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1.
Trees in farming systems can improve fertility of soils through mineralization of N in their litter. This study was to determine the quality parameters (i.e., chemical composition) of organic residues that are associated with N mineralization in soils under submerged and aerobic conditions, and to demonstrate that aeration conditions should be taken into account in categorization of organic residues as N sources in farming systems. Incubation experiments were conducted in Aeric Paleaquult soil under submerged and Oxic Paleustult soil under aerobic conditions. Treatments included litter and some fresh materials from trees as well as rice straw available in farming systems of Northeast Thailand. S. grandiflora and L. leucocephala (32 g kg−1 N) had the highest net N mineralization in both conditions. Some lower-quality (< 20 g kg−1 N) residues did exhibit low net N mineralization during the 16-week period under submerged conditions, but displayed almost no net N mineralization in aerobic conditions. Under submerged conditions, their net N mineralization was higher and more rapid. The nitrogen content of the residues was the most important factor controlling N mineralization under both conditions. Polyphenols exerted the highest negative influence on N mineralization in aerobic conditions, but exhibited no negative effect in submerged conditions. In categorizing organic residues for their effective use in soil fertility management, soil aeration conditions, as well as other environmental factors, should be taken into consideration in addition to residue quality.  相似文献   

2.
The Southeastern United States has a robust broiler industry that generates substantial quantities of poultry litter as waste. It has historically been applied to pastures close to poultry production facilities, but pollution of watersheds with litter-derived phosphorus and to a lesser extent nitrogen have led to voluntary and in some areas regulatory restrictions on application rates to pastures. Loblolly pine (Pinus taeda L.) forests are often located in close proximity to broiler production facilities, and these forests often benefit from improved nutrition. Accordingly, loblolly pine forests may serve as alternative land for litter application. However, information on the influence of repeated litter applications on loblolly pine forest N and P dynamics is lacking. Results from three individual ongoing studies were summarized to understand the effects of repeated litter applications, litter application rates, and land use types (loblolly pine forest and pasture) on N and P dynamics in soil and soil water. Each individual study was established at one of three locations in the Western Gulf Coastal Plain region. Annual applications of poultry litter increased soil test P accumulation of surface soils in all three studies, and the magnitude of increase was positively and linearly correlated with application rates and frequencies. In one study that was established at a site with relatively high soil test P concentrations prior to poultry litter application, five annual litter applications of 5 Mg ha−1 and 20 Mg ha−1 also increased soil test P accumulation in subsurface soils to a depth of up to 45 cm. Soil test P accumulations were greater in surface soils of loblolly pine stands than in pastures when both land use types received similar rates of litter application. In one study which monitored N dynamics, lower soil organic N, potential net N mineralization, potential net nitrification, and soil water N was found in loblolly pine stands than pastures after two annual litter applications. However, increases in potential net N mineralization, net nitrification, and soil water N with litter application were more pronounced in loblolly pine than in pasture soils. Loblolly pine plantations can be a viable land use alternative to pastures for poultry litter application, but litter application rate and frequency as well as differences in nutrient cycling dynamics between pine plantations and pastures are important considerations for environmentally sound nutrient management decisions.  相似文献   

3.
To detect the magnitude of indirect positive effects of deer and mice on seedling survival of some woody species in a Japanese temperate forest, we analyzed the data from an earlier field experiment using a hierarchical Bayesian approach. The forest studied was inhabited by sika deer (Cervus nippon) and mice (Apodemus spp.), and the floor was covered with dwarf bamboo, Sasa nipponica, which negatively affected tree seedlings and was in turn negatively affected by deer and mice. The field experiment was designed as the combination of exclusion or removal of these factors: deer, mice and dwarf bamboo. A hierarchical Bayesian model was constructed and the parameters were estimated by the Markov chain Monte Carlo method. The model successfully showed the indirect positive effects of deer and mice, which improved the survival rate of five cohorts of the seedlings of three tree species by ameliorating the direct negative effect of dwarf bamboo. The cohorts studied were formed by the seedlings of Abies homolepis that emerged in 1997 and 2002, those of Fraxinus lanuginosa f. serrata that emerged in 1998 and 2002, and those of Fagus crenata that emerged in 1999. The positive indirect effect was especially large in F. crenata, which is known to be severely affected by dwarf bamboo. The total effect of deer was shown to be positive for all cohorts except the A. homolepis cohort that emerged in 1997, at which time the dwarf bamboo had not yet fully recovered from the browsing pressure of deer. The total effect of mice was shown to be positive for all of the cohorts. We conclude that these positive effects were due to the large negative effect of dwarf bamboo on the seedlings.  相似文献   

