Effect of phosphorus nutrition on morphological characteristics of vesicular-arbuscular mycorrhizal colonization of maize

Does phosphorus influence performance of a native hemiparasite and its impact on a native legume?

Phosphorus (P) is an essential plant nutrient and can become limiting in terrestrial ecosystems where parasitic plant:host associations occur. Yet little is known on how P availability influences parasite performance and its impact on hosts. We investigated the performance of the Australian native stem hemiparasite Cassytha pubescens and its impact on the native leguminous shrub Acacia paradoxa in high or low P conditions in a glasshouse experiment. Infected plants had significantly lower total, shoot, root and nodule biomass and shoot:root ratio than uninfected plants, regardless of P supply. The significant negative effect of infection on arbuscular mycorrhizal colonisation of host roots was more severe in the high P treatment. Infection significantly decreased predawn quantum yield of A. paradoxa in low P but not high P conditions. This finding may be due to the parasite-induced significant enrichment of aluminium in host foliage in low P but not high P treatments. A. paradoxa had significantly lower foliar phosphorus concentration [P] and nitrogen concentration in low P than high P conditions. Parasite biomass and photosynthetic performance were unaffected by P, whereas C. pubescens had significantly lower stem [P] in the low P than high P treatment. Parasite carbon isotope composition was significantly higher than that of the host, especially in low P conditions. Our results show that: (a) native parasite growth and its negative impact on growth of this native shrub was unaffected by P supply and (b) soil P conditions may have no influence on stem hemiparasite:host associations in nature.

The effects of biochar and AM fungi (Funneliformis mosseae) on bioavailability Cd in a highly contaminated acid soil with different soil phosphorus supplies

Due to the increase of cadmium (Cd)-contaminated land area worldwide, effective measures should be taken to minimize the Cd bioavailability in crops. A study was performed to explore the effectiveness of biochar pyrolyzed from rice straw at 400 °C alone or combined with AM fungi (Funneliformis mosseae) on the corn growth and Cd uptake in corn in Cd-contaminated soil with different levels of phosphorus supplies. The results showed that biochar significantly reduced 66% and 38% of Cd uptake in shoot and root respectively (P < 0.001) attributed to the increase of soil pH and dissolved organic matter. In contrast, AM fungi inoculation of corn plants had little effect on Cd bioavailability due to the AM was suppressed by the highly contaminated acid soil (31.76 mg/kg), and had neither synergistic effect with biochar on decreasing the Cd bioavailability with high or low phosphorus supplies. This study demonstrated that biochar application could be a promising method to immobilize Cd in the contaminated soil to ensure the safety of agro-product while high Cd-contaminated soil would suppress the growth of mycorrhizae, so this remains an open question to be further studied.

The intensity of symbiotic relationships between arbuscular mycorrhizae and differentiated tree species regarding their age group and plant family in semi-arid Andine dynamical agroforestry system

As research on mycorrhiza progress and scientific knowledge about organic partnerships becomes more profound, mycorrhiza symbiosis is considered an essential parameter for the vitality of ecosystems. Concerning polyculture cultivation systems, the implementation of growth-promoting and nutrient-securing symbiotic partners is a crucial step towards preserving the dynamism of involved plants and thus decisive for the yield and success of such cultivation systems. In particular, arbuscular mycorrhizal fungi (AMF) show a considerable tendency in encouraging and maintaining a supply of water and nutrition for plants. Therefore, it was examined how intensive partnerships between AMF and trees in the semi-arid, dynamic agroforestry system of ‘Mollesnejta’ exist and how the species, family and age of trees are related to the respective degree of mycorrhizal intensity. This information is in turn used to decrypt relationships between nutrient provision and nutrient security in agroforestry systems and to improve them especially concerning current climate change. The results reveal that in the examined agroforestry system arbuscular mycorrhizal partnerships were found on all ten considered tree species in this study in the varying intensity of the mycorrhizal structure dependent on tree species and their plant family. Nevertheless, no statistical correlation between the number of mycorrhizal elements according to primary hyphae, ramification or vesicles about the age of the trees could be proven in this study.

