In this paper we propose and provide evidence for a mechanism, oxidative nitrogen scavenging (ONS), whereby seedlings of some grass species may extract nitrogen from symbiotic diazotrophic bacteria through oxidation by plant-secreted reactive oxygen species (ROS). Experiments on this proposed mechanism employ tall fescue (Festuca arundinaceae) seedlings to elucidate features of the oxidative mechanism. We employed 15N2 gas assimilation experiments to demonstrate nitrogen fixation, direct microscopic visualization of bacteria on seedling surfaces to visualize the bacterial oxidation process, reactive oxygen probes to test for the presence of H2O2 and cultural experiments to assess conditions under which H2O2 is secreted by seedlings. We also made surveys of the seedlings of several grass species to assess the distribution of the phenomenon of microbial oxidation in the Poaceae. Key elements of the proposed mechanism for nitrogen acquisition in seedlings include: 1) diazotrophic bacteria are vectored on or within seeds; 2) at seed germination bacteria colonize seedling roots and shoots; 3) seedling tissues secrete ROS onto bacteria; 4) bacterial cell walls, membranes, nucleic acids, proteins and other biological molecules are oxidized; 5) nitrates and/or smaller fragments of organic nitrogen-containing molecules resulting from oxidation may be absorbed by seedling tissues and larger peptide fragments may be further processed by secreted or cell wall plant proteases until they are small enough for transport into cells. Hydrogen peroxide secretion from seedling roots and bacterial oxidation was observed in several species in subfamily Pooideae where seeds possessed adherent paleas and lemmas, but was not seen in grasses that lacked this feature or long-cultivated crop species.

This article describes a process (termed ‘oxidative nitrogen scavenging’) where grasses scavenge organic nitrogen from microbes on and around roots. The authors propose a diurnal process where during the day roots produce and release hydrogen peroxide that oxidizes microbial exoenzymes around roots; at night hydrogen peroxide production ceases, then roots and symbiotic rhizobacteria secrete proteases that degrade the oxidized proteins to form peptides that are absorbed by roots. The existence of a mechanism for organic nitrogen scavenging in grasses emphasizes the nutritional importance of non-pathogenic microbes that associate with roots. Future applications of this process could result in new methods for the cultivation of crop plants.

Big-bracted dogwoods (Cornus sp.) are well-known plants in North America and eastern Asia where they occur as wild, generally spring-flowering understory trees. They are also popular ornamental landscape plants, and many economically important cultivars are propagated and sold across North America, Europe, and Asia. Starting in the late 1960s, Elwin Orton of Rutgers University in New Jersey (USA) utilized three geographically disjunct species of dogwoods, C. florida (eastern North America), C. nuttallii (western North America), and C. kousa (East Asia), in an extensive interspecific hybridization program. He was successful in developing the first-ever interspecific F 1 hybrids of these species, several of which have become staple items in the ornamental nursery trade due to their enhanced ornamental qualities and resistance to diseases. The original F 1 plants are still alive at Rutgers University. While they have been available for decades in horticultural commerce, the interspecific hybrid crosses were never formally described and their scientific hybrid names were never published. For the C. kousa × C. florida hybrids, the name Cornus 'rutgersensis' has been used on occasion in the horticultural trade, but without proper citation and description. Here, it is formally named Cornus × rutgersensis Mattera, T. Molnar, & Struwe, hybr. nov. For the C. kousa × C. nuttallii hybrids, no previous name has been used, and it is hereby named Cornus × elwinortonii Mattera, T. Molnar, & Struwe, hybr. nov. The need for providing scientific names for commonly used horticultural hybrids is discussed. Holotype material for both hybrid names was collected from the original F 1 hybrids for full documentation, typification, and description. The comparative intermediate development of leaves, inflorescence structures, and fruit types of the hybrids and their parents is discussed and illustrated. Etymology, phenology, and cultivation aspects of these hybrids and their cultivars including backcrosses to C. kousa are also presented. RESEARCH ARTICLE Launched to accelerate biodiversity research A peer-reviewed open-access journalRobert Mattera et al. / PhytoKeys 55: 93-111 (2015) 94

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