Enclosure experiment on the control mechanism of planktonic bacterial standing stock

In order to understand the control mechanisms of a large, stable bacterial standing stock, enclosure experiments were conducted in a eutrophic lake, where both bacterial productivity and grazing pressure were very high. Total bacterial number in the different enclosures ranged from 1.2 to 2.7×10⁷ cells mL⁻¹ throughout the experiment. The average bacterial cell production rate estimated from a grazer eliminating experiment was 6.3×10⁵ cells mL⁻¹ h⁻¹. Difference in the bacterial cell production rate between shaded and unshaded enclosures was not apparent. Bacteria showed a reduction in standing stock of only about 25–30% even after the supply of light was cut to 1%. Bacteria in the shaded enclosures then recovered their production rate in the first 12 days of perturbation. Grazing pressure in the shaded enclosures was not less than that for the control. Thus, it was considered a control mechanism of bacterial stable standing stock that the bacteria shifted their organic substrate from extracellular dissolved organic carbon freshly released from phytoplankton to that already stocked in the water column, though it is not known whether the dominant bacteria were the same.     

The effect of cropping and fertiliser nitrogen rates on nitrogen balance in soil

Summary Fertilizer/soil N balance of cropped and fallow soil has been studied in a pot experiment carried out with grey forest soil (southern part of Moscow region) at increasing rates of¹⁵N labelled ammonium sulfate (0; 8; 16; 32 mg N/100 g of soil). The fertilizer¹⁵N balance has been shown to depend upon its application rate and the presence of growing plants. Fertilizer N uptake efficiency was maximum (72.5%) and gaseous losses-minimum (12.5%) at the application rate of 16 mg N/100 g of soil. Fertilizer N losses from the fallow soil were 130–220% versus those from the cropped soil. At the application of fertilizer N the plant uptake of soil N was 170–240% and the amount of soil N as N–NH₄ exchangeable + N–NO₃ in fallow was 350–440% as compared to the control treatment without nitrogen (PK).After cropping without or with N fertilizer application at the rates of 8 and 32 mg N/100 g of soil, a positive nitrogen balance has been found which is likely due to nonsymbiotic (associative) N-fixation. It has been shown that biologically fixed nitrogen contributes to plant nutrition.     

Parthenogenesis in Tubificidae

The ability of tubificids to reproduce parthenogenetically following or in place of bisexual reproduction has been proved. During parthenogenesis the spermatogenesis ceases at an early stage of sexual cell development, which, together with some peculiarities of the structure of the sexual system, rules out the possibility of self-fertilization in the worms. For two years of cultivation the life cycles of 3 parthenogenetic generations in Tubifex tubifex and 2 in Limnodrilus hoffmeisteri were traced.     

大棚黄瓜霜霉病生态防治方法研究——温度控制试验研究初报

黄瓜霜霉病是对黄瓜生长发育危害最大的世界性病害。通过两年共10个处理的田间对比试验发现,大棚黄瓜霜霉病的发生发展与环境温度条件存在着十分密切的关系,在一定温度范围内(15℃—48℃),棚内日最高气温越高,发病期越晚,病越轻,产量越高。控制方法是:在大棚内日最低气温稳定大于10℃后,每隔一天对大棚进行一次40—47℃、并维持2小时左右的高温处理(其中大于42℃持续1.5小时左右,大于45℃持续1小时左右),然后大面积通风换气。方法简便易行、效果很好。     

Oligochaetes and eutrophication; an experiment over four years in outdoor mesocosms

Eight experimental ditch mesocosms were used to study the effect of eutrophication over four years. The experimental ditches had a sand or clay bottom. The ditches were treated with additions of phosphorus, phosphorus and nitrogen, or without additions (controls). Oligochaetes were sampled by deploying trays with substratum for colonization over twenty weeks. Both the important variables phosphorus, nitrogen and oxygen as well as the oligochaete species and numbers are presented. The effects of nutrient additions on phosphorus, nitrogen and oxygen concentrations were described together with changes in oligochaete species composition and numbers. The results were further analyzed by redundancy analysis (RDA). In the clay-lined ditches nutrient addition coincided with fluctuation in oxygen concentration. The higher the nutrient addition levels the longer the period of oxygen depletion became. During oxygen depletion the number of oligochaetes was strongly reduced or even became zero. The low nutrient status of the sandy bed in the sand-lined ditches slowed down the rate of colonization. Only a few tubificids were collected. Eutrophication effects were only observed at the highest nutrient addition level. Considerable variation is attributed to stochastic factors in the sand-lined ditches. Whether oligochaete species were present was related to the length of the colonization period. The substratum composition and food together with oxygen regime decided whether they become more or less abundant in ditches. Large-scale mesocosm experiments require time to develop. Only after the first colonization period variables of species presences and abundances can be employed to detect changes associated with eutrophication. Oligochaetes can be used to measure colonization as well as eutrophication processes.     

