• The importance of root hairs in the uptake of sparingly soluble nutrients is understood qualitatively, but not quantitatively, and this limits efforts to breed plants tolerant of nutrient-deficient soils. • Here, we develop a mathematical model of nutrient uptake by root hairs allowing for hair geometry and the details of nutrient transport through soil, including diffusion within and between soil particles. We give illustrative results for phosphate uptake. • Compared with conventional 'single porosity' models, this 'dual porosity' model predicts greater root uptake because more nutrient is available by slow release from within soil particles. Also the effect of soil moisture is less important with the dual porosity model because the effective volume available for diffusion in the soil is larger, and the predicted effects of hair length and density are different. • Consistent with experimental observations, with the dual porosity model, increases in hair length give greater increases in uptake than increases in hair density per unit main root length. The effect of hair density is less in dry soil because the minimum concentration in solution for net influx is reached more rapidly. The effect of hair length is much less sensitive to soil moisture.
No abstract is provided for this article.
Our studies are part of a programme of research into possible harmful effects of heavy metal‐contaminated sewage sludge being applied to soils supporting growth of trees. We have shown that ectomycorrhizal fungi vary in their growth response to heavy metals incorporated into agar plates. Lacearia laccata proved sensitive to Cu and Al when the concentration reached only 10 ppm but was tolerant of Zn at 10 ppm. Thelephora terrestris proved highly tolerant of Cu at 100 and 500 ppm in agar plates and Zn even at 1000 ppm. Mycelial growth in liquid media was inhibited between 200 and 400 ppm Cu. Growth of T. terrestris was reduced by 100 ppm Al. Suillus variegatus proved to be the most tolerant of Al on agar plates with growth increasing at least up to 100 ppm. It was sensitive to Cu at 100 ppm (but not consistently) and Zn at 1000 ppm. Abnormal morphological changes were observed in Scots pine mycorrhizas (T. terrestris) subjected to continuous application of Zn and Cu (as sulphates) in pots in the greenhouse. X‐ray micro‐analysis of the mycorrhizas in a scanning electron microscope revealed accumulation of Zn in the mycobiont‐hyphae. The studies indicate problems that might result from addition of excessive amounts of metals to soils with developing trees.
No abstract is provided for this article.
The exudation of soluble carbon compounds from Zea mays roots was investigated over a 10 day growth period under sterile and non-sterile solution culture c
The external morphology of spore-bearing gills of the agaric, Coprinus cinereus, has been studied, employing the Hexland cryo-apparatus attached to a Cambridge Stereoscan electron microscope. To assess the advantages of looking at frozen-hydrated material, a comparison has been made with similar tissue which had been chemically fixed and critical point-dried. Although good preservation of the basidiospores was achieved by the latter technique, the basidia were seen to have a wrinkled appearance and the cystidia were sometimes damaged with portions missing and never attained the ‘full-blown’ appearance of those on cryofixed gills. Additionally what appears to be a mucilaginous layer covering the gills, largely absent or indistinct in critical point-dried specimens but with remnants remaining as a fibrous network on the basidiospores, was preserved in frozen-hydrated ones.
Livestock slurry contains a large amount of particulate organic matter. When applied to soil these particles can act as carriers transporting phosphorus (P) through and over soils to watercourses. Little is known, however, about how slurry treatment (e.g. acidification and anaerobic digestion) may affect slurry particle size distribution and P forms within the particulate fraction. To characterize the small slurry particles, we separated untreated, acidified and anaerobically digested cattle slurry into 0.45–63 μm, <0.45 μm, <100 kDa and <3 kDa fractions and determined their P speciation. To understand the role of slurry particles on P leaching/translocation in soil, we applied the <63 μm, <0.45 μm and <100 kDa fractions of untreated and processed slurries to the surface of an unplanted agricultural, sand-textured soil in laboratory microcosms and studied P movement under a simulated rainfall regime. Results showed that the 0.45–63 μm particulate fraction accounted for >60% of total P content of the untreated and anaerobically digested cattle slurries. Acidification reduced the total P quantity of the 0.45–63 μm fraction by 26% through dissolution and desorption, resulting in a greater P in the <0.45 μm fraction. Anaerobic digestion increased the total P content of the 0.45–63 μm fraction, as the decomposition and breakdown of coarser particles transferred more P to this fraction. After application to soil, 3.3% of the added inorganic P and 1.7% of the added organic P was found in the leachate in the untreated <63 μm treatment. The 0.45–63 μm particulate fraction largely contributed to this P leaching, while the nanoparticulate fraction (3 kDa-0.45 μm) contained little P and had no appreciable effect on P leaching. Overall, acidification had no impact on P leaching. In contrast, anaerobic digestion increased inorganic P leaching by 67% and organic P leaching by 127%. In conclusion, our findings highlight the importance of the 0.45–63 μm fraction in P transport through soil, and the enhanced bioavailability and mobility of P following anaerobic digestion. These need greater consideration in future studies promoting the sustainable use of livestock waste and P recovery technologies.
Morphological features of narcissus flower stem surfaces in a scanning electron microscope varied according to the preparative techniques used. Thus epi-cuticular wax configurations were seen on unfixed and prefixed flowering stems, which had been freeze-dried, but not on those which were critical point dried.
An examination of roots of hybrid larch from a farm forestry site by scanning electron microscopy has revealed crystalline deposits encrusting mantle hyphae of the associated ectomycorrhizal fungus. Electron probe micro-analysis identified calcium in the crystals and X-ray diffraction showed them to be whewellite, the monohydrate form of calcium oxalate. The significance of the finding is discussed.
Soil carbon (C) and nitrogen (N) cycles are inextricably linked, yet the impacts of N availability upon soil C sequestration and turnover are poorly understood. According to stoichiometric theory, in the absence of nutrient limitation substrate decomposition will reach maximum rates, with C assimilated into microbial biomass at the expense of CO2 production. In this study, we added a 14C labelled low molecular weight substrate (glucose) to a sandy soil along with eleven increasing levels of N, phosphorus (P), and sulphur (S) in relative proportions as required for microbial biomass production. Adding a simple soluble substrate allowed us to explicitly examine changes in microbial transformations of added C, rather than changes resulting from extracellular enzyme activity or the extent of substrate decomposition. We hypothesized that as nutrient addition increased, an increasing proportion of the glucose-C provided would be incorporated into microbial biomass at the expense of CO2 production and stabilized as soil organic carbon (SOC). Instead, CO2 production from glucose-C increased significantly with nutrient addition without measurable changes in glucose-derived microbial biomass or SOC. This suggests that if there was greater glucose-derived microbial biomass produced under higher nutrient addition it was offset by a higher rate of microbial biomass turnover. We also found greater soil-derived microbial biomass at lower nutrient addition levels, potentially supporting the concept of microbial mining of soil organic matter (SOM) for nutrients under low nutrient availability. In conclusion, our data suggest that in a sandy soil with low capacity for physical protection of SOM, nutrient addition does not immediately promote C sequestration in the soil microbial community, and that the interaction between C stabilization and nutrient addition requires further work, especially for predicting ecosystem responses.
The unique mode of nutrition by carnivorous plants makes the facilitation of nutrient acquisition by mycorrhizal fungi seem unlikely. However, previously w
