Biogeochemistry (Ecology)

Eleven specimens in the Lewis and Clark Herbarium of The Academy of Natural Sciences have been sampled for biogeochemical studies-fatty acid and stable-isotope composition (delta^13C and DELTA^13C) of leaf tissues. These specimens are the earliest plant collections from the continental interior American Northwest, predating the Industrial Revolution that instigated dramatic changes in the chemistry of the world atmosphere. Comparisons are made of the preservational qualities of the Lewis and Clark specimens and modern collections, showing that the Lewis and Clark specimens are well-preserved at microscopical levels and thus are well suited for exploring their uses in biogeochemical analyses. This study demonstrates that herbarium specimens can provide data that are satisfactory to reconstruct temperature records from times and places for which climatological and other records were not kept, using biochemical proxies for growth temperature. The use of historic herbarium specimens with well-documented collection information (date and locality) can be used toward interpreting regional atmospheric chemistry, which can be applied to studies on larger geographical scales. Such forensic biogeochemical botany substantiates further the modern value of older collections in ways that were unimagined when the specimens were gathered. This is one of three complementary articles on the history, conservation, and use of the Lewis and Clark Herbarium.

Unprecedented and dramatic transformations are occurring in the Arctic in response to climate change, but academic, public, and political discourse has disproportionately focussed on the most visible and direct aspects of change, including sea ice melt, permafrost thaw, the fate of charismatic megafauna, and the expansion of fisheries. Such narratives disregard the importance of less visible and indirect processes and, in particular, miss the substantive contribution of the shelf seafloor in regulating nutrients and sequestering carbon. Here, we summarise the biogeochemical functioning of the Arctic shelf seafloor before considering how climate change and regional adjustments to human activities may alter its biogeochemical and ecological dynamics, including ecosystem function, carbon burial, or nutrient recycling. We highlight the importance of the Arctic benthic system in mitigating climatic and anthropogenic change and, with a focus on the Barents Sea, offer some observations and our perspectives on future management and policy.

Organic products in the neighboring municipalities of Nova
Friburgo and Cachoeiras de Macacú follow three primary
value chains that reach consumers through farmers markets,
home delivery baskets, and processing and distribution
industries. Organic products are mainly certified by the
participatory guarantee system. Within the first municipality,
a maximum of 86 products are distributed, where 60–70% of
the final value goes to the farmers, having a stronger set of
stakeholders. The second municipality has a maximum of 104
products distributed to final sale points, where 23–36% of the
final value goes to the farmers. Stakeholders have identified
the importance of their certification groups and potential
private alliances within the value chains.

The impact of experimentally intensified summer drought and precipitation on N2O and NO turnover and fluxes was investigated in a minerotrophic fen over a 2-year period. On three treatment plots, drought was induced for 6 and 10 weeks by means of roofs and drainage and decreased water table levels by 0.1–0.3 m compared with three nonmanipulated control plots. When averaged over the three treatment plots, both N2O and NO emission showed only little response to the drought. On the single plot scale, however, a clear impact of the treatment on N2O and NO fluxes could be identified. On the plot with the weakest water table reduction hardly any response could be observed, while on the plot with the greatest drainage effect, N2O and NO fluxes increased by 530% and 270%, respectively. Rewetting reduced NO emissions to background levels (0.05–0.15 μmol m−2 h−1), but heavily enhanced N2O emission (18–36 μmol m−2 h−1) for several days in the plots with largest water table reduction. These peaks contributed up to 40% to the cumulative N2O fluxes and were caused by rapid N2O production according to isotope abundance data. According to N2O concentrations and isotope abundance analysis N2O was mostly produced at depths between 0.3 and 0.5 m. During water table reduction net N2O production in 0.1 m depth steadily increased in the most effectively dried plot from 2 up to 44 pmol cm−3 day−1. Rewetting immediately increased net N2O production in the topsoil of the drought plots, showing rates of 18–174 pmol cm−3 day−1. This study demonstrates that drought and rewetting can temporarily increase N2O emission to levels that have to date only been reported from nutrient rich and degraded fens that have been drained for agricultural purposes.

