Euglena sp. as a suitable source of lipids for potential use as biofuel and sustainable wastewater treatment

Prolific algal growth in sewage ponds with high organic loads in the tropical regions can provide cost-effective and efficient wastewater treatment and biofuel production. This work examines the ability of Euglena sp. growing in wastewater ponds for biofuel production and treatment of wastewater. The algae were isolated from the sewage treatment plants and were tested for their nutrient removal capability. Compared to other algae, Euglena sp. showed faster growth rates with high biomass density at elevated concentrations of ammonium nitrogen (NH₄-N) and organic carbon (C). Profuse growth of these species was observed in untreated wastewaters with a mean specific growth rate (μ) of 0.28 day^?1 and biomass productivities of 132 mg ?L^?1? day^?1. The algae cultured within a short period of 8 days resulted in the 98 % removal of NH₄-N, 93 % of total nitrogen 85 % of ortho-phosphate, 66 % of total phosphate and 92 % total organic carbon. Euglenoids achieved a maximum lipid content of 24.6 % (w/w) with a biomass density of 1.24 g ?L^?1 (dry wt.). Fourier transform infrared spectra showed clear transitions in biochemical compositions with increased lipid/protein ratio at the end of the culture. Gas chromatography and mass spectrometry indicated the presence of high contents of palmitic, linolenic and linoleic acids (46, 23 and 22 %, respectively), adding to the biodiesel quality. Good lipid content (comprised quality fatty acids), efficient nutrient uptake and profuse biomass productivity make the Euglena sp. as a viable source for biofuel production in wastewaters.     

Elemental and biochemical composition of<Emphasis Type="Italic"> Nephrops norvegicus</Emphasis> (Linnaeus 1758) larvae from the Mediterranean and Irish Seas

The Norway lobster, Nephrops norvegicus, is a commercially exploited decapod which is widely distributed throughout the north-eastern Atlantic and the Mediterranean Sea. Ovigerous females originating from the Mediterranean and the Irish Seas were held in the laboratory until larvae hatched. Biomass and biochemical composition, as well as digestive gland structure, were examined in newly hatched larvae from these two regions. In addition, previously published data from a North Sea population were included in our comparison. Elemental analyses showed that the absolute quantities of dry mass (DM), carbon (C), nitrogen (N) and hydrogen (H) (collectively referred to as CHN) per individual, and the C:N mass ratios, were significantly lower, while the relative CHN, protein and lipid values (in % of DM) were higher in samples from the Irish Sea compared to larvae originating from either the Mediterranean or the North Sea. As in CHN, the absolute level of protein per individual was higher in larvae from the Mediterranean, while no significant differences were observed in the individual lipid contents. Likewise, the digestive gland structure at hatching did not show any differences between study areas. Intraspecific variability in biomass and chemical composition of newly hatched larvae from different regions may be related to differential patterns of reproduction in regions with different climatic conditions. Lobster larvae hatch in the Mediterranean Sea predominantly in winter when both water temperature and planktonic food availability are at a minimum, while hatching in the Irish Sea occurs under more favourable conditions in spring. Hence, significantly higher wet mass, dry mass and protein values in Mediterranean larvae may represent adaptive traits allowing for early posthatching survival and development under food-limited conditions in an oligotrophic environment.Communicated by H.-D. Franke     

