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Long-term dynamics of leaf and root decomposition and nitrogen release in a grey alder ( Alnus incana (L.) Moench) and silver birch ( Betula pendula Roth.) stands
Scandinavian Journal of Forest Research
Abstract
The decomposition of the leaf litter, fine roots (d < 2 mm) and coarser roots (2 ≤ d < 5 mm) of grey alder and silver birch, as well as of α-cellulose sheets using the litterbag method was studied in two experimental stands on Podzoluvisol soils in Southern Estonia. For both tree species, the coarser roots decomposed faster than the fine roots, (p < .05), tree species did not affect the decomposition rate of the roots (p > .5). The nitrogen (N) input to soil from aboveground litter was multiple times higher than the N flux from roots. The remaining relative ash-free mass of the leaves of grey alder and silver birch after three and a half years was similar. After 11 years the remaining relative ash-free mass of the fine and coarser roots of grey alder still accounted for around 10% of the initial value. For silver birch the remaining value was around 20% after 9 years. The litterbag method to underestimates in fertile soils the decomposition of organic matter and thus did not reflect the actual dynamics of decomposition.
... These variable effects of water availability may be related to the general environmental context of the studies, including the intensity of water stress and to plant species-specific differences, including root traits such as root diameter and root tissue density. Moreover, there are not enough studies that measured fluxes of nutrients by roots, by combining all three processes in a holistic manner Morozov et al. 2018;Palviainen et al. 2004). More studies manipulating water supply are needed to improve our understanding of the potential effect of lower water availability on fine root dynamics, and how nutrients move between the different pools. ...
... Both trees had similar lignin concentrations. Compared to previous studies with birch, we found similar concentrations for P, higher concentrations for N and K (Morozov et al. 2018), and lower concentrations for K (Palviainen et al. 2004). Pine had similar values for P, Ca, K, Mg compared to two previous studies, that however, were in the same study region Genet et al. 2005). ...
The insurance hypothesis predicts that forests with tree species mixtures may resist better to stressful environmental conditions than forests composed of only one tree species. Most of the currently available literature tested this hypothesis for aboveground productivity and its related response variables, but less is known about belowground processes. In my PhD thesis, I studied the drivers of belowground productivity and decomposition across climatic gradients and how they are affected by tree mixtures. I hypothesized that mixing of tree species with contrasting rooting patterns and fine root morphologies, would result in a release of competitive pressure belowground, and translate into higher fine root standing biomass and increased fine root productivity. Moreover, I hypothesized that roots with contrasting chemical and morphological characteristics in mixed stands would decompose faster, which may be particularly important under nutrient-limited conditions. Under water-limiting conditions, such as during extreme summer drought, I hypothesized overall slower decomposition but an attenuating effect of tree mixtures on decomposition due to improved micro-environmental conditions, in particular for leaves, since roots decompose in a more buffered soil environment. To test these hypotheses I examined the variation in tree root functional traits (across- and within-species), and its consequences for fluxes of C, N and P at the ecosystem scale. I addressed three main objectives and associated research questions to quantify the interactive effect of tree mixtures and climate on: 1) vertical root segregation and fine root standing biomass, 2) fine root dynamics and their associated nutrient fluxes and 3) fine root- and leaf litter decomposition. I could benefit from two different field experiments for my work, one with a 10-year-old tree-plantation experiment with birch and pine close to Bordeaux (ORPHEE experiment), the second along a latitudinal gradient of mature beech forests in the French Alps (BIOPROFOR experiment).I observed that roots from the birch and pine tree-plantation showed similar vertical distribution and similar belowground root standing biomass in tree mixtures compared to monocultures, contrary to my first hypothesis. However, the greater allocation of pine but not of birch to root growth within the top soil horizons under less water-limiting conditions suggests locally favourable conditions that may lead to soil depth-specific asymmetric competition. In the same experiment, fine root production and decomposition were similar in mixtures and in monocultures, in contradiction with my second hypothesis. Moreover, I did not observe any interactive effects of tree mixtures with stand density or water availability. Interestingly though, birch roots, but not pine roots released P during root decomposition, which suggests an important role of birch in the P-cycle and for P nutrition of trees on these P-limited sandy soils. In line with my third hypothesis, I observed a slower decomposition of leaf litter and fine roots in response to reinforced and prolonged summer drought, irrespective of the position along the latitudinal gradient in the Alps. However, this slower decomposition under drought was not attenuated in forest stands with mixed tree species compared to single species stands. Compared to leaf litter, fine roots decomposed slower and released less C. Interestingly, I found a net N release in decomposing fine roots but not in decomposing leaf litter, which suggests a distinct role of fine roots in the N cycle. In conclusion, I found that mixing tree species did not attenuate negative effects of climate change. However, this thesis demonstrates that promoting mixtures can still be beneficial for at least one of the admixed tree species, through species addition (i.e., complementing one tree species with another tree species), as one tree species may facilitate another via belowground fluxes of N and P.
... As noted in [19], in the first year of destruction, more than half the weight and more than 70% of the mass of carbon and lignin of fine (<2 mm in diameter) roots of pine trees are lost. A decrease in the rate of destruction of fine roots of deciduous and coniferous trees in the second year of exposure is also shown in works [30,32]. ...
The impact of industrial logging on the carbon cycle of boreal forests is characterized by significant uncertainties, which is largely due to the lack of information on carbon fluxes (in particular, soil respiration) in felling sites. The aim of study is to assess the effect of clear felling on CO2 emission from the soil surface of a coniferous-deciduous forest on a typical podzolic soil (Albic Retisol). The investigation was executed during the snowless periods (May-October) of 2020–2022 in a coniferous-deciduous forest and its felling site carried out in the winter of 2020. The carbon dioxide emission was measured by a LI COR 8100 gas analyzer. A brief description of the weather conditions during the years of research and the dynamics of soil temperature at a depth of 10 cm is given. A positive, statistically significant relationship between soil respiration and soil temperature at a depth of 10 cm (R2 = 0.17–0.75; p 0.001) was detected for the analyzed objects. The correlation with soil moisture was both positive and negative and statistically insignificant except data obtained in 2022 in the undisturbed control forest. The high values of CO2 flux during the snowless period were observed in July–August and was 3.90–5.62 gC/ m2/ day and 2.3–2.5 gC/m2/day in undisturbed forests and felled areas, respectively. In 2021, the peak of CO2 release shifted to June. Clear felling has a negative effect on the soil respiration of Albic Retisol that decreased by 1.2–1.9 times in the conditions of the middle taiga of the Komi Republic. The most (55–66%) of the C–CO2 efflux during the snowless period was emitted during the summertime, and the vegetation period (May–September) contribution was 84–88%. The obtained data will serve to determine the role of industrial logging in the carbon cycle of taiga forests.
... The release of N can be appreciated in the initial stages of the decomposition process, which probably is due mostly to leaches than to biological factors (Lanuza et al. 2019). Besides, according to Morozov et al. (2019), N retention in leaves in decomposition process, due to the lack of apparent net release, is associated to the low concentration in senescent leaves, high C:N relation and the presence of long-lasting leaves. ...
