Energetics in the global marinefauna: A connection between terrestrial diversification and change in the marine biosphere

Measurement of soil microbial biomass provides an early indication of changes in total soil organic matter due to straw incorporation

Influence of sorghum residues and tillage on soil organic matter and soil microbial biomass in an australian vertisol

Abstract. Initial soil development and enhanced nutrient retention are often important underlying environmental factors during primary succession. We quantified the accumulation rates of nitrogen (N) and soil organic matter (SOM) in a 37-year-long chronosequence of Leymus arenarius dunes on the pristine volcanic island Surtsey in order to illuminate the spatiotemporal patterns in their build-up. The Leymus dune area, volume and height grew exponentially over time. Aboveground plant biomass, cover or number of shoots per unit area did not change significantly with time, but root biomass accumulated with time, giving a root / shoot ratio of 19. The dunes accumulated on average 6.6 kg N ha−1 year−1, which was 3.5 times more than is received annually by atmospheric deposition. The extensive root system of Leymus seems to effectively retain and accumulate a large part of the annual N deposition, not only deposition directly on the dunes but also from the adjacent unvegetated areas. SOM per unit area increased exponentially with dune age, but the accumulation of roots, aboveground biomass and SOM was more strongly linked to soil N than time: a 1 g m−2 increase in soil N led on average to a 6 kg C m−2 increase in biomass and SOM. The Leymus dunes, where most of the N has been accumulated, will therefore probably act as hot spots for further primary succession of flora and fauna on the tephra sands of Surtsey.

The decrease of biodiversity related to the phenomena of global climate change is stimulating the scientific community towards a better understanding of the relationships between biodiversity and ecosystem functioning. In ecosystems where marked biodiversity changes occur at seasonal time scales, it is easier to relate them with ecosystem functioning. The objective of this work is to analyse the relationship between phytoplankton diversity and primary production in St. Andre coastal lagoon — SW Portugal. This lagoon is artificially opened to the sea every year in early spring, exhibiting a shift from a marine dominated to a low salinity ecosystem in winter. Data on salinity, temperature, nutrients, phytoplankton species composition, chlorophyll a (Chl a) concentration and primary production were analysed over a year. Modelling studies based on production-irradiance curves were also conducted. A total of 19 taxa were identified among diatoms, dinoflagellates and euglenophyceans, the less abundant group. Lowest diversities (Shannon— Wiener index) were observed just before the opening to the sea. Results show a negative correlation (p 90% of cell abundance) and production was maximal (up to 234.8 mg C m−3 h−1). Maximal photosynthetic rates (Pmax) (2.0–22.5 mg C mg Chl a −1 h−1) were higher under lower Chl a concentrations. The results of this work suggest that decreases in diversity are associated with increases in biomass and production, whereas increases correspond to opposite trends. It is suggested that these trends, contrary to those observed in terrestrial and in some benthic ecosystems, may be a result of low habitat diversity in the water column and resulting competitive pressure. The occurrence of the highest photosynthetic rates when Chl a is low, under some of the highest diversities, suggests a more efficient use of irradiance under low biomass-high diversity conditions. Results suggest that this increased efficiency is not explained by potential reductions in nutrient limitation and intraspecific competition under lower biomasses and may be a result of niche complementarity.

A mathematical model to describe polynuclear aromatic hydrocarbon (PAH) desorption, transport, and biodegradation in saturated soil was constructed by describing kinetics at a microscopic level and incorporating this description into macroscale transport equations. This approach is novel in that the macroscale predictions are made independently from a knowledge of microscale kinetics and macroscopic fluid dynamics and no adjustable parameters are used to fit the macroscopic response. It was assumed that soil organic matter, the principal site of PAH sorption, was composed of a continuum of compartments with a gamma distribution of desorption rate coefficients. The mass transport of substrates and microorganisms in a mesopore was described by diffusion and that in a macropore by one-dimensional advection and dispersion. Naphthalene was considered as a test PAH compound for initial model simulations. Three mechanisms of naphthalene biodegradation were considered: growth-associated degradation as a carbon and energy source for microbial growth; degradation for maintenance energy; and growth-independent degradation. The Haldane modification of the Monod equation was used to describe microbial growth rates and to account for possible growth inhibition by naphthalene. Multisubstrate interactions were considered and described with a noninteractive model for specific growth rates. The sensitivity of selected model parameters was analyzed under conditions when naphthalene was the sole growth-rate-limiting substrate. The time necessary to achieve a specific degree of naphthalene biodegradation was found to be proportional to the initial concentration of naphthalene in soil organic matter. The biodegradation rate of naphthalene increased when the sorption equilibrium constant of naphthalene was reduced. The presence of an alternative carbon source inhibited naphthalene biodegradation in spite of the calculated increase in biomass. (c) 1996 John Wiley & Sons, Inc.

