Utilization of evergreen and decidous oaks by the Californian oak moth Phryganidia californica

Summary The deciduous oak Quercus lobata was a better quality food source than the evergreen oak Q. agrifolia for the California oak moth Phryganidia californica: it supported higher growth rates, produced higher fecundity and survivorship, and higher efficiency of conversion of ingested food (ECI), efficiency of conversion of digested food (ECD) and efficiency of nitrogen utilization (NUE). Total polyphenols and astringency were similar in both oak speices, whereas water content was lower and leaf specific weight higher in Q agrifolia than in Q lobata. Nitrogen was higher in new leaves of Q agrifolia but higher in mature leaves of Q. lobata. Contrary to most other studies, total polyphenols and astringency were higher in new than in mature leaves. These results confirmed my hypothesis that the differences in leaf quality associated with the evergreen or deciduous life form would translate into food of differing quality for herbivores.     

Colonization and lignin decomposition of Camellia japonica leaf litter by endophytic fungi

Endophytic fungi occur on various types of leaf litter, but few studies have been done on their roles as saprophytes in decomposition. This study examined the succession of fungi in live, newly shed, and decomposing leaves at 2 months of decomposition of Camellia japonica and chemical changes in decomposing leaves colonized by endophytes. Coccomyces nipponicum, Lophodermium sp., Geniculosporium sp. 1, and Colletotrichum gloeosporioides were isolated from living leaves. Coccomyces nipponicum and Lophodermium sp. were also isolated frequently from newly shed and decomposing leaves. These two fungi caused a decrease of lignin content and bleaching in decomposing leaves under field and laboratory conditions. Total hyphal length in decomposing leaves was higher in bleached portions than in surrounding nonbleached portions, which probably reflected the early onset of hyphal growth of endophytes inside leaf tissue at leaf senescence or death. Incubation of newly shed leaves that were sterilized to exclude previously established endophytes resulted in no occurrence of bleached portions in decomposing leaves on the forest floor. This result indicated that these endophytes were incapable of colonizing leaves directly after litterfall and that the persistence of endophytes from live leaves was crucial for their colonization in decomposing leaves.     

Decomposition of Eucalyptus globulus leaves and three native leaf species (Alnus glutinosa, Castanea sativa and Quercus faginea) in a Portuguese low order stream

Leaf decomposition of the exotic evergreen Eucalyptus globulus (eucalyptus), and three native deciduous tree species, Alnus glutinosa (alder), Castanea sativa (chestnut) and Quercus faginea (oak), was compared in a second order stream in Central Portugal. Changes in dry weight, nitrogen and polyphenolic compounds and microbial colonization were periodically assessed for three months.Negative exponential curves fit the leaf weight loss with time for all leaf species. Mass loss rate was in the order alder (K = 0.0161) > chestnut (K = 0.0079) > eucalyptus (K = 0.0068) > oak (K = 0.0037). Microbial colonization followed the same pattern as breakdown rates. Evidence of fungal colonization was observed in alder after 3 days in the stream, whereas it took 21 days in oak leaves to have fungal colonization. Fungal diversity was leaf species-dependent and increased with time. In all cases, percent nitrogen per unit leaf weight increased, at least, at the initial stages of decay while soluble polyphenolics (expressed as percentage per unit leaf weight) decreased rapidly in the first month of leaves immersion.Intrinsic factors such as nitrogen and polyphenolic content may explain differences in leaf decomposition. The possible incorporation of eucalyptus litter into secondary production in a reasonable time span is suggested, although community balance and structure might be affected by differences in allochthonous patterns determined by eucalyptus monocultures.     

High Diversity of Fungi may Mitigate the Impact of Pollution on Plant Litter Decomposition in Streams

We investigated how a community of microbial decomposers adapted to a reference site responds to a sudden decrease in the water quality. For that, we assessed the activity and diversity of fungi and bacteria on decomposing leaves that were transplanted from a reference (E1) to a polluted site (E2), and results were compared to those from decomposing leaves either at E1 or E2. The two sites had contrasting concentrations of organic and inorganic nutrients and heavy metals in the stream water. At E2, leaf decomposition rates, fungal biomass, and sporulation were reduced, while bacterial biomass was stimulated. Fungal diversity was four times lower at the polluted site. The structure of fungal community on leaves decomposing at E2 significantly differed from that decomposing at E1, as indicated by the principal response curves analysis. Articulospora tetracladia, Anguillospora filiformis, and Lunulospora curvula were dominant species on leaves decomposing at E1 and were the most negatively affected by the transfer to the polluted site. The transfer of leaves colonized at the reference site to the polluted site reduced fungal diversity and sporulation but not fungal biomass and leaf decomposition. Overall, results suggest that the high diversity on leaves from the upstream site might have mitigated the impact of anthropogenic stress on microbial decomposition of leaves transplanted to the polluted site.     

