Heterotrophic respiration causes seasonal hysteresis in soil respiration in a warm-temperate forest

To assess the effect of changes in organic litter stock on seasonal changes in heterotrophic respiration (R _H), soil respiration (R _S), and total ecosystem respiration (R _E), we measured seasonal changes in leaf litter respiration (R _LL) by the chamber method and estimated the seasonal change in total R _H using the RothC model in a warm-temperate mixed deciduous?Cevergreen forest in Japan. Both R _E and R _S had seasonal hysteresis and were higher in spring than at the same temperature during autumn. Under warm and humid conditions, the rate of decomposition of newly supplied leaf litter in one?year was high (60% loss). Consequently, R _LL and R _H were higher in spring after leaf drop, when more fresh material was available, than in autumn. In this study, 42 and 88% of the difference in R _E and R _S between spring and autumn (soil temperature 16?C18°C) could be accounted for by the difference in R _H, respectively, and 71% of the difference in R _H could be accounted for by the difference in R _LL. This study showed that seasonal changes in heterotrophic respiration (R _LL and R _H) could be a major factor in the seasonal hysteresis of R _E and R _S.     

南北样带温带区栎属树种幼苗功能性状的变异研究

植物功能性状由生境条件和遗传因素共同决定,田间控制实验能够揭示植物功能性状在种内和种间的变异程度.采集南北样带温带区8个地点6种栎属树种的种子,通过田间栽培试验,以均一环境下1年生幼苗为对象,研究比较种内及种间比叶重、单位叶面积光合速率、单位叶重量光合速率、总干物质含量和根冠比5种功能性状的变化差异,并且分析幼苗功能性状与种子性状的关系.结果发现:栎属树种种间幼苗的功能性状变异系数高于种内,并且种内功能性状的差异较小,种间差异性较大,而比叶重和叶片光合速率无论在种间还是种内,其变异率都较小;总干物质量和根冠比与种子质量显著相关,随种子质量增加幼苗的总干物质量和根冠比呈现增加的趋势,比叶重和叶片光合速率与种子质量的相关性较小.     

Decomposition of tree root litter in a climatic transect of coniferous forests in northern Europe: A synthesis

The purpose of this study was to understand the variation in root litter mass‐loss rates in a climatic transect across a large region ranging from the Arctic Circle (66°N) in Scandinavia to Berlin (52°N) in north‐east Germany, dominated by coniferous monocultural forests. To investigate the combined influence of litter quality and climate, data were used from 37 sites and plots at which root litters of three coniferous species (Pinus sylvestris, Pinus contorta and Picea abies) had been incubated. In spite of the considerable climatic differences among sites, there were no strong relationships between any climatic variable and the lst‐yr mass loss (range 17.0–40.9%). For the lst‐yr mass loss, the average annual temperature was the most rate‐regulating factor for all litter combined, with a value for R ² _adj of 0.186. Substrate quality also had an influence. Thus, for the whole region lignin concentration was significant, with a value for R ² _adj of 0.142. For the separated groups of pine and spruce stands the value for r ² increased but the factor average temperature still dominated and for pine the R ² _adj reached a value of 0.346. Over the region N concentration in the fresh pine root litter was significant (R² _adj = 0.232). For the root litter of P. abies the average temperature in July was the strongest rate‐regulating climatic factor, with a value for R ² _adj of 0.381. A combination of temperature in July and the initial P concentration in the litter gave an R ² _adj value of 0.713 for P. abies litter, thus explaining about 71% of the variation.     

Communities of saprobic fungi on leaf litter of <Emphasis Type="Italic">Vismia guianensis</Emphasis> in remnants of the Brazilian Atlantic Forest

We examined the mycobiota associated with Vismia guianensis leaf litter in three Atlantic Forest remnants of Brazil’s semiarid region. Among the study sites, two remnants were protected forest reserves, whereas the third was influenced by major anthropogenic activities. Eighteen litter samples were collected in wet and dry seasons and were processed by particle filtration technique. A total of 4750 fungal isolates of 142 taxa were identified. Species richness was higher in litter samples collected during wet season. Nonmetric multidimensional scaling multivariate analysis showed differences in the composition of fungal communities among the sampling sites and the seasons. Analysis of similarity showed that the differences were statistically significant (R = 0.85; P = 0.0001). Our findings revealed that spatial and temporal heterogeneity, and human activities had significant impacts on the saprobic fungi of V. guianensis leaf litter.     