Litter decomposition and nutrient release are key factors in the nutrient cycling and availability in land uses and sustainable production systems. In three land uses systems (native forest-NF, coffee agroforestry system C-AFS, and pasture monoculture-PM), litter decomposition rate and nutrient release were estimated during 120 days. A total of 216 litterbags were systematically placed with 20 g of litter in dry matter basis each, which were extracted at 8, 23, 35, 50, 91, and 120 days later to estimate remnants dry matter (RDM %). No interaction was detected in litter decomposition rate between land use systems and decomposition time, presenting a different behavior between land uses in time. In contrast, land uses and time statistically affected (p \ 0.01) litter decomposition. The exponential model (RDM = 100.0e (-0.0056t) , SME = 23.5 for NF; RDM = 100.0e (-0.0064t) , SME = 25.5 for C-AFS; and RDM = 100.0e (-0.0457t) , SME = 136.8 for PM) presented the best fit to estimate the relative RDM (%) over time (t in days) in the three land uses. PM presented the greatest turnover rate at 120 days compared to AFS-C and NF (with a RDM of 14, 51 and 52%, respectively). The process of nutrient release was also faster in PM than in the other systems, with potassium as the fastest nutrient. These results suggest that the intervention in land use has an impact on rates of litter decomposition and nutrient, which affects nutrient cycling. The litter decomposition and nutrient release in agroforestry systems with coffee were
... Arrows identifies that differences in chemical element content are significant (p < 0.05) according to Tukey's test and Dunnett's T3 correction phosphorous) during the afforestation of grasslands at a higher rate than in the more fertile Endostagnic Umbrisols. Many other studies have reported the role of grey alder afforestation in soil enrichment with nitrogen (Uri et al. 2014;Innangi et al. 2017;Morozov et al. 2018) and carbon (Uri et al. 2017). The changes in topsoil (0-10 cm) are caused by the accumulation of alder leaf litter and formation of easy decomposable and nitrogen-rich biomass (Innangi et al. 2017). ...
Background
Natural afforestation of former agricultural lands with alder species is common in Europe. Symbiotic nitrogen fixation by actinomycetes associated with alder species has been widely used for improvement of soil properties of abandoned agricultural lands, but relatively little is known of the interactions of these processes with soil type and chemical composition. We conducted a space-for time study with soil sampling under and outside grey alder tree canopies on two different soil groups to explore effects of colonisation of former agricultural lands by alder on soil properties.
Results
The results were analysed using analysis of variance. During the first 25 years after afforestation of former agricultural lands there was a significant increase in content of C tot , N tot , K ⁺ , Fe ³⁺ , Mn ²⁺ and available P in the topsoil (0–10 cm and 11–20 cm) of Dystric Arenosols soils, which are deficient in organic matter. Such trends were not evident in organic matter rich Endostagnic Umbrisols soils, in which exchangeable K ⁺ concentration decreased and exchangeable Fe ³⁺ and Al ³⁺ concentration increased.
Conclusions
The results show that the effects of grey alder on soil chemical properties depend on initial soil properties. The invasion of agricultural land by grey alder leads to spatial variability of soil chemical properties creating a mosaic pattern.
The present work aims to bring together existing knowledge of the complex relationship between birch (Betula spp.) trees and their soil environment. Birches are currently receiving a growing interest due to their increasing prevalence in forests resulting from secondary succession, but also their use in site preparation in afforestation of post-agricultural lands. This paper shows that out understanding of the plant-soil relationship in birch forests is patchy and inconsistent. Perhaps understandably, the habitat requirements, management, growth and biomass production of birches are better understood than their wider role in the ecology and soil development in forest ecosystems. Observations reviewed in this paper paint an incomplete picture, existing data often originate from mixed forests and do not have direct import for newly created birch monocultures. One of the best understood features is the phytoremediation potential of this species. Other aspects, such as its effects on soil organic matter, enzymatic activity, meso- and macro-fauna are still little studied. In conclusion, we show that future research should utilise ad-hoc birch chronosequences generated by the abandonment of agricultural land and focus on uncovering the birch-soil feedbacks in forests dominated by these pioneer species.
Grey alder (Alnus incana) is a highly productive indigenous tree species, potential for short-rotation forestry in the Baltic and Nordic countries. The aim of the study was to investigate the development of a new forest generation, as well as the nitrogen (N) and carbon (C) storages and fluxes in a grey alder regenerating coppice (COP) after clear-cut and in an adjacent unharvested 21-year-old stand (MAT), which had reached its bulk maturity. The regeneration of COP was rapid and 5 years after clear-cut, stem mass was 6.4 t ha⁻¹. The nitrogen demand of the aboveground part of the 5-year-old COP trees was estimated to be roughly half of the corresponding value for MAT, depending mostly on leaf production. The annual N leaching flux in MAT was in the range of 16-29 kg ha⁻¹, the corresponding values for COP were roughly half of that. Net nitrogen mineralization did not differ significantly between MAT (117 kg ha⁻¹) and COP (129 kg ha⁻¹). For the soil respiration study, a 32-year-old grey alder stand growing at a similar site was included; soil respiration was significantly higher in MAT compared to COP in all study years in both studied stands.
Our understanding of fine-root decay processes is derived almost exclusively from litterbag studies. However, preparation of roots for litterbag studies and their subsequent decay within litterbags represent major departures from in situ conditions. We hypothesized that litterbag studies misrepresent fine-root decay and nutrient release rates during decomposition. To test these hypotheses, we developed a new intact-core technique that requires no a priori root processing, retains natural rhizosphere associations, and maintains in situ decay conditions. Using both litterbags and intact cores, we measured annual decay rates and nitrogen release from newly senesced fine roots of silver maple, maize, and winter wheat. After one year, mass loss was 10–23% greater, and nitrogen release was 21–29% higher within intact cores. Differences appeared to result from litterbag-induced
alterations to decomposer dynamics and from unavoidable changes to fine-root size-class composition within litterbags. Our results suggest that fine-root decay and nutrient turnover
occur significantly faster than estimated from litterbag studies. By minimizing disturbances to roots, soil, and rhizosphere associates prior to root decay, the intact-core technique provides an improved alternative for measuring fine-root decomposition.
Decomposition and nutrient release patterns of prunings of three woody agroforestry plant species (Acioa barteri, Gliricidia sepium and Leucaena leucocephala), maize (Zea mays) stover and rice (Oryza sativa) straw, were investigated under field conditions in the humid tropics, using litterbags of three mesh sizes (0.5, 2 and 7 mm) which allowed differential access of soil fauna. The decomposition rate constants ranged from 0.01 to 0.26 week−1, decreasing in the following order; Gliricidia prunings >Leucaena prunings > rice straw > maize stover >Acioa prunings. Negative correlations were observed between decomposition rate constants and C:N ratio (P < 0.004), percent lignin (P < 0.014) and polyphenol content (P < 0.053) of plant residues. A positive correlation was observed between decomposition rate constant and mesh-size of litterbag (P < 0.057). These results indicate that both the chemical composition of plant residues and nature of the decomposer played an important role in plant residue decomposition.Nutrient release differed with quality of plant residues and litterbag mesh-size. Total N, P, Ca and Mg contents of plant residues decreased with time for Gliricidia and Leucaena prunings, maize stover, and rice straw, and increased with time for Acioa prunings. There was some indication of N immobilization in maize stover and rice straw; P immobilization in Leucaena prunings and rice straw; and Ca immobilization in maize stover, rice straw and Gliricidia and Leucaena prunings. Acioa prunings immobilized N, P, Ca and Mg. All plant residues released K rapidly. Nutrient release increased with increasing mesh-size of litterbags, suggesting that soil faunal activities enhanced nutrient mobilization.
With this study we investigated the effective factors on annual amount of total litterfall and needle litterfall in Pinus brutia forests and estimated them with a regression model based on certain stand parameters. We studied 27 permanent plots representing different stand structure and environmental conditions in South-Western Turkey. Litterfall was collected in three month intervals corresponding to each of four seasons for a three-year period.
We found a significant relationship between litterfall and stand properties such as crown closure (%), basal area (m²ha⁻¹), stand stem volume (m³ha⁻¹), above-ground biomass (t ha⁻¹), mean annual volume increment (m³ha⁻¹yr⁻¹) and site index (T= 75). Similar relationships also hold true between litterfall and each of such climatic factors as seasonal mean temperature (°C), relative humidity (%) and temperature/precipitation ratio (dimensionless).
