Structure and functionality of soil microorganisms under conditions of manure and under supply
Λειτουργικές μορφές εδαφικών μικροοργανισμών μετά από χειρισμό οργανικής λίπανσης-άρδευσης
Κορδάτος, Χάρης Μιχαλάκη
The aim of this study was to investigate the biotic and abiotic effects οn the structure and the functionality of microbial soil community in a Mediterranean system. For this purpose 12 experimental plots (1m x 1m) were installed in an abandoned field. In these plots 2 levels of abiotic stress (low and high amount of rainfall) and 2 levels of biotic stress (with and without of organic fertilization) were applied. The 4 treatments resulted in the combination of independent variables. Τhe treatments were: 1) lot of water (20L that corresponds in the 150% of average monthly rainfall) without organic fertilization (cattle manure), 2) less water (7L that corresponds in the 50% of average monthly rainfall) without organic fertilization, 3) lot of water (20L) and organic fertilization (4 Kg/1m2), 4) less water (7L) and organic fertilization (4Kg/1m2). Two samplings were conducted; 3 and 6 months after the beginning of experiment respectively. Soil samples were collected from the first 15 cm of the soil surface. The soil samples were analyzed with the method of Eco Plates (BIOLOG) to assess the microbial functionality and with the method of Phospholipids fatty acids (PLFA) to assess microbial structure. In Eco Plates method, the consumption of substrates was measured for 144 hours every 24 hours using an automated plate reader. In the consumption of each substrate a sigmoid curve was adapted and the parameters (K, r and s) of this curve were analyzed. By the total of 31 substrates, 22 were consumed in all samples.
According to the values of parameter K, the discrimination among the soil samples, collected at the first sampling occasion, was among samples with manure and samples without manure. In the 2nd sampling, samples were discriminated according to the quantity of added water. Moreover samples collected from the treatment less H2O - with manure were discriminated clearly from those collected from less H2O - without manure. When the analysis was applied in the other two parameters (r: rate and s: time until point K/2 of curve) only samples collected from the treatment less H2O - without manure in the 1st sampling were discriminated from all the rest. Probably the incorporation of manure improves the physicochemical and mainly the soil moisture
conditions, resulting in changes in the functionality of microbial community when the amount of added water was equal to 50% of the average monthly rainfall. The effect of manure was insignificant where the added water is much more.
The method of PLFA gives the possibility of discrimination among basic groups of microorganisms such as Gram positive, Gram negative, Actinomycetes and Fungi. The statistical analysis of data with the neural networks they showed high concentrations of fatty acids cy 19:0 and 18:1ω9, trans in samples collected from the treatments lot H2O - with manure and less H2O - without manure that constitutes the extreme treatments that were applied. The presence of these fatty acids (cyclopropyl, trans) indicates soil disturbance. The cis/trans isomerization system and the transformation of cis double bonds to cyclopropane ring they are mechanisms that adapt fatty acids when these are exposed in various environmental stress.
The importance of each disturbance in the functionality of soil microbial community is changed with sampling time. The analysis of data with PCA showed that, despite the intense interventions (addition 150% of average monthly rainfall - with manure), changes caused in the functionality of soil bacteria are smaller than those caused by the alteration of climatic conditions from winter to summer.
Στην παρούσα εργασία ελέγχθηκε η επίδραση διαφορετικών τύπων καταπόνησης (βιοτική και αβιοτική) στη δομή και τη λειτουργικότητα της μικροβιακής εδαφικής κοινότητας σε ένα Μεσογειακό σύστημα.
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