Decomposing Leaf Litter Research Articles

Spectral Composition of Sunlight Affects the Microbial Functional Structure of Beech Leaf Litter During the Initial Phase of Decomposition

AimsThis study tests whether different spectral regions of sunlight affect the microbial decomposer assemblage in surface leaf litter in a beech understorey over the first 6 months following leaf senescence.MethodsWe performed a litterbag experiment employing filters attenuating combinations of UV-B, UV-A, blue, and green light as well as the whole spectrum of sunlight. We measured changes in microbial biomass and community structure, litter mass loss and litter chemistry during the first 6 months of decomposition.ResultsFungal and total microbial biomass were highest in the treatment excluding UV radiation, blue and green light. Exclusion of UV-B radiation decreased the fungal:bacterial biomass ratio and litter nitrogen content. Bacterial biomass was lower in the dark treatment compared to treatments receiving at least part of the solar spectrum. Our filter treatments affected microbial functional structure from the beginning of the experiment, whereas mass loss was only significantly affected after 6 months of decomposition and no effect was found on litter carbon content.ConclusionsThis study proves that sunlight, in a spectrally dependent manner, affects both microbial functional structure and biomass in temperate deciduous forests early in the decomposition process, with bacteria tending to dominate in sunlight and fungi in dark conditions. We found sunlight to be important in the decomposition in temperate forest understoreys despite the low irradiance characterizing these environments. However, long-term studies are required to estimate the relative contribution of sunlight among factors affecting the eventual incorporation of decomposing leaf litter into forest soils.

Diversity of silicon release rates among tropical tree species during leaf-litter decomposition

Leaf-litter is a significant source of biogenic Si, and differences among tree species in Si release rates during litter decomposition are important for quantifying Si cycles in forest ecosystems. We conducted two experiments to improve mechanistic understanding of Si release rates from dead leaves, using lowland tropical trees of Sarawak, Borneo. In the first experiment, we assessed Si leaching from leaf litter when they were shaken in water for four hours. In the second experiment, leaf litter samples were allowed to decompose in mesh bags in growth chambers for two months, in order to determine rates of decomposition and Si release, and to explore a relationship between decomposition rate and initial litter chemistry. Among the 12 species with large differences in initial leaf-litter Si concentration (0.72–80.0 mg Si g−1), Si leaching to water varied widely (0.04–0.16 mg Si g−1) and positively correlated with the initial Si concentration (R2 = 0.87; P < 0.001). Si release per unit leaf dry weight in the decomposition experiment was also positively correlated with initial litter Si concentration among six species (R2 = 0.998; P < 0.001). In contrast, proportion of initial Si content released did not exhibit a significant relationship with their decomposition rates, which were correlated with labile carbon content in leaf litter (e.g. hemicellulose). Our results suggest that Si release rates from decomposing leaf litter cannot be simply predicted from decomposition rates. The species differences in locations and stability of opal phytoliths and their resulting effects on Si dissolution rates should be considered.

Light and temperature mediate algal stimulation of heterotrophic activity on decomposing leaf litter

Abstract Recent evidence suggests that periphytic algae stimulate plant litter heterotrophs (fungi and bacteria) in the presence of light, but few studies have tested whether this stimulation varies across gradients of light, which may covary with temperature. We exposed field‐conditioned Typha domingensis litter to fully‐crossed, short‐term gradients of temperature (15, 20, 25, and 30°C) and light (0, 25, 53, 123, and 388 µmol quanta m−2 s−1) and measured responses of litter‐associated algal, fungal, and bacterial production rates and β‐glucosidase, β‐xylosidase, and phenol oxidase enzyme activities in the laboratory. Increased light stimulated algal production rates, from immeasurable production under darkness to &gt;200 µg algal C g−1 detrital C hr−1 at the highest light level, with the greatest light sensitivity and maximal photosynthetic rates at 25°C. In turn, increased light stimulated fungal production rates, especially at the two highest temperatures and most strongly at 25°C where light stimulated fungal production by a mean of 65 µg C g−1 detrital C hr−1, indicating 2.1‐fold stimulation by light. Bacterial production rates also responded to light, indicated by stimulation of a mean of 16 µg C g−1 detrital C hr−1 (1.6‐fold) at 15°C, but stimulation was weaker at higher temperatures. Enzyme activities increased strongly with elevated temperature but were not affected by light. Our experimental evidence suggests algae differentially stimulate litter‐associated bacteria and fungi in a light‐dependent manner that further depends on temperature. These findings advance understanding of the onset of algal stimulation of heterotrophy, including algal‐induced priming effects during litter decomposition, in response to common covarying environmental gradients subject to global change.

