Gerhard Eisenbeis

Organic residue decomposition: The minicontainer-system a multifunctional tool in decomposition studies

The Minicontainer-test, first described by Eisenbeis (1993), was designed to study the kinetics of organic residue decomposition at a microsite level. It is derived from the litterbag technique and consists of polyethylene minicontainers (volume about 1.5 cm3) filled with a test substrate (litter, straw, cellulose, etc.). The minicontainers (MCs) are closed at either end with plastic gauze discs of variable mesh size (e.g. 20 μm, 250 μm, 500 μm or 2 mm). A definite number of such units are inserted into PVC-bars, which can be implanted into the soil horizontally or vertically, or be exposed on the soil surface horizontally. The bars are very stable and can be exposed in different environments for months to years. If required, the bars can be removed temporarily and stored, e.g. during soil cultivation. Should fresh litter be used, two phases of decomposition can be distinguished: a fast initial phase, which can be mainly related to the effect of leaching, and a second slow phase depending mainly on the activity of soil organisms and litter quality. Several questions can be addressed to investigations using MCs, e.g. 1) parts of the soil fauna which are involved in decomposition (nematodes, microarthropods, and smaller specimens of the macrofauna, e.g. enchytraeidae, diplopods and dipteran larvae) can be extracted from the litter substrate using a miniscale high gradient extractor, 2) the organic mass loss of litter can be determined, 3) microbial biomass (Cmic, Nmic) can be assessed by fumigation extraction and 4) microbial activity (respiration) in the test substrate can also be assessed by use of standardised methods. Compared to litterbag studies, the larger number of small replicate units improves the statistical evaluation. Until today the Minicontainer-test has been applied in forestry and agriculture, e.g. studying the effects of liming, soil restoration and the application of insecticides, e.g. Diflubenzuron (Dimilin) and Btk (Bacillus thuringiensis var.kurstaki).

Physiological absorption of liquid water by Collembola: Absorption by the ventral tube at different salinities

Abstract The ability to absorb solutions has been examined in the coxal vesicles of the ventral tube in two sympatric surface dwelling Collembola ( Tomocerus sp. and Orchesella villosa ) from a beech forest. The net influx of distilled water and different sodium chloride solutions was measured, followed by examination of the effective surface of the vesicles which contacts the medium. The transport rate decreased with increasing salinity of the medium. Orchesella always showed higher absorption rates than Tomocerus , if the values were related to unit surface area. However, considering that the effective surface area of the vesicles of Tomocerus is larger, the total absorption rate by the ventral tube of Tomocerus exceeded that of Orchesella . Calculating the increase in the total water content. Orchesella compensated for its deficit faster than Tomocerus , because Orchesella is smaller in total weight and water content. In most cases the efficiency of the absorptive epithelium decreased during an absorption cycle; this also occurred before moulting. Some hours after moulting, the absorption rates increased to their former level. Comparing the rates of transpiration, absorption by the ventral-tube vesicles, and drinking, confirmed the dominant role of the ventral tube in the water balance of Collembola. It is an important factor in the strategy of adaptation from the hypogaic to the epigaic life.

Responses and adaptations of collembolan communities (Hexapoda: Collembola) to flooding and hypoxic conditions

Standard ecological methods (pitfall traps, trunk eclectors and soil cores) were used to evaluate collembolan community responses to different flooding intensities. Three sites of a floodplain habitat near Mainz, Germany, with different flooding regimes were investigated. The structures of collembolan communities are markedly different depending on flooding intensity. Sites more affected by flooding are dominated by hygrophilic and hygrotolerant species, whereas the hardwood floodplain is dominated by mesophilic species. The survival strategies of the hygrophilic and hygrotolerant species include egg diapause and passive drifting. The physiological adaptations to hypoxic conditions of several collembolan species were analyzed using a microcalorimeter. The activities were tested under normoxic and hypoxic/anoxic conditions as well as during post-hypoxic recovery. Lactate was increased after hypoxic intervals in the species studied, suggesting that, in addition to a massive decrease in metabolic rate, a modest glycolytic activity may be involved in the tolerance to hypoxia.

Effects of ecological flooding on the temporal and spatial dynamics of carabid beetles (Coleoptera, Carabidae) and springtails (Collembola) in a polder habitat

Abstract Within the scope of the Integrated Rhine Program an ecological flood gate and channel was inserted into the polder “Ingelheim” to enhance animal and plant diversity. In 2008, carabid beetles and springtails were collected, using pitfall traps, to measure the effects of ecological flooding and a strong precipitation event at a flood-disturbed and a dry location in this area. At both localities, xerophilic and mesophilic carabid beetle species were dominant throughout the study period. The total number of individuals of hygrophilic species was comparatively constant, while species number increased, partly due to the changed moisture conditions caused by ecological flooding and strong precipitation. Carabid beetle diversity and evenness decreased marginally when ecological flooding was absent. Springtails represent a less mobile arthropod order, and as such the impact of ecological flooding was stronger. An increase in both numbers of species and individuals of hygrophilic and hygrotolerant species occurred in the flood-disturbed location after ecological flooding. After the sites at both locations had dried, the number of individuals belonging to these species declined rapidly. In contrast to carabid species, the strong precipitation event showed no influence on hygrophilic springtail species. Thus, collembolan diversity and evenness decreased markedly in the absence of flooding. We showed that ecological flooding has an influence on the spatial and temporal dynamics of different arthropod groups that inhabit the polder “Ingelheim”. These findings demonstrate the importance of using different arthropod groups as bioindicators in determining the ecological value of a particular polder design.

