Fresh Litter Research Articles

Interventions to reduce the bacterial load in recycled broiler litter

Two experiments were undertaken to evaluate the bacterial load in recycled litter between broiler flocks following addition of quicklime (T1), windrowing (T2), shallow fermentation (T3), and control (no intervention, T4). The first experiment was developed in field conditions in which the broiler houses were accompanied by 6 consecutive flocks and the effect of the treatments was assessed on enterobacteria and aerobic mesophiles. The second experiment was conducted in an experimental broiler house with recycled litter for assessment of Salmonella Enteritidis phage type 4 (SE PT4). In the field study, T3 presented the best results in reducing enterobacteria in broiler litter in relation to the other treatments, with the highest reduction occurring in the first 3 flocks, tending to stabilization from the fourth flock onward for all the treatments assessed. From the third to sixth flocks, enterobacteria level at the end of the treatments (d 12) was lower than the average in the fresh litter, except in T4. All treatments reduced aerobic mesophiles throughout the flocks, where T2 showed the highest reduction. The percentage of dry matter in the broiler litter diminished in T4 and increased in T3 over the course of the flocks. In the second experiment, the drop in the SE PT4 level in the broiler litter first occurred in T2 and T3. However, all the treatments except for T4 eliminated SE PT4 within 12 d. The temperature of the broiler litter in T2 was higher in relation to the other treatments. The results show that litter treatment prior to reutilization by the successive broiler flock is required to reduce the level of residual bacteria. The fermentative treatments (T2 and T3) were found to be superior to the others in terms of reducing the bacterial load, with shallow fermentation standing out with the highest reduction of enterobacteria and equivalent SE PT4 elimination when compared to windrowing.

Impacts of warming and nitrogen addition on organic fraction release in fresh litter of Larix potaninii in alpine zone of the western Sichuan Province, China

The decomposition dynamics of organic components in fresh litter of Larix potaninii were monitored by in situ litter-bag incubation under four treatments, i.e., field condition (CK), nitrogen addition (AN, 2 g N·m-2), warming by top-open chamber (OTC), nitrogen addition with warming by top-open chamber (OTC+AN), from November to next September. Decomposition of water-soluble sugar, water-soluble phenol and total polyphenol were stimulated significantly under the treatment OTC, AN and OTC+AN during the first four months compared with the CK, but the difference of these components release narrowed with the extension of incubation time. Compared with CK, releases of dichloromethane-extractable fraction, acid soluble carbohydrates, acid soluble lignin, and acid insoluble lignin, were inhibited significantly under OTC, AN, and OTC+AN treatments, and the significance of inhibitory effect under the treatments was: OTC > OTC+AN > AN. Especially, in the treatment of OTC, half-life of dichloromethane-extractable fraction and acid inso-luble lignin in fresh litter were doubled, and that of hot-water soluble component was prolonged by more than 50% compared with CK. Half-life of water-soluble sugar, water-soluble phenol, total polyphenol, acid-soluble carbohydrate and acid-soluble lignin in fresh litter were respectively 182, 159, 127, 154 and 190 d in CK, and these components seem to be easily mineralized organic fraction. Meanwhile, half-life of hot-water soluble components, dichloromethane-extractable fraction, and acid insoluble lignin was 209, 302 and 318 d, respectively, indicating these fractions recalcitrant to decomposing in the fresh litter. Decomposition of all components in L. potaninii litter occurred in cold season from November to next March, which suggested that cold season was the most important period for litter decay in the alpine conifer. Generally it was assumed that microorganisms were inactive and decomposition of organic matters was slow in alpine soil during harsh winter, while the results of fresh litter incubation in situ showed that all components decomposed very fast during the period. Therefore, in alpine treeline, nitrogen deposition and warming would inhibit rather than promote decomposition of fresh litter, which would be conducive to carbon sequestration for the alpine soil ecosystem.

Biopore history determines the microbial community composition in subsoil hotspots

