Comparison of Major Nutrient Release Patterns of Quercus liaotungensis Leaf Litter Decomposition in Different Climatic Zones

Leaf litter decomposition of liaotong oak (Quercus liaotungensis Koize) under temperate, subtropical and tropical forests was examined using a litter bag technique. Decomposition rates and release dynamics of nutrients Ca, Cu, Fe, K, Mg, Mn and P were observed separately at all three sites for I to 2 a periods. The leaf litter mass loss of liaotong oak was simulated with Olson's exponential model. Significant differences of leaf litter mass loss were found in forests of all three climate zones. Litter decomposition was accelerated with the increase of both annual mean precipitation and temperature. Our results agreed with other studies demonstrating that litter decomposition processes were greatly affected not only by soil organisms (including soil fauna and microorganisms), but also by chemical factors. These chemical factors were important for controlling the release of nutrients, especially elements of Fe and Mn. We also found that Fe and Mn content increased in semi-decayed leaf litter as litter mass decreased. This result was presumably due to chelating process which accumulated soil Fe and Mn ions into the decomposing litter. In conclusion, our study allowed us to determine the classification of the characteristics of different nutrient release patterns.

Allelopathic effects of leaf litters of Eucalyptus camaldulensis on some forest and agricultural crops

Allelopathic effects of different doses of Eucalyptus camaldulensis leaf litters were investigated through an experiment in the green house of Institute of Forestry and Environmental Sciences, Chittagong, Bangladesh. Three popular agricultural crops： Falen （Vigna unguiculata）, Chickpea （Cicer arietinum）, Arhor （Cajanus cajan） and two widely used plantation trees： Sada koroi （Albizia procera） and Ipil ipil （Leucaena leucocephala） were selected as bioassay species. Experiment was set on tray at room temperature 27℃. The effects of different doses of leaf litter extracts were compared to the control. Results suggest that leaf litters of E, camaldulesis induced inhibitory effects, It was also found that the effect depend on concentration of extract and litterfall, type of receiver species. Higher concentration of the materials had the higher effect and vice versa. Though all the bioassay species were suppressed some of them showed better performance. Vigna unguiculata, Cicer arietinum are recommended in agroforestry based on this present Experiment output. In mixed plantation, Leucaena leucochephala is a better choice while compared to Albizia procera.

Leaching of dissolved organic matter from seagrass leaf litter and its biogeochemical implications

Dissolved organic matter（DOM） represents a significant source of nutrients that supports the microbial-based food web in seagrass ecosystems. However, there is little information on how the various fractions of DOM from seagrass leaves contributed to the coastal biogeochemical cycles. To address this gap, we carried out a 30-day laboratory chamber experiment on tropical seagrasses Thalassia hemprichii and Enhalus acoroides. After 30 days of incubation, on average 22% carbon（C）, 70% nitrogen（N） and 38% phosphorus（P） of these two species of seagrass leaf litter was released. The average leached dissolved organic carbon（DOC）, dissolved organic nitrogen（DON） and dissolved organic phosphorus（DOP） of these two species of seagrass leaf litter accounted for 55%, 95% and 65% of the total C, N and P lost, respectively. In the absence of microbes, about 75% of the total amount of DOC, monosaccharides（MCHO）, DON and DOP were quickly released via leaching from both seagrass species in the first 9 days. Subsequently, little DOM was released during the remainder of the experiment. The leaching rates of DOC, DON and DOP were approximately 110, 40 and 0.70 μmol/（g·d）. Leaching rates of DOM were attributed to the nonstructural carbohydrates and other labile organic matter within the seagrass leaf. Thalassia hemprichii leached more DOC, DOP and MCHO than E. acoroides. In contrast, E. acoroides leached higher concentrations of DON than T. hemprichii, with the overall leachate also having a higher DON： DOP ratio. These results indicate that there is an overall higher amount of DOM leachate from T. hemprichii than that of E. acoroides that is available to the seagrass ecosystem. According to the logarithmic model for DOM release and the in situ leaf litter production（the Xincun Bay, South China Sea）, the seagrass leaf litter of these two seagrass species could release approximately 4×10~3 mol/d DOC, 1.4×10~3 mol/d DON and 25 mol/d DOP into the seawater. In addition to providing readily available nutrients for the microbial food web, the remaining particulate organic matter（POM）from the litter would also enter microbial remineralization processes. What is not remineralized from either DOM or POM fractions has potential to contribute to the permanent carbon stocks.

