Aboveground nutrient cycling and forest development on poor sandy soil

The aboveground nutrient turnover of three ecosystems representing the main stages of heathland forest succession in NW Germany was investigated in a comparative study with regard to nutrient availability of the soil and light availability below the canopy. It was expected that nutrient availability would play a decisive role in forest development on nutrient poor acidic soil. The results show that the input of nutrients into the Calluna heathland is higher than the annual aboveground turnover of N, P, Ca, Mg, and K via litterfall. Compared to the pioneering birch-pine forest, the annual aboveground turnover of nutrients within the Calluna heathland, and therefore the nutrient availability is very low, while the light availability below the canopy is high. The increasing productivity of the growing successional forest is combined with an increasing nutrient turnover, mainly via litter fall. As a result, the increasing nutrient availability favours shade tolerant species with a higher nutrient demand at the late stages of succession. Consequently, the presumed terminal stage of succession, the oak-beech forest, is characterized by low light availability below the canopy and higher nutrient supply according to the resource-ratio hypothesis of Tilman (1985, 1986, 1988).     

Mycofloral succession onPinus densiflora needles on a moder site

Mycofloral succession on decaying pine needles in aPinus densiflora forest on a moder site was investigated in Sugadaira, Nagano Pref., central Japan. Dead needles on the tree, fallen needles obtained from two recognizable sublayers of the L layer and the upper sub-layer of the F₁ layer in the organic horizon were examined for their fungal flora using both washing and surface sterilization techniques. The major interior colonizer in freshly fallen needles varied with the season:Chaetopsina fulva in summer andSelenosporella curvispora in the other seasons.Thysanophora penicillioides was a remarkable external colonizer of freshly fallen needles in summer, while soil fungi were external colonizers of such needles in the other seasons. A possible successional change of major fungi with the needle decay was suggested. The observed seasonal alternation of the species colonizing freshly fallen needles was discussed in relation to climatic conditions. Contributions from Sugadaira Montane Research Center, No. 152.     

森林类型对土壤有机质、微生物生物量及酶活性的影响

以澳大利亚南昆士兰州典型森林类型——湿地松、南洋杉和贝壳杉林为对象,开展土壤可溶性有机碳和氮(SOC和SON)、微生物生物量碳和氮(MBC和MBN),以及土壤酶活性的研究,剖析森林类型对土壤质量的影响.结果表明:不同林型土壤SOC、SON含量分别在552 ～1154 mg·kg-1和20.11～57.32mg·kg-1;MBC、MBN分别在42～149 mg·kg-1和7～35 mg·kg-1.MBC、MBN之间呈显著相关.土壤几丁质酶、酸性磷酸酶、碱性磷酸酶和β-葡萄糖苷酶的活性分别为2.96 ～7.63、16.5 ～29.6、0.79 ～ 3.42和3.71 ～9.93 μg ·g-1·h-1,亮氨酸氨肽酶活性为0.18～0.46 μg·g-1·d-1.不同林型土壤SOC含量,以及土壤几丁质酶和亮氨酸氨肽酶活性为湿地松林、南洋杉林、贝壳杉林依次降低;而SON含量为南洋杉林＞贝壳杉林＞湿地松林,且南洋杉林的SON含量显著(P＜0.05)高于湿地松林;MBC和MBN以及碱性磷酸酶活性为贝壳杉林＞湿地松林＞南洋杉林;酸性磷酸酶和β-葡萄糖苷酶活性为湿地松林＞贝壳杉林＞南洋杉林.在土壤生物代谢因子中,MBC、MBN、SON和亮氨酸氨肽酶对不同森林类型土壤影响较大.     

