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51.
青甘边区黑河流域森林植被带及其昆虫区系的组成 总被引:1,自引:0,他引:1
黑河发源于青海、甘肃交界的祁连山区,是甘肃河西走廊最大的内陆河水系之一,水源丰富,流量稳定,这不仅取决于祁连山区大气降水和冰川融水,更重要的是与上游森林植被密不可分。但是,由于森林害虫猖獗成灾,严重威胁着这一地域森林的生存。近几年我们在森林昆虫普查的基础上,对黑河流域森林昆虫 相似文献
52.
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54.
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
55.
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
56.
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
57.
An igapó forest near the confluence of Rio Tarumã Mirim (Tarumãzinho) and Rio Negro has been studied. It is a typical ectotroph forest with a raw humus layer and suppressed litter decomposing activity by Higher (i.e., carpophore-producing) Fungi. The number of the latter is about one-fifth of that observed in the (anectotrophic) terra firme forest. All ectotrophically mycorrhizal fungi observed belonged in three families:Amanitaceae, Boletaceae, Russulaceae. Leguminosae are dominant, and of theseAldina latifolia andSwartzia cf.polyphylla were demonstrably ectomycorrhizal. The scarcity of mineral nutrients in the soils of igapó, campinarana and campina is overcome by direct cycling through ectomycorrhizae. This is in contrast to other black- and white-water inundated forest communities in Amazonia.Litter Decomposition and Ectomycorrhiza in Amazonian Forests3. Previous contributions seeSinger & Araujo (1979) andSinger & al. (1983). 相似文献
58.
Ingvar B. Andersson 《Hydrobiologia》1983,101(1-2):59-64
Total bacterial numbers in different strata of lake water and in inlet and outlet streams have been recorded during a yearly cycle. A calculated mean cell volume of 0.342 µm2 has then been used to estimate bacterial biomass in the lake. Change of biomass during the year was substantial and the range was from about 0.1 g · m–3 to about 1.0–1.2 g · m–3. The seasonal development included a spring-early summer increase followed by a decrease to the minimum in July–August. Correlation between epi- and hypolimnion was high and in both strata two dominant autumn peaks in biomass appeared. With the exception of the last autumn peak the development of bacterial biomass was closely related to development of phytoplankton biomass and production. 相似文献
59.
The roots and mycorrhizas of herbaceous woodland plants 总被引:4,自引:0,他引:4
60.
Thierry Becquer Denis Merlet Jean-Pierre Boudot James Rouiller Francis Gras 《Plant and Soil》1990,125(1):95-107
Nitrate uptake and leaching were measured during one year in a declined fir forest on the Vosges highlands (eastern France),
in order to investigate whether excess nitrification could be responsible for a deleterious acidification of the ecosystem.
Nitrate uptake by the vegetation was active mainly from spring to early fall, and then reached about 66 kg N ha-1. No significant leaching loss occurred during the growth period of the vegetation. Significant nitrate leaching occurred
in winter (about 17 kg N ha-1). During fall and winter the nitrification rate was of the same magnitude as values reported for other ecosystems, and, thus,
was not considered to be abnormaly strong. No abnormal temporal discoupling of nitrate production and nitrate uptake occurred
in the ecosystem, and forest decline must therefore have some other cause. 相似文献