Effect of grassland harvesting frequency and N-fertilization on stocks and dynamics of soil organic matter in the temperate climate

ABSTRACT

Management of grassland may affect the dynamics of soil organic carbon (SOC). Objectives were to analyze the effect of different harvesting frequencies and nitrogen fertilization regimes on SOC and total N stocks in a field trial on a sandy loam to loamy sand soil of a grassland site near Kiel (Germany). Additionally, effects on microbial biomass C (C_mic) and ergosterol (as proxy for fungi) contents, water-stable aggregate size-classes and density fractions were studied. In the surface soil (0–10 cm), SOC and total N stocks, amounts of large water-stable macroaggregates (> 2000 µm) and contents of C_mic and ergosterol were significantly higher under a five cut regime. C_mic (r_Spearman = 0.61) and ergosterol contents (r_Spearman = 0.67) were correlated with amounts of large water-stable macroaggregates suggesting that fungi and microbial biomass play an important role in binding of small macroaggregates into large macroaggregates. The free light fraction of SOM showed significantly higher C concentrations under three cut compared to five cut at 30–60 cm, presumably related to the C/N ratio and the decomposability of root litter. This study indicates the importance of cutting frequency on SOC and total N stocks, amounts of large macroaggregates and contents of C_mic and ergosterol.     

Metagenetics of fairy rings reveals complex and variable soil fungal communities

Although fairy rings are widely observed, little is known about the community processes associated with them. Here, we studied fairy rings in a natural grassland in northern Mongolia by sampling soils outside (future stage), directly under (present stage), and within (past stage) the rings, to represent different time stages during the expansion of fairy rings. Soil DNA was extracted for amplicon sequencing of the fungal ITS1 region. The present stage had reduced fungal diversity and different fungal communities toward the other stages. Most strikingly, there was an increase in the pathogenic fungus Gibberella baccata in the present stage of most rings and the saprotrophic fairy ring fungus Lepista luscina in several. However, no mushrooms of Lepista had been recorded from any of these rings during several years of observation. Known fairy ring fungi were not found in the present stage of every ring, even in some known rings to have previously displayed mushrooms of such species. It is possible that these fungi occurred or were more abundant at the unsampled leading edge of the ring. The increase in G. baccata is intriguing, but its importance, if any, is unclear. It is also unclear whether consortia of fungi or other microbes might be present in these rings. The absence or low abundance of the previously reported fairy ring fungal species suggests that their presence is transient, with rapid replacement by other fungi. No differences in soil parameters were found between the fairy ring stages, except for aluminum. There is a need for broader sampling, including analysis of non-fungal biota, to understand the functional diversity of fairy ring fungi and the consequences for plant communities.     

Ergosterol and microbial biomass relationship in soil

Ergosterol and microbial biomass C were measured in 26 arable, 16 grassland and 30 forest soils. The ergosterol content ranged from 0.75 to 12.94 g g^-1 soil. The geometric mean ergosterol content of grassland and forest soils was around 5.5 g g^-1, that of the arable soils 2.14 g g^-1. The ergosterol was significantly correlated with biomass C in the entire group of soils, but not in the subgroups of grassland and forest soils. The geometric mean of the ergosterol: microbial biomass C ratio was 6.0 mg g^-1, increasing in the order grassland (5.1), arable land (5.4) and woodland (7.2). The ergosterol:microbial biomass C ratio had a strong negative relationship with the decreasing cation exchange capacity and soil pH, indicating that the fungal part of the total microbial biomass in soils increased when the buffer capacity decreased. The average ergosterol concentration calculated from literature data was 5.1 mg g^-1 fungal dry weight. Assuming that fungi contain 46% C, the conversion factor from micrograms ergosterol to micrograms fungal biomass C is 90. For soil samples, neither saponification of the extract nor the more effective direct saponification during extraction seems to be really necessary.     

