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

peer reviewedAbstract 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

Integrated use of polyphosphate and P-solubilizing bacteria enhanced P use efficiency and growth performance of durum wheat

Coupling phosphate-solubilizing bacteria (PSB) with P fertilizers, including polyphosphates (PolyP), was reported as eco-efficient approach to enhance P use efficiency. Although PSB have been recently reported to hydrolyze PolyP, the plant growth promoting mechanisms of PolyP-PSB co-application were not yet uncovered. This study aims to evaluate the effect of a PSB consortium (PSBCs) on growth, P use efficiency (PUE), and wheat yield parameters under PolyP (PolyB) application. Co-application of PolyB-PSBCs significantly enhanced wheat growth at 75 days after sowing (DAS) compared to 30 DAS. A significant increase in shoot dry biomass (47%), shoot inorganic P content (222%), PUE (91%), and root P absorption efficiency (RPAE, 99%) was noted compared to unfertilized plants. Similarly, the PolyB-PSBCs co-application enhanced morphological root traits at 30 DAS, while acid phosphatase activities (root and rhizosphere), RPAE, and PUE were significantly increased at 75 DAS. The improved wheat P acquisition could be attributed to a lower investment in root biomass production, and significant induction of acid phosphatase activity in roots and rhizosphere soil under PolyB-PSBCs co-application. Consequently, the PolyB-PSBCs co-application significantly improved aboveground performance, which is reflected by increased shoot nutrient contents (P 300%, K 65%), dry weight (54%), and number (50%) of spikes. Altogether, this study provides relevant evidence that co-application of PolyP-PSBCs can be an integrated and environmentally preferred P fertilization approach owing to the dual effects of PolyP and PSBCs on wheat PUE

Inoculation with rhizobacterial consortia alleviates combined water and phosphorus deficit stress in intercropped faba bean and wheat

Our study aimed to assess the role of inoculation of faba bean/wheat intercrops with selected rhizobacterial consortia (composed of one rhizobium and two P solubilizing bacteria “PSB”) to alleviate the effects of combined water deficit and P limitation on faba bean/wheat intercropping vs. monocropping under greenhouse conditions. One Vicia faba L (Aguadulce) and one Triticum durum L. variety (Karim) were grown as a sole crop or were intercropped in pots containing a sterilized substrate (sand:peat 4:1 v/v) with either rock phosphate (RP) (unavailable P) or KH2PO4 in the nutrient solution (available P). Plant inoculation was performed using the rhizobacterial consortia C1 (Rhizobium laguerreae, Kocuria sp., and Pseudomonas sp.) and C2 (R. laguerreae, Rahnella sp., and Kocuria sp.). Two weeks after inoculation, the plants were subjected to water deficit with 40% substrate water holding capacity (WHC) vs. 80% WHC for the well-watered plants. The trial was assessed at the flowering stage, and the results showed that inoculation with both consortia (C1 and C2) improved faba bean biomass in terms of shoot, root, and nodules dry weight compared to inoculation with rhizobia alone. C2 improved these parameters by 19.03, 78.99, and 72.73%, respectively. The relative leaf water content decreased under combined stress, especially in response to C1 conferring significant improvement of this parameter in wheat intercrops. In faba bean under P limitation, inoculation with C2 increased stomatal conductance (gs), phosphatase, and phytase activity by 35.73, 166.94, and 26.16%, respectively, compared to plants inoculated with rhizobia alone. Furthermore, C2 also improved membrane stability under P deficit by 44.33 vs. 16.16% for C1 as compared to inoculation with rhizobia alone. In sole-cropped faba bean, inoculation with both consortia improved N accumulation compared to single inoculation with an increase of 70.75% under P limitation. Moreover, under combined stress, inoculation with C2 improved biomass and N content (112.98%) in intercropped wheat compared to the sole crop. Our findings revealed that consortium C2 might offer an agronomic advantage under water and P deficit and could serve as a useful inoculum for enhancing faba bean and wheat production in monocropping and intercropping systems

Synergistic action of phosphate solubilizing rhizobacteria and root functional traits enhances agronomic use efficiency of polyphosphate fertilizers