Allelopathic effects of Cinnamomum septentrionale leaf litter on Eucalyptus grandis saplings

Allelopathy plays an important role in plant-plant interactions, particularly through compounds released from litter exudates and decomposition. We conducted a greenhouse experiment to examine how additions of Cinnamomum septentrionale Hand. Mazz leaf litter (A) versus leaf litter aqueous extracts (B) can impact Eucalyptus grandis Hill ex Maid saplings, focusing on growth, physiology and photosynthesis. We show that both A and B significantly inhibited the growth and photosynthesis of E. grandis saplings, and this inhibition strengthened with increasing soil A content (range from 0 to 120 g pot−1) and concentrations of B (range from 0 to 80 g L−1). Additions of leaf litter or its aqueous extracts decreased chlorophyll content and intercellular CO2 concentration (Ci) while stomatal conductance (Gs) increased, reflecting that non-stomatal limitation might be the reason for the reduction of the photosynthetic rate. After treatment with A, the peroxidase (POD) and superoxide dismutase (SOD) activity were reduced, while there was a reduction in POD and non-changed SOD activity after treatment with B. Furthermore, sugar and proline levels declined under both A and B treatments. This study demonstrates that both A and B of C. septentrionale influenced the growth, chlorophyll synthesis and photosynthesis of E. grandis saplings, and caused oxidative damage in E. grandis. The Synthesis Effect (SE) indicates that B has stronger allelopathic effect than A under the same treatment. This stronger allelopathic effect of C. septentrionale leaf litter aqueous extracts than its decomposing leaf litter can be reflected by greater damage to membrane systems, and greater reductions of both chlorophyll content and photosynthesis on treated plants.

Functional diversity of ligninolytic fungi associated with leaf litter decomposition

AbstractFungi play central roles in leaf litter decomposition as they are capable of actively decomposing lignin and other recalcitrant components in leaf litter that impact the decomposition in terrestrial ecosystems. Quantitative evaluation is lacking, however, regarding the ability of diverse fungi to decompose leaf litter and the variability of ligninolytic activity among fungal taxa. In this comprehensive synthesis, I summarize the data of 1,232 individual pure culture tests conducted under standardized protocols to examine the functional diversity of fungi associated with leaf litter decomposition, with special emphasis on the ligninolytic activity. Fungal strains tested included 218 species in 69 families of Basidiomycota, Ascomycota, and Mucoromycotina that were derived from tropical and temperate forests to polar tundra. Fungal strains were inoculated adjacent to sterilized leaves and other substrata and incubated in the laboratory in order (a) to examine their functional potentialities in terms of the ability to cause mass loss of leaves and decompose recalcitrant components and (b) to explore the effect of litter quality and various environmental factors. The results of these tests revealed that ligninolytic abilities were specifically detected in fungal strains in such families as Mycenaceae and Marasmiaceae in Basidiomycota, and Rhytismataceae and Xylariaceae in Ascomycota. The ligninolytic activity varied among fungal taxa and with the quality and type of substrata, incubation temperature, and external supply of nutrients. This review provides integrative accounts of the functional diversity of ligninolytic fungi associated with leaf litter decomposition and enhances our understanding of the roles of fungal diversity in decomposition processes.

