Improving crop mineral nutrition

Background

Crops require adequate nutrition for the production of food, fibre and fuel, but soil conditions often limit the ability of crops to acquire mineral nutrients. To address this, mineral nutrients can be applied as inorganic or organic fertilisers to the soil or as liquid fertilisers to foliage. However, production and use of fertilisers can have negative environmental impacts. The articles in this Special Issue illustrate a number of ways to improve nutrient acquisition from the soil and their delivery through foliar application.

Scope

Articles highlighted here include those that discuss ways by which to assess a crop’s requirement for additional mineral elements, ways by which minerals can be supplied more effectively to crops both through roots and shoots, and ways by which the crop itself can be enhanced to acquire more mineral elements.

Conclusions

It is apparent from the information contained in this Special Issue that to improve the ability of crops to acquire mineral elements, a number of strategies are available. However, the success of any one intervention is dependent on how these strategies interact with the environment in which they are deployed and the suitability of the management system for the specific intervention.     

Root-shoot interactions in mineral nutrition

In this paper four classes of co-operative root-shoot interations are addressed. (I) Nitrogen concentrations in the xylem sap originating from the root and in the phloem sap as exported from source leaves are much lower than those required for growth by apices and developing organs. Enrichment of xylem sap N is achieved by xylem to xylem (X-X) transfer, by which reduced N, but not nitrate, is abstracted from the xylem of leaf traces and loaded into xylem vessels serving the shoot apex. Nitrogen enrichment of phloem sap from source leaves is enacted by transfer of reduced N from xylem to phloem (X-P transfer). Quantitative data for the extent of the contribution of X-X and X-P transfer to the nutrition of young organs of Ricinus communis L. and for their change with time are presented. (II) Shoot and root cooperate in nitrate reduction and assimilation. The partitioning of this process between shoot and root is shifted towards the root under conditions of nitrate- and K-deficiency and under salt stress, while P deficiency shifts nitrate reduction almost totally to the shoot. All four changes in partitioning can be attributed to the need for cation-anion balance during xylem transport and the change in electrical charge occurring with nitrate reduction. (III) Even maintenance of the specificity of ion uptake by the root may – in addition to its need for energy – require a shoot-root interaction. This is shown to be needed in the case of the maintenance of K/Na selectivity under the highly adverse condition of salt stress and absence of K supply from the soil. (IV) Hormonal root to shoot interactions are required in the whole plant for sensing mineral imbalances in the soil. This is shown and addressed for conditions of salt stress and of P deficiency, both of which lead to a strong ABA signalling from root to shoot but result in different patterns of response in the shoot.     

Morphology,nutrition and physiology of Sphaerotilus discophorus

Summary By means of hay infusion-Fe(OH)₃–MnCO₃ enrichment cultures, 11 pure strains of the filamentous, sheathed bacterium, Sphaerotilus discophorus were isolated from streams, rivers and lakes. The morphology of the colonies, filaments and cells are shown in a series of photographs. The strains grew well in dilute organic media but not in many of the common bacteriological media. All strains required thiamin and biotin for growth. Glucose, mannitol, salicin, raffinose, glycerol and other compounds were suitable energy sources and peptone and casein hydrolysate were satisfactory nitrogen sources for growth. The temperature range for growth was 5–35°C and the pH range 6.0–8.6.The sudanophilic granules of S. discophorus are composed of poly--hydroxybutyric acid which may be as much as 40% of the dry weight of the cells. Growth with iron and manganese salts results in extensive deposition of oxides on these metals on the filaments. Chemical analyses of 60 hr cultures showed that the iron content of the filaments ranged from 4.25–7.10% and manganese from 1.12–1.43%, calculated on a dry weight basis. Resting cell suspensions oxidized a variety of sugars, sugar alcohols, amino acids and other compounds and concomitantly assimilated about 90% of these substrates. The properties of S. discophorus are compared with those of S. natans.Based in part on a thesis presented by the senior author in partial fulfillment of the requirements for the degree of Doctor of Philosophy, Washington State University, 1963.     

Root developmental responses to phosphorus nutrition

Phosphorus is an essential macronutrient for plant growth and development. Root system architecture (RSA) affects a plant's ability to obtain phosphate, the major form of phosphorus that plants uptake. In this review, I first consider the relationship between RSA and plant phosphorus-acquisition efficiency, describe how external phosphorus conditions both induce and impose changes in the RSA of major crops and of the model plant Arabidopsis, and discuss whether shoot phosphorus status affects RSA and whether there is a universal root developmental response across all plant species. I then summarize the current understanding of the molecular mechanisms governing root developmental responses to phosphorus deficiency. I also explore the possible reasons for the inconsistent results reported by different research groups and comment on the relevance of some studies performed under laboratory conditions to what occurs in natural environments.     

Growth and mineral nutrition of two Chlorococcalean algae

The effect of composition of the medium and pH on the growth of Pediastrum duplex Meyen and Dictyosphaerium pulchellum Wood was studied. Both species showed preference to alkaline conditions. The ammonium nitrate grown colonies of D. pulchellum lacked mucilage and showed a more compact form, resembling D. pulchellum var. minitum Deflandre. From this it appears that D. pulchellum var. minitum is a nutritional variant of the species and not a stable variety.     

