187,136 research outputs found
N, P and K limitation of fine root growth along an elevation transect in tropical mountain forests
No full textIt is generally assumed that tree growth in tropical low-elevation forests is primarily limited by phosphorus while nitrogen limitation is more prominent in tropical montane forests where temperature is lower and the soils are poorly developed. We tested this hypothesis in mountain rainforests of South Ecuador by investigating the growth response of tree fine roots to N, P and K fertilization in ingrowth cores exposed at 1050 m (pre-montane) and 3060 m (upper montane) elevation. Root growth into unfertilized ingrowth cores (control treatment) was about 10 times slower at 3060 m than at 1050 m. At 1050 m, root growth was stimulated not only by P, but also by N and K. In contrast, N was the only element to promote root growth at 3060 m. The N concentration in fine root biomass dropped to nearly a third between 1050 and 3060 m, those of P, K, Ca and Mg decreased as well, but to a lesser degree. According to a (15)NO(3)(15)NH(4) tracer study along the slope, tree fine roots accumulated nitrate and ammonium in root biomass at similar rates between 1050 and 3060 m, despite lower temperatures higher upslope. We conclude that the nature of nutrient limitation of tree fine root growth changes with elevation from an apparent co-limitation by P together with N and K at 1050 m to predominant N limitation at 3060 m, which is also reflected by low foliar N concentrations. Increasing N limitation may have caused the high fine root biomass and root/shoot ratio in the high elevation forest, while the capability of the roots to acquire mineral N apparently was not affected by lower temperatures at high elevations. (C) 2010 Elsevier Masson SAS. All rights reserved
A 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
Nutrient dynamics along a precipitation gradient in European beech forests
No full textPrecipitation as a key determinant of forest productivity influences forest ecosystems also indirectly through alteration of the nutrient status of the soil, but this interaction is not well understood. Along a steep precipitation gradient (from 970 to 520 mm yr-1 over 150 km distance), we studied the consequences of reduced precipitation for the soil and biomass nutrient pools and dynamics in 14 mature European beech (Fagus sylvatica L.) forests on uniform geological substrate. We tested the hypotheses that lowered summer precipitation (1) is associated with less acid soils and a reduced accumulation of organic matter on the forest floor, and (2) reduces nutrient supply from the soil and leads to decreasing foliar and root nutrient concentrations. Soil acidity, the amount of forest floor organic matter, and the associated organic matter N and P pools decreased to about a half from wet to dry sites; the C/P and N/P ratios, but not the C/N ratio, of forest floor organic matter decreased. Net N mineralization (and nitrification) rate and the available P and K pools in the mineral soil did not change with decreasing precipitation. Foliar P and K concentrations (beech sun leaves) increased while N remained constant, resulting in decreasing foliar N/P and N/K ratios. N resorption efficiency increased toward the dry sites. We conclude that a reduction in summer rainfall significantly reduces the soil C, N and P pools but does not result in decreasing foliar N and P contents in beech. However, more effective tree-internal N cycling and the decreasing foliar N/P ratio towards the dry stands indicate that tree growth may increasingly be limited by N and not by P with decreasing precipitation.Open-Access-Publikationsfonds 201
Nutrient dynamics along a precipitation gradient in European beech forests
No full textPrecipitation as a key determinant of forest productivity influences forest ecosystems also indirectly through alteration of the nutrient status of the soil, but this interaction is not well understood. Along a steep precipitation gradient, we studied the consequences of reduced precipitation for the soil and biomass nutrient pools and dynamics in 14 mature European beech (Fagus sylvatica L.) forests on Triassic sandstone. We tested the hypotheses that lowered summer precipitation (1) is associated with less acid soils and (2) a reduced accumulation of organic matter on the forest floor, and (3) reduces nutrient supply from the soil and leads to decreasing foliar and root nutrient concentrations. Soil acidity, the amount of forest floor organic matter, and the associated organic matter N and P pools decreased to about a half from wet to dry sites; the C/P and N/P ratios, but not the C/N ratio, of forest floor organic matter were reduced as well. Net N mineralization and P and K pools in the mineral soil did not change with decreasing precipitation. Foliar P and K concentrations (beech sun leaves) increased while N remained constant, resulting in decreasing foliar N/P and N/K ratios. Estimated N resorption efficiency increased toward the dry sites. We conclude that a reduction in summer rainfall significantly reduces the soil C, N and P pools but does not result in decreasing foliar N and P contents in beech. However, the decreasing foliar N/P ratios towards the dry stands indicate that the importance of P limitation for tree growth declines with decreasing precipitation
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
Vulnerability analysis of the rare and endangered woodland fern <i>Polystichum braunii</i> in Germany: three possible causes of population decline
No full textBackground: Various rare and endangered temperate ferns are being threatened by their recent population decline, but there is limited understanding of the causes behind it. Aims: This study attempted to identify the possible drivers of regional population decline and extinction in the globally distributed woodland fern Polystichum braunii. Methods: A comparison was undertaken of the climatic, edaphic and phytosociological characteristics of sites with increasing, decreasing or recently extinct populations in Germany. Results: A significantly higher frequency of episodes of low relative air humidity (<60%) was found at sites with decreasing or extinct populations compared to habitats with population increases. Sites with decreasing or extinct populations were also characterised as having less summer precipitation (<500 mm year−1) and a shorter duration of snow cover (<110 days year−1) than sites with increasing populations. The latter had significantly higher moss cover (56% of the forest floor), but less cover by a tree litter layer (23%) compared to decreasing (36% and 38%) or recently extinct populations (22% and 52%). All increasing populations were located in intact Tilia – Acer ravine forests, while those suffering population decline were mostly located in Fagus-dominated forests. Conclusions: It was concluded that the probable causes of the recent decline in German P. braunii populations are reduced air humidity levels, decreasing snow duration or a shift from moss-covered to tree litter-covered forest floors due to climate warming or altered forest management
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Performance of seedlings of a shade-tolerant tropical tree species after moderate addition of N and P
No full textNitrogen deposition to tropical forests is predicted to increase in future in many regions due to agricultural intensification. We conducted a seedling transplantation experiment in a tropical premontane forest in Ecuador with a locally abundant late-successional tree species (Pouteria torta, Sapotaceae) aimed at detecting species-specific responses to moderate N and P addition and to understand how increasing nutrient availability will affect regeneration. From locally collected seeds, 320 seedlings were produced and transplanted to the plots of the Ecuadorian Nutrient Manipulation Experiment (NUMEX) with three treatments (moderate N addition: 50 kg N ha-1 yr-1, moderate P addition: 10 kg P ha-1 yr-1 and combined N and P addition) and a control (80 plants per treatment). After 12 months, mortality, relative growth rate, leaf nutrient content and leaf herbivory rate were measured.N and NP addition significantly increased the mortality rate (70 % vs. 54 % in the control). However, N and P addition also increased the diameter growth rate of the surviving seedlings. N and P addition did not alter foliar nutrient concentrations and leaf N:P ratio, but N addition decreased the leaf C:N ratio and increased SLA. P addition (but not N addition) resulted in higher leaf area loss to herbivore consumption and also shifted carbon allocation to root growth. This fertilization experiment with a common rainforest tree species conducted in old-growth forest shows that already moderate doses of added N and P are affecting seedling performance which most likely will have consequences for the competitive strength in the understory and the recruitment success of P. torta. Simultaneous increases in growth, herbivory and mortality rates make it difficult to assess the species’ overall performance and predict how a future increase in nutrient deposition will alter the abundance of this species in the Andean tropical montane forests
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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