Nutrient dynamics associated with leaf litter decomposition of three agroforestry tree species (Azadirachta indica, Dalbergia sissoo, and Melia azedarach) of Bangladesh

Azadirachta indica A. Juss, Dalbergia, sissoo Roxb., and Melia azedarach L. are little studied species in nutrient return capabilities from leaf litter decomposition to maintenance of the soil fertility despite their importance in agroforestry practices of Bangladesh. A leaf litter decomposition experiment was conducted using a litterbag teeh7 nique to assess the nutrient reaun efficiency of these species. The de- composition rate of leaf litter was highest for M. azedarach and lowest for D. sissoo. Rainfall and temperature of study sites showed a significant （p〈0.05） positive relationship with the rate of leaf litter decomposition. The highest decay constant was observed for M. azedarach （6.67）. Nitrogen and Phosphorus concentration in leaf litter showed a decreased trend sharply at the end of the first month, whereas rapid decrease of Potassium concentration was reported within 10 days. Conversely, higher concentration of nutrient was observed at the later stages of decomposition. All three species showed a similar pattern of nutrient release （K 〉 N 〉 P） during the decomposition process of leaf litter. Among the studied species, D. sissoo was best in terms of N and P return and A. indica was best in terms of K return.

Responses of Soil Fauna Structure and Leaf Litter Decomposition to Effective Microorganism Treatments in Da Hinggan Mountains,China

Microorganisms are nutritious resources for various soil fauna.Although soil fauna grazing affects microorganism composition and decomposition rate,the responses of soil fauna and leaf litter decomposition to added microorganism is little understood.In this study,in the coniferous and broad-leaved mixed forest of Tahe County in the northern Da Hinggan Mountains,China,three sampling sites(each has an area of 10 m2) were selected.The first two sites were sprinkled with 250 times(EM1) and 1000 times(EM2) diluted effective microorganism(EM) preparations evenly,and the third site was sprinkled with the same volume of water as a control site.The responses of soil fauna structure and leaf litter decomposition to EM treatment were conducted during three years.The results revealed that EM treatment resulted in significant increase of soil organic matter.The number of soil fauna in the EM1 and EM2 sites increased by 12.88% and 2.23% compared to the control site,and among them springtails and mites showed the highest increase.However,the groups of soil fauna in the EM1 and EM2 sites decreased by 6 and 9,respectively.And the changes in the diversity and evenness index were relatively complicated.EM treatment slowed the decomposition of broad-leaved litter,but accelerated the decomposition of coniferous litter.However,the decomposition rate of broad-leaved litter was still higher than that of coniferous litter.The results of this study suggested that the added microorganisms could help individual growth of soil fauna,and this method led to a change in the process of leaf litter decomposition.This paper did not analyze the activity of soil microorganisms,thus it is difficult to clearly explain the complex relationships among litter type,soil fauna and soil microorganisms.Further research on this subject is needed.