The mean annual litterfall considerably varied depending on stand characteristics and certain environmental factors. Both needle litterfall and total litterfall may be predicted for long term by regression models using certain stand parameters. Models developed for litterfall of P. brutia forests in this study may be used for national C inventory in Turkey.
European beech Fagus sylvatica and Norway spruce Picea abies are economically and ecologically important forest trees in large parts of Europe. Today, the beech forest reaches its northern distribution limit in south-eastern Norway and it is expected to expand northwards due to climate warming. This expansion will likely result in fundamental ecosystem changes. To increase our knowledge about the competitive balance between spruce and beech, we have investigated how beech and spruce litter affect spruce seedling emergence, growth and uptake of C and N. We did this in a seed-sowing experiment that included litter layer removal as well as reciprocal transplantations of litter layers between spruce and beech forests. Our results show that spruce seedling emergence was significantly impaired by both litter layer types, and especially so by the beech litter layer in the beech forest. The low seedling emergence in beech forests is concurrent with their lower light availability.
The effect of forest conservation on the organic carbon (C) stock of temperate forest soils is hardly investigated. Coarse woody debris (CWD) represents an important C reservoir in unmanaged forests and potential source of C input to soils. Here, we compared aboveground CWD and soil C stocks at the stand level of three unmanaged and three adjacent managed forests in different geological and climatic regions of Bavaria, Germany. CWD accumulated over 40–100 years and yielded C stocks of 11 Mg C ha⁻¹ in the unmanaged spruce forest and 23 and 30 Mg C ha⁻¹ in the two unmanaged beech–oak forests. C stocks of the organic layer were smaller in the beech–oak forests (8 and 19 Mg C ha⁻¹) and greater in the spruce forest (36 Mg C ha⁻¹) than the C stock of CWD. Elevated aboveground CWD stocks did not coincide with greater C stocks in the organic layers and the mineral soils of the unmanaged forests. However, radiocarbon signatures of the Oe and Oa horizons differed among unmanaged and managed beech–oak forests. We attributed these differences to partly faster turnover of organic C, stimulated by greater CWD input in the unmanaged forest. Alternatively, the slower turnover of organic C in the managed forests resulted from lower litter quality following thinning or different tree species composition. Radiocarbon signatures of water-extractable dissolved organic carbon (DOC) from the top mineral soils point to CWD as potent DOC source. Our results suggest that 40–100 years of forest protection is too short to generate significant changes in C stocks and radiocarbon signatures of forest soils at the stand level.
Characterization of decomposition dynamics of fine roots is essential for understanding vegetation–soil feedbacks and predicting ecosystem responses to future climate scenarios, given their more rapid turnover rates. Using a branch-order classification, we separated the fine root systems of Larix gmelinii into two classes: first- and second-order roots combined into one (lower-order); third- and fourth-order roots combined into another (higher-order). In a field experiment, we conducted a litterbag study to investigate fine root decomposition and its relationship with root order class and soil depth over 17 months. Despite their lower C:N ratio and smaller diameter, lower-order roots decomposed more slowly compared with higher-order roots over this period. This pattern also seems to hold true at each different depths (10, 20 and 30 cm) in the soil profile. Our data suggest that the slow decomposition rate of lower-order roots may result from their poor carbon quality. Moreover, we found that the decomposition rates of both lower-order and higher-order roots decreased linearly from 10 cm to 30 cm, which implied that a substantially larger fraction of fine root mass would be stabilized as soil organic carbon in the deeper rather than the upper soil layers.
Silver birch (Betula pendula Roth.) is one of the main pioneer tree species occupying large areas of abandoned agricultural lands under natural succession in Estonia. We estimated aboveground biomass (AGB) dynamics during 17 growing seasons, and analysed soil nitrogen (N) and carbon (C) dynamics for 10 year period in a silver birch stand growing on former arable land. Main N fluxes were estimated and nitrogen budget for 10-year-old stand was compiled. The leafless AGB and stem mass of the stand at the age of 17-years were 94 and 76 Mg ha⁻¹ respectively. The current annual increment (CAI) of stemwood fluctuated, peaking at 10 Mg ha⁻¹ yr⁻¹ at the age of 15 years; the mean annual increment (MAI) fluctuated at around 4-5 Mg ha⁻¹. The annual leaf mass of the stand stabilised at around 3 Mg ha⁻¹ yr⁻¹. The stand density decreased from 11600 to 2700 trees ha⁻¹ in the 8- and 17-year-old stand, respectively. The largest fluxes in N budget were net nitrogen mineralization and gaseous N2-N emission. The estimated fluxes of N2O and N2 were 0.12 and 83 kg ha⁻¹ yr⁻¹, respectively; N leaching was negligible. Nitrogen retranslocation from senescing leaves was approximately 45 kg ha⁻¹, N was mainly retranslocated into stembark. The N content in the upper 0-10 cm soil layer increased significantly (145 kg ha⁻¹) from 2004 to 2014; soil C content remained stable. Both the woody biomass dynamics and the N cycling of the stand witness the potential for bioenergetics of such ecosystems. © 2016, Finnish Society of Forest Science. all rights reserved.
A general model is presented in which the dynamics of decomposition in terrestrial ecosystems are determined by a set of hierarchically organized factors which regulate microbial activity at decreasing scales of time and space in the following order: climate - clay mineralogy + nutrient status of soil - quality of decomposing resources - effect of macroorganisms (i.e., roots and invertebrates). At the lower scale of determination, biological systems of regulation based on mutualistic relationships between macro- and microorganisms ultimately determine the rates and pathways of decomposition. Four such systems are defined, i.e., the litter and surface roots system, the rhizosphere, the drilosphere and the termitosphere in which the regulating macroorganisms are respectively litter arthropods and surface roots, live subterranean roots, endogeic earthworms, and termites. In the humid tropics, this general model is often altered because climatic and edaphic constraints are in many cases not important and because high temperature and moisture conditions greatly enhance the activity of mutualistic biological systems of regulation which exert a much stronger control on litter and soil organic matter dynamics. This general hypothesis is considered in the light of available information from tropical rain forests and humid savannas. Theoretical and practical implications regarding the biodiversity issue and management practices are further discussed. It is concluded that biodiversity is probably determined, at least partly, by soil biological processes as a consequence of enhanced mutualistic interactions, which enlarge the resource base available to plants. It is also concluded that any effort to restore or rehabilitate degraded soils in the humid tropics is promised to fail unless optimum levels of root and invertebrate activities are promoted and the resulting regulation effects operate in the four abovedescribed biological systems of regulation. Research required to substantiate and adequately test the present set of concepts and hypotheses are expressed.
The decomposition of Scots pine green needles and brown needle litter was followed. The nitrogen level was initially 1.2% in green and 0.40% in brown needles. The decomposition rate of the nitrogen-rich litter was initially higher than for the nutrient-poor but after three years the accumulated weight loss was similar in both cases. It was found that the decomposition rate of the lignin of the nitrogen-rich litter was significantly lower than that of the nitrogen-poor in the incubation period after 500 d. /// Изучали процессы разложения зеленой хвои шотландской сосны и бурой хвои в подстилке. Содержание азота вначале составляло в зеленой хвое 1,2% и в бурой - 0,40%. Скорость разложения опада, богатого азотом была в начале вьше, чем подстилки, бедной элементами питания; но через З года потеря массы уравнивалась в обоих случаях. Установлено, сто скорость разложения лигнина в опаде, богатом азотом, значительно ниже, чем в бедном опаде в течение инкубационного периода сроком 500 дней.
