Biofilm formation in drinking water affected by low concentrations of phosphorus

Abstract: There are geographical regions where microbial growth in drinking waters is limited by phosphorus instead of organic carbon. In these drinking waters even a low amount of phosphorus can strongly enhance microbial growth. The formation of biofilm can be limited by low availability of phosphorus in drinking waters with low content of phosphorus. The formation of biofilms on polyvinyl chloride plates was studied in laboratory experiments with water containing 48 microg/L assimilable organic carbon and 0.19 microg/L microbially available phosphorus. We found that low additions of phosphate (1-5 microg/L PO4(3-)-P) to water increased microbial growth in the water and in the biofilm. The effect of phosphorus on microbial growth could be detected by determining either the microbial cell production or the content of ATP in biofilms. Also, in steady-state biofilms, microbial concentrations were higher with phosphorus addition as enumerated by heterotrophic plate counts on R2A-agar and acridine orange direct counting. This work confirms the earlier findings of the importance of phosphorus for microbial growth in humic-rich drinking waters.     

A New Sensitive Bioassay for Determination of Microbially Available Phosphorus in Water

The content of assimilable organic carbon has been proposed to control the growth of microbes in drinking water. However, recent results have shown that there are regions where it is predominantly phosphorus which determines the extent of microbial growth in drinking waters. Even a very low concentration of phosphorus (below 1 μg of P liter⁻¹) can promote extensive microbial growth. We present here a new sensitive method to determine microbially available phosphorus concentrations in water down to 0.08 μg of P liter⁻¹. The method is a bioassay in which the analysis of phosphorus in a water sample is based on maximum growth of Pseudomonas fluorescens P17 when the energy supply and inorganic nutrients, with the exception of phosphorus, do not limit bacterial growth. Maximum growth (CFU) in the water sample is related to the concentration of phosphorus with the factor 373,200 ± 9,400 CFU/μg of PO₄-P. A linear relationship was found between cell growth and phosphorus concentration between 0.05 to 10 μg of PO₄-P liter⁻¹. The content of microbially available phosphorus in Finnish drinking waters varied from 0.1 to 10.2 μg of P liter⁻¹ (median, 0.60 μg of P liter⁻¹).     

Interaction between phosphorus and biodegradable organic carbon on drinking water biofilm subject to chlorination

Aims: To examine whether phosphorus and biodegradable organic carbon interact to impact biofilm density and physiological function of biofilm‐forming bacteria under conditions relevant to chlorinated drinking water distribution systems. Materials and Results: The 2 × 2 factorial experiments with low and high levels of phosphorus and biodegradable organic carbon were performed on 4 ‐week‐old drinking water biofilms in four separate pipe systems in the presence of chlorine. Experimental results revealed that biofilm heterotrophic plate count levels increased with the increase in biodegradable organic carbon concentration, showed no response to increases in levels of phosphorus and was not affected by interaction between phosphorus and biodegradable organic carbon. However, a significant positive interaction between phosphorus and biodegradable organic carbon was found to exist on biofilm mass and physiological function and/or metabolic potentials of biofilm communities; the effects of biodegradable organic carbon on biofilm mass and physiological function of biofilm‐forming bacteria were accelerated in going from low to high level of phosphorus. Conclusions: Biodegradable organic carbon was found to be the primary nutrient in regulating biofilm formation in drinking water regardless of the presence of chlorine. It can be therefore concluded that the removal of an easily biodegradable organic carbon is necessary to minimize the biofilm growth potential induced by the intrusion of phosphorus. Significance and Impact of the Study: Phosphorus introduced to drinking water may interact with biodegradable organic carbon, thus leading to measurable impact on the biofilm formation.     

