An analysis of yields of grasses in mixed and pure stands

To describe competition species must be compared with a standard. By conventional standards, such as grammes dry matter, tiller number and sq. cm leaf area, two species and even one species cannot be compared in the course of the season. Therefore a standard without dimensions was needed. Dividing yield of a species (expressed in any unit) in mixed culture by that in monoculture gave a figure without dimensions, called relative yield.Conclusions were based on my own pot experiments under controlled conditions and on field experiments of others.1. The rate at which one species replaces another is independent of the proportion of a species in the mixture.2. Competitive vigour of a grass species is independent of the other species or varieties associated with it in the mixture. This implies that if there are two experiments in which species A is competing with each of two morphologically identical varieties of species B, the result of competition between the varieties of B can be calculated. Competition in mixtures of two species will predict the competitive trend in more complex mixtures. In all these experiments the monocultures may never be omitted.3. When a treatment limits growth, in general competition changes at the expense of the more productive species. This is because there will be less competition for light as yield decreases, so benefiting the lower yielding species. Under these conditions the shoot/root ratio of the lower yielding species seems to decrease, another reason why the lower yielding species benefits in competition by suboptimum soil conditions. The above- ground production of a species with a large proportion of roots will respond less sharply to a shortage of minerals or water than a species with a higher shoot/root ratio. Hence, the change in competition in adverse conditions does not depend on the nature of the factor limiting growth.4. Sowing experiments show that pH considerably affects the development of seedlings, even though pH values within the range 4.2 - 6.8 does not affect competition between fully grown plants. In general the period of establishment and the competition afterwards should be stricktly separated. If this is omitted, completely erroneous conclusions may be drawn about the competitive ability of the species.5. Monocultures are preferred to mixed cultures for the following reasons.a. Because the higher yielding species in a mixture is not always the dominant species (Montgomery effect); the apparent advantage is often even a drawback. The risk of the lower yielding species becoming dominant should not be underestimated.b. The possibility that light is better utilized through the sod structure in a mixed culture can only be important during the period that the leaf canopy of the sod is not yet closed. In absolute terms this advantage is only small, especially if yields per cut are high; under grazing this possibility may be of more importance.c. A mixture of species with different growth rhythms might yield more. If so the increased yield will only be worthwhile if the species alter their order of dominance within the growing season. But changes in botanical composition are more gradual, so that this advantage of a mixture is lost.d. When the more productive species fails for some reason, the less productive species in the mixture could temporarily take over the production. But this temporary advantage may change into a persistent drawback, when recovery of the main species is hampered by the other species. On sown permanent grassland, especially under suboptimum conditions, less productive or otherwise undesirable species may in time invade the sward. It remains to be seen whether this is more efficiently prevented by a mixture or by a monoculture.e. The problem in sowing grassland is the choice of the highest yielding species under the prevailing conditions, rather than the choice of the highest yielding mixture

Competition between herbage plants

Starting from work with annuals a model of competition between herbage plants is discussed. It is shown that their mutual interference can only be described adequately if they are grown in mixture and also in monocultur

Osteoporosis care during the COVID-19 pandemic in the Netherlands: a national survey