4.
The foraging activities of nonindigenous feral hogs (Sus scrofa) create widespread, conspicuous soil disturbances. Hogs may impact forest regeneration dynamics through both direct effects, such as consumption of seeds, or indirectly via changes in disturbance frequency or intensity. Because they incorporate litter and live plant material into the soil, hogs may also influence ground cover and soil nutrient concentrations. We investigated the impacts of exotic feral hogs in a mixed pine-hardwood forest in the Big Thicket National Preserve (Texas, USA) where they are abundant. We established sixteen 10 m × 10 m plots and fenced eight of them to exclude feral hogs for 7 years. Excluding hogs increased the diversity of woody plants in the understory. Large seeded (>250 mg) species known to be preferred forage of feral hogs all responded positively to hog exclusion, thus consumption of Carya (hickory nuts), Quercus (acorns), and Nyssa seeds (tupelo) by hogs may be causing this pattern. The only exotic woody species, Sapium sebiferum (Chinese tallow tree), was more than twice as abundant with hogs present, perhaps as a response to increased disturbance. Hogs increased the amount of bare soil by decreasing the amounts of plant cover and surface litter. Plots with hogs present had lower soil C:N, possibly due to accelerated rates of nitrogen mineralization. These results demonstrate that hogs may influence future overstory composition and reduce tree diversity in this forest. Management of hogs may be desirable in this and other forests where large-seeded species are an important component of the ecosystem. Further, by accelerating litter breakdown and elevating nitrogen in the soil, hogs have the potential to impact local vegetation composition via nitrogen inputs as well.  相似文献   

5.
Chusquea ramosissima is a native monocarpic bamboo species growing in subtropical forests of northeastern Argentina, which can dominate gaps and open forests in the region, particularly after human disturbance. This bamboo species started to flower in different areas of northeastern Argentina in 2001, with the flowering peak during 2002 and 2003 and small isolated flowering events still occurring until 2010. We studied the effects of C. ramosissima flowering and die-back on microclimate, litter decomposition, nutrient availability, sapling growth, abundance and regeneration of tree canopy species. We wanted to know how environmental conditions and ecosystem processes change through time after bamboo flowering and if bamboo die-back would favor regeneration of canopy trees. Twenty 50 × 50 m plots of flowering and non-flowering bamboo were permanently marked and vegetation dynamics as well as nutrient cycling and microclimate studies were performed. C. ramosissima die-back enhanced growth and reduced mortality rate of tree saplings during the first year after flowering. Only growth of tree saplings previously established was enhanced by the flowering event and tree-species richness and saplings abundance of canopy trees did not change as expected due to bamboo flowering. The short-term effect of tree saplings growth was likely due to incident solar radiation at the forest floor which doubled in the first year after the bamboo flowering event. Increased light availability at the forest floor simultaneously promoted the growth of other understory plants such as ferns, lianas and Piper spp. that rapidly colonized gaps and intercepted a percentage of the incident solar radiation after the first year, which together with an increased litter layer due to the senescence of the bamboo, may have inhibited establishment of new tree individuals and affected tree growth. Contrary to predictions, soil water, litter decomposition and soil nutrients were not significantly affected by bamboo flowering. Thus, successful tree regeneration in gaps following bamboo flowering appears to be restricted to a very narrow window of increased light availability (i.e., 1 year) before growth of other understory plants and rapid re-colonization of bamboo. Changes in resource availability, and the opportunity for overstory regeneration after bamboo flowering events appears to depend on climatic and community characteristics of the ecosystem where the flowering event occurs and also, on the flowering patterns and their synchronicity.  相似文献   

