Salt Marsh Elevation Drives Root Microbial Composition of the Native Invasive Grass Elytrigia atherica

Salt marsh nitrogen cycling: where land meets sea

Salt marshes sit at the terrestrial-aquatic interface of oceans around the world. Unique features of salt marshes that differentiate them from their upland or offshore counterparts include high rates of primary production from vascular plants and saturated saline soils that lead to sharp redox gradients and a diversity of electron acceptors and donors. Moreover, the dynamic nature of root oxygen loss and tidal forcing leads to unique biogeochemical conditions that promote nitrogen cycling. Here, we highlight recent advances in our understanding of key nitrogen cycling processes in salt marshes and discuss areas where additional research is needed to better predict how salt marsh N cycling will respond to future environmental change.

Effect of allelochemicals sustained-release microspheres on the ingestion, incorporation, and digestion abilities of Daphnia magna Straus

Allelochemicals sustained-release microspheres (ACs-SMs) exhibited great inhibition effect on algae, however, few studies have focused on ACs-SMs toxicity on invertebrate. In this study, the effects of single high-concentration ACs (15 mg/L, SH-ACs), repeated low-concentration ACs (3 × 5 mg/L, RL-ACs) and ACs-SMs containing 15 mg/L ACs exposure on the ingestion, incorporation, and digestion of Daphnia magna Straus (DS) were investigated by stable isotope ¹⁵N labeling method. Meanwhile, the diversity and abundance of microflora in DS guts were determined by 16S rRNA genes and cloning methods. The results showed that SH-ACs exposure caused 50% and 33.3% death rates for newborn and adult DS, while RL-ACs exposure caused 10% death rate for newborn DS and no obvious effect on the activity of adult DS. And ACs-SMs exposure did not diminish the motility of both newborn and adult DS, indicating the lower acute toxicity of ACs-SMs. Furthermore, SH-ACs inhibited the ingestion (-6.45%), incorporation (-47.1%) and digestion (-53.8%) abilities of DS and reduced the microbial abundance (-27.7%) in DS guts. Compared with SH-ACs, RL-ACs showed relatively low impact on the ingestion (-3.23%), incorporation (-5.89%) and digestion (-23.9%) abilities of DS. Interestingly, ACs-SMs enhanced the ingestion (+9.68%), incorporation (+52.9%) and digestion (+51.3%) abilities of DS and increased the microbial abundance (+10.7%) in DS guts. Overall ACs and ACs-SMs reduced the diversity of microflora in DS guts. In conclusion, ACs-SMs can release ACs sustainably and prolong the sustained release time, which not only effectively reduce the toxicity of ACs, but also had positive effects on DS.

Seasonal and Zonal Succession of Bacterial Communities in North Sea Salt Marsh Sediments

Benthic microbial communities of intertidal zones perform important biogeochemical processes and provide accessible nutrients for higher organisms. To unravel the ecosystem services of salt marsh microbial communities, we analyzed bacterial diversity and metabolic potential along the land–sea transition zone on seasonal scales on the German North Sea Island of Spiekeroog. Analysis of bacterial community was based on amplicon sequencing of 16S rRNA genes and –transcripts. Insights into potential community function were obtained by applying the gene prediction tool tax4fun2. We found that spatial variation of community composition was greater than seasonal variations. Alphaproteobacteria (15%), Gammaproteobacteria (17%) and Planctomycetes (11%) were the most abundant phyla across all samples. Differences between the DNA-based resident and RNA-based active communities were most pronounced within the Planctomycetes (17% and 5%) and Cyanobacteriia (3% and 12%). Seasonal differences were seen in higher abundance of Gammaproteobacteria in March 2015 (25%) and a cyanobacterial summer bloom, accounting for up to 70% of the active community. Taxonomy-based prediction of function showed increasing potentials for nitrification, assimilatory nitrate and sulfate reduction from sea to land, while the denitrification and dissimilatory sulfate reduction increased towards the sea. In conclusion, seasonal differences mainly occurred by blooming of individual taxa, while the overall community composition strongly corresponded to locations. Shifts in their metabolism could drive the salt marsh’s function, e.g., as a potential nitrogen sink.

Genetically Modified Sugarcane Intercropping Soybean Impact on Rhizosphere Bacterial Communities and Co-occurrence Patterns

Strategies involving genes in the dehydration-responsive element binding (DREB) family, which participates in drought stress regulation, and intercropping with legumes are becoming prominent options in promoting sustainable sugarcane cultivation. An increasing number of studies focusing on root interactions in intercropping systems, particularly involving transgenic crops, are being conducted to better understand and thus, harness beneficial soil microbes to enhance plant growth. We designed experiments to investigate the characteristics of two intercropping patterns, soybean with wild-type (WT) sugarcane and soybean with genetically modified (GM) Ea-DREB2B-overexpressing sugarcane, to assess the response of the rhizosphere microbiota to the different cropping patterns. Bacterial diversity in the rhizosphere microbial community differed between the two intercropping pattens. In addition, the biomass of GM sugarcane that intercropped with soybean was significantly improved compared with WT sugarcane, and the aboveground biomass and root biomass of GM soybean intercropping sugarcane increased by 49.15 and 46.03% compared with monoculture. Furthermore, a beneficial rhizosphere environment for the growth of Actinobacteria was established in the systems intercropped with GM sugarcane. Improving the production mode of crops by genetic modification is a key strategy to improving crop yields and provides new opportunities to further investigate the effects of intercropping on plant roots and soil microbiota. Thus, this study provides a basis for selecting suitable sugarcane-soybean intercropping patterns and a theoretical foundation for a sustainable sugarcane production.

Fungal Biodiversity in Salt Marsh Ecosystems

This review brings together the research efforts on salt marsh fungi, including their geographical distribution and host association. A total of 486 taxa associated with different hosts in salt marsh ecosystems are listed in this review. The taxa belong to three phyla wherein Ascomycota dominates the taxa from salt marsh ecosystems accounting for 95.27% (463 taxa). The Basidiomycota and Mucoromycota constitute 19 taxa and four taxa, respectively. Dothideomycetes has the highest number of taxa, which comprises 47.12% (229 taxa), followed by Sordariomycetes with 167 taxa (34.36%). Pleosporales is the largest order with 178 taxa recorded. Twenty-seven genera under 11 families of halophytes were reviewed for its fungal associates. Juncus roemerianus has been extensively studied for its associates with 162 documented taxa followed by Phragmites australis (137 taxa) and Spartina alterniflora (79 taxa). The highest number of salt marsh fungi have been recorded from Atlantic Ocean countries wherein the USA had the highest number of species recorded (232 taxa) followed by the UK (101 taxa), the Netherlands (74 taxa), and Argentina (51 taxa). China had the highest number of salt marsh fungi in the Pacific Ocean with 165 taxa reported, while in the Indian Ocean, India reported the highest taxa (16 taxa). Many salt marsh areas remain unexplored, especially those habitats in the Indian and Pacific Oceans areas that are hotspots of biodiversity and novel fungal taxa based on the exploration of various habitats.