Effect of exposure to sunlight and phosphorus-limitation on bacterial degradation of coloured dissolved organic matter (CDOM) in freshwater

This study reports on the interacting effect of photochemical conditioning of dissolved organic matter and inorganic phosphorus on the metabolic activity of bacteria in freshwater. Batch cultures with lake-water bacteria and dissolved organic carbon (DOC) extracted from a humic boreal river were arranged in an experimental matrix of three levels of exposure to simulated sunlight and three levels of phosphorus concentration. We measured an increase in bacterial biomass, a decrease in DOC and bacterial respiration as CO(2) production and O(2) consumption over 450 h. These measurements were used to calculate bacterial growth efficiency (BGE). Bacterial degradation of DOC increased with increasing exposure to simulated sunlight and availability of phosphorus and no detectable growth occurred on DOC that was not pre-exposed to simulated sunlight. The outcome of photochemical degradation of DOC changed with increasing availability of phosphorus, resulting in an increase in BGE from about 5% to 30%. Thus, the availability of phosphorus has major implications for the quantitative transfer of carbon in microbial food webs.     

Priming and microbial nutrient limitation in lowland tropical forest soils of contrasting fertility

Priming is an increase in soil organic carbon decomposition following input of labile organic carbon. In temperate soils where biological activity is limited commonly by nitrogen availability, priming is expected to occur through microbial acquisition of nitrogen from organic matter or stimulated activity of recalcitrant-carbon degrading microorganisms. However, these priming mechanisms have not yet been assessed in strongly weathered tropical forest soils where biological activity is often limited by the availability of phosphorus. We examined whether microbial nutrient limitation or community dynamics drive priming in three lowland tropical forest soils of contrasting fertility (‘low’, ‘mid’ and ‘high’) by applying C₄-sucrose (alone or in combination with nutrients; nitrogen, phosphorus and potassium) and measuring (1) the δ¹³C-signatures in respired CO₂ and in phospholipid fatty acid (PLFA) biomarkers, and (2) the activities of enzymes involved in nitrogen (N-acetyl β-glucosaminidase), phosphorus (phosphomonoesterase) and carbon (β-glucosidase, cellobiohydrolase, xylanase, phenol oxidase) acquisition from organic compounds. Priming was constrained in part by nutrient availability, because priming was greater when sucrose was added alone compared to when added with nutrients. However, the greatest priming with sucrose addition alone was detected in the medium fertility soil. Priming occurred in parallel with stimulated activity of phosphomonoesterase and phenol oxidase (but not N-acetyl β-glucosaminidase); when sucrose was added with nutrients there were lower activities of phosphomonoesterase and phenol oxidase. There was no evidence according to PLFA δ¹³C-incorporation that priming was caused by specific groups of recalcitrant-carbon degrading microorganisms. We conclude that priming occurred in the intermediate fertility soil following microbial mineralization of organic nutrients (phosphorus in particular) and suggest that priming was constrained in the high fertility soil by high nutrient availability and in the low fertility soil by the low concentration of soil organic matter amenable to priming. This first study of priming mechanisms in tropical forest soils indicates that input of labile carbon can result in priming by microbial mineralization of organic nutrients, which has important implications for understanding the fate of organic carbon in tropical forest soils.     

Phosphorus Limitation of Microbial Processes in Moist Tropical Forests: Evidence from Short-term Laboratory Incubations and Field Studies

Although there is a widespread belief that phosphorus (P) limits basic ecosystem processes in moist tropical forests, direct tests of this supposition are rare. At the same time, it is generally believed that P does not limit soil microorganism respiration or growth in terrestrial ecosystems. We used natural gradients in P fertility created by soils of varying age underlying tropical rain forests in southwestern Costa Rica, combined with direct manipulations of carbon (C) and P supply, to test the effects of P availability on the decomposition of multiple forms of C, including dissolved organic carbon (DOC) and soil organic carbon (SOC). Results from a combination of laboratory and field experiments suggest that C decomposition in old, highly weathered oxisol soils is strongly constrained by P availability. In addition, P additions to these soils (no C added) also revealed that microbial utilization of at least labile fractions of SOC was also P limited. To our knowledge, this is the first direct evidence of P limitation of microbial processes in tropical rain forest soil. We suggest that P limitation of microbial decomposition may have profound implications for C cycling in moist tropical forests, including their potential response to increasing atmospheric carbon dioxide. Furthermore, this site is still relatively rich in P when compared to many other tropical forests on old soils; thus, we believe that P limitation of soil microorganisms throughout the humid tropics is a possibility.     