6.
We determined patterns of microsite suppression in dwarf bamboo Sasa nipponica when grazing deer were absent. This bamboo species is able to outcompete Hondo spruce (Picea jezoensis var. hondoensis) saplings under many environmental circumstances. We set up two 10 × 100 m plots inside a deer-proof fence within a subalpine forest on Mt. Ohdaigahara, central Japan, and two similarly sized plots outside the fence. Within the plots, we surveyed microsites where spruce saplings grew. We measured height and shoot elongation of all spruce saplings, and culm height and cover ratios of dwarf bamboo growing around each spruce sapling. Spruce sapling density and average height were higher inside the deer-proof fence than outside, as were bamboo height and cover. Thus, there was a negative effect of deer browsing on vegetation parameters outside the fence and a suppression of the negative effect of bamboo on spruce sapling growth inside the fence. Spruce sapling height was higher in tree-fall pits than in other microsites inside the fence, whereas both dwarf bamboo height and cover were lower in pits and rocky sites than elsewhere. In soil and collar microsites, spruce sapling shoot growth was lower and bamboo height and cover were higher than in pits and rocky sites. Inside the fence, dwarf bamboo cover was high, but pits and rocks suppressed its growth, allowing spruce saplings to flourish. To restore heavily damaged spruce forests with advanced saplings, it will be necessary to construct deer-proof fences and create and maintain microsites with pits and rocks.  相似文献   

7.
Carbon pools in two Quercus petraea (sessile oak) dominated chronosequences under different forest management (high forest and coppice with standards) were investigated. The objective was to study temporal carbon dynamics, in particular carbon sequestration in the soil and woody biomass production, in common forest management systems in eastern Austria along with stand development. The chronosequence approach was used to substitute time-for-space to enable coverage of a full rotation period in each system. Carbon content was determined in the following compartments: aboveground biomass, litter, soil to a depth of 50 cm, living root biomass and decomposing residues in the mineral soil horizons. Biomass carbon pools, except fine roots and residues, were estimated using species-specific allometric functions. Total carbon pools were on average 143 Mg ha−1 in the high forest stand (HF) and 213 Mg ha−1 in the coppice with standards stand (CS). The mean share of the total organic carbon pool (TOC) which is soil organic carbon (SOC) differs only marginally between HF (43.4%) and CS (42.1%), indicating the dominance of site factors, particularly climate, in controlling this ratio. While there was no significant change in O-layer and SOC stores over stand development, we found clear relationships between living biomass (aboveground and belowground) pools and C:N ratio in topsoil horizons with stand age. SOC pools seem to be very stable and an impact of silvicultural interventions was not detected with the applied method. Rapid decomposition and mineralization of litter, indicated by low O-horizon pools with wide C:N ratios of residual woody debris at the end of the vegetation period, suggests high rates of turnover in this fraction. CS, in contrast to HF benefits from rapid resprouting after coppicing and hence seems less vulnerable to conditions of low rainfall and drying topsoil.  相似文献   

8.
We examined the response of understory plants in mature maple-dominated forests of southern Québec, Canada, following about 30 years of high deer densities, using a deer exclosure experiment. An exclosure and a paired control of 625 m2 each were established on six sites in 1998. An exclosure and a paired control of 16 m2 were added at each of the same sites in 2003 but under a recent canopy gap to determine if light could enhance plant responses. We measured plant richness and abundance, and aboveground biomass of different plant groups for 8 years in the understory plots and for 3 years in the canopy gaps. Four herbaceous species were also monitored individually in the same plots. No significant differences between treatments were found in plots under forest cover, except for lateral obstruction at 0–50 cm height which was higher in the exclosures. Under canopy gaps, however, tree seedling and total plant abundance were higher in deer exclosures than in control plots. Trillium erectum recovered partially as individuals were taller, had larger leaves and more frequently produced a flower or a fruit in the absence of deer browsing under forest cover. To a lesser extent, Erythronium americanum and Maianthemum canadense also exhibited signs of recovery but were still at the single-leaf stage after 8 years of recovery. In general, the different plant groups exhibited little recovery following deer exclusion, possibly because of the low light levels that prevailed in the understory of undisturbed maple-dominated forests. The higher latitude of the present study could also contribute to the slow recovery rates of the different groups of plants compared to studies conducted in northeastern USA. Variability among sites and years had an effect on detection of statistically significant differences. Trends are however appearing over time, suggesting that many understory plants are recovering very slowly following deer exclusion. Our results emphasize the importance of studying large herbivore–forest interactions on different groups of plants, but also on specific species, and under different latitudes to be fully understood.  相似文献   

