Nelson Walter Osorio

Synergistic Influence of an Arbuscular Mycorrhizal Fungus and a P Solubilizing Fungus on Growth and P Uptake of Leucaena leucocephala in an Oxisol

An investigation was carried out to assess the role that P solubilizing micro-organisms play in the P nutrition of mycorrhizal and mycorrhiza-free Leucaena leucocephala (L am.). Soil microorganisms able to solubilize rock phosphate were isolated from the rhizosphere of L. leucocephala naturally growing on three different soils of Hawaii. The isolates were screened for their ability to solubilize rock phosphate in culture medium. The highest activity was observed with one of the fungal isolates, which was identified as Mortierella sp. It was multiplied and further evaluated with or without the mycorrhizal fungus Glomus aggregatum in a highly weathered soil for its effectiveness to enhance P uptake and growth of L. leucocephala. Phosphorus status of L. leucocephala pinnules monitored as a function of time revealed that plants colonized by both microorganisms had the highest P content followed by plants inoculated with the mycorrhizal fungus alone. Inoculation of soil with Mortierella sp. alone did not influence P content of plants measured at the time of harvest. However, Mortierella sp. increased the P content of mycorrhizal plants by 13% in the unfertilized soil and by 73% in the soil fertilized with rock phosphate. Shoot dry weight measurements showed that Mortierella sp. stimulated growth of nonmycorrhizal by 22%, while it stimulated the growth of myocorrhizal plants by 29% , regardless of P fertilization. The results suggest the existence of synergistic interaction between P solubilizing microorganisms and mycorrhizal fungi, although the degree of synergism was more pronounced in terms of P uptake than in terms of growth.

Soil Phosphate Desorption Induced by a Phosphate-Solubilizing Fungus

A series of in vitro experiments were carried out to evaluate the effectiveness of a phosphorus-solubilizing fungus to desorb phosphate (Pi) from soil samples differing in their Pi-sorption capacity. The results indicate that the fungus Mortierella sp. was effective in desorbing Pi from all soil samples tested by producing oxalic acid, and its effectiveness varied among soil orders. The effectiveness of the fungus was influenced by the soil Pi-sorption capacity, which could be used as a predictor of the effectiveness of microbes to increase soluble Pi via desorption from soils. The Pi desorption was most pronounced in a Mollisol followed by an Oxisol, an Ultisol, and then by three Andisols. The quantity of Pi desorbed by the fungus was also greater when the amount of sorbed Pi was high.

Strategies for Utilizing Arbuscular Mycorrhizal Fungi and Phosphate-Solubilizing Microorganisms for Enhanced Phosphate Uptake and Growth of Plants in the Soils of the Tropics

One of the major constraints for plant productivity in tropical regions is low soil phosphate (Pi) availability. Phosphate ions are rendered unavailable for plant uptake due to adsorption onto the surface of soil minerals and precipitation by free aluminum and iron ions. In highly weathered soils, this is so intense that plant crops commonly exhibit Pi-deficiency. High rates of soluble Pi-fertilizers are employed to meet plant P demands. However, the large quantity of Pi required in order to offset the high Pi-retention capacity of the soils and the high cost associated with it makes it inaccessible to the vast majority of growers in the region. An alternative means of improving plant Pi-uptake from insoluble native and applied rock phosphate is the use of arbuscular mycorrhizal (AM) fungi. These fungi form a symbiotic association with most plants and improve the efficiency of associated plants to take up Pi from the soil solution. Other soil microorganisms commonly known as phosphate-solubilizing microorganisms (PSM) can replenish soil solution Pi by solubilizing complex phosphorus compounds found in soil or added to it, mostly through the release of organic acids. In this chapter, an attempt is made to highlight the interactions of these two distinct groups of soil microorganisms and the mechanisms by which they facilitate plant available Pi and enhance plant growth in the soils of the tropics.

Effectiveness of Phosphate Solubilizing Microorganism in Increasing Plant Phosphate Uptake and Growth in Tropical Soils

Low soil phosphate availability is a major constraint for soil fertility in the tropics. Phosphate ions are either adsorbed onto the surface of soil minerals or precipitated by free aluminum and iron ions in acidic soils. In highly weathered soils, this is so intense that plant crops commonly exhibit phosphate deficiency. To overcome this problem, high rates of soluble phosphate fertilizers can be employed to increase the concentration of phosphate in soil solution. Nonetheless, the large quantity of phosphate required in these soils makes it an unviable solution to most farmers in poor developed countries of the tropics. One alternative is to use locally available rock phosphates that are cheaper than soluble phosphate fertilizers. However, the low solubility of rock phosphate limits their agronomic effectiveness in increasing plant phosphate and growth. An alternative means of improving plant phosphate uptake is the combined use of phosphate solubilizing microorganisms (PSMs) and arbuscular mycorrhizal fungi (AMF). The first group of soil microorganisms can enhance the dissolution of rock phosphate via the release of organic acids. The latter group of microorganisms forms symbiotic associations with plant roots and take up phosphate from the soil solution more efficiently than the unaided roots. Once the phosphate is absorbed by the mycorrhizal hyphae, it is delivered into the root tissue. In this text, I will illustrate the mechanisms and synergistic effects that they exhibited to improve plant phosphate uptake and growth.

