Low Soil Phosphorus Research Articles

Stacking of Pup1 QTL for low soil phosphorus tolerance and bacterial blight resistance genes in the background of APMS6B, the maintainer line of rice hybrid DRRH-3

Phosphorus (P) is one of the macronutrients essential for plant growth and development. Rice (Oryza sativa L.) is sensitive to P starvation and its deficiency influences many key plant functions, resulting in crop yield penalties. Although the hybrid rice segment is well-known for its yield heterosis, P deficiency and bacterial leaf blight diseases are evident limitations. APMS6B, the female parent of DRRH-3 is susceptible to low P and bacterial blight disease. In the present study, the improvement of APMS6B to P starvation and resistance to bacterial leaf blight (BB) was carried out using the marker-assisted backcross breeding approach. Kasalath (+Pup1 QTL) was used as a donor, and a promising IL (ATR 594-1) at BC1F4 generation was identified with 81.15% of recurrent parent genome recovery. Concurrently, this IL was intercrossed with GU-2 (+Xa21 and Xa38). Intercross F1s (ICF1) hybridity was confirmed through foreground selection having maximum RPGR (88.29%) and was selfed to produce ICF2. The resultant progenies were phenotyped for BB using Xoo inoculum (IX-020), simultaneously genotyped with gene-specific functional SSR markers forXa21 and Xa38. The identified BB-resistant plants were subjected to foreground selection for Pup1. Four promising ICF3 plants (BP-10-1, BP-10-3, BP-10-5, and BP-10-15 with Xa21, Xa38, and Pup1) along with parents and checks were screened both in low P plot (< 2 kg P2O5 ha−1) as well as in normal plot (> 25 kg P2O5 ha−1) during dry and wet seasons 2018. The field evaluation identified four promising intercrossed lines with better root growth in the primary root length of extracted zone and root volume. In addition, fewer reductions in grain yield (39.10%) under P starvation and less susceptibility indices values (< 1) for BB were observed. These lines may be exploited in the CMS conversion and development of climate-resilient, biotic and abiotic stress-tolerant rice hybrids.

Feasibility of variable rate application of diammonium phosphate fertilizer to wheat crop under center pivot irrigation system

A study was conducted, on a 30 ha wheat field under a solar energy powered center pivot irrigation system in a commercial farm located 400 km north of Khartoum, Sudan, to evaluate the feasibility of variable rate fertilizer application of Diammonium Phosphate (DAP) on wheat crop based on variable soil phosphorus content. Soil phosphorus content was divided into three categories (low: 3.75 to 4.50 ppm, medium: 4.51 to 5.25 ppm and high: 5.26 to 6.00 ppm) and a GIS soil phosphorus content map of the experimental field was generated. Three variable application rates (200 kg ha−1, 160 kg ha−1 and 120 kg ha−1) of granular DAP fertilizer were determined to fit the low, medium and high soil phosphorus contents, respectively. The the DAP fertilizer rate of 200 kg ha−1 was the rate practiced for wheat production in the experimental farm.The normalized Difference Vegetation Index (NDVI), measured at different wheat growth stages using sentinel-2 satellite images, and wheat grain yield were used to evaluate the response of wheat crop to the variable DAP fertilizer application rates. Excluding the tillering stage, the results showed significant differences in the NDVI values among different soil phosphorus levels and DAP fertilizer application rates at other growth stages, including stem elongation, grain filling and maturity stages. Moreover, wheat yield results showed significant differences among different soil phosphorus contents (P > F = 0.0001) and DAP fertilizer application rates (P > F = 0.0457). On the average, the highest yield of 2.449 t ha−1 was recorded in the field areas treated with the high DAP fertilizer application rate (200 kg ha−1), where the second highest yield of 2.441 t ha−1 was observed in field areas under the medium DAP fertilizer application rate (160 kg ha−1); however, no significant differences between these two yield values. Based on these results, the total savings of the DAP fertilizer was estimated to be 792 kg (equivalent to 475.2 $) in the experimental field (30 ha), only when the medium DAP fertilizer rate (160 kg ha−1) was used in the medium and high soil phosphorus zones, saving 15.84 $ ha−1 without affecting production.