Seasonal changes in litter fall and its quality from three sub-tropical fruit tree species at Nelspruit, South Africa

Litter fall from upper storey trees in agroforestry systems contributes to nutrient cycling for the benefit of all components of the system besides serving as mulch. This study examined the seasonal changes in the quantity and quality of leaf litter fall from three sub-tropical fruit trees viz: avocado (Persea americana L.), mango (Mangifera indica L.) and litchi (Litchi chinensis L.) which have potential for use in agroforestry. Leaf litter production was estimated using nylon mesh litter traps erected over five randomly selected trees of each species in a completely randomised design. Litter quality was determined by analysing ash content and polyphenol, carbon, cellulose, lignin and nutrient concentrations over a 2?year period (2007?C2008). Total annual leaf litter production during the study period (dry matter basis) was 8.3, 6.3 and 5.6?t?ha^?1?year^?1 for litchi, mango and avocado, respectively. In both years, leaf litter fall was greatest during autumn and lowest during winter in all species. There were no significant differences in S, Ca, Mg and Mn concentrations in the leaf litter, but polyphenol, N, P and K concentrations differed significantly (P?<?0.05) between species. It was concluded that litter quality from all three tree species was low and would require appropriate management to improve its quality.     

Forest composition,leaf litter,and songbird communities in oak- vs. maple-dominated forests in the eastern United States

Within the eastern deciduous forest region, forest composition varies, with some areas dominated by a mix of oaks (Quercus spp.) and other areas dominated by a mix of sugar maple (Acer saccharum) and other tree species. Prescribed fire is being used on an experimental basis to assess its effectiveness in restoring and maintaining oak-dominated forests. Maple-dominated forests are susceptible to invasion by non-native earthworms, such as Lumbricus terrestris, given the palatability of leaf litter and suitable soil conditions, especially in northern parts of the region. What are the implications of this variation on leaf litter availability and habitat for ground-nesting songbirds? We investigated this question by comparing forest composition, leaf litter, and songbird communities in maple-dominated forests in west-central Indiana and oak-dominated forests, recently burned and unburned, in southeastern Ohio. We also assessed abundance of earthworms and decomposition rates of different types of leaves in the maple-dominated forests in Indiana. Leaf litter and ground-nesting bird species were abundant in unburned oak-dominated forests, but were absent or nearly absent in recently burned oak-dominated forests and in maple-dominated forests. The lack of leaf litter and absence of ground-nesting bird species in maple-dominated forests may be due to the combination of abundant non-native earthworms, alkaline and calcium-rich soils, palatable leaves, and rapid leaf litter decomposition rates. Effects of burning on leaf litter and ground-nesting bird species in oak-dominated forests are probably temporary, as long as prescribed fires are not applied on a frequent or widespread basis. Our study is the first one to show a correlation between forest composition, leaf litter availability, earthworm abundance, and songbird populations. Many researchers are investigating effects of non-native earthworm invasions on ecosystem properties in eastern deciduous forests. We recommend that researchers should also monitor songbird populations to assess whether declines in ground-nesting bird populations are occurring in response to these changes.     