Coffee seedling growth as affected by mycorrhizal inoculation and organic amendment

An experiment was carried out to evaluate the effects of mycorrhizal inoculation and an organic amendment on coffee (Coffea arabica L.) seedling growth. A soil (fine, mixed, isothermic Typic Dystrudept) was either amended or unamended with composted coffee pulp (2:1 ratio, V:V), sterilized or not sterilized with Basamid™, and either inoculated or uninoculated with three mycorrhizal inocula: (i) Entrophospora colombiana, (ii) native Glomus spp., or (iii) a mix containing G. manihotis, G. fasciculatum, and E. colombiana. Plant growth and mycorrhizal activity were severely constrained in the unamended soil, which had low organic matter content, low pH, very high extractable aluminum (Al), and low availability of phosphorus (P), boron (B), calcium (Ca), magnesium (Mg), and potassium (K). Plants grew significantly better in the amended soil and further increases in coffee seedling height resulted with mycorrhizal inoculation. No significant differences were found among mycorrhizal inocula. In addition, sterilization significantly reduced plant growth in both amended and unamended soils.

Role of Litter Turnover in Soil Quality in Tropical Degraded Lands of Colombia

Land degradation is the result of soil mismanagement that reduces soil productivity and environmental services. An alternative to improve degraded soils through reactivation of biogeochemical nutrient cycles (via litter production and decomposition) is the establishment of active restoration models using new forestry plantations, agroforestry, and silvopastoral systems. On the other hand, passive models of restoration consist of promoting natural successional processes with native plants. The objective in this review is to discuss the role of litter production and decomposition as a key strategy to reactivate biogeochemical nutrient cycles and thus improve soil quality in degraded land of the tropics. For this purpose the results of different projects of land restoration in Colombia are presented based on the dynamics of litter production, nutrient content, and decomposition. The results indicate that in only 6–13 years it is possible to detect soil properties improvements due to litter fall and decomposition. Despite that, low soil nutrient availability, particularly of N and P, seems to be major constraint to reclamation of these fragile ecosystems.

Effect of Nitrogen Form on the Effectiveness of a Phosphate-Solubilizing Fungus to Dissolve Rock Phosphate

An in vitro experiment was carried out to evaluate the effect of nitrogen (N) form (NH4+ and/or NO3-) on the dissolution of rock phosphate (RP) by a phosphate solubilizing fungus (PSF) identified as Mortierella sp. In the presence of NH4Cl or NH4NO3, the solution of pH significantly decreased from an initial value of 7.6 to 3.4 and 3.7 respectively. In the presence of KNO3, the pH went down only to 6.7. As a result, significantly more P was detected in solution in the presence of NH4Cl (129.65 mg/L) than in the presence of NH4NO3 (109.25 mg/L). The concentration of P in solution in the presence of KNO3 was only 0.08 mg/L. The excess of NH4+ adversely affected the growth of Mortierella sp. However, this may have promoted a more active H+-pumping that decreased solution’s pH. In the presence of NO3- as the only source of N, Mortierella sp. not only dissolved a small amount of Pi from the RP but also immobilized most of it into its mycelia. In contrast, in the presence of NH4Cl, Mortierella sp. was effective to dissolve RP and the Pi released remaining in solution while only a little portion was immobilized by the fungal mycelia.

Silvopastoral Systems Enhance Soil Quality in Grasslands of Colombia

In the tropical drylands of Colombia, the soils subjected to traditional systems of livestock production are severely degraded and depleted of plant nutrients. Multistrata silvopastoral systems are viable alternatives to improve livestock production; however, it is unknown whether these systems can reduce the negative environmental impacts of traditional systems on soil quality. The objective of this study was to evaluate the effects of 13-year-old multistrata silvopastoral systems on soil quality parameters in degraded soils of the Sinu River Valley, Colombia. The results show that the trees in the silvopastoral systems increased or maintained soil pH values and nutrient availability (phosphorus, potassium, and calcium) with respect to the pastures with only grasses. The effects were significantly controlled by the types of plant species, particularly Guazuma ulmifolia and Cassia grandis.

Passive and Active Restoration Strategies to Activate Soil Biogeochemical Nutrient Cycles in a Degraded Tropical Dry Land

The potential use of two restoration strategies to activate biogeochemical nutrient cycles in degraded soils in Colombia was studied. The active model was represented by forest plantations of neem (Azadirachta indica) (FPN), while the passive model by successional patches of native plant species was dominated by mosquero (Croton leptostachyus) (SPM). In the field plots fine-litter traps and litter-bags were established; samples of standing litter and surface soil samples (0–10 cm) were collected for chemical analyses during a year. The results indicated that the annual contributions of fine litterfall in FPN and SPM were 557.5 and 902.2 kg ha−1, respectively. The annual constant of decomposition of fine litter (k) was 1.58 for neem and 3.40 for mosquero. Consequently, the annual real returns of organic material and carbon into the soil from the leaf litterfall decomposition were 146 and 36 kg ha−1 yr−1 for FPN and 462 and 111 kg ha−1 yr−1 for SPM, respectively. Although both strategies showed potential to activate soil biogeochemical cycles with respect to control sites (without vegetation), the superiority of the passive strategy to supply fine litter and improve soil properties was reflected in higher values of soil organic matter content and cation exchange capacity.

Germinação e crescimento de maracujazeiro roxo sob tratamentos pré-germinativos e inoculação micorrízica

Purple passion fruit (Passiflora edulis f. edulis Sims) is a tropical crop grown between 600 m and 2,000 m of altitude. Commercial crops are cultivated mainly in Brazil, Colombia, Peru and Ecuador, where it is consumed as a fresh fruit or produced for exportation to Europe (Ruggiero et al. 1996, Nakasone & Paull 1998, Riascos et al. 2011). In Colombia, this fruit is grown in Cundinamarca, Boyacá, Tolima and Huila, where the planted area ABSTRACT RESUMO