Major element residence times in humus from a beech forest: The role of element forms and recycling

This study presents the relationship between inputs of elements (especially biominerals), their recycling mechanisms and the average residence time of the major elements in mull humus.In forest ecosystems with generally low element inputs, decomposing leaf litter is an important source of soil nutrients. While the processes and the release speeds of elements, such as C, N and P, are well determined during litter degradation, less is known about elements like Fe, Al, Mg, Mn, Si, Ca, K, or Na, some of which are essential for tree nutrition.The objective of this study was to determine the average residence time of these elements in mull-type humus for 3 different soils: a Dystric Cambisol (S1), Eutric Cambisol (S2) and Rendzic Leptosol (S3), in the same beech grove of the northeast of France and to identify the main mechanisms controlling them.To achieve this goal, the approach used: 1) scanning electron microscope observation of the evolution and recycling of elements during litter degradation; 2) quantification of total inputs and their form (soluble/insoluble) in the litterfall and the contribution of exploitation residues; 3) quantification and evolution of litter stocks; and 4) calculation and comparison of the residence time of the elements according to their form.Calculation of inputs and stocks of elements in humus made it possible to assess the residence time of each elements. The average residence times were between 58.4 and 13.1 y for Fe and Al; 3.3 and 1.6 y for Si, N, S and Ca; 2.2 and 1.2 y for Mn, Mg, Na, P and C; and 0.6 and 0.8 y for K. The results were similar for the three soils except for the Mn stock and inputs, which were lower in S3, and for the Si input, which decreased from S1 to S3.The results of the study indicate that the residence times of K, P, Na, Mg and S decreased with the percentage of soluble forms. Conversely, they increased when elements were principally in the form of biominerals (Si, Ca), such as in plant tissues, organic molecules (N) and more resistant tissues, or intervened in sorption mechanisms (Al, Fe) and biotic recycling mechanisms, such as testate amoebae (Si, Ca, P, Mn) and fungal hyphae (Ca, Mn, P) and abiotic precipitation (Si).

Anthropogenic stressors affect fungal more than bacterial communities in decaying leaf litter: A stream mesocosm experiment.

Despite the progress made in environmental microbiology techniques and knowledge, the succession and functional changes of the microbial community under multiple stressors are still poorly understood. This is a substantial knowledge gap as microbial communities regulate the biogeochemistry of stream ecosystems. Our study assessed the structural and temporal changes in stream fungal and bacterial communities associated with decomposing leaf litter under a multiple-stressor scenario. We conducted a fully crossed 4-factor experiment in 64 flow-through mesocosms fed by a pristine montane stream (21 days of colonisation, 21 days of manipulations) and investigated the effects of nutrient enrichment, flow velocity reduction and sedimentation after 2 and 3 weeks of stressor exposure. We used high-throughput sequencing and metabarcoding techniques (16S and 18S rRNA genes) to identify changes in microbial community composition. Our results indicate that (1) shifts in relative abundances of the pre-existing terrestrial microbial community, rather than changes in community identity, drove the observed responses to stressors; (2) changes in relative abundances within the microbial community paralleled decomposition rate patterns with time; (3) both fungal and bacterial communities had a certain resistance to stressors, as indicated by relatively minor changes in alpha diversity or multivariate community structure; (4) overall, stressor interactions were more common than stressor main effects when affecting microbial diversity metrics or abundant individual genera; and (5) stressor effects on microbes often changed from 2 weeks to 3 weeks of stressor exposure, with several response patterns being reversed. Our study suggests that future research should focus more on understanding the temporal dynamics of fungal and bacterial communities and how they relate to ecosystem processes to advance our understanding of the mechanisms associated with multiple-stressor interactions.

Co-elevated CO2 and temperature and changed water availability do not change litter quantity and quality of pine and oak

Elevated CO2 concentration ([CO2]) and air temperature (Tair) as well as changed soil water availability (Wsoil) may affect quantity, chemistry, and microbial decomposability of tree leaf litter. However, our understanding is limited mainly to the effect of elevated [CO2]. This study investigated the effects of elevated [CO2] and Tair in combination with two Wsoil regimes on the quantity and chemistry including the ratio of lignin to nitrogen (lignin/N) of litter produced by Pinus densiflora and Quercus variabilis saplings, and microbial respiration of the soils amended with the litters. Either elevated [CO2] or high Wsoil alone increased litter production; meanwhile elevated Tair alone decreased litter production. However, co-elevation of [CO2] and Tair did not change litter production regardless of Wsoil regime for both species. Among litter chemistry, the lignin/N, which is a robust indicator of litter decomposability, of litter was changed in parallel with litter quantity (i.e., lignin/N ratio increased when litter quantity increased and vice versa) mainly due to dilution of N. Due to the opposite effect of warming and elevated [CO2] on litter quantity, lignin/N was not changed under co-elevated [CO2] and Tair at a given Wsoil regime for both species. Other litter chemistry including non-structural carbohydrates and minerals was also affected by [CO2], Tair, or Wsoil. However, changed litter chemistry did not change the CO2 emission from the soils amended with the litters; however, addition of litter with low lignin/N and high nutrients increased microbial biomass in the soil. This study enlarges our understanding of the effects of changed climatic variables on litter quantity, chemistry, and microbial decomposability and suggests that co-elevation of [CO2] and Tair may not cause a significant change in the litter parameters regardless of Wsoil. Study with mature trees at a natural forest should further improve our understanding.

