Ion Exchange Resin Bags Research Articles

Impacts of invasive Acacias on ion deposition in a coastal Bornean tropical heath forest

ABSTRACT The uncontrolled invasive spread of exotic Acacias is a growing concern for many tropical ecosystems, particularly due to their negative impact upon nutrient cycling. Studies investigating the effects of Acacia invasion on nutrient cycling have focused on litterfall and litter decomposition, although its impact on ion deposition in tropical ecosystems is less understood. We quantified and compared the rates of ion deposition (Ca2+, Mg2+, NH4 +, NO3 −) between Acacia-invaded and non-invaded tropical heath (Kerangas) forest sites in Brunei Darussalam, Southeast Asia. Ion exchange resin (IER) sampler, IER ring and IER bags were used to determine ion depositions via throughfall, in soils and in stream water respectively. Throughfall in Acacia-invaded heath forest sites recorded significantly higher NH4 + and Ca2+ depositions but lower Mg2+ than non-invaded, intact sites. For ion deposition in soil, all depths recorded significantly higher Ca2+ (except for 0 cm depth), Mg2+ and NH4 + depositions, but significantly lower NO3 − depositions, in Acacia-invaded sites. Ion deposition in stream water showed significant monthly variations, with Acacia-invaded sites recording significantly higher Mg2+ depositions in June, August and September 2015 but lower NH4 + depositions in June, July and September, lower NO3 − and Ca2+ depositions in June and September than non-invaded heath forest sites. Overall, these findings demonstrate that ion deposition via throughfall, in soil and in stream water were all affected by Acacia invasion, thus confirming the influence of alien invasive Acacias on nutrient cycling of tropical heath forests.

Drought boosts risk of nitrate leaching from grassland fertilisation

Both climate change and agricultural intensification are drivers of global nutrient cycles and biodiversity loss. A potentially great environmental threat can arise when these two drivers interact, for example, when farmers try to compensate reduced soil nutrient availability due to drought by the application of liquid organic fertiliser. As dry soils don't hold back nutrients very well, this approach can lead to nitrate leaching and potentially also to the pollution of drinking water. However, little is known about leaching from dry but fertilised grassland soil, and how this is affected by land use intensity and plant diversity.In this mesocosm study, we transferred 60 grassland sods differing in past land use intensity to a greenhouse and treated them with severe drought, fertilisation and both together. Drought was induced by almost entirely stopping irrigation for seven weeks. Fertilisation was done by three applications of slurry summing up to 168 kg total nitrogen per hectare (111 kg NH4-N). We assessed nutrient leaching risk with ion-exchange resin (IER) bags installed in the soil of all mesocosms. IER bags were retrieved after drought and extracts were analysed for concentrations of nitrate, ammonium, phosphate and potassium.Fertilisation partially buffered drought-induced losses in yield. However, the interaction of fertilisation and drought resulted in a drastic increase in nitrate leaching risk when soils are rewetted (>300%), while neither drought nor fertilisation alone were significant. Ammonium concentrations followed the same trend as nitrate, but less pronounced. Phosphate and potassium concentrations were not affected by the treatments. Past land use was hardly related to soil nutrient concentrations, rather was plant diversity. However, results indicate that plant diversity was not driving nitrate and ammonium concentrations under drought and/or fertilisation. This study reveals grassland fertilisation during drought to be a severe environmental problem due to significantly increased nitrate leaching risk.

Increased Nitrogen Availability in the Soil Under Mature Picea abies Trees Exposed to Elevated CO2 Concentrations

