Eucalypt seedlings lack a clear phosphate starvation response under low phosphorus availability

Abstract

In regions of low soil phosphorus (P) availability, such as many tropical and subtropical regions, the cultivation of eucalypts is common due to their adaptation to P-constrained soils. As in other trees, the molecular mechanisms underlying the phosphate starvation response (PSR) in eucalypts remain poorly understood. This study aimed to elucidate the molecular responses associated with PSR and assess the efficiency of P acquisition in five eucalypt species: Eucalyptus acmenoides, E. grandis, E. globulus, E. tereticornis, and Corymbia maculata. A greenhouse experiment was carried out in soil/substrate with low resin-extractable P (4.5 mg kg⁻¹, Low P) and sufficient P (10.8 mg kg⁻¹, Sufficient P) availability. After nine months growing in such conditions, various parameters were assessed, such as biomass production, P concentrations, P uptake efficiency (PUpE), and the expression of PSR-related genes. Overall, eucalypt plants exhibited a relatively weak response to low P availability, with slight variations in biomass production, P concentration, and PSR gene expression. C. maculata plants exhibited the highest PUpE under low P, while E. globulus exhibited the lowest. Among PSR-related genes, LPR1/2 in the roots of E. grandis, PDR2 in the roots of C. maculata, and phosphate transporters PHT1;6 and PHT1;8 in the roots of E. globulus, along with PHT1;12 in the roots of E. tereticornis, were induced under low P availability. Elevated PHT1 transcripts in the roots under sufficient P conditions, despite adequate leaf P concentrations, suggest potential interactions with other nutrient availability such as nitrogen, magnesium, and calcium, as well as symbiotic associations. Additionally, the upregulation SQD1 gene involved in membrane lipid remodeling in leaves of E. tereticornis, E. acmenoides, and C. maculata under low P suggests an improved P utilization efficiency. This study reveals the intricate and multifaceted nature of eucalypt responses to soil P availability. Despite the low P concentrations, eucalypt plants maintained foliar concentrations similar to those in the P-sufficient treatment suggesting a complex interplay of factors influencing PSR including nutrient balance.