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The effects of clear-cut on net nitrogen mineralization and nitrogen losses in a grey alder stand
... Generally, availability of N in forest ecosystems is limited and its low level inhibits the growth of trees. Although the total soil N pool can even be as large as 8-9 t ha −1 (Gundersen 1995;Becker et al. 2015), the amount of mineral N, which is available for the uptake by plants annually, forms only a small proportion (0.1-1%) of the total soil N pool (Helmisaari 1995). Available mineral N is produced from organic matter by in situ mineralization (Tate 1995) and net nitrogen mineralization (NNM) is one of the most important fluxes in the N cycle of boreal and temperate forests (Goodale and Aber 2001;Lovett et al. 2002). ...
... The NNM experiment was conducted by using the incubated polyethylene bags technique (Eno 1960), which was used also in our earlier studies (Uri et al. 2003(Uri et al. , 2008Becker et al. 2015, Notes: D 1,3average stand diameter at breast height, Haverage stand height, Gbasal area of stand, Nstand density, Site typeaccording to the Estonian classification (Lõhmus 1984). ...
... The internal diameter of the corer was 1.6 mm larger than its cutting edge to avoid compression and mixing of the soil, which could have affected NNM significantly (Raison et al. 1987;Persson and Wirén 1995;Stenger et al. 1995). Sampling and incubation were carried out at an approximately monthly interval, which is a conventional period allowing to observe changes in concentrations of the mineral forms of N (Adams et al. 1989); it has also been a standard period in previous similar studies (Uri et al. 2011;Becker et al. 2015Becker et al. , 2016Becker et al. , 2018. The samples were gathered by threes into composite samples and were transported to the laboratory on the same day. ...
Thinning changes the functioning of the whole forest ecosystem, including carbon and nitrogen (N) cycling. The input of organic matter and N into soil, as well as soil temperature and moisture regimes change, which may have an impact on the intensity of the net nitrogen mineralization (NNM) process. The main aims of this study were to estimate the effect of thinning on annual NNM as well as N leaching intensity in young silver birch and Scots pine stands. Thinning increased annual NNM flux in the silver birch stand, as well as annual net nitrification, while there was no change in the annual net ammonification flux. The effect of thinning on nitrification was more pronounced in the first post-thinning year. The 13-year dynamics of annual NNM in the birch stand revealed a significant decrease, which may be attributed to the effect of previous land use. The annual NNM flux in the Scots pine stand was practically equal in both plots; thinning did not affect N net mineralization intensity. The effect of thinning on the annual NNM flux was site and tree species specific. Thinning did not induce more intensive N leaching. Moreover, in the birch stand thinning even reduced N leaching.
... Grey alder is a suitable tree species for shortrotation forestry with an optimal rotation length of about 20-25 years (Aosaar et al. 2012;Uri et al. 2014). However, because of its low economic value, only very few publications have considered the impact of management on functioning and development of grey alder stands (Rytter 1995;Daugavietis et al. 2009;Becker et al. 2015). However, in the light of the Paris Agreement (2016), an increasing demand for renewable energy is predictable, which may also lead to more intensive management of grey alder stands for biomass. ...
... The N concentration was determined for the different fractions of the trees (leaves, twigs, branches, stemwood and stembark) and for the Table 2. The soil characteristics of the Voopste and Agali study sites Becker et al. 2015 herbs. For analysing N concentration in trees of MAT, three model trees were sampled in 2012. ...
... Assessment of NNM was based on the comparison of the nitrate and ammonium forms of N in the initial and incubated samples. The experiment of NNM is thoroughly described in Uri et al. (2003bUri et al. ( , 2008 and in Becker et al. (2015Becker et al. ( , 2016Becker et al. ( , 2018. Atmospheric deposition of N for this region has been estimated with the method of polyethylene gutter samplers in 1994-1996 and published by Mander et al. (1997). ...
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.
... Also a change in the leaching of N in the form of ammonium may be increased after drainage (Laine et al. 1995). When NNM studies mostly focus on mineral soils in different forest ecosystems (Connell et al. 1995;Goodale and Aber 2001;Andersson et al. 2002;Lõhmus et al. 2002;Pajuste and Frey 2003;Uri et al. 2008Uri et al. , 2011Becker et al. 2015Becker et al. , 2016, then relevant studies focusing on organic soils are still scarce. ...
... The NNM experiment was performed by using the method with incubated polyethylene bags (Eno 1960;Uri et al. 2008;Becker et al. 2015Becker et al. , 2016. Polyethylene bags ensure permeability to gases (O 2 , CO 2 , N 2 , etc.), but prevent leaching and the input of soluble N, as well as the direct nitrogen uptake by plants. ...
... The dynamics of NNM was studied in the 0-10 cm soil layer at all three study sites from May 2014 to June 2015. At all sites, sampling and incubation were performed at an approximately monthly interval, which has been reported to be an optimal period for changes in the concentration of the mineral forms of N (Adams et al. 1989), and has also been applied in our earlier studies (Uri et al. 2003(Uri et al. , 2008Becker et al. 2015Becker et al. , 2016. At each sampling session, 24 samples for incubation were taken from all study sites by using a cylindrical soil corer (Ø 48 mm). ...
The main aim of the current study was to estimate the annual net nitrogen mineralization (NNM) flux in stands of different tree species growing on drained peatlands, as well as to clarify the effect of tree species, soil properties and litter on annual NNM dynamics. Three study sites were set up in May 2014: a downy birch (Betula pubescens Ehrh.) stand and a Norway spruce (Picea abies (L.) Karst.) stand in Oxalis full-drained swamp (ODS) and a Scots pine (Pinus sylvestris L.) stand in Myrtillus full-drained swamp (MDS). The NNM flux was estimated using the in situ method with incubated polyethylene bags. The highest value of NNM was found in stands that were growing on fertile ODS: 127.5 kg N ha-1 yr-1 and 87.7 kg N ha-1 yr-1 , in the downy birch stand and in the Norway spruce stand, respectively. A significantly lower annual NNM flux (11.8 kg N ha-1 yr-1) occurred in the Scots pine stand growing in MDS. Nitrification was highest at fertile ODS sites and ammonification was the highest at the low fertility MDS site. For all study sites, positive correlation was found between soil temperature and NNM intensity. The difference in annual NNM between the downy birch stand and the Norway spruce stand growing on similar drained fertile peatlands was due to litter quality. The annual N input into the soil through leaf litter was the highest at the downy birch site where also the C/N ratio of litter was the lowest. The second highest N input into the soil was found in the spruce stand and the lowest in the pine stand.
... Infectious disease is therefore an important ecological and evolutionary driver whose action results in different strategies for trees to cope with pathogenic organisms. Resistance of trees is a complex phenomenon involving host pathogen interactions from molecular to ecological levels and relies on species-specific properties and individual characteristics, such as the ability to produce defensive compounds or to gather resources from the environment (Becker et al., 2015). ...
... incana) is widely distributed in the Northern Hemisphere and grows well both on mineral and organic soils (Hytönen and Saarsalmi, 2009;Müller et al., 2016). It can accumulate large amount of atmospheric nitrogen for biomass production with the aid of symbiotic Frankia bacteria in root nodules (Aosaar et al., 2013;Becker et al., 2015;Hytönen and Saarsalmi, 2009;Uri et al., 2002). It can regenerate from seeds but after cutting a new alder generation grows from stumps and root systems, and therefore reforestation actions are not needed in clear-cut areas (Uri et al., 2002). ...
... Unlike birch, grey alder seems to allocate resources for vegetative growth to keep damaged stumps alive after fungal infection. The better ability of grey alder to resist (survive from) C. purpureum infection one growing season after the treatment may relate to its ability to fix atmospheric nitrogen and use reserves support from other parts of the alder clone, i.e., to gather resources to endure pathogen infection (see the present study, Becker et al., 2015;Hamberg and Hantula, 2016;Hamberg et al., 2014;Hytönen and Saarsalmi, 2015;Rytter et al., 1991;Uri et al., 2004). Their ability to fix atmospheric nitrogen also enables grey alder to regenerate vigorously after cutting, forming both stump sprouts and root suckers, and thus increases their tolerance of the pathogen (Hytönen and Saarsalmi, 2015;Paukkonen et al., 1992). ...
We investigated the ability of birch (Betula pendula Roth. and B. pubescens Ehrh.) and grey alder (Alnus incana (L.) Moench) trees of different sizes to recover after cutting and artificial infection with a common decay fungus, Chondrostereum purpureum (Pers. Ex Fr.) Pouzar. In birch, resistance to C. purpureum was initially highest among stumps of 13 cm diameter but by the end of the experiment almost all stumps were dead, whereas in grey alder mortality happened more slowly than in birch and was the same across the size range of stumps. After two growing seasons when almost all the original stumps were dead due to fungal infection, alder root suckers developed around small alder stumps, showing a high level of compensation compared to birch. These results indicate that birch and alder have different strategies for survival after biocontrol treatment.
... The dry mass of different fractions was calculated for each model tree by multiplying the corresponding fresh mass by dry matter content. For estimation of AGB or stem mass, an allometric equation (1) was used. , (1) y -is the dependent variable (AGB, stem mass or the mass of the branches of a tree) D1.3 -is the diameter of the breast height a and b -are parameters ...
... For estimation of AGB or stem mass, an allometric equation (1) was used. , (1) y -is the dependent variable (AGB, stem mass or the mass of the branches of a tree) D1.3 -is the diameter of the breast height a and b -are parameters ...