Nutrient supplementation experiments with saltern microbial communities implicate utilization of DNA as a source of phosphorus

All environments including hypersaline ones harbor measurable concentrations of dissolved extracellular DNA (eDNA) that can be utilized by microbes as a nutrient. However, it remains poorly understood which eDNA components are used, and who in a community utilizes it. For this study, we incubated a saltern microbial community with combinations of carbon, nitrogen, phosphorus, and DNA, and tracked the community response in each microcosm treatment via 16S rRNA and rpoB gene sequencing. We show that microbial communities used DNA only as a phosphorus source, and provision of other sources of carbon and nitrogen was needed to exhibit a substantial growth. The taxonomic composition of eDNA in the water column changed with the availability of inorganic phosphorus or supplied DNA, hinting at preferential uptake of eDNA from specific organismal sources. Especially favored for growth was eDNA from the most abundant taxa, suggesting some haloarchaea prefer eDNA from closely related taxa. The preferential eDNA consumption and differential growth under various nutrient availability regimes were associated with substantial shifts in the taxonomic composition and diversity of microcosm communities. Therefore, we conjecture that in salterns the microbial community assembly is driven by the available resources, including eDNA.Subject terms: Metagenomics, Microbial ecology     

Ecoenzymatic stoichiometry of microbial nutrient acquisition in tropical soils

The relative activities of soil enzymes involved in mineralizing organic carbon (C), nitrogen (N), and phosphorus (P) reveal stoichiometric and energetic constraints on microbial biomass growth. Although tropical forests and grasslands are a major component of the global C cycle, the effects of soil nutrient availability on microbial activity and C dynamics in these ecosystems are poorly understood. To explore potential microbial nutrient limitation in relation to enzyme allocation in low latitude ecosystems, we performed a meta-analysis of acid/alkaline phosphatase (AP), β-1,4-glucosidase (BG), and β-1,4-N-acetyl-glucosaminidase (NAG) activities in tropical soils. We found that BG:AP and NAG:AP ratios in tropical soils are significantly lower than those of temperate ecosystems overall. The lowest BG:AP and NAG:AP ratios were associated with old or acid soils, consistent with greater biological phosphorus demand relative to P availability. Additionally, correlations between enzyme activities and mean annual temperature and precipitation suggest some climatic regulation of microbial enzyme allocation in tropical soils. We used the results of our analysis in conjunction with previously published data on soil and biomass C:N:P stoichiometry to parameterize a biogeochemical equilibrium model that relates microbial growth efficiency to extracellular enzyme activity. The model predicts low microbial growth efficiencies in P-limited soils, indicating that P availability may influence C cycling in the highly weathered soils that underlie many tropical ecosystems. Therefore, we suggest that P availability be included in models that simulate microbial enzyme allocation, biomass growth, and C mineralization.     

Soil Water Content and Organic Carbon Availability Are Major Determinants of Soil Microbial Community Composition

