Nutrient budgets in a dry heathland watershed in northeastern Spain

Dissolved nutrient inputs in bulk precipitation and outputs in streamwater were measured during 3 years of contrasting hydrological conditions in a 6.3-ha, grazed heathland watershed on schists in the Montseny mountains (NE Spain), drained by an intermittent stream. On average, 39% of the precipitation became streamflow. Bulk precipitation delivered positive net alkalinity (mean 0.22 keq/ha/yr), sulphate input was moderate (9.0 kg SO₄-S/ha/yr), and the mean input of inorganic N was not exceptionally high (6.6 kg/ha/yr). Ion concentrations were relatively low in streamwater; SO₄ ^2- was the dominant anion. Most concentrations in streamwater varied seasonally, with maxima in late summer or early autumn and minima in spring. This pattern probably resulted from increased availability of ions for leaching due to decomposition of organic matter and chemical weathering during the warm period. Nitrate concentrations were relatively high in winter and dropped sharply in early spring, probably because of biological uptake. Annual element outputs in streamwater varied between years and seemed to be controlled by both the amount of annual streamflow and its seasonal distribution. Annual inputs exceeded outputs for dissolved inorganic N. The watershed accumulated H⁺ and Ca²⁺, had net losses of Na⁺ and Mg²⁺, and was close to steady state for K⁺, SO₄ ^2-, Cl^- and alkalinity. The chloride budgets gave no evidence of substantial dry deposition in this system. The cationic denudation rate was negative (-0.14 keq/ha/yr) because Ca²⁺ retention was higher than net exports of Na⁺ and Mg²⁺ from silicate weathering. Low nutrient export and little production of alkalinity suggest that this watershed has a low buffering capacity.     

The Effects of Catalyst Layer Deposition Methodology on Electrode Performance

The catalyst layer of the cathode is arguably the most critical component of low‐temperature fuel cells and carbon dioxide (CO₂) electrolysis cells because their performance is typically limited by slow oxygen (O₂) and CO₂ reduction kinetics. While significant efforts have focused on developing cathode catalysts with improved activity and stability, fewer efforts have focused on engineering the catalyst layer structure to maximize catalyst utilization and overall electrode and system performance. Here, we study the performance of cathodes for O₂ reduction and CO₂ reduction as a function of three common catalyst layer preparation methods: hand‐painting, air‐brushing, and screen‐printing. We employed ex‐situ X‐ray micro‐computed tomography (MicroCT) to visualize the catalyst layer structure and established data processing procedures to quantify catalyst uniformity. By coupling structural analysis with in‐situ electrochemical characterization, we directly correlate variation in catalyst layer morphology to electrode performance. MicroCT and SEM analyses indicate that, as expected, more uniform catalyst distribution and less particle agglomeration, lead to better performance. Most importantly, the analyses reported here allow for the observed differences over a large geometric volume as a function of preparation methods to be quantified and explained for the first time. Depositing catalyst layers via a fully‐automated air‐brushing method led to a 56% improvement in fuel cell performance and a significant reduction in electrode‐to‐electrode variability. Furthermore, air‐brushing catalyst layers for CO₂ reduction led to a 3‐fold increase in partial CO current density and enhanced product selectivity (94% CO) at similar cathode potential but a 10‐fold decrease in catalyst loading as compared to previous reports.     

Anthropogenic N deposition increases soil organic matter accumulation without altering its biochemical composition