It is unclear how changing atmospheric composition will influence the plant–soil interactions that determine soil organic matter (SOM) levels in fertile agricultural soils. Positive effects of CO2 fertilization on plant productivity and residue returns should increase SOM stocks unless mineralization or biomass removal rates increase in proportion to offset gains. Our objectives were to quantify changes in SOM stocks and labile fractions in prime farmland supporting a conventionally managed corn–soybean system and the seasonal dynamics of labile C and N in soybean in plots exposed to elevated [CO2] (550 ppm) under free-air concentration enrichment (FACE) conditions. Changes in SOM stocks including reduced C/N ratios and labile N stocks suggest that SOM declined slightly and became more decomposed in all plots after 3 years. Plant available N (>273 mg N kg−1) and other nutrients (Bray P, 22–50 ppm; extractable K, 157–237 ppm; Ca, 2,378–2,730 ppm; Mg, 245–317 ppm) were in the high to medium range. Exposure to elevated [CO2] failed to increase particulate organic matter C (POM-C) and increased POM-N concentrations slightly in the surface depth despite known increases (≈30%) in root biomass. This, and elevated CO2 efflux rates indicate accelerated decay rates in fumigated plots (2001: elevated [CO2]: 10.5 ± 1.2 μmol CO2 m−2 s−1 vs. ambient: 8.9 ± 1.0 μmol CO2 m−2 s−1). There were no treatment-based differences in the within-season dynamics of SOM. Soil POM-C and POM-N contents were slightly greater in the surface depth of elevated than ambient plots. Most studies attribute limited ability of fumigated soils to accumulate SOM to N limitation and/or limited plant response to CO2 fertilization. In this study, SOM turnover appears to be accelerated under elevated [CO2] even though soil moisture and nutrients are non-limiting and plant productivity is consistently increased. Accelerated SOM turnover rates may have long-term implications for soil’s productive potential and calls for deeper investigation into C and N dynamics in highly-productive row crop systems.

Tropical forests store and sequester large amounts of carbon in above‐ and below‐ground plant biomass and soil organic matter (SOM), but how these are driven by abiotic and biotic factors remains poorly understood. Here, we test the effects of abiotic factors (light variation, caused by logging disturbance, and soil fertility) and biotic factors (species richness and functional trait composition) on biomass stocks (above‐ground biomass, fine root biomass), SOM and productivity in a relatively monodominant Guyanese tropical rainforest. This forest grows on nutrient‐poor soils and has few species that contribute most to total abundance. We, therefore, expected strong effects of soil fertility and species’ traits that determine resource acquisition and conservation, but not of diversity. We evaluated 6 years of data for 30 0.4‐ha plots and tested hypotheses using structural equation models. Disturbance increased productivity but decreased above‐ground biomass stocks. Soil phosphorus (P) enhanced above‐ground biomass and productivity, whereas soil nitrogen reduced fine root biomass. In contrast to expectations, trait values representing acquisitive strategies (e.g. high leaf nutrient concentration) increased biomass stocks, possibly because they indicate higher nutrient absorption and thus higher biomass build‐up. However, under harsh conditions where biomass increase is slow, acquisitive trait values may increase respiration and vulnerability to hazards and therefore increase biomass loss. As expected, species richness did not affect productivity. We conclude that light availability (through disturbance) and soil fertility—especially P—strongly limit forest biomass productivity and stocks in this Guyanese forest. Low P availability may cause strong environmental filtering, which in turn results in a small set of dominant species. As a result, community trait composition but not species richness determines productivity and stocks of biomass and SOM in tropical forest on poor soils. A plain language summary is available for this article.

Drivers of phytoplankton biomass and diversity in a macrotidal bay of the Amazon Mangrove Coast, a Ramsar site

The hypothesis that increasing nutrient supply increases the biomass of autotrophs pro- portionately more than the biomass of heterotrophs was tested by increasing (0, 1-, 2-, 4-, 8-, and 16- fold over the background loading of 5 mmol N m -2 d -1 , 1.6 mmol Si m -2 d -1 , and 0.25 mmol P m -2 d -1 ) the addition of nutrients to large (33 000 l) mesocosm units enclosing an oligotrophic coastal Mediter- ranean planktonic community. Autotrophic plankton biomass increased 50-fold along the range of nutrient inputs, whereas heterotrophic biomass increased only 10-fold. Heterotrophic biomass in- creased as the 1 ⁄5 power of the increase in the biomass of autotrophs, implying that the ratio of hetero- troph to autotroph biomass (HB/AB ratio) declined rapidly as the biomass of autotrophs increases with increasing nutrient inputs. The biomass distribution within the community shifted from an 'inverted pyramid' distribution, involving greater biomass of heterotrophs than that of autotrophs, at low nutrient inputs, to the conventional 'upward' pyramid pattern, where the biomass of autotrophs exceeds that of consumers, at the highest nutrient inputs. This shift stabilized after 4 d, and the pyra- mids remained quite constant for the rest of the experiment. The experimental test presented sup- ports the hypothesis that the relative biomass distribution between heterotrophs and autotrophs is regulated by nutrient supply.