Exploration of environmental factors governing soil microbial community composition is long overdue and now possible with improved methods for characterizing microbial communities. Previously, we observed that rice soil microbial communities were distinctly different from tomato soil microbial communities, despite management and seasonal variations within soil type. Potential contributing factors included types and amounts of organic inputs, organic carbon content, and timing and amounts of water inputs. Of these, both soil water content and organic carbon availability were highly correlated with observed differences in composition. We examined how organic carbon amendment (compost, vetch, or no amendment) and water additions (from air dry to flooded) affect microbial community composition. Using canonical correspondence analysis of phospholipid fatty acid data, we determined flooded, carbon-amended (+C) microcosm samples were distinctly different from other +C samples and unamended (–C) samples. Although flooding without organic carbon addition influenced composition some, organic carbon addition was necessary to substantially alter community composition. Organic carbon availability had the same general effects on microbial communities regardless of whether it was compost or vetch in origin. In addition, flooded samples, regardless of organic carbon inputs, had significantly lower ratios of fungal to bacterial biomarkers, whereas under drier conditions and increased organic carbon availability the microbial communities had higher proportions of fungal biomass. When comparing field and microcosm soil, flooded +C microcosm samples were most similar to field-collected rice soil, whereas all other treatments were more similar to field-collected tomato soil. Overall, manipulating water and carbon content selected for microbial communities similar to those observed when the same factors were manipulated at the field scale.     

Formation of biofilms in drinking water distribution networks,a case study in two cities in Finland and Latvia

The formation of biofilms in drinking water distribution networks is a significant technical, aesthetic and hygienic problem. In this study, the effects of assimilable organic carbon, microbially available phosphorus (MAP), residual chlorine, temperature and corrosion products on the formation of biofilms were studied in two full-scale water supply systems in Finland and Latvia. Biofilm collectors consisting of polyvinyl chloride pipes were installed in several waterworks and distribution networks, which were supplied with chemically precipitated surface waters and groundwater from different sources. During a 1-year study, the biofilm density was measured by heterotrophic plate counts on R2A-agar, acridine orange direct counting and ATP-analyses. A moderate level of residual chorine decreased biofilm density, whereas an increase of MAP in water and accumulated cast iron corrosion products significantly increased biofilm density. This work confirms, in a full-scale distribution system in Finland and Latvia, our earlier in vitro finding that biofilm formation is affected by the availability of phosphorus in drinking water.     

Environmental factors affect the response of microbial extracellular enzyme activity in soils when determined as a function of water availability and temperature

Microorganisms govern soil carbon cycling with critical effects at local and global scales. The activity of microbial extracellular enzymes is generally the limiting step for soil organic matter mineralization. Nevertheless, the influence of soil characteristics and climate parameters on microbial extracellular enzyme activity (EEA) performance at different water availabilities and temperatures remains to be detailed. Different soils from the Iberian Peninsula presenting distinctive climatic scenarios were sampled for these analyses. Results showed that microbial EEA in the mesophilic temperature range presents optimal rates under wet conditions (high water availability) while activity at the thermophilic temperature range (60°C) could present maximum EEA rates under dry conditions if the soil is frequently exposed to high temperatures. Optimum water availability conditions for maximum soil microbial EEA were influenced mainly by soil texture. Soil properties and climatic parameters are major environmental components ruling soil water availability and temperature which were decisive factors regulating soil microbial EEA. This study contributes decisively to the understanding of environmental factors on the microbial EEA in soils, specifically on the decisive influence of water availability and temperature on EEA. Unlike previous belief, optimum EEA in high temperature exposed soil upper layers can occur at low water availability (i.e., dryness) and high temperatures. This study shows the potential for a significant response by soil microbial EEA under conditions of high temperature and dryness due to a progressive environmental warming which will influence organic carbon decomposition at local and global scenarios.     

有机物添加下太岳山油松林土壤微生物元素组成的稳态分析

在山西太岳山地区,向油松林土壤中分别添加生物炭、玉米秸秆、蒙古栎叶、油松叶、木屑等5种有机物,测定各处理的土壤养分、酶及微生物生物量等指标,研究外源有机物添加下土壤酶化学计量特征及微生物元素组成的内稳性。结果表明: 添加木屑显著增加了土壤N(17.1%)、P(37.6%)含量,显著增加了微生物生物量碳(118.0%)、氮(41.0%)、磷(176.6%)。C、N、P获取酶(β-1,4-葡萄糖苷酶、β-1,4-N-乙酰氨基葡萄糖苷酶、亮氨酸氨基肽酶、酸性磷酸酶)活性总体上随添加有机物C/N值(生物炭<蒙古栎叶<油松叶<玉米秸秆<木屑)的增加而增加,其化学计量变化受土壤养分状态及微生物生物量的调控。酶活性相对比例及矢量特性表明,研究区微生物生长受到P的限制,且添加有机物没有缓解P的制约作用。微生物生物量碳、氮及化学计量比C∶N、C:P、N∶P属于绝对稳态型,而微生物生物量磷处于非稳态。微生物通过改变酶的分配策略保持微生物体元素及比例的相对稳定,仅有微生物生物量磷对土壤养分变化表现出不稳定性,可能因为P是研究区微生物生长的限制性元素。     

