Litter Nutrient Research Articles

Litter Decomposability Traits and Their Linkage with the Cycling of Nutrients in the Forest Ecosystems under the Lens of Climate Change: A Conceptual Overview

Litter decomposition is a key process that releases nutrients back to the ecosystem and therefore maintains the structure and functioning of the tropical forest ecosystems. The variations in the rate of litter decomposition among different ecosystems may be controlled by several factors including climate, litter quality and soil biota. However, the rapid change in the environmental conditions is expected to alter the rate of litter decomposition resulting in modified nutrient cycling. This modified cycling of the nutrient may disrupt the ecosystem structure and functions followed by the compromised quality of ecosystem services and functions. Thus, an improved understanding is needed about the factors affecting the decomposition rates to sustain biodiversity and ecosystem services in a changing environment. In this article, we tried to explain the various physical, chemical and biological factors that affect the litter decomposition and nutrient cycling in the forest ecosystem. To accomplish this, we synthesized the available information by carrying out a literature survey from available databases. We found that there is a shifting paradigm from climatic control to species traits control of litter decomposition rate and recently even moving beyond it considering the effects of soil biota and habitat effects too. Further, the rate of decomposition rate is linked with the cycling of nutrients and climatic effects are expected to cascade into ecosystem functions and their services. In order to get a clear picture, however, intensive studies are required to explore the coupling effects of climatic variation on the structure and functioning behaviour of the forest ecosystems to maintain biodiversity and their services in a changing environment.

Interspecific difference in N:P stoichiometric homeostasis drives nutrient release and soil microbial community composition during decomposition

Tree species can produce litter with large variation in nitrogen to phosphorus (N:P) ratios. Here we examined how litter N:P ratios affected decomposer community composition and nutrient release for two contrasting tree species in the Qinling Mountains, China. Two-year-old Quercus aliena var. acuteserrata and Pinus tabulaeformis seedlings were fertilized using nutrient solutions with varying N:P ratios for four months. The obtained litters with contrasting N:P stoichiometry were left to decompose on nutrient-free quartz sand for 12 weeks with microbial inoculum. Then, the post-decomposition microbial community composition was determined using a phospholipid fatty acid (PLFA) analysis. The Q. aliena litter stoichiometry was more homeostatic than P. tabulaeformis litter. Litter N:P ratio was significantly related to litter nutrient loss and mass loss for P. tabulaeformis but not always for Q. aliena. The soil microbial community compositions showed larger fungal to bacterial (F:B) ratios with increasing litter N:P ratios for Q. aliena but not P. tabulaeformis. Litter N:P ratio, as determined by species-specific homeostasis, showed an interspecific difference to affect the patterns of litter decomposition dynamics, as well as related soil microbial community composition. The less variation in the soil microbial community composition than plant litter stoichiometric characteristics during decomposition is likely an important mechanism that regulates the balance of biogeochemical cycles in the Qinling Mountains.

Carbon sequestration and nutrient cycling in agroforestry systems on degraded soils of Eastern Amazon, Brazil

Land degradation and rural poverty are widespread in the Eastern Brazilian Amazon. Slash-and-burn agriculture is the main source of livelihood in small farms but also a driver of degradation. In this context, Agroforestry Systems (AFS) are an alternative for climate change mitigation and land restoration, allying food security and ecosystem services reestablishment. We evaluated the increment of carbon stock (aboveground biomass, necromass, and soil) and standing litter nutrients in AFS and compared with natural succession. Treatments were established in 30 × 30 m plots with six repetitions (randomized block design) on a very degraded soil at UEMA School farm, in Eastern Amazon. In AFS, the 17 planted tree species of local interest (for fruit, timber, N-fixing) were associated with agricultural species and fertilized according to local standards. Carbon stock was measured in 2012 before the experiment setup (baseline) and in 2018. Aboveground carbon increment (Mg ha−1) was higher in AFS (26.79 ± 23.41) than in natural succession (1.13 ± 1.5), because of tree and shrub cover as a result of planting efforts. We found very high variability in plant development and carbon sequestration between plots. Soil organic carbon did not present increment between 2012 and 2018, and no differences between treatments were found in 2018. Species choice plays a keyhole for carbon sequestration and nutrient cycling reestablishment. Areas under natural succession presented very low resilience, evidencing the need for active restoration. Diverse agroforestry systems are an efficient strategy to restore forest cover on degraded soils of Amazon allying ecosystem services reestablishment and production.