Effects of N-enriched rock powder on soil chemistry,organic matter formation and plant nutrition in lignite-poor sandy mine spoil in the forest reclamation practice

The effects of a slow-release N-enriched rock powder on soil chemistry, on the development of the soil vegetation (field layer vegetation), on the nutritional status of pine seedlings (Pinus sylvestris L.), and on decomposition rates of cellulose in lignite-poor mine spoils were studied. In the initial phase after afforestation fertilization caused a significant increase in NO₃ ⁻-N concentrations in the soil solution of the top-soil (0–60 cm). Subsequently, NO₃ ⁻-N concentrations of all N fertilized treatments decreased with the exception of the highest N application area (500 kg N ha⁻¹). This decrease of NO₃ ⁻-N concentrations was related to the establishment of a field layer vegetation, which developed according to the amount of N applied. In the above-ground phytomass of the field layer vegetation a maximum N accumulation amount of 22 kg ha⁻¹ was measured. Cellulose decomposition increased with higher N application rates. In the second year after N-fertilization, the pine needles indicated insufficient supply for almost all nutrients except for N. The deficiency symptoms were most pronounced at the plots that had received the highest amounts of nitrogen. This phenomenon appears to be related to the competition by the field layer vegetation. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.     

Carbon and nitrogen cycling during old-field succession: Constraints on plant and microbial biomass

Soil C and N dynamics were studied in a sequence of old fields of increasing age to determine how these biogeochemical cycles change during secondary succession. In addition, three different late-successional forests were studied to represent possible "steady state" conditions. Surface soil samples collected from the fields and forests were analyzed for total C, H₂O-soluble C, total N, potential net N mineralization, potential net nitrification, and microbial biomass. Above-and belowground plant biomass was estimated within each of the old field sites.Temporal changes in soil organic C, total N and total plant biomass were best described by a gamma function [y =at ^b e ^ctd +f] whereas a simple exponential model [y =a(l – e^–bt ) + c] provided the best fit to changes in H₂O-soluble C, C:N ratio, microbial C, and microbial N. Potential N mineralization and nitrification linearly increased with field age; however, rates were variable among the fields. Microbial biomass was highly correlated to soil C and N pools and well correlated to the standing crop of plant biomass. In turn, plant biomass was highly correlated to pools and rates of N cycling.Patterns of C and N cycling within the old field sites were different from those in a northern hardwood forest and a xeric oak forest; however, nutrient dynamics within an oak savanna were similar to those found in a 60-yr old field. Results suggest that patterns in C and N cycling within the old-field chronosequence were predictable and highly correlated to the accrual of plant and microbial biomass.     

Carbon cycling and storage in world forests: biome patterns related to forest age

Forest age, which is affected by stand‐replacing ecosystem disturbances (such as forest fires, harvesting, or insects), plays a distinguishing role in determining the distribution of carbon (C) pools and fluxes in different forested ecosystems. In this synthesis, net primary productivity (NPP), net ecosystem productivity (NEP), and five pools of C (living biomass, coarse woody debris, organic soil horizons, soil, and total ecosystem) are summarized by age class for tropical, temperate, and boreal forest biomes. Estimates of variability in NPP, NEP, and C pools are provided for each biome‐age class combination and the sources of variability are discussed. Aggregated biome‐level estimates of NPP and NEP were higher in intermediate‐aged forests (e.g., 30–120 years), while older forests (e.g., >120 years) were generally less productive. The mean NEP in the youngest forests (0–10 years) was negative (source to the atmosphere) in both boreal and temperate biomes (?0.1 and –1.9 Mg C ha^?1 yr^?1, respectively). Forest age is a highly significant source of variability in NEP at the biome scale; for example, mean temperate forest NEP was ?1.9, 4.5, 2.4, 1.9 and 1.7 Mg C ha^?1 yr^?1 across five age classes (0–10, 11–30, 31–70, 71–120, 121–200 years, respectively). In general, median NPP and NEP are strongly correlated (R²=0.83) across all biomes and age classes, with the exception of the youngest temperate forests. Using the information gained from calculating the summary statistics for NPP and NEP, we calculated heterotrophic soil respiration (R_h) for each age class in each biome. The mean R_h was high in the youngest temperate age class (9.7 Mg C ha^?1 yr^?1) and declined with age, implying that forest ecosystem respiration peaks when forests are young, not old. With notable exceptions, carbon pool sizes increased with age in all biomes, including soil C. Age trends in C cycling and storage are very apparent in all three biomes and it is clear that a better understanding of how forest age and disturbance history interact will greatly improve our fundamental knowledge of the terrestrial C cycle.     

