Michael Runge

Relevance of element content of bark for the distribution of epiphytic lichens in a montane spruce forest affected by forest dieback

Element content in the bark on Norway spruce (Picea abies) was measured in a montane forest heavily affected by forest dieback and compared to that in a nearby intact stand. Bark contained less S, K, Fe, Mn, Pb, Cu, and H+ and more N, Ca, Mg, and Zn in the dieback-affected stand than in the intact one. Diversity of epiphytic lichen vegetation was higher in the dieback-affected stand than in the intact one. Cover of the foliose lichen Hypogymnia physodes was negatively correlated with Mn and Cu content of bark. Cover of the extremely acidophytic species Lecanora conizaeoides decreased with increasing Mg and increased with increasing Cu content of bark. The measurements support the hypothesis that chemical site factors are decisive for the high lichen diversity in dieback-affected montane spruce forests.

Stemflow chemistry and epiphytic lichen diversity in dieback-affected spruce forest of the Harz Mountains, Germany

Summary In the German Harz Mountains, epiphytic lichen diversity was found to be higher in a Picea abies forest affected by pollution-caused dieback than in a comparable healthy stand. Although amount and chemical composition of incident precipitation did not differ between the stands, element concentrations of S, H+, K, Fe, Mn, and Al in stemflow were significantly lower in the dieback-affected plot than in the healthy one. These lower concentrations are attributed to reduced interception and reduced leaching due to needle loss. Cover of Hypogymnia physodes decreased with increasing concentrations of many elements in stemflow and bark. Among these parameters, S concentration of stemflow is considered to influence directly H. physodes. Cover of the extremely toxitolerant Lecanora conizaeoides was less affected by chemical variables, but a significant dependence of cover on S concentration of stemflow, resulting in an optimum regression curve, could be established in this case. Total number of lichen species per sample tree decreased as concentrations of several elements increased, indicating that most lichen species had similar habitat requirements as H. physodes.

Water relations and photosynthetic performance in Larix sibirica growing in the forest-steppe ecotone of northern Mongolia

Shoot water relations were studied in Siberian larch (Larix sibirica Ledeb.) trees growing at the borderline between taiga and steppe in northern Mongolia. Larix sibirica is the main tree species in these forests covering 80% of Mongolias forested area. Minimum shoot water potentials (Psi(m)) close to the point of zero turgor (Psi(0)) repeatedly recorded throughout the growing season suggest that the water relations in L. sibirica were often critical. The Psi(m) varied in close relation to the atmospheric vapor pressure deficit, whereas Psi(0) was correlated with monthly precipitation. Young larch trees growing at the forest line to the steppe were more susceptible to drought than mature trees at the same sites. Furthermore, isolated trees growing on the steppe exhibited lower Psi(m) and recovered to a lower degree from drought overnight than the trees at the forest line. Indications of drought stress in L. sibirica were obtained in two study areas in Mongolias forest-steppe ecotone: one in the mountain taiga of the western Khentey in northernmost Mongolia, the other in the forest-steppe at the southern distribution limit of L. sibirica on Mt. Bogd Uul, southern Khentey. Larix sibirica growing in riverine taiga with contact to the groundwater table was better water-supplied than the larch trees growing at the forest line to the steppe. Larch trees from the interior of light taiga forests on north-facing slopes, however, exhibited more critical water relations than the trees at the forest line. Frequent drought stress in mature trees and even more in young larch trees at the forest-steppe borderline suggests that L. sibirica does not have the potential to encroach on the steppe under the present climate, except in a sequence of exceptionally moist and cool years. A regression of the present borderline between forest and steppe is likely to occur, as average temperatures are increasing everywhere and precipitation is decreasing regionally in Mongolias taiga forest region. Higher stomatal conductance concomitant to lower Psi(m) in trees of northern-slope forests compared to trees from the forest line to the steppe may be the result of a recent increase in drought intensity that affects better drought-adapted trees at the forest edge less than the trees in the forest interior. We conclude that drought is a key factor explaining the forest-steppe borderline in northern Mongolia. The proportion of forests within the present vegetation pattern of forests on north-facing slopes and the grasslands on south-facing slopes in Mongolias forest-steppe ecotone is not likely to increase under the present climate, but may decrease with increasing aridity due to global warming.