Biopores are hotspots of nutrient mobilisation and shortcuts for carbon (C) into subsoils. C processing relies on microbial community composition, which remains unexplored in subsoil biopores. Phospholipid fatty acids (PLFAs; markers for living microbial groups) and amino sugars (microbial necromass markers) were extracted from two subsoil depths (45–75 cm ; 75–105 cm) and three biopore types: (I) drilosphere of Lumbricus terrestris L., (II) 2-year-old root biopores and (III) 1.5-year-old root biopores plus six 6 months of L. terrestris activities. Biopore C contents were at least 2.5 times higher than in bulk soil, causing 26–35 times higher Σ PLFAs g-1 soil. The highest Σ PLFAs were found in both earthworm biopore types; thus, the highest soil organic matter and nutrient turnover were assumed. Σ PLFAs was 33% lower in root pores than in earthworm pores. The treatment affected the microbial community composition more strongly than soil depth, hinting to similar C quality in biopores: Gram-positives including actinobacteria were more abundant in root pores than in earthworm pores, probably due to lower C bioavailability in the former. Both earthworm pore types featured fresh litter input, promoting growth of Gram-negatives and fungi. Earthworms in root pores shifted the composition of the microbial community heavily and turned root pores into earthworm pores within 6 months. Only recent communities were affected and they reflect a strong heterogeneity of microbial activity and functions in subsoil hotspots, whereas biopore-specific necromass accumulation from different microbial groups was absent.

Warming and ozone exposure effects on silver birch (Betula pendula Roth) leaf litter quality, microbial growth and decomposition

Climate warming is expected to accelerate decomposition in boreal forests, but the concomitant effects of tropospheric ozone (O3), a phytotoxic greenhouse gas, alone and in combination with warming, are poorly understood. We studied how these two climatic factors affect leaf litter decomposition of two silver birch genotypes. We used field exposure for growing saplings and native and reciprocal transplant experiments for litter incubation to disentangle environmental and litter quality mediated effects of temperature and O3 on litter mass loss. We analysed litter C% and N% and microbial biomass (using qPCR) in fresh litter and after 217 and 257 days of incubation. Warming decreased fresh litter C% and N% and bacterial DNA, whereas elevated O3 increased N% and bacterial and fungal DNA, equally for both genotypes. In contrast, most effects on microbes during litter incubation varied between the two genotypes. Warming effects on microbes were mainly environmental, but despite having effects on litter quality and microbial growth, warming and O3 both had only weak or no effects on litter mass loss. Litter quality and microbial growth in northern birch stands are likely to change due to warming and O3 exposures, but effects on litter decomposition rate may remain weak.

Silica uptake and release in live and decaying biomass in a northern hardwood forest

In terrestrial ecosystems, a large portion (20-80%) of the dissolved Si (DSi) in soil solution has passed through vegetation. While the importance of this "terrestrial Si filter" is generally accepted, few data exist on the pools and fluxes of Si in forest vegetation and the rate of release of Si from decomposing plant tissues. We quantified the pools and fluxes of Si through vegetation and coarse woody debris (CWD) in a northern hardwood forest ecosystem (Watershed 6, W6) at the Hubbard Brook Experimental Forest (HBEF) in New Hampshire, USA. Previous work suggested that the decomposition of CWD may have significantly contributed to an excess of DSi reported in stream-waters following experimental deforestation of Watershed 2 (W2) at the HBEF. We found that woody biomass (wood+bark) and foliage account for approximately 65% and 31%, respectively, of the total Si in biomass at the HBEF. During the decay of American beech (Fagus grandifolia) boles, Si loss tracked the whole-bole mass loss, while yellow birch (Betula alleghaniensis) and sugar maple (Acer saccharum) decomposition resulted in a preferential Si retention of up to 30% after 16yr. A power-law model for the changes in wood and bark Si concentrations during decomposition, in combination with an exponential model for whole-bole mass loss, successfully reproduced Si dynamics in decaying boles. Our data suggest that a minimum of 50% of the DSi annually produced in the soil of a biogeochemical reference watershed (W6) derives from biogenic Si (BSi) dissolution. The major source is fresh litter, whereas only ~2% comes from the decay of CWD. Decay of tree boles could only account for 9% of the excess DSi release observed following the experimental deforestation of W2. Therefore, elevated DSi concentrations after forest disturbance are largely derived from other sources (e.g., dissolution of BSi from forest floor soils and/or mineral weathering).

Water, Rather than Temperature, Dominantly Impacts How Soil Fauna Affect Dissolved Carbon and Nitrogen Release from Fresh Litter during Early Litter Decomposition

