The impact of nutrient loading from Canada Geese (<Emphasis Type="Italic">Branta canadensis</Emphasis>) on water quality,a mesocosm approach

A mesocosm experiment determined the impact of Canada Goose (Branta canadensis) feces on water chemistry. After 30 days of fecal additions (treatments of 1.209, 2.419 g, and 12.090 g every 3 d to 0.811 m³ size mescosms), no significant changes in water column total phosphorus, nitrate, N:P ratios, total Kjeldahl nitrogen, chlorophyll-a, or phycocyanin were observed among treatment groups. Soluble reactive phosphorus showed a marginally significant increase in the high treatment group. A settling experiment suggested that goose feces and associated nutrients settled quickly to the sediment. Since fecal material settles quickly to the sediment, the impact of additional fecal material would not become evident in a lake until a wind event mixes the sediment into the water column or through alteration of the productivity or community structure of the benthos. Handling editor: K. Martens     

Hypophosphatemia is responsible for skeletal muscle weakness of vitamin D deficiency

A deficiency of vitamin D results in muscle weakness as well as rickets in children and osteomalacia in the adult. To study the basis for this weakness, severe vitamin D deficiency was produced in rats as revealed by a low level or absence of 25-hydroxyvitamin D₃ in the serum. Vitamin D deficiency was achieved by feeding purified diets to weanlings for 16 weeks. Muscle force, peak contraction (P), time-to-half contraction (T_1/2), time-to-peak contraction (T_P), and time-to-half recovery (T_1/2r) were measured. A significant reduction in muscle force was found when vitamin D deficiency was accompanied by hypophosphatemia. Within 2 days of correcting the hypophosphatemia, muscle strength was normalized. When serum calcium and serum phosphorus were maintained in the normal range in vitamin D-deficient rats, muscle weakness did not develop. Further, hypocalcemia together with vitamin D deficiency did not produce muscle weakness. These results strongly suggest that muscle weakness noted in rachitic patients is the result of the hypophosphatemia of vitamin D deficiency.     

Metabolomic analysis elucidates how shade conditions ameliorate the deleterious effects of greening (Huanglongbing) disease in citrus

Under tropical and subtropical environments, citrus leaves are exposed to excess sunlight, inducing photoinhibition. Huanglongbing (HLB, citrus greening), a devastating phloem-limited disease putatively caused by Candidatus Liberibacter asiaticus, exacerbates this challenge with additional photosynthetic loss and excessive starch accumulation. A combined metabolomics and physiological approach was used to elucidate whether shade alleviates the deleterious effects of HLB in field-grown citrus trees, and to understand the underlying metabolic mechanisms related to shade-induced morpho-physiological changes in citrus. Using metabolite profiling and multinomial logistic regression, we identified pivotal metabolites altered in response to shade. A core metabolic network associated with shade conditions was identified through pathway enrichment analysis and metabolite mapping. We measured physio-biochemical responses and growth and yield characteristics. With these, the relationships between metabolic network and the variables measured above were investigated. We found that moderate-shade alleviates sink limitation by preventing excessive starch accumulation and increasing foliar sucrose levels. Increased growth and fruit yield in shaded compared with non-shaded trees were associated with increased photosystem II efficiency and leaf carbon fixation pathway metabolites. Our study also shows that, in HLB-affected trees under shade, the signaling of plant hormones (auxins and cytokinins) and nitrogen supply were downregulated with reducing new shoot production likely due to diminished needs of cell damage repair and tissue regeneration under shade. Overall, our findings provide the first glimpse of the complex dynamics between cellular metabolites and leaf physiological functions in citrus HLB pathosystem under shade, and reveal the mechanistic basis of how shade ameliorates HLB disease.     