Mechanisms and Impact of Symbiotic Phosphate Acquisition

Phosphorous is important for life but often limiting for plants. The symbiotic pathway of phosphate uptake via arbuscular mycorrhizal fungi (AMF) is evolutionarily ancient and today occurs in natural and agricultural ecosystems alike. Plants capable of this symbiosis can obtain up to all of the phosphate from symbiotic fungi, and this offers potential means to develop crops less dependent on unsustainable P fertilizers. Here, we review the mechanisms and insights gleaned from the fine-tuned signal exchanges that orchestrate the intimate mutualistic symbiosis between plants and AMF. As the currency of trade, nutrients have signaling functions beyond being the nutritional goal of mutualism. We propose that such signaling roles and metabolic reprogramming may represent commitments for a mutualistic symbiosis that act across the stages of symbiosis development.

Effects of different soil remediation methods on inhibition of lead absorption and growth and quality of Dianthus superbus L

Heavy metal pollution in soil poses a serious threat to the growth of plants used in traditional Chinese medicine. Therefore, a pot experiment was conducted to study the effects of various soil remediation methods on the performance of Herba Dianthi (Dianthus superbus L.) grown on Pb-contaminated soil. The results show that inoculation of Herba Dianthi with arbuscular mycorrhizal fungi (AMF) led to a significant reduction in Pb uptake (P< 0.05), and increased root development and root-to-shoot ratio compared to untreated control plants, along with the highest content of active components. When planting with Trifolium repens, the reduction effect of Pb absorption was insignificant. Herba Dianthi showed improved growth and active ingredients, and the lowest Pb content, with AMF inoculation. The addition of EDTA decreased the growth of Herba Dianthi, but promoted the absorption of Pb. The inhibition of tumor cells was highest in E2. In conclusion, inoculation with AMF can ensure that plant lead content meets testing standards, helping to improve the quality of medicinal herbs.

Cereal mycorrhiza: an ancient symbiosis in modern agriculture

The majority of terrestrial plants live in association with symbiotic fungi that facilitate mineral nutrient uptake. The oldest and most prevalent of these associations are the arbuscular mycorrhizal (AM) symbioses that first evolved approximately 400 million years ago, coinciding with the appearance of the first land plants. Crop domestication, in comparison, is a relatively recent event, beginning approximately 10000 years ago. How has the dramatic change from wild to cultivated ecosystems impacted AM associations, and do these ancient symbioses potentially have a role in modern agriculture? Here, we review recent advances in AM research and the use of breeding approaches to generate new crop varieties that enhance the agronomic potential of AM associations.

Arbuscular mycorrhizal symbiosis is accompanied by local and systemic alterations in gene expression and an increase in disease resistance in the shoots

In natural ecosystems, the roots of many plants exist in association with arbuscular mycorrhizal (AM) fungi, and the resulting symbiosis has profound effects on the plant. The most frequently documented response is an increase in phosphorus nutrition; however, other effects have been noted, including increased resistance to abiotic and biotic stresses. Here we used a 16,000-feature oligonucleotide array and real-time quantitative RT-PCR to explore transcriptional changes triggered in Medicago truncatula roots and shoots as a result of AM symbiosis. By controlling the experimental conditions, phosphorus-related effects were minimized, and both local and systemic transcriptional responses to the AM fungus were revealed. The transcriptional response of the roots and shoots differed in both the magnitude of gene induction and the predicted functional categories of the mycorrhiza-regulated genes. In the roots, genes regulated in response to three different AM fungi were identified, and, through split-root experiments, an additional layer of regulation, in the colonized or non-colonized sections of the mycorrhizal root system, was uncovered. Transcript profiles of the shoots of mycorrhizal plants indicated the systemic induction of many genes predicted to be involved in stress or defense responses, and suggested that mycorrhizal plants might display enhanced disease resistance. Experimental evidence supports this prediction, and mycorrhizal M. truncatula plants showed increased resistance to a virulent bacterial pathogen, Xanthomonas campestris. Thus, the symbiosis is accompanied by a complex pattern of local and systemic changes in gene expression, including the induction of a functional defense response.