Effects of nutrient availability and neighbours on shoot growth,resprouting and flowering of Erica multiflora

Abstract. To test if low soil fertility and competition limit the performance of Mediterranean shrubs, and if the effects of competition on plant performance were modified by soil fertility, we subjected shrubs of Erica multiflora to a factorial field experiment of fertilization and removal of neighbours around target plants. After 18 months of treatment, fertilization had stimulated the growth of pre-existent sprouts and biomass allocation to stems into new sprouts, but decreased the frequency of sprout flowering. Removal of neighbours increased the number and biomass of new sprouts, the probability of sprout flowering and the biomass of flowers. Fertilization slightly enhanced sprout recruitment and the probability of sprout flowering when neighbours were removed, but did not modify the other parameters of plant performance. According to our results, both low soil fertility and competition limited plant performance. Competition was slightly more intense in fertilized plants, but only in determining sprout and flowering bud stimulation.     

A morphological study and hybridization analysis of Caloglossa leprieurii (Ceramiales, Rhodophyta) from Japan, Singapore and Australia

Morphological and hybridization experiments were performed on Caloglossa leprieurii (Montagne) J. Agardh collected from Japan, Singapore and Australia in order to evaluate taxonomic characters of this species. Within C. leprieurii at least four mating groups were recognized from the Indo-Pacific region. These mating groups could be characterized by the blade width at the inter-node and the cell-row numbers on the opposite side derived from the first axial cell at the main axis, though these properties showed a certain variability even in the same plant under both field and culture conditions. The phylogenetic relationship and geographic distribution of the four mating groups are discussed.     

Gravitropically-stimulated seedlings show autotropism in weightlessness

In a spaceflight experiment, autotropism by oat ( Avena sativa L.) coleoptiles following gravitropic responses was prominent in weightlessness: counter-reactions led to the straightening of the curved coleoptiles. This was not the case during clinorotation on earth. The autotropic reactions appeared to be related to the stimulus received during the stimulus period, i.e. the greater the response the greater the autotropic counter-reaction. Previous models of the gravitropic system which predicted that coleoptiles would not straighten in weightlessness are disproved. A modification to one of the models is proposed which includes the autotropic response observed in spaceflight. The nature of the counter-reactions in the absence of gravitropic stimulation is discussed.     

Natural regeneration of Pinus resinosa on burned and unburned sites in Newfoundland

Abstract. Natural regeneration of Pinus resinosa (red pine) seedlings around mature trees was studied in burned and unburned stands. Growth inhibitory effects of the forest organic matter on red pine seedlings was tested by a stair-step experiment using leachate of forest soil monoliths and also by a seed germination bio-assay using forest floor substrates. To test if higher burning temperatures can remove the allelopathic effects of red pine-Kalmia organic matter, a laboratory bio-assay was conducted by germinating red pine seeds on the organic matter burned at 200, 400, 600 and 800°C. Deposition of dry needles and a thick duff layer under red pine stands affected seedling establishment. Red pine seedling establishment increased with the decreasing thickness of duff layer away from the stump of the seed-bearing trees. Wildfire helped in removing the duff layer and increased seedling establishment. A high fuel load within a 0 - 1 m radius around the tree stump caused a deep burn of the organic matter including part of the soil seed reserve. On a burned-over surface, more seedlings established in a band between 1 and 2 m around the stump than inside and outside the band. Primary root growth of red pine was severely inhibited when the seedlings were grown in unburned forest floor organic matter where Kalmia was the principal understory species. Water leachate of a Pinus resinosa-Kalmia soil monolith was inhibitory to red pine seedling growth. In greenhouse conditions, the seedlings grew well in burned-over soil from a Pinus resinosa stand. Burned organic matter from a red pine forest showed an increase in pH with a burning temperature of 600°C. Primary root growth of red pine seedlings was similarly increased with increasing temperature up to 600°C; at higher temperatures the root length of seedlings did not increase any further.