秸秆还田条件下腐熟剂对不同质地土壤真菌多样性的影响

为因地制宜鉴选适宜的秸秆腐熟剂,在西辽河平原灌区选择秸秆还田的砂壤土和中壤土连作玉米地,分别配施中农绿康腐熟剂、人元腐熟剂和农富康腐熟剂(简称中农、人元、农富康),以秸秆还田不施腐熟剂为对照,在玉米吐丝期取0～15 cm、15～30 cm、30～45 cm土层样品,采用高通量测序技术,研究不同质地土壤秸秆还田配施腐熟剂情况下土壤真菌群落结构的多样性。结果表明,砂壤土秸秆还田配施腐熟剂处理特有OTU(operational taxonomic units)数均比对照多,中壤土则相反。所有处理土壤中被孢霉门(Mortierellomycota)、子囊菌门(Ascomycota)、担子菌门(Basidiomycota)相对丰度较高;优势属均为被孢霉属(Mortierella)和低温酵母(Guehomyces)。不同腐熟剂对土壤质地产生不同影响,中壤土秸秆还田配施中农和农富康对土壤真菌组成及丰度无显著影响,而配施人元显著改变中壤土真菌组成及丰度;砂壤土秸秆还田配施中农和人元显著增加土壤真菌组成及丰度。LEfSe分析可知,砂壤土秸秆还田配施中农、中壤土秸秆还田配施人元和农富康3个处理土壤真菌多样性存在差异,对真菌多样性差异发挥显著性作用的门为担子菌门、子囊菌门,纲为伞菌纲(Agaricomycetes),目为腔菌目(Pleosporales)和伞菌目(Agaricales),种为Mortierella fimbricystis。这种响应差异也体现在同一腐熟剂对中壤土和砂壤土不同土层真菌的影响;随土层的下移,砂壤土和中壤土对照中被孢霉属相对丰度先增加后下降,低温酵母相对丰度下降;施用腐熟剂后(中壤土农富康除外),深层土壤低温酵母相对丰度比表层土壤高。砂壤土秸秆还田配施中农后0～15 cm土层中上述2个优势菌属相对丰度显著提高;而中壤土秸秆还田配施人元增加0～15 cm土层低温酵母相对丰度和15～30 cm、30～45 cm土层被孢霉属相对丰度。由此可见,秸秆还田条件下腐熟剂与土壤质地间响应不同,所以秸秆腐熟剂配施应因地制宜。     

Phosphate solubilizing bacteria and fungi in desert soils: species,limitations and mechanisms

Desert soils are infertile, and the ability to improve them by P-fertilization is limited by the solubility of phosphate. We aimed to understand the function of phosphate solubilizing bacteria and the mechanisms behind phosphate solubilization in desert soils. Vegetated and barren desert soils, mine spoil and a fertile temperate grassland loam were sampled. Bacteria and fungi were isolated and identified, and their phosphate-solubilizing abilities were measured in vitro. The release of plant available PO₄, SO₄, NO₃ and NH₄ from desert soils did not compare with that of a grassland soil. Desert soils had substantially lower solubilization than grassland, 162 and 99–121 µg PO₄-P g^?1 dry soil, respectively. Phosphate-solubilizing bacteria and fungi were inhabiting the soils. Si addition increased phosphate solubilization of fungi by 50%. The isolated microbes were shown, using ³¹P nuclear magnetic resonance (NMR) analysis, to rapidly take-up both intracellular and extracellular phosphate during the phosphate solubilizing process. Desert soil had potentially active microbial populations that are capable to solubilize inorganic phosphorus; S and Si as the limiting factors. Acidification as the main mechanism to solubilize mineral phosphate was not as evident in our desert soils as in former studies dealing more fertile soils.     