The response of trees to increasing atmospheric CO2 concentrations is often mediated by the availability of nutrients. However, little is known about the influence of CO2 enrichment on nutrient availability in forests with mature trees. We studied processes in the soil under five 35-m-tall Norway spruce trees (Picea abies) in NW Switzerland that were exposed to a mean CO2 concentration of 550 ppm for 5 growing seasons using free air CO2 enrichment (FACE). We compared them with values from the soil under five control trees. Ceramic suction cups were installed in the soil under each tree to collect soil solution, and ion-exchange resin bags were buried in the soil to absorb ammonium and nitrate. Soil cores taken at the end of the experiment were used to measure the gross production of ammonium and nitrate by the 15N dilution technique. Although temporally and spatially variable, the nitrate concentration was higher in the soil solution under CO2-enriched trees. This effect was reflected in the resin bag extracts, which additionally indicated a trend of increased ammonium availability. Dissolved reduced N concentration (mainly dissolved organic N), however, was lower in the soil solution under CO2-enriched trees. K and Mg, and to a lesser extent Na and sulfate concentrations increased in the soil solution. P concentrations mostly remained below the detection limit. In spite of the higher concentrations of nitrate in soil extracts, gross N mineralization and nitrification rates were not affected by FACE. Needles from CO2-enriched trees contained slightly more N. No difference was observed for other nutrients. Overall, these results support the hypothesis of a priming effect, i. e. that FACE led to the production of more root exudates, which in turn stimulated soil biological activity, including mineralisation, over a time-span of at least several years. However, these tall trees showed no growth response to elevated CO2; hence, they gained no advantage from increased nitrate in the soil solution, presumably owing to other growth constraints including P and Mg availability.

Effects of Changes in Nitrogen Availability on Nitrogen Gas Emissions in a Tropical Forest During a Drought

AbstractAtmospheric nitrogen (N) deposition in tropical forests may increase substantially in coming decades, stimulating a concomitant increase of soil N gas emissions. At the same time, climate change may increase the prevalence of drought, altering the processes that produce these gases (dominantly aerobic nitrification and anaerobic denitrification). This alteration is of particular concern if global changes increase the fraction of N gas released as nitrous oxide (N2O; a greenhouse gas) relative to dinitrogen (N2). To simulate the effects of atmospheric N deposition on the amount and species of soil N gas emissions, we installed fertilized ion exchange resin bags across a hillslope in the Luquillo Experimental Forest of Puerto Rico. Our experiment took place during a severe drought, providing opportunities to consider how N addition and dry soil conditions interact. After 2 months of fertilization, we measured denitrification potential using a denitrification enzyme assay, which utilizes anoxic incubations where N and carbon limitation are relieved and nitrification is inhibited. We also measured N2 and N2O emissions using a Nitrogen Free Air Recirculation Method (NFARM), which quantifies emissions from both nitrification and denitrification. Data from these two methods suggest that N inputs stimulated N2O emissions associated with aerobic nitrification. Our data suggest that soil drying during the drought decreased N2 emissions associated with anaerobic denitrification and changed the spatial patterns of emissions in the landscape. Together these results suggest that, at least during a drought, N inputs increase N2O emissions associated with nitrification, which may represent a positive feedback to climate change.

Land use intensity, rather than plant species richness, affects the leaching risk of multiple nutrients from permanent grasslands.

The intensification of land use constitutes one of the main drivers of global change and alters nutrient fluxes on all spatial scales, causing landscape-level eutrophication and contamination of natural resources. Changes in soil nutrient concentrations are thus indicative for crucial environmental issues associated with intensive land use. We measured concentrations of NO3 -N, NH4 -N, P, K, Mg, and Ca using 1,326 ion-exchange resin bags buried in 20cm depth beneath the main root zone in 150 temperate grasslands. Nutrient concentrations were related to land use intensity, that is, fertilization, mowing, grazing intensities, and plant diversity by structural equationmodeling. Furthermore, we assessed the response of soil nutrients to mechanical sward disturbance and subsequent reseeding, a common practice for grassland renewal. Land use intensity, especially fertilization, significantly increased the concentrations of NO3 -N, NH4 -N, K, P, and also Mg. Besides fertilization (and tightly correlated mowing) intensity, grazing strongly increased NO3 -N and K concentrations. Plant species richness decreased P and NO3 -N concentrations in soil when grassland productivity of the actual year was statistically taken into account, but not when long-term averages of productivity were used. Thus, we assume that, in the actual study year, a distinct drought period might have caused the observed decoupling of productivity from fertilization and soil nutrients. Breaking up the grassland sward drastically increased NO3 -N concentrations (+146%) but reduced NH4 -N, P, and K concentrations, unbalancing soil nutrient stoichiometry and boosting the risk of N leaching. Reseeding the sward after disturbance did not have a short-term effect on nutrient concentrations. We conclude that renewal of permanent grassland should be avoided as far as possible and future grassland management has to strongly rise the effectiveness of fertilization. Additionally, grassland management might have to increasingly taking care of periods of drought, in which nutrient additions might not increase plant growth but potentially only facilitate leaching.

