Dudley bsa2013

Editor's Notes

1. First, what is water use efficiency?Instantaneous water use efficiency is The ratio of carbon gain to water lossbased on measurements of photosynthesis and transpiration at 1 point in timeWhen stomata are open on a leaf, carbon dioxide used in photosynthesis freely enters and photosynthetic rates are highHowever, water also escapes from these open stomata, resulting in proportionately high transpiration ratesThus WUEi is relatively low compared to when stomata are closedIn which case, transpiration decreases more than photosynthesis andWUEi is relatively high
2. Long-term WUE is based on the isotopic composition of C13 relative to C12 in tissue.C13 is relatively rare in the atmosphere, diffuses into the leaf at a slower rateAnd is discriminated against by rubiscoSo that when stomata are open relatively small amounts of C13 are used in growth and maintenanceHowever as stomata are closed for longer amounts of time (preventing not only entry of carbon dioxide but escape of water), C13 is used more due to a depletion of C12 inside the leafBecause the isotopic composition of C13 is standardized the average for C3 plants is ~-28, Thus the more positive this parameter (the closer to zero)the more C13 the plant has assimilated and the more water-use efficient it is said to beδX = [(Rsample / Rstandard) – 1] x 103More negative values correspond to higher transpiration ratesLess negative values are more efficient High stomatal conductance and low WUE = more negative ratios
3. Plant mating-systems refers to the pattern of union between male and female gametes within a speciesSpecies that are autogamous (to which I’ll be referring to as selfers) often flower earlier in the season with smaller petals and are found in more extreme habitats with limited geographic distributionCompared to their outcrossingcouterparts. In our own work, we have shown that selfersalso have higher photosynthetic and transpiration ratesthese trait differences found between selfers and outcrossers are consistent with different water use strategiesIn which selfers avoid water stress and outcrossers tend to tolerate itAfter early spring in CA, NO MORE RAIN
4. In which case, outcrossers are more likely to be exposed to lower water availability than selfers especially late in the growing seasonHere, I compare 2 pairs of sister taxa with habitat in californiaThe selferCxp and its sister subspecies Cxx andTheselfterce with its sister species cuI will be refer to each taxon henceforth as parviflora, xantiana, exilis and unguiculataPoint out dead grass in background of outcrosser CU
5. This study took place in sierra nevada of californiaIn Kern CoAround the Lake Isabella areaWe censused 2-4 populations per taxon twice in 2010Once, early, prior to floweringAnd once, late, after all plants in the census started to flower90 plants were randomly selected for each census period, independent of the other cohort
6. What we expect to find isThat WUE, both instantaneous and long-term, will increase across the growing season as late season water availability becomes more limitingIn addition, outcrossers will have greater water-use efficiencies than selfers and this difference is likely to be greater late in the season during flowering
7. Clear support for temporal increaseSupport early in the season for selfer having lower WUE
8. Support late in the season that selfer has lower WUENo support in either taxon for seasonal increase in WUE
9. Strong support for seasonal increase in WUE in both taxaNo support for selfer having lower WUE than the outcrosser
10. Strong support for seasonal increase in WUE No evidence that taxa differ in long term WUE
11. We predicted that WUE would increase as the growing season progressedWe found general support for this prediction with 2 notable exceptions
12. We also predicted that selfers would have lower wue than their outcrossing counterpartin only 2 comparisons did we find support for this prediction
13. Both predictions assume that WUE is important to plant fitnessWe addressed this by examining the relationship between WUE and fitness during floweringAgain, you can see in the background that during flowering in the outcrosser everything has already browned
14. Describe axes and points and lines and significanceWhat we find is that in general there is an increase in the number of reproductive organs with WUE, both instaneous and long-term
15. Consistent with what we would predict in drying soils and based on observations that higher WUE increases fitnessMay be a difference between buds+flrs+frts and ultimately the # of fruits produced