The influence of C3 and C4 vegetation on soil organic matter dynamics in contrasting semi-natural tropical ecosystems

This is a freely-available open access publication. Please cite the published version which is available via the DOI link in this record.Variations in the carbon isotopic composition of soil organic matter (SOM) in bulk and fractionated samples were used to assess the influence of C3 and C4 vegetation on SOM dynamics in semi-natural tropical ecosystems sampled along a precipitation gradient in West Africa. Differential patterns in SOM dynamics in C3/C4 mixed ecosystems occurred at various spatial scales. Relative changes in C/ N ratios between two contrasting SOM fractions were used to evaluate potential site-scale differences in SOM dynamics between C3- and C4-dominated locations. These differences were strongly controlled by soil texture across the precipitation gradient, with a function driven by bulk δ 13C and sand content explaining 0.63 of the observed variability. The variation of δ 13C with soil depth indicated a greater accumulation of C3-derived carbon with increasing precipitation, with this trend also being strongly dependant on soil characteristics. The influence of vegetation thickening on SOM dynamics was also assessed in two adjacent, but structurally contrasting, transitional ecosystems occurring on comparable soils to minimise the confounding effects posed by climatic and edaphic factors. Radiocarbon analyses of sand-size aggregates yielded relatively short mean residence times (τ ) even in deep soil layers, while the most stable SOM fraction associated with silt and clay exhibited shorter τ in the savanna woodland than in the neighbouring forest stand. These results, together with the vertical variation observed in δ 13C values, strongly suggest that both ecosystems are undergoing a rapid transition towards denser closed canopy formations. However, vegetation thickening varied in intensity at each site and exerted contrasting effects on SOM dynamics. This study shows that the interdependence between biotic and abiotic factors ultimately determine whether SOM dynamics of Published by Copernicus Publications on behalf of the European Geosciences Union. 5042 G. Saiz et al.: Influence of C3/C4 on SOM in tropical biomes C3- and C4-derived vegetation are at variance in ecosystems where both vegetation types coexist. The results highlight the far-reaching implications that vegetation thickening may have for the stability of deep SOM.UK National Environment Research CouncilAustralian Institute of Nuclear Science and Engineering (AINSE Ltd

The influence of C3 and C4 vegetation on soil organic matter dynamics in contrasting semi-natural tropical ecosystems

Variations in the carbon isotopic composition of soil organic matter (SOM) in bulk and fractionated samples were used to assess the influence of C3 and C4 vegetation on SOM dynamics in semi-natural tropical ecosystems sampled along a precipitation gradient in West Africa. Differential patterns in SOM dynamics in C3/C4 mixed ecosystems occurred at various spatial scales. Relative changes in C=N ratios between two contrasting SOM fractions were used to evaluate potential site-scale differences in SOM dynamics between C3- and C4-dominated locations. These differences were strongly controlled by soil texture across the precipitation gradient, with a function driven by bulk 13C and sand content explaining 0.63 of the observed variability. The variation of 13C with soil depth indicated a greater accumulation of C3-derived carbon with increasing precipitation, with this trend also being strongly dependant on soil characteristics. The influence of vegetation thickening on SOM dynamics was also assessed in two adjacent, but structurally contrasting, transitional ecosystems occurring on comparable soils to minimise the confounding effects posed by climatic and edaphic factors. Radiocarbon analyses of sand-size aggregates yielded relatively short mean residence times ( ) even in deep soil layers, while the most stable SOM fraction associated with silt and clay exhibited shorter in the savanna woodland than in the neighbouring forest stand. These results, together with the vertical variation observed in 13C values, strongly suggest that both ecosystems are undergoing a rapid transition towards denser closed canopy formations.However, vegetation thickening varied in intensity at each site and exerted contrasting effects on SOM dynamics. Thisstudy shows that the interdependence between biotic and abiotic factors ultimately determine whether SOM dynamics of C3- and C4-derived vegetation are at variance in ecosystems where both vegetation types coexist. The results highlight the far-reaching implications that vegetation thickening may have for the stability of deep SOM. © 2015, Copernicus Publications

