Jun Wasaki

High-temperature stress driven by global warming and phosphorus (P) deficiency resulting from the depletion of phosphate rock reserves pose serious threats to modern agriculture. However, our understanding of the combined effects of these stresses on plants remains limited. In this study, we employed a hydroponic culture system to investigate the physiological and transcriptomic responses of the model legume Lotus japonicus to simultaneous moderate high-temperature and low-P conditions. Both elevated temperature and low-P individually reduced shoot biomass. Under low-P conditions, shoot biomass remained significantly lower than in P sufficient plants. However, the relative reduction was smaller under elevated temperature than under favorable temperature. L. japonicus exhibited enhanced root-secreted acid phosphatase activity in under low-P alone and displayed an increased organic acid (e.g. malate and citrate) exudation rates under elevated temperature, irrespective of the P supply. Root transcriptome analysis identified up-regulation of the PEPC1 gene, encoding phosphoenolpyruvate carboxylase, suggesting its potential involvement in organic acid root exudation. Additionally, elevated temperatures promoted metal ion translocation and uptake, increased anthocyanin accumulation, and enhanced carbohydrate transport in shoots. Transcriptomic analysis further revealed that low-P stress altered heat shock protein expression, potentially associated with reduced ATP availability. These findings demonstrate that L. japonicus employs distinct and overlapping strategies to adapt to the combined stresses of elevated temperatures and P deficiency. These strategies include the adjustment of root exudation patterns, nutrient transport, and stress-responsive gene expression.

Phosphorus (P) is a critical macronutrient affecting ecosystem development. Unlike nitrogen, ecosystem P originates primarily from mineral-bound forms, particularly apatite, released during soil development. Although primary P minerals are sparingly soluble, they can be mobilised through diverse nutrient-acquisition strategies (NAS) of plants and their associated microorganisms. This review synthesises recent advances linking specialised root strategies, mycorrhizal associations, and nitrogen-acquisition mechanisms to primary P dissolution during early pedogenesis. We detail how specialised roots (e.g., cluster and dauciform roots) exude large quantities of carboxylates and protons to promote rapid mineral weathering, while mycorrhizal associations contribute through fungal secretion of carboxylates and the stimulation of P-solubilizing microorganisms in the hyphosphere. Furthermore, we elucidate a key biogeochemical coupling: nitrogen-acquisition strategies, specifically biological nitrogen fixation and ammonium uptake, intensify P mineral weathering both actively (carboxylates release to meet high metabolic P demands) and passively (proton excretion during charge balance maintenance). Evidence from chronosequences and controlled experiments demonstrated that specialised root and biological nitrogen fixation contributed more to P mineral weathering than mycorrhizal strategies and free-living microoragnism during carbon-limited early pedogenesis (< 100 years). We posit that conceptualizing NAS as integrated plant–microorganism systems are essential to resolving the dissolution mechanisms, particularly under the climate-driven expansion of young soils from glacier retreat and land erosion. Future research should prioritise identifying how specific root functional traits are matched with microbial partners to optimise C allocation and maximise mineral weathering, as well as elucidating key metabolic pathways to provide a mechanistic basis for ecosystem restoration and sustainable agriculture.

Acidic soils impose multiple stresses on plants and affect soil nutrient availability. Some elements are essential to many physiological processes within plants. Comprehensive studies on the ionomic profiles in plants are insightful for uncovering plant strategies for nutrient uptake and tolerance to environmental stress. This study aimed to elucidate plant nutrition strategies by comparing the ionomes of plants grown in highly acidic soils, so‐called solfatara fields, and in non‐solfatara fields, with average pH values of 3.89 and 5.29, respectively. A quadrat survey was conducted to investigate the effects of fumaroles, which emit volcanic gases and are characteristic of solfatara fields, on plant ionomes. Our study classified ionomic profiles in solfatara and non‐solfatara fields into two groups: aluminum (Al)‐accumulating and non‐Al‐accumulating plants. Among non‐Al‐accumulating plants, concentrations of manganese, magnesium, and sulfur were similar or higher in solfatara than in non‐solfatara fields. Among Al‐accumulating plants, the concentration of Al in Palhinhaea cernua was higher than in other species, and it did not differ significantly between solfatara and non‐solfatara fields. In the quadrat survey, only four species were found, and their ionomes did not change with distance from the fumarole. The most acidic area had a pH of 2.28, and only Fimbristylis dichotoma subsp. podocarpa was found there. Although it remains unclear whether these patterns reflect species traits or adaptive responses to environmental conditions, the results enable us to hypothesize that manganese, magnesium, and sulfur were associated with tolerance for very acidic soil exhibited by non‐Al‐accumulating plants.