... ∆W -is the annual dry mass increment of wood (g) W -is the dry mass of wood (g) r -is the radius of the analysed disk (mm) i -is the thickness of an annual ring (mm) For calculation of stem mass production, the relative increment of the wood and bark fractions was assumed to be equal. For the stemwood increment of stand, allometric relationship (1) was found between annual production of stem biomass and tree diameter (D1.3). ...
... The method is widely used and has been described in detail in many earlier studies (Eno, 1960;Adams et al., 1989;Hart et al., 1994; Uri Table 1 Main characteristics of the study areas . , 2008Becker et al., 2015). The thickness of the polyethylene bag film used was 18 lm, which prevented leaching and addition of soluble N as well as N uptake by plants but ensured permeability for gases (O 2 , CO 2 , N 2 , etc.). ...
... The leaching of nitrogen (N), phosphorus (P) and C was estimated with stainless steel plate lysimeters (Roots and Voll, 2011;Uri et al., 2011;Becker et al., 2015). At every study area, 14 plate stainless steel lysimeters (7 for the harvested sites + 7 for the control sites) were installed in the soil to a depth of 40 cm at random points on the diagonal traversing the plot. ...
... Irrespective of the treatment, the highest peak of NNM occurred in Orguse in May, but NNM was also high in June and July, which is in accordance with earlier results (Nadelhoffer et al., 1984;Uri et al., 2003;Becker et al., 2015). The proportion of nitrification was appreciable in both treatments, which is characteristic of fertile soils with a low C:N ratio (Table 4); also soil pH was more favourable for nitrification here, compared to the others areas. ...
Stumps of conifer trees are a prospective source of bioenergy and stump harvesting is a novel practice in forestry management in the Baltic and Nordic countries. However, as stump harvesting may cause possible environmental risks there has emerged a clear need for research focusing on sustainable forest management. Three Norway spruce (Picea abies) clear-cut areas on different soils in Estonia were selected for the present study. We analysed the effect of stump harvesting on net nitrogen mineralization (NNM) and on nutrient leaching. On dry and sandy Endogleyic Arenosol (Oxalis site type), stump harvesting reduced the annul NNM flux significantly; 134 and 202 kg N ha yr À1 at the harvested and at the control site, respectively. In clear-cut area where Endogleyic Cambisol was dominating (Hepatica site type), stump harvesting had no effect on NNM (92 vs 88 kg N ha yr À1). However, in a clear-cut area where the soil type was Endogleyic Albic Podzol (Myrtillus site type), stump harvesting increased the total annual NNM flux: 102 vs 70 kg N ha yr À1 at the harvested and at the control site, respectively. Stump harvesting affected also the proportion of nitrification and ammonification processes in NNM. At the Myrtillys site type stump harvesting increased the annual nitrogen (N) leaching flux. One year after stump harvesting, leaching at the harvested site was 11.7 vs 4.5 kg N ha À1 yr À1 at the control site. In the second year N leaching decreased and the difference levelled off. Increased N leaching was induced by a larger amount of water; average N concentration of the harvested and control sites did not differ. Although at the Oxalis site N leaching was larger at the harvested than at the control site, the total annual leached N flux was small ($2 kg N ha À1). At the fertile Hepatica site type treatment had no impact on N leaching, which was only ca 1 kg N ha À1 yr À1. Phosphorus (P) leaching was very small in all study areas, being below 0.1 kg P ha À1 yr À1. The effect of stump harvesting on annual NNM as well as on N leaching was soil specific and highly variable. Stump harvesting affected also the proportion of the nitrification and ammonification processes in total NNM. Considering the first short-term results obtained from different site types, we can conclude that harvesting of spruce stumps does not induce serious environmental hazards in relation of N cycling.
... That is due to most of N in the soil is locked up in organic forms, while the inorganic forms, such as ammonium (NH 4 + ) and nitrate (NO 3 − ), are the bulk of available N for plant uptake (Li et al., 2019). The in situ mineralization of native organic matter which transforms organic N to inorganic forms (Arslan et al., 2010) produces most of the available N for plant biomass as well as for microbial growth (Becker et al., 2015). In global terrestrial ecosystems, the annual cycle of soil N via ammonification and nitrification was estimated at 1450 Tg ammonium/year and 330 Tg nitrate/year, respectively (Kuypers et al., 2018). ...
... Specifically, five sampling points (one at the center and four at the corners of the plot) were selected in each plot. At each point, two PVC cores (4.6 cm diameter × 15 cm) were inserted into a depth of 10 cm because the top 0-10 cm layer is the most active soil part (Becker et al., 2015). One of PVC cores at each sampling point (initial sample) was sent to the laboratory in an icebox and stored at 4 • C. The other PVC core, covering with permeable plastic film on the top and gauze under the bottom to segregate the water and allow gas movement , was incubated in situ for one month. ...
The dynamic effects of forest regeneration pattern after clear-cutting primary forest on soil N mineralization (N min) have not been well investigated and whether the effects vary with season is unclear in eastern Tibetan Plateau. In this study, we compared soil net N min , i.e. net ammonification rate (net R a) and net nitrification rate (net R n) among Picea asperata-broadleaf mixed forest (natural regeneration after planting P. asperata, MF), natural secondary forest (natural without assisted regeneration, NF) and P. asperata plantation (reforestation after clear-cutting primary forest, PF) from June to November, and measured soil microbial community and enzyme activities. Forest regeneration pattern significantly altered net R a as well as net N min in June and November. Net R a of MF, NF and PF in June was − 0.29, − 0.52 and 0.04 mg kg − 1 d-1 , respectively. NF was likely to have higher net NH 4 + consumption in June presumably by the greater microbial utilization (biomass and enzymes) directly drove by the larger initial NH 4 + concentration. NF had higher net NH 4 + production (0.30 mg kg − 1 d-1) in November than MF (0.15 mg kg − 1 d-1) and PF (0.03 mg kg − 1 d-1). Net R n was insignificantly different among the regenerated forests and ranged between − 0.13 and 0.39 mg kg − 1 d-1 with a unimodal seasonal pattern. Nitrate dominated the inorganic N pool in PF while it was similar to ammonium in MF and NF in the middle of growing season, possibly suggesting an alteration of N preferences among the regenerated forests. Independent edaphic factors (including soil organic matter and available N) had greater explanations of net R a variability (19.0%), while net R n variability was more determined by enzyme activities (21.8%) and microbial community (13.1%). Overall, our results highlighted that the variations in soil net N min among three regenerated forests were dependent on season. Ammonium concentration before the start of growing season might play an important role in soil N dynamics. NF exhibited a larger N demand with regard to net R a , microbial induces and N-acquisition enzymes. These provided essential information for understanding soil N dynamics and for developing management practices of subalpine forests in eastern Tibetan Plateau.
... At the beginning of each incubation period, two PVC cores (5-cm diameter  12-cm height) were drove 10 cm into the soil at the central point of each plot. This soil depth was chosen because the most active part of the soil corresponds to the uppermost 0 to 10-cm layer (Becker et al., 2015). The soil sample in one of the PVC cores was stored in polyethylene bags at 4 C and immediately sent to the laboratory, where it was sieved (< 2-mm mesh) and frozen at À18 C (initial soil sample). ...
Societal Impact Statement
Heathlands are globally important ecosystems that provide key functions and services but are increasingly threatened by land use changes. We investigated how plant diversity and productivity influence nitrogen cycling under different management regimes. Our findings reveal that extensive grazing modulates the relationship between plant diversity and soil nitrogen dynamics, with contrasting effects in grazed versus abandoned sites. Increased plant species diversity and abundance of annual and perennial herbs in grazed sites were associated with enhanced N mineralization rates. These insights highlight the need for adaptive management strategies to address the challenges posed by land use changes and biodiversity loss in heathland ecosystems.
Summary
Abiotic controls on soil N‐transformations in heathlands are well understood; however, the effects of plant species diversity–productivity on N cycling remain unclear, particularly concerning grazing management.
We evaluated the feedbacks among plant species diversity, functional group productivity and soil properties, as well as their relationship with net N mineralization rates, in six heathlands dominated by Calluna vulgaris with differing management history (grazed at low intensity and abandoned).
Our findings revealed a pronounced increase in soil organic matter content with plant diversity in abandoned, species‐poor heathlands compared to the stronger feedback with soil total N in grazed, species‐rich sites, suggesting trade‐offs in the carbon‐to‐nitrogen ratio. Mean net ammonification, nitrification, and mineralization rates showed no significant differences between species‐rich and species‐poor heathlands. However, increased plant species diversity and abundance of productive functional groups in grazed sites were associated with enhanced N mineralization rates. In contrast, high species diversity in abandoned heathlands led to increased woody species productivity with traits related to nutrient conservation, which was linked to slower N mineralization rates.
These findings enhance our understanding of the effects of the diversity‐productivity relationship on nitrogen cycling in heathlands, providing insights for anticipating ecosystem responses to changing management regimes.
... After forest degradation, early successional species invade the habitat and radically alter vegetation and soil physicochemical properties (Lebrija-Trejos, Meave, Poorter, Pérez-García, & Bongers, 2010). Early successional forest ecosystems that grow after forest degradation or stand-replacement are highly valuable, especially in terms of carbon stock by pioneer tree species following ecosystem reconstruction (Becker et al., 2015; Lorenc-Pluci nska, Walentynowicz, & Niewiadomska, 2013;Preem et al., 2012;Swanson et al., 2011). The ability of Alnus trees to fix atmospheric nitrogen through symbiotic association with Frankia enables them to tolerate extremely harsh environmental conditions and accelerate the natural succession. ...