Effects of manganese on the viability of vegetative diaspores of the epiphytic lichen Hypogymnia physodes

Abstract Soredia of the lichen Hypogymnia physodes cultivated with Bolds basal medium on agar plates for 8 days exhibited decreasing growth rates along with increasing Mn concentrations above 3 mM. Ca and Mg added separately or in combination, alleviated Mn toxicity. The chlorophyll a and b content of the soredia was reduced under the influence of Mn and was positively correlated with the rate of grown soredia. Trebouxia cells of the soredia grown with excess Mn were smaller than control cells, had reduced chloroplasts and were partly collapsed; fungal hyphae were shortened and strongly swollen. Disintegrated cell walls occurred both in algal and fungal cells. Excess Mn was sequestered in extracellular encrustations together with phosphate as corresponding anion. Intracellularly, Mn was accumulated in polyphosphate granules both in algal and fungal cells. Mn uptake was correlated with significant loss of Na, Mg and Ca, particularly from the mycobiont. Fungal cell walls also lost significant amounts of P. The same damage symptoms occurred in cells of soredia both grown or not, but the former had a higher share of intact cells. Damaged cells of both types of soredia had equally increased Mn concentrations, whereas the total Mn content was higher in not grown soredia than in the grown ones due to the greater amount of damaged cells in the former. The Si–Mn ratio in cell walls of intact Trebouxia cells was significantly higher than in collapsed cells. The experimental evidence of Mn sensitivity of H. physodes soredia corresponds to studies of epiphyte vegetation in montane spruce forests of northern Germany that revealed decreasing cover values of H. physodes with an increasing Mn content of the substrate.

Correlations between the Mn/Ca ratio in stemflow and epiphytic lichen abundance in a dieback-affected spruce forest of the Harz Mountains, Germany

Summary Dieback-affected trees of a boggy stand of Picea abies in the Harz Mountains, northern Germany, bore a richer epiphytic lichen vegetation than healthy trees. Cover of the foliose epiphytic lichen Hypogymnia physodes decreased with increasing Mn/Ca ratio in stemflow. The total of lichen species per tree decreased both with the Mn/Ca ratio in stemflow and with the Mn concentration in bark. The results agree with experimental tests of Mn toxicity to H. physodes . Comparison with other dieback-affected spruce stands of the Harz Mountains revealed that Mn attained unusually high concentrations in the study site because of high Mn concentrations in the soil. Mn concentrations in soil, bark, stemflow, and incident precipitation suggest that Picea abies removes excess Mn taken up from the soil by the root system by transferring it into the bark. Mn in stemflow is supposed to derive primarily from leaching of Mn from bark and needles. SO 4 2– concentration that was found to be decisive for epiphytic lichen distribution in other dieback-affected spruce stands of the Harz Mountains was of subordinate significance to lichen vegetation in the present case.

Occurrence of pollution-sensitive epiphytic lichens in woodlands affected by forest decline: a new hypothesis

Summary Influences of forest dieback on epiphytic lichen vegetation in montane spruce forests of the Harz Mountains (Northern Germany) are described. The epiphytic lichen vegetation of damaged forest stands consists of more species and a higher number of endangered, loss toxitolerant lichen taxa than that of intact forest stands. Therefore, we tested the hypothesis that concentrations of potentially phytotoxic substances in stem flow are lower in damaged stands than in intact stands, because the higher needle surface of the latter should result in a higher pollutant interception. In accordance with this hypothesis, lower concentrations of the elements S, Zn, AI, and Mn and of hydronium ions were established in the stem flow of a damaged stand compared to an intact stand under identical climatological conditions. This phenomenon could be a precondition of the higher lichen diversity in the damaged stand.