Ectomycorrhizal fungi introduced with exotic pine plantations induce soil carbon depletion

Exotic pine plantations are promoted for their presumed capacity to provide a net sink of atmospheric C. Millions of hectares worldwide will be subjected to conversion into plantations during the next decades. However, pine introductions are known to result in a marked depletion of soil C, a phenomenon which has remained unexplained. We studied plantations in paramo grasslands of Ecuador, where the effect of the exotic introduction of radiata pines (Pinus radiata) and their accompanying ectomycorrhizal fungi can be studied in isolation from other ecosystem disturbances. We suggest that ectomycorrhizal fungi can extract C previously accumulated by paramo grasslands based on (a) a drastic simplification of the ectomycorrhizal community shown by direct DNA identification, (b) a loss of up to 30% soil C within <20 years of plantation, (c) stable C isotope values in fungal fruitbodies which are closer to grassland than pine values, and (d) radiocarbon dating of fruitbodies indicating relatively old C sources for fruitbody formation. Species number in the ectomycorrhizal guild drops to only three fungal species per plantation compared to approximately 100 in comparable native pine stands. Our results provide evidence for a dynamic role of ectomycorrhizal fungi in soil C processing, and question the strategy of introducing pine plantations as a general solution to reduce mounting atmospheric CO₂ levels.     

不同质地耕层土壤有效态微量元素含量特征

[目的]研究不同土壤质地下耕层土壤有效态微量元素含量特征,为合理制定农田土壤施肥方案和提高土壤养分资源利用率提供依据。[方法]以库车县不同质地耕层土壤(0—20cm)为调查对象,采用统计方法对土壤微量元素有效态含量特征进行分析。[结果](1)土壤有效态微量元素在壤土、砂壤土、黏土、黏壤土及砂土中含量差异显著(p0.05),且壤土和砂壤土的有效态微量元素含量相对较高;(2)土壤微量元素有效性综合指数排列顺序依次为:砂壤土(1.51)砂土(1.44)黏土(1.42)壤土(1.41)黏壤土(1.27);(3)土壤有机质与土壤有效态微量元素均具有极其显著的相关性(p0.01),pH值则与有效铜和有效锰相关显著(p0.05)。[结论]在不同土壤质地下,微量元素铁和锌含量较为缺乏,锰和铜含量则相对较为丰富,故应依据这一特性进行土地科学管理和施肥。     

Spatial changes of soil fungal and bacterial biomass from a sub-alpine coniferous forest to grassland in a humid, sub-tropical region

 Fungal and bacterial biomass were determined across a gradient from a forest to grassland in a sub-alpine region in central Taiwan. The respiration-inhibition and ergosterol methods for the evaluation of the microbial biomass were compared. Soil fungal and bacterial biomass both significantly decreased (P<0.05) with the shift of vegetation from forest to grassland. Fungal and bacterial respiration rates (evolved CO₂) were, respectively, 89.1 μl CO₂ g^–1 soil h^–1 and 55.1 μl CO₂ g^–1 soil h^–1 in the forest and 36.7 μl CO₂ g^–1 soil h^–1 and 35.7 μl CO₂ g^–1 soil h^–1 in the grassland surface soils (0–10 cm). The fungal ergosterol content in the surface soil decreased from the forest zone (108 μg g^–1) to the grassland zone (15.9 μg g^–1). A good correlation (R ²=0.90) was exhibited between the soil fungal ergosterol content and soil fungal CO₂ production (respiration) for all sampling sites. For the forest and grassland soil profiles, microbial biomass (respiration and ergosterol) declined dramatically with depth, ten- to 100-fold from the surface organic horizon to the deepest mineral horizon. With respect to fungal to bacterial ratios for the surface soil (0–10 cm), the forest zone had a significantly (P<0.05) higher ratio (1.65) than the grassland zone (1.05). However, there was no fungal to bacterial ratio trend from the surface horizon to the deeper mineral horizons of the soil profiles. Received: 30 March 2000     

Specific response of fungal and bacterial residues to one-season tillage and repeated slurry application in a permanent grassland soil