9.
Seasonal and spatial variability of litterfall and NO3− and NH4+ leaching from the litter layer and 5-cm soil depth were investigated along a slope in a tropical dry evergreen forest in northeastern Thailand. Using ion exchange resin and buried bag methods, the vertical flux and transformation of inorganic nitrogen (N) were observed during four periods (dry, early wet, middle wet, and late wet seasons) at 15 subplots in a 180-m × 40-m rectangular plot on the slope. Annual N input via litterfall and inorganic N leached from the litter layer and from 5-cm depth soil were 12.5, 6.9, and 3.7 g N m−2 year−1, respectively, whereas net mineralization and the inorganic N pool in 0–5-cm soil were 7.1 g N m−2 year−1 and 1.4 g N m−2, respectively. During the early wet season (90 days), we observed 82% and 74% of annual NO3− leaching from the litter layer and 5-cm soil depth, respectively. Higher N input via leaf litterfall in the dry season and via precipitation in the early wet season may have led to higher NO3− leaching rate from litter and surface soil layers during the early wet season. Large spatial variability in both NO3− vertical flux and litterfall was also observed within stands. Small-scale spatial patterns of total N input via litterfall were significantly correlated with NO3− leaching rate from the surface soil layer. In tropical dry evergreen forests, litterfall variability may be crucial to the remarkable seasonal changes and spatial variation in annual NO3− vertical flux in surface soil layers.  相似文献   

10.
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11.
Information on soil carbon sequestration and its interaction with nitrogen availability is rather limited, since soil processes account for the most significant unknowns in the C and N cycles. In this paper we compare three completely different approaches to calculate carbon sequestration in forest soils. The first approach is the limit-value concept, in which the soil carbon accumulation is estimated by multiplying the annual litter fall with the recalcitrant fraction of the decomposing plant litter, which depends on the nitrogen and calcium content in the litter. The second approach is the N-balance method, where carbon sequestration is calculated from the nitrogen retention in the soil multiplied with the present soil C/N ratio in organic layer and mineral topsoil. The third approach is the dynamic SMART2 model in combination with an empirical approach to assess litter fall inputs. The comparison is done by first validating the methods at three chronosequences with measured C pools, two in Denmark and one in Sweden, and then application on 192 intensive monitoring plots located in the Northern and Western part of Europe. Considering all three chronosequences, the N-balance method was generally most in accordance with the C pool measurements, although the SMART2 model was also quite consistent with the measurements at two chronosequences. The limit-value approach generally overestimated the soil carbon sequestration. At the intensive monitoring plots, the limit-value concept calculated the highest carbon sequestration, ranging from 160 to 978 kg ha−1 year−1, followed by the N-balance method which ranged from 0 to 535 kg ha−1 year−1. With SMART2 we calculated the lowest carbon sequestration from −30 to 254 kg ha−1 year−1. All the three approaches found lower carbon sequestration at a latitude from 60 to 70° compared to latitudes from 40 to 50 and from 50 to 60. Considering the validation of the three approaches, the range in results from both the N-balance method and SMART2 model seems most appropriate.  相似文献   

12.
Current management practices encourage conversion of red alder (Alnus rubra) riparian forests to conifers in the Pacific Northwest U.S. Patches of young naturally regenerated conifers are commonly present in alder dominated riparian areas and an understanding of the soil processes in these patches will be helpful in guiding future riparian management. Study objectives were to: (1) determine decomposition rates of red alder leaves in riparian alder and conifer patches, (2) relate decomposition rates to environmental factors and litter chemistry, and (3) determine nutrient release from decomposing alder leaves in these patches. Study sites were riparian areas adjacent to Brown and Le Bar creeks in the Skokomish River basin, Olympic National Forest, Washington. Red alder leaves were placed in litterbags in red alder and conifer riparian patches along each stream in November 2000 and collected after 1 and 3 years. There was rapid mass loss of alder leaves in the first year in both patch types, but decomposition was significantly faster (p < 0.05) in alder patches (43.2% mass remaining, k = 0.855 year−1) than in conifer patches (48.4% mass remaining, k = 0.734 year−1). There was little mass loss after the first year and no significant difference in decomposition rates. After 3 years mass remaining was 44.2% (k = 0.283 year−1) and 47.8% (k = 0.48 year−1) in alder and conifer patches, respectively. Decomposition rate differences were attributed more to the effects of the different litters in each patch and the influence on soil microbial and faunal communities than differences in soil temperature and moisture. The forest floor was deeper in conifer patches (3.7 cm) than alder (1.8 cm) patches. This was ascribed to slower decomposition rates in conifer patches, greater litterfall in conifer patches, and/or removal of alder surface litter by flooding. Alder patches were lower in elevation (0.8 m above bankfull width) than conifer patches (2.2 m). Forest floor and soil C and N concentrations and pHs were not significantly different in alder and conifer patches. Nutrient release from decomposing alder leaves was not significantly different in conifer and alder patches, although there was a trend for C, N, P, K, and Ca to be lost faster from leaves in alder patches than conifer patches in the first year. Red alder litter input to riparian conifer patches will initially decompose rapidly and provide nutrients, particularly N and P to conifers, as well as enhancing soil C since long-term decomposition rates are slow.  相似文献   

