Browsing by Author "Runge, M."

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. SO42- 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.

The inter-annual variability of four growth-related parameters (light-saturated photosynthesis A,,, leaf area index L, annual stem diameter growth S, and fine root production P) was investigated together with various leaf water status parameters in adult Fagus sylvatica and Quercus petraea trees during five summers with weak, moderate or severe soil water deficit. Study aims were (i) to identify differences in drought sensitivity among the tree organs (leaf, stem or root) and between the tree species, and (ii) to test the hypothesis that differences in whole-tree drought response are relevant for competition between Fagus and Quercus in Central European mixed stands. Drought had only weak or no influence on A,, and L of the two species during the 5 years; the only exception being a severe drought in 1990 with an A,,, reduction of Fagus by 30%. Stem diameter growth of Fagus was significantly smaller in dry than in wet summers; in contrast, no clear stem growth/moisture relationship was detected for Quercus during the study period. Soil water deficits apparently stimulated fine-root,growth of Fagus during the dry mid-summer 1995, thus compensating for root biomass losses due to high root mortalities in this period. Quercus fine-root biomass and productivity were not significantly influenced by this drought. A higher drought sensitivity of stem diameter growth, fine-root production and photosynthesis in Fagus corresponded to a larger inter-annual variability of the predawn leaf water potential between wet and dry summers and generally smaller leaf conductances of this species compared to Quercus. Quercus was less sensitive to drought in its growth processes, but showed larger inter-annual variabilities of the osmotic potentials of the leaf symplasm and of the seasonal minima of bulk leaf turgor compared to Fagus. Thus, Fagus is competitively superior in mixture with Quercus despite its higher sensitivity to soil water deficits. It is concluded that a whole-plant perspective rather than a leaf-centred view of drought response is needed to predict the consequences of water shortage for ecosystem-level processes, such as tree competition and succession driven by climate change. (C) 2001 Elsevier Science B.V. All rights reserved.

To provide an ecological basis for the regeneration and the sustainable use of the vegetation at the transition between eases and sandy desert, a joint European-Chinese research project is being conducted at the southern fringe of the Central-Asian Taklamakan desert (Xinjiang, China). The investigations are being carried out at five study sites located in the foreland of the river oasis of Qira (Cele). Four of these sites are dominated by one species each, which is indigenous on a local (Alhagi sparsifolia, Populus diversifolia, Tarmarix ramosissima) or regional scale (Calligonum spec.). The fifth site is free of vegetation. Subsequent to irrigation performed by artificial flooding, the effects of the consecutive desiccation and of harvest on the water relations of soil and plants (including water-use efficiency and drought tolerance), the demand and turnover of nutrients (especially of nitrogen) and productivity of the respective species are being investigated. The composition of the vegetation and the population biology of the local species are being studied. Concomitantly, socio-economic inquiries are being performed to register the population's demand for plant resources and to provide a basis for the calculation of the management costs. The results of the study should provide a basis for the regeneration of that kind of vegetation which is best suited to meet the population's demand for plant resources and shelter from sand drift. The selection of the vegetation will be made on the basis of its water-use efficiency, productivity and capability of regeneration. The first results and an outlook for the forthcoming research activities are presented.

Soredia of the lichen Hypogymnia physodes cultivated with Bold's 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 If. 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. (C) 2002 Elsevier Science B.V. All rights reserved.

The hypothesis that water relations and growth of phreatophytic Tamarix ramosissima Ledeb. and Populus euphratica Oliv. on dunes of varying height in an extremely arid Chinese desert depend on vertical distance to a permanent water table was tested. Shoot diameter growth of P. euphratica was inversely correlated with groundwater depth (GD) of 7 to 23 in (adj. R-2=0.69, P=0.025); growth of T. ramosissima varied independent of GD between 5 and 24 m (P=0.385). Pre-dawn (pd) and midday (md) water potentials were lower in T. ramosissima (minimum pd-1.25 MPa, and 3.6 MPa at 24 m GD) than in P. euphratica (minimum pd -0.9 MPa, and -3.05 MPa at 23 m GD) and did not indicate physiologically significant drought stress for either species. Midday water potentials of P. euphratica closely corresponded to GD throughout the growing season, but those of T. ramosissima did not. In both species, stomatal conductance was significantly correlated with leaf water potential (P. euphratica: adj. R-2=0.84, P<0.0001; T. ramosissima: adj. R-2=0.64, P=0.011) and with leaf-specific hydraulic conductance (P. euphratica: adj. R-2=0.79, P=0.001; T. ramosissima: adj. R-2=0.56, P=0.019); the three variables decreased with increasing GD in P. euphratica. Stomatal conductance of P. euphratica was more strongly reduced (>50% between -2 and -3 MPa) in response to decreasing leaf water potential than that of T. ramosissima (30% between -2 and -3 MPa). Tolerance of lower leaf water potentials due to higher concentrations of leaf osmotically active substances partially explains why leaf conductance, and probably leaf carbon gain and growth, of T. ramosissima was less severely affected by GD. Additionally; the complex below-ground structure of large clonal T. ramosissima shrub systems probably introduces variability into the assumed relationship of xylem path length with GD.

