The influence of sediment composition and leaf litter on the distribution of tubificid worms (Oligochaeta)

Summary The horizontal distribution of three species of tubificid worm (Tubifex tubifex, Limnodrilus hoffmeisteri and L. udekemianus in the sediment of a small stream was examined. Worm distribution was most strongly correlated with the distribution of leaf litter. This relationship was examined in the laboratory by means of choice chambers. It was concluded that; 1) the addition, to an inorganic substratum, of conditioned leaf material, enhanced its attractiveness to the worms; 2) a combination of silt-clay and leaf material was preferred by the worms to mixtures of leaf material and coarser inorganic substrata 3) some leaf species were more attractive to the worms than others; 4) there were differences between the worm species in their preferences for the various leaf species; 5) none of the three tubificid species was exclusively associated with its preferred leaf species; 6) worms would switch to less attractive leaf species if preferred alternatives were unavailable; 7) leaf material only attracted the worms once it had become conditioned; 8) this appeal was lost when the leaves were autoclaved; and 9) substratum choice was independent of worm size.We believe the worms were attracted to the leaves because the associated microfloras provided a concentration of bacterial food. Differences between the three tubificid species in their preferences for the various leaf species probably reduced trophic competition.     

Disparate effects of plant genotypic diversity on foliage and litter arthropod communities

Intraspecific diversity can influence the structure of associated communities, though whether litter-based and foliage-based arthropod communities respond to intraspecific diversity in similar ways remains unclear. In this study, we compared the effects of host-plant genotype and genotypic diversity of the perennial plant, Solidago altissima, on the arthropod community associated with living plant tissue (foliage-based community) and microarthropods associated with leaf litter (litter-based community). We found that variation among host-plant genotypes had strong effects on the diversity and composition of foliage-based arthropods, but only weak effects on litter-based microarthropods. Furthermore, host-plant genotypic diversity was positively related to the abundance and diversity of foliage-based arthropods, and within the herbivore and predator trophic levels. In contrast, there were minimal effects of plant genotypic diversity on litter-based microarthropods in any trophic level. Our study illustrates that incorporating communities associated with living foliage and senesced litter into studies of community genetics can lead to very different conclusions about the importance of intraspecific diversity than when only foliage-based community responses are considered in isolation. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The effect of earthworms and snails in a simple plant community

Snails and earthworms affected the dynamics of a simple, three-species plant community, in the Ecotron controlled environment facility. Earthworms enhanced the establishment, growth and cover of the legume Trifolium dubium, both via the soil and interactions with other plant species. Worms increased soil phosphates, increased root nodulation in T. dubium, and enabled T. dubium seedlings to establish in the presence of grass (Poa annua) litter, by increasing soil heterogeneity. Worms also buried the seeds of Poa annua and Senecio vulgaris, reducing the germination of new seedlings. Snails reduced nitrogen-fixing Trifolium dubium and increased cover of plant litter, thereby reducing ammonia-nitrogen concentrations in the soil. These effects and their interactions demonstrate that the detritivore food chain, and earthworms in particular, cannot be ignored if we are to understand the spatial and temporal dynamics of plant communities.     

Lumbricid earthworm invasion in the Carpathian Mountains and some other sites in Romania

Recent field research shows that the ubiquitous Lumbricus terrestris and Octolasion lacteum (the large parthenogenetic form) have invaded new habitats in Romania, replacing mostly endemic or rare species of the former earthworm communities which were recorded 20–30 years ago. Seven different cases of earthworm invasion are currently described. Invader species have larger ecological tolerances as compared with the endemic species.     

