A method for experimental warming of developing tree seeds with a common garden demonstration of seedling responses.

BACKGROUND: Forest dieback driven by rapid climate warming threatens ecosystems worldwide. The health of forested ecosystems depends on how tree species respond to warming during all life history stages. While it is known that seed development is temperature-sensitive, little is known about possible effects of climate warming on seed development and subsequent seedling performance. Exposure of seeds to high air temperatures may influence subsequent seedling performance negatively, though conversely, warming during seed development may aid acclimation of seedlings to subsequent thermal stress. Technical challenges associated with in-situ warming of developing tree seeds limit understanding of how tree species may respond to seed development in a warmer climate. RESULTS: We developed and validated a simple method for passively warming seeds as they develop in tree canopies to enable controlled study of climate warming on seedling performance. We quantified thermal effects of the cone-warming method across individual pine trees and stands by measuring the air temperature surrounding seed cones using thermal loggers and the temperature of seed cone tissue using thermocouples. We then investigated seedling phenotypes in relation to the warming method through a common garden study. We assessed seedling morphology, physiology, and mycorrhizal nodulation in response to experimental cone-warming in 20 seed-source-tree canopies on the San Francisco Peaks in northern Arizona, USA. The warming method increased air temperature surrounding developing seed cones by 2.1 °C, a plausible increase in mean air temperature by 2050 under current climate projections. Notable effect sizes of cone-warming were detected for seedling root length, shoot length, and diameter at root collar using Cohen's Local f2. Root length was affected most by cone-warming, but effect sizes of cone-warming on root length and diameter at root collar became negligible after the first year of growth. Cone-warming had small but significant effects on mycorrhizal fungal richness and seedling multispectral near-infrared indices indicative of plant health. CONCLUSIONS: The method was shown to reliably elevate the temperature surrounding seed cones and thereby facilitate experimental in-situ climate warming research on forest trees. The method was furthermore shown to influence plant traits that may affect seedling performance under climate warming.

Naphthalene degradation and incorporation of naphthalene-derived carbon into biomass by the thermophile Bacillus thermoleovorans.

The thermophilic aerobic bacterium Bacillus thermoleovorans Hamburg 2 grows at 60 degrees C on naphthalene as the sole source of carbon and energy. In batch cultures, an effective substrate degradation was observed. The carbon balance, including naphthalene, metabolites, biomass, and CO(2), was determined by the application of [1-(13)C]naphthalene. The incorporation of naphthalene-derived carbon into the bulk biomass as well as into specified biomass fractions such as fatty acids and amino acids was confirmed by coupled gas chromatography-mass spectrometry (GC-MS) and isotope analyses. Metabolites were characterized by GC-MS; the established structures allow tracing the degradation pathway under thermophilic conditions. Apart from typical metabolites of naphthalene degradation known from mesophiles, intermediates such as 2, 3-dihydroxynaphthalene, 2-carboxycinnamic acid, and phthalic and benzoic acid were identified for the pathway of this bacterium. These compounds indicate that naphthalene degradation by the thermophilic B. thermoleovorans differs from the known pathways found for mesophilic bacteria.

Tracing the transformation of labelled [1-13C]phenanthrene in a soil bioreactor.

[1-(13)C]-labelled phenanthrene was incubated in a closed bioreactor to study the flux and biotransformation of polycyclic aromatic hydrocarbon (PAH) in contaminated soils on a bulk and molecular level. The degradation of extractable phenanthrene was observed by GC-MS measurements and the mineralisation was monitored by (13)CO(2) production. The transformation of the (13)C-label into non-extractable soil-bound residues was determined by carbon isotopic measurements. With these data we were able to calculate a carbon budget of the (13)C-label. Moreover, the chemical structure of non-extractable bound residues was characterised by applying selective chemical degradation reactions to cleave xenobiotic subunits from the macromolecular organic soil matrix. The obtained low molecular weight products yielded (13)C-labelled compounds which were identified using IRM (isotope ratio monitoring)-GC-MS and structurally characterised with GC-MS. Most of the (13)C-labelled products obtained by chemical degradation of non-extractable bound residues are well-known metabolites of phenanthrene. Thus, metabolites of [1-(13)C]phenanthrene formed during biodegradation appear to be reactive components which are subsequently involved in the bound residue formation. Hydrolysable amino acids of the soil residues were significantly labelled with (13)C as confirmed by IRM-GC-MS measurements. Therefore, phenanthrene-derived carbon was transformed by anabolic microbial processes into typical biologically derived compounds. These substances are likely to be incorporated into humic-like material after cell death.