Organic and inorganic nitrogen nutrition of western red cedar, western hemlock and salal in mineral N-limited cedar-hemlock forests

Mechanisms of Carbon Sequestration in Highly Organic Ecosystems - Importance of Chemical Ecology

Organic matter decomposition plays a major role in the cycling of carbon (C) and nutrients in terrestrial ecosystems across the globe. Climate change accelerates the decomposition rate to potentially increase the release of greenhouse gases and further enhance global warming in the future. However, fractions of organic matter vary in turnover times and parts are stabilized in soils for longer time periods (C sequestration). Overall, a better understanding of the mechanisms underlying C sequestration is needed for the development of effective mitigation policies to reduce land-based production of greenhouse gases. Known mechanisms of C sequestration include the recalcitrance of C input, interactions with soil minerals, aggregate formation, as well as its regulation via abiotic factors. In this Minireview, we discuss the mechanisms behind C sequestration including the recently emerging significance of biochemical interactions between organic matter inputs that lead to C stabilization.

Light intensity affects the uptake and metabolism of glycine by pakchoi (Brassica chinensis L.)

The uptake of glycine by pakchoi (Brassica chinensis L.), when supplied as single N-source or in a mixture of glycine and inorganic N, was studied at different light intensities under sterile conditions. At the optimal intensity (414 μmol m(-2) s(-1)) for plant growth, glycine, nitrate, and ammonium contributed 29.4%, 39.5%, and 31.1% shoot N, respectively, and light intensity altered the preferential absorption of N sources. The lower (15)N-nitrate in root but higher in shoot and the higher (15)N-glycine in root but lower in shoot suggested that most (15)N-nitrate uptake by root transported to shoot rapidly, with the shoot being important for nitrate assimilation, and the N contribution of glycine was limited by post-uptake metabolism. The amount of glycine that was taken up by the plant was likely limited by root uptake at low light intensities and by the metabolism of ammonium produced by glycine at high light intensities. These results indicate that pakchoi has the ability to uptake a large quantity of glycine, but that uptake is strongly regulated by light intensity, with metabolism in the root inhibiting its N contribution.

Post-uptake metabolism affects quantification of amino acid uptake

• The quantitative significance of amino acids to plant nutrition remains controversial. This experiment determined whether post-uptake metabolism and root to shoot export differ between glycine and glutamine, and examined implications for estimation of amino acid uptake. • Field soil containing a Eucalyptus pauciflora seedling was injected with uniformly (13)C- and (15)N-labelled glycine or glutamine. I quantified (15)N and (13)C excess in leaves and roots and intact labelled amino acids in leaves, roots and stem xylem sap. A tunable diode laser quantified fluxes of (12)CO(2) and (13)CO(2) from leaves and soil. • 60-360 min after addition of amino acid, intact molecules of U-(13)C,(15)N glutamine were < 5% of (15)N excess in roots, whereas U-(13)C,(15)N glycine was 30-100% of (15)N excess in roots. Intact molecules of glutamine, but not glycine, were exported from roots to shoots. • Post-uptake metabolism and transport complicate interpretation of isotope labelling such that root and shoot contents of intact amino acid, (13)C and (15)N may not reflect rates of uptake. Future experiments should focus on reconciling discrepancies between intact amino acid, (13)C and (15)N by determining the turnover of amino acids within roots. Alternatively, post-uptake metabolism and transport could be minimized by harvesting plants within minutes of isotope addition.

Amino acid uptake by temperate tree species characteristic of low- and high-fertility habitats

The relationship between inorganic nitrogen (N) cycling and plant productivity is well established. However, recent research has demonstrated the ability of plants to take up low molecular weight organic N compounds (i.e., amino acids) at rates that often rival those of inorganic N forms. In this study, we hypothesize that temperate forest tree species characteristic of low-fertility habitats will prefer amino acids over species characteristic of high-fertility habitats. We measured the uptake of (15)N-labeled amino acids (glycine, glutamine, arginine, serine), ammonium (NH(4)(+)), and nitrate (NO(3)(-)) by four tree species that commonly occur in eastern North America, where their abundances have been correlated with inorganic N availability. Specific uptake rates of amino acids were largely similar for all tree species; however, high-fertility species took up NH(4)(+) at rates more than double those of low-fertility species, rendering amino acid N relatively more important to the N nutrition of low-fertility species. Low-fertility species acquired over four times more total N from arginine compared to NH(4)(+) and NO(3)(-); high-fertility species acquired the most N from NH(4)(+). Arginine had the highest uptake rates of any amino acid by all species; there were no significant differences in uptake rates of the remaining amino acids. Our results support the idea that the dominant species in a particular habitat are those best able to utilize the most available N resources.

