Foliar chemical concentrations in red alder stands of various ages

Summary Six stands of red alder (Alnus rubra Bong.) were sampled to assess the relationship between stand age and foliar chemical concentrations. The stands ranged in age from 9 to 45 years, and were located near Olympia, Washington, on sites of similar soil, aspect, and slope. Foliage was collected in July, and concentrations of most essential nutrients and aluminum were determined. Foliar concentrations of these elements varied among the different stands. Highest concentrations of N, P, Ca, S, Fe, and Al were found in trees of the youngest stand. Concentrations of N, P, S, and Fe were negatively correlated with stand age. The strongest correlation was obtained with P (r=–0.96,P<0.01), followed by N (r=–0.85,P=0.03). Results suggest that declining growth and deterioration of red alder stands with age may be related, at least in part, to limiting supplies of essential nutrients, especially P, N, and S.     

氮磷钾添加对罗汉松土壤微生物功能多样性的影响

为揭示罗汉松土壤微生物对不同氮磷钾养分水平的响应及规律,该研究以两年生罗汉松(Podocarpus macrophyllus)幼苗为试验树种,采用L9正交试验控制盆栽土壤的氮磷钾养分水平梯度,使用稀释平板涂布法和Biolog-ECO微平板法探讨不同土壤氮磷钾养分水平对罗汉松土壤微生物量和群落多样性及其对6种碳源的利用特征。结果表明:(1)随氮添加量的增加,土壤细菌(P<0.05)和放线菌数量(P<0.001)减少,真菌(P<0.001)及固氮菌数量(P<0.01)显著增加,土壤微生物群落的Pielou 指数(P<0.001)降低,Simpson指数(P<0.05)和McIntosh指数(P<0.001)升高,从而降低了土壤微生物对6种碳源的利用强度,特别是对难利用碳源胺类(P<0.001)、羧酸(P<0.001)、聚合物(P<0.001)及其他化合物(P<0.001)的利用强度显著降低。(2)磷添加量的增加显著降低了土壤微生物群落的Shannon指数(P<0.05)。(3)钾添加量的增加显著降低了土壤微生物群落的Shannon指数和Pielou指数及微生物群落对碳水化合物和氨基酸(P<0.01)两类易利用碳源的强度。综上所述,氮添加和钾添加是影响罗汉松土壤微生物群落功能多样性的主要因素,在罗汉松培育时应注意少量多次施肥,降低氮和钾的添加量,适当提高磷添加量,以促进罗汉松的生长及其可持续培育。该研究从微生物的角度为罗汉松施肥及管护提供了理论依据。     

Evaluation of laboratory-based measures of soil mineral nitrogen and potentially mineralizable nitrogen as predictors of field-based indices of soil nitrogen supply in potato production

Accurate estimation of soil nitrogen (N) supply in the field is required to optimize fertilizer N management and to minimize environmental N losses in humid environments. Laboratory-based measures of N availability were evaluated as predictors of field-based indices of soil N supply within potato production systems. Pre-plant soil samples (0–15 cm) were collected from a series of forty treatments in established potato trials located in Atlantic Canada and Maine, USA. Total plant N uptake at topkill with no fertilizer N applied (PNU_0N), PNU_0N plus soil mineral N to 30 cm depth at harvest and relative yield were considered as field-based indices of soil N supply. The potentially mineralizable N (N₀) was determined by aerobic incubation at 25°C and periodic leaching for 24 weeks. A series of laboratory-based measures of soil N supply were measured in soil samples. Pre-plant soil nitrate or total mineral N at 0–30 cm depth was the best single predictor of PNU_0N (r = 0.67 and 0.71, respectively) and relative yield (r = 0.58 and 0.61). The ultraviolet absorbance of 0.01 M NaHCO₃ extract at 205 nm (NaHCO₃-205) was suitable as a predictor of PNU_0N and relative yield in each growing season, however, the relationship between this parameter and PNU_0N or relative yield varied somewhat among years. A combination of pre-plant mineral N plus N mineralized in the first 2 weeks period of incubation after re-wetting is proposed as a more robust measure of N availability compared with use of mineral N alone.     