Feinstruktureller und histochemischer nachweis des transportepithels am ventraltubus symphypleoner collembolen (Insecta, Collembola)

SummaryFinestructurally the transporting epithelium of the ventral tube in symphypleonan Collembola (Sminthurides aquaticus Bourlet 1842) is characterized by infoldings of the apical and basal plasma membranes and abundant mitochondria. The cuticle above the transporting epithelium possesses the ability to accumulate chloride. The main function of the transporting epithelium in the ventral tube is probably the absorption of ions and water.ZusamnenfassungFeinstrukturell ist das Transportepithel am Ventraltubus symphypleoner Collembolen (Sminthurides aquaticus Bourlet 1842) durch Einfaltungen der apikalen und basalen Zellmembran und durch zahlreiche Mitochondrien gekennzeichnet. Die Cuticula oberhalb des Transportepithels besitzt die Fähigkeit zur Chloridakkumulation. Die wesentliche Funktion des Transportepithels besteht wahrscheinlich in der Absorption von Ionen und Wasser.

An extraction method for nematodes in decomposition studies using the minicontainer-method

The minicontainer-method is a new method developed to study biological processes related to soil litter decomposition. An adaptation of the classical Baermann-funnel technique is described which can be used, in association with the minicontainer method, to investigate the role of Nematoda in litter decomposition. The use of the extraction method is illustrated in a study of the effects of different tillage systems on the decomposition of rye straw and on the nematode density in minicontainers with different mesh sizes of 20 µm, 500 µm and 2 mm. Three tilled plots (conventional deep plough, cultivator and two-layer plough) and an untilled control were compared after periods of 4 weeks and 38 weeks. On both sample dates there were significant main effects of treatment and mesh size on the nematode density, and additionally, after 38 weeks significant treatment x soil depth interactions. After 4 weeks, there were significant main effects of treatment and soil depth on the decomposition, but no mesh size effects, whereas after 38 weeks, all experimental factors had a significant effect on the decomposition of the straw. Due to the small volume of litter substrate used in the minicontainer method, the efficiency of nematode extraction is high and the lack of oxygen in the minicontainers presents no serious problem during the extraction process. The method also allows the simultaneous extraction of a large number of samples within a short period of time. Our results indicate that the method is suitable to study the microdistribution of nematode activity within the soil profile and improves the possible applications of the minicontainer-method.

Fine structural and histochemical evidence of chloride cells in stonefly larvae 3. The floriform chloride cells

Abstract The larvae of Trinotoperla irrorata Tillyard (Gripopterygidae) possess remarkable chlorid cells consisting of one central cell and at least one adjacent cell grouped together into a small cell complex. They are termed floriform chloride cells because of the flower‐bud‐like structures seen by scanning electron miroscopy. Fine structural studies in combination with histochemical demonstration of chloride indicate that these cell complexes probably participate in osmoregulation by the absorption of salt.

Zur feinstrukturellen Anpassung des Transportepithels am Ventraltubus von Collembolen bei unterschiedlicher SalinitÄt

