Chemical analysis of wetland plants to evaluate the bioaccumulation and metabolism of hexachlorocyclohexane (HCH).

Hexachlorocyclohexanes (HCH) belong to the banned pesticides with short-time production and use during the last century. However, the consequences of this short period are still present as persistent environmental contamination. This study represents the large lab-scale experiment focused on the HCH accumulation and metabolism in selected wetland plants (Juncus effuses, Typha latifolia, Phragmites australis) and trees (Alnus glutinosa) after the exposure to the technical mix of HCH isomers (t-HCH) or δ-HCH at three different concentration. During the three-month exposure, morphological (biomass, height, relative chlorophyll content) and physiological (photosynthetic measurements - photosynthetic rate, stomatal conductance, transpiration and dark transpiration) parameters were measured to assess the HCH effect on plant's growth. The results showed that all selected plant species supported HCH removal from the soil. The total removal efficiency was lower for the t-HCH than for δ-HCH exposure, and the best results were provided by Alnus glutinosa tree. Also, no isomer preference was observed in plants exposed to t-HCH. Most HCH remained accumulated in the root biomass, and mainly α-HCH and δ-HCH were transported to the above-ground parts due to their physicochemical properties. Simultaneously, HCH uptake and metabolization to chlorobenzenes (CB) and chlorophenols (CP) occur. Non-targeted analysis showed that CP could be conjugated to glucose and malonyl in plant tissue, and secondary plant metabolism is affected positively and negatively after exposure to t-HCH depending on plant species and chemical concentration. Luteolin, quercetin and quercetin-3-O-glucoside found common to all species showed quantitative changes due to HCH. Nevertheless, most morphological and physiological parameters were adversely affected without statistical significance. This large-scale study provides information on the fate of HCH in the soil-plant system, the suitability of selected plants and their adaptation to chemical stress for use in the phytoremediation process.

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

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.

Acclimation to light and avoidance of photoinhibition in Typha latifolia is associated with high photosynthetic capacity and xanthophyll pigment content.

Tall monocots with long, linear leaves have lower canopy light attenuation than plants with horizontal leaves, yet little is known about their light acclimation and sun-shade responses. The genus Typha, common in nutrient-rich wetlands, is highly productive with dense canopies of such leaves. The objective of this study was therefore to investigate photosynthetic acclimation and pigment content in linear leaves of Typha latifolia L. in response to light availability. This was done in a growth experiment with two light intensities and in the field. In the laboratory, T. latifolia exhibited typical morphological, anatomical and gas exchange sun-shade responses. Net photosynthesis rates in high light were very high for a C3 plant (>40µmol CO2 m-2s-1) in both laboratory and field studies, and this was associated with stomatal conductances that were correspondingly high (maximum values >1.0mol H2O m-2s-1). The size of the xanthophyll (violaxanthin, antheraxanthin and zeaxanthin; VAZ) pool was also among the top 0.5% of all species. In the field, T. latifolia was able to maintain high net photosynthetic rates (26-41µmol CO2 m-2s-1) throughout its canopy and could avoid photoinhibition through high investment in the VAZ pool (0.7-1.3µmolg-1 DW total VAZ pigments). This pattern of acclimation is likely to be adaptive, explaining why this species is so successful and dominant in high-light, high-nutrient wetland environments.