Elemental Stoichiometric Ratios Research Articles

Early impacts of marginal land‐use transition to Miscanthus on soil quality and soil carbon storage across Europe

AbstractMiscanthus, a C4 perennial rhizomatous grass, is a low‐input energy crop suitable for marginal land, which cultivation can improve soil quality and promote soil organic carbon (SOC) sequestration. In this study, four promising Miscanthus hybrids were chosen to evaluate their short‐term potential, in six European marginal sites, to sequester SOC and improve physical, chemical, and biological soil quality in topsoil. Overall, no differences among Miscanthus hybrids were detected in terms of impacts on soil quality and SOC sequestration. SOC sequestration rate after 4 years was of +0.4 Mg C ha−1 year−1, but land‐use transition from former cropland or grassland showed contrasting SOC sequestration trajectories. In unfertilized marginal lands, cultivation of high‐yielding Miscanthus genotypes caused a depletion of K (−216 kg ha−1 year−1), followed by Ca (−56 kg ha−1 year−1), Mg (−102 kg ha−1 year−1) and to a lesser extent of N. On the contrary, the biological turnover of organic matter increased the available P content (+164 kg P2O5 ha−1 year−1). SOC content was identified as the main driver of changes in biological soil quality. High input of labile plant C stimulated an increment of microbial biomass and enzymatic activity. Here, a novel approach was applied to estimate C input to soil from different Miscanthus organs. Despite the high estimated plant C input to soil (0.98 Mg C ha−1 year−1), with significant differences among sites and Miscanthus hybrids, it was not identified as a driver of SOC sequestration. On the contrary, initial SOC and nutrients (N, P) content, as well as their elemental stoichiometric ratios with C, were the key factors controlling SOC dynamics. Introducing Miscanthus on marginal lands impacts positively soil biological quality over the short term, but targeted fertilization plans are needed to secure crop yield over the long term as well as the C sink capacity of this perennial cropping system.

Rethinking Aerobic Respiration in the Hyporheic Zone under Variation in Carbon and Nitrogen Stoichiometry.

Hyporheic zones (HZs)─zones of groundwater-surface water mixing─are hotspots for dissolved organic matter (DOM) and nutrient cycling that can disproportionately impact aquatic ecosystem functions. However, the mechanisms affecting DOM metabolism through space and time in HZs remain poorly understood. To resolve this gap, we investigate a recently proposed theory describing trade-offs between carbon (C) and nitrogen (N) limitations as a key regulator of HZ metabolism. We propose that throughout the extent of the HZ, a single process like aerobic respiration (AR) can be limited by both DOM thermodynamics and N content due to highly variable C/N ratios over short distances (centimeter scale). To investigate this theory, we used a large flume, continuous optode measurements of dissolved oxygen (DO), and spatially and temporally resolved molecular analysis of DOM. Carbon and N limitations were inferred from changes in the elemental stoichiometric ratio. We show sequential, depth-stratified relationships of DO with DOM thermodynamics and organic N that change across centimeter scales. In the shallow HZ with low C/N, DO was associated with the thermodynamics of DOM, while deeper in the HZ with higher C/N, DO was associated with inferred biochemical reactions involving organic N. Collectively, our results suggest that there are multiple competing processes that limit AR in the HZ. Resolving this spatiotemporal variation could improve predictions from mechanistic models, either via more highly resolved grid cells or by representing AR colimitation by DOM thermodynamics and organic N.

Soil Microbial Community and Soil Abiotic Factors Are Linked to Microorganisms’ C:N:P Stoichiometry in Larix Plantations

