Litter Addition Research Articles

Roots exert greater influence on soil respiration than aboveground litter in a subalpine Cambisol

Aboveground plant litter and roots are primary sources of soil organic carbon (SOC), profoundly affecting soil respiration and SOC dynamics. With global change, the quantities of aboveground plant litter and root inputs into soil are changing in the subalpine region; however, the impacts of these changes on soil respiration and the quantity and quality of SOC remain unclear. Here, a three-year detritus input and removal treatment (DIRT) experiment that included six treatments (namely, control, CK; double litter, DL; litter removal, NL; root exclusion, NR; root exclusion plus double litter, NRDL; and root exclusion plus litter removal, NRNL) was conducted in a subalpine Cambisol on the eastern edge of the Tibetan Plateau to assess the different effects of aboveground litter and roots on soil respiration and the quantity and quality of SOC dynamics. Among the treatments, the mean soil respiration in NL, NR and NRNL treatments significantly decreased by 21.7%, 31.9% and 40.5%, respectively, compared to the CK treatment. When with intact roots, double litter (DL) had a positive impact on soil respiration, resulting in a 13.2% increase in soil respiration compared to the CK treatment. In contrast, when with root exclusion (in the absence of roots), combined root exclusion and litter addition (NRDL) hardly influence soil respiration compared with the NR treatment, resulting in a 30.5% decrease in soil respiration. The soil respiration, labile SOC content and the abundance of soil microbes exhibited similar patterns among treatments. Roots excluded (NR, NRDL, NRNL) exerted a stronger effects on soil respiration, temperature sensitivity of soil respiration (Q10), labile SOC content and the recalcitrance index of carbon (RIC) than aboveground plant litter manipulation (CK, DL, NL). Correlation analysis and redundancy analysis revealed that soil respiration and its Q10 were regulated by the quantity and quality of SOC substrates and the abundance of soil microbes. Our results highlighted that roots exerted greater influence on the quantity and quality of SOC, the abundance of soil microbes, soil respiration and its Q10 than aboveground litter manipulation in subalpine Cambisol in response to future climate scenarios, especially the mediating effect of the presence of roots on the function of aboveground plant litter.

Soil enzyme activities responded differently to short-term litter input manipulation under coniferous and broad-leaved forests in the subalpine area of Southwest China

Litter plays an irreplaceable role in terrestrial ecosystem carbon (C), nitrogen (N) and phosphorus (P) cycling, and its decomposition is largely regulated by litter quality, soil properties and enzyme activities. However, how soil enzyme activities respond to change in litter input under different forest types remains unsolved. Here, we investigated soil enzyme activities involved in C (β-glucosidase, BG), N (N-acetyl-β-glucosaminidase, NAG; leucine aminopeptidase, LAP) and P (acid phosphatase, ACP) under short-term litter manipulations (i.e. Detritus Input and Removal Treatment-DIRT: control, CK; double litter, DL; no roots and double litter, NRDL; no litter, NL; no roots, NR; no roots and no litter, NRNL) and associated influencing drivers in a coniferous forest (Pinus yunnanensis) and a broad-leaved forest (Quercus pannosa) in the subalpine area of Southwest China. Our results showed that litter removal treatment significantly reduced enzyme activities under two forest soils, with the stronger effect of the NR treatment on decreased enzyme activities compared to the NL treatment, possibly because roots could provide more available C sources and nutrient to microorganism and also immediately interact with soil minerals. In contrast, the short-term litter addition did not significantly affect enzyme activities under both two forest soils. Additionally, the BG activities in coniferous forest soil were characterized by a lower effect size compared to those in broad-leaved forest soil under the litter removal (NL and NRNL) treatments, but the higher effect size of LAP and ACP activities were observed under the NRNL treatment in the coniferous forest soil. This finding was attributed to higher organic C sources in the coniferous forest soil which could promote other nutrients utilization by microorganisms, leading to more N and P enzyme productions. We observed that the enzyme activities in the coniferous forest soil were closely related to soil N, P contents and microbial traits (i.e., fungal and bacterial structure), while enzyme activities in the broad-leaved forest soil primarily depended on microclimates (soil temperature and moisture) and soil properties (pH, dissolved organic C and P contents) under short-term litter manipulations. Overall, our results revealed the different pattern and the regulatory mechanism of soil enzyme activities under litter input manipulation of two forests, thereby advancing understanding of soil enzyme dynamics in association with initial litter quality and soil properties under future global change.

