Werner Kofler

Effects of environmental conditions on onset of xylem growth in Pinus sylvestris under drought

We determined the influence of environmental factors (air and soil temperature, precipitation, photoperiod) on onset of xylem growth in Scots pine (Pinus sylvestris L.) within a dry inner Alpine valley (750 m a.s.l., Tyrol, Austria) by repeatedly sampling micro-cores throughout 2007-10 at two sites (xeric and dry-mesic) at the start of the growing season. Temperature sums were calculated in degree-days (DD) ≥5 °C from 1 January and 20 March, i.e., spring equinox, to account for photoperiodic control of release from winter dormancy. Threshold temperatures at which xylogenesis had a 0.5 probability of being active were calculated by logistic regression. Onset of xylem growth, which was not significantly different between the xeric and dry-mesic sites, ranged from mid-April in 2007 to early May in 2008. Among most study years, statistically significant differences (P<0.05) in onset of xylem growth were detected. Mean air temperature sums calculated from 1 January until onset of xylem growth were 230 ± 44 DD (mean ± standard deviation) at the xeric site and 205 ± 36 DD at the dry-mesic site. Temperature sums calculated from spring equinox until onset of xylem growth showed somewhat less variability during the 4-year study period, amounting to 144 ± 10 and 137 ± 12 DD at the xeric and dry-mesic sites, respectively. At both sites, xylem growth was active when daily minimum, mean and maximum air temperatures were 5.3, 10.1 and 16.2 °C, respectively. Soil temperature thresholds and DD until onset of xylem growth differed significantly between sites, indicating minor importance of root-zone temperature for onset of xylem growth. Although spring precipitation is known to limit radial growth in P. sylvestris exposed to a dry inner Alpine climate, the results of this study revealed that (i) a daily minimum air temperature threshold for onset of xylem growth in the range 5-6 °C exists and (ii) air temperature sum rather than precipitation or soil temperature triggers start of xylem growth. Based on these findings, we suggest that drought stress forces P. sylvestris to draw upon water reserves in the stem for enlargement of first tracheids after cambial resumption in spring.

Cell morphology, ultrastructure, and calcification pattern of Oocardium stratum , a peculiar lotic desmid

Cell morphology and ultrastructure of the desmid Oocardium stratum and its habitat conditions in two limestone-precipitating spring habitats in the Alps were studied. In spite of specific cell geometry, we found ultrastructural features (nucleus with nucleolus, Golgi apparatus, chloroplast structure, lipid bodies, cell wall texture) closely related to other desmids. The type of the mucilage pore apparatus perforating in high densities extended areas of the cell wall of Oocardium is of the Cosmarium type. Oocardium contrasts to Cosmarium by a peculiar bilateral cell geometry (lateral sphenoid shape) which is combined with a dislocated nucleus. Although the cell features of Oocardium did not differ between the two habitats, different calcification types (rhombohedral calcite versus fascicular-fibrous calcite) and calcification intensities were recorded. The spatial positioning and extension of the Oocardium niches differed considerably between the two springs in spite of high CO2 oversaturation at both sites.

EPILITHIC DIATOMS FROM RHEOCRENE SPRINGS IN THE EASTERN ALPS (VORARLBERG, AUSTRIA)

Benthic epilithic diatom assemblages were studied along with physico-chemical variables from 27 spring habitats situated in the western margin mountain area of the Eastern Alps (Vorarlberg, Austria) and were collected between the years 2003–2005. The sampling sites are situated in five of the seven aquatic ecoregions, as defined by the Austrian ecological quality assessments program of rivers. The sites occur over a wide altitudinal range (580 to 1800 m above sea level). The present study attempts to test the bioregional approach for the differentiation of rheocrene spring habitats, a spring type closely related to small running waters. Spring diatom assemblages primarily reflected the influence of the nutrient content, altitude, flow regime and mineral content but also are differentiated on a smaller scale by the main habitat peculiarities. The most frequent and abundant taxa were common elements of alpine lotic sites, the differentiation of assemblages appeared in the subdominant or even rare taxa (e.g. Gomphonema occultum, Encyonopsis microcephala, Delicata delicatula). Altogether the diatom composition comprised 197 taxa with >50% typical from lotic environments and 9% crenophilous taxa (having a strong affinity to springs, e.g. Delicata delicatula, Diatoma mesodori). Nitrate concentration and pH showed the greatest effect on the species composition but site-to-site characteristics also depended on the availability of substrates (e.g. wet rocks) and/or irregular discharge. Moisture indicator values, taking into consideration the distribution of taxa linked to water level fluctuations, were given for 57% of the species found (112 taxa). Fifteen percent of these taxa were generally occurring on wet and moist or temporarily dry places (springs—Navicula stromii, Rhopalodia gibba, moss habitats—Encyonopsis falaisensis, Pinnularia borealis) and another 4% nearly exclusively outside water bodies (e.g. Diadesmis gallica var. perpusilld). The latter group indicated either non-permanent sites or springs emerging from unstable ground. The number of threatened taxa (25%) according to the German Red List for diatoms was less than what was expected when compared to former studies based on Southern Alpine springs (50%) or Central Germany (31%). This reduction in red list species went along with higher nitrate concentrations, irregular discharge and minor human impact, since only 50% of the sites were still undisturbed.

