Tree Litter Research Articles

Differential effects of forest-floor litter and roots on soil organic carbon formation in a temperate oak forest

Both forest-floor litter and roots are known to be involved in the formation of soil organic carbon (SOC), but it remains elusive how the two contrasting types of plant carbon sources would differentiate in their effects on SOC. Here we used field-based soil mesocosms to study the responses of SOC components (i.e. mineral-associated organic C [MAOC], particulate organic C [POC], and dissolved organic C [DOC]) and pathways of production (i.e. plant-derived vs. microbial-derived C compounds) to multi-year treatments of forest-floor litter and roots in a temperate oak forest in central China. After eight years, the concentrations of both POC and MAOC were significantly higher in plots with presence of forest-floor litter than in those exclusive of both forest-floor litter and roots at the soil depth of 0–5 cm; roots predominantly affected POC but not the total SOC. The contributions from the forest-floor litter and roots to total SOC and its components were all non-additive; the plots with co-occurrence of forest-floor litter and roots had 49.7% less total SOC, 36.6% less POC, and 54.7% less MAOC, than the sum of the plots with only forest-floor litter or roots, at the soil depth of 0–5 cm. The concentrations of both lignin phenols and microbial biomass carbon (MBC) were significantly higher in plots with only forest-floor litter than in those exclusive of both forest-floor litter and roots down to a depth of 20 cm, and the plant-derived neutral sugars were significantly higher in plots with only forest-floor litter than in those exclusive of both forest-floor litter and roots at the soil depth of 0–10 cm. In contrast, the concentration of lignin phenols was significantly higher in plots with only roots than in those exclusive of both forest-floor litter and roots below the depth of 5 cm, and the concentrations of MBC and microbial-derived neutral sugars were higher in plots with only roots than in those exclusive of both forest-floor litter and roots at the soil depth of 0–10 cm. The plots with co-occurrence of forest-floor litter and roots had a significantly higher concentration of lignin phenols at all soil depths investigated, as well as higher concentrations of the plant- and microbial-derived neutral sugars and MBC at the soil depth of 0–5 cm, than those exclusive of both forest-floor litter and roots; the effects were all non-additive such that the plots with co-occurrence of forest-floor litter and roots had less plant- and microbial-derived C compounds than the sum of the values between the plots with only forest-floor litter and the plots with only roots. The contributions of amino sugars to SOC did not significantly respond to either the treatments with forest-floor litter and roots or soil depth, albeit variable MBC concentrations. In addition, our results show that the microbial-derived neutral sugars were positively correlated with plant-derived neutral sugars. Findings in this study provide empirical evidence on the primacy of forest-floor litter in SOC pool at the soil depth of 0–5 cm, and demonstrate the differential roles and contributions between forest-floor litter and roots in the pathways of SOC formation and spatial differentiation of carbon compounds.

Restitution of fresh organic matter to the soil by woody plants in the fields of ANR in the Maradi region of central eastern Niger

Niger, like other Sahelian countries, has experienced severe droughts that have led to the disappearance of vegetation cover in most regions and have led populations to adopt restoration techniques. This is the case of the practice of assisted natural regeneration (ANR) developed in the Maradi region. The objective of this study is therefore to quantify the fresh organic matter (FOM) of woody plants in ANR fields. The study fields were selected in two ANR terroirs (Boussaragui and Dan Saga). The direct method was used to quantify litter inputs from trees, shrubs and woody clumps that contribute to soil organic carbon stock (SOCS). Tree litter was quantified by a trap door and tussock litter by collection after clearing. The results of this work show that litterfall in the dry season occurs throughout the season, at different times depending on the terroir, with a shift in production peaks between plots in the same terroir. The average dry season litter production is 265.52 and 937.62 kg. ha-1 for Boussaragui and Dan Saga respectively. Trees and shrubs produce more litter and thus return more FOM to the soil than do tussocks. This study thus reveals that woody plants in ANR fields contribute significantly to improving the organic carbon stock of cultivated sandy soils.

