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101.
102.
V. P. Shabaev 《Plant and Soil》1986,91(2):249-256
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. 相似文献
103.
E. Wada R. Imaizumi Y. Kabaya T. Yasuda T. Kanamori G. Saito A. Nishimune 《Plant and Soil》1986,93(2):269-286
Summary Plants from agricultural and natural upland ecosystem were investigated for15N content to evaluate the role of symbiotic N2-fixation in the nitrogen nutrition of soybean. Increased yields and lower δ15N values of nodulating soybeansvs, non-nodulating isolines gave semi-quantitative estimates of N2 fixation. A fairly large discrepancy was found between estimations by δ15N and by N yield at 0 kg N/ha of fertilizer. More precise estimates were made by following changes in plant δ15N when fertilizer δ15N was varied near15N natural abundance level. Clearcut linear relationships between δ15N values of whole plants and of fertilizer were obtained at 30 kg N/ha of fertilizer for three kinds of soils. In experimental
field plots, nodulating soybeans obtained 13±1% of their nitrogen from fertilizer, 66±8% from N2 fixation and 21±10% from soil nitrogen in Andosol brown soil; 30%, 16% and 54% in Andosol black soil; 7%, 77% and 16% in
Alluvial soil, respectively. These values for N2 fixation coincided with each corresponding estimation by N yield method.
Other results include: 1)15N content in upland soils and plants was variable, and may reflect differences in the mode of mineralization of soil organics,
and 2) nitrogen isotopic discrimination during fertilizer uptake (δ15N of plant minus fertilizer) ranged from −2.2 to +4.9‰ at 0–30 kg N/ha of fertilizer, depending on soil type and plant species.
The proposed method can accurately and relatively simply establish the importance of symbiotic nitrogen fixation for soybeans
growing in agricultural settings. 相似文献
104.
Review article number 6 : Plant molluscicides 总被引:1,自引:0,他引:1
A review on the application of plant molluscicides in the control of schistosomiasis is presented. Laboratory bioassays are discussed, together with criteria for activity. An attempt has been made to provide a comprehensive list of known molluscicidal natural products. 相似文献
105.
Timothy J. Fahey Joseph B. Yavitt John A. Pearson Dennis H. Knight 《Biogeochemistry》1985,1(3):257-275
Storage and flux of nitrogen were studied in several contrasting lodgepole pine (Pinus contorta spp.latifolia) forests in southeastern Wyoming. The mineral soil contained most of the N in these ecosystems (range of 315–860 g · m–2), with aboveground detritus (37.5–48.8g · m–2) and living biomass (19.5–24.0 g · m–2) storing much smaller amounts. About 60–70% of the total N in vegetation was aboveground, and N concentrations in plant tissues were unusually low (foliage = 0.7% N), as were N input via wet precipitation (0.25 g · m–2 · yr–1), and biological fixation of atmospheric N (<0.03 g · m–2 · yr–1, except locally in some stands at low elevations where symbiotic fixation by the leguminous herbLupinus argenteus probably exceeded 0.1 g · m–2 · yr–1).Because of low concentrations in litterfall and limited opportunity for leaching, N accumulated in decaying leaves for 6–7 yr following leaf fall. This process represented an annual flux of about 0.5g · m–2 to the 01 horizon. Only 20% of this flux was provided by throughfall, with the remaining 0.4g · m–2 · yr–1 apparently added from layers below. Low mineralization and small amounts of N uptake from the 02 are likely because of minimal rooting in the forest floor (as defined herein) and negligible mineral N (< 0.05 mg · L–1) in 02 leachate. A critical transport process was solubilization of organic N, mostly fulvic acids. Most of the organic N from the forest floor was retained within the major tree rooting zone (0–40 cm), and mineralization of soil organic N provided NH4 for tree uptake. Nitrate was at trace levels in soil solutions, and a long lag in nitrification was always observed under disturbed conditions. Total root nitrogen uptake was calculated to be 1.25 gN · m–2 · yr–1 with estimated root turnover of 0.37-gN · m–2 · yr–1, and the soil horizons appeared to be nearly in balance with respect to N. The high demand for mineralized N and the precipitation of fulvic acid in the mineral soil resulted in minimal deep leaching in most stands (< 0.02 g · m–2 · yr–1). These forests provide an extreme example of nitrogen behavior in dry, infertile forests. 相似文献
106.
BioControl - Insects associated with the Sitka spruce weevil,Pissodes strobi (Peck), on Sitka spruce,Picea sitchensis (Bong.) Carr. were sampled at 9 locations in British Columbia. Fourteen species... 相似文献
107.
108.
Dong Ming 《Plant Ecology》1987,72(1):35-44
Masson Pine (Pinus massoniana Lamb.) is a pioneer in forest succession in the subtropics of East Asia. However, the species persits, though with decreasing
abundance, throughout the various successional phases. Agestructure, spatial pattern, density, population biomass, and their
dynamics are described for a population in Sichuan, China, on the basis of a census of all individuals in the population while
substituting space with time. In the course of succession, the population density increases and its rate of growth decreases
until self-thinning starts; during the phase of self-thinning density decrease and continues to decrease even afterwards,
but the rate of growth increase markedly after self-thinning has stopped. The development of population biomass (Bp) during
the early succession from shrub-grassland to the early stages of mixed pine and broad-leaved forest can be described by a
logistic equation. Later, Bp decrease rapidly. These changes are governed partly by inherent biological features of P. massoniana and partly by the invasion, establishment and development of shade-tolerant evergreen broad-leaved trees. Both self- and
alien-thinning occur. Soil conditions affect the rates of these processes. 相似文献
109.
George M. White 《Cell biochemistry and biophysics》1987,11(1):25-33
Computers, the human mind, and social systems have common problems of inadequate memory and insufficient data manipulation
speed. In each of these domains, information compression techniques have evolved to reduce storage and processing needs. Among
the techniques for information compression, coding of information in procedures stands out as exceptionally powerful. Procedural
information coding also gives rise to behavior that may be defined as intelligent. It is found in the human mind, in machines
and in social systems. Its use in human thought is aided by language development which promotes regular review of abstract
procedures. A practical consequence of better understanding of procedural information coding is the possibility of training
people to exhibit greater mental capacity, a controversial possibility. This paper explores the impact of data processing
resource limitations, data compression and procedural thinking in men and machines. 相似文献
110.
The effects of in vivo ultrasound irradiation of the spleen on immunological functions were assessed with an in vitro natural killer (NK) cell cytotoxic assay. Anesthetized hamsters were exposed to 1 MHz ultrasound at intensity levels currently being used clinically for therapeutic diathermy and hyperthermia (1-5 W/cm2, for 500 sec with constant beam scanning). Hyperthermic levels in the spleen ranged from 38-43 degrees C. Significant depression of natural killer (NK) cell activity was seen 4 h after spleen irradiation as compared to sham irradiated and normal animals. A return towards normal levels was observed in experimental groups at 24 h after exposure. Sham and normal animals were not significantly different in NK activity, indicating no significant stress-related immunosuppressive effects due to handling. Differential leukocyte counts taken for each exposure condition showed significant lymphopenia at 4, 8, and 16 h after exposure, near normal levels at 24 h, and complete recovery by 48 h. The number of circulating mononuclear cells at 4 h showed a dose-related suppression as the exposure intensities were increased. 相似文献