Ana de Santiago

Effect of Trichoderma asperellum strain T34 on iron, copper, manganese, and zinc uptake by wheat grown on a calcareous medium

Rhizosphere microbes may enhance nutrient uptake by plants. Here we studied the effect of Trichoderma asperellum inoculation on the uptake of Fe, Cu, Mn, and Zn by wheat (Triticum aestivum L) grown in a calcareous medium. To this end, an experiment involving two factors, namely Fe enrichment (ferrihydrite enrichment and non-enrichment of the growing medium), and inoculation/non-inoculation with Trichoderma asperellum strain T34, was performed twice under the same conditions. The increase in Fe availability as a result of ferrihydrite enrichment did not enhance plant dry matter production. The effect of T34 on the concentration of Fe, Cu, Mn and Zn, and the total amount of Cu, Mn, and Zn in the aerial parts differed depending on the degree of ferrihydrite enrichment. Inoculation with T34 increased Fe concentration in Fe-deficient media, thus revealing a positive effect of this microorganism on Fe nutrition in wheat. However, T34 significantly decreased the concentration and total amount of Cu, Mn, and Zn in the aerial parts, but only in ferrihydrite-enriched medium. This adverse effect of T34 on Cu, Mn, and Zn uptake by wheat plants may have been related to conditions of restricted availability where potential competition for nutrients between microorganisms and plants can be more marked.

Effects of humic substances on iron nutrition of lupin

Poorly crystalline Fe oxides and organic matter are two important factors affecting Fe nutrition of plants. The main objective of this work was to study the contribution of humic substances to Fe nutrition of a typical Fe-chlorosis sensitive plant (white lupin, Lupinus albus L.). An experiment was performed involving two growing media (siliceous and calcareous) and different Fe sources: control without additional Fe added to the growing media, ferrihydrite (FH), FH + humic substances (HS, at two rates, 0.1 and 0.3xa0g C kg−1 growing media), Fe complexed to humic substances (Fe–HS), and Fe–EDDHA (as an effective Fe source in calcareous media). Chlorophyll meter readings and dry matter production (DM) were significantly greater with Fe–EDDHA and Fe–HS when compared with the other treatments in calcareous media. The positive effect of complexed Fe (to EDDHA or HS) on Fe nutrition can be, at least partially, related to an increase in Fe(III)-reducing capacity by roots, which seems to be improved by an enhanced root development. No positive effect on Fe nutrition was observed with the application of HS in a ferrihydrite enriched growing media (FH + HS) at 4xa0weeks, particularly with the application of HS at 0.3xa0g C kg−1 in calcareous media. Thus, the effect of HS on Fe availability was only positive if some Fe is complexed to HS. The efficiency of HS with Fe complexed (Fe–HS) in preventing Fe chlorosis was found to be similar to Fe–EDDHA. This is important not only for the knowledge of factors affecting Fe availability in soils, but also with a view of using Fe–HS complexes as effective products to correct this nutritional problem.

Humic substances increase the effectiveness of iron sulfate and Vivianite preventing iron chlorosis in white lupin

The main objective of this work was to study the influence of humic substances (HS) on the effectiveness of Fe sulfate and Vivianite in preventing Fe chlorosis in white lupin with a view of performing cost-effective methods to overcome the problem. Two consecutive crops were performed using calcareous sand treated with different Fe sources (FeSO4·7H2O and Vivianite, at three different rates, and Fe-EDDHA) and five HS rates. Vivianite was more effective and persistent than Fe sulfate in increasing Soils and Plant Analysis Development (SPAD) readings and lupin yield expressed as dry matter (DM), probably due to the type of alteration products formed upon Vivianite oxidation. The effect of Fe sulfate and Vivianite in preventing Fe chlorosis was significantly increased by HS, and the best results were obtained with Vivianite and HS applied at 0.32xa0g Fe kg−1 and 0.06xa0g kg−1 growing media, respectively. SPAD readings with this treatment accounted for 85% and 70% of those obtained with Fe-EDDHA in the first and second crop, respectively, whereas DM production was greater with the Vivianite + HS treatment than with Fe-EDDHA. These results showed the potential effectiveness of treatments based on the application of Vivianite and HS in overcoming Fe chlorosis. However, HS applied with Fe sources at rates of 0.5 and 1xa0g kg−1 growing media decreased SPAD readings and plant yield. These positive and negative effects of HS in preventing Fe chlorosis were more evident with Fe sulfate and Vivianite than with chelated Fe, probably due to the effect of HS on the solubility of Fe forms of the growing medium.

ADVERSE EFFECTS OF HUMIC SUBSTANCES FROM DIFFERENT ORIGIN ON LUPIN AS RELATED TO IRON SOURCES

Humic substances improve the efficiency of different iron (Fe) sources overcoming Fe deficiency chlorosis of plants. However, applied at high rates, they can promote negative effects on plants. The main objective of this work was to study the potential adverse effect of three humic acids from different origin when they were applied with two effective Fe sources for plants: Fe- ethylenediaminedihydroxyphenylacetic acid (EDDHA) and Vivianite. To this end, an experiment with lupin (Lupinus albus L.) was performed involving two factors: (i) Fe source, and (ii) humic substances from three different origin (composted cork, leonardite, and compost obtained from a mixture of olive husk with cotton gin trash) applied at 0, 0.1, and 0.5 g organic carbon (C) kg−1 of growing media. At the rates used, humic substances promoted adverse effects on plant development, chlorophyll meter readings, and Fe content in lupin grown in calcareous media. Overall, the effect on dry matter and Fe content in plants was more relevant when Fe was supplied with Vivianite, the effect on chlorophyll meter readings being more significant when Fe was applied as Fe-EDDHA. Differences were also observed depending on the source of humic substances, those from leonardite promoting the greatest decrease in dry matter in roots and shoots. These humic substances possessed the highest values of spectroscopy index for aromaticity (A254 ). On the other hand, the application of humic substances from olive husk compost, which exhibited the lower aromaticity index, resulted in the smallest decrease in dry matter production and chlorophyll meter readings. Dry matter in roots decreased logarithmically with increased values of the estimates of the amounts of aromatic compounds accumulated in the growing media (R2 = 0.92; P < 0.01) with Vivianite as Fe source. Thus, the effects decreasing dry matter production, particularly in roots, and chlorophyll meter readings can be ascribed at least partially to the presence of phytotoxic aromatic compounds in humic substances.

Interaction between beet vinasse and iron fertilisers in the prevention of iron deficiency in lupins

BACKGROUNDnRecycling of organic byproducts for use as soil amendments or fertilisers may enhance the productivity of soils. The aim of this study was to investigate the potential of sugar beet vinasse to correct iron chlorosis in crops when applied in conjunction with Fe fertilisers such as vivianite and ferrous sulfate (FS). An experiment involving two factors (Fe source and dialysed sugar beet vinasse (DBV) rate) was performed using white lupin (Lupinus albus L.) and calcareous sand as growing medium.nnnRESULTSnAlthough vivianite provided lower chlorophyll contents than Fe-chelate, dry matter production was not significantly different between the two Fe sources. Vivianite was more effective than FS in preventing iron chlorosis in white lupin, but not when DBV was applied. DBV significantly increased chlorophyll content in plants treated with FS after 3 weeks of growth.nnnCONCLUSIONnDBV increased the effect of FS in preventing iron deficiency chlorosis in white lupin. This was due, at least in part, to the inhibition of the precipitation of Fe oxides by organic compounds and to the increase in the content of Fe complexed by organic compounds in the growing medium, as revealed by sequential Fe fractionation.