Effect of wheat straw and cellulose degrading fungi of genus Trichoderma on soil respiration and cellulase, betaglucosidase and soil carbon content

D. Draganova*, I. Valcheva, Y. Kuzmanova, M. Naydenov

Department of Microbiology and Ecological Biotechnologies, Faculty of Plant Protection and Agroecology, Agricultural University, 12 Mendeleev, 4000 Plovdiv, Bulgaria

(Manuscript received 12 June 2018; accepted for publication 31 August 2018)

Abstract. Due to the intensive soil exploitation and increased mineral fertilization, the degradation of plant residues in the soil is becoming more difficult and slower over the years. This disturbs the structure of the soil and the nutritional balance and leads to a reduction in soil fertility. To solve the problem, microorganisms capable of degrading plant residues in the soil can be used. The purpose of this study was to investigate the effect of fungi of genus Trichoderma on the biodegradation of wheat straw in the soil by observation of the change in cellulase enzyme activity in the soil and the increase in soil biological activity. The highest basal soil respiration was noted at T2TUR (65.76 μgCO2) and T6 (53.69 μgCO2). During the entire straw degradation period, the highest endoglucanase activity was observed at T4 (285.0 μgGlu) and T6 (275.56 μgGlu), whereas the highest β-glucosidase was noted at T6 (5220.3 μgPNP/g/h) and T1UKR (5020.0 μgPNP/g/h). The presence of cellulose-degrading fungi positively affected the increase in the total amount of microbial biomass at the end of the study period, whereas the amount of Corg was increased in all straw amended variants. At the beginning of the process, CMCase correlated with the microbial carbon (r=0.896 for Cmic) and β-glucosidase activity was closely connected with both soil organic carbon and microbial carbon (r=0.819 for Corg and r=0.866 for Cmic). At the end of the investigated period a stronger correlation with Corg was observed.

Influence of organic nitrogen amendment, containing amino acids on the cellulase and xylanase, produced by Trichoderma spp. isolates

D. Draganova*, I. Valcheva, Y. Kuzmanova, M. Naydenov

Department of Microbiology and Ecological Biotechnologies, Faculty of Plant Protection and Agroecology, Agricultural University, 4000 Plovdiv, Bulgaria (Manuscript received 14 June 2017; accepted for publication 8 August 2017)

Abstract. Cellulases and hemicellulases are amount the main hydrolytic enzymes, involved in the bioconversion of lignocellulose material by microorganisms. Filamentous fungi of the genus Trichoderma are one of the most studied and good producer of cellulases and hemicellulases. The nutrients balance, especially carbon to nitrogen ratio, is one of the main factors of the biodegradation. The ability of 37 local isolates of Trichoderma sp. to produce cellulases and xylanase were tested in solid state cultivation on wheat straw as a substrate whit two variants: 1. the straw was only moistured with destilated water (CN 80:1); 2. the C:N ratio of the straw was adjusted to 30:1 using organic nitrogen amendment. There is a significant difference in the enzymatic activity of the isolates in their cultivation on straw with CN 80 and CN 30. The highest carboxymethylcellulase (CMCase) activity at CN 80 showed T1T (110.19U/ml), and in the variant at CN 30 – TD (369.07U/ml). The highest β-glucosidase activity on both variants CN 80 and CN 30 was established for TG (2743.1U/ml – 12679.9U/ml). The highest xylanase activity at CN 80 and CN 30 was measured on T4I (21311.5U/ml – 47937.5U/ml). After ONA addition, all enzymes activities have increased several times, indicating the enhancing effect of the additive. The average activity of CMCase increased 6.1 times, the average β – glucosidase activity increased 5.1 times, while the xylanase activity increased 4.9 times for all tested isolates. The increase in activity of the investigated enzymes showed different patterns.