The possibility of predicting solute uptake and plant growth response from independently measured soil and plant characteristics

Summary The growth and nitrogen uptake response of rape plants to nitrate concentration at the root surface were studied in solution culture in a controlled environment cabinet over a period of 24 days. NO₃ ^– was supplied at the rates of 10^–5 M, 5×10^–5 M, 10^–4 M, 10^–3 M and 10^–2 M in solution and was maintained near these levels.With increasing mean N concentration in the tissues, the relative growth rate and leaf area ratio increased and unit leaf rate decreased slightly. Values of all three growth parameters decreased with plant age.The shoot: root dry weight ratios and their N content ratios increased with increasing mean per cent N in the plant. The length or surface area per unit dry weight of roots was correlated negatively with per cent N and positively with age.The maximum mean inflow of nitrate to rape roots decreased sharply with age. The concentration at which half maximal mean inflow was attained was 3.44×10^–5 M NO₃ ^–.     

The possibility of predicting solute uptake and plant growth response from independently measured soil and plant characteristics

Summary A model of the way the rate of growth of a plant may be affected by the level of supply of a nutrient is presented. Growth rate is linked to the nutrient level of the photosynthetic tissues, which is assumed to control changes in the net assimilation rate, the leaf area per unit shoot weight, the shoot: root ratio, the root surface area, and the distribution of nutrient between root and shoot. The uptake of nutrient depends on the concentration of nutrient at the root surface, the root surface area and its absorbing power. All these relationships may be determined in stirred solution culture. A method of applying this information to soil grown plants is suggested.Soil Science Laboratory, Department of Agricultural Science, University of Oxford     

The effect of methods of application of sawdust on plant growth,plant nutrient uptake and soil chemical properties

Summary Sawdust fromCanarium schweinfurthii (Engl.), a common source of timber in the rainforest zone of Nigeria was subjected to various treatments to improve the nutrient content and aid the decomposition of the otherwise highly-lignified material. The treatments were then either incorporated into the soil or added to the soil surface as a mulch in both greenhouse and field studies. The greenhouse studies involved two six-week sowings in the same soil while the field study involved 3 season sowings (2 rainly, one dry season) using maize (Zea mays L.var. Western yellow) as a test crop.Results indicated that in the greenhouse, incorporation of untreated sawdust led to significant reductions in maize growth, dry matter yield and uptake of N and other nutrients. While the incorporated inorganically amended sawdust treatment produced significantly higher dry matter yield, that produced by the surface-applied organically amended treatment was significantly higher than the incorporated treatment. Except for untreated sawdust, the incorporation of organically and inorganically amended sawdust increased the contents insoil of N, available P, and exchangeable K.     

The response of plant mitochondria to media of high solute content

The state-3 rate of respiration of potato tuber mitochondria is inhibited by concentrations of KCl or NaCl above 125 mM, and by concentrations of sucrose, lactose, or maltose above 500 mM, but not at all by mannitol, glucose, glycine, or proline up to a concentration of 1500 mM in the medium. Mitochondria from cauliflower, beetroot, cucumber, rock melon, and watermelon behave very similarly to those from potato tuber. The variable response to different solutes proves that the reduction in respiration is not a simple function of the chemical potential of water in the medium. Disruption of potato mitochondria by ultrasonic vibration does not relieve the inhibition of succinate oxidation caused by KCl or sucrose. However, treatment with detergent abolishes completely the inhibition of respiration by sucrose. Inhibition of succinate dehydrogenase [Succinate:PMS, oxidoreductase (EC.1.3.99.1)] and malate dehydrogenase [L-Malate:NAD oxidoreductase (EC.1.1.1.37)] activities by sucrose is less than the inhibition of succinate- and malate-dependent oxygen uptake by the potato mitochondria. Limited substrate uptake and, alternatively, reduced electron flow as a consequence of a direct effect of solute on the mitochondrial membrane are considered as possible mechanisms of inhibition.     

