Photosynthetic variation and responsiveness to CO2 in a widespread riparian tree

Abstract

Phenotypic responses to rising CO2 will have consequences for the productivity and management of the world's forests. This has been demonstrated through extensive free air and controlled environment CO2 enrichment studies. However intraspecific variation in plasticity remains poorly characterised in trees, with the capacity to produce unexpected trends in response to CO2 across a species distribution. Here we examined variation in photosynthesis traits across 43 provenances of a widespread, genetically diverse eucalypt, E. camaldulensis, under ambient and elevated CO2 conditions. Genetic variation suggestive of local adaptation was identified for some traits under ambient conditions. Evidence of genotype by CO2 interaction in responsiveness was limited, however support was identified for quantum yield (φ). In this case local adaptation was invoked to explain trends in provenance variation in response. The results suggest potential for genetic variation to influence a limited set of photosynthetic responses to rising CO2 in seedlings of E. camaldulensis, however further assessment in mature stage plants in linkage with growth and fitness traits is needed to understand whether trends in φ could have broader implications for productivity of red gum forests.

Fig 1. Distribution of E. camaldulensis provenances sampled in this study.

Occurrence records (underlaid) spanning the species natural range were obtained from the Atlas of Living Australia (http://www.ala.org.au. Accessed 12 May 2016). National Surface Hydrology Polygon obtained from Geoscience Australia [82]. Figure produced using ArcGIS v. 10.3.

Fig 2. Box plots illustrate variation among provenances, grouped by subspecies, for each photosynthetic trait, presented as the mean, 1^st and 3^rd quartiles of the distribution and outliers within whiskers spanning 1.5 times the interquartile range (IQR).

Subspecies are ordered based on their approximate south to north latitudinal position.

Fig 3. Association of provenance BLUEs (least square means) for selected traits and climate parameters.

For principal components, arrows against the y axis indicate the relative shift in environmental variables based on loadings with increasing values of the PC estimate. Likewise arrows against the vertical axis indicate relative shift in trait values based on loadings with decreasing values of the PC estimate.

Fig 4

Associations between photosynthetic responses, a) ΔAmax and b) Δφ, between CO₂ regimes for test plants. The dashed lines at Δtrait = 1 is the expected response ratio if no change is observed between treatment.

Fig 5

Association between quantum yield (φ) and mean annual temperature at site of origin across for the a) ambient and b) elevated [CO₂] treatments, and c) relationship between φresponse ratio (Δφ) and provenance mean annual temperature. Units for WorldClim temperature data are in ^oC*10.