13.
Lowland evergreen rainforests in southern Chile growing on highly productive soils and accessible sites have been subjected to traditional and industrial logging of valuable timber trees. Old-growth rain forests in this area are characterized by highly conservative N cycles, which results in an efficient N use of ecosystems. We hypothesize that different logging practices, by changing forest structure and species composition, can alter the quantity and quality (i.e. C/N ratio) of litterfall and soil organic matter and soil microbial processes that determine N storage and availability. To test this hypothesis we investigated chemical properties, microbial N transformations, N fluxes and N storage in soils of lowland evergreen rainforests of Chiloé Island after 10 years since industrial selective logging (ISL) and in stands subjected to traditional selective logging (TSL) by landowners in small properties. We compared them to reference unlogged old-growth stands (OG) in the same area. Tree basal area was more reduced in the stands subjected to ISL than to TSL. Litterfall inputs were similar in both logging treatments as in OG stands. This was due to greater biomass of understory species after logging. In TSL understory tree species determined a higher litterfall C/N ratio than ISL. We found higher soil N availability and content of base cations in surface soils of logged forests than in OG. The litter horizon of OG forest had significantly higher rates of non-symbiotic N fixation than logged forests. In the ISL treatment there was a trend toward increasing soil denitrification and significantly higher NO3–N/Nt ratio in spring waters, which led to a stronger δ15N signal in surface and deep soils. We conclude that massive understory occupation by the shade-intolerant native bamboo Chusquea quila in ISL led to enhanced litter quality (lower C/N ratios) relaxing the tightness of the N cycle, which increased soil N availability leading to a higher proportion of nitrate in spring waters and higher gaseous N losses. In contrast, under TSL a higher litterfall C/N ratio slowed decomposition and net N mineralization rates thus reducing the chances for N losses, and enhancing C and N storage in soil. We suggest that sustainable logging practices in these rain forests should be based on lower rates of canopy removal to enhance colonization of the understory by shade-tolerant trees, which are associated with a more efficient N cycle.  相似文献   

14.
Changes in temperature, precipitation, and atmospheric carbon dioxide (CO2) concentration that are expected in the coming decades will have profound impacts on terrestrial ecosystem net primary production (NPP). Nearly all models linking forest NPP with soil carbon (C) predict that increased NPP will result in either unchanged or increased soil C storage, and that decreased NPP will result in decreased soil C storage. However, linkages between forest productivity and soil C storage may not be so simple and direct. In an old-growth coniferous forest located in the H.J. Andrews Experimental Forest, OR, USA, we experimentally doubled needle litter inputs, and found that actual soil respiration rates exceeded those expected due to the C added by the extra needles. Here, we estimated that this ‘priming effect’ accounted for 11.5–21.6% of annual CO2 efflux from litter-amended plots, or an additional 137–256 g C m−2 yr−1 loss of stored C to the atmosphere. Soil priming was seasonal, with greatest amounts occurring in June–August coincident with peaks in temperature and dry summer conditions. As a result of priming, mineral soil was more resistant to further mineralization during laboratory incubations. Soil lignin-derived phenols in the Double Litter plots were more oxidized than in the control, suggesting that the soil residue was more degraded. Our hypothesis that excess dissolved organic C produced from the added litter provided the link between the forest floor and mineral soil and a substrate for soil priming was not supported. Instead, the rhizosphere, and associated mycorrhizal fungi, likely responded directly to the added aboveground litter inputs. Our results revealed that enhanced NPP may lead to accelerated processing of some stored soil C, but that the effects of increased NPP on ecosystem C storage will be based on a net balance among all ecosystem C pools and are likely to be ecosystem-dependant. Forest C models need to include these complex linkages between forest productivity and soil C storage.  相似文献   

