Soluble Nitrogen Compounds Research Articles

Mechanisms of aluminum‐induced growth stimulation in tea (Camellia sinensis)

AbstractBeneficial effects of aluminum (Al) on plant growth have been reported for plant species adapted to acid soils. However, mechanisms underlying the stimulatory effect of Al have not been fully elucidated. The aim of this study was to determine the possible contribution of photosynthesis, antioxidative defense, and the metabolism of both nitrogen and phenolics to the Al‐induced growth stimulation in tea (Camellia sinensis [L.] Kuntze) plants. In hydroponics, shoot growth achieved its maximum at 50 μM Al suply (24 μM Al3+ activity). A more than threefold increase of root biomass was observed for plants supplied with 300 μM Al (125 μM Al3+ activity). Total root length was positively related to root Al concentrations (r = 0.98). Chlorophyll a and carotenoid concentrations and net assimilation rates were considerably enhanced by Al supply in the young but not in the old leaves. Activity of nitrate reductase was not influenced by Al. Higher concentrations of soluble nitrogen compounds (nitrate, nitrite, amino acids) and reduction of protein concentrations suggest Al‐induced protein degradation. This occurred concomitantly with enhanced net CO2‐assimilation rates and carbohydrate concentrations. Aluminum treatments activated antioxidant defense enzymes and increased free proline content. Lowering of malondialdehyde concentrations by Al supply indicates that membrane integrity was not impaired by Al. Leaves and roots of Al‐treated plants had considerably lower phenolic and lignin concentrations in the cell walls, but a higher proportion of soluble phenolics. In conclusion, Al‐induced growth stimulation in tea plants was mediated by higher photosynthesis rate and increased antioxidant defense. Additionally, greater root surface area may improve water and nutrient uptake by the plants.

Is wood pre‐treatment essential for tree‐ring nitrogen concentration and isotope analysis?

Tree-ring nitrogen concentrations and isotope ratios (δ(15)N) are gaining in popularity for environmental research although their use is still debated because of nitrogen mobility in tree stems. Modern studies generally present results on wood that is pre-treated to remove soluble nitrogen compounds and to minimize the impact of radial translocation on tree-ring nitrogen environmental records. However, the necessity to use such pre-treatment has never been fully assessed. Here we compare the nitrogen concentrations and δ(15)N values of two wood preparation protocols applied to beech and red spruce tree rings for the removal of soluble compounds from ring pairs with non pre-treated tree rings. For both tree species, pre-treatment did not minimize the radial patterns of tree-ring nitrogen concentrations and the increasing concentration trends that are coincident with the heartwood-sapwood boundary. Therefore, even if the tree-ring nitrogen concentrations are slightly modified by pre-treatment, these concentrations are considered to reflect internal stem processes rather than environmental conditions in both species. The δ(15)N values were similar for untreated and pre-treated ring pairs, suggesting that wood pre-treatment did not substantially change the δ(15)N values and temporal trends in ring series. In addition, tree-ring δ(15)N series of untreated and pre-treated wood did not show any sign of influence of the heartwood-sapwood boundary in either tree species, indicating that nitrogen translocation did not generate significant isotopic fractionation. We therefore suggest that untreated ring δ(15)N values of beech and red spruce trees can be used for environmental research.

Feedback of carbon and nitrogen cycles enhances carbon sequestration in the terrestrial biosphere

AbstractThe efforts to explain the ‘missing sink’ for anthropogenic carbon dioxide (CO2) have included in recent years the role of nitrogen as an important constraint for biospheric carbon fluxes. We used the Nitrogen Carbon Interaction Model (NCIM) to investigate patterns of carbon and nitrogen storage in different compartments of the terrestrial biosphere as a consequence of a rising atmospheric CO2 concentration, in combination with varying levels of nitrogen availability. This model has separate but closely coupled carbon and nitrogen cycles with a focus on soil processes and soil–plant interactions, including an active compartment of soil microorganisms decomposing litter residues and competing with plants for available nitrogen. Biological nitrogen fixation is represented as a function of vegetation nitrogen demand. The model was validated against several global datasets of soil and vegetation carbon and nitrogen pools. Five model experiments were carried out for the modeling periods 1860–2002 and 2002–2100. In these experiments we varied the nitrogen availability using different combinations of biological nitrogen fixation, denitrification, leaching of soluble nitrogen compounds with constant or rising atmospheric CO2 concentrations. Oversupply with nitrogen, in an experiment with nitrogen fixation, but no nitrogen losses, together with constant atmospheric CO2, led to some carbon sequestration in organismic pools, which was nearly compensated by losses of C from soil organic carbon pools. Rising atmospheric CO2 always led to carbon sequestration in the biosphere. Considering an open nitrogen cycle including dynamic nitrogen fixation, and nitrogen losses from denitrification and leaching, the carbon sequestration in the biosphere is of a magnitude comparable to current observation based estimates of the ‘missing sink.’ A fertilization feedback between the carbon and nitrogen cycles occurred in this experiment, which was much stronger than the sum of separate influences of high nitrogen supply and rising atmospheric CO2. The demand‐driven biological nitrogen fixation was mainly responsible for this result. For the modeling period 2002–2100, NCIM predicts continued carbon sequestration in the low range of previously published estimates, combined with a plausible rate of CO2‐driven biological nitrogen fixation and substantial redistribution of nitrogen from soil to plant pools.