黄土高原土石山区土壤密度的坡面变化——以六盘山香水河小流域为例

[目的]土壤密度是最基本的森林土壤水文物理性质参数,为了定量描述土壤密度随坡位的变化和影响因素,研究不同坡面土壤密度的空间异质性。[方法]在宁夏六盘山半湿润区香水河小流域,选择华北落叶松人工林和天然灌丛2个典型坡面,按坡位从上到下设置连续样地。2014年进行了森林土壤调查,在样地内掘土壤剖面,采用环刀法,分层测定土壤密度。[结果]在1 m深土层内,土壤密度(Y,g.cm-3)随土层(X,cm)加深呈线性增大,拟合关系式:华北落叶松坡面为Y1=0.755 5+0.007 7X(R2=0.99),天然灌丛坡面为Y2=0.919 5+0.004 7X(R2=0.98),其原因包括植被根系活动、土壤生物活动、砾石含量等的土层差异;在2个坡面上,0 100 cm土层平均土壤密度均有明显坡位差异,且2个坡面的沿坡整体变化趋势不相同,华北落叶松坡面从坡顶到坡脚是先逐渐增大,后趋于稳定;天然灌丛坡面从坡顶到坡脚是"增大-减小-增大"的趋势,不同土层土壤密度的坡面变化也各不相同。在华北落叶松林坡面引起土壤密度坡位差异的主要原因是海拔,而在天然灌丛坡面是植物生长状况;2个坡面的土壤密度平均值均出现在相对坡长的0.4 0.5处。坡面上各样地的平均土壤密度和坡面平均值的差值(Z,g.cm-3)随相对水平坡长(样地离开坡顶水平距离和整个坡面水平坡长的比)(X,m)变化的回归关系式分别为:华北落叶松坡面Z1=-0.139X2+0.25X-0.080 1(R2=0.93),天然灌丛坡面Z2=0.494 4X3-0.767 2X2+0.340 3X-0.040 5(R2=0.95)。[结论]华北落叶松林坡面和天然灌丛坡面的土壤密度都存在明显的坡位变化,但变化格局和主要影响因素不同。基于土壤密度坡面变化的拟合关系,可实现从特定坡位测定值推算坡面平均值的尺度转换。     

Zur Ökologie der Arthropodenfauna einer Stadtlandschaft und ihrer Umgebung II. Pflanzengallen und Pflanzenminen

The distribution of 17 dominant gall-inducing arthropods and 12 leaf miners on woody plants was analysed in the city of Kiel and surrounding habitats. The number of species and the diversity of the fauna in the two landscapes did not differ very much.Pemphigus bursarius, Schizoneura ulmi undStigmella argentipedella preferred trees in the city. In the city predominated plant parasites that hibernate on their host plant, while species overwintering in the litter on the ground or in the soil were suppressed. Important habitat factors may be mechanical perturbations near the ground (removal of leaf litter, pavement on the ground, trampling, digging of the soil). The number of species declined with decreasing size of the habitat islands (wood — bushes, hedges — individually growing trees or groups of trees on grassland — road trees), the species hibernating in the vegetation layer were favoured.     

Variability in Populus leaf anatomy and morphology in relation to canopy position, biomass production, and varietal taxon

Twelve poplar (Populus) genotypes, belonging to different taxa and to the sections Aigeiros and Tacamahaca, were studied during the third growing season of the second rotation of a high density coppice culture. With the objective to highlight the relationships between leaf traits, biomass production and taxon as well as the influence of canopy position, anatomical and morphological leaf characteristics (i.e. thickness of epidermis, of palisade and spongy parenchyma layers, density and length of stomata, leaf area, specific leaf area (SLA) and nitrogen concentration) were examined for mature leaves from all genotypes and at two canopy positions (upper and lower canopy). Above ground biomass production, anatomical traits, stomatal and morphological leaf characteristics varied significantly among genotypes and between canopy positions. The spongy parenchyma layer was thicker than the palisade parenchyma layer for all genotypes and irrespective of canopy position, except for genotypes belonging to the P. deltoides × P. nigra taxon (section Aigeiros). Leaves at the upper canopy position had higher stomatal density and thicker anatomical layers than leaves at the lower canopy position. Leaf area and nitrogen concentration increased from the bottom to the top of the canopy, while SLA decreased. Positive correlations between biomass production and abaxial stomatal density, as well as between biomass production and nitrogen concentration were found. A principal component analysis (PCA) showed that genotypes belonging to the same taxon had similar anatomical characteristics, and genotypes of the same section also showed common leaf characteristics. However, Wolterson (P. nigra) differed in anatomical leaf characteristics from other genotypes belonging to the same section (section Aigeiros). Hybrids between the two sections (Aigeiros × Tacamahaca) expressed leaf characteristics intermediate between both sections, while their biomass production was low.     

Low light acclimation in five temperate broad-leaved tree species of different successional status: the significance of a shade canopy

?Context

Tree species differ largely in their capability to produce characteristic shade leaves with effective morphological and physiological acclimation to low light.