... Between the end of July 2019 and the end of April 2020, measurements of net soil N mineralization were conducted at each sampling point (sampling once every three months) using the in situ incubation method with PVC cores, in accordance with the methodology outlined by Raison et al. [47]. At each sampling point, two PVC cores (6 cm in diameter and 20 cm in height) were inserted to a depth of 10 cm, which was identified as the most active soil layer (0-10 cm) [48]. Soil temperature was measured in situ at a depth of 5 cm using a temperature probe. ...
Soil nitrogen (N) mineralization typically governs the availability and movement of soil N. Understanding how factors, especially functional genes, affect N transformations is essential for the protection and restoration of forest ecosystems. To uncover the underlying mechanisms driving soil N mineralization, this study investigated the effects of edaphic environments, substrates, and soil microbial assemblages on net soil N mineralization in boreal forests. Field studies were conducted in five representative forests: Larix principis-rupprechtii forest (LF), Betula platyphylla forest (BF), mixed forest of Larix principis-rupprechtii and Betula platyphylla (MF), Picea asperata forest (SF), and Pinus sylvestris var. mongolica forest (MPF). Results showed that soil N mineralization rates (Rmin) differed significantly among forests, with the highest rate in BF (p < 0.05). Soil properties and microbial assemblages accounted for over 50% of the variability in N mineralization. This study indicated that soil environmental factors influenced N mineralization through their regulatory impact on microbial assemblages. Compared with microbial community assemblages (α-diversity, Shannon and Richness), functional genes assemblages were the most important indexes to regulate N mineralization. It was thus determined that microbial functional genes controlled N mineralization in boreal forests. This study clarified the mechanisms of N mineralization and provided a mechanistic understanding to enhance biogeochemical models for forecasting soil N availability, alongside aiding species diversity conservation and fragile ecosystem revitalization in boreal forests.
... The majority of published studies quantifying nutrient leaching under N-fixing trees were carried out for alder (Alnus spp.) trees in temperate regions and found that the presence of N-fixing trees generally causes soil acidification and increases leaching of N and cations. However, the extent of this increase depends on stand age, site fertility and soil retention capacity (Becker et al., 2015;Binkley et al., 1992;Uri et al., 2011, Perakis et al., 2013. In forests dominated by N-fixing black locust (Robinia pseudoacacia), soil pH was lower and nutrient leaching to 60 cm depth was higher compared to adjacent temperate pine-oak forests (Montagnini et al., 1991). ...
... Thus, these datasets fail to accurately represent conditions over the entire vegetation cycle, resulting in large uncertainties. Since 1980s, a large number of long-term field N 2 O experiments has been conducted throughout the world, providing sufficient representative data for field data-oriented analysis (27,28). ...
Nitrous oxide (N 2 O) emissions are highly variable due to the complex interaction of climatic and ecological factors. Here, we obtained in-situ annual N 2 O emission flux data from almost 180 peer-papers to evaluate the dominant drivers of N 2 O emissions from forests and unfertilized grasslands at a global scale. The average value of N 2 O emission fluxes from forest (1.389 kg Nha ⁻¹ yr ⁻¹ ) is almost twice as large as that from grassland (0.675 kg Nha ⁻¹ yr ⁻¹ ). Soil texture and climate are the primary drivers of global forest and grassland annual N 2 O emissions. However, the best predictors varied according to land use and region. Soil clay content was the best predictor for N 2 O emissions from forest soils, especially in moist or wet regions, while soil sand content predicted N 2 O emissions from dry or moist grasslands in temperate and tropical regions best. Air temperature was important for N 2 O emission from forest, while precipitation was more efficient in grassland. This study provides an overall understanding of the relationship between natural N 2 O emissions and climatic and environmental variables. Moreover, the identification of principle factors for different regions will reduce the uncertainty range of N 2 O flux estimates, and help to identify region specific climate change mitigation and adaptation strategies.
... Thirdly, soil disturbances brought by replanting seedlings increased substrate availability in the deeper layer which might enhance the denitrification (Zhang et al., 2021a). Furthermore, thinning reduced the absorption of effective N by root systems markedly, which increased labile N pool and reinforced soil nitrification and denitrification ( Fig. 5; Table 3) (Becker et al., 2015;Frazer et al., 1990;Kellman and Kavanaugh, 2008;Yashiro et al., 2008). Noteworthy, in our current research, NO 3 − -N leaching loss occurred during the first year after thinning. ...
Thinning and replanting are effective forest management measures to improve the stand structure and species composition of artificial forests. However, the effects of thinning and replanting on soil N2O and CH4 fluxes and their associations with changes in soil environment factors have been poorly understood in plantation forests. A 36-month field experiment was conducted to elucidate the effects of thinning and replanting different species on soil N2O and CH4 fluxes and related environmental factors in Cunninghamia lanceolata plantation on shallow soil. The experiment consisted of five treatments, uncut control (CK), moderate thinning + replanting evergreen seedlings (MTE), moderate thinning + replanting deciduous seedlings (MTD), heavy thinning + replanting evergreen seedlings (HTE), heavy thinning + replanting deciduous seedlings (HTD). Compared with the control, moderate and heavy thinning increased cumulative N2O emissions by 12.4% and 21.4%, respectively, and reduced CH4 cumulative uptake by 35.4% and 38.8%, respectively. However, the effects on soil N2O and CH4 fluxes replanting deciduous or evergreen seedlings were insignificant. The results showed that thinning increased N2O emissions and decreased CH4 uptake due to the increased soil temperature, labile C and N concentrations. Soil temperature was the dominant factor, and mineral N was a contributing factor affecting N2O and CH4 fluxes. The study concludes that thinning increased the global warming potential with N2O contributing more than CH4 (113.5%: −13.5%). Our findings highlight that thinning increased N2O emissions and decreased CH4 uptake with the increasing intensity and the replanting had no different effects between deciduous and evergreen seedlings on the fluxes of N2O and CH4 during the early years following thinning.
... The mean height of the forest stand is 17.5 m, the mean stem diameter at breast height is 15.6 cm and the growing stock is 245 m 3 ha −1 (based on Uri et al. (2014) and Becker et al. (2015)). In the forest floor, the following herbs dominate: Filipendula ulmaria (L.) Maxim., Aegopodium podagraria L., Cirsium oleraceum (L.) Scop., Geum rivale L., Crepis paludosa (L.) Moench,), shrubs (Rubus idaeus L., Frangula alnus L., Daphne mezereum L.) and young trees (A. ...
The carbon (C) budgets of riparian forests are sensitive to climatic variability. Therefore, riparian forests are hot spots of C cycling in landscapes. Only a limited number of studies on continuous measurements of methane (CH4) fluxes from riparian forests is available. Here, we report continuous high-frequency soil and ecosystem (eddy-covariance; EC) measurements of CH4 fluxes with a quantum cascade laser absorption spectrometer for a 2.5-year period and measurements of CH4 fluxes from tree stems using manual chambers for a 1.5 year period from a temperate riparian Alnus incana forest.
The results demonstrate that the riparian forest is a minor net annual sink of CH4 consuming 0.24 kg CH4-C ha⁻¹ y⁻¹. Soil water content is the most important determinant of soil, stem, and EC fluxes, followed by soil temperature. There were significant differences in CH4 fluxes between the wet and dry periods. During the wet period, 83% of CH4 was emitted from the tree stems while the ecosystem-level emission was equal to the sum of soil and stem emissions. During the dry period, CH4 was substantially consumed in the soil whereas stem emissions were very low. A significant difference between the EC fluxes and the sum of soil and stem fluxes during the dry period is most likely caused by emission from the canopy whereas at the ecosystem level the forest was a clear CH4 sink. Our results together with past measurements of CH4 fluxes in other riparian forests suggest that temperate riparian forests can be long-term CH4 sinks.
... C leaching was measured using stainless steel plate lysimeters in both studied stands (Roots and Voll, 2011;Uri et al., 2011;Becker et al., 2015;Morozov et al., 2019). Lysimeters were installed and water was sampled as described in our parallel study (Aun et al., 2021): 7 stainless steel plate lysimeters were installed at random points across the area to a soil depth of 40 cm to both sample plots in studied stands. ...
Thinning is the main silvicultural method for improving stand growth and wood quality, however, despite the relevance and extensive use of thinning in forest management, its effect on stand carbon (C) balance is still poorly studied at the ecosystem level. The present case study estimated the two-year post-thinning effect on the C balance of a pole stand and a middle-aged Scots pine stand growing on mesotrophic sandy soils. Moderate thinning from below reduced the stand C storage by 21–24%, however, the amount of C accumulated in woody biomass, which was removed by logging, is expected to recover in both stands in the following four years. The reduced biomass of the trees contributed to the decreased annual net primary production (NPP) of the stand by 9–11%. The absolute value of net ecosystem production decreased by 0.9 and 0.7 t C ha⁻¹ yr⁻¹ in the pole and the middle-aged stand, respectively; still, both thinned plots maintained their C sink status. The production of the herbaceous understorey as well as the production of needles increased in the younger stand after thinning, but this could not compensate for C loss at the stand level. The effect of thinning on the production of mosses and dwarf shrubs was not expressed in either stand, probably due to the too short post-thinning period. Thinning did not significantly affect either total soil respiration or the heterotrophic respiration (Rh). However, it increased the contribution of Rh to total soil respiration, which can be attributed to decreased fine root biomass and root respiration, while the aboveground litterfall was not significantly changed after thinning. Fine root production, which accounted for the main belowground litter input, was significantly lower in both thinned plots. Moderate thinning in the pole and the middle-aged Scots pine stand did not change the ecosystem into a C source and the induced C loss will be compensated during a short post-thinning period.
