Spreading recruitment over time to cope with environmental variability

10 paginas, 3 figuras, 2 tablas.-- El PDF es la versión de autor.Seedling establishment is one of the most vulnerable life cycle stages, and a key component for the population dynamics in short-lived plants. In unpredictable environments, timing of emergence is critical for the success of plant performance, and different adaptive bet-hedging strategies have evolved to reduce the risk of failure in recruitment. In this study we describe the spatio-temporal pattern of seedling emergence (overall rate and timing) and survival in four contrasting Mediterranean habitats for Plantago coronopus, a small herb with dimorphic seeds. We then explore the importance of spreading germination within years, as well as the role of the two types of seeds from a broader temporal perspective. Populations strongly differed for all recruitment components analyzed in a given year, but this spatial differentiation diluted when a longer period was considered. Apical (smaller) seeds germinated later and in a significantly lower proportion than basal (larger) seeds. Both late emergents and seedlings from apical seeds had lower survival probability in a rainy year. However, our results suggest that in a population having the lowest production of apical seeds, late emergents coming from apical seeds may constitute a large fraction of yearly recruitment and that their performance was non-significantly different from that of early emergents over the 4-year study period. This study provides evidence of the importance of two related traits (spreading seedling emergence through time by producing dimorphic seeds) as bet-hedging strategies to cope with environmental unpredictability. This is at least partly accomplished by increasing the potential of recruitment in favourable years, instead of buffering such important process in extremely bad years.This study was funded by the Spanish Ministry of Science, under projects BOS2002-01162 and CGL2006-08507 to MBG.Peer reviewe

A miniDOAS instrument optimised for ammonia field measurements

We present a differential optical absorption spectroscopy (DOAS) instrument, called "miniDOAS", optimised for optical open-path field-measurements of ambient ammonia (NH3) alongside nitrogen oxide (NO) and sulfur dioxide (SO2). The instrument is a further development of the miniDOAS presented by Volten et al. (2012). We use a temperature-controlled spectrometer, a deuterium light source and a modified optical arrangement. The system was set up in a robust, field-deployable, temperature-regulated housing. For the evaluation of light spectra we use a new high-pass filter routine based upon robust baseline extraction with local regression. Multiple linear regression including terms of an autoregressive–moving-average model is used to determine concentrations. For NH3 the random uncertainty is about 1.4 % of the concentration, and not better than 0.2 µg m−3. Potential biases for the slope of the calibration are given by the precision of the differential absorption cross sections (±3 %) and for the offset by the precision of the estimation of concentration offsets (cref) introduced by the reference spectrum Iref. Comparisons of miniDOAS measurements to those by NH3 acid trap devices showed good agreement. The miniDOAS can be flexibly used for a wide range of field trials, such as micrometeorological NH3 flux measurements with approaches based upon horizontal or vertical concentration differences. Results from such applications covering concentration dynamics of less than one up to several hundreds of µg m−3 are presented

Ammonia emissions from a grazed field estimated by miniDOAS measurements and inverse dispersion modelling

Ammonia (NH3) fluxes were estimated from a field being grazed by dairy cattle during spring by applying a backward Lagrangian stochastic model (bLS) model combined with horizontal concentration gradients measured across the field. Continuous concentration measurements at field boundaries were made by open-path miniDOAS (differential optical absorption spectroscopy) instruments while the cattle were present and for 6 subsequent days. The deposition of emitted NH3 to "clean" patches on the field was also simulated, allowing both "net" and "gross" emission estimates, where the dry deposition velocity (vd) was predicted by a canopy resistance (Rc) model developed from local NH3 flux and meteorological measurements. Estimated emissions peaked during grazing and decreased after the cattle had left the field, while control on emissions was observed from covariance with temperature, wind speed and humidity and wetness measurements made on the field, revealing a diurnal emission profile. Large concentration differences were observed between downwind receptors, due to spatially heterogeneous emission patterns. This was likely caused by uneven cattle distribution and a low grazing density, where "hotspots" of emissions would arise as the cattle grouped in certain areas, such as around the water trough. The spatial complexity was accounted for by separating the model source area into sub-sections and optimising individual source area coefficients to measured concentrations. The background concentration was the greatest source of uncertainty, and based on a sensitivity/uncertainty analysis the overall uncertainty associated with derived emission factors from this study is at least 30–40 %

