Search

Nutrient supplies to plants from ants are well known from specialised myrmecophytic symbioses and from plants growing in soil close to ant nests. However, above-ground nutrient pathways may play a largely unrecognised role also in less specialised ant-plant interactions-the numerous facultative relationships, where ants forage on plants., In a laboratory experiment, weaver ants ( Oecophylla smaragdina) were confined to the canopies of coffee ( Coffea arabica) seedlings, excluding any ant-to-plant transfer of nutrients via the soil strata. When ants were fed 15N-labelled glycine and subsequently deposited faecal droplets on the seedlings, coffee leaves showed increased levels of 15N and total nitrogen compared to control plants without ants. This was evident for both exposed leaves and leaves covered in plastic bags (i.e. not directly exposed to ants). Thus, nitrogen from ant excretions was absorbed through the coffee leaves, and subsequently, translocated within the plants and possibly leading to the observed higher shoot/root (wet weight) ratios observed on ant-plants compared to controls., Synthesis. These results reveal an undescribed foliar uptake of ant-provided nutrients. If this is a general mechanism, a vast amount of ant-plant interactions involves fertilisation. Foliar fertilisation by ants may be an important steady benefit to plants, which has driven the evolution of ant-plant mutualisms in parallel with the well-recognised but probably more fluctuating benefit from herbivore protection. Given the world-wide abundance of plant canopies foraged by ants, this nutrient pathway may be of high ecological significance. [ABSTRACT FROM AUTHOR]

Landscaping paradigms that encourage high-input, intensively managed and mono-culture turf/lawn landscapes have raised concerns about water quality. We conducted a watershed-scale assessment of landscaping practices that included turf, urban, forest, native meadow, and mixed landuse watersheds with a professional golf course and a parking lot. The turf site was moderately managed and had lower fertilizer inputs than those typically used by homeowners and golf courses. Stream water sampling was performed during base flow and storm events. Highest nitrate and total nitrogen concentrations in runoff were observed for the mixed watershed draining the golf course. In contrast, concentrations in base flow from the turf watershed were lower than expected and were comparable to those measured in the surrounding meadow and forest sites. Total nitrogen concentrations from the turf site increased sharply during the first storms following fertilization, suggesting that despite optimal management there exists a risk for nutrient runoff following fertilization. Overall, this study suggests that turf or lawns, when managed properly, pose minimal water quality risk to surface waters. Rate, timing of application, and the type of fertilizer appear to be the key factors affecting water quality. Better education of homeowners and landscaping professionals with regard to these factors may be a cost-effective strategy to reduce nonpoint source pollution. [ABSTRACT FROM AUTHOR]

A key part of the uncertainty in terrestrial feedbacks on climate change is related to how and to what extent nitrogen (N) availability constrains the stimulation of terrestrial productivity by elevated CO2 ( eCO2), and whether or not this constraint will become stronger over time. We explored the ecosystem-scale relationship between responses of plant productivity and N acquisition to eCO2 in free-air CO2 enrichment ( FACE) experiments in grassland, cropland and forest ecosystems and found that: (i) in all three ecosystem types, this relationship was positive, linear and strong ( r2 = 0.68), but exhibited a negative intercept such that plant N acquisition was decreased by 10% when eCO2 caused neutral or modest changes in productivity. As the ecosystems were markedly N limited, plants with minimal productivity responses to eCO2 likely acquired less N than ambient CO2-grown counterparts because access was decreased, and not because demand was lower. (ii) Plant N concentration was lower under eCO2, and this decrease was independent of the presence or magnitude of eCO2-induced productivity enhancement, refuting the long-held hypothesis that this effect results from growth dilution. (iii) Effects of eCO2 on productivity and N acquisition did not diminish over time, while the typical eCO2-induced decrease in plant N concentration did. Our results suggest that, at the decennial timescale covered by FACE studies, N limitation of eCO2-induced terrestrial productivity enhancement is associated with negative effects of eCO2 on plant N acquisition rather than with growth dilution of plant N or processes leading to progressive N limitation. [ABSTRACT FROM AUTHOR]

Almost all models of plant resource limitation are grounded in either one or both of two simple conceptual models: Liebig's Minimum Hypothesis (LMH), the idea that plants are limited by the resource in shortest supply, and the Multiple Limitation Hypothesis (MLH), the idea that plants should adjust to their environment so that all essential resources are equally limiting. Despite the differences in their predictions, experiments have so far failed to discriminate between them. In a simple factorial nitrogen and water addition experiment in a Minnesota grassland, we observed shifts in allocation that, as in previous studies, are not all explained by a single theory. We found that leaf biomass responded positively to nitrogen additions but did not respond to water additions. We found that fine-root biomass increased in response to water additions, but only at low nitrogen levels, and that fine-root biomass decreased in response to nitrogen additions, but only at high water levels. To understand these responses we built a physiologically based model of plant competition for water, nitrogen, and space to predict plant allocation to fine roots and leaves. Critically, we include in our model the inherent variability of soil moisture and treat light, water, and nitrogen as resources with distinct mechanistic roles. Experimental results showed that plants were nitrogen and water limited. The model explains the experimental results, under conditions of co-limitation, as follows. Foliage increases with nitrogen additions but not water additions because leaf construction is constrained by nitrogen uptake. When water is added, plants spend a larger fraction of the growing season limited by light (and effectively nitrogen) than by water. Thus, water additions cause fine-root biomass to increase because of the increased importance of nitrogen limitation. The response of fine-root biomass to water additions decreases with nitrogen additions because these additions reduce nitrogen limitation. In general, our results are explained by sequential resource limitation. The rate of carbon assimilation may be limited by a single resource at any one moment, but the identity of the limiting resource(s) changes throughout the growing season. [ABSTRACT FROM AUTHOR]

