Unravelling the complexity of salt marsh ‘Fucus cottonii’ forms (Phaeophyceae,Fucales)

Genetic affiliation, nuclear DNA content, and gamete functioning were examined in small salt marsh Fucus from three localities in western Ireland. Individuals with small and dioecious receptacles were found at all localities, but production of germlings was only evident at Locality 1. Here, the Fucus vegetation formed a morphological cline from F. vesiculosus with bladders in the mid-intertidal to small Fucus individuals lacking bladders in the salt marsh of the upper intertidal. Measurements of nuclear DNA content ranged from 1–1.8 pg at this locality, with F. vesiculosus individuals in the lower range. At the two other localities, the small salt marsh Fucus consisted of distinct morphological entities. Microsatellite analyses revealed that individuals at Locality 2 were derived mainly from F. vesiculosus, whereas those from Locality 3 were hybrids between F. vesiculosus and F. spiralis with greatest affiliation to F. spiralis. While the small salt marsh Fucus forms from Locality 2 had high nuclear DNA content (c. 4 pg) and were probably octoploids, the small salt marsh Fucus from Locality 3 formed two groups: one with high (3.9–4.6 pg) and one with low (1.5–1.9 pg) nuclear DNA content. Nuclear DNA content measured in individuals from Locality 3 varied between 1.1–2.8 pg in F. vesiculosus and 2–3.5 pg in F. spiralis, and showed a more or less stepwise increase in both species, consistent with polyploidy. We hypothesize that the small salt marsh Fucus forms originate from genome size changes in the parental taxa.     

Litter decomposition promotes differential feedbacks in an oligotrophic southern Everglades wetland

The differential accumulation or loss of carbon and nutrients during decomposition can promote differentiation of wetland ecosystems, and contribute to landscape-scale heterogeneity. Tree islands are important ecosystems because they increase ecological heterogeneity in the Everglades landscape and in many tropical landscapes. Only slight differences in elevation due to peat accumulation allow the differentiation of these systems from the adjacent marsh. Hydrologic restoration of the Everglades landscape is currently underway, and increased nutrient supply that could occur with reintroduction of freshwater flow may alter these differentiation processes. In this study, we established a landscape-scale, ecosystem-level experiment to examine litter decomposition responses to increased freshwater flow in nine tree islands and adjacent marsh sites in the southern Everglades. We utilized a standard litterbag technique to quantify changes in mass loss, decay rates, and phosphorus (P), nitrogen (N) and carbon (C) dynamics of a common litter type, cocoplum (Chrysobalanus icaco L.) leaf litter over 64 weeks. Average C. icaco leaf degradation rates in tree islands were among the lowest reported for wetland ecosystems (0.23 ± 0.03 yr⁻¹). We found lower mass loss and decay rates but higher absolute mass C, N, and P in tree islands as compared to marsh ecosystems after 64 weeks. With increased freshwater flow, we found generally greater mass loss and significantly higher P concentrations in decomposing leaf litter of tree island and marsh sites. Overall, litter accumulated N and P when decomposing in tree islands, and released P when decomposing in the marsh. However, under conditions of increased freshwater flow, tree islands accumulated more P while the marsh accumulated P rather than mineralizing P. In tree islands, water level explained significant variation in P concentration and N:P molar ratio in leaf tissue. Absolute P mass increased strongly with total P load in tree islands (r ² = 0.81). In the marsh, we found strong, positive relationships with flow rate. Simultaneous C and P accumulation in tree island and mineralization in adjacent marsh ecosystems via leaf litter decomposition promotes landscape differentiation in this oligotrophic Everglades wetland. However, results of this study suggest that variation in flow rates, water levels and TP loads can shift differential P accumulation and loss leading to unidirectional processes among heterogeneous wetland ecosystems. Under sustained high P loading that could occur with increased freshwater flow, tree islands may shift to litter mineralization, further degrading landscape heterogeneity in this system, and signaling an altered ecosystem state.     