模拟增温和氮沉降对中亚热带杉木幼林土壤有效氮的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 模拟增温和氮沉降对中亚热带杉木幼林土壤有效氮的影响 DOI: 10.5846/stxb201512302599 作者: 作者单位: 福建师范大学地理科学学院,福建师范大学地理科学学院,福建师范大学地理科学学院,福建师范大学地理科学学院,福建师范大学地理科学学院,福建师范大学地理科学学院,福建师范大学地理科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点基础研究发展计划（2014CB954003）；国家自然科学基金项目（31130013） Effects of soil warming and nitrogen deposition on available nitrogen in a young Cunninghamia lanceolata stand in mid-subtropical China Author: Affiliation: School of Geographical Science, Fujian Normal University,,,,,School of Geographical Science, Fujian Normal University, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以中亚热带杉木（Cunninghamia lanceolata）幼苗为研究对象，设置埋设电缆以加热土壤增温（+5℃）结合模拟氮沉降的实验，施氮水平分别为对照（CT，0 kg hm-2 a-1）、施低氮（LN，40 kg hm-2 a-1）和施高氮（HN，80 kg hm-2 a-1），用离子交换树脂袋法研究了土壤有效氮对模拟增温和施氮的短期响应。经过为期1a的研究，结果表明：土壤有效氮主要集中在夏冬季，而且硝态氮是土壤有效氮的主要存在形态；增温显著增加土壤有效氮含量（P < 0.05），各月间的有效氮含量与气温和降雨量有关；总体来看，氮沉降显著增加土壤有效氮含量（P < 0.05），而且随氮沉降水平的升高而增加。低氮处理下，大多数月份的土壤有效氮含量显著增加，高氮处理下，各月的有效氮含量均显著高于对照处理；增温×氮沉降在各月间均显著增加土壤有效氮含量（P < 0.05），并随氮沉降水平的升高而增加。而且，两者的交互作用对有效氮的增幅显著大于任一单一因子的作用。说明增温和氮沉降两者的交互作用对土壤有效氮的影响具有叠加效应。因此，增温和氮沉降及其交互作用短期内都会显著增加土壤有效氮含量，为植物生长提供充足的养分。 Abstract:Soil available nitrogen is a small but crucial component in the nitrogen pool, as productivity in ecosystems is closely linked to nitrogen availability. Since the world's first Industrial Revolution, global warming has increased and nitrogen deposition has increased; therefore, there is a strong focus on soil available nitrogen. To study the short-term response of soil available nitrogen to climate change (warming, nitrogen deposition), we conducted an experiment in four micro-plots planted with young Cunninghamia lanceolata in a mid-subtropical region, which was subjected to experimentally increased soil temperature (W, +5℃) and inorganic nitrogen concentration in artificial precipitation (control[CT], 0 kg hm-2 a-1; low nitrogen addition[LN], 40 kg hm-2 a-1; and high nitrogen addition[HN], 80 kg hm-2 a-1) by using NH4NO3. Soil available nitrogen was measured monthly by using ion exchange resin bags. After one year, the results showed that soil available nitrogen concentrated primarily in the summer and winter, and nitrate nitrogen was the main form of available nitrogen. Increasing the soil temperature significantly increased the soil available nitrogen content (P < 0.05). In addition, the soil available nitrogen content was related to monthly air temperature and rainfall. Overall, nitrogen deposition significantly increased the soil available nitrogen content (P < 0.05). Under low nitrogen treatment, soil available nitrogen content increased significantly in most months; under high nitrogen, soil available nitrogen was significantly higher every month than that in the control treatment. With the combined treatment of increased soil temperature and nitrogen deposition, the soil available nitrogen content increased significantly each month, more than that by either increased temperature or nitrogen deposition alone. This indicated that increased soil temperatures and nitrogen deposition had a combined effect on soil available nitrogen content. Therefore, increased temperature and nitrogen deposition, individually or combined, increased soil available nitrogen content considerably, and thus could provide plants with sufficient nitrogen for productive growth. 参考文献 相似文献 引证文献

No effects of Epichloë endophyte infection on nitrogen cycling in meadow fescue (Schedonorus pratensis) grassland