The National Forest Soil Inventory (NFSI) provides the Greenhouse Gas Reporting in Germany with a quantitative assessment of organic carbon (C) stocks and changes in forest soils. Carbon stocks of the organic layer and the mineral topsoil (30 cm) were estimated on the basis of approx. 1.800 plots sampled from 1987-1992 and re-sampled from 2006-2008 on a nationwide grid of 8 x 8 km. Organic layer C stock estimates were attributed to surveyed forest stands and CORINE land cover data. Mineral soil C stock estimates were linked with the distribution of dominant soil types according to the Soil Map of Germany (1:1,000,000) and subsequently related to the forest area. It appears that the C pool of the organic layer was largely depending on tree species and parent material, while the C pool of the mineral soil varied among soil groups. We identified the organic layer C pool as stable although C was significantly sequestered under coniferous forest at lowland sites. The mineral soils however sequestered 0.41 Mg C ha(-1 ) yr(-1) . Carbon pool changes were supposed to depend on stand age and forest transformation as well as an enhanced biomass input. Carbon stock changes were clearly attributed to parent material and soil groups as sandy soils sequestered higher amounts of C, while clayey and calcareous soils showed small gains and in some cases even losses of soil C. We further showed that the largest part of the overall sample variance was not explained by fine-earth stock variances, rather by the C concentrations variance. The applied uncertainty analyses in this study links the variability of strata with measurement errors. In accordance to other studies for Central Europe, the results showed that the applied method enabled a reliable nationwide quantification of the soil C pool development for a certain period. This article is protected by copyright. All rights reserved.
Afforestation has been proposed as a strategy to mitigate the often high greenhouse gas (GHG) emis-sions from agricultural soils with high organic matter con-tent. However, the carbon dioxide (CO 2) and nitrous ox-ide (N 2 O) fluxes after afforestation can be considerable, de-pending predominantly on site drainage and nutrient avail-ability. Studies on the full GHG budget of afforested or-ganic soils are scarce and hampered by the uncertainties associated with methodology. In this study we determined the GHG budget of a spruce-dominated forest on a drained organic soil with an agricultural history. Two different ap-proaches for determining the net ecosystem CO 2 exchange (NEE) were applied, for the year 2008, one direct (eddy co-variance) and the other indirect (analyzing the different com-ponents of the GHG budget), so that uncertainties in each method could be evaluated. The annual tree production in 2008 was 8.3 ± 3.9 t C ha −1 yr −1 due to the high levels of soil nutrients, the favorable climatic conditions and the fact that the forest was probably in its phase of maximum C assimilation or shortly past it. The N 2 O fluxes were deter-mined by the closed-chamber technique and amounted to 0.9 ± 0.8 t C eq ha −1 yr −1 . According to the direct measure-ments from the eddy covariance technique, the site acts as a minor GHG sink of −1.2 ± 0.8 t C eq ha −1 yr −1 . This con-trasts with the NEE estimate derived from the indirect ap-proach which suggests that the site is a net GHG emitter of 0.6 ± 4.5 t C eq ha −1 yr −1 . Irrespective of the approach ap-plied, the soil CO 2 effluxes counter large amounts of the C sequestration by trees. Due to accumulated uncertainties in-volved in the indirect approach, the direct approach is consid-ered the more reliable tool. As the rate of C sequestration will likely decrease with forest age, the site will probably become a GHG source once again as the trees do not compensate for the soil C and N losses. Also forests in younger age stages have been shown to have lower C assimilation rates; thus, the overall GHG sink potential of this afforested nutrient-rich or-ganic soil is probably limited to the short period of maximum C assimilation.
Background and aims
Root decomposition studies have rarely considered the heterogeneity within a fine-root system. Here, we investigated fine root (< 0.5 and 0.5–2 mm in diameter) decomposition and accompanying nutrient dynamics of two temperate tree species—Betula costata Trautv and Pinus koraiensis Sieb. et Zucc.
Methods
Both litterbag and intact-core techniques were used to examine decomposition dynamic and nutrient release of the two size class roots over a 498-day period. Moreover, we examined differences between the two approaches.
Results
The very fine roots (< 0.5 mm) with an initially lower C:N ratio, decomposed more slowly than 0.5–2 mm roots of both tree species. The differences in mass loss between size classes were smaller when using the intact-core technique compared with litterbag technique. In contrast to root biomass loss, net N release was much higher in the fine roots (< 0.5 mm). All fine roots initially released N (0–75 days), but immobilized N to varying extent in the following days (75–498 days) during decomposition.
Conclusions
Our results suggest that the slow decomposition rate of very fine roots (< 0.5 mm) may be determined by their high concentration of acid-unhydrolyzable structural components. Additionally, the heterogeneity within a bulk fine-root system could lead to differences in their contribution to soil in terms of carbon and nitrogen dynamics.
Background and aims
Roots of the lowest branch orders have the highest mortality rate, and may contribute predominately to plant carbon (C) and nutrient transfer into the soil. Yet patterns and controlling factors of the decomposition of these roots are poorly understood.
Methods
We conducted a two-year field litterbag study on different root orders and leaf litter in four temperate and four subtropical tree species.
Results
Five species showed slower decay rates in lower- (order 1–2) than higher-order (order 3–5) roots, and all species showed slower decay rates in lower-order roots than leaf litter. These patterns were strongly related to higher acid-insoluble fraction in lower- than higher-order roots, and in roots than in leaf litter, but were unrelated to initial N concentration. Litter N was predominantly in recalcitrant forms and limited amount of N was released during the study period;only 12 % of root N and 26 % of leaf litter N was released in 2 years.
Conclusions
We conclude that the slow decomposition of lower-order roots may be a common phenomenon and is mainly driven by their high acid-insoluble fraction. Moreover, litter N, especially root N, is retained during decomposition and may not be available for immediate plant uptake.
In the Northern and Baltic countries, grey alder is a prospective tree species for short-rotation forestry. Hence, knowledge about the functioning of such forest ecosystems is critical in order to manage them in a sustainable and environmentally sound way. The 17-year-long continuous time series study is conducted in a grey alder plantation growing on abandoned agricultural land. The results of above- and below-ground biomass and production of the 17-year-old stand are compared to the earlier published respective data from the same stand at the ages of 5 and 10 years. The objectives of the current study were to assess (1) above-ground biomass (AGB) and production; (2) below-ground biomass: coarse root biomass (CRB), fine root biomass (FRB) and fine root production (FRP); (3) carbon (C) and nitrogen (N) accumulation dynamics in grey alder stand growing on former arable land. The main results of the 17-year-old stand were as follows: AGB 120.8 t ha−1; current annual increment of the stem mass 5.7 t ha year−1; calculated CRB 22.3 t ha−1; FRB 81 ± 10 g m−2; nodule biomass 31 ± 19 g m−2; fine root necromass 11 ± 2 g m−2; FRP 53 g DM m−2 year−1; fine root turnover rate 0.54 year−1; and fine root longevity 1.9 years. FRB was strongly correlated with the stand basal area and stem mass. Fine root efficiency was the highest at the age of 10 years; at the age of 17 years, it had slightly reduced. Grey alder stand significantly increased N and Corg content in topsoil. The role of fine roots for the sequestration of C is quite modest compared to leaf litter C flux.
