Aluminum (Al) toxicity and phosphorus (P) deficiency are widely recognized as major constraints to agricultural productivity in acidic soils. Under this scenario, the development of ryegrass plants with enhanced P use efficiency and Al resistance is a promising approach by which to maintain pasture production. In this study, we assessed the contribution of growth traits, P efficiency, organic acid anion (OA) exudation, and the expression of Al-responsive genes in improving tolerance to concurrent low-P and Al stress in ryegrass (Lolium perenne L.). Ryegrass plants were hydroponically grown under optimal (0.1 mM) or low-P (0.01 mM) conditions for 21 days, and further supplied with Al (0 and 0.2 mM) for 3 h, 24 h and 7 days. Accordingly, higher Al accumulation in the roots and lower Al translocation to the shoots were found in ryegrass exposed to both stresses. Aluminum toxicity and P limitation did not change the OA exudation pattern exhibited by roots. However, an improvement in the root growth traits and P accumulation was found, suggesting an enhancement in Al tolerance and P efficiency under combined Al and low-P stress. Al-responsive genes were highly upregulated by Al stress and P limitation, and also closely related to P utilization efficiency. Overall, our results provide evidence of the specific strategies used by ryegrass to co-adapt to multiple stresses in acid soils.

Improving plant ability to acquire and efficiently utilize phosphorus (P) is a promising approach for developing sustainable pasture production. This study aimed to identify ryegrass cultivars with contrasting P use efficiency, and to assess their associated biochemical and molecular responses. Nine ryegrass cultivars were hydroponically grown under optimal (0.1 mM) or P-deficient (0.01 mM) conditions, and P uptake, dry biomass, phosphorus acquisition efficiency (PAE) and phosphorus utilization efficiency (PUE) were evaluated. Accordingly, two cultivars with high PAE but low PUE (Ansa and Stellar), and two cultivars with low PAE and high PUE (24Seven and Extreme) were selected to analyze the activity and gene expression of acid phosphatases (APases), as well as the transcript levels of P transporters. Our results showed that ryegrass cultivars with high PAE were mainly influenced by root-related responses, including the expression of genes codifying for the P transporter LpPHT1;4, purple acid phosphatase LpPAP1 and APase activity. Moreover, the traits that contributed greatly to enhanced PUE were the expression of LpPHT1;1/4 and LpPHO1;2, and the APase activity in shoots. These outcomes could be useful to evaluate and develop cultivars with high P-use efficiency, thus contributing to improve the management of P in grassland systems.

Although silicon (Si) and lignin are accumulated on plant cell walls and both confer resistance to multiple biotic and abiotic stresses [¹,²], the impact of Si on lignin production in plants grown under phosphorus (P) stress still remains unknown. We evaluated the effect of Si on the lignin accumulation pattern and expression of lignin biosynthesis-related genes in wheat plants grown at different P levels. Two wheat cultivars differing in tolerance to P deficiency (Púrpura-sensitive and Fritz-tolerant) were hydroponically grown in a continuously aerated nutrient solution, as proposed by [³]. Ten days later, plants were treated with P (0, 0.01 or 0.1 mM) in combination with Si (0, 1 or 2 mM). Twenty-one days after the initiation of treatments, plants were harvested and lignin concentration, the lignin distribution pattern and the gene expression of phenylalanine ammonia lyase (TaPAL) and cinnamyl alcohol dehydrogenase (TaCAD) were analyzed in shoots. The lignin concentration of both wheat cultivars did not vary at different P doses; nevertheless, 2 mM Si increased lignin accumulation mainly at either 0 mM P (cv. Púrpura) or 0.01 mM P (cv. Fritz), with a more noticeable effect in Púrpura than in Fritz. This increase was in agreement with the stronger intensity of Safranine O staining observed after Si was added to both cultivars grown at sufficient or deficient P levels and supports previous findings showing the alleviative role of Si by increasing lignin production under stressful conditions [⁴,⁵,⁶,⁷,⁸]. Such an effect may be related to either increased hydrogen peroxide production or peroxidase activity in cell walls, as well as to the modulation of the activity and/or gene expression of some key enzymes involved in lignin biosynthesis. In this way, we also found that Si induced the expression of lignin biosynthesis genes. The up-regulation of TaPAL was detected in cv. Púrpura grown at low P levels, with a further increase observed in plants treated with Si. Similar to Si addition to P-stressed plants of cv., Fritz caused a 1.5-fold increase in the transcript level of TaPAL. Similarly, the expression level of TaCAD increased 1.7-fold as a result of the Si supply to both cultivars grown at low P. Overall, our results show that Si induced the biosynthesis of lignin in shoots of wheat plants grown under P stress. Acknowledgments. FONDECYT Regular Project N° 1201257 and FONDECYT Postdoctoral Project N° 3200901.

