Genome-Wide Association Study for Root Morphology and Phosphorus Acquisition Efficiency in Diverse Maize Panels.

Maximizing soil exploration through modifications of the root system is a strategy for plants to overcome phosphorus (P) deficiency. Genome-wide association with 561 tropical maize inbred lines from Embrapa and DTMA panels was undertaken for root morphology and P acquisition traits under low- and high-P concentrations, with 353,540 SNPs. P supply modified root morphology traits, biomass and P content in the global maize panel, but root length and root surface area changed differentially in Embrapa and DTMA panels. This suggests that different root plasticity mechanisms exist for maize adaptation to low-P conditions. A total of 87 SNPs were associated to phenotypic traits in both P conditions at -log10(p-value) ≥ 5, whereas only seven SNPs reached the Bonferroni significance. Among these SNPs, S9_137746077, which is located upstream of the gene GRMZM2G378852 that encodes a MAPKKK protein kinase, was significantly associated with total seedling dry weight, with the same allele increasing root length and root surface area under P deficiency. The C allele of S8_88600375, mapped within GRMZM2G044531 that encodes an AGC kinase, significantly enhanced root length under low P, positively affecting root surface area and seedling weight. The broad genetic diversity evaluated in this panel suggests that candidate genes and favorable alleles could be exploited to improve P efficiency in maize breeding programs of Africa and Latin America.

Root morphological and physiological traits are committed to the phosphorus acquisition of the desert plants in phosphorus-deficient soils.

BACKGROUND: Phosphorus (P) deficiency in desert ecosystems is widespread. Generally, desert species may allocate an enormous proportion of photosynthetic carbon to their root systems to adjust their P-acquisition strategies. However, root P-acquisition strategies of deep-rooted desert species and the coordination response of root traits at different growth stages to differing soil P availability remains unclear. In this study, a two-year pot experiment was performed with four soil P-supply treatments (0, 0.9, 2.8, and 4.7 mg P kg-1 y-1 for the control, low-, intermediate-, and high-P supply, respectively). Root morphological and physiological traits of one- and two-year-old Alhagi sparsifolia seedlings were measured. RESULTS: For two-year-old seedlings, control or low-P supply significantly increased their leaf Mn concentration, coarse and fine roots' specific root length (SRL), specific root surface area (SRSA), and acid phosphatase activity (APase), but SRL and SRSA of one-year-old seedlings were higher under intermediate-P supply treatment. Root morphological traits were closely correlated with root APase activity and leaf Mn concentration. One-year-old seedlings had higher root APase activity, leaf Mn concentration, and root tissue density (RTD), but lower SRL and SRSA. Two-year-old seedlings had higher root APase activity, leaf Mn concentration, SRL and SRSA, but a lower RTD. Root APase activity was significantly positively correlated with the leaf Mn concentration, regardless of coarse or fine roots. Furthermore, root P concentrations of coarse and fine roots were driven by different root traits, with root biomass and carboxylates secretion particularly crucial root traits for the root P-acquisition of one- and two-year-old seedlings. CONCLUSIONS: Variation of root traits at different growth stages are coordinated with root P concentrations, indicating a trade-off between root traits and P-acquisition strategies. Alhagi sparsifolia developed two P-activation strategies, increasing P-mobilizing phosphatase activity and carboxylates secretion, to acclimate P-impoverished in soil. The adaptive variation of root traits at different growth stages and diversified P-activation strategies are conducive to maintaining the desert ecosystem productivity.

Elevated CO2 and temperature increase arbuscular mycorrhizal fungal diversity, but decrease root colonization, in maize and wheat.