Systemic Epichloe endophytes produce alkaloids that protect their grass hosts against pathogens and herbivores. These alkaloids, together with other endophyte induced changes in litter quality, may decelerate the decomposition of infected grass litter, but so far no study has tested whether the effects on decomposition rate translate into changes in N cycling in infected grasslands. Here we test if the Epichloe uncinata infection of meadow fescue, Schedonorus pratensis decelerates litter decomposition and N release, increases soil C and N accumulation and lowers the availability of mineral N in the soil under infected grass. To analyze grass litter and soil attributes, samples were collected from endophyte infected (E+) and non-infected (E-) field plots, established seven years earlier. At the time of the study, the frequency of E+ plants was 80–90 % and 0–3 % in the E+ and E- plots, respectively. Litter decomposition rate and litter N release were examined using litter mesh bags, placed on field ground. Soil mineral N availability was estimated using ion exchange resin bags that were buried in the soil. Epichloe uncinata infection did not affect meadow fescue litter N%, litter mass loss or litter N release. Neither did soil C and N content and resin NH4 and NO3 contents differ between the E+ and E- grass plots. E+ litter did not decompose faster in E+ than E- plots, i.e. no home-field advantage was observed. We did not find evidence that Epichloe uncinata infection would decelerate N cycling and reduce N mineralization in meadow fescue grasslands. This suggests that the infection may not decrease the benefit of the endophyte-grass symbiosis by reducing soil fertility.

Treeline soil warming does not affect soil methane fluxes and the spatial micro-distribution of methanotrophic bacteria

The impact of a warmer climate on CH4 fluxes from soils is highly uncertain, because soil warming may affect methanotrophic bacteria in two opposed ways: CH4 assimilation in soils might be increased by the decreasing soil moisture often associated with soil warming. In contrast, CH4 oxidation might be suppressed by higher NH4+ concentrations in warmed soils resulting from an accelerated nitrogen mineralization. We investigated effects of soil warming on soil-atmosphere CH4 fluxes in the last two years of a six-year long field experiment at a Swiss alpine treeline. Specifically, we measured CH4 fluxes using static chambers, and characterized N cycling by quantifying soil N2O emissions and NH4+ and NO3− concentrations. We further labeled intact soil cores with C14H4 and traced the labeled bacteria using an auto-radiographic technique to study the potential warming-related changes in the micro-distribution of methanotrophic bacteria within the soils. Our results did not show a significant effect of soil warming on net CH4 fluxes after five and six years of soil warming. In general, soils were a net sink for CH4 but CH4 emissions were observed occasionally. One reason for the unaltered CH4 fluxes might be the negligible warming effects on soil water contents in the treeline environment with frequent rainfalls. In the warmed soils, soil moisture was lower in the litter layer, but not deeper in the soils. Therefore, soil warming did not affect gas transport rates into deeper soil layers where methanotrophic bacteria were located. Another reason might be the general absence of substantial warming effects on mineral N, with NH4+ concentrations being marginally significantly higher in warmed soils only in ion exchange resin bags (P < 0.1) but not in soil extracts. Auto-radiographic image analysis of soil cores revealed an overall heterogeneous 14C distribution and a warming-induced shift of methanotrophic bacteria toward the soil surface. The absence of responses of CH4 fluxes to warming in this alpine treeline ecosystem is likely related to the rather minimal changes in the putative drivers soil moisture and NH4+ concentration.

Seasonal dynamics of soil nitrogen availability and phosphorus fractions under urban forest remnants of different vegetation communities in Southern China

Urban forest remnants are a useful tool to study forest response to global change with urbanization. Soil nutrient status in urban forests has not been well understood, especially under the pressure of rapid urbanization in developing countries. In this study, ion-exchange resin bags and a modified Hedley P fractionation procedure were used to measure seasonal dynamics of soil N forms (ammonium and nitrate) and P fractions (available, labile, slow, occlude and weathered mineral P) under urban forest remnants across a successional sequence and non-forest land in the city of Nanchang, Southern China. Results showed that soil N availability varied with season and vegetation community (P<0.05). Soil P fractions showed minimal seasonal variation except available P, while their averages generally increased with forest development from non-forest land to coniferous forest to conifer-broadleaf mixed forest to evergreen broad-leaved forest. The ratios of fresh soil N forms to P fractions generally decreased with forest development, while N forms absorbed by resins to P fractions generally increased from non-forest land to coniferous forest, then decreased from conifer-broadleaf mixed forest to evergreen broad-leaved forest. It is suggested that urban older forest remnants could easily move to N saturation status and soil P enrichment, causing urban water pollution due to the accumulative effect of elevated atmospheric N deposition and exogenous P input with urbanization.