While soil responses to organic and inorganic phosphorus (P) fertilizers have been widely studied, plant physiological and molecular responses remain insufficiently characterized. Such an understanding is necessary to develop sustainable P fertilization strategies that enhance plant performance in soils with P limitations. This study investigated the impact of poultry manure (PM) and its combination with phytase enzyme on molecular plant responses involved in P use efficiency (PUE) of ryegrass plants growing on a P-deficient Andisol. A greenhouse experiment under controlled conditions was performed to evaluate soil properties, plant biomass, P uptake, plant performance, and the expression of P transporters under the following P treatments: P deficiency (PD), mineral fertilizers (F), PM alone, and PM combined with phytase. The combination of PM and phytase enhanced soil P availability by 60% and increased soil P enzyme activities 2.6-fold, facilitating the mineralization of organic P. This resulted in a 63% increase in shoot P concentration and a 35% enhancement in shoot biomass. Additionally, oxidative stress markers decreased, with lipid peroxidation in roots reduced up to five-fold, while antioxidant activity increased 1.6-fold. Molecular analysis revealed that the expression of the P transporter gene LpPHT1;4 was upregulated 9.3-fold, indicating an improved capacity for P acquisition and utilization. These findings suggest that phytase-mediated hydrolysis of organic P and the activation of plant P transporters are key mechanisms driving enhanced P uptake and efficiency in P-deficient soils.

Volcanic Andisols in southern Chile severely limit pasture productivity due to their high phosphorus (P) sorption capacity. This study evaluated how contrasting P sources shape the rhizosphere microbiome of perennial ryegrass (Lolium perenne) and the pathways linking microbial community composition, plant biochemical responses, and biomass production under P-limiting conditions. A greenhouse experiment using an Andisol (Freire series) tested four P sources; Triple Superphosphate (TSP), Phosphate Rock (PR), Cattle Dung (CD), and Poultry Manure (PM); at two nitrogen (N) rates (100 and 200 mg kg⁻¹) alongside an unfertilized control. Rhizosphere communities were characterized by 16S rRNA amplicon sequencing coupled with functional gene prediction (PICRUSt2), antioxidant enzyme activity and lipid peroxidation markers (superoxide dismutase, catalase, malondialdehyde), P-starvation transporter and phosphatase gene expression (LpPHT1;1, LpPHT1;4, LpPAP1), and soil chemistry. P source was the dominant driver of both plant performance and community composition, with N rate exerting a secondary, modulatory role; attenuating P-starvation gene expression at higher doses and subtly influencing community beta-diversity. Soil P availability, pH, and exchangeable aluminum collectively explained 81.4% of community variance. Path analysis revealed that the rhizosphere microbiome had no significant direct effect on shoot P uptake but was strongly associated with reduced foliar oxidative stress (β = -0.759, p < 0.001), with its indirect effect on shoot biomass fully mediated through this antioxidant buffering response. Organic amendments enriched predicted genes related to P mineralization and biological N–P cycling while suppressing denitrification-associated genes. These findings suggest that in high P-fixing volcanic soils, rhizosphere community shifts benefit plant growth primarily by alleviating P deficiency-induced oxidative stress rather than by directly enhancing P uptake, highlighting the agronomic value of organic amendments beyond nutrient supply alone.