Symbiotic N2 fixation by soybean in organic and conventional cropping systems estimated by 15N dilution and 15N natural abundance

Nitrogen (N) is often the most limiting nutrient in organic cropping systems. N₂ fixing crops present an important option to improve N supply and to maintain soil fertility. In a field experiment, we investigated whether the lower N fertilization level and higher soil microbial activity in organic than conventional systems affected symbiotic N₂ fixation by soybean (Glycine max, var. Maple Arrow) growing in 2004 in plots that were since 1978 under the following systems: bio-dynamic (DYN); bio-organic (ORG); conventional with organic and mineral fertilizers (CON); CON with exclusively mineral fertilizers (MIN); non-fertilized control (NON). We estimated the percentage of legume N derived from the atmosphere (%Ndfa) by the natural abundance (NA) method. For ORG and MIN we additionally applied the enriched ¹⁵N isotope dilution method (ID) based on residual mineral and organic ¹⁵N labeled fertilizers that were applied in 2003 in microplots installed in ORG and MIN plots. These different enrichment treatments resulted in equal %Ndfa values. The %Ndfa obtained by NA for ORG and MIN was confirmed by the ID method, with similar variation. However, as plant growth was restricted by the microplot frames the NA technique provided more accurate estimates of the quantities of symbiotically fixed N₂ (Nfix). At maturity of soybean the %Ndfa ranged from 24 to 54%. It decreased in the order ORG > CON > DYN > NON > MIN, with significantly lowest value for MIN. Corresponding Nfix in above ground plant material ranged from 15 to 26 g N m^-2, with a decreasing trend in the order DYN = ORG > CON > MIN > NON. For all treatments, the N withdrawal by harvested grains was greater than Nfix. This shows that at the low to medium %Ndfa, soybeans did not improve the N supply to any system but removed significant amounts of soil N. High-soil N mineralization and/or low-soil P availability may have limited symbiotic N₂ fixation.     

Litterfall and nutrient returns in red alder stands in western Washington

Summary Litterfall was collected over 1 year from eight natural stands of red alder growing on different sites in western Washington. The stands occurred at various elevations and on different soils, and differed in age, basal area, and site index. Most litterfall was leaf litter (average 86 percent). Amounts of litterfall and leaf litter varied significantly (P<0.05) among the sites. Average weights of litterfall and leaf litter in kg ha^–1 yr^–1, were 5150 and 4440, respectively. Weight of leaf litter was not significantly (P<0.05) related to site index, stand age, or basal area. The sites varied significantly (P<0.05) in concentrations of all elements determined in the leaf litter, except Zn. Average chemical concentrations were: N, 1.98 percent; P, 0.09 percent; K, 0.44 percent; Ca, 1.01 percent; Mg, 0.21 percent; S, 0.17 percent; SO₄–S, nil; Fe, 324 ppm; Mn, 311 ppm; Zn, 53 ppm; Cu, 13 ppm; and Al, 281 ppm. There were significant correlations between some stand characteristics and concentrations of some elements, and among the different chemical components of the leaf litter. Important correlations were found between stand age and P concentration (r=–0.84,P<0.01); weight of leaf litter and P concentration (r=0.74,P<0.05); weight of leaf litter and K concentration (r=0.71,P<0.05); concentrations of N and S (r=0.81,P<0.05); and concentrations of Fe and Al (r=0.98,P<0.01). Returns of the different elements to the soil by leaf litter varied among the different sites. Average nutrient and Al returns, in kg ha^–1 yr^–1, were: N, 82; Ca, 41; K, 19; Mg, 8; S, 7; P, 4; Fe, 1; Mn, 1; Al, 1; Zn, 0.2, and Cu, <0.1.     

