古尔班通古特沙漠生物土壤结皮对土壤氮库垂直分布特征的影响

生物土壤结皮在干旱区氮素地球化学循环中具有重要作用,研究不同生物土壤结皮下不同形态氮素含量的变化,解析生物土壤结皮对土壤养分影响过程和范围,有助于进一步理解生物土壤结皮的生态功能。本研究以古尔班通古特沙漠藻-地衣混生结皮和藓类结皮两种生物土壤结皮为研究对象,以裸沙为对照,测定生物土壤结皮层和0—100 cm内8个土层全氮、无机氮、可溶性有机氮、游离态氨基酸氮、微生物生物量氮等氮库含量,和土壤脲酶、硝酸盐还原态酶、亮氨酸氨基肽酶等土壤胞外酶活性。结果表明：1)结皮层各形态氮素含量和各土壤酶活性显著高于其下层土壤,结皮层和结皮下各层土壤氮库整体上表现为藓类结皮>藻-地衣混生结皮>裸沙;土壤氮库各形态氮素含量和土壤酶活性在垂直分布上均呈现先显著下降(0—20 cm)后稳定(20—100 cm)的趋势;在20—30 cm土层,除裸沙的无机氮、铵态氮以及藻-地衣混生结皮的硝态氮外,其余速效氮(无机氮、硝态氮、铵态氮)含量具有增加的特点。2)土壤各氮库含量与全磷、有机碳、电导率、土壤脲酶和亮氨酸氨基肽酶活性呈正相关,与pH、土壤含水率呈负相关。3)利用氮循环相关指标建立土壤氮循环多功能...     

Chemical speciation of Zn in acidic soils: suitable soil extractant for assessing Zn availability to maize (Zea mays L.)

Abstract

Chemical fractions of soil Zn namely: water soluble (WS), exchangeable (EX), Pb displaceable (Pb-disp.), acid soluble (AS), Mn oxide occluded (MnOX), organically bound (OB), amorphous Fe oxide occluded (AFeOX), crystalline Fe oxide occluded (CFeOX), residual (RES) were determined in 20 surface (0–15 cm) samples of acidic soils from the provinces of Uttarakhand and Uttar Pradesh, India. The chemical fractions of soil Zn in acidic soils were found to be in the following descending order of Zn concentration: RES > CFeOX > Pb-Disp. > AFeOX > MnOX > AS > OB > EX > WS. These soil samples were also extracted by: DTPA (pH 7.3), DTPA (pH 5.3), AB-DTPA (pH 7.6), Mehlich 3 (pH 2.0), Modified Olsen, 0.01 N CaCl₂, 1 M MgCl ₂ and ion exchange resins. Chemical fractions and the soil extractable content of Zn estimated by different soil extractants were significantly correlated with some general soil properties. Maize (cv. Pragati) plants were grown in these soils for 35 days after emergence and Zn uptake by plants was compared with the amount of Zn extracted by different soil extractants and chemical fractions of Zn. Among chemical fractions of soil Zn, Pb-displaceable and acid soluble chemical fractions of soil Zn showed a significant and positive correlation with Zn uptake by maize. Path coefficient analysis also revealed that the acid soluble Zn fraction showed the highest positive and direct effect on Zn uptake (P=0.960). Among different multinutrient soil extractants evaluated for their suitability to assess Zn availability in acidic soils, DTPA (pH=5.3) was most suitable soil extractant, as the quantity of soil Zn extracted by this extractant showed a significant and positive correlation with the dry matter yield, Zn concentration and uptake by maize plants.     

Consecutive zinc balance trials in growing rats

Rats were fed a purified egg white-based diet containing 5 ppm Cu and 2, 14, or 57 ppm Zn. Zinc and copper balances were determined for eight consecutive weekly trial periods. The zinc-deficient group almost ceased to gain weight and was in slightly negative zinc balance. Groups of rats fed 14 and 57 ppm Zn gained weight at equal rates. These groups were in strongly positive zinc balance for four weeks; thereafter, they fed 57 ppm Zn retained about two times as much zinc as did the group fed the diet containing 14 ppm Zn. All groups were in null or slightly negative copper balance throughout the trial. These results suggest that zinc accumulation may be homeostatically controlled to a level in excess of that needed for maximum growth.     