Diversity and species distribution of ectomycorrhizal fungi along productivity gradients of a southern boreal forest

Coniferous forests with diverse ectomycorrhizal fungus (EMF) communities are associated with nutrient-poor, acidic soils but there is some debate whether EMF can be equally adapted to more productive, nitrogen-rich sites. We compared EMF species distribution and diversity along a replicated productivity gradient in a southern boreal forest of British Columbia (Canada). Roots from subalpine fir (Abies lasiocarpa) saplings of the understory were sampled and EMF species were identified by morphotypes supplemented with ITS rDNA analysis. There were significant changes in the distribution and abundance of 74 EMF species along the productivity gradient, with as little as 24% community similarity among contrasting sites. Species richness per plot increased asymptotically with foliar nitrogen concentrations of subalpine fir, demonstrating that many EMF species were well suited to soils with high rates of nitrogen mineralization. EMF species abundance in relation to site productivity included parabolic, negative linear, and positive exponential curves. Both multi-site and more narrowly distributed EMF were documented, and a diverse mix of mantle exploration types was present across the entire productivity gradient. The results demonstrate strong associations of EMF fungal species with edaphic characteristics, especially nitrogen availability, and a specialization in EMF communities that may contribute to the successful exploitation of such contrasting extremes in soil fertility by a single tree host.

Uptake of organic nitrogen by plants

Languishing for many years in the shadow of plant inorganic nitrogen (N) nutrition research, studies of organic N uptake have attracted increased attention during the last decade. The capacity of plants to acquire organic N, demonstrated in laboratory and field settings, has thereby been well established. Even so, the ecological significance of organic N uptake for plant N nutrition is still a matter of discussion. Several lines of evidence suggest that plants growing in various ecosystems may access organic N species. Many soils display amino acid concentrations similar to, or higher than, those of inorganic N, mainly as a result of rapid hydrolysis of soil proteins. Transporters mediating amino acid uptake have been identified both in mycorrhizal fungi and in plant roots. Studies of endogenous metabolism of absorbed amino acids suggest that L- but not D-enantiomers are efficiently utilized. Dual labelled amino acids supplied to soil have provided strong evidence for plant uptake of organic N in the field but have failed to provide information on the quantitative importance of this process. Thus, direct evidence that organic N contributes significantly to plant N nutrition is still lacking. Recent progress in our understanding of the mechanisms underlying plant organic N uptake may open new avenues for the exploration of this subject.

Characterization of an amino acid permease from the endomycorrhizal fungus Glomus mosseae

Arbuscular mycorrhizal (AM) fungi are capable of exploiting organic nitrogen sources, but the molecular mechanisms that control such an uptake are still unknown. Polymerase chain reaction-based approaches, bioinformatic tools, and a heterologous expression system have been used to characterize a sequence coding for an amino acid permease (GmosAAP1) from the AM fungus Glomus mosseae. The GmosAAP1 shows primary and secondary structures that are similar to those of other fungal amino acid permeases. Functional complementation and uptake experiments in a yeast mutant that was defective in the multiple amino acid uptake system demonstrated that GmosAAP1 is able to transport proline through a proton-coupled, pH- and energy-dependent process. A competitive test showed that GmosAAP1 binds nonpolar and hydrophobic amino acids, thus indicating a relatively specific substrate spectrum. GmosAAP1 mRNAs were detected in the extraradical fungal structures. Transcript abundance was increased upon exposure to organic nitrogen, in particular when supplied at 2 mm concentrations. These findings suggest that GmosAAP1 plays a role in the first steps of amino acid acquisition, allowing direct amino acid uptake from the soil and extending the molecular tools by which AM fungi exploit soil resources.