The role of the understory in litter DOC and nutrient leaching in boreal forests

Dissolved organic carbon (DOC) derived from plant litter plays an important role in the ecosystem carbon balance and soil biogeochemistry. However, in boreal coniferous forests no integrated understanding exists of how understory vegetation contributes to litter leaching of DOC, nitrogen (N) and phosphorus (P) with different bioavailability at the forest stand level. We characterized water extractable leachates from fresh and decayed litter of dominant canopy and understory sources in a boreal coniferous forest, in order to explore the contribution of understory vegetation as a source of both total and bioavailable forms of DOC, N and P. Recently produced litter from deciduous species (including Vaccinium myrtillus) yielded the highest amounts of DOC. However, this leaching potential decreased exponentially with mass loss through litter decay. The DOC lability generally showed little interspecific variation, although wood derived DOC was more recalcitrant. Lability decreased progressively with litter aging. Water extractable nutrients increased proportionally with DOC, and roughly a quarter (N) or half (P) had directly bioavailable inorganic forms. Scaled to annual litterfall at the forest stand, understory vegetation contributed ~ 80% of the water extractable DOC and nutrients from fresh litter, with > 60% coming from Vaccinium myrtillus alone. However, as litter decomposes, the data suggest a lower leaching potential is maintained with a larger contribution from needle, wood and moss litter. Our study shows that understory vegetation, especially V. myrtillus, is a key driver of litter DOC and nutrient leaching in boreal coniferous forests.

Long-Term Fire Regime Modifies Carbon and Nutrient Dynamics in Decomposing Eucalyptus pilularis Leaf Litter

The changes in fire regimes expected under climate change are likely to disrupt the biogeochemical cycling of carbon (C) and nutrients in forest ecosystems. Plant litter decomposition is a critical step in the terrestrial biogeochemical cycle, and is an important determinant of fire fuel load and forest C balance. We conducted a 277-day leaf litter decomposition experiment in an Australian eucalypt forest to test whether three contrasting, long-term fire regimes (no burning [NB], 4-yearly burning, and 2-yearly burning) were associated with different C and nutrient dynamics during litter decomposition. Fire regime had strong effects on many litter properties, including overall rates of decomposition and C loss, which were greatest in the NB treatment, suggesting that fire regime can modify the rate at which C is returned from litter to soil or the atmosphere. This has potentially important implications for soil C storage and atmospheric CO2 concentrations under a changing climate. High-frequency fire was associated with litter nutrient depletion and high microbial nutrient demand, but did not affect nutrient loss rates from decomposing litter, suggesting conservative use and retention of nutrients by the litter microbial biomass. These effects differed qualitatively between 2- and 4-yearly burning regimes, and they show how decadal-scale increases in fire frequency might contribute to soil nutrient depletion by disrupting decomposition. Many effects of fire regime on litter properties throughout decomposition were sensitive to litter bag re-collection date, suggesting that seasonal factors moderate the effects of fire regime, and that the role of fire regime-altered litter chemistry in shaping decomposition may be secondary to that of fire regime-altered environmental variables. Together, our findings highlight the potential consequences of long-term increases in prescribed fire frequency for litter decomposition and the storage and cycling of C and nutrients in eucalypt forests, and reveal the specific importance of average burn frequency in this context.