Accumulating evidence indicates that future rates of atmospheric N deposition have the potential to increase soil C storage by reducing the decay of plant litter and soil organic matter (SOM). Although the microbial mechanism underlying this response is not well understood, a decline in decay could alter the amount, as well as biochemical composition of SOM. Here, we used size‐density fractionation and solid‐state ¹³C‐NMR spectroscopy to explore the extent to which declines in microbial decay in a long‐term (ca. 20 yrs.) N deposition experiment have altered the biochemical composition of forest floor, bulk mineral soil, as well as free and occluded particulate organic matter. Significant amounts of organic matter have accumulated in occluded particulate organic matter (~20%; oPOM); however, experimental N deposition had not altered the abundance of carboxyl, aryl, alkyl, or O/N‐alkyl C in forest floor, bulk mineral soil, or any soil fraction. These observations suggest that biochemically equivalent organic matter has accumulated in oPOM at a greater rate under experimental N deposition, relative to the ambient treatment. Although we do not understand the process by which experimental N deposition has fostered the occlusion of organic matter by mineral soil particles, our results highlight the importance of interactions among the products of microbial decay and the chemical and physical properties of silt and clay particles that occlude organic matter from microbial attack. Because oPOM can reside in soils for decades to centuries, organic matter accumulating under future rates of anthropogenic N deposition could remain in soil for long periods of time. If temperate forest soils in the Northern Hemisphere respond like those in our experiment, then unabated deposition of anthropogenic N from the atmosphere has the potential to foster greater soil C storage, especially in fine‐texture forest soils.     

Male tree weta are attracted to cuticular scent cues but do not discriminate according to sex or among two closely related species

Recognition of conspecifics is an essential precursor of successful mating. Where related species coexist, species discrimination might be important, but because related species are similar, species signal recognition may actually be low. Chemical cues such as cuticular hydrocarbons (CHCs) are frequently used by insects to identify suitable sexual partners. We predicted that New Zealand tree weta (Hemideina spp.), a genus of nocturnal ensiferan Orthoptera that live both allopatrically and sympatrically, use chemical signals from either frass or CHCs to find mates. In a series of six laboratory trials using both H. thoracica and H. crassidens, we found that male tree weta, but not female tree weta, occupied cavities primed with female cuticular cues more often than cavities without. However, males did not discriminate between chemical cues of male and female conspecifics, or between conspecifics and heterospecifics. In field trials, tree weta did not occupy artificial cavities primed with either female frass or female cuticular cues more often than unscented cavities. However, in both trials weta preferentially returned to cavities that had already been occupied earlier in the trials. A final field trial confirmed the presence of mixed species harems during the mating season in one region of sympatry. Our results suggest that selection on sex and species specific chemical cues that could be used to find conspecific mates is weak. Mixed species aggregations suggest that identification of conspecific mating cues has not evolved to be species specific. We infer that for male tree weta, the cost of mating with heterospecifics is likely less than not mating at all.     

An examination of current Hg deposition and export in Fenno-Scandian catchments

The input and output flux data of total Hg (THg) and methylmercury (MeHg) from three catchments located in different geographical regions in Sweden and one catchment in southern Finland were compared to elucidate the role of current atmospheric Hg/MeHg deposition with regard to waterborne Hg/MeHg output.There was a negative co-variaton between the open field THg inputs and the ratio of THg output to open field input. The highest ratio (and lowest input) occurring in N. Sweden and S. Finland, while the lowest output ratio (and highest inputs) occurred in southwest Sweden. A much larger variation was found in the ratio of output to open field input for MeHg (14 to 160%). Examinations of MeHg input/output data in relation to catchment charateristics suggest that riparian peat, mires and wet organic soil contributed to the large MeHg output from certain catchments, probably due to in situ production of MeHg. This finding is consistent with other studies which have found that catchment characteristics such as wetland area, flow pathways, seasonal temperature and water flow are important in controlling the output of MeHg. These catchment characteristics govern the fate of the contemporary input of Hg and MeHg as well as the mobilization of the soil pools.     