Water-column mixing is known to have a decisive impact on plankton communities. The underlying mechanisms depend on the size and depth of the water body, nutrient status and the plankton community structure, and they are well understood for shallow polymictic and deep stratified lakes. Two consecutive mixing events of similar intensity under different levels of herbivory were performed in enclosures in a shallow, but periodically stratified, eutrophic lake, in order to investigate the effects of water-column mixing on bacteria abundance, phytoplankton abundance and diversity, and rotifer abundance and fecundity. When herbivory by filter-feeding zooplankton was low, water-column mixing that provoked a substantial nutrient input into the euphotic zone led to a strong net increase of bacteria and phytoplankton biomass. Phytoplankton diversity was lower in the mixed enclosures than in the undisturbed ones because of the greater contribution of a few fast-growing species. After the second mixing event, at a high biomass of filter-feeding crustaceans, the increase of phytoplankton biomass was lower than after the first mixing, and diversity remained unchanged because enhanced growth of small fast-growing phytoplankton was prevented by zooplankton grazing. Bacterial abundance did not increase after the second mixing, when cladoceran biomass was high. Changes in rotifer fecundity indicated a transmission of the phytoplankton response to the next trophic level. Our results suggest that water-column mixing in shallow eutrophic lakes with periodic stratification has a strong effect on the plankton community via enhanced nutrient availability rather than resuspension or reduced light availability. This fuels the basis of the classic and microbial food chain via enhanced phytoplankton and bacterial growth, but the effects on biomass may be damped by high levels of herbivory.

The microcalorimetric method was used to calculate the metabolic enthalpy change per mol of glucose degraded by soil microorganisms, ΔH met. This parameter has been calculated by microcalorimetry for many organic, inorganic and biochemical reactions, but there is only some information about its quantification for microbial growth reactions in soils. Values of ΔH met were calculated for different soil samples collected in Galicia (Spain) and Campinas (Săo Paolo, Brazil). Exponential microbial growth was stimulated in all soil samples by the addition of glucose and power-time curves were recorded. Results showed changes in the values of ΔH met calculated for all the soil samples, suggesting a dependence of this value with the microbial growth rate constant, with the percentage of growth, with the initial number of microorganisms of soil samples, with the quantity of glucose added and with the strain of bacteria growing in soil. The interpretation of variations of ΔH met provides important qualitative and quantitative information. It reports data that allow to interpret from a qualitative point of view, the increase in biomass as a consequence of the degradation of the organic matter in soil, to understand changes in the percentages of soil organic matter and to know if the microbial population growing in differential soil samples is homogeneous. Therefore, to report that value would be very important in ecological studies, but beforehand, it is necessary to solve some problems that can appear in the experiments done to make the quantification .

Is there a linear relationship between priming effect intensity and the amount of organic matter input?