Marker assisted pedigree breeding based improvement of the Indian mega variety of rice MTU1010 for resistance against bacterial blight and blast and tolerance to low soil phosphorus.

Rice production is affected by many biotic and abiotic stresses; among them, bacterial blight (BB) and blast diseases and low soil phosphorous stress cause significant yield losses. The present study was carried out with the objective of combining the BB resistance gene, Xa21, the blast resistance gene, Pi54, and the low soil phosphorous tolerance QTL/gene, Pup1, into the genetic background of the Indian mega-rice variety, MTU1010 (Cottondora Sannalu), through marker-assisted pedigree breeding. RP5973-20-9-8-24-12-7 [a near isogenic line (NIL) of MTU1010 possessing Pup1] and RP6132 [a NIL of Akshayadhan possessing Xa21 + Pi54] were crossed and ‘true’ F1s were identified, using the target gene-specific markers and selfed. F2 plants, which are homozygous for all the three target genes/QTLs, were identified using PCR based markers and were advanced further through the pedigree method of breeding, with selection based on phenotypic traits specific for MTU1010. At the F5 generation, a set of 15 promising triple positive homozygous lines were identified and screened for their resistance against BB and blast diseases and tolerance to low soil P. Among them, two lines (LPK 30-18-16 and LPK 49-15-22) showed higher yields as compared to MTU1010, along with the desirable long slender grain type in both low soil P and normal soil P plots, and also exhibited high levels of resistance against BB and blast diseases, with lesser grain shattering as compared to MTU1010. These lines are being advanced for multi-location trials for validating their performance.

Phosphorus puts a mortgage on restoration of species‐rich grasslands on former agricultural land

Large‐scale biodiversity loss is one of the most urgent global issues. The Convention on Biological Diversity created a vision to ecologically restore ecosystems by 2050. The European Union follows this ambition, and member states are required to select Special Areas of Conservation (SACs) to develop and restore; one example is species‐rich semi‐natural grassland. Species‐rich grassland restoration requires time for restoring both abiotic conditions, e.g. low soil phosphorus concentrations, and biotic conditions, e.g. introduction of missing species. For 507 grasslands (in northern Belgium) situated in SACs, we calculated the time needed for restoring necessary phosphorus‐poor conditions. Only 11% of the grasslands already met the strictest phosphorus‐target. We found that less than a fourth of the other 452 grasslands will reach this phosphorus‐target by 2050 through mowing. P‐mining, a more intensive technique involving fertilization of nitrogen and potassium, could help achieve this phosphorus‐target on about slightly more than a third of these grasslands by 2050. The soil iron concentration strongly affected the restoration times. A total of 65% of the grasslands will require alternatives like topsoil removal or selection of a different, less ambitious grassland target. These calculations do not include the time needed for biotic restoration. Because grassland restoration is a long‐term process, we advocate better protection of still existing species‐rich grasslands. Restoration is a last resort in safe‐guarding biodiversity.

Ozone does not diminish the beneficial effects of arbuscular mycorrhizas on Medicago sativa L. in a low phosphorus soil.

Enriched surface ozone (O3) can impose harmful effects on plants. Conversely, arbuscular mycorrhizal (AM) symbiosis can enhance plant tolerance to various environmental stresses and facilitate plant growth. The interaction of AM fungi and O3 on plant performance, however, seldom has been investigated. In this study, alfalfa (Medicago sativa L.) was used as a test plant to study the effects of O3 and AM symbiosis on plant physiology and growth under two O3 levels (ambient air and elevated O3 with 60nmol·mol-1 O3 enrichment) and three AM inoculation treatments (inoculation with exogenous or indigenous AM fungi and non-inoculation control). The results showed that elevated O3 decreased plant net photosynthetic rate and biomass, and increased malondialdehyde concentration, while AM inoculation (with both exogenous and indigenous AM fungi) could promote plant nutrient acquisition and growth irrespective of O3 levels. The positive effects of AM symbiosis on plant nutrient acquisition and antioxidant enzyme (superoxide dismutase and peroxidase) activities were most likely offset by increased stomatal conductance and O3 intake. As a result, AM inoculation and O3 generally showed no significant interactions on plant performance: although elevated O3 did not diminish the beneficial effects of AM symbiosis on alfalfa plants, AM symbiosis also did not alleviate the harmful effects of O3 on plants.

