温带灌木生态系统的动态特征--生物量和元素循环

本文通过对北京郊区的一个经皆伐以后，自然发育二十多年的次生灌木生态系统的定量研究，结果如下： 1）该生态系统年中最高生物量可达20.30 t/ha，但没有明显的年净增加，从而推出该系统可能进入一种比较稳定的平衡状态，生物量最高出现于秋季（生长季末）;最低为春季（生长季始），这主要是由于从秋季到春季经历了凋落和休眠的过程。另外，灌木的地下部分生物量与地上之比接近1，这也是对灌木生长发育特征的反映。 2）植物各个部位--侧根，主根，主枝，侧枝，叶---有不同的烧失量，但三种植物几乎有相似的顺序，即：主枝>侧枝><主根>侧根>叶（荆条的叶与侧根有相反的顺序）。烧失量反映了有机物质在植物各个部位的含量。 3）十种元素（N，K，Ca，Mg，Na，Cu，Zn，Fe，Al，Mn）在同一种植物，同种元素在不同植物，植物的不同部位，都有不同的含量，并且随着季节的变化而变化。 4）降水中所含的元素是生态系统营养的重要来源，尤其是一些大量元素如K, Na, Ca, Mg等。一般地冠流中的元素含量要高于降水中的，冠流中元素浓度与降水中的比值，不同的元素是不相同的，其中K为2-7倍，Na为1-3倍，Ca, Mg为1-2倍，对同一元素，比值的大小降水的时间有一定的关系，也即有时间性的变化。 5）土壤的水分含量不仅由于雨季和旱季而发生变化，还随土壤的不同的而异，而这种变化又随着季节性而不同。 6）营养元素输入--输出预算表明，各个元素基本上没有明显的存留，甚至有微量的亏损，但仍可以判断，该生态系统基本上处于一种较稳定的平衡状态。

北京东灵山地区森林植物养分利用效率研究

本文选择东灵山地区具有代表性的11种植物，研究了植物叶片养分元素动态特征以及各个层次物种、生活型和生境等对植物叶片养分元素再吸收的影响。主要结论如下： 1、不同物种间、以及相同物种在不同森林类型内的叶片C素含量变化程度较小;11个物种之间叶片N素养分浓度差很大，但各种植物叶片的N素含量的季节变化比较一致，大多数情况下表现为单峰型或双峰变化曲线;各种森林类型中11种植物叶片P的最高含量都出现在生长初期，以后开始下降。 2、在物种水平、养分再吸收是一种重要的养分保存机制，N素和P素再吸收率大约为50%，对这两种养分元素而言，相同生境下生长的不同植物种的养分再吸收率不同，存在显著差异，而同一植物种不同生境下养分再吸收率之间也存在差异，而S素的差异则不显著。 3、同一生活型在不同的森林类型中养分再吸收率差异不明显，同一森林类型中不同生活型的养分再吸收率差异也不明显;高养分再吸收率不是低养分环境所选择的优势性状，低养分环境中的物种主要通过延长叶片寿命和加强低养分浓度状况下的物质合成来适应低养分环境。 4、除了土壤pH值外，土壤容重、土壤有机质、土壤全氮、土壤阳离子交换量在三种生境下都表现出一定的差异性。华北落叶松林生境下的土壤养分含量较丰富，其次是落叶阔叶混交林，辽东栎林相对前二种生境其土壤养分相对低一些，但在三种生境之间养分元素再吸收率差异不显著，植物养分再吸收没有或微弱地受控于土壤养分获得的能力。

Methane and carbon dioxide fluxes from a shallow hypereutrophic subtropical Lake in China

Up to now, there have been few studies in the annual fluxes of greenhouse gases in lakes of subtropical regions. The fluxes of methane (CH4) and carbon dioxide (CO2) across air-water interface were measured in a shallow, hypereutrophic, subtropical Lake Donghu (China) over a year cycle, using a static chamber technique. During the year, Lake Donghu emitted CH4 and CO2; the average flux of CH4 and CO2 was 23.3 +/- 18.6 and 332.3 +/- 160.1 mg m(-2) d(-1), respectively. The fluxes of CH4 and CO2 showed strong seasonal dynamics: CH4 emission rate was highest in summer, remaining low in other seasons, whereas CO2 was adsorbed from the atmosphere in spring and summer, but exhibited a large emission in winter. Annual carbon (C) budget across air-water interface in Lake Donghu was estimated to be 7.52 +/- 4.07 x 10(8) g. CH4 emission was correlated positively with net primary production (NPP) and temperature, whereas CO2 flux correlated negatively with NPP and temperature; however, there were no significant relationships between the fluxes of CH4 and CO2 and dissolved organic carbon, a significant difference from boreal lakes, indicating that phytoplankton rather than allochthonous matter regulated C dynamics across air-water interface of subtropical lake enriched nutrient content. (c) 2005 Elsevier Ltd. All rights reserved.