长期施肥黄土旱塬农田土壤-微生物-植物系统碳氮磷生态化学计量特征

探讨长期不同施肥制度对农田土壤、植物生态系统的碳(C)、氮(N)、磷(P)含量及其生态化学计量比的影响,可为揭示该系统能量平衡和养分循环,实现农业生态系统元素平衡及可持续发展提供参考意义。以位于黄土高原半干旱地区的长武国家黄土高原农业生态实验站长期施肥试验为研究对象,选取不施肥(CK)、单施氮肥(N)、单施磷肥(P)、施氮磷肥(NP)、单施有机肥(M)、氮肥配施有机肥(NM)、磷肥配施有机肥(PM)、氮磷肥配施有机肥(NPM)8个处理,分析了黄土旱塬典型农田土壤-微生物-植物生态系统中C、N、P含量及其生态化学计量变化规律。研究结果表明:1)长期单施有机肥和化肥配施有机肥处理可显著提高土壤和有机质C、N、P含量。2)氮、磷肥的输入显著降低了土壤和小麦C∶N、N∶P,施P显著降低了有机态C∶P和小麦C∶P;有机肥配施对微生物生物量和小麦C∶N∶P的影响更为明显。3)长期有机肥配施条件下土壤养分和小麦化学计量比存在较强的相关关系。微生物生物量碳与有机C、N、P呈显著正相关,土壤微生物生物量氮与土壤N、P总量呈显著正相关,微生物生物量磷与土壤C、N、P总量含量呈显著负相关;植株碳含量与微生物...     

Protein, lipid, water and caloric contents of immature rainbow trout, Salmo gairdneri Richardson, growing at different rates

Protein, lipid, water and caloric contents of immature rainbow trout, relative to size of whole fish, growing at different rates were examined by use of allometric analysis (y = ax^b, Huxley, 1932). Fish grew at different rates as a result of differences in ration size (satiation, or 4–5% of dry body weight), temperature (7 and 12°C) and bGH (bovine growth hormone) administration. In fingerlings, protein, lipid and caloric contents tended to increase (v. body weight) as a percentage of body composition, whereas above fingerling size, protein decreased while lipid and caloric contents still increased. These trends occurred regardless of growth rate differences. The correlations between protein, lipid, caloric contents and body weight were high so reliable estimates of body components can be made from body weight for all experimental treatments. At satiation rations (7 and 12°C), there were no significant differences in protein content, but lipid and caloric contents were significantly higher in control fish. At low rations, protein and caloric contents were lower than those at satiation rations and lipid was lower than in the control group. On a dry weight basis, in uninjected fish at 12°C, ration size did not influence the percentage composition (protein and lipid) but the low ration group had lower energy values per unit of body dry weight. At low temperature (7°C satiation), fish had lower lipid and higher protein content (dry weight basis) than their controls (12°C satiation), thereby resembling bGH injected fish at satiation rations. Values of caloric content estimated from protein and lipid values by use of standard conversion factors differed sufficiently from caloric values directly determined by bomb calorimetry to suggest that caloric values of lipids may change during growth. The increase in body caloric content during growth apparently results mainly from an increase in the percentage of lipid. The similarity of body composition between different growth rate groups implied a tendency for conservation of relative proportions of components such that body composition can be approximated from body weight. Equations were also given to describe the relationship between water content and body constituents, and the relationship between condition factor (K) and both the body dry weight and lipid content.     

Effects of phosphorous, nitrogen, and carbon limitation on biomass composition in batch and continuous flow cultures of the heterotrophic dinoflagellate Crypthecodinium cohnii

We have used phosphate, nitrogen, or carbon limited batch and continuous flow cultures to study how growth and biochemical composition of the dinoflagellate Crypthecodinium cohnii CCMP 316 is affected by nutrient limitation. Specific contents of phosphorous, proteins, and starch were differently affected by nutrient limitation. The specific phosphorous content in C. cohnii varied 10-20 times depending on phosphate availability in the medium. When phosphate was available it was taken up in excess and stored to be re-utilized during phosphate limitation. The specific protein content varied twofold. At most conditions, proteins made up 12-15% of the biomass dry weight but when cells were nitrogen limited, the specific protein content was only half this value. Floridean starch was the major cell constituent of C. cohnii accounting for 40-50% of the biomass dry weight. Only during carbon limitation did the specific starch content decrease. In contrast was the specific lipid content almost unaffected by nutrient availability and lipids accounted for 12-15% of the biomass dry weight irrespectively of which nutrient that was limiting. Lipid production does therefore not depend on nutrient limitation in C. cohnii and lipids are produced even by carbon limited cells. Cultures grown under phosphate limitation resulted in formation of cells with maximal specific contents of all the three major cell constituents; starch, lipid, and protein.     