Phyllosphere fungi on living and decomposing leaves of giant dogwood

Phyllosphere fungi on living leaves and their succession on decomposing leaves were studied on giant dogwood (Swida controversa). A total of 12 and 34 fungal species were isolated from the interior and surface, respectively, of living leaves, and 15 frequent species were considered as phyllosphere fungi. Six of these 15 species were also frequent on decomposing litter. Characteristic successional trends were observed in the 6 phyllosphere fungi during decomposition. The sum of frequencies of endophytes decreased as decomposition progressed, and no endophytes were isolated from the litter at the 11th month of decomposition. The sum of frequencies of epiphytes increased as decomposition progressed. Endophytes and epiphytes showed different responses to litter mass loss and concentrations of nitrogen, lignin, and total carbohydrates during the decomposition process. These results suggested that epiphytes may survive on decomposing leaves as primary decomposers on the ground, thereby excluding endophytes by competition for available energy sources, and that epiphytes may have a greater contribution to decomposition than endophytes in dogwood leaves.     

Arbuscular mycorrhizal fungi colonize decomposing leaves of<Emphasis Type="Italic"> Myrica parvifolia</Emphasis>,<Emphasis Type="Italic"> M. pubescens</Emphasis> and<Emphasis Type="Italic"> Paepalanthus</Emphasis> sp.

Hyphae and vesicles of arbuscular mycorrhizal fungi (AMF) were found within the decomposing leaves of Myrica parvifolia, M. pubescens and Paepalanthus sp. at three montane sites in Colombia. Hyphae, vesicles, and arbuscule-like structures were also found within scale-like leaves of the rhizomes of Paepalanthus sp. The litter found in the vicinity of the roots was divided into three decomposition layers. The highest AMF colonization occurred in the most decomposed leaves, which were in close association with roots. In contrast, there were no differences in AMF colonization of roots present in the different decomposition layers. Colonization of decomposing leaves by AMF did not differ between the two closely related species M. parvifolia and M. pubescens, nor between two sites (Guatavita and Zipacón, Colombia) differing in soil fertility. Occurrence of vesicles in decomposing leaves was correlated with abundant AMF extraradical hyphae among the leaves. We propose that AMF enter decomposing leaves mechanically through vascular tissue. As a consequence, AMF are well positioned to obtain and efficiently recycle mineral nutrients released by decomposer microorganisms before their loss by leaching or immobilization in soil.     

Mass loss and nitrogen dynamics in decomposing acid forest litter in the Netherlands at increased nitrogen deposition

Litterbag experiments were carried out in five forest ecosystems in the Netherlands to study weight loss and nitrogen dynamics during the first two years of decomposition of leaf and needle litter. All forests were characterized by a relatively high atmospheric nitrogen input by throughfall, ranging from 22–55 kg N ha^–1 yr^–1.Correlation analysis of all seven leaf and needle litters revealed no significant relation between the measured litter quality indices (nitrogen and lignin concentration, lignin-to-nitrogen ratio) and the decomposition rate. A significant linear relation was found between initial lignin-to-nitrogen ratio and critical nitrogen concentration, suggesting an effect of litter quality on nitrogen dynamics.Comparison of the decomposition of oak leaves in a nitrogen-limited and a nitrogen-saturated forest suggested an increased nitrogen availability. The differences in capacities to retain atmospheric nitrogen inputs between these two sites could be explained by differences in net nitrogen immobilization in first year decomposing oak leaves: in the nitrogen-limited oak forest a major part (55%) of the nitrogen input by throughfall was immobilized in the first year oak leaf litter.The three coniferous forests consisted of two monocultures of Douglas fir and a mixed stand of Douglas fir and Scots pine. Despite comparable litter quality in the Douglas fir needles in all sites, completely different nitrogen dynamics were found.     