IRT1, an Arabidopsis transporter essential for iron uptake from the soil and for plant growth

Plants are the principal source of iron in most diets, yet iron availability often limits plant growth. In response to iron deficiency, Arabidopsis roots induce the expression of the divalent cation transporter IRT1. Here, we present genetic evidence that IRT1 is essential for the uptake of iron from the soil. An Arabidopsis knockout mutant in IRT1 is chlorotic and has a severe growth defect in soil, leading to death. This defect is rescued by the exogenous application of iron. The mutant plants do not take up iron and fail to accumulate other divalent cations in low-iron conditions. IRT1-green fluorescent protein fusion, transiently expressed in culture cells, localized to the plasma membrane. We also show, through promoter::beta-glucuronidase analysis and in situ hybridization, that IRT1 is expressed in the external cell layers of the root, specifically in response to iron starvation. These results clearly demonstrate that IRT1 is the major transporter responsible for high-affinity metal uptake under iron deficiency.     

The role of microorganisms in mediating and facilitating the uptake of plant nutrients from soil

Summary No root systems in nature are without a microbial population. These may be freeliving or symbiotic.The incidence and nutrition of the freeliving microorganisms is discussed. Shortage of substrate makes it unlikely that the N-fixers in the population can fix useful amounts of N. There is a possibility that P supply is improved, but an analysis of possible processes shows them to be rather unlikely, and evidence for them to be poor. Manganese and iron uptake can be altered by microbial activity. Growth of plants can be affected by non-nutritional bacterial effects.The ecology of Rhizobium in the soil is briefly discussed, and the varying needs of different identified strains is stressed.Mycorrhizal infection of plants leads to large growth increases in appropriate conditions. This is almost always linked to increased P uptake, but zinc and copper nutrition can also be improved. The processes involved are briefly discussed. Rapid and extensive infection is important; it is very sensitive to temperature. New modelling methods are now becoming available to measure the behaviour of the fungal infections. The microorganisms require C compounds from the plant, and new measurements of this cost are discussed. The possibility of practical use of mycorrhizal fungi seem to be improving.Keynote address     

The contribution of plant traits and soil microbes to phosphorus uptake from low-phosphorus soil in upland rice varieties

Plant and Soil - Popular African upland rice variety Nerica4 performs poorly under phosphorus (P) deficiency; the objective was to identify plant and soil traits likely to improve its P efficiency....     

Transient three-dimensional modeling of soil water and solute transport with simultaneous root growth,root water and nutrient uptake

A three-dimensional solute transport model was developed and linked to a three-dimensional transient model for soil water flow and root growth. The simulation domain is discretized into a grid of finite elements by which the soil physical properties are spatially distributed. Solute transport modeling includes passive and active nutrient uptake by roots as well as zero- and first-order source/sink terms. Root water uptake modeling accounts for matric and osmotic potential effects on water and passive nutrient uptake. Root age effects on root water and nutrient uptake activity have been included, as well as the influence of nutrient deficiency and ion toxicity on root growth. Examples illustrate simulations with different levels of model complexity, depending on the amount of information available to the user. At the simplest level, root growth is simulated as a function of mechanical soil strength only. Application of the intermediate level with root water and nutrient uptake simulates the influence of timing and amount of NO3 application on leaching. The most comprehensive level includes simulation of root and shoot growth as influenced by soil water and nutrient status, temperature, and dynamic allocation of assimilate to root and shoot.     

Effect of liming on mineralization of soil nitrogen as measured by plant uptake and nitrogen released during incubation

The effect of lime rates on oat yield and N uptake was measured in a 6-years pot experiment, using 12 acid surface soils (pH 4.7 to 6.0). Mineralization of nitrogen was measured by incubation of soil samples taken after harvest each year from the different lime treatments.Nitrogen uptake was significantly correlated with total N in the soils. Averaged over all 12 soils liming only to pH 7 or above, increased the oat yield significantly. Liming increased the N concentration of grain and the N uptake significantly during a 4-years period, indicating the effect of lime on N mineralization.The mineralization of organic N measured by incubation in the non-limed samples was highly correlated with the total N concentration, but it was not significantly related to the original pH of the soils. The amounts of N released as well as the duration of the lime effect on mineralization varied among soils. When pH was raised to 7 or above, considerable increases in N mineralization occurred in some soils. Based on average values, liming increased N mineralization significantly during a 3-years period. After 3 years, the lime treatments differed only slightly from the non-limed treatments.     