Anthropogenic climate change threatens ecosystem multifunctionality. Arbuscular mycorrhizal (AM) fungi are important symbionts that participate in mediating many ecosystem processes, and thus being potentially essential link in the chain of responses to climate change. Yet, how climate change affect the abundance and community structure of AM fungi associated with different crops remains elusive. Here, we investigated the changes in rhizosphere AM fungal communities and growth performance of maize and wheat grown in Mollisols under experimentally elevated CO2 (eCO2, +300 ppm), temperature (eT, +2 °C) and both in-combination (eCT) with open-top chambers, representing a scenario likely to occur by this century's end. The results showed that eCT significantly shifted AM fungal communities in both rhizospheres compared with control, but with no remarkable variation of the overall communities in maize rhizosphere, suggesting their greater resistance to climate change. Both eCO2 and eT increased rhizosphere AM fungal diversity, and conversely they reduced mycorrhizal colonization of both crops, probably since AM fungi had distinct adaptive strategies to climate change in rhizospheres (i.e., r-strategy) and roots (K-strategy), while the colonization intensity positively correlated with a decreased phosphorus (P)-uptake in two crops. Furthermore, co-occurrence network analysis showed that eCO2 strongly decreased the modularity and betweenness centrality of network structure than that of eT and eCT in both rhizospheres, along with the reduced network robustness, implied their destabilized communities under eCO2, while root stoichiometry (C:N and C:P ratio) was the most important factor associating with taxa in networks regardless of climate change. Overall, those findings suggest that rhizosphere AM fungal communities in wheat appear to be more sensitive to climate change than that in maize, further highlighting the importance of effective monitoring and managing AM fungi, which may allow crops to maintain critical levels of mineral nutrients (at least P) under future global change.

Phosphorus acquisition strategies of wheat are related to biochar types added in cadmium-contaminated soil: Evidence from soil zymography and root morphology.

Biochar application for the remediation of cadmium (Cd)-contaminated soils may result in a relative deficiency of phosphorus (P) due to the disruption of soil nutrient balance. However, the P acquisition strategies of plants in such situation are still unclear. In this study, analyses on soil zymography and root morphology were combined for the first time to investigate the effects of pristine and P-modified biochars from apple tree branches on the P acquisition strategies of wheat under Cd stress. The results show that the application of pristine biochar exacerbated the soil's relative P deficiency. Wheat was forced to improve foraging for P by forming longer and thinner roots (average diameter 0.284 mm) as well as releasing more phosphatase to promote P mobilization in the soil. Moreover, bioavailable Cd affected the P acquisition strategies of wheat through stimulating the release of phosphatase from roots. The P-modified biochar maintained high levels of Olsen-P (>100 mg kg-1) in the soil over time by slow release, avoiding the creation of relative P deficiency in the soil; and increased the average root diameter (0.338 mm) and growth performance index, which promoted shoot growth (length and biomass). Furthermore, the P-modified biochar reduced DTPA-extracted Cd concentration in soils by 79.8 % (pristine biochar by 26.9 %), and decreased the Cd translocation factor from root to shoot as well as Cd concentration in the shoots. Therefore, P-modified biochar has a great potential to regulate the soil element balance (carbon, nitrogen, and P), promote wheat growth, and remediate the Cd-contaminated soil.

Polyphosphate application influences morpho-physiological root traits involved in P acquisition and durum wheat growth performance.

BACKGROUND: Among phosphate (P) fertilizers, polyphosphates (PolyPs) have shown promising results in terms of crop yield and plant P nutrition. However, compared to conventional P inputs, very little is known on the impact of PolyPs fertilizers on below- and above-ground plant functional traits involved in P acquisition. This study aims to evaluate agro-physiological responses of durum wheat variety ´Karim´ under different PolyPs applications. Three PolyPs fertilizers (PolyA, PolyB, and PolyC) versus one orthophosphate (OrthoP) were applied at three doses; 30 (D30), 60 (D60), and 90 (D90) kg P/ha under controlled conditions. The PolyPs (especially PolyB and PolyC) application at D60 significantly increased morphophysiological root traits (e.g., RL: 42 and 130%; RSA:40 and 60%), shoot inorganic P (Pi) content (159 and 88%), and root P acquisition efficiency (471 and 296%) under PolyB and PolyC, respectively compared to unfertilized plants. Above-ground physiological parameters, mainly nutrient acquisition, chlorophyll content and chlorophyll fluorescence parameters were also improved under PolyB and PolyA application at D60. A significant and positive correlation between shoot Pi content and rhizosphere soil acid phosphatase activity was observed, which reveal the key role of these enzymes in PolyPs (A and B) use efficiency. Furthermore, increased P uptake/RL ratio along with shoot Pi indicates more efficient P allocation to shoots with less investment in root biomass production under PolyPs (especially A and B). CONCLUSIONS: Under our experimental conditions, these findings report positive impacts of PolyPs on wheat growth performance, particularly on photosynthesis and nutrient acquisition at D60, along with modulation of root morpho-physiological traits likely responsible of P acquisition efficiency.

Phosphate solubilizing bacteria can significantly contribute to enhance P availability from polyphosphates and their use efficiency in wheat.

