The significance of atmospheric nutrient inputs and canopy interception of precipitation during ecosystem development in piñon-juniper woodlands of the southwestern USA

In arid ecosystems, widely spaced vegetation and prolonged dry periods may enhance canopy capture of nutrients from dry deposition. Additionally, differences in precipitation type, plant canopy architecture, and soil nutrient limitation could affect canopy exchange of atmospherically derived nutrients. We collected bulk precipitation and throughfall underneath piñon pine (. Pinus edulis) and one-seed juniper (. Juniperus monosperma) along a substrate age gradient to determine if canopy interception or throughfall chemistry differed among tree species, season, or substrate age. The Substrate Age Gradient of Arizona consists of four sites with substrate ages ranging from 1ky to 3000ky-old, which exhibit classic variations in soil nitrogen (N) and phosphorus (P) availability with substrate age. Greater nutrient inputs below canopies than in intercanopy areas suggest throughfall contributes to the "islands of fertility" effect. Canopy interception of precipitation did not differ between tree species, but was greater in the summer/fall than winter/spring. We found that net canopy retention of atmospherically derived N was generally greater when N availability in the soil was low, but retention also occurred when N availability was relatively high. Taken together, our results were inconclusive in determining whether the degree of soil nutrient limitation alters canopy exchange of plant growth-limiting nutrients. © 2013 Elsevier Ltd

Proximate controls on semiarid soil greenhouse gas fluxes across 3 million years of soil development

Soils are important sources and sinks of three greenhouse gases (GHGs): carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). However, it is unknown whether semiarid landscapes are important contributors to global fluxes of these gases, partly because our mechanistic understanding of soil GHG fluxes is largely derived from more humid ecosystems. We designed this study with the objective of identifying the important soil physical and biogeochemical controls on soil GHG fluxes in semiarid soils by observing seasonal changes in soil GHG fluxes across a three million year substrate age gradient in northern Arizona. We also manipulated soil nitrogen (N) and phosphorus availability with 7 years of fertilization and used regression tree analysis to identify drivers of unfertilized and fertilized soil GHG fluxes. Similar to humid ecosystems, soil N2O flux was correlated with changes in N and water availability and soil CO2 efflux was correlated with changes in water availability and temperature. Soil CH4 uptake was greatest in relatively colder and wetter soils. While fertilization had few direct effects on soil CH4 flux, soil nitrate was an important predictor of soil CH4 uptake in unfertilized soils and soil ammonium was an important predictor of soil CH4 uptake in fertilized soil. Like in humid ecosystems, N gas loss via nitrification or denitrification appears to increase with increases in N and water availability during ecosystem development. Our results suggest that, with some exceptions, the drivers of soil GHG fluxes in semiarid ecosystems are often similar to those observed in more humid ecosystems

Snowmelt timing alters shallow but not deep soil moisture in the Sierra Nevada

Roughly one-third of the Earth's land surface is seasonally covered by snow. In many of these ecosystems, the spring snowpack is melting earlier due to climatic warming and atmospheric dust deposition, which could greatly modify soil water resources during the growing season. Though snowmelt timing is known to influence soil water availability during summer, there is little known about the depth of the effects and how long the effects persist. We therefore manipulated the timing of seasonal snowmelt in a high-elevation mixed-conifer forest in a Mediterranean climate during consecutive wet and dry years. The snow-all-gone (SAG) date was advanced by 6 days in the wet year and 3 days in the dry year using black sand to reduce the snow surface albedo. To maximize variation in snowmelt timing, we also postponed the SAG date by 8 days in the wet year and 16 days in the dry year using white fabric to shade the snowpack from solar radiation. We found that deeper soil water (30-60 cm) did not show a statistically significant response to snowmelt timing. Shallow soil water (0-30 cm), however, responded strongly to snowmelt timing. The drying effect of accelerated snowmelt lasted 2 months in the 0-15 cm depth and at least 4 months in the 15-30 cm depth. Therefore, the legacy of snowmelt timing on soil moisture can persist through dry periods, and continued earlier snowmelt due to climatic warming and windblown dust could reduce near-surface water storage and availability to plants and soil biota. Key Points The hydrological signal of snowmelt timing was strongest in shallow soil Effects of snowmelt timing on soil moisture lasted 2-4 months Advancing snowmelt timing by 2-3 weeks depleted shallow soil water by one third © 2014. American Geophysical Union. All Rights Reserved

Soil carbon and nitrogen erosion in forested catchments: Implications for erosion-induced terrestrial carbon sequestration

