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Responses of wheat (Triticum aestivum) to complete submergence are not well understood as research has focused on waterlogging (soil flooding). The aim of this study was to characterize the responses of 2 wheat cultivars differing vastly in submergence tolerance to test if submergence tolerance was linked to shoot carbohydrate consumption as seen in rice. Eighteen-day-old wheat cultivars Frument (intolerant) and Jackson (tolerant) grown in soil were completely submerged for up to 19 days while assessing responses in physiology, gene expression, and shoot metabolome. Results revealed 50% mortality after 9.3 and 15.9 days of submergence in intolerant Frument and tolerant Jackson, respectively, and significantly higher growth in Jackson during recovery. Frument displayed faster leaf degradation as evident from leaf tissue porosity, chlorophyll a, and metabolomic fingerprinting. Surprisingly, shoot soluble carbohydrates, starch, and individual sugars declined to similarly low levels in both cultivars by day 5, showing that cultivar Jackson tolerated longer periods of low shoot carbohydrate levels than Frument. Moreover, intolerant Frument showed higher levels of phytol and the lipid peroxidation marker malondialdehyde relative to tolerant Jackson. Consequently, we propose to further investigate the role of ethylene sensitivity and deprivation of reactive O 2 species in submerged wheat.

Environmental metabolomics has become interesting in marine ecological studies. One example is the revealing of new insights in stress response of Zostera marina. This is essential to understand how, at which level and to what extend aquatic plants adapt, tolerate and react to environmental stressors. We exposed Z. marina to water column anoxia and assessed the diurnal metabolomic response by GC-TOF-MS based metabolomics identifying 109 known and 217 unknown metabolites. During day time photosynthetic oxygen production prevents severe effects of anoxia on the metabolome (complete set of small-molecule metabolites). Night time water column anoxia caused a shift in metabolic composition and concentration (trajectories of PLS-DA) in particular an increase in pyruvate and lactate indicating an activation of fermentation in the plant. Concurrent increase of alanine, succinate and GABA suggests the presence of the GABA shunt pathway, a strategy to decrease pyruvate levels by transamination. The down regulation of TCA cycle intermediates illustrates the inactivity of TCA due to lack of oxygen, which results in an accumulation of pyruvate and followed by fermentation to lactic acid. We demonstrate the applicability of metabolomics to assess environmental stress responses of Zostera marina.

Sulfide intrusion in seagrasses represents a global threat to seagrasses. In contrast seegrasses grow in hostile sediments, where they are constantly exposed to sulfide intrusion. Little is known about the strategies to survive sulfide intrusion, if there are detoxification mechanisms and sulfur nutrition in general. By a global review of sulfide intrusion, coupled with a series of field studies and in situ experiments we elucidate sulfide intrusion and different strategies of seagrasses to sustain sulfide intrusion. Using stable isotope tracing, scanning electron microscopy with x-ray analysis to trace sulfur compounds and as well as metabolomics upon sulfide and anoxia exposure we identified different strategies to cope with sulfidic sediments. 1) Avoidance, by reoxidation of gaseous sulfide in the arenchyma to elemental sulfur and sulfate; where precipitation of sulfide occurred as non-toxic elemental sulfur on the inner wall of the root lacunae. 2) Tolerance by incorporation, where gaseous sulfide is incorporated by enzymatic uptake and accumulated as organic sulfur, representing a non-toxic storage compound. We found considerable amounts of sediment sulfides incorporated in seagrasses indicating a possible role of sulfide in the sulfur nutrition beside the detoxification function. Our results suggest different adaptations of Z. marina to reduced sediments and sulfide intrusion ranging from bacterial and chemical reoxidation of sulfide to sulfate to incorporation of sulfide into organic sulfur compounds in the plant.

Sulfide intrusion in seagrasses represents a global threat to seagrasses and thereby an important parameter in resilience of seagrass ecosystems. In contrast seegrasses colonize and grow in hostile sediments, where they are constantly exposed to invasion of toxic gaseous sulfide. Remarkably little is known about the strategies of seagrasses to survive sulfide intrusion, their potential detoxification mechanisms and sulfur nutrition in general.By a global review of sulfide intrusion, coupled with a series of field studies and in situ experiments we elucidate sulfide intrusion and different strategies of seagrasses to sustain sulfide intrusion. Using stable isotope tracing, scanning electron microscopy with x-ray analysis, tracing sulfur compounds combined with ecosystem parameters we found different spatial, intraspecific and interspecific strategies to cope with sulfidic sediments. 1) Tolerance, by elimination (eg. Zostera marina); where we found precipitation of sulfide as non-toxic elemental sulfur on the inner wall of the root lacunae. 2) Utilization (eg. Z. marina), where seagrasses detoxify and incorporate sulfides by active uptake and metabolize to sulfate, representing a non-toxic storage compound. 3) Avoidance, by barriers in tissue (eg. suberin layers in Posidonia) and/or radial root oxygen loss to reoxidize sulfide. Foliar sulfate and metabolic uptake of gaseous sulfide via roots as main sulfur source represents an evolutionary adaption of submerged plants, to our knowledge not present in terrestrial plants at that level. Sulfide is not necessarily toxic but used as sulfur nutrition, presupposing healthy seagrass ecosystems that can support detoxification mechanisms. Presence or absence of those mechanisms determines susceptibility of seagrass ecosystems to sediment sulfide and thereby their resilience, which is important knowledge for management of seagrasses under global pressure.

Intensive recreational SCUBA diving threatens coral reef ecosystems. The reefs at Dahab, South Sinai, Egypt, are among the world’s most dived (>30,000dives y−1). We compared frequently dived sites to sites with no or little diving. Benthic communities and condition of corals were examined by the point intercept sampling method in the reef crest zone (3 m) and reef slope zone (12 m). Additionally, the abundance of corallivorous and herbivorous fish was estimated based on the visual census method. Sediments traps recorded the sedimentation rates caused by SCUBA divers. Zones subject to intensive SCUBA diving showed a significantly higher number of broken and damaged corals and significantly lower coral cover. Reef crest coral communities were significantly more affected than those of the reef slope: 95% of the broken colonies were branching ones. No effect of diving on the abundance of corallivorous and herbivorous fish was evident. At heavily used dive sites, diver-related sedimentation rates significantly decreased with increasing distance from the entrance, indicating poor buoyancy regulation at the initial phase of the dive. The results show a high negative impact of current SCUBA diving intensities on coral communities and coral condition. Corallivorous and herbivorous fishes are apparently not yet affected, but are endangered if coral cover decline continues. Reducing the number of dives per year, ecologically sustainable dive plans for individual sites, and reinforcing the environmental education of both dive guides and recreational divers are essential to conserve the ecological and the aesthetic qualities of these dive sites.