Post-fire spread of alien plant species in a mixed broad-leaved forest of the Insubric region

How do tree species regenerate and which ecological conditions are required after forest fire in the Insubric region of the Alps? Are indigenous stand-forming tree species resistant over the invasion of alien plant species after such a disturbance? We addressed these questions in a case study in the Swiss canton of Ticino. In April 2006, a surface fire with severe intensity burnt a forest area of 55 ha on a south-facing slope (400-800 m.a.s.l.). The dominant trees in the investigated area were chestnut (Castanea sativa Mill.), beech (Fagus sylvatica L.) and deciduous oaks (Quercus spp.) mixed with tree species of intermediate height. Vegetation data were collected in May and August 2009 by systematic sampling. Resprouting of the survived trees and generative regeneration were analysed by counting vegetative shoots from sprouting stools, of seedling age, height and damage rate, respectively. Different vegetation structures related to low or high fire intensity were clearly visible three years after the forest fire, creating various habitats for both new invaders and seedlings of the stand-forming trees. The dominant chestnut was the only tree species that regenerated effectively by sprouting from stools. Seedlings of the stand-forming trees grew in high abundance under shadow conditions close to their mother trees which provided the seed source. In contrast, pioneer trees invaded patches where full light was available. Under such conditions the two main woody alien plant species, Ailanthus altissima and Robinia pseudoacacia, grew in high abundance. Due to the different ecological requirements of indigenous and alien tree seedlings, not any interaction between the two groups was detected.     

Effects of leaf litter on woody seedlings in xeric successional communities

We investigated the effect of leaf litter on the establishment of Eucalyptus incrassata, a mallee eucalypt. It has been suggested that litter accumulation may hinder seedling establishment, and that the removal of litter may be one of the mechanisms through which fire enhances recruitment. We conducted factorial experiments testing the effects of three kinds of leaf litter on E. incrassata seeds and seedlings at three contiguous sites with different land use histories. One site was an uncleared E. incrassata open mallee woodland (Mallee site), one a cleared area that had been ungrazed for about five years (Pasture site) and the third an area of mallee rolled some 40 years ago and permitted to regenerate (Regrowth site). Litter had no effect on emergence of planted E. incrassata seeds, but emergence differed between sites. Overall, the percentage of seeds that germinated and emerged was substantial (mean 35.2% ± 25.9%). Seedling shoot biomass did not differ between sites or litter treatments. Although seedlings grown in Pasture litter suffered higher mortality rates, overall mortality rates were low (mean 13.2% ± 15.5%), suggesting that leaf litter has little effect on recruitment rates during winter and spring. We conclude that leaf litter does not affect emergence or growth in young E. incrassata seedlings during winter and spring, when most establishment occurs. Our results emphasize the difficulty in predicting litter effects on recruitment.     

Nitrogen in shoot litter,root litter and root exudates from nitrogen-fixingAlnus incana

Summary A pot experiment withAlnus incana (L.) Moench growing in sand was set up to compare the amounts of nitrogen released from plants shoot litter with that released below ground as root litter and/or root exudation. No nitrogen fixation by free-living microorganisms was found in the sand and the increased nitrogen content of the plant + soil system was therefore due to nitrogen fixation byFrankia in the alder root-nodules. Most of the nitrogen released from the plants was in the nitrogen-rich leaf and other shoot litter. Only small amounts of nitrogen were found in the drainage water from the pots and were recorded as increased nitrogen content of the sand.     

Neurochemical characterization of nervous elements innervating the body wall of earthworms (Lumbricus, Eisenia): immunohistochemical and pharmacological studies