Effects of leaf litter extraction fluid from dominant forest tree species on functional characteristics of soil microbial communities

The effects of extraction fluids from the leaf litter from different dominant tree species on the functional characteristics of the soil microbial community were studied to understand how changes in soil quality and synergism between plants and soil contribute to the process of forest succession. Leaf litter from dominant tree species at different stages of succession were collected and extracted with sterile deionized water. After treating the soil of abandoned land with the different extraction fluids, we analyzed changes in carbon utilization of the soil microbial community in Biolog EcoPlates, then considered these results with those of our previous study on forest vegetation succession in the Malan forest. The leaf litter enhanced the metabolic capacity and functional diversity of the soil microbes, especially in the following combinations： the leaf litter of Quercus liaotungensis-Pinus tabulae- formis, P. tabulaeformis-Betula platyphylla, Q. liaotun- gensis and P. tabulaeformiss. Second, when litter from onespecies evaluated, the species enhanced metabolism and diversity in the order of their successional relationship： B. Platyphylla 〈 P. tabulaeformis 〈 Q. liaotungensis. After soils were treated with different leaf litters at 25 ℃ for 7 days, the sorting pattern of the PCA values, based on the similarity of carbon source utilization by the soil microbes, corresponded to the successional pattern on the basis of the similarity of community composition of forest plants. Thus, changes in soil properties caused by leaf litter from different dominant trees probably play a unique role in the successional pattern of a forest community. We thus pro- pose a successional mechanism that underlies the natural succession process within the Malan forest region. When the dominant forest species of the climax successional stage develops during the early successional stages, its forest litter probably alters soil properties such that the soil becomes unsuitable for the gradual growth and regenera- tion of the original dominant tree species but promotes the growth and establishment of later-invasive plants. In this way, the originally dominant species is replaced by the newly dominant tree species during forest succession.

Leaf litter ecological fate in the Schelde Estuary in Belgium

Two dominant species of Willow( Salix triandra )and Reed (Phragmites australis) along the Schelde Estuary(in Belgium)were selected in this research. The pigments of higher plant was used as biomarkers, the decomposition process of the two species were studied after they fall into the Schelde Estuary. After statistical analysis(Spearman rank order correlation, P <0 05), the results has shown the decomposition dynamics pattern of the pigments, and the willow showed different pattern in comparing with the reed, e.g. Chlorophyll a decomposition dynamics for willow is: y 1=12196 x 2 - 175895 x +1E+06+ k , R 2=0 5706 while for reed is: y 2=-37878 x 2+229782 x +734282+ k , R 2=0 9065 The precise time of the leaf litter spent in the water was also calculated as were less than 24 days, 24-37 days, longer than 37 days(willow)and less than 24 days, longer than 24 days(reed), the leaf litter fate of the two dominant species in the Schelde Estuary was also compared.

Allelopathic effects of Leucaena leucocephala leaf litter on some forest and agricultural crops grown in nursery

An experiment was conducted to assess the effect of leaf litter of Leucaena leucocephala on two forest crops Sada koroi （Albizia procera）, Ipil ipil （L. leucocephala） and three agricultural crops Falen （Vigna unguiculata）, Chickpea （Citer arietinum） and Arhor （Cajanus cajan） in the nursery of the Institute of Forestry and Environmental Sciences, Chittagong University, Bangladesh, in a Randomized Block Design. Results suggested that leaf litters ofL. leucocephala induced inhibitory effects on germination and growth of bioassay. It was also found that the effect depended on concentration of extract and litterfall, type of receptor species. Higher concentration of the materials had the higher effect and vice versa. Growth response of receptor crops varied with the variation of leaf litter application. The study revealed that application of low-dose leaf litter specially litter of 10 g·m^-2 had stimulating effect on shoot growth of C. arietinum, Vunguiculata and A. procera. While in all other cases significant inhibitory effect was observed and it was significantly increased with the increase of leaf litter application. However, the trend of inhibition was uneven with treatments. Root growth was found to be more affected than shoot growth.

