中亚热带主要树种凋落叶在杉木人工林中分解及氮磷释放过程

采用分解网袋法研究了马尾松(Pinus massoniana)、桤木(Alnus cremastogyne)、木荷(Schima superba)、青冈(Cycloblanopsis glauca)等树种凋落叶在21年生杉木人工林内的分解速率和养分释放过程。经过13个月的分解实验,4种供试凋落叶以青冈分解最快,质量失重率为33.5%,其次为桤木和木荷,马尾松分解最慢,其质量失重率仅为29.9%。4种凋落叶分解50%和95%所需要的时间分别为21～26个月和94～112个月。在凋落叶分解过程中,除桤木凋落叶中氮含量下降外,其他3种凋落叶的氮含量均增加,但凋落叶的C/N均降低;在凋落叶分解的前3个月,凋落物中磷含量快速下降,此后变化很小,C/P呈增加趋势。在凋落叶分解过程中,马尾松凋落叶对氮素表现为固持作用,而其他3种凋落叶对氮素表现为净释放,4种凋落叶的磷素均表现为净释放。4种供试材料中桤木较适合与杉木混交种植。     

不同贮藏方式对河西走廊四种茄科植物种子萌发的影响

种子扩散后的贮藏条件对其萌发有着重要影响.本文探讨了4种贮藏条件(室温、冬季枯落物表层、枯落物覆盖、冬季浅层覆土)对河西走廊4种茄科植物黑果枸杞(Lycium ruthenicumr)、黄果枸杞(L.barbarum var.auranticarpum)、红果龙葵(Solanum alatum)和曼陀罗(Darura stramonium)种子萌发的影响.结果表明:经冬季浅层覆土(1 cm)和枯落物覆盖的黑果枸杞种子萌发率(96.5％和75.5％)和黄果枸杞种子萌发率(65.3％、53.6％)显著提高,萌发速率加快;未萌发的黑果枸杞和黄果枸杞种子保持较高活性;黑果枸杞种子经冬季枯落物表层和室温存放后萌发率为57.5％,未萌发种子活性丢失率较高(47.5％和31％);黄果枸杞种子经枯落物表层存放后,萌发率为39.3％,未萌发种子部分活性丢失(38％);经各种贮藏后的红果龙葵种子萌发率均较高(＞90％),曼陀罗种子萌发率极低(＜10％),种子保持较高活性(50.5％ ～81.5％).黑果枸杞和黄果枸杞种子萌发对贮藏条件具有一致性的响应,即经过冬季浅层覆土和枯落物覆盖后萌发率均显著提高、萌发速率加快、萌发历程缩短,说明冬季的湿冷环境能够打破黑果枸杞和黄果构杞种子休眠,并保持种子活性;而冬季干燥寒冷环境可使部分种子失活,不利于种群的建植和自然更新.种子萌发对湿冷的需求反映了温带植物繁衍种族的自然机制,保证了幼苗存活和建植的最大化.     

喀斯特峰丛洼地植被演替过程中土壤养分的积累及影响因素

以桂西北环江县典型喀斯特峰丛洼地为对象,利用空间代替时间的方法,于2009年分析了植被演替过程中表层土壤(0～15 em)养分的变化及其主要控制因素.结果表明:随着植被正向演替(草地-灌丛-次生林-原生林),表层土壤的有机碳、全氮和全磷等含量显著增加,分别由演替初期(草地)的29.1、2.48和0.72 g·kg-1增加为演替后期(原生林)的73.9、8.10和1.6g·kg-1.土壤阳离子交换量与有机碳和全氮密切相关,是喀斯特土壤C、N积累的主要控制因素;凋落物中的P含量、C/P和N/P是土壤全磷积累的主要控制因素,较高的凋落物P含量、N/P以及较低的C/P有利于土壤中P的积累;而坡度、坡向和裸岩率等地形因子对土壤养分的影响较小.     

Context‐specific effects of the identity of detrital mixtures on invertebrate communities

Many aquatic ecosystems are sustained by detrital subsidies of leaf litter derived from exogenous sources. Although numerous studies have examined the effects of litter species richness and identity on decomposition processes, it remains unclear how these effects extend to associated invertebrate communities or how these effects vary spatially according to local environmental context. Using field enrichment experiments, we assessed how the species richness, assemblage composition, and supply of detrital litter resources interact to affect benthic communities of three temperate Australian estuarine mudflats. Our experiments utilized eight litter sources that are presently experiencing human‐mediated changes in their supply to estuarine mudflats. Contrary to predictions, we did not detect effects of the species richness of detrital mixtures on benthic communities. Macroinvertebrate community structure and, in particular, abundance were, instead, influenced by the assemblage composition of detrital mixtures. At two of the three sites, plots receiving the most labile detrital mix, containing the ephemeral algae Chaetomorpha and Ulva, supported the fewest macroinvertebrates of all the experimental enrichments. The large effect of detrital mix identity on macroinvertebrate communities is of concern given present trends of proliferation of macroalgae at the expense of more refractory seagrasses and marsh grasses. As such environmental degradation continues, it will be important to more fully understand under what environmental contexts such compositional changes in detrital resources will have the most detrimental effects on important prey resources for commercially important fish and wading shorebirds.     

