Extent Of Nutrient Limitation Research Articles

Nitrogen and phosphorus additions alter nutrient dynamics but not resorption efficiencies of Chinese fir leaves and twigs differing in age.

It is unclear how or even if phosphorus (P) input alters the influence of nitrogen (N) deposition in a forest. In theory, nutrients in leaves and twigs differing in age may show different responses to elevated nutrient input. To test this possibility, we selected Chinese fir (Cunninghamia lanceolata) for a series of N and P addition experiments using treatments of +N1 - P (50 kg N ha(-1) year(-1)), +N2 - P (100 kg N ha(-1) year(-1)), -N + P (50 kg P ha(-1) year(-1)), +N1 + P, +N2 + P and -N - P (without N and P addition). Soil samples were analyzed for mineral N and available P concentrations. Leaves and twigs in summer and their litters in winter were classified as and sorted into young and old components to measure N and P concentrations. Soil mineral N and available P increased with N and P additions, respectively. Nitrogen addition increased leaf and twig N concentrations in the second year, but not in the first year; P addition increased leaf and twig P concentrations in both years and enhanced young but not old leaf and twig N accumulations. Nitrogen and P resorption proficiencies in litters increased in response to N and P additions, but N and P resorption efficiencies were not significantly altered. Nitrogen resorption efficiency was generally higher in leaves than in twigs and in young vs old leaves and twigs. Phosphorus resorption efficiency showed a minimal variation from 26.6 to 47.0%. Therefore, P input intensified leaf and twig N enrichment with N addition, leaf and twig nutrients were both gradually resorbed with aging, and organ and age effects depended on the extent of nutrient limitation.

Plant diversity is linked to nutrient limitation of dominant species in a world biodiversity hotspot

AbstractQuestionsWhat is the role of nutrient limitation of dominant species in maintaining plant species diversity at small spatial scales, particularly in biodiversity hotspots?LocationSouthwest of Western Australia.MethodsThe extent of nutrient limitation was determined by measuring variation in the foliar nutrients of dominant plant species and total above‐ground biomass in relation to soil N and P across 16 plots. Plant species richness and evenness for the same plots were then regressed against foliar N:P and δ15N of the dominant species.ResultsFoliar N and P content as well as above‐ground biomass increased, while foliar N:P decreased with increasing soil N and P, suggesting that dominant species are limited by both N and P in southwest Australia. In contrast, foliar δ15N values only increased with decreasing soil P, indicating that δ15N enrichment reflects low P availability. Species richness increased at sites where foliar N:P was higher and δ15N more enriched, suggesting that a relatively greater number of rare plant species co‐exist where the growth of dominant vegetation is more nutrient‐limited.ConclusionsThe mechanisms that allow an exceptionally high number of plant species to co‐exist at small spatial scales in a southwest Australian biodiversity hotspot are linked to the extent to which the dominant plant species are limited in N and P. In addition, on nutrient‐impoverished soils, a foliar N:P ratio >16 can reflect N as well as P limitation. While foliar δ15N also reflects availability of soil P, it is not necessarily a reliable indicator of nutrient limitation in southwest Australia, and perhaps in other environments where plants are highly adapted to low‐nutrient conditions.

Nutrient limitations in wet, drained and rewetted fen meadows: evaluation of methods and results

Restoration of wet grassland communities on peat soils involves management of nutrient supply and hydrology. The concept of nutrient limitation was discussed as well as its interaction with drainage and rewetting of severely drained peat soils. Different methods of assessing nutrient limitation were compared and the type and extent of nutrient limitation were determined for several wet grassland communities. It was concluded that a full-factorial field fertilisation experiment is the most preferable method. Plant tissue analyses and soil chemical analyses were considered less suitable, although they may provide helpful additional information. Fertilisation experiments in the laboratory using sods or using test plants appear to be the proper means to study mechanisms or processes, but have a restricted predictive value for field situations. Generalising the results, it seems that many relativily undisturbed grassland plant communities on peaty soils are characterised by N limitation. Phosphate limitation for vegetation on peat soils is mainly observed in specific circumstances such as extreme calcium richness, high concentrations of Fe or as a result of drainage or long-term hay cropping. The latter two may also cause K limitation. Rewetting is regarded as a prerequisite in restoring wet grassland communities. Further restoration measures to influence nutrient availability depend on aims of the management and the individual site conditions.

