STUDY ON MICROBIAL COMMUNITIES AND SOIL ORGANIC MATTER IN IRRIGATED AND NON-IRRIGATED VERTISOL FROM BOIANU

Transcription

1 Available online at Soil Forming Factors and Processes from the Temperate Zone 11 (2012) 1-8 STUDY ON MICROBIAL COMMUNITIES AND SOIL ORGANIC MATTER IN IRRIGATED AND NON-IRRIGATED VERTISOL FROM BOIANU Gabi-Mirela Matei a,*, S. Matei a, Victoria Mocanu a, I. Seceleanu a, Valentina Coteţ a, Sorina Dumitru a a National Research-Development Institute for Soil Science, Agrochemistry and Environment Protection-Bucharest, Bd. Marasti 61, , Sector 1, Bucharest, Romania Studiul comunităţilor microbiene şi al materiei organice în vertosolul irigat şi neirigat de la Abstract Irrigation, when administered correctly, confers the producers the possibility to overcome drought effects and obtain higher yields, supplementing the quality of food for animals or human consumers. In the mean time, soil erosion, pathogens attack and nutrients or pesticides spreading can be prevented by an adequate management of irrigation water. As a consequence, soil microbial community structure, composition and activities, as well as the organic matter quality can be different from those in non-irrigated soil. Research have been carried out in order to assess changes in bacterial and fungal communities and activity in irrigated Vertisol from, as compared with non-irrigated. The paper presents the results concerning the taxonomical composition of bacterial and fungal microflora in the horizons of the two soil profiles, as well as the level of CO 2 released by microorganisms. Chromatographic aspects of humus fractions were used to characterize the organic matter in irrigated and nonirrigated soil. Increased moisture and lowered temperature in Ap horizon of irrigated soil increased bacterial counts (18 x10 6 viable cells x g -1 dry soil) and their metabolic activity expressed by carbon dioxide released (46.838mg CO 2 x g -1 dry soil) comparatively with non- irrigated soil. Fungal microflora was more abundant after 25-50cm under irrigation. Species diversity slightly increased under irrigation in both upper and lower part of soil profile. In irrigated soil, associations of species belonging to bacterial genera Pseudomonas and Bacillus were dominant in surface and white actinomycetes in the depth. Fungal consortia of Penicillium, Aspergillus and Fusarium dominated in both soil profiles. Irrigation induced changes in the quantity and quality of soil organic matter, as well as in the aspect of their migration pattern, as revealed on circular chromatograms Author(s) CC Attribution 3.0 Unsuported License. Keywords: irrigation, bacteria, fungi, soil respiration, microbial community Corresponding author: * address: so_matei602003@yahoo.com

2 1. INTRODUCTION Irrigation gives farmers the opportunity to obtain higher yields by accessing the source of water when climatic conditions are unfavorable and cultures are in critical stages of development. When applied correctly, irrigation protects against seasonal variability and drought. In addition, irrigation supports livestock production potential by providing additional fodder and by increasing the value of soils otherwise considered low productive. Proper management of irrigation water can prevent soil erosion, nutrient leaching, spreading pesticides, pathogens and weeds, caused by improper application of water supplements (Oved et al., 2001). Research was conducted to assess changes in bacterial and fungal communities and their physiological activity in irrigated compared with non-irrigated Vertisols from. 2. MATERIALS AND METHODS Microbiological analyses performed on soil samples include bacterial and fungal population density estimation, taxonomic composition analysis of microbial communities and their global level of activity. Decimal dilutions were made of soil, and plated on specific solid culture media, respectively Topping for aerobic heterotrophic bacteria and Czapek for saprophytic fungi (Papacostea, 1976). Colonies developed after incubation were counted and the density of bacteria and fungi was reported to gram of dry soil. Taxonomic identification was performed according to determinative manuals for bacteria (Bergey & Holt, 1994) and fungi (Domsch & Gams, 1972; Samson & Reenen-Hoekstra, 1988). The global physiological activities of microflora were determined by the method of substrate-induced respiration (Ștefanic, 1991) and expressed in mg CO 2 /100g soil. Pfeiffer chromatograms were made to evidence graphically the qualitative differences between analyzed soils. 3. RESULTS AND DISCUSSION Data analysis revealed differences concerning species composition of bacterial and fungal microflora in soil horizons of irrigated and non-irrigated profiles, as well as the amount of CO 2 released by microorganisms. Chromatographic aspects of humic fraction characterizing organic matter were also different in irrigated and non-irrigated soil profiles. For profile P1 (Table 1), quantitative estimates of bacterial microflora showed that the Ap horizon 0-20 cm from the surface was populated with a moderate number of bacteria ( x 10 6 viable cells x g -1 dry soil), while the other horizons presented low numbers of bacteria, their populations diminishing gradually from surface to depth up to x 10 6 viable cells x g -1 dry soil in horizon C> 130cm. Microscopic fungi developed in very high numbers in the Ap horizon (0-20cm) ( x 10 3 cfu x g -1 dry soil) and presented less numerous effectives on the depths, with a distribution different from bacteria. Unevenness is due to the fact that the usual trend to decrease in number with depth is changed in the transition horizons A / B and B / C, where identified higher numbers of fungi than in horizons above each, respectively than in Az and By. 2

