Soil burial has a greater effect on litter decomposition rate than nitrogen enrichment in alpine grasslands

高寒草地土壤掩埋对凋落物分解速率的影响大于氮素富集 由于高寒草地退化、鼠害严重、大风频繁等原因,凋落物被频繁掩埋在土壤中。但凋落物的位置变化和氮富集对高寒草原凋落物分解速率和养分动态影响的认识尚不清楚。为了研究凋落物 位置变化(地表、掩埋10 cm和悬空60 cm)和氮富集对高寒草原优势植物凋落物分解的影响,本研究依托2009年在新疆天山巴音布鲁克高寒草原设置的长期模拟氮沉降研究平台,以对照和氮富集处理样方的优势植物羊茅(Festuca ovina)和赖草(Leymus tianschanicus)凋落物为试验材料,测定分解过程中凋落物质量损失和碳氮磷含量的变化特征。研究结果表明,掩埋凋落物分解速率显著快于地表凋落物,悬空处理凋落物分解速率慢于地表凋落物。氮富集显著影响凋落物质量,进而影响凋落物分解。而凋落物质量残留在对照与氮富集土壤掩埋之间无显著差异。这些结果表明,氮富集通过凋落物质量而不是通过土壤环境因素,影响短期凋落物分解。不同处理的所有试验凋落物均有碳和磷的释放现象。对照处理的凋落物,凋落物氮以累积为主,而氮富集处理的凋落物,凋落物氮以释放为主。这表明凋落物分解可能受到氮元素限制,氮富集改变了凋落物分解调控的氮循环过程。本研究提供了直接证据,掩埋处理的凋落物有更快的质量损失和碳元素释放,土壤掩埋是旱地凋落物分解速率比模型预测的快的一个候选解释。     

Limited evidence that mixing leaf litter accelerates decomposition or increases diversity of decomposers in streams of eastern Canada

Most studies of terrestrial litter decomposition in streams and rivers have used leaves from a single tree species, but leaf packs in streams in eastern North America are usually mixtures of two or more species. Litter mixtures may decay more quickly than either of the component species. If so, estimates of stream energy and nutrient budgets may be inaccurate. In northern Nova Scotia, Canada, we measured mass loss from binary mixtures (1:1 mass ratio) of leaf litter in mesh bags, using freshly fallen or air-dried litter from five species of canopy trees. We repeated the experiment eight times, in summer and fall, in two streams and a small river, over 3 years. In some trials we enumerated benthic invertebrate and fungal colonization of decaying litter. Although there were marked differences in mass loss rates among litter types, decomposition was accelerated in mixtures relative to the mean of the component species in only three of eight trials, and only in mixtures containing N-rich speckled alder leaves. Mixing yellow birch and red maple leaves inhibited decomposition. Diversity (Shannon–Weaver Index), species richness, and abundance of aquatic hyphomycete fungi, as indexed by conidial production, were never greater (and sometimes less) on litter mixtures than on the component species. Total numbers, taxonomic richness and diversity of benthic invertebrates generally, and litter-feeding species in particular, were not augmented by mixing litter types. Litter mixtures appear to dilute a preferred substrate with patches of a less preferred substrate. Our results provide only weak support for the contention that combining two litter types leads to acceleration of decomposition rates. Handling editor: K. Martens     

Effects of mixing pine and broadleaved tree/shrub litter on decomposition and N dynamics in laboratory microcosms