Effects of soil fauna on leaf litter decomposition under different land uses in eastern coast of China

Soil fauna decompose litter, whereas land use changes may significantly alter the composition and structure of soil fauna assemblages. However, little is known of the effects of land-use on the contribution of soil fauna to litter decomposition. We studied the impacts of soil fauna on the decomposition of litter from poplar trees under three different land uses （i.e. poplar-crop integrated system, poplar plantation, and cropland）, from December 2013 to December 2014, in a coastal area of Northern Jiangsu Province. We collected litter samples in litterbags with three mesh sizes （5, 1 and 0. 01 mm, respectively） to quantify the contribution of various soil fauna to the decomposition of poplar leaf litter. Litter decomposition rates differed significantly by land use and were highest in the cropland, intermediate in the poplar-crop integrated system, and lowest in the poplar plantation. Soil fauna in the poplar-crop integrated system was characterized by the highest numbers of taxa and individuals, and highest Margalef＇s diversity, which suggested that agro-forestry ecosystems may support a greater quantity, distribution, and biodiversity of soil fauna than can single-species agriculture or plantation forestry. The individuals and groups of soil fauna in the macro-mesh litterbags were higher than in the meso-mesh litterbags underthe same land use types. The average contribution rate of meso- and micro-fauna to litter decomposition was 18.46%, which was higher than the contribution rate of macro-fauna （3.31%）. The percentage of remaining litter mass was inversely related to the density of the soil fauna （P 〈 0.05） in poplar plantations; however, was unrelated in the poplar-crop integrated system and cropland. This may have been the result of anthropogenic interference in poplar-crop integrated systems and croplands. Our study suggested that when land-use change alters vegetation types, it can affect species composition and the structure of soil fauna assemblages, which, in turn, affects litter decomposition.

Determination of Nutrient Contents in the Leaf Litter of <i>Diospyros crassiflora</i>S. (Hiern-FWTA) Plantation in Okwuta-Ibeku, Umuahia, Abia State, Nigeria

Determination of nutrient contents in Diospyros crassiflora leaf litter was carried out in the Forestry Research Institute of Nigeria (FRIN), Okwuta-Ibeku, Umuahia, Abia State, Nigeria in 2016 and 2017. Three 1 m × 1 m trays were randomly positioned for collection of leaf litter production from 4/5 years old Diospyros crassiflora species in each block (10 m × 25 m) within the plantation totaling 1.5 ha. A Randomised Complete Block Design (RCBD) with three replicates was used to study the mean monthly leaf litterfall of Diospyros crassiflora. Leaf litter was collected from each of the three litter trays per block and placed in paper bags every 28th day of each month from January-December in 2016 and in 2017. Fifteen grammes (15 g) of properly mixed and oven-dried samples of D. crassiflora leaf litter were milled and sieved in 1 mm sieve;0.3 g was used to determine nutrient elements and their concentrations. The data obtained from mineral nutrient contents of D. crassiflora leaf litter was analysed using analysis of variance. Result reveals the mean concentrations of nitrogen (1.41 and 1.41 mg·l-1), phosphorus (0.18 and 0.18 mg·l-1), potassium (0.68 and 0.68 mg·l-1), sodium (0.35 and 0.30 mg·l-1), calcium (1.57 and 1.56 mg·l-1), magnesium (0.32 and 0.31 mg·l-1), chlorine (0.25 and 0.24 mg·l-1), Organic carbon (0.03 and 0.03 mg·l-1) and Organic matter (1.17 and 1.18 mg·l-1) etc. in D. crassiflora leaf litter in January-December (2016 and 2017). The study shows almost uniform distribution of mineral elements concentrations in 2016 and 2017.

Effect of Leaf Litter Treatment on Soil Microbial Biomass

Soil microbial biomass is an active fraction of soil organic matter. It shows quicker response than soil organic matter to any change in the soil environment. Being an index of soil fertility, it plays a key role in the decomposition of litters and fast release of available nutrients. Leaf litters of leguminous and non-leguminous species in alone and mixed form were applied as treatments in the soil to observe the changes in the magnitude of soil microbial biomass. Soil microbial biomass C and N were determined by chloroform fumigation extraction method. Increment in the concentration of microbial biomass C and N was higher in the treatments with leguminous leaf litter (497 - 571 μgCg?1, 48 - 55 μgNg?1) than the non-leguminous one (256 - 414 μgCg?1;22 - 36 μgNg?1). However, when non-leguminous litters were mixed with leguminous litters then the values increased distinctly (350 - 465 μgCg?1, 28 - 48 μgNg?1). On the basis of increment in soil microbial biomass, leaf litters of the species considered potential to improve soil nutrients are—Cassia siamea and Dalbergia sissoo from leguminous trees, Anthocephalus + Cassia and Shorea + Dalbergia from mixed form of non-leguminous and leguminous one and Eichhornia crassipes, an alien aquatic macrophyte. The leaf litters of these species can be used as source of organic matter to improve the crop yield.