Neolithic to Bronze Age (4850–3450 cal. BP) fire management of the Alpine Lower Engadine landscape (Switzerland) to establish pastures and cereal fields

Agro-pastoral activities in the past act as environmental legacy and have shaped the current cultural landscape in the European Alps. This study reports about prehistoric fire incidents and their impact on the flora and vegetation near the village of Ardez in the Lower Engadine Valley (Switzerland) since the Late Neolithic Period. Pollen, charcoal particles and non-pollen palynomorphs preserved in the Saglias and Cutüra peat bog stratigraphies were quantified and the results compared with the regional archaeological evidence. Anthropogenic deforestation using fire started around 4850 cal. BP at Saglias and aimed at establishing first cultivated crop fields (e.g. cereals) and small pastoral areas as implied by the positive correlation coefficients between charcoal particles and cultural and pastoral pollen indicators, as well as spores of coprophilous fungi. Pressure on the natural environment by humans and livestock continued until 3650 cal. BP and was followed by reforestation processes until 3400 cal. BP because of climatic deterioration. Thereafter, a new, continuous cultivation/pastoral phase was recorded for the Middle to Late Bronze Age (3400–2800 cal. BP). After rather minor human impact during the Iron Age and Roman Period, intensive agriculture was recorded for the Medieval Period. The area around Ardez was used for crop cultivation from about 1000 cal. BP until the start of the ‘Little Ice Age’ (600 cal. BP). Despite a land-use reorganisation, the following gradual decrease in agricultural activities led to the extant mixture of a cultivated, grazed and forested landscape in the Lower Engadine. In addition, this study demonstrates the excellent value of the fungus Gelasinospora as a highly local marker of past and today’s fire incidents, as well as of the use of micro-charcoals from pollen slides and macro-charcoals (>150 µm) from pollen sample residues for the reconstruction of short- and long-term fire histories.

Tree water status and growth of saplings and mature Norway spruce (Picea abies) at a dry distribution limit

We evaluated the size effect on stem water status and growth in Norway spruce (Picea abies (L.) Karst.) occurring at the edge of its natural range in a dry inner Alpine environment (750 m asl, Tyrol, Austria). Intra-annual dynamics of stem water deficit (ΔW), maximum daily shrinkage (MDS), and radial growth (RG) were compared among saplings (stem diameter/height: 2.2 cm/93 cm; n = 7) and mature adult trees (25 cm/12.7 m; n = 6) during 2014. ΔW, MDS, and RG were extracted from stem diameter variations, which were continuously recorded by automatic dendrometers and the influence of environmental drivers was evaluated by applying moving correlation analysis (MCA). Additionally, we used Morlet wavelet analysis to assess the differences in cyclic radial stem variations between saplings and mature trees. Results indicate that saplings and mature trees were experiencing water limitation throughout the growing season. However, saplings exhibited a more strained stem water status and higher sensitivity to environmental conditions than mature trees. Hence, the significantly lower radial increments in saplings (0.16 ± 0.03 mm) compared to mature trees (0.54 ± 0.14 mm) is related to more constrained water status in the former, affecting the rate and duration of RG. The wavelet analysis consistently revealed more distinct diurnal stem variations in saplings compared to mature trees. Intra-annual RG was most closely related to climate variables that influence transpiration, i.e., vapor pressure deficit, relative air humidity, and air temperature. MCA, however, showed pronounced instability of climate–growth relationships, which masked missing temporal or significant correlations when the entire study period (April–October) was considered. We conclude that an increase in evaporative demand will impair regeneration and long-term stability of drought-prone inner Alpine Norway spruce forests.