Longstanding observations suggest that dissolved materials are lost from fresh litter through leaching, but the role of soil fauna in controlling this process has been poorly documented. In this study, a litterbag experiment employing litterbags with different mesh sizes (3 mm to permit soil fauna access and 0.04 mm to exclude fauna access) was conducted in three habitats (arid valley, ecotone and subalpine forest) with changes in climate and vegetation types to evaluate the effects of soil fauna on the concentrations of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) during the first year of decomposition. The results showed that the individual density and community abundance of soil fauna greatly varied among these habitats, but Prostigmata, Isotomidae and Oribatida were the dominant soil invertebrates. At the end of the experiment, the mass remaining of foliar litter ranged from 58% for shrub litter to 77% for birch litter, and the DOC and TDN concentrations decreased to 54%–85% and increased to 34%–269%, respectively, when soil fauna were not present. The effects of soil fauna on the concentrations of both DOC and TDN in foliar litter were greater in the subalpine forest (wetter but colder) during the winter and in the arid valley (warmer but drier) during the growing season, and this effect was positively correlated with water content. Moreover, the effects of fauna on DOC and TDN concentrations were greater for high-quality litter and were related to the C/N ratio. These results suggest that water, rather than temperature, dominates how fauna affect the release of dissolved substances from fresh litter.

Measuring the effect of freezing on hydrolytic and oxidative extracellular enzyme activities associated with plant litter decomposition

Extracellular enzymes are the proximate drivers of biogeochemical cycling in ecosystems. In terrestrial environments, studies of extracellular enzyme activities (EEAs) in soils far outpace studies in substrates such as leaf litter. Despite recent methodological advances that have made EEA assays feasible for researchers conducting large-scale studies, there are still a number of methodological uncertainties that exist, particularly when working with less studied substrates (i.e. grassland leaf litter). These uncertainties are of particular importance when considering the logistics of sample processing after collecting samples in large numbers and/or from distant field sites. Studies of soil handling suggest that while assaying biochemical and molecular markers in fresh samples is ideal, that freezing samples is often a viable solution if the former is not feasible. Due to the inherent differences of litter and soil materials and associated microenvironments, we can draw only limited conclusions from the results of studies on sample handling using soil. As a result, we investigated the effect of two typical freezing temperatures (−20° and −80°C) on subsequent EEAs in decomposing leaf litter material. We incubated litter material from six grassland plant communities for 12 weeks at 25°C, then measured the EEA of five hydrolytic and two oxidative enzymes in fresh litter, and in litter that was frozen for four weeks at either −20° or −80°C. Results indicate that freezing only affected the activity of N-acetyl-β glucosaminidase (NAG), an enzyme that was affected by freezing in prior soil studies. We observed an approximate 35% increase in NAG activity with freezing. The remaining six EEAs measured were not observed to be affected by freezing, and the level of freezing (i.e. temperature) did not influence any of the seven EEAs measured, suggesting that freezing is a suitable alternative when laboratory analyses on fresh litter samples are not logistically possible.

Eutrophication triggers contrasting multilevel feedbacks on litter accumulation and decomposition in fens.

Eutrophication is a major threat for the persistence of nutrient-poor fens, as multilevel feedbacks on decomposition rates could trigger carbon loss and increase nutrient cycling. Here, we experimentally investigate the effects of macronutrient (NPK) enrichment on litter quality of six species of sedge (Carex sp.), which we relate to litter decomposition rates in a nutrient-poor and nutrient-rich environment. Our research focused on four levels: we examined how eutrophication alters (1) fresh litter production ("productivity shift"), (2) litter stoichiometry within the same species ("intraspecific shift"), (3) overall litter stoichiometry of the vegetation under the prediction that low-competitive species are outcompeted by fast-growing competitors ("interspecific shift"), and (4) litter decomposition rates due to an altered external environment (e.g., shifts in microbial activity; "exogenous shift"). Eutrophication triggered a strong increase in fresh litter production. Moreover, individuals of the same species produced litter with lower C:N and C:P ratios, higher K contents, and lower lignin, Ca and Mg contents (intraspecific shift), which increased litter decomposability. In addition, species typical for eutrophic conditions produced more easily degradable litter than did species typical for nutrient-poor conditions (interspecific shift). However, the effects of nutrient loading of the external environment (exogenous shift) were contradictory. Here, interactions between litter type and ambient nutrient level indicate that the (exogenous) effects of eutrophication on litterdecomposition rates are strongly dependent of litter quality. Moreover, parameters of litter quality only correlated with decomposition rates for litter incubated in nutrient-poor environments, but not in eutrophic environments. This suggests that rates of litter decomposition can be uncoupled from litter stoichiometry under eutrophic conditions. In conclusion, our results show that eutrophication affects litter accumulation and -decomposition at multiple levels, in which stimulatory and inhibitory effects interact. The cumulative effect of these interactions ultimately determine whether peatlands remain sinks or become sources of carbon under eutrophic conditions.

