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961.
应用模拟试验的方法,研究了“草基-鱼塘”系统中的能量转化与养分循环.结果表明,该系统中饲草对太阳能的利用率为0.83%,鱼对饲料能的转化率为7.3%.与以粮食作为鱼饲料比较,单位面积草地的产鱼当量是粮食作物的1.6倍.鱼对饲料N、P、K的转化率分别为16.8%、32.3%和2.0%.塘泥沉积的N、P分别占饲料的23.4%和56.1%;猪对饲料N、P、K的转化率分别为20.5%、33.7%和4.6%,猪粪尿回收饲料N为36.4%、P为63.8%、K为39.4%.猪-草-鱼结合的基塘系统其能量和养分转化效率均高于单一的养鱼系统. 相似文献
962.
The effects of tidalrestrictions by diking on salt marshbiogeochemistry were interpreted by comparingthe hydrology, porewater chemistry and solidphase composition of both seasonally floodedand drained diked marshes with adjacentnatural salt marshes on Cape Cod,Massachusetts. Flooding periods weregreatest in natural and least in drainedmarshes.Differences between the chemistry of thenatural and diked marshes depended upon thedepth of the water table and the supply ofsulfate for anaerobic metabolism. Drainedmarsh sediments were highly acidic (pH <4)with porewaters rich in dissolved Fe; thenatural and diked flooded marshes had pH 6–7.5and Fe orders of magnitude lower. Porewater nutrients, sulfides and alkalinitywere much lower in both flooded and draineddiked marshes than in the natural marsh.Sediments of the drained marsh had subsided90 cm relative to the natural site due toorganic matter decomposition and compaction. However, despite the loss of organic matter,much of the P and N was retained, withNH4 likely protected from nitrificationby low pH and PO4 adsorbed on Fe and Aloxides. Iron, and to a lesser degree sulfur,had also been well retained by the sediment. Despite eight decades of diking, substantialamounts of reduced S, representing potentialacidity, persisted near the top of the watertable.In contrast, the surface of the seasonallyflooded marsh was only 15 cm below thenatural marsh. Accretion since dikingamounted to 25 cm and involved proportionallyless mineral matter.The restoration of seawater flow to bothseasonally flooded and drained diked marsheswill likely extend flooding depth andduration, lower redox, increase cationexchange, and thereby increase NH4,Fe(II), and PO4 mobilization. Increasedporewater nutrients could benefitrecolonizing halophytes but may also degradesurface water quality. 相似文献
963.
Export of DOC from forested catchments on the Precambrian Shield of Central Ontario: Clues from 13C and 14C 总被引:3,自引:2,他引:1
S.L. Schiff R. Aravena S.E. Trumbore M.J. Hinton R. Elgood P.J. Dillon 《Biogeochemistry》1997,36(1):43-65
Export of dissolved organic carbon (DOC) from forested catchmentsis governed by competing processes of production, decomposition, sorptionand flushing. To examine the sources of DOC, carbon isotopes (14Cand 13C) were analyzed in DOC from surface waters, groundwatersand soils in a small forested catchment on the Canadian Shield in centralOntario. A significant fraction (greater than 50%) of DOCin major inflows to the lake is composed of carbon incorporated into organicmatter, solubilized and flushed into the stream within the last 40 years. Incontrast, 14C in groundwater DOC was old indicating extensiverecycling of forest floor derived organic carbon in the soil column beforeelution to groundwater in the lower B and C soil horizons. A small uplandbasin had a wide range in 14C from old groundwater values atbaseflow under dry basin conditions to relatively modern values during highflow or wetter antecedent conditions. Wetlands export mainly recently fixedcarbon with little seasonal range. DOC in streams entering the small lakemay be composed of two pools; an older recalcitrant pool delivered bygroundwater and a young labile pool derived from recent organic matter.The relative proportion of these two pools changes seasonally due thechanges in the water flowpaths and organic carbon dynamics. Althoughchanges in local climate (temperature and/or precipitation) may alterthe relative proportions of the old and young pools, the older pool islikely to be more refractory to sedimentation and decomposition in thelake setting. Delivery of older pool DOC from the catchment andsusceptibility of this older pool to photochemical decomposition mayconsequently be important in governing the minimum DOC concentrationlimit in lakes. 相似文献
964.