Comparison of Disturbed and Undisturbed Soil Core Methods to Estimate Nitrogen-Mineralization Rates in Manured Agricultural Soils

Ion exchange resin / soil cores are a common in situ approach to estimating soil nitrogen (N) mineralization rates. However, no studies compare the two common methods of core preparation (disturbed and undisturbed). The objective of our study was to compare N mineralized and soil temperature in disturbed versus undisturbed cores of manured agricultural soils. Undisturbed cores were prepared by driving aluminum tubes (25 cm long with 10 cm inner diameter) into soil, removing the tubes, and then inserting an ion-exchange resin bag beneath the soil at the bottom of the tube. Disturbed cores were prepared with the same materials, but soil was excavated, mixed, and then filled into tubes fitted with ion-exchange resin bags at the bottom. Soil from six agricultural fields (five of which had more than 10 years of regular dairy manure application) was incubated over four time periods during summer and winter. A total of 13 soil / incubation-period combinations were tested. Disturbed cores tended to have more N mineralized than undisturbed cores (P < 0.10), especially in cores prepared with the lowest clay content soil. However, variability of N mineralized was lower in disturbed cores than undisturbed cores for 11 of the 13 soil / incubation periods. This lower variability was significant in two of the four incubation periods (P < 0.10). There was little difference in mean soil temperatures in disturbed versus undisturbed cores or within cores versus outside but adjacent to cores. However, in summer, the daily temperature range inside cores was significantly greater than the temperature range in soil outside cores (P < 0.01).

Characteristics of Soil CO2Efflux in Even-aged Alder Compared to Korean Pine Plantations in Central Korea

We investigated the relationship between vegetation type and soil carbon dynamics in even-aged alder (Alnus hirsuta) and Korean pine (Pinus koraiensis) plantations in central Korea. Both forests were located on the same soil parent material and occupied similar topographic positions. Soil <TEX>$CO_2$</TEX> efflux in the two plantations was determined using a dynamic chamber method accompanied by measurements of soil moisture content and temperature. Mean soil temperature was similar in the two plantations, but mean soil water content was significantly higher in the alder plantation than in the pine plantation. In both plantations, seasonal patterns in soil <TEX>$CO_2$</TEX> efflux exhibited pronounced variation that corresponded to soil temperature. Soil water content did not affect the seasonal variation in soil <TEX>$CO_2$</TEX> efflux. However, in summer, when soil temperature was above <TEX>$17^{\circ}C$</TEX>, soil <TEX>$CO_2$</TEX> efflux increased linearly with soil water content in the alder plantation. Estimated <TEX>$Q_{10}$</TEX> was 3.3 for the alder plantation and 2.7 for the pine plantation. Mean soil respiration during the measurement period in the alder plantation was 0.43 g <TEX>$CO_2\;m^{-2}\;h^{-1}$</TEX>, which was 1.3 times higher than in the pine plantation (0.33 g <TEX>$CO_2\;m^{-2}\;h^{-1}$</TEX>). Higher soil <TEX>$CO_2$</TEX> efflux in the alder plantation might be related to nitrogen availability, particularly the concentration of <TEX>$NO_3{^-}$</TEX>, which was measured using the ion-exchange resin bag method.

The Wetland Disturbance Index: Links with Soil and Water Nitrate Concentrations

Human activities have increased deleterious nitrogen inputs to terrestrial and aquatic ecosystems. The lessening of nitrogen inputs to streams can be achieved through the protection and restoration of riparian zones, including headwater wetlands. However, although headwater streams and their associated habitats account for the majority of the drainage area of rivers in Pennsylvania (U.S.A.), it is unknown how nitrogen cycling rates vary in headwater wetlands that differ in anthropogenic disturbance level. Thirteen forested headwater wetland sites within the Upper Juniata watershed, a major drainage basin of the Susquehanna-Chesapeake watershed, were selected based on a previously described, rapid assessment/disturbance index. The objective of this study was to determine whether relative soil nitrogen availability was correlated with a disturbance gradient created from the rapid assessment/disturbance index. Soil nitrogen at each site was collected with free ion exchange resin bags and analyzed for ammonium and nitrate. Results indicated that the disturbance index was predictive of relative soil nitrate availability (R2 = 0.69, p < 0.05). We conclude that the disturbance index is an effective, rapid assessment tool that could be used by managers to locate headwater wetlands with potentially high soil nitrate availability.