Effects of forest clearing and succession on the carbon and nitrogen content of soils in Puerto Rico and US Virgin Islands

Soil samples from mature and secondary forests and agricultural sites in three subtropical life zones of Puerto Rico and the US Virgin Islands were collected to determine the effects of forest conversion to agriculture and succession on soil organic carbon (C) and nitrogen (N) contents. Site characteristics that may affect soil C and N (slope, elevation, aspect, and texture) were as uniform as possible. Carbon contents (to 50 cm depth or bedrock) of cultivated sites, as a percent of corresponding mature forests, were lower in the wet (44%) and moist (31%) than in the dry (86%) life zones whereas N contents were relatively high regardless of life zone (60–130% of the mature forests). Conversion of forests to pasture resulted in less soil C and N loss than conversion to crops. The time for recovery of soil C and N during succession was approximately the same in all three life zones, about 40–50 yr for C about 15–20 yr for N. However, the rate of recovery of soil C was faster in the wet and moist life zone, whereas N appeared to recover faster in the dry life zone. Evidence for loss of soil C during cultivation and gain during succession to soil depths of 50–100 cm is presented.     

Bacterial diversity in relation to secondary production and succession on surfaces of the kelp Laminaria hyperborea

Kelp forests worldwide are known as hotspots for macroscopic biodiversity and primary production, yet very little is known about the biodiversity and roles of microorganisms in these ecosystems. Secondary production by heterotrophic bacteria associated to kelp is important in the food web as a link between kelp primary production and kelp forest consumers. The aim of this study was to investigate the relationship between bacterial diversity and two important processes in this ecosystem; bacterial secondary production and primary succession on kelp surfaces. To address this, kelp, Laminaria hyperborea, from southwestern Norway was sampled at different geographical locations and during an annual cycle. Pyrosequencing (454-sequencing) of amplicons of the 16S rRNA gene of bacteria was used to study bacterial diversity. Incorporation of tritiated thymidine was used as a measure of bacterial production. Our data show that bacterial diversity (richness and evenness) increases with the age of the kelp surface, which corresponds to the primary succession of its bacterial communities. Higher evenness of bacterial operational taxonomical units (OTUs) is linked to higher bacterial production. Owing to the dominance of a few abundant OTUs, kelp surface biofilm communities may be characterized as low-diversity habitats. This is the first detailed study of kelp-associated bacterial communities using high-throughput sequencing and it extends current knowledge on microbial community assembly and dynamics on living surfaces.     

Modeling changes in soil organic matter in Amazon forest to pasture conversion with the Century model

Land use and land cover changes in the Brazilian Amazon region have major implications for regional and even global carbon cycling. We analyzed the effects of the predominant land use change, conversion of tropical forest to pasture, on total soil C and N, using the Century ecosystem model and data collected from the Nova Vida ranch, Western Brazilian Amazon. We estimated equilibrium organic matter levels, plant productivity and residue carbon inputs under native forest conditions, then simulated deforestation following the slash and burn procedure. Soil organic matter dynamics were simulated for pastures established in 1989, 1987, 1983, 1979, 1972, 1951, and 1911. Using input data from the Nova Vida ranch, the Century model predicted that forest clearance and conversion to pasture would cause an initial decline in soil C and N stocks, followed by a slow rise to levels exceeding those under native forest. Simulated soil total C and N levels (2500 g C m^?2 and 245 g N m^?2 in the 0–20 cm layer) prior to conversion to pasture were close to those measured in the native forest. Simulated above‐ and below‐ground biomass for the forest and pasture were comparable with literature values from this region. The model predicted the long‐term changes in soil C and N under pasture inferred from the pasture chronosequence, but there was considerable variation in soil C stocks for pastures <20 years in age. Differences in soil texture between pastures were relatively small and could not account for much of the variability between different pastures of similar ages, in either the measured or simulated data. It is likely that much of the variability in C stocks between pastures of similar ages is related to initial C stocks immediately following deforestation and that this was the largest source of variability in the chronosequence. Internal C cycling processes in Century were evaluated using measurements of microbial biomass and soil δ¹³C. The relative magnitude and long‐term trend in microbial biomass simulated by the model were consistent with measurements. The close fit of simulated to measured values of δ¹³C over time suggests that the relative loss of forest‐derived C and its replacement by pasture‐derived C was accurately predicted by the model. After 80 years, almost 90% of the organic matter in the top 20 cm was pasture derived. While our analysis represents a single ‘case study’ of pasture conversion, our results suggest that modeling studies in these pasture systems can help to evaluate the magnitude of impacts on C and N cycling, and determine the effect of management strategies on pasture sustainability.     

