Non‐pathogenic association of L‐form bacteria (pseudomonas syringae pv. phaseolicola) with bean plants (Phaseolus vulgaris L.) and its potential for biocontrol of halo blight disease

L‐forms of the halo blight pathogen, Pseudomonas syringae phaseolicola, were maintained in a medium which suppressed cell wall synthesis. These L‐forms, unlike revertants (walled forms derived from unstable L‐forms) and cell walled (parent) organisms, did not elicit a hypersensitive response in tobacco leaves. Association of L‐forms with Phaseolus vulgaris was established by seed imbibition in L‐form suspensions compared with appropriate control treatments (5% mannitol or heat‐killed cells). Seedling emergence and plant growth was not affected by L‐form imbibition. The association was detected by agglutination assays using polyclonal antibody. The L‐form association was localized to the lower shoot tissue and was progressively lost with age of plants. Plants with associated L‐forms had vigour and shoot weights equivalent to controls and showed no disease symptoms. The cell walled form could not be isolated from plants showing positive agglutination. On challenge with the pathogen, plants associated with L‐forms showed significantly less disease symptoms than controls. Stem extracts, from associated plants, were inhibitory to in vitro cultures of both L‐forms and parent forms of Ps. syr. phaseolicola. These results indicate that L‐form associations confer induced systemic resistance to bean plants and might be developed as novel biocontrol systems.     

Use of disease progress curves to study the effects of the biocontrol agent Sporidesmium sclerotivorum on lettuce drop

At the end of the spring 1987 growing season, the mycoparasite Sporidesmium sclerotivorum was applied at 0, 0.2, 2 or 20 kg ha^‐1 to lettuce plants infected with Sclerotinia minor. Disease incidence was monitored in the same plots for five subsequent crops (three fall and two spring crops) without additional application of either pathogen or mycoparasite. Logistic growth curves were fitted to the data to describe disease progression over time for each inoculum level within each of the five crops. Within each crop, increasing the quantity of mycoparasite inoculum resulted in positive horizontal displacement of the curve with respect to time. As quantities of inoculum of S. sclerotivorum increased, inflection points of the disease progress curves increased at a decreasing rate. Thus, additional mycoparasite inoculum resulted in ever‐smaller increases in inflection point, and after a certain threshold level of mycoparasite inoculum (< 0.2 kg ha^‐1), increases in inflection point did not result in meaningful increases in harvestable lettuce. Maximum rates of disease increase were not different among the treatments within each crop, but were different between crops. Maximum rates of disease increase averaged 3.4, 3.4, 2.1, 3.6 and 1.5% day^‐1 for the fall 1987, spring 1988, fall 1988, spring 1989, and fall 1989, respectively. At all inoculum levels, the fall epidemics began later after planting than the spring epidemics.     

Stature variation in the British American Colonies: French and Indian War records, 1755-1763

Personnel records kept by military units of American colonials during the French and Indian War (1755-1763) are analyzed for relationships between environmental factors and stature. A robust American economy and direct access to high-quality food were apparently critical to tallness of this white American male sample. American-born men were taller at all ages than those who had migrated from Europe. January temperatures, rural versus urban birth, and ethnicity also showed stature relationships within the American-born group; thermal effects were by far the strongest of the non-nutritional factors.     

Limnologic consequences of the decline in hemlock 4800 years ago in three Southern Ontario lakes

Four thousand eight hundred years ago hemlock (Tsuga canadensis) populations were decimated throughout eastern North America. We have studied the effects of this loss from the terrestrial community on three Southern Ontario lakes: Little Round Lake, Sunfish Lake, and McKay Lake. This study includes the use of cladocerans, diatoms, chrysophytes, and bacterial pigments to assess the limnologic changes that occurred in these lakes. Each lake experienced a change in trophic status that coincided with the loss of hemlock from its catchment, but the change in the aquatic biota was different in each lake. The lakes' size may have been the most influential factor governing the response to this terrestrial disturbance.     