Atmospheric nitrogen deposition in south-east Scotland: Quantification of the organic nitrogen fraction in wet, dry and bulk deposition

Water soluble organic nitrogen (WSON) compounds are ubiquitous in precipitation and in the planetary boundary layer, and therefore are a potential source of bioavailable reactive nitrogen. This paper examines weekly rain data over a period of 22 months from June 2005 to March 2007 collected in 2 types of rain collector (bulk deposition and “dry + wet” deposition) located in a semi-rural area 15 km southwest of Edinburgh, UK (N55°51′44″, W3°12′19″). Bulk deposition collectors are denoted in this paper as “standard rain gauges”, and they are the design used in the UK national network for monitoring precipitation composition. “Dry + wet” deposition collectors are flushing rain gauges and they are equipped with a rain detector (conductivity array), a spray nozzle, a 2-way valve and two independent bottles to collect funnel washings (dry deposition) and true wet deposition. On average, for the 27 weekly samples with 3 valid replicates for the 2 types of collectors, dissolved organic nitrogen (DON) represented 23% of the total dissolved nitrogen (TDN) in bulk deposition. Dry deposition of particles and gas on the funnel surface, rather than rain, contributed over half of all N-containing species (inorganic and organic). Some discrepancies were found between bulk rain gauges and flushing rain gauges, for deposition of both TDN and DON, suggesting biological conversion and loss of inorganic N in the flushing samplers.

Plankton biomass in secondary ponds treating piggery waste

This study aimed at analyzing the plankton biomass found in a piggery waste treatment system, composed of a high rate algal pond (HRAP), two maturation ponds (MP1, MP2) (System A) and a water hyacinth pond (WHP) (System B). The ponds were disposed in series and the study was performed for 32 weeks. The physicochemical variables monitored were: pH, temperature, dissolved oxygen, soluble chemical oxygen demand, nitrogen compounds and total phosphorus. The plankton biomass was identified at genus level and the ecology index was calculated so as to describe its development in the ponds. Results showed lower specific richness, which was associated to the mono-specific Chlorella sp population. The protozoa density was conversely proportional to the green algae density. The higher species diversity occurred in the WHP and MP2. The green algae presented high relative density (>97 %). The Jaccard index reached 100% if Chlorella sp and sometimes diatoms were found in the system's inlet and outlet. The productivity of algal biomass was lower than 10 gTSS/m²/d in the maturation ponds, which was maintained in the HRAP. The green algae coefficient of variation (CV) varied from 0 to 1.5 in the HRAP and WHP, but was constant at 0.9 to the 10th week in MP1 and around 0.5 during all the experimental period for MP2. For the chlorophyll a, this coefficient varied in all the ponds.

Increased negative anomalies of sedimentary organic matter δ13C and δ15N values in the East Sea (Sea of Japan) during the full glaciation of the late Quaternary