Evidence for Early Human Presence at High Altitude in the Ötztal Alps (Austria/Italy)

The present article reports on the results and interpretation of a total of 235 radiocarbon dates from Alpine sites in the Otztal region. Out of these, 88 age determinations were performed on equipment and artifacts associated with the Neolithic Iceman (discovered in 1991), and on a variety of plant and animal specimens collected at his discovery site. Since the material was dispersed over a larger area, 14 C dates were important to establish the deposition time of the respective samples. About half of the samples fall into the time period where the Iceman lived, documenting synchronous deposition, whereas the others spread out over several thousand years before and after his lifetime. The other set of samples (147) were collected along the Otztal Valley to the north, with a few samples collected also south of the Alpine watershed. The samples were mainly from soil profiles and peat bogs above the present-day timberline. Overall, the analysis of the data indicates human presence in these high regions of the Alps throughout the Holocene. While the older botanical and archaeological finds indicate activities of hunting and foraging, the younger ones (after ~5000 BC) point to an intensification of pasturing. This suggests that early human activity was concentrated at altitudes where natural pastures were found, which were probably more favorable than locations at the bottom of the valleys where flooding and other hazards existed. Early users may have come from south of the water divide spreading into the northern regions, particularly during the summer season. It is possible that the Iceman perished at one of his crossings over the probably well-known high-altitude mountain pass due to reasons not yet fully resolved. DOI: 10.2458/56.17919

Planktonic needle-shaped Nitzschia species from Lake Victoria, Africa, revisited

Thin needle-shaped species of Nitzschia Hassall were found to form a key component of the diatom plankton in the deep Kenyan waters of Lake Victoria. An attempt was made to classify the six most common Nitzschia species of this growth form type on the basis of morphology, although they exhibit only small differences. Nitzschia lacustris Hustedt, previously described from Lake Victoria, was confirmed and recorded as an essential element of the phytoplankton. Three species were close to N. bacata Hustedt, N. graciliformis Lange-Bertalot & Simonsen and N. nyassensis O. Müller, but could not be definitively identified due to specific morphological deviations from the original descriptions, such as the overall size range, striation density and valve outline. Nitzschia bacata and N. nyassensis have repeatedly been recorded from the East African Great Lakes. Two more taxa are proposed as new to science, N. kavirondoensis sp. nov. and N. rusingae sp. nov., since neither could be matched to descriptions of the existing nitzschielloid taxa around N. acicularis (Kützing) W. Smith. Their morphological features were documented by light and scanning electron microscopy and differentiated from similar taxa recorded from Africa and other parts of the world.

Siderocelis irregularis (Chlorophyta, Trebouxiophyceae) in Lake Tanganyika (Africa)*

Siderocelis irregularis Hindák, representing a genus Siderocelis (Naumann) Fott that is known from European temperate waters, was identified as a common phytoplankter in Lake Tanganyika. It was found aposymbiotic as well as ingested (possibly endosymbiotic) in lake heterotrophs, mainly Strombidium sp. and Vorticella spp. The morphology and ultrastructure of the species, studied with LM, SEM and TEM, are described with emphasis on the structure of the cell wall and the pyrenoid.

Мicroscopic investigations (LM, TEM and SEM) and identification of Chlorella isolate R-06/2 from extreme habitat in Bulgaria with a strong biological activity and resistance to environmental stress factors

An extremophilic Chlorella strain R-06/2, isolated from a geothermal spring (+42 °C) in the region of Rupite village (SW Bulgaria), was investigated for species identification. This was done by observation of the cell morphology, reproduction and ultrastructure by light microscopy, scanning electron microscopy and transmission electron microscopy, and by investigation of the cell-wall chemistry. The pyrenoid ultrastructure with a double-layered thylakoid traversing the matrix, the shape of the starch envelope, as well as the cell wall, composed of glucosamine and developed around young autospores, were the features that allowed us to classify the thermophilic strain Chlorella R-06/2 as Chlorella vulgaris Beijerinck 1890.

Robustness of xylem properties in conifers: analyses of tracheid and pit dimensions along elevational transects

In alpine regions, tree hydraulics are limited by low temperatures that restrict xylem growth and induce winter frost drought and freezing stress. While several studies have dealt with functional limitations, data on elevational changes in functionally relevant xylem anatomical parameters are still scarce. In wood cores of Pinus cembra L. and Picea abies (L.) Karst. trunks, harvested along five elevational transects, xylem anatomical parameters (tracheid hydraulic diameter dh, wall reinforcement (t/b)2), pit dimensions (pit aperture Da, pit membrane Dm and torus Dt diameters) and respective functional indices (torus overlap O, margo flexibility) were measured. In both species, tracheid diameters decreased and (t/b)2 increased with increasing elevation, while pit dimensions and functional indices remained rather constant (P. cembra: Dt 10.3 ± 0.2 μm, O 0.477 ± 0.005; P. abies: Dt 9.30 ± 0.18 μm, O 0.492 ± 0.005). However, dh increased with tree height following a power trajectory with an exponent of 0.21, and also pit dimensions increased with tree height (exponents: Dm 0.18; Dt 0.14; Da 0.11). Observed elevational trends in xylem structures were predominantly determined by changes in tree size. Tree height-related changes in anatomical traits showed a remarkable robustness, regardless of the distributional ranges of study species. Despite increasing stress intensities towards the timberline, no adjustment in hydraulic safety at the pit level was observed.