Decay stages and meteorological factors affect microbial community during leaf litter in situ decomposition

Litter microorganisms play a crucial role in the biological decomposition in forest ecosystems;however,the coupling effect of meteorological and substrate changes on it during the different stages of leaf decomposition in situ remains unclear.Hence,according to meteorological factors dynamics,a one-year field litter of Quercus wutaishanica in situ decomposition experiment was designed for four decay stages in a warm temperate forest.Microbial community composition was characterized using Illumina sequencing of fungal ITS and bacterial 16S genes.Bacterial(6.6)and fungal(3.6)Shannon indexes were the largest after 125 days’litter decomposition(October).The relative abundance of Acidobacteria after 342 days and Bacteroidetes after 125 days were 3 and 24 times higher than after 31 days,respectively.Some non-dominant species(bacteria:Firmicutes,Planctomycotes,and Verrucomicrobia;fungi:Chytridiomycota and Glomeromomycota)may be absent or present at different decomposition stages due to litter properties or meteorological factors.Chemoheterotrophy and aerobic-chemoheterotrophy were the dominant bacterial functional groups,and the dominant fungal functional groups were saprotrophs,pathotrophs,and symbiotrophs.Precipitation and relative humidity significantly affected bacteria.Temperature,sunlight intensity,and net radiation significantly affected fungi.Besides,among the relative contributions of changes in bacterial and fungal community structure,leaf litter properties alone explained the variation of 5.51%and 10.63%.Microbial diversity and decay stage directly affected the litter mass-loss rate,with meteorological factors(precipitation,relative humidity,air temperature,and sunlight intensity)being indirect.Our findings highlight the importance of microbial diversity for leaf litter decomposition and the influence of meteorological factors.

Microcosm study on fate and dynamics of mangrove tannins during leaf litter leaching

Background Mangrove tannins can participate in wetland biogeochemical cycling.However,their fate and dynamics during leaf litter leaching have yet to be elucidated in coastal aquatic environments.Methods By using a simulated microcosm experiment,changes in leaf litter mass and tannin compounds,including total phenolics(TP),extractable condensed tannins(ECT),and bound condensed tannins(BCT),were examined in the litters and leachates of four common mangrove species:Kandelia obovata(Ko),Aegiceras corniculatum(Ac),Sonneratia apetala(Sa),and Avicennia marina(Am).Results Leaching caused a notable decline in litter mass,TP,and ECT in the leaf litter of Ko,Ac,Sa,and Am,while BCT increased significantly in Ko and Ac.Loss in foliar TP was higher than in leaf litter mass,and loss in foliar ECT was higher than in TP of Ko and Ac,but Sa showed the opposite result.The temporal changes of TP and ECT concentrations in leachates followed a similar trend,with an initial increase followed by a decrease.ECT dynamics in Ko and Ac leachates correlated with their TP concentrations,while in Sa leachate,the peak ECT occurred 72 h later than its TP peak.The leachate ECT concentrations were highest in Ac,followed by Ko,and significantly lower in Sa.The peak TP and ECT proportions in leachates accounted for 9.2-23.9%and 7.7-9.4%of the total decreases in foliar TP and ECT,respectively.Conclusion During the leaching process,tannins’fate was species-specific,while the dynamics were almost similar.