From Litter to Humus in a Norwegian Spruce Forest: Long-Term Studies on the Decomposition of Needles and Cones

The aim of this review and synthesis is to illustrate the gradual transformation of needles and cones from litter to humus. Individual needles may follow quite different decomposition pathways, which contributes to a diverse humus structure. In the litter layer (Oi), about 40% of the needles were excavated by special mites that produced slowly decomposable excrements. In the fermentation layer (Oe), needles which happened to be in close contact with fine roots decomposed more rapidly. Cones decomposed slower than needles during the first 3–5 years, so the role of cones in carbon (C) storage may be greater than indicated by their fraction of fresh litter. Over a 13 years period, potassium (K), magnesium (Mg) and phosphorus (P) in cones was released, while the total amount of calcium (Ca), manganese (Mn), iron (Fe) and aluminium (Al) increased strongly. Nitrogen concentration increased but the total nitrogen content remained rather constant. After 13 years, the cones had sunk about 6 cm into the soil and lost 60% of their dry weight but were morphologically intact. A cone monitored for 28 years was fully recognizable and had not yet reached the stable Oa layer. The most inert decomposition products in the Oa layer were fragments of needles and cone scales, microarthropod excrements and chitinous insect remains.

How do microbial communities in top- and subsoil respond to root litter addition under field conditions?

Contrasting microbial community composition and activity at different soil depths may affect root litter decomposition. These effects have up to now been investigated mainly in laboratory studies, which may not be able to take into account complex in situ conditions. Our study aimed to analyze the composition and activity of microbial communities after addition of 13C labeled wheat root litter to a loamy soil under grassland at 30, 60 and 90 cm depths, during a three-year field experiment. We investigated the dynamics of bacterial and fungal abundances and community structures by DNA genotyping and pyrosequencing of 16S and 18S rDNAs. The genetic structures of bacterial and fungal communities were evaluated by automated ribosomal intergenetic spacer analysis. The functions of these communities were analysed by determination of extracellular enzyme activities and viable microbial communities involved in 13C labeled organic matter decomposition studied by 13C PLFAs.The abundance of fungal and bacterial communities (16S and 18S rDNAs and PLFA) and the potential activities of enzymes involved in the C- and N-cycles were significantly higher at the top 30 cm compared with deeper soil throughout the experiment. Both were stimulated by fresh litter input. A trend to decreasing bacterial and fungal richness was noted after root litter addition at 30 cm, while richness of bacteria at 90 cm and those of fungi at 60 and 90 cm increased. Moreover, root litter addition caused a reduction of the Shannon Weaver Diversity index and a shift in microbial community structure at all three depths, which was more pronounced for bacteria at 30 and 60 cm and for fungi at 90 cm. The changes during litter degradation resulted in similar dynamics of most enzyme activities at all depths. Chitinase activity was enhanced after 29 months compared to initial conditions indicating the availability of high amounts of microbial detritus. The degrading microbial community as assessed by 13C PLFA showed similar temporal dynamics at all three depths. Fungal contribution to this community decreased during later stages of litter degradation, while the contribution of Gram+ bacteria increased. We conclude that litter addition led to convergence of microbial communities of top- and subsoil through stimulation of copiotrophic populations. Soil microbial community structures are thus connected with the amount of fresh litter input. Enzyme activities and 13C PLFA reflect to some extent the changes occurring during degradation, i.e. exhaustion of fresh plant material and accumulation of detritus.

Temporal variation in the strength of podzolization as indicated by lysimeter data

This study examines trends in podzolization – both temporally and with depth – as indicated by translocation of dissolved organic carbon (DOC), iron (Fe) and aluminum (Al) in soil water. Water as saturated flow was captured by zero-tension lysimeters installed below the O, E and B horizons of six Spodosol pedons in Michigan, USA. Over a 2-year timespan, we sampled soil water on 36 different dates, resulting in 505 samples. All samples were analyzed for DOC, whereas Fe and Al contents were determined for a subset of 227 samples.Cumulative water fluxes are high during both spring snowmelt and the fall (autumn) season, when much water is moving as saturated flow. Water flux rates are much greater during snowmelt, and when averaged over all horizons, 1.15 times more water is translocated through the soil during snowmelt than in fall, even though the latter is routinely twice as long. Translocation of DOC out of the O horizon is a dominant process in these soils during snowmelt, peaking in mid-snowmelt. It peaks again – even higher – in fall, as rains strip C from fresh litter. Overall, little DOC leaves the soil system; B horizons are effective traps for C being transported in soil water. Surprisingly, E horizons retain DOC in almost all seasons, but particularly in fall and early snowmelt, as water percolates through C-rich, fresh litter. The thick, bright, C-poor E horizons in these soils suggest that, over long timescales, in situ mineralization of C exceeds the net retention of DOC from the O horizons above. Translocation of Fe and Al in soil water also has a distinct annual bimodality, largely following that of DOC. This component of podzolization peaks in mid-snowmelt and again late in fall. On an annual basis, considerably more Al moves in soil water than Fe; 1.9 times more Al than Fe is translocated out of E horizons, and 1.8 times more Al is lost from B horizons.Our study supports existing pedogenic theory for the snowy midlatitudes, in which snowmelt is seen as a key period for podzolization. Daily rates of translocation of metals and DOC moving in saturated flow during snowmelt are considerably higher than for any other time of year. Our study also sheds new light on the importance of fall rains to podzolization. Although the daily rates of translocation for fall are much less than during snowmelt, the greater length of the season, the relatively high frequency of rain events, and the abundance of fresh C combine to make fall an important period for translocation of metals and DOC. Thus, our study highlights that podzolization here has a short but intense “pulse” during snowmelt, and a second, less intense but longer period during fall. Little podzolization occurs during winter, and during summer, translocation occurs only during infrequent, large storms.