Der Einfluss symbiotischer Bodenpilze auf den Stickstoffzyklus

To increase nutrient use efficiency and reduce nutrient losses are key aspects for sustainable agriculture. Arbuscular mycorrhizal fungi (AMF) are an import and widespread group of plant-symbiotic soil fungi. Here we investigate the role of those soil microorganisms, for effective nutrient recycling. We conducted greenhouse and lysimeter experiments to compare the cycling of important plant nutrients in systems with high and low abundance of AMF. AMF increased plant N nutrition, reduced leaching losses of mineral N, and prevented emissions of N2O, an important greenhouse gas. The results show the importance of AMF for an effective nutrient management. Farmers should implement strategies to promote AMF in the soil, as they are an indispensable compound of sustainable agriculture

A miniDOAS instrument optimised for ammonia field measurements

We present a differential optical absorption spectroscopy (DOAS) instrument, called "miniDOAS", optimised for optical open-path field-measurements of ambient ammonia (NH3) alongside nitrogen oxide (NO) and sulfur dioxide (SO2). The instrument is a further development of the miniDOAS presented by Volten et al. (2012). We use a temperature-controlled spectrometer, a deuterium light source and a modified optical arrangement. The system was set up in a robust, field-deployable, temperature-regulated housing. For the evaluation of light spectra we use a new high-pass filter routine based upon robust baseline extraction with local regression. Multiple linear regression including terms of an autoregressive-moving-average model is used to determine concentrations. For NH3 the random uncertainty is about 1.4% of the concentration, and not better than 0.2 mu g m(-3). Potential biases for the slope of the calibration are given by the precision of the differential absorption cross sections (+/- 3 %) and for the offset by the precision of the estimation of concentration offsets (c(ref)) introduced by the reference spectrum I-ref. Comparisons of miniDOAS measurements to those by NH3 acid trap devices showed good agreement. The miniDOAS can be flexibly used for a wide range of field trials, such as micrometeorological NH3 flux measurements with approaches based upon horizontal or vertical concentration differences. Results from such applications covering concentration dynamics of less than one up to several hundreds of mu g m(-3) are presented

Ammonia emission after slurry application to grassland in Switzerland

Loss of ammonia (NH3) after field application of livestock slurry contributes between 30% and 50% of agricultural NH3 emissions from European countries. The objectives of this study were to re-evaluate NH3 emissions following application of cattle and pig slurry to grassland in Switzerland and to investigate the effectiveness of abatement techniques. In 17 field experiments, NH3 emissions were determined with a micrometeorological approach, relating the emission to the measured concentration by means of atmospheric dispersion modelling. The cattle slurry applied exhibited an average dry matter content of 3.3% (range between 1.0% and 6.7% dry matter). The emission after application of cattle slurry spread with a splash plate (referred to as reference technique) ranged from 10% to 47% of applied Total Ammoniacal Nitrogen (% of TAN) and averaged to 25% of TAN. This range of losses is lower by approx. a factor of two compared to measurements from earlier Swiss experiments. Applications with trailing hose and trailing shoe systems yielded an average reduction of 51% and 53%, respectively, relative to the reference technique. A regression analysis showed that the dry matter content of the slurry and the air temperature are important drivers for NH3 emission

Reduced Nitrous Oxide Emissions From Drained Temperate Agricultural Peatland After Coverage With Mineral Soil

