Heterogeneous nutrient supply promotes maize growth and phosphorus acquisition: additive and compensatory effects of lateral roots and root hairs

Background and AimsRoot proliferation is a response to a heterogeneous nutrient distribution. However, the growth of root hairs in response to heterogeneous nutrients and the relationship between root hairs and lateral roots remain unclear. This study aims to understand the effects of heterogeneous nutrients on root hair growth and the trade-off between root hairs and lateral roots in phosphorus (P) acquisition.MethodsNear-isogenic maize lines, the B73 wild type (WT) and the rth3 root hairless mutant, were grown in rhizoboxes with uniform or localized supply of 40 (low) or 140 (high) mg P kg⁻¹ soil.ResultsBoth WT and rth3 had nearly two-fold greater shoot biomass and P content under local than uniform treatment at low P. Significant root proliferation was observed in both WT and rth3 in the nutrient patch, with the WT accompanied by an obvious increase (from 0.7 to 1.2 mm) in root hair length. The root response ratio of rth3 was greater than that of WT at low P, but could not completely compensate for the loss of root hairs. This suggests that plants enhanced P acquisition through complementarity between lateral roots and root hairs, and thus regulated nutrient foraging and shoot growth. The disappearance of WT and rth3 root response differences at high P indicated that the P application reduced the dependence of the plants on specific root traits to obtain nutrients.ConclusionsIn addition to root proliferation, the root response to a nutrient-rich patch was also accompanied by root hair elongation. The genotypes without root hairs increased their investment in lateral roots in a nutrient-rich patch to compensate for the absence of root hairs, suggesting that plants enhanced nutrient acquisition by regulating the trade-off of complementary root traits.     

Root hairs are the most important root trait for rhizosheath formation of barley (Hordeum vulgare), maize (Zea mays) and Lotus japonicus (Gifu)

Background and AimsRhizosheaths are defined as the soil adhering to the root system after it is extracted from the ground. Root hairs and mucilage (root exudates) are key root traits involved in rhizosheath formation, but to better understand the mechanisms involved their relative contributions should be distinguished.MethodsThe ability of three species [barley (Hordeum vulgare), maize (Zea mays) and Lotus japonicus (Gifu)] to form a rhizosheath in a sandy loam soil was compared with that of their root-hairless mutants [bald root barley (brb), maize root hairless 3 (rth3) and root hairless 1 (Ljrhl1)]. Root hair traits (length and density) of wild-type (WT) barley and maize were compared along with exudate adhesiveness of both barley and maize genotypes. Furthermore, root hair traits and exudate adhesiveness from different root types (axile versus lateral) were compared within the cereal species.Key ResultsPer unit root length, rhizosheath size diminished in the order of barley > L. japonicus > maize in WT plants. Root hairs significantly increased rhizosheath formation of all species (3.9-, 3.2- and 1.8-fold for barley, L. japonicus and maize, respectively) but there was no consistent genotypic effect on exudate adhesiveness in the cereals. While brb exudates were more and rth3 exudates were less adhesive than their respective WTs, maize rth3 bound more soil than barley brb. Although both maize genotypes produced significantly more adhesive exudate than the barley genotypes, root hair development of WT barley was more extensive than that of WT maize. Thus, the greater density of longer root hairs in WT barley bound more soil than WT maize. Root type did not seem to affect rhizosheath formation, unless these types differed in root length.ConclusionsWhen root hairs were present, greater root hair development better facilitated rhizosheath formation than root exudate adhesiveness. However, when root hairs were absent root exudate adhesiveness was a more dominant trait.     