est. Microbial biomass and activity in soils are frequently studied in tropical dry forests, but scarce information is available about the relationships between functional bacterial groups and soil fertility, where relief interacts with rainfall seasonality. The culturable-bacterial groups and nutrients were studied during two consecutive years in soils from two topographic areas of different relief (hilltop vs hillslope) in a tropical dry forest from Chamela Jalisco, Mexico. We expected that seasonal and spatial variation in soil resources availability affects the abundance of functional culturable-bacterial groups. To evaluate this, fifteen soil cores (1kg), 0-5cm depth, were taken in the dry, early rainy and rainy seasons, from each of the ten replicate plots in hilltop and hillslope areas located in three microbasins. We found that hilltop soils were more organic and had higher concentration of labile C and total nutrient forms than hillslope soils, for which these soils had higher counts of colony-forming units (CFU) of total heterotrophic and P solubilizing bacteria. In both hilltop and hillslope soils, C and nutrient concentrations, as well as the counts of CFU of heterotrophic and P solubilizing bacteria generally decreased from the dry to the rainy season during the two study years. In contrast, the counts of CFU nitrifying and cellulolytic bacteria were higher at the hillslope than at the hilltop soils. The seasonal pattern of both groups was opposite to that of heterotrophic bacteria, presumably associated with a decrease in soil labile C and organic matter quality. In conclusion, our study suggests that available C appears to be the main factor that controls the structure of soil bacterial groups and soil fertility, where relief, rainfall seasonality and intra- and inter-annual variations are critical factors that interactively modify bacterial dynamics related to soil C availability in the tropical dry forest.

This book is an attempt to address the study of soil organic matter (SOM) using an easy-to-read language; that is addressed to people which in general should have some technical training in agricultural or environmental issues. I have avoided writing a book with a strictly scientific format, given to this segment is already amply covered. In all case, I have selected tables and figures looking for a better understanding of the text. It would be possible that following reading book chapters will require more specific scientific language; for this reason, efforts were made to give enough scientific background in the Introduction and the first chapters (at least concerning to the most important concepts). Much of the written herein has been endorsed by foreign experience or obtained from our scientific works performed during years and published in international scientific media. This work begins with an Introduction and the subsequent 12 chapters describe the different aspects of the SOM from different approaches; the final chapter (Epilogue) conjugates the previous chapters and establishes the final conclusions. As indicated, the structure of this book allows a progression from basic to more difficult concepts. However, people with basic knowledge on SOM can directly afford the chapters of interest. The Prologue, written by Prof. Dr. Gonzalo ALMENDROS, a recognized authority in the field of humic substances, shows the state of art of this subject and different approaches to the study of the SOM, and it may serve as a test to the readers to know if they have enough knowledge on humus. My total gratitude to Dr. José A. ESPINOSA because he encourage me to write this book; I expect this book can be useful to the Latin-American readers. The advantage of this book over other specialist literature is the easy-to-read language used to explain a very complex and difficulty subject, as the SOM is.

Chromite ores in Forumad area from Sabzevar ophiolite belt, northeastern Iran are surrounded by magmatic dunite that is rich in nickel as compared with other ultramafics. Chromium is intensively bonded within chromite and is not an essential element for plant's life cycle, whereas Ni is more bioavailable and is an essential constituent of plant enzymes. Determined bio-concentration factor (BCF) for Ni in Salsola orientalis S.G. Gmel., the predominant plant species on the soils developed on dunite zones from 20 locations (average 0.81) indicated that Ni can be successfully used as a pathfinder for tracing the chromite ore bodies hosting dunites in the studied area. In soils developed on serpentinized ultramafics, maximum total concentrations of 719, 1150, 181, 617, 4481, 2314, and 20,790 μg g−l were determined for Ni, Cr, Co, Mn, Fe, Mg, and Ca, respectively by using Atomic Absorption Spectroscopy (AAS). Dry climate, low rainfall and high temperature of the area lead to grow a specific flora including annual and perennial herbaceous plants. The chemical data showed  excellent correlation coefficient between Cr and Ni (0.91) in soils developed on dunite zones. Investigation on 107 species from 30 families, growing on the studied soils indicated that S. orientalis could consider as promising plant for prospecting of chromite ores in Sabzevar ophiolite belt in reconnaissance survey.

The availability of organic carbon (C) affects microbial processes and nitrogen (N) dynamics in the soil. The microbial theory suggests that depending on C and N availability, microbial populations affect N transformations in the soil. However, other chemical and physical factors may be regulating the interaction between heterotrophic and nitrifying microbial populations, but is completely unknown if high nitrification rates are explained by bacterial competition by C and N in tropical soils. This paper shows how population ecology can address and propose hypotheses to explain the role of bacterial competition by C and N on the nitrification. Two models were here proposed: the first explains how bacterial intraspecific competition by C between heterotrophic microorganisms, determines N availability for nitrifying chemolitotrophic bacteria; whereas the second explains the interspecific competition between nitrifying bacteria that do not compete with heterotrophic by available C, but if by ammonium. The hypotheses are based on the competition model of Lotka-Volterra to explain how the two types of competition determine the dominance of heterotrophic bacterial populations on nitrifiers, which could explain the high nitrification rates in tropical soils. Finally, we exposed the perspectives and limitations on conceptual hypothetical model proposed for understanding the processes linked to soil N availability.