Variation in litter decomposition-temperature relationships between coniferous and broadleaf forests in Huangshan Mountain, China

A study was conducted to identify the differences in the decompositions of leaf litter, lignin and carbohydrate between coniferous forest and broadleaf forest at 20℃ and 30℃ in Huangshan Mountain, Anhui Province, China. Results showed that at 20℃ mass loss of leaf litter driven by microbial decomposers was higher in broadleaf forest than that in coniferous forest, whereas the difference in mass loss of leaf litter was not significant at 30℃. The temperature increase did not affect the mass loss of leaf litter for coniferous forest treatment, but significantly reduced the decomposition rate for broadleaf forest treatment. The functional decomposers of microorganism in broadleaf forest produced a higher lignin decomposition rate at 20℃, compared to that in coniferous forest, but the difference in lignin decomposition was not found between two forest types at 30℃. Improved temperature increased the lignin decomposition for both broadleaf and coniferous forest. Additionally, the functional group of microorganism from broadleaf forest showed marginally higher carbohydrate loss than that from coniferous forest at both temperatures. Temperature increase reduced the carbohydrate decomposition for broadleaf forest, while only a little reduce was found for coniferous forest. Remarkable differences occurred in responses between most enzymes （Phenoloxidase, peroxidase, !5-glucosidase and endocellulase） and decomposition rate of leaf litter to forest type and temperature, although there exist strong relationships between measured enzyme activities and decomposition rate in most cases. The reason is that more than one enzyme contribute to the mass loss of leaf litter and organic chemical components. In conclusion, at a community scale the coniferous and broadleaf forests differed in their temperature-decomposition relationships.

Mercury in leaf litter in typical suburban and urban broadleaf forests in China

To study the role of leaf litter in the mercury （Hg） cycle in suburban broadleaf forests and the distribution of Hg in urban forests, we collected leaf litter and soil from suburban evergreen and deciduous broadleaf forests and from urban forests in Beijing. The Hg concentrations in leaf litter from the suburban forests varied from 8.3 to 205.0 ng/g, with an average （avg） of （49.7 ± 36.9） ng/g. The average Hg concentration in evergreen broadleaf forest leaf litter （50.8 ± 39.4） ng/g was higher than that in deciduous broadleaf forest leaf litter （25.8 ± 10.1） ng/g. The estimated Hg fluxes of leaf litter in suburban evergreen and deciduous broadleaf forests were 179.0 and 83.7 mg/（ha·yr）, respectively. The Hg concentration in organic horizons （O horizons） （（263.1 ± 237.2） ng/g） was higher than that in eluvial horizons （A horizons） （（83.9 ± 52.0） ng/g）. These results indicated that leaf litterfall plays an important role in transporting atmospheric mercury to soil in suburban forests. For urban forests in Beijing, the Hg concentrations in leaf litter ranged from 8.8–119.0 （avg 28.1 ± 16.6） ng/g, with higher concentrations at urban sites than at suburban sites for each tree. The Hg concentrations in surface soil in Beijing were 32.0–25300.0 ng/g and increased from suburban sites to urban sites, with the highest value from Jingshan （JS） Park at the centre of Beijing. Therefore, the distribution of Hg in Beijing urban forests appeared to be strongly influenced by anthropogenic activities.

Fungal community succession on decomposing leaf litter across five phylogenetically related tree species in a subtropical forest