Contrasting phosphate acquisition of mycorrhizal fungi with that of root hairs using the root hairless barley mutant

Comparisons between plant species or cultivars differing in root hair length have indicated a major impact of root hairs on the mycorrhizal dependency of plants with respect to phosphate (P) uptake. The current study aimed to investigate this relationship by comparing directly the mycorrhizal dependency of a spontaneous root hairless mutant, brb , in Hordeum vulgare cv Pallas and its wild type. Both brb and wild type were grown at different soil P levels in association with different mycorrhizal fungi. P uptake of brb and wild type was similar at high P levels, but P uptake by non-mycorrhizal brb plants at low P levels was substantially lower than that of the non-mycorrhizal wild-type plants. However, P uptake of the mutant was much increased by mycorrhizas and with one fungus, the additional P uptake was effectively translated into increased plant growth. Roots of the mutant contained typical colonization structures and a radioactive tracer confirmed P transport by the extraradical mycelium. This is the first direct evaluation of the relative effectiveness of root hairs and mycorrhizas. Mycorrhizas effectively substituted root hairs in P uptake, whereas the additional P was most often used less effectively in promoting plant growth than P provided by root hairs.     

Analyses of mutants of three genes that influence root hair development in Zea mays (Gramineae) suggest that root hairs are dispensable

Root hairs are specialized epidermal cells that are thought to play an important role in plant nutrition by facilitating the absorption of water and nutrients. Three maize mutants with abnormal root hair morphologies (rthl, rth2, and rth3) have been isolated from Mutator transposon stocks. All three root hair mutant phenotypes are controlled by single recessive alleles. The rthl mutant initiates normal-looking root hair primordia that fail to elongate. The normal-looking root hair primordia of the rth2 mutant elongate to only approximately one-fifth to one-fourth the length of wild type root hairs. Like rth1 primordia, rth3 primordia undergo little elongation. However, unlike the relatively normal-looking rth1 primordia, rth3 primordia are distinctly abnormal when viewed through a scanning electron microscope. The rth1 mutant exhibits pleiotropic nutrient deficiencies, while the rth2 and rth3 mutants grow vigorously. This finding suggests that under some environmental conditions, root hairs are less important to plant growth than has been previously thought. The rthl, rth2, and rth3 genes have been mapped to chromosomes 1L, 5L, and 1S, respectively, via crosses with BA translocation stocks. The rth2 allele exhibits reduced transmission through the male gametophyte, but a normal rate of transmission through female gametophytes; rth1 and rth3 are transmitted at normal rates.     

Relative importance of an arbuscular mycorrhizal fungus (Rhizophagus intraradices) and root hairs in plant drought tolerance

Both arbuscular mycorrhizal (AM) fungi and root hairs play important roles in plant uptake of water and mineral nutrients. To reveal the relative importance of mycorrhiza and root hairs in plant water relations, a bald root barley (brb) mutant and its wild type (wt) were grown with or without inoculation of the AM fungus Rhizophagus intraradices under well-watered or drought conditions, and plant physiological traits relevant to drought stress resistance were recorded. The experimental results indicated that the AM fungus could almost compensate for the absence of root hairs under drought-stressed conditions. Moreover, phosphorus (P) concentration, leaf water potential, photosynthetic rate, transpiration rate, stomatal conductance, and water use efficiency were significantly increased by R. intraradices but not by root hairs, except for shoot P concentration and photosynthetic rate under the drought condition. Root hairs even significantly decreased root P concentration under drought stresses. These results confirm that AM fungi can enhance plant drought tolerance by improvement of P uptake and plant water relations, which subsequently promote plant photosynthetic performance and growth, while root hairs presumably contribute to the improvement of plant growth and photosynthetic capacity through an increase in shoot P concentration.     

