氮、磷养分有效性对森林凋落物分解的影响研究进展

通过对相关研究文献的综述结果表明,氮(N)和磷(P)是构成蛋白质和遗传物质的两种重要组成元素,限制森林生产力和其他生态系统过程,对凋落物分解产生深刻影响。大量的凋落物分解试验发现在土壤N有效性较低的温带和北方森林,凋落物分解速率常与底物初始N浓度、木质素/N比等有很好的相关关系,也受外源N输入的影响;而在土壤高度风化的热带亚热带森林生态系统中,P可能是比N更为重要的分解限制因子。然而控制试验表明,N、P添加对凋落物分解速率的影响并不一致,既有促进效应也有抑制效应。为了深入揭示N、P养分有效性对凋落物分解的调控机制,"底物的C、N化学计量学"假说、"微生物的N开采"假说以及养分平衡的理论都常被用于解释凋落物分解速率的变化。由于微生物分解者具有较为稳定的C、N、P等养分需求比例,在不同的养分供应的周围环境中会体现出不同的活性,某种最缺乏的养分可能就是分解的最重要限制因子。未来的凋落物分解研究,应延长实验时间、加强室内和野外不同条件下的N、P等养分添加控制试验,探讨驱动分解进程的微生物群落结构和酶活性的变化。     

Studies on litter decomposition processes in a temperate forest ecosystem. I. Change of organic matter in oak (Quercus liaotungensis Koidz.) twigs

The litter bag method was used in this study on the decomposition of twigs of an oak (Quercus liaotungensis Koidz.) which is dominant in the warm temperate deciduous forests. This continual 5-year investigation was to measure the changes of organic compounds in twig litter. The decomposition of oak twigs based on rates of the mass loss during the first 5 years was simulated using the Olson exponential equation. The simulated data fitted well with the observed values. Oak twigs were predicted to reach 95% mass loss within 21 years. During the first 5 years, the concentration of protein in the remaining litter increased from 3.5% to 5.5%, while the concentration of hemicellulose decreased from 16.0% to 8.0%. However, there was no obvious change in the concentrations of lignin and cellulose. The losses of lignin, crude-cellulose and hemicellulose could be well simulated using the Olson exponential equation. However, this was not true for cellulose and protein.     

不同水分条件下毛果苔草枯落物分解及营养动态

于2009年5月至2010年5月采用分解袋法,研究了三江平原典型湿地植物毛果苔草枯落物分解对水分条件变化的响应,探讨了典型碟形洼地不同水位下枯落物分解1a时间内的分解速率与N、P等营养元素动态。分解1a内,无积水环境下枯落物失重率为34.99%,季节性积水环境下为27.28%,常年积水环境下随水位增加枯落物失重率分别为26.99%与30.67%,表明积水条件抑制了枯落物的分解。枯落物的分解随环境变化表现出阶段性特征,分解0—122 d内随水位增加枯落物失重率分别为16.09%、24.25%、23.53%与26.60%,即生长季内积水条件促进了枯落物有机质的分解及重量损失。而随实验进行,分解122—360 d内随水位增加毛果苔草枯落物的失重率分别为18.90%、3.02%、3.46%、4.03%,即在非生长季土壤冻融期积水条件抑制了枯落物分解(P<0.05)。水分条件对毛果苔草枯落物N元素的影响表现为积水条件促进生长季内枯落物的N固定,水位最高处毛果苔草N浓度显著高于无积水环境(P<0.05)。但进入冻融期后积水环境下枯落物N浓度与含量降低;其中季节性积水限制了枯落物的N积累能力,至分解360d时与初始值相比表现出明显的N释放(P=0.01)。毛果苔草枯落物分解61d时P出现富集,其中积水条件下P的富集作用增强,但与水位不相关。分解1a后毛果苔草枯落物表现为P的净释放,不同水分条件下枯落物P元素损失没有明显差异(P>0.05)。     

Evaluation of the faster initial decomposition of tropical floating leaves ofNymphaea elegans Hook

Contributions of abiotic and biotic processes to the decomposition of floating leaves ofNymphaea elegans were separately evaluated by comparing the rate obtained from anin situ experiment of submerging dry leaf material in a lake, and that from a laboratory experiment of submerging dry leaf material in lake water with a bio-fixing reagent. It took 8 days to decompose 79.4% of the initial dry weight of the floating leaf ofN. elegans in a tropical lake. Of the dry weight loss, 32.9% and 67.1% were atributed to abiotic and biotic decomposition, respectively. The relationship between decomposition rate and the mesh size of the leaf litter bags was examined by the application of a mathematical model. A reasonable value of decomposition loss at an early stage could be obtained using a bag with a mesh opening of 9.9 mm². The decomposition rate of floating leaves is faster than that of other aquatic plants. Rapid decomposition ofN. elegans leaves may be attributed to the fact that the plant has a low carbon to nitrogen ratio.     