Mycorrhizae enhance reactive minerals but reduce mineral-associated carbon.

Soil organic carbon (C) is the largest active C pool of Earth's surface and is thus vital in sustaining terrestrial productivity and climate stability. Arbuscular mycorrhizal fungi (AMF) form symbioses with most terrestrial plants and critically modulate soil C dynamics. Yet, it remains unclear whether and how AMF-root associations (i.e., mycorrhizae) interact with soil minerals to affect soil C cycling. Here we showed that the presence of both roots and AMF increased soil dissolved organic C and reactive Fe minerals, as well as litter decomposition and soil CO2 emissions. However, it reduced mineral-associated C. Also, high-resolution nanoscale secondary ion mass spectrometry images showed the existence of a thin coating (0.5-1.0 μm thick) of 56 Fe16 O- (Fe minerals) on the surface of 12 C14 N- (fungal biomass), illustrating the close physical association between fungal hyphae and soil Fe minerals. In addition, AMF genera were divergently related to reactive Fe minerals, with Glomus being positively but Paraglomus and Acaulospora negatively correlated with reactive Fe minerals. Moreover, the presence of roots and AMF, particularly when combined with litter addition, enhanced the abundances of several critical soil bacterial genera that are associated with the formation of reactive minerals in soils. A conceptual framework was further proposed to illustrate how AMF-root associations impact soil C cycling in the rhizosphere. Briefly, root exudates and the inoculated AMF not only stimulated the decomposition of litter and SOC and promoted the production of CO2 emission, but also drove soil C persistence by unlocking mineral elements and promoting the formation of reactive minerals. Together, these findings provide new insights into the mechanisms that underlie the formation of reactive minerals and have significant implications for understanding and managing soil C persistence.

The real and apparent priming effects following litter incorporation as modeled under different moisture regimes

The addition of litter (maize straw) to soil accelerates activity of microorganisms and significantly changes the mineralization of soil organic carbon (SOC), which are referred to as “apparent” and “real” priming effects (PEs). In this study, the mechanisms of PEs under different moisture conditions were explored using a simple mechanistic model that was dependent on the size of the SOC pool (%C), microbial biomass, and microbial activity (the proportion of actively growing microbial biomass relative to the total soil biomass). In an incubation experiment, soil cores were incubated with 13C-labeled maize straw (δ13C = 600.9 ± 2.53‰) under two moisture regimes: constant moisture (60% of water holding capacity throughout incubation) and drying and rewetting treatments (7-day long drying and rewetting cycles in a 76-day laboratory incubation). Microcosms were sampled after 1, 7, 10, 15, 21, 60, and 76 days, and cumulative soil respiration, microbial biomass and cumulative PEs were measured during the incubation period. The model was parameterized with native SOC and 13C-labeled litter carbon (C) data and simulated microbial metabolic processes, microbial turnover, soil organic matter (SOM) dynamics, and apparent and real PEs. The model contained two special features. The first feature was the assumption of sequential utilization of native SOC and litter-derived C with distinctly different stability and properties, where the organic carbon (OC) must first be solubilized into dissolved organic carbon (DOC) before it can be consumed by microorganisms. The second feature was the first attempt to evaluate the continuous turnover of native SOC, native SOM-derived and litter-derived microbial biomass C under varying moisture conditions. The optimized model explained 93% of the observed cumulative priming effect (CPE) under constant moisture and 94% of the CPE under drying and rewetting treatments, respectively. The simulation results showed that the conversion of native SOC and litter C to DOC was rate-limited, and positive apparent PE dominated the priming process. Although more C was allocated to respiration rather than growth, the compensation by a longer turnover time of microbial C eventually led to a higher sequestration of soil C under the drying and rewetting treatment compared to those under constant moisture. The turnover time of native SOC was significantly affected by the turnover of native-SOM derived and litter-derived microbial biomass C, and the turnover of litter-derived microorganisms may play a key role in regulating real PE. This study demonstrates that the combination of mathematical modeling and 13C-labeled litter varying in solubility and recalcitrance can effectively distinguish C sources and elucidate the mechanisms of PEs in soils under different moisture regimes.

