Soil extracts are routinely used to quantify dissolved organic nutrient concentrations in soil. Here we studied the loss and transformation of low molecular weight (LMW) components of DOC (14C-glucose, 1 and 100μM) and DON (14C-amino acid mixture, 1 and 100μM) during extraction of soil (0–6h) with either distilled water or 0.5M K2SO4. The extractions were performed at 20°C, at 4°C, or in the presence of an inhibitor of microbial activity (HgCl2 and Na-azide). We showed that both glucose and amino acids became progressively lost from solution with increasing shaking time. The greatest loss was observed in H2O extracts at 1μM for both substances (>90% loss after 15min). Lower temperature (4°C) and presence of K2SO4 both resulted in reduced loss rates. The presence of microbial inhibitors effectively eliminated the loss of glucose and amino acids. We conclude that microbial transformation of LMW-DOC and DON during H2O or K2SO4 extraction of soil may affect the estimation of their concentrations in soil. This finding has significant implications for methods that rely on chemical extractions to estimate LMW-C components of DOC and DON.
Die Addition der Elemente von ′J F′ oder von ′BrF′an Alkene kann durch die in situ Darstellung dieser Elektrophile aus Halogen‐AgF erfolgen.
Organic acids such as citrate and oxalate have been implicated in enhancing many rhizosphere processes including nutrient acquisition. This study was condu
Root hairs project from the surface of the root to aid nutrient and water uptake and to anchor the plant in the soil. Their formation involves the precise control of cell fate and localized cell growth. We are now beginning to unravel the complexities of the molecular interactions that underlie this developmental regulation. In addition, after years of speculation, nutrient transport by root hairs has been demonstrated clearly at the physiological and molecular level, with evidence for root hairs being intense sites of H+-ATPase activity and involved in the uptake of Ca2+, K+, NH4 +, NO3 −, Mn2+, Zn2+, Cl− and H2PO4 −.
In this report, the nonlinear energy method for fracture toughness determination has been applied to cyclic loading conditions. The nonlinear energy toughness for cyclic loading, G(fc), was obtained from an envelope of the cyclic load-displacement record for thin center-cracked sheet specimens of 7075-T6 aluminum alloy. A cyclic loading program, in which each succeeding load peak approached the static load in an exponential manner, was applied to these specimens. With constant specimen dimensions, different load increments were used for different specimens, which resulted in varying cyclic lives. The specimens used in these tests exhibited a significant reduction in G(fc) with increasing cyclic life in a manner analogous to the classical S-N diagram. This reduction in life for 7075-T6 was significantly less than for 2024-T3, which had been evaluated previously although 2024-T3 has considerably higher toughness. (Author)
Policy decision making for agricultural greenhouse gas mitigation is hindered by scientific uncertainty regarding the effectiveness of mitigation measures. Successful on-farm adoption of measures is contingent upon farmer perception of the relative practicality of implementing the measure and associated incentives and advice. In the absence of a comprehensive evidence base we utilised Best–Worst Scaling, a discrete choice survey method, to elicit expert and farmer opinion on the relative effectiveness and practicality of mitigation measures to reduce greenhouse gas emissions from sheep production systems. The method enabled individual mitigation measures to be ranked on a ratio scale of effectiveness (expert opinion) and practicality (farmer opinion). Six measures were identified as possessing the combined qualities of effectiveness and practicality and are considered priority candidates for policy promotion. The overall preferred measure was the use of legumes in pasture reseed mixes. Estimation and analysis of the distribution of individual respondent scores revealed heterogeneity in farmers’ perceptions of practicality, suggesting that flexible policies are required to enable farmers to select mitigation measures most suited to their farm type and locality. Practical measures with below average effectiveness may be widely adopted with limited regulation, incentivisation or advice, whilst some highly effective measures with lower practicality are likely to present greater obstacles to adoption.
SummaryApplications of growth regulators to detached peach laterals in winter had variable effects on flower bud abscission. GA3 and GA4+7 increased bud abscission while IAA, BA and ABA inhibited abscission. Ethephon had a variable effect. Interactions were obtained between the compounds generally with IAA or GA playing the major role. GA had a peak of activity during a critical period in late winter indicating a variation in responsiveness. Variations in sensitivity to GA were obtained for different cultivars. Field applications of GA3, GA4+7, and ethephon to Elberta peach trees in winter, alone and in various combinations, promoted bud abscission.
A warming climate and expected changes in average and extreme rainfall emphasise the importance of understanding how the land surface routes and stores surface water. The availability and movement of water within an ecosystem is a fundamental control on biological and geophysical activity, and influences many climatic feedbacks. A key phenomenon influencing water infiltration into the land surface is soil hydrophobicity, or water repellency. Despite repellency dictating the speed, volume and pattern of water infiltration, there is still major uncertainty over whether this critical hydrological process is biologically or physicochemically controlled. Here we show that soil water repellency is likely driven by changes in the plant and soil microbial communities in response to environmental stressors. We carried out a field survey in the summers of 2013 to 2016 in a variety of temperate habitats ranging across arable, grassland, forest and bog sites. We found that moderate to extreme repellency occurs in 68% of soils at a national scale in temperate ecosystems, with 92% showing some repellency. Taking a systems approach, we show that a wetter climate and low nutrient availability alter plant, bacterial and fungal community structure, which in turn are associated with increased soil water repellency across a large-scale gradient of soil, vegetation and land-use. The stress tolerance of the plant community and associated changes in soil microbial communities were more closely linked to changes in repellency than soil physicochemical properties. Our results indicate that there are consistent responses to diverse ecosystem stresses that will impact plant and microbial community composition, soil properties, and hydrological behaviour. We suggest that the ability of a biological community to induce such hydrological responses will influence the resilience of the whole ecosystem to environmental stress. This highlights the crucial role of above-belowground interactions in mediating climatic feedbacks and dictating ecosystem health.
The effect of inorganic N additions on the biodegradation and microbial use of organic N pools in soil is poorly understood. To examine the effects of inorganic N on the mineralization rates of amino acids, four soils under contrasting management regimes were subjected to increasing loadings of NH 4 NO 3 , ranging from 0 to 120 kg N ha −1 In addition, the effect of soil sieving and storage temperature and time on amino acid mineralization was also investigated. At times ranging from 1 to 40 d after the addition of the inorganic N, the mineralization kinetics of an equimolar mixture of fifteen 14 C‐labeled amino acids was followed for a subsequent 24‐h period. The rate of 14 CO 2 evolution was soil dependent, with half‐lives ranging from 2 h for topsoils to 25 h for subsoils. For all soils, at all times, and at all inorganic‐N loadings, the addition of inorganic N appeared to have little effect on the mineralization kinetics of the amino acids to 14 CO 2 In addition, the presence of inorganic N also had no major effect on the C use efficiency of the microbial biomass. It is speculated that N release from the amino acids into the soil by the microbial biomass may also be little affected by inorganic‐N additions. Sieving and storage of soil at either 4 or 18°C for up to 40 d had little impact on amino acid mineralization rate. Experiments with potential microbial disrupting agents (autoclaving, CHCl 3 fumigation, HgCl 2 , and freeze–thaw) all indicated that the observed mineralization of amino acid C was due to microbial activity. We conclude therefore that inorganic N and soil storage has little effect on the microbial use of readily assimilatable amino acids.