Loss of soil carbon and nitrogen indicates climate change-induced alterations in a temperate forest ecosystem

Climate warming is expected to influence terrestrial biogeochemical cycles by modifying the quality and quantity of plant litter input to soils. Although a growing number of studies recognize the importance of plant litter input in influencing the loss of soil organic matter (SOM) through a phenomenon called the priming effect (PE), the exact mechanisms behind PE are not well known. Importantly, most PE research is based on short term pot experiments in which fresh organic matter (FOM) input is represented by a single addition of compounds of unnaturally simple chemical composition. Furthermore, only a few studies exist in which the PE was explored in terms of organic C (SOC) and total N content in the soil. Here, we report results of a 3-year long litter manipulation study conducted under natural conditions in a broadleaved Korean pine forest in N-E China. We show that the extra supply (twice the normal input) of aboveground tree litter composing of conifer needles, leaves and small twigs was associated not only with slightly decreased SOC (by 5%) but especially that of soil total N (STN) (by 15%) content in the top soil (0–5 cm depth). In contrast, removal of litter resulted in an increased (ca. 15%) amount of both SOC and STN during the study when compared to control soils receiving natural litter input. Despite the enhanced leaf litter decomposition rate in the treatment receiving extra litter, the changes in SOC and STN were related neither to soil microbial biomass nor to community composition. The amount of N lost (40.0 g m−2) in the soil due to litter addition was ca. three times the amount of N added (12.3 g m−2) via the litter, while the amount of C lost (238 g m−2) was about one third of that added (940 g m−2), suggesting that soil N in our research site is more prone to the PE than soil C. As we did not manipulate belowground FOM input, our results suggest that input of aboveground litter rather than that by roots explained the PE in our study. Results of our long-term study conducted under natural conditions in undisturbed forest soils highlight the large potential of recalcitrant, aboveground litter to affect the PE, which should not go unnoticed when predicting the role of forest soils under conditions (such as climate warming) when these soils act as C sinks.

Sodium as a subsidy in the spring: evidence for a phenology of sodium limitation

Understanding the factors that mediate carbon (C) cycling is increasingly important as anthropogenic activities and climate change alter ecosystems. Decomposition rates mediate C cycling and are in part regulated by sodium (Na) where Na is limiting up to some threshold after which Na becomes stressful and reduces decomposition rates (i.e., the Sodium Subsidy-Stress hypothesis). An overlooked pathway by which decomposers encounter increased salts like NaCl is through plants, which often take up Na in proportion to soil concentrations. Here we tested the hypothesis that Na addition through litter (detritus) and water and their interaction would impact detrital processing and leachate chemistry. Laboratory riparian soil mesocosms received either artificial litter (100% cellulose sponges) soaked in 0.05% NaCl (NaClL) or just H2O (H2OL: control) and half of each litter treatment received weekly additions of 150 ml of either 0.05% NaCl water (NaClW) or just H2O (H2OW: control). After 8 weeks decomposition was higher in NaCl addition treatments (both NaClL and NaClW and their combo) than controls (H2OL + H2OW) but reflected a unimodal relationship where the saltiest treatment (NaClL + NaClW) was only marginally higher than controls indicating a subsidy-stress response. Previous studies in this system found that Na addition in either water or litter decreased decomposition. However, differences may reflect a phenology of Na demand where Na-limitation increases in the spring (this study). These results indicate that our understanding of how Na impacts detrital processes, C cycling, and aquatic-terrestrial linkages necessitates incorporation of temporal dynamics.

A northward range shift of sugar maple (Acer saccharum) in Eastern Canada should reduce soil carbon storage, with no effect on carbon stability

Climate change is shifting the home range of sugar maple (Acer saccharum Marsh.) northward, onto the southern range of balsam fir (Abies balsamea (L.) Mill.). Such a shift from coniferous to deciduous forests will result in more labile tree litter, potentially decreasing soil organic carbon (SOC) storage in the forest floor. However, microbial processing of deciduous litter may be more efficient, leading to more stable SOC as mineral-associated organic matter (C-MAOM) in the mineral soil. To test these hypotheses, we surveyed 15 stands of each tree species along the sugar maple–balsam fir ecotone in Eastern Canada. In each of the 30 stands, we dug three soil pits and measured SOC stocks in the forest floor and across five mineral soil depths. Mineral soil samples were incubated 51 weeks and monitored for CO2 emission rates, to quantify the bioreactive SOC pool. We also derived two indices of microbial SOC processing based on δ13C signatures and assessed the proportion of C-MAOM at each soil depth. SOC stocks were 21% lower in sugar maple than in balsam fir stands, mainly because of thicker forest floors in the latter. Soil CO2 emissions were higher in samples from sugar maple stands during the first 10 weeks of the incubation, but higher in samples from balsam fir stands thereafter. Consequently, the bioreactive SOC pool did not differ between tree species. Microbial SOC processing was higher under sugar maple than under balsam fir in only a subset of stands occurring in one region. Likewise, the effect of tree species on C-MAOM was significant in only one region, but contrary to expectations (i.e. balsam fir > sugar maple). We conclude that a northward shift of sugar maple will reduce SOC storage but will not increase SOC stability in the mineral soil, potentially creating positive feedback on global warming.