Litterfall,litter decomposition,and flux of particulate organic material in a coastal plain stream

Import of allochthonous material in terms of litterfall in a 3rd order stream in Mississippi coastal plain was 386g dry wt/m²/yr. Litter materials consisting of deciduous leaves, pine needles, and woody twigs collected during different seasons showed some differences in ash-free dry weight, caloric, carbon, hydrogen, nitrogen and phosphorus contents. In situ decomposition to particulate form of deciduous and pine litter enclosed in nylon litter bags showed 15% and 65%, respectively, of the litter remaining after 334 days. Downstream net transport of suspended particulate organic material in the river averaged 688,290 kg dry wt/yr with a range of 456,061 to 920,518 kg dry wt/yr. There was a tendency for the particulate organic matter load of the water to increase during ebbtide and to decrease during floodtide.Supported by the National Aeronautics and Space Administration (NASA Grant No. NGL-25-001-40) and by the National Science Foundation Biological Oceanography Section (NSF Grant No. GA-35715).     

安徽巢湖蓝藻早期成岩过程中微生物作用的实验室模拟

通过实验室模拟蓝藻的早期成岩过程,获得微生物转化无定形体样品,并对样品进行光学显微镜和扫描电子显微镜形态观察,以及生化成分和碳氢氮元素分析,为干酪根早期演化过程研究提供现代对比实例。研究结果表明:蓝藻在模拟过程中不断被降解,到模拟实验的第95天,蓝藻产荧光物质基本被降解完全,样品呈无定形体状。微生物作用使多糖和蛋白质含量下降,粗脂肪含量上升到12.96%;经微生物转化作用后,蓝藻中的C,N元素含量明显减少,N元素含量比新鲜蓝藻中N元素含量降低了26.98%。可见早期成岩过程中微生物作用使蓝藻形态朝无定体转化,有利于脂类成分的增加,利于成烃。     

Extraction of hydrocarbons from freshwater green microalgae (Botryococcus sp.) biomass after phycoremediation of domestic wastewater

This study was undertaken to analyze the efficiency of Botryococcus sp. in the phycoremediation of domestic wastewater and to determine the variety of hydrocarbons derived from microalgal oil after phycoremediation. The study showed a significant (p < 0.05) reduction of pollutant loads of up to 93.9% chemical oxygen demand, 69.1% biochemical oxygen demand, 59.9% total nitrogen, 54.5% total organic carbon, and 36.8% phosphate. The average dry weight biomass produce was 0.1 g/L of wastewater. In addition, the dry weight biomass of Botryococcus sp. was found to contain 72.5% of crude oil. The composition analysis using Gas Chromatogram - Mass Spectrometry (GC-MS) found that phthalic acid, 2-ethylhexyltridecyl ester (C₂₉H₄₈O₄), contributed the highest percentage (71.6%) of the total hydrocarbon compounds to the extracted algae oil. The result of the study suggests that Botryococcus sp. can be used for effective phycoremediation, as well as to provide a sustainable hydrocarbon source as a value-added chemical for the bio-based plastic industry.     