15.
The aim of the present study was to quantify the effects of roe deer browsing relative to the effects of soil preparation, shelterwood density (light) and seed fall. Ultimately, the goal was better silvicultural guidelines to support the use of natural beech regeneration in the close-to-nature forestry context. In spring 1995, an experiment on natural regeneration with three experimental stands (0.28–0.6 ha) was installed in a beech (Fagus sylvatica) dominated broadleaved forest inhabited by a dense roe deer (Capreolus capreolus) population (24 deer km−2). The autumn of 1995 offered a large beech mast (stand average 307–1168 beechnuts m−2).Treatments installed included fencing to exclude deer, soil preparation, shelterwood thinning, and the relevant control treatments. Roe deer and soil preparation had dramatic effects on regeneration from the moment the seedlings sprouted in the spring 1996. The regeneration sprouted only sparsely in the unprepared seedbed producing only 5 seedlings m−2 (average across fence treatments) after 2 months, which was reduced to 1 sapling m−2 8 years later. Deer had no significant effect on the regeneration density of the unprepared seedbed. In contrast, the cultivated seedbeds produced initially (after 2 months) up to 191 seedlings m−2 protected by fence, whereas the densities in the unfenced treatments peaked by 22 seedlings m−2. By the end of the study, these densities were reduced to 22 saplings m−2 in the permanently fenced mineral soil seedbed and to 2 saplings m−2 in the unfenced mineral soil seedbed. Regeneration height outside the permanent fence was generally only half the height of the regeneration inside. Additionally, we found significantly positive effects of increasing light and seed fall on regeneration density and of light on regeneration growth.We conclude that the roe deer only reduced the regeneration density of the dense regenerations established in the cultivated seedbeds. However, the regeneration density of the unprepared seedbed was not sufficient to support a future high quality stand. We found no treatment that within the timeframe of this study could support successful regeneration establishment outside the permanent fences. Whether this will change in the future with more time given for the regeneration to establish is yet to be revealed.  相似文献   

16.
We compared different potential indicators of nitrogen (N) availability across 50 beech forests growing on a wide range of soils in northeastern France. Among the 50 sites measured, high elevation acidic soils had the highest potential net N mineralization in the A horizon (PNM0–5 cm), while low elevation neutral and calcareous soils had the lowest (PNM0–5 cm). We found that (PNM0–5 cm) was negatively correlated with soil pH (R2 = 0.47***) and positively correlated with microbial C/N (R2 = 0.34***). However, when high elevation sites were excluded from analyses, the relationship between PNM0–5 cm and soil pH as well as microbial C/N became weaker (R2 = 0.23*** for both variables). We found no relationship between PNM0–5 cm and organic N concentration, soil C/N, or vegetation-based indices for N availability (Ellenberg N and Ecoplant C/N). Bivariate linear regression analyses showed that 69% of the variability in percent nitrification (%Nitrif) was explained by both soil pH (0–5 cm) and soil C/N. Percent nitrification was strongly correlated with vegetation-based indices for N availability. The Ellenberg N and R (pH index) values together explained 74% of the variation in %Nitrif. No relationship was found between %Nitrif and soil δ15N (natural abundance in 15N). Of the 76 plant species evaluated, the probability of presence of 61 plant species was significantly correlated with %Nitrif while the probability of presence of 27 plant species only was correlated with PNM0–5 cm. From these results, we believe that the use of plant community composition or the combination of soil pH and C/N are robust indicators of N availability.  相似文献   

17.
Soil properties were compared in adjacent 50-year-old Norway spruce, Scots pine and silver birch stands growing on similar soils in south-west Sweden. The effects of tree species were most apparent in the humus layer and decreased with soil depth. At 20-30 cm depth in the mineral soil, species differences in soil properties were small and mostly not significant. Soil C, N, K, Ca, Mg, and Na content, pH, base saturation and fine root biomass all significantly differed between humus layers of different species. Since the climate, parent material, land use history and soil type were similar, the differences can be ascribed to tree species. Spruce stands had the largest amounts of carbon stored down to 30 cm depth in mineral soil (7.3 kg C m−2), whereas birch stands, with the lowest production, smallest amount of litterfall and lowest C:N ratio in litter and humus, had the smallest carbon pool (4.1 kg C m−2), with pine intermediate (4.9 kg C m−2). Similarly, soil nitrogen pools amounted to 349, 269, and 240 g N m−2 for spruce, pine, and birch stands, respectively. The humus layer in birch stands was thin and mixed with mineral soil, and soil pH was highest in the birch stands. Spruce had the thickest humus layer with the lowest pH.  相似文献   

