Accumulation and Translocation of Phosphorus, Calcium, Magnesium, and Aluminum in Pinus massoniana Lamb. Seedlings Inoculated with Laccaria bicolor Growing in an Acidic Yellow Soil

Abstract

Research Highlights: We demonstrate that ectomycorrhizal (ECM) fungi improve plant aluminum (Al)-tolerance in the field and Laccaria bicolor S238A is a promising ECM isolate. Furthermore, we interpret the underlying nutritional mechanism that ECM inoculation facilitates aboveground biomass production as well as nutrients accumulation and translocation. Background and Objectives: Al toxicity is a primary limiting factor for plants growing in acidic soils. Hydroponic/sand culture studies have shown that some ECM fungi could enhance plant Al-tolerance. However, the underlying mechanisms of ECM fungi in improving plant Al-tolerance in the field are still unknown. To fill this knowledge gap, the present study aimed to examine roles of ECM inoculation in biomass production, accumulation and translocation of nutrients and Al in the host plant grown in the field under Al treatment. Materials and Methods: 4-week-old Pinus massoniana seedlings were inoculated with three Laccaria bicolor isolates (L. bicolor 270, L. bicolor S238A or L. bicolor S238N) and grown in an acidic yellow soil under 1.0 mM Al treatment for 12 weeks in the field. Biomass production, accumulation and translocation of P, Ca, Mg, and Al were investigated in these 16-week-old P. massoniana seedlings. Results: All three of these L. bicolor isolates improved biomass production as well as P, Ca and Mg accumulation in P. massoniana seedlings. Moreover, the three ECM isolates facilitated the translocation of P, Ca, and Mg to aboveground in response to Al treatment, particularly when seedlings were inoculated with L. bicolor S238A. In addition, both L. bicolor 270 and L. bicolor S238A had no apparent effects on Al accumulation, while enhanced Al translocation to aboveground. In contrast, L. bicolor S238N decreased Al accumulation but had no significant effect on Al translocation. Conclusions: ECM fungi in the field improved plant Al-resistance by increasing nutrient uptake, and this was mostly due to translocation of P, Ca, and Mg to aboveground, not by decreasing the uptake and translocation of Al.

Laccaria bicolor Mobilizes both Labile Aluminum and Inorganic Phosphate in Rhizosphere Soil of Pinus massoniana Seedlings Field Grown in a Yellow Acidic Soil

“…In addition, Lactarius deliciosus and Suillus luteus cultured in vitro on Pachlewski liquid medium could reduce active Al 3ϩ concentrations while increasing P availability in response to Al stress (24). Compared with their non-ECM-inoculated counterparts, both biomass production and P uptake were significantly higher in L. bicolor-inoculated P. massoniana grown in acid yellow soil (25) and Pisolithus tinctorius-inoculated Pinus densiflora cultured on perlite containing Al 3ϩ (26). In a neutral purple soil (pH 6.8), Al-bound P (Al-P) and Ca-bound P (Ca-P) decreased significantly when the soil was incubated in vitro with Boletus sp.…”

“…Growth inhibition is an index used extensively for the assessment of Al toxicity (5,36). Numerous studies have demonstrated that various ECM fungi, including L. bicolor (25), P. tinctorius (26,31,37), and P. involutus (38), could enhance plant growth and Al tolerance in acidic culture media. P. tinctorius inoculation also enhanced P. strobus shoot but not root growth with ϩAl treatment (31).…”

“…In particular, information regarding whether ECM fungi play a role in the immobilization of activated Al in the field is limited. Based on the increased uptake of P and Al in ECM fungi (30) or ECM seedlings (25) in previous studies, we hypothesized that ECM fungal association can improve the availability of P and Al in the field (Fig. 1c).…”

“…Meanwhile, Wang et al (24) showed that ECM fungi, including L. deliciosus and S. luteus, produce oxalates, which could decrease active Al 3ϩ concentrations via formation of chelates. The uptake of Al was also enhanced in L. bicolor-inoculated P. massoniana (25), P. tinctorius-inoculated Pinus strobus seedlings (31), and Hebeloma crustuliniforme-inoculated Picea abies (32). In addition, studies have reported that the acidification of rhizosphere soil could facilitate the dissolution of labile Al (33).…”

“…Scholl et al (34) and Zhou et al (35) also found that exchangeable Al concentrations in soil solution were increased when ECM fungi dissolved soil mineral particles to release P. Similarly, a previous in vitro study showed that L. bicolor S238A and L. bicolor S238N increased the mycelial uptake of Al after addition of Al (30). Accumulations of Al in an acidic soil (pH 4.64) were significantly higher in three ECM isolate-inoculated P. massoniana seedlings than in non-ECM seedlings (25). At present, the role of ECM inoculation with regard to inorganic P (IP) availability after Al treatment in acidic soil remains poorly understood.…”