Search

Potassium (K) is a major element for proper plant nutrition in addition to nitrogen and phosphorus. Soil 2:1 clay minerals serve as a K reservoir for plants because they can fix anhydrous K+ ions in their interlayer sites (formation of “illite-like” layers) and such “fixed” ions can nonetheless be taken up by plants. The objective of the study was to determine if modifications of the illite structure can be observed within one season of maize growth and if these changes are impacted by fertilization and Arbuscular Mycorrhizal Fungi (AMF) inoculation. To do so, clay fractions recovered from (1) soil adhering to maize roots (“rhizosphere” soil), (2) soil sampled in the vicinity of maize roots but not adhering to the roots (“non rhizosphere” soil) and (3) soil sampled in adjacent un-planted fallow soil (“fallow” soil) were investigated using X-ray diffraction. The results indicated that extraction of K occurs during growth of the plants (40 days after sowing) and modifies the illite structure differently in the rhizosphere compared to the soil not adhering to the roots. At the end of the growth period (130 days) more K was present in the clay minerals than after 40 days growth except in the rhizosphere of AMF-inoculated roots, showing that mycorrhiza activity tended to affect a slightly greater loss of K compared to non-mycorrhiza clays in the rhizosphere. No influence of K fertilization on soil clay illite structure was observed suggesting that added K has been either already been taken up by maize plants after 40 days, either leached or adsorbed elsewhere than in the 2:1 clay mineral interlayer sites (organic matter or external sites). The results showed that clay modifications can be observed at the scale of a growing season and suggest that K+ ions can be extracted by the plants from the illitic layers (in illite minerals and illite layers of mixed layered smectite/illite minerals) and re-stored (being lost from plants and returning to the soil) within one growing season.

Background Increasing the presence of beneficial soil microorganisms is a promising sustainable alternative to support conventional and organic fertilization and may help to improve crop health and productivity. If the application of single bioeffectors has shown satisfactory results, further improvements may arise by combining multiple beneficial soil microorganisms with natural bioactive molecules. Methods In the present work, we investigated in a pot experiment under greenhouse conditions whether inoculation of two phosphate-solubilizing bacteria, Pseudomonas spp. (B2) and Bacillus amyloliquefaciens (B3), alone or in combination with a humic acids (HA) extracted from green compost and/or a commercial inoculum (M) of arbuscular mycorrhizal fungi (AMF), may affect maize growth and soil microbial community. Phospholipid fatty acid (PLFA) and denaturing gradient gel electrophoresis (DGGE) fingerprinting analysis were performed to detect changes in the microbial community composition. Results Plant growth, N and P uptake, and mycorrhizal root colonization were found to be larger in all inoculated treatments than in the uninoculated control. The greatest P uptake was found when B. amyloliquefaciens was applied in combination with both HA and arbuscular mycorrhizal fungi (B3HAM), and when Pseudomonas was combined with HA (B2HA). The PLFA-based community profile revealed that inoculation changed the microbial community composition. Gram+/Gram− bacteria, AMF/saprotrophic fungi and bacteria/fungi ratios increased in all inoculated treatments. The greatest values for the AMF PLFA marker (C16:1ω5) and AMF/saprotrophic fungi ratio were found for the B3HAM treatment. Permutation test based on DGGE data confirmed a similar trend, with most significant variations in both bacterial and fungal community structures induced by inoculation of B2 or B3 in combination with HA and M, especially in B3HAM. Conclusions The two community-based datasets indicated changes in the soil microbiome of maize induced by inoculation of B2 or B3 alone or when combined with humic acids and mycorrhizal inoculum, leading to positive effects on plant growth and improved nutrient uptake. Our study implies that appropriate and innovative agricultural management, enhancing the potential contribution of beneficial soil microorganisms as AMF, may result in an improved nutrient use efficiency in plants.