... After forest degradation, early successional species invade the habitat and radically alter vegetation and soil physicochemical properties (Lebrija-Trejos, Meave, Poorter, Pérez-García, & Bongers, 2010). Early successional forest ecosystems that grow after forest degradation or stand-replacement are highly valuable, especially in terms of carbon stock by pioneer tree species following ecosystem reconstruction (Becker et al., 2015; Lorenc-Pluci nska, Walentynowicz, & Niewiadomska, 2013;Preem et al., 2012;Swanson et al., 2011). The ability of Alnus trees to fix atmospheric nitrogen through symbiotic association with Frankia enables them to tolerate extremely harsh environmental conditions and accelerate the natural succession. ...
Nitrogen‐fixing Nepalese alder (Alnus nepalensis D. Don.) is a rapidly‐growing pioneer tree species that often forms pure stands in areas affected by landslides, but also occurs mixed with other late‐successional species in the central Himalaya. In this study, we assessed the distribution of carbon in vegetation and soil in a chronosequence of A. nepalensis (3‐270 years old) forest stands and evaluated its correlation with the stand and alder total basal area (TBA). The study was conducted in six different naturally occurring forest stands in a chronosequence viz., alder‐early regenerating (AER), alder‐late regenerating (ALR), alder young‐mixed (AYM), alder mature‐oak (Quercus leucotrichophora) mixed (AMOM), alder mature‐rhododendron (Rhododendron arboreum) mixed (AMR), and alder old‐oak (Q. leucotrichophora) mixed (AOOM) forests. The chronosequence consisted of three young unreserved, AER, ALR, and AYM (age 3‐25) and three older reserved, AMOM, AMR, and AOOM (age 80‐270) stands. We used structural equation modeling (SEM) to quantify the contribution of various carbon pools on ecosystem carbon stock. Forest carbon stock significantly increased (P<0.05) with forest age and TBA, indicating that succession is the driving factor of the forest ecosystem processes, carbon accumulation, and therefore, change in vegetation biomass carbon and soil carbon in the chronosequence of A. nepalensis forests. Total vegetation biomass carbon (tree, shrubs, herbs, and litter) contained ~ 12.54 ‐289.85 Mg ha‐1 (79.11‐ 57.77 % total carbon stock), and soil carbon (depths of 0‐10 cm in AER, 0‐30 cm in AYM, 0‐100 cm in remaining forest stands) contained ~3.31‐210.13 Mg ha‐1 (20.8‐42 % total carbon stock) and positively increased with stand and A. nepalensis total basal area. The tree layer biomass carbon stock was considerably higher than the understory (shrubs, herbs, and forest floor). The soil carbon stock was reported to be influenced by the successional stages. Therefore, these findings reflect that the A. nepalensis forest development in the central Himalaya lead to storage of large amount of carbon stock in both plant biomass and soil.
... Leaching of C was estimated using stainless steel plate lysimeters (Roots and Voll, 2011;Uri et al., 2012;Becker et al., 2015;Morozov et al., 2019). In all study stands, 14 stainless steel plate lysimeters were installed (7 for TP + 7 for CP) in the soil at a depth of 40 cm at random points across the plot. ...
Although thinning is a widely used silvicultural method, its effect on stand carbon (C) cycling is still poorly studied at the ecosystem level. The present case study estimated the two-year post-thinning effect on the C balance of a pole and a middle-aged silver birch stand. The results demonstrate the multifaceted impact of thinning on the different C fluxes of deciduous forest ecosystems.
The effect of thinning on the C budget of the studied stands was modest: net ecosystem production (NEP) decreased by 1.2 and 1.6 t C ha⁻¹ yr⁻¹ in the pole and the middle- aged stand, respectively; still, both stands remained C sinks. Lower annual production in the thinned stands as a result of the decreased standing biomass of the trees was the main factor for reduced C sequestration capacity. Thinning increased the C accumulation of the herbaceous plants in both stands, however, it did not compensate for the lower C accumulation by the trees. In general, thinning did not affect significantly the soil respiration fluxes; the small post-thinning increase of the annual soil heterotrophic flux, 0.33–0.68 t C ha ⁻¹, was most probably related to elevated soil temperature during the active growing season. The annual aboveground litter flux, i.e. the labile C source of Rh, was not significantly changed by thinning. Fine root production and the belowground C input to the soil remained at the same level in the pole stand and decreased slightly in the middle-aged stand. We conclude that the high production ability and fast C accumulation recovery of silver birch stands growing on fertile soils leads to a balanced C budget already during the short post-thinning period.
... The average values of N 2 O fluxes for the whole study period (kg N 2 O-N ha -1 yr -1 ) were comparable with the respective values for beech stands (0.17 by Brumme et al. 1999;0.05-0.22 by Dannemann et al. 2008), but significantly lower than for riparian grey alder stand (0.20 to 2.70 by Teiter and Mander 2005;Mander et al. 2008Mander et al. , 2014, for a grey alder plantation (0.50 by Uri et al. 2011), for a 32-year-old natural grey alder stand and the clear-cut area (1.03 and 0.54 by Becker et al. 2015). Brumme et al. (1999) generalized literature data from 21 temperate forests and found the mean annual fluxes of N 2 O-N to be 0.39 ± 0.27 kg ha −1 yr −1 . ...
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.
... It is also unclear to what extent the observed shifts in community structure and function are dependent on the altered soil properties. So far most of the previous work has been based on low resolution methods, such as microbial biomass, phospholipid fatty acid or single functional process, such as enzyme activity, litter decomposition rates and nitrogen mineralization potential (Tan, Chang and Kabzems 2008;Becker et al. 2015). Current high-throughput sequencing approaches make it possible to investigate forest soil microbial communities with far greater sample numbers, sequence coverage and phylogenetic resolution (Nacke et al. 2011;Baldrian et al. 2012). ...
To understand the temporal responses of soil prokaryotic communities to clear cutting disturbance, we examined the changes in soil bacterial and archaeal community composition, structure and diversity along a chronosequence of forest successional restoration using high throughput 16S rRNA gene sequencing. Our results demonstrated that clear-cutting significantly altered soil bacterial community structure, while no significant shifts of soil archaeal communities were observed. The hypothesis that soil bacterial communities would become similar to those of surrounding intact primary forest with natural regeneration was supported by the shifts in the bacterial community composition and structure. Bacterial community diversity patterns induced by clear cutting were consistent with the intermediate disturbance hypothesis. Dynamics of bacterial communities was mostly driven by soil properties, which collectively explained more than 70% of the variation in bacterial community composition. Community assembly data revealed that clear-cutting promoted the importance of the deterministic processes in shaping bacterial communities, coinciding with the resultant low resource environments. But assembly processes in the secondary forest returned a similar level compared to the intact primary forest. These findings suggest that bacterial community dynamics may be predictable during the natural recovery process.
Interactions between soil fungi and soil environmental factors regulate soil nitrogen (N) mineralization rates on the eastern Qinghai-Tibetan Plateau. Some studies have also illuminated differences in soil N mineralization rate based on different mycorrhizal forests, but the associated effect of soil fungal functional guilds and soil environmental factors underlying this process are not well-understood. Three primary forests respectively dominated by Abies fargesii var. faxoniana (ectomycorrhizal, EcM), Cupressus chengiana (arbuscular mycorrhizal, AM) and Rhododendron phaeochrysum (ericoid mycorrhizal, ErM) trees were selected in this area. Meanwhile, soil net N mineralization rate, soil fungal composition and soil enzyme activity among these three mycorrhizal forests were studied. Our results showed that there were significant differences in the seasonal variation of soil net N mineralization rates among three mycorrhizal forests. Soil net N mineralization rate in the AM forest was faster. EcM fungi and saprotroph are the main functional guilds in these three mycorrhizal forests. Meanwhile, the relative abundances of soil fungal functional guilds, soil temperature and soil peroxidase activity could explain 85.0% in the difference of soil net ammonification rate among three mycorrhizal forests. In addition, soil temperature, soil water-filled pore space and soil ammonium content play a central role in controlling the differing soil net nitrification rate among three mycorrhizal forests. Our results suggest differences in soil net mineralization among different mycorrhizal forest types are driven mainly by soil net ammonification. Soil fungal functional guilds and temperature regulate the rate of soil net ammonification by modulating soil peroxidase activity.
Clear-cutting is an extensively used silvicultural method in the Nordic and Baltic countries, which strongly influences the site’s carbon (C) budget. In the current study, C budgets for a young silver birch stand chronosequence (2–8-year-old) were compiled using the C budgeting method. High variability of annual NEP between stands of similar ages occurred, as the C accumulation ability of young stands was site specific. Heterotrophic respiration (Rh), the main C efflux from the ecosystem, varied between (3.7 and 6.3 t C ha⁻¹ yr⁻¹) across all stands. Modelling of the annual NEP dynamics across the chronosequence revealed the C compensation point at a stand age of 6 years. The estimated cumulative C loss for the period when NEP was negative was almost 5 t C ha⁻¹ and the amount of lost C could have been recaptured already in a 10-year-old stand. The C sink capacity of the studied sites depended mostly on the production of herbaceous plants until the production of the new tree generation became the main driver of ecosystem’s net primary production. Hence, site’s C accumulation capacity largely depends on the density and quality of the new forest regeneration.