Rhizosphere microbes significantly enhance phosphorus (P) availability from a variety of unavailable P pools in agricultural soils. However, little is known about the contribution of root-associated microorganisms, notably P solubilizing bacteria (PSB), to enhance the use of polyphosphate (PolyP) fertilizers as well as the key mechanisms involved. This study assesses the ability of four PSB (Bacillus siamensis, Rahnella aceris, Pantoea hericii, Bacillus paramycoides) and their consortium (Cs) to enhance the release rate of available P from two types of PolyP ("PolyB" and "PolyC") with a focus on the key role of phosphatase enzyme activities and organic acids production. Wheat growth performance and P acquisition efficiency were evaluated in response to co-application of PSB and PolyP. Results showed that inoculation with PSB, notably Cs, significantly enhanced available P from PolyC, PolyB and tri-calcium P. Increased available P in response to inoculation with PSB significantly correlated with medium acidification, organic acids production (notably glycolic acid) and induced activities of acid phosphatase and pyrophosphatase. In planta, the co-application of PSB-PolyP improved wheat plant biomass, root growth and P acquisition, with best results obtained from Cs-PolyP co-application as compared to uninoculated and unfertilized plants. At seedling stage, the co-application of Cs-PolyP (PolyB and PolyC) enhanced root hairs length (125 % and 131 %), root length (26 % and 37 %) and root inorganic P (Pi) content (160 % and 182 %), respectively compared to uninoculated plants. Similarly, at tillering stage, plant biomass (35 % and 47 %), Pi content (43 % and 253 %), P translocation (215 % and 315 %) and soil phosphatases (213 % and 219 %) significantly improved under PolyB and PolyC application, respectively. Findings from this study demonstrate the key role of PSB to enhance the use of PolyP through production of organic acids and phosphatases, exhibiting differential traits patterns between the two PolyP. Improved wheat growth and root P acquisition in response to PSB-PolyP co-application can be attributed to induced rhizosphere processes leading to enhanced available P taken up by roots.

Plant phosphorus acquisition links to phosphorus transformation in the rhizospheres of soybean and rice grown under CO2 and temperature co-elevation.

Climate change is likely to influence the reservoir of soil phosphorus (P) as plants adaptably respond to climate change in the perspective of P acquisition capability via root proliferation and mediating biochemical properties in the rhizosphere to access various soil P fractions. It is particularly important in cropping soils where P fertilizer plus soil P is required to synchronize crop P demand for the production sustainability under climate change. However, few studies have examined the effect of CO2 and temperature co-elevation on plant P acquisition, P fractions and relevant functional genes in the rhizosphere of different crops. Thus, the present study investigated the effect of elevated CO2 and warming on P uptake of soybean and rice grown in Mollisols, and soil P fractions and relevant biochemical properties and microbial functions in the rhizosphere with or without P application. Open-top chambers were used to achieve elevated CO2 of 700 ppm combined with warming (+ 2 °C above ambient temperature). CO2 and temperature co-elevation increased P uptake in soybean by 23% and 28% under the no-P and P application treatments, respectively; and in rice, by 34% and 13%, respectively. CO2 and temperature co-elevation depleted organic P in the rhizosphere of soybean, but increased in the rhizosphere of rice. The phosphatase activity negatively correlated with organic P in the highland soil while positively in the paddy soil. The P mineralization likely occurs in soybean-grown soils under climate change, while the P immobilization in paddy soils. CO2 and temperature co-elevation increased the copy numbers of P functional genes including phoD, phoC, pstS and phnX, in soils with P application. These results indicate that the P application would be requested to satisfy the increased P demand in soybean under climate change, but not in rice in paddy soils where soil P availability is sufficient. Therefore, elevated CO2 and temperature facilitated the crop P uptake via biochemical and microbial pathways, and P functional genes played an essential role in the conversion of P.

Common and specific responses to iron and phosphorus deficiencies in roots of apple tree (Malus × domestica).

