Published this week in the Journal of Degraded and Mining Lands Management (13(4):11435–11446), the study by Ariyanti, Cahyani and Cahyono (Sebelas Maret University, Surakarta) starts from a practical observation: the rhizosphere soils of plants already growing on a contaminated landfill are natural reservoirs of indigenous arbuscular mycorrhizal fungi (AMF) and phosphate-solubilizing bacteria (PSB), so they should be cheap, pre-adapted inoculum for revegetating the same sites. The team tested that idea directly. They collected rhizosphere soil from three phytoremediator shrubs — Calotropis gigantea (R1), Jatropha gossypiifolia (R2) and Senna alata (R3) — at the Putri Cempo landfill in Surakarta, Indonesia (7°32′16.7″ S, 110°51′15.6″ E), spiked it with Pb(NO₃)₂ to 300 mg Pb kg⁻¹, added rock phosphate at 100 kg ha⁻¹, and grew uniform C. gigantea stem cuttings in a 3×2 factorial (rhizomyco source × ±PSB, four replicates, 800 g soil + 200 g zeolite per pot). The PSB inoculum was isolate BRhizS7 (phosphate solubilization index 4.38) applied at 10⁸ CFU mL⁻¹; plants were harvested two months later. The starting soils were mildly contaminated (37–47 mg Pb kg⁻¹, pH 7.2–7.3) and differed in their native microbiology: S. alata rhizosphere carried the most AMF spores (325 per 100 g soil) and PSB (3 × 10⁵ CFU g⁻¹), Jatropha the fewest of both (146 spores per 100 g; 0.5 × 10⁵ CFU g⁻¹).
The decoupling: spore multiplication is not symbiotic function
The headline result is a warning about how mycorrhizal inoculants are selected and quality-controlled. Jatropha rhizosphere soil (R2) produced the greatest propagation potential — the fold-increase in AMF spore density relative to the starting population — while Senna soil (R3) produced the least. Plant response ran in exactly the opposite order: R3 supported the highest C. gigantea biomass and Pb uptake, R2 the lowest. PSB inoculation supercharged spore production in the Calotropis rhizosphere (a 4.28-fold jump over the uninoculated control, to 884.72 spores per 50 g soil versus 340.28 in the control) — yet that same Calotropis rhizomyco was outperformed for growth and Pb uptake by the introduced Senna community. The authors’ conclusion is blunt: “AMF propagation potential does not necessarily reflect symbiotic effectiveness,” and the indigenous community “is not necessarily the most effective symbiotic community for its host plant.” Genus-level identification adds a twist: the best-performing R3 soil contained only Acaulospora, while the poorer R1 and R2 soils carried three genera each (R1: Acaulospora, Glomus, Gigaspora; R2: Acaulospora, Glomus, Scutellospora) — functional compatibility, not richness, carried the benefit. Consistent with earlier work the paper cites, intermediate spore densities can outperform high ones because dense colonization taxes host carbohydrate.
What the phosphate bacteria actually did to the lead
PSB inoculation significantly increased fresh and dry biomass (p < 0.01 in both cases) and significantly enhanced soil Pb reduction (p < 0.01; rhizomyco source p < 0.05, interaction p < 0.05). The largest single-treatment reduction occurred in the PSB-inoculated Jatropha soil — though it was statistically tied with the other two PSB combinations. Mechanistically the authors invoke solubilization: PSB convert sparingly soluble Pb compounds to Pb²⁺ (they cite work showing PbCO₃ solubilization by Pb-resistant PSB), which raises bioavailability, plant uptake, and depletion of soil Pb. But the follow-through is the part that should change how the result gets used: with PSB, Pb concentration and uptake went up in the roots and down in the shoots. Root bioaccumulation factors exceeded 1 in almost every treatment (the two exceptions being the uninoculated Calotropis and Jatropha soils, at 0.90 and 0.75), and every translocation factor was below 1. The correlation structure says the same thing from another angle: AMF spore density correlated negatively with shoot Pb concentration (r = −0.80, p < 0.001) and positively with root Pb uptake (r = 0.63, p < 0.001), while shoot Pb uptake correlated negatively with chlorophyll content (r = −0.41, p < 0.05) — keeping Pb out of shoots protected photosynthesis. The paper’s own verdict, which we endorse: C. gigantea here is functioning as a phytostabilizer, not a phytoextractor. That matches the genus’s prior profile — the congener Calotropis procera was reported with a root BAF of 1.83 and TF of 0.96 in urban soils — and it is consistent with this site’s standing argument that Pb is the hardest metal to push into harvestable shoots.