Ramial wood amendments (Piliostigma reticulatum) mitigate degradation of tropical soils but do not replenish nutrient exports

Restoring degraded soils to support food production is a major challenge for West African smallholders who have developed local innovations to counter further degradation. The objective of this study was to evaluate a local farmer's technique that uses ramial wood (RW) as soil amendment (Piliostigma reticulatum shrub). Three treatments were applied in an experimental plot in Burkina Faso: control (no amendment), low RW (3 Mg fresh mass·ha−1·yr−1), and high RW (12 Mg fresh mass·ha−1·yr−1). RW was chipped to <5‐cm pieces and either buried or mulched. Topsoil carbon (C), nitrogen (N), and phosphorus (P) in control and low‐RW treatments declined after 7 years of continuous sorghum cultivation. Use of high‐RW amendment stabilized soil C content while N and P declined, thus not replenishing nutrient exports. Net contribution to soil C in the layer measuring 0–15 cm was 15% of the applied C in the high‐RW amendments. Although biomass and grain yields were higher in high‐RW treatments, crop productivity declined throughout the experiment for all treatments. Termite casts on RW treatments evidenced the potential role of wood‐foraging termites in diluting the impact of RW on soil fertility build‐up and soil water content. We conclude that mitigating soil degradation under semiarid conditions in Burkina Faso would require large amounts of woody amendments, particularly if the level of termite activity is high. Additional nutrient sources would be needed to compensate for removal in exported products so that biomass and grain production can be stabilized or increased.Estación Experimental Agropecuaria BarilocheFil: Félix, Georges F. Wageningen University. Farming Systems Ecology; HolandaFil: Clermont-Dauphin, Cathy. Montpellier SupAgro- Centre de Coopération Internationale en Recherche Agronomique pour le Développement-Institut National de la Recherche Agronomique. Eco&Sols; FranciaFil: Hien, Edmond. Laboratoire Mixte International. Intensification Ecologique des Sols Cultivés en Afrique de l'Ouest; Burkina FasoFil: Groot, Jeroen C.J. Wageningen University. Farming Systems Ecology; HolandaFil: Penche, Aurelien. Laboratoire Mixte International. Intensification Ecologique des Sols Cultivés en Afrique de l'Ouest; Burkina FasoFil: Barthès, Bernard G. Universidad Montpellier; FranciaFil: Manlay, Raphaël J. AgroParisTech; FranciaFil: Tittonell, Pablo Adrian. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche; ArgentinaFil: Cournac, Laurent. Montpellier SupAgro- Centre de Coopération Internationale en Recherche Agronomique pour le Développement-Institut National de la Recherche Agronomique. Eco&Sols; Franci

Advanced Camera for Surveys Observations of Young Star Clusters in the Interacting Galaxy UGC 10214

We present the first Advanced Camera for Surveys (ACS) observations of young star clusters in the colliding/merging galaxy UGC 10214. The observations were made as part of the Early Release Observation (ERO) program for the newly installed ACS during service mission SM3B for the Hubble Space Telescope (HST). Many young star clusters can be identified in the tails of UGC 10214, with ages ranging from ~3 Myr to 10 Myr. The extreme blue V-I (F606W-F814W) colors of the star clusters found in the tail of UGC 10214 can only be explained if strong emission lines are included with a young stellar population. This has been confirmed by our Keck spectroscopy of some of these bright blue stellar knots. The most luminous and largest of these blue knots has an absolute magnitude of M_V = -14.45, with a half-light radius of 161 pc, and if it is a single star cluster, would qualify as a super star cluster (SSC). Alternatively, it could be a superposition of multiple scaled OB associations or clusters. With an estimated age of ~ 4-5 Myr, its derived mass is < 1.3 x 10^6 solar masses. Thus the young stellar knot is unbound and will not evolve into a normal globular cluster. The bright blue clusters and associations are much younger than the dynamical age of the tail, providing strong evidence that star formation occurs in the tail long after it was ejected. UGC 10214 provides a nearby example of processes that contributed to the formation of halos and intra-cluster media in the distant and younger Universe.Comment: 6 pages with embedded figures, ApJ in pres