Biochemical composition of Streptocephalus dichotomus Baird Branchinella kugenumaensis (Ishikawa)

Summary Estimations of total nitrogen, non-protein nitrogen protein, amino acids, lipid, carbohydrate, ash and water contents are carried out for the two fairy shrimps Streptocephalus dichotomus and Branchinella kugenumaensis.The mean values for S. dichotomus are: T.N. - 12.13%; N.P.N. - 3.49%; Protein - 54.71%; Lipid - 11.01%; Carbohydrate - 7.43% and ash - 10.44% and for B. kugenumaensis are: T.N. - 12.63%; N.P.N. - 4.92%; Protein - 48.21%; Lipid - 17.14%; Carbohydrate - 8.93% and ash - 9.17% expressed as percentage dry weight.The protein ash contents are higher in S. dichotomus while non-protein nitrogen, lipid and carbohydrate are higher in B. kugenumaensis.These biochemical fractions show no significant difference between males and females in both S. dichotomus and B. kugenumaensis.The work on Streptocephalus dichotomus formed a part of a thesis submitted for the Degree of Doctor of Philosophy to the University of Madras in 1970.     

Allochthonous and autochthonous carbon sources for fish in floodplain lagoons of an Australian dryland river

Dryland rivers associated with arid and semi-arid land areas offer an opportunity to explore food web concepts and models of energy sources in systems that experience unpredictable flooding and long dry spells. This study investigated the sources of energy supporting three species of fish feeding at different trophic levels within floodplain lagoons of the Macintyre River in the headwaters of the Murray-Darling river system, Australia. Stable isotope analyses revealed that fish consumers derived, on average, 46.9% of their biomass from zooplankton, 38.1% from Coarse Particulate Organic Matter (CPOM) and 24.0% from algae. Ambassis agassizii derived on average 57.6% of its biomass carbon from zooplankton and 20.4–27.8% from algae or CPOM. Leiopotherapon unicolor derived most of its carbon from zooplankton and CPOM (38.3–39.5%), with relatively high contributions from algae compared to the other species (33.3%). An average of 48.4% of the biomass of Nematalosa erebi was derived from zooplankton, with CPOM contributing another 38.1%. Zooplankton was the most important source of organic carbon supporting all three fish species in floodplain lagoons. Phytoplankton, and possibly, particulate organic matter in the seston, are the most likely energy sources for the planktonic suspension feeders (zooplankton) and, consequently, the fish that feed on them. These results indicate a stronger dependence of consumers on autochthonous sources and on locally produced organic matter from the riparian zone (i.e., the Riverine Productivity Model), than on other resources.     

Organic nitrogen of tomato waste hydrolysate enhances glucose uptake and lipid accumulation in Cunninghamella echinulata

Aims: To investigate the effect of organic nitrogen on lipogenesis during growth of Cunninghamella echinulata on tomato waste hydrolysate (TWH) media. Methods and Results: Cunninghamella echinulata grown on a TWH medium rapidly took up glucose and produced large amounts of lipids. However, when some quantities of the organic nitrogen were removed from TWH (by acid followed by alkaline precipitation of proteins) the uptake of glucose was dramatically reduced and large quantities of fungal biomass having low lipid content were produced. Nevertheless, when glycerol was used as carbon source instead of glucose, the uptake rate as well as the biomass production and the lipid accumulation processes were unaffected by the TWH organic nitrogen removal. Finally, when the fungus was grown on a glucose supplemented TWH medium that contained no assimilable organic nitrogen (after further precipitation of proteins with methanol), the produced biomass contained non-negligible quantities of lipids, although glucose uptake remained low. Lipid analysis showed that the produced lipids comprised mainly of neutral lipids, which were preferentially consumed during lipid turnover. Lipid production on the original TWH medium having glucose as carbon source was 0·48 g of lipid per gram of dry biomass, corresponding to 8·7 g of lipid per litre of growth medium. The produced lipids contained 11·7%γ-linolenic acid (GLA), hence the GLA yield was more than 1 g l⁻¹. Conclusions: Organic nitrogen compounds found in TWH favour glucose (but not glycerol) uptake and lipid accumulation in C. echinulata. Significance and Impact of the Study: Agro-industrial wastes containing organic nitrogen, such as tomato waste, are produced in vast amounts causing severe environmental problems. These wastes could be used as fermentation feedstock to produce microbial lipids.     