No CO2 fertilization effect on plant growth despite enhanced rhizosphere enzyme activity in a low phosphorus soil

No CO2 fertilization effect on plant growth despite enhanced rhizosphere enzyme activity in a low phosphorus soil

Variability of root traits, seed size and tolerance to low soil phosphorus in common bean (Phaseolus vulgaris L.)

Variability of root traits, seed size and tolerance to low soil phosphorus in common bean (Phaseolus vulgaris L.)

Interactions between biochar, arbuscular mycorrhizal fungi and photosynthetic processes in potato (Solanum tuberosum L.)

Pyrolyzed biomass, generating biochar for use as soil amendment, is recognized as a promising strategy for carbon sequestration. Current understanding of the interactions between biochar, arbuscular mycorrhizal (AM), and plant photosynthesis, in terms of biochemical processes and CO2 uptake, is fragmentary. The aim of this study was to investigate the effects on photosynthesis in potato including maximum rate of carboxylation by Rubisco (Vcmax), maximum rate of electron transport rate for RuBP-regeneration (Jmax), mesophyll conductance (gm) and other plant traits. Four types of biochar (wheat or miscanthus straw pellets pyrolyzed at temperatures of either 550 °C or 700 °C) were amended into low phosphorus soil. Potato plants were inoculated with the AM fungus Rhizophagus irregularis (M+) or not (M−). The results showed that four types of biochar generally decreased nitrogen and phosphorus content of potato, especially the biochars pyrolyzed at high temperature. This negative effect of biochar on nutrient content was alleviated by AM. It was found that Vcmax was limited by low plant nitrogen content as well as leaf area and phosphorus content. Plant phosphorus content also limited Jmax, which was mutually constrained by Vcmax of leaves. Low gm was an additional limiting factor for photosynthesis. The gm was positively correlated to nitrogen content, which influenced the leaf anatomical structure by alteration of leaf mass per area. In conclusion, the influence of interactions between quality of biochar and AM symbiosis on photosynthesis of potato seems to relate to effects on plant nutrient content and leaf structures. Accordingly, a model for the dependence of Vcmax on nitrogen and phosphorus content and their interactive effect exhibited a high correlation coefficient. As potato plants form AM symbiosis under natural field conditions, the extent and interaction with the quality of amended biochar can be a determining factor for plant nutrient content, growth and yield.

Enhancement of sorghum grain yield and nutrition: A role for arbuscular mycorrhizal fungi regardless of soil phosphorus availability

Societal Impact StatementSorghum is an important cereal crop that provides calories and nutrients for much of the world's population, and it is often grown with low fertiliser input. Optimising the yield, nutritive content and bioavailability of sorghum grain with minimal input is of importance for human nutrition, and arbuscular mycorrhizal (AM) fungi have previously shown potential to assist in this. Across sorghum genetic diversity, AM fungi improved the yield, nutrition and zinc and iron bioavailability of grain in a low phosphorus soil. Thus, food production systems that effectively manage AM fungi may improve consumer outcomes.Summary Sorghum is a C4 cereal crop that is an important source of calories and nutrition across the world, predominantly cultivated and consumed in low‐ and middle‐income countries. Sorghum can be highly colonised by arbuscular mycorrhizal (AM) fungi, and the plant‐fungal association can lead to improvements in biomass and nutrient uptake. High‐throughput phenotyping allows us to non‐destructively interrogate the ‘hidden’ effects of AM fungi on sorghum growth and phenology. Eight genetically diverse sorghum genotypes were grown in a soil amended with 2 or 20 mg P kg−1 and inoculated with an AM fungal culture of Rhizophagus irregularis. High‐throughput phenotyping uncovered the ‘hidden’ effects of AM fungi on growth and phenology, while grain biomass, nutrition, Zn and Fe bioavailability and root AM colonisation was determined after destructive harvest. Sorghum plants colonised by AM fungi generally performed better than non‐AM control plants, with greater yield, harvest indices, and grain P, Zn and Fe contents. During the early growth stages, AM colonisation led to temporary growth depressions. There were also AM fungal and P fertilisation effects on sorghum time‐of‐flowering. The sorghum genotype with the highest AM colonisation could barely produce grain when non‐inoculated. The two genotypes that failed to mature had very low AM colonisation. Generally, the genetically diverse sorghum genotypes were highly responsive to AM colonisation and produced more grain of greater nutritive quality when colonised, without adverse consequences for micronutrient bioavailability.

