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2 Polish Journal of Ecology

2 2000

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Response of microbial communities to biomanipulation of the numbers of epigean macroarthropods in a field experiment in meadow

Stefaniak O., Dziedzic T., Gorlach K.

Polish Journal of Ecology

2000

Vol. 48, nr 4

311-326

The objective of our investigations was to analyse if experimental exclusion ofmacroarthropods patrolling soil surface affects numbers, composition and enzymatic activity of microbial communities. The experiments were carried out in mesocosms containing soil cores taken from the meadow or filled with sand (100 cm^2, 15 cm deep), inserted into the soil profile in Arrhenatheretalia mown meadow. Two types of mesocosms have been compared: open (O) - accessible for macrofauna, with openings cut in netting in soil/litter interface, or closed (C), made from the same nylon material (mesh size 0,24 mm), but without openings. In the mesocosms, litter bags containing 9,5 g dry wt of above ground parts of Dactylis glomerata were placed on the soil or sand surface. The experiments have been repeated in the two successive growing seasons (1992, 1993) and lasted from spring, (time of exposure) till autumn. The abundance of microbes in the litter increased gradually from very low initial numbers till the peak (higher by 4-6 orders of magnitude) in autumn, in the period of high moisture content of the habitat (18 or 23 weeks after the exposure, respectively in two experiments). In this last period only, significant differences were recorded between microbial numbers in litter exposed in open and closed mesocosms. The numbers of total bacteria and Actinomycetes were in the most analysed cases (6 per 8 analyses) significantly higher in closed mesocosms. Fungi were more abundant in open ones (3 per 4 cases). Differences between enzymatic activity in the litter placed in these two series of mesocosms were not significant. Highly significant positive correlation was found between litter decomposition rate and the estimated number of microbes in it (P,0,05). The dynamics of microbes in the sand followed a similar trend of gradual increase from springm till autumn, as in the litter. Seasonal dynamics in the soil was different and variable. On the contrary to the litter, in soil and sand higher microbial numbers and higher enzymatic activity were found, in most analysed cases, inmesocosms accessible for macrofauna (O) (higher - 20, lower - 5 cases). It was the consequence of higher input of invertebrate ejecta and higher organic matter content in these mesocosms.

Effect of macroarthropods on microbial and faunal numbers and organic matter content in soil

Kajak A., Kusińska A., Stanuszek S., Stefaniak O., Szanser M., Wasylik A., Wasilewska L.

Polish Journal of Ecology

2000

Vol. 48, nr 4

339-354

A field exclusion experiment in Arrhenatherrethalia mown meadow was carried out in mesocosms to analyse the role of epigeic, mobile macroarthropods in decomposition processes. A mineral bag technique allowed assessment of annual organic matter accumulation in the sandy substrate of mesocosms. Higher total organic C content was recorded in the top substrate layer (0-3 cm) in mesocosms accessible for macroarthropods, than in closed, inaccessible ones (17 and 23% more, respectively, in the two years), as well as higher amount of C in humus acids (6 and 36% more in two years). Possible reasons for these differences were considered. The total plant biomass, the litter disappearenc3 rate and water content in litter did not differ significantly between the types of mesocosms. In the top layer of mesocosms accessible for macroarthropods higher content of comminuted plant material (38,9 g m^-2) and arthropods feces (12.3 g^-2) were found compared to the amount in closed mesocosms (17,1 and 2,1 g m^-2 respectively). But the particulate organic matter derived from comminuted plant remnants and from fecal pellets accounted, in the period of the highest content, for about a half of the total carbon accumulated in the top substrate layer. In the litter of the open mesocosms reduced number of fungivorous mites and aphids was found, coupled with higher density of bacterivorous nematodes and higher abundance of fungi. The density of fungivorous mites was negatively correlated with the intensity of area patrolling by Araneae (tau = -0.79, P=0,0028) and Staphylinidae (tau = -0.58, P = 0.03). The elimination of aphids was positively correlated with area patrolling by the last group (tau = 0.81, P = 0.005). These results suggest that predation by macroarthropods changed proportions between fungi- and bacteriovorous invertebrates and as a consequence proportions between fungi and bacteria.