Adaptation to oak and other fibrous,phenolic-rich foliage by a small mammal,Neotoma fuscipes

Summary Neotoma fuscipes, a small mammalian herbivore with apparently generalized food habits, was laboratory tested to determine its degree of dietary specialization. Woodrats from both oak woodland and coastal sage communities preferred Quercus agrifolia leaves (containing 40% phenolics and about 16% condensed tannin) over foliage from other dominant species. Approximately one-third of the oak phenolics and less than 10% of the oak condensed tannin remained in the feces. Their performance on pure oak leaves was comparable to that on a mixed diet of Quercus, Salvia, Eriogonum, and Rhus, with respect to weight maintenance, digestive efficiency and total amount ingested. Digestive efficiency was low on the oak diet (55%) relative to Salvia (77%), and to achieve similar weight levels, approximately twice as much oak as Salvia was ingested. Woodrats retained more nitrogen as oak consumption increased. Intake of oak and other foods increased with each experimental day. A sympatric species, N. lepida, was unable to maintain weight on oak leaves, although its digestive and polyphenolic-degrading capabilities, and nitrogen retention efficiency were equivalent to those of N. fuscipes. On a weight-adjusted basis, N. lepida ate about half as much oak per day as N. fuscipes. Oak intake may have been reduced by an inability to rapidly degrade fiber, which constitutes about 30% of the oak diet. In natural populations, N. fuscipes selectively feeds on evergreen sclerophyll vegetation high in fiber, tannins and related polyphenolics. Individuals ingest 2–3 plant types at a time, with a single species (oak when available) constituting most of the material consumed. Neotoma lepida diets are also dominated by a single species. The diversity of plant types eaten by different populations of N. lepida suggests that local dietary specializations may be developmentally acquired.     

Field study of beech (t Fagus sylvatica L.) and melojo oak (t Quercus pyrenaica Willd) leaf litter decomposition in the centre of the Iberian Peninsula

The effect of the canopy on leaf decomposition of beech (t Fagus sylvatica) and melojo oak (t Quercus pyrenaica) was studied during a period of 660 days in a mountain forest of central Spain; response of leaves to leaching was also studied to determine the effects of rainfall after leaf fall. Beech leaves lost 5.8% of their weight by leaching, whereas melojo oak leaves lost 13%. Under both types of canopy, beech leaves showed almost no difference in their decomposition patterns, with decay constants of 0.31 and 0.32 respectively. Melojo oak leaves showed quite a different behaviour under both canopies; decay constant was 0.47 under t Quercus pyrenaica and 0.77 under beech canopy. Total immobilization of nitrogen was less in the melojo oak forest. Effects of summer dryness were sharper in the melojo oak forest, where decomposition stopped during the summer. This delay in the decomposition might have been due to the lower canopy density in the melojo oak forest. The decomposition patterns of the leaves of both species, under the canopy of the other species, suggests what might happen in mixed stands. Thus, the presence of melojo oaks in beech forest would increase decay and decrease nitrogen immobilization. The presence of beech trees in melojo oak forests would improve microclimatic conditions and increase decay, whereas beech litter on the soil would immobilizate more nitrogen.     

四川盆地亚热带常绿阔叶林凋落叶多酚类物质在不同降雨期间的降解特征

植物多酚类物质是森林凋落物中的重要组分,其含量的多寡在一定程度上决定了凋落物的分解速率。然而,凋落物分解过程中多酚类物质的降解动态仍不十分清楚。因此,以四川盆地亚热带常绿阔叶林最具代表性的3个针叶树种马尾松(Pinus massoniana)、柳杉(Cryptomeria fortunei)、杉木(Cunninghamia lanceolata)和3个阔叶树种香樟(Cinnamomum camphora)、红椿(Toona ciliata)、麻栎(Quercus acutissima)凋落叶为对象,采用凋落物分解袋法,研究了6种凋落叶多酚类物质在第一年不同降雨期间的降解特征。结果表明:自微量降雨期起至雨季前期止,6种凋落叶多酚类物质具有一致的降解动态,降解率均表现为随着降水量的增加而增加;自雨季后期之后,多酚类物质含量均处于稳定状态。第一个分解年,6种凋落叶多酚类物质降解率大小顺序依次为:红椿(100%)柳杉(97.81%)杉木(94.45%)麻栎(93.67%)马尾松(93.06%)香樟(91.64%)。分解初期旱季两时期(微量降雨期和春季少雨期),6种凋落叶多酚类物质均有较大的降解量,其降解率占全年降解率的42.16%—71.20%。并且,除香樟以外的5种凋落叶多酚类物质大量降解释放发生在雨季前期,占全年降解率的44.46%—55.72%。此外,凋落叶多酚类物质初始含量与其降解率呈显著的二次函数关系。可见,降雨是湿润亚热带常绿阔叶林区凋落物多酚类物质降解的关键驱动因子之一,树种组成是影响凋落物多酚类物质降解的内部因素。     