?Aims

By examining the sun/shade leaf differentiation in leaf morphology, foliar nitrogen and photosynthetic capacity in five temperate tree species of different successional status, we aimed at identifying those leaf traits that determine the development of a typical shade crown with low light-acclimated leaves.

?Methods

Leaf morphology, foliar N content, photosynthetic capacity (V _cmax, J _max and A _max) and leaf dark respiration (R _d) were measured in the canopies of 26 adult trees of Fraxinus, Acer, Carpinus, Tilia and Fagus species.

?Results

Six traits (the sun/shade leaf differentiation in specific leaf area, leaf size, A _max per leaf area or per mass, photosynthetic N use efficiency and R _d) were found to characterise best the degree of low light acclimation in shade leaves. All five species exhibited certain modifications in leaf morphology and/or physiology in response to low light; Fagus sylvatica showed the highest and Fraxinus excelsior the lowest shade leaf acclimation.

?Conclusions

Our results indicate that the five early/mid- to late-successional species have developed species-specific low light acclimation strategies in their shade crowns which differ in terms of the relative importance of leaf morphological and physiological acclimation.     

Interannual variability of net ecosystem production for a broadleaf deciduous forest in Sapporo, northern Japan

To estimate net ecosystem production (NEP), ecosystem respiration (R _E), and gross primary production (GPP), and to elucidate the interannual variability of NEP in a cool temperate broadleaf deciduous forest in Sapporo, northern Japan, we measured net ecosystem exchange (NEE) using an eddy covariance technique with a closed-path infrared gas analyzer from 2000 to 2003. NEP, R _E, and GPP were derived from NEE, and data gaps were filled using empirical regression models with meteorological variables such as photosynthetic active radiation and soil temperature. In general, NEP was positive (CO₂ uptake) from May to September, either positive or negative in October, and negative (CO₂ release) from November to the following April. NEP rapidly increased during leaf expansion in May and reached its maximum in June or July. The four-year averages (±?standard deviation) of annual NEP, GPP, and R _E were 443?±?45, 1,374?±?39, and 931?±?11?g?C?m^?2?year^?1, respectively. The lower annual NEP and GPP in 2000 may have been caused by lower solar radiation in the foliated season. During the foliated season, monthly GPP varied from year to year more than monthly R _E. Variations in the amount of incoming solar radiation may have caused the interannual variations in the monthly GPP. Additionally, in May, the timing of leaf expansion had a large impact on GPP. Variations in GPP affected the interannual variation in NEP at our site. Thus, interannual variation in NEP was affected by the incoming solar radiation and the timing of leaf expansion.     

Natural abundance N in soil and litter across a nitrate-output gradient in New Hampshire

Stable isotopes of nitrogen are potentially a valuable tool for regional assessments of nitrogen saturation because they provide an integrated measure of the past nitrogen cycling history of a site. We measured δ¹⁵N of soil and litter, as well as net nitrification potential, at three sites across a nitrate-loss gradient in the White Mountains, New Hampshire to test the hypotheses: (1) that δ¹⁵N in soil and litter increase across a spatial gradient of nitrate loss; and (2) that δ¹⁵N in soil and litter is elevated when nitrification is elevated. δ¹⁵N was found not to vary significantly among the three sites. Patterns of leaf litter and forest floor δ¹⁵N, however, were strongly influenced by species composition in individual plots. Beech litter had significantly higher δ¹⁵N than yellow birch, sugar maple, and red maple. The conifer-dominated plots had significantly lower δ¹⁵N in both the organic soil horizons and in litter than did the hardwood-dominated plots. When we adjusted for spatial heterogeneity in mineral soil δ¹⁵N values by using an enrichment factor, δ¹⁵N_foliar − δ¹⁵N_Bs, in place of absolute soil δ¹⁵N values, a positive relationship was found with net nitrification for hardwoods. δ¹⁵N may also be a useful tool for evaluating species differences in nitrogen cycling and nitrogen uptake. The distinct pattern we observed of decreasing δ¹⁵N across the continuum from hardwood-dominated to conifer-dominated sites may suggest that local drivers (for example, nitrification rate) regulate the absolute value of foliar δ¹⁵N, while species-driven factors (e.g., timing and type of uptake) control the foliar δ¹⁵N value of one species relative to another in the same plot.     