Question: Can above-ground biomass of naturally growing Alhagi sparsifolia shrubs be estimated non-destructively? Location: Qira oasis (37degrees01'N, 80degrees48'E, 1365 m a.s.l.) at the southern fringe of the Taklamakan desert, Xinjiang, NW China. Methods: Two methods were compared to estimate above-ground biomass (AGB) of Alhagi. At first shrub AGB was estimated by manual ground measurements (called 'allometric approach') of length, width and height of 50 individuals. Subsequently regression equations were established between calculated shrub canopy volume and shrub AGB (r(2) = 0.96). These equations were used to calculate AGB from manual ground measurements in 20 sample plots within the Alhagi field. Secondly, kite-based colour aerial photography coupled with the use of a Geographic Information System (called 'GIS approach') was tested. First and second order polynomial regressions between AGB data of the 50 individual shrubs and their respective canopy area allowed to automatically calculate the AGB of all remaining shrubs covered by the photograph (r(2) = 0.92 to 0.96). The use of non-linear AGB regression equations required an automatised separation of shrubs growing solitary or in clumps. Separation criteria were the size and shape of shrub canopies. Results: The allometric approach was more reliable but also more time-consuming than the GIS-based approach. The latter led to an overestimation of Alhagi dry matter in densely vegetated areas. However, this systematic error decreased with increasing size of the surveyed area. Future research in this field should focus on improvements of AGB estimates in areas of high shrub density.

River oases at the southern fringe of the Taklamakan desert in NW China are surrounded by belts of spontaneous vegetation that protect the oases from sand drift. As an important source of forage, fuel and construction wood, this foreland vegetation is also a component part of the agricultural system of the oases but has been, and still is, destroyed through overuse. Within a broader study that aimed to provide a basis for a sustainable management of this foreland vegetation, biomass and production were studied in four vegetation types dominated either by Alhagi sparsifolia, Calligonum caput-medusae, Populus euphratica, or Tamarix ramosissima that were thought to occur under different regimes of natural flooding in the foreland of Qira (Cele) oasis, Xinjiang, NW China. Shoot biomass components were closely correlated to basal area (Calligonum, Populus, Tamarix) or shrub volume and projection area (Alhagi), enabling non-destructive estimation of stand biomass from shoot diameters or shrub dimensions with sufficient precision using allometric regression equations. Relationships between shoot basal area and biomass of the woody species (Calligonum, Populus and Tamarix) agreed with predictions by a theoretical model of plant vascular systems, suggesting that they are determined by hydraulic and mechanical requirements for shoot architecture. Average aboveground biomass densities of typical stands in late summer were 2.97 Mg/ha in Alhagi, 3.6 Mg/ha in a row plantation and 10.9 Mg/ha in homogenous stands of Calligonum, 22-29 Mg/ha in 22 year-old Populus forests and 1.9-3.1 Mg/ha in Tamarix-dominated vegetation. Annual aboveground production including wood and assimilation organs ranged from 2.11 to 11.3 Mg/ha in plantations of Calligonum, 3.17 to 6.12 Mg/ha in Populus, and 1.55 to 1.74 Mg/ha (based on total ground area) or 3.10 to 7.15 Mg/ha (in homogenous stands) in Tamarix. Production of Alhagi is equal to peak biomass. A thinning treatment simulating use by the local population enhanced productivity of Calligonum, Populus and Tamarix. A complete harvest of Alhagi in late August decreased production in the following year. An artificial flood irrigation treatment did not sufficiently increase soil water content except in the uppermost layer and had no clear beneficial effect on growth of the four species and even a negative effect on Alhagi, which was due to increased competition from annual species. As biomass and production with or without artificial irrigation were much higher than values expected for rain-fed desert vegetation at a mean annual precipitation of 35 mm, it is concluded that the existence of all vegetation types studied is probably based on permanent access to groundwater and that natural floods or precipitation do not contribute to their water supply. The effects of agricultural groundwater use in the oasis on groundwater in the foreland of the oasis need further study. Sustainable use of this productive vegetation is possible but requires proper management.

Element content in the bark of 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. (C) 2001 Elsevier Science Ltd. All rights reserved.

Epiphytic lichen diversity in a dieback-affected forest of red spruce (Picea rubens Sarg.) and balsam fir (Abies balsamea (L.) Mill.) on Whiteface Mountain, New York, U.S.A., was higher on dead compared with living trees and on fir compared with spruce. Diversity differed more between living and dead spruce than between living and dead fir. Cover of all lichen species that occurred on more than 50% of the sample trees, except for two species, decreased with increasing mean concentration of NO3- in stemflow. Concentrations of NO3- were higher on living spruce compared with dead spruce and with living and dead fir. The negative correlations between lichen cover and NO3- concentration may reflect either a decrease of lichen abundance caused by toxic effects of higher NO3- concentrations or a removal of NO3- from stemflow by epiphytic lichens. Experimental exposure of Hypogymnia physodes to NaNO3 reduced chlorophyll concentrations. This result, together with estimations of lichen and needle biomass, indicates that a dependence of lichen cover on NO3- concentrations in stemflow may be the cause for the negative correlations. The sulphur concentration in stemflow did not affect lichen abundance on Whiteface Mountain. The manganese concentration in stemflow may have an effect on single species.