Comparison between antifungal and antibacterial activities of several strains of Epicoccum purpurascens from the Mediterranean area

The antimicrobial activities of seven Epicoccum purpurascens strains isolated either from evergreen oak leaves (Quercus ilex) collected over a period of one year, or from the atmosphere were compared in vitro. Two strains sporulated and conspicuously inhibited the growth of Staphylococcus aureus and Trichophyton mentagrophytes. Thin-layer chromatographic studies showed the existence of some compounds, such as flavipin, which were common to all the strains. Epicorazine B was present in the extracts of only the two most active strains.     

Fine Scale Patterns in Microbial Extracellular Enzyme Activity during Leaf Litter Decomposition in a Stream and its Floodplain

Microorganisms mediate the decomposition of leaf-litter through the release of extracellular enzymes. The surfaces of decomposing leaves are both chemically and physically heterogeneous, and spatial patterns in microbial enzyme activity on the litter surface should provide insights into fine-scale patterns of leaf-litter decomposition. Platanus occidentalis leaves were collected from the floodplain of a third-order stream in northern Mississippi, enclosed in individual litter bags, and placed in the stream channel and in the floodplain. Replicate leaves were collected approximately monthly over a 9-month period and assayed for spatial variation in microbial extracellular enzyme activity and rates of organic matter (OM) decomposition. Spatial variation in enzyme activity was measured by sampling 96 small discs (5-mm diameter) cut from each leaf. Discs were assayed for the activity of enzymes involved in lignin (oxidative enzymes) and cellulose (β-glucosidase, cellobiohydrolase) degradation. Rates of OM loss were greater in the stream than the floodplain. Activities of all enzymes displayed high variability in both environments, with severalfold differences across individual leaves, and replicate leaves varied greatly in their distribution of activities. Geostatistical analysis revealed no clear patterns in spatial distribution of activity over time or among replicates, and replicate leaves were highly variable. These results show that fine-scale spatial heterogeneity occurs on decomposing leaves, but the level of spatial variability varies among individual leaves at the measured spatial scales. This study is the first to use geostatistical analyses to analyze landscape patterns of microbial activity on decomposing leaf litter and in conjunction with studies of the microbial community composition and/or substrate characteristics, should provide key insights into the function of these processes.     

Chilling-Induced Photoinhibition in Two Oak Species: Are Evergreen Leaves Inherently Better Protected Than Deciduous Leaves?

We compared the sensitivity to cold stress, in terms of photosynthetic capacity and changes in chlorophyll fluorescence of photosystem 2 (PS2), of an evergreen and a deciduous oak species, which co-occur in the southeastern United States. We predicted that the evergreen species, Quercus virginiana, which must endure winter, is likely to have an inherently greater capacity for energy dissipation and to be less susceptible to chilling stress than the deciduous species, Quercus michauxii. Short-term cold stress in both species lead to greater than 50 % reduction in maximum photosynthetic rates, 60-70 % reduction in electron transport, and irreversible quenching of PS2 fluorescence. The kinetics of recovery in the dark after exposure to 1 h high irradiance (1000 μmol m^-2 s^-1) and chilling (5 °C) showed that the evergreen Q. virginiana exhibited more protective q_E and less irreversible quenching (q_I) than the deciduous Q. michauxii. The large q_E which we observed in Q. virginiana suggests that the capacity for photoprotection at low temperatures is not induced by a long-term acclimation to cold but preexists in evergreen leaves. This capacity may contribute to the ability of this species to maintain leaves during the winter. This revised version was published online in June 2006 with corrections to the Cover Date.     