Nutrient and Temperature Limitation of Bacterioplankton Growth in Temperate Lakes

Limitation of bacterioplankton production by nutrients and temperature was investigated in eight temperate lakes in summer. Six of the lakes were resampled in autumn. The lakes differ in nutrient content, water color, and concentration of dissolved organic carbon. Nutrients (phosphorus, nitrogen, and organic carbon) were added alone and in all possible combinations to filtered lake water inoculated with bacteria from the lake. After incubation for 36–40 h at in situ temperatures (ranging from 7 to 20°C), the response in bacterioplankton production was determined. The effect of increased temperature on bacterioplankton growth was also tested. Bacterioplankton production was often limited by phosphorus alone, organic carbon alone, or the two in combination. Phosphorus limitation of bacterioplankton production was more common in the summer, whereas limitation by organic carbon was more frequently observed in the autumn. There was a close balance between limitation by phosphorus and organic carbon in the epilimnion in the summer. In the hypolimnion in the summer, bacterioplankton growth was primarily phosphorus-limited. The effect of phosphorus additions decreased with increasing phosphorus concentrations in the lakes. However, there were no correlations between the effect of added organic carbon and water color, dissolved organic carbon concentration, or phosphorus concentration. When temperature was low (in the hypolimnion in the summer, and throughout the water column in the autumn) temperature also limited bacterioplankton production. Thus, temperature and inorganic nutrients or organic compounds can limit bacterioplankton growth both alone and simultaneously. However, at low temperatures, temperature is the most important factor influencing bacterioplankton growth.     

Effects of Assimilable Organic Carbon and Free Chlorine on Bacterial Growth in Drinking Water

Assimilable organic carbon (AOC) is one of the most important factors affecting the re-growth of microorganisms in drinking water. High AOC concentrations result in biological instability, but disinfection kills microbes to ensure the safety of drinking water. Free chlorine is an important oxidizing agent used during the disinfection process. Therefore, we explored the combined effects of AOC and free chlorine on bacterial growth in drinking water using flow cytometry (FCM). The initial AOC concentration was 168 μg.L^-1 in all water samples. Without free chlorine, the concentrations of intact bacteria increased but the level of AOC decreased. The addition of sodium hypochlorite caused an increase and fluctuation in AOC due to the oxidation of organic carbon. The concentrations of intact bacteria decreased from 1.1×10⁵ cells.mL^-1 to 2.6×10⁴ cells.mL^-1 at an initial free chlorine dose of 0.6 mg.L^-1 to 4.8×10⁴ cells.mL^-1 at an initial free chlorine dose of 0.3 mg.L^-1 due to free chlorine originating from sodium hypochlorite. Additionally, free chlorine might be more obviously affected AOC concentrations than microbial growth did. These results suggested that AOC and free chlorine might have combined effects on microbial growth. In this study, our results showed concentrations determined by FCM were higher than those by HPC, which indicated that some E. coli detected by FCM might not be detected using HPC in drinking water. The level of free chlorine might restrain the consumption of AOC by inhibiting the growth of E. coli; on the other hand, chlorination might increase the level of AOC, thereby increase the potential for microbial growth in the drinking water network.     