Nitrogen enrichment amplifies the effects of litter treatments on soil microorganisms and ecosystem functions in grazed and non-grazed grasslands

Litter removal or addition and nitrogen (N) enrichment are two important methods for restoring grasslands. Despite the litter alteration and N enrichment effect on soil microorganisms in different ecological systems of independent have got the good evaluation, it is still unknown how N enrichment modifies the effects of litter removal and addition on soil microorganisms and ecosystem function in different grasslands. Here, we conducted two independent experiments to assess the effects of litter addition/removal and N enrichment on soil microorganisms and ecosystem functions in a typical grassland. In a litter-removal experiment, we evaluated how N addition regulated the effect of litter removal in a long-term non-grazed grassland. In a litter-addition experiment, we evaluated how N addition regulated the effect of litter addition in a long-term over-grazed grassland. We found that the response of plant communities to removal/addition of litter and N enrichment was relatively minor in both non-grazed and grazed grasslands; the high precipitation during the sampling year may mask the effects of the litter and N treatments on plant community. Litter addition in the grazed grassland increased fungal and AMF biomass and decreased bacteria: fungi ratio, but litter removal in the non-grazed grassland had only minor effects on soil microbial variables. Litter removal in the non-grazed grassland and litter addition in the grazed grassland had different effects on soil carbon (Cmin) and N mineralization (Nmin), but N enrichment consistently reduced soil Cmin and Nmin in non-grazed and grazed grasslands. In addition, N enrichment amplified the effects of litter treatments on soil microorganisms and mineralization. These findings indicate that removal of litter from non-grazed grasslands and addition of this litter to grazed grasslands may help to restore grasslands, and the amount of N enrichment should be adjusted to optimize the positive effect of nitrogen enrichment and weaken the negative effect of nitrogen enrichment. Overall, our experimental results revealed that the effects of litter treatment on soil microorganisms and mineralization in grazed and non-grazed semi-arid grasslands are amplified by N enrichment.

Trace metal uptake in forage systems receiving long‐term applications of alum‐treated or untreated poultry litter

AbstractTreating poultry litter with alum (Al2[SO4]3·14H2O) is a commonly used best management strategy for reducing ammonia (NH3) volatilization and phosphorus (P) runoff and leaching. However, little is known about how this amendment affects trace metal availability and uptake by forages, as well as potential issues with phytotoxicity, toxicity to grazing animals, and overall yield. The objective of this study was to determine longitudinal effects of alum‐treated poultry litter, untreated litter, ammonium nitrate, and an unfertilized control on trace metal (As, Cu, Se, and Zn) and S concentrations and uptake by tall fescue (Festuca arundinacea Schreb.), yield, as well as availability in soil over 20 years. Greater (p < 0.05) Mehlich‐3 extractable soil As and subsequent forage As uptake occurred with alum beyond the 6.72 Mg ha−1 rate; however, forage As concentrations were not affected by alum. Forage yields were greater with alum‐treated and untreated litters than with ammonium nitrate applied at the same N rate. Treating litter with alum generally did not improve tall fescue yields, except at the lowest litter rate (2.24 Mg ha−1). Alum treatment of poultry litter has been shown to be a cost‐effective best management practice that reduces ammonia volatilization, which improves air quality and poultry production, while reducing P and heavy metal runoff and ultimately improving water quality. Given that trace metal and S concentrations in forages were all in the normal ranges, treating poultry litter with alum does not pose issues with respect to metal phytotoxicity and/or toxicity to grazing animals.

Pilot Study on the Action of Thymus vulgaris Essential Oil in Treating the Most Common Bacterial Contaminants and Salmonella enterica subsp. enterica Serovar Derby in Poultry Litter.