The effect of limited nitrogen (N) or water availability on fine root growth and turnover was examined in two deciduous species,
Alnus incana L. and Salix viminalis L., grown under three different regimes: (i) supply of N and water in amounts which would not hamper growth, (ii) limited
N supply and (iii) limited water supply. Plants were grown outdoors during three seasons in covered and buried lysimeters
placed in a stand structure and filled with quartz sand. Computer-controlled irrigation and fertilization were supplied through
drip tubes. Production and turnover of fine roots were estimated by combining minirhizotron observations and core sampling,
or by sequential core sampling. Annual turnover rates of fine roots <1 mm (5–6 year−1) and 1–2 mm (0.9–2.8 year−1) were not affected by changes in N or water availability. Fine root production (<1 mm) differed between Alnus and Salix, and between treatments in Salix; i.e., absolute length and biomass production increased in the order: water limited < unlimited < N limited. Few treatment
effects were detected for fine roots 1–2 mm. Proportionally more C was allocated to fine roots (≤2 mm) in N or water-limited
Salix; 2.7 and 2.3 times the allocation to fine roots in the unlimited regime, respectively. Estimated input to soil organic carbon
increased by ca. 20% at N limitation in Salix. However, future studies on fine root decomposition under various environmental conditions are required. Fine root growth
responses to N or water limitation were less pronounced in Alnus, thus indicating species differences caused by N-fixing capacity and slower initial growth in Alnus, or higher fine root plasticity in Salix. A similar seasonal growth pattern across species and treatments suggested the influence of outer stimuli, such as temperature
and light.
Habitat features and macroinvertebrate communities were surveyed in 66 predominantly upland streams throughout Wales and Scotland to assess the efficacy of riparian management (as buffer strips) in protecting stream resources during commercial forestry. Marginal habitat characteristics differed between streams with different riparian management. Streams with "harder' margins occurred where the banks were covered with either conifers or broadleaves. Streams with "softer' margins occurred in seminatural moorland, and where a buffer strip of moorland vegetation had been retained along the stream at the planting stage. Streams in conifer forest in which a riparian buffer strip had been cleared retrospectively were intermediate. For any given pH, aluminium concentrations were significantly higher in streams draining conifer catchments than in streams draining whole catchments of moorland or deciduous woodland. The taxon richnesses of Ephemeroptera, Plecoptera, Trichoptera and all taxa combined, in both riffles and margins, declined significantly with increasing acidity and aluminium concentration. Primary ordination axes form both habitats correlated with taxon richness, and hence also with pH and aluminium. However, there were significant effects on the ordination scores by riparian management, due mostly to reduced taxon richnesses in conifer sites without buffer strips. -from Authors
Root turnover is fastest in the finest roots of the root system (first root order). Additionally, tissue chemistry varies among even the finest root orders and between white roots and older, pigmented roots. Yet the effects of pigmentation and order on root decomposition have rarely been examined. We separated the first four root orders (all <1 mm) of four temperate tree species into three classes: white first- and second-order roots; pigmented first- and second-order roots; and pigmented third- and fourth-order roots. Roots were enclosed in litterbags and buried under their own and under a common species canopy in a 34-year-old common garden in Poland. When comparing decomposition of different root orders over 36 months, pigmented third- and fourth-order roots with a higher C:N ratio decomposed more rapidly, losing 20-40% of their mass, than pigmented first- and second-order roots, which lost no more than 20%. When comparing decomposition of roots of different levels of pigmentation within the same root order over 14 months, pigmented (older) first- and secondorder roots lost ∼10% of their mass, while white (younger) first- and second-order roots lost ∼30%. In contrast to root mass loss, root N content declined more rapidly in the first- and second-order roots than in third- and fourth-order roots. In higher-order roots, N increased in the first 10 months from ∼110% to nearly 150% of initial N content, depending on species; by the end of the study N content had returned to initial levels. These findings suggest that, in plant communities where root mortality is primarily of pigmented first- and second-order roots, microbial decomposition may be slower than estimates derived from bulk fine-root litterbag experiments, which typically contain at least four root orders. Thus, a more mechanistic understanding of root decomposition and its contribution to ecosystem carbon and nutrient dynamics requires a fundamental shift in experimental methods that stratifies root samples for decomposition along more functionally based criteria such as root order and pigmentation, which parallel the markedly different longevities of these different root classes.
In northern coniferous forests nutrient release from litter occurs primarily in late stages of decomposition when mainly extensively lignified parts remain. An important regulating factor in these stages is the turnover rate of lignin and related compounds. Two factors which influence the decomposition rate of lignin are 1) nitrogen concentration which retards decomposition and 2) concentration of celluloses which increase the turnover rate. The amount and composition of humus which is formed may be dependent on the initial lignin concentration of the litter, which in its turn varies among species. These results from studies in northern coniferous forests are discussed in an ecosystem context.
Our understanding of fine-root decay processes is derived almost exclusively from litterbag studies. However, preparation of roots for litterbag studies and their sub- sequent decay within litterbags represent major departures from in situ conditions. We hypothesized that litterbag studies misrepresent fine-root decay and nutrient release rates during decomposition. To test these hypotheses we developed a new intact-core technique that requires no a priori root processing, retains natural rhizosphere associations, and main- tains in situ decay conditions. Using both litterbags and intact cores, we measured annual decay rates and nitrogen release from newly senesced fine roots of silver maple, maize, and winter wheat. After one year, mass loss was 10-23% greater, and nitrogen release was 21-29% higher within intact cores. Differences appeared to result from litterbag-induced alterations to decomposer dynamics and from unavoidable changes to fine-root size-class composition within litterbags. Our results suggest that fine-root decay and nutrient turnover occur significantly faster than estimated from litterbag studies. By minimizing disturbances to roots, soil, and rhizosphere associates prior to root decay, the intact-core technique provides an improved alternative for measuring fine-root decomposition.
Decomposition of fine roots (<1 mm in diameter) of the clones of Salix viminalis, S. dasyclados and α-cellulose sheets (50 x 10 x 1 mm) was studied in a 6-years old Salix spp. plantation established on abandoned agricultural land in Estonia. The substrates were incubated in litterbags (mesh size 0.14 mm) in 5-10 cm topsoil, in non-fertilised plots for one year. Changes in the ash-free weight of the fine roots were best described by negative exponential models (S. viminalis R2 = 0.98, S. dasyclados R 2 = 0.96), and by a linear model for α-cellulose (R2 = 0.63). The sheets of α-cellulose decomposed roughly twice as rapidly as the fine roots (S. viminalis k = 0.325, S. dasyclados k = 0.165). The remaining (of the initial) ash-free weights of the fine roots were 73.3±0.8% (mean±SE) and 85.8± 2.2% respectively, and of the α-cellulose 35.9±8.5%, in the end of the one year of decomposition. The amount of acid detergent (AD) lignin in the fine-roots of S. viminalis increased significantly and did not change in S. dasyclados, suggesting higher activity of microbial decomposers in the first substrate. Of the studied quality parameters, the AD lignin was the major factor determining the different rate of decomposition of the fine roots of S. viminalis and S. dasyclados. Nitrogen was recycled in the fine root sub-system in both Salix species. This knowledge can be applied in the management of Salix plantations, aimed at bioenergy production.
It is recognized that human activities, such as fossil fuel burning, land-use change, and forest harvesting at a large scale, have resulted in the increase of greenhouse gases in the atmosphere since the onset of the industrial revolution. The increasing amounts of greenhouse gases, particularly CO2 in the atmosphere, is believed to have induced climate change and global warming. With the ability to remove CO2 from the atmosphere through photosynthesis, forests play a critical role in the carbon cycle and carbon sequestration at both global and local scales. It is necessary to understand the relationship between forest soil carbon dynamics and carbon sequestration capacity, and the impact of forest management practices on soil CO2 efflux for sustainable carbon management in forest ecosystems. This paper reviews a number of current issues related to (1) carbon allocation, (2) soil respiration, and (3) carbon sequestration in the forest ecosystems through forest management strategies. The contribution made by forests and forest management in sequestrating carbon to reduce the CO2 concentration level in the atmosphere is now well recognized. The overall carbon cycle, carbon allocation of the above- and belowground compartments of the forests, soil carbon storage and soil respiration in forest ecosystems and impacts of forest management practices on soil respiration are described. The potential influences of forest soils on the buildup of atmospheric carbon are reviewed.
