avoid food shortages. However, the implementation of intensive agricultural practices such as excessive irrigation, tillage, and chemical fertilizers to increase crop productivity has devastated soil and farmland quality. [1,2] Particularly, acidification, salinization, and organic matter decomposition in soils typically coincide with agriculture practices, which adversely affect crop productivity and soil fertility. [3][4][5] Additionally, the inefficient absorption of conventional chemical NPK (i.e., nitrogen, phosphorus, and potassium) fertilizers by plants are among the main drivers of environmental eutrophication. [6] Therefore, many efforts are being made to develop novel strategies to overcome these drawbacks, including new types of fertilizers that can both maximize crop nutrient use efficiency and restore soil quality. [7,8] Novel smart fertilizer structures should not only be sensitive to crop rhizosphere, thus selectively releasing NPK or other crop macronutrients, but should also be made with non-toxic and low-cost materials. Crop nutrient use is maximized when the sensing ability of smart fertilizers is coupled with slow-releasing activity,

Structurally stable humic substances (HSs) in soils are tightly associated with soil fertility, and it is thus important to understand how soil HSs are naturally formed. It is believed that microbial metabolism on plant matter contributes to natural humification, but detailed microbial species and their metabolisms inducing humic functionality (e.g., direct plant stimulation) need to be further investigated.

No abstract

No abstract

We investigated the ability of microbial volatile organic compounds (MVOCs) emitted by Bacillus megaterium (a well-known MVOC producer) to modify the dissolution kinetics and surface of hydroxyapatite, a natural soil mineral. Facilitated phosphate release was induced by the airborne MVOCs in a time-dependent manner. Use of each standard chemical of the MVOCs then revealed that acetic and oxalic acids are crucial for the phenomenon. In addition, the ability of such MVOCs to engineer the apatite surfaces was evidenced by FT-IR spectra showing the COO– band variation with incubation time and the prolonged acceleration of phosphate release during the negligible acidification of the hydroxyapatite-containing solutions. The formation of calcium oxalate was revealed through SEM-EDS and XRD analyses, suggesting that MVOC oxalic acid interacts with calcium ions, leading to the precipitation of calcium oxalate, thus preventing the recrystallization of calcium phosphates. Gel- and soil-based plant cultivation tests employing Arabidopsis thaliana and solid calcium phosphates (i.e., nano- and microsized hydroxyapatites and calcium phosphate dibasic) demonstrated that these MVOC mechanisms facilitate plant growth by ensuring the prolonged supply of plant-available phosphate. The relationship between the growth enhancement and the particle size of the calcium phosphates also substantiated the MVOC sorption onto soil minerals related to plant growth. Given that most previous studies have assumed that MVOCs are a molecular lexicon directly detected by the dedicated sensing machinery of plants, our approach provides a new mechanistic view of the presence of abiotic mediators in the interaction between plants and microbes via MVOCs.