A multidisciplinary evaluation of restoration measures in a degraded Cirsio‐Molinietum fen meadow

Abstract. An integrated multidisciplinary approach including descriptive and experimental research of environmental and biotic factors was used to evaluate an attempt to restore a species‐rich fen meadow, phytosociologically belonging to the Cirsio‐Molinietum. Expert judgement and preliminary research indicated that soil acidification, due to drainage in the surrounding area, caused the degeneration of the fen meadow. Flooding the meadow with surface water was applied in order to stop acidification. A small irrigated wetland (helophyte filter) was constructed to reduce nutrient availability in the surface water. Sod cutting was applied in a small area as well. The two measures were evaluated through: (1) measurements of hydrological and soil factors, (2) seed bank analysis, (3) recording species composition in permanent plots, (4) assessing the type and extent of nutrient limitation using a full‐factorial fertilization experiment, (5) assessing the effect of liming on vegetation biomass, and (6) recording the growth of three introduced fen meadow species in the liming experiment.The research was carried out in a degraded site with intact vegetation, a degraded site where the top soil was removed by sod cutting and a reference site with intact Cirsio‐Molinietum vegetation. Groundwater levels in the degraded and the stripped site differed slightly from those of the reference site but they were within the range of Cirsio‐Molinietum requirements. Groundwater quality slightly improved in the stripped site. Top‐soil removal considerably reduced the macro‐nutrient contents and caused a stronger P‐deficiency. No increase in soil pH was observed immediately after top‐soil removal. A small increase in soil pH was found after five years in the stripped site, indicating a slight recovery from acidification. Liming after top‐soil removal had little effect on the soil pH after six months but stimulated the growth of established species such as Agrostis canina. Few viable seeds of characteristic fen meadow species were present in the seed banks of both degraded and well developed fen meadow sites. The species composition after top soil removal reflected the seed bank of the degraded fen meadow and establishment of characteristic fen meadow species was poor, even after five years. The introduced species (Carex hostiana, C. panicea, Cirsium dissectum) survived during the first year in both the degraded and the stripped site. Liming initially stimulated the growth of two species, but in the second year this effect disappeared. After two years, none of the introduced species survived at the stripped site. The restoration measures failed so far, probably because acidification could not be counteracted satisfactorily.Finally, it was concluded that our multidisciplinary approach enables us to draw proper conclusions and that it is suitable for other restoration attempts as well.

Molecular tools in marine ecology

Molecular tools have diverse applications in marine ecology. In microbial systems, DNA sequences of rRNA and other genes have identified a variety of novel lineages of bacteria inhabiting marine environments that have resisted traditional culture methods. However, relatively few natural populations have been characterized due to the rather labor-intensive methodologies employed. Recent technological developments such as in situ PCR and flow cytometry promise to greatly enhance the speed at which microbial taxa can be identified and enumerated in field collected water and substrate samples; such advances will allow future work to employ the spatial and temporal field sampling required to monitor the impact of natural and anthropogenic changes in the environment. This approach also holds promise for examining physiological status of field collected cells, garnering information on such elusive parameters as growth rates and the extent of nutrient limitation under natural conditions. Studies of macrobiota have similarly benefited from the use of molecular approaches to species identification. This has been particularly true with regard to distinguishing among larval forms of closely related taxa which are nearly identical morphologically. Genetic variation within species assayed by molecular tools has been useful in examining the stability of populations through time and in assessing patterns of recruitment to geographically separated populations. Enhanced understanding of these ecological problems will also require intensive spatial and temporal monitoring of both larval and adult populations. Often, the newer techniques based on DNA sequence variation have practical advantages over allozyme techniques: e.g., PCR allows assay of minute quantities of DNA that may come from ethanol preserved samples. However, when ample allozyme variation exists to address a given issue, these older techniques may be favored on a variety of criteria, including speed and cost. Hence, choice of methodology should be based on the expected efficiency of a given approach to a specific problem rather than the apparent sophistication of the method itself.

Characterisation of the type and extent of nutrient limitation in grassland vegetation using a bioassay with intact sods

An important methodological problem in plant ecology concerns the way in which the type and extent of nutrient limitation in terrestrial communities should be assessed. Conclusions on nutrient limitation have been founded mainly on soil extractions, fertiliser trials and tissue nutrient concentrations. In order to avoid some of the problems associated with these methods, we employed a special technique using intact sods which rooted both in the intact soil and in a nutrient solution, from which N, P and K were omitted stepwise. The method was applied to hay-field communities which differed in their history of fertiliser application. Four fields were compared which were not fertilised for 2, 6, 19 or 45 years, while hay making continued. This was done to restore former species-rich grassland communities. We tested the hypothesis that the increase in species diversity in these grasslands was attended by an increase in the number of limiting nutrients. We observed clear shifts in the type and extent of nutrient limitation. Fields which were recently fertilised were characterised by nitrogen and potassium limitation, while phosphorus limitation increased in importance towards the later stages of succession. In the last field (45 years unfertilised) N, P and K equally limited production at the community level. These conclusions differed from those drawn from a fertiliser trial in these same four fields, which failed to detect phosphorus limitation. It is concluded that the use of this method provides a valuable extra source of information while studying relationships between nutrient limitation and species diversity in grassland communities.