Plant growth–promoting bacteria improve maize growth through reshaping the rhizobacterial community in low-nitrogen and low-phosphorus soil

Plant growth–promoting bacteria improve maize growth through reshaping the rhizobacterial community in low-nitrogen and low-phosphorus soil

Effects of elevated CO2 concentration and nitrogen addition on foliar phosphorus fractions of Mikania micranatha and Chromolaena odorata under low phosphorus availability.

Invasive plants rapidly spread in habitats with low soil phosphorus (P) availability and have triggered a sharp decline in the diversity of native species. However, no studies have explored how widespread invasive species acclimate to low soil P availability via changing foliar P fractions, especially under elevated atmospheric CO2 concentrations ([CO2 ]) and nitrogen (N) deposition. Here, an open-top chamber experiment was conducted to explore the effect of nutrient addition and elevated [CO2 ] on leaf traits and foliar functional P fractions (i.e., Pi, metabolite P, lipid P, nucleic acid P, and residual P) of two aggressive invasive species (Mikania micranatha and Chromolaena odorata). We found that foliar N/P ratios were more than 20, and P addition significantly increased plant biomass. Both results indicated P-limited plant growth at our studied site. Elevated [CO2 ], N and N + P addition greatly increased plant biomass, photosynthetic rates, and photosynthetic P-use efficiency (PPUE) in invasive species, but PPUE decreased with increasing P addition. Nitrogen addition slightly decreased the concentration of leaf total P, decreased foliar residual P, but increased metabolite P concentrations in invasive species. Similar changes in foliar P fractions were found under N + P addition. Phosphorus addition increased foliar P concentrations, which was strongly correlated with an increase in metabolite P concentrations in invasive species. Elevated [CO2 ] alleviated these effects and increased PPUE. The present results suggest that future elevated [CO2 ] and N deposition allow the invasive species to acclimate to low soil P availability and support their successful invasion by greatly reducing P allocation to non-metabolite foliar P fractions (i.e., nucleic acid P and residual P) to meet their demand of metabolite P for photosynthesis and exhibit a high PPUE.

Phosphorus availability increases pathobiome abundance and invasion of rhizosphere microbial networks by Ralstonia.

Soil disease-suppressiveness depends on complex interactions among pathogens, native microbiota, and physicochemical properties, while these interactions remain understudied. Comparing field and microcosm experiments, we investigated the significance of these interactions in disease emergence or suppression using structural equation modelling (SEM) and receiver operating characteristic curve (ROC) analyses. We observed significant differences in the relative abundance of pathogenic and beneficial microbes, alpha and beta diversity indices between disease-conducive and -suppressive rhizosphere soils. The pathogenic (Ralstonia) and beneficial (Bacillus) taxa dominated disease-conducive and -suppressive rhizosphere soils, respectively. Moreover, the co-occurrences of Ralstonia with native microorganisms were positive and negative in the disease-conducive and -suppressive soils, respectively. These results suggest the supportive (Rudaea) and suppressive (Enterobacter, Bacillus) role of indigenous microbes in the invasion of soil and plant systems by Ralstonia. The SEM and ROC analysis predicted that Ralstonia invaded rhizospheric microbial networks and caused peanut wilt under high than low soil phosphorus conditions. Our results suggest the importance of soil phosphorus availability in altering the microbial interactions, thus leading to soil invasion by Ralstonia. Thus, we conclude by saying that feeding soil with high amounts of available phosphorus could deplete plant-beneficial microbes and increase the pathobiome abundance that may compromise plant health.

