Shifting abundances of communities associated with nitrogen cycling in soils promoted by sugarcane harvest systems

Sugarcane cultivation supports Brazil as one of the largest world sugar and ethanol producer. In order to understand the impact of changing sugarcane harvest from manual to mechanized harvest, we studied the effect of machinery traffic on soil and consequently soil compaction upon soil microbial communities involved in nitrogen cycling. The impact of sugarcane harvest was dependent on soil depth and texture. At deeper soil layers, mechanized harvesting increases the abundance of nitrogen fixers and denitrifying communities (specifically nosZ clade I and II) while manual harvesting increases the abundance of ammonia oxidizers (specifically AOA) and increases denitrifying communities (nosZ clade I and II) on top and at intermediate depth. The effect of change on the harvest system is more evident on sandy soil than on clay soil, where soil indicators of compaction (bulk density and penetration resistance) were negatively correlated with soil microorganisms associated with the nitrogen cycle. Our results point to connections between soil compaction and N transformations in sugarcane fields, besides naming biological variables to be used as proxies for alterations in soil structure.     

Effects of nitrogen limitation on water relations of jack pine (Pinus banksiana Lamb.) seedlings

The water relations of shoots of young jack pine (Pinus banksiana Lamb.) seedlings were examined 6 and 15 weeks after the initiation of four different dynamic nitrogen (N) treatments using a pressure-volume analysis. The N treatments produced a wide range of needle N concentrations from 12 to 32 mg g^?1 dry mass and a 10-fold difference in total dry mass at 15 weeks. Osmotic potential at full turgor did not change over the range of needle N concentrations observed. Osmotic potential at turgor-loss point, however, declined as N concentrations decreased, indicating an increased ability of N-deficient jack pine plants to maintain turgor. The increase could be attributed largely to an increase in cell wall elasticity, suggesting that elasticity changes may be a common, significant adaptation of plants to environmental stresses. Dry mass per unit saturated water almost doubled as needle N level dropped from 32 to 12 mg g^?1 and was inversely correlated to the bulk modulus of elasticity. This suggests that cell wall elasticity is determined more by the nature of its cross-linking matrix than by the total amount of cell wall material present. Developmental change was evident in the response of some water relation variables to N limitation.     

Response of Picea rubens seedlings to intermittent mist varying in acidity, and in concentrations of sulfur-, and nitrogen-containing pollutants

Two-year-old red spruce seedlings ( Picea rubens Sarg .) growing in. field chambers were repeatedly exposed to acidic mist with a factorial combination of 3 fluctuating levels of acidity: median pH values of 3.0 (range of 2.5 to 3.5), 3.5 (range of 3.0 to 4.0), and 4.0 (range of 3.5 to 4.5). and 3 ion compositions: sulfate. nitrate and ammonium, and a combination of all 3 ions. The experiment was performed during the growing season over a period of 3.5 months. Mist exposures were intermittent with 5 wet-dry cycles for each 16-h overnight exposure period, Foliar necrosis occurred on seedlings treated with the most acidic mist and was most severe when the mist contained sulfate. At a median pH of 3.5, a value close to that of cloud water occurring in the eastern United States, injury developed with sulfuric acid mist, but not. when the mist contained nitric acid. The combination of high acidity and sulfate significantly decreased volume of aboveground tissues, while high acidity and nitrate increased volume. Root and needle dry weights were not affected. However, high acidity of mist was associated with increased leader shoot length. These results indicate, that there is a risk of foliar injury and changes in growth of red spruce with cloud water at a median acidity of pH 3.5 or below, especially when there are high concentrations of sulfate and low concentrations of nitrate.     

Evaluation of automated analysis of 15N and total N in plant material and soil

Simultaneous determination of ¹⁵N and total N using an automated nitrogen analyser interfaced to a continuous-flow isotope ratio mass spectrometer (ANA-MS method) was evaluated. The coefficient of variation (CV) of repeated analyses of homogeneous standards and samples at natural abundance was lower than 0.1%. The CV of repeated analyses of ¹⁵N-labelled plant material and soil samples varied between 0.3% and 1.1%. The reproductibility of repeated total N analyses using the automated method was comparable to results obtained with a semi-micro Kjeldahl procedure. However, the automated method gave results which were 3% to 5% higher than those obtained with the Kjeldahl procedure. Since only small samples can be analysed, careful sample homogenization and fine grinding are very important. Evaluation of a diffusion method for preparing nitrate and ammonium in solution for automated ¹⁵N analysis showed that the recovery of inorganic N in the NH₃ trap was lower when the N was diffused from water than from 2 M KCl. The results also indicated that different proportions of the NO₃ ^- and the NH₄ ⁺ in aqueous solution were recovered in the trap after combined diffusion. The method is most suited for diffusing either NO₃ ^- or NH₄ ⁺ alone, but can be used for combined diffusion of the two ions.     

Dinitrogen fixation and infection of grass leaves byPseudomonas rubrisubalbicans andHerbaspirillum seropedicae

Bacteria causing mottled stripe disease in sugar cane, known asPseudomonas rubrisubalbicans, were shown to be able to fix molecular N₂ and to grow on it. The root associated diazotroph known asHerbaspirillum seropedicae, after artificial inoculation caused mottled stripe disease symptoms on sorghum and Napier grass but not on sugar cane. Both bacteria could be reisolated from leaves even 60 days after. Sugar cane leaves contained large numbers of these bacteria even in the uninoculated controls. Additional physiological characteristics of six strains ofP. rubrisubalbicans were compared with those of twoH. seropedicae strains and were shown to be very similar.     

Evidence for increases in vegetation species richness across UK Environmental Change Network sites linked to changes in air pollution and weather patterns

We analysed trends in vegetation monitored at regular intervals over the past two decades (1993–2012) at the twelve terrestrial Environmental Change Network (ECN) sites. We sought to determine the extent to which flora had changed and link any such changes to potential environmental drivers. We observed significant increases in species richness, both at a whole network level, and when data were analysed within Broad Habitat groupings representing the open uplands, open lowlands and woodlands. We also found comparable increases in an indicator of vegetation response to soil pH, Ellenberg R. Species characteristic of less acid soils tended to show more consistent increases in frequency across sites relative to species with a known tolerance for strongly acidic soils. These changes are, therefore, broadly consistent with a response to increases in soil solution pH observed for the majority of ECN sites that, in turn, are likely to be driven by large reductions in acid deposition in recent decades. Increases in species richness in certain habitat groupings could also be linked to increased soil moisture availability in drier lowland sites that are likely to have been influenced by a trend towards wetter summers in recent years, and possibly also to a reduction in soil nitrogen availability in some upland locations. Changes in site management are also likely to have influenced trends at certain sites, particularly with respect to agricultural practices. Our results are therefore indicative of widescale responses to major regional-scale changes in air pollution and recent weather patterns, modified by local management effects. The relative consistency of management of ECN sites over time is atypical of much of the wider countryside and it is therefore not appropriate to scale up these observations to infer national scale trends. Nevertheless the results provide an important insight into processes that may be operating nationally. It will now be necessary to test for the ubiquity of these changes using appropriate broader spatial scale survey data.     

First report on egg deposition and egg morphology of the endangered endemic Romanian perch

The surface of the whitish translucent egg of Romanichthys valsanicola is sculptured in an irregular honeycomb–like pattern. The micropyle consists only of a type I micropylar channel.