Effects of Snow Cover on Carbon Dioxide Emissions and Their δ13C Values of Temperate Forest Soils with and without Litter

The presence of litter and winter snow cover can affect the decomposition of organic matter in forest soils and changes in δ13C values of soil-respired carbon dioxide (CO2). However, limited information is available on the responses of CO2 emissions from forest soils and their δ13C values to snow cover and litter addition over the year. We experimentally manipulated snow cover to study the impacts of light and heavy artificial snow cover on soil heterotrophic respiration and its δ13C values, using undisturbed large soil columns collected from two typical temperate forests in Northeastern China. Based on the average temperatures of surface forest soils in four seasons of the year in this study region, the simulations of autumn freeze–thaw, winter freeze, spring freeze–thaw, and the growing season were sequentially carried out under laboratory conditions. A set of novel analysis systems, including automated chamber equipment and laser spectroscopy analysis with high-frequency measurements for CO2 concentrations and the 13C/12C isotopic ratios in CO2, was used to study the effects of artificial snow cover and the presence of litter on soil heterotrophic respiration and its δ13C values. During the autumn freeze–thaw simulation, there were larger CO2 emissions and less negative δ13C values of soil-respired CO2 upon heavy snow cover than upon light snow cover, indicating that the presence of increased snow cover prior to winter freeze can increase the decomposition of organic C in subsurface soils under temperate forests. The δ13C values of soil-respired CO2 in all treatments were, on average, less negative as the simulated spring freeze–thaw proceeded, which was contrary to the variations of the δ13C during the autumn freeze–thaw simulation. Soil heterotrophic respiration and its δ13C values during the spring freeze–thaw simulation were, on average smaller upon heavy snow cover than upon light snow cover, which differed from those during the autumn freeze–thaw and growing season simulations, respectively. Taken together, the results highlight that the effects of snow cover on soil heterotrophic respiration and its δ13C values under temperate forests may vary with different seasons of the year and the presence of litter.

Contribution of microbial necromass to soil organic carbon formation during litter decomposition under incubation conditions.

We conducted a 512-day incubation experiment to study the dynamics of microbial necromass and soil carbon fraction in the 'litter-soil' transformation interface soil layer (TIS) during litter decomposition, using a perennial C3 herb, Stipa bungeana, in the loess hills. The results showed that soil microbial necromass was dominated by fungi in the early and middle stages, and by bacteria in the late stage. The contribution of fungal necromass C to mineral-associated organic C (MAOC) was significantly higher (38.7%-75.8%) than that of bacteria (9.2%-22.5%) and 2-3 times more than the contribution rate of bacterial necromass. Soil organic C (SOC) content was decreasing during litter decomposition. The input of plant C resources stimulated microbial utilization of soil C fractions. The continuous decrease in particulate organic C during the early and late stages of decomposition was directly responsible for the decrease in SOC content. In contrast, the fluctuating changes in microbial necromass C and MAOC played an indirect role in the reduction of SOC. The increase in soil microbial necromass C caused by a single exogenous addition of litter did not directly contribute to SOC accumulation.

Drivers of contrasting boreal understory vegetation in coniferous and broadleaf deciduous alternative states

AbstractAlternative states defined by tree‐canopy dominance result in different ecosystem functioning and shape habitat conditions for the understory vegetation. One example in the boreal forest is the alternation between broadleaf deciduous and coniferous forests. Disturbances related to natural fires and human land uses have produced changes in tree‐canopy dominance in the boreal region where coniferous forests change to broadleaved forests, affecting understory community dynamics and their related ecosystem processes and functions. To analyze the factors driving changes in understory vegetation and the resistance of its vegetation to shifts between alternative states, we compared the effects of changes in the system between two contrasting boreal forest types (black spruce vs. trembling aspen) in adjacent stands with similar topoedaphic conditions. We performed a 5‐year in situ experiment using alternative states as a theoretical framework including two approaches: (1) the ecosystem approach, manipulating environmental conditions of light, litter, and nutrients in each forest type to determine the main mechanisms associated with tree‐canopy dominance that affect the diversity and composition of understory communities; and (2) the community approach, physically exchanging understory communities between alternative states, to determine their resistance under a new tree‐canopy dominance through time, as well as the resilience of the forest understory after a small‐scale disturbance. Results indicate that the understory vegetation of trembling aspen forests were resistant through time both after changes in local conditions in the ecosystem approach and in the new black spruce‐dominated alternative state in the community approach. In contrast, mosses and ericaceous plants that typically dominate the forest floor of black spruce forests were negatively affected by the physical effect of broadleaf litter addition in our ecosystem approach and they were not resistant when transplanted to trembling aspen forests in the community approach, as they decreased in abundance and were invaded by aspen understory community species over time. The understory vegetation is a key forest ecosystem driver that can contribute to maintain the resilience of the boreal system and help to preserve their ecosystem services, which is a key aspect to consider in forest management faced with the effects of climate change.