Effects of manipulated herbivore inputs on nutrient flux and decomposition in a tropical rainforest in Puerto Rico

Forest canopy herbivores are known to increase rates of nutrient fluxes to the forest floor in a number of temperate and boreal forests, but few studies have measured effects of herbivore-enhanced nutrient fluxes in tropical forests. We simulated herbivore-induced fluxes in a tropical rainforest in Puerto Rico by augmenting greenfall (fresh foliage fragments), frassfall (insect feces), and throughfall (precipitation enriched with foliar leachates) in replicated experimental plots on the forest floor. Background rates of greenfall and frassfall were measured monthly using litterfall collectors and augmented by adding 10× greenfall or 10× frassfall to designated plots. Throughfall fluxes of NH(4), NO(3) and PO(4) (but not water) were doubled in treatment plots, based on published rates of fluxes of these nutrients in throughfall. Control plots received only background flux rates for these compounds but the same minimum amount of distilled water. We evaluated treatment effects as changes in flux rates for NO(3), NH(4) and PO(4), measured as decomposition rate of leaf litter in litterbags and as adsorption in ion-exchange resin bags at the litter-soil interface. Frass addition significantly increased NO(3) and NH(4) fluxes, and frass and throughfall additions significantly reduced decay rate, compared to controls. Reduced decay rate suggests that nitrogen flux was sufficient to inhibit microbial decomposition activity. Our treatments represented fluxes expected from low-moderate herbivore outbreaks and demonstrated that herbivores, at these outbreak levels, increase ecosystem-level N and P fluxes by >30% in this tropical rainforest.

Soil moisture condition and soil nitrogen dynamics in a pure Alnus japonica forest in Korea

This study was conducted to examine the influences of soil-moisture conditions on soil nitrogen (N) dynamics, including in situ soil N mineralization, N availability, and denitrification in a pure Alnus japonica forest located in Seoul, central Korea. The soil N mineralization, N availability, and denitrification were determined using the buried bag incubation method, ion exchange resin bag method, and acetylene block method, respectively. The annual net N mineralization rate (kg N ha−1 year−1) and annual N availability (mg N bag−1) were 40.26 and 80.65 in the relatively dry site, −5.43 and 45.39 in the moist site, and 7.09 and 39.17 in the wet site, respectively. The annual net N mineralization rate and annual N availability in the dry site were significantly higher than those in the moist and wet sites, whereas there was no significant difference between the moist and wet sites. The annual mean denitrification rate (kg N ha−1 year−1) in the dry, moist, and wet sites was 2.37, 2.76, and 1.59, respectively. However, there was no significant difference among sites due to the high spatial and temporal variations. Our results indicate that soil-moisture condition influenced the in situ N mineralization and resin bag N availability in an A. japonica forest, and treatments of proper drainage for poorly drained sites would increase soil N mineralization and N availability and consequently be useful to conserve and manage the A. japonica forest.

Soil nitrogen availability varies with plant genetics across diverse river drainages

Understanding covariance of plant genetics and soil processes may improve our understanding the role of plant genetics in structuring soils and ecosystem function across landscapes. We measured soil nitrogen (N) and phosphorus (P) availability using ion exchange resin bags within three river drainages across Utah and Arizona, USA. The three drainages spanned more than 1,000 km in distance, 8° of latitude, and varying climatic regimes, but were similarly dominated by stands of Populus fremontii (S. Watts), P. angustifolia (James), or natural hybrids between the two species. Soil N availability was consistently greater in P. fremontii stands compared to P. angustifolia stands, and hybrid stands were intermediate. However, we found that the influence of overstory type on soil P availability depended on the river drainage. Our study suggests that, even with a near doubling of mean soil N availability across these drainages, the relative genetic-based effects of the dominant plant on N availability remained consistent. These results expand upon previous work by: 1) providing evidence for linkages between plant genetic factors and ecosystem function across geographic scales; and 2) indicating that plant genetic-based effects on nutrient dynamics in a given ecosystem may differ among nutrients (e.g., N vs. P).