Influence of cultural practices on edaphic factors related to root disease in Pinus nursery seedlings

Conifer seedlings grown in bare-root nurseries are frequently damaged and destroyed by soil-borne pathogenic fungi that cause root rot. Relationships between nursery cultural practices, soil characteristics, and populations of potential pathogens in the soil were examined in three bare-root tree nurseries in the Midwestern USA. Soil-borne populations of Fusarium spp. and Pythium spp. were enumerated as a function of soil depth in the upper 42 cm; red and white pine seedling root systems were assessed visually for signs of root rot. Soil organic carbon and resistance to cone penetration (as a function of depth) were augmented by saturated hydraulic conductivity (K_sat), water retention characteristic, texture and pH at selected depths. Cone index (CI) provided accurate ‘fingerprints’ of cultural practices in each nursery. A tillage pan due to rotary tillage was detected by CI in the Minnesota and Wisconsin nurseries, but no such tillage pan was indicated in the Michigan nursery, which did not use rotary tillage. Curves of CI also indicated differing maximum depth of tillage disturbance between nurseries; maximum rooting depth based on 3 MPa CI were different among nurseries. Vertical distribution of soil-borne Fusarium spp. reflected the vertical incorporation pattern associated with the type of tillage implement used to incorporate cover crop residue prior to Pinus seedling establishment. Peak numbers of Fusarium spp., from 250 to 950 colony-forming units (cfu g-1 dry soil) were recorded between 12 – 24 cm depth in two nurseries using a moldboard plow for incorporation while steadily decreasing populations, from 1800 to 250 cfu g-1 dry soil, were found from 0 to 15 cm in the third nursery using a disc. Vertical distribution of the Fusarium spp. also correlated with organic carbon levels, which suggested that cover-crop incorporation and conifer rooting had determined the location of soil-borne Fusarium spp. propagules. K_sat suggest that tillage pans caused by rotary tillage may impede drainage during nearly daily irrigation enough to cause physiological stress to the seedlings and predispose them to disease. Low levels of mortality (from < 1% to 5%) were observed in two-year-old Pinus seedlings while disease severity varied by nursery and seedling species. Tillage should be used to control depth placement of biomass residue and pathogenic fungal propagules, and adjusted to prevent tillage pans within the seedling root zone. More studies are needed to determine the impact of these cultural controls on the need and application depth of fumigation for pathogen control. This revised version was published online in August 2006 with corrections to the Cover Date.     