We studied the relationships between soil nutrient availability and microbial biomass and activity of two contrasting soil conditions in a tropical deciduous forest in western Mexico. Hilltops have higher pH, water, dissolved organic C, and ammonium concentrations than hillslopes. Our main hypothesis was that soil microbial biomass, microbial activity and bacterium species richness would be higher in soils with high availability of nutrients. Fifteen soil cores, 0–5 cmdepth, were taken inthe dry, early rainy andrainy season, fromeach of the ten replicate plots in hilltop and hillslope positions located on three contiguous small watersheds. We measured moisture, C, N and P availability, potential C mineralization, net nitrification, microbial biomass and culturable heterotrophic and nitrifying bacteria in composite samples from each plot. Microbial biomass, species richness of culturable heterotrophic bacteria and C mineralization were significantly higher on hilltops than on hillslopes. Net nitrification was, in contrast, significantly higher on hillslopes than on hilltops and counts of culturable nitrifying bacteria were also significantly higher in the rainy-season samples. Hilltops and hillslopes had low similarity in composition of culturable heterotrophic bacterial species, particularly during the rainy season. The results suggested that C and N availability and seasonal changes in soil moisture are important controlling factors for some soil culturable-bacterial species, which may affect both C mineralization and nitrification in these tropical deciduous forest soils.

Silicon is a non-essential element for plant growth. Nevertheless, it affects plant
stress resistance and in some plants, such as grasses, it may substitute carbon (C)
compounds in cell walls, thereby influencing C allocation patterns and biomass
production. How variation in silicon supply over a narrow range affects nitrogen
(N) and phosphorus (P) uptake by plants has also been investigated in some detail.
However, little is known about effects on the stoichiometric relationships between
C, N and P when silicon supply varies over a broader range. Here, we assessed the
effect of silicon on aboveground biomass production and C:N:P stoichiometry of
common reed, Phragmites australis, in a pot experiment in which three widely
differing levels of silicon were supplied. Scanning electron microscopy (SEM)
showed that elevated silicon supply promoted silica deposition in the epidermis of
Phragmites leaves. This resulted in altered N:P ratios, whereas C:N ratios changed
only slightly. Plant growth was slightly (but not significantly) enhanced at intermediate
silicon supply levels but significantly decreased at high levels. These findings
point to the potential of silicon to impact plant growth and elemental stoichiometry
and, by extension, to affect biogeochemical cycles in ecosystems dominated by
Phragmites and other grasses and sedges

Short-term nutrient fluxes of a groundwater-fed, flow-through lake Nutrient fluxes take place in lakes through different flow paths, and the importance of their nutrient flux changes depend on the biogeochemical processes involved. In flow-through lakes, the hydrological control of these flux processes appears to be very important, but the significance of other processes is poorly understood. To test this significance, we analyzed C, N and P fluxes on a weekly scale during mid-stratification in a Spanish calcareous lake fed by agriculturally-drained streams and groundwater. As expected, hydrologic flow paths were more important than those of biogenic fluxes for the nutrient budgets. The organic C (OC hereafter), total N and total P surface inflows and outflows differed. While C and N surface hydrological fluxes covaried, P input or output fluxes were unrelated with those of other nutrients. Net groundwater C and P fluxes covaried, but they were not related with those of N. The accumulations of OC, N and P were also related with each other. All of the biogenic fluxes were highly variable. Primary production by emergent plants (Cladium) were higher than water column photosynthesis, the latter being net autotrophic most of the time. Particulate nutrient settling rates were within the range of those in oligotrophic lakes. Denitrification was not as high as expected in the nitrate-rich water of this lake, which was limited by low levels of soluble reactive phosphorus and dissolved organic carbon. CO 2 degassing from the surface to the atmosphere was always positive, suggesting net heterotrophy, but this was the opposite of previous results. These conflicting results could be reconciled by the high hydrological inputs of inorganic carbon, which yielded more carbon dioxide to be outgassed. Albeit low, the CO 2 production from CaCO 3 formation could sometimes be a source of CO 2. However, the biogenic fluxes were higher than expected in flow-through lakes, mostly arising from the role of littoral emergent plants in nutrient fluxes, which was often neglected in biogeochemical budget studies. Furthermore, no relationship was found between water renewal time and accumulation, thus emphasizing the significance of biogenic fluxes on nutrient retention. At the ecosystem level, our study highlighted both the importance of the hydrogeological setting of the basin on nutrient fluxes and the importance of emergent vegetation on lake nutrient budgets. RESUMEN Flujos de nutrientes a corto plazo en un lago fluvial alimentado por aguas subterráneas Los flujos de nutrientes tienen lugar en los lagos siguiendo líneas de flujo diferentes, cuya importancia depende de los procesos biogeoquímicos implicados en ellos. En los lagos fluviales el control hidrológico de estos flujos es muy notable, pero la importancia de otros procesos sobre dicho control aún se conoce mal. Con objeto de mejorar el conocimiento de estos aspectos limnológicos, analizamos aquí los flujos de C, N y P a escala semanal durante el periodo central de la estratificación en un lago calcáreo español (laguna Conceja, Centro de España), alimentado por ríos y agua subterránea que han drenado zonas agrícolas. El transporte hidrológico fue más importante que los flujos biogénicos en los balances de nutrientes. Las entradas de carbono orgánico, nitrógeno y fósforo totales fueron diferentes de las salidas. Aunque los flujos hidrológicos superficiales de C y N covariaron, las entradas y salidas de P no lo hicieron. Los flujos subterráneos de C y P covariaron, pero no se relacionaron con los de N. Las acumulaciones de C orgánico, N y P estuvieron relacionadas entre sí. Todos los flujos biogénicos de nutrientes fueron muy variables. La producción primaria debida a las plantas emergentes (Cladium) fue mayor que la fotosíntesis en la columna de agua, la cual experimentó una autotrofia neta durante la mayor parte del periodo de estudio. La sedimentación de los nutrients particulados estuvo dentro del rango de la observada en otros lagos oligotróficos. La desnitrificación no fue tan alta como la esperada a juzgar por el elevado contenido en nitrato del lago, lo cual se debió a la limitación por las escasas concentraciones de fósforo reactivo soluble y carbono orgánico disuelto. El 16481_Limnetica 35(1), pàgina 147, 20/05/2016