Pine Forest Floor Carbon Accumulation in Response to N and PK Additions: Bomb <Superscript>14</Superscript>C Modelling and Respiration Studies

The addition of nitrogen via deposition alters the carbon balance of temperate forest ecosystems by affecting both production and decomposition rates. The effects of 20 years of nitrogen (N) and phosphorus and potassium (PK) additions were studied in a 40-year-old pine stand in northern Sweden. Carbon fluxes of the forest floor were reconstructed using a combination of data on soil ¹⁴C, tree growth, and litter decomposition. N-only additions caused an increase in needle litterfall, whereas both N and PK additions reduced long-term decomposition rates. Soil respiration measurements showed a 40% reduction in soil respiration for treated compared to control plots. The average age of forest floor carbon was 17 years. Predictions of future soil carbon storage indicate an increase of around 100% in the next 100 years for the N plots and 200% for the NPK plots. As much as 70% of the increase in soil carbon was attributed to the decreased decomposition rate, whereas only 20% was attributable to increased litter production. A reduction in decomposition was observed at a rate of N addition of 30 kg C ha^–1 y^–1, which is not an uncommon rate of N deposition in central Europe. A model based on the continuous-quality decomposition theory was applied to interpret decomposer and substrate parameters. The most likely explanations for the decreased decomposition rate were a fertilizer-induced increase in decomposer efficiency (production-to-assimilation ratio), a more rapid rate of decrease in litter quality, and a decrease in decomposer basic growth rate.     

Microclimate and substrate quality controls on nitrogen mineralization in a New England high salt marsh

New England high salt marsh primary productivity is limited by N, but variation in plant N availability across salt marsh vegetation zones has not been quantified. To investigate this, we measured in situ net N mineralization rates throughout the growing season in three zones of a Maine high salt marsh, Juncus gerardii, Spartina patens, and mixed perennial forb. We also measured microclimate factors (soil temperatures and moistures) and substrate quality parameters (soil organic matter, soil total nitrogen, soil C:N ratio) to see if either related to differences in net N mineralization. To determine the relative importance of substrate quality and microclimate, we measured N mineralization of the different soil types in the laboratory, holding microclimate parameters constant. We also investigated the relative importance of microclimate and substrate statistically, with principal components analysis and multiple regression. In situ net N mineralization rates were significantly higher in the forb zone than in graminoid zones, but graminoid zone N mineralization rates did not vary significantly from each other. Soil temperatures, moistures, carbon, and nitrogen were all significantly higher in the forb zone than in graminoid zones, but C:N ratio did not vary significantly across zones. Principal components analysis and multiple regression revealed that microclimate was a more significant predictor of total N mineralized over the course of the growing season than was substrate quality. In contrast, when microclimate conditions were held constant, forb zone N mineralization was still significantly higher than that of graminoid zones, suggesting that substrate quality does exert some control on this process. Thus, both microclimate and substrate quality appear to influence N mineralization rates across vegetation zones of this Maine salt marsh.     

氮负荷增强对闽江河口芦苇残体分解及其养分释放的影响

选择闽江河口鳝鱼滩西北部的纯芦苇湿地为研究对象,基于野外氮负荷增强分解试验,探讨了氮负荷增强对芦苇残体分解及其养分释放的影响。试验设置了4个氮负荷水平,即NL0（无氮负荷处理,0 g N m^-2 a^-1）、NL1（低氮负荷处理,12.5 g N m^-2 a^-1）、NL2（中氮负荷处理,25.0 g N m^-2 a^-1）和NL3（高氮负荷处理,75.0 g N m^-2 a^-1）。结果表明,不同氮负荷处理下残体的分解速率整体表现为NL2（0.00284 d^-1）>NL1（0.00263 d^-1）>NL0（0.00257 d^-1）>NL3（0.00250 d^-1）,低氮和中氮负荷总体促进了残体分解,而高氮负荷抑制了残体分解,原因主要与不同处理下残体分解过程中基质质量及pH的明显改变有关。不同氮负荷处理下,残体中的全碳（TC）含量在分解期间均呈不同波动变化特征;全氮（TN）和全磷（TP）含量均在分解初期（0-30 d）骤然降低,之后则呈不同波动变化,其中TN含量呈波动上升变化,而TP含量呈小幅波动变化。残留率是影响不同氮负荷处理下残体分解期间碳（C）、氮（N）和磷（P）净释放的共性因素,而氮负荷增强导致的残体基质质量（C/N、C/P、N/P）和主要环境因子（pH、电导率（EC））改变影响了其释放强度。研究发现,在氮负荷增强背景下残体养分的累积与释放发生了明显改变,闽江河口氮负荷水平的增加整体将抑制芦苇残体中C、N养分的释放,但其在分解中后期（90-240 d）可能对P养分释放具有较为明显的促进作用。     