Critical phosphorus requirements of Trifolium species: The importance of root morphology and root acclimation in response to phosphorus stress.

Differences in root morphology and acclimation to low-phosphorus (P) soil were examined among eight legume species from the Trifolium Section Tricocephalum to understand how these root attributes determine P acquisition. Ornithopus sativus was included as a highly P-efficient benchmark species. Plants were grown as microswards in pots with five rates of P supplied in a topsoil layer to mimic uneven P distribution within a field soil profile. Topsoil and subsoil roots were harvested separately to enable measurement of the nutrient-foraging responses. Critical P requirement (lowest P supply for maximum yield) varied over a threefold range, reflecting differences in root morphology and acclimation of nutrient-foraging roots to P stress. Among the species, there was a 3.2-fold range in root length density, a 1.7-fold range in specific root length, and a 2.1-fold range in root hair length. O. sativus had the lowest critical P requirement, displayed a high root length density, the highest specific root length, and the longest root hairs. Acquisition of P from P-deficient soil was facilitated by development of a large root hair cylinder (i.e. a large root-soil interface). This, in turn, was determined by the intrinsic root morphology attributes of each genotype, and the plasticity of its root morphology response to internal P stress. Root acclimation in low-P soil by all species was mostly associated with preferential allocation of mass to nutrient-foraging roots. Only O. sativus and four of the Trifolium species adjusted specific root length beneficially, and only O. sativus increased its root hair length in low-P soil.

Novel major QTLs associated with low soil phosphorus tolerance identified from the Indian rice landrace, Wazuhophek.

With an objective of mapping novel low soil P (Phosphorus) tolerance loci in the non-Pup1 type donor rice line, Wazuhophek, we screened a recombinant inbred line (RIL) mapping population consisting of 330 lines derived from the cross Wazuhophek x Improved Samba Mahsuri (which is highly sensitive to low soil P) in a plot with low soil P for tolerance associated traits. Molecular mapping with SSR markers revealed a total of 16 QTLs (seven major and nine minor QTLs), which are associated with low soil P tolerance related traits. Interestingly, a QTL hotspot, harbouring 10 out of 16 QTLs were identified on the short arm of chromosome 8 (flanked by the makers RM22554 and RM80005). Five major QTLs explaining phenotypic variance to an extent of 15.28%, 17.25%, 21.84%, 20.23%, and 18.50%, associated with the traits, plant height, shoot length, the number of productive tillers, panicle length and yield, respectively, were located in the hotspot. Two major QTLs located on chromosome 1, associated with the traits, total biomass and root to shoot ratio, explaining 15.44% and 15.44% phenotypic variance, respectively were also identified. Complex epistatic interactions were observed among the traits, grain yield per plant, days to 50% flowering, dry shoot weight, and P content of the seed. In-silico analysis of genomic regions flanking the major QTLs revealed the presence of key putative candidate genes, possibly associated with tolerance.

Short-term microbial responses to soluble inorganic P input in a tropical lowland rain forest in Amazonia