Foliage litter quality and annual net N mineralization: comparison across North American forest sites

The feedback between plant litterfall and nutrient cycling processes plays a major role in the regulation of nutrient availability and net primary production in terrestrial ecosystems. While several studies have examined site-specific feedbacks between litter chemistry and nitrogen (N) availability, little is known about the interaction between climate, litter chemistry, and N availability across different ecosystems. We assembled data from several studies spanning a wide range of vegetation, soils, and climatic regimes to examine the relationship between aboveground litter chemistry and annual net N mineralization. Net N mineralization declined strongly and non-linearly as the litter lignin:N ratio increased in forest ecosystems (r ² = 0.74, P < 0.01). Net N mineralization decreased linearly as litter lignin concentration increased, but the relationship was significant (r ² = 0.63, P < 0.01) only for tree species. Litterfall quantity, N concentration, and N content correlated poorly with net N mineralization across this range of sites (r ² < 0.03, P = 0.17–0.26). The relationship between the litter lignin:N ratio and net N mineralization from forest floor and mineral soil was similar. The litter lignin:N ratio explained more of the variation in net N mineralization than climatic factors over a wide range of forest age classes, suggesting that litter quality (lignin:N ratio) may exert more than a proximal control over net N mineralization by influencing soil organic matter quality throughout the soil profile independent of climate. Received: 16 December 1996 / Accepted: 8 February 1997     

Linking Foliar Chemistry to Forest Floor Solid and Solution Phase Organic C and N in Picea abies [L.] Karst Stands in Northern Bohemia

Dissolved organic carbon and nitrogen (DOC and DON) produced in the forest floor are important for ecosystem functions such as microbial metabolism, pedogenesis and pollutant transport. Past work has shown that both DOC and DON production are related to litterfall and standing stocks of C and N in the forest floor. This study, conducted in spring, 2003, investigated variation in forest floor water extractable DOC (WEDOC) and DON (WEDON) and forest floor C and N as a function of lignin, cellulose and N contained in live canopy foliage across eight Picea abies [L.] Karst stands in northern Bohemia. Based on Near Infrared Spectroscopy (NIR) analysis of foliar materials, lignin:N and cellulose:N content of the youngest needles (those produced in 2002) were positively and significantly related to WEDOC (R² = 0.82–0.97; P<0.01) and to forest floor C:N ratio (R = 0.72–0.78; P<0.01). Foliar N was strongly and negatively related to WEDOC and C:N ratio (R = −0.91 and 0.72; P<0.05) among our study sites. WEDON was positively correlated to foliar lignin:N (R = 0.48; P<0.05; n=40). Forest floor C pools were not positively correlated with foliar lignin and cellulose and forest floor N pools were not positively correlated with foliar N. Instead, a significant negative correlation was found between forest floor N pools and foliar cellulose (R=−0.41; P<0.05), and between forest floor C pools and foliar N (R = −0.44; P<0.05). From a remote sensing standpoint, our results are important because canopy reflectance properties are primarily influenced by the most recent foliage, and it was the chemistry of the most recently produced needles that showed a stronger relationship with forest floor WEDOC and C:N ratio suggesting forest floor production of WEDOC can be calculated regionally with remote sensing.     

Chemical soil properties under five age series ofAlnus nepalensis plantations in the Eastern Himalayas

Summary Five age series stands ofAlnus nepalensis D. Don monocultures have been selected from the Pankhasari range of the Kalimpong forest division in the Eastern Himalayas. Chemical soil propeties such as organic carbon, total nitrogen, CN ratio, available phosphorus and exchangeable cations (Ca⁺², K⁺ and Na⁺) were analysed in all these different ages of plantation stands from the surface to 1 m deep profiles to find out the long term effect ofA. nepalensis on the soil quality of these erosion vulnerable slopes.Organic carbon, available phosphorus and total nitrogen content per-hectare increased with increasing plantation stand age. Analysis of variance for nutrients showed significant variation in depth (total nitrogenP<0.001; organic carbon,P<0.001; available phosphorus,P<0.05; exchangeable Ca⁺²,P<0.01; and exchangeable K⁺,P<0.01) and between plantation stands (organic carbon,P<0.05; and available phosphorusP<0.05). High value of total nitrogen content (34.97t ha^–1) was obtained in 46 yr old stand. Soil pH is low. It increased down the depth and in older plantations. These stands with high soil total nitrogen and organic carbon content show increased fertility of the stands. The cover ofA. nepalensis in rocky, landslide and ecosion prone slopes of the Eastern Himalayas, serves to protect and improve soil quality.     

