Rhizosphere priming of two near-isogenic wheat lines varying in citrate efflux under different levels of phosphorus supply

Understanding how various forms of phosphorus stress affect microbiome functions and boost plant disease resistance: Insights from metagenomic analysis

The plant's response to phosphorus (P) starvation suppresses its immunity and regulates rhizosphere microbial colonization. However, the impact of various P forms on plant disease resistance and microbial composition remains underreported. This paper examines the soybean rhizosphere microbiome facing co-stress from Fusarium oxysporum and diverse P forms. Macrogenomic analysis evaluates whether P addition enhances plant disease resistance and rhizosphere microbial function, and if such effects relate to P forms. Results show that different P forms mitigate F. oxysporum-induced plant inhibition by promoting P turnover. P forms predominantly affect microbial composition, followed by soil and plant properties. In soybean, the phosphate transport strategy (ugpA/Q) was selected to maintain high P to enhance immunity in the KH2PO4 treatment, while organo-P mineralization (phnH/F/W/G) was selected for superphosphate treatment. The Frankiales, a P-turnover microorganism, copiotrophic microorganisms, and indicator bacteria of plant properties, initially increase after F. oxysporum inoculation and then decrease post P addition, regardless of P forms. Additionally, the rhizosphere microbial community's metabolic activities and compounds significantly aid soybean defense against F. oxysporum, with functional types depending on P forms. Therefore, these findings establish a novel approach to enhance host defense against soil-borne diseases through P nutrition regulation to mediate host-driven metabolic activities of microbial communities.

Stimulation of primed carbon under climate change corresponds with phosphorus mineralization in the rhizosphere of soybean

Elevated CO2 and temperature likely alter photosynthetic carbon inputs to soils, which may stimulate soil microbial activity to accelerate the decomposition of soil organic carbon (SOC), liberating more phosphorus (P) into the soil solution. However, this hypothesis on the association of SOC decomposition and P transformation in the plant rhizosphere requires robust soil biochemical evidence, which is critical to nutrient management for the mitigation of soil quality against climate change. This study investigated the microbial functional genes relevant to P mineralization together with priming processes of SOC in the rhizosphere of soybean grown under climate change. Soybean plants were grown under elevated CO2 (eCO2, 700 ppm) combined with warming (+ 2 °C above ambient temperature) in open-top chambers. Photosynthetic carbon flow in the plant-soil continuum was traced with 13CO2 labeling. The eCO2 plus warming treatment increased the primed carbon (C) by 43 % but decreased the NaHCO3-extratable organic P by 33 %. Furthermore, NaHCO3-Po was negatively correlated with phosphatase activity and microbial biomass C. Elevated CO2 increased the abundances of C degradation genes, such as abfA and ManB, and P mineralization genes, such as gcd, phoC and phnK. The results suggested that increased photosynthetic carbon inputs to the rhizosphere of plants under eCO2 plus warming stimulated the microbial population and metabolic functions of both SOC and organic P mineralization. There is a positive relationship between the rhizosphere priming effect and P mineralization. The response of microorganisms to plant-C flow is decisive for coupled C and P cycles, which are likely accelerated under climate change.

Ecosystem-dependent responses of soil carbon storage to phosphorus enrichment

Phosphorus deposition can stimulate both plant carbon inputs and microbial carbon outputs. However, how P enrichment affects soil organic carbon (SOC) storage and the underlying mechanisms remain unclear. We conducted a meta-analysis of 642 SOC observations from 213 field P addition experiments world-wide and explored the regulations of plant inputs, microbial outputs, plant characteristics, and environmental and experimental factors on SOC responses. We found that, globally, P addition stimulated SOC by 4.0% (95% CI: 2.0-6.0%), but the stimulation only occurred in forest and cropland rather than in grassland. Across sites, the response of SOC correlated with that of plant aboveground rather than belowground biomass, suggesting that the change in plant inputs from aboveground was more important than that from belowground in regulating SOC changes due to P addition. Among multiple factors, plant N fixation status and mean annual temperature were the best predictors for SOC responses to P addition, with SOC stimulation being higher in ecosystems dominated by symbiotic nitrogen fixers and ecosystems in high-temperature regions like tropical forests. Our findings highlight the differential and ecosystem-dependent responses of SOC to P enrichment and can contribute to accurate predictions of soil carbon dynamics in a P-enriched world.