Effect of Litter Removal and Addition on Root Exudation and Associated Microbial N Transformation in a Pinus massoniana Plantation

In forest ecosystems, variations in aboveground litter input caused by global changes, substantially alter soil N cycling. In field-grown plants, few studies have directly measured root exudation rates and quantified their effects on N transformations under litter manipulation. We quantified soil N transformation rate responses to litter manipulation in a Pinus massoniana plantation, and unravelled the effect of root exudation on soil N transformations. We measured in situ P. massoniana root exudation rates as well as soil microbial biomass, soil C and N concentrations, the activities of four soil enzymes involved in soil N transformations, and net N mineralization and net nitrification rates after experimental litter removal and litter addition treatments. Litter removal and litter addition treatments had little impact on soil C and N concentrations, microbial biomass, soil enzyme (urease, hydroxylamine reductase, nitrate reductase, and nitrite reductase) activity, and net N mineralization rates. However, both litter removal and addition increased net N nitrification rates. Additionally, litter removal significantly decreased root C exudation rates (in April 2021 and annually), whereas litter addition had no significant effects on root C exudation rates across all seasons. Furthermore, root C exudation rates were positively associated with urease and nitrate reductase activities, but negatively associated with hydroxylamine reductase and nitrite reductase activities, as well as net N nitrification rate. Overall, we demonstrated that root exudates may be an important physiological adjustment by which trees respond to changes in litter input caused by global environmental changes, regulating underground N biochemical processes. Furthermore, we provide new evidence from root exudates for understanding the potential influence of litter inputs on soil N cycling. A strong correlation exists between root exudates and N transformation, shedding new light on the dynamics of rhizosphere nutrient cycling crucial for maintaining forest ecosystem stability and productivity under changing environmental conditions.

Root litter quality drives the dynamic of native mineral-associated organic carbon in a temperate agricultural soil.

Understanding the fate and residence time of organic matter added to soils, and its effect on native soil organic carbon (SOC) mineralisation is key for developing efficient SOC sequestration strategies. Here, the effect of litter quality, particularly the carbon-to-nitrogen (C:N) ratio, on the dynamics of particulate (POC) and mineral-associated organic carbon (MAOC) were studied. In a two-year incubation experiment, root litter samples of the C4-grass Miscanthus with four different C:N ratios ranging from 50 to 124 were added to a loamy agricultural topsoil. In an additional treatment, ammonium nitrate was added to the C:N 124 litter to match the C:N 50 litter input ratio. Soils were size-fractionated after 6, 12 and 24 months and δ13C was measured to determine the proportion of new and native POC and MAOC. Litter quality was further assessed by mid-infrared spectroscopy and compound peak analysis. Litter quality strongly affected SOC dynamics, with total SOC losses of 42.5 ± 3.0% in the C:N 50 treatment and 48.9 ± 3.0% in the C:N 124 treatment after 24 months. Largest treatment effects occurred in mineralisation of native MAOC, which was strongly primed by litter addition. The N amendment in the C:N 124 treatment did not alleviate this potential N mining flux. Litter quality plays a major role in overall SOC dynamics, and priming for N mining from the MAOC pool could be a dominant mechanism. However, adding N did not compensate for poor litter quality, highlighting the role of litter quality beyond stoichiometric imbalances.

Native grass sod and plug production as an alternative technique to restore neotropical rupestrian grassland after mining

