西藏高原自然生态系统转化为农田后提高了土壤的净矿化和净硝化

A comparative study was conducted to determine the NH4^＋ and NO3^- concentrations in soil profiles and to examine the net nitrogen （N） mineralization and nitrification in adjacent forest, grassland, and cropland soils on the Tibetan Plateau. Cropland soil showed significantly higher inorganic N concentrations in soil profiles compared with forest and grassland soils. NO3^- -N accounted for 70%-90^ of inorganic N in cropland soil, while NH4^＋ -N was the main form of inorganic N in forest and grassland soils. The average net N mineralization rate at 0 20 cm depth was approximately twice in cropland soil （1.48 mg kg^-1 d^-1） as high as in forest （0.83 mg kg^-1 d^-1） or grassland soil （0.72 mg kg^-1 d^-1）. Cropland showed strong net nitrification, with the net rate almost equal to the total net N mineralization. Urea addition stimulated soil respiration, particularly in forest soil. Most urea-N, however, remained as NH4^＋ in forest and grassland soils, while NO3^- was the main form of inorganic N to increase in cropland soil. Higher rates of net nitrification in cropland soils suggest that land use change on the Tibetan Plateau may lead to high N losses through nitrate leaching.     

城郊土壤不透水表面有土壤机碳转化及其相关性质的研究

Installation of impervious surface in urban area prevents the exchange of material and energy between soil and other environmental counterparts, thereby resulting in negative effects on soil function and urban environment. Soil samples were collected at 0-20 cm depth in Nanjing City, China, in which seven sites were selected for urban open soils, and fourteen sites with similar parent material were selected for the impervious-covered soils, to examine the effect of impervious surface on soil properties and microbial activities, and to determine the most important soil properties associated with soil organic carbon （SOC） transformation in the urban soils covered by impervious surfaces. Soil organic carbon and water-soluble organic carbon （WSOC） concentrations, potential carbon （C） and nitrogen （N） mineralization rates, basal respiration, and physicochemical properties with respect to C transformation were measured. Installation of impervious surface severely affected soil physicochemical properties and microbial activities, e.g., it significantly decreased total N contents, potential C mineralization and basal respiration rate （P 〈 0.01）, while increased pH, clay and Olsen-P concentrations. Soil organic carbon in the sealed soils at 0-20 cm was 2.35 kg m-2, which was significantly lower than the value of 4.52 kg m-2 in the open soils （P 〈 0.05）. Canonical correlation analysis showed WSOC played a major role in determining SOC transformation in the impervious-covered soil, and it was highly correlated with total N content and potential C mineralization rate. These findings demonstrate that installation of impervious surface in urban area, which will result in decreases of SOC and total N concentrations and soil microbial activities, has certain negative consequences for soil fertility and long-term storage of SOC.     

酸雨对土壤有机碳氮潜在矿化的影响

Acid rain is a serious environmental problem worldwide. In this study, a pot experiment using forest soils planted with the seedlings of four woody species was performed with weekly treatments of pH 4.40, 4.00, 3.52, and 3.05 simulated acid rain （SAR） for 42 months compared to a control ofpH 5.00 lake water. The cumulative amounts of C and N mineralization in the five treated soils were determined after incubation at 25 ℃ for 65 d to examine the effects of SAR treatments. For all five treatments, cumulative CO2-C production ranged from 20.24 to 27.81 mg kg^-1 dry soil, net production of available N from 17.37 to 48.95 mg kg^-1 dry soil, and net production of NO3-N from 9.09 to 46.23 mg kg^-1 dry soil. SAR treatments generally enhanced the emission of CO2-C from the soils; however, SAR with pH 3.05 inhibited the emission. SAR treatments decreased the net production of available N and NO3-N. The cumulative CH4 and N2O productions from the soils increased with increasing amount of simulated acid rain. The cumulative CO2-C production and the net production of available N of the soil under Acmena acuminatissima were significantly higher （P 〈 0.05） than those under Schima superba and Cryptocarya concinna. The mineralization of soil organic C was related to the contents of soil organic C and N, but was not related to soil pH. However, the overall effect of acid rain on the storage of soil organic matter and the cycling of important nutrients depended on the amount of acid deposition and the types of forests.     