Changes in streamside riparian forest canopy and leaf litter nutrient flux to soils during an emerald ash borer infestation in an agricultural landscape

The invasive forest insect pest, emerald ash borer (EAB), is causing rapid, widespread ash tree mortality across eastern North America. Riparian (streamside) forests in agricultural landscapes often represent residual patches of high quality forest habitat that, owing to their strong land/water ecological linkages, can be critical for maintaining stream water quality and aquatic and terrestrial biodiversity. When riparian forests contain high numbers of ash trees, EAB can pose a risk of disrupting some of those land/water linkages thereby reducing riparian and aquatic habitat quality. We tracked ash tree mortality, streamside forest canopy cover, leaf litter deposition rates, and nutrient flux to soils in 18 riparian forest plots with an average of 24% ash by stem density over a 5 year period from early to late stages of an EAB invasion (2010–2015). Ash tree mortality increased from an average of 10–98% over 5 years in most plots, but when blue ash were dominant, final ash mortality was about 34%. Despite the nearly complete mortality of ash trees in almost all plots by 2015, the average canopy openness measured at 1.5 m above ground only increased to about 9%, which was significantly higher than the 2010 average of 6% open. Final canopy openness was significantly but weakly (r2 = 0.24) associated with the proportion of ash in riparian plots, indicating highly patchy openness resulting from ash mortality. Ash leaf litter deposition to streamside traps declined by 84% and elm declined by 20%, whereas leaf deposition from the other four most common contributors to riparian leaf litter increased by up to 37% over the same period. The large reductions in ash litter deposition were sufficient to reduce macro-nutrient flux to the streamside forest floor and therefore likely to streams. Amounts of N, C, P, K, and Ca delivered to the streamside soils via leaf litter fall were all consistently, some of them significantly, lower by 2014 than in the baseline year of 2010. Although total leaf litter mass returned to near pre-infestation levels by 2014, the altered composition of leaf litter caused a persistent reduction in nutrient flux to riparian soils. We also measured stem density of regenerating ash saplings ( 0.5 m height) at the end of the study period and found them to be abundant with an average of 2084 stems/ha. Our results provide an empirical demonstration of EAB-induced disruptions to ecological linkages and processes in riparian forests, at least over the short term.

Species‐specific root proliferation of tree seedlings in tropical litter: do nutrients matter?

Litter decomposition mobilizes nutrients that sustain ecosystem productivity, but decomposition by‐products may also hamper root proliferation by phytotoxicity. The aim of this study was to assess the litter substrate preferences of tropical tree seedlings in relation to litter chemical traits.We characterized 44 litter types (11 species at four decomposition ages; 0, 30, 90 and 180 days) for nutrients (N, P, K, Mg, Mn, Na, Fe and Zn) and proximate chemical parameters (cellulose, extractive, lignin and C) and tested the effect of such litter materials on seedling root growth of Albizia procera, Dalbergia sissoo and Terminalia arjuna. Albizia procera root growth was inhibited by all litter types and ages, including conspecific materials, while different heterospecific litters had inhibitory or stimulatory effect on D. sissoo and T. arjuna root growth, compared to the control. Interestingly, inhibitory and stimulatory effects of heterospecific litters significantly changed with litter age, although with no clear‐cut pattern among target species and litter species and age, while conspecific litters consistently inhibited root growth when aged, but not when fresh. Litter nutrient, extractive, C, cellulose and lignin showed no consistent association with root growth of tested plants. Albizia procera root growth was positively associated with Na content and N:P ratio. Dalbergia sissoo root growth was positively associated to C:N and lignin:N ratios, and negatively to K, Na and Zn content. Finally, T. arjuna root was positively associated to cellulose and N:P ratio, but negatively to extractive. We conclude that studied nutrient, cellulose and lignin do not consistently explain the species‐specific response of root of tree seedlings to decomposing litter.