The opportunity, and the two real risks
The opportunity is a deployable establishment protocol. Landfill-cap revegetation with C. gigantea stem cuttings is attractive for reasons the paper notes well: it is a non-food, non-feed fiber plant (so root-bound Pb has no food-chain route), it propagates vegetatively for uniform planting material, and the Senna-associated Acaulospora community plus a local PSB isolate is the kind of cheap, site-derived inoculum that field programs actually scale. The soil-fertility side improved too — organic C rose 16.03–46.22% across treatments, and PSB-inoculated pots gained 41.58% organic C and 2.77% available P over initial soil, with available P tracking dry biomass at r = 0.78 (p < 0.01).
The first risk is chemical. Standard practice for Pb-contaminated soil is the opposite maneuver: add phosphate to precipitate pyromorphite and immobilize Pb. This system deliberately runs the reverse — phosphate plus PSB to mobilize Pb²⁺ into the rhizosphere, betting the plant will capture it. That bet only pays while a vigorous, continuous root system is present. On a real landfill cap, a drought or cover failure that kills the stand leaves freshly mobilized Pb²⁺ in the soil solution, more leachable than the aged, sorbed Pb it replaced. The second risk is inferential: this is a two-month greenhouse pot trial (n = 4 per treatment) with Pb added as a soluble nitrate salt — freshly labile, not the strongly sorbed Pb of an aged landfill — in a zeolite-amended medium, starting from soil at ~37–47 mg Pb kg⁻¹ that was then spiked. The direction of the effects is credible and internally coherent; the magnitudes and the “which rhizomyco wins” ranking should be treated as one-soil, one-season hypotheses until a field trial says otherwise. Reviewers of the piece also flagged an internal reporting quirk the journal should clean up: initial AMF spore densities are given per 100 g soil while final densities are per 50 g, and the prose once credits R1 with the largest soil-Pb reduction as a main effect while the post-hoc comparison names R2B1 (statistically tied with the other PSB treatments) — worth knowing before citing any single number from that section.
Where it connects
No Calotropis species page exists yet in this database, so the honest home for this story is the /metals/lead/ hub, alongside the Pb phytostabilization literature this result extends. If the Senna-derived Acaulospora consortium replicates in field trials — the authors themselves flag this as the open question, whether the effect is host-specific or transferable across phytoremediators — it would be one of the cleaner examples of cross-species microbiome transfer in metal-plant practice, and C. gigantea would deserve a proper species entry as a Pb phytostabilizing shrub with an agronomic propagation route. The inoculum-selection lesson generalizes further, to nickel agromining too: any program that screens AMF or bacterial inoculants by how fast they multiply, rather than by what the host plant does with them, is optimizing the wrong variable.
Source: Ariyanti FID, Cahyani VR, Cahyono O (2026), Journal of Degraded and Mining Lands Management 13(4):11435–11446, DOI 10.15243/jdmlm.2026.134.11435, gold OA (received 2026-07-27, accepted 2026-09-30). The full text was read via the publisher’s PDF. Every number quoted above — the 300 mg kg⁻¹ Pb spike, the Table 1 soil and microbiology values, the 16.03–46.22% organic C range, the 41.58%/2.77% PSB effects, the BAF values 0.90 and 0.75, the 4.28-fold propagation increase, the 884.72 vs 340.28 spore densities, the correlation coefficients and significance levels, and the C. procera BAF 1.83/TF 0.96 context — was verified verbatim against the retrieved text by three independent reviewers on three different model vendors, each retrieving the primary source independently; no discrepancies were found. Values that appear only in figure bar charts (tissue Pb concentrations and percentage soil-Pb reductions per treatment) are not quoted, because the prose does not state them; qualitative trends from figures are attributed as such. See /methodology/ for how we source and check analysis pieces.