施肥对黄土旱塬区黑垆土土壤肥力及硝态氮累积的影响

本文以长期定位试验为依托,研究了黄土高原旱塬区黑垆土大田对比试验和长期定位施肥对土壤肥力及硝态氮累积和淋溶的影响。结果表明:长期施用有机肥能够明显增加土壤养分,氮磷和有机肥配施效果显著;和1984年土壤养分状况相比,大田对比试验土壤有机质增加了27.1%,全氮和全磷提高了84.2%和34.8%,有效氮、有效磷和速效钾增加了46.9%、540.0%和10.2%,养分水平与长期定位试验中氮磷配施相近。长期定位试验中氮磷配施或与有机肥配施能够有效地减少土壤剖面中硝酸盐的累积和淋溶,氮肥单施硝态氮累积量最大,为1006.4kg/hm2,大田对比试验土壤硝态氮总累积量较长期定位试验中施用氮肥处理的总累积量少。

水肥处理对黄瓜土壤养分、酶及微生物多样性的影响

以津优1号黄瓜为试材,设3个土壤相对含水量水平(50%～60%、70%～80%、90%～100%)和2个肥料追施量(600kgN·hm-2和420kgP2O5·hm-2,420kgN.hm-2和294kgP2O5·hm-2)处理,研究了不同水肥供应对日光温室黄瓜土壤养分、酶活性及微生物多样性的影响.结果表明:土壤中NH4+-N含量随施肥量的增加而提高,随土壤相对含水量的增加而降低;水肥供给的增加有利于提高土壤中速效磷含量和蔗糖酶活性;肥料增加使土壤中蛋白酶活性降低,而水分降低使土壤中脲酶活性提高.土壤中微生物多样性与土壤中养分含量无显著相关性,与土壤脲酶活性呈显著正相关,与蔗糖酶活性呈显著负相关.土壤相对含水量70%～80%、氮肥追施量600kgN·hm-2和420kgP2O5.hm-2处理的土壤养分含量、蔗糖酶、磷酸酶和脲酶活性较高,且土壤中微生物多样性和均匀度显著高于其他处理,土壤生产潜力最优.

长期施肥对黄土旱塬区土壤—植物系统中氮、磷养分的影响

对1984年建立的长期试验田,分析了2005年小麦产量、养分吸收及土壤养分变化。结果表明,单施磷肥增产25.6%,单施氮肥增产48.1%,其吸氮、磷量也相应增加,但收获指数显著低于对照;氮磷配施增产幅度为101.3%3~02.8%,养分吸收量增加显著,最佳施肥量为N2P2(N 90 kg/hm2、P 56.4 kg/hm2)。施肥明显改变了耕层土壤养分的含量,也影响了养分在土壤剖面的分布。氮磷配施是培肥土壤的有效途径,耕层土壤全磷增加了8.3%~45.2%,速效磷增加54.8%9~17.8%。中等施氮(N 90 kg/hm2)水平下,随着磷的增加,耕层土壤全磷累积和施磷量的关系为y=0.002x-0.112。速效磷含量增加和磷肥用量的关系为y=9.6537Ln(x)-35.371,施肥对60 cm以下磷素影响较小。

土壤改良剂与氮肥配施对玉米生长及其养分含量的影响

采用盆栽试验研究了秸秆配方、废料配方和胶土配方3种改良剂与氮肥配施对玉米植株生长状况、生物量、叶绿素含量、全N及全P含量的影响。结果表明:3种改良剂与0.5 g/盆氮肥配施可以显著提高株高、茎粗、叶面积、地上地下生物量、叶绿素含量及植株全N含量,且以秸秆配方配施效果最佳,过量施用氮肥(1.0 g/盆)时,各指标与0.5 g氮肥水平下的值相比增加幅度甚小,茎粗和地下生物量甚至有下降的趋势。改良剂因素和氮肥因素对全P含量也有一定的影响,但二者交互作用对其并未产生显著性影响。因此,在施加改良剂的条件下可以适当地减少肥料的使用量,在满足植物体吸收利用前提下,既减少了养分投入和浪费,又减轻了对环境的污染。