Ecological stoichiometry is an essential tool to understand carbon (C), nitrogen (N), and phosphorus (P) cycles and nutrient limitations. Plantations are usually managed to maintain specific age structures, but the impact of such management on microbial biomass and stoichiometric ratios remains unclear. We compared the stand ages of four Larix principis-rupprechtti Mayr. Plantations that were 15 years old, (young plantation, Lar15), 24 years old, (middle aged plantation, Lar24), 40 years old, (near-mature plantation, Lar40), and 50 years old, (mature plantation, Lar50), respectively, to determine the main factors that drive differences in the C:N:P stoichiometry of microorganisms. We demonstrated that the temperature, moisture, and nutrient concentrations in surface soil increased significantly with forest age. The stoichiometric ratios of elements in soil and microorganisms reached their maxima in the Lar40 and Lar50 plantations. Additionally, forest stand ages had a great influence on the biomass of microbial communities. Moreover, soil microbial community and soil abiotic factors are closely related to soil microorganisms’ C:N:P stoichiometric ratios. Specifically, changes in the microbial biomass C:N (MBC:MBN) were primarily correlated with bacteria, Gram-positive bacteria (G+), temperature, NH4+-N, and moisture in soil. Shifts in G+, actinobacteria, soil temperature, and total phosphorus were primarily associated with variation in microbial biomass C:P (MBC:MBP). Alterations in microbial biomass N:P (MBN:MBP) were correlated with bacteria, NH4+-N, water content, Gram-negative bacteria, and soil temperature. Overall, these results suggest that microbial elemental stoichiometric ratios could be affected by stand age and emphasize the importance of microbial communities and soil abiotic factors in shifting this dynamic change process.

Effects of Saltwater Pulses on Soil Microbial Enzymes and Organic Matter Breakdown in Freshwater and Brackish Coastal Wetlands

Coastal freshwater and brackish wetlands are exposed to pulses of saltwater during times of reduced freshwater flows (i.e., dry seasons, droughts), periodic storm surges, and increased tidal extent associated with rising seas. The effects of saltwater pulses on belowground processing rates of detrital organic matter as mediated by microbial activities are uncertain. Our objectives were to quantify whether and how pulses of saltwater (i) change soil porewater physicochemistry, (ii) change soil microbial extracellular enzyme activities, and (iii) change root litter breakdown over time in freshwater and brackish marshes. From 2014 to 2016, we simulated saltwater intrusion as monthly in situ pulsed additions of artificial seawater in experimental dosing chambers (1.4 m diameter) within freshwater and brackish marshes of Everglades National Park. At monthly intervals, we collected soil porewater chemistry, and measured microbial extracellular enzymes, elemental stoichiometric ratios, and breakdown rates (k) of incubated (0–30 cm depth) root litter and compared these responses over time. Saltwater pulses increased sulfate and nitrogen concentrations in porewater at the freshwater site. However, saltwater pulses generally decreased porewater constituents (e.g., dissolved organic carbon, dissolved nitrogen and phosphorus species) at the brackish site. One saltwater pulse increased root litter k by 1.25-fold in the brackish marsh. However, long-term (740 days) k in brackish wetlands, and both short- and long-term k in freshwater wetlands, were not affected by 24 monthly pulses of saltwater. Enzyme activities fluctuated with time and did not respond to multiple saltwater pulses. Our results suggest that detrital organic matter stocks and associated soil microbial activities are relatively resistant to single and multiple (n = 24) pulses of saltwater.

Hydrothermal assisted growth of CdSe nanoparticles and study on its dielectric properties

In this work, we have synthesized cadmium selenide (CdSe) nanoparticles by using cadmium chloride (CdCl2) as cadmium ion and sodium selenosulfate (Na2SeSO3) as selenium ion sources through a simple, convenient and cost-effective hydrothermal route at 180 °C temperature for 24 h. Aqueous ammonia was employed as a complex reagent to adjust the pH of the solution. Structural analysis of the obtained product was carried out by using x-ray diffractometer, which revealed that the final product has a cubic structure of CdSe with average crystallite size 13.15 nm. The cauliflower-like CdSe nanostructures were confirmed from the scanning electron microscopy and high-resolution transmission electron microscopy. EDS analysis indicates that the obtained product has a good elemental stoichiometric ratio. The electron diffraction pattern reveals the polycrystalline nature of CdSe. From UV–visible absorption spectral analysis, the optical energy bandgap of CdSe nanoparticles was found to be 1.90 eV. XPS spectra presented Cd 3d3/2, Cd 3d5/2 and Se 3d3/2 peaks at 411.04, 404.29 and 53.52 eV respectively. The CdSe nanoparticles exhibit photoluminescence with two distinct emission bands at 632 nm and 720 nm. FTIR study was used towards the understanding of the formation mechanism and bonding on the surface of the resulting nanoparticles. The dielectric properties of a pelletized sample of CdSe nanoparticles were carried out at room temperature.