两类温带森林下土壤氮的有效性指标比较

To evaluate the validity of different indices in estimating soil readily mineralizable N, soil microbial biomass （Nmic）, soil active N （SAN）, soluble organic N （SON）, net N mineralization rate （NNR） and gross N mineralization rate （GNR） in mineral soils （0-10 cm） from six forest stands located in central Germany were determined and compared with two sampling times： April and November. Additionally, soil density fractionation was conducted for incubated soils （with addition of ^15NH4-N and glucose, 40 days） to observe the sink of added ^15N in different soil fractions. The study showed that Nmic and NNR in most stands differed significantly （P 〈 0.05） between the two sampling times, but not GNR, SAN and SON. In November, no close relationships were found between GNR and other N indices, or between Nrnic, SON, and SAN and forest type. However, in April, GNR was significantly correlated （P 〈 0.05） with Nmic, SAN, and NNR along with Nmlc under beech being significantly higher （P 〈 0.05） than under conifers. Furthermore, density fractionation revealed that the light fraction （LF, 0.063-2 mm, 〉 1.7 gcm^-3） was not correlated with the other N indices. In contrast, results from the incubation study proved that more 15N was incorporated into the heavy fraction （HF 〈 0.063 ram, 〉 1.7 g cm^-3） than into LF, indicaing that more labile N existed in HF than in LF. These findings suggested that attention should be paid to the differences existing in N status between agricultural and forest soils.     

印度热带森林干旱扰动土壤的微生物碳, 氮, 磷的研究

Variations in microbial biomass C (MB-C),N (MB-N) and P (MB-P) along a gradient of different dominant vegeta- tion covers (natural forest,mixed deciduous forest,disturbed savanna and grassland ecosystems) in dry tropical soils of Vindhyan Plateau,India were studied from January 2005 to December 2005.The water holding capacity,organic C,total N,total P and soil moisture content were comparatively higher in forest soils than in the savanna and grassland sites.Across different study sites the mean annual MB-C,MB-N and MB-P at 0-15 cm soil depth varied from 312.05 ± 4.22 to 653.40 ± 3.17,32.16 ± 6.25 to 75.66 ± 7.21 and 18.94 ± 2.94 to 30.83 ± 23.08 μg g ?1 dry soil,respectively.At all the investigated sites,the maximum MB-C,MB-N and MB-P occurred during the dry period (summer season) and the minimum in wet period (rainy season).In the present study,soil MB-C,MB-N and MB-P were higher at the forest sites compared to savanna and grassland sites.The differences in MB-C,MB-N and MB-P were significant (P 0.001) among sites and seasons.The MB-C (P 0.0001),MB-N (P 0.001) and MB-P (P 0.0001) were positively correlated with organic C,while the relationship between soil moisture and MB-C,MB-N and MB-P (P 0.001,P 0.01 and P 0.0001,respectively) was negative.The decreasing order of MB-C,MB-N and MB-P along study ecosystems was natural forest mixed deciduous forest savanna grassland.The results suggested that deforestation and land use practices (conversion of forest into savanna and grassland) caused the alterations in soil properties,which as a consequence,led to reduction in soil nutrients and MB-C,MB-N and MB-P in the soil of disturbed sites (grassland and savanna) compared to undisturbed forest ecosystems.     

好氧条件下两种水稻土的氮素总转化速率比较

Although to date individual gross N transformations could be quantified by ~(15)N tracing method and models,studies are still limited in paddy soil.An incubation experiment was conducted using topsoil(0-20 cm) and subsoil(20-60 cm) of two paddy soils,alkaline and clay(AC) soil and neutral and silt loam(NSL) soil,to investigate gross N transformation rates.Soil samples were labeled with either ~(15)NH4_NO_3 or NH_4~(15)NO_3,and then incubated at 25 °C for 168 h at 60%water-holding capacity.The gross N mineralization(recalcitrant and labile organic N mineralization) rates in AC soil were 1.6 to 3.3 times higher than that in NSL soil,and the gross N nitrification(autotrophic and heterotrophic nitrification) rates in AC soil were 2.4 to 4.4 times higher than those in NSL soil.Although gross NO_3~- consumption(i.e.,NO_3~- immobilization and dissimilatory NO_3~- reduction to NH_4~+ rates increased with increasing gross nitrification rates,the measured net nitrification rate in AC soil was approximately 2.0 to 5.1 times higher than that in NSL soil.These showed that high NO_3~- production capacity of alkaline paddy soil should be a cause for concern because an accumulation of NO_3~- can increase the risk of NO_3~- loss through leaching and denitrification.     