Mycorrhiza alters the profile of root hairs in trifoliate orange

Root hairs and arbuscular mycorrhiza (AM) coexist in root systems for nutrient and water absorption, but the relation between AM and root hairs is poorly known. A pot study was performed to evaluate the effects of four different AM fungi (AMF), namely, Claroideoglomus etunicatum, Diversispora versiformis, Funneliformis mosseae, and Rhizophagus intraradices on root hair development in trifoliate orange (Poncirus trifoliata) seedlings grown in sand. Mycorrhizal seedlings showed significantly higher root hair density than non-mycorrhizal seedlings, irrespective of AMF species. AMF inoculation generally significantly decreased root hair length in the first- and second-order lateral roots but increased it in the third- and fourth-order lateral roots. AMF colonization induced diverse responses in root hair diameter of different order lateral roots. Considerably greater concentrations of phosphorus (P), nitric oxide (NO), glucose, sucrose, indole-3-acetic acid (IAA), and methyl jasmonate (MeJA) were found in roots of AM seedlings than in non-AM seedlings. Levels of P, NO, carbohydrates, IAA, and MeJA in roots were correlated with AM formation and root hair development. These results suggest that AMF could alter the profile of root hairs in trifoliate orange through modulation of physiological activities. F. mosseae, which had the greatest positive effects, could represent an efficient AM fungus for increasing fruit yields or decreasing fertilizer inputs in citrus production.     

Roothairless5, which functions in maize (Zea mays L.) root hair initiation and elongation encodes a monocot‐specific NADPH oxidase

Root hairs are instrumental for nutrient uptake in monocot cereals. The maize (Zea mays L.) roothairless5 (rth5) mutant displays defects in root hair initiation and elongation manifested by a reduced density and length of root hairs. Map‐based cloning revealed that the rth5 gene encodes a monocot‐specific NADPH oxidase. RNA‐Seq, in situ hybridization and qRT‐PCR experiments demonstrated that the rth5 gene displays preferential expression in root hairs but also accumulates to low levels in other tissues. Immunolocalization detected RTH5 proteins in the epidermis of the elongation and differentiation zone of primary roots. Because superoxide and hydrogen peroxide levels are reduced in the tips of growing rth5 mutant root hairs as compared with wild‐type, and Reactive oxygen species (ROS) is known to be involved in tip growth, we hypothesize that the RTH5 protein is responsible for establishing the high levels of ROS in the tips of growing root hairs required for elongation. Consistent with this hypothesis, a comparative RNA‐Seq analysis of 6‐day‐old rth5 versus wild‐type primary roots revealed significant over‐representation of only two gene ontology (GO) classes related to the biological functions (i.e. oxidation/reduction and carbohydrate metabolism) among 893 differentially expressed genes (FDR <5%). Within these two classes the subgroups ‘response to oxidative stress’ and ‘cellulose biosynthesis’ were most prominently represented.     

Nitrogen limitation impairs plant control over the arbuscular mycorrhizal symbiosis in response to phosphorus and shading in two European sand dune species

The symbiosis of plants with arbuscular mycorrhizal fungi (AMF) may become parasitic if the cost:benefit ratio (carbon:phosphorus ratio) increases. In case of mycorrhizal parasitism, a plant may prevent growth depression through the reduction of root colonization as a form of control over the symbiosis. In this greenhouse study, we attempted to manipulate the cost:benefit ratio of the arbuscular mycorrhizal symbiosis by shading and/or phosphorus (P) fertilization in the differentially mycotrophic plant species Hieracium pilosella and Corynephorus canescens. By repeated sampling of soil cores, we assessed the temporal progress of plant investment towards mycorrhizal structures as a measure of plant control over the AMF. Unexpectedly, we found no obvious treatment effects on mycorrhizal growth dependency (MGD), most likely caused by constant N-limitation in AM plants being enhanced by P-fertilization and shade probably not exacerbating plant C-budget for AMF. This highlights the importance of N:P:C stoichiometry for the outcome of the symbiosis. Nevertheless, we found possible control mechanisms in shaded H. pilosella, with considerably higher resource investments into root than into hyphal growth, while root colonization was only marginally suppressed. This control only manifested after 4 weeks of growth under potentially detrimental conditions, emphasizing the importance of time in plant control over the arbuscular mycorrhizal symbiosis. In contrast, the less mycotrophic C. canescens did not exhibit obvious changes in mycorrhizal investments in reaction to shading and P-fertilization, possibly because the low mycotrophy and AMF colonization already imposes a functioning control mechanism in this species. Our study suggests that highly mycotrophic plants may have a stronger need to keep AMF in check than less mycotrophic plants, which may have implications for the role of mycotrophy in the outcome of symbiotic interactions in natural situations.     