This study was carried out to compare the ecological function of exotic pine (Pinus radiata—Pr) and native pine (Pinus tabulaeformis—Pt) in terms of litter decomposition and its related N dynamics and to evaluate if the presence of broad-leaved tree species (Cercidiphyllum japonicum—Cj) or shrub species (Ostryopsis davidiana—Od) litter would promote the decomposition of pine needles and N cycling. Mass remaining, N release of the four single-species litters and mixed-species (Pt + Cj; Pr + Cj; Pt + Od; Pr + Od) litters and soil N dynamics were measured at microcosm scale during an 84-day incubation period. The Pt and Pr litter, with poorer substrate quality, indicated slower decomposition rates than did the Cj and Od litter. Due to their high C/N ratios, the N mass of Pt and Pr litter continuously increased during the early stage of decomposition, which showed that Pt and Pr litter immobilized exogenous N by microbes. No significant differences of soil inorganic, dissolved organic and microbial biomass N were found between the Pt and Pr microcosm at each sampling. The results showed that the exotic Pr performed similar ecological function to the native Pt in terms of litter decomposition and N dynamics during the early stage. The presence of Cj or Od litter increased the decomposition rates of pine needle litter and also dramatically increased soil N availability. So it is feasible for plantation managers to consider the use of Cj as an ameliorative species or to retain Od in pine plantations to promote the decomposition of pine litter and increase nutrient circulation. The results also suggested that different species litters induced different soil dissolved organic nitrogen (DON). As a major soluble N pool in soil, DON developed a different changing tendency over time compared with inorganic N, and should be included into soil N dynamic under the condition of our study.     

Bilateral olfaction: two is better than one for navigation

Do animals require bilateral input to track odors? A recent study reveals that fruit fly larvae can localize odor sources using unilateral inputs from a single functional sensory neuron, but that an enhanced signal-to-noise ratio provided by dual inputs is helpful in more challenging environments.     

放牧对青藏高原东部两种典型高寒草地类型凋落物分解的影响

为认识放牧对青藏高原东部中生性的高寒草甸草地和半湿生的沼泽草地凋落物分解的影响,在这两种草地上分别设置了围栏和放牧样地,研究了其各自的混合凋落物样品和4个优势物种(发草Deschampsiacaespitos、鹅绒委陵菜Potentilla anserine、木里苔草Carexmuliensis、藏嵩草Kobresiatibetica)凋落物的分解和养分释放动态,这4个优势物种也大致代表了当地沼泽草地生态系统在放牧和气候变暖驱动下逆行演替不同阶段的优势物种类群。结果表明,各优势物种凋落物的分解速率有显著差异;放牧在总体上促进了凋落物的分解,但不同物种的响应有所不同;放牧对凋落物C的释放影响不显著或有抑制作用,但对N、P的释放具有一定促进作用。对各优势物种凋落物分解和养分释放模式的分析表明,群落逆行演替过程中,凋落物分解和C释放加速,可能促进沼泽湿地退化的正反馈效应。草甸草地的退化标志物种鹅绒委陵菜具有较高的凋落物质量和分解速度,反映了中生条件下植物应对牲畜啃食采用"逃避"而非"抵抗"策略的趋向。     

Effects of malaria double infection in birds: one plus one is not two

Avian malaria parasites are supposed to exert negative effects on host fitness because these intracellular parasites affect host metabolism. Recent advances in molecular genotyping and microscopy have revealed that coinfections with multiple parasites are frequent in bird-malaria parasite systems. However, studies of the fitness consequences of such double infections are scarce and inconclusive. We tested if the infection with two malaria parasite lineages has more negative effects than single infection using 6 years of data from a natural population of house martins. Survival was negatively affected by both types of infections. We found an additive cost from single to double infection in body condition, but not in reproductive parameters (double-infected had higher reproductive success). These results demonstrate that malaria infections decrease survival, but also have different consequences on the breeding performance of single- and double-infected wild birds.     

When one is better than two: RNA with dual functions

The central dogma of biology, until not long ago, held that genetic information stored on DNA molecules was translated into the final protein products through RNA as intermediate molecules. Then, an additional level of complexity in the regulation of genome expression was added, implicating new classes of RNA molecules called non-coding RNA (ncRNA). These ncRNA are also often referred to as functional RNA in that, although they do not contain the capacity to encode proteins, do have a function as RNA molecules. They have been thus far considered as truly non-coding RNA since no ORF long enough to be considered, nor protein, have been associated with them. However, the recent identification and characterization of bifunctional RNA, i.e. RNA for which both coding capacity and activity as functional RNA have been reported, suggests that a definite categorization of some RNA molecules is far from being straightforward.Indeed, several RNA primarily classified as non-protein-coding RNA has been showed to hold coding capacities and associated peptides. Conversely, mRNA, usually regarded as strictly protein-coding, may act as functional RNA molecules. Here, we describe several examples of these bifunctional RNA that have been already characterized from bacteria to mammals. We also extend this concept to fortuitous acquisition of dual function in pathological conditions and to the recently highlighted duality between information carried by a gene and its pseudogenes counterparts.     