Peatlands drained for agriculture emit large amounts of nitrous oxide (N2O) and thereby contribute to global warming. In order to counteract soil subsidence and sustain agricultural productivity, mineral soil coverage of drained organic soil is an increasingly used practice. This management option may also influence soil-borne N2O emissions. Understanding the effect of mineral soil coverage on N2O emissions from agricultural peatland is necessary to implement peatland management strategies which not only sustain agricultural productivity but also reduce N2O emissions. In this study, we aimed to quantify the N2O emissions from an agriculturally managed peatland in Switzerland and to evaluate the effect of mineral soil coverage on these emissions. The study was conducted over two years on a grassland on drained nutrient-rich fen in the Swiss Rhine Valley which was divided into two parts, both with identical management. One site was not covered with mineral soil (reference "Ref"), and the other site had a similar to 40 cm thick mineral soil cover (coverage "Cov"). The grassland was intensively managed, cut 5-6 times per year, and received c. 230 kg N ha(-1) yr(-1) of nitrogen fertilizer. N2O emissions were continuously monitored using an automatic time integrating chamber (ATIC) system. During the experimental period, site Ref released 20.5 +/- 2.7 kg N ha(-1) yr(-1) N2O-N, whereas the N2O emission from site Cov was only 2.3 +/- 0.4 kg N ha(-1) yr(-1). Peak N2O emissions were mostly detected following fertilizer application and lasted for 2-3 weeks before returning to the background N2O emissions. At both sites, N2O peaks related to fertilization events contributed more than half of the overall N2O emissions. However, not only the fertilization induced N2O peaks but also background N2O emissions were lower with mineral soil coverage. Our data suggest a strong and continued reduction in N2O emissions with mineral soil cover from the investigated organic soil. Mineral soil coverage, therefore, seems to be a promising N2O mitigation option for intensively used drained organic soils when a sustained use of the drained peatland for intensive agricultural production is foreseen, and potential rewetting and restoration of the peatland are not possible

Soil carbon loss from drained agricultural peatland after coverage with mineral soil

Drainage for agriculture has turned peatlands from a net sink to a net source of carbon (C). In order to reduce the environmental footprint of agricultural peatland drainage, and to counteract soil subsidence, mineral soil coverage is becoming an increasingly used practice in Switzerland. To explore the effect of mineral soil coverage on soil C loss and the source of CO2 frompeatland drained for agriculture, we utilized the radiocarbon signature (F14C) of soil C and emitted CO2 in the field. The experiment, located in the Swiss Rhine Valley, was carried out on two adjacent drained organic soils, either without mineral soil cover (reference ‘Ref’), or covered with mineral soil (thickness ~ 40 cm) (coverage ‘Cov’) 13 years ago. Drainage already commenced 130 years ago and the site was managed as meadow since the 1970ies. Drainage induced 41–75 kg Cm−2 loss, which is equivalent to annual C loss rates of 0.49–0.58 kg C m−2 yr−1 and 0.31–0.63 kg C m−2 yr−1 for Cov and Ref, respectively. Mineral soil coverage had no significant effect on the amount of heterotrophic respiration, however, at Cov, the radiocarbon signature of heterotrophic CO2 was significantly (p < 0.01) younger than at Ref, indicating that mineral soil coverage moved the source of decomposition of soil organic carbon (SOC) from a higher share of old peat towards a higher share of relatively younger material. In summary, our study lends support to the hypothesis that mineral soil coverage might reduce the decomposition of old peat underneath, and may therefore be a promising peatland management technique for the future use of drained peatland for agriculture

Cross-Linking Cellulosic Fibers with Photoreactive Polymers: Visualization with Confocal Raman and Fluorescence Microscopy

The properties of paper sheets can be tuned by adjusting the surface or bulk chemistry using functional polymers that are applied during (online) or after (offline) papermaking processes. In particular, polymers are widely used to enhance the mechanical strength of the wet state of paper sheets. However, the mechanical strength depends not only on the chemical nature of the polymeric additives but also on the distribution of the polymer on and in the lignocellulosic paper. Here, we analyze the photochemical attachment and distribution of hydrophilic polydimethylacrylamide-<i>co</i>-methacrylate-benzophenone P­(DMAA-<i>co</i>-MABP) copolymers with defined amounts of photoreactive benzophenone moieties in model paper sheets. Raman microscopy was used for the unambiguous identification of P­(DMAA-<i>co</i>-MABP) and cellulose specific bands and thus the copolymer distribution within the cellulose matrix. Two-dimensional Raman spectral maps at the intersections of overlapping cellulose fibers document that the macromolecules only partially surround the cellulose fibers, favor to attach to the fiber surface, and connect the cellulose fibers at crossings. Moreover, the copolymer appears to accumulate preferentially in holes, vacancies, and dips on the cellulose fiber surface. Correlative brightfield, Raman, and confocal laser scanning microscopy finally reveal a reticular three-dimensional distribution of the polymer and show that the polymer is predominately deposited in regions of high capillarity (i.e., in proximity to fine cellulose fibrils). These data provide deeper insights into the effects of paper functionalization with a copolymer and aid in understanding how these agents ultimately influence the local and overall properties of paper