The molecular composition of water-soluble lignins isolated from four non-food bioenergy crops (cardoon CAR, eucalyptus EUC, and two black poplars RIP and LIM) was characterized in detail, and their potential bioactivity towards maize germination and early growth evaluated. Lignins were found to not affect seed germination rates, but stimulated the maize seedling development, though to a different extent. RIP promoted root elongation, while CAR only stimulated the length of lateral seminal roots and coleoptile, and LIM improved only the coleoptile development. The most significant bioactivity of CAR was related to its large content of aliphatic OH groups, C-O carbons and lowest hydrophobicity, as assessed by (31)P-NMR and (13)C-CPMAS-NMR spectroscopies. Less bioactive RIP and LIM lignins were similar in composition, but their stimulation of maize seedling was different. This was accounted to their diverse content of aliphatic OH groups and S- and G-type molecules. The poorest bioactivity of the EUC lignin was attributed to its smallest content of aliphatic OH groups and largest hydrophobicity. Both these features may be conducive of a EUC conformational structure tight enough to prevent its alteration by organic acids exuded from vegetal tissues. Conversely the more labile conformational arrangements of the other more hydrophilic lignin extracts promoted their bioactivity by releasing biologically active molecules upon the action of exuded organic acids. Our findings indicate that water-soluble lignins from non-food crops may be effectively used as plant biostimulants, thus contributing to increase the economic and ecological liability of bio-based industries.

Water-soluble humic-like lignins from energy crops had been previously shown to significantly improve plant development due to their chemical composition and supramolecular arrangement. Here, humic-like lignins isolated from Giant Reed were tested in several bioassays to verify whether the biostimulation was due to a hormone-mimic (auxin- and gibberellin-like) activity. The water-soluble lignins were applied on tomato seeds harboured with the auxin reporter DR5::GUS (β-glucuronidase), to visualize the auxin responses in roots. Moreover, auxin- or gibberellin (GA)-mimetic activities were assessed by the Audus test on watercress and chicory seeds, respectively, with increasing concentrations of water-soluble lignin. The latter showed a significant GA-like effect, whereas it did not produce auxin-like activity at any assayed concentration. The water-soluble lignins may either directly function as GA on plant and seed development or positively perturb GA-related hormonal balances, thereby influencing GA-mediated physiological mechanisms. These findings suggest that humic-like residual lignins from energy crops may be useful in intensified sustainable agriculture as seed germination enhancers and biostimulants of plant growth.

Identification of organic P species is important to understand their origin, turnover in soils and their effects on soil fertility. Attention has been recently devoted to microbial inocula, referred to as Bioeffectors, that are capable to increase P bioavailability and plant uptake. Nevertheless, little is known on the effect of Bioeffectors on soil P forms and their dynamics in agricultural soils upon different P fertilization. We investigated the effects of the application of different commercial inocula strains (Trichoderma harzianum T 22, Pseudomonas sp., and Bacillus amyloliquefaciens) alone or in combination with different P fertilizers (triple superphosphate, rock phosphate, and both composted cow- and horse-manure) on soil organic P forms. P forms were characterized by liquid-state 31P–NMR spectroscopy, while plant P uptake from P-treated soil was followed in a greenhouse pot experiment under maize cultivation. NMR spectra showed that the type of P fertilizer and bioeffectors inoculation, affected the abundance and the composition of organic P forms. The specific capacity of all bioeffectors, and especially Pseudomonas, was related to an increased content of diesters P forms. Pseudomonas, and, to a lesser extent, B. amyloliquefaciens showed the largest increase in combination with organic P amendments, which also provided the largest plant P uptake. This suggests a key role of Diester-P forms in determining P availability in agroecosystems. Microbial inoculation plays an important role in the dynamics of soil P, inducing a rapid P cycling that prevents P fixation and losses from soils, thus enhancing the P fertilizer use efficiency in agricultural soils.

Four water extractable organic matter (WEOM) were obtained from composts made out of residues of: 1. artichoke (C-CYN), 2. artichoke/fennel (C-CYNF), 3. tomato/woodchips (C-TOM), 4. Municipal solid waste (C-MSW), and their bioactivity was tested for maize seed germination and maize seedling growth. The molecular properties of both original composts and their WEOM were characterized by spectroscopic ((13)C-CPMAS- and (1)H NMR, FTIR-ATR), thermochemolysis-GC/MS, and thermal methods (TGA, DSC). While all WEOM had significant effects on plant growth, CYN-WEOM was the only material that concomitantly increased germination rate and primary and lateral root length of maize seedlings. The lignin-rich WEOM from green composts were generally more effective than those obtained from equally hydrophobic, but mainly alkyl-rich municipal organic wastes. A flexible conformational structure, due to the balanced content of aromatic compounds and carbohydrates, appeared to facilitate the release of bioactive molecules from WEOM suprastructures and stimulate plant growth.

