Phylogenetic analysis of P_i-responsive transporters of <i>Petunia hybrida</i> compared to <i>Arabidopsis</i> transporters for nitrate, nitrite, and peptides.

<p>For the EST sequences listed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090841#pone-0090841-t001" target="_blank">Table 1</a> the full-length predicted cDNA sequences were derived from the petunia genome sequence. Predicted petunia protein sequences were compared with <i>Arabidopsis thaliana</i> transporters for nitrate and nitrite (NRT and Nitr1, respectively), and for peptide transporters (PTR). Note the clear separation of the nitrate transporter subfamilies NRT1 and NRT2. The NRT1 family also comprises the nitrite transporter AtNitr1 and several peptide transporters, of which only two are represented (AtPTR2 and AtPTR5). Petunia has two very closely homologous representatives of the high affinity nitrate transporter family NRT2 (cn8666 and cn7864). In addition, there is a putative nitrite transporter (corresponding to the EST sequences CL1918 and cn5943), and two additional members of the low affinity NRT1 family. Genes boxed in green were analyzed by qPCR (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090841#pone-0090841-g008" target="_blank">Figure 8</a>). Cn8665, which is almost identical to cn8666, and CL5245, which is predicted to encode a nitrogen limitation adaptation gene (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090841#pone-0090841-t001" target="_blank">Table 1</a>), were omitted from phylogenetic analysis.</p

<i>R. irregularis</i> increases nutrient content of plants supplied with water or with nutrient solution.

<p>Nutrient levels in leaves were determined 36 days after inoculation in the plants shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090841#pone-0090841-g003" target="_blank">Figure 3</a>. Values are the mean of three biological replicates. Error bars represent standard deviations. Asterisks indicate significant differences between mycorrhizal roots (black columns) and non-mycorrhizal controls (white columns). (<b>a</b>) Plants were fertilized with basic nutrient solution. Values are expressed relative to the non-mycorrhizal fertilized controls that were set to 100% for each nutrient. (<b>b</b>) As in (a), but without nutrient solution. Values are expressed relative to the non-colonized water-treated controls that were set to 100% for each nutrient.</p

Shoot weight, shoot/root ratio and N/P ratio as indicators of nutritional status.

<p>Treatments were as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090841#pone-0090841-g003" target="_blank">Figure 3</a>, shown are the values of the final time point (48 days after inoculation). Columns represent the average of three biological replicates, error bars represent standard deviations. Asterisks indicate significant differences between mycorrhizal and non-mycorrhizal plants (white vs. black columns), crosses indicate significant differences between the non-mycorrhizal nutrient treatments vs. the non-mycorrhizal water treatment (i.e. between the different white columns). (a) Shoot weight of plants grown with <i>R. irregularis</i> (black column) or without (white columns) under different nutritional conditions. (b) Shoot/root ratio of plants inoculated with <i>R. irregularis</i> (black columns) or without (white columns) under various nutritional conditions. A ratio of 3.5–4 indicates that plants are well supplied with mineral nutrients, whereas a ratio around 2 indicates that plants are starved and allocate relatively large amounts of resources to the root system to compensate nutritional deficits. (c) N/P ratio of the same plants as in (a),(b). In the absence of exogenous P_i supply, mycorrhizal plants (black columns) exhibited lower N/P ratios than non-mycorrhizal controls, reflecting increased mycorrhizal P_i supply. Administration of 5 mM KH₂PO₄ reduced N/P ratio even stronger than AM, in particular if only P_i was supplied.</p

Exogenous phosphate and nitrate inhibit root colonization by <i>Rhizophagus irregularis</i>.

<p>Plants inoculated with <i>Rhizophagus irregularis</i> were watered with the basic nutrient solution, additionally supplemented with the indicated nutrient concentrations. The first column to the left in each graph corresponds to the concentration in the basic nutrient solution, except for KH₂PO₄ (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090841#pone.0090841.s004" target="_blank">Table S2</a>); the other columns represent elevated nutrient levels as indicated. Columns represent the average of four replicate plants with standard deviations.</p

Inhibition of AM colonization by exogenous phosphate depends on the supply with other nutrients.

<p>KH₂PO₄ was applied to inoculated plants at the indicated concentrations either with basic nutrient solution (black columns) or alone (white columns). Additional treatments involved the application of KH₂PO₄ with only micronutrients (light grey) or only macronutrients (dark grey), respectively. Columns represent the average of four replicate plants with standard deviations. Asterisks indicate significant differences between phosphate alone (white bars) and phosphate with micronutrients (light grey bars), respectively, vs. the treatment with a combination of P_i and basic nutrient solution (black bars).</p

Correction: Phosphorus and Nitrogen Regulate Arbuscular Mycorrhizal Symbiosis in <i>Petunia hybrida</i>

<p>Correction: Phosphorus and Nitrogen Regulate Arbuscular Mycorrhizal Symbiosis in <i>Petunia hybrida</i></p

Withdrawal of individual nutrients interferes with the inhibitory effect of P_i.

<p>Effects of withdrawal of individual nutrients from the basic nutrient solution applied together with 5₂PO₄. Omitted nutrients were replaced by other nutrients to maintain osmotic relationships. The strong inhibitory effect of P_i (P) was reduced particularly by removal of nitrate (P-N), but also to a lesser extent by removal of S, K, Ca, and Fe. The control treatment (c) represents fertilization with low P_i levels (0.03 mM). Columns represent the average of six biological replicates, error bars represent the standard deviations. Asterisks indicate significant differences between the treatments lacking individual nutrients and the treatment with basic nutrient solution and high P_i.</p

Presentation_1.PDF

<p>Application of nitrogen (N) fertilizers, predominantly as urea, is a major source of reactive N in the environment, with wide ranging effects including increased greenhouse gas accumulation in the atmosphere and aquatic eutrophication. The soil microbial community is the principal driver of soil N cycling; thus, improved understanding of microbial community responses to urea addition has widespread implications. We used next-generation amplicon sequencing of the 16S rRNA gene to characterize bacterial and archaeal communities in eight contrasting agricultural soil types amended with 0, 100, or 500 μg N g^-1 of urea and incubated for 21 days. We hypothesized that urea amendment would have common, direct effects on the abundance and diversity of members of the microbial community associated with nitrification, across all soils, and would further affect the broader heterotrophic community resulting in decreased diversity and variation in abundances of specific taxa. Significant (P < 0.001) differences in bacterial community diversity and composition were observed by site, but amendment with only the greatest urea concentration significantly decreased Shannon indices. Expansion in the abundances of members of the families Microbacteriaceae, Chitinophagaceae, Comamonadaceae, Xanthomonadaceae, and Nitrosomonadaceae were also consistently observed among all soils (linear discriminant analysis score ≥ 3.0). Analysis of nitrifier genera revealed diverse, soil-specific distributions of oligotypes (strains), but few were correlated with nitrification gene abundances that were reported in a previous study. Our results suggest that the majority of the bacterial and archaeal community are likely unassociated with N cycling, but are significantly negatively impacted by urea application. Furthermore, these results reveal that amendment with high concentrations of urea may reduce nitrifier diversity, favoring specific strains, specifically those within the nitrifying genera Nitrobacter, Nitrospira, and Nitrosospira, that may play significant roles related to N cycling in soils receiving intensive urea inputs.</p