Volatile methanol and acetone additions increase labile soil carbon and inhibit nitrification

Recent efforts to understand the contribution of low-molecular weight compounds to carbon dynamics in soil ecosystems has resulted in a framework that suggests that low-molecular weight, labile carbon compounds can be directly assimilated by microbial biomass before being stabilized on soil colloids. However, this model primarily focuses on dissolved organic matter inputs and overlooks the potential importance of volatile organic compounds (VOCs). Here we determined the effects of two VOCs commonly emitted from soil and decomposing leaf litter (methanol, and acetone) on soil respiratory dynamics during a 28-day lab experiment. At the end of the experiment we quantified carbon and nitrogen concentrations in dissolved organic matter, microbial biomass, particulate organic matter, mineral associated organic matter, the labile carbon pool, and we quantified nitrifying microorganism abundance. Our results demonstrate that VOCs (i.e. methanol and acetone) increase soil respiration, contribute to labile soil C, and inhibit nitrification. Our VOC additions resulted in respiration spikes 4.1–5.5-fold greater than the control for acetone and methanol, respectively, though respiration returned back to control levels within 144 h after additions. Our VOC additions resulted in a 1.6–1.7-fold increase in labile soil carbon, suggesting that litter-derived VOCs could enter soil C pools following microbial metabolism. Additionally, soils exposed to VOCs contained ~ 2.25-fold less total dissolved nitrogen, and ~ 34–220-fold less nitrate. Ammonia oxidizing archaea were ~ 1.5 fold less abundant in VOC treated soils than in the control. After VOC additions were ceased, nitrate levels increased at approximately the same rate in all treatments, suggesting an inhibitory effect of methanol and acetone on nitrifying microorganisms. These results indicate that common decomposition derived VOCs play an important yet under-recognized role in driving the formation of soil organic matter as well as increasing the immobilization of nitrogen in soil ecosystems.

Effect of Black Cherry (Prunus serotina) Litter Extracts on Germination and Growth of Scots Pine (Pinus sylvestris) Seedlings

In the managed forest of temperate Europe, black cherry (Prunus serotina) is one of the most important invader species. Among the ecological traits enabling its expansion in forest stands, the role of chemical compounds released naturally by this plant into the environment still remains unclear. The aim of this study was to determine the influence of black cherry leaf litter on the germination and growth of Scots pine (Pinus sylvestris) seedlings. Laboratory bioassays with extracts from newly fallen and decomposed leaves showed a phytotoxic effect on root elongation and a slightly weaker negative effect on stem growth of pine shoots. The inhibitory effect increased with the gradient of leaf extract concentration. Furthermore, a significant negative correlation was observed between condensed tannin content in decomposed leaf litter of the black cherry and the pine root growth. The results are discussed in the context of black cherry litter properties which could interfere with natural regeneration of pine forests.

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.

Indian pollinators of cocoa,Theobroma cacaoL.