The dynamics of fungal and bacterial residues to a one-season tillage event in combination with manure application in a grassland soil are unknown. The objectives of this study were (1) to assess the effects of one-season tillage event in two field trials on the stocks of microbial biomass, fungal biomass, microbial residues, soil organic C (SOC) and total N in comparison with permanent grassland; (2) to determine the effects of repeated manure application to restore negative tillage effects on soil microbial biomass and residues. One trial was started 2 years before sampling and the other 5 years before sampling. Mouldboard ploughing decreased the stocks of SOC, total N, microbial biomass C, and microbial residues (muramic acid and glucosamine), but increased those of the fungal biomarker ergosterol in both trials. Slurry application increased stocks of SOC and total N only in the short-term, whereas the stocks of microbial biomass C, ergosterol and microbial residues were generally increased in both trials, especially in combination with tillage. The ergosterol to microbial biomass C ratio was increased by tillage, and decreased by slurry application in both trials. The fungal C to bacterial C ratio was generally decreased by these two treatments. The metabolic quotient qCO₂ showed a significant negative linear relationship with the microbial biomass C to SOC ratio and a significant positive relationship with the soil C/N ratio. The ergosterol to microbial biomass C ratio revealed a significant positive linear relationship with the fungal C to bacterial C ratio, but a negative one with the SOC content. Our results suggest that slurry application in grassland soil may promote SOC storage without increasing the role of saprotrophic fungi in soil organic matter dynamics relative to that of bacteria.     

Long‐term effects of leguminous cover crops on microbial indices and their relationships in soils of a coconut plantation of a humid tropical region

In this study, leguminous crops like Atylosia scarabaeoides, Centrosema pubescens, Calopogonium mucunoides, and Pueraria phaseoloides. grown as soil cover individually in the interspaces of a 19‐yr‐old coconut plantation in S. Andaman (India) were assessed for their influence on various microbial indices (microbial biomass C, biomass N, basal respiration, ergosterol, levels of ATP, AMP, ADP) in soils (0–50 cm) collected from these plots after 10 years. The effects of these cover crops on . CO₂ (metabolic quotient), adenylate energy charge (AEC), and the ratios of various soil microbial properties viz., biomass C : soil organic C, biomass C : N, biomass N : total N, ergosterol : biomass C, and ATP : biomass C were also examined. Cover cropping markedly enhanced the levels of organic matter and microbial activity in soils after the 10‐yr‐period. Microbial biomass C and N, basal respiration, . CO₂, ergosterol and levels of ATP, AMP, ADP in the cover‐cropped plots significantly exceeded the corresponding values in the control plot. While the biomass C : N ratio tended to decrease, the ratios of biomass N : total N, ergosterol : biomass C, and ATP : biomass C increased significantly due to cover cropping. Greater ergosterol : biomass C ratio in the cover‐cropped plots indicated a decomposition pathway dominated by fungi, and high . CO₂ levels in these plots indicated a decrease in substrate use efficiency probably due to the dominance of fungi. The AEC levels ranged from 0.80 to 0.83 in the cover‐cropped plots, thereby reflecting greater microbial proliferation and activity. The ratios of various microbial and chemical properties could be assigned to three different factors by principal components analysis. The first factor (PC1) with strong loadings of ATP : biomass C ratio, AEC, and . CO₂ reflected the specific metabolic activity of soil microbes. The ratios of ergosterol : biomass C, soil organic C : total N, and biomass N : total N formed the second factor (PC2) indicating a decomposition pathway dominated by fungi. The biomass C : N and biomass C : soil organic C ratios formed the third principal component (PC3), reflecting soil organic matter availability in relation to nutrient availability. Overall, the study suggested that Pueraria phaseoloides. or Atylosia scarabaeoides were better suited as cover crops for the humid tropics due to their positive contribution to soil organic C, N, and microbial activity.     

Decomposition of wheat straw differing in nitrogen content in soils under conventional and organic farming management