Lycophytes, one of the earliest‐diverging vascular plant lineages, occur in diverse and often extreme environments, yet their ecological adaptation strategies remain poorly understood. Ionomics, characterized by elemental composition, offers insights into how evolutionary history and environmental conditions shape plant function. Here, we investigated how lineage and soil type influence ionomic profiles in terrestrial lycophytes by analyzing shoot elemental concentrations in three Lycopodiaceae species and four Selaginellaceae species collected across Japan, including serpentine soils and solfatara fields. Element concentrations were quantified by inductively coupled plasma mass spectrometry, with nitrogen and phosphorus measured colorimetrically. Statistical analyses included heatmap clustering and principal component analysis. Across non‐solfatara environments, Lycopodiaceae and Selaginellaceae showed distinct ionomic profiles at the family level within the sampled taxa, with variation appearing to be more strongly affected by lineage differences than by living environment. In Selaginellaceae, individuals from serpentine soils showed higher magnesium, iron, and arsenic, reflecting serpentine soil characteristics. Lycopodiaceae showed higher aluminum, copper, potassium, rubidium, and manganese, whereas Selaginellaceae had higher calcium, magnesium, phosphorus, nitrogen, strontium, and zinc. For Palhinhaea cernua (Lycopodiaceae), which occurred in both solfatara and non‐solfatara fields, shoots from the acidic solfatara environment contained higher sulfur, nitrogen, and phosphorus while maintaining consistently high aluminum concentrations, supporting its status as an aluminum hyperaccumulator. Overall, lycophytes demonstrate family‐specific elemental homeostasis that is conserved across environments, alongside characteristic shifts in extreme soils. These findings provide a foundation for understanding ecological diversification in the earliest‐diverging vascular plants and highlight ionomics as an effective approach for exploring their environmental adaptation strategies.

Most Proteaceae and some Fabaceae species produce specialised cluster roots (CRs), and are abundant in severely phosphorus (P)‐impoverished soils in southwest Australia. Two types of CRs, compound and simple, have been identified. However, the difference in their P‐mining strategies remains unclear. Therefore, we conducted glasshouse and field experiments to compare the P‐acquisition strategies among 18 CR‐producing species in Proteaceae and Fabaceae. Proteaceae produced a significantly larger mass of CRs than Fabaceae. Particularly, Banksia species produced the largest mass of compound CRs and exhibited the greatest net plant‐absorbed P in pots and consistently higher mature leaf manganese concentration in the field. In contrast, Hakea and Grevillea species produced less mass of simple CRs but three times as much soil adhered to their CRs per CR dry weight, resulting in greater absorbed P per CR weight. All plants depleted similar P compounds from soil and accessed c . 52% of P that was not extracted by a NaOH‐EDTA solution, suggesting that both CRs shared a common physiological function for mining scarcely available P. This study highlights two divergent P‐acquisition strategies: greater biomass investment in compound CRs versus greater P‐acquisition efficiency in simple CRs.

Several plant species adapted to low-phosphorus (P) conditions develop cluster roots, specialized structures that release organic acids and acid phosphatases (APases) to increase inorganic phosphate (Pi) availability. White lupin (Lupinus albus L.) is used as a model for studying cluster root function. Using a positron-emitting tracer imaging system (PETIS), we previously observed spot-like carbon (C) secretion patterns in the cluster roots of white lupin, the amounts of which differed widely among spots, suggesting variation in secretion activity among cluster roots. Here, we combined PETIS with RNA-Seq to investigate transcriptomic differences between cluster roots with varying secretion activities. We identified 564 genes positively correlated and 135 genes negatively correlated with secretion levels. Among the positively correlated genes, we found three aluminum-activated malate transporter genes and two multidrug and toxic compound extrusion genes, likely involved respectively in malate and citrate secretion. Two APase genes encoding putative secreted enzymes were also upregulated. All Pi transporter genes except PHO1;6H were stably expressed, whereas PHO1;6H was significantly upregulated in high-C-secreting roots. Our findings highlight putative genes potentially involved in Pi mobilization, offering insights into plant adaptation to P deficiency.