Iron and phosphorus are abundant elements in soils but poorly available for plant nutrition. The availability of these two nutrients represents a major constraint for fruit tree cultivation such as apple (Malus × domestica) leading very often to a decrease of fruit productivity and quality worsening. Aim of this study was to characterize common and specific features of plant response to Fe and P deficiencies by ionomic, transcriptomic and exudation profiling of apple roots. Under P deficiency, the root release of oxalate and flavonoids increased. Genes encoding for transcription factors and transporters involved in the synthesis and release of root exudates were upregulated by P-deficient roots, as well as those directly related to P acquisition. In Fe-deficiency, plants showed an over-accumulation of P, Zn, Cu and Mn and induced the transcription of those genes involved in the mechanisms for the release of Fe-chelating compounds and Fe mobilization inside the plants. The intriguing modulation in roots of some transcription factors, might indicate that, in this condition, Fe homeostasis is regulated by a FIT-independent pathway. In the present work common and specific features of apple response to Fe and P deficiency has been reported. In particular, data indicate similar modulation of a. 230 genes, suggesting the occurrence of a crosstalk between the two nutritional responses involving the transcriptional regulation, shikimate pathway, and the root release of exudates.

Physiological and transcriptomic data highlight common features between iron and phosphorus acquisition mechanisms in white lupin roots.

In agricultural soil, the bioavailability of iron (Fe) and phosphorus (P) is often below the plant's requirement causing nutritional deficiency in crops. Under P-limiting conditions, white lupin (Lupinus albus L.) activates mechanisms that promote P solubility in the soil through morphological, physiological and molecular adaptations. Similar changes occur also in Fe-deficient white lupin roots; however, no information is available on the molecular bases of the response. In the present work, responses to Fe and P deficiency and their reciprocal interactions were studied. Transcriptomic analyses indicated that white lupin roots upregulated Fe-responsive genes ascribable to Strategy-I response, this behaviour was mainly evident in cluster roots. The upregulation of some components of Fe-acquisition mechanism occurred also in P-deficient cluster roots. Concerning P acquisition, some P-responsive genes (as phosphate transporters and transcription factors) were upregulated by P deficiency as well by Fe deficiency. These data indicate a strong cross-connection between the responses activated under Fe or P deficiency in white lupin. The activation of Fe- and P-acquisition mechanisms might play a crucial role to enhance the plant's capability to mobilize both nutrients in the rhizosphere, especially P from its associated metal cations.

Physiological and RNA sequencing data of white lupin plants grown under Fe and P deficiency.

This DIB article provides details about transcriptional and physiological response of Fe- and P-deficient white lupin roots, an extensive and complete description of plant response is shown in the research article "Physiological and transcriptomic data highlight common features between iron and phosphorus acquisition mechanisms in white lupin roots" Venuti et al. [1]. White lupin plants were grown under hydroponic system and three different nutritional regimes: Fe deficiency (-Fe), P deficiency (-P), or Fe and P sufficiency (+P + Fe). Depending on nutritional treatment, white lupin plants showed changes in the fresh weights, in root external acidification and FeIII-reductase activity. Moreover, the transcriptomic changes occurring in apices and clusters of Fe-deficient lupin roots were investigated and compared with differences of gene expression occurring in P-deficient plants (-P) and in Fe- and P-sufficient plants (+P + Fe). Transcriptomic data are available in the public repository Gene Expression Omnibus (http://www.ncbi.nlm.nih.gov/geo) under the series entry (GSE112220). The annotation, mapping and enrichment analyses of differentially modulated transcripts were assessed.

Arbuscular mycorrhizal fungi alleviate arsenic toxicity to Medicago sativa by influencing arsenic speciation and partitioning.

In a pot experiment, Medicago sativa inoculated with/without arbuscular mycorrhizal (AM) fungus Rhizophagus irregularis were grown in four levels (0, 10, 25, and 75 mg/kg) of arsenic (As)-polluted soil to investigate the influences of AM symbiosis on plant As tolerance. The results showed that mycorrhizal inoculation significantly increased plant biomass, while As addition decreased mycorrhizal colonization and hyphal length density. Mycorrhizal inoculation dramatically improved plant phosphorus (P) nutrition, restricted As uptake and retained more As in roots by upregulating the expression of the AM-induced P transporter gene MsPT4 and the metallothionein gene MsMT2. High soil As content downregulated MsPT4 expression. Dimethylarsenic acid (DMA) was detected only in the shoots of mycorrhizal plants, indicating that AM fungi likely play an essential role in As detoxification by biological methylation. The present investigation allowed deeper insights into the As detoxification mechanisms of AM associations and demonstrated the important role of AM fungi in plant resistance under As-contaminated conditions.