Hydrologic control of litter decomposition in seasonally flooded prairie marshes

The effect of seasonal inundation on the decomposition of emergent macrophyte litter (Scolochloa festucacea) was examined under experimental flooding regimes in a northern prairie marsh. Stem and leaf litter was subjected to six aboveground inundation treatments (ranging from never flooded to flooded April through October) and two belowground treatments (nonflooded and flooded April to August). Flooding increased the rate of mass loss from litter aboveground but retarded decay belowground. Aboveground, N concentration decreased and subsequently increased earlier in the longer flooded treatments, indicating that flooding decreased the time that litter remained in the leaching and immobilization phases of decay. Belowground, both flooded and nonflooded litter showed an initial rapid loss of N, but concentration and percent of original N remaining were greater in the nonflooded marsh throughout the first year. This suggested that more N was immobilized on litter under the nonflooded, more oxidizing soil conditions. Both N concentration and percent N remaining of belowground litter were greater in the flooded than the nonflooded marsh the second year, suggesting that N immobilization was enhanced after water-level drawdown. These results suggest different mechanisms by which flooding affects decomposition in different wetland environments. On the soil surface where oxygen is readily available, flooding accelerates decomposition by increasing moisture. Belowground, flooding creates anoxic conditions that slow decay. The typical hydrologic pattern in seasonally flooded prairie marshes of spring flooding followed by water-level drawdown in summer may maximize system decomposition rates by allowing rapid decomposition aboveground in standing water and by annually alleviating soil anoxia.     

Studies on two species of Asellus in Rutland Water

The study comprised a comparison of the ecology of two species of Asellus (A. aquaticus and A. meridianus), and had two main aims. First the energy budget of the population of A. aquaticus, which is one of the most abundant species in the reservoir was assessed. Secondly, the two species appear to be ecologically very similar and it has been assumed by many workers that they are in competition. The study aimed to investigate how these two species might be able to coexist.The population dynamics of both species and the interaction between them is under study, as are their relations with the other benthic animals recorded in the reservoir (see Bullock et al. 1982). The sampling programme to cover variations in depth and substratum is also described by Bullock et al. 1982. A. aquaticus occurs in both arms while A. meridianus exists only in the south arm. A preliminary examination of the available data reveals that the density of A. aquaticus has increased in the south arm while the density of A. meridianus decreased drastically in February 1980. Since then low numbers of A. meridianus have been recorded every month even in the summer (breeding) season. It is noteworthy that simultaneously the number of predators, particularly Helobdella stagnalis, increased in comparison with previous years.It was therefore decided to study the predation on Asellus in the laboratory as well as in the field by using a serological technique. Antisera were produced against each species of Asellus by injections into rabbits of precipitated proteins (antigens). Thus a positive reaction obtained from a homogenised predator when tested with the specific antiserum indicates which species of Asellus had been consumed and the percentage of predators which had fed on Asellus in every sample could be calculated. The results obtained to date reveal that considerable numbers of Asellus spp. are removed from the environment by the predators (Helobdella stagnalis, Erpobdella octoculata, Polycelis tenuis. Dendrocoelum lacteum and Dugesia lugubris).Size class structures of the population of both species were constructed to study their life cycles and to estimate the population production. Comparitive respirometry of the two species was carried out at 4 °C, 10 °C and 16 °C, using a Gilson differential respirometer. This study aimed firstly to assess one of the essential parameters in the energy budget study of A. aquaticus and secondly, since A. aquaticus appears to be more active than A. meridianus, it would be expected that a comparison of their metabolic rate at different temperature would reveal marked differences between two species. It was found that there was no significant difference between the two species at 4 °C and 10 °C, but A. aquaticus had a significantly higher metabolic rate than A. meridianus at 16 °C.Consumption and assimilation of decaying oak leaves and of Cladophora glomerata (both of which are available in the environment) by two species of Asellus are being measured at present in the laboratory at three different temperatures (4 °C, 10 °C and 16 °C), and will contribute to the estimation of energy budgets.     