Owing to its ability to produce large amounts of biomass in a short period of time, grey alder can be considered to be a prospective tree species for short-rotation forestry (SRF) in Eastern Europe and the Nordic countries. Relatively scanty data is available about grey alder yield and growth dynamics. Seven yield-tables from six countries and several pub-lished studies have been included in this review. The main aim of the review was to sum up and analyze published data; to evaluate the potential for biomass production and to summarize the existing relevant knowledge for giving recommendations about the optimal principles on managing alder stands. According to different yield-tables, the mean annual increment (MAI) of 20-year-old stands varied from 2.56 m 3 ha À1 to 4.75 m 3 ha À1 (dry matter). In favourable conditions, the growth of alder stands can be rapid and biomass production high. The highest woody biomass of annual production reported in literature amounts to 17 t ha À1 y À1 . A rotation length of 15.20 years is recommended by the majority of authors. The rotation period is longer in northern countries (Norway, Finland) than in southern countries. According to yield-tables, it coincides with the start of the decrease in MAI in most cases. Approximately 60 t ha À1 e90 t ha À1 of stemwood can be produced during one rotation. The density of the natural grey alder stand is typically very high. The optimal initial density of grey alder may not exceed 10,000 ha À1 in the case of plantations and the optimal number of trees per hectare before harvesting should range between 3000 ha À1 and 6000 ha À1 .
The dynamics of the above-ground biomass production of a grey alder plantation on abandoned farmland was investigated during 11 years after establishment. In the 12-year-old stand, the total biomass of the above-ground part of the stand was 68.8 t dry matter (DM) ha(-1) and the current annual production (CAP) was 14.0 t DM ha(-1) year(-1). The predicted mean annual increment (MAI) reached is maximum at the age of 16 years, which indicates bulk maturity (the stand age when CAI = MAI) and appropriate rotation time for obtaining maximum biomass production. In the case of short-rotation forestry, initial stand density should not be higher than 6500-6000 trees per hectare. Below-ground biomass accounted for 18 and 16 per cent of total stand biomass at a stand age of 5 and 10 years, respectively. The biomass of the nodules was estimated at 155 +/- 63 kg DM ha(-1) and the biomass of the fine roots was estimated at 870 +/- 130 kg DM ha(-1) in the 10-year-old grey alder stand. Of the fine roots, 80 per cent and almost all nodules were located in the upper 0-20 cm soil layer in both the 5-year-old and the 10-year-old stand. The value of leaf area index increased with stand age, ranging between 1.38 and 5.43 m(2) m(-2) during the development of the stand. Specific leaf area varied in different years from 11.1 to 13.5 m(2) kg(-1).
Tree litter decomposition on disturbed post-mining sites has been mainly studied within successional gradients, whereas almost no results were shown from afforested spoil heaps. Litterfall and its decomposition rate are considered the most important ecological processes for soil restoration during stand development on such initial forest habitats. These processes allow development of a functional ecosystem and productive forest stands. Moreover, the pedogenesis process on such “soilless”’ habitats can be significantly improved and accelerated by tree species selection during afforestation.
The main aim of the study was to determine litter decomposition rates of nine tree species used for afforestation of a lignite mine spoil heap. We assumed that leaf litter decomposition rates would differ among tree species studied and that the site conditions would significantly influence this process.
Our study was conducted on the spoil heap of the lignite open cast mine in Bełchatów, central Poland. We studied leaf litter decomposition of Alnus glutinosa, Betula pendula, Pinus sylvestris, Quercus robur, Q. rubra and Robinia pseudoacacia in pure stands of these species (home stands), and litter decomposition of Acer pseudoplatanus, A. glutinosa, Fagus sylvatica, Prunus serotina, Q. rubra, and R. pseudoacacia in Scots pine stands. We used the litterbag method. The experiments lasted for three years and the samples were collected every three months.
Leaf litter decomposition calculated for home stands after three years of decomposition was 94.4% of the initial leaf mass for A. glutinosa, 70.9% for R. pseudoacacia, 70.1% for P. sylvestris, 68.3% for B. pendula, 66.9% for Q. rubra and 61.5% for Q. robur. In Scots pine stands, after three years of the experiment, 92.3% of the initial leaf mass decomposed for P. serotina, 85.7% for A. glutinosa, 83.5% for A. pseudoplatanus, 65.2% for R. pseudoacacia, 50.9% for Q. rubra and 40.1% for F. sylvatica. A. glutinosa, R. pseudoacacia and Q. rubra leaves decomposed significantly faster in home stands than in Scots pine stands. Site aspect significantly influenced litter decomposition of the species studied, with higher rates mostly on the western slope.
Our study revealed that the decision on tree species used for afforestation might shorten the period needed for soil restoration and achievement of sustainability of novel ecosystems. Proper selection of main and admixture tree species for afforestation of the post-mining sites might reduce the renewal period of the soilless and newly created habitats, which may provide noticeable ecological and economical effects during stand management.
Litterbag is a standard apparatus used in plant litter decomposition studies. Decreasing bag mesh size hampers litter decomposition due to exclusion of large-bodied consumers and interferences with agents of litter fragmentation. The combined use of coarse and fine mesh bags in field studies is thus relevant for assessing the contribution of macrodetritivores and microbial decomposers to litter decomposition. The present paper examines methods for analyzing the effect of litterbag mesh size on decomposition. I present here a new approach derived from a mathematical analysis of the first-order decay model (i.e. the Olson's model) and use it to reanalyze a large dataset of litter decay rates in two different mesh size litterbags. The presented calculation method for the extent and rate of litter fragmentation overcomes several shortcomings of previously used indices. I also highlight potential pitfalls associated with using the Olson's model to analyze the effect of litterbag mesh size on decomposition.
Estimation of the carbon (C) storages and fluxes in different forest ecosystems is essential for understanding their C sequestration ability. The net ecosystem production (NEP) and the net primary production (NPP) in five downy birch (Betula pubescens) stands, aged between 12 and 78 years, growing on fertile well-drained Histosols, were studied. Drainage of swamp forests is a large-scale manipulation, which causes significant shifts at the ecosystems level, altering C and nutrient cycling a great deal. Young and middle-aged downy birch stands (12–30-year-old) acted as C sink ecosystems, accumulating 1.4–3.0 t C ha⁻¹ yr⁻¹. In the 38-year-old stand NEP was roughly zero; annual C budget was almost in balance. The over-matured downy birch stand (78-year-old) acted as a C source emitting 0.95 t C ha⁻¹ yr⁻¹. Annual woody biomass increment of the stand was the main factor which affected the forest to act as a C accumulating system. Although the highest heterotrophic respiration (Rh) values were measured in the middle-aged stands, mean soil C emission did not differ significantly between the studied stands. Annual total soil respiration (Rs) and Rh ranged from 7.4 to 8.8 t C ha⁻¹ and 4.7 to 6.2 t C ha⁻¹, respectively. Soil temperature appeared to be the dominant driver of the soil CO2 effluxes. Temperature sensitivity (Q10 value) of respiration rates (3.0–5.5), as well as the Rh/Rs (0.6–0.7) varied irrespective of stand age. Both the annual aboveground litter (1.5–1.9 t C ha⁻¹ yr⁻¹) and fine root litter (0.9–1.5 t C ha⁻¹ yr⁻¹) input fluxes were quite similar for the studied stands. However, the annual organic C input into the soil via above- and belowground litter was smaller than the annual Rh efflux, indicating that continuous mineralization of the peat layer reduces the soil organic C pool. The main share of the C stock in the drained swamp downy birch stands was soil C; the storage of C accumulated in the woody biomass of the trees accounted for only 5–20% of the total C storage of the ecosystem.