Glacio-eustatic sea-level fluctuations and subsequent paleoceanographic changes in the East Sea (Sea of Japan) have been identified by unique sedimentary features and their geochemical properties throughout the late Quaternary sediments. These events were synchronous basin wide. The effect of sea-level change in the East Sea is fundamental to the anoxia of bottom water resulting from the stagnant, strongly stratified water column with limited ventilation during the glacial periods. The four sediment cores collected from the Japan Basin, Yamato Basin and Korea Plateau in the East Sea showed extraordinarily co-varied δ 1 3C and δ 15N values of sedimentary organic matter, representing distinct negative anomalies of both isotopes for the thick dark laminated mud layers formed during full glaciations (MIS 2 and MIS 6) of the late Quaternary. The most plausible cause to induce such peculiar isotope variations is the enhanced contribution of terrestrial organic detritus, in addition to the anoxic diagenetic condition in the bottom water during the glacial times, both of which are characterized by relatively low δ 13C and δ 15N values. The aeolian contribution of terrigenous particles in the form of Kosa supplied from inland China was intensified in the East Sea during the last glacial maximum. During the glacial periods, the anoxic decay of sedimentary organic matter may lead not only to the reduction of δ 13C values attributed to the selective preservation of 13C-depleted organic compounds, but also to the decrease of δ 15N values due to the addition of 15N-depleted organic matter by using soluble nitrogenous compounds and the bacterial growth adding 15N-depleted biomass to the residual materials. Thus, the results argue against the utility of δ 1 3C and δ 15N values of sedimentary organic matter as a proxy of paleoproductivity and atmospheric pCO 2 levels in a marginal sea environment such as the East Sea.

Alterations in Nitrogen Metabolites after Putrescine Treatment in Alfalfa under Drought Stress

Alfalfa (Medicago sativa, Siwa 1) seeds were subjected to drought stress during germination by using polyethylene glycol (PEG 4000) for studying the changes in some enzyme activities involved in nitrogen metabolism and the content of nitrogenous compounds during the first four days of growth after putrescine (Put) treatment. Decreasing the external water potential reduced activities of glutamate-pyruvate transferase (GPT), glutamate-oxaloacetate transferase (GOT) and RNase. Some free amino acids such as proline and glycine increased, while alanine and aspartic acid decreased. Nucleic acids content also decreased. Polyamines e.g., spermidine (Spd) and spermine (Spm) increased at the water potential -0.4 MPa. Put treatment increased activities of GOT, GPT and RNase. Furthermore, Put treatment increased nucleic acids content and the endogenous polyamines under drought stress. Drought stress was imposed during seedling stage by decreasing soil moisture content. GOT, GPT and RNase activities increased in leaves of alfalfa seedlings under drought stress. Soluble nitrogenous compounds accumulated under drought stress, while nucleic acids content decreased. Except glutamic acid, all free amino acids detected increased under drought stress. Put treatment decreased activities of GOT, GPT and RNase, as well as reduced the accumulation of the total soluble nitrogenous compounds, but increased DNA, RNA and protein contents.

Seasonal courses of key parameters of nitrogen, carbon and water balance in European beech (Fagus sylvatica L.) grown on four different study sites along a European North–South climate gradient during the 2003 drought

During the growing season of the exceptionally dry and warm year 2003, we assessed seasonal changes in nitrogen, carbon and water balance related parameters of mature naturally grown European beech (Fagus sylvatica L.) along a North–South transect in Europe that included a beech forest stand in central Germany, two in southern Germany and one in southern France. Indicators for N balance assessed at all four sites were foliar N contents and total soluble non-protein nitrogen compounds (TSNN) in xylem sap, leaves and phloem exudates; C and water balance related parameters determined were foliar C contents, δ13C and δ18O signatures. Tissue sampling was performed in May, July and September. The N related parameters displayed seasonal courses with highest concentrations during N remobilization in May. Decreased total foliar N contents as well as higher C/N ratios in the stands in central Germany and southern France compared to the other study sites point to an impaired N nutrition status due to lower soil N contents and precipitation perception. TSNN concentrations in leaves and phloem exudates of all study sites were in ranges previously reported, but xylem sap content of amino compounds in July was lower at all study sites when compared to literature data (c. 1 μmol N mL−1). In September, TSNN concentrations increased again at the two study sites in southern Germany after a rain event, whereas they remained constant at sites in central Germany and southern France which hardly perceived precipitation during that time. Thus, TSNN concentrations in the xylem sap might be indicative for water balance related N supply in the beech trees. TSNN profiles at all study sites, however, did not indicate drought stress. Foliar δ13C, but not foliar C and δ18O followed a seasonal trend at all study sites with highest values in May. Differences in foliar δ13C and δ18O did not reflect climatic differences between the sites, and are attributed to differences in altitude, photosynthesis and δ18O signatures of the water sources. Except of low TSNN concentrations in the xylem sap, no physiological indications of drought stress were detected in the trees analysed. We suppose that the other parameters assessed might not have been sensitive to the drought events because of efficient regulation mechanisms that provide a suitable physiological setting even under conditions of prolonged water limitation. The uniform performance of the trees from southern France and central Germany under comparably dry climate conditions denotes that the metabolic plasticity of mature beech from the different sites studied might be similar.