Regulating plant tissue growth by mineral nutrition

The objective of this study was to determine if the growth of sweet orange (Citrus sinensis (L.) Osbeck cv. ‘Valencia’) nonembryogenic callus could be regulated and controlled via the mineral nutrient components of the medium. The 14 salts comprising Murashige and Skoog (MS) basal medium were subdivided into five component groups. These five groups constituted the independent factors in the design. A five-dimensional hypervolume constituted the experimental design space. Design points were selected algorithmically by D-optimality criteria to sample of the design space. Growth of the callus at each design point was measured as % increase of fresh weight at 14 d. An analysis of variance was conducted and a response surface polynomial model generated. Model validation was conducted by mining the polynomial for design points to two regions—“MS-like” growth and MS + 25% growth and comparing callus growth to predicted growth. Five of the eight selected MS-like points and three of the six MS + 25% growth points validated, indicating regions within the design space where growth was equivalent to MS, but the salt combinations were substantially different from MS, and a smaller region where growth exceeded MS by greater than 25%. NH₄NO₃ and Fe were identified as important factors affecting callus growth. A second experiment was conducted where NH₄NO₃ and Fe were varied, thus creating a two-dimensional slice through the region of greatest callus growth and provided increased resolution of the response.     

Tree mineral nutrition is deteriorating in Europe

The response of forest ecosystems to increased atmospheric CO₂ is constrained by nutrient availability. It is thus crucial to account for nutrient limitation when studying the forest response to climate change. The objectives of this study were to describe the nutritional status of the main European tree species, to identify growth‐limiting nutrients and to assess changes in tree nutrition during the past two decades. We analysed the foliar nutrition data collected during 1992–2009 on the intensive forest monitoring plots of the ICP Forests programme. Of the 22 significant temporal trends that were observed in foliar nutrient concentrations, 20 were decreasing and two were increasing. Some of these trends were alarming, among which the foliar P concentration in F. sylvatica, Q. Petraea and P. sylvestris that significantly deteriorated during 1992–2009. In Q. Petraea and P. sylvestris, the decrease in foliar P concentration was more pronounced on plots with low foliar P status, meaning that trees with latent P deficiency could become deficient in the near future. Increased tree productivity, possibly resulting from high N deposition and from the global increase in atmospheric CO₂, has led to higher nutrient demand by trees. As the soil nutrient supply was not always sufficient to meet the demands of faster growing trees, this could partly explain the deterioration of tree mineral nutrition. The results suggest that when evaluating forest carbon storage capacity and when planning to reduce CO₂ emissions by increasing use of wood biomass for bioenergy, it is crucial that nutrient limitations for forest growth are considered.     

Sodium in the mineral nutrition ofAvena Sativa

Summary In pot experiments with oats on sandy soil poor in sodium and potassium a study was made of the effect of the addition of Na₂SO₄ and K₂SO₄ on the mineral composition of the straw.The addition of sodium at 200 ppm Na significantly increased the phosphorus content of the straw and there was a slight further increase with 200 ppm Na plus 200 ppm K, but the phosphorus content never exceeded 0.13 per cent.Sodium and potassium caused a highly significant decrease in the silica content of the straw. Decreased lodging in soils inundated with sea water can therefore not be ascribed to an increase of silica content.The calcium and the cellulose contents of the straw were both significantly reduced by sodium and potassium.     

Modeling optimal mineral nutrition for hazelnut micropropagation

Micropropagation of hazelnut (Corylus avellana L.) is typically difficult because of the wide variation in response among cultivars. This study was designed to determine the required mineral nutrient concentrations for micropropagation of C. avellana cultivars using a response surface design analysis. Driver and Kuniyuki Walnut (DKW) medium mineral nutrients were separated into five factors: NH₄NO₃, Ca(NO₃)₂, mesos (MgSO₄ and KH₂PO₄), K₂SO₄, and minor nutrients (boron, copper, manganese, molybdenum, and zinc) ranging from 0.5× to 2× the standard DKW medium concentrations with 33 treatments for use in modeling. Overall quality and shoot length for all cultivars were influenced by ammonium and nitrate nitrogen, mesos and minors. Reduced Ca(NO₃)₂ improved multiplication while higher amounts increased shoot length for most cultivars. Uptake of nutrients varied among the cultivars. Calcium and magnesium concentrations were greater in the shoots that grew well compared to poorly-growing and control treatments. All five cultivars showed improved growth on some treatments and the models indicated that shoots grown on an optimized medium would be even better. This model indicates that NH₄NO₃, Ca(NO₃)₂, mesos, and minors all had significant effects on hazelnut growth and multiplication and should be optimized in future experiments.     

Screening Arabidopsis for mutants in mineral nutrition

Arabidopsis thaliana is a small herbaceous plant which is used as a model plant for defining the molecular basis of many plant processes. The advantages of this plant for genetic studies are its small, well-characterized genome, a short life cycle, large seed set and small seed size. The analysis of mutants of this plant has proved useful in understanding basic plant processes. To isolate Arabidopsis mutants in mineral nutrition, we have devised a method of screening based on X-ray fluorescence spectrometry (XRFS) analysis of leaves. We have identified three mutants in P and Mn nutrition after screening over 100 000 seedlings. These mutants show either excessive accumulation of P or Mn in shoots or an inabilty to accumulate normal concentrations of P.