Estimation of the carbon (C) storages and fluxes in different forest ecosystems is essential for understanding their C sequestration ability. Grey alder (Alnus incana (L.) Moench) is a fast growing tree species with a great potential for short-rotation forestry in the Nordic and Baltic countries and its stands are considered C accumulating ecosystems. We hypothesized that grey alder stands growing at fertile sites act as C sinks in the young and middle-age stages, while mature stands become C sources as a consequence of declined net primary production (NPP). Net ecosystem production (NEP) was studied in five grey alder stands aged between 9 and 40 years. It was found that the NEP of the studied grey alder stands of different ages varied from −1.98 to +4.14 t C ha⁻¹ yr⁻¹. The oldest grey alder stand proved to be a weak C source (−0.77 t C ha⁻¹ yr⁻¹). However, also young alder stands regenerated in a clear-cut area may emit C in the earlier stage, owing to previous cutting and decomposition of organic residues matter. In this aspect, the land use history is of great significance.
Biomass from woody crops is regarded as a future major source of renewable energy. Wood production therefore has to be enhanced to meet the energy needs of an increasing population. This can be reached by using fast-growing tree species. Grey alder (Alnus incana (L.) Moench.) is an indigenous and fast-growing species, which is well adapted to the harsh climate of northern Europe, and could complement other biomass-oriented species used today. This study aimed to assess the potential for wood production and carbon (C) sequestration in biomass and soil of grey alder plantations under north European conditions. The estimates were based on literature data on above- and below ground biomass production, including fine roots, biomass allocation patterns and litter decomposition. By applying logistic functions on production figures and adding an estimated breeding response, grey alder would be able to produce on average 6–7 Mg ha−1 yr−1 of above ground woody biomass during a rotation up to 25 years. This would significantly contribute to increased biomass availability in the Nordic and Baltic countries when applied on agricultural land. By assuming that grey alder will mostly be used on areas suitable for the species, e.g. sites with harsh climate or moist conditions, an estimate of 560,000 ha of newly abandoned agricultural land will be available. Thus, afforestation of those areas with grey alder would result in a total annual increase of aboveground woody biomass of 3.7 Tg, corresponding to 69,000 TJ yr−1. Grey alder would also be an efficient C sink when used on newly abandoned agricultural land. Using the same areas as for biomass the annual C sequestration in biomass and soil would reach 2.6 Tg C. These figures show that grey alder has a potential to be a significant contributor for increasing biomass supply and capture C in northern Europe.
Transects were established on two hillslopes and two study nitrogen budgets in two complex riparian buffer zones receiving different nitrogen loading. In the heavily loaded site the average total-N content decreased from 23 mg l-1 to 3.1 mg l-1 in a 40-years-old riparian grey alder forest (80 % removal). At the site with low loading the average removal of total-N was 48 %. In both transects the budget of N fluxes was established. In the older forest it was estimated as high as 321.1 kg ha-1 yr-1, being 285.3 kg ha-1 yr-1 in the younger one. Considering all inputs and outputs, the N removal efficiency in grey alder stands slows down with increase of age. In the same time, immobilization in soil is increasing. This suggests that grey alder buffer communities should be managed by regeneration cutting and tending to keep their nitrogen removal rate high.
Stumps and coarse roots form the largest part of the coarse woody debris in managed boreal forests but their contribution to nutrient cycling and carbon balance of forest ecosystems is poorly understood. Decomposition and nutrient (C, N, P, K, Ca) release from Norway spruce (Picea abies) coarse roots (diameters 5-10 cm and >10 cm) and stumps were studied in southern Finland in a chronosequence of stands clear-cut 0, 5, 10, 20, 30 and 40. years ago. Density, mass and the amount of C decreased significantly faster from stumps than from coarse roots. The average annual decomposition rate constants (k-values) for the whole 40-year study period were 0.040 for stumps, 0.024 for >10 cm diameter roots and 0.034 for 5-10 cm diameter roots. The release of N was extremely slow since stumps, >10 cm roots and 5-10 cm roots still contained 97%, 107% and 96% of the initial amounts of N, respectively, after 40. years of decomposition. The amount of P was significantly higher in 40-year decomposed stumps (115%) than in >10 cm (71%) and 5-10 cm (61%) roots. Stumps, >10 cm roots and 5-10. cm roots lost 79%, 79% and 81% of their initial amount of K, and 51%, 47% and 45% of their initial amount of Ca, respectively, during the 40-year period. The results indicate that coarse roots and stumps are long-term C pools and sources of nutrients for vegetation in boreal forests.
The dynamic changes of root systems were investigated in a 15-20 yr old Scots pine Pinus sylvestris stand at Ivantjärnsheden in Central Sweden. Two independent strata were designated for the purposes of sampling, one of them dominated by clones of Calluna vulgaris and the other by Cladonia lichens. Considerable variations in the fine-root quantity during the season were recorded for P. sylvestris, C. vulgaris and Vaccinium vitis-idaea. The root dynamics of P. sylvestris in the -2 respectively, in the total stand. The cumulative annual total in dead fine roots was 121 ± 20, 25 ± 13 and 104 ± 25 g m-2. Estimates, which are optimal figures derived from different calculation methods, are given ± one standard error. These results suggest a production and supply of dead fine-root material to the soil, considerably higher than that conventionally expected. /// Исследовли динамику изменений корневых систем в 15-20-летнем лесу Pinus sylvestris Ивантерсхеден (Центральная Швеция). 2. независимых участка ис-пользованы для сбора материала: в одном доминировали клоны Calluna vulgaris, в другом - лишайники Cladonia. Установлены существенные различия в количестве тонких корешков в течение сезона для P. sylvestris, C. vulgaris и Vaccinium vitis-idaea. Динамика корней P. sylvestris класса 2 для всего леса. Масса мертвых корней за год составляла 121 ± 20, 25 ± 13 и 104 ± 25 Γ / M2. Оптимальные показатели, измеренные разными методами, дали одну стандартную ошибку. Результаты показали, что продукция и поступление отдельных корешков в почву значительно вьше, чем рпедполагалось ранее.
Decomposition of live fine roots was studied in a mixed deciduous forest in Virginia, a mixed deciduous forest and a Pinus resinosa plantation in Massachusetts and an Acer saccharum-Quercus borealis forest in Wisconsin. Decomposition rates were similar in all forests and roots <0.5 mm diameter lost dry matter more slowly than those 0.5-3.0 mm diameter. Dry matter losses were initially rapid, but after 10-20% of the initial mass was lost the rates slowed significantly. After 4 yr, roots had lost 20-60% of their initial mass. A composite exponential decay model, including a labile and a recalcitrant fraction, described the dry matter losses better than a simple exponential decay model. The low rates of decomposition and N release indicated that fine roots account for a large portion of the organic matter and N in the forest soils.-Authors
The relationships between the nine most common earthworm specieas from Estonia to soil and vegetation factors were analysed by redundancy analysis. Two groups could be identified: one consists of the endogeic species Allolobophora caliginosa, A. chlorotica, A. rosea and Lumbricus rubellus of which A. chlorotica and A. rosea prefer habitats with high phytomass production; the ohter group contains Lumbricus castaneus and Dendrobaena octaedra. In the latter group the earthworm communities are separated mainly by the influence of soil nitrogen and moisture content. Diversity of earthworm communities was low on agriculturally managed land and was positively correlated to total soil nitrogen.