Remobilised nitrogen and root uptake of nitrate for spring leaf growth,flowers and developing fruits of pear (Pyrus communis L.) trees 总被引:1,自引:0,他引:1
Both uptake of fertiliser N and remobilisation of stored N were quantified for the early growth of spur and shoot leaves, flowers and fruit development of pear trees. One-year old Abbé F. trees grafted on quince C rootstocks were fertilised with a generous N supply for one year and while dormant during the winter, transferred to sand cultures. Each tree received 3 g of labelled nitrate-N at the end of winter and in early spring. Leaves, flowers and fruit were sampled on 5 separate occasions and the recovery of labelled N used to distinguish the remobilisation of N and the root uptake of nitrate. Remobilisation of stored N accounted for most of the N present in leaves and flowers during blossoming. Remobilisation of nitrogen stopped between petal fall and the beginning of fruit development. Root uptake of nitrate linearly increased over time and at the last sampling, 55 days after bud burst, fertiliser N contributed approximately half of the total N recovered in both spur and shoot leaves, the remainder coming from remobilisation. Flowers and fruits based their N metabolism more on remobilisation as compared to the leaves. This pattern of internal cycling of N is discussed in relation to fertilisation strategies for pear trees. 相似文献
965.
The phase-shift presaturation technique for water suppression is further improved with effective phase cycling. In the two-dimensional NMR COSY, NOESY and HMQC experiments of biosamples, the water sup-pression factor reaches the order of 10 , making it possible to detect 13C NMR signals in extremely diluted (2 mmol/L) aqueous solutions. 相似文献
966.
McCormick Paul V. Shuford III Robert B. E. Backus John G. Kennedy William C. 《Hydrobiologia》1997,362(1-3):185-210
We sampled periphyton in dominant habitats at oligotrophic and eutrophic sites in the northern Everglades during the wet and
the dryseasons to determine the effects of nutrient enrichment on periphytonbiomass, taxonomic composition, productivity,
and phosphorus storage. Arealbiomass was high (100–1600 g ash-free dry mass [AFDM]m−2) in oligotrophic sloughs and in stands of the emergentmacrophyte Eleocharis cellulosa, but was low in adjacent stands of
sawgrass,Cladium jamaicense (7–52 g AFDM m−2). Epipelon biomasswas high throughout the year at oligotrophic sites whereas epiphyton andmetaphyton biomass varied seasonally
and peaked during the wet season.Periphyton biomass was low (3–68 g AFDM m−2) and limitedto epiphyton and metaphyton in open-water habitats at eutrophic sites andwas undetectable in cattail stands (Typha
domingensis) that covered morethan 90% of the marsh in these areas. Oligotrophic periphytonassemblages exhibited strong seasonal
shifts in species composition and weredominated by cyanobacteria (e.g., Chroococcus turgidus, Scytonema hofmannii)during the
wet season and diatoms (e.g. Amphora lineolata, Mastogloiasmithii) during the dry season. Eutrophic assemblages were dominated
byCyanobacteria (e.g., Oscillatoria princeps) and green algae (e.g., Spirogyraspp.) and exhibited comparatively little seasonality.
Biomass-specific grossprimary productivity (GPP) of periphyton assemblages in eutrophic openwaters was higher than for comparable
slough assemblages, but areal GPP wassimilar in these eutrophic (0.9–9.1 g C m−2d−1) and oligotrophic (1.75–11.49 g C m−2d−1) habitats. On a habitat-weighted basis, areal periphytonGPP was 6- to 30-fold lower in eutrophic areas of the marsh due to
extensiveTypha stands that were devoid of periphyton. Periphyton at eutrophic siteshad higher P content and uptake rates than
the oligotrophic assemblage, butstored only 5% as much P because of the lower areal biomass.Eutrophication in the Everglades
has resulted in a decrease in periphytonbiomass and its contribution to marsh primary productivity. These changesmay have
important implications for efforts to manage this wetland in asustainable manner.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
967.
Michael Doebeli Graeme D. Ruxton 《Evolution; international journal of organic evolution》1997,51(6):1730-1741
We study the evolution of dispersal rates in a two patch metapopulation model. The local dynamics in each patch are given by difference equations, which, together with the rate of dispersal between the patches, determine the ecological dynamics of the metapopulation. We assume that phenotypes are given by their dispersal rate. The evolutionary dynamics in phenotype space are determined by invasion exponents, which describe whether a mutant can invade a given resident population. If the resident metapopulation is at a stable equilibrium, then selection on dispersal rates is neutral if the population sizes in the two patches are the same, while selection drives dispersal rates to zero if the local abundances are different. With non-equilibrium metapopulation dynamics, non-zero dispersal rates can be maintained by selection. In this case, and if the patches are ecologically identical, dispersal rates always evolve to values which induce synchronized metapopulation dynamics. If the patches are ecologically different, evolutionary branching into two coexisting dispersal phenotypes can be observed. Such branching can happen repeatedly, leading to polymorphisms with more than two phenotypes. If there is a cost to dispersal, evolutionary cycling in phenotype space can occur due to the dependence of selection pressures on the ecological attractor of the resident population, or because phenotypic branching alternates with the extinction of one of the branches. Our results extend those of Holt and McPeek (1996), and suggest that phenotypic branching is an important evolutionary process. This process may be relevant for sympatric speciation. 相似文献
968.