Impacts of monosodium glutamate industrial wastewater on plant growth and soil characteristics

Research into utilization of monosodium glutamate industrial wastewater (MSGW) as a plant nutrient source was undertaken. The physico-chemical and microbiological characteristics of MSGW were analyzed in detail. Effect of MSGW on early growth of Chinese cabbage (Brassica rapa L. cv. Pekinensis) and maize (Zea mays L. cv. Bright Jean) was tested by the seed germination bioassay. Subsequently, in a greenhouse pot experiment using the same plant species, effects of MSGW application rates on the plant biomass yield, nitrogen content and soil properties were analyzed. The MSGW was characterized by high levels of N (56.7 g l^?1), organic C (344.6 g l^?1), total solids (600 g l^?1) and other minerals. At MSGW concentrations below 1%, germination indices for both the plant species were significantly (p < 0.01) higher than the control. Further, the greenhouse study results indicated significant increase in the plant biomass yield at MSGW application rates of 5000 and 7500 l ha^?1. As the MSGW dose increased, the biomass yield decreased, decreasing the N-use efficiency. Maize showed significantly higher wastewater N-use efficiency compared to the Chinese cabbage. Although the total culturable bacterial and fungal counts in the raw MSGW were low, addition of MSGW to the soil increased the soil microbial activities and soil respiration. Soil organic C was also increased by the addition of MSGW, due to the presence of significant amounts of organic C in the wastewater. This preliminary study demonstrates that by proper management of the pH and optimization of application rate, MSGW can be utilized as a nutrient source for plant growth. Further long-term field studies to evaluate the environmental impact of MSGW usage in agriculture are being designed to reduce the environmental risks associated with the reuse of this underutilized wastewater in the agriculture.     

Relation of soil moisture and air conditioning irrigation to plant water balance,growth characteristics and nutrients uptake in rye and wheat

The results of experiments conducted with autumn rye and summer wheat on sandy loam soil at the Institute for Cereal Production of the Martin-Luther University, Halle-Wittenberg (G.D.R.) have revealed that an increase in soil moisture improved the plant water balance, width of stomata, shoot growth, tiller density, leaf area and growth rate. Net assimilation rate, however, decreased with the increase in soil moisture above 50 per cent water holding capacity. Increased soil moisture improved contents of nitrogen, potassium and phosphorus only during early stages of growth, but their uptake was not reduoed at maturity. Air conditioning irrigation proved superior in respect to all above mentioned characteristics, except the uptake of potassium, which decreased with air conditioning irrigation at higher soil moisture relations.     

Effect of soil volume and plant density on mycorrhizal infection and growth response

Summary The effect of soil volume and plant density on mycorrhizal infection and growth response was studied with onion. There was a significant negative correlation between percentage vesicular-arbuscular mycorrhizal infection and root density. The growth response due to mycorrhiza decreased when less soil was available for the plant. The root: shoot ratio decreased with increasing plant density in both mycorrhizal and non-mycorrhizal plants. Pot size did not affect the root: shoot ratio.     

Soil solute concentration and water uptake by single lupin and radish plant roots

Application of computer assisted tomography to gamma and X-ray attenuation measurements and Na⁺-LIX microelectrodes were used to determine the spatial distributions of soil water content and Na⁺ concentrations respectively near single roots of eighteen day old lupin and radish plants. These quantities were monitored at root depths of 3, 6 and 9 cm and at zero, 2, 4, 6, and 8 hour intervals from the diurnal commencement of transpiration. The plants were subjected to two levels of transpirational demand and five Na⁺ soil solution concentration levels. Water extraction rates for the lupin and radish roots increased continuously with time but were substantially reduced with increasing Na⁺ concentration in the treatment. Water uptake was uniform along the length of the essentially constant diameter lupin roots but decreased along the tapering radish roots as the diameter and hence the surface area per unit length of the roots decreased. The accumulation of Na⁺ at the root surfaces of both plants increased gradually with time in a near linear fashion and was slightly higher under the higher transpiration demand. These increases were not exponential as would be expected with non-absorption by the roots and this is considered to be due to back diffusion at the relatively high water contents used. At these water contents matric potentials had a much smaller influence on transpiration than osmotic potentials. The relationships between leaf water potentials (Ψ₁) and osmotic potentials at the root surfaces were linear with the decreases in Ψ₁ almost exactly reflecting the decreases in Ψ_π indicating rapid plant adjustment. Leaf water potentials decreased progressively with time and the relationships between leaf water potential and the transpiration rate were also linear supporting the suggestion of constant plant resistances at any given concentration.     