Cocoa is the third important beverage crop grown for its beans which are mainly used in the chocolate industry. It is the only tree species of economic importance in the family Malvaceae. Cocoa flowers are produced in large numbers but only few of them develop into fruits. Self-incompatibility is a special feature present in cocoa. Pollination is a major concern in this crop. A field experiment was carried out in the farmer's holdings at Sethumadai, Pollachi and at Coconut Research Station, TNAU, Aliyar Nagar during 2013-2014 to study the Indian pollinators of cocoa. Results of the field experiment on pollinators of cocoa revealed that cocoa is pollinated by small midges, Forcipomyia spp. belonging to the family Ceratopogonidae, Diptera. Results of field experiments to study the mechanism of pollination revealed that caging of two cocoa entries viz., CCRP 1 and CCRP 2 with 100 kg of decomposed leaf litter as pollinator breeding substrate resulted in the production of 27 matured pods in both the trees over a period of four months. Whereas, the same entries, under similar setup without pollinator breeding substrate resulted in no pod set in both the trees over a period of four months. These results proved the entomophilous nature of cocoa. From the field experiments, Forcipomyia spp. is identified as a potential pollinator of cocoa in India. Decomposed banana pseudostem and decomposed leaf litter were identified as the best pollinator breeding substrates.

Relationships between fungal community composition in decomposing leaf litter and home‐field advantage effects

Abstract Increasing evidence suggests that specific interactions between microbial decomposers and plant litter, named home‐field advantage (HFA), influence litter breakdown. However, we still have limited understanding of whether HFA relates to specific microbiota, and whether specialized microbes originate from the soil or from the leaf microbiome. Here, we disentangle the roles of soil origin, litter types and the microbial community already present on the leaf litter in determining fungal community composition on decomposing leaf litter and HFA. We collected litters and associated soil samples from a secondary succession gradient ranging from herbaceous vegetation on recently abandoned ex‐arable fields to forest representing the end stage of succession. In a greenhouse, sterilized and unsterilized leaf litters were decomposed for 12 months in soils from early‐ to late‐successional stages according to a full‐factorial design. At the end, we examined fungal community composition on the decomposing litter. Fungal communities on decomposed late‐successional litter in late‐successional soil differed from those in early‐ and mid‐successional stage litter and soil combinations. Soil source had the strongest impact on litter fungal composition when using sterilized litter, while the impact of litter type was strongest when using unsterilized litter. Overall, we observed HFA, as litter decomposition was accelerated in home soils. Increasing HFA did not relate to the dissimilarity in overall fungal composition, but there was increasing dissimilarity in the relative abundance of the most dominant fungal taxon between decomposing litter in home and away soils. We conclude that early‐, mid‐ and late‐succession litter types did not exert strong selection effects on colonization by micro‐organisms from the soil species pool. Instead, fungal community composition on decomposing litter differed substantially between litter types for unsterilized litter, suggesting that the leaf microbiome, either directly or indirectly, is an important determinant of fungal community composition on decomposing leaves. HFA related most strongly to the abundance of the most dominant fungal taxa on the decomposing litter, suggesting that HFA may be attributed to some specific dominant fungi rather than to responses of the whole fungal community. A plain language summary is available for this article.

The potential for mass ratio and trait divergence effects to explain idiosyncratic impacts of non‐native invasive plants on carbon mineralization of decomposing leaf litter

Abstract Invasive plant effects on litter decomposition tend to be idiosyncratic among species and ecosystems, which may arise from variation in the invader’s relative abundance (mass ratio effect), from its relative functional difference to other species (trait divergence effect) and/or from species’ litter mixing that causes non‐additive decomposition rates relative to single‐species decomposition. We use experimental microcosms to quantify the potential for mass ratio and trait divergence to explain effects of invasive litters on carbon mineralization rates of decomposing litter mixtures and to generate non‐additive dynamics in two distinct forest litter types. The relative strength and direction of the mass ratio and trait divergence effects on carbon mineralization values were moderated by interactions between each effect and the canopy litter mixture. In both maple–poplar and oak–hickory litter mixtures, we found that the strength of the trait divergence effect increased with increasing proportions (mass ratio) of understorey litter in the litter mixtures, suggesting that interactions between these two mechanisms are important for moderating the influence of understorey invasions. Similarly, the addition of understorey litter always caused synergistic, non‐additive impacts on carbon mineralization, increasing carbon mineralization on average by 34%. For both litter mixtures, non‐additivity increased with increasing trait divergence between understorey and canopy litter. Our findings show the potential for pronounced context‐dependency in the impact of non‐native invasive species that arise via multiple mechanism and their interactions. As such, they suggest the necessity of accounting for frequently theorized but infrequently tested mechanisms relating to mass ratio and trait divergence. Accounting should improve understanding of when mass ratio and trait divergence affect ecosystem process rates, and hence build confidence in mechanistic projections of invader impacts. A plain language summary is available for this article.