Quantitative partition of protein,carbohydrate and fat pools in growing pigs

A model combining data from balance experiments with data from oxidation of nutrients demonstrating the pools of protein, carbohydrate and fat and their partition in the body was presented.

Data from more than 200 experiments with growing pigs were used to fill up the “black boxes”; in the model and to discuss the pattern between catabolic and anabolic processes of the different nutrients.

With a ME‐intake of 1.3 MJ/kg^0.75 the proportion of retained protein from the protein pool varied from 50 to 75% depending on the age of animals and the protein quality. At a low protein intake and ME of 0.6 MJ/kg^0.75 the utilization of protein was reduced to about 25% as a substantial part of the protein pool was oxidized.

The carbohydrate group from the protein sources constituted less than 5% of the carbohydrate pool. The oxidation of carbohydrates was between 50–75% of the pool in all experiments, while the rest was used for lipogenesis. Even on a low feeding level the pattern occurred indicating a requirement for specific substances formed in the body.

Lipogenesis constituted 46–96% of the fat pool depending of the amount on digested fat in the different experiments. No oxidation of fat was observed in experiments with pigs (30–90 kg LW) on a high feeding level in spite of the broad variation in the amount of digested fat, indicating a complete storage of the fat pool into body fat. In experiments with piglets (3–9 kg LW) on the same energy intake fat oxidation of about 30% occurred, probably caused by the high energy requirement of the piglets. With a ME‐intake of 0.6 MJ/kg^0.75 the oxidation of fat was higher than the fat pool for pigs between 30–60 kg LW, thereby causing oxidation of body fat to cover the energy requirements.     

Disentangling species and functional group richness effects on soil N cycling in a grassland ecosystem

Species richness (SR) and functional group richness (FGR) are often confounded in both observational and experimental field studies of biodiversity and ecosystem function. This precludes discernment of their separate influences on ecosystem processes, including nitrogen (N) cycling, and how those influences might be moderated by global change factors. In a 17‐year field study of grassland species, we used two full factorial experiments to independently vary SR (one or four species, with FGR = 1) and FGR (1–4 groups, with SR = 4) to assess SR and FGR effects on ecosystem N cycling and its response to elevated carbon dioxide (CO₂) and N addition. We hypothesized that increased plant diversity (either SR or FGR) and elevated CO₂ would enhance plant N pools because of greater plant N uptake, but decrease soil N cycling rates because of greater soil carbon inputs and microbial N immobilization. In partial support of these hypotheses, increasing SR or FGR (holding the other constant) enhanced total plant N pools and decreased soil nitrate pools, largely through higher root biomass, and increasing FGR strongly reduced mineralization rates, because of lower root N concentrations. In contrast, increasing SR (holding FGR constant and despite increasing total plant C and N pools) did not alter root N concentrations or net N mineralization rates. Elevated CO₂ had minimal effects on plant and soil N metrics and their responses to plant diversity, whereas enriched N increased plant and soil N pools, but not soil N fluxes. These results show that functional diversity had additional effects on both plant N pools and rates of soil N cycling that were independent of those of species richness.     

两种典型土壤胶体对镉的生物有效性的影响

采用黑麦草盆栽试验,研究了人工Cd污染(10.91mg·kg-1)黄棕壤和红壤(简称原土)及其胶体组分(简称胶体)和去胶后组分(简称去胶)Cd的生物有效性,并研究了EDTA对Cd解吸和生物有效性的影响.结果表明:(1)各处理黑麦草株高、地上部干重、根干重、总生物量都表现为胶体＞原土＞去胶,胶体上总生物量分别是原土和去胶处理的(1.31±0.02)倍和(1.82±0 21)倍.(2)黑麦草体内Cd浓度、及其对Cd的富集系数都表现为胶体＜原土＜去胶,表明胶体中Cd的生物有效性＜原土＜去胶.(3)黄棕壤各组分Cd的解吸率分别表现为胶体和原土约为0,去胶组分为(10.5±3.5)%,红壤各组分平均为(20.8±1 9)%,但加入EDTA则明显增加了Cd的解吸,导致黑麦草体内Cd浓度显著增加,黑麦草地上部干重、根干重、总生物量降低.EDTA对Cd的活化作用表现为去胶＞原土＞胶体,黄棕壤＞红壤,EDTA对各处理植株Cd总量的影响与此吻合.这说明,土壤镉的生物有效性受土壤胶体及其pH等的强烈影响.     