3 Table 1. Microbiological characteristics of soil profiles from Bacteria (x10 6 viable cells x g -1 dry soil) Profile Horizon Depth (cm) P1 Non-irrigated Fungi (x 10 3 cfu x g -1 dry soil) Ap Az A / B Bz By B/C C > P2 Irrigated Ap Az B B B/C C C2 > Global activity of microflora (Fig.1) is low throughout the whole profile, reflected by lower values of soil respiration, which varies also inconsistent on the profile, influenced especially by fluctuations in the fungal group, from mg CO 2 /100g soil in Ap horizon (0-20cm) to mg CO 2 /100g soil in the bottom of the profile (C>130 cm), with the lowest values ( mg CO 2 /100g soil) recorded in Bz horizon (57-81 cm). Soil respiration potential Horizon (mg CO 2 /100g soil) Ap Az A/B Bz By B/C Non-irrigated C Fig. 1. Soil respiration potential of non-irrigated profile P1 from 3

4 In terms of species composition and species richness, biodiversity peak occurred in the surface horizon Ap (0-20cm), for both bacteria and fungi, the other horizons were populated with a smaller number of species of microorganisms. Dominant bacterial species in non-irrigated profile P1 (Table 2) belong to the genus Bacillus, with a frequent presence of the species B. cereus, B. circulans and B. mesentericus on most horizons and the weaker presence of the genus Pseudomonas. Actinomycetes from Albus and Fuscus series appear in most horizons, except horizons By and B / C. Fungi have a higher species diversity in Ap (0-20) and B / C (98-130cm) horizons with 6 and 5 species, with Penicillium and Aspergillus species well represented. The rest of profile horizons were also populated with other species important for their role in recycling organic matter, such as Stachybotrys chartarum, Cladosporium spp., Paecilomyces marquandii (Table 3). For irrigated profile P2, the number of bacteria is also moderate in Ap (90-25cm) horizon, but the value of x 10 6 viable cells x g -1 dry soil is slightly higher comparatively with nonirrigated P1. Values reflecting soil colonization with moderate numbers of bacteria ( x 10 6 viable cells x g -1 dry soil) were also calculated for horizon B / C ( cm), the rest of horizons being sparsely populated with numbers an order of magnitude smaller than these (minimum x 10 6 viable cells x g -1 dry soil in C2> 160cm). Unlike the non-irrigated profile P1, where fungi grow in large numbers only in Ap 0-20cm, in irrigated profile P2, both Ap (0-25cm) and Az (25-50cm) are favorable to the growth of large numbers of microscopic fungi (Table 1). In the rest of the profile horizons, the number of fungal structures is lower by an order of magnitude, but the decrease is not uniform with depth. Table 2. Taxonomic composition of soil bacterial microflora from Profile Horizon Depth (cm) Bacteria - Taxonomic composition P1 Non-irrigated Ap 0 20 Bacillus cereus, Pseudomonas sp., Bacillus circulans, Bacillus mesentericus, Bacillus megaterium Actinomycetes Series Fuscus and Albus Az Bacillus cereus, Bacillus megaterium, Actinomycetes Series Albus A / B Bacillus mesentericus, Pseudomonas acidophila, Bacillus circulans, Actinomycetes Series Fuscus Bz Bacillus mesentericus, Pseudomonas acidophila, Bacillus circulans, Actinomycetes Series Albus By Bacillus circulans, Bacillus cereus B/C Pseudomonas sp., Bacillus circulans C > 130 Bacillus circulans Actinomycetes Series Fuscus P2 Irrigated Ap 0 25 Pseudomonas fluorescens, Pseudomonas sp., Bacillus circulans, Bacillus polymixa, Actinomycetes Series Fuscus Az Bacillus megaterium, Pseudomonas fluorescens, Pseudomonas acidophila,, Bacillus cereus B Pseudomonas sp., Bacillus circulans B Bacillus circulans Actinomycetes Series Albus B/C Pseudomonas pseudogleyi Actinomycetes Series Albus C Actinomycetes Series Albus C2 > 160 Actinomycetes Series Albus 4