Cardamom, mandarin and nitrogen-fixing trees in agroforestry systems in India's Himalayan region. I. Litterfall and decomposition

Litterfall and decomposition were studied in agroforestry systems involving large cardamom (Amomum subulatum) and mandarin (Citrus reticulata) in the Sikkim Himalaya, India. There were stands with N₂-fixing trees (Alnus nepalensis over large cardamom, and Albizia stipulata over mandarin agroforestry) or without them (native non-symbiotic mixed tree species) in both systems. The total annual litter (litter + crop residue) production was higher in the Alnus-cardamom than in the forest-cardamom stand and in the mandarin than in the Albizia-mandarin stand. The ratio of litter production to floor litter was higher in the N₂-fixing stands than in the non-N₂-fixing stands, indicating a faster litter turnover in the former. Tree litterfall occurred throughout the year, but with marked peaks during November to April. Total soluble polyphenolics of fresh litter were higher in N₂-fixing species than in mixed tree species and crops. Half-life values for ash-free mass were shortest in the leaves of N₂-fixing species. N loss was higher from N₂-fixing Alnus and Albizia leaves, whereas P loss was faster and nearly equal in Alnus leaf litter and cardamom residue in cardamom, and Albizia leaf litter and crop residue in mandarin agroforestry systems. The P turnover in N₂-fixing Alnus and Albizia twigs was faster than in the twigs of mixed tree species. The N₂-fixing tree species increased the N and P cycling through production of more above-ground litter and influenced greater release of these nutrients.     

Impact of plant species on the formation of carbon and nitrogen stock in soils under semi-desert conditions

The unique forest ecosystems investigated were created on the place of natural steppe biogeocoenoses 60?years ago. The aim of the study was to elucidate the effect of plant species on the formation of organic C and N stocks in soils and to estimate nitrogen availability for artificial wood plantation. For this purpose, 290 soil samples were taken from four forest monocultures (Quercus robur L., Pinus sylvestris L., Cotinus coggygria Scop., and Acer tataricum L.) and from virgin steppe ecosystem. The amounts and stocks of organic C, total and readily nitrified N, and seasonal dynamics of NO₃ ^? and NH₄ ⁺ ions activities were determined. It was shown that the species composition of the stands influenced the stock of organic C and N in soils. The storages of C and total N differed by 74 and 4.4?Mg/ha^?1, respectively, in the litter and upper horizons (0–40-cm layer) in the stands studied. The differences in distribution of stocks of these elements in virgin steppe and artificial forest ecosystems were found. Organic C and N stocks increased 1.6–6.6 times in the forest litter compared to the steppe one, while in 5–40-cm layer, the storages of C and N decreased by 20–35% compared to the virgin soil. The impact of litter on total N content in arid climate was limited in 0–5-cm layer. The deficit of mineral N compounds was observed in autumn in soil with low stock of total N.     

A comparison of decomposition dynamics among green tree leaves,partially decomposed tree leaf litter and their mixture in a warm temperate forest ecosystem

Decomposition dynamics were compared among green tree leaves, partially decomposed tree leaf litter (i.e., decayed tree leaf litter on forest floor) and a mixture of the two in a warm temperate forest ecosystem in central China to test the influence of litter chemical quality on the degree of decomposition. The study was conducted in situ at two contrasting forest sites, an oak forest dominated by Quercus aliena var. acuteserrata Maxim., and a mixed pine and oak forest dominated by Pinus armandii Franch. and Q. aliena var. acuteserrata. We found marked differences in the rate of decomposition among litter types at both forest sites; the litter decomposition constant, k, was about 39 % greater at the oak forest site and more than 70 % greater at the pine-oak forest site, for green leaves than for partially decomposed leaf litter. The decomposition dynamics and temporal changes in litter chemistry of the three litter types also greatly differed between the two forest sites. At both forest sites, the higher rate of decomposition for the green leaves was associated with a higher nitrogen (N) content and lower carbon to N ratio (C/N) and acid-unhydrolyzable residue to N ratio (AUR/N). We did not find any non-additive effects when mixing green leaves and partially decomposed leaf litter. Our findings support the contention that litter chemical quality is one of the most important determinants of litter decomposition in forest ecosystems at the local or regional scale, but the effect of litter chemical quality on decomposition differs between the contrasting forest types and may vary with the stage of decomposition.     