亚热带典型树种根毛特征及其与共生真菌的关系

根毛和共生真菌增加了吸收面积,提高了植物获取磷等土壤资源的能力。由于野外原位观测根表微观结构较为困难,吸收细根、根毛、共生真菌如何相互作用并适应土壤资源供应,缺乏相应的数据和理论。该研究以受磷限制的亚热带森林为对象,选取了21种典型树种,定量了根毛存在情况、属性变异,分析了根毛形态特征与共生真菌侵染率、吸收细根功能属性之间的关系,探讨了根表结构对低磷土壤的响应和适应格局。结果表明:1)在亚热带森林根毛不是普遍存在的, 21个树种中仅发现7个树种存有根毛, 4个为丛枝菌根(AM)树种, 3个为外生菌根(ECM)树种。其中,马尾松(Pinus massoniana)根毛出现率最高,为86%;2)菌根类型是理解根-根毛-共生真菌关系的关键,AM树种根毛密度与共生真菌侵染率正相关,但ECM树种根毛直径与共生真菌侵染率负相关; 3) AM树种根毛长度和根毛直径、ECM树种根毛出现率与土壤有效磷含量呈负相关关系。该研究揭示了不同菌根类型树种根毛-共生真菌-根属性的格局及相互作用,为精细理解养分获取策略奠定了基础。     

Root hair phenotypes influence nitrogen acquisition in maize

Background and AimsThe utility of root hairs for nitrogen (N) acquisition is poorly understood.MethodsWe explored the utility of root hairs for N acquisition in the functional–structural model SimRoot and with maize genotypes with variable root hair length (RHL) in greenhouse and field environments.Key ResultsSimulation results indicate that long, dense root hairs can improve N acquisition under varying N availability. In the greenhouse, ammonium availability had no effect on RHL and low nitrate availability increased RHL, while in the field low N reduced RHL. Longer RHL was associated with 216 % increase in biomass and 237 % increase in plant N content under low-N conditions in the greenhouse and a 250 % increase in biomass and 200 % increase in plant N content in the field compared with short-RHL phenotypes. In a low-N field environment, genotypes with long RHL had 267 % greater yield than those with short RHL. We speculate that long root hairs improve N capture by increased root surface area and expanded soil exploration beyond the N depletion zone surrounding the root surface.ConclusionsWe conclude that root hairs play an important role in N acquisition. We suggest that root hairs merit consideration as a breeding target for improved N acquisition in maize and other crops.     

Interactions between root hair length and arbuscular mycorrhizal colonisation in phosphorus deficient barley (Hordeum vulgare)

Aims

Phosphorus (P) limits crop yield and P-fertilisers are frequently applied to agricultural soils. However, supplies of quality rock phosphate are diminishing. Plants have evolved mechanisms to improve P-acquisition and understanding these could improve the long-term sustainability of agriculture. Here we examined interactions between root hairs and arbuscular mycorrhizal (AM) colonisation in barley (Hordeum vulgare L.).

Methods

Barley mutants exhibiting different root hair phenotypes, wild type barley and narrowleaf plantain (Plantago lanceolata L.) were grown in the glasshouse in P-sufficient and P-deficient treatments and allowed to develop AM colonization from the natural soil community. Plants were harvested after 6 weeks growth and root hair length, AM-fungal colonisation, shoot biomass and P-accumulation measured.

Results

Under P-deficient conditions, root hair length and AM colonisation were negatively related suggesting that resources are allocated to root hairs rather than to AM fungi in response to P-deficiency. There was evidence that barley and narrowleaf plantain employed different strategies to increase P-acquisition under identical conditions, but root hairs were more effective.

Conclusions

This research suggests future barley breeding programmes should focus on maintaining or improving root hair phenotypes and that pursuing enhancements to AM associations under the prevalent agricultural conditions tested here would be ineffectual.     