Is vegetation in equilibrium with climate? How to interpret late-Quaternary pollen data

Current methods for estimating past climatic patterns from pollen data require that the vegetation be in dynamic equilibrium with the climate. Because climate varies continuously on all time scales, judgement about equilibrium conditions must be made separately for each frequency band (i.e. time scale) of climatic change. For equilibrium conditions to exist between vegetation and climatic changes at a particular time scale, the climatic response time of the vegetation must be small compared to the time scale of climatic variation to which it is responding. The time required for vegetation to respond completely to climatic forcing at a time scale of 10⁴ yr is still unknown, but records of the vegetational response to climatic events of 500-to 1000-yr duration provide evidence for relatively short response times. Independent estimates for the possible patterns and timing of late-Quaternary climate changes suggest that much of the vegetational evidence previously interpreted as resulting from disequilibrium conditions can instead be interpreted as resulting from the individualistic response of plant taxa to the different regional patterns of temperature and precipitation change. The differences among taxa in their response to climate can lead a) to rates and direction of plant-population movements that differ among taxa and b) to fossil assemblages that differ from any modern assemblage. An example of late-Holocene vegetational change in southern Quebec illustrates how separate changes in summer and winter climates may explain the simultaneous expansion of spruce (Picea) populations southward and beech (Fagus) populations northward.     

Vegetation responses to past climatic variation

Vegetation responses to climatic change can be studied retrospectively by utilizing the Quaternary fossil record. There has been controversy over the extent to which major changes in vegetation patterns at the continental scale lag behind the climatic changes that drive them, and to what extent vegetation can ever be said to be in equilibrium with climate. The equilibrium question has no single answer. The predominant mode of vegetation response to climatic change depends on the space and time frame and resolution of the data set in which the response is observed.Vegetation (as observed on particular space and time scales) can be in dynamic equilibrium with climate if its response time is sufficiently fast in relation to the rate of climatic change to which it is observed to be responding. Several processes can be involved in the response: successional, migrational, edaphic, and evolutionary. Successional response times can be deduced from forest succession models. The other processes are less well understood and different ideas exist concerning their rates. According to one hypothesis, migrational lags caused delays of thousands of years in the postglacial dynamics of forest composition. The alternative hypothesis explains these changes as dynamic equilibrium responses to changes in climatic seasonality and climatic anomaly patterns. Neither hypothesis need be universally true; gradient analysis and forest succession models are among the techniques that can be used in inferential tests of these hypotheses for particular space-time regions.Dynamic equilibrium may often be a reasonable approximation for the responses of the broadest continental-scale forest patterns to orbitally induced climatic changes. But as spatial and temporal frames of observation are diminished and resolution increased, biotic processes must eventually come to dominate. At sufficiently fine scales the main observable phenomena are successional responses to natural disturbance events. The late-Quaternary record of vegetation change allows a choice of observation scales and thus provides a continuum of possibilities for study, ranging from long-term dynamic bioclimatology to more conventional vegetation dynamics.I thank Margaret Davis, Honor Prentice, Jim Ritchie, Al Solomon, Geoff Spaulding and Tom Webb for their reviews of earlier drafts. Research supported by a US Department of Energy, Carbon Dioxide Research Division, grant to Brown University and a Swedish Natural Science Research Council grant to the project SlsSimulation of Natural Forest Dynamics.I thank Margaret Davis, Honor Prentice, Jim Ritchie, Al Solomon, Geoff Spaulding and Tom Webb for their reviews of earlier drafts. Research supported by a US Department of Energy, Carbon Dioxide Research Division, grant to Brown University and a Swedish Natural Science Research Council grant to the project SlsSimulation of Natural Forest Dynamics.     