This is a survey study concerning osteoporosis care during the COVID-19 pandemic in the Netherlands. Respondents reported that osteoporosis care stagnated and lower quality of care was provided. This leads to the conclusion that standardization of osteoporosis care delivery in situations of crisis is needed.Purpose: During the initial phase of the COVID-19 pandemic, there was no guidance of professional societies or guidelines on the organization of osteoporosis care in case of such a crisis, and treatment relied on local ad hoc strategies. Experiences from the current pandemic need to be taken into account for the near future, and therefore, a national multidisciplinary survey was carried out in the Netherlands.Methods: A survey of 17 questions concerning the continuation of bone mineral density measurements by Dual Energy X-ray absorptiometry (DXA), outpatient clinic visits, and prescription of medication was sent to physicians, nurses, nurse practitioners, and physician assistants working in the field of osteoporosis.Results: 77 respondents finished the questionnaire, of whom 39 (50.6%) reported a decline in DXA-scanning and 36 (46.8%) no scanning at all during the pandemic. There was an increase in remote consultations for both new and control patient visits (n = 48, 62.3%; n = 62, 81.7% respectively). Lower quality of care regarding fracture prevention was reported by more than half of the respondents (n = 44, 57.1%). Treatment with intravenous bisphosphonates and denosumab was delayed according to 35 (45.4%) and 6 (6.3%) of the respondents, respectively.Conclusion: During the COVID-19 pandemic, osteoporosis care almost completely arrested, especially because of the discontinuation of DXA-scanning and closing of outpatient clinics. More than half of the respondents reported a substantial lower quality of osteoporosis care during the COVID pandemic. To prevent an increase in fracture rates and a decrease in patient motivation, adherence and satisfaction, standardization of osteoporosis care delivery in situations of crisis is needed.Diabetes mellitus: pathophysiological changes and therap

The PL calibration for Milky Way Cepheids and its implications for the distance scale

The rationale behind recent calibrations of the Cepheid PL relation using the Wesenheit formulation is reviewed and reanalyzed, and it is shown that recent conclusions regarding a possible change in slope of the PL relation for short-period and long-period Cepheids are tied to a pathological distribution of HST calibrators within the instability strip. A recalibration of the period-luminosity relation is obtained using Galactic Cepheids in open clusters and groups, the resulting relationship, described by log L/L_sun = 2.415(+-0.035) + 1.148(+-0.044)log P, exhibiting only the moderate scatter expected from color spread within the instability strip. The relationship is confirmed by Cepheids with HST parallaxes, although without the need for Lutz-Kelker corrections, and in general by Cepheids with revised Hipparcos parallaxes, albeit with concerns about the cited precisions of the latter. A Wesenheit formulation of Wv = -2.259(+-0.083) - 4.185(+-0.103)log P for Galactic Cepheids is tested successfully using Cepheids in the inner regions of the galaxy NGC 4258, confirming the independent geometrical distance established for the galaxy from OH masers. Differences between the extinction properties of interstellar and extragalactic dust may yet play an important role in the further calibration of the Cepheid PL relation and its application to the extragalactic distance scale.Comment: Accepted for Publication (Astrophysics & Space Science

Alkynamide phthalazinones as a new class of TbrPDEB1 inhibitors

Several 3′,5′-cyclic nucleotide phosphodiesterases (PDEs) have been validated as good drug targets for a large variety of diseases. Trypanosoma brucei PDEB1 (TbrPDEB1) has been designated as a promising drug target for the treatment of human African trypanosomiasis. Recently, the first class of selective nanomolar TbrPDEB1 inhibitors was obtained by targeting the parasite specific P-pocket. However, these biphenyl-substituted tetrahydrophthalazinone-based inhibitors did not show potent cellular activity against Trypanosoma brucei (T. brucei) parasites, leaving room for further optimization. Herein, we report the discovery of a new class of potent TbrPDEB1 inhibitors that display improved activities against T. brucei parasites. Exploring different linkers between the reported tetrahydrophthalazinone core scaffold and the amide tail group resulted in the discovery of alkynamide phthalazinones as new TbrPDEB1 inhibitors, which exhibit submicromolar activities versus T. brucei parasites and no cytotoxicity to human MRC-5 cells. Elucidation of the crystal structure of alkynamide 8b (NPD-048) bound to the catalytic domain of TbrPDEB1 shows a bidentate interaction with the key-residue Gln874 and good directionality towards the P-pocket. Incubation of trypanosomes with alkynamide 8b results in an increase of intracellular cAMP, validating a PDE-mediated effect in vitro and providing a new interesting compound series for further studies towards selective TbrPDEB1 inhibitors with potent phenotypic activity