三种苦苣苔对石灰土和红壤的适应性分析

为探讨苦苣苔科植物对其岩溶生境的适应性,该研究选取黄花牛耳朵(Primulina lutea)、紫花报春苣苔(Pri.purpurea)和桂林蛛毛苣苔(Paraboea guilinensis)三种苦苣苔科植物,将其栽种在石灰土及红壤两种不同类型的土壤中,观测记录其生长性状并对其叶片元素含量进行测定和比较。植株采集过程中,同时采集自然生境中三种苦苣苔科植物叶片及取样植物基部土壤,并对叶片及土壤元素的含量进行测定,作为今后苗圃试验的参照。结果表明:三种苦苣苔科植物在两种土壤上的生长状况及适应性具有差异,其在石灰土上生长良好,在红壤上生长较差;在两种不同土壤中,除N外,桂林蛛毛苣苔的叶片其他元素(P、K、Mn、Mg、Ca、Zn、Cu)差异极显著(P0.01);除P外,紫花报春苣苔的叶片其他元素(N、K、Mn、Mg、Ca、Zn、Cu)差异极显著(P0.01);除N、Cu、Ca外,黄花牛耳朵的叶片元素(P、K、Mn、Mg、Zn)差异极显著(P0.01);三种植物的叶片元素比值,除少数值没有差异外,大部分指标差异都极显著;对叶片元素与栽培土壤元素的相关性分析,发现植物叶片Mn元素与土壤中N、Ca、Mg、Zn、Mn、有机质含量等呈正相关,土壤P元素与叶片中N、P元素呈正相关,而与叶片中Zn元素呈负相关关系。在其他栽培条件一致的条件下,土壤因素及物种差别是造成黄花牛耳朵、紫花报春苣苔和桂林蛛毛苣苔适应性产生差异的主要原因。     

Differential Controls of Water Input on Litter Decomposition and Nitrogen Dynamics in the Patagonian Steppe

Studies of the effects of precipitation on litter decomposition and nitrogen mineralization in arid and semiarid environments have demonstrated contradictory results. We conducted a manipulative experiment with rainout shelters in the semiarid Patagonian steppe, aimed at assessing the direct effects of water availability on litter decomposition and net nitrogen mineralization while isolating the indirect effects. We created four levels of precipitation input: control and three levels (30, 55 and 80%) of precipitation interception and we examined litter decomposition and nutrient release of a dominant grass species, Stipa speciosa, inorganic soil nitrogen, and in situ net nitrogen mineralization over two consecutive years. Litter decomposition rates (k, year⁻¹) varied significantly (P < 0.001) among precipitation interception treatments and were positively correlated with incoming annual precipitation (APPT, mm/year) (k = 0.0007 × APPT + 0.137). In contrast, net N mineralization was not correlated with incoming precipitation. Soil NO₃⁻ significantly decreased with increasing precipitation input, whereas soil NH₄⁺ concentration did not differ among precipitation interception treatments. Controls of water input on litter decomposition appear to be different from controls on N mineralization in the semiarid Patagonian steppe. We suggest that although water availability affects both the mineralization of C and N, it differentially affects the movement and fate of the inorganic products. A consequence of the accumulation of inorganic N during dry episodes is that periods of maximum water and soil nutrient availability may occur at different times. This asynchrony in the availability of N and water in the soil may explain the observed lags in the response of primary production to increases in water availability.     