Plant phosphorus-acquisition and -use strategies affect soil carbon cycling

Increased anthropogenic nitrogen (N) deposition is driving N-limited ecosystems towards phosphorus (P) limitation. Plants have evolved strategies to respond to P limitation which affect N cycling in plant-soil systems. A comprehensive understanding of how plants with efficient P-acquisition or -use strategies influence carbon (C) and N cycling remains elusive. We highlight how P-acquisition/-use strategies, particularly the release of carboxylates into the rhizosphere, accelerate soil organic matter (SOM) decomposition and soil N mineralisation by destabilising aggregates and organic-mineral associations. We advocate studying the effects of P-acquisition/-use strategies on SOM formation, directly or through microbial turnover.

Wheat root trait plasticity, nutrient acquisition and growth responses are dependent on specific arbuscular mycorrhizal fungus and plant genotype interactions

This study aimed to examine how interactions at both plant genotype and arbuscular mycorrhizal fungus species levels affected the expression of root traits and the subsequent effect on plant nutrition and growth. We used two wheat cultivars with contrasting phosphorus (P) acquisition efficiencies (Tukan and Crac) and two arbuscular mycorrhizal (AM) fungi (Rhizophagus intraradices and Claroideoglomus claroideum). Plant growth, as well as morphological and architectural root traits, were highly dependent on the myco-symbiotic partner in the case of the less P-acquisition efficient cultivar Tukan, with mycorrhizal responses ranging from -45 to 54 % with respect to non-mycorrhizal plants. Meanwhile, these responses were between only -7 and 5 % in the P-acquisition efficient cultivar Crac. The AM fungal species produced contrasting mechanisms in the improvement of plant nutrition and root trait responses. Colonization by R. intraradices increased Ca accumulation, regardless of the cultivar, but reduced root growth on Tukan plants. On the other hand, C. claroideum increased P content in both cultivars, with a concomitant increase in root growth and diffusion-based nutrient acquisition by Tukan. Moreover, plants in symbiosis with R. intraradices showed greater organic acid concentration in their rhizosphere compared to C. claroideum-colonized plants, especially Tukan (24 and 35 % more citrate and oxalate, respectively). Our results suggest that the responses in plant-AM fungal interactions related to nutrient dynamics are highly influenced at the fungus level and also by intra-specific variations in root traits at the genotype level, while growth responses related to improved nutrition depend on plant intrinsic acquisition efficiency.

Root traits benefitting crop production in environments with limited water and nutrient availability

BACKGROUND

Breeding for advantageous root traits will play a fundamental role in improving the efficiency of water and nutrient acquisition, closing yield gaps, and underpinning the "Evergreen Revolution" that must match crop production with human demand.

SCOPE

This preface provides an overview of a Special Issue of Annals of Botany on "Root traits benefitting crop production in environments with limited water and nutrient availability". The first papers in the Special Issue examine how breeding for reduced shoot stature and greater harvest index during the Green Revolution affected root system architecture. It is observed that reduced plant height and root architecture are inherited independently and can be improved simultaneously to increase the acquisition and utilisation of carbon, water and mineral nutrients. These insights are followed by papers examining beneficial root traits for resource acquisition in environments with limited water or nutrient availability, such as deep rooting, control of hydraulic conductivity, formation of aerenchyma, proliferation of lateral roots and root hairs, foraging of nutrient-rich patches, manipulation of rhizosphere pH and the exudation of low molecular weight organic solutes. The Special Issue concludes with papers exploring the interactions of plant roots and microorganisms, highlighting the need for plants to control the symbiotic relationships between mycorrhizal fungi and rhizobia to achieve maximal growth, and the roles of plants and microbes in the modification and development of soils.