Physiological Performance of Beech (Fagus sylvatica L.) at its Southeastern Distribution Limit in Europe: Seasonal Changes in Nitrogen, Carbon and Water Balance

To assess the physiological performance of drought-sensitive European beech ( Fagus sylvatica L.) under the dry Mediterranean climate prevailing at its southeastern distribution limit in Europe, we analyzed seasonal changes in carbon, nitrogen and water balance of naturally grown adult trees. We determined the foliar C and N contents, delta13C and delta18O signatures, total soluble non-protein nitrogen compounds (TSNN) in xylem, leaves, and phloem, as well as leaf water potential and photosynthetic quantum yield in northern Greece during 2003. Tissue sampling was performed in May, July, and September, while field measurements were conducted regularly. Climatic conditions for the 2003 growing season fall within the typical range of the studied area. The N- and C-related parameters displayed distinct seasonal courses. TSNN was highest in May in all tissues, and asparagine (Asn) was then the most abundant compound. Thereafter, TSNN decreased significantly in all tissues and both its concentration and composition remained constant in July and September. In both months, glutamate (Glu) prevailed in leaves, gamma-aminobutyric acid (GABA) in phloem exudates from twigs and trunks, and arginine (Arg) in the xylem sap, where loading with amino acids was rather low during that period, amounting to only 0.8 micromol N ml-1 in September. Highest total foliar N and C contents were detected in May, and the elevated abundance of nutrients as well as an increased foliar delta13C signature at the beginning of the growing season is attributed to remobilization processes. The signatures of delta18O, quantum yield and leaf water potentials varied only slightly throughout the growing season. Although summer precipitation at the study site was considerably lower compared to what is usual for typical central European beech forests, no intensive drought responses of the physiological apparatus were detected in the studied beech trees. This suggests efficient internal regulation mechanisms, constantly ensuring a favourable physiological status under the relatively dry Mediterranean climate.

Soluble N compound profiles and concentrations in European beech (Fagus sylvatica L.) are influenced by local climate and thinning

We assessed seasonal changes of total soluble nonprotein nitrogen compounds (TSNN) in adult European beech trees (Fagus sylvatica, L.) growing under different local climate during the growing season immediately following a thinning treatment and 3 years later. In both years, samples of leaves, xylem sap and phloem exudates from beech trees growing in thinned and unthinned (control) stands on a dry, warm SW exposed and a cooler, moist NE exposed site were collected in May, July and September. In May of both years, asparagine (Asn) and glutamine (Gln) were most abundant in leaves and xylem, respectively, whereas arginine (Arg) dominated in the phloem. In July, TSNN concentrations decreased in all tissues and sites, but differences in water availability between aspects were reflected in TSNN concentrations. In September, differences in the increase of Arg concentration in the phloem were related to differences in the onset of senescence between treatments. Thinning treatment increased amino compound concentrations of beech tissues in July on both aspects, particularly at the NE thinned site. It is supposed that, the N balance of adult beech is favoured by both, the thinning treatments as well as the cool-moist climate prevailing at the NE aspect.

Ecophysiology of selected tree species in different plant communities at the periphery of the Atlantic Forest of SE-Brazil II. Spatial and ontogenetic dynamics in Andira legalis, a deciduous legume tree

Andira legalis Vell. Toledo (Leguminosae, Papilionoideae) is a deciduous tree of the coastal vegetation of Brazil. It was studied in the restinga ecosystems of the Atlantic coast along a moisture gradient of open dry restinga (annual precipitation 800 mm, water table high at 0.9–1.2 m but partially saline), intermediate restinga (annual precipitation 1164 mm, water table low at 2–3 m) and wet restinga (annual precipitation 1000 mm, water table high at 0.5–1 m). In addition, a comparison of the ecophysiological performance was made of A. legalis in the wet restinga and a dune forest (water table low at 2–6 m). Plants of A. legalis at a given site and even within clonal stands show considerable phenological plasticity, where especially timing of leaf shedding and new bud break, leaf expansion and maturation varies between neighbouring individuals and all stages can be observed at the same time. We used analyses of soluble carbohydrate carbon compounds, soluble non-protein nitrogen compounds, stable isotope signatures (δ13C, δ15N) and parameters of fluorescence of chlorophyll a for describing metabolic relations and photosynthetic behaviour and to deduce possible variations in ecophysiological strategies in response to site conditions. The phenological plasticity is described in relation to predominant metabolite levels in leaves, roots, xylem and phloem, but its ecological advantage—perhaps related to staggered resource acquisition and susceptibility to predators—remains an open question. For overall ecophysiological performance among the environmental factors root access to the ground water table appeared to be more essential than significantly different precipitation regimes, as plants in the intermediate restinga appeared to be more stressed than those in the other two open restingas. Shading in the dune forest was also an important environmental constraint.