Seed germination and seedling physiology of Larix kaempferi and Pinus densiflora in seedbeds with charcoal and elevated CO2

We investigated the effect of ectomycorrhizal colonization, charcoal and CO₂ levels on the germination of seeds of Larix kaempferi and Pinus densiflora, and also their subsequent physiological activity and growth. The seeds were sown in brown forest soil or brown forest soil mixed with charcoal, at ambient CO₂ (360 μmol mol⁻¹) or elevated CO₂ (720 μmol mol⁻¹), with or without ectomycorrhiza. The proportions of both conifer seeds that germinated in forest soil mixed with charcoal were significantly greater than for seeds sown in forest soil grown at each CO₂ level (P < 0.05; t-test). However, the ectomycorrhizal colonization rate of each species grown in brown forest soil mixed with charcoal was significantly lower than in forest soil at each CO₂ treatment [CO₂] (P < 0.01; t-test). The phosphorus concentrations in needles of each seedling colonized with ectomycorrhiza and grown in forest soil were greater than in nonectomycorrhizal seedlings at each CO₂ level, especially for L. kaempferi seedlings (P < 0.05; t-test), but the concentrations in seedlings grown in brown forest soil mixed with charcoal were not increased at any CO₂ level. Moreover, the maximum net photosynthetic rate of each seedling for light and CO₂ saturation (P _max) increased when the seedlings were grown with ectomycorrhiza at 720 μmol mol⁻¹ [CO₂]. Ectomycorrhizal colonization led to an increase in the stem diameter of each species grown in each soil treatment at each CO₂ level. However, charcoal slowed the initial growth of both species of seedling, constraining ectomycorrhizal development. These results indicate that charcoal strongly assists seed germination and physiological activity.     

The role of monoterpenes in soil nitrogen cycling processes in ponderosa pine

The effects of select monoterpenes on nitrogen (N) mineralization and nitrification potentials were determined in four separate laboratory bioassays. The effect of increasing monoterpene addition was an initial reduction in NO₃ ^–-N production (nitrification inhibition), followed by a reduction in the sum of NH₄ ⁺-N and NO₃ ^–-N (inhibition of net N mineralization and net immobilization at high monoterpene additions. Monoterpenes could produce this pattern by inhibiting nitrification, reducing net N mineralization, enhancing immobilization of NO₃ ^–-N relative to NH₄ ⁺-N, and/or stimulating overall net immobilization of N by carbon-rich material.Initial monoterpene concentrations in the assay soils were about 5% of the added amount and were below detection after incubation in most samples.Potential N mineralization-immobilization, nitrification, and soil monoterpene concentrations were determined by soil horizon for four collections from a ponderosa pine (Pinus ponderosa) stand in New Mexico. Concentrations of monoterpenes declined exponentially with soil depth and varied greatly within a horizon. Monoterpene content of the forest floor was not correlated with forest floor biomass. Net N mineralization was inversely correlated with total monoterpene content of all sampled horizons. Nitrification was greatest in the mineral soil, intermediate in the F-H horizon, and never occurred in the L horizon. Nitrification in the mineral soil was inversely correlated with the amount of monoterpenes in the L horizon that contain terminal unsaturated carbon-carbon bonds (r ² = 0.37, P 0.01). This pattern in the field corresponded to the pattern shown in the laboratory assays with increasing monoterpene additions.     

Sorption of phosphorus by the iron oxide-impregnated filter paper (Pi soil test) embedded in soils

Incubation experiments were carried out to evaluate the feasibility of extracting phosphorus from soil by embedding iron oxide-impregnanted filter paper strips (P_i strips) in soils having a wide range in pH, texture, and extractable-P contents. Under flooded conditions, the amount of P extracted by the P_i strips increased with the period of submergence and embedding time of the P_i strips. Under unsaturated conditions, the P_i strips were found to extract P from soils over a wide range in moisture conditions; however, keeping the soil at moisture level between saturation and field capacity was found to result in maximal sorption of P by the strips. An embedding time of 16 h was found to be adequate.Phosphorus extracted by embedding P_i strips in soil columns for 16 h at field capacity moisture level correlated significantly with P extracted by shaking the soil with 0.01 M CaCl₂ solution and a P_i strip for 16 h in the laboratory (r=0.94^**). The P extracted by embedding P_i strips correlated best with Bray 1 P in acid soils (r=0.97^**) and with Olsen P in alkaline and calcareous soils (r=0.96^**). The results of the studies demonstrate the feasibility of developing a nondestructive method of monitoring changes in plant-available P in situ under field conditions.     