The indiscriminate use of antimicrobials in poultry farms is linked to the increase in multi-resistant bacteria. Accordingly, based on the antimicrobial properties of Thyme Essential Oil (TEO), the present study evaluated the effects of TEO on the reduction of common microbial contaminants and Salmonella on poultry litter. A litter bulk sample was collected in a broiler farm and qualitative/quantitative investigations identified Escherichia coli and Mammaliicoccus lentus. The experimental contamination with Salmonella Derby wild strain was also performed. All pathogens showed phenotypic and genotypic resistance to different classes of antibiotics. The litter, split in different units, was treated with aqueous solutions of TEO at different concentrations (5% to 1.25%), demonstrating its effectiveness in reducing the total number of bacteria. The strongest antibacterial action was observed at the lowest concentration against Enterobacteriaceae, with a growth reduction compared to the positive control of 73.3% and 77.8% against E. coli and Salmonella Derby, respectively, while towards M. lentus the reduction was 50%. Our data confirm the antimicrobial activity of TEO and suggest its possible application for the treatment of poultry litter as an effective and natural approach for the prevention of diseases caused by the most common bacteria that colonize poultry farms, counteracting the onset of antibiotic resistance.

Effects of litter placement, soil moisture and temperature on soil carbon dioxide emissions in a sandy grassland soil

AbstractSemiarid grasslands contribute significantly to global soil carbon (C) storage. Carbon loss from these systems via microbial decomposition is controlled by abiotic and biotic factors such as soil moisture and temperature and C input. Plant litter in these systems can be present above the soil surface or mixed with surface soil by trampling, especially in intensively grazed areas. A quantitative understanding of abiotic factors' interactive effect is critical for predicting soil C dynamics in response to grassland management and environmental conditions changes. Therefore, we conducted a 3‐month laboratory incubation experiment to quantify the impact of litter placement and soil moisture on soil carbon dioxide (CO2) emissions under three controlled temperatures. The treatments including three litter placements (no litter, litter on top and litter mixed with surface soil) and three soil moisture levels (23%, 37% and 50% water‐filled pore space [WFPS]) were incubated at three temperatures (10°C, 20°C and 30°C). Carbon dioxide fluxes were measured every 2 weeks. Soil CO2 fluxes were higher for all moisture and litter treatments initially and declined overtime at 20°C and 30°C. Mixing litter with soil increased the cumulative CO2 emissions by 24% and 19.5% at 20°C and 30°C, respectively, compared to no litter. Also, soil‐litter mixing compared with litter on top showed a 14.3% and 21.6% increase in cumulative CO2 emissions at temperatures of 20°C and 30°C, respectively. At all temperatures, 37% and 50% WFPS resulted in similar cumulative CO2 emissions. The results from this study indicate that rising temperatures from 10°C to 30°C accelerate the effect of soil litter mixing on increasing CO2 emissions compared to litter on top and no litter.

Assessment of Earthworm Services on Litter Mineralisation and Nutrient Release in Annual and Perennial Energy Crops (Zea mays vs. Silphium perfoliatum)

Abundant and functionally diverse earthworm communities in perennials deliver ecosystem services like increasing nutrient availability by incorporating organic matter. This study aimed to analyse the decomposition of annual and perennial energy crop residues, and the subsequent nutrient release, depending on earthworm functional diversity. In a laboratory experiment, two ecological earthworm groups—anecics (detritivorous Lumbricus terrestris (L.)) and endogeics (geophagous Aporrectodea caliginosa and A. rosea)—were incubated with wilted cup plant (Silphium perfoliatum) and maize (Zea mays) litter for 4 or 8 weeks. Decomposition and consumption rates were calculated. The C, N and P in litter and casts were analysed. Mineralisation was a function of earthworm biomass and the number of individuals. Functional diversity had no beneficial effect. Decomposition was found to be highest in treatments with detritivorous earthworms, i.e., higher earthworm biomass, yet consumption and nutrient turnover in relation to earthworm biomass were higher in treatments with geophages indicating enhanced competition. N limitation became apparent in both litter treatments and was predominant with cup plant litter. N limitation and recalcitrant cell wall compounds affected consumption rates and the egestion of total C and P. While N in casts was lower than expected, P was increased. We observed that the effects manifested at different stages of decomposition of maize and cup plant, highlighting differences in temporal development of decomposition and nutrient turnover between litter types. Our results indicate that earthworms promote decomposition of recalcitrant litter and nutrient turnover, but N limitation may hamper nutrient release. Cup plant systems offer a suitable habitat for soil-dwelling organisms, but management approaches must consider the adequate input of organic matter as an energy and nutrient source to enhance ecosystem service provision.

