Long-term soil warming decreases microbial phosphorus utilization by increasing abiotic phosphorus sorption and phosphorus losses

Phosphorus (P) is an essential and often limiting element that could play a crucial role in terrestrial ecosystem responses to climate warming. However, it has yet remained unclear how different P cycling processes are affected by warming. Here we investigate the response of soil P pools and P cycling processes in a mountain forest after 14 years of soil warming (+4 °C). Long-term warming decreased soil total P pools, likely due to higher outputs of P from soils by increasing net plant P uptake and downward transportation of colloidal and particulate P. Warming increased the sorption strength to more recalcitrant soil P fractions (absorbed to iron oxyhydroxides and clays), thereby further reducing bioavailable P in soil solution. As a response, soil microbes enhanced the production of acid phosphatase, though this was not sufficient to avoid decreases of soil bioavailable P and microbial biomass P (and biotic phosphate immobilization). This study therefore highlights how long-term soil warming triggers changes in biotic and abiotic soil P pools and processes, which can potentially aggravate the P constraints of the trees and soil microbes and thereby negatively affect the C sequestration potential of these forests

Community profiling and gene expression of fungal assimilatory nitrate reductases in agricultural soil

Although fungi contribute significantly to the microbial biomass in terrestrial ecosystems, little is known about their contribution to biogeochemical nitrogen cycles. Agricultural soils usually contain comparably high amounts of inorganic nitrogen, mainly in the form of nitrate. Many studies focused on bacterial and archaeal turnover of nitrate by nitrification, denitrification and assimilation, whereas the fungal role remained largely neglected. To enable research on the fungal contribution to the biogeochemical nitrogen cycle tools for monitoring the presence and expression of fungal assimilatory nitrate reductase genes were developed. To the ∼100 currently available fungal full-length gene sequences, another 109 partial sequences were added by amplification from individual culture isolates, representing all major orders occurring in agricultural soils. The extended database led to the discovery of new horizontal gene transfer events within the fungal kingdom. The newly developed PCR primers were used to study gene pools and gene expression of fungal nitrate reductases in agricultural soils. The availability of the extended database allowed affiliation of many sequences to known species, genera or families. Energy supply by a carbon source seems to be the major regulator of nitrate reductase gene expression for fungi in agricultural soils, which is in good agreement with the high energy demand of complete reduction of nitrate to ammonium

Stable ¹⁵N enrichment of aphids correlates with phloem-feeding duration.

<p>The calculated values of the µg excess ¹⁵N uptake of <i>R. padi</i> aphids (N = 30) are plotted against the time that aphids spent in defined EPG phases on barley plants. Either the phloem-feeding phase E2 (A) or the sum of defined non-feeding phases are plotted (B). The non-feeding time includes the time aphids spent cell puncturing (C), had derailed stylet mechanics (F), were xylem drinking (G) and saliva injecting (E1). Pearson's product moment correlation between ¹⁵N uptake and phloem-feeding A, t = 8.95, cor = 0.86, p<0.001 and ¹⁵N uptake and non-feeding B, t = −2.03, cor = −0.36, p = 0.05 (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0083085#pone-0083085-t002" target="_blank">Table 2</a>). The feeding experiment was conducted for up to 24 hours and the feeding behaviour was recorded with EPG. The µg excess ¹⁵N uptake of control aphids was zero.</p

A cost-effective high-throughput microcosm system for studying nitrogen dynamics at the plant-microbe-soil interface. Plant Soil 317

Abstract In the present study a new microcosm system was evaluated for its suitability to investigate nitrogen dynamics between soils, plants and microbes. Five different agricultural soils were homogenized and transferred in the test tubes, and kept under controlled conditions in a climate chamber for 4weeks. Soils differed clearly in nitrogen pools and microbial population structures but less in their activities. Bacterial and fungal community compositions and soil properties, except gross N transformation rates, remained stable and reproducible during the test period in all soils

High ¹⁵N enrichment is characterised by few feeding interruptions.

<p>The µg excess ¹⁵N uptake of individual <i>R. padi</i> aphids is plotted against the number of feeding interruptions. Green stars (N = 21), experimental time up to 24 hours. Orange stars (N = 8), experimental time from 4 to 6 hours. A zero value of no feeding behaviour is excluded in the plot and the statistical analyses. Pearson's product moment correlation for 20 hours, t₍₂₀₎ = −3.02, cor = −0.56, p = 0.007; for 4 to 6 hours, t₍₆₎ = −0.73, cor = −0.28, p = 0.495.</p