Long-Term Nitrogen Storage and Soil Nitrogen Availability in Post-Fire Lodgepole Pine Ecosystems

Long-term, landscape patterns in inorganic nitrogen (N) availability and N stocks following infrequent, stand-replacing fire are unknown but are important for interpreting the effect of disturbances on ecosystem function. Here, we present results from a replicated chronosequence study in the Greater Yellowstone Ecosystem (Wyoming, USA) directed at measuring inorganic N availability (ionexchange resin bags) and ecosystem N pools among 77 lodgepole pine stands that varied in age and density. Inorganic N availability ranged from 0.07 to 3.20 lN bag -1 d -1 and nitrate (NO3 ) was, on average, 65% of total resin-sorbed N. Total ecosystem N stocks (live + detrital + soil) averaged 109.9 ± 3.0 g N m -2 (range = 63.7‐185.8 g N m -2 ). Live N was 14%, detrital N was 29%, and soil N was 57% of total stocks. Soil NO3 , total ecosystem N, live N, and detrital N generally increased with stand age, but soil N stocks decreased. Models (AICc) to predict soil N availability and N stocks included soil P, soil Ca, bulk density, and pH in addition to age (adj R 2 ranged from 0.18 to 0.53) and density was included only for live N stocks. Patterns of N stocks and N availability with density were strongest for young stands (<20 years) regenerating from extensive fire in 1988; for example, litterfall N stocks increased with density (adj R 2 = 0.86, P < 0.001) but inorganic N availability declined (adj R 2 = 0.47, P < 0.003). Across the complex Yellowstone landscape, we conclude that N stocks and N availability are best predicted by a combination of local soil characteristics in addition to factors that vary at landscape scales (stand density and age). Overall, total ecosystem N stocks were recovered quickly following standreplacing fire, suggesting that moderate increases in fire frequency will not affect long-term landscape N storage in Greater Yellowstone.

Changes in soil nitrogen availability due to stand development and management practices on semi‐arid sandy lands, in northern China

AbstractSoil nitrogen (N) availability is one of the limiting factors for plant growth on sandy lands. Little is known about impacts of afforestation on soil N availability and its components in southeastern Keerqin sandy lands, China. In this study, we measured N transformation under sandy Mongolian pine (Pinus sylvestris var. mongolica Litv.) plantations of different ages (grassland, young, middle‐aged, close‐to‐mature) and management practices (non‐grazing and free‐grazing) during the growing seasons using the ion exchange resin bag method. Results showed that, for all plots and growing season, soil NH‐N, NO‐N, mineral N, and relative nitrification index, varied from 0·18 to 1·54, 0·96 to 22·05, 1·23 to 23·58 µg d−1 g−1 dry resin, and 0·76 to 0·97, respectively, and NO‐N dominated the available N amount due to intense nitrification in these ecosystems. In general, the four indices significantly increased in the oldest plantation, with corresponding values in non‐grazing sites lower than those in free‐grazing sites (p &lt; 0·05). Our studies indicated that it is a slow, extended process to achieve improvement in soil quality after afforestation of Mongolian pine in the study area. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Lead contamination of an agricultural soil in the vicinity of a shooting range

In this study, coupled Pb concentration/Pb isotope data were used to evaluate the effect of a shooting range (operational for over 30 years) on Pb contamination of adjacent agricultural soils and the associated environmental risks. Lead was mainly concentrated in the arable layer of the contaminated agricultural soils at total concentrations ranging from 573 to 694 mg kg(-1). Isotopic analyses ((206)Pb/(207)Pb) proved that Pb originated predominantly from the currently used pellets. Chemical fractionation analyses showed that Pb was mainly associated with the reducible fraction of the contaminated soil, which is in accordance with its predominant soil phases (PbO, PbCO(3)). The 0.05 M EDTA extraction showed that up to 62% of total Pb from the contaminated site is potentially mobilizable. Furthermore, Pb concentrations obtained from the synthetic precipitation leaching procedure extraction exceeded the regulatory limit set by the United States Environmental Protection Agency for drinking water. Ion exchange resin bags showed to be inefficient for determining the vertical distribution of free Pb(2 + ) throughout the soil profile. Increased Pb concentrations were found in the biomass of spring barley (Hordeum vulgare L.) sampled at the studied site and two possible pathways of Pb uptake have been identified: (1) through passive diffusion-driven uptake by roots and (2) especially through atmospheric deposition, which was also proved by analyses of a bioindicator species (bryophyte Hypnum cupressiforme Hedw.). This study showed that shooting ranges can present an important source of Pb contamination of agricultural soils located in their close vicinity.

