1,721,117 research outputs found
Air humidity as an ecological factor for woodland herbs: leaf water status, nutrient uptake, leaf anatomy, and productivity of eight species grown at low or high vpd levels
No full textEcologists have widely neglected the long term impact of vpd (the water vapor saturation deficit of the air) on plant growth and development. This paper tests the hypothesis that the prevailing vpd level during growth has a significant influence on the ecology of temperate woodland herbs, independently of soil moisture status. Eight herbaceous species (Scrophularia nodosa, Digitalis purpurea, Campanula trachelium, Rumex sanguineus, Geum urbanum, Hieracium sylvaticum, Hordelymus europaeus, Brachypodium sylvaticum) were grown in climate chambers at four different saturation deficits (vpd = 120,580,930 or 1210 Pa) with unlimited water supply in solution cultures in order to experimentally analyse long-term effects of vpd on shoot water relations, plant morphology and plant growth rate. In their natural forest floor environment these species are exposed to vpd levels of 200 to 600 Pa on summer days. After 50 to 90 days of cultivation I compared the four vpd treatments with respect to dry matter production, leaf anatomy, leaf conductance, transpiration rate, bulk leaf water potential (V,), leaf water content (0,), and shoot nutrient concentrations. Productivity was significantly higher at 120 than at 580, 930 or 12 10 Pa in seven of eight species. Plants grown at low vpd had larger leaves and leaf epidermal cells, and a lower stomatal frequency than plants of high-vpd treatments which indicates a stimulation of leaf expansion by high air humidities. Low saturation deficits also affected leaf anatomy (less compact leaf mesophyll with larger fractional air space) but did not alter mesophyll cell dimensions. Leaf water potential and leaf water content were more favorable at 120 Pa than at higher vpd levels in all eight species although a clear dependence of leaf water status (psi(1) and theta(1)) on transpiration rate did not exist. Shoot nutrient concentrations generally were lower at low than high vpd which reflects a nutrient dilution effect caused by an increased carbon assimilation of the low vpd plants. In contrast, no correlation was found between transpiration rate and shoot concentrations of Ca or other mineral nutrients. I conclude that vpd acts as a soil water-independent growth-controlling factor for hygromorphic woodland herbs. Environments with a vpd of 100 to 500 Pa improve leaf water status and stimulate leaf expansion of these species which leads to enhanced growth. Other growth-relevant parameters (leaf conductance, transpiration rate and nutrient uptake), which were also affected by vpd, had only a minor or no influence on productivity
Effects of Norway spruce monocultures on the structure of bird communities in a submontane-montane forested landscape of Central Germany
No full textThe present study investigates the effects of Norway spruce plantations on the structure of breeding bird communities in a former beech dominated forested landscape in submontane to montane elevation in Northern Hesse, Germany. Three plots of 16.5 - 19.8 ha were established in each of the following settings: (i) structurally-rich spruce stands with a mosaic of young and old patches, (ii) homogeneously structured mature spruce stands (,monocultures, and (iii) old-growth beech stands which may resemble the potential natural vegetation of the region. Based on a survey of bird territories in summer 1997, 37 species were identified in total as breeding birds in the 9 plots; 17 species occurred in both spruce and beech forests, 6 species were restricted to spruce stands and 12 to beech stands only. Strucrurally-rich spruce stands showed a substantially higher number of bird species per plot area (19 on average) and a higher density of bird territories (30.4 per 10 ha) than either spruce monocultures (11 species, 23.8 territories per lip ha) or beech stands (17 and 21.2, respectively). The breeding bird community of spruce monocultures showed a low species evenness and lacked species that nest in hollows or near the ground. In general, distinct differences exist in the species composition of spruce and beech stands. A number of apical deciduous forest birds are missing in coniferous stands. The pygmy owl (Glaucidium passerinum) mac serve as a good indicator of species-rich bird communities in spruce-dominated landscapes as this species depends on high vertical and horizontal forest heterogeneity. It is concluded that spruce plantations may represent valuable habitats with respect to biodiversity conservation in temperate forests if forest management maintains a small-scale mosaic consisting of patches of different age
Genotypic variation in drought response of silver birch (Betula pendula): leaf water status and carbon gain
No full textTo assess genotypic variation in drought response of silver birch (Betula pendula Roth), we studied the plasticity of 16 physiological traits in response to a 12-14-week summer drought imposed on four clones in two consecutive years. In a common garden experiment, 1-year-old clonal trees from regions with low (550 mm year(-1)) to high rainfall (1270 mm year) were grown in 45-1 pots, and leaf gas exchange parameters, leaf water potentials, leaf osmotic potentials and leaf carbon isotope signatures were repeatedly measured. There were no clonal differences in leaf water potential, but stomatal conductance (g(s)), net photosynthesis at ambient carbon dioxide concentration, photosynthetic water-use efficiency, leaf carbon isotope composition (delta(13) C) and leaf osmotic potentials at saturation (Pi(0)) and at incipient plasmolysis (Pi(p)) were markedly influenced by genotype, especially g(s) and osmotic adjustment. Genotypes of low-rainfall origin displayed larger osmotic adjustment than genotypes of high-rainfall origin, although their Pi(0) and Pi(p) values were similar or higher with ample water