The response of sorghum and sunflower to short-term waterlogging

Summary The effect of waterlogging on water use and nutrient uptake in sunflower and sorghum was investigated in relation to stage of development of the crops and the timing and duration of waterlogging. Waterlogging at the vegetative and floral initiation stages of plant growth induced a reduction in water use of sunflower, with corresponding declines in leaf expansion and leaf water potential; in sorghum, the transpiration rates were much lower than for sunflower and relatively unaffected by waterlogging. Waterlogging at anthesis, however, caused an immediate reduction in water use in sunflower with a similar but delayed effect in sorghum. The differences in response of these two species are discussed in relation to the relative importance of water stress and nutrient uptake. Plant analysis at maturity indicated that waterlogging at any growth stage reduced both total and seed phosphorus in sunflower; similar effects were recorded with sorghum, with the exception of anthesis waterlogging which did not reduce nutrient uptake. Waterlogging effects on plant potassium levels were variable.     

Access permeability of ionic channels. Dependence on aqueous jump distance

The access diffusion permeability of pores with diameters comparable to the aqueous jump distance is characterized using a rate theory analysis for the aqueous diffusion process. It is found that this process gives rise to two permeability terms, one associated with bulk diffusion and the other a jump from the aqueous solution into a position where it has access to the channel. The latter term dominates for small channel diameters and vice versa for large channel diameters. The properties of access diffusion with respect to concentration polarization is shown to be different in the two limits of large and small values of the channel radius. A necessary criterion for bulk access diffusion to be rate limiting is given in terms of measured channel conductance G, aqueous jump distance lambda and aqueous resistivity rho, G greater than pi lambda/rho, which does not require a knowledge of channel geometry.     

Aluminum sulfate treatment: Short-term effect on complex phosphorus compounds in a eutrophic lake

Application of aluminum sulfate to the hypolimnion of West Twin Lake, a hardwater eutrophic lake in northeastern Ohio, did not efficiently remove complex phosphorus compounds from the water column. The majority of the complex phosphorus compounds remaining after alum treatment released P0₄ following brief treatment with alkaline phosphatase.     

Change in pattern diversity during secondary succession in Estonian forests

Comparisons of observed variance in species diversity (exp LT) and in species richness with expectation assuming a random and independent distribution of species are used to assess the relative importance during succession of niche limitation (Wilson, Gitay & Agnew 1987; limitation of the abundance or occurrence of species by competitive interactions) and nucleation (Yarranton & Morrison 1974; the development of a community through chance establishment or persistence followed by vegetative expansion from those nuclei). Wilson, Gitay & Agnew (1987) and Palmer (1987) suggest a deficit (i.e. lower than expected) in variance of richness is consistent with a ‘niche limitation’ process where competitive sorting makes patches more similar in species number than would be expected. In contrast, variance that is greater than expected is consistent with and could result from underlying environmental heterogeneity (i.e. ‘waterhole effect’). We extend these ideas to suggest that, in addition, a deficit in variance of diversity (expLT) can be interpreted as indicating niche limitation. Further, we suggest that a deficit of variance in richness need not be interpreted as resulting from niche limitation, but could result from limited dispersal and establishment followed by localized spread that causes quadrats to have less compositional overlap than might be expected if species were distributed at random. However, there is little reason to expect that such nucleation would cause a similar reduction in the variance of diversity. First, expLT is relatively insensitive to the presence or absence of rare species, and second, if local competitive processes do restrict the values of exp LT through some form of niche limitation, this could well be independent of the specific species involved. Thus, a combination of lower than expected variance in richness and high variance in diversity suggests nucleation to be important, particularly if the mean pairwise similarity between samples is lower than expected. We first examine a secondary successional sere with stands representing post-logging and mature forest. The variance of diversity is low in the establishment phase, but not in subsequent phases where the tree canopy is well developed. Significantly low variance of species richness is observed in a young forest just entering the thinning phase. Thus, nucleation may be taking place in the establishment phase of forest development, and is almost certainly important in the early thinning phase. Second, we examine communities in the process of equilibration following fertilization, logging, and paludification. All these communities have a low variance in diversity (exp LT) suggesting niche limitation.