSOR EMISSIONS.

23 Because ozone increases both stomatal aperture and leaf biomass in some species, polluted plants will lose more water. Tissues will become water stressed, particularly under drought, inducing a secondary effect of ozone to close stomata via hydraulic signals, and reduce biomass growth/productivity. it Effect of ozone on the response of stomatal conductance to soil drying. Re-calculated from Wilkinson & Davies Effect of ozone on fresh biomass in well-watered watered and droughted Anthoxanthum odoratum rol) Stomata al conductanc ce (% ww cont WW control WW + ozone DD control 120 DD + ozone (am) 2 1(pm) Time from start of soil drying treatment (days) Fresh bio omass (g) WW 1 WW 2 DD 3 DD 4 5 ctrl ozone ctrl ozone