supply. Genotypes of low-rainfall origin had higher g(s) than genotypes of high-rainfall origin under both ample and limited water supply, indicating a higher water consumption that might increase competitiveness in drought-prone habitats. Although most parameters tested were significantly influenced by genotype and treatment, the genotype x treatment interactions were not significant. The genotypes differed in plasticity of the tested parameters and in their apparent adaptation to drought; however, among genotypes, physiological plasticity and drought adaptation were not related to each other. Reduction of g(s) was the first and most plastic response to drought in all genotypes, and allowed the maintenance of high predawn leaf water potentials during the drought. None of the clones exhibited non-stomatal limitation of photosynthesis. Leaf g(s) photosynthetic capacity, magnitude of osmotic adjustment and VC were all markedly lower in 2000 than in 1999, indicating root limitation in the containers in the second year
Vegetation structure at the breeding sites of the partridge (Perdix perdix L.) in Central Europe and its possible importance for population density
No full textThis paper analyses the abundance of breeding pairs and the location of nesting sites of partridges as related to vegetation structure in the nest surroundings in two areas with very different partridge densities and arable landscape patterns (Central Germany and Eastern Poland). Study objective was to identify underlying causes of the more than 100 fold difference in population density of this species in these two areas of Central Europe. Our results suggests that the very limited availability of appropriate nesting habitats with an open canopy structure and low leaf area index is one of the key factors being responsible for the very low recent population density, and the past rapid decline, of partridge in the modern agricultural landscape of western Central Europe
In situ measurement of fine root water absorption in three temperate tree species - Temporal variability and control by soil and atmospheric factors
No full textMiniature heat balance-sap flow gauges were used to measure water flows in small-diameter roots (3-4 mm) in the undisturbed soil of a mature beech-oak-spruce mixed stand. By relating sap flow to the surface area of all branch fine roots distal to the gauge, we were able to calculate real time water uptake rates per root surface area (J(S)) for individual fine root systems of 0.5-1.0m in length. Study aims were (i) to quantify root water uptake of mature trees under field conditions with respect to average rates, and diurnal and seasonal changes of J(S), and (ii) to investigate the relationship between uptake and soil moisture theta, atmospheric saturation deficit D, and radiation 1. On most days, water uptake followed the diurnal course of D with a midday peak and low night flow. Neighbouring roots of the same species differed up to 10-fold in their daily totals of J(S) ( < 100-2000 g m(-2) d(-1)) indicating a large spatial heterogeneity in uptake. Beech, oak and spruce roots revealed different seasonal patterns of water uptake although they were extracting water from the same soil volume. Multiple regression analyses on the influence of D, I and theta on root water uptake showed that D was the single most influential environmental factor in beech and oak (variable selection in 77% and 79% of the investigated roots), whereas D was less important in spruce roots (50% variable selection). A comparison of root water uptake with synchronous leaf transpiration (porometer data) indicated that average water fluxes per surface area in the beech and oak trees were about 2.5 and 5.5 times smaller on the uptake side (roots) than on the loss side (leaves) given that all branch roots < 2 mm were equally participating in uptake. Beech fine roots showed maximal uptake rates on mid-summer days in the range of 48-205 g m-2 h(-1) (i.e. 0.7-3.2 mmol m(-2) s(-1)), oak of 12-160 g m(-2) h(-1) (0.2-2.5 mmol m(-2) s(-1)). transpiration rates ranged from 3 to 5 and from 5 to 6 mmol m(-2) s(-1) for sun canopy leaves of beech and oak, respectively. We conclude that instantaneous rates of root water uptake in beech, oak and spruce trees are above all controlled by atmospheric factors. The effects of different root conductivities, soil moisture, and soil hydraulic properties become increasingly important if time spans longer than a week are considered. (c) 2005 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved
Vegetation structure at the breeding sites of the partridge (Perdix perdix L.) in Central Europe and its possible importance for population density
No full textThis paper analyses the abundance of breeding pairs and the location of nesting sites of partridges as related to vegetation structure in the nest surroundings in two areas with very different partridge densities and arable landscape patterns (Central Germany and Eastern Poland). Study objective was to identify underlying causes of the more than 100 fold difference in population density of this species in these two areas of Central Europe. Our results suggests that the very limited availability of appropriate nesting habitats with an open canopy structure and low leaf area index is one of the key factors being responsible for the very low recent population density, and the past rapid decline, of partridge in the modern agricultural landscape of western Central Europe
A comparison of four different fine root production estimates with ecosystem carbon balance data in a Fagus-Quercus mixed forest (vol 239, pg 237, 2002)
No full textA comparison of four different fine root production estimates with ecosystem carbon balance data in a Fagus-Quercus mixed forest