Estimation of symbiotically fixed nitrogen in field grown soybeans: An application of natural15N/14N abundance and a low level15N-tracer technique

Summary Plants from agricultural and natural upland ecosystem were investigated for¹⁵N content to evaluate the role of symbiotic N₂-fixation in the nitrogen nutrition of soybean. Increased yields and lower δ¹⁵N values of nodulating soybeansvs, non-nodulating isolines gave semi-quantitative estimates of N₂ fixation. A fairly large discrepancy was found between estimations by δ¹⁵N and by N yield at 0 kg N/ha of fertilizer. More precise estimates were made by following changes in plant δ¹⁵N when fertilizer δ¹⁵N was varied near¹⁵N natural abundance level. Clearcut linear relationships between δ¹⁵N values of whole plants and of fertilizer were obtained at 30 kg N/ha of fertilizer for three kinds of soils. In experimental field plots, nodulating soybeans obtained 13±1% of their nitrogen from fertilizer, 66±8% from N₂ fixation and 21±10% from soil nitrogen in Andosol brown soil; 30%, 16% and 54% in Andosol black soil; 7%, 77% and 16% in Alluvial soil, respectively. These values for N₂ fixation coincided with each corresponding estimation by N yield method. Other results include: 1)¹⁵N content in upland soils and plants was variable, and may reflect differences in the mode of mineralization of soil organics, and 2) nitrogen isotopic discrimination during fertilizer uptake (δ¹⁵N of plant minus fertilizer) ranged from −2.2 to +4.9‰ at 0–30 kg N/ha of fertilizer, depending on soil type and plant species. The proposed method can accurately and relatively simply establish the importance of symbiotic nitrogen fixation for soybeans growing in agricultural settings.     

The Effect of Mixing Prunings of Two Tropical Shrub Legumes (Calliandra Houstoniana and Indigofera zollingeriana) with Contrasting Quality on N Release in the Soil and Apparent N Degradation in the Rumen

Lack of synchronization between N released from prunings applied to the soil as green manures and crop uptake as well as optimization of protein digestibility for ruminants, remain major research objectives for the selection of multipurpose tree and shrub legumes (MPT) for mixed smallholder systems in the tropics. Prunings of the high tannin, low quality MPT Calliandra houstoniana CIAT 20400 (Calliandra) and the tannin free, high quality MPT Indigofera zollingeriana (Indigofera) were mixed in the proportions 100:0, 75:25, 50:50, 25:75, and 0:100 (w/w) in order to measure the aerobic rate and extent of N release in a leaching tube experiment, and the anaerobic extent of N degradation in an in vitro gas production experiment. Parameters measured in Calliandra:Indigofera mixtures were compared to theoretical values derived from single species plant material (i.e. 100:0 and 0:100). Aerobic N release and apparent anaerobic N degradation increased with increasing proportion of the high quality legume (Indigofera) in the mixture. While N release in the soil was lower than theoretical values in the mixture 50% Calliandra/50% Indigofera, this was not the case with apparent anaerobic N degradation with the same mixture. Aerobic N immobilization was more pronounced for the mixture 75% Calliandra/25% Indigofera than for 100% Calliandra and negative interaction was observed with apparent anaerobic N degradation in the mixture 75% Calliandra/25% Indigofera. Plant quality parameters that best correlated with aerobic N release and apparent anaerobic N degradation in the rumen were lignin + bound condensed tannins (r=−0.95 and −0.95 respectively, P<0.001). In addition, a positive correlation (r=0.89, P<0.001) was found between aerobic N release in the leaching tube experiment and apparent N degradation in the in vitro anaerobic gas production experiment. Results show that mixing prunings of MPT materials with contrasting quality is an effective way to modify aerobic N release pattern as well as apparent anaerobic N degradation and could possibly be applied to minimize N losses in the rumen and in the soil. In addition, apparent anaerobic N degradation was identified as good predictor of aerobic N release in the soil, which has resource saving implications when screening MTP to be used as green manures.     

