Feather mosses utilize various sources of nitrogen (N): they absorb N deposited on leaf tissue, they host N2 fixing cyanobacteria, and they are able to take up N directly from soil. In addition to their importance as primary producers in boreal ecosystems, feather mosses play a significant role in N cycling. However, estimates of their ability to take up N from soil in situ are scarce. Further, connecting uptake of N from soil with N2 fixation could significantly improve our understanding of their role in ecosystem N cycling, but to date this issue has not been addressed. We report results from an uptake experiment in which we tracked 13C-carbon (C), 15N-alanine and 15N-ammonium chloride (NH4Cl) into feather moss (Pleurozium schreberi (Brid.) Mitt.)-soil cores taken along natural fertility gradients in Northern Sweden. The varying fertility conditions coincided with a N2 fixation gradient in the feather moss. We found that P. schreberi takes up C and N directly from soil. However, the moss did not show a preference for inorganic or organic N sources and only 1.4% of the added amino acid appeared to be taken up from soil in an intact form. No differences in uptake of C or N from soil along the fertility gradients were detected. Nitrogen fixation rates in the moss were thus not correlated with C or N-uptake from soil. Nitrogen fixation as well as uptake of C and N from soil seem to be unaffected by C or N availability in the soil, suggesting that the moss can cover its nutrient demand by absorption of throughfall N and via associated N2-fixing cyanobacteria without soil-N supplementation. We suggest further, that the moss can represent a (temporary) N-sink in the boreal forest, and that the moss' mechanism of uptake and release thereby will characterize the ecosystem N cycle.
Summary Despite considerable attention over the last 25 yr, the importance of early protein breakdown products to plant nitrogen (N) nutrition remains uncertain. We used rhizosphere injection of 15 N‐, 13 C‐ and 14 C‐labelled inorganic N and amino acid ( l ‐alanine), with chase periods from 1 min to 24 h, to investigate the duration of competition for amino acid between roots ( Triticum aestivum ) and soil microorganisms. We further investigated how microbial modification of l ‐alanine influenced plant carbon (C) and N recovery. From recovery of C isotopes, intact alanine uptake was 0.2–1.3% of added. Soil microbes appeared to remove alanine from soil solution within 1 min and release enough NH 4 + to account for all plant 15 N recovery (over 24 h) within 5 min. Microbially generated inorganic or keto acid C accounted for < 25% of the lowest estimate of intact alanine uptake. Co‐location of C and N labels appears a reasonable measure of intact uptake. Potential interference from microbially modified C is probably modest, but may increase with chase period. Similarly, competition for l ‐alanine is complete within a few minutes in soil, whereas NO 3 − added at the same rate is available for > 24 h, indicating that long chase periods bias outcomes and fail to accurately simulate soil processes.
No abstract is provided for this article.
Alleviation of subsoil acidity with lime or gypsum increases carbon (C) accumulation in deep layers by stimulating root growth and C and nitrogen (N) inputs at depth. However, the effects of these amendments combined with N fertilization on soil CO2 emissions remain controversial. We evaluated the effects of superficial lime and gypsum application and N-fertilizer on C and N dynamics and microbial C use efficiency (MicCUE) in samples taken from the topsoil (0–10 cm) and subsoil (40–60 cm) of a no-till field experiment carried out in Brazil. We performed a short-term laboratory incubation with 14C-glucose and 14C-arginine to assess C and N mineralization dynamics. Liming increased topsoil pH but had no effect on subsoil acidity. A higher content of organic C, total N, and microbial biomass C and N were found in the topsoil. The addition of soil corrective (lime and gypsum) and N fertilizer had no effect on MicCUE of added 14C-glucose. However, the MicCUE of 14C-arginine was affected by the soil layer, and was higher in the subsoil. After the addition of arginine, net NH4 +-N production was highest in the topsoil control, while net NO3 −-N content was highest with lime + gypsum plus residual N in the same layer. We conclude that while lime and gypsum ameliorate soil acidity, they have minimal effect on C cycling through the microbial biomass, particularly in the subsoil.