Despite the importance of grasses in the structure and functioning of tropical grasslands, there is still a lack of efficient and economically viable techniques to produce and introduce grasses in restoration projects. Here, we evaluated the sod and plug‐plant production and planting of a native grass from Brazilian rupestrian grasslands, Sporobolus metallicolus, in a post‐bauxite mining. To produce the sod, we used post‐mining substrate and its mixture with commercial substrate. Then, we sowed 270 seeds of S. metallicolus on a 4‐cm layer of substrate in 144‐cm2 trays. Eighty days after sowing, we subdivided the contents of each tray (substrate + plant) into 4 × 3–cm plug‐plants. Plug‐plants were planted in the degraded area with and without the incorporation of litter from an adjacent conserved rupestrian grassland. We also evaluated the cost of production of each plug‐plant. The mixture of substrates provided greater plant growth and rooting, obtaining plug‐plants with an average of 13 individuals, dry mass of 270 mg, and estimated cost of US$ 0.0045. In the degraded area, the addition of litter increased shoot biomass gain. Plant survival was 100% with and without litter addition and the plants started seed dispersal at 7 months after planting. The production of S. metallicolus plugs with the mixed substrate and the growth of plants in the post‐mined area showed promising results and reduced costs, indicating technical and financial feasibility. The presented techniques can be an option for introducing grasses in degraded areas and optimize the use of seeds.

Exogenous Carbon Addition Reduces Soil Organic Carbon: The Effects of Fungi on Soil Carbon Priming Exceed Those of Bacteria on Soil Carbon Sequestration

Soil organic carbon (SOC) forms the largest terrestrial organic carbon (C) pool, which is regulated by complex connections between exogenous C input, microbial activity, and SOC conversion. Few studies have examined the changes in natural abundance C due to microbial activity after exogenous C inputs in karst lime soils in China. In this research, the 13C isotope tracer technique was employed to investigate the priming effect of SOC on typical lime soil (0~20 cm) of 13C_litter and 13C_calcium carbonate (CaCO3) through a mineralization incubation experiment. Samples were collected at 5, 10, 20, 40, 60, and 80 days of incubation and analyzed for SOC mineralization, SOC distribution across fractions (>250 μm, 53~250 μm, and <53 μm), and soil microbial diversity. A control consisting of no exogenous C addition was included. SOC mineralization and SOC priming were considerably higher (15.48% and 61.00%, respectively) after litter addition compared to CaCO3. The addition of either litter or CaCO3 reduced the total organic C (TOC) and macroaggregate (>250 μm) and microaggregate (53~250 μm) C fractions by 2150.13, 2229.06, and 1575.06 mg C kg−1 Cbulk on average and increased the mineral particulate C fraction (<53 μm) by 1653.98 mg C kg−1 Cbulk. As the incubation time extended, a significantly positive correlation was apparent between SOC priming and soil fungal diversity, as well as between the mineral particulate C fraction and soil bacterial diversity. The effect of soil fungal diversity on SOC priming (R = 0.40, p = 0.003) significantly exceeded that of bacterial diversity on SOC sequestration (R = 0.27, p = 0.02). Our results reveal that after adding litter or CaCO3, soil fungi stimulate SOC mineralization and decomposition and soil bacteria enhance SOC sequestration, with the effects of fungi being more pronounced. These findings can provide a theoretical basis for understanding C sequestration and emission reduction in karst lime soils.

Positive responses of soil nutrients and enzyme activities to AM fungus under interspecific and intraspecific competitions when associated with litter addition

Arbuscular mycorrhizal fungi mediated-litter decomposition is essential for soil carbon and nutrient cycling. Plant competition profoundly influences soil C, nutrients, glomalin-related soil protein, and enzymes. However, it is unclear how a combined AM fungus and litter addition affects soil properties under interspecific and intraspecific competitions. With 170-day-old Broussonetia papyrifera and Carpinus pubescens seedlings, three treatments of intraspecific or interspecific plant competition, AMF Claroideoglomus etunicatum inoculation or not, and leaf litter addition to soil substrate or not were examined to address differences in plant biomass production, soil organic carbon, total nitrogen and total phosphorus, EE-GRSP, DE-GRSP and T-GRSP, and activity of alkaline phosphatase, catalase and urease. The results were as follows: Root, shoot and total biomass increased in B. papyrifera but decreased in C. pubescens under AM mycorrhization in both intraspecific and interspecific competitions. Under mycorrhization, intraspecific, not interspecific, competition increased SOC and ratios of C/N, C/P, DE-GRSP and T-GRSP. Mycorrhization plus litter addition increased SOC, ratios of C/N, C/P and N/P, EE-GRSP, DE-GRSP, T-GRSP, and alkaline phosphatase activity under intraspecific competition, while soil TN, TP, and catalase and urease activities. Soil C, N, P, EE-GRSP or T-GRSP positively associated with catalase, urease or alkaline phosphatase activities. These results showed that alterations in intra- and interspecific competition induced by AM fungus positively respond to soil C, nutrient, GRSP, and enzyme activities, thus plant competition is a key factor in regulating soil properties. Overall, we suggest that interspecific competition enables AMF to increase soil N and P accumulations and related enzyme activities, while intraspecific competition confers more significant benefits than interspecific competition in improving soil C and GRSP accumulations under a combined AMF and litter addition. The findings highlight the importance of plant competition in improving soil function through AM fungus, which is conducive to understand the mechanisms of plant restoration and nutrient cycling in degraded ecosystems.