Relationships between soil,fallow period,weeds and rice yield in slash-and-burn systems of Laos

Decline in soil fertility accelerated by shorter fallow periods was expected to be a major constraint in slash-and-burn rice production systems in northern Laos. In this paper we describe relationships between fallow period, soil fertility parameters, weeds and rice yield. Soil infertility is not perceived a major yield constraint by the farmers. Of the various soil parameters observed only soil organic matter showed consistent association with rice yield (r=0.42, p<0.01). Fallow period and rice yield showed no association and the relationship between fallow and organic matter was very weak (r=0.16, p<0.01). Rice yield was negatively related to densities of Ageratum conyzoides and Lygodium flexuosum. Soil loss during the cropping period ranged from 300–29.300 kg ha^–1. For the same period organic matter, total N, available P and available K content in the top 0–3 cm decreased by 11,12,17, and 17%, respectively, and loss of total N for the soil depth of 0–25 cm was estimated at 400 kg ha^–1. Soil physical properties, moisture stress and available N are the most likely detriments to rice yields. Further attempts to relate soil properties to rice yield should include repeated measurements during the cropping season and observations on soil physical properties.The research presented was supported by the Provincial Agriculture Service, Luang Prabang, Laos, and the Swiss Development Cooperation.     

Decreased α1-Adrenergic Receptor Binding in the Cerebral Cortex and Brain Stem during Pancreatic Regeneration in Rats

The purpose of this study was to investigate the role of brain α₁-adrenergic receptor binding in the rat model of pancreatic regeneration using 60–70% pancreatectomy. The α₁-adrenergic receptors kinetics was studied in the cerebral cortex and brain stem of sham operated, 72 h pancreatectomised and 7 days pancreatectomised rats. Scatchard analysis with [³H]prazosin in cerebral cortex and brain stem showed a significant decrease (P < 0.01), (P < 0.05) in maximal binding (B _max) with a significant decrease (P < 0.001), (P < 0.01) in the K _d in 72 h pancreatectomised rats compared with sham respectively. Competition analysis in cerebral cortex and brain stem showed a shift in affinity during pancreatic regeneration. The sympathetic activity was decreased as indicated by the significantly decreased norepinephrine level in the plasma (P < 0.001), cerebral cortex (P < 0.01) and brain stem (P < 0.001) of 72 h pancreatectomised rats compared to sham. Thus, from our results it is suggested that the central α₁-adrenergic receptors have a functional role in the pancreatic regeneration mediated through the sympathetic pathway.     

Effect of lime, dicyandiamide and soil water content on ammonia and nitrous oxide emissions following application of liquid hog manure to a marshland soil

The loss of nitrogen (N) from field-applied animal manure through ammonia (NH₃) volatilisation and nitrous oxide (N₂O) emission is of major environmental concern. Both lime and dicyandiamide (DCD) have been suggested as amendments that can mitigate N₂O emissions, but simultaneously increase the risk of NH₃ volatilisation. This study evaluated the impact of lime and DCD on NH₃ and N₂O emissions following application of liquid hog manure. Hydrated lime (Ca(OH)₂) was added to an acidic soil to achieve three pH levels (4.7, 6.3 and 7.4). Soil samples (100 g) were then placed in 500 ml screw-top Mason-jars and de-ionised water was added to bring the samples to 50, 70 and 90% water-filled pore space (WFPS). Slurry was applied at a rate equivalent to 116,000 l ha⁻¹, while DCD was applied at 30% of the NH₄-N rate applied. Jars were sealed and incubated at 21°C for 21 d. Ammonia volatilisation was quantified using boric acid traps, while N₂O gas concentration was analysed using gas chromatography. Dicyandiamide had no effect (P>0.05) on either NH₃ or N₂O emissions. Both NH₃ and N₂O emissions increased (P<0.05) as WFPS increased, with emissions ranging from 0.9 to 1.4 kg NH₃-N ha⁻¹ and 123 to 353 g N₂O-N ha⁻¹, respectively. Liming decreased (P<0.01) N₂O emissions from 547 to 46 g N₂O-N ha⁻¹, but increased (p<0.01) NH₃ volatilisation from 0.36 to 1.92 kg NH₃-N ha⁻¹. Results suggest that liming to a pH ≥6.3 can reduce N₂O emissions, however, this reduction will be accompanied by a substantial loss of NH₃. Section Editor: H. Lambers     