Changes in organic matter composition of forest soil treated with a large amount of urea to promote ammonia fungi and the abilities of these fungi to decompose organic matter

Organic matter composition (lignin, holocellulose, 50% (v/v) methanol extract, water-soluble carbohydrate (WSC) and phenolics (WSP), petroleum ether extract, and ash) of A₀ layer soil treated with 700 g/m² of urea to promote ammonia fungi was investigated in a Japanese red pine (Pinus densiflora) forest. Nine species of fungi were found during the study period of 18 months after the treatment. Of these, seven species belong to the ammonia fungi. WSC content of the treated soil was lower than that of the control. Methanol extract content increased initially after the treatment, then decreased to below the control level. There were no consistent differences in other components between the treated plot and the control. The abilities to decompose cellulose, lignin, chitin, protein and lipid in 18 strains in 10 species of the ammonia fungi were also screened. Cellulose was not lysed byPseudombrophila deerata, Hebeloma spp. andLaccaria bicolor. Strong lignolytic activity was shown byLyophyllum tylicolor, Coprinus echinosporus andP. deerata. Chitin was decomposed byAmblyosporium botrytis, L. tylicolor, C. echinosporus andHebeloma vinosophyllum. All strains possessed proteolytic and lipolytic activities. Supply of glucose to the culture media resulted in weaker enzyme activities except for lignolytic ability.     

Relations between understorey vegetation,site productivity,and environmental factors in Pinus sylvestris L. stands in southern Finland

Relations between understorey vegetation, site productivity, and environmental factors in mature stands of Pinus sylvestris L. in southern Finland were studied using data from 234 sample plots. The (weighted) Pearson product-moment correlation between site index and the first ordination axis of detrended correspondence analysis (DCA) was 0.83. The correlation was clearly better where site index was above 21 m (r=0.83) than where it was less (r=0.33). Partial canonical correspondence analysis (CCA) indicated that the residual compositional variation, not related to site fertility as expressed by site index, can be partly ascribed to high moisture regime with poor drainage (paludification), soil deposit type, soil stoniness, and macroclimate, and in part to unexplained sources. The unique influence of canopy cover on the vegetation composition was non-significant (p<0.05) and that of stand age too small to be detected in the vegetation data. The results support Cajander's forest site type theory according to which there exists a dominant relationship between understorey vegetation and site productivity in boreal forest ecosystems. Cladonia sectio Cladonia lichens, exluding Cladonia uncialis, were treated collectively, and abbreviated as Cladonia spp. The most frequent of these species were C. gracilis, C. cornuta, C. fimbriata, C. deformis, C. cenotea, C. botrytes, C. crispata, C. pyxidata, C. cornuta, and C. furcata.     

树木外生菌根菌与环境因子关系研究进展

土壤、气候和立地因子等环境因子影响树木外生菌根菌的种类及数量。本文通过查阅大量国内外文献 ,综述了外生菌根菌与土壤、季节气候及立地因子等环境因子的相互关系 ,探讨了环境因子对外生菌根菌的影响 ,揭示了外生菌根菌研究中所关注的环境因子问题。同时 ,提出了外生菌根菌与环境因子关系今后研究的主要内容与方向 ,旨在为森林生态系统的可持续经营和退化森林生态系统的恢复、改造等提供科学依据。     

Impact of spruce forest and grass vegetation cover on soil micromorphology and hydraulic properties of organic matter horizon

Two organic matter horizons developed under a spruce forest and grass vegetation were chosen to demonstrate the impact of a different vegetation cover on the micromorphology, porous system and hydraulic properties of surface soils. Micromorphological studies showed that the decomposed organic material in the organic matter horizon under the grass vegetation was more compact compared to the decomposed organic material in the organic matter horizon under the spruce forest. The detected soil porous system in the organic matter horizon under the spruce forest consisted of two clusters of pores with different diameters that were highly connected within and between both clusters. The soil porous system in the organic matter horizon under the grass vegetation consisted of one cluster of pores with the larger diameters and isolated pores with the smaller diameter. The retention ability of the organic matter horizon under the grass vegetation was higher than the retention ability of the organic matter horizon under the spruce forest. Presented at the International Conference on Bioclimatology and Natural Hazards, Poľana nad Detvou, Slovakia, 17–20 September 2007.     