四种园林植物的热值与养分特征

测定了蔷薇科植物美人梅、樱花和木兰科植物白玉兰、广玉兰不同组分的热值、养分和灰分含量,探讨4种植物不同发育阶段根系、枝干和叶等器官的热值分配特征及其影响因子.结果表明:4种植物不同组分干质量热值和去灰分热值在17.02~21.93 kJ.g-1和18.42~22.57 kJ.g-1之间;叶片和细根具有较高的干质量热值和去灰分热值,去灰分热值随着根系和茎干(枝)的发育呈减小趋势.美人梅和樱花的干质量热值和去灰分热值总体上高于白玉兰和广玉兰.细根干质量热值和去灰分热值与其养分和灰分含量呈极显著相关(P<0.01).随着根系的发育,干质量热值和去灰分热值与有机碳含量的相关性逐渐降低,不同器官干质量热值与全氮含量相关性最强.

长期定位施肥对黑垆土剖面养分分布特征的影响

对黄土高原旱地 1 5年连续施肥后土壤剖面养分分布的研究发现 ,施化肥对土壤剖面有机质、全N、全P含量的影响深达 1 0 0cm以下 ,所有施肥处理有机质、全N、全P、NO3- N、有效P含量在耕层 (0～ 2 0cm)都有不同程度增加 ;40～ 60、60～ 80cm土层有机质、全N、全P都低于长年不施肥处理 ,造成土壤下层养分的亏缺。长期大量施用氮肥造成N素养分下淋累积 ;长期大量施用磷肥土壤耕层有效P显著提高 ,而 2 0cm以下土层变化不大。

Biochemical compositions of two dominant bloom- forming species isolated from the Yangtze River Estuary in response to different nutrient conditions

Variations of cellular total lipid, total carbohydrate and total protein content of two dominant bloom-forming species (Skeletonema costatum and Prorocentrum donghaiense) isolated from the Yangtze River Estuary were examined under six different nutrient conditions in batch cultures. Daily samples were collected to estimate the cell growth, nutrient concentration and three biochemical compositions content during 7 days for S. costatum and the same sampling procedure was done every other day during 10 days for P. donghaiense. Results showed that for S. costatum, cellular total lipid content increased under phosphorus (P) limitation, but not for nitrogen (N) limitation; cellular carbohydrate were accumulated under both N and P limitation: cellular total protein content of low nutrient concentration treatments were significantly lower than that of high nutrient concentration treatments. For P. donghaiense, both cellular total lipid content and total carbohydrate content were greatly elevated as a result of N and P exhaustion, but cellular total protein content had no significant changes under nutrient limitation. In addition, the capability of accumulation of three biochemical constituents of P. donghaiense was much stronger than that of S. costatum. Pearson correlation showed that for both species, the biochemical composition of three constituents (lipid, carbohydrate and protein) had no significant relationship with extracellular N concentration, but had positive correlation with extracellular and intracellular P concentration. The capability of two species to accumulate cellular total lipid and carbohydrate under nutrient limitation may help them accommodate the fluctuating nutrient condition of the Yangtze River Estuary. The different responses of two species of cellular biochemical compositions content under different nutrient conditions may provide some evidence to explain the temporal characteristic of blooms Caused by two species in the Yangtze River Estuary. (C) 2008 Elsevier B.V. All rights reserved.

Nutrient structure of seawater and ecological responses in Jiaozhou Bay, China

Nutrient concentrations in seawater, and C, N, P, Si and chlorophyll a content in different-sized particulates were measured in Jiaozhou Bay, and C, N, P, Si composition in different-sized fractions of phytoplankton and their ecological responses to nutrient structure of the seawater were studied. Microphytoplankton and nanophytoplankton were dominant in Jiaozhou Bay. High C (16.50-20.97 unol L-1), N (2.46-2.99 mu mol L-1) and low P (0.06-0.12 mu mol L-1), Si (0.18-0.57 mu mol L-1) content, and high N/P (24.7-64.6) and low SUP (4.4-10.8), Si/N (0.06-0.20) ratios were found in all sized groups of particulates. These values reflected the elemental compositions of different-sized fractions of phytoplankton as being an ecological response to the nutrients in the seawater. The ratios deviated significantly from the Redfield values. The nutrient composition of seawater and particulates and their relationship to chlorophyll a showed that phytoplankton growth was possibly limited by Si. Si limitation appears favorable for controlling the ecological equilibrium of Jiaozhou Bay. Different-sized fractions of phytoplankton had different suitability to nutrient structures of the seawater. Among phytoplankton size groups, nanophytoplankton and microphytoplankton growths were more adaptable in eutrophic Jiaozhou Bay, and more competitive for assimilation of Si. This is consistent with their diatom-dominated composition, controlling the biomass and productivity of phytoplankton in Jiaozhou Bay. (c) 2006 Elsevier Ltd. All rights reserved.