An incubation experiment was carried out to investigate the interactions of two straw qualities differing in N content and two soils differently accustomed to straw additions. One soil under conventional farming management (CFM) regularly received straw, the other soil under organic farming management (OFM) only farmyard manure. The soils of the two sites were similar in texture, pH, cation‐exchange capacity, and glucosamine content. The soil from the OFM site had higher contents of organic C, total N, muramic acid, microbial biomass C and N (C_mic and N_mic), but a lower ergosterol content and lower ratios ergosterol to C_mic and fungal C to bacterial C. The straw from the CFM had threefold higher contents of total N, twofold higher contents of ergosterol and glucosamine, a 50% higher content of muramic acid, and a 30% higher fungal C–to–bacterial C ratio. The straw amendments led to significant net increases in C_mic, N_mic, and ergosterol. Microbial biomass C showed on average a 50% higher net increase in the organic than in the CFM soil. In contrast, the net increases in N_mic and ergosterol differed only slightly between the two soils after straw amendment. The CO₂ evolution from the CFM soil always exceeded that from the OFM, by 50% or 200 µg (g soil)^–1 in the nonamended control soil and by 55% or additional 600 µg (g soil)^–1 in the two straw treatments. In both soils, 180 µg g^–1 less was evolved as CO₂‐C from the OFM straw. The metabolic quotient qCO₂ was nearly twice as high in the control and in the straw treatments of the CFM soil compared with that of the OFM. In contrast, the difference in qCO₂ was insignificant between the two straw qualities. Differences in the fungal‐community structure may explain to a large extent the difference in the microbial use of straw in the two soils under different managements.     

人工草地建设对甘南草原土壤理化特性和微生物数量特征的影响

研究甘南草原高寒草甸退化草地人工种草后土壤理化性质和微生物数量特征,为退化草地的修复与利用提供参考。于2017年5,7,10月分别采集播种燕麦、黑麦及其未播种的草地土壤,测定其理化特性及微生物数量特征。结果表明:人工种植的黑麦草地土壤水分均大于燕麦人工草地,5,7月人工草地土壤含水量均显著大于对照草地,但10月差异不显著(P>0.05);pH在各月份不同播种方式下差异均不显著(P>0.05);土壤全氮、全磷在不同月份间差异亦不显著(P>0.05),但黑麦人工草地5月10—20cm层的有机碳、10月40—50cm层的全氮含量均显著大于燕麦人工草地及对照样地(P<0.05),7月20—30cm层燕麦人工草地的有机碳含量显著大于黑麦人工草地及对照草地;5月0—30cm层燕麦人工草地和黑麦人工草地的细菌数量显著高于对照草地的细菌数量(P<0.05),7月0—10cm层人工草地细菌数量显著高于对照草地(P<0.05),10月黑麦人工草地0—30cm层细菌数量均显著高于对照草地(P<0.05);5,10月真菌数量在0—10cm层人工草地显著高于对照草地(P<0.05),7月10—30cm层人工草地的真菌数量、0—10cm层的放线菌数量均显著高于对照草地(P<0.05);冗余分析发现,土壤细菌和真菌的变化具有联动性,且与土壤有机质、全氮、全磷等养分呈正相关。综上,人工种草后土壤养分的变化导致了土壤微生物数量的差异,这需要在草地管理中予以重视。     

长期氮沉降和地上凋落物处理对半干旱区沙质草地表层土壤碳氮组分的影响

为揭示半干旱区沙质草地生态系统中表层土壤C、N组分对长期氮添加和地上凋落物处理的响应特征,以科尔沁沙地西南部国家野外科学观测研究站建立的长期(9年)氮添加和凋落物处理样地为平台,测定并分析该样地表层土壤环境因子、铵态氮、硝态氮、总有机碳、不同碳氮组分。结果表明:(1)持续9年的氮添加和地上凋落物处理对表层土壤环境因子和不同碳氮组分无交互作用;(2)氮添加处理显著降低土壤pH(p<0.01),增加土壤中硝态氮的含量(p<0.05),其增长幅度为37.57%,并显著增加溶解性有机氮(DON)和易变活性氮(LON)的含量(p<0.01,p<0.05);(3)地上凋落物去除显著降低土壤总有机碳(TOC)、易变缓性碳(IOC)、微生物生物量碳(MBC)和微生物生物量氮(MBN)含量(p<0.05);(4)经过9年氮添加和地上凋落物处理,半干旱区沙质草地表层土壤中不同碳氮组分与土壤环境因子间相关性并不密切。即长期氮添加和地上凋落物处理会改变表层土壤不同碳、氮组分的含量,但并未显著改变各碳、氮组分的比值。研究结果为揭示长期氮添加和地上凋落物处理对半干旱区沙质草地土壤C、N贮存和预测未来土壤生物地球化学元素动态研究提供参考资料。     