SummaryThe transporting epithelium in the ventral tube of some Collembola-Species —Podura aquatica, Lepidocyrtus ruber, Sminthurides aquaticus andTomocerus vulgaris — was examined about any finestructural changes caused by different salinities.Podura aquatica was compared by two populations from periodic salt lakes in the “Neusiedler-lake-region” withLepidocyrtus ruber from the supralitoral of the middle-sea coast on the isle of Elba/Italy, as an example for longtime adaptation. In the animals from a highly saline substrate the typical structures of transporting epithelia were reduced: most of all the apical folded border and the number of mitochondria. Living on a periodic salt lake of lower salinityPodura aquatica showed a fine structure similar to that discovered under normal conditions. InSminthurides aquaticus andTomocerus vulgaris, as examples of short time adaptation, the apical folded border of the transporting epithelium revealed as the most sensible structure against stronger changes of salinity. At 100 mOsm sea salt-, respectively 250, 500 and 1000 mOsm NaCl-solution the folded border was shortened, the fold number was diminuated and more irregular and partly the folded border had completely disappeared. More invaginations of the apical cell membrane were found instead. Often they were seen lying parallel to the cuticle. Thus they are interpreted to function as an isolatory mechanism. As for the abundance of mitochondria and the expansion of the basal labyrinth no regular measurable changes could be found. A comparison with the chloride cells respectively chloride epithelia of aquatic insects points out that the uptake of ions is probably regulated by variation of the resorptive surface beneath the cuticle.ZusammenfassungDas Transportepithel am Ventraltubus verschiedener Collembolen-Arten —Podura aquatica, Lepidocyrtus ruber, Sminthurides aquaticus undTomocerus vulgaris — wurde auf salinitÄtsabhÄngige VerÄnderungen der Feinstruktur hin untersucht. Als Beispiel langfristiger Adaptation wurdePodura aquatica aus zwei Populationen von Salzlaken des Neusiedlersee-Gebietes mitLepidocyrtus ruber aus dem Supralitoral der Mittelmeerküste der Insel Elba/Italien verglichen. Die Tiere von stark salzhaltigem Substrat zeigten eine Rückbildung der für Transportepithelien typischen Strukturen, in erster Linie eine Reduzierung des apikalen Faltensaumes und der Mitochondriendichte. Auf einer Salzlake geringerer SalinitÄt ergab sich fürPodura aquatica eine Feinstruktur, die der unter Normalbedingungen nahekommt. Für die Beispiele kurzfristiger Adaptation —Sminthurides aquaticus, Tomocerus vulgaris — erwies sich von der Feinstruktur her der apikale Faltensaum als der Ort grö\ter SensibilitÄt gegenüber stÄrkeren SalinitÄtsschwankungen. Bei 100 mOsm Meersalz-, bzw. 250, 500 und 1000 mOsm NaCl-Lösung verkürzte sich der Faltensaum, die Faltendichte wurde geringer und unregelmÄ−Biger, teilweise kam es zu völligem Schwund. Anstelle des Faltensaumes traten auch verstÄrkt Invaginationen der apikalen Zellmembran auf, vielfach stapelartig geschichtet oder parallel zur Cuticula. Dies wird im Sinne eines Isolationsmechanismus gedeutet. Keine me\baren VerÄnderungen ergaben sich für die Mitochondriendichte und die Ausdehnung des basalen Labyrinths. Der Vergleich mit den Chloridzellen bzw. Chloridepithelien aquatischer Insekten legt nahe, da\ die Ionenaufnahme durch Variation der resorptiven OberflÄche gesteuert wird.

Zur morphologie des ventraltubus von Tomocerus-SPP (collembola: tomoceridae) unter besonderer berücksichtigung der muskulatur, der cuticularen strukturen und der ventralrinne

Abstract The ventral tube of the Tomocerus spp. is an abdominal appendage. Microtubercles are arranged on its surface in different patterns. Their arrangement on surfaces, which are free from bristles and scales, is considered to reduce transpiration. All bristles are mechanoreceptors, but the scales are without sensory components. The ventral channel shows a tubular structure near the head and on the front side of the ventral tube. In the thoracic region, the channel is extended, and on tendon-plates it is even interrupted. For this reason, the ventral channel is considered to be unsuitable for transport of fluid. The division of the hemocoel in a frontal and a caudal cavity serves to facilitate hemolymph flow around the transporting cells in the tube vesicles. The fat body in the tube base also assists in the flow, possibly by contraction of the tube cylinder. Many excretory granules are accumulated in the fat body. The external formation of the ventral tube into basal plate, tube cylinder, tube flaps, and tube vesicles corresponds to the highly specialized and segmentated muscle system. There are 14 muscle pairs which are differentiated in proximal, lateral and distal muscles. The function of the proximal muscles is to move the tube cylinder and control its position, the lateral muscles move the tube flaps and support the erection of the tube cylinder, and the distal muscles retract the tube vesicles. The basal plate and tube cylinder can be homologized to the coxa. The structure that separates both parts serves, as in legs, as insertion for muscles, as do the basicosta and merocosta in higher insects. Embryologically, the ventral tube is considered to be a derivative of a real limb. Finally, the abdominal appendages with vesicles are discussed for all orders of Apterygota.

Wasserhaushalt, Osmo- und lonenregulation sowie Exkretion

Mit den Teilgebieten Wasserhaushalt, Osmo- und Ionenregulation und Exkretion werden wichtige Grundfunktionen von Insekten behandelt, die masgeblich zu ihrer erfolgreichen Evolution beigetragen haben. Wesentlich hierfur ist die Fahigkeit zur Regulation im Hinblick auf eine ausgeglichene Wasser- und Stoffbilanz, die es ermoglicht, die vielfaltigsten Lebensraume im aquatischen und terrestrischen Bereich zu besiedeln. Mit dem Wasserhaushalt werden Phanomene der Wasserzufuhr, des Wasserverlustes und der Verteilung des Wassers zwischen den groseren Kompartimenten des Insektenkorpers besprochen. Insekten sind als relativ kleine Tiere mit einem grosen Oberflachen/Volumen-Verhaltnis oft extremen Anforderungen ausgesetzt. Die Fahigkeit zur Wasserkonservierung bei Landbewohnern gilt dabei als eines der physiologischen Kardinalprobleme ihrer Existenz. Neben einer ausgeglichenen Wasserbilanz sind fur das Funktionieren des Insektenkorpers stabile osmotische Verhaltnisse und weitgehend konstante Ionenverhaltnisse von Bedeutung (osmotische — und ionale Homoostase).