Nitrogen sequestration capacity of two salt marshes from the Tagus estuary

The role of salt marshes as nitrogen sink is examined taking into consideration the seasonal variation of above and belowground biomass of Spartina martima and Halimione portulacoides in two marshes from Tagus estuary, Pancas and Corroios, and the degradation rates of belowground litter. Total nitrogen was determined in plant components, decomposing litter and sediment. Biomass was higher in Corroios, the saltier marsh, with 7190 g m⁻² y⁻¹ dw of S. maritima and 6593 g m⁻² y⁻¹ dw of H. portulacoides and the belowground component contributed to 96% and 90% of total biomass, respectively. In the other marsh, Pancas, belowground biomass contributed to 56% and 76% of total biomass for S. maritima and H. portulacoides, respectively. Litterbag experiment showed that between 25% and 50% of nitrogen is lost within the first month and remained relatively constant in the next four months. Slower decomposition is observed in sediments with higher nitrogen concentration (max. 0.7% N in the saltier marsh). Higher concentrations of N were found in the sediment upper layers. Considering the sediment-root system, most of the nitrogen is stored in the sediment compartment and only about 1–4% of the total N was found in the roots. Considering these results, Tagus salt marshes act as a sink for nitrogen.     

马尾松林两种林下植被土壤碳氮特征及其与凋落物质量的关系

以飞播马尾松林为研究对象,通过典型样地调查和样品测定,采用配对样本t检验和冗余分析（RDA）方法分析芒萁类和禾草类两种林下植被类型土壤碳、氮特征及其与凋落物质量之间的关系。结果表明：（1）土壤有机碳、微生物量碳、可溶性有机碳、全氮、速效氮、微生物量氮和可溶性有机氮含量在0-10、10-20 cm土层均表现为禾草类显著高于芒萁类（P < 0.05）,而在20-40、40-80 cm土层两种植被类型碳氮指标的大小未表现出相同的变化规律,且差异不显著（P > 0.05）。（2）两种植被类型凋落物半分解和未分解层的C含量及C/N值均表现为芒萁类显著高于禾草类（P < 0.05）,而N含量则表现为禾草类显著高于芒萁类（P < 0.05）;同一植被类型的未分解层C含量及C/N值均显著大于半分解层,N含量则半分解层显著大于未分解层（P < 0.05）。（3）0-10 cm土层两种类型凋落物C/N值和C含量均与土壤碳氮各指标呈显著负相关（P < 0.05）,N含量与土壤碳氮各指标的相关性不显著（P > 0.05）;10-20 cm土层,芒萁类的半分解层C/N值与土壤碳氮各指标存在显著相关性（P < 0.05）,禾草类的凋落物C含量与土壤碳氮各指标也存在显著相关性（P < 0.01）。林下植被凋落物C/N值越小,其分解速率越快,有利于土壤养分的积累,禾草类凋落物C/N值低于芒萁类是导致其土壤碳氮指标高于芒萁类的重要原因。     

闽江河口春季互花米草入侵过程对短叶茳芏沼泽土壤碳氮分布特征的影响

2014年4月,选择闽江口鳝鱼滩湿地中未被入侵的短叶茳芏群落(A)、互花米草入侵斑块边缘(B)以及互花米草入侵斑块中央(C)为研究对象,基于时空互代研究方法,探讨了互花米草入侵序列下湿地土壤碳氮空间分布特征的差异。结果表明,互花米草入侵显著降低了土壤的NO_3~--N含量(P0.05),但整体增加了NH_4~+-N含量,这与其入侵后导致湿地土壤颗粒组成发生显著变化(砂砾含量增加33.81%),进而促进了土壤的矿化作用和硝化作用,并有助于硝态氮的垂直淋失有关。互花米草入侵整体增加了土壤的碳氮含量和C/N比,与入侵进程和入侵前相比,互花米草入侵后湿地土壤的碳储量分别增加了8.73%和24.37%,氮储量则分别增加了10.22%和17.87%,这主要与其对闽江口湿地植物群落格局、养分生物循环以及强促淤作用引起的土壤颗粒组成等显著改变有关。研究发现,闽江口互花米草入侵对短叶茳芏湿地土壤碳氮含量的影响相对于江苏盐城、长江口以及杭州湾湿地的影响可能更为显著,其互花米草入侵较大改变了土壤中陆源和海源有机质的来源比例,使得入侵后湿地土壤养分的自源性增强。     

High Organic Carbon Export Precludes Eutrophication Responses in Experimental Rocky Shore Communities