Loss of total phenols from leaf litter of two shrub species: dual responses to alpine forest gap disturbance during winter and the growing season

高山森林林窗能够通过调控水热动态进而控制林下生态系统过程。因此,本研究旨在通过两种典型灌木[华西箭竹(Fargeisia nitida (Mitford) Keng f.)和康定柳(Salix paraplesia Schneid.)]凋落叶分解,探索林窗干扰对分解过程中总酚释放的影响。我们在一个典型的岷江冷杉林(Abies faxoniana Rehd.)样地,通过设置不同林窗位置(林窗中心南侧、林窗中心北侧、林缘、扩展林缘和林下)进行了凋落物分解实验;并在两年的不同关键时期：雪被形成期、雪被覆盖期、雪被融化期、生长季节初期和生长季节后期,对两种灌木凋落叶分解袋进行采样,并测试其总酚释放率和微生物丰富度(真菌和细菌)。实验结束后,我们发现,雪被厚度、冻融循环以及真菌细菌比对凋落叶的总酚释放具有显著影响。在两年的雪被形成期、雪被覆盖期、雪被融化期和生长季节后期,真菌和细菌丰富度表现出从林窗中心到林下逐渐降低的趋势,而在两年的生长季节初期,其表现出从林窗中心到林下逐渐增加的趋势。而从不同林窗位置来比较,两种灌木凋落叶的总酚释放率仅在第一年各关键时期表现出同真菌细菌丰富度类似的规律。此外,在第一年的冬季,以及从整个第一年和整个两年分解时间段来看,林窗中心位置两种凋落叶的总酚释放率皆较其他林窗位置高。这些研究结果表明,高山森林林窗的形成能够促进凋落叶总酚的释放,尽管其释放对林窗干扰的响应在不同关键时间具有不同的表现。总之,在高寒生物区,林窗的更替消失以及在气候变化背景下冬季变暖导致的雪被覆盖厚度和持续时间的减少会降低凋落叶总酚的释放率。     

Bax forms two types of channels, one of which is voltage-gated

When activated, the proapoptotic protein Bax permeabilizes the mitochondrial outer membrane, allowing the release of proteins into the cytosol and thus initiating the execution phase of apoptosis. When activated Bax was reconstituted into phospholipid membranes, we discovered a new, to our knowledge, property of Bax channels: voltage gating. We also found that the same Bax sample under the same experimental conditions could give rise to two radically different channels: Type A, which is small, well behaved, homogeneous, and voltage-gated, and Type B, which is large, noisy, and voltage-independent. One Type B channel can be converted irreversibly into a population of Type A channels by the addition of La³⁺. This conversion process appears to involve a two-dimensional budding mechanism. The existence of these two types of Bax channels suggests a process for controlling the degree of mitochondrial outer membrane permeabilization.     

Leaf litter decomposition of sweet chestnut is affected more by oomycte infection of trees than by water temperature

Riparian forests are subjected to multiple disturbances, such as tree diseases caused by invasive pathogens, whose consequences on stream functioning are unknown. We assessed the impact of Phytophthora cinnamomi infection, and interactions with temperature, on microbial decomposition of Castanea sativa leaves. Leaves from healthy, symptomatic and highly symptomatic trees were incubated in the laboratory at 13 and 18 °C for 64 d. Infection significantly increased polyphenolic concentration and leaf toughness, reducing leaf decomposition and microbial respiration rates irrespective of temperature. Aquatic hyphomycete communities differed significantly in leaves from highly symptomatic trees. Fungal biomass was highest at 18 °C, irrespective of tree health status. None of the parameters were influenced by the tree health status × temperature interaction, suggesting that temperature rise may not synergistically increase the cross-ecosystem effects caused by P. cinnamomi in streams where litter decomposition is microbial-driven. Infection by P. cinnamomi alters the nutritional quality of leaves affecting the functioning of aquatic ecosystems.     