Dry weight and chemical composition (CHN) in relation to population density of cultivatedTisbe holothuriae (Copepoda,Harpacticoida)

The harpacticoid copepodTisbe holothuriae was cultivated at different densities in a running-water system. Dry weight and chemical composition (CHN) of both females and egg-sacs have been determined. Dry weight decreased significantly with increasing density from 3,48 to 1.94μg in egg-sacs, and from 10.80 to 6.58μg in females. Increasing density in both egg-sacs and females results in decrease of carbon, nitrogen and hydrogen contents, expressed as a percentage of dry weight of egg-sacs and females, respectively. Carbon decreases from 52.56 to 50.57% (egg-sacs) and 45.80 to 39.95% (⧫), nitrogen from 12.63 to 11.94% and 10.72 to 9.73% and hydrogen from 9.08 to 7.78% and 7.47 to 6.17%. The dry weight and elemental compositions of the egg-sacs varied in accordance with that of the females, however, a higher percentage of elemental content was observed in egg-sacs. The energy equivalents were calculated from the carbon content. This indicates that more energy was transferred from the maternal body into egg-sacs. The ratio of carbon to nitrogen did not show any marked variations; no clear relation appeared between C:N and density, indicating a relatively constant chemical composition in both females and egg-sacs.     

Biomass and elemental composition (C.H.N.) of the rotifer Brachionus plicatilis cultured as larval food

Changes in dry weight, carbon, nitrogen, hydrogen and ash content of the rotifer Brachionus plicatilis were investigated during population growth in culture. Also caloric equivalent was estimated from carbon content. Body dry weight and weight of C, N, and H increased with increasing the egg/female ratio of the population, while ash content remained constant. As percentage of dry weight, C content increased with fecundity, H and N remained constant and ash content decreased. The caloric equivalent ranged from 1278 µcal to 4406 µcal for rotifers from 314 µg to 846 µg of dry weight.     

Seasonal variations in carbon and nitrogen content of Acartia clausi (Copepoda,Calanoida) in the Gulf of Trieste (Northern Adriatic Sea)

A yearly study was made on total and cephalothorax lengths, dry weight, carbon and nitrogen contents and C:N ratio of the species Acartia clausi (Copepoda, Calanoida) which is always abundant, particularly in spring, in the net zooplankton community of the Gulf of Trieste (Northern Adriatic Sea). The samples of net zooplankton were carried out every month at the permanent station located 200 m offshore and preserved for about one year in 4% buffered formalin to insure weight loss stabilization. A. clausi was separated from other zooplankton specimens; washed and dried. For each monthly sample the average total and cephalothorax lengths and the average dry weight of adult organisms of A. clausi were measured. The mean carbon and nitrogen contents, as a percentage of dry weight, were determined by using a CHN analyser. Linear regression models were computed on the log-transformed data in order to check the relationships between dry weight, total and cephalothorax lengths, carbon and nitrogen contents and C:N ratio of A. clausi. The best of the various established correlations, was between dry weight and carbon content. Our study pinpointed a high seasonal variability of the C:N ratio, mainly due to seasonal fluctuations in the nitrogen content.     

Trockengewicht und Kaloriengehalt sich entwickelnder Heringseier

Dry weight and caloric content of eggs from spring spawning western Baltic Sea herrings have been determined employing the bomb calorimetry technique. Water temperature throughout incubation was kept at 8.0°±0.2° C. Average dry weight and caloric content values of one pist fertilized egg are 0.170 mg (0.124 mg without chorion) and 0.748 cal (without chorion), respectively. The caloric content per egg decreases progressively during the incubation period (Fig. 2). The same holds for the dry substance of the egg (Fig. 1). Energy extraction efficiency related to dry weight is 67.8%, the efficiency related to dry organic substance 70.4%, and the caloric efficiency 63.7%.     

