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. 2021 Sep 3;128(4):469-480.
doi: 10.1093/aob/mcab089.

Shade and salinity responses of two dominant coastal wetland grasses: implications for light competition at the transition zone

Emil Jespersen  1 , Gro H Kirk  1 , Hans Brix  1 , Franziska Eller  1 , Brian K Sorrell  1
Affiliations

Shade and salinity responses of two dominant coastal wetland grasses: implications for light competition at the transition zone

Emil Jespersen et al. Ann Bot. .

Abstract

Background: Coastal wetlands are threatened by the increased salinity that may result from sea level rise. Salinity stress alters species zonation patterns through changes in competitive outcome between species differing in salinity tolerance. This study therefore aimed to understand how salinity and light affect two dominant and competing coastal wetland grasses that differ in salt tolerance, height and photosynthetic metabolism.

Methods: The C4 species Spartina anglica and the C3 species Phragmites australis were grown at five salinity levels (0, 7, 14, 21 and 28 ppt) and two light fluxes (100 % and 50 % of natural daylight) in an outdoor experimental setup for 102 d with full access to nutrients.

Key results: Salinity reduced the biomass, height and shoot density of P. australis from 81.7 g dry weight (DW), 0.73 m and 37 shoots per pot at a salinity of 0 ppt to 16.8 gDW, 0.3 m and 14 shoots per pot at a salinity of 28 ppt. Biomass, height and shoot density of S. anglica did not respond or were only slightly reduced at the highest salinity of 28 ppt. High salinity also resulted in a higher tissue concentration of N and P in P. australis. Both species had low ability to acclimate to the lower light flux. Shade acclimation in S. anglica occurred via modest changes in specific leaf area, pigment content and biomass allocation.

Conclusions: High salinity reduced traits important for light competition and increased the nutrient concentration in P. australis leaf and root biomass, while this was overall unaffected in S. anglica. This is likely to reduce the competitive ability of P. australis over S. anglica for light because at high salinities the former cannot effectively shade the lower-growing S. anglica. Neither species effectively acclimates to shade, which could explain why S. anglica does not occur in the understorey of P. australis at low salinities.

Keywords: Phragmites australis; Spartina anglica; C4 photosynthesis; Salt tolerance; ion regulation; light competition; salt exclusion; shade acclimation; sodium.

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Figures

Fig. 1.
Fig. 1.
Changes in total biomass (A), shoot height (Height), number of shoots per pot (Density) (B) and the fraction of biomass allocated to roots (RMF) and leaves (LMF) (C) in S. anglica (SA) and P. australis (PA) to the two light fluxes (LL low light, 50 % full sunlight; HL high light, 100 % full sunlight) and five salinity levels (0, 7, 14, 21, 28 ppt). Values are mean ± s.e. (n = 8).
Fig. 2.
Fig. 2.
Response of chlorophyll pigments (Chl) (A), specific leaf area (SLA) (B) and water in the leaf (Leaf water) (C) in S. anglica (SA) and P. australis (PA) to changes in light fluxes (LL low light, 50 % full sunlight; HL high light, 100 % full sunlight) and salinity (0, 14, 28 ppt). Values are mean ± s.e. (n = 5–7).
Fig. 3.
Fig. 3.
Changes in percentage N (A) and percentage P (B) per biomass in root and leaf tissue in S. anglica (SA) and P. australis (PA) to the two light fluxes (LL low light, 50 % full sunlight; HL high light, 100 % full sunlight) and five salinity levels (0, 7, 14, 21, 28 ppt). Values are mean ± s.e. (n = 8).
Fig. 4.
Fig. 4.
Comparison of K and Na concentration in the leaf (A) and root (B) tissue and the total concentration of Ca, K, Mg and Na in the leaf and root tissue (C) of S. anglica (SA) and P. australis (PA) to the two light fluxes (LL low light, 50 % full sunlight; HL high light, 100 % full sunlight) and five salinity levels (0, 7, 14, 21, 28 ppt). Values are mean ± s.e. (n = 8).
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