Below‐ground biological responses to pyrogenic organic matter and litter inputs in grasslands

SummaryTerrestrial ecosystems are often burned by both managed and wildfires. During a fire, the above‐ground biomass that would typically accumulate and be decomposed as litter on the soil surface is combusted. Pyrogenic organic matter (PyOM) remaining after a fire is a considerably more recalcitrant organic input to the soil than fresh litter. The activity and community composition of soil organisms responsible for decomposition of organic matter and nutrient recycling in the soil could thus be affected by altered resource availability caused by frequent fires.We examined the effect of PyOMvs. fresh litter inputs to soil biota at both an annually burned and an infrequently burned tallgrass prairie site by tracing13C‐ and15N‐labelled litter and PyOMinto growing plant roots, microbial phospholipid fatty acids (PLFAs) and soil nematodes for 1 year.Litter‐derived C or N was incorporated into microbes, nematodes and roots, while PyOMcontributed minimally to soil microbes and plant roots and was not detectable in nematodes. Soil microbial and nematode abundances in the PyOMamended plots did not significantly differ from the bare soil plots, but nematodes were more abundant and microbialPLFAs less abundant in litter‐amended plots. The annually burned site had less predator and omnivore nematodes, with increased abundance of microbial feeders and greater microbial uptake of litter C.An alteration of the soil food web structure caused by burning and the removal of the litter layer, along with the accumulation of non‐microbially decomposed PyOMin the soil, contributes to the limitation of N cycling in frequently burned ecosystems.ALay Summaryis available for this article.

Litter heterogeneity modulates fungal activity, C mineralization and N retention in the boreal forest floor

The implications of forest floor heterogeneity for fungal activity, nutrient retention and carbon sequestration within the forest floor remain poorly documented. This information would be particularly relevant to situations where large changes in fresh litter occur such as following stand replacing disturbances. Numerous laboratory studies have documented mycelial translocation of simple forms of C and nutrients between contrasting substrates, allowing fungi to overcome local deficiencies. In slightly more complex but less controlled conditions, we assessed how factors contributing to forest floor heterogeneity—decay state, litter origin and tree species—individually affect fungal activity during decomposition. We also assessed how the juxtaposition of litters of contrasting nutrient and C status (decay state) alter fungal activity within individual substrates. We expected fungal biomass to be reallocated to C-rich litters while lignocellulolytic activity would increase in all juxtaposed litters. A microcosm experiment was conducted in which wood and leaf litters of one softwood species (Pinus banksiana) and one hardwood species (Populus tremuloïdes) were incubated alone or in combination with litters of contrasting decay states. Litter mass loss, change in N content, C mineralization, fungal biomass, specific respiration rate and lignocellulolytic activity were measured after 15 and 30 weeks. The decay state of litter had the most pronounced and consistent effects on fungal activity, with higher fungal biomass and lignocellulolytic enzyme activity in well decomposed litters and higher mass loss, C mineralization and specific respiration rate in fresh litters. In juxtaposed litters, fungal biomass was initially reallocated to fresh litters when incubated with well decomposed litters. Cellulolytic activity also increased by 30% in juxtaposed fresh litters while Mn-peroxidase activity increased by 42% in both fresh and well decomposed litters. With the longer incubation period, C mineralization and specific respiration of fungal biomass increased in juxtaposed well decomposed wood, indicating an increase in overflow metabolism presumably in response to an increase in labile C. Fresh litters that were juxtaposed increased their N content while that of single litters decreased. A better understanding of fine scale mechanisms affecting litter decomposition could improve our ability to forecast ecosystem response to disturbance.