Spatial and temporal variation of atmospheric nitrogen deposition in the North China Plain

A monitoring network of nine sites was established to determine the spatial and temporal variation of atmospheric nitrogen (N) deposition in the North China Plain (NCP) over a two-year period. The annual bulk deposition of inorganic N in the North China Plain ranged from 18.4 to 38.5 kg/hm² and averaged 28.0 kg/hm². The concentration of NH₄ -N and NO₃^--N in rainwater averaged 3.76 and 1.85 mg/L, respectively, which were significantly higher than the values at background sites in China (normally less than 0.5 mg/L). Annual bulk deposition of inorganic N in the Beijing area (32.5 kg/hm²) was higher than that in Shandong and Hebei provinces (21.2 kg/hm² on an average). Also bulk N deposition was much greater in Dongbeiwang and Fangshan than in Yanqing and Shunyi counties. Significant spatial variation of bulk deposition was observed in the Beijing area because of variation of precipitation, and 60% of bulk deposition occurred from June to September. Bulk deposition of NH₄ -N was 2.0 times that of NO₃^--N deposition at the rural monitoring sites. However, the situation was reversed at the Beijing Academy of Agricultural-Forestry Sciences (BAAFS), the unique urban monitoring site. The results suggest that reduced N in precipitation is dominant in rural regions, but oxidized N is the major form in urban regions. The positive relationship between inorganic N deposition and precipitation can be fitted by a power equation (r²= 0.67), showing an increase of NH₄ -N and NO₃^--N inputs with increased precipitation. Wet deposition of N accounted for 73% of the bulk deposition, implying that dry deposition of N, particularly NH₄ -N from dust, is important in the North China Plain.     

土壤微生物对气候变暖和大气N沉降的响应

气候变暖和大气N沉降是近一、二十年来人们非常关注的全球变化现象,它们所带来的一系列生态问题已成为全球变化研究的重要议题。它们不仅影响地上植被生长和群落组成,还直接或间接地影响土壤微生物过程,而土壤微生物对此做出的响应正是生态系统反馈过程中非常重要的环节。该文分别从气候变化对土壤微生物的影响(土壤微生物量、微生物活动和微生物群落结构)和土壤微生物对气候变化的响应(凋落物分解、养分利用与循环以及养分的固持与流失)两个角度,综述近期土壤微生物对气候变暖和大气N沉降响应与适应的研究进展。气候变暖和大气N沉降对土壤微生物的影响更多地反映在微生物群落的结构和功能上,而土壤微生物量、微生物活动和群落结构的变化又会通过改变凋落物分解、养分利用和C、N循环等重要的土壤生态系统功能和过程做出响应,形成正向或负向反馈,加强或削弱气候变化给整个陆地生态系统带来的影响。然而,到目前为止土壤微生物的响应对陆地生态系统产生的最终结果仍是未决的关键性问题。     

Nitrogen deposition enhances moss growth,but leads to an overall decline in habitat condition of mountain moss‐sedge heath

Ecosystems are subject to multiple, natural and anthropogenic environmental influences, including nitrogen (N) deposition, land use and climate. Assessment of the relative importance of these influences on biodiversity and ecosystem functioning is crucial for guiding policy and management decisions to mitigate global change; yet, few studies consider multiple drivers. In the UK, ongoing loss of the internationally important arctic/alpine moss‐sedge community, Racomitrium heath, has been linked to elevated N deposition, high grazing pressures and their combination; however, the relative importance of these drivers remains unclear. We used environmental gradients across the habitat's European distribution (UK, Faroes, Norway and Iceland) to investigate the relative impact of N deposition and grazing pressure, as well as climate, on the condition of the dominant moss species, Racomitrium lanuginosum. Key variables including tissue chemistry, growth and cover were measured at 36 sites, and multiple linear regressions were used to examine the relative importance of the drivers across sites. Our results clearly show that regional variation in the condition of R. lanuginosum across Europe is primarily associated with the impacts of N deposition, with climate (air temperature) and grazing pressure playing secondary roles. In contrast to previous experimental studies, we found moss growth to be stimulated by elevated N deposition; this apparent discrepancy may result from the use of artificially high N concentrations in many experiments. Despite increased growth rates, we found that moss mat depth and cover declined in response to N deposition. Our results suggest that this is due to increased decomposition of material in the moss mat, which ultimately leads to loss of moss cover and habitat degradation. This study clearly demonstrates both the key role of N deposition in degradation of Racomitrium heath and the importance of observational studies along natural gradients for testing predictions from experimental studies in the real world.     