Effects of forest cover types and environmental factors on soil respiration dynamics in a coastal sand dune of subtropical China

Trees on sand dunes are more sensitive to environmental changes because sandy soils have extremely low water holding capacity and nutrient availability. We investigated the dynamics of soil respiration(Rs) for secondary natural Litsea forest and plantations of casuarina,pine, acacia and eucalyptus. Results show that significant diurnal variations of Rsoccurred in autumn for the eucalyptus species and in summer for the pine species, with higher mean soil respiration at night. However, significant seasonal variations of Rswere found in all five forest stands. Rschanged exponentially with soil temperatures at the 10-cm depth; the models explain 43.3–77.0% of Rs variations. Positive relationships between seasonal Rsand soil moisture varied with stands. The correlations were significant only in the secondary forest, and the eucalyptus and pine plantations. The temperature sensitivity parameter(Q10 value) of Rsranged from 1.64 in casuarina plantation to 2.32 the in secondary forest; annual Rswas highest in the secondary forest and lowest in the pine plantation. The results indicate that soil temperatures and moisture are the primary environmental controls of soil respiration and mainly act through a direct influence on roots and microbial activity. Differences in root biomass, quality of litter,and soil properties(pH, total N, available P, and exchangeable Mg) were also significant factors.     

Structure and composition of the seed bank in monospecific and tree species-rich temperate broad-leaved forests

How tree species diversity affects ecosystem functioning is a topic of intensive research. This study compares monospecific and species-rich broad-leaved forests under similar bedrock and climate conditions for the size and composition of their seed bank. We tested the hypotheses that (i) the actual herb-layer vegetation has an only weak influence on the composition of the seed bank, (ii) the species diversity of the seed bank increases with tree-layer diversity, and (iii) tree species forming a more persistent litter layer reduce the number of germinating seeds. The number of seeds and their species composition were investigated in soil cores taken from three soil depths (0–5, 5–10 and 10–20 cm; n = 4, with each 6 sub-samples) in 9 study plots differing in tree species diversity (3 monospecific Fagus plots, 3 plots with Fagus, Fraxinus and Tilia, and 3 plots with Fagus, Fraxinus, Tilia, Carpinus and Acer). Tree species diversity had a much stronger influence on the size and composition of the seed bank than herb-layer diversity or composition, the latter revealing only a low similarity to the corresponding seed bank. The number and species diversity of emerging seedlings decreased significantly with the amount of acidifying Fagus litter, but increased with litter mass of Tilia and other trees with nutrient-rich, rapidly decomposing litter. We conclude that tree species diversity does not influence the seed bank through effects on herb-layer composition, but mostly through differential disturbance histories of the stands and litter quality effects on germination and soil chemistry. From the contrasting effects of Fagus and Tilia leaf litter, it appears that effects of tree species identity are more relevant than influences of tree species diversity itself.     

Phenotypic variation in <Emphasis Type="Italic">Phoebe bournei</Emphasis> populations preserved in the primary distribution area

Phoebe bournei (Hemsl.) Yang is a rare and protected plant in China. This study was conducted to determine the phenotypic variation in this species and to document phenotypic variation within and among populations of P. bournei. Nested analysis of variance, coefficient of variation, multiple comparisons, principal component analysis (PCA) and correlation analysis were used to analyze ten phenotypic traits in ten natural populations of P. bournei from both the northeastern and the primary region of the range of this species. Significant differences among and within populations were observed in leaf and seed phenotypic traits. Variation among populations (34.92%) was greater than that within populations (26.19%). The mean phenotypic differentiation coefficient was 53.77% among populations, indicating that variation among populations comprised the majority of the phenotypic variation of P. bournei. The coefficient of variance (CV) of ten traits varied from 6.44 to 18.45%, with an average of 12.03%. The CV of leaf traits among populations (15.64%) was higher than that of seed traits (8.60%), indicating that seed traits were more stable. The results from CV and PCA indicated that leaf area, leaf length and thousand seed weight were the main factors accounting for the observed phenotypic variations. Significant or highly significant correlations were observed among most leaf and/or in seed phenotypic traits, whereas no significant correlations were observed between phenotypic traits and geographic factors. Based on cluster analysis, the ten populations can be divided into three clusters. These clusters were not a result of geographic distances.     

