Adão de Siqueira Ferreira

Changes in Diversity, Abundance, and Structure of Soil Bacterial Communities in Brazilian Savanna Under Different Land Use Systems

The Brazilian Savanna, also known as “Cerrado”, is the richest and most diverse savanna in the world and has been ranked as one of the main hotspots of biodiversity. The Cerrado is a representative biome in Central Brazil and the second largest biome in species diversity of South America. Nevertheless, large areas of native vegetation have been converted to agricultural land including grain production, livestock, and forestry. In this view, understanding how land use affects microbial communities is fundamental for the sustainable management of agricultural ecosystems. The aim of this work was to analyze and compare the soil bacterial communities from the Brazilian Cerrado associated with different land use systems using high throughput pyrosequencing of 16S rRNA genes. Relevant differences were observed in the abundance and structure of bacterial communities in soils under different land use systems. On the other hand, the diversity of bacterial communities was not relevantly changed among the sites studied. Land use systems had also an important impact on specific bacterial groups in soil, which might change the soil function and the ecological processes. Acidobacteria, Proteobacteria, and Actinobacteria were the most abundant groups in the Brazilian Cerrado. These findings suggest that more important than analyzing the general diversity is to analyze the composition of the communities. Since soil type was the same among the sites, we might assume that land use was the main factor defining the abundance and structure of bacterial communities.

Change in Soil Microbial and Enzyme Activities in Response to the Addition of Rock-Phosphate-Enriched Compost

Phosphorus (P) is considered a nonrenewable resource that plays a key role in agriculture and such studies are needed to evaluate alternative sources of this element. In the current study, objectives were to evaluate soil microbial respiration and enzymatic activity resulting from the addition of rock-phosphate-enriched organic compost to soil under incubation conditions. An organic-mineral compost (OMC) was produced by aerobically composting a mixture of coffee grain trash (62%), bovine manure (7%), phosphate rock (28%), and gypsum (3%) for 3 months. Different amounts of OMC were added in a portion (100 g) of soil, and then this mixture was incubated for 28 days. After this time, soil microbial respiration (SMR), biochemical parameters, and available P were evaluated. The addition of OMC led to significant increase in SMR, dehydrogenase, fluorescein diacetate hydrolysis, β-glucosidase, and phosphatase activity, which were dependent on the added amounts of the compost. The values of available P in soil increased significantly (13 times) with the OMC addition when compared to the control.The assay showed that P-enriched OMC application impacted soil function and improved soil biochemical properties. These results suggest that this practice may be of great importance for soil fertilization.

Aspectos morfofisiológicos de plantas de milho e bioquímico do solo em resposta à adubação nitrogenada e à inoculação com Azospirillum brasilense

Nitrogen (N) is a macronutrient that positively affects grain yields in maize crops, being its appropriate management indispensable for a sustainable agriculture, including the use of alternative resources such as diazotrophic bacteria. The aims of this work were to evaluate morphophysiological aspects of maize plants and activity of soil enzymes (urease and fosfatase) due to mineral N fertilization and Azospirillum brasilense inoculation. Two trials were conducted under greenhouse conditions with cerrado soil. A randomized block design was set up with treatments distributed as a 3 x 3 factorial. The first factor corresponded to N rates (0; 100 and 200 kg ha-1) and the second factor to an A. brasilense inoculant (0; 100 and 200 mL ha-1). At the end of this experiment, another trial was done to determine the possible residual effect of inoculation and nitrogen fertilization. Nitrogen application promoted maize plants growth, and increased chlorophyll and nutrient contents. Intensified activity of rhizosphere enzymes related to ammonium and inorganic phosphorus availability was also observed. In addition, N fertilization had residual effect on plant development in the test evaluating the residual effect of the fertilizer. The combination of 200 mL ha-1 of A. brasilense with 200 kg ha-1 of N increased the physiological response of the maize crop.

Influence of Phosphorus and Carbon on Soil Microbial Activity in a Savannah Agroecosystem of Brazil

The microbial activity of soil plays an important role in the regulation of the transformation of carbon (C) and phosphorus (P). However, the activity of soil microbes is strongly related to the type of land-use system. The present work aimed to compare the microbial activity and metabolic responses of three different land-use systems to P (0 to 600 mg kg−1 of dry soil) and C additions in an Oxisol of the Brazilian savannah. The land-use systems studied were savannah vegetation (SV), 32-year-old pine plantation (PP), and 11-year-old no-tillage system (NT). The following analyses were carried out: amount of C carbon dioxide (CO2) evolved, total organic carbon (TOC), total glucose (TG), microbial biomass carbon (MBC), and metabolic yields (Y) from P and C additions to the soil. The different land-use systems affected the respiratory activity of microbiota, indicating an increase in SV and a decrease in PP when compared to the SV system under incubation for 17 days. The addition of P resulted in an increase of respiratory activity. The responses were adjusted by the Michaelis–Menten equation for all three land-use systems. The greatest TOC and lowest MBC were observed in NT and PP, respectively, when compared to SV. However, a lower content of TG was observed in NT in comparison to SV. Under bioassay conditions, the results confirm the greater microbial demand for P in PP and SV than in NT. The NT system showed greater metabolic yields when glucose was applied to the soil, suggesting that the response of microbiota in this system depends on easily available forms of C, as shown by the sugar content. The results showed expressive metabolic differences among the systems, suggesting that different soil uses change the dynamic of the responses of soil microorganisms.