Can Litter (Dead Herbage) Management Affect the Production and Composition of a Desert Steppe Community?

To examine the effect of litter on ANPP and species composition (using ground cover) in a Desert Steppe community by removing or adding litter, during plant dormancy, in a single event in either fall or spring. Litter was removed or added in three intensity treatments (heavy, moderate, control—undisturbed) as the main plot and season (fall or spring) as the secondary treatment in a split-plot design with five replications. The experiments were repeated in each of 5 years while three of those were resampled twice. The year effect was analyzed by classifying them into high or low precipitation categories and including those in the statistical model. We found few treatment effects one year after treatment and no persistent effect. Therefore, we focus our examination on the first year only. The total ANPP of individual plant types, or their proportions, were not affected by litter treatment or its interaction with season of treatment or precipitation category. Only the ground cover of selected species was influenced by the treatment. The ground cover of Stipa breviflora was greater with heavy litter removal in fall but unaffected by litter removal in spring while Neopallasia pectinata had a greater cover with moderate or heavy removal in years when precipitation was low. Litter addition resulted in a greater ground cover of Neopallasia pectinata and reduced the cover of Convolvulus ammannii in years of low precipitation. The marginal effectiveness of litter treatments on the plan community in the Desert Steppe suggests that it need not be a factor for consideration in grazing management.

The interspecific competition of tree plants in the presence of AM fungi and litter facilitates root morphological development and nutrition when compared with intraspecific competition.

Arbuscular mycorrhizal (AM) fungi can affect plant growth by regulating competition. Nutrient-deficient karst habitats contain abundant plants that compete for nutrients through interspecific or intraspecific competition, involving the nutritional transformation of litter decomposition. However, how plant competition in the presence of AM fungi and litter affects root development and nutrition remains unclear. A potted experiment was conducted, including AM fungus treatment with or without Glomus etunicatum, the competition treatment concerning intraspecific or interspecific competition through planting Broussonetia papyrifera and Carpinus pubescens seedlings, and the litter treatment with or without the mixture of B. papyrifera and C. pubescens litter leaves. The root morphological traits were analyzed, and nitrogen (N), phosphorus (P), and potassium (K) were measured. The results showed that AM fungus differently affected the root morphological development and nutrition of both competitive plants, significantly promoting B. papyrifera roots in the increase of dry weight, length, volume, surface area, tips, and branches as well as N, P, and K acquisitions regardless of litter addition. However, there was no apparent influence for C. pubescens roots, except for the diameter in the interspecific competition with litter. The root dry weight, length, volume, surface area, and tips of B. papyrifera under two competitive styles were significantly greater than C. pubescens regulated by AM fungus, presenting significant species differences. The responses of the relative competition intensity (RCI) on root morphological and nutritional traits indicated that AM fungus and litter both asymmetrically alleviated more competitive pressure for B. papyrifera than C. pubescens, and the interspecific competition facilitated more root morphological development and nutrition utilization by endowing B. papyrifera root superiority relative to C. pubescens compared with the intraspecific competition. In conclusion, interspecific competition is more beneficial for plant root development and nutrition than intraspecific competition in the presence of AM fungus and litter via asymmetrically alleviating competitive pressure for different plants.