Forage radish and cereal rye cover crop effects on mycorrhizal fungus colonization of maize roots

Forage radish (Raphanus sativus L. var. longipinnatus) is being used by increasing numbers of farmers as a winter cover crop in the Mid-Atlantic USA. It is a non-host to arbuscular mycorrhizal fungi (AMF) and releases anti-fungal isothiocyanates (ITCs) upon decomposition in the winter. Field experiments were conducted to determine the effect of forage radish and cereal rye (Secale cereale L.) cover crops on arbuscular mycorrhizal fungus colonization of and P acquisition by a subsequent maize (Zea mays L.) silage crop. Cover crop treatments included forage radish, rye, a mix of forage radish and rye, and no cover crop. Mycorrhizal fungus colonization of maize roots at the V4 stage following forage radish cover crops was not significantly different from that in the no cover crop treatment. In 3 out of 6 site-years, a rye cover crop increased AMF colonization of V4 stage maize roots compared to no cover crop. These findings suggest that forage radish cover crops do not have a negative effect on AMF colonization of subsequent crops.     

接种AMF对菌根植物和非菌根植物竞争的影响

为了研究丛枝菌根真菌(arbuscular mycorrhizal fungus, AMF)对菌根植物与非菌根植物种间竞争的影响,以玉米(菌根植物)和油菜(非菌根植物)作为供试植物,分别进行间作、尼龙网分隔和单作,模拟这两种植物之间不同的竞争状态,接种丛枝菌根真菌Glomus intraradices和Glomus mosseae,比较菌根植物和非菌根植物的生长和磷营养状况,分析AMF侵染对植物种间竞争作用的影响。结果显示,与单作相比,间作模式下玉米的生物量及磷营养状况有所降低,但其菌根依赖性却有所提高。与不接种相比,接种处理显著降低了间作体系油菜根系的磷含量和磷吸收量,但趋于改善菌根植物玉米的磷营养状况。因此,接种AMF可以降低非菌根植物的磷营养状况及生物量,使得菌根植物的相对竞争能力明显提高,说明AMF在维持物种多样性方面有着重要的作用。     

The growth defect of lrt1, a maize mutant lacking lateral roots, can be complemented by symbiotic fungi or high phosphate nutrition

The growth of three maize (Zea mays L.) mutants, each impaired in the formation of one individual element of its root system, was compared under "natural" limiting phosphate conditions (0.1 mM). Mutant plants exhibiting a reduction in root hairs (rth3-1) or a depletion of crown and brace roots (rtcs) grew as well as the corresponding wild-type plants. However, mutant plants lacking lateral roots (lrt1) showed a strong reduction in plant growth. The growth defect of lrt1 was overcome when it was grown in association with an arbuscular mycorrhizal fungus, Glomus mosseae. Establishment of symbiosis was associated with the occurrence of a new type of lateral root. These new lateral roots were stunted and highly branched, giving rise to a bush-like structure. Supply of high phosphate (1 microM) ameliorated the growth of lrt1 plants too, but less efficiently than the symbiosis did. Hence, arbuscular mycorrhizal fungi as well as phosphate functionally complemented the lrt1 mutation.     

Arbuscular mycorrhizas and their role in plant growth, nitrogen interception and soil gas efflux in an organic production system

Background and aims

Roots and mycorrhizas play an important role in not only plant nutrient acquisition, but also ecosystem nutrient cycling.

Methods

A field experiment was undertaken in which the role of arbuscular mycorrhizas (AM) in the growth and nutrient acquisition of tomato plants was investigated. A mycorrhiza defective mutant of tomato (Solanum lycopersicum L.) (named rmc) and its mycorrhizal wild type progenitor (named 76R) were used to control for the formation of AM. The role of roots and AM in soil N cycling was studied by injecting a ¹⁵N-labelled nitrate solution into surface soil at different distances from the 76R and rmc genotypes of tomato, or in plant free soil. The impacts of mycorrhizal and non-mycorrhizal root systems on soil greenhouse gas (CO₂ and ¹⁴⁺¹⁵N₂O and ¹⁵N₂O) emissions, relative to root free soils, were also studied.