Discovery of Two Distant Type Ia Supernovae in the Hubble Deep Field North with the Advanced Camera for Surveys

We present observations of the first two supernovae discovered with the recently installed Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. The supernovae were found in Wide Field Camera images of the Hubble Deep Field North taken with the F775W, F850LP, and G800L optical elements as part of the ACS guaranteed time observation program. Spectra extracted from the ACS G800L grism exposures confirm that the objects are Type Ia supernovae (SNe Ia) at redshifts z=0.47 and z=0.95. Follow-up HST observations have been conducted with ACS in F775W and F850LP and with NICMOS in the near-infrared F110W bandpass, yielding a total of 9 flux measurements in the 3 bandpasses over a period of 50 days in the observed frame. We discuss many of the important issues in doing accurate photometry with the ACS. We analyze the multi-band light curves using two different fitting methods to calibrate the supernovae luminosities and place them on the SNe Ia Hubble diagram. The resulting distances are consistent with the redshift-distance relation of the accelerating universe model, although evolving intergalactic grey dust remains as a less likely possibility. The relative ease with which these SNe Ia were found, confirmed, and monitored demonstrates the potential ACS holds for revolutionizing the field of high-redshift SNe Ia, and therefore of testing the accelerating universe cosmology and constraining the "epoch of deceleration".Comment: 11 pages, 8 embedded figures. Accepted for publication in Ap

CMB polarimetry with BICEP: instrument characterization, calibration, and performance

BICEP is a ground-based millimeter-wave bolometric array designed to target the primordial gravity wave signature on the polarization of the cosmic microwave background (CMB) at degree angular scales. Currently in its third year of operation at the South Pole, BICEP is measuring the CMB polarization with unprecedented sensitivity at 100 and 150 GHz in the cleanest available 2% of the sky, as well as deriving independent constraints on the diffuse polarized foregrounds with select observations on and off the Galactic plane. Instrument calibrations are discussed in the context of rigorous control of systematic errors, and the performance during the first two years of the experiment is reviewed.Comment: 12 pages, 15 figures, updated version of a paper accepted for Millimeter and Submillimeter Detectors and Instrumentation for Astronomy IV, Proceedings of SPIE, 7020, 200

Foliar trait contrasts between African forest and savanna trees: Genetic versus environmental effects

Journal ArticleVariations in leaf mass per unit area (Ma) and foliar concentrations of N, P, C, K, Mg and Ca were determined for 365 trees growing in 23 plots along a West African precipitation gradient ranging from 0.29 to 1.62m a-1. Contrary to previous studies, no marked increase in Ma with declining precipitation was observed, but savanna tree foliar [N] tended to be higher at the drier sites (mass basis). Generally, Ma was slightly higher and [N] slightly lower for forest vs savanna trees with most of this difference attributable to differences in soil chemistry. No systematic variations in [P], [Mg] and [Ca] with precipitation or between trees of forest vs savanna stands were observed. We did, however, find a marked increase in foliar [K] of savanna trees as precipitation declined, with savanna trees also having a significantly lower [K] than those of nearby forest. These differences were not related to differences in soil nutrient status and were accompanied by systematic changes in [C] of opposite sign. We suggest an important but as yet unidentified role for K in the adaption of savanna species to periods of limited water availability; with foliar [K] being also an important factor differentiating tree species adapted to forest vs savanna soils within the 'zone of transition' of Western Africa.Natural Environment Research Council TROBIT Consortium projectRoyal Society - University Research Fellowshi

Absolute polarization angle calibration using polarized diffuse Galactic emission observed by BICEP