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.

Epiphytic lichen diversity in a boggy stand of Norway spruce (Picea abies) was studied in the eastern Harz Mountains, northern Germany. Spruce trees at wet sites were affected by forest dieback, whereas trees on drier sites remained unaffected. Lichen diversity was higher on dieback-affected trees than on healthy ones. The foliose lichen Hypogymnia physodes was significantly more frequent on dead trees, whereas the crustose, extremely toxitolerant Lecanora conizaeoides occurred more frequently on healthy trees. Stemflow concentrations of NH4+ NO3-, PO3-, and SO42- were lower on affected trees. This is attributed to reduced interception from the atmosphere due to needle loss. Cover of H. physodes decreased with increasing mean SO42- concentration in stemflow. The total of lichen species per sample tree also decreased with increasing SO42- concentration in stemflow, indicating that most species reacted in a similar way as H. physodes. Cover of L. conizaeoides increased with increasing SO42- concentration, but decreased at higher SO42- concentrations. Bark chemistry had a minor influence on lichen diversity. (C) 2002 The British Lichen Society. Published by Elsevier Science Ltd. All rights reserved.

The indigenous vegetation surrounding the river oases on the southern rim of the Taklamakan Desert has drastically diminished due to overexploitation as a source of fodder, timber and fuel for the human population. The change in the spatial extent of landscape forms and vegetation types around the Qira oasis was analyzed by comparing SPOT satellite images from 1998 with aerial photographs from 1956. The analysis was supplemented by field surveys in 1999 and 2000. The study is part of a joint Chinese-European project with the aim of assessing the current state of the foreland vegetation, of gathering information on the regeneration potential and of suggesting procedures for a sustainable management. With 33 mm of annual precipitation, plants can only grow if they have access to groundwater, lakes or rivers. Most of the available water comes into the desert via rivers in the form of seasonal flooding events resulting from snow melt in the Kun Lun Mountains. This water is captured in canal systems and used for irrigation of arable fields. Among the eight herbaceous and woody vegetation types and the type of open sand without any plant life that were mapped in 2000 in the oasis foreland, only the latter, the oasis border between cultivated land and open Populus euphratica forests and Tamarix ramosissima-Phragmites australis riverbed vegetation could be clearly identified on the photographs from 1956. The comparison of the images revealed that the oasis increased in area between 1956 and 2000. Shifting sand was successfully combated near to the oasis borders but increased in extent at the outward border of the foreland vegetation. In contrast to expectations, the area covered with Populus trees was smaller in 1956 than today due to some new forests in the north of the oasis that have grown up since 1977. Subfossil wood and leaf remnants of Populus euphratica that were found in many places in the foreland must have originated from forests destroyed before 1956. In the last 50 years, the main Qira River has shifted its bed significantly northward and developed a new furcation with a large new bed in 1986. The natural river dynamics are not only an important factor in forming the oasis' landscape but also in providing the only possible regeneration sites for all occurring plant species. The conclusion of the study is that the oasis landscape has changed considerably in the last 50 years due to natural floodings and to vegetation degradation by human overexploitation. The trend towards decreasing width of the indigenous vegetation belt resulting from the advancing desert and the expansion of arable land is particularly alarming because a decrease in its protective function against shifting sand can be expected in the future.

Water relation characteristics of the desert legume Alhagi 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 that Alhagi 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 that Alhagi plants were not drought stressed and xylem sap flow measurements indicated that Alhagi plants used large amounts of water during the summer months. Flood irrigation had no influence on water relations in Alhagi probably because Alhagi plants produced only few fine roots in the upper soil layers. The data indicate that Alhagi 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 of Alhagi 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 and regions.

Water relations of Alhagi sparsifolia Shap. at the transition zone between oases and sandy desert were studied in the southern fringe of Taklamakan Desert. Results showed that A. sparsifolia maintained the positive turgor during the summer. The steady high predawn water potential (psi(P)) indicated A. sparsifolia had sufficient hydration and water supply in growing season. In July, water deficit caused by drought stress had no effect on the transpiration of A. sparsifolia. Therefore, drought stress is not a main factor affecting the survival of plants. The physiological adaptation to drought of A. sparsifolia was shown mainly at the leaf level by significant difference (DeltaII) and relative water content (RWC) between the osmotic pressure at full turgor and at turgor loss, by occurring of osmotic adjustment, by high percentage of dry mass-related water content ( WCsat), by RWC at turgor loss point ( RWCp) in stable level and low RWC of the saturated symplast (RWCsym). However, the morphological features of transpiring surface reduction and deep root system seem to be the main way for the plant to adapt to the extreme drought environment. Result also suggests that one time of irregular irrigation in summer will not be helpful to recover water status of A. sparsifolia in location where the water table is very low.