Arbuscular mycorrhizal fungi alleviate the heavy metal toxicity on sunflower (Helianthus annuus L.) plants cultivated on a heavily contaminated field soil at a WEEE-recycling site.

An 8-week pot experiment was conducted to investigate the growth and responses of sunflower (Helianthus annuus L.) to arbuscular mycorrhizal (AM) fungal inoculations on a heavily heavy metal (HM)-contaminated (H) soil and a lightly HM-enriched (L) soil, both of which were collected from a waste electrical and electronic equipment (WEEE)-recycling site. Compared with the L soil, the H soil induced significantly larger (P<0.05) concentrations of Cd, Cu, Pb, Cr, Zn and Ni in sunflower (except for root Cr and shoot Ni), which impaired the thylakoid lamellar folds in leaves. The biomasses and P concentrations of shoots and roots, as well as the total P acquisitions per pot were all significantly decreased (P<0.05). Both Funneliformis mosseae (Fm) and F. caledonium (Fc) inoculation significantly increased (P<0.05) root mycorrhizal colonization. For the L soil, AM fungal inoculations had no significant effects on the soil-plant system, except for a decrease of soil pH and increases of soil available P and DTPA-extractable Zn concentrations with the Fm-inoculated treatment. For the H soil, however, AM fungal inoculations significantly increased (P<0.05) the biomasses and P concentrations of shoots and roots, as well as the total P acquisitions per pot, and significantly reduced (P<0.05) the concentrations of HMs in shoots (except for Cu and Pb with Fm- and Fc- inoculated treatments, respectively) and alleviated the toxicity symptoms of HMs in thylakoid structure of leaves. AM fungal inoculations in the H soil also significantly increased (P<0.05) the shoot uptake of HMs (except for Cr), and tended to decrease the total concentrations of HMs in soils. This suggests the potential application of AM fungi for both reducing HM stress and promoting phytoextraction of HM-contaminated soils caused by WEEE recycling.

How functional is a trait? Phosphorus mobilization through root exudates differs little between Carex species with and without specialized dauciform roots.

Root structures secreting carboxylates and phosphatases are thought to enhance a plant's phosphorus (P) acquisition. But do closely related species with and without such structures really differ in root exudation, P mobilization, or ecological niche? We investigated this by comparing 23 European Carex species with and without 'dauciform roots' (DRs). Plants grown in pots with sand were screened for DR formation, phosphatase activities, carboxylate exudation, and utilization of various organic and inorganic P compounds. Ecological niches were compared using ecological indicator values and nutrient concentrations of plant shoots in natural habitats. Species of subgenus Carex formed DRs, while species of subgenus Vignea did not. Species with DRs had higher root diesterase activity than species without DRs, exuded more citrate but less oxalate and less total carboxylates, and allocated less biomass to roots. Species with and without DRs showed similar growth responses to different forms of P and different amounts of P supplied; their natural habitats do not differ in soil fertility or degree of P limitation. Despite some differences in physiological function, DRs did not influence the P acquisition and nutritional niche of European Carex species, suggesting that species with and without DRs do not exhibit distinct P-acquisition strategies.

Balanced allocation of organic acids and biomass for phosphorus and nitrogen demand in the fynbos legume Podalyria calyptrata.

Podalyria calyptrata is from fynbos soils with low availability of phosphorus (P) and nitrogen (N). We investigated the physiological basis for tolerance of low P supply in nodulated P. calyptrata and examined responses to increased supply of combined-N as Ca(NO3)2 and P. It was hypothesized that increasing supply of combined-N would stimulate P-acquisition mechanisms and enhance plant growth with high P supply. Biomass, leaf [N] and [P], organic acid and phosphatase root exudates, and phosphoenolpyruvate carboxylase (PEPC) and malate dehydrogenase (MDH) activity in nodules and roots were examined in two N×P experiments. Low P supply decreased leaf [P] and limited growth, decreasing the nodule:root ratio but increasing nodular PEPC and MDH activity for enhanced P-acquisition or P-utilization. At low P supply, a N-induced demand for P increased root exudation of citrate and PEPC and MDH activity in roots. Greater combined-N supply inhibited nodulation more at low P supply than at high P supply. With a P-induced demand for N the plants nodulated prolifically and increased combined-N supply did not enhance plant growth. The physiological basis for N2-fixing P. calyptrata tolerating growth at low P supply and responding to greater P supply is through balanced acquisition of P and N for plant demand.