Survey and monitoring of insect pollinators of cocoa

Cocoa is the third important beverage crop grown for its beans which are mainly used in chocolate industry. Cocoa flowers are produced in large numbers but only few of them develop into fruits. Field experiments were carried out to study the insect pollinators of cocoa through survey and monitoring in major cocoa growing districts of Tamil Nadu during 2013–2014. Maximum of 114 pollinators emerged from the decomposed leaf litter collected from thirteen years old cocoa plantations at Sethumadai, Coimbatore district. Positive correlation was observed between age of the trees and number of pollinators emerged. Another field experiment was conducted to monitor the pollinators of cocoa by installing coloured sticky traps during 2013–2014 in the farmers’ holdings at Sethumadai, Coimbatore district. The highest number of pollinators was trapped on the blue sticky traps followed by white sticky traps. Abundance of cocoa pollinators in the field was positively correlated with weather parameters viz soil moisture and rainfall and negatively correlated with soil temperature.

Arthrinium urticae . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Arthrinium urticae , which is usually observed on dead leaves and stems, and decomposed leaf litter, but has also been recorded as an endophyte. Some information on its associated organisms and substrata, habitat, dispersal and transmission, economic impacts and conservation status is given, along with details of its geographical distribution (Asia (India (Assam, Kerala), Turkey), Caribbean (Cuba), Europe (Belgium, Poland, UK)).

Temporal and Vertical Variation of Selected Extracellular Enzyme Activities on Tree Litter Degradation of a Subtropical Forest

The present study focused on the soil enzyme activities through in situ incubation of litter decomposition pits across major seasons in a subtropical forest of Bengal. This study examined the activities of extracellular enzymes (amylase, cellulase and invertase) and their relationship with the types of litter decay and soil physiochemical properties at different depths of the soil matrix. The higher decay constant (k) of decomposed leaf litter was recorded for Tectona and lower for Albizia in the studied three seasons. The results also revealed that the activities of soil extracellular enzymes were higher in rainy season compared to winter in all experimental sites with respect to control. Among the studied enzymes, invertase was significantly higher in different decomposed sites at the surface soils compared to other enzymes during the rainy season. The results also demonstrated that the enzyme activities gradually declined from the surface soil to subsurface soil at the different decomposed sites. However, in surface soil, the amylase and invertase activities were highest in Tectona litter-containing soil and cellulase activity was highest in Shorea litter-containing soil in all the studied seasons. On the other hand, soil parameters such as moisture, organic carbon and available nitrogen were significantly correlated with enzyme activities in different decomposed sites. The results suggest that the activity of the extracellular enzymes involved in litter decomposition varies in different species and seasons.

Is intensity of plant root mycorrhizal colonization a good proxy for plant growth rate, dominance and decomposition in nutrient poor conditions?

AbstractQuestionsMycorrhizae may be a key element of plant nutritional strategies and of carbon and nutrient cycling. Recent research suggests that in natural conditions, intensity of mycorrhizal colonization should be considered an important plant feature. How are inter‐specific variations in mycorrhizal colonization rate, plant relative growth rate (RGR) and leaf litter decomposability related? Is (arbuscular) mycorrhizal colonization linked to the dominance of plant species in nutrient‐stressed ecosystems?LocationTeberda State Biosphere Reserve, northwest Caucasus, Russia.MethodsWe measured plant RGR under mycorrhizal limitation and under natural nutrition conditions, together with leaf litter decomposability and field intensity of mycorrhizal colonization across a wide range of plant species, typical for alpine communities of European mountains. We applied regression analysis to test whether the intensity of mycorrhizal colonization is a good predictor of RGR and decomposition rate, and tested how these traits predict plant dominance in communities.ResultsForb species with a high level of field mycorrhizal colonization had lower RGR under nutritional and mycorrhizal limitation, while grasses were unaffected. Litter decomposition rate was not related to the intensity of mycorrhizal colonization. Dominant species mostly had a higher level of mycorrhizal colonization and lower RGR without mycorrhizal colonization than subordinate species, implying that they were more dependent on mycorrhizal symbionts. There were no differences in litter decomposability.ConclusionsIn alpine herbaceous plant communities dominated by arbuscular mycorrhizae, nutrient dynamics are to a large extent controlled by mycorrhizal symbiosis. Intensity of mycorrhizal colonization is a negative predictor for whole plant RGR. Our study highlights the importance of mycorrhizal colonization as a key trait underpinning the role of plant species in carbon and nutrient dynamics in nutrient‐limited herbaceous plant communities.