模拟N沉降下不同林龄马尾松林凋落叶分解-土壤C、N化学计量特征

模拟N沉降对森林生态系统的影响是当今全球变化生态学研究的一个热点问题,土壤碳库对N沉降比较敏感,N沉降增加了凋落叶分解过程中外源N含量,间接影响凋落叶分解的化学过程并改变凋落叶分解速率,因此,研究模拟N沉降下凋落叶分解-土壤C-N关系对预测森林C吸存有重要意义。利用原位分解袋法研究了模拟N沉降下三峡库区不同林龄马尾松林(Pinus massoniana)凋落叶分解过程中凋落叶-土壤C、N化学计量响应及其关系;N沉降水平分对照(CK,0 g m~(-2)a~(-1))、低氮(LN,5 g m~(-2)a~(-1))、中氮(MN,10 g m~(-2)a~(-1))和高氮(HN,15 g m~(-2)a~(-1))。结果表明:分解540 d后,N沉降促进20年生和30年生马尾松林凋落叶分解,46年生马尾松林中仅低氮处理促进凋落叶分解,4种处理均是30年生分解最快,说明同一树种起始N含量低的凋落叶对N沉降呈正响应,N沉降处理促进起始N含量低的凋落叶分解,起始N含量高的凋落叶分解过程中易达到"N饱和"。N沉降抑制20年生和46年生凋落叶C释放(低于对照0.62%—6.69%),促进30年生C释放(高于对照0.28%—5.55%);30年生和46年生林分N固持量均高于对照(高于对照0.15%—21.34%),20年生则低于对照(5.70%—13.87%),说明模拟N沉降处理促进起始C含量低的凋落叶C释放和起始N含量低的凋落叶N固持。N沉降处理下仅30年生马尾松林土壤有机碳较对照增加,且土壤有机质与凋落叶C、N和分解速率呈正相关,与凋落叶C/N比呈显著负相关;土壤总氮与凋落叶分解速率、凋落叶N含量呈正相关,土壤有机碳/总氮比与凋落叶C、N含量呈正相关;对照处理中凋落叶分解指标对土壤养分影响顺序是分解速率凋落物C含量凋落物C/N比凋落物N含量,低、中、高氮处理中则是凋落物C含量分解速率凋落物N含量凋落物C/N比。研究表明低土壤养分含量马尾松林对N沉降呈正响应,N沉降促进低土壤养分马尾松林凋落叶分解并提高土壤肥力;凋落叶质量和土壤养分含量低的生态系统土壤C对N沉降响应更显著。     

Effects of rhizome age on the decomposition rate of Phragmites australis rhizomes

The change in dried rhizome samples that were left to decompose was investigated to elucidate the effects of rhizome age on the decomposition rate of Phragmites australis. Rhizomes were classified into five age categories and placed 30 cm below the soil surface of a reed stand. After 369 days of decay, new (i.e., aged less than one year) rhizomes had lost 84% of their original dry mass, compared with a loss of 41–62% for that of older rhizomes. The exponential decay rates of older rhizomes were nearly identical to that of aboveground biomass. The nitrogen (N) concentration increased to two times its original values, but the phosphorus (P) concentration remained constant after an initial loss by leaching. The carbon to nitrogen (C:N) and carbon to phosphorus ratios (C:P) leveled out at 22:1 to 38:1 and 828:1 to 1431:1, respectively, regardless of rhizome age. The results are important to understand the nutrient cycles of reed-dominant marsh ecosystems.     