Results

The formation of AM significantly enhanced plant growth and nutrient acquisition, including interception of recently applied NO ₃ ^? . Whereas roots caused a small but significant decrease in ¹⁵N₂O emissions from soils at 23?h after labeling, compared to the root-free treatment, arbuscular mycorrhizal fungi (AMF) had little effect on N₂O emissions. In contrast soil CO₂ emissions were higher in plots containing mycorrhizal root systems, where root biomass was also greater.

Conclusions

Taken together, these data indicate that roots and AMF have an important role to play in plant nutrient acquisition and ecosystem N cycling.     

Mycorrhizal symbiosis and Lygodium microphyllum Invasion in South Florida—a biogeographic comparison

Lygodium microphyllum (Old World Climbing Fern) is one of the most problematic weeds in south Florida, invading numerous habitats from mangroves to pine flatwoods natural ecosystems. Much of the research efforts on L. microphyllum has been focused on reproductive potential, spore release, growth under different environmental conditions, belowground rhizome dormancy and survival strategies that describes its invasiveness. However, the role of an important mutualistic association with arbuscular mycorrhizal fungi (AMF) in the competitive ability and successful invasion of L. microphyllum by enhancing nutrient uptake has not been previously considered. Analysis of field root and soil samples from the ferns introduced and native range as well as a 7-week growth chamber experiment were done to determine the level of mycorrhizal colonization in the roots of L. microphyllum and the dependency on mycorrhizal fungi for growth and phosphorus (P) uptake. The field root samples showed that L. microphyllum was heavily colonized by AMF in relatively drier conditions, which are commonly found on some Florida sites compared to more common wetter sites where the fern is found in its native Australia. The results from the growth chamber experiment showed that the mycorrhizal treatment plants had significantly higher relative growth rate and biomass compared to the non-mycorrhizal plants. Similarly, L. microphyllum was highly dependent on the mycorrhizal fungi for growth and P uptake. Our results suggest that AMF play a significant role in vegetative reproduction and likely enhance the invasiveness of L. microphyllum in south Florida natural areas.     

<Emphasis Type="Italic">OsNOX3</Emphasis>, encoding a NADPH oxidase,regulates root hair initiation and elongation in rice

Root hairs play important roles in plant nutrient and water acquisition. To better understand the genetic mechanism controlling root hair development in rice (Oryza sativa L.), a rice mutant with root hair defects was isolated and characterized. Cryo-scanning electron microscope showed that the density and length of root hairs in the mutant were significantly reduced compared to the wild type (WT). Map-based cloning and complementation test revealed that the mutation occurred in a NADPH oxidase gene OsNOX3 (LOC_Os01g61880). The OsNOX3 displays high sequence similarity with the previously characterized NOX genes RTH5 in maize and RHD2 in Arabidopsis, which play critical roles in root hair development. Expression pattern analysis indicated that OsNOX3 was expressed in various tissues throughout the plant with high expression in roots and root hairs. Subcellular localization analysis confirmed that OsNOX3 was located on the plasma membrane. Staining assays showed that the content of superoxide and hydrogen peroxide were significantly reduced in root hair tips of Osnox3 when compared to WT. Our results showed critical roles of OsNOX3 in regulating both root hair initiation and elongation in rice, which is similar to RTH5 but different from RHD2, confirming the difference of genetic mechanisms regulating root hair morphogenesis in monocot and dicot plants.     

