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852.
The ratio between (Ca +K +Mg) and Al in nutrientsolution has been suggested as a predictive tool forestimating tree growth disturbance. However, the ratiois unspecific in the sense that it is based on severalelements which are all essential for plant growth;each of these may be growth-limiting. Furthermore,aluminium retards growth at higher concentrations. Itis therefore difficult to give causal and objectivebiological explanations for possible growthdisturbances. The importance of the proportion ofbase-cations to N, at a fixed base-cation/Al ratio, isevaluated with regard to growth of Picea abies.The uptake of elements was found to be selective;nutrients were taken up while most Al remained insolution. Biomass partitioning to the roots increasedafter aluminium addition with low proportions of basecations to nitrogen. We conclude that the low growthrates depend on nutrient limitation in thesetreatments. Low growth rates in the high proportionexperiments may be explained by high internal Alconcentrations. The results strongly suggest thatgrowth rate is not correlated with the ratio in therooting medium and question the validity of usingratios as predictive tools for estimating forestdamage. We suggest that growth limitation of Picea abies in the field may depend on lowproportions of base cations to nitrate. It istherefore important to know the nutritional status ofthe plant material in relation to the growth potentialand environmental limitation to be able to predict andestimate forest damage. 相似文献
853.
Nyberg Lars Lundström Ulla Söderberg Ulf Danielsson Rolf van Hees Patrick 《Water, Air, & Soil Pollution: Focus》2001,1(1-2):241-263
In 1994, a large survey of soil chemistry was undertaken in thecounty of Värmland in central Sweden (Lundström et al., 1998).The southern part of the county was affected by soilacidification whereas there were no such indications in thenorthern part. To investigate the influence of soil chemistryon the trees at the specific sites, the survey was continued byan analysis of needle chemistry (Norway spruce) which wasundertaken at 150 of the 180 sites, and of tree growth at 65 ofthe 180 sites. Growth was expressed as a ratio between expectedgrowth, estimated with a national, empirical growth model, andthe growth observed in the field. In statistical analyses,using rank correlation, PCA and PLS, there were only weakindications of an influence of soil chemistry on needlechemistry and on tree growth. A moderate correlation betweennitrogen and sulphur in needles was found, which wasinterpreted as an effect of deposition and of processes in thetree canopy. No obvious regional pattern of the growth ratiowas found, in contrast to the clear pattern of soilacidification. The statistical analysis could not with anycertainty point out any of the soil chemistry variables asespecially important for the tree growth ratio. 相似文献
854.
Erisman J. W. Hensen A. Fowler D. Flechard C. R. Grüner A. Spindler G. Duyzer J. H. Weststrate H. Römer F. Vonk A. W. Jaarsveld H. v. 《Water, Air, & Soil Pollution: Focus》2001,1(5-6):17-27
Between 1993 and 1999 two EU funded projects wereexecuted aimed at (i) the development of drydeposition monitoring methods for core sites andlarge scale application, (ii) the installation andrunning of three core sites in Europe and (iii) the improvement and validation of models used forregional application. This article provides anoverview of the development of depositionmonitoring stations and the main results of thethree core sites, which were operated between1995 and 1998. Furthermore, the results of thedevelopment of a low cost monitoring system arepresented. Continuous measurements were made ofboth wet and dry deposition of sulphur andnitrogen components and base cations. The 4 yearsof data show a decrease in sulphur loads and notrend for the other components. It is shown thatthe surface affinities for sulphur depositionalso changed during the years, underpinning theneed for dry deposition monitoring. A conditionaltime average gradient system was successfullydeveloped and tested and provides a good meansfor low cost monitoring of dry deposition fluxes.The costs can be reduced by a factor of 3–4 without losing the accuracy of the annual average gas fluxes. 相似文献
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Jörgen I. Johnsson Karin Kjällman-Eriksson 《Behavioral ecology and sociobiology》2008,62(10):1613-1620
Little is known about how cryptic colouration influences prey search in near-surface aquatic habitats, although such knowledge
is critical for understanding the adaptive value of colour crypsis as well as the perceptive constraints influencing foraging
behaviour in these environments. This study had two main aims: (1) to investigate how background colour matching by prey affects
foraging efficiency by brown trout parr and (2) to investigate how foraging ability on cryptic and conspicuous prey is affected
by fish size at age (reflecting dominance). We addressed these questions by training wild brown trout parr to forage individually
on live brown-coloured maggots on a cryptic (brown) or conspicuous (green) background. A separate experiment confirmed the
absence of trout preference for brown or green substrate. The results show that prey background colour matching increases
search time in brown trout. Search time generally decreased by learning, but conspicuous prey remained an easier prey to find
throughout the six training trials. Thus, perceptive constraints appear to limit search efficiency for cryptic prey, suggesting
that cryptic colouration can confer survival benefits to prey in natural environments. Smaller fish generally found conspicuous
prey faster than larger individuals, whereas search time for cryptic prey was not influenced by body size. This suggests that
smaller individuals compensate for inferior competitive ability by increasing foraging activity rather than improving cognitive
ability. The technique of varying cognitive demands in behavioural tasks could be used more in future studies aimed at distinguishing
motivational effects from cognitive explanations for variation in behavioural performance. 相似文献
859.
Social information use is a process across time, space, and ecology, reaching heterospecifics 总被引:2,自引:0,他引:2
Decision making can be facilitated by observing other individuals faced with the same or similar problem, and recent research suggests that this social information use is a widespread phenomenon. Implications of this are diverse and profound: for example, social information use may trigger cultural evolution, affect distribution and dispersal of populations, and involve intriguing cognitive traits. We emphasize here that social information use is a process consisting of the scenes of (1) event, (2) observation, (3) decision, and (4) consequence, where the initial event is a scene in such a process of another individual. This helps to construct a sound conceptual framework for measuring and studying social information use. Importantly, the potential value of social information is affected by the distance in time, space, and ecology between the initial observation and eventual consequence of a decision. Because negative interactions between individuals (such as direct and apparent competition) also depend on the distance between individuals along these dimensions, the potential value of information and the negative interactions may form a trade-off situation. Optimal solutions to this trade-off can result in adaptively extended social information use, where using information gathered some time ago, some distance away, and from ecologically different individuals is preferred. Conceivably, using information gathered from a heterospecific individual might often be optimal. Many recent studies demonstrate that social information use does occur between species, and the first review of published cases is provided here. Such interaction between species, especially in habitat selection, has important consequences for community ecology and conservation. Adaptively extended social information use may also be an important evolutionary force in guild formation. Complex coevolutionary patterns may result depending on the effect of information use on the provider of information. 相似文献
860.
Ulrike Schulte-Oehlmann Jörg Oehlmann Wilhelm Püttmann 《Environmental Sciences Europe》2007,19(3):168-179