Behavioural and chemical mechanisms behind a Mediterranean ant–ant association

1. Interspecific competition among ants is common, and so is competitive exclusion among dominant ant species. In contrast, specific associations between non‐parasitic ant species are rare, especially in the temperate zones. As an exception, the subordinate ant Camponotus lateralis frequently co‐occurs with the dominant Crematogaster scutellaris but rarely with other dominant ants. 2. This association is one of various associations between Camponotus and Crematogaster species across the world. However, the mechanisms behind these co‐occurences are largely unknown. 3. In the present study, we therefore investigated the association of Ca. lateralis and Cr. scutellaris. We studied the spatial association of the nests, interspecific aggression, both species' cuticular hydrocarbon profiles, and their propensity to follow the other species' pheromone trails. 4. Crematogaster scutellaris usually attacked and displaced the generally submissive Ca. lateralis, but was significantly less aggressive at jointly used trails. Camponotus nests were always in close proximity to Crematogaster nests. 5. The cuticular hydrocarbons of both species consisted of alkanes with chain lengths between C21 and C35. The two species had 25 hydrocarbons in common, including mono‐, di‐, and tetramethyl alkanes. Despite this qualitative similarity, however, the quantitative hydrocarbon composition differed between the two species. 6. Camponotus lateralis followed artificial trails containing trail pheromones of Cr. scutellaris, but the latter did not follow Ca. lateralis trail pheromones. Interspecific trail‐following by Camponotus, but not vice versa, has been observed in another Camponotus–Crematogaster association and may be a more general mechanism that facilitates associations between the two ant genera.     

Atmospheric Deposition to the Turkey Lakes Watershed: Temporal Variations and Characteristics

We investigated the atmospheric concentrations and deposition fluxes of major ions to the Turkey Lakes Watershed (TLW) between 1980 and 1996. During that time, daily SO₄ ²⁻ concentrations in precipitation decreased markedly, while NO₃ ⁻, NH₄ ⁺, and H⁺ concentrations remained roughly constant. It appears that precipitation acidity did not decrease in spite of declining SO₄ ²⁻ concentrations due to a concurrent and counterbalancing decrease in the concentrations of Ca²⁺, Mg²⁺, and K⁺ in precipitation. The reasons for the decline in base cations are unknown, but this decline is probably related to decreasing emissions of soil-derived particles from agricultural, industrial, and road sources. A similar situation was seen during the same period in other parts of Canada, the eastern United States, and Europe. Wet, dry, and total (wet + dry) deposition fluxes of sulphur (S) and nitrogen (N) were estimated annually for the years 1980–96. The 17-year mean annual total (wet + dry) deposition of S to the watershed was estimated at 38.5 mmol m⁻² y⁻¹ (range 24.3–50.3). Total S deposition decreased by 35% from the early 1980s (1982–84) to the mid-1990s (1994–96), a decline consistent with the 23% decline in annual SO₂ emissions in eastern North America during the same period. In contrast, the annual total (wet + dry) deposition of oxidized N ranged from 39.8 to 60.4 mmol m⁻² y⁻¹, with a 15-year mean of 50.1 mmol m⁻² y⁻¹ and a net increase of 10% between the early 1980s (1983–85) and the mid-1990s (1994–96). This is in keeping with a 10% increase in NO_x emissions in eastern North America during the same period. For both S and N (oxidized), wet deposition dominated over dry deposition as the major mechanism for atmospheric input to the watershed. Annually, wet deposition accounted for approximately two-thirds of the total atmospheric deposition of both S and N. Dry S deposition was due more to gaseous SO₂ deposition (two-thirds of dry S deposition) than to particulate SO₄ ²⁻ deposition (one-third of dry S deposition). Dry deposition of oxidized N, however, was dominated (95%) by gaseous HNO₃ deposition, with minimal input from particulate NO₃ ⁻ deposition. Compared to several selected watershed/forest sites in Canada, the United States, and Europe, the estimated total deposition of S and N at the TLW was relatively high during the measurement period. Received 5 October 1999; accepted 1 March 2001.