Community assembly history is increasingly recognized as a fundamental determinant of community structure. However, little is known as to how assembly history may affect ecosystem functioning via its effect on community structure. Using wood-decaying fungi as a model system, we provide experimental evidence that large differences in ecosystem functioning can be caused by small differences in species immigration history during community assembly. Direct manipulation of early immigration history resulted in three-fold differences in fungal species richness and composition and, as a consequence, differences of the same magnitude in the rate of decomposition and carbon release from wood. These effects - which were attributable to the history-dependent outcome of competitive and facilitative interactions - were significant across a range of nitrogen availabilities observed in natural forests. Our results highlight the importance of considering assembly history in explaining ecosystem functioning.

Assembly history, or the order of species arrival, can have wide-ranging effects on species, communities and ecosystems. However, it remains unclear whether assembly history primarily affects individual species, with effects attenuating at the level of communities and ecosystems or, alternatively, has consistent effect sizes across increasing levels of ecological organisation. We address this question using a field-based manipulation of assembly history of wood-inhabiting fungi. The largest effect sizes were observed for the frequency of some individual species, and mean effect sizes were lower for community metrics of fungi immigrating from the regional species pool. There was little evidence, however, of attenuation in effect sizes at the ecosystem level (carbon, nitrogen, decomposition) in comparison to the species or community level. These results indicate that assembly history can have strong effects on ecosystem properties even under natural levels of environmental variability.

Both top-down (grazing) and bottom-up (resource availability) forces can determine the strength of priority effects, or the effects of species arrival history on the structure and function of ecological communities, but their combined influences remain unresolved. To test for such influences, we assembled experimental communities of wood-decomposing fungi using a factorial manipulation of fungivore (Folsomia candida) presence, nitrogen availability, and fungal assembly history. We found interactive effects of all three factors on fungal species composition and wood decomposition 1 year after the fungi were introduced. The strength of priority effects on community structure was affected primarily by nitrogen availability, whereas the strength of priority effects on decomposition rate was interactively regulated by nitrogen and fungivores. These results demonstrate that top-down and bottom-up forces jointly determine how strongly assembly history affects community structure and function.

Strains of Xanthomonas isolated in New Zealand from diseased endemic and introduced plants, investigated in a multi-locus sequence analysis (MLSA), were distributed primarily in two species. Strains from Dysoxylum, Hardenbergia, Liquidambar, Magnolia and Mahonia were members of Xanthomonas arboricola. Strains of Xanthomonas campestris pv. laureliae, X. campestris pv. eucalypti and strains from Aralia, Diospyros, Dysoxylum, Eriostemon, Eucalyptus, Metrosideros and Olea formed a population distinct from all known Xanthomonas spp. These latter strains have a unique fatty acid methyl ester profile and are considered to be members of a new Xanthomonas species, for which the name Xanthomonas dyei is proposed. Xanthomonas campestris pv. eucalypti and X. campestris pv. laureliae are considered to be pathovars of the new species and their reclassification as X. dyei pv. eucalypti and X. dyei pv. laureliae, respectively, is proposed. Strains previously identified as Pseudomonas syringae pv. dysoxyli from Dysoxylum spectabile, including the pathotype strain, were examined and found not to represent the pathogen originally described as P. dysoxyli. Other strains (proved to be pathogenic) from diseased D. spectabile, corresponding to the original description of P. dysoxyli, are members of X. dyei and the new combination X. dyei pv. dysoxyli is proposed. The geographic and evolutionary origins of X. dyei, apparently endemic to Australasia, and the adaptation of strains to the introduced host plants Aralia, Diospyros, Eriostemon, Metrosideros and Olea, are discussed. The origins of the X. arboricola strains isolated from Dysoxylum, Hardenbergia, Liquidambar, Magnolia and Mahonia pose a conundrum.

Fluorescent pseudomonads isolated from diseased tissue of a number of unrelated hosts, viz, chinese gooseberry, cauliflower, pumpkin, lupin, tomato, passionfruit, poppy, pea, and grape, are identified as Pseudomonas viridiflava (Burkholder 1930) Dowson 1939. The pathogenicity of Ps. viridiflava from these hosts is confirmed and characters of the isolates ilre compared.