A time series phospholipid fatty acid (PLFA) 13 C-labeling study was undertaken to determine methanotrophic taxon, calculate methanotrophic biomass, and assess carbon recycling in an upland brown earth soil from Bronydd Mawr (Wales, United Kingdom). Laboratory incubations of soils were performed at ambient CH 4 concentrations using synthetic air containing 2 parts per million of volume of 13 CH 4 . Flowthrough chambers maintained a stable CH 4 concentration throughout the 11-week incubation. Soils were analyzed at weekly intervals by gas chromatography (GC), GC-mass spectrometry, and GC-combustion-isotope ratio mass spectrometry to identify and quantify individual PLFAs and trace the incorporation of 13 C label into the microbial biomass. Incorporation of the 13 C label was seen throughout the experiment, with the rate of incorporation decreasing after 9 weeks. The ␦ 13 C values of individual PLFAs showed that 13 C label was incorporated into different components to various extents and at various rates, reflecting the diversity of PLFA sources. Quantitative assessments of 13 C-labeled PLFAs showed that the methanotrophic population was of constant structure throughout the experiment. The dominant 13 C-labeled PLFA was 18:17c, with 16:15 present at lower abundance, suggesting the presence of novel type II methanotrophs. The biomass of methane-oxidizing bacteria at optimum labeling was estimated to be about 7.2 ؋ 10 6 cells g ؊1 of soil (dry weight). While recycling of 13 C label from the methanotrophic biomass must occur, it is a slower process than initial 13 CH 4 incorporation, with only about 5 to 10% of 13 C-labeled PLFAs reflecting this process. Thus, 13 C-labeled PLFA distributions determined at any time point during 13 CH 4 incubation can be used for chemotaxonomic assessments, although extended incubations are required to achieve optimum 13 C labeling for methanotrophic biomass determinations.

Exposure of mineral soils to atmospherically relevant concentrations of (13)CH(4) (2 ppmv) followed by (13)C-phospholipid fatty acid stable isotope probing allows assessment of the high-affinity methanotrophic bacterial sink in hitherto unattainable detail. Utilizing this approach, inorganic fertilizer-treated soils from a long-term agricultural experiment were shown to display dramatic reduction, by > 70%, of the methanotrophic bacterial cell numbers. Reduction in the methane sink capacity of the soils was slightly lower than the directly observed reduction in methanotrophic bacterial counts, indicating that the inhibitory effects on high-affinity methanotrophic bacteria are not fully expressed through CH(4) oxidation rates. The results emphasize the need to rigorously assess commonly applied agricultural practices with respect to their unseen negative impacts on soil microbial diversity in relation to terrestrial sinks for atmospheric trace gases.

Agricultural landscapes provide financial livelihoods for farming communities in rural areas. However, such agroenvironments can significantly impact the local floral biodiversity and introduce harmful invasive species to the ecosystem. Despite the prominence of plantations throughout the tropics, their effects on local flora are limited to only a few specific cash crops and geographical regions. Here, we compared the species richness and structural diversity of vegetation in natural forest fragments and three types of vanilla plantation within the Sava region of north‐east Madagascar ranging from those within or adjacent to existing forests, to intensively cultivated plantations. We recorded data on plant species abundance, diameter at breast height and canopy cover within multiple sites of each habitat. We used abundance data to calculate species richness indices, and we compared these metrics between habitats. Forested habitats contained a significantly higher floral species richness, structural diversity and more endemic and regionally native species than nonforested, anthropogenic vanilla plantations. However, our results suggest that the high floral species richness and structural diversity of natural forests can be partially achieved in vanilla plantations, depending on the site's management regime; traditionally managed vanilla plantations located close to natural forests can support diverse floral communities. These encouraging findings for plant conservation and sustainable agroforestry in Madagascar suggest that that newly created vanilla plantations and already existing nonforested plantations should endeavour to follow the more traditional forested approach to enhance the future sustainability and promote floristic diversity.

The impacts of land-use change and long-term agricultural practices on the bacterial and methanotrophic biomass in the soils comprising the Classical Experiments at Rothamsted Research were investigated by using 13 CH 4 phospholipid fatty acid stable isotope probing (PLFA SIP). Nine sites were studied, including six arable plots, two regenerated woodlands and a regenerated grassland. The regenerating sites had all been in arable cropping for at least 200 years (and probably much longer) before commencing regeneration approximately 120 years ago. Six sites were plots within the Broadbalk Wheat Experiment, which had been cultivated, and on which winter wheat was grown annually for 163 years with different fertilizer and manure treatments; the field had been in arable cropping for at least 200 years previously. Triplicate soil samples were incubated under 2 ppmv 13 CH 4 for up to 100 days. Extraction and 13 C-PLFA analysis revealed that overall methanotrophic biomass was smaller in the Rothamsted soils compared with the other mineral soils studied to date, as indicated by poor 13 C incorporation. High-affinity methanotrophs similar to known type II methanotrophs were most abundant in all of the soils studied, except in two plots receiving farmyard manure (FYM and FYM + N). Manuring resulted in a shift to a population similar to known type I methanotrophs. Methanotrophic biomass was elevated in soils that had received the largest input of N fertilizer, though without detectable differences in CH 4 oxidation rates, indicating the potential mediation of atmospheric CH 4 oxidation by non-methanotrophs, which are most likely to be nitrifying bacteria.

The amounts and delta(13)C values of CH4 at subambient concentrations in soil gas were determined along depth profiles in a U.K. grassland (Bronydd Mawr) and woodland (Leigh Woods). The data were used to determine in situ kinetic isotope effects (KIEs) associated with uptake of atmospheric CH4 by high-affinity methanotrophic bacteria that inha bit soil. Three independent calculation approaches yielded similar mean KIEs of 1.0211 +/- 0.0020 (n=18) for Bronydd Mawr and 1.0219 +/- 0.0010 (n=24) for Leigh Woods. Soil methanotrophy KIEs were largely invariant among oak, beech, and pine forest soils of different ages at Leigh Woods but exhibited a statistically significant relationship with methanotroph biomass in individual plots at Bronydd Mawr and Leigh Woods quantified previously by 13C stable isotope probing. This finding, albeit based upon a small data set suggests that 13C and 12C partitioning associated with the global soil sink for atmospheric CH4 may occur in part as a result of biological as well as physical processes. An accurate assessment of the relative importance of each process to the total KIE requires confirmation that significant partitioning of (13)CH4 and (12)CH4 occurs in pore spaces as a result of differences in diffusion rates.