Diversity patterns of leaf-associated aquatic hyphomycetes along a broad latitudinal gradient

Information about the global distribution of aquatic hyphomycetes is scarce, despite the primary importance of these fungi in stream ecosystem functioning. In particular, the relationship between their diversity and latitude remains unclear, due to a lack of coordinated surveys across broad latitudinal ranges. This study is a first report on latitudinal patterns of aquatic hyphomycete diversity associated with native leaf-litter species in five streams located along a gradient extending from the subarctic to the tropics. Exposure of leaf litter in mesh bags of three different mesh sizes facilitated assessing the effects of including or excluding different size-classes of litter-consuming invertebrates. Aquatic hyphomycete evenness was notably constant across all sites, whereas species richness and diversity, expressed as the Hill number, reached a maximum at mid-latitudes (Mediterranean and temperate streams). These latitudinal patterns were consistent across litter species, despite a notable influence of litter identity on fungal communities at the local scale. As a result, the bell-shaped distribution of species richness and Hill diversity deviated markedly from the latitudinal patterns of most other groups of organisms. Differences in the body-size distribution of invertebrate communities colonizing the leaves had no effect on aquatic hyphomycete species richness, Hill diversity or evenness, but invertebrates could still influence fungal communities by depleting litter, an effect that was not captured by the design of our experiment.     

Leaf decomposition and nutrient release of dominant species in the forest and lake in the Jiuzhaigou National Nature Reserve,China

AimsLitter decomposition is an important ecological process in nutrient cycling and productivity of ecosystems. Our objective is to quantify the differences of litter decomposition and nutrient release (N and P) under the forest and in an alpine lake among the dominant tree species in the Jiuzhaigou National Nature Reserve.
Methods Fresh leaf litters of Abies ernestii, Pinus tabulaeformis, Betula albo-sinensis, and Salix cupularis were collected and placed in bags under the forest and in an alpine lake for a year.
Important findings The mass remaining ratio (MR) of the leaf litters was well predicted with Olson’s decay model (r > 0.93, p < 0.01). The time for 99% decomposition was the shortest for S. cupularis (6.80 a), followed by B. albo-sinensis (10.34 a), A. ernestii (18.88 a), and P. tabulaeformis (27.21 a). These values were 1.48-, 1.55-, 1.80-, and 1.65-folds of the corresponding values in the lake, respectively. Both MR and nitrogen remaining ratio (NR) had significantly negative correlations with the leaf initial N concentration, but significantly positive correlations with the initial C:N. The nutrient release was significantly different among the four species and between the two sites (i.e., forest and alpine lake). The N release of S. cupularis was consistent between forest and the lake (i.e. directly released in the beginning of decomposition), while other species had an obvious N enrichment process before it released. The release of P among was similar among the four species and between the two sites, with a release—enrichment—release pattern. Overall, the leaf litter decomposition appeared as an intricate process that was affected by the litter chemistry and and the environment. The fast litter decomposition in the lake may have a profound influence on the water quanlity in the Jiuzhaigou National Nature Reserve.     

高山森林林窗对凋落叶分解的影响

林窗对降水和光照等环境条件的再分配以及分解者群落的影响可能深刻作用于森林凋落物分解过程,但有关高山森林林窗大小对凋落物分解的影响尚无研究报道。采用凋落物分解袋法,研究了川西高山森林不同大小林窗对非生长季节和生长季节红桦(Betula albo-sinensis)和岷江冷杉(Abies faxoniana)凋落叶质量损失的影响。结果显示,经过1a的分解,不同生境下红桦和岷江冷杉凋落叶分别分解了27.25%—30.12%和27.04%—27.96%,其中非生长季节占53.83%—60.18%和50.23%—59.09%。林窗对红桦和岷江冷杉凋落叶质量损失的影响因物种不同而呈现季节差异。总体上,林窗加快了岷江冷杉凋落叶的分解而延缓了红桦凋落叶的分解。与郁闭林下相比,林窗显著增加了2种凋落叶非生长季节的质量损失速率,显著降低了生长季节2种凋落叶的质量损失速率;2种凋落叶质量损失速率在非生长季节随林窗面积增大而加快,在生长季节随林窗面积增大而减慢。林窗显著影响了初冻期、深冻期和融化期岷江冷杉凋落叶的质量损失率,但对红桦凋落叶质量损失率影响不显著。可见,高山森林凋落物分解过程受到林窗的显著影响,并且阔叶和针叶凋落叶在非生长季节和生长季节对林窗的响应具有明显差异。     

Soil depth- and root diameter-related variations affect root decomposition in temperate pine and oak forests

Aims Assessment of factors regulating root decomposition is needed to understand carbon and nutrient cycling in forest ecosystems. The objective of this study is to examine the effects of soil depth and root diameter on root decomposition and to analyze the relationship of root decomposition with factors such as soil environmental conditions and initial litter quality.