In non-flooded lowland rain forests with low soil phosphorus (P) in parts of Amazonia, P cycling largely occurs via leaf litter recycling by arbuscular mycorrhizal (AM) fungal symbionts. Occasional high input of P into these ecosystems occurs during drought years with increased litterfall. As the length and frequency of drought events are projected to increase in the region, a single-dose nutrient addition experiment was carried out to test how this would impact P cycling. An application rate of 4 kg P ha–1 was used, which corresponds to twice the amount of litter-derived P in an average year. It was hypothesized that i) the added mineral P would be immobilized by soil microorganisms, leading to measurable increase in soil microbial biomass carbon (C) and P and ii) AM colonization rate would be reduced by the pulse in mineral P available for plant uptake. The results did not support either of our hypotheses. The addition of P did not have an effect on AM root colonization, nor was P immobilized by soil microbiota during the experimental period. The lack of a difference between the control and treatment at our study site could be attributed to the relatively low one-off dose of P applied that did not change either the colonization rate of roots by AM fungi or the amount of soil available labile P. To obtain a mechanistic understanding of the availability, capture, and use of P by plant-symbiont associations in tropical rain forest ecosystems, further integrated studies of the soil-plant system combining long-term nutrient manipulations, modeling, and experimental approaches are required.

Encourage farmers to adopt sustainable water and nutrient management in arid agroecosystems: problems, solutions and future studies

Crop production is seriously threatened by drought. Greater availability of nitrogen and phosphorus through intercropping with grain legumes and incubation with Phosphate Solubilizing Bacteria (PSB) can alleviate the negative effect of water stress on some crops. However, row crop-grain legume intercropping and using PSB bacteria is not welcomed or widely accepted by smallholder farmers in arid regions. The problem is that N-fixation by grain legumes cannot complementarily satisfy nitrogen demand of row crop especially in low phosphorus soils of these regions under restricted irrigation. The efficiency of PSB bacteria also is very low in the alkaline soil of this region. It suggests that some amount of nitrogen fertilizer should be used in this intercropping system. Nitrogen also consumption improves the efficiency of PSB bacteria. So, consumption of some nitrogen, and incubation with PSB bacteria meet entirely the need for phosphorus fertilizer. Significant water saving by restricting irrigation without significant yield loss in row crop and grain legumes can be regarded as an advantage of this method. So, farmers can cultivate more land with the same amount of water. In such a situation, even small foliage of the grain legumes, as green manure can convince the farmers to use the row crop -grain legumes intercropping system even under restricted irrigation conditions. Futures studies must focus on a better understanding of competition and facilitation of two crops for water and nutrients. They also must pay attention to nitrogen × PSB bacteria, and Phosphorus × rhizobacteria synergic interactions on yield of and sources use efficiency of both crops. These studies may help to better water and plant nutrition management in a way that is environmentally safe and economical for farmers.

Species-abundance distribution patterns of Quercus aliena var. acutiserrata forest in Taibai Mountain, China.

The statistical model (log-normal model), niche models (Zipf model, broken stick mo-del, niche preemption model), and neutral model were used to fit the species-abundance distribution patterns based on the measurements of environmental factors and inventory data of trees with DBH≥1 cm in a 1.5 hm2 plot in the primary forest (PF) and a 1.5 hm2 plot in the secondary forest (SF). The results showed that species-abundance distribution was affected by habitat heterogeneity in Q. aliena var. acutiserrata forest. Topography had a predominant impact on the species-abundance distribution in PF. Species distribution was affected by both neutral and niche processes, with neutral process having a less prominent effect in large convexity habitats. While the neutral model was rejected by the K-S and Chi-square test in low convexity habitats, the species-abundance distribution satisfied the assumption of niche theory. Niche process and neutral process were equally important in the community in areas with steep slopes, while niche differentiation was the dominant in flat areas. In SF, the main factors affecting species distribution were soil nutrients. The niche process was the mainly ecological process affected species-abundance distribution in habitats with high soil available phosphorus, while the niche and neutral processes existed simultaneously in habitats with low soil phosphorus availability. There was a significant scale effect on the species-abundance distribution pattern of Q. aliena var. acutiserrata forests in Taibai Mountain. The niche and neutral processes could protect the species-abundance distribution at the 20 m×20 m scale in PF, while the niche process could explain the species-abundance distribution at the 40 m×40 m and 70 m×70 m scales. The niche and neutral processes combined acted on the species abundance distribution at the 20 m×20 m, 40 m×40 m and 70 m×70 m scales in SF, with niche process being more important than neutral process. Moreover, besides the scale and habitat heterogeneity, the species-abundance distribution patterns of Q. aliena var. acutiserrata forests differed significantly between primary forest and secondary forest under anthropogenic disturbance.