Phosphorus Acquisition Strategies within Arbuscular Mycorrhizal Fungal Community of a Single Field Site

Diversity in phosphorus (P) acquisition strategies was assessed among eight isolates of arbuscular mycorrhizal fungi (AMF) belonging to three Glomus species, all obtained from the same field site. Maize (Zea mays L. cv. Corso) was used as a test plant. Compartmented cultivation containers coupled with ³³P radioisotope labeling of soil P were employed to estimate (1) the distance from the roots that AMF were able to acquire soil P from, (2) the rate of soil colonization, (3) the efficiency of uptake of soil P by AMF, (4) benefits provided to maize in terms of P acquisition and growth. Glomus mosseae and G. intraradices took up P 10 cm from roots, whereas G. claroideum only up to 6 cm from the roots. G. mosseae most rapidly colonized the available soil volume and transported significant amounts of P to maize from a distance, but provided no net P uptake benefit to the plants. On the other hand, both G. intraradices and three out of four G. claroideum isolates significantly improved net P uptake by maize. These effects seem to be related to variability between and to a limited extent also within AMF species, in mycelium development, efficiency of hyphal P uptake and effects on plant P acquisition via the root pathway. In spite of absence of maize growth responses to inoculation with any of the AMF isolates, this study indicates remarkable functional diversity in the underground component of the studied field site.     

Effects of using different host plants and long-term fertilization systems on population sizes of infective arbuscular mycorrhizal fungi

The effect of cultivation of mycorrhizal and non-mycorrhizal plants and mineral fertilization on the arbuscular mycorrhizal fungal (AMF) community structure of maize (Zea mays L.) plants was studied. Soil samples were collected from two field experiments treated for 5 years with three fertilization systems (Control – no fertilization; Mineral – NPK fertilization; and Organic – Farmyard manure fertilization). Soil samples containing soil and root fragments of rapeseed (Brassica napus L., non-mycorrhizal plant) and wheat (Triticum aestivum L., mycorrhizal plant) collected from the field plots were used as native microbial inoculum sources to maize plants. Maize plants were sown in pots containing these inoculum sources for four months under glasshouse conditions. Colonization of wheat roots by AMF, AMF community structure, AMF diversity (Shannon’s index), AMF dominance (Simpson’s index) and growth of maize were investigated. Sixteen AMF species were identified from rhizosphere soil samples as different species of genera Acaulospora, Claroideoglomus, Dentiscutata, Funneliformis, Gigaspora, Quatunica, Racocetra, and Rhizoglomus. Maize plants grown in manure-fertilized soils had a distinct AMF community structure from plants either fertilized with mineral NPK-fertilizer or non-fertilized. The results also showed that inoculum from non-mycorrhizal plants combined with mineral fertilization decreased AMF diversity (Shannon’s index), AMF dominance (Simpson’s index) and growth of maize. Our findings suggest that non-mycorrhizal plants, such as B. napus, can negatively affect the presence and the effects of soil inoculation on maize growth. Also, our results highlight the importance of considering the long-term effect of rapeseed cultivation system on the reduction of population sizes of infective AMF, and its effect on succeeding annual crops.     

Stimulation of root hair elongation in Arabidopsis thaliana by low phosphorus availability

Low phosphorus availability stimulates root hair elongation in many plants, which may have adaptive significance in soil phosphorus acquisition. We investigated the effect of low phosphorus on the elongation of Arabidopsis thaliana root hairs. Arabidopsis thaliana plants were grown in plant culture containing high (1000 mmol m^?3) or low (1 mmol m^?3) phosphorus concentrations, and root hair elongation was analysed by image analysis. After 15d of growth, low-phosphorus plants developed root hairs averaging 0.9 mm in length while high-phosphorus plants of the same age developed root hairs averaging 0.3 mm in length. Increased root hair length in low-phosphorus plants was a result of both increased growth duration and increased growth rate. Root hair length decreased logarithmically in response to increasing phosphorus concentration. Local changes in phosphorus availability influenced root hair growth regardless of the phosphorus status of the plant. Low phosphorus stimulated root hair elongation in the hairless axr2 mutant, exogenously applied IAA stimulated root hair elongation in wild-type high-phosphorus plants and the auxin antagonist CM PA inhibited root hair elongation in low-phosphorus plants. These results indicate that auxin may be involved in the low-phosphorus response in root hairs.