Soil stoichiometry of Pinus massoniana forest in red soil erosion area under different management patterns

We investigated the concentrations of carbon (C), nitrogen (N), and phosphorus (P) and C:N:P stoichiometry in soil and litter of Pinus massoniana forest under four different management patterns: inefficient forest transformation, mixture of arbor with shrub and herb, shallow ditch grass planting, and being banned in serious erosion and degradation of red soil in southern China. Our findings could provide scientific basis for soil erosion control and vegetation restoration in this area. The results showed that there were significant differences in soil organic carbon (SOC), TN, TP and litter nutrient content among different management patterns. The nutrient contents in soil and litter under all the four management patterns were significantly higher than that of control, with mixture of arbor with shrub and herb having the highest concentrations. The concentrations of SOC, TN and TP decreased with the increases of soil layer. However, the shallow ditch grass planting mana-gement pattern presented as follows: the concentrations of SOC, TN and TP decreased first and then increased with the increases of soil layer, with the lowest value in 5-20 cm soil layer. There were significant differences in soil C:N, C:P, N:P and litter C:P among different management patterns, and the soil spatial variation was C:N>C:P>N:P. Excepted for mixture of arbor with shrub and herb, C:N was still at a lower level in the other management patterns, and soil C:P and N:P showed higher values overall. Litter C:N, C:P and N:P had opposite change pattern, with inefficient forest transformation and mixture of arbor with shrub and herb being much smaller than the control. Soil C:N and C:P were mainly controlled by SOC content and litter C content, and soil N:P was mainly controlled by soil TP content and litter P content. Soil stoichiometry was affected by soil water content, soil bulk density, pH, and other factors. The relationship between litter and soil nutrients was closely related and showed similar changes.

Litter dynamics recover faster than arthropod biodiversity during tropical forest succession

AbstractLitterfall and litter decomposition are key elements of nutrient cycling in tropical forests, a process in which decomposer communities such as macro‐arthropods play a critical role. Understanding the rate and extent to which ecosystem function and biodiversity recover during succession is useful to managing the growing area of tropical successional forest globally. Using a replicated chronosequence of forest succession (5–15, 15–30, 30–45 years, and primary forest) on abandoned pastures in lowland tropical wet forest, we examined litterfall, litter chemistry, and effects of macro‐arthropod exclusion on decomposition of two litter types (primary and 5‐ to 15‐years‐old secondary forest). Further, we assessed macro‐arthropod diversity and community composition across the chronosequence. Overstory cover, litterfall, and litter nutrients reached levels similar to primary forest within 15–30 years. Young secondary forest litter (5–15 years) had lower initial N and P content, higher C:N, and decayed 60 percent faster than primary forest litter. The presence of macro‐arthropods strongly mediated decomposition and nutrient release rates, increasing litter mass loss by 35–44 percent, N released by 53 percent, and P release by 84 percent. Forest age had no effect on soil nutrients, rates of litter decomposition, nutrient release, or macro‐arthropod influence. In contrast, abundance and community composition of macro‐arthropods remained significantly lower and distinct in all ages of secondary compared with primary forest. Order richness was lower in 5–15 years of secondary compared with primary forest. Our results suggest that in highly productive tropical wet forest, functional recovery of litter dynamics precedes recovery of decomposer community structure and biodiversity.Abstract in Spanish is available with online material.

Temporal and stoichiometric patterns of algal stimulation of litter‐associated heterotrophic microbial activity

