Nitrogen (N) and phosphorus (P) availability limit plant growth in most terrestrial ecosystems. This review examines how variation in the relative availability of N and P, as reflected by N: P ratios ...of plant biomass, influences vegetation composition and functioning. Plastic responses of plants to N and P supply cause up to 50-fold variation in biomass N: P ratios, associated with differences in root allocation, nutrient uptake, biomass turnover and reproductive output. Optimal N: P ratios - those of plants whose growth is equally limited by N and P - depend on species, growth rate, plant age and plant parts. At vegetation level, N: P ratios <10 and >20 often (not always) correspond to N- and P-limited biomass production, as shown by short-term fertilization experiments; however long-term effects of fertilization or effects on individual species can be different. N: P ratios are on average higher in graminoids than in forbs, and in stress-tolerant species compared with ruderals; they correlate negatively with the maximal relative growth rates of species and with their N-indicator values. At vegetation level, N: P ratios often correlate negatively with biomass production; high N: P ratios promote graminoids and stress tolerators relative to other species, whereas relationships with species richness are not consistent N: P ratios are influenced by global change, increased atmospheric N deposition, and conservation managment.
Aims Dauciform roots (DR) are formed by some Cyperaceae under phosphorus (P) deficiency. To advance our understanding of their physiological function, I ask: Is DR formation regulated by shoot P ...status or external P supply? How does it respond to nitrogen (N)? Do DR enhance root monoesterase, diesterase or phytase activities and ability to utilize organic P? Methods Greenhouse experiments were carried out with two Carex species grown in sand with (1) different combinations of N and P supply, (2) local supply of N or P to root halves, and (3) different organic P forms. Results Carex flava produced DR in all treatments. The density of DR and phosphatase activities increased with N supply; they were regulated by shoot P status and external N (but not P) supply. All phosphatase activities increased with DR density. Carex muricata produced no DR and had lower diesterase activity than C. flava but both species grew equally well with diester-P. Conclusions DR and phosphatase activities are regulated by both N and P supply. Similar growth responses to nutrients in both species suggest small costs and benefits of DR under experimental conditions but confirmation is needed for plants grown on natural soils.
1. Nitrogen and phosphorus supply influences the rate of litter decomposition and nutrient dynamics during decomposition. Besides the total amount of N and P available to decomposers, their relative ...supply (N : P ratio) might be important, e.g. through an influence on the composition and activity of microbial communities. 2. We carried out two experiments using laboratory microcosms to test that (i) N : P ratios (in either litter or the environment) determine whether N or P limits the rate of decomposition, (ii) the 'critical' N : P ratio between N and P limitation depends on overall nutrient availability, (iii) litter colonization by fungi and bacteria depends on the N : P ratio, and (iv) N : P ratios determine if proportionately more N or P is retained or immobilized by the litter. 3. In one experiment, cellulose as a nutrient-free litter analogue was incubated on sand fertilized with varying N : P supply ratios, whereas in a second experiment, Carex leaf litter with varying N : P ratios was incubated on nutrient-free sand. 4. Results essentially support our hypotheses. Cellulose decomposition was N- or P-limited depending on the N : P supply ratio. The shift from N to P limitation occurred at N : P supply ratios of 1·7-45, depending on overall nutrient supply. Bacteria were most abundant on cellulose at low N : P supply ratios, when decomposition was N-limited, while fungi were relatively more important at high N : P ratios, when decomposition was P-limited. The amounts of mineral N and P immobilized on cellulose and those released from litter, both in absolute terms and relative to supply, depended on the type of nutrient limitation (N vs. P). 5. The N : P ratio of nutrients available to decomposers appears to be an important determinant of plant litter decomposition, the relative importance of fungi and bacteria in litter-associated microbial communities, and litter nutrient dynamics.
Root structures secreting carboxylates and phosphatases are thought to enhance a plant’s phosphorus (P) acquisition. But do closely related species with and without such structures really differ in ...root exudation, P mobilization, or ecological niche? We investigated this by comparing 23 European Carex species with and without ‘dauciform roots’ (DRs).
Plants grown in pots with sand were screened for DR formation, phosphatase activities, carboxylate exudation, and utilization of various organic and inorganic P compounds. Ecological niches were compared using ecological indicator values and nutrient concentrations of plant shoots in natural habitats.