Intestinal Microbiota of Broiler Chickens As Affected by Litter Management Regimens.

Poultry litter is a mixture of bedding materials and enteric bacteria excreted by chickens, and it is typically reused for multiple growth cycles in commercial broiler production. Thus, bacteria can be transmitted from one growth cycle to the next via litter. However, it remains poorly understood how litter reuse affects development and composition of chicken gut microbiota. In this study, the effect of litter reuse on the microbiota in litter and in chicken gut was investigated using 2 litter management regimens: fresh vs. reused litter. Samples of ileal mucosa and cecal digesta were collected from young chicks (10 days of age) and mature birds (35 days of age). Based on analysis using DGGE and pyrosequencing of bacterial 16S rRNA gene amplicons, the microbiota of both the ileal mucosa and the cecal contents was affected by both litter management regimen and age of birds. Faecalibacterium, Oscillospira, Butyricicoccus, and one unclassified candidate genus closely related to Ruminococcus were most predominant in the cecal samples, while Lactobacillus was predominant in the ileal samples at both ages and in the cecal samples collected at day 10. At days 10 and 35, 8 and 3 genera, respectively, in the cecal luminal microbiota differed significantly in relative abundance between the 2 litter management regimens. Compared to the fresh litter, reused litter increased predominance of halotolerant/alkaliphilic bacteria and Faecalibacterium prausnitzii, a butyrate-producing gut bacterium. This study suggests that litter management regimens affect the chicken GI microbiota, which may impact the host nutritional status and intestinal health.

Homogenization of detrital leachate in an old-growth coniferous forest, OR: DOC fluorescence signatures in soils undergoing long-term litter manipulations

Characterizing the relationship between plant detrital inputs and the resulting dissolved organic carbon (DOC) leachate is vital to understanding the ultimate fate of root carbon, fallen wood and needles in forested watersheds. Similarly, elucidating chemical differences in the soil DOC pool may help to explain which DOC fractions are sorbed to mineral surfaces and contribute to accumulation of soil organic carbon, are respired as CO2, or are exported to nearby catchments. In order to test the hypothesis that soils with different detrital inputs impart a detectable signal on DOC in mineral soil, soil solution DOC was sampled from the Detrital Input and Removal Treatment (DIRT) plots located in the H.J. Andrews Experimental Forest, OR. Multiple types of fresh litter extracts, along with lysimeter and soil extracts from DIRT treatment plots were characterized using UV-Vis and fluorescence spectroscopy coupled with the Cory and McKnight (Environ Sci Technol 39:8142–8149, 2005) parallel factor analysis (PARAFAC) model. Principal component analysis of 13 unique fluorophores distinguished using PARAFAC show that litter and soil extracts (Douglas-fir needles, wood of decomposition Class 2, Class 3 and Class 5, O-horizon, and 0–5 cm A-horizon) each have distinct fluorescence signatures. However, while litter-leached DOC chemistry varies by litter type, neither lysimeter-collected DOC or soil extracts in the DIRT plots show statistically significant differences in fluorescence signatures among treatments, even after 17 years of litter manipulations. The lack of observed differences among DIRT treatments suggests that both abiotic interactions and microbial activity effectively homogenize organic carbon constituents within the dissolved pool. Minor but observable changes in PARAFAC components and optical indices during a 1-month biodegradation incubation of litter and soil extracts indicate that while biodegradation significantly alters DOC chemistry, abiotic mechanisms are also critical to DOC transformation in these soils with high sorption capacity. Although leachates from different plant detrital sources have distinct carbon chemical signatures, these DOC signatures are effectively homogenized after passage through mineral soil. These results highlight the dominant role of both biotic and abiotic interactions in controlling the chemistry of DOC in shallow soils.