The distribution and chemical neuroanatomy of nervous elements and certain pharmacological–physiological characteristics of the innervation of the body wall in earthworms are described. Solitary sensory bipolar cells can be found among the epithelial cells. These bipolar cells contain serotonin, tyrosine hydroxylase, histamine, gamma-amino-butyric acid (GABA), Eisenia tetradecapeptide, proctolin or rhodopsin in various combinations. In the body wall, the plexus submuscularis is composed of nerve fibres only, whereas the plexus subepithelialis and muscularis also contain solitary nerve cells. These cells display histamine, GABA or neuropeptide Y immunoreactivity. The fibres of the three plexuses are reactive to serotonin, histamine, Eisenia tetradecapeptide, proctolin, GABA and neuropeptide Y antibodies. FMRFamide-immunoreactive fibres of the plexus muscularis originate from the central nervous system, whereas axons containing the other studied molecules are derived from both peripheral and central structures. High pressure liquid chromatography assays have revealed serotonin, dopamine and histamine in the body wall. Contractions of the body wall musculature can be elicited with serotonin and FMRFamide. Serotonin-evoked contractions are suppressed by the application of GABA. Serotonin acts both directly on the muscle cell receptors and indirectly through initiating transmitter release from the nervous elements, whereas the FMRFamide-induced contractions seem to be mediated through the muscle cell receptors only. The pharmacological profiles of the serotonin and GABA receptors resemble those of the vertebrate 5-HT₃ and GABA_B receptor types. Our findings indicate that both the sensory and efferent system of the annelid body wall operate by means of a variety of neuroactive compounds, suggesting a complex role of signalling systems in the regulation of this organ.This work was supported by the Hungarian Scientific Research Fund (OTKA; grant nos. T 34106 and T 34160). Márta Wilhelm is in receipt of a János Bolyai Scholarship.     

Effects of water and nutrient supply on amount and on nutrient concentration of litterfall and forest floor litter in Eucalyptus globulus plantations

A field experiment was initiated in March 1986 in central Portugal to evaluate the influence of water and nutrient supply on the productivity of E. globulus. The treatments applied were, irrigation plus fertiliser, irrigation and the application of fertilisers in rainfed plots. The control received neither fertilisers nor irrigation. The annual pattern litterfall was measured over a period of 5 years and the litter layer was quantified 6 years after planting. The amount of litterfall varied with the treatments. Simultaneous water and nutrient supply increased significantly litterfall, in respect to control. In rainfed conditions the timing of the maximum of litterfall was anticipated relative to the irrigated plots. However, the time of maximum litterfall did not coincide with the dry season but rather with period of maximum growth in each treatment. The N and P concentration was higher in the litterfall of the two fertilised treatments than in the others. The lowest concentrations of N and P in the leaf litter were coincident with the summer period in all treatments. The withdrawal of N and P ranged between 32 and 65% according to treatment and season. The deliverance of nutrients through litterfall was strongly increased by simultaneous water and nutrient supply. The supply of fertilisers in rainfed conditions promoted higher deliverance of nutrients than in the plots irrigated only. The mass of the litter layer was significantly increased by simultaneous water and nutrient supply. Application of fertilisers induced an increase in N and P concentration and a decrease in C/N ratio of the litter layer. Treatments and C/N values did not influence apparently the proportion of carbon, N and P released through mineralization from the litter layer. The non-fertilized treatments showed a more efficient N cycling than the others.     

Processing of leaf litter in a northern jarrah forest stream,Western Australia: I. Seasonal differences

Seasonal differences in the processing of jarrah (Eucalyptus marginata) leaves were examined in a small forest stream of the Darling Range, Western Australia. Processing rates in both summer and winter were very low, placing this species in the slow category (k < 0.005) of Petersen & Cummins (1974).Macroinvertebrates did not contribute to the processing of jarrah leaves during summer and autumn, coincident with the period of peak litter fall. The low quality of detritus entering the streams, and possibly some adverse interactions with the physical and chemical environment, inhibits processing during the summer months. As a consequence, a significant proportion of the coarse-particle detritus entering these streams may be exported unprocessed at the onset of high winter flows.In contrast with previous studies, jarrah leaves were processed at a faster rate during winter than summer. This seasonal difference can, in part, be attributed to the increased density and proportion of shredders at this time. Despite this, the processing of jarrah leaves during winter was very slow and must reflect the poor quality of this detritus as food for invertebrate consumers.     