Herbivory by Leaf-cutting Ants: Nutrient Balance between Harvested and Refuse Material1

From an ecological standpoint, the symbiosis between leaf-cutting ants and their fungus can be described as an herbivore feeding on plant material harvested by the ants, metabolized by the fungus, and finally removed by the ants as refuse. Here, we report on a nutrient balance (soluble and insoluble carbon and nitrogen compounds) between harvested and refuse material collected from six Acromyrmex lundi nests from a semiarid woodland in Córdoba, Argentina. The nutrient balance was calculated using cellulose as an indicator. Harvested material had low protein (10%) and high fiber content (57%). Refuse material was rich in fiber (53%), total nitrogen (2%), and ash content (28%). Balance was negative for soluble carbon and phenols. Soluble fibers, lignin, and true protein remained unchanged. Surprisingly, crude protein and all soluble nitrogen fractions had a positive balance, suggesting additional nitrogen sources besides plant material. Phenol utilization by the leaf-cutting ant fungus suggests that phenols are not harmful to the fungus. Inability to metabolize insoluble carbon compounds and a net nitrogen gain in the refuse material were peculiar and interesting features of the ant–fungus system.

Changes in soluble nitrogenous compounds, caseins and free amino acids during ripening of artisanal prato cheese; a Brazilian semi-hard cows variety

Proteolytic changes, during ripening (1–60 days) of 12 batches of artisanal Prato cheese, a Brazilian semihard cows’milk variety, were evaluated by determining the soluble nitrogenous compounds, caseins and their degradation products and free amino acids. Levels of pH 4.4-soluble nitrogen (pH 4.4-SN) and 12% TCA-soluble N, expressed as% TN, at the end of ripening were 21.4 and 12.5, respectively.% Aminoacid nitrogen/TN increased significantly ( P<0.05) during ripening to final values of 4.32. The degradation patterns of α s1- and β-caseins were similar in all cheese batches and α s1-casein was hydrolysed more extensively than β-casein during ripening. The total content of free amino acids increased aproximately 8 times throughout ripening with average final values of 2454 mg/100 g total solids. γ-Amino butyric acid, leucine, lysine, glutamic acid, tryptophan and phenylalanine were the most abundant free amino acids in all batches studied, representing of 62% of total free amino acids.

Influence of starter and adjunct lactobacilli culture on ripening of miniature washed-curd cheeses

Ten strains of Lactobacillus were tested as adjunct cultures in combination with two different Lactocococcus lactis starters in miniature washed-curd cheeses manufactured under controlled bacteriological conditions. Growth of lactobacilli seemed to depend on the strain used, but was not influenced by the starter strain (either L. lactis subsp. lactis lL416 or L. lactis subsp. cremoris AM2). Lactococcal counts in miniature cheeses with AM2 starter and added lactobacilli were higher than in control cheeses without lactobacilli. Consistently good survival (~100% after four weeks) was observed for IL416, regardless of the presence of adjunct culture). In contrast, AM2 starter cell viability decreased slowly over the same time period. Gross composition and protein analyses were performed on the miniature cheeses. Our results indicate that production of soluble nitrogenous compounds was influenced by the lactobacilli adjunct, and depended on the starter strain. We conclude that the use of different combinations of starter and adjunct cultures can result in marked differences in bacterial populations and product properties. Such studies may be used to choose the combination of strains necessary to obtain a product with particular properties.