A Simulative Study on Effects of Climate Warming on Nutrient Contents and In Vitro Digestibility of Herbage Grown in Qinghai-Xizang Plateau

The increasing trend of air temperature along with the climate warming has been accepted gradual-ly by scientists and by the general public. Qinghai-Xizang Plateau, a unique geographic unit due to high-altitude climate, is one of the most susceptible regions to climate warming. Its ecosystem is very fragile and sensi-tive to climate change. In order to get a better understanding of the impacts of climate warming on the nutrient contents of herbage grown in Qinghai-Xizang Plateau, a simulative study was implemented at Daban Moutain by using temperature differences resulted from sites selected at different altitudes and nutrient contents and in vitro digestibility were determined for assessing the quality of the grown herbage. There were significant downtrends in crude protein (CP), ether extract (EE) and nitrogen free extract (NFE) contents of herbage along with the increase of temperature. It had a positive correlation between temperature and content of acid detergent fibre (ADF), acid detergent lignin (ADL) in herbage. In vitro digestibility of herbage decreased along with the in-crease of temperature. The results of this study indicated that climate warming significantly influence nutrient contents and in vitro digestibility of herbage grown in Qinghai-Xizang Plateau. It is suggested that the future climate warming especially the gradual rise of the night temperature could cause negative effect on herbage quality grown in Qinghai-Xizang Plateau by decreasing CP, EE, and NFE contents and increasing some indi-gestible ingredients such as crude fibre (CF), neutral detergent fibre (NDF), ADF, and ADL. This, conse-quently, decreases the ruminant assimilation ability.

Effect of Nb Content on the Microstructure and Mechanical Properties of Zr-Cu-Ni-Al-Nb Glass Forming Alloys

(Zr65Al10Ni10Cu15)(100-x) Nb-x glass forming alloys with Nb contents ranging from 0 to 15 at.% were prepared by water-cooled copper mould cast. The alloys with different Nb contents exhibited different microstructures and mechanical properties. Unlike the monolithic Zr65Al10Ni10Cu15 bulk metallic glass, only a few primary bee beta-Ti phase dendrites were found to distribute in the glassy matrix of the alloys with x = 5. For alloys with x = 10, more beta-phase dendrites forms, together with quasicrystalline particles densely distributed in the matrix of the alloys. For alloys with x = 15, the microstructure of the alloy is dominated by a high density of fully developed P-phase dendrites and the volume fraction of quasicrystalline particles significantly decreases. Room temperature compression tests showed that the alloys with x = 5 failed at 1793 MPa and exhibited an obvious plastic strain of 3.05%, while the other samples all failed in a brittle manner. The ultimate fracture strengths are 1793, 1975 and 1572 MPa for the alloys with x = 0, 10 and 15 at.% Nb, respectively.

Water Content Distribution in the Surface Layer of Maoping Slope

The water content distribution in the surface layer of Maoping slope has been studied by testing the water content at 31 control sites. The water content profiles at these sites have also been determined. The water content distributions at different segments have been obtained by using the Kriging method of geostatistics. By comparing the water content distributions with the landform of the slope, it was shown that the water content is closely dependent on the landform of the slope. The water content distribution in the surface layer provided a fundamental basis for landslide predication and treatment.

Effect of Fe content on the thermal stability and dynamic mechanical behavior of NdAlNiCu bulk metallic glasses

The dependence of microstructure and thermal stability on Fe content of bulk Nd60Al10Ni10Cu20-xFex (0 less than or equal to x less than or equal to 20) metallic glasses is investigated by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD) and high-resolution transmission electron micrograph (HRTEM). All samples exhibit typical amorphous feature under the detect limit of XRD, however, HRTEM results show that the microstructure of Nd60Al10Ni10Cu20-xFex alloys changes from a homogeneous amorphous phase to a composite structure consisting of clusters dispersed in amorphous matrix by increasing Fe content. Dynamic mechanical properties of these alloys with controllable microstructure are studied, expressed via storage modulus, the loss modulus and the mechanical damping. The results reveal that the storage modulus of the alloy without Fe added shows a distinct decrease due to the main a relaxation. This decrease weakens and begins at a higher temperature with increasing Fe content. The mechanism of the effect of Fe addition on the microstructure and thermal stability in this system is discussed in terms of thermodynamics viewpoints. (C) 2004 Elsevier B.V. All rights reserved.