Composition of organic matter in sediments facing a river estuary (Tyrrhenian Sea): relationships with bacteria and microphytobenthic biomass

The relationships between the biochemical composition of sediment organic matter and bacteria and microphytobenthic biomass distribution, were investigated along the coast of Northern Tuscany (Tyrrhenian Sea). Organic matter appeared to be of highly refractory composition. Among the three main biochemical classes, proteins were the major component (0.96 mg g^-1 sediment d.w.) followed by total carbohydrates (0.81 mg g^-1 sediment d.w.) and lipids (8.1 µg g^-1 sediment d.w.). Bacterial number in surface sediments (0–2 cm) ranged from 1.7 to 24.5 × 10⁸ cells g^-1 of sediment dry weight showing a strong decrease with sediment depth. In surface sediments, significant correlations were found between bacterial biomass and protein concentration. Bacterial activity (measured by the frequency of dividing cells) was significantly related to lipid concentration. Bacterial and microphytobenthic biomass accounted for 3.1 and 18.1% respectively of the sediment organic carbon. In surface sediments bacterial lipids accounted, on average, for 27 % of total lipids, whereas bacterial proteins and carbohydrates accounted for 2.5 and 0.5% of total proteins and carbohydrates, respectively.The benthic degradation process indicated that lipids were a highly degradable compound (about 35% in the top 10 cm). Carbohydrate decreased for 25.6% in the top 10 cm, whereas proteins increased with depth, thus indicating that this compound may resist to diagenetic decomposition.These data suggest that specific organic compounds need to be measured rather than bulk carbon and nitrogen measurements in order to relate microbial biomass to the quality of organic matter.     

Experimental evidence of food-independent larval development in endemic Jamaican freshwater-breeding crabs

In an experimental study, we compared reproductive and developmental traits of endemic sesarmid crabs from Jamaica living in landlocked limnic or terrestrial habitats. Laboratory rearing and behavioral observations showed that the larval development of Sesarma windsor, Sesarma dolphinum (both from freshwater brooks), and Metopaulias depressus (the bromeliad crab) invariably consists of two nonfeeding zoeal stages and a facultatively lecithotrophic megalopa. In a quantitative study of life-history processes characterizing this developmental mode, we provide for S. windsor first data of biomass and elemental composition (dry mass, W; carbon, hydrogen, nitrogen, collectively, CHN) during development from the egg through successive larval stages. These data show that larval independence of food is based on an enhanced female energy allocation in reproduction, reflected in unusually large egg size (1.45-1.70 mm), as well as high contents of C and H (about 60% and 9%, respectively) and high C : N ratios (7.6-8.4) in eggs and early larvae. During zoeal development, about 6% of initial W and 9% of N but 13% each of C and H were lost; similar losses occurred during megalopal development in continued absence of food. These patterns reflect the metabolic utilization of stored organic matter, with preferential degradation of lipid reserves. Fed megalopae gained greater amounts of W and N as compared with C and H (increments of 37% and 38% vs. 25% and 19%, respectively), indicating preferential investment of nutritional energy in proteins required for the formation of new tissues and organs, while generally decreasing proportions of CHN within total W suggested an increasing mineralization of the exoskeleton. Although survival and molt cycle duration of the megalopa stage were not affected by absence of food, significant effects were found in the size of first-stage juvenile crabs, indicating a trade-off between nutritional flexibility in the last larval stage and postmetamorphic fitness. Similar patterns of development and biomass in M. depressus as well as preliminary data obtained for S. dolphinum and Sesarma fossarum suggest that reproductive and developmental traits may be similar in all endemic Jamaican sesarmids. These traits are interpreted as life-history adaptations to development in landlocked habitats, probably playing a key role during adaptive radiation.     