Lateral movement of organic matter (OM) due to erosion is now considered an important flux term in terrestrial carbon (C) and nitrogen (N) budgets, yet most published studies on the role of erosion focus on agricultural or grassland ecosystems. To date, little information is available on the rate and nature of OM eroded from forest ecosystems. We present annual sediment composition and yield, for water years 2005-2011, from eight catchments in the southern part of the Sierra Nevada, California. Sediment was compared to soil at three different landform positions from the source slopes to determine if there is selective transport of organic matter or different mineral particle size classes. Sediment export varied from 0.4 to 177 kg ha-1, while export of C in sediment was between 0.025 and 4.2 kg C ha-1 and export of N in sediment was between 0.001 and 0.04 kg N ha-1. Sediment yield and composition showed high interannual variation. In our study catchments, erosion laterally mobilized OM-rich litter material and topsoil, some of which enters streams owing to the catchment topography where steep slopes border stream channels. Annual lateral sediment export was positively and strongly correlated with stream discharge, while C and N concentrations were both negatively correlated with stream discharge; hence, C: N ratios were not strongly correlated to sediment yield. Our results suggest that stream discharge, more than sediment source, is a primary factor controlling the magnitude of C and N export from upland forest catchments. The OM-rich nature of eroded sediment raises important questions about the fate of the eroded OM. If a large fraction of the soil organic matter (SOM) eroded from forest ecosystems is lost during transport or after deposition, the contribution of forest ecosystems to the erosion-induced C sink is likely to be small (compared to croplands and grasslands)

A positive relationship between the abundance of ammonia oxidizing archaea and natural abundance δ15N of ecosystems

We present a significant relationship between the natural abundance isotopic composition of ecosystem pools and the abundance of a microbial gene. Natural abundance 15N of soils and soil DNA were analysed and compared with archaeal ammonia oxidizer abundance along an elevation gradient in northern Arizona and along a substrate age gradient in Hawai'i. There was a significant positive correlation between the abundance of archaeal amoA genes and natural abundance δ15N of total soil or DNA suggesting that ammonia oxidizing archaea play an important role in ecosystem N release. © 2013 Elsevier Ltd

Tracing the source of soil organic matter eroded from temperate forest catchments using carbon and nitrogen isotopes

Soil erosion continuously redistributes soil and associated soil organic matter (SOM) on the Earth's surface, with important implications for biogeochemical cycling of essential elements and terrestrial carbon sequestration. Despite the importance of soil erosion, surprisingly few studies have evaluated the sources of eroded carbon (C). We used natural abundance levels of the stable and radioactive isotopes of C (13C and 14C) and stable isotope of nitrogen (15N) to elucidate the origins of SOM eroded from low-order catchments along the western slopes of the Sierra Nevada of California, USA. Our work was conducted in two relatively undisturbed catchments (low elevation = 1800 m, and high elevation = 2300 m) of the Kings River Experimental Watersheds (KREW) in the Sierra National Forest. Sediment captured in basins at the outlet of each gauged watershed were compared to possible source materials, which included: upland surficial organic horizons (i.e., forest floor) and mineral soils (0–0.6 m) from three landform positions (i.e., crest, backslope, and toeslope), stream bank soils (0–0.6 m), and stream-bed materials (0–0.05 m). We found that most of the organic matter (OM) in the captured sediments was composed of O-horizon material that had high C concentrations. Radiocarbon analyses also showed that the captured OM is composed of modern (post-1950) C, with fraction modern values at or above 1.0. Our results suggest that surface (sheet) erosion, as opposed to channeling through established streams and episodic mass wasting events, is likely the largest source of sediment exported out of these minimally disturbed, headwater catchments. The erosional export of sediment with a high concentration of C, especially in the form of relatively undecomposed litter from the O horizon, suggests that a large fraction of the exported C is likely to be decomposed during or after erosion; hence, it is unlikely that soil erosion acts as a significant net sink for atmospheric CO2 in these low-order, temperate forest catchments

Closely Related Tree Species Differentially Influence the Transfer of Carbon and Nitrogen from Leaf Litter Up the Aquatic Food Web

Decomposing leaf litter in streams provides habitat and nutrition for aquatic insects. Despite large differences in the nutritional qualities of litter among different plant species, their effects on aquatic insects are often difficult to detect. We evaluated how leaf litter of two dominant riparian species (Populus fremontii and P. angustifolia) influenced carbon and nitrogen assimilation by aquatic insect communities, quantifying assimilation rates using stable isotope tracers (13C, 15N). We tested the hypothesis that element fluxes from litter of different plant species better define aquatic insect community structure than insect relative abundances, which often fail. We found that (1) functional communities (defined by fluxes of carbon and nitrogen from leaf litter to insects) were different between leaf litter species, whereas more traditional insect communities (defined by relativized taxa abundances) were not different between leaf litter species, (2) insects assimilated N, but not C, at a higher rate from P. angustifolia litter compared to P. fremontii, even though P. angustifolia decomposes more slowly, and (3) the C:N ratio of material assimilated by aquatic insects was lower for P. angustifolia compared to P. fremontii, indicating higher nutritional quality, despite similar initial litter C:N ratios. These findings provide new evidence for the effects of terrestrial plant species on aquatic ecosystems via their direct influence on the transfer of elements up the food web. We demonstrate how isotopically labeled leaf litter can be used to assess the functioning of insect communities, uncovering patterns undetected by traditional approaches and improving our understanding of the association between food web structure and element cycling

Vegetable consumption pattern of households in selected areas of the old rivers state in Nigeria

