Photosynthesis of co-existing Phragmites haplotypes in their non-native range: are characteristics determined by adaptations derived from their native origin?

Loc Xuan Nguyen,Brian K Sorrell,Franziska Eller,Luciana Achenbach,Carla Lambertini,Hans Brix

doi:10.1093/aobpla/plt016

Abstract

The Gulf Coast of North America (GC) is a ‘hot spot’ of Phragmites diversity as several lineages (defined according to the haplotypes of their chloroplast DNA) differing in origin, genetic traits and phenotype co-exist and interbreed in this area. We analysed differences in photosynthetic characteristics among and within four haplotypes to understand if differences in gas exchange can be attributed to adaptations acquired in their native ranges. We collected rhizomes of four GC haplotypes (I2, M1, M and AI; including the phenotypes ‘Land-type’, ‘Delta-type’, ‘EU-type’ and ‘Greeny-type’) and propagated them in a common controlled environment to compare photosynthesis–irradiance responses, CO2 responses, chlorophyll fluorescence, the activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), specific leaf area (SLA), pigment contents, stomatal density and guard cell length. The maximum light-saturated photosynthetic rate, Amax, in the haplotype I2 (Land-type) and haplotype M1 (Delta-type) (34.3–36.1 µmol CO2 m−2 s−1) was higher than that in the invasive Eurasian haplotype M (22.4 ± 2.3 µmol CO2 m−2 s−1). The Amax of haplotype AI (Greeny3-type) was 29.1 ± 4.0 µmol CO2 m−2 s−1 and did not differ from the Amax of the other haplotypes. The carboxylation rate (Vcmax) and electron transport rate (Jmax) followed the same pattern as Amax. The haplotypes also differed in SLA (17.0–24.3 m2 kg−1 dry mass) and pigment content, whereas stomatal density and guard cell length, Rubisco activity and chlorophyll fluorescence did not differ significantly among haplotypes. The high photosynthetic activity and gas-exchange capacity of the two haplotypes originating in tropical Africa and the Mediterranean area (haplotypes I2 and M1) are apparently adaptations derived from their native ranges. Hence, the haplotypes can be regarded as ecotypes. However, it remains unclear how these differences relate to plant competitiveness and fitness in the GC of North America environment.

Highlights

The common reed, Phragmites australis (Cav.) Trin. ex Steud, is a cosmopolitan emergent wetland grass occurring on all continents except Antarctica and in subtropical to cold temperate climates (Brix 1999; Clevering and Lissner 1999)
The aim of this study was to assess whether Phragmites haplotypes co-occurring in the Mississippi River Delta differ in their photosynthetic characteristics and whether these differences are shared by all genotypes of the same haplotype, being attributable to ecotypes, or alternatively have resulted after colonization of the delta
As genotypes clustered according to haplotype in the principal component analysis (PCA) when significant variation among genotypes was considered, such differences appear to be within the normal variation range within haplotypes

Summary

Introduction

The common reed, Phragmites australis (Cav.) Trin. ex Steud, is a cosmopolitan emergent wetland grass occurring on all continents except Antarctica and in subtropical to cold temperate climates (Brix 1999; Clevering and Lissner 1999). In the Mississippi River Delta at the Gulf Coast of North America, five maternal lineages of Phragmites, defined according to their chloroplast DNA haplotypes (Saltonstall 2002) and hereafter termed haplotypes, have been identified (Hauber et al 2011; Lambertini et al 2012a). These haplotypes differ in their geographic origin and to a large extent in their phenotype. This variation pattern is probably due to gene flow among haplotypes in the Gulf Coast, as evidenced by nuclear DNA variation (Lambertini et al 2012a)

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