Invasive litter, not an invasive insectivore, determines invertebrate communities in Hawaiian forests

In Hawaii, invasive plants have the ability to alter litter-based food chains because they often have litter traits that differ from native species. Additionally, abundant invasive predators, especially those representing new trophic levels, can reduce prey. The relative importance of these two processes on the litter invertebrate community in Hawaii is important, because they could affect the large number of endemic and endangered invertebrates. We determined the relative importance of litter resources, represented by leaf litter of two trees, an invasive nitrogen-fixer, Falcataria moluccana, and a native tree, Metrosideros polymorpha, and predation of an invasive terrestrial frog, Eleutherodactylus coqui, on leaf litter invertebrate abundance and composition. Principle component analysis revealed that F. moluccana litter creates an invertebrate community that greatly differs from that found in M. polymorpha litter. We found that F. moluccana increased the abundance of non-native fragmenters (Amphipoda and Isopoda) by 400% and non-native predaceous ants (Hymenoptera: Formicidae) by 200%. E. coqui had less effect on the litter invertebrate community; it reduced microbivores by 40% in F. moluccana and non-native ants by 30% across litter types. E. coqui stomach contents were similar in abundance and composition in both litter treatments, despite dramatic differences in the invertebrate community. Additionally, our results suggest that invertebrate community differences between litter types did not cascade to influence E. coqui growth or survivorship. In conclusion, it appears that an invasive nitrogen-fixing tree species has a greater influence on litter invertebrate community abundance and composition than the invasive predator, E. coqui.     

Fine root growth and nutrient release in decomposing leaf litter in three contrasting vegetation types in central Amazonia

We tested the hypothesis that the growth of fine roots upward into the leaf litter, forming a ‘surface root mat’, found widely in Amazonian forests, is of adaptive value for plants of poor soils because it makes possible more rapid uptake of limiting nutrients. We assessed the effect of invasion by fine roots on the rates of loss of dry mass and nutrient content of leaf litter over 1 year in three plots in each of three contrasting forest types in central Amazonia: the stunted facies of heath forest known as campina (SHF), the taller facies of heath forest known as campinarana (THF), both on spodosols, and the surrounding lowland evergreen rain forest (LERF) on ultisol. Pairs of bags filled with freshly fallen leaves from the trees of Clitoria fairchildiana (Fabaceae) were placed on the litter layer; in order to prevent roots entering the control bag in each pair that bag was lifted from the forest floor and turned over each week, while the treatment bag was left undisturbed. From each plot, four pairs of litter bags were retrieved after 30, 60, 120, 180, 270 and 360 d, and all roots that had grown into the litterbags were carefully removed. The leaves and roots from each bag were oven-dried for nutrient analysis. In no forest type was there a significant difference in the rate of loss of dry matter from the litter between the bags with and without roots. The amounts of roots invading the litter bags increased significantly in the sequence SHF < THF < LERF. In no forest did the presence of roots have a significant effect on the rate of disappearance of N or P from the leaf material, or on the rate of accumulation of Fe and Al. In the SHF there was no significant effect of invasion by roots on the rates of disappearance of Ca, Mg, Mn or Zn, but in the THF, the rates of disappearance of these four elements between 270 and 360 d were significantly greater in the presence of roots. In the LERF the results were similar, but the effects of roots started earlier—the rates of disappearance of Ca and Mg were significantly enhanced between 120 and 360 d. The results from the SHF may be interpreted to suggest that the growth of fine roots (and their fungal associates) upward into leaf litter is unlikely to be explained wholly by their role in the efficient recovery of mineral nutrients.     