Examining trophic-level nematode community structure and nitrogen mineralization to assess local effective microorganisms’ role in nitrogen availability of swine effluent to forage crops

Culturing and using effective microorganisms from locally derived microorganisms has become a common practice employed by farmers throughout Central America as well as parts of South America and Southeast Asia to control foul odors and flies around compost piles and livestock facilities. These local, effective microorganisms (LEM) are applied in a concentrated solution fermented from carbohydrate-rich substrates inoculated with locally-sourced, actively decomposing leaf litter. Despite its growing prevalence among small-scale farmers in some parts of the world, there is little published research that explores the beneficial or detrimental effects of changing the biome of animal-based nutrients and the soils to which LEM are applied. The objectives of this study were to evaluate the effect of combining LEM with swine effluent to fertilize annual ryegrass (Lolium multiflorum) on plant-available nitrogen, nematode community structure, and forage productivity. Forage performance was good across all of the treatments – with relative feed quality (RFQ) values above 200 and 100 in the March and May harvests respectively. In the first, second and third sampling dates, soils from 0 to 5 cm depth showed more nitrogen mineralized in LEM-treated soils than in control soils (p = 0.178, p < 0.0001 and p = 0.027) respectively. After nutrient applications, soil-nematode community structure (0–10 cm) at the trophic group level changed over time. Most changes were similar between treatments, however, plant parasitic nematode populations were found to be significantly higher in LEM-treated plots in all but one of the sampling dates. LEM is gaining popularity as a natural amendment and although we have shown that it does increase N availability and changes trophic-level nematode community structure, more research is needed to optimize the potential of these benefits.

Effects of decomposing leaf litter of Leucaena leucocephala on photosynthetic traits of Cynodon dactylon and Medicago sativa

Leucaena leucocephala is an introduced species, which has been widely used in mountain ecological restoration in southwestern China. To investigate the allelopathic effects of decomposing L. leucocephala leaf litter, the photosynthetic physiology of seedlings of two recipient plants, Cynodon dactylon and Medicago sativa, were measured in this controlled study. As the amount of decomposing L. leucocephala leaf litter increased, the net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) decreased continuously, and the intercellular CO2 concentration (Ci) increased continuously in both recipient plants. In M. sativa, all abovementioned indices differed significantly compared with the control group: Pn, Gs, and Tr decreased by 41.69, 59.35, and 48.02%, respectively, and Ci increased by 28.53%. In C. dactylon, Gs decreased significantly by 27.27%. Analysis of the photosynthesis–light response curve indicated that the maximum net photosynthetic rate (Pnmax) and dark respiration rate (Rd) of C. dactylon, as well as Pnmax and light saturation point (Lsp) of M. sativa, decreased significantly as the amount of decomposing L. leucocephala leaf litter increased. These results indicated that the photosynthetic traits, light adaptation ability and physiological metabolism of recipient plants were affected by the treatment. The decreased photosynthesis was caused by the changes in pigments and soluble sugar contents induced by L. leucocephala leaf litter and is therefore considered to be associated with non-stomatal limitations. In addition, as the amount of decomposing L. leucocephala leaf litter increased, M. sativa showed decreased chlorophyll (Chla) and carotenoid (Car) contents, while C. dactylon showed decreased Chla and Chl(a + b) contents. However, both recipient plants exhibited significantly increases in their soluble sugar content. Overall, M. sativa was more sensitive than C. dactylon to the allelopathic effects induced by decomposing L. leucocephala leaf litter.