Fungi are an essential component of the ecosystem.They play an integral role in the decomposition of leaf litter and return nutrients to the ecosystem through nutrient cycling.They are considered as the“key players”in leaf litter decomposition,because of their ability to produce a wide range of extracellular enzymes.Time-related changes of fungal communities during leaf litter decomposition have been relatively well-investigated.However,it has not been established how the tree species,tree phylogeny,and leaf litter chemistry influence fungal communities during decomposition.Using direct observations and a culturing approach,this study compiles fungi found in freshly collected leaf litter from five phylogenetically related,native tree species in Taiwan:Celtis formosana(CF),Ficus ampelas(FA),Ficus septica(FS),Macaranga tanarius(MT),and Morus australis(MA).We investigated(i)the effects of tree species(including tree phylogeny)and leaf litter chemistry on fungal community succession,and(ii)specific patterns of fungal succession(including diversity and taxonomic community assembly)on decomposing leaf litter across the selected tree species.We hypothesized that host species and leaf litter chemistry significantly affect fungal community succession.A total of 1325 leaves(CF:275,FA:275,FS:275,MT:275 and MA:225)were collected and 236 fungal taxa were recorded(CF:48,FA:46,FS:64,MT:42 and MA:36).Tree species relationships had variable associations on the fungal communities,as even closely related tree species had strongly differing communities during decomposition.A high number of species were unique to a single tree species and may indicate‘host-specificity’to a particular leaf litter.The overlap of microfungal species in pair wise comparisons of tree species was low(7–16%),and only 1–2%of microfungal species were observed in leaves of all tree species.The percentage of occurrences of fungal communities using Hierarchical Cluster Analyses(HCA)showed that there were at least four succession stages in each tree species during decomposition.Fungal diversity increased at the beginning of each tree species leaf decay,reached peaks,and declined at the final stages.Overall,our findings demonstrate that tree species and leaf litter chemistry are important variables in determining fungal diversity and community composition in leaf litter.Referring to the establishment of fungal discoveries from this experimental design,two new families,two new genera,40 new species and 56 new host records were reported.This study provides a host-fungus database for future studies on these hosts and increases the knowledge of fungal diversity in leaf litter.

Leaf litter decomposition characteristics and controlling factors across two contrasting forest types

Plant leaf litter decomposition provides a source of energy and nutrients in forest ecosystems.In addition to traditional environmental factors,the degradation process of litter is also affected by plant functional traits and litter quality.However,at the community level,it is still unclear whether the relative importance of plant traits and litter quality on the litter decomposition rate is consistent.A year-long mixed leaf litter decomposition experiment in a similar environment was implemented by using the litterbag method in seven typical forest types in Dongling Mountain,Beijing,North China,including six monodominant communities dominated by Juglans mandshurica,Populus cathayana,Betula dahurica,Betula platyphylla,Pinus tabuliformis and Larix gmelinii var.principis-rupprechtii and one codominant community dominated by Fraxinus rhynchophylla,Quercus mongolica and Tilia mongolica.The results showed that there were considerable differences in the litter decomposition rate(k-rate)among the different forest types.The community weighted mean(CWM)traits of green leaves and litter quality explained 35.60%and 9.05%of the k-rate variations,respectively,and the interpretation rate of their interaction was 23.37%,indicating that the CWM traits and their interaction with litter quality are the main factors affecting the k-rate variations.In the recommended daily allowance,leaf nitrogen content,leaf dry matter content,leaf tannin content and specific leaf area were the main factors affecting the k-rate variations.Therefore,we suggest that future studies should focus on the effects of the CWM traits of green leaves on litter decomposition at the community level.

Effects of multiple but low pesticide loads on aquatic fungal communities colonizing leaf litter

In the first tier risk assessment（RA） of pesticides, risk for aquatic communities is estimated by using results from standard laboratory tests with algae, daphnids and fish for single pesticides such as herbicides, fungicides, and insecticides. However, fungi as key organisms for nutrient cycling in ecosystems as well as multiple pesticide applications are not considered in the RA. In this study, the effects of multiple low pesticide pulses using regulatory acceptable concentrations（RACs） on the dynamics of non-target aquatic fungi were investigated in a study using pond mesocosm. For that, fungi colonizing black alder（Alnus glutinosa） leaves were exposed to multiple, low pulses of 11 different pesticides over a period of 60 days using a real farmer＇s pesticide application protocol for apple cropping.Four pond mesocosms served as treatments and 4 as controls. The composition of fungal communities colonizing the litter material was analyzed using a molecular fingerprinting approach based on the terminal Restriction Fragment Length Polymorphism（t-RFLP） of the fungal Internal Transcribed Spacer（ITS） region of the ribonucleic acid（RNA） gene（s）. Our data indicated a clear fluctuation of fungal communities based on the degree of leaf litter degradation. However significant effects of the applied spraying sequence were not observed. Consequently also degradation rates of the litter material were not affected by the treatments. Our results indicate that the nutrient rich environment of the leaf litter material gave fungal communities the possibility to express genes that induce tolerance against the applied pesticides. Thus our data may not be transferred to other fresh water habitats with lower nutrient availability.

