Bacteria are vital components of lake systems, driving a variety of biogeochemical cycles and ecosystem services. Bacterial communities have been shown to have a skewed distribution with a few abundant species and a large number of rare species. The contribution of environmental processes or geographic distance in structuring these components is uncertain. The discrete nature of lakes provides an ideal test case to investigate microbial biogeographical patterns. In the present study, we used 16S rRNA gene metabarcoding to examine the distribution patterns on local and regional scales of abundant and rare planktonic bacteria across 167 New Zealand lakes covering broad environmental gradients. Only a few amplicon sequence variants (ASVs) were abundant with a higher proportion of rare ASVs. The proportion of locally abundant ASVs was negatively correlated with the percentage of high productivity grassland in the catchment and positively with altitude. Regionally rare ASVs had a restricted distribution and were only found in one or a few lakes. In general, regionally abundant ASVs had higher occupancy rates, although there were some with restricted occupancy. Environmental processes made a higher contribution to structuring the regionally abundant community, while geographic distances were more important for regionally rare ASVs. A better understanding of the processes structuring the abundance and distribution of bacterial communities within lakes will assist in understand microbial biogeography and in predicting how these communities might shift with environmental change.

<p>Plant-plant productivity relationships within ecosystem and community ecology are contentiously debated in the literature due to the numerous factors involved making conclusions hard to draw and disentangle. There are several widely established and supported plant-plant productivity relationships. Increasing species richness can allow for greater niche complementarity, which in turn increases overall above and below ground productivity. Plants with different functional traits can differentially affect a plant community depending on the arrival time of the plant. These priority effects allow certain plants to outcompete others and persist in a community across different temporal scales. Plant species differ in their ability to interact with certain species of symbiotic partners in the soil (Arbuscular mycorrhizal fungi, AMF). This interaction generalism of a plant species indicates the ability of a plant to host many or few AMF species (generalist or specialist, respectively). However, there remains a limited understanding of plant-fungi relationships especially with respect to community productivity and the temporal effects of adding contrasting types of interaction generalism into an established community. The aim of this study was to determine the effects of the addition of an interaction specialist or generalist plant species into an established plant community on the overall community productivity. Three communities that differed in plant species richness were grown for 38 days at which point either a generalist or specialist was added. Community treatments were carried out in field soil, sterile soil and sterile soil reinoculated with viable field soil, separating the effects of plant niche-partitioning for plant-fungi interaction partners from the effects of niche-partitioning for other resources (e.g. soil nutrients). Community productivity was tested using different productivity measures; 1) carbon flux as the Net Ecosystem Exchange (NEE) of the community, 2) total above and below ground plant biomass, 3) neutral lipid fatty acid (NLFA) AMF biomarker, 16:1w5, extracted from total soil and total root mass to assess AMF biomass. It was difficult to disentangle the effects of species richness and interaction generalism on carbon flux in communities, with soil type clearly impacting these relationships. In all soil types, an increase in community plant richness had the greatest effect on carbon draw down and biomass productivity with respect to both plant and AMF biomass. In non-sterilised soil, interaction generalism, specifically the addition of a specialist alongside increased species richness corresponded to increased carbon drawdown. In the context of previous research, this study further highlighted the complexity of factors driving plant-plant-fungi relationships, but clearly identifies the positive role that species richness is having. Although the role of plant-fungi relationships in overall community productive remains unclear, this study provides a platform for future research to be undertaken.</p>

<p>Plant-plant productivity relationships within ecosystem and community ecology are contentiously debated in the literature due to the numerous factors involved making conclusions hard to draw and disentangle. There are several widely established and supported plant-plant productivity relationships. Increasing species richness can allow for greater niche complementarity, which in turn increases overall above and below ground productivity. Plants with different functional traits can differentially affect a plant community depending on the arrival time of the plant. These priority effects allow certain plants to outcompete others and persist in a community across different temporal scales. Plant species differ in their ability to interact with certain species of symbiotic partners in the soil (Arbuscular mycorrhizal fungi, AMF). This interaction generalism of a plant species indicates the ability of a plant to host many or few AMF species (generalist or specialist, respectively). However, there remains a limited understanding of plant-fungi relationships especially with respect to community productivity and the temporal effects of adding contrasting types of interaction generalism into an established community. The aim of this study was to determine the effects of the addition of an interaction specialist or generalist plant species into an established plant community on the overall community productivity. Three communities that differed in plant species richness were grown for 38 days at which point either a generalist or specialist was added. Community treatments were carried out in field soil, sterile soil and sterile soil reinoculated with viable field soil, separating the effects of plant niche-partitioning for plant-fungi interaction partners from the effects of niche-partitioning for other resources (e.g. soil nutrients). Community productivity was tested using different productivity measures; 1) carbon flux as the Net Ecosystem Exchange (NEE) of the community, 2) total above and below ground plant biomass, 3) neutral lipid fatty acid (NLFA) AMF biomarker, 16:1w5, extracted from total soil and total root mass to assess AMF biomass. It was difficult to disentangle the effects of species richness and interaction generalism on carbon flux in communities, with soil type clearly impacting these relationships. In all soil types, an increase in community plant richness had the greatest effect on carbon draw down and biomass productivity with respect to both plant and AMF biomass. In non-sterilised soil, interaction generalism, specifically the addition of a specialist alongside increased species richness corresponded to increased carbon drawdown. In the context of previous research, this study further highlighted the complexity of factors driving plant-plant-fungi relationships, but clearly identifies the positive role that species richness is having. Although the role of plant-fungi relationships in overall community productive remains unclear, this study provides a platform for future research to be undertaken.</p>