Impact of ectohumus application in birch and pine nurseries on the presence of soil mites (Acari), Oribatida in particular

Abstract Intensively used forest nurseries are characterised by degradation processes that lead to a drop in the quality of seedlings. The main reason of this problem is a decrease in biological soil diversity. Therefore, an attempt of nursery soil enrichment by introducing ectohumus – as compost and fresh litter – from the pine forest was carried out. The research was carried out in 2009–2011 in the Bielawy forest nursery near the city of Toruń, Poland. The objective of the study was to determine the impact of organic fertilisation (compost made up of forest humus) and mulching using fresh ectohumus on the density and community composition of Acari mites and on species composition of oribatid mites (Oribatida) in the nurseries of silver birch and Scots pine. Mites, especially oribatid mites, were treated as bioindicators of soil biological activity. Research has shown that mulching using fresh ectohumus caused a multiple increase in the density of mites, especially in saprophagous mites Oribatida. Oribatid mites were clearly more numerous in birch cultivation than in that of pine. Overall, 27 species of oribatid mites were found. Mulching resulted in a significant growth in species diversity in both cultivations. The most numerous oribatid mite in the area under the study was Oribatula tibialis. This species was present in all plots and showed clear preference for birch cultivation. Tectocepheus velatus and Oppiella nova, common and known to be present in a variety of environments, were slightly less numerous.

Molecular characterization of soil organic matter from native vegetation–pasture–sugarcane transitions in Brazil

Replacing pastures (PA) with sugarcane (SG) has been deemed an agronomically feasible strategy for sugarcane expansion in Brazil. However, there are some uncertainties about the environmental impacts regarding this land use change (LUC), mainly related to soil organic matter (SOM), a key factor of environmental sustainability of Brazilian ethanol. LUC-related losses of SOM can overcome the C savings from biofuels. The molecular composition of SOM was evaluated to understand the C dynamics regarding LUC from PA to SG, using native vegetation (NV) as reference. Our study area was located in the south-central region of Brazil. Soil sampling was performed at three depths (0–0.1m, 0.2–0.3m and 0.9–1m) in three representative sites with known LUC history and management practice since 1970. Pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) was chosen to study SOM chemistry. Content and isotopic composition of soil organic C and N were also determined. The LUC caused decreases on C and N contents and on δ13C isotopic values. Depth was the major factor that influenced SOM composition, while the influence of LUC was mainly evident in surface soils and diminished rapidly with depth. The main difference in SOM composition undergoing the conversion PA-SG was a higher contribution from compounds associated to fresh litter inputs. The high contribution from fresh litter, having a relatively low mean residence time and increasing decomposition rates, is probably a major factor that drives C losses in areas undergoing sugarcane expansion.

改变碳输入对亚热带人工林土壤微生物生物量和群落组成的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 改变碳输入对亚热带人工林土壤微生物生物量和群落组成的影响 DOI: 10.5846/stxb201310142473 作者: 作者单位: 1,福建师范大学地理科学学院 作者简介: 通讯作者: 中图分类号: S718.5 基金项目: 国家自然科学基金项目(41371269);教育部新世纪优秀人才支持计划(DB-168);福建省杰出青年科学基金项目(2060203) Changes of above- and belowground carbon input affected soil microbial biomass and community composition in two tree species plantations in subtropical China Author: Affiliation: College of Geographical Sciences, Fujian Normal University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:通过在亚热带杉木(Cunninghamia lanceolata)和米老排(Mytilaria laosensis)人工林中设置互换凋落物、去除凋落物、去除凋落物+去除根系和对照处理来分析改变地上、地下碳输入对人工林土壤微生物生物量和群落组成的影响。结果显示,改变地上、地下碳输入对土壤微生物生物量碳、氮的影响因树种而异。在米老排林中,土壤微生物生物量不受碳源的限制。而在杉木林中,加入米老排凋落物、去除凋落物和去除凋落物+去除根系3种处理中土壤微生物生物量碳、氮具有明显增加的趋势。磷脂脂肪酸分析结果显示,杉木林中,添加高质量的米老排凋落物后,革兰氏阳性细菌、阴性细菌、丛枝菌根真菌、放线菌和真菌群落生物量分别显著增加了24%、24%、53%、25%、28%,革兰氏阴性细菌和丛枝菌根真菌的相对丰度均有显著增加。与对照相比,杉木林中去除凋落物后革兰氏阳性细菌、阴性细菌、丛枝菌根真菌、放线菌和真菌群落生物量分别显著增加了22%、29%、44%、25%、52%,真菌与细菌比值显著增加了21%。但是,去除凋落物+去除根系处理对两个树种人工林土壤微生物群落组成均无显著影响。米老排和杉木林土壤微生物生物量碳、氮的季节变化格局不同,土壤养分有效性可能是驱动土壤微生物生物量季节变化的主要因子。未来研究需要关注凋落物和根系在不同树种人工林中对土壤微生物群落的相对贡献。 Abstract:We employed Detritus Input and Removal Experiment (DIRT) to examine the effects of carbon (C) input on soil microbial biomass and community composition in 19-year-old Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) and Mytilaria laosensis forests in subtropical China. The treatments included:(1) reciprocal litter transplant; (2) litter removal; (3) no inputs (litter removal+ root trenching); and (4) control. Each treatment had four 2 m×2 m plots. From January to December 2012, we collected the top 5 cm soil layer samples monthly from C. lanceolata and M. laosensis plots. Chloroform fumigation-extraction was used to determine the soil microbial biomass C and nitrogen (N) contents. Phospholipid fatty acid (PLFA) analysis was used to characterize the microbial community composition in soil samples collected in June 2012. Results suggested that the C input manipulations induced differences in soil microbial biomass and community composition were dependent on tree species. C input manipulations had no significant effects on soil microbial biomass C and N under M. laosensis. However, the concentrations of microbial biomass C and N seemed to increase under C. lanceolata. PLFA analysis showed that M. laosensis litter significantly increased the contents of bacterial PLFAs, fungal PLFAs and actinomycetes, and significantly enhanced the percent abundance of gram-negative bacteria and arbuscular mycorrhizal fungi under C. lanceolata. Litter removal significantly increased the contents of gram-positive bacteria, gram-negative bacteria, arbuscular mycorrhizal fungi, actinomycetes and fungi by 22%, 29%, 44%, 25% and 52%, respectively, and also increased the fungi to bacteria ratio by 21% compared with the control in C. lanceolata soil. However, litter removal and root trenching did not change soil microbial community composition in C. lanceolata and M. laosensis soils. Seasonal patterns of microbial biomass C and N were different between C. lanceolata and M. laosensis plantations. Nutrient availability rather than soil temperature, moisture or fresh litter input, may determine seasonal fluctuation of soil microbial biomass in this study. Our results suggested that further studies are required to confirm the relative contribution of above- and belowground C inputs in different tree species plantations in subtropical China. 参考文献 相似文献 引证文献