Characteristics of chimpanzee (Pan troglodytes) ejaculates collected by rectal probe electrostimulation and by artificial vagina

This study compares characteristics of ejaculates collected from 16 adult male chimpanzees using rectal probe electrostimulation (RPE) and from 10 adult male chimpanzees trained to use an artificial vagina (AV). Ejaculate weight, semen volume, and sperm number were significantly lower (P < 0.01) and percentage liquefaction was significantly higher (P < 0.01) in ejaculates collected by RPE. Percentages of motile sperm and of live sperm in semen did not differ significantly between the two collection methods. Total amounts of protein and of α-glucosidase activity were significantly lower (P < 0.01) in seminal fluid from RPE samples. For ejaculates collected by RPE, semen volume correlated positively with protein (r = 0.8640, P < 0.001), fructose (r = 0.6976, P < 0.001), and citrate (r = 0.6976, P < 0.001); sperm number correlated positively with α-glucosidase activity (r = 0.6547, P < 0.001); and protein correlated positively with fructose (r = 0.5906, P < 0.002), citrate (r = 0.5926, P < 0.002) and α-glucosidase activity (r = 0.6006, P < 0.001). For ejaculates collected by AV, semen volume correlated positively with percentage liquefaction (r = 0.6058, P < 0.001), protein (r = 0.8055, P < 0.001), fructose (r = 0.6606, P < 0.001), and citrate (r = 0.8272, P < 0.001); sperm number correlated positively with percentage of motile sperm (r = 0.4196, P 0.004); percentage of motile sperm correlated positively with percentage of live sperm (r = 0.4388, P < 0.002); and, protein correlated positively with fructose (r = 0.6947, P < 0.002) and with citrate (r = 0.5926, P < 0.002). These data show that there is a significant difference in semen parameters and in biochemical parameters of ejaculates obtained by RPE and by AV. © 1995 Wiley-Liss, Inc.     

In situ annual nitrogen mineralization predicted by simple soil properties and short-period field incubation

A typical method to determine nitrogen mineralization is year-round field incubation of undisturbed soil cores. As this technique is very laborious, the aim of the present study was to establish less time consuming methods to assess the annual N mineralization. Options considered were reducing the period of subsequent field incubations to less than a full year, and prediction using simple (direct) soil measurements. In situ annual N mineralization was measured in 74 semi-natural, unfertilized sites under year-round vegetation cover by sequential incubation of undisturbed soil cores during 2 full years. The sites classify into 14 very different plant community types and encompass a wide range of edaphic conditions. A high correlation with the annual N mineralization was maintained when sequential incubations were restricted to the period early March–mid August (r=0.98). Shorter periods may also be used, as long as they lie within the period early March–mid August and cover 3 months at least. The average annual N mineralization could be predicted accurately using the soil mineral nitrogen pool (N_min), moisture content and pH as the predictor variables. In a multiple regression model based on log-transformed values, the R ² was 0.835. Samples (preferably bulked) are best taken in early March, just before the start of the growing season. Higher N_min contents (moisture and pH assumed constant) indicated higher annual N mineralization rates. Higher moisture contents (at constant N_min and pH) generally indicated lower annual rates. Soil pH showed a quadratic relation (at fixed N_min and moisture) with maximum annual mineralization occurring at a pH-CaCl₂ value of 5.5–5.6. N_min appeared to be the most important predictor variable. Even within plant community types (with a reduced range of conditions), its relationship with the annual N mineralization persisted. Frequently studied factors, such as total soil N, organic matter content, C:N ratio, soluble organic N and particle size composition, only showed low and insignificant correlations, although stronger relationships have sometimes been reported. It is assumed this discrepancy is caused by the smaller range of conditions usually studied. This revised version was published online in June 2006 with corrections to the Cover Date.