Developmental patterns of larval growth in the edible spider crab, Maja brachydactyla (Decapoda: Majidae)

The large edible spider crab Maja brachydactyla Balss, 1922, an overexploited coastal fishery resource in Galicia (NW Spain), is considered as a potential aquaculture candidate. Patterns of its larval growth were studied under controlled laboratory conditions (constant 18 ± 1 °C; 36‰ salinity; photoperiod ca. 12:12 h; lipid-enriched Artemia metanauplii provided as food). From hatching through complete larval development and metamorphosis to the first juvenile crab instar, changes in carapace size, dry weight (DW), ash content, elemental composition (carbon, hydrogen, nitrogen; CHN), and proximate biochemical composition (total proteins, lipids, carbohydrates; Pr, L, Ch) were measured in successive stages (zoea I, II, megalopa, crab I). Body size may be described as a linear function of the number of molting cycles, whereas the amounts of DW, CHN, Pr, L, and Ch per individual increased exponentially (3 to 9 fold). The highest growth rates were observed in L, C and H, the lowest in DW, Pr and N. As a consequence of these patterns, the C:N mass ratio as well as the fractions of L, C and H (in % of DW) increased significantly, while those of Pr and N decreased from 26% to 16% of DW. Throughout development, however, Pr remained the principal biochemical component of total DW. Positive correlations between biochemical and CHN data allow for estimates of Pr from N and of L from C values per individual. The patterns of larval growth observed in M. brachydactyla are, in general, similar to those previously described for other brachyuran crabs with a planktotrophic mode of larval development.     

酸性矿山废水污染的水稻田土壤中重金属的微生物学效应

采样调查了广东大宝山地区受酸性采矿废水长期污染的亚热带水稻田的土壤理化性质 ,重金属 Cu、Pb、Zn、Cd的全量及其 DTPA浸提量 ,以及微生物生物量及其呼吸活性等指标。利用主成分和逐步回归分析了影响土壤重金属的有效性及其微生物学效应的因素。结果表明 :土壤高含硫 ,强酸性 ,有机碳、全氮较低 ,4种金属的全量普遍超标。DTPA可提取态金属含量较高 ,不仅与其全量呈显著正相关 ,而且与土壤酸度和粘粒含量正相关 ,和 Mn含量负相关。过量的金属显著降低了土壤微生物生物量 C、N、微生物商、生物量 N/全 N比 ,并抑制了微生物呼吸强度和对有机碳的矿化率 ,导致了土壤 C/N比的升高。同时 ,金属对微生物群落及生理代谢指标 ,如微生物生物量 C/N比和代谢商的影响不显著。 DTPA可提取态金属 ,特别是 DTPA- Cu是导致微生物生物量和活性指标变化的主要因素。以有机碳 (或全氮 )为基数的复合微生物指标降低了土壤性质差异造成的干扰 ,较单一指标更能准确指示微生物对金属胁迫的反应。土壤硫没有对金属有效性和微生物指标产生明显影响 ,但其氧化过程可能引起酸化和金属离子的释放     

Carbon and nitrogen limitations of soil microbial biomass in desert ecosystems

Microbial biomass nitrogen was measured in unamended (dry) and wetted soils in ten shrubland and grassland communities of the Chihuahuan desert, southern New Mexico, by the fumigation-extraction method. Microbial biomass-N in dry soils was undetectable. Average microbial biomass-N in wetted soils among all plant communities was 15.3 μg g^-1 soil. Highest values were found in the communities with the lowest topographic positions, and the minimum values were detected in the spaces between shrubs. Microbial biomass was positively and significantly correlated to soil organic carbon and extractable nitrogen (NH₄ ⁺ + NO₃ ^-). In a stepwise multiple regression, organic carbon and extractable nitrogen accounted for 40.9 and 5.6%, respectively, of the variance in microbial biomass-N among all the samples. Among communities, the soil microbial biomass was affected by the ratio of carbon to extractable nitrogen. Our results suggest a succession in the control of microbial biomass from nitrogen to carbon when the ratio of carbon to nitrogen decreases during desertification.