Fungal colonization and decomposition of Castanopsis sieboldii leaves in a subtropical forest

Fungi play a crucial role in the decomposition of lignin in fallen leaves but few studies have examined the functional roles of ligninolytic fungi associated with the decomposition of fallen leaves on tropical forest soils. This study examined fungal populations responsible for lignin decomposition in Castanopsis sieboldii leaves in a subtropical evergreen broad-leaved forest in southern Japan. Fallen leaves of C. sieboldii are characterized by the occurrence of bleached portions attributable to fungal colonization of leaf tissues and decomposition of lignin. The bleached area accounted for 29.7%, on average, of the total area of C. sieboldii fallen leaves in the study site. Leaf mass per unit area (LMA) and lignin content were lower in the bleached area than in the surrounding nonbleached area of the same leaves, indicating that removal of lignin enhanced mass loss from leaf tissues and created small-scale heterogeneity of decomposition within single leaves. An unidentified species of Lachnocladiaceae (Basidiomycetes) was isolated frequently from the bleached area and caused selective decomposition of lignin in leaves under pure culture conditions, indicating that this fungus was responsible for the bleaching. The greater hyphal length of basidiomycetes in the bleached area than in the nonbleached area supported the finding that this Lachnocladiaceae sp. was associated with the bleaching. The relatively rapid decomposition of C. sieboldii leaves on the subtropical forest soil is partly attributable to colonization of the litter by this Lachnocladiaceae sp.     

Tracing site‐specific isotopic signatures along a Blue Tit Cyanistes caeruleus food chain

Food chains culminating with temperate insectivorous passerines are well described, yet whether trophic webs can be site‐specific remains a largely unexplored question. In the case of site‐ or habitat‐specificity of food webs, stable isotope signatures of bird feathers may enable assignment of unmarked individuals to a site or a habitat of origin. We address this question in landscapes that include contrasting forest habitat patches with either deciduous Downy Oak Quercus humilis or evergreen Holm Oak Quercus ilex as dominant tree species. First, we examine the spatial variation across habitats and sites in the stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) along the oak leaf–Tortrix moth Tortrix viridana caterpillar–Blue Tit Cyanistes caeruleus food chain. Secondly, we assess whether the isotopic signatures allow for correct assignment of individual birds to their site or habitat of origin. At the scale of the landscape, stable isotope values enabled identification of the different components of the Blue Tit food chain: from oak leaves to Blue Tit nestlings and yearling birds. However, isotopic signatures were site‐specific (i.e. geographical) more than habitat‐specific (i.e. deciduous vs. evergreen oaks). Discriminant analyses correctly assigned 85% of nestlings and 83% of resident yearling birds, indicating a pronounced effect of site on Blue Tit feather isotopic signatures. We thereby demonstrate that isotopes reflect a stronger association of locally born birds to the local features of their habitat than that of un‐ringed yearling birds, whose plumage may have grown while in a wider geographical area. This study provides evidence of site‐specific isotopic signatures from oak leaves to Blue Tit feathers at a fine spatial scale.     

Fungal communities on decaying leaves in streams: a comparison of two leaf species

Decomposition of leaf litter is a microbial mediated process that helps to transfer energy and nutrients from leaves to higher trophic levels in woodland streams. Generally, aquatic hyphomycetes are viewed as the major fungal group responsible for leaf litter decomposition. In this study, traditional microscopic examination (based on identification of released conidia) and phylogenetic analysis of 18S rRNA genes from cultivated fungi were used to compare fungal community composition on decomposing leaves of two species (sugar maple and white oak) from a NE Ohio stream. No significant differences were found in sporulation rates between maple and oak leaves and both had similar species diversity. From the 18S rRNA gene sequence data, identification was achieved for 12 isolates and taxonomic affiliation of 12 of the remaining 14 isolates could be obtained. A neighbor-joining tree (with bootstrap values) was constructed to examine the taxonomic distribution of the isolates relative to sequences of known operational taxonomic units (OTUs). Surprisingly, only 2 of the isolates obtained were aquatic hyphomycetes based on phylogenetic analysis. Overall, there were no differences between the two leaf types and a higher diversity was observed via culturing and subsequent 18S rRNA gene sequencing than by conidia staining. These differences resulted from the fact that traditional microscopy provides estimates of aquatic hyphomycete diversity while the other approach revealed the presence of both aquatic hyphomycete and non-aquatic hyphomycete taxa. The presence of this broad array of taxa suggests that the role of aquatic hyphomycetes relative to other fungi be re-evaluated. Even though the functional role of these non-aquatic hyphomycetes taxa is unknown, their presence and diversity demonstrates the need to delve further into fungal community structure on decomposing leaves.     