Effects of seagrass leaf litter decomposition on sediment organic carbon composition and the key transformation processes

Seagrass leaf litters are an important source of sediment organic carbon(SOC). However, the mechanisms of seagrass leaf litter decomposition influencing SOC composition and the key transformation processes remain unknown. We performed a laboratory chamber experiment to compare the labile organic carbon(OC) composition and the enzyme activities governing SOC transformation between the seagrass group(seagrass leaf litter addition) and the control group. The results showed that the seagrass leaf litter decomposition significantly elevated the salt-extractable carbon(SEC) content and the SEC/SOC. Additionally,the levels of invertase, polyphenol oxidase, and cellulase in the seagrass leaf litters addition group were generally higher than in the control group, which could elevate recalcitrant OC decomposition. Following 24 days incubation, addition of seagrass leaf litter increased the amount of CO_2 released, but decreased the SOC content. Therefore, seagrass leaf litter decomposition leached abundant dissolved OC, which enhanced the activity and transformation of SOC.

云南乌蒙山国家级自然保护区珙桐林生态化学计量特征

【目的】探究国家Ⅰ级珍稀濒危植物珙桐生态化学计量特征,揭示珙桐林生态系统养分元素状况和生长限制因子。【方法】在云南乌蒙山国家级自然保护区不同海拔段设置4个样地,编号分别为Ⅰ、Ⅱ、Ⅲ、Ⅳ,利用单因素方差分析及多重比较等方法研究珙桐林叶片-凋落物-土壤3种组分C、N、P含量及其比值的差异性、相关性,用冗余分析方法探究土壤化学计量特征的响应因子。【结果】珙桐叶片C、N、P平均含量分别为520.97、22.73、1.43 g/kg,凋落物C、N、P平均含量分别为459.87、10.96、1.35 g/kg,土壤C、N、P平均含量分别为74.81、7.94、0.79 g/kg,叶片、凋落物、土壤C、N、P平均含量表现为叶片>凋落物>土壤。不同样地同一组分间土壤C、N、P含量差异显著,表现为Ⅳ>Ⅲ>Ⅱ>Ⅰ(Ⅰ:58.47±1.88、5.73±0.41、0.06±0.02 g/kg;Ⅱ:64.45±2.29、6.82±0.19、0.61±0.08 g/kg;Ⅲ:75.94±1.32、7.88±0.16、1.11±0.06 g/kg;Ⅳ:100.39±1.24、11.32±0.25、1.36±0.10 g/kg),叶片、凋落物差异不显著;同一样地不同组分间C含量差异显著,表现为叶片>凋落物>土壤,N、P含量差异不显著;不同样地同一组分、同一样地不同组分间C∶N、C∶P、N∶P存在显著差异。叶片、凋落物、土壤C、N、P含量及比值间相关性显著;海拔、非毛管孔隙度和坡度、毛管孔隙度、粉砂粒含量是影响土壤养分含量的关键环境因子。【结论】云南乌蒙山国家级自然保护区珙桐林不同海拔样地间土壤C、N、P含量及其比值存在显著差异,叶片、凋落物差异不明显,根据生态化学计量特征表明样地Ⅳ珙桐生长受P元素限制,海拔、非毛管孔隙度、坡度、毛管孔隙度、粉砂粒含量是影响珙桐林土壤养分循环的关键环境因子。