土壤紧实度对伴矿景天生长及镉锌吸收性的影响研究

采集黏土、壤黏土和砂质壤土,分别设置无压实、低紧实度及高紧实度3种处理,通过盆栽试验研究了土壤紧实度对Cd、Zn超积累植物伴矿景天生长和Cd、Zn吸收性的影响。结果表明,与无压实处理比较,砂质壤土、壤黏土和黏土中伴矿景天地上部生物量在低紧实度下显著下降66.8%~83.5%、59.9%~60.4%和57.9%~71.4%;高紧实度处理却显著提高了伴矿景天的根系活力(142%~241%)。高紧实度处理显著降低了壤黏土上伴矿景天地上部Cd和Zn含量,但低紧实度对砂质壤土和黏土上伴矿景天地上部Cd和Zn含量无显著影响。与无压实处理比较,低紧实度显著降低了砂质壤土、壤黏土和黏土上伴矿景天的Cd吸取量,分别下降50.4%~73.8%、61.4%~74.9%和43.4%~63.3%,Zn吸取量下降48.7%~79.5%、73.6%~79.0%和46.1%~63.5%;土壤紧实度对壤黏土上伴矿景天的镉锌吸取效率影响最明显。     

Does biochar interfere with standard methods for determining soil microbial biomass and phenotypic community structure?

Due to its high sorption affinity for organic compounds, biochar may interfere with extraction procedures involving such compounds used for microbially-related assays commonly applied to soils. Here we assessed the impact of two biochars (derived from pine bark and produced at 300 and 600 °C) at three concentrations (0, 12.5, and 50 g kg⁻¹) in three distinct arable soils with contrasting textural classes (loamy sand, sandy loam, and clay) on the determination of soil microbial biomass C by fumigation–extraction, fungal biomass by ergosterol analysis, and microbial community structure as defined by phospholipid fatty acid (PLFA) profiling. Biochar did not affect the apparent concentration of soil microbial biomass C and had no significant impact on apparent PLFA profiles. By contrast, the apparent extraction efficiency of ergosterol was affected dependent on soil type, biochar production temperature, and biochar concentration. Nonetheless, ergosterol contents of biochar-amended soils can be accurately estimated by correcting for reduced recovery using an ergosterol spike.     

Long‐term effects on soil microbial properties of heavy metals from industrial exhaust deposition

Soil samples were taken at 0—10 cm and 10—20 cm depth from 7 clay‐marsh sites used as grassland close to Nordenham in the north of Lower Saxony, Germany. The sites had been contaminated by deposition of heavy metals from industrial exhausts, the level of contamination varying according to their distances from a lead factory. The soils were analyzed to assess the depth‐specific effects of NH₄NO₃ extractable and total amounts of Zn, Pb, and Cu on basal respiration, adenylates, ergosterol, and biomass C estimated by fumigation extraction (FE) and substrate‐induced respiration (SIR). Most of the chemical and biological properties studied decreased with depth, but depth‐specific differences in the relationships between these properties rarely occurred. The biomass C/soil organic C ratio was at a relatively high level, but most consistently reflected pollution as a decrease with increasing heavy metal load, independently of the method used for biomass C estimation. However, the SIR estimates were on average 44 % lower than those of FE, mainly due to pH effects. The metabolic quotient SIR‐qCO₂ increased with increasing NH₄NO₃ extractable and total heavy metal contents, but also with decreasing pH, whereas the FE‐qCO₂ remained unaffected by heavy metals and pH. The ATP/FE‐biomass C ratio was on average 8.2 μmol g^—1 and negatively affected by soil pH, but also by total Zn, NH₄NO₃ extractable Zn and Cu. The ergosterol/FE‐biomass C ratio was on average 0.29 %, i.e. at a very low level, and increased with increasing heavy metal content. This indicates a change in the community structure towards fungi.     