Abstract Periphyton communities associated with submerged plant detritus contain interacting autotrophic and heterotrophic microbes, and are sites of extracellular enzymatic activity. The strength and nature of these interactions might be expected to change over time as microbial communities develop on plant litter. Microbial interactions and enzymatic activity can be altered by nutrient availability, suggesting that litter stoichiometry could also affect these phenomena. We grew wetland plants under ambient and nutrient‐enriched conditions to generate plant litter of differing nutrient content. In two experiments, we investigated: (1) the influence of algal photosynthesis on fungal and bacterial production and the activities of four extracellular enzymes throughout a 54‐day period of microbial colonisation and growth; and (2) the influence of litter stoichiometry on these relationships. Ambient and nutrient‐enriched standing‐dead plant litter was collected and then submerged in wetland pools to allow for natural microbial colonisation and growth. Litter samples were periodically retrieved and transported to the laboratory for experiments manipulating photosynthesis using the photosystem II inhibitor DCMU (which effectively prevents algal photosynthetic activity). Algal (14C‐bicarbonate), bacterial (3H‐leucine), and fungal (14C‐acetate) production, and β‐glucosidase, β‐xylosidase, leucine aminopeptidase, and phosphatase activities (MUF‐ or AMC‐labelled fluorogenic substrates) were measured under conditions of active and inhibited algal photosynthesis. Photosynthesis stimulated overall fungal and bacterial production in both experiments, although the strength of stimulation varied amongst sampling dates. Phosphatase activity was stimulated by photosynthesis during the first, but not the second, experiment. No other enzymatic responses to short‐term photosynthesis manipulations were observed. Microbial communities on high‐nutrient litter occasionally showed increased extracellular enzyme activity, fungal growth rates, and bacterial production compared to communities on non‐enriched litter, but algal and fungal production were not affected. Litter stoichiometry had no effects on fungal, bacterial, or enzymatic responses to photosynthesis, but the mean enzyme vector analysis angle (a measure of P‐ versus N‐acquiring enzyme activity) was positively correlated to litter N:P, suggesting that elevated litter N:P led to an increase in the relative activity of P‐acquiring enzymes. These results supported the hypothesis that algal photosynthesis strongly influences heterotrophic microbial activity on macrophyte leaf litter, especially that of fungi, throughout microbial community development. However, the strength of this photosynthetic stimulation does not generally depend on small differences in litter nutrient content. Stimulation of microbial heterotrophs by algal photosynthesis could drive diurnal shifts in periphyton community and aquatic ecosystem function, as well as linking green (photoautotroph‐based) and brown (detrital‐based) food webs.

Understanding the relationship between soil properties and litter chemistry in three forest communities in tropical forest ecosystem.

In this study, we investigated the relationship between soil properties and litter chemistry in three forest communities, i.e., Sal mixed forest (SMF), dry mixed forest (DMF), and teak plantation forest (TPF), in tropical deciduous forest ecosystem in North India. Fresh leaf litter and soil samples were collected at two soil depths (0-15 and 15-30 cm) from all these three forest communities. Litter bag experiment was also conducted to know differences in litter nutrients after its decomposition. The concentrations (mg kg-1) of different nutrients such as sodium (Na) 2.6, potassium (K) 38.5, calcium (Ca) 425, and carbon (C) 45.54% were highest in fresh litter collected from DMF. Total organic carbon (g kg-1) was significantly higher in SMF (19.23) in comparison to DMF (18.41) and TPF (13.61) at 0-15-cm soil depth. Na, K, Ca, available P, total P, available N, and total N were highest in DMF soil. We observed significantly positive correlation between all nutrients of litter and soil. Although soil bulk density (BD) and particle density (PD) showed their significant negative correlation with litter C, total porosity was positively correlated. Similarly, litter Na has its significant negative correlation with BD and positive correlation with PD. The litter chemistry played a significant role in changing soil pH and TOC. All litter nutrients, except total P, have their significant positive correlation with soil pH. Total P, C, and N of litter have their significant positive correlation with total soil organic carbon. This indicates that litter chemistry and soil properties have specific relation among them despite unique species composition in each forest community.