Soil microbial response to glucose and phosphorus addition under agricultural systems in the Brazilian Cerrado

Conventional tillage (CT) and no-tillage (NT) management systems alter soil nutrient availability and consequently modify soil microbial response to nutrient additions such as carbon (C) and phosphorus (P). The objective of this study is to evaluate microbial response to the addition of C (glucose) and P (Na2HPO4.7H2O) under CT and NT in the brazilian Cerrado. In response to glucose addition, the NT system yielded higher microbial respiration rates and glucose consumption than the CT system. The best microbial response to C addition was after 0 - 12 h incubation in NT and 0 - 24 h in CT. The addition of P produced higher demand under CT than NT. After incubation, biochemical indicators such as microbial respiration, glucose consumption, dehydrogenase activity and metabolic yield confirmed the higher glucose demands under NT and higher phosphorus demands under CT. These results demonstrate that C and P addition alter significantly the microbial response, suggesting that soil microorganisms present nutrient differential demands between CT and NT management systems.

The combination of compost or biochar with urea and NBPT can improve nitrogen-use efficiency in maize

The addition of organic residues to agricultural soils has been used as a practical alternative to improve crop quality and health. The objective of this work was to evaluate maize physiological and nutritional responses to the application of compost and biochar combined with urea (N) and N-(n-butyl) thiophosphoric triamide (NBPT). The experiment was performed in plastic pots with 3 kg of soil under greenhouse conditions for 30 days. The compost and biochar were applied at the rate of 0.3 ton ha-1, using an amount of nutrient (nitrogen, phosphorus and potassium) demanded by crop growth. The physiological responses of maize were monitored by measuring the plant height, stalk diameter, leaf chlorophyll content, shoot dry weight and root dry weight. The nutritional responses of maize were assessed by using the nutrient concentration and the total nutrient assimilation by the plants. The results showed that the addition of compost or biochar did not alter the maize physiological response compared to the addition of mineral fertilizer used under the same conditions. However, a difference occurred in the maize nutritional responses to the compost and biochar amendments combined with urea and NBPT. The greatest N concentration in maize was observed in the treatment consisting of biochar combined with urea + NBPT. All the treatments in which compost or biochar was applied in combination with urea and NBPT presented greater total N assimilation compared to the treatment with conventional fertilization. The results of this survey showed that the combination of urea and NBPT improved the nitrogen-use efficiency of maize.

Assessment and kinetics of soil phosphatase in Brazilian Savanna systems

The activity and kinetics of soil phosphatases are important indicators to evaluate soil quality in specific sites such as the Cerrado (Brazilian Savanna). This study aimed to determine the activity and kinetic parameters of soil phosphatase in Cerrado systems. Soil phosphatase activity was assessed in samples of native Cerrado (NC), no-tillage (NT), conventional tillage (CT) and pasture with Brachiaria brizantha (PBb) and evaluated with acetate buffer (AB), tris-HCl buffer (TB), modified universal buffer (MUB) and low MUB. The Michaelis-Menten equation and Eadie-Hofstee model were applied to obtain the kinetic parameters of soil phosphatase using different concentrations of p-nitrophenol phosphate (p-NPP). MUB showed the lowest soil phosphatase activity in all soils whereas AB in NC and NT presented the highest. Low MUB decreased interferences in the assessment of soil phosphatase activity when compared to MUB, suggesting that organic acids interfere on the soil phosphatase activity. In NC and NT, soil phosphatase activity performed with TB was similar to AB and low MUB. Km values from the Michaels-Menten equation were higher in NC than in NT, which indicate a lower affinity of phosphatase activity for the substrate in NC. Vmax values were also higher in NC than in NT. The Eadie-Hofstee model suggests that NC had more phosphatase isoforms than NT. The study showed that buffer type is of fundamental importance when assessing soil phosphatase activity in Cerrado soils.

CRESCIMENTO MICELIAL E SÍNTESE DE PROTEÍNAS DECHOQUE TÉRMICO EM TRÊS ISOLADOS DE FUNGOS ECTOMICORRÍZICOS SOB CONDIÇÕES DE TEMPERATURAS SUPRA-ÓTIMAS

SUMMARY : MYCELIAL GROWTH AND SYNTHESIS OF HEAT SHOCKPROTEINS BY ECTOMICORRHIZAL FUNGI UNDER SUPRA-OPTIMAL TEMPERATURE CONDITIONS In most organisms, the synthesis of heat shock proteins is a transient physiologicalchange in the cell exposed to supra-optimal temperatures. The physiological response toheat shock is particularly dependent on the cell type and on the capacity of the organismsto respond to environmental alterations. In this study the mycelial growth and synthesis ofheat shock proteins of two Pisolithus isolates (RV82 and RS24) and one Paxillus involutusisolate to supra-optimal temperatures was evaluated. Mycelial growth was evaluatedunder sublethal, lethal and heat shock temperature conditions with appropriate growthmedium on Petri plates. Proteins in the mycelium of the isolates were marked usingradioactive amino acid ( 3 H-leucine) and the radioactivity was quantified in scintillationsolution. Synthesis of heat shock proteins (HSPs) were evaluated by polyacrylamide gels(SDS-PAGE and 2D-PAGE). The two Pisolithus isolates RS24 and RV82 were more tolerantto high temperatures than P. involutus. The Pisolithus isolates differed regarding thesynthesis of stress proteins since high and low molecular mass proteins were synthesized.In response to the heat shock, the RV82 isolate synthesized putative heat shock proteins ofthe groups HSP70, HSP28, HSP26 and sHSPs (15–18 kDa), while the RS24 isolatesynthesized putative heat shock proteins of the groups HSP86, HSP60, HSP55, HSP35and sHSPs (12–18 kDa). The low heat tolerance of the P. involutus isolate was attributedto its incapacity of synthesizing HSPs. Our results suggest that the induction of thethermotolerance mechanism differs among ectomicorrhizal fungi isolates.Index terms: heat stress, heat shock proteins, HSPs, Pisolithus sp., Paxillus involutus.