Defining phosphorus efficiency in plants

The many different definitions for "nutrient efficiency" make the use of the term ambiguous. We evaluated nutrient efficiency using data from a study of response to phosphorus (P) supply in white clover (Trifolium repens L.) and lucerne (Medicago sativa L.). Application of various criteria identified in the literature as measures of nutrient efficiency did not clarify differences between purportedly P efficient and inefficient germplasm. Germplasm differed in maximum shoot and total dry mass and in solution P concentration ([P]_s) required to achieve 80% maximum yield, but not in P concentration of tissue ([P]_t), internal P utilization, or P uptake per unit of fine root dry mass. Differences in yield may have resulted from factors other than efficient use of P. To reduce the confounding effects that other factors have on nutrient efficiency, it is essential that equivalent yields of germplasm be demonstrated where nutrients are not limiting. Mechanisms that enable enhanced nutrient efficiency can be identified less ambiguously using this approach.Joint contribution of the Minn. Agric. Exp. Stn. and the USDA-ARS     

Nutrient fluxes in the shifting cultivation system of south-west Côte d'Ivoire

At two sites, one with a 4-year-old (4-Y) secondary vegetation and the other with a 20-year-old (20-Y) vegetation, the influence of burning slashed vegetation on crop performance was studied during three seasons. In the first season after clearing, also the influence on weed growth was studied. At both sites, burning significantly decreased the number of weed seedlings. The lowest number of seedlings was found on the burnt plots of the 20-Y site. Burning increased yield and nutrient uptake significantly in the first and second season after clearing. In the third season after burning, only at the 4-Y site a significantly higher yield and nutrient uptake were found. At the 20-Y site the effect had disappeared. Calculations of efficiency of utilization of absorbed N, P and K indicated that P was the least available nutrient, also after burning. At both sites three consecutive crops absorbed approximately 40% of P applied in ash, while the cumulative recovery of K was at least 36% at the 4-Y site and at least 59% at the 20-Y site. On non-burnt plots, yields were not lower in the third season than in the first season after clearing, thus indicating that the inherent soil fertility did not decrease. Hence, yield decline on the burnt plots could be ascribed to ash depletion. It was concluded that in the local shifting cultivation system, the combination of ash depletion and infestation of weeds are the main reasons for abandoning the fields.     

Environmental correlates of gastrointestinal parasitism in montane and lowland baboons in Natal,South Africa

We compared the gastrointestinal parasites of the baboon,Papio cynocephalus ursinus, living in montane (altitude, >1800 m) and coastal lowland (altitude, 100–200 m) habitats in Natal, South Africa, using fecal analysis. While the montane animals harbored a smaller number of species, helminth egg-output rates were higher in them than in the lowland animals. The decrease in parasite diversity with increasing altitude was expected, but the difference in helminth egg output was not. It may be due to a combination of food shortage, which characterizes the montane environment, especially at the end of winter, and the high proportion of soil-contaminated items in the diets of the montane animals.     

Stable isotopic structure of aquatic ecosystems

Isotopic, biogeochemical and ecological structure can provide a new dimension for understanding material flows, and the simultaneous function and structure of an ecosystem. Distributions ofδ ¹³C andδ ¹⁵N for biogenic substances in the Nanakita river estuary involving Gamo lagoon in Japan were investigated to construct isotope biogeochemical and ecological structure for assessing fate and transfer of organic matter, and food web structure. The isotopic framework of the ecosystem was successfully described in aδ ¹⁵N–δ ¹³C map. In this estuary the variations of isotope ratios of biogenic substances were clearly explained by the mixing of land-derived organic matter, and marine-derived organic matter. A trophic-level effect of¹⁵N enrichment was clearly observed. Organisms were classified into three groups depending upon the contribution of land-derived organic matter in a food chain. Almost all biota except mollusca in the lagoon depend on organic matter of marine origin. The contributions of both land and marine organic matter were comparable for mollusca in the lagoon.     

槟榔（Areca catechu L.）的民族植物学

本文从民族植物学的观点介绍了我国南方各省嚼槟榔的习俗、历史及演变,分析了这个习俗的形成原因及槟榔的药用价值。作者认为咀嚼槟榔有成瘾性,但是否对人的中枢神经系统有损害,必须进一步研究。作者对这种习俗提出了几点看法和建议,对槟榔的开发利用有重要参考价值。     

The Value of a hoard: not just energy

We present a stochastic dynamic programming model of the contributionof stored food to winter survival. Using the acorn woodpecker(Melanerpes formtcivorus) as a model organism, we demonstratethat a hoard of small energetic value can impart considerableimprovement in the probability of surviving the winter and soimprove fitness. With this model we hope to resolve Koenig andMumme's paradox, that acorn woodpeckers expend much time andeffort to create and maintain hoards of acorns which provideno more that 16% of their energetic needs over the period inwhich they are used. We further demonstrate that the contributionof hoarded acorns to survival depends on the variability inforaging outcome, independently of the energetic value of thehoard in absolute terms. We point out that the results applyin principle to all hoarding animals and suggest a number offurther elaborations of the model.     