Species of subgenus Carex formed DRs, while species of subgenus Vignea did not. Species with DRs had higher root diesterase activity than species without DRs, exuded more citrate but less oxalate and less total carboxylates, and allocated less biomass to roots. Species with and without DRs showed similar growth responses to different forms of P and different amounts of P supplied; their natural habitats do not differ in soil fertility or degree of P limitation.
Despite some differences in physiological function, DRs did not influence the P acquisition and nutritional niche of European Carex species, suggesting that species with and without DRs do not exhibit distinct P-acquisition strategies.
Interspecific hybrid endophytes of the genus Epichloë (Ascomycota, Clavicipitaceae) are prevalent in wild grass populations, possibly because of their larger gene variation, resulting in increased ...fitness benefits for host plants; however, the reasons are not yet known. We tested hypotheses regarding niche expansion mediated by hybrid endophytes, population-dependent interactions and local co-adaptation in the woodland grass Hordelymus europaeus, which naturally hosts both hybrid and non-hybrid endophyte taxa.
Seedlings derived from seeds of four grass populations made endophyte free were re-inoculated with hybrid or non-hybrid endophyte strains, or left endophyte free. Plants were grown in the glasshouse with or without drought treatment.
Endophyte infection increased plant biomass and tiller production by 10–15% in both treatments. Endophyte types had similar effects on growth, but opposite effects on reproduction: non-hybrid endophytes increased seed production, whereas hybrid endophytes reduced or prevented it completely.
The results are consistent with the observation that non-hybrid endophytes in H. europaeus prevail at dry sites, but cannot explain the prevalence of hybrid endophytes. Thus, our results do not support the hypothesis of niche expansion of hybrid-infected plants. Moreover, plants inoculated with native relative to foreign endophytes yielded higher infections, but both showed similar growth and survival, suggesting weak co-adaptation.
Background and aims Plants can develop various root traits which may contribute to their nutrient acquisition. We investigated the occurrence of five root traits among species of genus Carex to ...determine their frequency, mutual associations and dependence on taxonomy (subgenus) or habitat. Methods Root samples of 40 species were collected in their natural habitats within Russia and Belarus. They were examined microscopically to quantify the abundance of AM-fungal hyphae (H), arbuscules (A) and vesicles (V), dark septate endophyte (DSE), typical (long) root hairs (TRH), bulbous (shortened) root hairs (BRH) and dauciform roots (DR). Results The frequency of root traits decreased in the order TRH (100% of the species), DSE (80%), BRH (43%), A and V (25%) and DR (23%). Most species possessed 2–4 different traits, but up to five were possible, even on a single plant. Traits occurred largely independently of each other. DR were only found in subgenus Carex and mainly in grasslands. DSE and BRH were more abundant in subgenus Carex. BRH were most abundant in wetlands, TRH were shortest and thinnest in grasslands. Conclusions A diversity of root traits exists in the genus Carex, with variation both among and within species. The abundance and size of traits exhibits some taxonomic and ecological patterns, which differ for each trait.
The ability of some invasive plant species to produce biochemical compounds toxic to native species, called allelopathy, is thought to be one of the reasons for their success when introduced to a ...novel range, an idea known as the Novel Weapons Hypothesis. However, support for this hypothesis mainly comes from bioassays and experiments conducted under controlled environments, whereas field evidence is rare. In a field experiment, we investigated whether three plant species invasive in Europe,
Solidago gigantea
,
Impatiens glandulifera
and
Erigeron annuus
, inhibit the germination of native species through allelopathy more than an adjacent native plant community. At three sites for each invasive species, we compared the germination of native species that were sown on invaded and non-invaded plots. Half of these plots were amended with activated carbon to reduce the influence of potential allelopathic compounds. The germination of sown seeds and of seeds from the seedbank was monitored over a period of 9 weeks. Activated carbon generally enhanced seed germination. This effect was equally pronounced in invaded and adjacent non-invaded plots, indicating that invasive species do not suppress germination more than a native plant community. In addition, more seeds germinated from the seedbank on invaded than on non-invaded soil, probably due to previous suppression of germination by the invasive species. Our field study does not provide evidence for the Novel Weapons Hypothesis with respect to the germination success of natives. Instead, our results suggest that if invasive species release allelopathic compounds that suppress germination, they do so to a similar degree as the native plant community.
Purpose
WisQoL (Wisconsin Stone Quality of Life questionnaire) is a disease specific, health related quality of life measure designed for patients who form kidney stones. The goal of this study was ...to develop and validate a German version of WisQoL.