季节性冻融期间土壤动物对高山草甸两种凋落叶失重的贡献

季节性冻融期间高山草甸凋落叶的分解可为生长季节植物生长提供必要的养分,对于维持生态系统物质循环和养分平衡具有重要作用。然而,土壤动物对凋落叶分解是否具有明显的贡献仍然缺乏一致认识。因此,以高山草甸代表性植物黄花亚菊(Ajania nubigena)和黑褐苔草(Carex atrofusca)凋落叶为研究对象,采用不同孔径凋落叶袋排除土壤动物的方法,研究冬季不同冻融时期(冻结前期、冻结期和融化期)土壤动物对凋落叶失重的贡献。整个季节性冻融期间土壤动物对黄花亚菊和黑褐苔草两种凋落叶失重率的作用分别为12.07%和4.03%,总贡献率分别为46.39%和24.14%。土壤动物对两种凋落叶失重率的作用均在融化期最大,而土壤动物对黄花亚菊凋落叶失重率的作用在冻结初期最小,土壤动物对黑褐苔草凋落叶失重率的作用在冻结期最小。整个季节性冻融期,土壤动物对凋落叶失重率的作用和贡献率与正积温和凋落叶初始C、N浓度和C/N比均呈显著的正相关关系。因此,季节性冻融期间土壤动物对高山草甸凋落叶分解具有明显的贡献,但这些过程受冻融格局和凋落叶初始质量的调控。     

灌丛群落叶功能型及其与凋落物水分涵养性能的关系——以广西三种典型灌丛群落为例

牡荆、红背山麻杆和羊蹄甲群落是三种在广西壮族自治区具有较为重要水土保持功能的典型灌丛。通过野外勘察选择了受干扰程度较低的群落作为研究样地。通过测定样方中优势物种的叶功能性状和凋落物的水分涵养特征,揭示了灌丛群落的叶功能型及其与凋落物水分涵养性能的关系,以求更好地发挥灌丛在区域退化生态系统中生态恢复和水土保持的作用。研究结果表明,(1)三种灌丛群落的叶功能性状有着十分明显的差异,群落的叶功能型因此而分化形成了以羊蹄甲为代表的低干物质、低有机质与高比叶面积(低LOMC+LDMC-高SLA)的类型,以及以红背山麻杆群落和牡荆灌丛群落为代表的高干物质、高有机质与低比叶面积(高LDMC+LOMC-低SLA)的类型。后者因叶片磷含量(LPC)的不同,再进一步分化。(2)三种灌丛群落凋落物的水分涵养性能由于群落凋落物的水分涵养特征存在显著差异出现分化。红背山麻杆和牡荆灌丛的凋落物蓄积量(LS)和自然含水率(NWC)显著高于羊蹄甲灌丛,而它们的最大持水率(MWHR)则低于羊蹄甲灌丛。红背山麻杆和牡荆灌丛的最大拦蓄量(MIC)和有效拦蓄量(EIC)因此而显著高于羊蹄甲灌丛。(3)灌丛群落的叶功能性状SLA、LDMC、LOMC、LPC等分别与MIC和EIC等水分涵养性能特性存在显著相关性。叶功能型为低LDMC+LOMC-高SLA的羊蹄甲灌丛群落具有较低的水分涵养性能,而叶功能型为高LDMC+LOMC-低SLA的红背山麻杆和牡荆灌丛群落具有较高的水分涵养性能。为了提高生态系统的水土保持功能,在进行退化生态系统生态恢复时应尽可能选择叶功能型为高LDMC+LOMC-低SLA的群落类型。     

Litter decomposition in a temperate and a tropical stream: the effects of species mixing,litter quality and shredders

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