Consistent performance of invasive plant species within and among islands of the Mediterranean basin

Since the success of an invasive species depends not only upon its intrinsic traits but also on particular characteristics of the recipient habitat, assessing the performance of an invader across habitats provides a more realistic analysis of risk. Such an analysis will not only provide insights into the traits related to invasiveness, but also the habitat characteristics that underpin vulnerability to invasion that, taken together, will facilitate the selection of management strategies to mitigate the invader’s effect. In the present study, we considered the Mediterranean basin islands as an excellent study region to test how the same invasive species perform in different habitats within a single island, and to scale up differences among islands with similar climate. We tested how the performance of three widespread plant invaders with clonal growth but contrasting life-history traits, a deciduous tree Ailanthus altissima, a succulent subshrub Carpobrotus spp., and an annual geophyte Oxalis pes-caprae, varied depending upon the species identity, habitat, and invaded island. The environmental parameters considered were habitat type, elevation, species diversity in the invaded plot, and several soil traits (% C, % N, C/N, pH, and relative humidity). The study documents that the performance of these three important and widespread plant invaders is dependent mainly on species identity, and less upon the invaded island’s general features. Likewise, differences in performance among habitats were only significant in the case of Ailanthus, whereas Carpobrotus and Oxalis appear to perform equally well in different environments. Ailanthus thus appears to have a broader spectrum of invasiveness, being able to invade a larger number of habitat types. On the contrary, Carpobrotus spp. have not yet invaded habitats different from those where the species have been originally introduced and where they are still commonly spread by humans. Oxalis distribution is mainly related to agricultural activities and disturbed sites, and the total area infested by this geophyte may be more reflection of the extent of suitable habitats than of invasiveness or ecological impact. Our results confirm the potential for these species to significantly alter the functioning of ecosystems in the Mediterranean islands and highlight the risk to other islands not yet invaded.     

马尾松人工纯林凋落松针数量及基质质量动态

凋落物是森林生态系统的重要组成部分,其产量与基质质量是影响植物-土壤间养分循环的重要因素。以3种密度马尾松人工纯林为研究对象,分析松针凋落模式及基质质量变化规律,比较不同林分密度间松针凋落特性差异,探讨松针基质质量、产量及气候因素间的关系。结果表明:松针凋落数量动态变化属双峰型,在2月呈现一个小高峰,在10/11月达最高峰。3种密度林分中各月凋落松针的N、P浓度均差异显著(P0.05),全年最高值出现在4—6月,8—12月的松针N、P浓度显著低于其他时段;不同月份凋落松针木质素浓度也差异显著(P0.05),在2月木质素含量达峰值,7、8月含量较低;3种密度林分中各月凋落松针的C/N、C/P、L/N和L/P比存在显著差异(P0.05),4—6月呈现最低值,9/11/12月则出现最高值,相差达2—3倍,且均高于养分释放临界值,不利于松针N素和P素的释放。林分密度对松针凋落数量和N浓度影响显著(P0.05),中等密度林分松针凋落数量高于低、高密度林分,中、高密度林分凋落松针N浓度显著高于低密度林分。凋落松针基质质量与自身凋落数量密切相关,并且受气温和降水量的影响。凋落松针N、P浓度与凋落数量呈显著负相关(P0.05),C/N、C/P、L/N、L/P比与凋落数量呈显著正相关(P0.05),说明更多凋落物产量将伴随着更低的基质质量,将有更慢的分解速度。     

Biomass and litter dynamics in a Melaleuca forest on a seasonally inundated floodplain in tropical,northern Australia