Evaluation of Biochar as a Litter Amendment for Commercial Broiler Production

SUMMARY Litter amendments are commonly used in commercial broiler production to improve litter quality and overall house conditions. While litter amendments used to limit the formation of gaseous ammonia have been studied extensively, there has been little evaluation of materials to limit water activity in the litter. The large surface area and high porosity of biochar (BC), or charcoal that is used for environmental or agricultural applications, are physical characteristics of the material that aid in water absorption and could lead to altered water activity in commercial broiler litter. This study examined the influence of a pre-flock application of BC on broiler performance, health, and litter quality and determined the water holding capacity (WHC) of pine shavings (PS) at varying BC inclusion rates. Surface application of BC to PS at a rate of 0.97 kg/m2 did not influence performance, health, or litter nutrient content in male broilers reared to 35 d of age. The addition of BC to PS increased WHC and was influenced by BC particle size. The addition of BC at 10 to 20% by weight to PS increased WHC by 21.6 and 32.2%, respectively, over that of PS. The data herein indicate that BC used a litter amendment has no negative effects on performance and health and may improve litter quality through increased water absorption.

Vertical distribution of 137Cs in forest soil after the ground fires

We studied the influence of forest fires on vertical pattern of 137Cs specific activity concentration in forest soils. Our experiments were organized in Bazar forestry of State Enterprise (SE) “Narodychi Forestry” (Ukraine). We sampled soil in the study sites where grassfires occurred at different times, and determined the specific activity of 137Cs in all soil horizons. We determined that the forest fires and burned forest litter intensify mineralization of forest litter nutrients and increase the radionuclide content in upper layers of soil mineral part. In the following years, the radionuclides gradually move to deeper soil horizons and the difference between the burned and control areas decreases. We determined the depth of soil layer, where the changes in 137Cs specific activity occur caused by the forest fires. The time required for restoration of the original distribution is calculated. The results obtained allow us to identify a group of plants (by the location of the root system) that may have increased levels of contamination in the years following a forest fire and to determine the period when we must conduct additional radiological control of them. We suggested the recommendations on usage of non-timber forest products on the territories contaminated with radionuclides.

Annual biomass loss and potential value of urban tree waste in the United States

Urban trees provide numerous benefits to society, but upon removal, this resource is underutilized and often considered a waste product to be discarded. However, urban trees have a potential to be utilized for various products, create jobs and an income stream for cities. The latest data on urban forests in the United States were used to estimate the potential annual value that could be derived from urban tree waste. Assuming a mortality rate of 2%, annual urban woody biomass loss in the U.S. equates to about 46 million tonnes of fresh-weight merchantable wood or 7.2 billion board feet of lumber or 16 million cords of firewood. The potential annual value from urban wood waste ranges between $89-786 million depending upon the product derived (e.g., wood chips to lumber). States with the greatest urban wood product potential are Florida ($6.6–57.6 million/year) and Georgia ($6.0–52.7 million/year). Along with woody biomass, annual leaf loss has a potential to produce value. The value of nutrients in annual leaf litter is estimated at $551 million per year. In addition to direct revenue from sales, other environmental benefits can be derived through tree waste utilization that reduces landfill waste, use of fertilizers and fossil fuel use in energy production. There are various reasons why this potential maximum value from urban tree waste is not and likely cannot be attained, but its current use and value can be increased. Creating markets and systems to utilize urban tree removals and leaves can help enhance income for urban forest management as well as create social and environmental goods.