The effects of cropping corn on the extractability of zinc added to a calcareous soil

The effects of cropping corn on the decrease in the extractability of Zn added to a calcareous soil were studied by a pot experiment and chemical extractions. The results show that the concentrations of Zn exchangeable with MgCl₂ (EXC-Zn) and extractable with DTPA (DTPA-Zn) in the soils with added Zn decreased with time. The processes associated with the decrease in extractability in DTPA of Zn added to soil can be described aptly by a diffusion equation which gives the proportion of added Zn in the non-DTPA fraction as a function of the square root of incubation time. This result suggests that the diffusion of Zn cations into microporous solids is a rate-limiting reaction. The relative diffusion rate coefficients (D/r²) were found to be 1.95×10^-10 and 3.34×10^-10 sec^-1 in the soils with added Zn of 20 and 60 mg kg^-1, respectively. Compared with uncropped soil, the concentrations of DTPA-Zn in the soils with added Zn were decreased by cropping. The decrease of DTPA-Zn in the soils in the presence of corn can be attributed to both its acquisition by corn and other processes associated with the growing of corn. The activity of plant roots would appear to enhance the process of decrease in the extractability in DTPA of Zn added to the soil. The source of Zn uptake by corn was affected by the loading or activity of Zn in soil. In the soil with low available Zn, the DTPA non-extractable Zn (non-DTPA-Zn) was mobilized and taken up by corn. In the soils with high available Zn, e.g. the recently added Zn, only EXC-Zn and a part of the DTPA-Zn were taken up by corn.     

Parameters of availability of zinc in orchard soils in relation to zinc nutrition of apple

Summary Labile pool, selective distribution coefficient and adsorption maxima of zinc were measured. Labile pool decreased while selective distribution coefficient increased with increasing depth in all soil profiles. The values of adsorption maxima of zinc corresponded to selective distribution coefficient. The relative efficiency of four extractantsviz 0.05M CA(NO₃)₂ 0.1M Mg(NO₃)₂; 0.01M EDTA–NH₄OAc and 0.005M DTPA-triethanolamine mixture in predicting the availability of native soil zinc to apple was tested. The correlation study indicated that all extractants are good index of zinc availability to apple trees. DTPA-extractable zinc is as efficient as its labile pool(E-value) in predicting the availability of native soil zinc to apple trees. This study also suggested that soil profile should be sampled upto a depth of 30–60 cm for providing a better prediction of availability of native soil zinc to apple trees.     

Effect of phosphorus application on transformation of zinc fraction in soil and on the zinc nutrition of lowland rice

We have studied in the laboratory the effect of different levels of P application on the transformation on native as well as of applied zinc in a rice-growing soil under two moisture regimes viz., flooded and nonflooded. Application of P caused a decrease in the water soluble plus exchangeable and organic complexed with a concomitant increase in the amorphous and crystalline sesquioxide bound forms of native soil zinc. Application of P also caused a decrease in the transformation of applied Zn into the water soluble plus exchangeable and organically complexed and an increase in the amorphous and crystalline sesquioxide bound forms of zinc. The above effects of P were more pronounced in soil under flooded than under nonflooded moisture regimes. The water soluble plus exchangeable and the organically complexed forms of Zn are considered to play an important role in Zn nutrition of lowland rice, while the role of the amorphous and crystalline sesquioxide bound forms are less important in this regard.The results of greenhouse experiments showed that P application caused a progressive decrease in the Zn concentration in shoot and root. This was attributed at least partly to the decrease in the water soluble plus exchangeable and organically complexed forms of Zn and an increase in the amorphous and crystalline sesquioxide bound forms in soil due to P application.     