Influence of long-term conservation tillage on soil and rhizosphere microorganisms

 In long-term field experiments on sandy loam and loamy sand soils, the influence of conservation and conventional tillage on soil and rhizosphere microorganisms was studied. Conservation tillage stimulated rhizosphere bacteria on winter wheat, winter barley, winter rye and maize in different soil layers. Particularly the populations of Agrobacterium spp. and Pseudomonas spp. were increased. On the sandy loam, N₂ fixation and nodulation of pea plants were significantly increased. No influence of different soil tillage was determined on the colonization of the rhizosphere by mycorrhiza and saprophytic fungi. Stubble residues infected with Gaeumanomyces graminis were infectious for a longer time on the soil surface than after incorporation into the soil. Received: 10 March 1998     

Does soil ergosterol concentration provide a reliable estimate of soil fungal biomass?

Our aim was to determine if soil ergosterol concentration provides a quantitative estimate of the soil fungal biomass concentration, as is usually assumed. This was done by comparing soil ergosterol measurements with soil fungal biomass (fungal biomass C) concentrations estimated by microscopic measurements and by the selective inhibition technique linked to substrate-induced respiration (SIR). The measurements were compared in a silty-clay loam soil given a range of previous treatments designed to increase or decrease the soil fungal biomass and so also to change the soil ergosterol concentration. The treatments used were ryegrass amendment, to increase the total and fungal biomass, and CHCl₃-fumigation and the addition of the biocides, captan, bronopol and dinoseb, to decrease both ergosterol and fungal biomass C concentrations. The mineralization of ergosterol following addition to sand innoculated with soil extract, and to a sandy loam soil, was also determined. The added ergosterol was little, if at all, degraded following addition to either sand or the unfumigated or fumigated soil during a 10 d aerobic incubation. Similarly, pesticide addition did not significantly change soil ergosterol concentrations yet the soil fungal biomass C concentration decreased significantly. Thus, the ratio: (soil ergosterol concentration/soil fungal biomass C concentration) was much higher in the pesticide-treated soils than the control soil. Following ryegrass amendment, soil ergosterol concentration increased from about 6-12 μg⁻¹ soil within 5 d and then decreased gradually to about 7 μg g⁻¹ soil by 20 d incubation. Changes in fungal biomass C (measured by direct microscopy) closely mirrored changes in soil ergosterol over this period. However, when the amended soil was fumigated and then incubated for a further 5 d, the initial ergosterol concentration declined from 7 to 5 μg g⁻¹ soil by 20 d incubation (a decline of about 0.4). The comparable decline in fungal biomass C was about eight-fold. Thus the ratio of ergosterol to fungal biomass C increased from 0.005 to about 0.01. There was a significant correlation (r>0.84, P<0.001) between soil ergosterol concentration and fungal biomass measured by either SIR or microscopy. However, three data points played a vital role in the correlation. When these points were excluded the relationship was very poor (r<0.4). Our results therefore suggest that substantial amounts of ergosterol may exist, other than in living cells, for considerable periods, with little, if any mineralization. Thus, these results indicate that ergosterol and fungal biomass C concentrations are not always closely correlated, due to the slow metabolism of ergosterol in recently dead fugal biomass and/or the existence of exocellular ergosterol in soil.     

土壤质地对柱花草生长发育、生物量及土壤肥力变化的影响

采用大田试验的方法,在云南省元谋县小雷宰流域内壤土、砂壤土和重壤土3种质地土壤上,以热研5号柱花草为材料,研究土壤质地对柱花草生长发育、生物量及土壤有机质、有机碳、全氮和全磷的影响。试验结果表明:3种土壤质地上种植柱花草,柱花草地上部和地下部生长量和生物量表现幼苗期增加缓慢,而分枝期后增加快的趋势。壤土耕性好,兼有砂土和重壤土的优点,有利柱花草地上部分的生长发育,柱花草地上部生长量、生物量及改善土壤肥力方面显著高于重壤土。砂壤土有利于柱花草根系向深层土壤生长,柱花草地下部生长量、生物量及根瘤显著高于种植在重壤土。在3种土壤质地种植柱花草后,土壤有机质、有机碳、全氮和全磷均有上升趋势。综合而言,通气性和保肥保水能力居中的壤土更适合柱花草的生长发育及干物质的积累。