Leaves of various tree and shrub species, treated with X-rays to kill animals, were allowed to decompose (usually for two years) in field conditions in open-ended glass tubes containing soil. Hazel, ash, oak, and birch, were each studied for three two-year periods: 1966-68, 1967-69, 1968-70. Apart from hazel, no litter showed significant within-species differences in weight loss with time. Where the curves of percentage of original weight remaining against time showed no significant differences for the same species in different years, the data were pooled. Throughout, an asymptotic regression fitted the data better than an exponential regression. Each litter showed an initially rapid weight loss for up to 20 days. In some cases, even the asymptotic regression did not fit the data well during this period. Chemical analyses (C, H, N, LOI) suggested that no significant change of composition of the leaves with time could be clearly detected because of the variability of the composition of the litters. However, oak, hazel, elm, and lime showed marked fluctuations in nitrogen content with time. In some cases there were quite large gains in nitrogen. Carbon/nitrogen ratios showed a clear decrease with time. /// Листья различных видов деревьев и кусгарников, обработанные Х-лучами, для уничтожения животных, помещали в полевые условия для разложения на 2 года, в стеклянных трубках с почвой, открытых с обоих концов. Исследованы лещина, ясень, дуб и береза в течение трех двухлетних периодов: 1966-68, 1967-69, 1968-70 гг. За исключением лещины, в остальных видах листвы не зарегистрированы различия в скорости потери веса в пределах одного вида. Там, где кривые процентного отношения веса к исходному с течением времени не показали значительных различий, у одного вида в разные годь, данные обобщены. Во всех случаях асимптотная регрессия подходит болыпе, чем экспоненциальная. У каждого вида листвы вначале зарегистрирована быстрая потеря веса в течение 20 дней. В некоторых случаях даже асимптотная регрессия в этот период не соответствует данным. Химические анализы (C, H, N, LOI) показали, что существенные различия в составе листвы в течение этих периодов не могли быть установлены вследствие изменчивости состава листвы. Однако, у дуба лещины, вяза и липы зарегистрированы существенные временные колебания в содержании азота. В некоторых случаях установлено болышое увеличение содержания азота. Отнощение C/N заметно снижалось со временем.
Processing of leaves of five riparian plant species [sugar maple (Acer saccharum), speckled alder (Alnus rugosa), eastern hemlock (Tsuga canadensis), red-stem dogwood (Cornus sericea) and sweet gale (Myrica gale)] was studied during the summer in a northern Michigan stream. In June 1992, dried green leaves (∼5g) of each species were placed into coarse-mesh bags and tethered in a riffle. Mass loss and macroinvertebrate colonization were measured after 2, 14, 28 and 42 days. In general, decay rates were fast (k = 0.017 - 0.134), with most species losing >80% of mass within 28 days. The order of decomposition (in declining rate) was: maple = dogwood > alder > sweet gale = hemlock. Macroinvertebrate numbers in the leaf packs were highest at 14 days, but densities per unit remaining mass increased steadily during the experiment. Midge larvae (Diptera: Chironomidae) and netspinning caddisflies (Trichoptera: Hydropsychidae) comprised 54% and 44%, respectively, of the macroinvertebrates, which generally lacked typical shredder taxa. Of several measurements of leaf chemistry, toughness and morphology, leaf surface area per unit mass was the best predictor of processing rate. Hemlock and sweet gale may contain secondary compounds that inhibit decomposition. Leaf processing rates were among the highest observed for any North American stream, which may be related to high microbial activity at summer water temperatures, good nutritional status of fresh leaves, and abundant macroinvertebrates. Summer inputs of leaves to woodland streams are transient but possibly important energy resources for some stream organisms.
Despite its importance to energy flow and nutrient cycling the process of fine root decomposition has received comparatively little detailed research. Disruption of the fine root-soil interface during preparation of root litterbags for decomposition studies could affect decay rates and nutrient mobilization in part by altering the community of decay organisms. We compared rates of decomposition and nutrient release from fine roots of pine between litterbags and intact cores and characterized the fungal community in the decomposing roots. Fine root decomposition was about twice as fast overall for intact cores than litterbags, and rapid mobilization of N and P was observed for roots in cores whereas nutrients were immobilized in litterbags. Fungal communities characterized using 454 pyrosequencing were considerably different between decaying roots in intact cores and litterbags. Most interesting, taxa from ectomycorrhizal fungal orders such as Boletales, Thelephorales and Cantharellales appeared to be more common in decaying roots from cores than litterbags. Moreover, the rate of N and P mobilization from decaying fine roots was highly correlated with taxa from two orders of ectomycorrhizal fungi (Thelephorales, Cantharellales). Although we caution that DNA identified from the decaying roots cannot be conclusively ascribed to active fungi, the results provide tentative support for a significant role of ectomycorrhizal fungi in decomposition and nutrient mobilization from fine roots of pine.
Mass loss and changes in chemical composition during the decay of a variety of forest litters decomposing at several very different sites were measured. -from Authors
Litter decomposition was studied in short-rotation forest stands on a low-humified peat bog using the litter-bag technique. Leaf and twig litters, mainly from willows and grey alder, were compared with regard to weight and nutrient losses. The study sites included untreated, limed and limed plus fertilized plots. The application of solid fertilizers, containing mainly phosphorus and potassium, once every second year (F treatment), was compared with daily irrigation-fertilization during the growing seasons. The application of liquid fertilizer (IL treatment) included all essential nutrients in balanced proportions.
Short-rotation energy forestry is one of the potential ways for management of abandoned agricultural areas. It helps sequestrate carbon and mitigate human-induced climate changes. Owing to symbiotic dinitrogen (N2) fixation by actinomycetes and the soil fertilizing capacity and fast biomass growth of grey alders, the latter can be suitable species for short-rotation forestry. In our study of a young grey alder stand (Alnus incana (L.) Moench) on abandoned arable land in Estonia we tested the following hypotheses: (1) afforestation of abandoned agricultural land by grey alder significantly affects the soil nitrogen (N) status already during the first rotation period; (2) input of symbiotic fixation covers an essential part of the plant annual N demand of the stand; (3) despite a considerable N input into the ecosystem of a young alder stand, there will occur no significant environmental hazards (N leaching or N2O emissions). The first two hypotheses can be accepted: there was a significant increase in N and C content in the topsoil (from 0.11 to 0.14%, and from 1.4 to 1.7%, respectively), and N fixation (151.5kgNha−1yr−1) covered about 74% of the annual N demand of the stand. The third hypothesis met support as well: N2O emissions (0.5kgNha−1yr−1) were low, while most of the annual gaseous N losses were in the form of N2 (73.8kgNha−1yr−1). Annual average NO3–N leaching was 15kgNha−1yr−1 but the N that leached from topsoil accumulated in deeper soil layers. The soil acidifying effect of alders was clearly evident; during the 14-year period soil acidity increased 1.3 units in the upper 0–10cm topsoil layer.
The climatic influence on plant litter decomposition has been successfully correlated on a regional level by using estimated actual evapotranspiration (AET) and annual mass loss. This approach was applied to decomposition studies carried out in a transect along Sweden with litter incubated in four different forest types. A unified needle litter was used and among 14 Scots pine sites about 80% of the mass-loss rate could be explained. A simple model was made on the influence of both climate and nutrient concentrations (nitrogen and phosphorus) on mass-loss rate. About 90% of the first-year mass loss could be explained by this approach. As early decomposition stages were studied (<40%) no influence of lignin was observed.
Above- and below-ground net primary production was estimated for 40-year-old Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) stands growing on sites with apparently large differences in productivity potential. Aboveground net production was estimated from direct measurements of tree growth; belowground productivity was derived from data obtained by sorting live and dead roots from soil cores used in combination with measurements of root growth on observation windows.Aboveground net production was 13.7 t•ha−1 on the high productivity site and 7.3 t•ha−1 on the low productivity site. Belowground dry matter production on the high productivity site was 4.1 t•ha−1 compared with 8.1 t•ha−1 for the poorer site. On the more productive site, 8% of total stand dry matter production was in fine roots in contrast to over 36% on the poorer site. The difference in total net production (aboveground plus belowground) between the two sites was small (2.4 t•ha−1). Apparent differences in aboveground productivity may, to a large extent, result from the need for a greater investment in the fine roots on harsher sites.