Tree-distance and tree-species effects on soil biota in a temperate agroforestry system

AimsCropland agroforestry systems are land-use systems with numerous environmental advantages over monoculture croplands including promotion of soil life. This study aimed to investigate tree-species and tree-distance effects on soil biota in a temperate agroforestry system.MethodsOur study was conducted at a paired alley-cropping and monoculture cropland system. The tree rows of the agroforestry system comprised of blocks of poplar Fritzi Pauley, poplar Max 1 or black locust. Within the agroforestry system, soil microbial and earthworm communities were collected along transects spanning from the center of the tree rows into the crop rows. Archaea, bacteria, and fungi were quantified using real-time PCR. The community composition of fungi and earthworms was deciphered using amplicon sequencing and morphological identification, respectively.ResultsTree rows promoted the abundance of bacteria and earthworms, which we attribute mainly to tree litter input and the absence of tillage. Fungal community composition was altered by the tree rows, resulting in an increased proportion of ectomycorrhizal fungi in the tree-row associated mycobiome. The proportion of Blumeria graminis, the causal agent of powdery mildew, increased with increasing distance from the trees. We suggest that enhanced microbial antagonism, increased earthworm densities and/or altered microclimate contributed to the suppression of B. graminis in vicinity of the trees. Tree-species effect had a minor influence on the abundance and composition of soil communities at our study site.ConclusionsIn comparison to monoculture cropland, agroforestry benefits the abundance, diversity, and function of soil biota and may enhance soil suppressiveness.

Evaluation of the Combined C/N ratio, DO Set Point, and HRT Influence on Nitrogen Removal Rate in One-Stage Reactor Through Partial Nitrification Anammox Process During Treatment of Synthetic Digestate of Poultry Litter Wastewater

Highlights A one-stage reactor PN/A process was developed and evaluated. The highest TN removal rate was 87.3% for the PN/A process to treat synthetic wastewater containing poultry litter at room temperature. Bacterial composition of mature sludge community of wastewater was investigated in this study. Adjusted parameters controlled the growth of AOB and NOB. Abstract. Anammox is an increasingly common process used for the treatment of municipally rejected water and even mainstream wastewater due to its low oxygen demand. However, anammox is not commonly utilized in the treatment of poultry litter because of its high organic content, which would inhibit the anammox process. One-stage partial nitrification and anammox (PN/A) process was developed and evaluated for removing total nitrogen (TN) content from synthetic digestate of poultry litter using a sequencing batch biofilm reactor (SBBR). Independent variables including carbon to nitrogen ratio (C/N) at 1, 2, and 3, dissolved oxygen level (DO, mg/L) at 0.2, 0.35, and 0.5, and hydraulic retention time (HRT, h) at 24, 48, and 72 were examined using Central Composite Design (CCD) coupled with Response Surface Methodology (RSM) to optimize the TN removal rate. Results showed that the one-stage PN/A process achieved an optimal TN removal rate of 87.3% and an optimal NH4+-N removal rate of 100% when C/N, DO, and HRT were 1, 0.5 mg/L, and 72 h, respectively. The quadratic regression model developed (p = 0.0018) perfectly fitted the nitrogen removal efficiency of the SBBR. The uncertainty analysis showed an error range of 0.12% to 0.96% for the model's accuracy within the DO, C/N ratio, and HRT ranges tested. The bacterial consortium analysis suggested that the control of the growth of ammonium oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) was achieved. Keywords: Anammox, Comammox, Nitrospira, Partial nitrification, Poultry litter wastewater.

Effect of biochar on growth performance, gas concentration and broiler leg health of broilers

This experiment was conducted to investigate the effect of adding biochar to the diet and litter on growth performance, gas concentration, hock burning and dermatitis in the foot pads of broilers. In the experiment, 300 One day old chicks were randomly distributed to 5 treatments 3 replicates each treatment , with (20) birds .T1: as control treatment. T2: (2) kg biochar / 100 kg feed). T3: (4 kg biochar l / 100 kg feed). T4: (2 kg biochar / 100 kg litter). T5: (4 kg biochar / 100 kg litter) . The results of the statistical analysis of the average live body weight and feed conversion factor of broilers showed a significant superiority of the treatments with added biochar to the feed compared to the treatments with added biochar to the litter and the control group. While the results for ammonia gas NH3 levels, the hock burn and footpad dermatitis suggested that the addition of biochar to the litter treatments produced the best results compared to the biochar-added diet group and the control group.