Prescribed burning and mechanical thinning effects on belowground conditions and soil respiration in a mixed-conifer forest,California

Soil respiration (R_S) is a major carbon pathway from terrestrial ecosystems to the atmosphere and is sensitive to environmental changes. Although commonly used mechanical thinning and prescribed burning can significantly alter the soil environment, the effect of these practices on R_S and on the interactions between R_S and belowground characteristics in managed forests is not sufficiently understood. We: (1) examined the effects of burning and thinning treatments on soil conditions, (2) identified any changes in the effects of soil chemical and physical properties on R_S under burning and thinning treatments, and (3) indirectly estimated the changes in the autotrophic soil respiration (R_A) and heterotrophic soil respiration (R_H) contribution to R_S under burning and thinning treatments. We conducted our study in the Teakettle Experimental Forest where a full factorial design was implemented with three levels of thinning, none (N), understory thinning (U), and overstory thinning (O; September to October 2000 for thin burn combination and June and July 2001 for thin only treatments) and two levels of burning, none (U) and prescribed burning (B; fall of 2001). R_S, soil temperature, soil moisture, litter depth, soil total nitrogen and carbon content, soil pH, root biomass, and root nitrogen (N) concentration were measured between June 15 and July 15, 2002 at each plot. During this period, soil respiration was measured three times at each point and averaged by point. When we assumed the uniform and even contribution of R_A and R_H to R_S in the studied ecosystem without disturbances and a linear relationship of root N content and R_A, we calculated the contributions of R_A to R_S as 22, 45, 53, 48, and 45% in UU, UO, BN, BU, and BO, respectively. The results suggested that after thinning, R_S was controlled more by R_H while after burning R_S was more influenced by R_A. The least amount of R_S variation was explained by studied factors under the most severe treatment (BO treatment). Overall, root biomass, root N concentration, and root N content were significantly (p < 0.01) correlated with soil respiration with correlation coefficients of 0.37, −0.28, and 0.29, respectively. This study contributes to our understanding of how common forestry management practices might affect soil carbon sequestration, as soil respiration is a major component of ecosystem respiration.     

Effects of litter quality and parent material on organic matter characteristics and N-dynamics in Luxembourg beech and hornbeam forests

To test effects of litter quality and soil conditions on N-dynamics, we selected seven forests in Luxembourg dominated by beech (Fagus sylvatica, L.) and hornbeam (Carpinus betulus L.), and located on acid loam, decalcified marl or limestone, and measured organic matter characteristics, microbial C and N and net N-mineralization in a laboratory incubation experiment. Organic layer characteristics were significantly affected by species, with lower litter decay and higher accumulation under the less palatable beech, even on limestone. However, beech and hornbeam did not show any differences in N-cycling at all. Instead of species, N-cycling was affected by site conditions, albeit different than expected. Microbial N generally increased from acid loam to limestone, but acid loam showed higher net N-mineralization, especially in the organic layer. Also, acid loam showed high instead of low efficiency of N-mineralization per unit microbe, in both organic layer and mineral topsoil. In addition, acid loam showed net consumption of DOC instead of release in both soil layers, which suggests that not N, but C was a limiting factor to decomposition. In contrast, limestone showed low net N-mineralization in the organic layer, despite high mass and well-decomposed organic matter, and low efficiency of N-mineralization per unit microbe in both organic layer and mineral topsoil. DOC was net released instead of consumed, which supported that not C, but N was a limiting factor. The general lack of differences in net N-cycling between species, but relatively clear site effects, is discussed in relation to different microbial strategies. Acid soil may have high net N-release despite low biological activity, because N-requirements of fungi are also low, while in calcareous soil, high bacterial N-demand may counteract high gross N-release. Thus, species producing litter that decomposes rapidly may be planted to improve soil conditions and plant biodiversity, but litter quality effects on N-availability may be less important than soil conditions.