Mycorrhizal fungi can form symbiotic associations with tree species, which not only play an important role in plant survival and growth, but also in soil carbon (C) and nitrogen (N) cycling. However, the understanding of differences in soil C and N cycling patterns among forests with different mycorrhizal types is still incomplete. In order to determine the similarities and differences of soil C and N cycling patterns in different mycorrhizal forest types, three primary forests dominated by ectomycorrhizal (EcM), arbuscular mycorrhizal (AM) and ericoid mycorrhizal (ErM) trees respectively were studied on the eastern Qinghai-Tibetan Plateau. Indicators associated with soil C and N cycling, including leaf litter quality, soil C and N contents, soil C and N fluxes, and soil microbial biomass C and N contents were measured in each mycorrhizal type forest. The results showed that leaf litter quality was significantly lower with high C:N ratio and lignin: N ratio in ErM forest than that in AM and EcM forests. Soil CO 2 flux (508.25 ± 65.51 mg m ⁻² h ⁻¹ ) in AM forest was significantly higher than that in EcM forest (387.18 ± 56.19 mg m ⁻² h ⁻¹ ) and ErM forest (177.87 ± 58.40 mg m ⁻² h ⁻¹ ). Furthermore, soil inorganic N content was higher in the AM forest than that in EcM and ErM forests. Soil net N mineralization rate (−0.02 ± 0.03 mg kg ⁻¹ d ⁻¹ ) was lower in ErM forest than that in EcM and AM forests. We speculated that AM and EcM forests were relatively characterized by rapid soil C cycling comparing to ErM forest. The soil N cycling in EcM and ErM forests were lower, implying they were ‘organic’ N nutrition patterns, and the pattern in ErM forest was more obvious.
Riparian forests are known as hot spots of nitrogen cycling in landscapes. Climate warming speeds up the cycle. Here we present results from a multi-annual high temporal-frequency study of soil, stem, and ecosystem (eddy covariance) fluxes of N 2 O from a typical riparian forest in Europe. Hot moments (extreme events of N 2 O emission) lasted a quarter of the study period but contributed more than half of soil fluxes. We demonstrate that high soil emissions of N 2 O do not escape the ecosystem but are processed in the canopy. Rapid water content change across intermediate soil moisture was a major determinant of elevated soil emissions in spring. The freeze-thaw period is another hot moment. However, according to the eddy covariance measurements, the riparian forest is a modest source of N 2 O. We propose photochemical reactions and dissolution in canopy-space water as reduction mechanisms.
Riparian forests are known as hot spots of N cycling in landscapes and climate warming speeds up the cycle. Here we present results from the first multi-annual high temporal-frequency study of soil, stem and ecosystem (eddy covariance) fluxes of N2O from a typical riparian forest in Europe.
Hot moments (extreme events of N2O emission) last a quarter of the study period but contribute more than a half of soil fluxes. For the first time we demonstrate that high soil emissions of N2O do not reach the ecosystem level. During the drought onset, soil N2O emission peaks at intermediate soil water content. Rapid water content change is the main determinant of the emissions. The freeze–thaw period is another hot moment. However, according to the eddy covariance measurements the riparian forest is a modest source of N2O. We propose photochemical reactions and dissolution in canopy-space water as consumption mechanisms.
In the LIFE REstore project, vegetation was surveyed in 32 extracted peatlands in the period from 2016 to 2018. The surveyed peatlands included both former block-cut and vacuum harvested areas. Typical vegetation types occurring in the former peat extraction areas were identified, and influence of drainage, water table and other factors was evaluated. The results of LIFE REstore inventory were supplemented with data from similar studies carried out in Latvia. In total, results from 39 cutaway peatland areas in Latvia have been included in this study. Several scenarios of spontaneous revegetation were identified. They were distinguished by dominant properties of residual peat layer, peat extraction methods, and moisture conditions. Each scenario includes several succession stages. Overall, the results describe the process of spontaneous revegetation in various conditions in Latvia, although not all variations could be included in this overview. The main factors determining the course of spontaneous revegetation in cutaway peatlands are groundwater table, type and properties of residual peat, its physical and chemical properties, as well as hydro-chemical parameters of water bodies. The restoration of peat-forming mire vegetation and hence the peat accumulation process is possible only in wet conditions, which is important when planning rehabilitation for mire ecosystem and its functions, including carbon sequestration, regulation of water and nutrient cycling, and soil formation.
The results of this inventory were used to identify the factors which should be taken into account in planning rehabilitation of peatlands damaged by peat extraction, i.e. restoration of peat-forming vegetation. Abandonment of such degraded peatlands leading to natural succession cannot be considered rehabilitation in cases when the impact of drainage system is not eliminated.
Riparian buffer zones are considered to be important elements of agricultural watersheds, in that they control nutrient and carbon fluxes. Although the water purification effect of riparian ecosystems has been well studied, there is little knowledge of their internal cycling, especially in the area of gaseous emissions. We measured fluxes of nitrous oxide (N2O), dinitrogen (N2), methane (CH4), and carbon dioxide (CO2) in riparian grey alder stands in southern Estonia and black alder stands in Brandenburg, Germany. Dinitrogen emission was the most important component in N retention in the studied riparian grey alder forests. In 2001-2003, the median values of N2 emission in the grey alder sites significantly exceeded the N2 emission rates in the black alder sites, varying from 700 to 1200 and from 360 to 400 kg N2-N ha-1 year-1, respectively. In contrast, the median values of N 2O flux were higher in the black alder sites than in the grey alder sites, i.e., 0.9-2.6 and 0.2-0.7 kg N2O-N ha-1 year -1, respectively. The black alder sites acted as a sink for CH 4, whereas the grey alder sites emitted a small amount of CH 4. The CO2-C flux was higher in the black alder stands. The estimated N2-N emission in the grey alder stands for 1994-1995 was 51.2, whereas N2O-N emission was 0.5 kg N ha-1 year-1. The significant increase in N2 emission from 1994-1995 to 2001-2003 can be related to changes in microbial activity during the succession of the pioneer grey alder stand into a more stable mixed forest community. Due to CO2 fluxes and N2O fluxes from sites with altered water regime, the estimated GWP of the studied riparian alder stands was relatively high. Further investigations should concentrate on the factors that regulate rates of N2O and N2 emission from riparian buffer zones.
The effect of red alder (Alnus rubra Bong.) on soil phosphorus (P) availability in conifer forests of the Pacific Northwest has been the focus of several recent studies. One study at the Thompson Research Center in Washington State, found Bray No. 2 extractable P to be lower in soils under pure alder than in soils under adjacent stands of pure conifer. The Thompson study, and others in forests of the Northwest, have also found that the quantity of P in aboveground litter fall is greater for conifer stands mixed with alder than in adjacent pure conifer stands, suggesting equal or greater soil P availability under the influence of alder. We assessed the effect of low densities of red alder on soil P, using a modified Hedley sequential P fractionation scheme, in a Douglas-fir (Pseudotsuga menziesii (Mirb.) France) plantation in coastal Oregon. We determined that soils under plots with 190 alder stems/ha and 740 Douglas-fir stems/ha had greater inorganic P availability than pure Douglas-fir plots (740 stems/ha). Inorganic P fractions, sequentially extracted from soils at 0-0.15 m depths by anion exchange resins, by sodium hydroxide, and by hydrochloric acid, were 65-225% greater in plots with alder. Soil phosphatase activity was nearly three times greater in plots mixed with alder. No significant pH differences between the treatments were found. We conclude that red alder appears to increase the availability of soil P at our site, but note that increased P supplies may not prevent a P limitation on productivity for either alder or conifers.
Australia’s harvested native forests are extremely diverse in terms of species-mix, disturbance history and ecology, forest productivity and C storage. Our understanding of the effects of harvesting on C storage and greenhouse gas (GHG) emissions from these systems is incomplete, and this paper consolidates current Australian knowledge, places this in a global context, and identifies areas requiring further study. The uptake of CO2 and the re-accumulation of forest C stocks after harvesting or other disturbance is largely dependent on forest primary production. However, in Australian native forests, knowledge of rates of primary production for the diverse range of species and management practices present is poor. Soil respiration rates following harvest have also been largely unquantified for Australian systems. It is essential that both these parameters are quantified if estimates of net ecosystem production (NEP) are to be made. It is generally acknowledged that harvested forests have a negative NEP, and thus are sources of C, immediately following harvest, but attain a positive NEP as the forest regrows and photosynthetic capacity increases. The magnitude and time course of these changes are largely unknown for most Australian forest systems. In addition, little data are available to quantify the effect on soil C storage, and where estimates have been made these are often subject to methodological uncertainty and are thus highly contentious. Following harvest, the changes that occur to soil structure, moisture content, and N cycling may also influence CH4 and N2O flux, although these fluxes also remain largely unquantified in harvested Australian forests. Given the significant changes to NEP, CH4 and N2O fluxes observed after forest harvest in international studies, it is expected that GHG fluxes would typically increase from Australian native forests following harvest, and then slowly decrease over time as biomass accumulates, and N2O and CH4 fluxes return to background levels. However, it is currently difficult to quantify the magnitude and time course of these changes due to a lack of both gas flux and primary production measurements. Clearly, further research effort to quantify these parameters throughout Australia is required in order to obtain a more reliable picture of the effects of harvesting and other disturbances on forest GHG balance.
2010): Effects of nitrogen-fixing and non-nitrogen-fixing tree species on soil properties and nitrogen transformation during forest restoration in southern China, Soil Science and Plant Nutrition, 56:2, 297-306 This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.