Litter inputs exert greater influence over soil respiration and its temperature sensitivity than roots in a coniferous forest in north-south transition zone

The changes in carbon inputs of litter and roots to forest soils caused by climate change will result in a serious cascade effect on soil respiration and its temperature sensitivity (Q10). To differentiate and quantify the effects of surface litter and living roots on soil respiration and Q10, and further explore the role of abiotic factors and microbial properties on soil respiration and Q10, a short-term (two years) detritus input and removal treatment experiment was conducted in a coniferous forest of central China. Soil temperature, soil moisture, C/N, microbial biomass and community composition were analyzed to explore the drive mechanisms of soil respiration and Q10 in response to carbon inputs. The results showed that litter addition increased soil respiration by 22 %, while litter or roots removal did not affect soil respiration, which might be ascribed to the “priming effects” mediated by fresh plant litter. We also found that litter addition increased Q10, while litter removal decreased Q10. Litter addition significantly enhanced the microbial biomass for any single functional group and altered soil microbial community composition. Structural equation model further proved that microbial biomass and community composition exerted stronger impacts on Q10 than do soil abiotic factors. Soil moisture, microbial biomass and community structure were main factors in predicting soil respiration. The study highlights the important role of litter inputs compared with living roots in carbon cycling in short-term and deepens our understanding on the complex relationships among soil respiration, soil micro-environment and microbial community composition.

Does liming improve microbial carbon use efficiency after maize litter addition in a tropical acidic soil?

Soil pH is one of the main drivers of soil microbial functions, including carbon use efficiency (CUE), the efficiency of microorganisms in converting substrate C into biomass, a key parameter for C sequestration. We evaluated liming effects after maize-litter addition on total CUE (including microbial residues), CUE of microbial biomass (CUEMB), and fungal biomass on an acidic Acrisol with a low C. We established a 6-week incubation experiment to compare limed and unlimed Acrisol treatments and a reference soil, a neighboring Nitisol with optimal pH. Fungal biomass (ergosterol) increased ~ 10 times after litter addition compared with soils without litter, and the final amount was greater in the limed Acrisol than the Nitisol. Litter addition induced a positive priming effect that increased with increasing pH. The increases in soil pH also led to increases in litter-derived CO2C and decreases in particulate organic matter (POM)C. Thus, in spite of increasing microbial biomass C, CUE decreased with increasing pH and CUEMB was similar across the three soils. CUEMB was positively associated with saprotrophic fungi, implying that fungi are more efficient in incorporating litter-derived C into microbial, especially fungal biomass after 42 days. By including undecomposed maize litter and microbial residues, CUE provided a more comprehensive interpretation of pH and liming effects than CUEMB. Nevertheless, longer-term studies may provide further information on substrate-C turnover and the persistence of liming and pH effects.

Litter addition as a tool for restoring hydrological processes and controlling erosion in riparian forests disturbed by fine sediment deposition

Riverscape aggradation due to the deposition of fine particles above natural forest litter can change the soil, sediment, and water properties, damage riparian vegetation, and reduce environmental integrity, especially in headwater streams. Litter addition techniques that enhance surface roughness and permeability can decrease the interference of fine particles on the ecosystem, representing a low‐tech alternative to recover disturbed riparian areas. We aimed to evaluate run‐off, percolation, storage coefficients, run‐off volume, and sediment yield using a rainfall simulator and the mitigation potential provided by the addition of forest litter to limnological variables—turbidity, total suspended solids (TSS), electrical conductivity, pH, nitrogen—which are indicators of integrity that can reflect streams' aggradation. Fifteen soil samples from a disturbed area (silt and clay deposits aboveground), five from an undisturbed area (sandy soil), and superficial forest litter were obtained from riparian areas adjacent to two small streams in Carajás National Forest, Brazil. The addition of litter showed great potential to mitigate erosive processes and to reestablish hydrological processes in the disturbed soil. The run‐off volume and sediment yield were 2–4 times lower in litter addition treatments compared to non‐litter addition. Litter addition also improved run‐off water quality, especially turbidity and TSS, which were 12–16 times and 3–13 times lower, respectively. The experimental addition of litter has shown encouraging results to be applied in situ as a sustainable, low‐cost, and simplified nature‐based solution to contribute to the restoration of degraded riparian forests and reduce in‐stream silt and clay aggradation.

Combined addition of plant litter altered remediating effects on petroleum‐contaminated soil in Northern Shaanxi, China