Nitrogen availability is not affected by frequent fire in a South African savanna

Abstract:There is a perception that sustained frequent fires cause nitrogen limitation over the long term (50–100 y) by volatilizing the nitrogen in soil, plant biomass and litter. Here we test this perception in a South African savanna located in the Kruger National Park. At our study site we compare the effects of 50 y of fire exclusion, season (August and February) and frequency (triennial and annual August and triennial February) of burn on nitrogen cycling and availability. We do this using three different methods to determine nitrogen mineralization; in situ incubations, laboratory incubations and ion-exchange resin bags. On each treatment we established two parallel transects 100 m apart with 10 sampling points per treatment along these transects. Daily mineralization rates for in situ incubations were determined monthly from August 2004 to June 2005 at each of the sampling points. Ion-exchange resin bags were buried (5 cm) at the same points and left in the field from August 2004 to August 2005. In February 2005 five randomly located soil samples from each of the four treatments were collected for laboratory incubations using a 7-cm-diameter soil auger. Regardless of method used our results show that there are no significant differences in daily nitrogen mineralization rates after 50 y of different burning treatments from annual burning to fire exclusion. In fact, both in situ and laboratory incubations show that nitrogen availability is higher on the annual burn than the fire exclusion (0.16 μg g−1soil d−1vs. 0.11 μg g−1soil d−1and 0.46 μg g−1soil d−1vs. 0.30 μg g−1soil d−1respectively). Perceived negative effects of fire on ecosystem functioning has curbed the use of fire as a management tool with fire often actively suppressed in savanna. The results of our study show that fire can be used more vigorously in mesic African savanna to manipulate tree:grass ratios without negatively affecting the nitrogen cycle.

Nitrogen immobilization by wood-chip application: Protecting water quality in a northern hardwood forest

Forest harvesting disrupts the nitrogen cycle, which may affect stream water quality by increasing nitrate concentrations, reducing pH and acid neutralizing capacity, and mobilizing aluminum and base cations. We tested the application of wood chips derived from logging slash to increase immobilization of N after harvesting, which should reduce nitrate flux to streams. In August 2004, a stand of northern hardwoods was patch-clearcut in the Catskill Mountains, NY, and four replicates of three treatments were implemented in five 0.2-ha cut patches. Wood chips were applied to the soil surface at a rate equivalent to the amount of slash smaller than eight inches in diameter (1× treatment). A second treatment doubled that rate (2×), and a third treatment received no chips (0×). Additionally, three uncut reference plots were established in nearby forested areas. Ion exchange resin bags and soil KCl-extractions were used to monitor nitrate availability in the upper 5–10 cm of soil approximately every seven weeks, except in winter. Resin bags indicated that the wood chips retained 30% or 42% of the nitrate pulse, while for KCl extracts, the retention rate was 78% or 100% of the difference between 0× and uncut plots. During the fall following harvest, wood-chip treated plots had resin bag soil nitrate concentrations about 25% of those in 0× plots ( p = 0.0001). In the first growing season after the cut, nitrate concentrations in wood-chip treated plots for KCl extracts were 13% of those in 0× treatments ( p = 0.03) in May and about half those in 0× treatments ( p = 0.01) in July for resin bags. During spring snowmelt, however, nitrate concentrations were high and indistinguishable among treatments, including the uncut reference plots for resin bags and below detection limit for KCl extracts. Wood chips incubated in litterbags had an initial C:N of 125:1, which then decreased to 70:1 after one year of field incubation. These changes in C:N values indicate that the wood-chip application can potentially immobilize between 19 and 38 kg N ha −1 in the first year after harvesting, depending on the rate of wood-chip application. Our results suggest that the application of wood chips following harvesting operations can contribute to the protection of water quality and warrant additional research as a new Best Management Practice following cutting in regions that receive elevated levels of atmospheric N deposition.