Changes in the structure and function of microbial communities in drinking water treatment bioreactors upon addition of phosphorus

Phosphorus was added as a nutrient to bench-scale and pilot-scale biologically active carbon (BAC) reactors operated for perchlorate and nitrate removal from contaminated groundwater. The two bioreactors responded similarly to phosphorus addition in terms of microbial community function (i.e., reactor performance), while drastically different responses in microbial community structure were detected. Improvement in reactor performance with respect to perchlorate and nitrate removal started within a few days after phosphorus addition for both reactors. Microbial community structures were evaluated using molecular techniques targeting 16S rRNA genes. Clone library results showed that the relative abundance of perchlorate-reducing bacteria (PRB) Dechloromonas and Azospira in the bench-scale reactor increased from 15.2% and 0.6% to 54.2% and 11.7% after phosphorus addition, respectively. Real-time quantitative PCR (qPCR) experiments revealed that these increases started within a few days after phosphorus addition. In contrast, after phosphorus addition, the relative abundance of Dechloromonas in the pilot-scale reactor decreased from 7.1 to 0.6%, while Zoogloea increased from 17.9 to 52.0%. The results of this study demonstrated that similar operating conditions for bench-scale and pilot-scale reactors resulted in similar contaminant removal performances, despite dramatically different responses from microbial communities. These findings suggest that it is important to evaluate the microbial community compositions inside bioreactors used for drinking water treatment, as they determine the microbial composition in the effluent and impact downstream treatment requirements for drinking water production. This information could be particularly relevant to drinking water safety, if pathogens or disinfectant-resistant bacteria are detected in the bioreactors.     

Diverse responses of pqqC- and phoD-harbouring bacterial communities to variation in soil properties of Moso bamboo forests

Phosphate-mobilizing bacteria (PMB) play a critical role in the regulation of phosphorus availability in the soil. The microbial genes pqqC and phoD encode pyrroloquinoline quinone synthase and bacterial alkaline phosphatase, respectively, which regulate inorganic and organic phosphorus mobilization, and are therefore used as PMB markers. We examined the effects of soil properties in three Moso bamboo forest sites on the PMB communities that were profiled using high-throughput sequencing. We observed differentiated responses of pqqC- and phoD-harbouring PMB communities to various soil conditions. There was significant variation among the sites in the diversity and structure of the phoD-harbouring community, which correlated with variation in phosphorus levels and non-capillary porosity; soil organic carbon and soil water content also affected the structure of the phoD-harbouring community. However, no significant difference in the diversity of pqqC-harbouring community was observed among different sites, while the structure of the pqqC-harbouring bacteria community was affected by soil organic carbon and soil total nitrogen, but not soil phosphorus levels. Overall, changes in soil conditions affected the phoD-harbouring community more than the pqqC-harbouring community. These findings provide a new insight to explore the effects of soil conditions on microbial communities that solubilize inorganic phosphate and mineralize organic phosphate.     

Soil microorganisms respond to five years of climate change manipulations and elevated atmospheric CO2 in a temperate heath ecosystem

Background and aims

Soil microbial responses to global change can affect organic matter turnover and nutrient cycling thereby altering the overall ecosystem functioning. In a large-scale experiment, we investigated the impact of 5 years of climate change and elevated atmospheric CO₂ on soil microorganisms and nutrient availability in a temperate heathland.

Methods

The future climate was simulated by increased soil temperature (+0.3 °C), extended pre-summer drought (excluding 5–8 % of the annual precipitation) and elevated CO₂ (+130 ppm) in a factorial design. Soil organic matter and nutrient pools were analysed and linked to microbial measures by quantitative PCR of bacteria and fungi, chloroform fumigation extraction, and substrate-induced respiration to assess their impact of climate change on nutrient availability.

Results

Warming resulted in higher measures of fungi and bacteria, of microbial biomass and of microbial growth potential, however, this did not reduce the availability of nitrogen or phosphorus in the soil. Elevated CO₂ did not directly affect the microbial measures or nutrient pools, whereas drought shifted the microbial community towards a higher fungal dominance.