Effects of different N fertilizers on the activity of Glomus mosseae and on grapevine nutrition and berry composition

Grapevine N fertilization may affect and be affected by arbuscular mycorrhizal (AM) fungal colonization and change berry composition. We studied the effects of different N fertilizers on AM fungal grapevine root colonization and sporulation, and on grapevine growth, nutrition, and berry composition, by conducting a 3.5-year pot study supplying grapevine plants with either urea, calcium nitrate, ammonium sulfate, or ammonium nitrate. We measured the percentage of AM fungal root colonization, AM fungal sporulation, grapevine shoot dry weight and number of leaves, nutrient composition (macro- and micronutrients), and grapevine berry soluble solids (total sugars or degrees Brix) and total acidity. Urea suppressed AM fungal root colonization and sporulation. Mycorrhizal grapevine plants had higher shoot dry weight and number of leaves than non-mycorrhizal and with a higher growth response with calcium nitrate as the N source. For the macronutrients P and K, and for the micronutrient B, leaf concentration was higher in mycorrhizal plants. Non-mycorrhizal plants had higher concentration of microelements Zn, Mn, Fe, and Cu than mycorrhizal. There were no differences in soluble solids ( degrees Brix) in grapevine berries among mycorrhizal and non-mycorrhizal plants. However, non-mycorrhizal grapevine berries had higher acid content with ammonium nitrate, although they did not have better N nutrition and vegetative growth.

Ethnoveterinary medicines used for ruminants in British Columbia, Canada

BACKGROUND

The use of medicinal plants is an option for livestock farmers who are not allowed to use allopathic drugs under certified organic programs or cannot afford to use allopathic drugs for minor health problems of livestock.

METHODS

In 2003 we conducted semi-structured interviews with 60 participants obtained using a purposive sample. Medicinal plants are used to treat a range of conditions. A draft manual prepared from the data was then evaluated by participants at a participatory workshop.

RESULTS

There are 128 plants used for ruminant health and diets, representing several plant families. The following plants are used for abscesses: Berberis aquifolium/Mahonia aquifolium Echinacea purpurea, Symphytum officinale, Bovista pila, Bovista plumbea, Achillea millefolium and Usnea longissima. Curcuma longa L., Salix scouleriana and Salix lucida are used for caprine arthritis and caprine arthritis encephalitis. Euphrasia officinalis and Matricaria chamomilla are used for eye problems. Wounds and injuries are treated with Bovista spp., Usnea longissima, Calendula officinalis, Arnica sp., Malva sp., Prunella vulgaris, Echinacea purpurea, Berberis aquifolium/Mahonia aquifolium, Achillea millefolium, Capsella bursa-pastoris, Hypericum perforatum, Lavandula officinalis, Symphytum officinale and Curcuma longa. Syzygium aromaticum and Pseudotsuga menziesii are used for coccidiosis. The following plants are used for diarrhea and scours: Plantago major, Calendula officinalis, Urtica dioica, Symphytum officinale, Pinus ponderosa, Potentilla pacifica, Althaea officinalis, Anethum graveolens, Salix alba and Ulmus fulva. Mastitis is treated with Achillea millefolium, Arctium lappa, Salix alba, Teucrium scorodonia and Galium aparine. Anethum graveolens and Rubus sp., are given for increased milk production. Taraxacum officinale, Zea mays, and Symphytum officinale are used for udder edema. Ketosis is treated with Gaultheria shallon, Vaccinium sp., and Symphytum officinale. Hedera helix and Alchemilla vulgaris are fed for retained placenta.

CONCLUSION

Some of the plants showing high levels of validity were Hedera helix for retained placenta and Euphrasia officinalis for eye problems. Plants with high validity for wounds and injuries included Hypericum perforatum, Malva parviflora and Prunella vulgaris. Treatments with high validity against endoparasites included those with Juniperus communis and Pinus ponderosa. Anxiety and pain are well treated with Melissa officinalis and Nepeta caesarea.