Phosphorus uptake and toxicity are delimited by mycorrhizal symbiosis in P-sensitive Eucalyptus marginata but not in P-tolerant Acacia celastrifolia

Silicon attenuates nutritional disorder of phosphorus in seedlings of Eucalyptus grandis × Eucalyptus urophylla

BACKGROUND

Nutritional disorders of phosphorus (P), due to deficiency or toxicity, reduce the development of Eucalyptus spp. seedlings. Phosphorus deficiency often results in stunted growth and reduced vigor, while phosphorus toxicity can lead to nutrient imbalances and decreased physiological function. These sensitivities highlight the need for precise management of P levels in cultivation practices. The use of the beneficial element silicon (Si) has shown promising results under nutritional stress; nevertheless, comprehensive studies on its effects on Eucalyptus spp. seedlings are still emerging. To further elucidate the role of Si under varying P conditions, an experiment was conducted with clonal seedlings of a hybrid Eucalyptus spp. (Eucalyptus grandis × Eucalyptus urophylla, A207) in a soilless cultivation system. Seedlings were propagated using the minicutting method in vermiculite-filled tubes, followed by treatment with a nutrient solution at three P concentrations: a deficient dose (0.1 mM), an adequate dose (1.0 mM) and an excessive dose (10 mM), with and without the addition of Si (2mM). This study assessed P and Si concentration, nutritional efficiency, oxidative metabolism, photosynthetic parameters, and dry matter production.

RESULTS

Si supply increased phenolic compounds production and reduced electrolyte leakage in seedlings provided with 0.1 mM of P. On the other hand, Si favored quantum efficiency of photosystem II as well as chlorophyll a content in seedlings supplemented with 10 mM of P. In general, Si attenuates P nutritional disorder by reducing the oxidative stress, favoring the non-enzymatic antioxidant system and photosynthetic parameters in seedlings of Eucalyptus grandis × Eucalyptus urophylla.

CONCLUSION

The results of this study indicate that Eucalyptus grandis × Eucalyptus urophylla seedlings are sensitive to P deficiency and toxicity and Si has shown a beneficial effect, attenuating P nutritional disorder by reducing the oxidative stress, favoring the non-enzymatic antioxidant system and photosynthetic parameters.

Species-specific effects of mycorrhizal symbiosis on Populus trichocarpa after a lethal dose of copper

Poplars have been identified as heavy metals hyperaccumulators and can be used for phytoremediation. We have previously established that their symbiosis with arbuscular mycorrhizal fungi (AMF) may alter their uptake, tolerance and distribution to excess concentrations of heavy metals in soils. In this study we hypothesised that mycorrhizal symbiosis improves the tolerance of poplars to lethal copper (Cu) concentrations, but this influence may vary among different AMF species. We conducted an experiment in a growth chamber with three Cu application levels of control (0 mg kg-1), threshold-lethal (729 mg kg-1) and supra-lethal (6561 mg kg-1), and three mycorrhizal treatments (non-mycorrhizal, Rhizophagus irregularis, and Paraglomus laccatum) in a completely randomized design with six replications. The poplars did not grow after application of 729 mg Cu kg-1 substrate, and mycorrhizal symbiosis did not help plants to tolerate this level of Cu. This can be explained by the toxicity suffered by mycorrhizal fungi. Translocation of Cu from roots to shoots increased when plants were colonised with R. irregularis and P. laccatum under threshold-lethal and supra-lethal applications of Cu, respectively. This result shows that mycorrhizal mediation of Cu partitioning in poplars depends on the fungal species and substrate Cu concentration. Multi-model inference analysis within each mycorrhizal treatment showed that in plants colonised with R. irregularis, a higher level of mycorrhizal colonisation may prevent Cu transfer to the shoots. We did not observe this effect in P. laccatum plants probably due to the relatively low colonisation rate (14%). Nutrient concentrations in roots and shoots were impacted by applied substrate Cu levels, but not by mycorrhizas. Magnesium (Mg), potassium (K), and manganese (Mn) concentrations in roots reduced with enhancing applied substrate Cu due to their similar ionic radii with Cu and having common transport mechanism. Synergistic effect on shoot concentration between applied substrate Cu levels and Mg, K, calcium, iron (Fe), and zinc was observed. Root Cu concentration was inversely related with root K and Mn concentrations, and shoot Cu concentration had a positive correlation with shoot Fe and K concentrations. Overall, mycorrhizal symbiosis has the potential to enhance plant health and their resilience to Cu toxicity in contamination events. However, it is important to note that the effectiveness of this symbiotic relationship varies among different mycorrhizal species and is influenced by the level of contamination.

Pioneer Tree Bellucia imperialis (Melastomataceae) from Central Amazon with Seedlings Highly Dependent on Arbuscular Mycorrhizal Fungi

Bellucia imperialis is one of the most abundant pioneer tree species in anthropized areas of the Central Amazon, and has ecological importance for the environmental resilience of phosphorus (P)-depleted areas. Thus, we investigated whether B. imperialis depends on symbiosis with arbuscular mycorrhizal fungi (AMF) to grow and establish under the edaphic stresses of low nutrient content and low surface moisture retention capacity of the substrate. We tried three AMF inoculation treatments: (1) CON-no mycorrhizae; (2) MIX-with AMF from pure collection cultures, and (3) NAT-with native AMF, combined with five doses of P via a nutrient solution. All CON treatment seedlings died without AMF, showing the high mycorrhizal dependence of B. imperialis. Increasing P doses significantly decreased the leaf area and shoot and root biomass growth for both the NAT and MIX treatments. Increasing P doses did not affect spore number or mycorrhizal colonization, but decreased the diversity of AMF communities. Some species of the AMF community showed plasticity, enabling them to withstand shortages of and excess P. B. imperialis was shown to be sensitive to excess P, promiscuous, dependent on AMF, and tolerant of scarce nutritional resources, highlighting the need to inoculate seedlings to reforest impacted areas.