Conclusions

Although we were not able to show strong interactive effects of the global change factors, warming and drought changed both nutrient availability and microbial community composition in the heathland soil, which could alter the ecosystem carbon and nutrient flow in the long-term.     

草甸草原土壤碳/氮矿化潜力及土壤微生物水分敏感性对极端干旱的响应

土壤碳、氮矿化是生态系统养分循环的关键过程,受到水分供给的强烈影响。本研究对极端干旱处理(连续3年生长季减少66%降水)的内蒙古草甸草原野外取土,采用超低温冻干后再调节土壤水分至3%、8%、13%、18%、25%和35% 6个水平进行室内培养,研究极端干旱处理后土壤碳/氮矿化潜力以及土壤微生物对水分变化的敏感性。结果表明: 与对照(自然降雨)相比,极端干旱处理后,6个培养水平的平均土壤氮矿化潜力显著提高14.2%,但未显著影响土壤碳矿化潜力。极端干旱显著提高土壤微生物生物量氮和土壤可溶性有机碳26.8%和26.9%。无论是对照还是极端干旱处理,土壤氮矿化潜力、碳矿化潜力和微生物生物量碳和氮均随着土壤含水量增加而增加,而可溶性有机碳从较低水分的培养水平(3%和8%)到较高水分的培养水平(>13%)显著降低,表明底物的扩散起到重要作用。极端干旱处理显著提高了碳矿化初始脉冲强度,表明极端干旱提高了土壤微生物对水分的敏感性。极端干旱显著降低了土壤碳矿化潜力/氮矿化潜力的比值,表明长期干旱可能会降低土壤碳、氮循环过程的耦合作用。极端干旱对土壤碳矿化和氮矿化过程的影响存在差异,激发了土壤微生物对水分的敏感性,弱化了碳、氮循环过程的耦合关系,并进一步影响中国北方草甸草原生态系统的生物地球化学循环过程及草地生产力。     

Seasonal and Spatial Controls over Nutrient Cycling in a Pacific Northwest Prairie

West Coast prairies in the US are an endangered ecosystem, and effective conservation will require an understanding of how changing climate will impact nutrient cycling and availability. We examined how seasonal patterns and micro-heterogeneity in edaphic conditions (% moisture, total organic carbon, % clay, pH, and inorganic nitrogen and phosphorus) control carbon, nitrogen, and phosphorus cycling in an upland prairie in western Oregon, USA. Across the prairie, we collected soils seasonally and measured microbial respiration, net nitrogen mineralization, net nitrification, and phosphorus availability under field conditions and under experimentally varied temperature and moisture treatments. The response variables differed in the degree of temperature and moisture limitation within seasons and how these factors varied across sampling sites. In general, we found that microbial respiration was limited by low soil moisture year-round and by low temperatures in the winter. Net nitrogen mineralization and net nitrification were never limited by temperature, but both were limited by excessive soil moisture in winter, and net nitrification was also inhibited by low soil moisture in the summer. Factors that enhanced microbial respiration tended to decrease soil phosphorus availability. Edaphic factors explained 76% of the seasonal and spatial variation in microbial respiration, 35% of the variation in phosphorus availability, and 29% of the variation in net nitrification. Much of the variation in net nitrogen mineralization remained unexplained (R ² = 0.19). This study, for the first time, demonstrates the complex seasonal controls over nutrient cycling in a Pacific Northwest prairie.     

土壤酶计量揭示了武夷山黄山松林土壤微生物沿海拔梯度的碳磷限制变化

了解土壤胞外酶活性和酶计量的变化对评估山地生态系统土壤养分有效性和微生物的营养限制状况具有重要意义.然而,亚热带山地森林土壤微生物的营养限制状况对海拔梯度变化的响应及其驱动因素尚不清楚.本研究以武夷山不同海拔(1200～2000 m)黄山松林为对象,测定了土壤基本性质、微生物生物量以及与碳(C)、氮(N)、磷(P)循环...