中国亚热带耕作雏形土及强酸土的可蚀性与渗透性关系

To evaluate the validity of different indices in estimating soil readily mineralizable N, soil microbial biomass (Nmic), soil active N (SAN), soluble organic N (SON), net N mineralization rate (NNR) and gross N mineralization rate (GNR) in mineral soils (0-10 cm) from six forest stands located in central Germany were determined and compared with two sampling times: April and November. Additionally, soil density fractionation was conducted for incubated soils (with addition of ¹⁵NH₄-N and glucose, 40 days) to observe the sink of added ¹⁵N in different soil fractions. The study showed that Nmic and NNR in most stands differed significantly (P ≤ 0.05) between the two sampling times, but not GNR, SAN and SON. In November, no close relationships were found between GNR and other N indices, or between Nmic, SON, and SAN and forest type. However, in April, GNR was significantly correlated (P ≤ 0.05) with Nmic, SAN, and NNR along with Nmic under beech being significantly higher (P ≤ 0.05) than under conifers. Furthermore, density fractionation revealed that the light fraction (LF, 0.063-2 mm, > 1.7 g cm^-3) was not correlated with the other N indices. In contrast, results from the incubation study proved that more ¹⁵N was incorporated into the heavy fraction (HF < 0.063 mm, > 1.7 g cm^-3) than into LF, indicaing that more labile N existed in HF than in LF. These findings suggested that attention should be paid to the differences existing in N status between agricultural and forest soils.     

Effect of indaziflam on microbial activity and nitrogen cycling processes in an orchard soil

Indaziflam is a preemergent herbicide widely used for the control of weeds in pecan (Carya illinoinensis) orchards in the southwestern region of the United States. Given the paucity of data regarding the effect of indaziflam on the biochemical properties of soils supporting pecan production, this study was conducted to evaluate the effects of different application rates of indaziflam on soil microbial activity, diversity, and biochemical processes related to nitrogen (N) cycling. During two consecutive growing seasons (2015 and 2016), soil samples were obtained from experimental mesocosms consisting of soil-filled pots where pecan saplings were grown and treated with indaziflam applied at two different rates (25 and 50 g active ingredient (ai) ha^-1, with the higher rate being slightly lower than the recommended field application rate of 73.1 g ai ha^-1). Soil samples were collected approximately one week before and one week after herbicide application for determination of soil microbial biomass and diversity, N mineralization, and β-glucosaminidase activity. Soil samples collected from the control mesocosms without herbicide application were treated in the laboratory with two rates of indaziflam (75 and 150 g ai ha^-1) to determine the immediate effect on microbial activity. No significant effect of herbicide treatment on soil respiration and microbial biomass was detected. The results showed a slight to moderate decrease in microbial diversity (7% in 2015 and 44% in 2016). However, decreased β-glucosaminidase activity with herbicide treatment was observed in soils from the mesocosms (33%) and soils treated with indaziflam in the laboratory (45%). The mineral N pool was generally dominated by ammonium after indaziflam application, which was consistent with the drastic decrease (75%) in nitrification activity measured in the laboratory experiment. The results of this study indicate that indaziflam, even when applied at higher than recommended rates, has limited effects on soil microbial activity, but may affect N cycling processes.     

温度变化对森林土壤氮矿化的影响

Nitrogen mineralization in forest soil wa studied in laboratory by incubating undisturbed soil cores enclosed within PVC columns at different temperatures to compare the effect of flucttuating temperature with that of constant temperaature,and to find out whether soil nitrification shows linearity over time .The results showed that there was no significant difference between soil nitrification at fluctuating temperature and that at constant temperature,and suggested that it must be careful to make the conclusion that soil nitrification has linearity over time.     