A Medicago truncatula phosphate transporter indispensable for the arbuscular mycorrhizal symbiosis

The arbuscular mycorrhizal (AM) symbiosis is a mutualistic endosymbiosis formed by plant roots and AM fungi. Most vascular flowering plants have the ability to form these associations, which have a significant impact on plant health and consequently on ecosystem function. Nutrient exchange is a central feature of the AM symbiosis, and AM fungi obtain carbon from their plant host while assisting the plant with the acquisition of phosphorus (as phosphate) from the soil. In the AM symbiosis, the fungus delivers P(i) to the root through specialized hyphae called arbuscules. The molecular mechanisms of P(i) and carbon transfer in the symbiosis are largely unknown, as are the mechanisms by which the plant regulates the symbiosis in response to its nutrient status. Plants possess many classes of P(i) transport proteins, including a unique clade (Pht1, subfamily I), members of which are expressed only in the AM symbiosis. Here, we show that MtPT4, a Medicago truncatula member of subfamily I, is essential for the acquisition of P(i) delivered by the AM fungus. However, more significantly, MtPT4 function is critical for AM symbiosis. Loss of MtPT4 function leads to premature death of the arbuscules; the fungus is unable to proliferate within the root, and symbiosis is terminated. Thus, P(i) transport is not only a benefit for the plant but is also a requirement for the AM symbiosis.

Plant nitrogen capture from organic matter as affected by spatial dispersion, interspecific competition and mycorrhizal colonization

• The capture of nitrogen (N) by plants from N-rich complex organic material differing in spatial (uniform dispersion or discrete patches) heterogeneity was measured, as well as the subsequent impact on N capture of the addition of a mycorrhizal inoculum ( Glomus hoi ). • The organic material was dual-labelled with ¹⁵ N and ¹³ C to follow plant uptake of N (as ¹⁵ N) and to determine the amounts of original ¹³ C and ¹⁵ N which remained in the soil at harvest. The organic material was added to microcosm units containing Lolium perenne or Plantago lanceolata in intra or interspecific competition. • Plant N capture from the dispersed organic material was more than twice that from the discrete patch (dispersed: 17%; discrete: 8%). There was no effect of species composition or the mycorrhizal inoculum on total plant N capture except when in interspecific plant competition. Here, N capture was dependent on the root length produced and was always higher when the mycorrhizal inoculum was present. • Mycorrhizal colonization increased N capture from the organic material when in interspecific plant competition but not in monoculture.

Growth and phosphorus nutrition of a Paris-type arbuscular mycorrhizal symbiosis

•  Paris -type arbuscular mycorrhizas (AM) are reportedly the most common morphological type of AM; however, most research has focused on the Arum -type. Asphodelus fistulosus , a common weed in southern Australia, forms Paris -type AM when colonised by Glomus coronatum . It is often found in sites with low nutrient levels, and may therefore be dependent on its AM associations for growth and phosphorus (P) nutrition. •  A. fistulosus was inoculated with G. coronatum and grown in pots containing a soil/sand mixture with P added to give five soil P concentrations. The plants were grown in a glasshouse and harvested 6 and 9 wk after planting, at which times growth, P nutrition and colonisation were measured. •  At low soil P, A. fistulosus showed very marked positive responses to colonisation both in P uptake and growth; both responses decreased with increasing P supply. Colonisation was not greatly reduced by increasing P supply. •  This study appears to be one of the first detailed investigations of P responses in a Paris -type AM, providing insight into what is reportedly the more common but less well studied morphological type of AM.