Air moisture is one of the main factors causing the greenhouse effect, but humidity has not been thoroughly studied at the ecosystem level. In 2006 a free-air humidity manipulation (FAHM) facility was established in Estonia to investigate the effect of humidity on the performance of two tree species—silver birch (Betula pendula Roth.) and hybrid aspen (Populus tremula L. × P. tremuloides Michx.). The trial is located on an Endogleyic Planosol of former arable land and offers the opportunity to change relative air humidity through controlled artificial misting and drying. We measured the CO2, CH4 and N2O emission from the FAHM system using closed chamber and gas-chromatograph techniques from July 2009 to October 2010. Measurements were carried out once a month in three humidification (h) plots and in three control (c) plots. The vegetation period was rainy in 2009, but the next summer was relatively dry. The dry summer interacted better with the humidification. The CO2 flux decreased when the air moisture was higher than in the control plots. The soil acted as a sink for methane. Less CH4 was oxidized in the soil with increased humidity. Emission of N2O did not correlate with air humidity, although one could observe a clear tendency that there was a smaller N2O flux during the period with increased humidity. Expectedly, CO2 emission and CH4 consumption demonstrated strong positive correlations with soil temperature.
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.
To study the fluxes of the radiative active trace gases CHâ, COâ, and NâO, a gas sampling and analytical device was developed. It is a useful tool for accurate gas sampling in the field and enables the subsequent fully automated analysis of the gas samples in the laboratory. The computer-controlled analytical system consists of a gas chromatograph equipped with a flame ionization detector (FID), an electron capture detector (ECD), and a pressure-controlled autosampler for 64 sample containers. The system automates sample injection, the analysis of CHâ, COâ, and NâO in each sample and the subsequent evacuation of the sample containers. It is equipped with a second alternative sample inlet for manual syringe injection. This inlet is suitable for analyzing small volumes of gas samples (3 mL). The gas sampling system for use in the field consists of evacuated sample bottles (100 mL) with Teflon cocks combined with a small battery-driven field sampler with a pressure sensor. This device enables an on-site control of the vacuum integrity of the sample bottles during sampling and purging of the dead volumes between the sampler induction pipe and the sample container. 11 refs., 4 figs.
Successive rotations of nitrogen-fixing red alder (Alnus rubra Bong.) may alter soil properties, potentially influencing future tree growth and nutrition. We examined the effects of red alder on soil properties and next-rotation alder leaf and leaf litter element concentrations. A conversion experiment was initiated in 1984 by clearcutting a 50-year-old red alder stand and an adjacent 50-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) France) stand. Both areas were replanted with red alder, yielding first- and second-rotation alder plots. Prior to conversion, the 50-year-old alder plot had higher total soil C, N, and extractable Ca, Mg, and Al, while pH and available P were lower. The second-rotation plot had lower leaf P, Ca, and Mg concentrations than the first-rotation plot in 1988 and 1989; it also had lower leaf K, Mn, and Fe concentrations in 1989. The second-rotation plot had lower leaf litter N, P, K, Mg, and Fe concentrations, and litter-fall mass and element transfer rates were 30-49% those of the first rotation. The findings indicate a potential decrease In availability of most macronutrients when growing repeated rotations of red alder on glacial till derived soils.
Nitrogen mineralization is a critical ecosystem process that is difficult to measure. Among several in situ methods used to estimate N mineralization rates in soils, the buried bag and covered-cylinder methods are two of the most common. Few studies have compared N mineralization rates from these two in situ methods, and it is still unclear if they provide analogous results. We compared both techniques, and two different core diameters, to determine if the different methods produce comparable results. Contrary to our expectations, larger cores were not more representative than smaller due to the importance of site-specific soil characteristics, especially rockiness. Dissimilarities in means, and weak and inconsistent correlations between methods, suggested that the different methods may not be equivalent. Our results suggest that the method optimization depends on specific site conditions, at least in forest soils, and that comparison among studies using different in situ methods should be made with caution until more standardization is achieved.
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).
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.
Nearly all northeastern U.S. forests have been disturbed by wind, logging, fire, or agriculture over the past several centuries. These disturbances may have long-term impacts on forest carbon and nitrogen cycling, affecting forests' vulnerability to N saturation and their future capacity to store C. We evaluated the long-term (80-110 yr) effects of logging and fire on aboveground biomass, foliar N (%), soil C and N pools, net N mineralization and nitrification, and NO3- leaching in northern hardwood forests in the White Mountain National Forest, New Hampshire. Historical land-use maps were used to identify five areas each containing previously logged, burned, and relatively undisturbed (oldgrowth) forests. Aboveground biomass averaged 192 Mg/ha on the historically disturbed sites and 261 Mg/ha on the old-growth sites, and species dominance shifted from early-successional and mid-successional species (Betula papyrifera and Acer rubrum) to late-successional species (Fagus grandifolia and particularly A. saccharum). Forest floors in the old-growth stands had less organic matter and lower C:N ratios than those in historically burned or logged sites. Estimated net N mineralization did not vary by land-use history (113 kg·ha-1·yr-1); mean (± 1 SE) nitrification rates at old-growth sites (63 ± 4.3 kg·ha-1·yr-1) doubled those at burned (34 ± 4.4 kg·ha-1·yr-1) and logged (29±4.7 kg·ha-1-yr-1) sites. Across all plots, nitrification increased as forest floor C:N ratio decreased, and NO3- concentrations in streamwater increased with nitrification. These results indicate that forest N cycling is affected by century-old disturbances. The increased nitrification at the old-growth sites may have resulted from excess N accumulation relative to C accumulation in forest soils, due in part to low productivity of old-aged forests and chronic N deposition.
The occurrence of different mycorrhizas of the grey alder, Alnus incana (L.) Moench., in Sweden was investigated. Root sampling was carried out in planted and natural grey alder stands, representing different soil types, geographical sites, and plant ages. Mycorrhizal infection of roots was found to be frequent at all investigated sites, except for some planted peat bogs, where alders do not occur naturally. At the latter sites, mycorrhizal infection was less frequent and consisted only of ectomycorrhizas. Young trees here were non-mycorrhizal. At all other sites vesicular-arbuscular mycorrhiza (VAM) was found to be the almost exclusive type of mycorrhiza in first-year seedlings. In trees older than one year ectomycorrhiza was the dominating type. In the planted stands up to five years of age no fruitbodies of ectomycorrhizal fungi were found. In such stands the ectomycorrhizas generally had thin, translucent mantles and could be observed only by microscopic examination. In one old plantation (27 years) and in the natural stands sporocarps of several specific "alder fungi" were found. Here, the mycorrhizal root tips had thick, mostly whitish mantles. The Hartig net was in all cases confined to penetration between epidermal cells. Soil collected from one alder site and two non-alder biotopes readily infected grey alder seedlings with Frankia and VAM fungi whereas a peat soil failed to infect seedlings with any symbiont. In vitro inoculation of nodulated seedlings with Glomus mossae (Nicol. & Gerd.) Gerdemann & Trappe resulted in VAM-infection. Simultaneous syntheses with isolates of alder-specific, and other, ectomycorrhizal fungi, using three different methods, failed. On the basis of these results an endomycorrhizal-ectomycorrhizal succession after the first growth season in Alnus incana is concluded. A subsequent succession of ectomycorrhizal species from early-stage to late-stage ones is discussed.
Alnus incana nodules were incubated in situ and assayed for nitrogen-fixing activity by the acetylene reduction method. The effects of air and soil temperature and light intensity (at the tree stem) on the acetylene reduction activity were examined, and diurnal and seasonl fluctuations in acetylene reducing activity were studied. Rates of acetylene reduction obtained varied between 0.4 and 84.8 μmoles of ethylene per g dry weight of nodule per h with a seasonal average of 8.6 μmoles g-1 h-1. Based on field assays an annual rate of fixation of 43 kg N/ha was estimated for a 30 year old A. incana stand. /// Почки Alnus incana исследованы in situ, и в них исследована активность азотфиксации методом восстановления ацетилена. Лзмеряли влияние температуры воздуха и почвы и осбещенности (на стволе) на активность восстановления ацетилена и определяли суточные и сезонные колебания активности данного процесса. Полученные результаты колебались в пределах 0.4-84.4 ммолей этилена на г сухого веса почек в час, средние данные за сезон - 8.6 ммолей/г/час. На основании полевых исследований годовая скорость фиксации составляет 43 кг азота/га, что было получено при исследовании в 30-летнем насаждении A. incana.
We evaluated the effects of stand density on nitrogen (N"2) fixation, net primary production (NPP) photosynthate partitioning, and canopy characteristics in 5-yr-old red alder (Alnus rubra Bong.) plantations. Our study used acetylene reduction and dimension analysis techniques. Trees in low-density stands (initially spaced 2.74 x 2.74 m) had the highest mass, and surface-area components as well as N"2 fixation. Mid-density stands (initially spaced 1.22 x 1.82 m) had the highest per-unit-area values for leaf mass, canopy volume, branch mass and surface area, root and stump mass, net branch production, aboveground net production, and N"2 fixation. The highest density stands (initially spaced 0.61 x 1.22 m) had the highest values per unit area of the variables: wood volume, bole and total aboveground dry mass, and net bole production. Nodule dry mass per unit area was approximately equal in the mid- and high-density stands, averaging 146 kg/ha. A high correlation between N"2 fixation and leaf mass per tree (r = 0.892) supports an earlier hypothesis (Gordon and Wheeler 1978) about field-grown alder. The lack correlation between leaf mass and N"2 fixation per unit area (averaging 2.15 Mg/ha and 70 kg@?ha^-^1@?yr^-^1, respectively) suggests that high-density stands allocated less photosynthate to nodules of N"2 fixation.