We investigated in field experiments whether soil application of a commercial mycorrhizal inoculum (CI) with and without addition of phosphorus (P) fertilizers provided greater maize (Zea mays L.) yields and more soil available P than indigenous fungi alone. A field experiment was established with and without applications of commercial inoculum of arbuscular mycorrhizal fungi (AMF) in combination with three fertilizer rates (NPK = N200P90K160; NK = N200P0K160; and control = N0P0K0). Plant and soil (bulk and rhizosphere soil) samples were collected. Results showed that application of CI, in the NK treatment, resulted in plant growth, grain yield and P uptake similar to that found in treatments that received P fertilizer (NPK). After 40 days, inoculation increased available soil P concentrations, both in the NPK and NK treatments. This indicates that inoculated roots mobilize more P and plants may have uptaken more P from soil. The results suggest that AMF inoculation can be used as a component of integrated nutrient management strategies.

In a greenhouse pot experiment, lettuce plants (Lactuca sativa L.) were grown in a Hg-contaminated sandy soil with and without inoculation with arbuscular mycorrhizal fungi (AMF) (a commercial inoculum containing infective propagules of Rhizophagus irregularis and Funneliformis mosseae) amended with different rates of a humic acid (0, 1, and 2 g kg(-1) of soil), with the objective of verifying the synergistic effects of the two soil treatments on the Hg tolerance of lettuce plants. Our results indicated that the plant biomass was significantly increased by the combined effect of AMF and humic acid treatments. Addition of humic matter to soil boosted the AMF effect on improving the nutritional plant status, enhancing the pigment content in plant leaves, and inhibiting both Hg uptake and Hg translocation from the roots to the shoots. This was attributed not only to the Hg immobilization by stable complexes with HA and with extraradical mycorrhizal mycelium in soil and root surfaces but also to an improved mineral nutrition promoted by AMF. This work indicates that the combined use of AMF and humic acids may become a useful practice in Hg-contaminated soils to reduce Hg toxicity to crops.

We have studied the effects of P fertilization and AMF inoculation on the growth of escarole (Chicorium endivia L.) plants, grown in both As-non-contaminated (Padula) and As-contaminated (La Botte) soils and As and P uptake by these plants. Our study demonstrated that the combined use of AMF inoculation and P fertilization can significantly increase the production of biomass of escarole plants, even if grown in highly As-contaminated soils. In addition, this dual agricultural practice has also allowed to reduce the translocation of the harmful element from roots to leaves minimizing, hence, the accumulation of highly toxic levels of As in the edible part of the escarole. Therefore, the combined use of AMF inoculation and P fertilization may alleviate the As toxicity to sensitive plants as Cichorium endivia, by promoting their growth, limiting As assimilation and improving P nutrition.

We have studied the uptake and distribution of arsenic (As) and phosphorus (P) in roots, shoots and berries of tomato plants, grown on uncontaminated soil, irrigated with As-contaminated solutions at four concentrations (0, 0.5, 2 and 4 mg L -1 ), in presence or absence of P fertilization.The biomass of tomato plants decreased with increasing As concentration in irriga-tion water, especially tomato berries. In addition, the reduction of biomasses was significantly greater in plants non-fertilized with P. The beneficial effect generated with the P addition indicated that this nutrient played an important role in alleviating As toxicity in tomato plants. The higher the As concentration in irrigation water the higher the As concentration in plant tissues; most of the As absorbed by plants was accumulated in their roots. Phosphorus application has allowed to reduce As trans-location toward tomato berries, enhancing plant P status. These observations may be useful for certain areas of the World, in which As-contaminated waters are used for agricultural purposes.Keywords: tomato, arsenic, uptake, phosphorus fertilization, contamination.