岩溶区和非岩溶区两种优势植物凋落叶分解的比较研究

应用野外分解网袋法对岩溶地区和非岩溶地区两种优势树种桂花和青冈栎凋落叶的分解速率和养分释放规律进行研究。结果表明:分解1年后,凋落叶失重率桂花大于青冈栎,同一物种岩溶区大于非岩溶区。凋落叶各元素浓度随分解时间变化也有一定差异,C含量均表现为初期上升,后下降,最后上升的趋势;N含量前半年呈波动状态,后半年逐渐上升;P含量处波动状态,总体呈上升趋势。N、P含量和凋落叶失重率均表现为极显著正相关,而C:N、C:P、N:P与凋落叶失重率呈极显著负相关(P<0.01),说明凋落叶分解过程中失重率与N、P含量及C:N、C:P、N:P关系密切。凋落叶桂花N、P含量比青冈栎高,分解速率也比较快。     

The decomposition of mangrove litter in a subtropical mangrove forest

Decomposition of Avicennia marina (Forsk.) Vierh. leaf and woody litter (twigs) was studied using litter bag experiments in a subtropical mangrove forest at two tidal levels (high and low) with different inundation regimes and during two seasons (summer and winter). Losses in dry weight were best described by a single exponential model which showed loss rates of both leaves and twigs were significantly higher low down on the shoreline (greater inundation) and in summer. The time (days) required for the loss of half of the initial dry weight (t ₅₀) was summer: high 59, low 44; winter: high 98, low 78. For twigs the values (days) were summer: high 383, low 179; winter; high 1327, low 1207. There is an exponential relationship between leaf litter t ₅₀'s and latitude which indicates the importance of temperature and therefore season, to the dynamics of organic cycling and export in mangrove systems.     

3个温带阔叶树种根系长期分解速率研究

根系分解对土壤碳固持和养分长期有效性具有重要意义,但目前对根系的长期分解模式仍知之甚少。比较3个温带阔叶树种不同直径根系7 a分解动态,可为生态过程模型提供数据支撑。在帽儿山生态站采用分解袋法对白桦（Betula platyphylla）、春榆（Ulmus davidiana var.japonica）、水曲柳（Fraxinus mandshurica）的5个直径等级（< 1 mm）、（1-2 mm）、（2-5 mm）、（5-10 mm）、（10-20 mm）根系进行了7 a野外分解实验。重复测量方差分析表明：时间、树种、直径与树种交互作用、树种与时间交互作用显著影响根系质量保持率。根系质量保持率随时间呈指数下降趋势,7 a间根系经历早期快速分解和后期慢速分解两个阶段,实验结束时根系仍剩余相当部分的初始质量（24%-56%）。利用Olson指数衰减模型估计各树种根系分解系数发现：白桦根系分解系数与根直径间具有显著的线性正相关关系,水曲柳具有显著对数正相关关系,春榆的关系不显著。3个树种短期分解系数均高估根系分解速率,而且不能完全代表长期分解系数的种内、种间差异。研究结果对理解根系长期分解速率随直径变化模式提供了数据支撑。     

Impact of soil mesofauna on the decomposition of two main species litters in a Pinus koraiensis mixed broad-leaved forest of the Changbai Mountains

In most terrestrial ecosystems, the majority of aboveground net primary productivity enters the decomposition system as plant litter. The decomposition of plant litter plays a critical role in regulating build up of the forest soil organic matter, releasing of nutrients for plant growth, and influencing the carbon cycling. Soil fauna are considered to be an important factor in the acceleration litter decomposition and nutrient transformations. Mechanisms of soil faunal contribution to litter decomposition include digestion of substrates, increase of surface area through fragmentation and acceleration of microbial inoculation into litter. The Pinus koraiensis mixed broad-leaved forest is one of the typical forest vegetation types in Changbai Mountain. Previously, major studies carried here were focused on climate, soil and vegetation; however, on litter decomposition and the role of soil fauna in this forest ecosystem were limited. In this paper, we conducted a litter decomposition experiment using litterbag method to explore the contribution of soil fauna on litter decomposition and provide a scientific basis for maintaining a balanced in P. koraiensis mixed broad-leaved forest in Changbai Mountains. During 2009 and 2010, we used litterbags with different mesh sizes to examine the decomposition of two dominant tree species (P. koraiensis, Fraxinus mandshurica) in studied site. The results showed that the process of litter decomposition can be separated into two apparent stages. The initial decomposition process at former six months was slow, while accelerated the final six months. The former six months (from October 2009 to April 2010) was winter and spring. There was low temperature and almost no activity of soil fauna and microbes. The final six months (from June to October 2010), decomposition rates increased. In summer and autumn, both temperature and moisture increases, abundance of soil fauna was much than before and was most active. The remaining mass of P. koraiensis was higher than that of F. mandshurica in two mesh size litterbags after 1 year decomposition, meanwhile litter in 2 mm mesh size litterbag had higher decomposition rate than that of 0.01 mm for two species litter. The Collembola, Acari, Enchytraeidae Lithobiomorpha and Diptera larvae were mainly fauna groups in the litterbags. The composition of soil fauna community was difference between P. koraiensis and F. mandshurica during litter decomposition. 24 different soil fauna groups and 1431 individual were obtained in P. koraiensis litterbags; Isotomidae, Tomoceridae and Oribatida were dominant groups; while 31 different soil fauna groups and 1255 individual were obtained in F. mandshurica litterbags; Isotomidae, Hypogastruridae Oribatida and Mesostigmata were dominant groups. The rate of litter decomposition was positively correlated with the individual and group density of soil fauna. Contribution rate to litter decomposition was 1.70% for P. koraiensis and 4.83% for F. mandshurica. Repeated measures ANOVA showed that litter species, time and soil fauna had a significant impact on the rate of litter decomposition (P < 0.05). Our results suggested that soil fauna could accelerate litter decomposition and, consequently, nutrient cycling in P. koraiensis mixed broad-leaved forest, Changbai Mountains.     