We present a method of cross-calibrating the polarization angle of a polarimeter using BICEP Galactic observations. \bicep\ was a ground based experiment using an array of 49 pairs of polarization sensitive bolometers observing from the geographic South Pole at 100 and 150 GHz. The BICEP polarimeter is calibrated to +/-0.01 in cross-polarization and less than +/-0.7 degrees in absolute polarization orientation. BICEP observed the temperature and polarization of the Galactic plane (R.A= 100 degrees ~ 270 degrees and Dec. = -67 degrees ~ -48 degrees). We show that the statistical error in the 100 GHz BICEP Galaxy map can constrain the polarization angle offset of WMAP Wband to 0.6 degrees +\- 1.4 degrees. The expected 1 sigma errors on the polarization angle cross-calibration for Planck or EPIC are 1.3 degrees and 0.3 degrees at 100 and 150 GHz, respectively. We also discuss the expected improvement of the BICEP Galactic field observations with forthcoming BICEP2 and Keck observations.Comment: 13 pages, 10 figures and 2 tables. To appear in Proceedings of SPIE Astronomical Telescopes and Instrumentation 201

Neemazal ® as a possible alternative control tool for malaria and African trypanosomiasis?

Background: Research efforts to identify possible alternative control tools for malaria and African trypanosomiasis are needed. One promising approach relies on the use of traditional plant remedies with insecticidal activities. Methods: In this study, we assessed the effect of blood treated with different doses of NeemAzal ® (NA, neem seed extract) on mosquitoes (Anopheles coluzzii) and tsetse flies (Glossina palpalis gambiensis) (i) avidity to feed on the treated blood, (ii) longevity, and (iii) behavioural responses to human and calf odours in dual-choice tests. We also gauged NeemAzal ® toxicity in mice. Results: In An. coluzzii, the ingestion of NA in bloodmeals offered by membrane feeding resulted in (i) primary antifeedancy; (ii) decreased longevity; and (iii) reduced response to host odours. In G. palpalis gambiensis, NA caused (i) a knock-down effect; (ii) decreased or increased longevity depending on the dose; and (iii) reduced response to host stimuli. In both cases, NA did not affect the anthropophilic rate of activated insects. Overall, the most significant effects were observed with NA treated bloodmeals at a dose of 2000 μg/ml for mosquitoes and 50 μg/ml for tsetse flies. Although no mortality in mice was observed after 14 days of follow-up at oral doses of 3.8, 5.6, 8.4 and 12.7 g/kg, behavioural alterations were noticed at doses above 8 g/kg. Conclusion: This study revealed promising activity of NA on A. coluzzii and G. palpalis gambiensis but additional research is needed to assess field efficacy of neem products to be possibly integrated in vector control programmes

The influence of C₃ and C₄ vegetation on soil organic matter dynamics in contrasting semi-natural tropical ecosystems

Variations in the carbon isotopic composition of soil organic matter (SOM) in bulk and fractionated samples were used to assess the influence of C3 and C4 vegetation on SOM dynamics in semi-natural tropical ecosystems sampled along a precipitation gradient in West Africa. Differential patterns in SOM dynamics in C3/C4 mixed ecosystems occurred at various spatial scales. Relative changes in C / N ratios between two contrasting SOM fractions were used to evaluate potential site-scale differences in SOM dynamics between C3- and C4-dominated locations. These differences were strongly controlled by soil texture across the precipitation gradient, with a function driven by bulk δ13C and sand content explaining 0.63 of the observed variability. The variation of δ13C with soil depth indicated a greater accumulation of C3-derived carbon with increasing precipitation, with this trend also being strongly dependant on soil characteristics. The influence of vegetation thickening on SOM dynamics was also assessed in two adjacent, but structurally contrasting, transitional ecosystems occurring on comparable soils to minimise the confounding effects posed by climatic and edaphic factors. Radiocarbon analyses of sand-size aggregates yielded relatively short mean residence times (τ) even in deep soil layers, while the most stable SOM fraction associated with silt and clay exhibited shorter τ in the savanna woodland than in the neighbouring forest stand. These results, together with the vertical variation observed in δ13C values, strongly suggest that both ecosystems are undergoing a rapid transition towards denser closed canopy formations. However, vegetation thickening varied in intensity at each site and exerted contrasting effects on SOM dynamics. This study shows that the interdependence between biotic and abiotic factors ultimately determine whether SOM dynamics of C3- and C4-derived vegetation are at variance in ecosystems where both vegetation types coexist. The results highlight the far-reaching implications that vegetation thickening may have for the stability of deep SOM. Â © Author(s) 2015