The influence of starter and adjunct lactobacilli culture on the ripening of washed curd cheeses

Ten strains of lactobacillus from the CNRZ collection were tested as adjunct culture in miniature washed curd cheeses manufactured under controlled bacteriological conditions with two different starters, Lactococcus lactis subsp. lactis IL 416 and Lactococcus lactis subsp. cremoris AM2. Lactobacilli growth seemed to be dependent on the Lactobacillus strain but was not influenced by the starter strain or counts. Lactococci counts were higher in the miniature cheeses with AM2 starter and added lactobacilli than in the control cheeses without lactobacilli. Gross composition and hydrolysis of s1 casein were similar for miniature cheeses with and without lactobacilli. In the miniature cheeses manufactured with IL416 starter, the lactobacilli adjunct slightly increased the soluble nitrogen content, but that was not verified in the AM2 miniature cheeses. Phosphotungstic acid nitrogen content increased in miniature cheeses manufactured with IL416 when Lactobacillus plantarum 1572 and 1310 adjunct cultures were added. That was also verified for several Lactobacillus strains, specially Lactobacillus casei 1227, for miniature cheeses manufactured with AM2 starter. Free fatty acid content increased in miniature cheeses made with lactobacilli adjuncts 1310, 1308 and 1219 with IL416 starter, and with strains 1218, 1244 and 1308 for miniature cheeses with AM2 starter. These results indicate that production of soluble nitrogen compounds as well as free fatty acid content could be influenced by the lactobacilli adjunct, depending on the starter strain.

Soluble nonprotein nitrogen compounds indicate changes in the nitrogen status of beech seedlings due to climate and thinning

Summary • We assessed the effect of climatic and canopy density changes on the seasonal patterns of total soluble nonprotein N (TSNN) in naturally regenerated beech (Fagus sylvatica) seedlings grown on limestone. • Leaves, roots, wood and phloem exudates from seedlings grown in control and thinned stands on a dry, warm SW-exposed site and a moist, cooler NE-exposed site were examined. The concentrations of amino compounds, ammonium and nitrate, comprising TSNN, were determined in May (new leaf expansion), July (mid-summer) and September (end of the growing season). • In May, Asn was augmented in leaves and roots at the NE site, whereas Arg dominated in leaves and phloem at the SW site. In July, all TSNN compounds declined, independent of site and treatment. In September, TSNN, and particularly Arg, increased in roots, phloem and wood at the SW site, compared with the NE. • TSNN indicates changes in the N status of beech seedlings, due to altered growth conditions. The drier and warmer climate at the SW site, relative to the NE, resulted in earlier N remobilization in spring and storage in autumn. Thinning improved the N status at the NE site, but impaired it at the SW site, by affecting differently the climatic conditions and soil nutrient balance of each site.

Changes in Nitrogen Compounds in Berries of Six Grape Cultivars during Ripening over Two Years

Nitrogen compounds (free amino acids, peptides, and proteins) in the berries (juice, skins, and seeds) of six grape cultivars were studied to determine the amount of protein and changes in protein during ripening. Proteins were extracted totally and effectively from the skin and seeds at pH 12 with water. The amount of protein in juice and skins increased over time during ripening, whereas the amount of protein in seeds changed only slightly. Approximately 63% of total soluble and/or extractable nitrogen compounds in berries were proteins. Free amino acids and peptides comprised approximately 20 and 17% of all nitrogen compounds, respectively. Seeds contained on average approximately 50% of all the nitrogen compounds found in berries, primarily in the form of proteins. Juice and skins both contained approximately 25% of nitrogen compounds, and in juices these were primarily in the form of free amino acids. Proteins from these three tissues were rich in aspartic acid and glutamic acid, and similar amino acid compositions of proteins were observed in two different growing seasons for the same tissue of the same cultivar. Moreover, these compositions did not change appreciably during ripening. Amino acid compositions of proteins from the same tissue of different cultivars were similar. In comparisons of compositions of proteins from the three different tissues, a greater degree of similarity was observed between proteins from the juice and skin than between proteins from the juice and seeds or between proteins from the skin and seeds. Acknowledgments: The authors express their gratitude to Mr. Tohru Hosaka, of the Institute of Enology and Viticulture, Yamanashi University, for his technical assistance.

Proteolytic activity of Penicillium chrysogenum and Debaryomyces hansenii during controlled ripening of pork loins

The role of micro-organisms on the ripening process of dry-cured ham, particularly with respect to proteolysis, is not clear. This is partially due to the lack of an adequate system to study changes on a sterile control meat product for long ripening times. Using a meat system based on sterile pork loins ripened under aseptic conditions for 106 days, the contribution to the proteolysis of two micro-organisms isolated from dry-cured ham has been established. Changes were studied by SDS-PAGE of sarcoplasmic and myofibrillar proteins, capillary zone electrophoresis (CZE) of low ionic strength-soluble nitrogen compounds, and HPLC of free amino acids. Debaryomyces hansenii Dh345 did not show any significant proteolytic activity. However, Penicillium chrysogenum Pg222 showed high proteolytic activity on myofibrillar proteins resulting in an increase in soluble nitrogen compounds. For this, P. chrysogenum Pg222 should be considered to be used as starter culture in meat products made using long ripening times.