Effect of adding biochar to the diet and litter on the rate of diet consumption, relative humidity and gut health of broilers (Ross308)

This experiment was conducted to investigate the effect of adding biochar to the diet and litter on growth performance and broilers the hock burn and footpad dermatitis. In the experiment, 300 One day old chicks were randomly distributed to 5 treatments 3 replicates each treatment , with (20) birds per replicate and with an average weight (39.7) g. T1: Without adding biochar in the diet and litter. T2: (2) kg of biochar / 100 kg of diet). T3: (4 kg of biochar l / 100 kg of diet). T4: (2 kg of biochar / 100 kg of litter). T5: (4 kg of biochar / 100 kg of litter) . The results of the statistical analysis of the weekly diet consumption rate indicated a significant superiority of the treatments of adding biochar to the diet over the treatments of adding biochar to the litter and the control group . While the results of relative humidity, level ammonia NH3 level indicated that adding biochar to the litter treatments recorded the best results compared to the group adding biochar to the diet and the control group. As for the results of the microbial characteristics, it was shown that the treatments of adding biochar to the diet recorded the best results compared with the group adding biochar to the litter and the control group, which recorded a decrease in the number of colon bacteria and an increase in the number of lactic acid bacteria. While the relative humidity results indicated that adding biochar to the litter treatments recorded the best results compared to the group adding biochar to the diet and the control group.
 The aim of this study is to evaluate biochar as a food additive and a positive stimulant of the intestinal flora in maintaining the health of the broiler digestive system. Besides, due to its absorbent properties, it can reduce the moisture content of the litter and improve the overall environment of broiler breeding halls.

Evaluating the Effects of Pine and Miscanthus Biochar on Escherichia coli, Total Aerobic Bacteria, and Bacterial Communities in Commercial Broiler Litter.

Escherichia coli (E. coli) is a commensal bacteria found in the gastrointestinal tract of poultry; however, some strains are pathogenic and can cause a wide range of diseases. In addition, some strains of pathogenic E. coli can survive in the litter between flocks, making litter management critical for reducing E. coli-associated infections. Biochar (BC) is a porous, carbonaceous material that may be a beneficial litter amendment to reduce moisture and microbial loads. The objectives of this study were to evaluate the effects of pine BC, miscanthus BC, and Poultry Litter Treatment (PLT) on E. coli, total aerobic bacteria populations, and bacterial communities when added to used broiler litter. Pine and miscanthus BC were mixed into poultry litter at inclusion rates of 5%, 10%, 20%, 25%, and 30% w/w. PLT was surface applied at a rate of 0.73 kg/m2. Baseline E. coli and aerobics were measured after a 48-hr litter incubation period and just prior to adding litter treatments. Escherichia coli and aerobics were enumerated 2 and 7 days after adding treatments. Overall, pine BC at 30% had the lowest E. coli and aerobic counts (5.98 and 6.44 log 10 colony-forming units [CFU]/g, respectively); however, they were not significantly different from the control (P ≤ 0.05). At day 2, 30% pine BC inclusion rate treatment resulted in a significant reduction in E. coli and aerobic bacteria counts compared to the control. Miscanthus BC application did not result in significant reductions in E. coli or aerobic bacteria at days 2 or 7. PLT had the highest E. coli (7.07 log 10 CFU/g) and aerobic counts (7.21 log 10 CFU/g) overall. Bacterial community analysis revealed that the alpha and beta diversity between pine BC- and PLT-treated litter were significantly different. However, neither BC type significantly impacted bacterial diversity when compared to the control. Differences in E. coli and aerobic counts between BC types may be attributed to variations in feedstock physiochemical properties.