The influence of compost on the growth of bean plants irrigated with As-contaminated waters and its influence on the mobility of As in the soils and the uptake of As (as NaAs III O 2 ) by plant components was studied at various compost application rates (3·10 4 and 6·10 4 kg ha −1 ) and at three As concentrations (1, 2 and 3 mg kg −1 ). The biomass and As and P concentrations of the roots, shoots and beans were determined at harvest time, as well as the chlorophyll content of the leaves and nonspecific and specifically bound As in the soil. The bean plants exposed to As showed typical phytotoxicity symptoms; no plants however died over the study. The biomass of the bean plants increased with the increasing amounts of compost added to the soil, attributed to the phytonutritive capacity of compost. Biomass decreased with increasing As concentrations, however, the reduction in the biomass was significantly lower with the addition of compost, indicating that the As phytotoxicity was alleviated by the compost. For the same As concentration, the As content of the roots, shoots and beans decreased with increasing compost added compared to the Control. This is due to partial immobilization of the As by the organic functional groups on the compost, either directly or through cation bridging. Most of the As adsorbed by the bean plants accumulated in the roots, while a scant allocation of As occurred in the beans. Hence, the addition of compost to soils could be used as an effective means to limit As accumulation in crops from As-contaminated waters.

The role of phosphorus (P) application and arbuscular mycorrhizal fungi (AMF) on growth, arsenic (As) and P accumulation in lettuce plants growing in an As-polluted soil (total As 250 mg kg−1), was investigated. In particular, it was tested whether application of a commercial inoculum (CI), with (+P at 90 kg P ha−1) and without (−P at 0 kg P ha−1) P fertilizer, supported greater plant growth and provided more P, enhancing As tolerance, than indigenous fungi alone. The influence of these treatments on As and P availability in the rhizosphere and bulk soils was also investigated. Greenhouse pot experiments were established where plants were grown with and without commercial inoculum (+CI, −CI) in unsterilized conditions. Inoculation with commercial inoculum and P application together considerably increased plant biomass, by enhancing host plant P nutrition and lowering shoot and root As concentrations compared to plants inoculated only with native AMF. In the rhizosphere of +CI+P plants there was P soil depletion compared to −CI+P. The results evidenced that, with P addition, inoculation with commercial inoculum alleviated the toxicity of excessive As by improving P nutrition without increasing As concentrations in the plant, emphasizing the role of beneficial microbes and P fertilizer to improve soil fertility in As-contaminated soil.

A greenhouse study was carried out to determine the possibility of using Lolium perenne for revegetation of soil from a former ferrous metallurgical plant (Naples, South Italy) contaminated by Cu, Pb and Zn at levels above current Italian regulatory limits. Surface soil samples (0-40 cm) from the facility area where raw minerals were disposed (RM1 and RM2), from a nearby unpolluted cultivated soil (C) as control and a 1:3 mixture of the control with the polluted ones (RM1+C and RM2+C) were utilized for the experiment. Revegetation trials were conducted in the greenhouse. At 90 days from seeding, shoot length, chlorophyll content, biomass yield, plant metal uptake and changes of organic carbon content and metal distribution among soil extractable phases defined by sequential extraction were determined. In the mixed substrates (RM1+C and RM2+C) concentrations of Cu, Pb and Zn were still two to three times higher than the Italian regulatory limits. Plants were healthy with 100% survival in all substrates, with no macroscopic symptoms of metal toxicity. The high pH of the soil could be one of the most important parameters responsible for the limited plant availability of the metals. On RM1, RM2 and mixed media, plants experienced retarded growth, reduced shoot length and biomass yield and higher total chlorophyll content compared to those cropped on the control soil, without any evident phytotoxic symptoms. In RM1 and RM2, the plant contents of Cu (19.3 and 12.6 mg kg(-1)), Pb (0.98 and 0.67 mg kg(-1)) and Zn (99 and 88 mg kg(-1)) were higher than that of plants grown on non-contaminated soil (Cu 10.1, Pb0.2, Zn 79 mg kg(-1)), but still in the range of physiologically acceptable levels. The distribution of metals in soil was slightly affected by Lolium growth with changes only regarding the organic-bound Cu and Zn pool, with reduction up to 24%. Results indicated that an acceptable healthy vegetative cover can be achieved on the contaminated soil by the proposed revegetation approach and that metals will remain stable over the study period with slight variation of the more available metal forms.