ABSTRACT Nitrogen species distribution during coal pyrolysis with Ca addition in N2, CO2 and Ar was studied at 1000 °C using a horizontal tube furnace. In particular, the effect of Ca on the distribution of nitrogen species in N2 and CO2 atmospheres, which were closer to pyrolysis processes of conversional air and oxy-fuel combustion in comparison with inert Ar environment, was investigated for the first time in this work. It was found that Ca has a great effect on nitrogen species distribution during both coal and demineralized coal pyrolysis; on the other hand, CO2 causes the formation of NO. Demineralization increases the formation of HCN and char nitrogen, but there is little effect on NH3 formation during pyrolysis in N2, in contrast to pyrolysis in Ar atmosphere, which decreases NH3 formation. A significant reduction in char yield was found after char gasification in CO2 at 1000 °C. With two different Ca-based additives, i.e., (CH3COO)2Ca and Ca(OH)2, char yield decreases with the increasing amount of Ca additives in both cases. The effect of Ca on HCN and NH3 formation during pyrolysis depends on both the form of Ca and the amount of addition. In most cases, HCN and NH3 formation decreases with Ca addition in Ar, but increases in N2. Ca addition slightly promotes HCN formation during pyrolysis in CO2. There is no NH3 detected during pyrolysis in CO2 because of the reaction of NH3 and CO2 in the background. In addition, NO concentration decreases sharply with increasing the amount of Ca addition in the atmosphere of CO2, which means that Ca has an effect not only on pyrolysis, but also on gasification of char in CO2. In most cases, char nitrogen increases with Ca addition in N2 or Ar. © 2012 Curtin University of Technology and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

• Here, nitrogen (N) uptake and metabolism, and related gene expression, were analyzed in germinating spores of Glomus intraradices to examine the mechanisms and the regulation of N handling during presymbiotic growth. • The uptake and incorporation of organic and inorganic N sources into free amino acids were analyzed using stable and radioactive isotope labeling followed by high-performance liquid chromatography (HPLC), gas chromatography–mass spectrometry (GC-MS) and liquid scintillation counting and the fungal gene expression was measured by quantitative polymerase chain reaction (Q-PCR). • Quiescent spores store Asp, Ala and Arg and can use these internal N resources during germination. Although not required for presymbiotic growth, exogenous N can also be utilized for the de novo biosynthesis of amino acids. Ammonium and urea are more rapidly assimilated than nitrate and amino acids. Root exudates do not stimulate the uptake and utilization of exogenous ammonium, but the expression of genes encoding a putative glutamate dehydrogenase (GDH), a urease accessory protein (UAP) and an ornithine aminotransferase (OAT) were stimulated by root exudates. The transcript levels of an ammonium transporter (AMT) and a glutamine synthetase (GS) were not affected. • Germinating spores can make effective use of different N sources and the ability to synthesize amino acids does not limit presymbiotic growth of arbuscular mycorrhizal (AM) spores. [ABSTRACT FROM AUTHOR]

Nitrogen is required for adequate residue production from cereal cover crops used in notill cotton (Gossypium hirsutum L.) production, but residues can immobilize N needed by cotton. We conducted a 3-yr field study on a Decatur silt loam (clayey, kaolinitic, rhermic Rhodic Paleudulr) in northern Alabama to test N fertilizer practices for cotton grown with a rye (Secale cereale L.) cover crop and conservation tillage. Nitrogen rates applied to the rye cover crop were 0, 34, and 67 kg N ha-1 and cotton N rates were 0, 45, 90, and 135 kg N ha-1. Additionally, 15N microplors were established in cover crop N treatments of 34 kg N ha-1 and in cotton treatments of 90 kg N ha-1. Data collected included cover crop aerial biomass, cover crop C/N ratios, cotton leaf N at first flower, lint yield, lint quality, and 15N in plant and soil samples. Cotton grown in unfertilized rye treatments needed 57 to 60% (38-40 kg N ha-1) more N to maximize yields above median conventional tillage N recommendations (67 kg N ha-1). Cover crop N rates of 67 kg N ha-1 maximized cover crop biomass production for soil protection and soil organic matter aggradation. If the cover crop was fertilized, minimum cotton N applications of 70 and 76 kg N ha-1 were needed for economic optimum and maximum lint yield, respectively. We speculate that cotton N rates may be decreased in the future as new N and C pool equilibria are reached. [ABSTRACT FROM AUTHOR]