Decomposition and colonisation by invertebrates of native and exotic leaf material in a small stream in New England (Australia)

In many parts of south-eastern Australia, native riparian vegetation has been cleared and exotic willows planted. In order to evaluate some of the possible effects of this practice, the decomposition and colonisation by invertebrates of the leaves of three native plant species along with those of willow were examined.Decomposition of leaves of the willow Salix babylonica L. and the indigenous macrophyte Myriophyllum propinquum A. Cunn. was much faster than for leaves of the indigenous trees Eucalyptus blakelyi Maiden and Casuarina cunninghamiana Miq. Both macroinvertebrates and current were found to have a significant influence upon decomposition. The pattern of preferential colonisation suggested that plant detritus represented a primary food source for invertebrates and not simply a refuge. Colonisation was found to be a function of the stage of decomposition, regardless of plant species. The lower temporal availability of willow leaves compared to the native evergreen tree leaves appears to be insufficient to enhance the production of the benthic macroinvertebrates.     

The Balearic Islands: a reservoir of cpDNA genetic variation for evergreen oaks

Aim To analyse the role of the Balearic Islands as a refuge area for evergreen Quercus (cork oak: Quercus suber L., holm oak: Q. ilex L., kermes oak: Q. coccifera L.), by using molecular, historical and palaeobotanical data. Location The Western Mediterranean Basin (Balearic Islands, eastern Iberia, Provence, Sardinia, Corsica, Sicily, Malta, Italy, Northern Africa). Methods We sampled 108 populations and used the PCR‐RFLP technique with five universal cpDNA primers to define haplotypes in the sampled populations. Diversity, differentiation parameters and spatial analysis of the populations, using a spatial version of amova , were linked to the geological history of the Western Mediterranean Basin in order to explain the present spatial pattern of the evergreen Quercus populations in the Balearics. Results Evergreen Quercus cpDNA shows a complex structure, with remnants of ancient diversity in the Balearics. Balearic populations of holm oak are related to Iberian populations, while for cork and kermes oaks, we found both Tyrrhenian and Iberian haplotypes. Main conclusions The complex spatial patterns of cpDNA in Balearic evergreen Quercus appears explicable in terms of a combination of physical (vicariance and long distance dispersal) and biological (introgressive hybridization) factors. The Balearics constitute a glacial refuge area and a reservoir of genetic variation with traces of ancient diversity from Messinian–Pliocene stages.     

Species diversity of freshwater hyphomycetes in some streams of Pakistan. III. Autumnal colonization of freshwater hyphomycetes on bait leaves

Significantly more species of freshwater hyphomycetes colonized bait leaves of alder (16 species) and willow (14 species) during early submersion period (1 wk) than those of oak (8 species). Production of conidia was also higher on alder and willow leaves than on oak leaves. Higher amounts of dry mass were lost from the alder (28.6%) and willow leaves (29.4%) than from the oak leaves (18.7%). Rapid loss of dry mass was accompanied by rapid development of a fungal community. Fungal species took a longer time (6 wk) to reach their peak of occurrence on oak than on willow and alder leaves (3–4 wk).Flagellospora curvula dominated the assemblages of freshwater hyphomycetes on alder and willow leaves, andLunulospora curvula dominated the assemblage on oak leaves. The freshwater hyphomycete community showed higher values of species diversity (H value) on oak leaves than on alder and willow leaves.     

长白山白桦(Betula platyphlla)纯林和白桦山杨 (Populus davidiana)混交林凋落物的分解

采用交互分解实验,研究长白山白桦叶片和白桦、山杨与水曲柳混合叶片在白桦纯林和白桦山杨混交林内的分解过程。两年的分解实验结果表明,两种类型叶片均存在一个快速分解阶段和一个慢速分解阶段,森林类型和凋落物类型对凋落物分解率的影响在快速分解阶段不显著而在慢速分解阶段显著;混交林内的环境促进了凋落物分解和养分元素释放;在同一林型内,底物质量高的混合叶片其分解率和养分元素释放率均大于底物质量低的白桦叶片;凋落物的底物质量在一定程度上可以抵消森林类型对凋落物分解的影响;白桦山杨混交林混合叶片分解速率和养分元素释放率要显著大于白桦纯林内的白桦叶片,说明白桦山杨混交林的物质循环速度和养分元素供应能力要显著大于白桦纯林。