The effects of nutrient additions on growth of the red alder (Alnus rubra Bong.) are not well known. We examined the growth and nutritional responses of 10 young (0-4 years old at time of fertilization) red alder plantations on eastern Vancouver Island to additions of phosphorus (P), added as triple super phosphate, and a blended fertilizer (F) containing elements other than nitrogen (N), P, and calcium (Ca). Site fertility classes ranged from poor to very rich and soil moisture regime classes ranged from moderately dry to very moist. Nutrients were added in single-tree plots and responses were measured for up to 3 years after fertilization. In plantations fertilized within 1 year of planting, P additions increased heights (average of 17%), basal diameters (28%), and stem volumes (68%) over a 3-year period and increased 1st-year foliar concentrations of P, N, and S. The fertilizer supplying other elements also increased concentrations of N and S, along with potassium (K), boron (B), zinc (Zn), and manganese (Mn), but increased volume by only 16%. These data suggest that deficiencies of P are more likely to limit the growth of young red alder than are deficiencies of other elements. Older plantations (more than 2 years postplanting) were less responsive to fertilization than were younger plantations (less than 2 years postplanting). Growth of young red alder appears limited by P availability when soil Bray-P and foliar P concentrations are less than approximately 12 mg kg -1 and 2 g kg -1, respectively.
The effect of clear-cutting on in situ carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) trace gas exchange between soil and atmosphere was studied during one growing season in two Atlantic temperate forest sites located in Nova Scotia, Canada. The flux, the storage and the concentration (four depths) of the three main greenhouse gases (GHGs) were measured up to ten times in 2005 (between March and November) in two clear-cut and two forest plots (paired sites). Air temperature and soil moisture were also monitored simultaneously with GHG. All three GHG showed high temporal variability and variability between plots during the time covered by this study. Our results also showed that there was still a treatment effect on GHG three years post-harvest. Clear-cutting increased CO2 production and storage in one of our site and CH4 uptake in both sites, but was inconsistent for N2O during the sampling period. With the exception of CO2, the correlation between GHG, and air temperature and soil moisture was absent. This suggests that GHG emissions in these two Acadian forests are mainly affected by other biological and physical factors. Finally, our study showed that measures of one GHG could not be used to infer measures of another GHG.
In the article the authors provide a formal definition of nitrogen saturation and set forth a series of testable hypotheses regarding the states of forest-ecosystem response to chronic nitrogen deposition. These hypotheses are used to suggest early indicators of nitrogen saturation and to discuss the potential implications of nitrogen saturation of forest ecosystems over large geographic areas. Possible effects include elevated concentrations of nitrate, aluminum, and hydrogen in streams, which would decrease water quality; frost damage or other disruptions of physiological function that would reduce productivity in conifer stands; increase cation leaching from soils and nitrate losses that would lead to reduced soil fertility and increased acidity; and possible increases in emissions of trace gases such as nitrous oxide, which may alter atmospheric chemistry and contribute to the warming of Earth's atmosphere (the greenhouse effect).
Forest soils show a considerable level of spatial heterogeneity. It was previously reported that soil moisture content affects microbial biomass and respiration in the soil as well as enzyme-catalyzed processes; as such it can be one of the potential drivers of heterogeneity of microbial distribution and decomposition in forest soils. The moisture mass content in samples of Quercus petraea forest soil varied substantially and ranged between 0.35–0.70gg−1 soil wet mass in the litter horizon and 0.10–0.60gg−1 in the humus horizon within a single sampling of a 144m2 area as well as of a 0.11m2 area. Soil moisture content positively and significantly correlated with microbial (bacterial and fungal) biomass, explained up to 60% of the total variability in microbial biomass and a significant difference in the ratio of fungal to bacterial biomass was found among the samples with high and low moisture content. Also the activity of several extracellular enzymes involved in decomposition (i.e., laccase, Mn-peroxidase, endo-1,4-β-glucanase, endo-1,4-β-xylanase, cellobiohydrolase, β-glucosidase, β-xylosidase, chitinase and acid phosphatase) correlated with soil moisture, although the response varied among soil horizons and sampling dates. The effect of moisture on enzyme activities was probably partially mediated by the changes in biomass content. Forest soil was demonstrated to be a mosaic of small dry and moist patches where the differences in microbial biomass content or enzyme activities vary by tens of percents due to differential moisture content.
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.
Constraints on nitrogen fixation are the ultimate causes of N limitation of primary production, but hypotheses concerning limitations to N2 fixation remain largely untested in natural terrestrial ecosystems. We examined limitations to N 2 fixation by thinleaf alder (Alnus tenuifolia) in two stages of primary forest succession on the Tanana River floodplain (interior Alaska, USA) and focused on the hypothesis that N 2 fixation was limited by low soil P availability. Paired control and P fertilized plots were established at four replicate early successional alder stands and four later successional poplar ( Populus bal- samifera) stands (dense alder understories with mature poplar overstories) and N 2 fixation was estimated with an acetylene reduction assay. In alder stands, P fertilization increased total nodule dry biomass and increased total ecosystem N inputs, but it had little effect on nitrogenase activity per unit nodule dry mass (specific acetylene reduction activity, ARA). Specific ARA increased only in late July when soil temperature and ARA were at their maximum values. In contrast, fertilization had no effect on these measures in poplar stands where reduced soil moisture may have superseded limitation by P. We detected no differ- ences in specific ARA, total nodule biomass, or N inputs, between alder and poplar stands but all of these measures were highly variable. Leaf area of the alder canopy emerged as the best predictor of ecosystem inputs of fixed N among control plots. Alders resorbed high amounts of P but little N (consistent with low P availability and a high P demand and a high N availability in alder), and P fertilization reduced P resorption but had no effect on N resorption. The timing of N2 fixation and N resorption indicate that late-season increases in leaf N, following a midseason reduction in leaf N, were driven by N2 fixation in excess of plant N demands as nodules continued fixing N while alder leaves senesced. These results have shown that P limits N2 fixation in alder stands in this nitrogen-limited sere, but that factors limiting N2 fixation can change over short successional time scales.
Forest harvest results in the removal of a large reservoir of terrestrial carbon with potential significant effects on net CO2 emissions, but concomitant effects on other atmospheric trace gas fluxes are poorly understood.We measured CO2, CH4 and N2O fluxes between soils and the atmosphere over 3 years at a recently harvested site under Pinus radiata on a volcanic soil of high-fertility status using replicated, large, in situ chambers to enclose three harvest residue treatments. Temporal changes in CO2 and N2O emissions were also measured over a wider harvested area using small chambers. The residue (slash) treatments were a control (‘no-slash’), ‘normal-slash’ typical of the site and ‘high-slash’ (three times normal-slash). Mass loss was inversely related to all size categories of slash, and averaged 98% for litter and 34% for large wood (76–120mm diameter). C:N ratios generally declined as a result of increased N concentrations. Overall, CO2-C production was significantly higher (P=0.02) in the ‘normal-slash’ (by 27%) and ‘high-slash’ (by 72%) than in the ‘no-slash’ treatments. An interaction between treatment and time explained (P=0.05) the CO2-C flux data better than did the interaction between treatment and soil moisture (P=0.07). Evidence from small-chamber CO2-C flux data collected over a wider area before and after harvest suggested little apparent effect of soil disturbance during harvest. Averaged over 3 years, the annual CO2-C efflux from the large chambers was 8.3±1.1Mgha−1.Methane uptake was apparently depressed by surface soil disturbance during harvest, because it increased after harvest by 70% in the ‘normal-slash’ and ‘high-slash’ treatments to average 12±1kg CH4 ha−1year−1. Neither NH4+ nor NO3−-N concentrations had any measurable effect on CH4 uptake. Despite the high N fertility of the harvest site, N2O emissions were low overall (0.56±0.17kg N2O-N ha−1year−1) and differed little between treatments, apart from a spike shortly after harvest.Overall, during the time frame of the first commitment period under the Kyoto Protocol, the three greenhouse gases (CO2, CH4 and N2O) contributed 87, −1 and 14%, respectively, to combined emissions on a CO2-equivalent basis from this fertile harvest site.
Nitrous oxide is produced from denitrification and nitrification processes in soils, and contributes to global warming and stratospheric ozone depletion. Laboratory experiments with six soils ranging in clay content between 4–12% were designed to investigate the effect of water and temperature on the partitioning of N2O from denitrification and nitrification. The nitrification rates at 70% field capacity (FC) were significantly higher in the loamy soils (980–1440 μg N kg−1 soil day−1) than in the sandy soils (60–460 μg N kg−1 soil day−1). The nitrous oxide produced by nitrification differed similarly between the soil types resulting in ratios of N2ON relative to NO3−N, which were only ranging from 0.28 to 0.48% with an average of 0.39%, indicating a rather constant relationship between nitrification and nitrous oxide emission. Maximum nitrification rates occured at 20°C and 100% filed capacity (FC) and was 13 at 40% FC. At lower temperatures only small responses to changes in soil moisture were observed. The percentage of N2ON produced by nitrification increased with increased siol moisture (0.49% at 40% FC and 0.93% at 100% FC) and decreased with increasing temperature (0.49% at 5°C and 0.17% at 20°C). The denitrification activity (N2 + N2O) in the sandy loam soil responded significantly to both increased soil moisture and increased temperature, whereas the coarse sandy soil only reacted to increased temperature. In the coarse sandy soil the Q10-values were in the range from 1.9 to 3.4, and the values were ranging from 4.9 to 8.9 in the sandy loam soil. As for the denitrification activity also the N2 to N2O ratio increased exponentially with increasing temperature, which implies a linear relationship between the log(N2 to N2O ratio) and the temperature. The N2 to N2O ratios were lower in the coarse sandy soil than in the sandy loam soil, and were in the range from 0 to 16.
