Plant–microbe interactions play crucial roles in species invasions but are rarely investigated at the intraspecific level. Here, we study these interactions in three lineages of a globally distributed plant, Phragmites australis. We use field surveys and a common garden experiment to analyze bacterial communities in the rhizosphere of P. australis stands from native, introduced, and Gulf lineages to determine lineage-specific controls on rhizosphere bacteria. We show that within-lineage bacterial communities are similar, but are distinct among lineages, which is consistent with our results in a complementary common garden experiment. Introduced P. australis rhizosphere bacterial communities have lower abundances of pathways involved in antimicrobial biosynthesis and degradation, suggesting a lower exposure to enemy attack than native and Gulf lineages. However, lineage and not rhizosphere bacterial communities dictate individual plant growth in the common garden experiment. We conclude that lineage is crucial for determination of both rhizosphere bacterial communities and plant fitness.

Citation: Meyerson, L. A., P. Py sek, M. Lu canov a, S. Wigginton, C.-T. Tran, and J. T. Cronin. 2020. Plant genome size influences stress tolerance of invasive and native plants via plasticity. Ecosphere 11(5):Abstract. Plant genome size influences the functional relationships between cellular and whole-plant physiology, but we know little about its importance to plant tolerance of environmental stressors and how it contributes to range limits and invasion success. We used native and invasive lineages of a wetland plant to provide the first experimental test of the Large Genome Constraint Hypothesis (LGCH)-that plants with large genomes are less tolerant of environmental stress and less plastic under stress gradients than plants with small genomes. We predicted that populations with larger genomes would have a lower tolerance and less plasticity to a stress gradient than populations with smaller genomes. In replicated experiments in northern and southern climates in the United States, we subjected plants from 35 populations varying in genome size and lineage to two salinity treatments. We measured traits associated with growth, physiology, nutrition, defense, and plasticity. Using AICc model selection, we found all plant traits, except stomatal conductance, were influenced by environmental stressors and genome size. Increasing salinity was stressful to plants and affected most plant traits. Notably, biomass in the high-salinity treatment was 3.0 and 4.9 times lower for the invasive and native lineages, respectively. Plants in the warmer southern greenhouse had higher biomass, stomate density, stomatal conductance, leaf toughness, and lower aboveground percentage of N and total phenolics than in the northern greenhouse. Moreover, responses to the salinity gradient were generally much stronger in the southern than northern greenhouse. Aboveground biomass increased significantly with genome size for the invasive lineage (43% across genome sizes) but not for the native. For 8 of 20 lineage trait comparisons, greenhouse location 9 genome size interaction was also significant. Interestingly, the slope of the relationship between genome size and trait means was in the opposite direction for some traits between the gardens providing mixed support for LGCH. Finally, for 30% of the comparisons, plasticity was significantly related to genome size-for some plant traits, the relationship was positive, and in others, it was negative. Overall, we found mixed support for LGCH and for the first time found that genome size is associated with plasticity, a trait widely regarded as important to invasion success.

Advanced N‐removal onsite wastewater treatment systems (OWTS) rely on nitrification and denitrification to remove N from wastewater. Despite their use to reduce N contamination, we know little about microbial communities controlling N removal in these systems. We used quantitative polymerase chain reaction and high‐throughput sequencing targeting nitrous oxide reductase (nosZ) and bacterial ammonia monooxygenase (amoA) to determine the size, structure, and composition of communities containing these genes. We analyzed water samples from three advanced N‐removal technologies in 38 systems in five towns in Rhode Island in August 2016, and in nine systems from one town in June, August, and October 2016. Abundance of nosZ ranged from 9.1 × 103 to 9 × 108 copies L−1 and differed among technologies and over time, whereas bacterial amoA abundance ranged from 0 to 1.9 × 107 copies L−1 and was not different among technologies or over time. Richness and diversity of nosZ—but not amoA—differed over time, with median Shannon diversity indices ranging from 2.61 in October to 4.53 in August. We observed weak community similarity patterns driven by geography and technology in nosZ. The most abundant nosZ‐ and amoA‐containing bacteria were associated with water distribution and municipal wastewater treatment plants, such as Nitrosomonas and Thauera species. Our results show that nosZ communities in N‐removal OWTS technologies differ slightly in terms of size and diversity as a function of time, but not geography, whereas amoA communities are similar across time, technology, and geography. Furthermore, community composition appears to be stable across technologies, geography, and time for amoA. Core Ideas We describe N‐cycling bacterial communities in advanced N‐removal septic systems. Geographic factors are weak drivers of community composition in nosZ. Technology design is a weak driver of community composition in nosZ. Community composition of amoA is similar across time, space, and among technologies Time drives differences in nosZ—but not amoA—diversity and abundance.

Biological nitrogen removal (BNR) systems are increasingly used in the United States in both centralized wastewater treatment plants (WWTPs) and decentralized advanced onsite wastewater treatment systems (OWTS) to reduce N discharged in wastewater effluent. However, the potential for BNR systems to be sources of nitrous oxide (N 2 O), a potent greenhouse gas, needs to be evaluated to assess their environmental impact. We quantified and compared N 2 O emissions from BNR systems at a WWTP (Field's Point, Providence, RI) and three types of advanced OWTS (Orenco Advantex AX 20, SeptiTech Series D, and Bio-Microbics MicroFAST) in nine Rhode Island residences (n = 3 per type) using cavity ring-down spectroscopy. We also used quantitative polymerase chain reaction to determine the abundance of genes from nitrifying (amoA) and denitrifying (nosZ) microorganisms that may be producing N 2 O in these systems. Nitrous oxide fluxes ranged from −4 ´ 10 −3 to 3 ´ 10 −1 mmol N 2 O m −2 s −1 and in general followed the order: centralized WWTP > Advantex > SeptiTech > FAST. In contrast, when N 2 O emissions were normalized by population served and area of treatment tanks, all systems had overlapping ranges. In general, the emissions of N 2 O accounted for a small fraction (<1%) of N removed. There was no significant relationship between the abundance of nosZ or amoA genes and N 2 O emissions. This preliminary analysis highlights the need to evaluate N 2 O emissions from wastewater systems as a wider range of technologies are adopted. A better understanding of the mechanisms of N 2 O emissions will also allow us to better manage systems to minimize emissions. Comparison of N 2 O Emissions and Gene Abundances between Wastewater Nitrogen Removal SystemsElizabeth Quinn Brannon,* Serena M. Moseman-Valtierra, Brittany V. Lancellotti, Sara K. Wigginton, Jose A. Amador, James C. McCaughey, and George W. Loomis H umans substantially modify global nitrogen (N) cycles by industrially fixing N for fertilizer and ultimately releasing reactive N back to the environment through various mechanisms, including wastewater treatment. The continued growth of the human population will lead to further increases in excess reactive N, increasing the need for N remediation (Galloway et al., 2003). In recent years, remediation has focused on upgrading centralized wastewater treatment plants (WWTPs) to include biological nitrogen removal (BNR). Since one in five US homes are serviced by conventional onsite wastewater treatment systems (OWTS) (USEPA, 2013) they can also be large sources of N (Zhu et al., 2008;USEPA, 2015). The use of OWTS can be advantageous relative to centralized WWTPs, as they recharge groundwater supplies, require less infrastructure, and have lower energy costs (USEPA, 2013). To ameliorate N inputs to the environment, conventional OWTS are also being upgraded to advanced OWTS that include BNR.Although BNR systems at WWTPs and OWTS vary in design, all employ nitrifying (conversion of ammonium to nitrate) and denitrifying (convers...