The functional role of organic acid anions in soil has been intensively investigated, with special focus on (i) microbial respiration and soil carbon dynamics, (ii) nutrient solubilization or (iii) metal detoxification and reduction of plant metal uptake. Little is known about the interaction dynamics of organic acid anions with the soil matrix and the potential impact of adsorption and desorption processes on the functional significance of these effects. The aim of this study was to characterize experimentally the adsorption and desorption dynamics of organic acid anions in five agricultural soils differing in iron and aluminium oxide contents and using citrate as a model carboxylate. Results showed that both adsorption and desorption processes were fast in all soils, reaching a steady state within approximately 1 hour. However, for a given total soil citrate concentration (ct) the steady state was critically dependent on the starting conditions of the experiment, whether most of the citrate was initially present in solution (cl) or held on the solid phase (cs). Specifically, desorption-led processes resulted in significantly smaller steady-state solution concentrations than adsorption-led processes, indicating that hysteresis occurred. As it is not possible to distinguish between different adsorption and desorption pools in soil experimentally, a new dynamic hysteresis model that relies only on measured soil solution concentrations was developed. The model satisfactorily explained experimental data and was able to predict dynamic adsorption and desorption behaviour. To demonstrate its use, we applied the model to two relevant situations involving exudation and microbial degradation. The study highlighted the complex nature of citrate adsorption and desorption dynamics in soil. We conclude that existing models need to incorporate both temporal and hysteresis components to describe realistically the role and fate of organic acids in soil processes.
A scanning electron microscope has been employed to explore the ultrastructural features of stem lesions in peas caused by the fungal pathogen Sclerotinia sclerotiorum and to determine the mode of entry of this fungus into potato leaves. Wax rodlets covered the parchment-like tissue of the stem lesion of peas but were relatively sparse on the healthy stem surface. Hyphae from agar discs supporting growth of the fungus penetrated stomatal openings on the adaxial leaf surfaces of potato plants.
The overall aim of this study was to evaluate the benefit of mixing two large volume wastes, namely mineral processing waste and source-segregated green waste compost, on the growth performance of plants targeted towards high (horticulture/agriculture) and low (amenity/restoration) value markets. The secondary aims were to evaluate the influence of mineral waste type on plant growth performance and to undertake a simple economic analysis of the use of mineral–compost mixtures in land restoration. Our results showed that in comparison to organic wastes, mineral wastes contained a low available nutrient content which reduces compost quality. This is supported by growth trials with tomato, wheat and grass which showed that, irrespective of mineral source, plants performed poorly in compost blended with mineral waste in comparison to those grown in green waste or peat-based compost alone. In terms of consumer confidence, unlike other wastes (e.g. biosolids and construction/demolition waste) the mineral quarry wastes can be expected to be free of potentially toxic elements, however, the production costs of compost–mineral waste mixtures and subsequent transport costs may limit its widespread use. In addition, handling of the material can be difficult under wet conditions and effective blending may require the purchase of specialist equipment. From our results, we conclude that mineral fines may prove useful for low quality, low value landscaping activities close to the source of production but are unsuited to high value markets.
Der trigonal‐bipyramidale Titelkomplex (I) wird durch die Bestrahlung von Dodecacarbonyltriruthenium in n‐Hexan unter N 2 in Gegenwart von Triphenylstibin gebildet und isoliert.
The impact of Erythrina poeppigiana on soil characteristics, at three different positions relative to the shade tree and from three different soil depths,
Summary The ability of plants to compete effectively for nitrogen (N) resources is critical to plant survival. However, controversy surrounds the importance of organic and inorganic sources of N in plant nutrition because of our poor ability to visualize and understand processes happening at the root–microbial–soil interface. Using high‐resolution nano‐scale secondary ion mass spectrometry stable isotope imaging (Nano SIMS ‐ SII ), we quantified the fate of 15 N over both space and time within the rhizosphere. We pulse‐labelled the soil surrounding wheat ( Triticum aestivum ) roots with either or 15 N‐glutamate and traced the movement of 15 N over 24 h. Imaging revealed that glutamate was rapidly depleted from the rhizosphere and that most 15 N was captured by rhizobacteria, leading to very high 15 N microbial enrichment. After microbial capture, approximately half of the 15 N‐glutamate was rapidly mineralized, leading to the excretion of , which became available for plant capture. Roots proved to be poor competitors for 15 N‐glutamate and took up N mainly as . Spatial mapping of 15 N revealed differential patterns of 15 N uptake within bacteria and the rapid uptake and redistribution of 15 N within roots. In conclusion, we demonstrate the rapid cycling and transformation of N at the soil–root interface and that wheat capture of organic N is low in comparison to inorganic N under the conditions tested.