高寒草甸土CO2流通和氮矿化之间的关系以及对外加碳或氮的响应

In nutrient-limited alpine meadows,nitrogen(N) mineralization is prior to soil microbial immobilization;therefore,increased mineral N supply would be most likely immobilized by soil microbes due to nutrient shortage in alpine soils.In addition,low temperature in alpine meadows might be one of the primary factors limiting soil organic matter decomposition and thus N mineralization.A laboratory incubation experiment was performed using an alpine meadow soil from the Tibetan Plateau.Two levels of NH4NO3(N) or glucose(C) were added,with a blank without addition of C or N as the control,before incubation at 5,15,or 25 ℃ for 28 d.CO2 efflux was measured during the 28-d incubation,and the mineral N was measured at the beginning and end of the incubation,in order to test two hypotheses:1) net N mineralization is negatively correlated with CO2 efflux for the control and 2) the external labile N or C supply will shift the negative correlation to positive.The results showed a negative correlation between CO2 efflux and net N immobilization in the control.External inorganic N supply did not change the negative correlation.The external labile C supply shifted the linear correlation from negative to positive under the low C addition level.However,under the high C level,no correlation was found.These suggested that the correlation of CO2 efflux to net N mineralization strongly depend on soil labile C and C:N ratio regardless of temperatures.Further research should focus on the effects of the types and the amount of litter components on interactions of C and N during soil organic matter decomposition.     

Phosphorus‐enriched soils of urban and suburban Nanjing and their effect on groundwater phosphorus

Neither the phosphorus (P)‐rich soils in urban areas nor their environmental implications have been adequately studied. This study investigated soils of typical urban function zones in Nanjing/China, like park, residential areas, school yards, campus as well as suburb vegetable land and garbage filling sites, and meantime ground water in situ. Typical soils were also experimentally leached for P leaching evaluation. All studied soils were enriched with P with enrichment ratios varying from 2 to 10 for total P and 5 to 22 for NaHCO₃‐extractable P, as compared with the original parent soils. The C : P ratios also indicated strong enrichment of P in urban soils. In urban areas the maximum P layer appeared as buried under different depth while in suburban soils as epipedon. The various morphology of P distribution suggested different soil formation patterns, which were related to the land use history. Groundwater P was significantly correlated with the maximum extractable P content of P in soil profiles and even better with the weighted average P content of the whole profile or P content of the soil layer at or close to groundwater table. Dissolved P in experimental leachate was comparable with that of groundwater but higher than environmentally acceptable level. Furthermore, there was a significant correlation between solution P and different extractable P forms of the studied soils. Simple P tests can provide an evaluation of the potential risk of urban soils in discharging P to water system.     

Organic compounds and heavy metals in the atmosphere of the city of Caracas,Venezuela — I: Atmospheric particles

Aliphatic and aromatic hydrocarbons, fatty acids and heavy metals (Pb, Cu, Ni, Zn, Fe and Cd) were analyzed in atmospheric particulate matter in the city of Caracas, Venezuela. Samples were taken from 6 stations within the metropolitan area of Caracas, characterized as industrial (one), urban (two), suburban (two) and rural (one). In addition, the concentration and composition of the organic compounds was monitored over a 5 month period at an urban site to determine seasonal and temporal variabilities. In general terms, the concentrations of pollutants decreased from industrial and urban sites to suburban to rural. A similar trend was observed for preliminary toxicity tests carried out on the particulate extracts. The concentration levels of most of the pollutants were high for the industrial and urban sites, and comparable with those of other major cities worldwide.     

Temporal and spatial variations in nitrogen transformations in deciduous forest ecosystems along an urban-rural gradient

Ecosystem processes such as N transformations have seldom been studied in urban and suburban areas. Here we report the temporal and spatial variations in soil N measured continuously over 16 months in remnant forests dominated by northern red oak (Quercus rubraL.) along a 130 km urban-rural transect in the New York City metropolitan area. Urban, suburban and rural forests all exhibited clear seasonal patterns in soil N concentrations and transformation rates. Concentrations of extractable inorganic N were highest in early spring, while net N mineralization and nitrification rates were highest in summer. Peak N mineralization and nitrification in urban stands tended to occur a month earlier than in rural stands. Daily net N mineralization rates averaged 4.45 mg N kg⁻¹ soil organic matter (SOM) in urban stands, 3.51 in suburban stands, and 2.49 in rural stands. In urban and suburban forests, between 23.2-73.8% of the annual net N mineralized was nitrified, but in rural forests, net nitrification was mostly below the detection limit. Annual net N mineralization rates, expressed on an areal basis (to a depth of 7.5 cm), averaged 11.6 g m⁻² in urban forests, 11.3 g m⁻² in suburban sites, and 7.3 g m⁻² in rural forests. N returns in oak litter fall were 2.15, 1.32, and 1.81 g m⁻² in urban, suburban, and rural stands, respectively. The elevated N transformation rates and nitrate production, in combination with possible pollution constraints on tree growth in urban environments, raises concern that these urban and suburban forests may be approaching an N saturated status.     