Gravimetricvs. respirometric determination of metabolic efficiency in caterpillars ofPieris brassicae

Conventional gravimetry and a combination of gravimetry and respirometry were compared for their precision in measuring respiration and metabolic efficiency of growth of final stadiumPieris brassicae L. (Pieridae, Lepidoptera) caterpillars. This was done both for caterpillars feeding on an artificial diet and for caterpillars feeding on excised leaf material of a host plant,Brassica oleracea L. Gravimetry produced significantly greater variation in the total amount of matter respired and the metabolic efficiency than indirect calorimetry for caterpillars feeding on plant material, while the two methods gave similar results for the caterpillars reared on a meridic artificial diet. Respirometry (indirect calorimetry) revealed that caterpillars feeding on the artificial diet were growing with a higher metabolic efficiency than caterpillars feeding on the host plant. This difference was not revealed by conventional gravimetry. It is argued that metabolic efficiencies as derived from gravimetric budget calculations are subject to a number of random errors that distort precise determination of metabolic efficiencies in studies involving plant food.     

Rotifer population dynamics in response to increased bacterial biomass and nutrients: a mesocosm experiment

The impact of organic nutrients and massive addition of bacteria was followed in lake water mesocosms in a eutrophic lake. Increased DOM initiated a sequence of trophic responses indicated by rapid increases in bacterioplankton, protozoa, and algal biomass. The populations of Keratella cochlearis and Keratella quadrata showed a distinct response by rapid increase in birth rate followed by maxima of production and abundance. This succession clearly reflected the trophic position of these rotifer populations in the food chain. A reverse response was observed in Conochilus unicornis.     

Exogenous 13C glucose oxidation during exercise: North American vs Western European studies

The purpose of this study was to test the hypothesis that the well-documented changes in background ¹³C enrichment of expired CO₂ observed in response to exercise and carbohydrate ingestion, in subjects living on a North American diet, are not present in subjects living on a Western European diet. The experimental protocol used by Pirnay et al. in 1977 and by Krzentowski et al. in 1984 in subjects living on a Western European diet (4 h of exercise on a treadmill at 50% VO_2max with ingestion of 100 g of glucose in 400 ml of water) was duplicated as closely as possible in six subjects living on a North American diet. The actual amounts of exogenous glucose oxidized, computed with a high artificial ¹³C enrichment of glucose (+189.7 ¹³C PDB-1) which allows one to neglect the 1–2 changes in ¹³C background, were [mean (SEM)] 54.7 (5.4) and 84.2 (3.4) g over 2 h and 4 h of exercise, respectively. These values compare well with data computed by Pirnay et al. [56.6 (13.1) and 94.9 (4.2) g] and by Krzentowski et al. [55.0 (6.2) and 88.0 (4.5) g] using a natural enrichment of glucose (–11.21 and –10.63 ¹³C PDB-1, respectively) assuming no change in ¹³C background in their Western European subjects. Under the same assumption and using a natural enrichment of glucose (–11.30 ¹³C PDB-1) the oxidation of exogenous glucose was overestimated by 30–40% in our North American subjects. This result indicates that because of a lower input of ¹³C in their diet, the difference between the isotopic composition of carbohydrate and fat stores are smaller, and changes in ¹³C background are small or absent in response to moderate workload in Western European subjects, when compared to their North American counterparts.     

赣榆县厉庄地埂利用型式试验

在赣榆县厉庄以大金鸡菊、紫穗槐和红柳三种经济植物进行了地埂利用型式试验,取得了比较明显的水土保持效果和改善农田小环境的生态效益。栽植后第三年植物覆盖率达90％或100％;地面蒸发量减少15.2～17.7％;截留降水量为0.5～0.7mm;大气相对湿度提高3.7～5.4％;土壤养分也有不同程度的增加。经济效益估测每亩地埂可收到300～600元,比种黄豆高5～9倍。效益最好的是红柳,大金鸡菊次之,紫穗槐较低。