The extraction by soil and absorption by plants of applied zinc and cadmium

In five consecutive years lettuce, spinach, spring wheat, endive and maize were grown in pots and the effects of native and soil-applied Zn and Cd on plant Zn and Cd concentrations were studied. The normal interactive pattern was antagonistic, Zn reducing plant Cd uptake, and conversely, but less so. Only in loam soil Zn and Cd were synergistic to some extent, plant Zn uptake increasing with applied Cd.When relating total soil Cd/Zn to plant Cd/Zn separate sets of data could be distinguished for loam and sandy soil, each fitting a straight line. The use of 0.1 M CaCl₂ instead of total extractable soil Cd/Zn makes the two sets of data to coalesce around a single straight line. All crops were found to show a positive linear relationship between 0.1 M CaCl₂-extractable soil Cd/Zn and plant Cd/Zn.     

茶园土壤及与茶叶中微量元素锌硒含量相关性的研究

植物生长的环境适应及其内含物质功能和变化规律的研究已成为热点问题。该研究对贵州省地标品牌湄潭翠芽、凤冈锌硒茶4个样地12个样点茶园土壤及其对应种植点茶叶样品中锌硒含量变化进行了检测与分析。结果表明:(1)4个样地中,3个样地的锌含量都是原土高于种植土,而硒含量没有明显规律性变化;各主产区土壤锌硒含量的标准差均大于均值的5%,土质均匀度都较低;(2)4个样地新叶(一芽二叶)与老叶的锌含量都呈现显著差异,而硒在新叶和老叶中的含量差异无明显变化规律;(3)锌元素在茶树体内转移现象明显,由老叶向新叶中转移,新叶中含量较高;硒元素在新叶和老叶中的含量变化不明显。新叶中锌的含量与其0~20 cm表层土样和21~40 cm深层土样中锌的含量呈极显著正相关(P0.01),相关系数为0.768;而新叶硒的含量与0~20 cm表层土中硒含量呈显著正相关(P0.05)。茶叶中锌硒主要是通过茶树根系从土壤中吸收和传输,但其吸收转移效率不由土壤中的含量多少直接决定,还受到茶园土壤质地、茶园温湿度等环境管控因素的影响,锌硒微量元素参与茶树体内的生理作用和代谢途径具有较大的差异。因此,进一步探索茶树吸收与转化锌硒微量元素的存在形态和作用机理,了解不同产区茶叶中微量元素锌硒含量与其茶园土壤的关系,对于生产适宜于人类身体健康适当锌硒含量的有机茶具有重要意义。     

土壤中外源锌对不同植物毒性的敏感性分布

采用逻辑斯蒂克分布(log-logistic distribution)模型结合物种敏感性分布方程Burr-III分析,研究了2种不同土壤中添加不同水平的外源Zn后对8种不同植物毒性的剂量-效应关系及不同植物对外源Zn毒害的敏感性差异。结果表明,土壤中添加低浓度(<100mg·kg-1)Zn能对植物生长产生刺激效应,而过量的Zn则产生明显毒害作用。土壤中Zn毒性的阈值浓度(ECx)在不同植物间有较大差异,这主要与植物种类及土壤性质差异有关。不同土壤中Zn植物毒性的敏感性分布结果表明,不同植物对Zn毒性的敏感性频次分布有明显差异,其中叶菜类植物对土壤中Zn的毒害较为敏感,而禾本科类植物(如玉米)对Zn具有较强的抗性,不同类型植物对土壤中Zn毒害的敏感性分布频次顺序与土壤性质无关。     

川南天然常绿阔叶林人工更新后土壤氮库与微生物的季节变化

对川南天然常绿阔叶林及其人工更新成檫木林、柳杉林和水杉林后土壤不同形态氮素含量、微生物数量和脲酶活性进行研究,并探讨了它们之间的相互关系。结果表明：土壤全氮、微生物量氮、铵态氮和硝态氮含量、细菌、真菌和放线菌数量及脲酶活性,各林分均为秋季＞春季＞冬季＞夏季,各季节均为天然常绿阔叶林＞檫木林＞水杉林＞柳杉林。这说明天然常绿阔叶林人工更新后土壤不同形态氮素含量、微生物数量和脲酶活性下降,土壤保肥和供肥能力降低,而各人工林下降程度不同。土壤不同形态氮素含量与微生物数量和脲酶活性之间呈显著正相关,说明微生物数量及脲酶活性的变化能够表征土壤氮素含量变化。研究结果为保护天然常绿阔叶林、选择适宜的更新树种和天然常绿阔叶林人工更新后林地土壤的科学管理提供依据,也为退耕还林中树种的选择提供参考。     