Volatile hydrocarbons in and around Vienna,Austria

Atmospheric hydrocarbons (HCs) have been determined during a winter and a spring sampling period at several urban and a semi-rural site in the Vienna region. HC relative concentration patterns were generally consistent, however large concentration differences were observed at the various sampling sites. Concentration ratios for ‘semi-rural’, ‘suburban’ and ‘city street level’ sites were 1:2.5:10 for the winter case. HC concentrations at a 52 m high building were around 40% of the values at street level for species emitted by traffic. The relative abundances of aromatics (47%), alkanes (37%) and alkenes (11%) in the vienna urban atmosphere compare well with results from Berlin, while in other cities under comparison (e.g. Washington, Sydney, and Leningrad) alkanes are the most abundant volatile HC class (45 to 69%).     

Ion Fluxes with Bulk and Throughfall Deposition along an Urban–Suburban–Rural Gradient

Fluxes of principal anions and cations with bulk and throughfall deposition during the growing period (April–September) were investigated for three years (2001–2003) at three sites differently exposed to the second biggest Lithuanian city – Kaunas. Fluxes of all investigated anions (SO₄ ^2?, NO₃ ^? and Cl^?) and most cations were found to be the highest in suburban area to compare with both – Rural and urban sites. The highest seasonal variability of monthly ion fluxes and the highest differences between throughfall and bulk fluxes (net throughfall) were recorded in suburban area. The highest throughfall enrichment by sulphur was detected in spring and the beginning of summer (April, May) in urban and especially in suburban sites. For nitrogen compounds (NO₃ ^?, NH₄ ⁺) positive net throughfall values were characteristic for urban and suburban sites and negative for rural site almost during the entire growing period. Uptake of NH₄ ⁺ ions was detected to be much higher of that for nitrates in rural area (46% vs. 22%). The most intensive enrichment of throughfall fluxes by K⁺ ions took place during the summer time (May, June, July), however, intensity of potassium leaching at the same amount of precipitation was the highest in suburban area.     

Changes of isopod assemblages along an urban–suburban–rural gradient in Hungary

Responses of isopod assemblages to urbanisation were studied along an urban–suburban–rural gradient representing a decrease in the intensity of human disturbance. Pitfall trapping collected six species (Armadillidium vulgare, Porcellio scaber, Porcellium collicola, Trachelipus ratzeburgii, Cylisticus convexus, and Trachelipus rathkii). A. vulgare occurred abundantly in all sites reflecting the broad tolerance and invasive nature of this species. Indicator species analysis demonstrated that P. scaber and T. rathkii were significant quantitative character species for the urban site, while T. ratzeburgii was characteristic for the natural habitats (suburban and rural sites). CANOCO revealed that ground and air temperature show positive correlation with the distribution of P. scaber and T. rathkii, and negative correlation with T. ratzeburgii. Nested ANOVA on trap level showed that there were no significant differences between the number of isopod species and individuals, and the diversity of isopod assemblages in the three studied areas. Significant differences were observed at site level. The results did not support the hypothesis that diversity should decrease in response to habitat disturbance. They also contradicted the intermediate disturbance hypothesis; species richness was not the highest in the moderately disturbed suburban area. Multivariate methods detected that the isopod assemblages of the rural and suburban areas were relatively similar, while that of the urban area was relatively separated.     

评价城市土壤磷素淋溶风险的化学指标

Soils from urban and suburban areas are normally enriched with phosphorus (P). Sixteen urban soils with a wide range of total P concentrations under typical urban land uses were sampled and analyzed for extractable P concentrations using water, sodium bicarbonate and citric acid. Meanwhile the soils were artificially leached in columns and P concentrations in the leachates were determined. With linear regression a two-stage linear relationship was found to exis tbetween concentrations of P in the leachates and soil P contents obtained by various chemical measurements, i.e., there was a “change-point” denoting the critical threshold value for extractable P between the regression lines, above which concentrations of P in leachates increased substantially. These threshold “change-point” values were 1.5 mg kg^-1 for water-soluble P and CaCl2-P, 25 mg kg^-1 for Olsen-P, and 250-350 mg kg^-1 for citric acid-P with the sharpest change and the best predictor [τ2 (upper) = 0.928, τ2 (lower) = 0.807] appearing for Olsen-P. These “change-points” were considered important criteria in assessing the risk of P leaching from urban soils and could be used as standards to delineate and target hazardous areas in urban and suburban areas.     