Radiocesium immobilization to leaf litter by fungi during first-year decomposition in a deciduous forest in Fukushima

Vast forest areas in eastern Japan have been contaminated with radio-isotopes by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. Radiocesium (radioCs) is known to remain bioavailable in forest ecosystems for a long time, and it is necessary to terminate the cycling process to decontaminate the forest ecosystem. We observed radiocesium concentrations of leaf litter during decomposition on a forest floor where radiocesium (137Cs) contamination was ∼155 kBq/m2. Litter bag experiments were conducted with newly fallen mixed deciduous leaf litter in a deciduous forest (alt. 610 m) about 50 km from the FDNPP. Litter bags were retrieved in April, June, August, October, and December 2012. Fresh litter 137Cs concentration was ∼3000 Bq/kg in December 2011. During the decomposition process on the forest floor, litter 137Cs concentration increased rapidly and exceeded 25,000 Bq/kg after 6 months, whereas potassium (K) concentration in the litter was rather stable, indicating that radiocesium and K showed contrasting dynamics during the early decomposition phase. Nitrogen, phosphorus, and 137Cs contents were positively correlated to fungal biomass, evaluated by phospholipid fatty acids in the litter during decomposition. The increase of radiocesium concentration mainly occurred during from April to October, when fungal growth peaked. Therefore, this suggests fungal translocation of nutrients from outside the litter substrate (immobilization) is the mechanism to increase radiocesium in the decomposing litter. The amount of 137Cs contained in the 1-year-old decomposed leaf litter was estimated to be 4% per area of the soil-contaminated 137Cs.

Decomposing cones of Norway spruce (Picea abies (L.) H. Karst.): dry weight loss, chemical changes, and vertical transport in a Norwegian raw humus soil profile

Naturally shed cones of Norway spruce (Picea abies) were placed on the forest floor, partly on moss-covered ground, and partly on vegetation-free needle mats. Numbered sticks allowed individual recovery after 1, 3, 5, 7, 9, 11, and 13 years. During the first nine years, cones decomposed fastest in the moss site. After 13 years, dry weight loss was about 60% in both habitats, but cones still retained their shape. In the moss site, cones were then situated in the middle of the organic layer, with their underside about 3 cm above the bleached layer. Cones in the needle mat profile had sunk less. One cone with rather intact shape was found below a nylon strip laid out 28 years earlier. Compared to needle litter from Norway spruce and Scots pine, spruce cones had low concentrations of Ca, Mn, and Fe. The concentration of these elements, as well as N, Al, and S, was greatly increased during decomposition. Ca, Mn, Fe, and Al were immobilized for a long time, as their total amount per cone increased with time. Cones decomposed slower than needles, so their role in humus composition and carbon storage may be greater than indicated by their fraction of fresh litter.