Effects of nitrogen and cutting management on root growth and productivity of a Kentucky bluegrass (Poa pratensis L.) and white clover (Trifolium repens L.) pasture

Nitrogen (N) and defoliation effects on productivity, root growth and soil nitrate (NO3-) in a Kentucky bluegrass and white clover pasture were examined. Nitrogen was applied annually in two equally split applications at rates of 0, 80 or 160 kg N ha -1. After reaching 12.7 cm, plants were cut to 2.5, 5.1 or 7.6 cm. Herbage was analyzed for yield, crude protein (CP), neutral detergent fiber and acid detergent fiber. Root samples were divided into three depths: 0.0--5.1, 5.1--10.2 and 10.2--20.3 cm, and analyzed for volume, dry weight and length. Soil NO3- was measured. At the 2.5 cm cut yield and fiber concentrations were higher; CP concentration was lower. Roots in the top depth had lower volume, dry weight and length. When no N was added, CP concentration of herbage and soil NO3 - concentration were lower, and root volume and dry weight were lower in the 0.0--5.1 cm depth. Cutting to 2.5 cm stopped root growth; more herbage was harvested but the material was more mature, decreasing CP and increasing fiber

Arsenic-phosphorus interactions in the soil-plant-microbe system: dynamics of uptake, suppression and toxicity to plants

High arsenic (As) concentrations in the soil, water and plant systems can pose a direct health risk to humans and ecosystems. Phosphate (Pi) ions strongly influence As availability in soil, its uptake and toxicity to plants. Better understanding of As(V)-Pi interactions in soils and plants will facilitate a potential remediation strategy for As contaminated soils, reducing As uptake by crop plants and toxicity to human populations via manipulation of soil Pi content. However, the As(V)-Pi interactions in soil-plant systems are complex, leading to contradictory findings among different studies. Therefore, this review investigates the role of soil type, soil properties, minerals, Pi levels in soil and plant, Pi transporters, mycorrhizal association and microbial activities on As-Pi interactions in soils and hydroponics, and uptake by plants, elucidate the key mechanisms, identify key knowledge gaps and recommend new research directions. Although Pi suppresses As uptake by plants in hydroponic systems, in soils it could either increase or decrease As availability and toxicity to plants depending on the soil types, properties and charge characteristics. In soil, As(V) availability is typically increased by the addition of Pi. At the root surface, the Pi transport system has high affinity for Pi over As(V). However, Pi concentration in plant influences the As transport from roots to shoots. Mycorrhizal association may reduce As uptake via a physiological shift to the mycorrhizal uptake pathway, which has a greater affinity for Pi over As(V) than the root epidermal uptake pathway

Highly efficient xylem transport of arsenite in the arsenic hyperaccumulator Pteris vittata

The hyperaccumulator Pteris vittata translocates arsenic (As) from roots to fronds efficiently, but the form of As translocated in xylem and the main location of arsenate reduction have not been resolved. Here, P. vittata was exposed to 5 mu M arsenate or arsenite for 1-24 h, with or without 100 mu M phosphate. Arsenic speciation was determined in xylem sap, roots, fronds and nutrient solutions by high-performance liquid chromatography (HPLC) linked to inductively coupled plasma mass spectrometry (ICP-MS). The xylem sap As concentration was 18-73 times that in the nutrient solution. In both arsenate- and arsenite-treated plants, arsenite was the predominant species in the xylem sap, accounting for 93-98% of the total As. A portion of arsenate taken up by roots (30-40% of root As) was reduced to arsenite rapidly. The majority (c. 80%) of As in fronds was arsenite. Phosphate inhibited arsenate uptake, but not As translocation. More As was translocated to fronds in the arsenite-treated than in the arsenate-treated plants. There was little arsenite efflux from roots to the external solution. Roots are the main location of arsenate reduction in P. vittata. Arsenite is highly mobile in xylem transport, possibly because of efficient xylem loading, little complexation with thiols in roots, and little efflux to the external medium

Protocol: genetic transformation of the fern Ceratopteris richardii through microparticle bombardment

BACKGROUND: The inability to genetically transform any fern species has been a major technical barrier to unlocking fern biology. Initial attempts to overcome this limitation were based on transient transformation approaches or achieved very low efficiencies. A highly efficient method of stable transformation was recently reported using the fern Ceratopteris richardii, in which particle bombardment of callus tissue achieved transformation efficiencies of up to 72%. As such, this transformation method represents a highly desirable research tool for groups wishing to undertake fern genetic analysis. RESULTS: We detail an updated and optimized protocol for transformation of C. richardii by particle bombardment, including all necessary ancillary protocols for successful growth and propagation of this species in a laboratory environment. The C. richardii lifecycle comprises separate, free-living gametophyte and sporophyte stages. Callus is induced from the sporophyte apex through growth on cytokinin-containing tissue culture medium and can be maintained indefinitely by sub-culturing. Transgene DNA is introduced into callus cells through particle bombardment, and stable genomic integration events are selected by regeneration and growth of T(0) sporophytes for a period of 8 weeks on medium containing antibiotics. Selection of T(1) transgenic progeny is accomplished through screening T(1) gametophytes for antibiotic resistance. In many cases sexual reproduction and development of transgenic embryos requires growth and fertilization of gametophytes in the absence of antibiotics, followed by a separate screen for antibiotic resistance in the resultant sporophyte generation. CONCLUSIONS: Genetic transformation of C. richardii using this protocol was found to be robust under a broad range of bombardment and recovery conditions. The successful expansion of the selection toolkit to include a second antibiotic for resistance screening (G-418) and different resistance marker promoters increases the scope of transformations possible using this technique and offers the prospect of more complex analysis, for example the creation of lines carrying more than one transgene. The introduction of a robust and practicable transformation technique is a very important milestone in the field of fern biology, and its successful implementation in C. richardii paves the way for adoption of this species as the first fern genetic model. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13007-015-0080-8) contains supplementary material, which is available to authorized users