桂林岩溶石山檵木群落不同恢复阶段凋落物层酶对凋落物分解的影响

该文选取桂林岩溶石山檵木群落不同恢复阶段(灌木阶段、乔灌阶段和小乔林阶段)作为研究对象,探究凋落物层酶对凋落物分解速率的影响。结果表明:不同恢复阶段凋落物经1 a分解后,凋落物剩余率分别为灌木阶段(59.58%)、乔灌阶段(61.79%)和小乔林阶段(62.02%)。不同恢复阶段凋落物分解速率随演替的进行而减小。3个不同恢复阶段凋落物层多酚氧化酶、脲酶、蔗糖酶活性均在12月份最低,多酚氧化酶活性均在3月份最高,脲酶和蔗糖酶活性均在6月份最高。3个恢复阶段纤维素酶活性变化规律趋势一致,均在6月份酶活性最高,灌木阶段纤维素酶活性在3月份最低,乔灌阶段和小乔林阶段纤维素酶活性均在9月份最低。3个不同恢复阶段的凋落物层酶活性在不同时期均表现为蔗糖酶脲酶纤维素酶多酚氧化酶。不同恢复阶段凋落物层酶活性对凋落物分解速率影响不同。灌木阶段凋落物层蔗糖酶活性与分解速率呈显著正相关(P 0.05),乔灌阶段脲酶活性与分解速率呈显著正相关(P 0.05),小乔林阶段各酶活性与分解速率相关不显著。蔗糖酶、脲酶和多酚氧化酶是影响灌木阶段凋落物分解速率的重要因素,脲酶、纤维素酶和多酚氧化酶是影响乔灌和小乔林阶段分解速率的重要因素。     

减雨对南亚热带马尾松人工林凋落物分解的影响

为探究气候变化背景下降雨格局改变对马尾松人工林凋落物分解及养分释放过程的影响,以南亚热带马尾松(Pinus massoniana)人工林为研究对象,设置穿透雨减少50%和不减雨(对照)处理,开展连续观测野外降水控制实验。采用凋落物分解袋法,研究了减雨处理对南亚热带马尾松人工林凋落叶分解速率及养分释放的影响,以及凋落叶分解速率的影响因素。结果表明:凋落叶分解2年后,减雨处理和对照林凋落叶残留率分别为38.09%和38.06%;凋落叶分解过程中碳元素表现为淋溶-富集-释放,而氮元素表现为富集,减雨50%在一定程度上促进了氮的富集,但未达到显著水平。相关分析表明,凋落叶的残留率与氮浓度和月积温呈显著负相关,与碳/氮呈显著正相关。本研究发现,减雨50%并未改变马尾松凋落叶分解速率和养分释放模式,凋落叶的残留率与氮浓度、碳/氮及月积温密切相关。     

Elevated UV-B radiation has no effect on litter quality and decomposition of two dune grassland species: evidence from a long-term field experiment