18.
Through the long-term measurement and development of a method for partitioning the products of decomposing litter, the impact of chemical components of forest debris on soil organic carbon (SOC) accumulation was studied in a forest succession series in South China. We quantified how litter quality is strongly correlated with the partitioning of respiration, dissolved organic carbon (DOC) and fragments of decomposing litter. In the succession sequence of 60-year-old pine forest (PF), to 80-year-old mixed pine and evergreen broadleaved forest (MF) to more than 400-year-old monsoon evergreen broadleaved forest (MEBF), the litter C/N ratios and lignin contents were gradually decreasing, which in turn were correlated with increasing litter decomposition constants (k-values), gradually shortening residence times of standing litter pool. And, 53.5%, 65.6% and 76.2% of the gravimetric litter mass losses were going belowground through both DOC and fragmentation. Correspondingly, the SOC accumulation rates in the top 20 cm of mineral soils for the three forests from 1978 to 2008 were 26 ± 4, 33 ± 5 and 67 ± 5 g C m−2 yr−1, respectively. Results of the study support the idea that in order to increase carbon sequestration in soils and long-term functional ability of forest ecosystems to act as carbon sinks, “Kyoto Forests” should be designed and reconstructed with a high diversity of broadleaved species, especially containing nitrogen-fixing trees.  相似文献   

19.
The effect of harvest residue management options on biomass and nutrient accumulation in understory vegetation, as well as the contribution of understory to nutrient cycling, were assessed during the early rotation stage of a Eucalyptus globulus Labill. plantation in Central Portugal. The effects of residue management options on early tree growth were also evaluated. Treatments established at the time of plantation and replicated four times in a simple completely randomised design included removal of harvest residues (R), incorporation of residues into the soil by harrowing (I) and maintenance of residues on the soil surface (S). Understory biomass was sampled in the spring between 2002 and 2006, and every 2 months between March 2006 and March 2007. The latter samples were stratified into biomass, standing dead mass and litter for net above ground primary production (NAPP) assessment. Samples were oven dried, weighed and analysed for nutrient contents. Results showed that understory standing biomass strongly increased from the first to the third year and that quantities of nutrients accumulated in ground vegetation followed similar patterns between the three treatments. Nutrient accumulation in ground vegetation was greater than in tree biomass until at least the second spring after plantation. Bimonthly sampling revealed treatment R to have the largest amounts of standing biomass, standing dead mass, litter and nutrient immobilisation, while treatment S exhibited the lowest values. NAPP (4th–5th year) was 639, 511 and 362 g m−2 year−1, respectively in R, I and S, corresponding the standing biomass increase to 277, 183 and 143 g m−2 year−1. These values are comparable to those observed for litter fall in similar stands (age and tree density) in the same area. The contribution of ground vegetation to nutrient accumulation in the system was unaffected by harvest residue management methods, but further research is necessary in order to establish whether slash management options influence long term tree growth and vegetation dynamics.  相似文献   

20.
Black cottonwood (Populus trichocarpa Torr. and Gray) is a deciduous tree species that extends from Alaska through coastal regions of western Canada into the northwestern United States and as far south as Baja California. We examined the influence of black cottonwood on soil fertility within a forest dominated by Douglas-fir [Pseudotsuga menziessi (Mirb.) Franco], western hemlock [Tsuga heterophylla (Raf.) Sarg], and western red cedar (Thuja plicata Donn ex. D. Don.). Six circular 0.008 ha plots with a single cottonwood tree in the center of conifers were paired with six conifer plots (of the same size) without cottonwood. Litterfall, litter decomposition, properties of forest floor and mineral soil, and N mineralization were compared between plot types. Cottonwood litter had higher concentrations of almost all elements relative to conifer litter. Mass loss did not differ between cottonwood and fir/hemlock litter on cottonwood sites. Twice the amount of mull-like humus form (vermimull and mullmoder, 56%) was found in cottonwood plots compared to 28% in conifer plots. Higher pH (4.4) was found in the forest floor under cottonwood compared to conifer (3.9). Total N concentration (3.33 g/kg) and base saturation (68%) were higher in the mineral soil under cottonwood compared to conifers (2.98 g/kg total N and 50% base saturation). Net ammonification and net mineralization were both lower under cottonwood. These results suggest a variable effect of cottonwood on soil fertility within coastal western hemlock forests with some soil variables changed in a favourable direction and some in an unfavourable direction.  相似文献   

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