No full textThe controversy on how to measure fine root production of forests (P) most accurately continues. We applied four different approaches to determine annual rates of P in an old-growth temperate Fagus sylvatica-Quercus petraea stand: sequential soil coring with minimum-maximum calculation, sequential coring with compartmental flow calculation, the ingrowth core method, and a recently developed root chamber method for measuring the growth of individual fine roots in situ. The results of the four destructive approaches differed by an order of magnitude and, thus, are likely to introduce large errors in estimating P. The highest annual rates of P were obtained from the sequential coring approach with compartmental flow calculation, intermediate rates by sequential coring with minimum-maximum calculation, and low ones by both the root growth chamber and ingrowth core approaches. A carbon budget for the stand was set up based on a model of annual net carbon gain by the canopy and measurements on carbon sink strength (annual leaf, branch and stem growth). The budget implied that a maximum of 27% of the net carbon gain was available for allocation to fine root growth. When compared to the carbon budget data, the sequential coring/compartmental flow approach overestimated annual fine root production substantially; whereas the ingrowth core and root growth chamber approaches grossly underestimated P rates. With an overestimation of about 25% the sequential coring/minimum-maximum approach demonstrated the best agreement with the carbon budget data. It is concluded that the most reliable estimate of P in this temperate forest will be obtained by applying the sequential coring/minimum-maximum approach, conducted with a large number of replicate samples taken on a few dates per season, in conjunction with direct root growth observation by minirhizotrons
Genotypic variation in drought response of silver birch (Betula pendula): leaf water status and carbon gain
No full textTo assess genotypic variation in drought response of silver birch (Betula pendula Roth), we studied the plasticity of 16 physiological traits in response to a 12-14-week summer drought imposed on four clones in two consecutive years. In a common garden experiment, 1-year-old clonal trees from regions with low (550 mm year(-1)) to high rainfall (1270 mm year) were grown in 45-1 pots, and leaf gas exchange parameters, leaf water potentials, leaf osmotic potentials and leaf carbon isotope signatures were repeatedly measured. There were no clonal differences in leaf water potential, but stomatal conductance (g(s)), net photosynthesis at ambient carbon dioxide concentration, photosynthetic water-use efficiency, leaf carbon isotope composition (delta(13) C) and leaf osmotic potentials at saturation (Pi(0)) and at incipient plasmolysis (Pi(p)) were markedly influenced by genotype, especially g(s) and osmotic adjustment. Genotypes of low-rainfall origin displayed larger osmotic adjustment than genotypes of high-rainfall origin, although their Pi(0) and Pi(p) values were similar or higher with ample water supply. Genotypes of low-rainfall origin had higher g(s) than genotypes of high-rainfall origin under both ample and limited water supply, indicating a higher water consumption that might increase competitiveness in drought-prone habitats. Although most parameters tested were significantly influenced by genotype and treatment, the genotype x treatment interactions were not significant. The genotypes differed in plasticity of the tested parameters and in their apparent adaptation to drought; however, among genotypes, physiological plasticity and drought adaptation were not related to each other. Reduction of g(s) was the first and most plastic response to drought in all genotypes, and allowed the maintenance of high predawn leaf water potentials during the drought. None of the clones exhibited non-stomatal limitation of photosynthesis. Leaf g(s) photosynthetic capacity, magnitude of osmotic adjustment and VC were all markedly lower in 2000 than in 1999, indicating root limitation in the containers in the second year
Genotypic variation in drought response of silver birch (Betula pendula Roth): leaf and root morphology and carbon partitioning
No full textThis study investigates the drought response of four genotypes of Betula pendula with a focus on leaf and root morphological traits, leaf phenology and carbon partitioning between shoot and root. Potted one-year-old clonal plants of four genotypes from regions with low to high annual rainfall (550-1270 mm year(-1)) were subjected to drought periods of 12-14 weeks in two subsequent years. Well-watered control plants of the four genotypes differed significantly with respect to total leaf area per plant (LA) and specific leaf area (SLA), whereas differences in total fine root surface area (RA), root specific area (SRA), and the fine root:leaf mass ratio (FR:LM) were not significant. Highest LA and SLA were found in the clone originating from the driest environment. In complementary physiological investigations this clone was found to have the highest water use as well which was interpreted as competitive superiority in terms of water consumption. Drought resulted in an increase in SLA in all genotypes, and a decrease in LA. Leaf area reduction was more pronounced in the genotypes from high than in those from low rainfall origin. The ratio of total root to leaf surfaces remained more or less constant after drought application despite an increase in FR:LM. This is explained by a decrease in SRA resulting from a reduced abundance of very small fine rootlets (diameter < 0.2 mm) in the drought-treated plants. The loss in total root surface area due to a reduction in finest root mass was compensated for by a relative increase in total root dry mass per plant. Comparison of results from the first and second drought period indicated a marked influence of timing of drought, root system size, and putative root limitation on plant drought response. We conclude that leaf and root morphology, the total leaf and root surfaces, and the morphological response to drought in birch are to a large extent under genetic control
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