From studies on living plant tissues it has been inferred that elevated UV‐B radiation could negatively affect litter quality and subsequent decomposition. However, in general, the effects of UV‐B radiation on litter chemistry and decomposition reported in the literature are variable and are often only marginally (if at all) significant. This might be due to the ecologically unrealistic conditions under which these experiments were performed. We investigated the effects of elevated UV‐B radiation on litter quality and subsequent decomposition on initial litter chemistry and long‐term (2 years) decomposition of freshly senesced Carex arenaria and Calamagrostis epigejos leaf litter under ecologically realistic conditions. This material was collected from a dune grassland that had received UV‐B radiation treatments for three growing seasons. It was then used in a 2‐year decomposition study using litter bags. We found no significant effects of elevated UV‐B radiation on any of the litter chemistry parameters in either of the two species, nor did we find significant effects on litter decomposition. However, we did find significant differences in litter decomposition between the species. These differences were related to the interspecific differences in litter chemistry, particularly the litter phenolics concentration. These results show that litter quality and decomposition in dune grasslands are, also under ecologically realistic conditions, not affected by UV‐B radiation. Instead, litter decomposition is determined by constitutive interspecific differences in litter chemistry. In conclusion, with our results added to the already existing literature, the preponderance of evidence now clearly suggests that elevated UV‐B radiation has very little, if any, impact on litter quality and subsequent decomposition in real ecosystems.     

高山林线交错带高山杜鹃的凋落物分解

凋落物分解是维持生态系统生产力、养分循环、土壤有机质形成的关键生态过程。高山林线交错带是陆地生态系统中对气候变化响应的敏感区域。季节变化和海拔梯度上的植被类型差异可能会影响该区域凋落物的分解,进而对高山生态系统的碳氮循环产生重要影响。采用凋落物分解袋的方法,研究了川西高山林线交错带优势种高山杜鹃(Rhododendron lapponicum)凋落叶在雪被期和生长季的分解特征。结果显示:(1)季节变化和植被类型对高山杜鹃凋落物的分解均具有显著影响(P0.05),凋落叶的质量损失主要发生在生长季且在高山林线最大,暗针叶林中雪被期的质量损失略高于生长季,但差异不显著;(2)林线交错带上高山杜鹃凋落叶分解缓慢,一年干物质失重率为9.62%,拟合分解系数k为0.145;(3)高山杜鹃凋落叶的质量变化主要体现在纤维素降解显著且集中在雪被期,木质素无明显降解,在高山林线上C/N、C/P、木质素/N变化幅度较小且C、N、P的释放表现得稳定而持续。结果表明,季节性雪被对林线交错带内高山杜鹃分解的影响不仅局限在雪被期内,雪被融化期间频繁的冻融作用和雪融水淋洗作用可能会促进高山杜鹃凋落物在生长季初期的分解。总的来看,在气候变暖的情景下,雪被的缩减、生长季的延长和高山杜鹃群落的扩张可能加速高山林线交错带高山杜鹃凋落物的分解。     

两种栽培型广藿香内生真菌群落组成变化

为探索内生真菌与广藿香互作间对宿主活性成分形成机制的影响,该研究以成分差异较大的牌香和湛香为对象,采用传统形态学方法对所获菌株归类,通过真菌通用引物ITS1/ITS4扩增菌株rDNA-ITS序列,鉴定其分类地位并研究其多样性。结果表明:(1)用PDA和LBA培养基对苗期、分枝期和成株期广藿香茎叶组织块进行内生真菌分离,共获得3070株菌株,其中牌香(PX)分离出1624株,鉴定出1319株,分属于36属;湛香(ZX)分离出1446株,鉴定出994株,分属于33属。牌香分离出7种特有内生真菌,分别为香柱菌(Epichloe typhina)、盘长孢状刺盘孢菌(Colletotrichum gloeosporioides)、座腔孢菌(Botryosphaeria sp.)、丝核菌(Rhizoctonia sp.)及截盘多毛孢菌(Truncatella sp.),并首次分离到疫霉菌(Phytophthora sp.)和指疫霉菌(Sclerophthora sp.),这2种菌属于卵菌门内生菌。湛香分离出拟青霉菌(Paecilomyces sp.)和尾孢菌(Cercospora sp.)2种特有内生真菌。(2)牌香和湛香优势内生真菌相同,均为链格孢菌(Alternaria sp.)和刺盘孢菌(Colletotrichum sp.),其中牌香中相对分离频率为9.48%和7.81%,湛香为10.16%和8.65%。(3)从苗期到成株期,牌香和湛香内生真菌定殖率逐渐增高,依次为牌香8月(97.78%)>7月(72.50%)>5月(55.28%);湛香8月(91.11%)>7月(63.06%)>5月(46.67%)。平均定殖率为牌香75.19%,湛香66.95%。(4)随着生长期延长,牌香和湛香内生真菌多样性呈递增趋势,同时2种广藿香内生真菌平均相似性系数为0.86。可见,牌香和湛香内生真菌种类丰富,各有独特的内生真菌,且不同生长期内生真菌种群组成不同。该研究结果为筛选活性内生真菌菌株,探究内生真菌影响广藿香活性成分合成与积累奠定了基础。     