The effect of Cd2+ on photosynthetic reactions of mesophyll protoplasts

Photosynthetic CO₂-fixation of mesophyll protoplasts of lambs lettuce [Valerianella locusta (L.) Betcke] was inhibited by short time exposure to Cd⁺. Inhibition was due to uptake of the metal ion into the protoplasts and increased with increasing Cd²⁺ concentrations and the time of preincubation. A 10 min pretreatment at 2 mM Cd²⁺ reduced CO₂-fixation by 40–60%. Inhibition of photosynthesis was independent of the light intensity to which the protoplasts were exposed. Measurement of the lightinduced electrochromic pigment absorption change at 518nm and chlorophyll fluorescence studies revealed that primary photochemical reactions associated with the thylakoid membranes were not affected by the metal ion. Also, light activation of the ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) was not inhibited by Cd²⁺. Under rate-limiting CO₂ concentrations, inhibition of CO₂-fixation was smaller than at V_max of CO₂ reduction indicating that the carboxylation reaction of the Calvin cycle is not susceptible to Cd²⁺. Cd²⁺ treatment of protoplasts significantly extended the lagphase of CO₂-supported O₂-evolution and partly inhibited light activation of the glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.13) and the ribulose-5-phosphate kinase (EC 2.7.1.19). Measurement of relative concentrations of [¹⁴C]-labeled Calvin cycle intermediates showed that Cd²⁺ caused a decrease in the 3-phosphoglycerate/triose phosphate ratio and an increase in the triose phosphate/ribulose-1,5-bisphosphate ratio. It is concluded that in protoplasts Cd²⁺ affects photosynthesis mainly at the level of dark reactions and that the site of inhibition may be localized in the regenerative phase of the Calvin cycle.     

Utilization of carbon and nitrogen sources and acid/alkali production by cowpea rhizobia

Summary Sixteen slow-growing strains of rhizobia (15 cowpea rhizobia and oneR. japonicum) were examined to determine the effects of carbon and nitrogen sources on acid/alkali production in culture media. We found that the pH changes of the medium were more influenced by nitrogen sources than carbon sources (with the exception of ribose). When ammonium sulphate was used as a nitrogen source, all the cowpea rhizobia strains produced acid. When yeast-extract was used as a nitrogen source, however, a heterogenous pattern for acid/alkali production was found. The majority of the strains produced alkali from nitrate, glutamate and urea irrespective of carbon sources and acid from ribose irrespective of nitrogen sources.     

Differences in hair density of Japanese monkeys (Macaca fuscata fuscata) with locality and age

The hair density of free-ranging Japanese monkeys (Macaca fuscata fuscata) living in three different areas was investigated. The Japanese monkeys had thicker hair than other macaques. The hair density in the Japanese monkeys varied with locality: the northern monkeys had thicker hair than the southern ones. The density did not vary markedly with age up to 3 years of age, but then decreased gradually up to adult age (≧7 years old). The remarkable growth of the trunk suggested that the total number of hairs increased with age, especially during the period as a juvenile.     

元江干热河谷山地五百年来植被变迁探讨

元江河谷是云南省最干热地区之一,在海拔800—900米以下的山地上广泛分布着稀树灌草丛。根据《元江府志》(1714年编纂)、《元江州志》(1826年编纂)、《元江志稿》(1922年编篡)及对现存植被的考察,本文探讨了元江干热河谷山地五百年来植被的变迁。 元江县森林复盖率的减少与人口的增加有密切关系,十七世纪中期以前,森林复盖率在75％以上,十八、十九世纪时为70％左右,1958年为61.5％,1975年为27.3％,至1982年则为19.3％。研究表明,在十九世纪以前,这个地区分布的主要植被是热带季雨林,甚而热带季节雨林,以后热带稀树灌草丛则迅速发展。植被的历史变化与土壤流失密切相关。植物群落的演变是由以乔木树种为优势演变为以灌木种类为优势,再演变为以多年生草木植物为优势,而最后则成为裸地。本文也讨论了这个地区植被恢复的方法。