Effects of recycled bentonite addition on soil properties, plant growth and nutrient uptake in a tropical sandy soil

The only way to increase the low CEC of sandy tropical soils over the long term is to apply high CEC materials such as 2:1 clay minerals. Acid activated bentonite is used in Thailand in the vegetable oil industry during the clarification process. The waste bentonite is discarded afterwards. The aim of the study was to compare the effects of the addition of these oil bentonites (OB) with the addition of cation beneficiated bentonite (BB) on soil properties and plant growth. Palm, rice and soybean OB, and bentonite beneficiated with calcium, magnesium, and potassium were applied at rates between 5 and 40 t ha⁻¹ to an Arenic Acrisol. Three consecutive crops of sorghum were grown in pots. Biomass and plant nutrient content were determined at each growth phase, and selective soil properties were measured at the start and the end of the study. Beneficiated bentonite was not water repellent, but the addition of OB resulted in soil water repellency. The application of bentonite at the rate of 40 t ha⁻¹ increased the cation exchange capacity (CEC) from 0.6 cmolc kg-1 in the control to 1.9 and 0.7 cmol_c kg⁻¹ in the BB and OB, respectiveley. The lower value of the CEC for OB compared to BB was probably due to the activation process and oil coating. OB applications at rates higher than 20 t ha⁻¹ did not increase biomass, and biomass decreased with increasing water repellency. The other treatments produced a higher biomass than the control. However biomass was below potential because of widespread nitrogen deficiency. Exchangeable K was exhausted in two crops, whatever the initial level, stressing the issue of K management in this soil type. Soybean OB is a promising material for soil chemical properties and biomass production, probably because of its low oil content.     

DNA from soil mirrors plant taxonomic and growth form diversity

Ecosystems across the globe are threatened by climate change and human activities. New rapid survey approaches for monitoring biodiversity would greatly advance assessment and understanding of these threats. Taking advantage of next-generation DNA sequencing, we tested an approach we call metabarcoding: high-throughput and simultaneous taxa identification based on a very short (usually <100 base pairs) but informative DNA fragment. Short DNA fragments allow the use of degraded DNA from environmental samples. All analyses included amplification using plant-specific versatile primers, sequencing and estimation of taxonomic diversity. We tested in three steps whether degraded DNA from dead material in soil has the potential of efficiently assessing biodiversity in different biomes. First, soil DNA from eight boreal plant communities located in two different vegetation types (meadow and heath) was amplified. Plant diversity detected from boreal soil was highly consistent with plant taxonomic and growth form diversity estimated from conventional above-ground surveys. Second, we assessed DNA persistence using samples from formerly cultivated soils in temperate environments. We found that the number of crop DNA sequences retrieved strongly varied with years since last cultivation, and crop sequences were absent from nearby, uncultivated plots. Third, we assessed the universal applicability of DNA metabarcoding using soil samples from tropical environments: a large proportion of species and families from the study site were efficiently recovered. The results open unprecedented opportunities for large-scale DNA-based biodiversity studies across a range of taxonomic groups using standardized metabarcoding approaches.     

Assessment of methylammonium as an analog for ammonium in plant uptake from soil

We tested radioactive methylammonium (¹⁴CH₃NH _inf3 ^sup+ ) as a tracer for ammonium (NH₄ ⁺) in root uptake measurements from soil. Tomato (Lycopersicon esculentum Moll. cv T5) in 3 L pots filled with loamy sand soil received 40, 200, or 600 μmol ¹⁴CH₃NH₃ ⁺ or ¹⁵NH₄ ⁺. During a 4 h period, the plants absorbed ¹⁴CH₃NH₃ ⁺ at slower rates than ¹⁵NH₄ ⁺. Estimates of NH₄ ⁺ absorption based on ¹⁵NH₄ ⁺ absorption were 0.9–7.9 μmol NH₄ ⁺ g⁻¹ plant dry weight h⁻¹, whereas those based on ¹⁴CH₃NH₃ ⁺ absorption were 0.2–1.0 μmol NH₄ ⁺ g⁻¹ plant dry weight h⁻¹. After 4 h, approximately one-half of the applied ¹⁵N was not recovered in the plants or soil KCl extracts; apparently, this ¹⁵N was either immobilized or nitrified and denitrified by soil biota. By contrast, almost all the ¹⁴CH₃NH₃ ⁺ remained in the soil solution after 4 h, but after a 10 d incubation, approximately 20% had been released as ¹⁴CO₂. These differences in plant absorption rates and movement through soil pools indicate that CH₃NH₃ ⁺ cannot be used reliably as an NH₄ ⁺ analog in soil.