Methods
The German version of the WisQoL was developed following a standardized multistep process. Patients were recruited prior to stone treatment, and completed the questionnaire as well as the SF-36v2 (36-Item Short Form Health Survey). This was repeated 1, 3, and 6 months after stone surgery. Scores of the 28 questionnaire items were summarized into sum scores for four domains and a total score. The psychometric properties of the questionnaire were statistically analyzed.
Results
The German WisQoL demonstrated excellent internal consistency (Cronbach’s
α
> 0.90 for all domains at all visits). All inter-domain associations were positive. The test–retest reliability for patients with unchanged self-reported health state was considered satisfactory (Spearman’s rho for total score 0.70 95% CI 0.55 to − 0.80). The German WisQoL demonstrated good convergent validity with the validated SF-36v2 (correlation between corresponding items 0.44 to 0.64). All domain scores showed significant sensitivity to change induced by stone treatment (
p
≤ 0.05). Total WisQoL scores generally improved during the first 3 months following stone treatment, and remained stable thereafter.
Conclusion
The German WisQoL proved to be a reliable and robust instrument to evaluate health related quality of life measures of kidney stone patients in the clinical setting. It is expected to be of use for further research in patients with kidney stones.
1. Different grass species dominate grasslands fertilized with nitrogen (N) or phosphorus (P), possibly due to the impact of N : P stoichiometry on competitive interactions. How species compete for ...nutrients, and whether the mechanisms are similar for N and P, is still not fully understood. 2. We investigated whether the outcome of competition between Alopecurus pratensis and Agrostis capillaris depends on N : P stoichiometry, and on the ability to acquire supplied N or P. Monocultures and mixtures of the two species were grown in pots at nine combinations of N and P supply (N : P ratios 1∙7, 15 and 135, all at three supply levels). After 3 months, we determined plant biomass, morphological traits and nutrient concentrations of plant tissues. 3. N : P supply ratios had similar effects on the growth of the two species but contrasting effects on their competitive strength, as assessed by comparing growth in competition to growth in monoculture: Alopecurus was the stronger competitor under N limitation (N : P ratio 1∙7), whereas Agrostis was an equal or stronger competitor under P limitation (N : P ratio 135). This result resembled patterns of species distribution observed in the field. 4. The strong competitive response of Alopecurus at the low N : P supply ratio was associated with a high investment in root biomass and root length, and a high nitrogen productivity. The competitive response of Agrostis at the high N : P supply ratio was associated with low root mortality and high root phosphatase activity. 5. Our results obtained under N limitation support the pre-emption theory in which plants with the highest root length are able to acquire more N from the soil than their competitors, and therefore can suppress their growth. Under P limitation, however, plant investment in root length could not explain competitor suppression. Here, other factors important in competition for P, such as mycorrhizal hyphal length, root longevity, or exudation rates of P releasing compounds, merit investigation.
Digital tools like 3D laser-based photonic scanners, which can assess external anthropometric measurements for population based studies, and predict body composition, are gaining in importance. Here ...we focus on a) systematic deviation between manually determined and scanned standard measurements, b) differences regarding the strength of association between these standard measurements and body composition, and c) improving these predictions of body composition by considering additional scan measurements. We analysed 104 men aged 19-23. Bioelectrical Impedance Analysis was used to estimate whole body fat mass, visceral fat mass and skeletal muscle mass (SMM). For the 3D body scans, an Anthroscan VITUSbodyscan was used to automatically obtain 90 body shape measurements. Manual anthropometric measurements (height, weight, waist circumference) were also taken. Scanned and manually measured height, waist circumference, waist-to-height-ratio, and BMI were strongly correlated (Spearman Rho>0.96), however we also found systematic differences. When these variables were used to predict body fat or muscle mass, explained variation and prediction standard errors were similar between scanned and manual measurements. The univariable predictions performed well for both visceral fat (r.sup.2 up to 0.92) and absolute fat mass (AFM, r.sup.2 up to 0.87) but not for SMM (r.sup.2 up to 0.54). Of the 90 body scanner measures used in the multivariable prediction models, belly circumference and middle hip circumference were the most important predictors of body fat content. Stepwise forward model selection using the AIC criterion showed that the best predictive power (r.sup.2 up to 0.99) was achieved with models including 49 scanner measurements. The use of a 3D full body scanner produced results that strongly correlate to manually measured anthropometric measures. Predictions were improved substantially by including multiple measurements, which can only be obtained with a 3D body scanner, in the models.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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