Nitrate production was studied in the field by incubation of the soil in pint polyethylene bags during the 1958–59 winter season. This technique permits the diurnal changes in soil temperature to be taken into consideration in studying microbial processes, such as nitrification.
Laboratory studies showed that the rate of nitrification in soil contained in the bags was equal to that contained in ventilated bottles. The bags were tightly closed against the soil and secured with rubber bands. Only slight losses in soil moisture occurred during a 6‐week period of incubation. Polyethylene is permeable to oxygen and carbon dioxide. No nitrate difused through the polyethylene bags in a 24‐week period.
Field studies were made using bags of soil buried at a depth of 4 inches for periods of 1 to 6 weeks. Although soil temperatures at this depth were never below freezing, they varied sufficiently to result in considerable changes in the rate of nitrate production.
This technique should also prove to be of considerable value in evaluating nitrification in climates where the soil is frozen or at a temperature near freezing during a portion of the year.
To determine the long-term effect of alder on soil fertility, biogeochemical fluxes were measured and calculated for two pairs of adjacent, 55-yr-old stands dominated by conifers, primarily Douglas-fir (Pseudotsuga menziesii), and by ocnifers and nitrogen-fixing red alder (Alnus rubra). At a low-fertility site in the Wind River Experimental Forest in southwestern Washington, biomass of the alder-conifer stand (289 Mg/ha) exceeded that of the conifer stand (171 Mg/ha), and the aboveground net primary production (ANPP) of the alder-confier stand (10.3 Mg[center dot]ha[sup [minus]1][center dot]yr[sup [minus]1]). At a more fertile site in the Cascade Head Experimental Forest in western Oregon, both biomass and ANPP were higher than at Wind River, and biomass and ANPP were higher in the conifer stand (584 Mg/ha and 19.2 Mg[center dot]Ha[sup [minus]1][center dot]yr[sup [minus]1]) than in the alder-conifer stand (342 Mg/ha and 10.7 Mg[center dot]ha[sup [minus]1][center dot]Yr[sup [minus]1]). Nitrogen accretion in the alder-conifer stand at Wind River average 54 kg[center dot]ha[sup [minus]1][center dot]yr[sup [minus]1] for the 52 yr since stand establishment, with a current rate of N fixation of [approx] 75 kg[center dot]ha[sup [minus]1][center dot]yr[sup [minus]1]. For the alder-conifer stand at Cascade Head, N accretion averaged 73 kg[center dot]ha[sup [minus]1][center dot]yr[sup [minus]1] for 55 yr, with a current N-fixation rate of 85 kg[center dot]ha[sup [minus]1][center dot]yr[sup [minus]1]. The cycling of all nutrients appeared very malleable under the influence of alder. 59 refs., 1 fig., 7 tabs.
Three comparisons examined acetylene reduction rate and nodule biomass of red alder (Alnusrubra Bong.) and Sitka alder (Alnussinuata (Regel) Rydb.) on Vancouver Island, British Columbia. The first showed that the acetylene reduction rates of Sitka alder on four sites in early July 1979 varied from 8.8 to 22.0 μmol C 2 H 2 •g ⁻¹ dry nodule per hour; smaller nodules had the higher rates. In the second comparison, red alder and Sitka alder acetylene reduction rates for young plants were similar when assayed on the same day on the same site. Finally, acetylene reduction rates and nodule biomass were determined for both species growing in closed canopy stands on adjacent sites. In this pair of 20-year-old stands, red alder had double the acetylene reduction rate and three times the nodule biomass of the Sitka alder. Combining the nodule biomass estimates with the seasonal average reduction rates yielded current annual nitrogen fixation estimates (using C 2 H 2 ) of 130 kg•ha ⁻¹ •year ⁻¹ for the red alder plot and 20 kg•ha ⁻¹ •year ⁻¹ for the Sitka alder plot. These estimates are within published ranges for the species. The lower fixation rate of Sitka alder is still substantial, relative to the nitrogen demands of conifers, and its shrub-like growth form makes it an attractive management alternative to red alder for biological nitrogen fixation in mixed conifer–alder plantations.
A facility for free air humidity manipulation (FAHM) was established to investigate the effect of increased air humidity on trees’ performance and their canopy functioning with respect to rising air humidity predicted for Northern Europe. The FAHM system enables air relative humidity (RH) to be increased up to 18 units (%) over the ambient level during mist fumigation, depending on the wind speed inside the experimental stand. Water was dispersed inside 14×14m experimental plots in the form of mist with an average particle size of 50μm from June to August in 2008, and from May to September in 2009. The average increase in RH was 7 units (%) over the whole period of humidification in 2008 (P
Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] stem growth per unit of leaf area was compared in the presence and absence of Sitka alder (Alnus sinuata) and red alder (Alnus rubra). The apparent effect of the alders differed with the method used to calculate the ratio. When Douglas-fir's rating was calculated from conversion ratios for sapwood area to leaf area as measured at each site, it was increased 40 percent by the presence of Sitka alder and 250 percent by red alder. This increased stem growth per unit of leaf area probably resulted from both greater net photosynthetic rates and a shift in within-tree photosynthate allocation. Forest Sci. 30:259-263.
We studied greenhouse gas (GHG) fluxes in two differently loaded riparian Alnus incana-dominated forests in agricultural landscapes of southern Estonia: a 33-year-old stand in Porijõgi, in which the uphill agricultural activities had been abandoned since the middle of the 1990s, and a 50-year-old stand in Viiratsi, which still receives polluted lateral flow from uphill fields fertilized with pig slurry. In Porijõgi, closed-chamber based sampling lasted from October 2001 to October 2009, whereas in Viiratsi the sampling period was from November 2003 to October 2009. Both temporal and spatial variations in all GHG gas fluxes were remarkable. Local differences in GHG fluxes between micro-sites (“Edge”, “Dry” and “Wet” in Porijõgi, and “Wet”, “Slope” and “Dry” in Viiratsi) were sometimes greater than those between sites. Median values of GHG fluxes from both sites over the whole study period and all microsites did not differ significantly, being 45 and 42 mg CO2–C m−2 h−1, 8 and 0.5 μg CH4–C m−2 h−1, 1.0 and 2.1 mg N2–N m−2 h−1, and 5 and 9 μg N2O–N m−2 h−1, in Porijõgi and Viiratsi, respectively. The N2:N2O ratio in Viiratsi (40–1200) was lower than in Porijõgi (10–7600). The median values-based estimation of the Global Warming Potential of CH4 and N2O was 19 and 185 kg CO2 equivalents (eq) ha−1 yr−1 in Porijõgi and −14 and 336 kg CO2 eq ha−1 yr−1 in Viiratsi, respectively. A significant Spearman rank correlation was found between the mean monthly air temperature and CO2, CH4 and N2 fluxes in Porijõgi, and N2O flux in Viiratsi, and between the monthly precipitation and CH4 fluxes in both study sites. Higher groundwater level significantly increases CH4 emission and decreases CO2 and N2O emission, whereas higher soil temperature significantly increases N2O, CH4 and N2 emission values. In Porijõgi, GHG emissions did not display any discernable trend, whereas in Viiratsi a significant increase in CO2, N2, and N2O emissions has been found. This may be a result of the age of the grey alder stand, but may also be caused by the long-term nutrient load of this riparian alder stand, which indicates a need for the management of similar heavily loaded riparian alder stands.
The effect of land use type on the dynamics and annual rate of net nitrogen mineralization (NNM) in a naturally generated silver birch stand and in a grassland, both on abandoned agricultural land, was assessed in situ in the upper 0–20 cm soil layer using the method of buried polyethylene bags. Annual NNM rate in the birch stand (156 kg N ha−1 year−1) was higher than in the grassland (102 kg N ha−1 year−1); in both cases NNM covered a major part of the plants annual nitrogen demand. The rate of NNM in the upper 0–10 cm soil layer in the birch stand (99 kg N ha−1 year−1) exceeded the respective rate of NNM in the grassland (51 kg N ha−1 year−1) roughly two times. In the grassland the rates of NNM in the 0–10 and 10–20 cm layers were equal; in the birch stand NNM in the 0–10 cm layer was 1.7 times higher than in deeper 10–20 cm layer. The intensity of daily NNM in the upper 0–10 cm soil layer in the birch stand was the highest in June and in the grassland in May, 776 and 528 mg kg−1 N day−1, respectively. In our study no significant correlation was found between NNM and the environmental factors monthly mean soil temperature, soil moisture content and pH.The share of net nitrification in NNM in the birch stand and in the grassland was similar, 60% and 63%, respectively. In the deeper topsoil layer (10–20 cm) net nitrification made up a significantly higher proportion in NNM in the grassland than in the birch stand, 58% and 35%, respectively; this may increase nitrogen leaching from the deeper soil layers.Most probably, more intensive NNM did not lead to higher N leaching or emission losses from ecosystems in the birch stand compared with the grassland because an essential amount of nitrogen is retained in tree biomass.