The vegetable consumption pattern of households in selected areas in the old  Rivers State (now Rivers and Bayelsa States) in Nigeria was investigated. Areas studied were Port Harcourt the State capital, Igwuruta, Ahoada and Kaiama. Resultsshowed that mothers consumed 59 ± 0.45g to 130 ± 2.04g/person/day of   vegetables between the months of May and July, the peak season of vegetable production. Factors that influenced vegetable consumption were found to be chiefly season and culture. Other factors were availability/price for 43.8% of households in Kaiama, a riverine community, while taste and nutrition knowledge wielded minor influences. Leafy vegetables were consumed at least four times per week in Igwuruta and Port Harcourt, while households in Ahoada and Kaiama, where culture had strong influence, consumed them only occasionally. Vegetables consumed were mainly pumpkin leaves (Telfairia occidentialis) and okro (Abelmoschus esculentus) in areas where season played a strong role. In areas where culture had a strong  influence, bitterleaf, a leafy vegetable that undergoes rigorous process of squeezing and washing and is only scantly used in soups, was the vegetable of choice. Other vegetables less frequently consumed were Amaranthus hybridus, Pterocarpus spp.,Gnetum africanum and Piper guineense leaves. These were used chiefly in varioussoup dishes eaten as accompaniments with the starchy staples. Other dishes inwhich leafy vegetables were consumed were pottage in those areas of high  vegetable consumption, and occasionally in stew by all households investigated. Household size of 5 to 8 persons consumed their soup dishes between two and four days, while larger households of nine and above ate their soups in one day. However, households with deep freezer facilities stored their soup dishes for up to seven days. In spite of the reasonable consumption of vegetables during the peak season of production, reports of micronutrient deficiencies in Nigeria are rife, indicating a need for intervention. Possible reasons for the high prevalence of  micronutrient deficiencies are seasonal variations in vegetable production,  inadequate processing and preservation of vegetables for all year distribution and culture which may limit adequate consumption of leafy vegetables even when they are in abundance. This situation underscores the need for nutrition education,  coupled with a program on dietary diversification to create awareness, increase production, processing, preservation and consumption of vegetables.Key words: Vegetable consumption, season, culture, nutrition education Le modèle de consommation de légumes tel que pratiqué par des ménages dans desrégions sélectionnées de l’ancien Etat de ‘Rivers’ (aujourd’hui Etats de Rivers et deBayelsa) au Nigeria a fait l’objet de recherche. Les régions étudiées étaient Port  Harcourt, la Capitale de l’Etat, Igwuruta, Ahoada et Kaiama. Les résultats ont montré que des mères consommaient entre 59 ± 0.45g et 130 ±  2.04g/personne/jour de légumes entre les mois de mai et de juillet, la saison  maximale de production de légumes. Il s’est avéré que les facteurs qui ont influencé la consommation de légumes étaient principalement la saison et la culture. D’autres facteurs étaient la disponibilité/le prix pour 43.8% des ménages de Kaiama, une  communauté riveraine, tandis que le goût et la connaissance en matière de nutrition ont joué une influence mineure. Les légumes verts étaient consommés au moins quatre fois par semaine à Igwuruta et à Port Harcourt, tandis que les ménages  d’Ahoada et de Kaiama, où la culture a une forte influence, ne les consommaient que de temps à autre. Les légumes consommés étaient principalement les feuilles de courge (Telfairia occidentialis) et okro (Abelmoschus esculentus) dans les régions où la saison jouait un grand rôle. Dans les régions où la culture a une forte  influence, la feuille amère, un légume vert qui subit un processus rigoureux qui consiste à le presser et le laver, et qui n’est utilisé que légèrement dans les soupes, était le légume favori. D’autres légumes moins fréquemment consommés étaient les feuilles d’Amaranthus hybridus, de Pterocarpus spp., devGnetum africanum et de Piper guineense. Ces légumes étaient utilisés surtout dans les différentes variétésde soupes mangées comme des accompagnements avec les aliments de base  riches en féculents. D’autres plats dans lesquels des légumes verts étaient  consommés étaient des potages dans ces régions de grande consommation de légumes, et de temps à autre en ragoût par tous les ménages qui ont fait l’objet de l’étude. Les ménages d’une taille de 5 à 8 personnes consommaient leurs plats de soupes entre deux et quatre jours, tandis que de plus grands ménages de neuf  personnes et plus mangeaient leurs soupes en une journée. Cependant, les  ménages qui ont des réfrigérateurs conservaient leurs plats de soupes jusqu’à sept jours. En dépit de la consommation raisonnable de légumes pendant la saison maximale de production, les rapports sur les carences en micronutriments au Nigeria vont bon train, indiquant une nécessité d’intervention. Les raisons possibles qui expliquent cette prévalence élevée des carences en micronutriments sont les variations saisonnières en production de légumes, un traitement inadéquat et une mauvaise conservation des légumes à répartir sur toute l’année, ainsi qu’une culture qui peut limiter une consommation adéquate des légumes verts même lorsqu’il y en a en abondance. Cette situation met en exergue la nécessité d’une éducation portant sur la nutrition, complétée par un programme sur la diversification  alimentaire en vue d’une prise de conscience, d’une augmentation de la production, du traitement, de la conservation et de la consommation des légumes.Mots-clés: Consommation de légumes, saison, culture, éducation portant sur la nutritio