Relative susceptibility to predation of two species of caterpillar on plantain

Summary The relative susceptibility to predators of a cryptic generalist caterpillar (Spilosoma congrua: Arctiidae) and a non-cryptic specialist (Junonia coenia: Nymphalidae) using the same hostplant species (Plantago lanceolata) was examined. In a laboratory experiment using predatory stinkbugs (Podisus maculiventris), more Junonia caterpillars than Spilosoma caterpillars were killed (70% vs. 16%). This result was a consequence of the Spilosoma spending some time under cover, moving frequently, feeding on leaves while under or adjacent to them, and spending little time on the leaves. In a field experiment using predatory wasps (Polistes fuscatus), the wasps found 7 times as many of the Junonia as the Spilosoma, and overall 6 times as many Junonia were killed as Spilosoma. Initially, 71% of the Junonia caterpillars encountered by wasps were killed, but by the fourth day of the test, only 22% of the Junonia encountered by wasps were killed. Over three full days of observations, a constant 50% of the Spilosoma caterpillars encountered by the wasps per day were killed. For the Junonia, evasion of predators rested on passive chemical defense. For the Spilosoma, evasion depended on being unapparent, speedy movement between feeding and resting sites and, if found, on fleeing immediately and quickly. These results indicate that Spilosoma caterpillars, by way of cryptic and escape behaviors, can be less susceptible to insect predators than Junonia caterpillars.     

Meiofauna promotes litter decomposition in stream ecosystems depending on leaf species

Litter decomposition, a fundamental process of nutrient cycling and energy flow in freshwater ecosystems, is driven by a diverse array of decomposers. As an important component of the heterotrophic food web, meiofauna can provide a trophic link between leaf‐associated microbes (i.e., bacteria and fungi)/plant detritus and macroinvertebrates, though their contribution to litter decomposition is not well understood. To investigate the role of different decomposer communities in litter decomposition, especially meiofauna, we compared the litter decomposition of three leaf species with different lignin to nitrogen ratios in litter bags with different mesh sizes (0.05, 0.25, and 2 mm) in a forested stream, in China for 78 days. The meiofauna significantly enhanced the decomposition of leaves of high‐and medium‐ quality, while decreasing (negative effect) or increasing (positive effect) the fungal biomass and diversity. Macrofauna and meiofauna together contributed to the decomposition of low‐quality leaf species. The presence of meiofauna and macrofauna triggered different aspects of the microbial community, with their effects on litter decomposition varying as a function of leaf quality. This study reveals that the meiofauna increased the trophic complexity and modulated their interactions with microbes, highlighting the important yet underestimated role of meiofauna in detritus‐based ecosystems.     

美国南卡罗来纳州森林湿地十种典型植物凋落叶的分解特征

凋落叶分解是控制森林湿地物质循环的重要生态过程,是全球C、N等元素循环的重要一部分。以美国南卡罗来纳州10种典型植物的凋落叶为研究对象,通过2a的分解实验测定分解阶段凋落叶的生物量残留率、分解速率常数k和C、N残留百分比,探讨初始凋落叶化学性质对分解速率常数k的影响。结果表明:(1)十种凋落叶生物量在两年内降解至初始的14.5%—66.2%,种间差异可达4倍以上;分解速率常数k在0.26—1.64a~(-1)之间,针叶分解速率阔叶分解速率;(2)分解速率常数k与初始凋落叶酸溶性组分(AS)极显著正相关(P0.001),与初始C含量、酸不溶组分(AIF)和AIF/N比均显著负相关(P0.05);(3)凋落叶C残留百分比持续下降至10.2%—66.1%,而N残留百分比因物种与分解阶段不同呈现不同变化规律。结果表明,森林湿地中凋落叶初始C组分差异是其分解速率的种间极大差异的主要原因,评估森林湿地的C、N循环应充分考虑种间差异。