Assessment of Variability among Humus Forms and Soil Properties in Relation to Tree Species and Forest Operations in the Kheyrud Forest, Nowshahr

Tree species and litter play a key role in the functioning of forest ecosystems as influential factors affecting soil ecological processes and the distribution of humus forms. This study investigates the morphology of humus under the litter of different trees on compacted skid trails at different time intervals after skidding operations (6, 10, and 20 years) in the Kheyrud forest, Nowshahr. Each skid trail was identified with three replications in pure beech, beech-hornbeam and mixed beech stands and a total of 81 profiles with dimensions of 30 × 30 cm, drilled and classified using the European Humus Group Proposal (EHGP). According to the results, the mull of the most dominant humus was under the mixed beech litter, while in the pure beech litter the amphi humus was the most abundant form of humus. Three types of humus mull, moder, and amphi were observed in the skid trail under the beech-hornbeam litter. Oligomull was the most abundant form of humus mull in the skid trail under mixed beech litter, while in the trails under pure beech Eumacroamphi, Eumesoamphi, and Hemimoder were the most common forms of humus amphi and moder. Also, the thickness of the organic layer (Organic litter, Organic fragmentation, and Organic humus) was higher in all skid trails under the pure beech litter as compared to other treatments, while from younger trails (6 years) to older trails (20 years), the thickness of the organic-mineral horizon (Ah) increased under the beech mixed litter. We can conclude that different litter types were the main factor to control the presence of different forms of humus after forest operations.

Litter quality and living roots affected the formation of new mineral-associated organic carbon but did not affect total mineral-associated organic carbon in a short-term incubation

Storing carbon (C) in soil organic matter (SOM) is critical for mitigating climate change as well as for providing food security under extreme weather events. Mineral-associated organic matter (MAOM), which is the organic matter attached to silt and clay, has a longer residence time than the light, sand-sized particulate organic matter (POM). Hence, increasing the C in this fraction is thought to be important for long-term C storage. However, the influence of litter quality and living plants on new MAOM formation and MAOM turnover is unclear. We hypothesized that lower C:N litter would form MAOM more efficiently and result in more MOAM than higher C:N litter because lower C:N litter favors biomass production of microbes, which are thought to be an important precursor of MAOM. In addition, we hypothesized that living plants would amplify the effect of litter quality on MAOM formation and turnover because roots growing with low C:N litter would be less N-stressed and rely less on MAOM turnover to access N than roots growing in high C:N litter. We conducted a greenhouse study where soil was mixed with four different plant litter treatments: a control without litter, soybean (Glycine max) with C:N = 21, buckwheat (Fagopyrum esculentum) with C:N = 35, and sudex (Sorghum bicolor [L.] Moench × S. sudanense [P.] Staph.) with C:N = 65. The four litter treatments were incubated with and without living oats (Avena sativa). The incubation was maintained for 40 days, and over this period soybean and buckwheat lost 89 % of their initial dry matter while sudex lost 69 % of its initial dry matter. Contrary to our expectation, the litter with the higher C:N (sudex) had the greatest proportion of degraded C transferred to MAOM (i.e., the litter MAOM-C transfer efficiency). However, the litter MAOM-C transfer efficiency was not associated with the total MAOM-C at the end of the incubation. The presence of living plants increased the amount of MAOM-C derived from soybean and sudex litter, but it did not increase the total MAOM-C. Thus, our results demonstrate that high C:N litter can efficiently form new MAOM-C, which can be enhanced by the presence of living plants, but the greater MAOM-C formation may be accompanied by a loss of pre-existing MAOM-C.

Mixed-litter effects of fresh leaf semi-decomposed litter and fine root on soil enzyme activity and microbial community in an evergreen broadleaf karst forest in southwest China.