The rhizosphere is the narrow zone where interactions between plant roots, soil and a myriad of microorganisms affect nutrients biogeochemical cycling (including phosphorus (P)) and crop productivity. Given the dependency of today’s agriculture and food production on external P inputs, exploring the ability of roots and their microbial symbionts to sense the rhizosphere P limitation is emerging as a potential strategy to optimize P use efficiency. Indeed, dual use of P-solubilizing rhizobacteria (PSB) and polyphosphate (PolyP) fertilizers, that may exhibit slow P release property, can be considered as an integrated P management practice in agricultural soils to enhance P fertilizers use efficiency. In line with that, our recent published studies (Khourchi et al., 2022b, 2022a) showed that roots and PSB significantly increased P availability from PolyP under both soils and in vitro conditions. This hydrolysis process was catalyzed by the exuded P-hydrolyzing enzymes (phosphatases) and organic acids. For instance, the increased P uptake and P availability are accompanied with enhanced acid phosphatase activity in the rhizosphere of inoculated wheat plants under PolyP application. Moreover, the greenhouse-based experiments demonstrated that inoculation with PolyPhydrolyzing bacteria improved crop performance and P acquisition by modulating morphophysiological root traits (root length, root hair length and root acid phosphatases). These beneficial effects of PolyP and PSB can be attributed to induced rhizosphere processes such as rhizosphere acidification and exudation of phosphatases directly involved in PolyP hydrolysis. Indeed, PolyP hydrolysis can be synchronized with the crop P requirement, leading to an optimized and efficient P acquisitio

Polyphosphate fertilizer use efficiency strongly relies on soil physicochemical properties and root-microbial activities

peer reviewedLimited phosphorus (P) bioavailability restricts global agriculture and food production. This element is considered the least plant-available nutrient, and it is highly susceptible to immobilization in the soil matrix. Among the mineral fertilizers used to increase soil P fertility, polyphosphates (PolyP) consist of polymers of OrthoP residues and have been shown to improve crop P uptake and resulting yields more than other forms of P amendments. PolyP fertilizers are also known for their progressive hydrolysis, improving P availability in the rhizosphere and plant P uptake throughout crop growth stages. However, PolyP behavior in soils is still understudied, including rhizosphere traits likely to be involved in PolyP use efficiency within the soil-root-microbe interface. To improve our knowledge of PolyP behavioral properties in the soil–plant continuum, this review is among the first studies to compile, discuss, and propose ideas regarding this research while focusing on the key soil biochemical factors responsible for PolyP hydrolysis and use by crop roots. A combination of exuded P-hydrolyzing enzymes and acidification of the rhizosphere can presumably mobilize available P from PolyP and thereby improve crop P acquisition. The importance of root-associated microbes (exhibiting high P-mobilization capacities) is also discussed as a promising rhizosphere trait that could contribute greatly to boost PolyP hydrolysis and thus increase PolyP agronomic efficiency

Faba bean variety mixture can modulate faba bean-wheat intercrop performance under water limitation

Commercial legume varieties vary in terms of their drought tolerance when grown as sole crops, though relatively little is known about how legume variety selection affects cereal–legume intercrop performance under drought conditions. This study aims to test the hypothesis that positive rhizosphere interactions in faba bean–wheat intercrops will confer a “buffering capacity” on faba bean and wheat performance under water stress and that this effect will (i) depend on faba bean varietal selection and (ii) be enhanced with increasing faba bean varietal diversity. In a greenhouse experiment, three commercial faba bean (Vicia faba L.) varieties [Gloria (G), Alexia (A), Julia (J)] were grown in sole crop or intercropped with spring wheat (Triticum aestivum L.) under well-watered or water-stress conditions. Under intercropping, either one, two, or all three faba bean varieties were grown together with wheat to test the effect of intraspecific diversity on a cereal–legume intercrop performance. Consistent with the proposed hypothesis, we found that, under well-watered and water-stress conditions, wheat and faba bean shoot biomass production and nitrogen (N) acquisition improved with intercropping and that faba bean variety and variety mixture strongly modulated the intercropping effect. Interestingly, in both well-watered and water-stress conditions, wheat dry biomass and N accumulation were greatest in intercrops containing Gloria, while nodule number, nodule weight, and N accumulation in faba bean were greatest for intercrops containing Alexia and Julia (AJ). The effect of varietal diversity was inconsistent. Intercrops with two faba bean varieties tended to have positive or neutral effects on measured wheat and faba bean variables. However, overall performance under intercropping was generally reduced when all three faba bean varieties were planted with wheat. The effect of faba bean species diversity can buffer faba bean–wheat intercrop performance against water stress, and intercropping tended to have positive or neutral effects on the measured wheat and faba bean variables, notably with two-varietal faba bean mixtures