AbstractIn the present study, we assessed whether the nonadditive effects of mixed litter decomposition on soil biological and chemical properties, which was usually recognized in clean soils, could be used to enhance the efficiency of petroleum‐contaminated soil necrophytoremediation. In particular, six common plant species from the petroleum production region of Northern Shaanxi, China were collected, forming nine mixture types. The single and mixed litters were used to treat petroleum‐contaminated soil with a proportion of 45 g kg−1 at 25°C and a constant humidity for 150 days. The possible nonadditive effects on the efficiency of removing contaminants and recovering the damaged soil traits caused by the mixed litter addition were then investigated. The results indicate that monospecific litter treatments significantly increased the degradation rates of petroleum contaminants, the available N and P contents, and the catalase and dehydrogenase activities by 36%–74%, 28%–455%, and 8%–102%, respectively (p < 0.05). The mixed addition of the litters from Lespedeza davurica and Artemisia scoparia or those from Agropyron cristatum and Bromus inermis caused significant synergistic effects, enhancing the overall petroleum component removal, replenishing nutrients (particularly nitrogen) or stimulating enzymatic activities (especially for sucrase, phosphatase, catalase, and urease). The observed values of the corresponding indicators following mixed litter treatment were observed to significantly increase by 12%–18%, 23%–58%, and 9%–24% (p < 0.05), relative to their predicted values, which were calculated based on the observed values from the monospecific litter treatments and the proportion of the litter in the mixture. However, other litter combinations may weaken the remediation effects of the litter addition. In general, a high content of nutrients, primary metabolites (e.g., soluble sugars and amino acids), and the potential bio‐surfactants and co‐metabolized substrates (including terpenoids and flavonoids) of mixed litters enhanced the remediation efficiency of mixed litters. Notably, an increase in the chemical diversity of mixed litter may weaken its synergistic effects on the degradation of petroleum components and the simulation of soil polyphenol oxidase activity. Our results demonstrate that appropriate litter mixing combinations can effectively enhance the efficiency of necrophytoremediation, thus providing new approaches for the more convenient and economical remediation of petroleum‐contaminated soil.

Effects of substitution of fermented chicken litter with concentrate on nutrient digestibility and performance of sheep

The study aimed to investigate the effects of supplementing fermented chicken litter on feed consumption, nutrient digestibility (dry matter/DM, organic matter/OM, crude fiber/CF, extract ether/EE, crude protein/CP), total digestible nutrients (TDN), and average daily gain (ADG) in sheep. A completely randomized design with 4 treatments and 3 replications, namely T0 = concentrate without the addition of fermented litter, T1 = 90% concentrate + 10% fermented litter, T2 = 80% concentrate + 20% fermented litter, T3 = 70% concentrate + 30% fermented litter and T4 = 60% concentrate + 40% fermented litter was used. The parameters studied were dry matter digestibility (DMD), organic matter digestibility (OMD), extract ether digestibility (EED), crude fiber digestibility (CFD), crude protein digestibility (CPD), TDN, feed consumption and average daily gain. The results revealed that sheep fed different levels of fermented litter did not affect OMD, DMD, EED, CPD, CFD, TDN, dry matter consumption, and average daily gain (ADG). It was concluded that fermented chicken litter can be incorporated in sheep diet, without considerable negative effects.

Biochar mitigates allelopathic effects in temperate trees.

Many invasive and some native tree species in North America exhibit strong allelopathic effects that may contribute to their local dominance. Pyrogenic carbon (PyC; including soot, charcoal, and black carbon) is produced by the incomplete combustion of organic matter and is widespread in forest soils. Many forms of PyC have sorptive properties that can reduce the bioavailability of allelochemicals. We investigated the potential for PyC produced by controlled pyrolysis of biomass ("biochar" [BC]) to reduce the allelopathic effects of black walnut (Juglans nigra) and Norway maple (Acer platanoides), a common native tree species and a widespread invasive species in North America, respectively. Seedling growth of two native tree species (Acer saccharinum [silver maple] and Betula papyrifera [paper birch]) in response to leaf-litter-incubated soils was examined; litter incubation treatments included leaves of black walnut, Norway maple, and a nonallelopathic species (Tilia americana [American basswood]) in a factorial design with varying dosages; responses to the known primary allelochemical of black walnut (juglone) were also examined. Juglone and leaf litter of both allelopathic species strongly suppressed seedling growth. BC treatments substantially mitigated these effects, consistent with the sorption of allelochemicals; in contrast no positive effects of BC were observed in leaf litter treatments involving controls or additions of nonallelopathic leaf litter. Treatments of leaf litter and juglone with BC increased the total biomass of silver maple by ~35% and in some cases more than doubled the biomass of paper birch. We conclude that BCs have the capacity to largely counteract allelopathic effects in temperate forest systems, suggesting the effects of natural PyC in determining forest community structure, and also the applied use of BC as a soil amendment to mitigate allelopathic effects of invasive tree species.