Litter decomposition is the main process that affects nutrient cycling and carbon budgets in mixed forests. However, knowledge of the response of the soil microbial processes to the mixed-litter decomposition of fresh leaf, semi-decomposed leaf and fine root is limited. Thus, a laboratory microcosm experiment was performed to explore the mixed-litter effects of fresh leaf, semi-decomposed leaf and fine root on the soil enzyme activity and microbial community in an evergreen broadleaf karst forest in Southwest China. Fresh leaf litter, semi-decomposed litter and fine root in the Parakmeria nitida and Dayaoshania cotinifolia forests, which are unique protective species and dominant species in the evergreen broadleaf forest, were decomposed alone and in all possible combinations, respectively. Our results showed that the mass loss of fresh leaf litter in three mixed-litter treatment was significantly higher than that in two mixed-litter treatment in the P. nitida and D. cotinifolia forests. Mass loss of fine root in the single litter treatment was significantly lower in the P. nitida forest and higher in the D. cotinifolia forest compared to that in the other litter treatments. There were insignificant differences in the activities of β-glucosidase (BG) and leucine aminopeptidase (LAP) between control and mixed-litter treatment in the P. nitida forest and between control and single litter treatment in the D. cotinifolia forest. The N-acetyl-β-D-glucosaminidase (NAG) activity was significantly increased by the single litter decomposition of fresh leaf and fine root and three mixed-litter decomposition in the P. nitida and D. cotinifolia forests. The activity of acid phospomonoesterase (AP) in the decomposition of fresh leaf litter was lower in the P. nitida forest and higher in the D. cotinifolia forest compared to that in control. The most dominant soil bacteria were Proteobacteria in the P. nitida forest and were Actinobacteria and Proteobacteria in the D. cotinifolia forest. Shannon, Chao1, ACE and PD indexes in the mixed-litter decomposition of fresh leaf and semi-decomposition litter were higher than that in control in P. nitida forest. There were insignificant differences in observed species and indexes of Chao1, ACE and PD between litter treatments in the D. cotinifolia forest. Richness of mixed-litter significantly affected mass loss, soil enzyme activity and microbial diversity in the P. nitida forest. Litter N concentration and the presence of fresh leaf litter were significantly correlated with the mass loss and soil enzyme activity in the P. nitida and D. cotinifolia forests. These results indicated that the presence of fresh leaf litter showed a non-negligible influence on mixed-litter decomposition and soil enzyme activity, which might be partly explained by litter initial quality in the P. nitida and D. cotinifolia forests.

Nitrogen and Carbon Mineralization from Green and Senesced Leaf Litter Differ between Cycad and Angiosperm Trees.

Plant leaf litter decomposition is directly influenced by the identity of the source plants and the leaf age. Defoliation of forests by tropical cyclones (TC) transfers copious amounts of high-quality green leaf litter to soils. We used a soil amendment approach with the incubated buried bag method to compare carbon (C) and nitrogen (N) mineralization dynamics of green and senesced leaf litter from cycad Cycas micronesica and angiosperm Morinda citrifolia trees on the island of Guam. Soil priming increased the decomposition of pre-existing organic C, and were greater for green leaf litter additions than senesced leaf litter additions. Available N content increased by day 14 and remained elevated for the entire 117-d incubation for soils amended with green M. citrifolia litter. In contrast, available N content increased above those in control soils by day 90 and above those in soils amended with senesced litter by day 117 for green C. micronesica litter. The net N mineralization rate was higher than control soils by 120% for the senesced litter treatments and 420% for the green litter treatments. The results reveal a complex but predictable interplay between TC defoliation and litter quality as defined by tree identity. We have illuminated one means by which increased frequency of intense TCs due to climate change may alter the global C and N cycles.

Effects of resource size on invertebrate assemblages in water-filled treeholes

Water-filled treeholes are important habitat patches for aquatic invertebrates in forest ecosystems. A detailed understanding of the interspecies relationships that occur within them will help in understanding how invertebrate diversity is maintained in forests, particularly with respect to resource utilization. The sequential use of the same food resource among several different species is called a processing chain. In this study, we focused on the aspects of leaf litter in the treeholes as a food and habitat resource, and tested the following hypotheses using artificial containers as treeholes with three different leaf litter samples categorized as “untreated”, “fragmented”, and “pulverized”: (1) inorganic ions would leach out as leaf fragmentation progresses, resulting in water acidification, which consequently affects invertebrates. (2) filter-feeder species that consume microorganisms and fine particle organic matter increase as leaf fragmentation progresses. (3) differences in the size of leaf litter fragments affect the inhabitant species and cause differences in the assemblage structure of invertebrates. We observed an increase in pH and dissolved oxygen (DO) with increasing the fragmentation of leaf litter; however, the results were marginally non-significant. The assemblage composition of aquatic invertebrates did not show clear patterns in relation to the leaf litter treatments. Invertebrate assemblages from treeholes with pulverized leaf litter appeared to be associated with increasing DO. We found that the filter-feeder Tripteroides bambusa (Diptera: Culicidae) was dominant under conditions where treeholes contained fine particles of leaf litter, while the benthic inhabitant Ceratopogonidae sp. (Diptera) dominated under conditions with coarse leaf litter fragments. Our results suggest that fragmentation of leaf litter may have different effects on the different dominant species. We conclude that resource processing does not necessarily have positive effects on the species.