Soil Carbon and Nutrient Dynamics Following Cessation of Anthropogenic Disturbances in Degraded Subtropical Forests

AbstractSoil carbon (C) and nutrient availability is fundamental to terrestrial biodiversity and functionality. In recent decades, the restoration of degraded forests has become a major concern worldwide, and recent studies have demonstrated that soil C and nitrogen (N) increase over time following restoration. However, our understanding of the responses of soil phosphorus (P), calcium (Ca), potassium (K) and magnesium (Mg) and elemental stoichiometric ratios to restoration remains elusive. We employed a chronosequence to examine the responses of C and macronutrients in three soil layers (0–10 cm, 10–20 cm and 20–30 cm) to the time (0 to 31 years) since the cessation of anthropogenic disturbances in the degraded subtropical forests of Eastern China. We found that stand basal area, soil water content, organic matter content and C concentration and stock increased, while soil pH and bulk density decreased over time, with the most pronounced effects within the 0–10 cm layer. Total and available N and K as well as available P and total Mg increased, while total P in the 20–30 cm layer and Ca in all soil layers decreased over time. The mass concentration ratios of soil C to total N and available N, P and K decreased, whereas those for C to total P and Ca as well as total N to total P and available N to available P increased over time. Our results suggest that soil C accumulation and biologically driven nutrients increase, while nutrients that are driven primarily through geochemical mechanisms decrease with live biomass accumulation following restoration. Copyright © 2017 John Wiley & Sons, Ltd.

Ecological Stoichiometry of Ocean Plankton.

Marine plankton elemental stoichiometric ratios can deviate from the Redfield ratio (106C:16N:1P); here, we examine physiological and biogeochemical mechanisms that lead to the observed variation across lineages, regions, and seasons. Many models of ecological stoichiometry blend together acclimative and adaptive responses to environmental conditions. These two pathways can have unique molecular mechanisms and stoichiometric outcomes, and we attempt to disentangle the two processes. We find that interactions between environmental conditions and cellular growth are key to understanding stoichiometric regulation, but the growth rates of most marine plankton populations are poorly constrained. We propose that specific physiological mechanisms have a strong impact on plankton and community stoichiometry in nutrient-rich environments, whereas biogeochemical interactions are important for the stoichiometry of the oligotrophic gyres. Finally, we outline key areas with missing information that is needed to advance understanding of the present and future ecological stoichiometry of ocean plankton.

Photosynthetic efficiency, cell volume, and elemental stoichiometric ratios in Thalassirosira weissflogii under phosphorus limitation

Nutrient limitation is known to inhibit growth and metabolism and to alter elemental stoichiometric ratios in phytoplankton. In this study, physiological changes in Thalassirosira weissflogii were measured under different dissolved inorganic phosphate (DIP) regimes in semi-continuous cultures to revisit the utility of the Redfield ratio for assessing nutrient limitation. The results showed that cell size increased with decreasing DIP availability. In the P-depleted treatment (f/2-P) the cell size was 1.48 times larger than that in the P-limited (f/100) treatment and 2.67 times larger than that in the P-saturated treatment (f/2 and f/10). The fucoxanthin to chlorophyll a ratio (Fuco/chl a) was relatively stable (about 0.3) in P-saturated cultures and was 10 times higher than that in P-limited and P-depleted cultures. During the experimental period, the photosynthetic efficiency index, ΔF/Fm′, was relatively stable at ∼0.50 in the P-saturated cultures, but quickly declined with decreasing DIP availability. Although cellular P content showed a significant difference between the P-saturated culture (1.6 pg/cell) and the P-limited culture (0.7 pg/cell), the N/P ratio in T. weissflogii did not show a trend with DIP availability and fluctuated slightly around 25. Our results suggest that cell division in T. weissflogii is not strictly size-gated but is probably regulated by a biochemical, and hence, an elemental stoichiometric ratio threshold, and that deviation of the cellular N/P ratio from the Redfield ratio is not a reliable indicator of algal nutrient stress.