Search

At the Harvard Forest, Petersham, MA, the impact of 20 years of annual ammonium nitrate application to the mixed hardwood stand on soil bacterial communities was studied using 16S r RNA genes pyrosequencing. Amplification of 16 S r RNA genes was done using DNA extracted from 30 soil samples (three treatments × two horizons × five subplots) collected from untreated (control), low N-amended (50 kg ha−1 year−1) and high N-amended (150 kg ha−1 year−1) plots. A total of 1.3 million sequences were processed using qiime. Although Acidobacteria represented the most abundant phylum based on the number of sequences, Proteobacteria were the most diverse in terms of operational taxonomic units ( OTUs). Uni Frac analyses revealed that the bacterial communities differed significantly among soil horizons and treatments. Microsite variability among the five subplots was also evident. Nonmetric multidimensional scaling ordination of normalized OTU data followed by permutational manova further confirmed these observations. Richness indicators and indicator species analyses revealed higher bacterial diversity associated with N amendment. Differences in bacterial diversity and community composition associated with the N treatments were also observed at lower phylogenetic levels. Only 28-35% of the 6 936 total OTUs identified were common to three treatments, while the rest were specific to one treatment or common to two. [ABSTRACT FROM AUTHOR]

Polyamines (putrescine, spermidine, and spermine) are low molecular weight, open-chained, organic polycations which are found in all organisms and have been linked with stress responses in plants. The objectives of our study were to investigate the effects of chronic N additions to pine and hardwood stands at Harvard Forest, Petersham, MA on foliar polyamine and inorganic ion contents as well as soil and soil solution chemistry. Four treatment plots were established within eachstand in 1988: control, low N (50 kg N ha-1 yr-1 as NH4NO3), low N + sulfur (74 kg S ha-1 yr-1 as Na2SO4), and high N (150 kg N ha-1 yr-1 as NH4NO3). All samples were analyzed for inorganic elements; foliage samples were also analyzed for polyamines and total N. In the pine stand putrescine and total N levels in the foliage were significantly higher for all N treatments as compared to the control plot. Total N content was positively correlated with polyamines in the needles (P ≤ 0.05). Both putrescine and N contents were also negatively correlated with most exchangeable cations and total elements in organic soil horizons and positively correlated with Ca and Mg in the soil solution (P≤ 0.05). In the hardwood stand, putrescine and total N levels in the foliage were significantly higher for the high N treatment only ascompared to the control plot. Here also, total foliar N content was positively correlated with polyamines (P ≤ 0.05). Unlike the case with the pine stand, in the hardwood stand foliar polyamines and N were significantly and negatively correlated with foliar total Ca, Mg, and Mn (P ≤ 0.05). Additional significant (P ≤ 0.05) relationshipsin hardwoods included: negative correlations between foliar polyamines and N content to exchangeable K and P and total P in the organic soil horizon; and positive correlations between foliar polyamines and N co [ABSTRACT FROM AUTHOR]