Leaf litter identity alters the timing of lotic nutrient dynamics

Abstract The effects of resource quality on ecosystems can shift through time based on preferential use and elemental needs of biotic consumers. For example, leaf litter decomposition rates are strongly controlled by initial litter quality, where labile litter is processed and depleted more quickly than recalcitrant litters. We examined the effect of this processing continuum on stream nutrient dynamics. We added one of four different litter compositions differing in litter quality (cottonwood [Populus deltoides], labile; sycamore [Platanus occidentalis], recalcitrant; bur oak [Quercus macrocarpa], recalcitrant; and mixed [equivalent mixture of previous three species]) to 12 large (c. 20 m long, with riffle, glide and pool sections) outdoor stream mesocosms to assess the effect of litter species composition on whole‐stream nutrient uptake. Nutrients were dosed once weekly for 8 weeks to measure uptake of NH4–N, NO3–N, and PO4–P. We also measured changes in litter C, N, and P content on days 28 and 56 of the study. Nutrient uptake rates were highly variable, but occasionally very different among litter treatments (c. 5× between highest and lowest uptake rates by species). Uptake rates were generally greatest in cottonwood (labile) streams early in the study. However, during the last 4 weeks of the study, bur oak streams (recalcitrant) took up more nutrients than cottonwood streams, resulting in more cumulative NO3–N uptake in bur oak than in cottonwood streams. Cumulative NO3–N uptake was greater in mixed streams than expected (non‐additive) on two dates of measurement, but was generally additive. Changes in litter nutrient content largely corroborated nutrient uptake patterns, suggesting strong N immobilisation early in the study and some N mineralisation later in the study. P was strongly retained by most litters, but especially bur oak. Nutrient content of litter also largely changed additively, suggesting minimal evidence for non‐additive diversity effects on nutrient source/sink status. Our results demonstrate that litter species identity can have whole‐ecosystem effects on stream nutrient dynamics, with important implications for the form and fate of nutrients exported downstream. Further, diverse litter assemblages may serve as temporal stabilisers of ecosystem processes, such as nutrient sequestration, due to microbial nutrient requirements and differential decomposition rates, or the classic litter processing continuum.

Do Silvi-Medicinal Plantations Affect Tree Litter Decomposition and Nutrient Mineralization?

In a silvi-medicinal system, the plant secondary metabolites (PSMs) released from medicinal herbs could affect tree litter decomposition and nutrient release. However, the specific effects of PSMs on arboreous litter decomposition are still not well understood. In this study, the extracts of nine types of medicinal herbs were used to treat Pinus armandii Franch. and Larix gmelinii (Rupr.) Kuzen. litter during a simulated half-year decomposition. The effects of the extracts on the decomposition and the N and P release of the conifer litter were investigated. The results indicated that most of the medicinal herb extracts significantly inhibited the late decomposition of P. armandii litter, whereas only two of them accelerated the entire decomposition process. Only a few significantly affected the decomposition of the L. gmelinii litter. Four of the nine types of extract significantly inhibited the N and P release of the P. armandii litter, while 3/9 and 6/9 inhibited the N and P release of the L. gmelinii litter, respectively. The accelerating effects of the extracts on the cellulase activity and the inhibitory effects on the polyphenol oxidase activity might be responsible for the early acceleration and late inhibition of litter decomposition, while the effects of the extracts on the activities of protease and phosphatase might not be the main reason for the inhibitory or accelerating effects on the N and P release. In general, the inhibitory effects of medicinal herbs on the nutrient cycling of ecosystems should be taken into consideration when building silvi-medicinal systems, especially in P. armandii forests.

In situ leaf litter production, decomposition and nutrient release of dry Afromontane trees

ABSTRACTThe litter fall production, decomposition and subsequent nutrient release of Carrisa edulis, Juniperus procera, Maytenus obscura and Olea europaea was monitored in the dry Afromontane fores...

Effects of Acacia invasion on leaf litter nutrient and soil properties of coastal Kerangas forests in Brunei Darussalam