Effect of Soluble Nutrient Content in Wood on its Susceptibility to Soft Rot and Bacterial Attack in Ground Test

Summary The objective of the study was to investigate whether soluble sugars and nitrogenous compounds in wood have an impact on susceptibility of wood to decay in ground contact, which is important in the field of test methodology and standardization. Kiln drying of Scots pine planks caused a distinct gradient of low-molecular weight (LMW) sugars and nitrogenous compounds in the 0–2 mm zone at the surface of the timber, whereas the deeper zones had constant and low contents of soluble substances. Strips, containing different content of soluble nutrients, were cut and exposed in two types of soil; the former one being rich in soft rot fungi, the latter one being rich in soft rot fungi and bacteria. The strips rich in nutrients showed an average of 16 % of mass loss whereas samples poorer in nutrients were less affected (8–9 %) after 120 days of exposure in the soil rich in soft rot fungi. A pure culture test with the soft rot fungus Phialophora mutabilis confirmed the above-mentioned observation. The result is in favour of taking samples with approximately equal content of soluble nutrients to decrease the variability of test results, e.g., mass losses. The garden compost, rich in both soft rot fungi and bacteria, caused severe mass loss (40–48 %) of the strips after 120 days of exposure. No difference in the mass losses of the samples was measured. The choice of test soil as well as the nutrient status of the samples can lead to completely different results and, consequently, conclusions.

Metabolic responses of Norway spruce (Picea abies) trees to long-term forest management practices and acute (NH4 )2 SO4 fertilization: transport of soluble non-protein nitrogen compounds in xylem and phloem.

From laboratory experiments with seedlings and young trees of Norway spruce (Picea abies L. Karst.), a cycling pool of soluble non-protein N compounds is thought to be indicative of the N-nutritional status of trees. In order to test whether this assumption can be transferred to mature trees grown in the field, xylem sap and phloem exudate were collected from spruce trees in two remote forest stands: (1) a N-limited stand (Villingen site), and (2) a stand where trees are sufficiently supplied with N from the soil (Schluchsee site). Trees at these sites were c. 80-100 (Villingen site) and c. 40-60 (Schluchsee site) yr old. In addition to untreated control areas, one entire watershed area at both sites was subjected to (NH2 )2 SO4 fertilization to the soil. In the xylem sap of the spruce roots at both sites Gln, Asp and Arg were the dominant total soluble non-protein nitrogen (TSNN) compounds. In the xylem sap of the trunk and the twigs Arg was virtually absent and Gln plus Asp dominated TSNN. On average, TSNN in the xylem sap of trees at the Schluchsee site was 1·5-2-fold higher than those at Villengen. Highest TSNN contents in the xylem sap were found during growth and development of current year tissues, while the lowest TSNN contents were found in summer. At the Villingen site (NH4 )2 SO4 fertilization caused an increase in the Gln content in the xylem sap of all tree sections analysed as well as an increase in the Arg content in the xylem sap of the roots. At the Schluchsee site only a small increase in TSNN contents of the xylem was observed, mostly in the xylem sap of the roots. In phloem exudates TSNN contents were much higher in trees on the Schluchsee than on the Villingen site. The seasonal pattern of TSNN in phloem exudates was similar to the seasonal pattern found in the xylem sap. During spring and early summer Gln was the predominant TSNN compound in phloem exudates, but during late summer and autumn Arg became predominant. At the Villingen site (NH4 )2 SO4 fertilization caused a significant increase in TSNN contents in phloem exudates of twigs and roots, but at Schluchsee an increase in TSNN was found only in phloem exudates of the roots. At both field sites Arg that was not transported to the shoot by xylem transport, was allocated from the leaves to the roots by phloem transport and was cycled within the root system by both xylem and phloem transport. From these results it is calculated that shoot-to-root signalling by long-distance transport of amino compounds can also contribute to the regulation of N-nutrition of mature spruce trees. Apparently, the internal cycling of individual N compounds within spruce trees differs considerably.