Information about forestry insularity of plants on soil nutrients will be critical for selecting plant species for agrosilvopastoral or fertility reclamation programs in dry ecosystems. We explored the effects of four Mimosa species (M. lacerata, M. luisana, M. polyantha and M. texana var. filipes) and of rainfall seasonal variation on soil nutrients in a semiarid ecosystemlocated at the Tehuaca ´ n-Cuicatla ´ n Valley, Mexico. Soil samples were taken from outside and under the canopy at three positions (trunk, middle, edge) in all four Mimosa species; ten plants per species. The soil pH, organic matter (SOM), organic carbon (SOC), total nitrogen (Nt), available phosphorus (Pi), and major cations (Ca, Mg, K and Na) were determined. Our results showed that Mimosa species improve the soil under their canopies creating fertile islands with higher SOM, SOC, total N and Pi cycling than the soil in open areas (OA). The insularity effect was significantly species-dependent, where SOM, SOC, Nt and Pi decreased consistently from trunk to OA in all four Mimosa species; however, magnitude varied among species. Likewise, differences in the quantity of soil cations were observed among Mimosa species; though, an insularity gradient trunk-open area was not observed. All these effects were consistent across the species studied and showed little seasonal variability, suggesting a strong forestry insularity of Mimosa species on soil fertility. Of all the four Mimosa species studied, M. lacerata was the most effective in accumulating SOM and nutrients in the soil, for which it would be a good option to implement in agrosilvopastoral or fertility reclamation programs in this semiarid ecosystem.

Seasonal variation of dissolved organic C (DOC) and its effects on microbial activity and N dynamics were studied during two consecutive years in soils with different organic C concentrations (hilltop and hillslope) in a tropical deciduous forest of Mexico. We found that DOC concentrations were higher at the hilltop than at the hillslope soils, and in both soils generally decreased from the dry to the rainy season during the two study years. Microbial biomass and potential C mineralization rates, as well as dissolved organic N (DON) and NH4+ concentrations and net N immobilization were higher in soils with higher DOC than in soils with lower DOC. In contrast, net N immobilization and NH4+ concentration were depleted in the soil with lowest DOC, whereas NO3 concentrations and net nitrification increased. Negative correlations between net nitrification and DOC concentration suggested that NH4+ was transformed to NO3 by nitrifiers when the C availability was depleted. Taken together, our results suggest that available C appears to control soil microbial activity and N dynamics, and that microbial N immobilization is facilitated by active heterotrophic microorganisms stimulated by high C availability. Soil autotrophic nitrification is magnified by decreases in C availability for heterotrophic microbial activity. This study provides an experimental data set that supports the conceptual model to show and highlight that microbial dynamics and N transformations could be functionally coupled with DOC availability in the tropical deciduous forest soils.