5 Table 3. Taxonomic composition of soil fungal microflora from Profile Horizon Depth (cm) Fungi - Taxonomic composition P1 Non-irrigated Ap 0 20 Verticillium tenerum, Aspergillus terreus, Penicillium funiculosum, Penicillium verrucosum, Acremonium strictum, Phialophora fastigiata Az Stachybotrys chartarum, Fusarium oxysporum A / B Geotrichum candidum Bz Cladosporium herbarum, Penicillium vermiculatum, Penicillium citrinum By Cladosporium cladosporioides B/C Penicillium janthinellum, Penicillium verrucosum, Paecilomyces marquandii, Aspergillus glaucus, Aspergillus terreus C > 130 Aspergillus terreus P2 Irrigated Ap 0 25 Fusarium oxysporum, Paecilomyces marquandii, Aspergillus wentii, Penicillium sp., Penicillium verrucosum, Rhizopus stolonifer,aspergillus terreus Az Pencillium vermiculatum, Fusarium oxysporum, Aspergillus terreus, Penicillium sp., Aspergillus versicolor, Penicillium funiculosum B Fusarium oxysporum, Penicillium brasilianum B Trichoderma viride, Cladosporium cladosporioides B/C Penicillium brasilianum, Penicillium aurantiogriseum, Cladosporium sphaerospermum C Alternaria alternata, Penicillium sp., Paecilomyces sp., Aspergillus glaucus C2 > 160 Penicillium sp., Aspergillus glaucus In the transitional horizon B / C and the subjacent horizons there are conditions that maintain the existence of fungi numbers larger than in B horizons. Global microbial activities (Fig.2), influenced by the large numbers of microorganisms from surface horizons, reach values above 30 mg CO 2 /100g soil, considered as moderate level, in Ap (0-25cm) ( mg CO 2 /100g soil) and Az (25-50cm) ( CO 2 /100g mg soil). In the remaining profile horizons, values are low, with variations as a function of favoring conditions for the development of representatives of bacteria and fungi. Horizon Soil respiration potential (mg CO2 /100g soil) Ap Az B1 B2 B/C C1 Irrigated C2 Fig. 2 Soil respiration potential of irrigated profile P2 from In terms of taxonomy, bacteria are more diverse in the surface horizons A, where fluorescent and non-fluorescent pseudomonads dominate, accompanied by various species of bacillaceae. Actinomycetes from Albus Series are well developed in horizons B and especially C (Table 2). Pseudomonas pseudogleyi represents the dominant species in the transition horizon B / C ( cm). The maximum number of fungal species identified in irrigated profile P2 is 7 vs. 6 in nonirrigated profile P1 (Table 3). The dominant species in the surface and the B1 (50-86cm) horizon is 5

6 Fusarium oxysporum. Otherwise, a greater share in the community of the genus Penicillium comparatively with Aspergillus which maintains the same position as in P1 is revealed by the analysis of community structure. The dominant species in horizon B2 (86-114cm), Trichoderma viride is known as a very effective enzyme-producer and antagonist for plant pathogens. Fig.3 Chromatogram of non-irrigated soil (P1) Fig.4 Chromatogram of irrigated soil (P2) Pfeiffer chromatograms revealed a central area of pale pink color, narrower at P1 (Fig. 3) and broader at P2 (Fig.4), diffuse, with more obvious and marked rays. The grayish-white area without rays is larger in P1 chromatogram, while in the P2, it is very small (1-2mm). Peripheral areas have brown-grey appearance similar in the two profiles, but the brown contour is lighter and thinner in P1 than in P2, where chromatogram edges are vivid, well outlined, in shades of dark brown, almost black. All this indicates that there are differences between the two soils concerning the quantity and quality of their constituents, their different migration appearing evident on chromatograms configuration. 4. CONCLUSIONS Increased humidity and lower temperature in the Ap horizon of irrigated soil favored increasing number of bacteria (18 x 10 6 viable cells x g -1 dry soil) and their metabolic activity, expressed by the amount of released carbon dioxide (CO mg x g -1 dry soil), compared with non-irrigated soil. Fungal microflora was more abundant starting from the depth of 25-50cm, under irrigation. Species diversity in irrigation conditions increased slightly both in surface and in the bottom of soil profile. In irrigated soil, associations of bacterial species that belonged to the genera Pseudomonas and Bacillus were dominant in the surface, and actinomycetes from Series Albus in depth. Fungal consortia with species of genera Penicillium, Aspergillus, Fusarium were dominant in both soil profiles. Irrigation induces changes in the quantity and quality of fulvic acids evidenced in the appearance model of migration of the circular chromatograms. 6

7 References Bergey, D. H., and Holt, John G. (1994). Bergey's manual of determinative bacteriology. Baltimore: Williams & Wilkins. Domsch, K. H., and Gams, W. (1972). Fungi in agricultural soils. New York: Halsted Press Division. Oved, T., Shaviv, A., Goldrath, T., Mandelbaum, R. T., and Minz, D. (2001). Influence of effluent irrigation on community composition and function of ammonia-oxidizing bacteria in soil. Applied and environmental microbiology, 67(8), Papacostea, P. (1976). Biologia solului. București: Ed. Științifică și Enciclopedică. Samson, Robert A., and Reenen-Hoekstra, Ellen S. van. (1988). Introduction to food-borne fungi. Baarn: Centraalbureau voor Schimmelcultures, Institute of the Royal Netherlands Academy of Arts and Sciences. Ștefanic, G. (1991). Assay of the potential level of soil respiration with an oxygen-generating respirometer. Bull. Acad. Sci. Agric. Forest., 21,

8