Litterfall from a Melaleuca forest was investigated as part of chemical cycling studies on the Magela Creek floodplain in tropical, northern Australia. The forest contained two species of tree, Melaleuca cajaputi and Melaleuca viridiflora, with a combined average density of 294 trees ha^–1. The M. viridiflora trees had diameter breast height measurements ranging from 11.8 to 62.0 cm, median class 25.1–30.0cm and a mean value of 29.2±1.0 cm, compared to 13.0 to 66.3 cm, 30.1–35.0cm and 33.5±1.0cm for M. cajaputi trees. A regression model between tree height, diameter breast height and fresh weight was determined and used to calculate average tree weights of 775±1.6kg for M. viridiflora and 1009±1.6kg for M. cajaputi, and a total above-ground fresh weight of 263±0.3t ha^–1. The weight of litter recorded each month on the ground beneath the tree canopy ranged from 582±103 to 2176±376 g m^–2 with a monthly mean value of 1105±51 g m^–2. The coefficient of variation of 52% on this mean indicates the large spatial and temporal variability in litter distribution over the study site. This variability was greatly affected by the pattern of water flow and litter transport during the Wet season. Litterfall from the trees was evaluated using two techniques - nets and trays. The results from these techniques were not significantly different with annual litterfall collected in the nets being 705 ± 25 g m^–2 and in the trays 716±49 g m^–2. The maximum monthly amount of litterfall, 108 ±55g m^–2, occurred during the Dry season months of June–July. Leaf material comprised 70% of the total annual weight of litter, 480±29 g m^–2 in the nets and 495 ± 21 g m^–2 in the trays. The tree density and weight of litter suggest that the Melaleuca forests are highly productive and contribute a large amount of material to the detrital/debris turnover cycle on the floodplain.     

The breakdown of buried and surface-placed leaf litter in an upland stream

The breakdown of buried leaves (Eucalyptus viminalis) was investigated using surface-placed and buried leaf packs in a riffle of the Acheron River, Victoria. Leaf packs buried to a depth of 10 cm were rapidly colonized by invertebrates, with the total numbers of individuals and species exceeding those on surface leaf packs. A larger proportion of leaves in buried leaf packs was grazed in comparison with those on the surface, with the intensity of grazing also being higher for leaves in buried packs. Both surface and buried leaf packs broke down rapidly with no significant difference in weight loss with time. The high level of breakdown of buried E. viminalis leaf litter observed in this study suggests that the hyporheos of Australian headwater streams may significantly contribute to the decomposition of particulate organic matter.     

Leaf litter decomposition and nutrient dynamics in a subtropical forest after typhoon disturbance

Decomposition of typhoon-generated and normal leaf litter and their release patterns for eight nutrient elements were investigated over 3 yr using the litterbag technique in a subtropical evergreen broad-leaved forest on Okinawa Island, Japan. Two common tree species, Castanopsis sieboldii and Schima wallichii, representative of the vegetation and differing in their foliar traits, were selected. The elements analyzed were N, P, K, Ca, Mg, Na, Al, Fe and Mn. Dry mass loss at the end of study varied in the order: typhoon green leaves > typhoon yellow leaves > normal leaves falling for both species. For the same litter type, Schima decomposed faster than Castanopsis. Dry mass remaining after 2 yr of decomposition was positively correlated with initial C:N and C:P ratios. There was a wide range in patterns of nutrient concentration, from a net accumulation to a rapid loss in decomposition. Leaf litter generated by typhoons decomposed more rapidly than did the normal litter, with rapid losses for N and P. Analysis of initial quality for the different litter types showed that the C:P ratios were extremely high (range 896 – 2467) but the P:N ratios were < 0.05 (range 0.02 – 0.04), indicating a likely P-limitation for this forest. On average 32% less N and 60% less P was retranslocated from the typhoon-generated green leaves than from the normal litter for the two species, Castanopsis and Schima. An estimated 2.13 g m^–2 yr^–1 more N and 0.07 g m^–2 yr^–1 more P was transferred to the soil as result of typhoon disturbances, which were as high as 52% of N and 74% of P inputted from leaf litter annually in a normal year. Typhoon-driven maintenance of rapid P cycling appears to be an important mechanism by which growth of this Okinawan subtropical forest is maintained.     