Differential expression of zinc efficiency during the growing season of barley

Considerable genetic variation exists in zinc (Zn) efficiency among cereal species and genotypes within the same species. Currently, the mechanisms of Zn efficiency are not understood well; however, the research so far suggests that overall Zn efficiency can be partitioned into uptake, utilisation and translocation or remobilisation efficiency, all or some of which collectively determine the level of Zn efficiency in a particular genotype. In a growth room study, using two barley genotypes differing in Zn efficiency (Zn-efficient Unicorn and Zn-inefficient Amagi Nijo), we attempted to determine which of these components of Zn efficiency contributed to greater Zn efficiency in Unicorn, by examining growth responses to Zn over a wide range of Zn fertilisation rates (0, 0.05, 0.2, 0.8, 3.2 and 12.8 mg Zn/kg soil) during the entire growth period. Zn-efficient Unicorn showed less severe Zn deficiency symptoms, produced more dry matter, and grain yield under Zn deficient conditions compared with Zn-inefficient Amagi Nijo. These responses also varied with the level of Zn deficiency stress and growth stage. Most importantly, the greater Zn efficiency (e.g., ability to grow well under Zn deficiency) at maturity of Unicorn was due to greater translocation of Zn from vegetative to reproductive organs or greater ability to produce higher grain yield with limited Zn rather than Zn uptake from soil which was similar in both genotypes. Zn-efficient Unicorn also had a lower critical deficiency concentration for grain (12 mg Zn/kg DW) than the Zn-inefficient Amagi Nijo (18 mg Zn/kg DW), suggesting a lower requirement for metabolic processes in Zn-efficient Unicorn. The critical deficiency concentration in the grain has the potential to diagnose Zn-deficient soils. The results also show that grain Zn concentration can be increased by Zn fertilisation, with significant increases occurring above the Zn fertilisation rate that is adequate for production of grain. However, genetic variation in grain Zn concentration should be explored and wild relatives of barley may offer potential for crop improvement for this trait.     

Effects of different levels of dietary zinc on the gilthead,Sparus aurata during the growing season

Gilthead were fed three diets. Diet A was the control diet, whereas diets B and C were supplemented with 300 and 900 mg Zn/kg, respectively. Fish fed with diet C, at the end of the experiment, showed the lowest weight. Zinc concentrations presented the higher values in gills, liver, and kidney. Muscle and brain had the lower mean values and showed a tight control of zinc levels. These results reinforce the hypothesis that zinc in the CNS should be strictly controlled in order to maintain the functional role of the metal. Significant differences in tissue zinc concentrations were obtained between fish fed different amounts of zinc, the metal concentrations being higher in tissues of fish fed diet C. The tissue decrease of zinc, found at the end of the experiment, may depend on a lower feed consumption or on different zinc requirements during the cold season. These changes, even if not univocal among the three diets, may be associated with the life cycle of fish. Furthermore, copper concentrations were little affected by the different concentrations of zinc in the three diets; liver and kidney presented the highest concentrations; liver showed a significant decrease in copper content at the end of the experiment. We conclude that: zinc concentrations of the diet may affect the gilthead weights and the tissual metal content; and zinc concentrations in the diets, depending on the growth rate, may be varied depending on the season.     

Effect of excessive dietary fluoride on nutrient digestibility and retention of iron, copper, zinc, and manganese in growing pigs

Ninety-six crossbred growing pigs were used to evaluate the effects of fluoride levels on growth performance, nutrient digestibility, and the retention of minerals in tissues. Four dietary treatments were formulated by supplementing fluorine (as NaF) to a corn-soybean basal diet (39.75 mg/kg F) to provide the following added fluorine levels: 0, 50 100, and 150 mg/kg fluorine. The results showed pigs of the 100 and 150 mg/kg fluorine-added groups had decreased average daily gain (ADG) and increased feed gain ratio (F/G) compared to the control (p<0.05). Apparent digestibility of protein and calcium in 100 and 150 mg/kg fluorinetreated groups was significantly lower than that of the control (p<0.05). On the other hand, iron, copper, zinc, and manganese levels in most tissues of the 100 and 150 mg/kg fluorine groups were markedly changed compared to the control (p<0.05). However, growth performance, nutrient digestibility, and mineral concentrations in all tissues of pigs were not significantly affected by the addition of 50 mg/kg fluorine (p>0.05). Thus, this study suggested that excess fluoride levels could decrease growth performance and change the retention of iron, copper, zinc, and manganese in pigs.     