Detecting psychogeriatric problems in primary care: factors related to psychiatric symptoms in older community patients

Objective The aim was to determine the relationship and influence of different variables on the psychiatric symptomatology of older people who reside in the community, as detected by family practitioners.Design A cross-sectional and multi-centre study.Setting Twenty-eight general practices and two psychiatric practices in Huesca, Spain, from 19 primary care health centres.Subjects A sample of 324 patients aged over 65 years, representative of the older people who reside in the community in the province of Huesca.Main outcome measures Symptoms of depression (Yesavage GDS), cognitive impairment (MMSE), anxiety (GADS), psychotic symptoms, obsessive symptoms and hypochondriacal ideas (GMS) were measured by family practitioner and were detected following specific questions from the Geriatric Mental State (GMS-B) examination, following DSM-IV criteria, being defined as 'concern and fear of suffering, or the idea of having a serious disease based on the interpretation of somatic symptoms'. Sociodemographic, physical and somatic, functional and social data were evaluated. Analysis was carried out in three phases: univariate, bivariate and multivariate with logistic regression.Results At the time of the study, 46.1% of the older people studied suffered from some psychiatric symptom; 16.4% had cognitive impairment, 15.7% anxiety, 14.3% depression, 6.1% hallucinations and delusions, 7.2% hypochondriacal ideas and 4.4% obsessive symptoms. Female gender was significantly associated with depression (prevalence ration (PR) 3.3) and anxiety (PR 3.9). Age was a factor associated with cognitive impairment (PR 4.4). Depression was significantly related to severity of the physical illness (PR 61.7 in extremely severe impairment). Isolation (PR 16.3) and being single (PR 13.4) were factors which were strongly associated with anxiety; living in a nursing home was associated with psychotic symptoms (PR 7.6).Conclusions Severity of physical illness, isolation, living in a nursing home and female gender, among others, are related to psychiatric symptoms in community-residing older people identified in primary healthcare centres.     

Effects of length of forest fallow on fertility dynamics in a Mexican ultisol

Changes with time in the fertility of a Mexican ultisol were evaluated from analyses of soil samples from fields representing 50 years of pineapple slash-and-burn agriculture. Sixteen fields with similar soil profile charactersitics representing eight ages of forest fallow were sampled. The fields, within an area of 5 km² of nearly level tropical forest, had been cleared by hand, initially intercropped with corn and manioc, followed with 3 to 4 y of pineapple, and then abandoned. The surface soils contained relatively high levels of C and N (5% and 0.3% respectively), were strongly acid (pH 5 to 5.5), and supplied very low levels of available P and K. Soil contents of both C and N declined rapidly after clearing to levels approximately 20% lower at 10y, then increased steadily during the fallow period to values not different from their initial levels. Since little of the N released was utilized by the low-yielding, P-deficient crops, this loss of C, N and accompanying cations is a most serious consequence of this rotation. Both the exchangeable and reserve K levels of these ultisols are low. Thus, K is identified as second to P as a growth limiting factor and the most difficult fertility management problem.     

Element concentrations in the boreal forest moss Hylocomium splendens: variation related to gradients in vegetation and local environmental factors

This study aims at assessing the suitability of Hylocomium splendens as a biomonitor for heavy metal deposition and contributing to the understanding of mineral nutrient uptake mechanisms in forest floor bryophytes. Concentrations of Ca, Mg, K, Cd, Cu and Pb were determined in Hylocomium splendens segment samples collected at 196 permanent vegetation plots from eleven monitoring areas, where the vegetation-environment relationships had previously been thoroughly studied. Element concentrations in Hylocomium splendens were related to environmentally interpreted vegetational gradients, cover of understorey vascular plants, and local environmental conditions, including element concentrations in humus, soil moisture and tree impact, by means of correlation analyses performed separately for each area. A combined test was performed for each Hylocomium splendens variable over all eleven areas, showing that concentrations of Ca, Cd and Mg in Hylocomium splendens were strongly correlated with the main vegetational gradient and with pH and concentrations of Ca and total N in humus, indicating considerable uptake of nutrients by Hylocomium splendens from water that has been in contact with humus. These relationships were less strong in the climatically most humid areas. Concentrations of all elements were more or less strongly correlated with one or more variables reflecting tree influence (tree density as measured by basal area and two crown influence indices) reflecting that throughfall precipitation, modified by leaching from the canopy, partly accounts for input of elements, especially for K, Cd and Mg. Only concentrations of Pb, Cd and Cu were significantly correlated, negatively, with vascular plant cover, indicating that supply of elements by leaching from understorey vascular plant foliage is negligible. The concentration of Cu in Hylocomium splendens was only weakly correlated, and the concentration of Pb unrelated to vegetational gradients and most environmental conditions. The results indicate that atmospheric deposition accounts for most of the input of Pb, confirming the suitability of Hylocomium splendens as a biomonitor for this element. For elements such as Cd local environmental conditions should be carefully considered, even when data from regional moss surveys are to be interpreted. This revised version was published online in June 2006 with corrections to the Cover Date.     