杭州市城市土壤重金属的潜在可淋洗性研究

研究了杭州市城市土壤 8个重金属元素 (Cd、Co、Cr、Cu、Ni、Pb、Zn、Mn)的含量、形态和潜在可淋洗性。结果表明 ,该城市土壤中Cd、Cr、Cu、Ni、Pb、Zn和Mn均有明显的积累 ,其中Cd、Co、Cr和Ni主要以稳定的残余态为主 ,而Cu、Pb、Zn和Mn则以可提取态为主 ,因此在强还原、强酸性或有利于有机质分解条件下Cu、Pb、Zn、Mn的释放潜力较高。用荷兰能源研究中心的淋洗方法 (pH4 0 )测试表明 ,该市城市土壤的重金属可淋洗性较低 ,在一般条件下该城市土壤重金属不会有较大的释放 ,这与该城市土壤中酸可提取态重金属比例较低并含有较高的有机质及粘粒含量有关     

东亚季风与城市活动影响下南京市大气沉降多元特征研究

Atmospheric deposition, a major pathway of metals entering into soils, plays an important role in soil environment, especially in urban regions where a large amount of pollutants are emitted into atmosphere through various sources. In order to understand the characteristics of atmospheric deposition in urban area and its relation with natural and anthropogenic sources, a three-year study of atmospheric deposition at three typical sites, industrial zone (IN), urban residential area (RZ) and suburban forested scenic area (FA), was carried out in Nanjing, a metropolitan city in eastern China from 2005 to 2007. The bulk deposition rate and element composition of atmospheric deposition varied spatio-temporally in the urban zones of Nanjing. The concentrations of Cu, Zn, Pb and Ca in the atmospheric deposits were strongly enriched in the whole Nanjing region; however, anthropogenic pollutants in atmospheric deposits were diluted by the input of external mineral dust transported from northwestern China. Source apportionment through principal component analysis (PCA) showed that the background atmospheric deposition at the FA site was the combination of external aerosol and local emission sources. The input of long-range transported Asian dust had an important influence on the urban background deposition, especially in spring when the continental dust from the northwestern China prevailed. Marine aerosol source was observed in summer and autumn, the seasons dominated by summer monsoon in Nanjing. In contrast, the contribution of local anthropogenic emission source was constant regardless of seasons. At the RZ and IN sites, the atmospheric deposition was more significantly affected by the nearby human activities than at the FA site. In addition, different urban activities and both the winter and summer Asian monsoons had substantial impacts on the characteristics of dust deposition in urban Nanjing.     

Are urban parks refuges for bumble bees Bombus spp. (Hymenoptera: Apidae)?

Declines in bee populations have been documented in several parts of the world. Bees are dependent upon flowering plants for resources, and flowering plants often depend upon bees for pollination services. Bees can therefore serve as indicator species of habitat degradation due to these relationships with flowering plants. This study investigates how the bumble bee community in San Francisco has responded to urbanization and which urban park characteristics are important for the current community’s structure. To answer these questions we sampled bumble bees, in 18 urban parks and two nearby wild parks. We estimated park characteristics and used multiple regression analysis to determine which characteristics predicted bumble bee abundance and species richness. Bumble bee abundance was positively associated with resource availability or proxies of resource availability; “natural area” (areas that contain remnant fragments that have been largely unchanged by human activity) in 2003 and nest site abundance and openness of the surrounding matrix in both 2003 and 2004. Bumble bee species richness was negatively associated with abundance of a dominant species, Bombus vosnesenskii, in 2004. The importance of the surrounding matrix suggests that these parks do not act as islands. Accordingly, area of park did not explain species richness, while abundance of the dominant competitor did. The species that was most influenced by competition, Bombus sitkensis, uses rodent holes as nest sites and is possibly excluded from nest sites by the early emerging B. vosnesenskii, another subterranean nester. The species least influenced by competition, Bombus melanopygus, is able to use both rodent holes and abandoned bird nests as nest sites.