Modification of soil aggregation by watering regime and roots growing through beds of large aggregates

The influence of root growth and soil watering regime on aggregation was studied under controlled conditions. The study examined the influence of pea (Pisum sativum cv Greenfeast), ryegrass (Lolium rigidum cv Wimmera) and wheat (Triticum aestivum cv Kite) roots on changes in aggregation and on the properties of the aggregates. The soil was a non swelling red-brown earth which was either kept wet or was allowed to wet and dry during the experiment. Root growth increased the percentage of small sized aggregates (<18 mm diameter), organic carbon, tensile strength and stability of aggregates in comparison with a non planted soil. Changes in aggregate size distribution and properties of the aggregates were related to root length density of the species and also to the soil watering regime. Root length density was in the order ryegrass>pea>wheat. Wetting and drying of soil increased the strength and stability of aggregates. Incubating aggregates allowed some roots to decompose but did not increase the strength or stability of aggregates compared with unincubated soil. The results of this experiment are of practical significance in soil structural management, and in studies of soil aggregation dynamics. It may be possible to use plant roots to alter the size and properties of aggregates.     

Effects of histidine on tissue zinc distribution in rats

Histidine has been reported to affect body zinc status by increasing urinary zinc excretion. The effects of experimental histidinemia on distribution of⁶⁵Zn in anesthetized rats were studied. Infusion ofl-histidine at a rate sufficient to raise plasma concentrations to approximately 2mm for 6h starting 48 h after a single intraperitoneal⁶⁵Zn injection did not alter⁶⁵Zn activities in a variety of tissues when compared with anesthetized uninfused animals. However, plasma⁶⁵Zn and erythrocyte⁶⁵Zn were decreased, and liver⁶⁵Zn was increased. If⁶⁵Zn was injected intravenously during histidine infusion, net accumulation of zinc by some tissues was increased, but uptake by others was reduced relative to uninfused animals. In all cases, however, uptake expressed relative to plasma⁶⁵Zn levels was increased when allowance was made for the more rapid fall in plasma⁶⁵Zn during histidine infusion. Similar infusions ofd-histidine produced quantitatively similar effects. Since enzymatic mechanisms and amino acid carriers would be expected to show stereoselectivity, such processes are unlikely to be involved in the zinc distribution changes described. The possibility of zinc transport by a hitherto unidentified carrier is discussed. These experiments confirm that histidinemia can affect zinc status, but any associated changes in urinary zinc excretion do not seem adequate to account for the tissue changes found.     

Experimental study of the effect of hydrology and mechanical soil disturbance on plant communities in Mediterranean temporary pools in Western Morocco

Physical soil disturbance and the hydrology of temporary pools affect the biomass, species composition and richness of plant communities. Disturbance liberates sites for the random recruitment of new individuals. The addition of seeds modifies the structure of the communities. In order to verify these hypotheses concerning the vegetation of temporary pools, an experiment was carried out using 72 soil samples collected from a pool in Western Morocco and placed in containers. Three types of laboratory treatments were applied, each combined with control treatments: soil disturbance (control/disturbed), hydrology (flooded, saturated and dry) and seed addition (sowing/no sowing). The total biomass, the annual and perennial species richness were calculated for each sample to test the effects of disturbance, hydrology and seed addition on the biomass and species richness of the various plant communities. The results show that disturbance reduces the total biomass, especially of perennials, but without significantly increasing the richness of annuals. Seed addition does not affect the total biomass and reduces total richness only in saturated soil, where biomass production is high. The most extreme stress conditions (drought and flooding) limit the abundance of species and therefore competition. Guest editors: B. Oertli, R. Cereghino, A. Hull & R. Miracle Pond Conservation: From Science to Practice. 3rd Conference of the European Pond Conservation Network, Valencia, Spain, 14–16 May 2008