Evaluation of Diverse Wheat (Triticum aestivum) and Triticale (× Triticosecale) Genotypes for Low Phosphorus Stress Tolerance in Soil and Hydroponic Conditions

Identification of “donors” possessing superior traits to adapt to low phosphorus (P) soils is a primary requirement to develop efficient crop plants for sustainable agricultural production. Diverse wheat (Triticum aestivum L., 89) and triticale (×Triticosecale Wittmack, 15) genotypes were phenotyped in soil with low and sufficient P for two seasons and once in the hydroponic system. Principal component analysis of relative biomass and grain weight revealed four clusters each for wheat and triticale. In low P soil, genotypes in the efficient cluster showed lesser reduction in total biomass, grain weight, total P uptake, and harvest index (HI), and improved P acquisition efficiency (PAE) and P harvest index (PHI) as compared to the inefficient cluster. In hydroponics, reduction in total biomass was less while root biomass and PAE increased at low P in the efficient genotypes. Out of 22 (soil) and 38 (hydroponics) P-efficient wheat genotypes, nine were overlapping in both screens while in P-inefficient cluster, out of 23 (soil) and 5 (hydroponics), three were common. A few P-efficient genotypes identified were DL784-3, DBW 16, and GW 322 and triticale TREAT, whereas P inefficient were C306 and ABACUS PVR (triticale). The selections in hydroponics are likely to be relevant in the field as demonstrated by overlapping of genotypes in both the mediums. Genotypic variations in P efficiency were strongly associated with P utilization rather than P uptake.

Low soil phosphorus availability triggers maize growth stage specific rhizosphere processes leading to mineralization of organic P

In this study, we examine the rhizosphere processes influencing organic P (Po) utilization in soil with low inorganic P (Pi) availability and how they change with plant development. Interactions between plants and the rhizosphere microbial community triggered by P deficiency may provide insights into the role of P availability on degradation of soil organic matter (SOM). Maize (Zea mays) plants were grown in low P containing soil. Soil pH, potential acid phosphatase activities, soil C and P pools, microbial biomass C and P, microbial community structure, and plant P content were analyzed at different vegetative growth stages (VGS). At early VGS, the plants were P deficient which correlated with greater rhizosphere potential acid phosphatase activity, degradation of SOM and a reduction in the Po pool. At late VGS, the plants appeared to recover which correlated with a decrease in Meh (III) extractable P, an increase in microbial biomass C and P, change in microbial community structure, and greater total P (TP) in the plant biomass. The mineralization of organic C and Po are coupled in low P soil where N is not limited. The overall findings from this study advance our understanding of the coupled biogeochemical rhizosphere processes controlling P cycling at different plant growth stages and notably the importance of Po to the overall P needs of plants in soil with low Pi availability.

Dissecting the phenotypic response of maize to low phosphorus soils by field screening of a large diversity panel

Maize (Zea mays L.) is an important crop worldwide, but in many regions is increasingly faced with the issue of phosphorus (P)-deficient soils. The aim of this study was to screen for low P-tolerance in maize and to dissect the underlying phenotypic response. To this end, we evaluated a panel of 380 diverse inbred lines in the field under low and normal P conditions for 17 morphological, biomass- and yield-related traits. All traits showed a significant genotypic variation and a moderate to high repeatability for each P condition. Under P deficiency, all traits were significantly lower compared to the control with normal P availability. The variance due to the interaction between genotype and P condition was significant for most traits, but generally small compared to the genotypic variance. Regarding the low P tolerance index, i.e. the phenotype under low P relative to the control, we observed a generally similar response within the morphological, biomass- or yield-related traits. Interestingly, genotypes showing little yield reduction under low P appear to achieve this tolerance through different strategies. Based on our results, low-P tolerant and low-P sensitive lines were identified, which can be used for further genetic research as well as to improve this globally important trait in maize breeding.