Water relation characteristics ofAlhagi sparsifolia and consequences for a sustainable management

Water relation characteristics of the desert legumeAlhagi sparsifolia were investigated during the vegetation period from April to September 1999 in the foreland of Qira oasis at the southern fringe of the Taklamakan Desert, Xinjiang Uygur Autonomous Region of China. The seasonal variation of predawn water potentials and of diurnal water potential indicated thatAlhagi plants were well water supplied over the entire vegetation period. Decreasing values in the summer months were probably attributed to increasing temperatures and irradiation and therefore a higher evapotranspirative demand. Data from pressure-volume analysis confirmed thatAlhagi plants were not drought stressed and xylem sap flow measurements indicated thatAlhagi plants used large amounts of water during the summer months. Flood irrigation had no influence on water relations inAlhagi probably becauseAlhagi plants produced only few fine roots in the upper soil layers. The data indicate thatAlhagi sparsifolia is a drought-avoiding species that utilizes ground water by a deep roots system, which is the key characteristic to adjust the hyper-arid environment. Because growth and survival ofAlhagi depends on ground water supply, it is important that variations of ground water depth are kept to a minimum. The study will provide a theoretical basis for the restoration and management of natural vegetation around oasis in arid regions.

Keimlings- und Jungpflanzenentwicklung der Buche (Fagus sylvatica L.) in Abhängigkeit vom Al/Ca-Verhältnis des Bodenextraktes

Summary Germination and development of beech seedlings have been studied over a period of 200 d on soil variants with varying ratios between their water extractable Al- and Ca-contents. In the soil variants with p H-values The frequency of root tip damages and the number of seedlings, unable to establish because of radicle damages after contact with the soil increased with increasing Al/Ca-ratios. In general, no significant correlations could be established between root damages and water extractable Ca-, Mg- and K-contents. These results are interpreted as disturbances in cell metabolism and division in the root tip meristem, caused directly by Al-ions. Then, the antagonistic effect of Ca follows from the significance of the Ca-ions in maintaining the selective permeability of the plasmalemma. As a consequence from these results Al-toxicity cannot be excluded as a cause of disturbances in beach seedling establishment and development in acid soils.

Contributions to a Sustainable Management of the Indigenous Vegetation in the Foreland of Cele Oasis — A Project Report from the Taklamakan Desert

The ecological situation of oases at the southern border of the Taklamakan desert is shortly described, and the importance of a vegetation from indigenous species at the transition from the oases to the desert is emphasized. This vegetation serves as a shelter against sand drift and as a source of livestock feed as well as of fuel and construction material. Its destruction through overexploitation and other interventions during the last decades has considerably promoted sand drift and the deterioration of arable land. Therefore, a management of this protective vegetation is to be developped that leads to a sufficient regeneration and that ensures both its preservation and its use. A research project that is carried through jointly by Chinese and European scientists shall yield an ecological basis for this sustainable management.

Are Fe and P availabilities involved in determining the occurrence and distribution of Calluna vulgaris (L.) Hull in semi-arid grasslands on calcareous soils?

Calluna vulgaris (L.) Hull is primarily found on acid soils and is generally classified as a calcifuge species. Therefore, its occasional growth in semi-arid grassland on shallow calcareous soils gave rise to the question as to whether special soil conditions, deviating from the typical conditions in calcareous soils, enable this unusual occurrence. In an attempt to answer this question, we analysed selected soil factors, comparing plots where C. vulgaris was growing besides calcicole species (=CF plots) with neighbouring plots where only calcicole species were present (=CC plots). Main emphasis was placed on Fe and P availability because results from growth experiments indicate that the availability of either Fe or P to calcifuges causes calcifuge species to fail on calcareous soils. The results of our investigations do not support the hypothesis that the occurrence of C. vulgaris in semi-arid calcareous grasslands depends on higher Fe and/or P availability. Rather, its growth on carbonate-buffered soils shows that this species is not really calcifuge. Since the CF plots differ from the CC plots either by a lower inclination or by a more northerly exposition, we assume that the primary establishment and this species’ distribution pattern in the investigated semi-arid grassland are not dependent on soil chemical factors, but are governed by topography and its consequences for soil humidity and drought stress.