Exotic Acacia were introduced to Brunei Darussalam in the 1990s for plantation forestry and land rehabilitation but are now regarded as invasive. We assessed the effects of Acacia on litter nutrient composition and soil physicochemical properties of Brunei’s coastal Kerangas (heath) forests. Soil and litter samples were collected from ten 20 x 20 m plots in Acacia-invaded Kerangas forests (IKF) and ten uninvaded (UKF) plots. Soil samples were analyzed for pH, gravimetric water content and nutrient concentrations whereas litter samples were analyzed for total nutrients only. We recorded significantly higher concentrations of litter total N and P in the IKF than the UKF plots. In contrast, no significant differences were detected in soil properties, except for topsoil available P and subsoil exchangeable Ca which were both lower in the IKF plots. A significant positive correlation was detected between litter N and topsoil N in the IKF plots. We suggest that the fairly recent timescale of Acacia invasion (< 25 years) of the IKF sites resulted in the lack of significant increase of soil nutrients. In conclusion, Acacia invasion into Brunei’s forests can potentially alter both leaf litter and soil physicochemical properties of Kerangas forests, in particular affecting nutrient availability. This alteration of ecosystem may further enhance the invasion success of Acacia, making restoration attempts more challenging.

Leaf Nutrients and Macroinvertebrates Control Litter Mixing Effects on Decomposition in Temperate Streams

Plant litter decomposition is an essential ecosystem function in temperate streams. Both riparian vegetation and decomposer communities are major determinants of the decomposition efficiency and the interactions occurring within litter mixtures. However, the extent to which such litter mixture interactions are affected by combined shifts in litter traits and decomposer community is not well understood. We used leaf litter from 10 European tree species in order to study litter decomposition and litter mixture effects occurring in two-species litter mixtures in a temperate forested stream of northwestern France. The study distinguished between (1) decomposition involving microorganisms alone or together with invertebrates, and (2) decomposition involving litter mixtures of similar or dissimilar nutrient content. Increasing mean litter nutrient concentration favored both microbial activity and litter decomposition rate. Surprisingly, the highest litter mixture effects occurred in mixtures containing two nutrient-rich litters and occurred mainly in macroinvertebrate presence. Both the “mass ratio hypothesis,” expressed as the community-weighted mean traits (TraitCWM), and the “niche complementarity hypothesis,” expressed as the functional dissimilarity of litter traits (TraitFD), contributed to explain litter mixture effects. However, TraitCWM was found to be a better predictor than TraitFD. Finally, when evaluating the individual contributions of litter nutrients, calcium and magnesium appeared as important drivers of litter mixture effects. Our findings suggest that the mass ratio hypothesis overrules the niche complementarity hypothesis as a driver of litter diversity effects. Our study highlights the key importance of macroinvertebrates and of leaf nutrients, such as Ca and Mg, which are often neglected in decomposition studies in streams.

Soil fauna promote litter decomposition but do not alter the relationship between leaf economics spectrum and litter decomposability

The leaf economics spectrum (LES) describes co-variation in leaf functional traits relevant to carbon and nutrient economics across plant species. It has been proposed that LES can be a useful predictor of litter decomposability, thereby influencing ecosystem carbon and nutrient cycling. However, the role of soil fauna in mediating the LES-decomposability relationship is largely unexplored. We evaluated leaf litter decomposability of 21 co-occurring tree species in a subtropical forest in China. We used litterbags with different mesh sizes to control litter accessibility to meso- and macrofauna. We quantified 9 leaf functional traits and 12 litter traits, and investigated how these traits were related to the losses of litter mass, carbon and nitrogen under different fauna treatments. Litter mass loss varied from 32.3 to 80.6% after 400 days of decomposition in the field. Meso- and macrofauna presence increased on average litter mass loss by 8.4%, carbon loss by 11% and nitrogen loss by 14.4%. Litter nutrient contents and stoichiometry generally had no significant effect on decomposition rates. Instead, structure-related traits such as toughness, lignin and labile compounds were generally strongly related to decomposition rates, suggesting that decomposition processes are strongly limited by energy availability. We found significant linear relationships between LES and litter mass or carbon loss, but not nitrogen loss. However, meso- and macrofauna presence did not significantly alter the regression slopes of these relationships, suggesting that meso- and macrofauna exert similar effects on decomposition of litter originating from tree species characterized by different life strategies. This study advances our understanding of the soil fauna in driving litter decomposition in subtropical forests.