Phosphorus (P) is the most limiting nutrient for plant growth and productivity in many regions worldwide especially in the tropics. Aside intrinsic low P availability controlled by physicochemical and biological reactions, erosion and yield harvest are also very crucial in P depletion. These processes are massively intensified through anthropogenic activities, such as land-use change, the predominant global change of this century due to increasing population and food demand. Land-use change in consequence, affects P mobilization directly or indirectly through major modification of soil properties and functions. Hence, profound knowledge on abiotic and biotic factors affecting various P pools is necessary to understand the P dynamics and mobilization and to obtain a more effective soil management practices towards P conservation. Most studies were focused only on assessing the effects of land-use change on available P, but the other P pools such as Fe-bound P and microbial biomass P which are very important as reserve P pools especially in P-depleted soil were rarely considered. Therefore, this thesis aims at assessing the impacts of land-use on abiotic and biotic processes controlling forms, distribution and availability of P in soil. The P sequential fractionation approach following Hedley method (1982) was used to assess the various P pools. The Hedley fractionation method estimates the P forms that have potential contribution to available P over a growing season. The extent of the method on extracting P from various pools and the mechanisms behind P dynamics was validated in an incubation experiment using 33P tracer isotope. The incorporation of 33P-labeled KH2PO4 was traced in available P, microbial biomass P and Fe-bound P pools in an acidic P-depleted soil (Cambisol) depending on availability of carbon and nitrogen provided via applying glucose and ammonium sulfate, respectively. The Hedley fractionation was very efficient and accurate in extracting various P forms. The P immobilization via microbial uptake and fixation by the Fe and Al oxides was almost instantaneous. Applying glucose boosted microbial growth and so demand for P, resulting in increased 33P recovery and P content in microbial biomass. The microbial biomass P, as the most important labile P reservoir prohibits P fixation and increases the availability of P to plants during biomass turnover. In contrast, the high 33P recovery in Fe-bound P pool showed the dominance of P adsorption by Fe and Al oxides on P fixation and so less availability for plants. The potential contribution of earthworms (another biotic factor) on P availability was also investigated. By coupling 14C imaging and direct zymography for the first time, we visualized and localized the effects of earthworms on distribution of litter and C compounds as well as enzymes activity throughout soil profile. Earthworms bury above ground litter, produce casts and mucus that enhance the activity of beneficial soil microorganisms, colonizing earthworms' biopores and so affect the P mobilization. Indeed, increase in microbial biomass P in the biopores and the activity of phosphatase enzymes which is responsible in hydrolyzing recalcitrant forms of organic P to become available for plants, were recorded. In the second part of this thesis, we found out that the change of forests to: (a) intensively-managed oil palm and rubber plantations in the tropics and; (b) organic and conventional farming in sub-tropics alters the distribution of P pools through controlling abiotic and biotic reactions in soil. Organic and inorganic fertilizers application increases easily-available inorganic P. However, by decrease of easily-available organic P, moderately-available and non-available P intensifies. This means that fertilization maintains soil fertility only for a short time and fertilization is not sustainable in the long run due to the depletion of P reserves. The mechanisms of depletion in this easily-available P pool through land-use change are: 1) soil erosion; 2) microbial mineralization of soil organic matter (SOM) and 3) P export via yield products. The intensified reduction in SOM contents induced by land-use change is the major influencing factor on P mobilization. Decreasing SOM furthermore, promotes soil compaction and reduces soil water holding capacity that leads to flooding. In the third part of this thesis, we demonstrated that anaerobic conditions which may take place following flooding accompanying decreasing SOM contribute to P mobilization and so the potential uptake of P by plant roots. The extent of microbial-mediated reduction process leading to dissolution of ferric oxides is apparently determined by the SOM content. SOM is the source of carbon and energy which enables microorganisms to efficiently reduce Fe3+. Therefore, soils under forest and agroforest, with relatively high SOM content, resulted in a faster and higher P release than the plantation soils. Furthermore, increasing bulk density and in consequence flooding in soils under rubber and particularly under oil palm plantations led to lengthier anaerobic conditions and so more Fe3+ reduction and P release. In conclusion, land-use change leads to major modification of soil properties and functions that affect abiotic and biotic mechanisms controlling the dominant type of P pool and their distribution in a soil, and determine the dynamics of P pools transformation and P availability for plants. Among all the affecting factors, the mechanisms controlling P mobilization and availability are more closely linked to SOM content. Thus, ecologically-based managements to reduce SOM content loss are necessary to have the highest P availability for plants and so higher yield.

Soil nitrogen cycling is determined by the competition between mycorrhiza and ammonia-oxidizing prokaryotes.

The capacity of epifauna to control algal proliferation following nutrient input depends on responses of both grazers and upper trophic level consumers to enrichment. We examined the responses of Thalassia testudinum (turtle grass) epifaunal assemblages to nutrient enrichment at two sites in Florida Bay with varying levels of phosphorus limitation. We compared epifaunal density, biomass, and species diversity in 2 m2 plots that had either ambient nutrient concentrations or had been enriched with nitrogen and phosphorus for 6 months. At the severely P-limited site, total epifaunal density and biomass were two times higher in enriched than in unenriched plots. Caridean shrimp, grazing isopods, and gammarid amphipods accounted for much of the increase in density; brachyuran crabs, primary predatory fish, and detritivorous sea cucumbers accounted for most of the increase in biomass. At the less P-limited site, total epifaunal density and biomass were not affected by nutrient addition, although there were more caridean shrimp and higher brachyuran crab and pink shrimp biomass in enriched plots. At both sites, some variation in epifaunal density and biomass was explained by features of the macrophyte canopy, such as T. testudinum and Halodule wrightii percent cover, suggesting that enrichment may change the refuge value of the macrophyte canopy for epifauna. Additional variation in epifaunal density and biomass was explained by epiphyte pigment concentrations, suggesting that enrichment may change the microalgal food resources that support grazing epifauna. Increased epifaunal density in enriched plots suggests that grazers may be able to control epiphytic algal proliferation following moderate nutrient input to Florida Bay.