Summary Breakdown of dry matter and release of nutrients from decomposing leaf litter and forest-floor material were measured in a
34-year-old red pine (Pinus resinosa Ait.) plantation in central Wisconsin using (1) leaf-litter bags (2) litterfall and forest-floor nutrient data and an exponential
decay function, and (3) nutrient flux data and a mass balance equation. After one year of decomposition, 77% of the original
dry matter in leaf-litter bags remained. The release of macronutrients in decomposing leaf litter was K>Mg>P, S>N>Ca, and
the release of micronutrients and aluminum was Mn, B>Al>Cu>Zn. Nitrogen in decomposing leaf litter showed the leaching, accumulation,
and final release phases delineated by Berg and Staff4. Half-lives of dry matter and nutrients in the forest floor ranged from 0.5 (K) to 39 (Al) yr. Forest-floor turnover rates
of the various elements followed the same trends as in leaf-litter bags except that Ca turned over more readily than P, S,
and N and Zn turned over more readily than the other micronutrients. A forest-floor nutrient balance sheet confirmed that
the macronutrients N and Ca are accumulating most readily in the forest floor. The overall implications of these trends for
tree nutrition are discussed. 相似文献
969.
Respiring rat liver mitochondria are known to spontaneously release the Ca2+ taken up when they have accumulated Ca2+ over a certain threshold, while Sr2+ and Mn2+ are well tolerated and retained. We have studied the interaction of Sr2+ with Ca2+ release. When Sr2+ was added to respiring mitochondria simultaneously with or soon after the addition of Ca2+, the release was potently inhibited or reversed. On the other hand, when Sr2+ was added before Ca2+, the release was stimulated. Ca2+-induced mitochondrial damage and release of accumulated Ca2+ is generally believed to be due to activation of mitochondrial phospholipase A (EC 3.1.1.4.) by Ca2+. However, isolated mitochondrial phospholipase A activity was little if at all inhibited by Sr2+. The Ca2+ -release may thus be triggered by some Ca2+ -dependent function other than phospholipase. 相似文献
970.
Relationships between soil microbial properties and aboveground stand characteristics of conifer forests in Oregon 总被引:4,自引:0,他引:4
Eight forest sites representing a large range of climate, vegetation, and productivity were sampled in a transect across Oregon to study the relationships between aboveground stand characteristics and soil microbial properties. These sites had a range in leaf area index of 0.6 to 16 m2 m–2 and net primary productivity of 0.3 to 14 Mg ha–1 yr–1.Measurements of soil and forest floor inorganic N concentrations and in situ net N mineralization, nitrification, denitrification, and soil respiration were made monthly for one year. Microbial biomass C and anaerobic N mineralization, an index of N availability, were also measured. Annual mean concentrations of NH
4
+
ranged from 37 to 96 mg N kg–1 in the forest floor and from 1.7 to 10.7 mg N kg–1 in the mineral soil. Concentrations of NO
3
–
were low ( < 1 mg N kg–1) at all sites. Net N mineralization and nitrification, as measured by the buried bag technique, were low on most sites and denitrification was not detected at any site. Available N varied from 17 to 101 mg N kg–1, microbial biomass C ranged from 190 to 1230 mg Ckg–1, and soil respiration rates varied from 1.3 to 49 mg C kg–1 day–1 across these sites. Seasonal peaks in NH
4
+
concentrations and soil respiration rates were usually observed in the spring and fall.The soils data were positively correlated with several aboveground variables, including leaf area index and net primary productivity, and the near infrared-to-red reflectance ratio obtained from the airborne simulator of the Thematic Mapper satellite. The data suggest that close relationships between aboveground productivity and soil microbial processes exist in forests approaching semi-equilibrium conditions.Abbreviations IR
infrared
- LAI
leaf area index
-
k
c
proportion of microbial biomass C mineralized to CO2
- NPP
net primary productivity
- TM
Thematic Mapper 相似文献