Germination and early growth of <Emphasis Type="Italic">Ailanthus</Emphasis> and tulip poplar in three levels of forest disturbance

Increasing rates of forest disturbance may provide greater opportunity for invasion of nonnative species, thereby altering the successional trajectory of native plant communities. In the eastern U.S., invasive Ailanthus altissima and native Liriodendron tulipifera have similar life histories and niches and often co-occur. To examine how disturbance affects the establishment of these species, we performed field experiments to evaluate the response of sown seeds and transplanted seedlings to three levels of disturbance on north- and south-facing aspects. L.␣tulipifera germination was severely limited by low seed viability and had significantly lower germination than A. altissima in all sites. The effect of disturbance regime on A. altissima germination depended on aspect in the second growing season. In contrast, mean seedling survival, biomass, leaf area and leaf area ratio were greater for L. tulipifera in all field sites. Overall, the north-facing selective cut forest provided a disproportionately large number of suitable microsites for L. tulipifera establishment. Collectively, this study demonstrated that different timber harvest practices produce heterogeneous mosaics of suitable microsites for germination and establishment. Limited L. tulipifera germination may be a serious constraint to population establishment if seeds are deposited for the first time immediately after a disturbance event. However, if sufficient viable seeds of both species exist, L. tulipifera out-performs the invasive in the first two years following disturbance. This may explain why A. altissima has shown explosive population growth in a limited number of sites in the past century.     

马尾松人工林林窗大小对四种凋落叶质量损失和养分释放的影响

马尾松人工林乔木层植物凋落物的分解对林地养分平衡和系统物质循环具有重要意义,并可能受不同大小林窗下微环境差异的影响。采用凋落物袋分解法,以马尾松(Pinus massoniana)人工林人为砍伐形成的7个不同大小林窗(G1:100 m~2、G2:225 m~2、G3:400 m~2、C4:625 m~2、G5:900 m~2、G6:1225m~2、G7:1600 m~2)为研究对象,林下(G0)为对照,研究林窗大小对红椿(Toona ciliata)、桢楠(Phoebe zhennan)、香樟(Cinnamomum camphora)和马尾松4种乡土树种凋落叶质量损失及养分释放的影响。结果显示:1)林窗大小(G0-G7)显著影响林窗中心放置的红椿和桢楠凋落叶N和P释放率、香樟凋落叶失重率和N、P、K释放率以及马尾松凋落叶P和K释放率。相对于林下,中小型林窗(G1-G4)的凋落叶失重率和N、P释放率明显较大,而大型林窗(G6-G7)的凋落叶K释放率明显较大。2)林窗内放置位置显著影响红椿、桢楠和马尾松凋落叶的K释放率及香樟凋落叶的P释放率。红椿和桢楠的凋落叶K释放率从林窗中心到边缘显著减少,而马尾松凋落叶K释放率及香樟P释放率从林窗中心到边缘显著增加。3)4种凋落叶类型中红椿凋落叶分解最快,其分解50%和95%所需时间分别为5.29和23.14个月。上述结果表明,林窗大小和林窗内位置对凋落物质量损失及其养分释放具有显著影响,但影响大小及趋势随物种初始基质质量的差异具有明显变化,研究结果为亚热带低山丘陵区马尾松人工低效林的科学经营及管理提高了一定的科学依据。     

Activities and properties of cellulase and xylanase associated with Phragmites leaf litter in a seawater lake

The activities and properties of cellulases and xylanases associated with Phragmites communis leaves were followed during the course of their decomposition from autumn to summer in a seawater lake. Cellulases and xylanases of low optimum pH (4 or less) were detected on aerial dead leaves before submergence. These enzymes remained on the leaves immediately after submergence, but were replaced by enzymes with a higher optimum pH (about 5.5 to 6.5), the activity of which increased rapidly during the initial two weeks. The enzyme activities then declined with water temperature until about day 100, but gradually increased again thereafter. This successive change in enzyme activities closely correlated with that of the decomposition rates of cellulose and xylan. The molecular weight distribution of the cellulases and xylanases changed markedly in the latter half of the experimental period, which suggested a change in the flora of active decomposer microorganisms.