西双版纳热带次生林林窗干热季气温分布特征的初步分析

利用西双版干热季次生林林窗的温度观测资料,探讨了林窗４方位的气温时空变化特征。由于林窗不同区域所受太阳辐射的影响不同,加之林缘热力效应的综合作用,林窗中存在明显的气温差异,特别是最高气温差异显著;气温最高值和气温日较差最大值不在林窗中央而出现在林窗东侧林缘树冠垂线处。     

Effects of soil organic matter and nitrogen supply on competition between Festuca ovina and Deschampsia flexuosa during inland dune succession

We tested the prediction that the successional replacement of plant species during succession on inland sand dunes results from the effects of an increase in nitrogen mineralization on competitive interactions. The growth and competitive strength of Festuca ovina and Deschampsia flexuosa on soil substrates with different amounts of soil organic matter or nitrogen supply were measured. Small tillers of Festuca ovina and Deschampsia flexuosa were grown in monocultures and 1:1-mixtures on soil columns with undisturbed layers of soil organic matter from different successional age. There was (a) no visible soil organic matter, (b) a thin soil organic layer (0.5 cm) and (c) a thicker soil organic layer (6.0 cm) present on the soil columns. The species were also grown on columns with no visible soil organic matter (bare sand) with two different levels of N fertilization to mimic the increased N mineralization in the older successional stages.In monoculture, Festuca produced more biomass on the substrates with a soil organic layer compared to the unfertilized sand substrate. It also produced more biomass on sand substrates with N fertilization. Deschampsia produced more biomass in treatments with a soil organic layer compared to the bare sand treatments, but did not respond to the ammonium-nitrate addition. In competition, Festuca seemed to be the stronger competitor on the unfertilized sand substrate. Festuca was also the better competitor on the N fertilized sand treatments, while on the treatments with a soil organic layer Deschampsia was the winning species. Our results do not support the hypothesis that an increase in N supply is responsible for the replacement of Festuca by Deschampsia that concur with the accumulation of soil organic matter during succession in inland dunes.     

Growth response of Pinus radiata to multiple applications of nitrogen fertilizer and evaluation of the quantity of added nitrogen remaining in the forest system

Over a period of nine years, 922 kg ha^-1 of N was added in eight applications to a 16 year old P. radiata stand in a low rainfall area in north-east Tasmania, Australia. Fertilizing lifted current annual increment from 8.5 m³ha^-1 for the unfertilized plots, to 31 m³ha^-1. Increased growth was associated with improved health of the trees. Biomass measurements showed that there was a large increase in needle retention as well as needle mass on the fertilized trees. Concentration of N was also higher in fertilized trees. Fertilized plots contained 467 kg ha^-1 more N than unfertilized plots. This represented about 50 percent of the N applied. Most of this extra N was in the forest crop and in the surface 10 cm of the soil. There was no increase in organic carbon in the surface soil with the result that the C/N ratio was reduced from a very high 28 to 17.Despite the high growth rates attained in the N fertilized plots, the failure to increase soil organic matter and the loss from the site of much of the applied N indicated that long term improvement of growth of these low rainfall sites was unlikely. Growth would only be maintained with continued N fertilizer additions.