We studied the effect of nutrient inputs on the carbon (C) budget of rocky shore communities using a set of eight large experimental mesocosms. The mesocosms received a range of inorganic nitrogen (N) and phosphorus (P) additions, at an N:P ratio of 16. These additions were designed to elevate the background concentration, relative to that in eutrophic Oslofjord (Norway) waters, by 1, 2, 4, 8, 16, 32 μmol dissolved inorganic nitrogen (DIN)l⁻¹ (and the corresponding P increase). Two unamended mesocosms were used as controls. The nutrients were added continuously for 27 months before gross primary production (GPP), respiration (R), net community production (NCP), and dissolved organic carbon (DOC) production were assessed for the dominant algal species (Fucus serratus) and for the whole experimental ecosystem. Inputs and outputs of DOC and particulate organic carbon (POC) from the mesocosms were also quantified. The F. serratus communities were generally autotrophic (average P/R ratio = 1.33 ± 0.12), with the GPP independent of the nutrient inputs to the mesocosms, and maintained a high net DOC production during both day (0.026 ± 0.008 g C m⁻² h⁻¹) and night (0.015 ± 0.004 g C m⁻² h⁻¹). All the experimental rocky shore ecosystems were autotrophic (P/R ratio = 2.04 ± 0.28), and neither macroalgal biomass nor production varied significantly with increasing nutrient inputs. Most of the excess production from these autotrophic ecosystems was exported from the systems as DOC, which accounted for 69% and 58% of the NCP of the dominant community and the experimental ecosystem, respectively, the rest being lost as POC. High DOC release and subsequent export from the highly energetic environments occupied by rocky shore communities may prevent the development of eutrophication symptoms and render these communities resistant to eutrophication. Received 10 October 2001; accepted 18 July 2002.     

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。     

Bioturbation of Burrowing Crabs Promotes Sediment Turnover and Carbon and Nitrogen Movements in an Estuarine Salt Marsh

Ecological functions of bioturbation in ecosystems have received increasing attention over the recent decades, and crab burrowing has been considered as one of the major bioturbations affecting the physical and chemical processes in salt marshes. This study assessed the integrated effects of crab excavating and burrow mimic trapping on sediment turnover and vertical C and N distributions in a Chinese salt marsh in the Yangtze River estuary. Crab burrowing increased soil water content and the turnover of carbon and nitrogen and decreased bulk soil density. Vertical movement of materials, nutrient cycling and reuse driven by crab burrowing might be obstructed by vegetation (Phragmites australis and Spartina alterniflora communities). The amount of soil excavated by crab burrowing was higher than that deposited into burrow mimics. In Phragmites marshes, Spartina marshes and unvegetated mudflats, net transport of soil to the marsh surface was 171.73, 109.54, and 374.95 g m⁻² d⁻¹, respectively; and the corresponding estimated soil turnover time was 2.89, 4.07 and 1.83 years, respectively. Crab burrowing in salt marshes can mix surface and deeper soil over a period of years, accelerating litter decomposition and promoting the efficient reuse of nutrients by plants. Therefore, bioturbation affects soil physical processes and functioning of ecosystems, and needs to be addressed in ecosystem management.     

高原山地石漠化过程中土壤团聚体稳定性及其化学计量特征

石漠化演替过程中不同石漠化等级土壤团聚体稳定性及其碳、氮、磷化学计量特征是评价石漠化地区土壤恢复效应的有效途径.该文以五个不同石漠化等级的样地为研究对象,利用湿筛法分析0～20 cm土层土壤不同粒级团聚体分布状况、稳定性水平和化学计量特征.结果表明:(1)相较而言,无石漠化样地中>2 mm和0.25～2 mm两级水稳性...     

Stable carbon and nitrogen isotope signatures of decomposing tropical macrophytes

The Pantanal of Mato Grosso, Brazil, is a large, seasonal wetland, which exhibits high macrophyte productivity at the beginning of the rainy season, when the floodplain becomes flooded. During inundation, from December through May, there is rapid turnover of decomposing macrophyte litter, which is subsequently colonized and consumed by various organisms. In this paper, the variation in the carbon and nitrogen isotope signatures of decomposing macrophytes and detritus was determined to provide an isotopic baseline for the elucidation of higher trophic levels. Seven abundant macrophyte species, Cyperaceae sp., Pontederia lanceolata, Cabomba furcata, Salvinia auriculata, Eichhornia crassipes, Nymphaea amazonum and Paspalum repens, were exposed in mesocosm decomposition experiments lasting 21 or 100 days. Stable isotope ratios of carbon and nitrogen and the atomic C/N ratios were determined for decomposing plant material, particulate organic matter (POM), the microbial film, and aquatic invertebrate larvae. The ¹³C values for the macrophytes did not change during decomposition. However, the variability of ¹⁵N was high (range of ± 6 ) due to microbial activity. There was no consistent difference in the isotopic signatures of macrophytes and POM. C/N ratios decreased from 17 to 50 in macrophytes, to 7 to 12 in POM. The isotopic signatures and C/N ratios of the microbial film were the same as those of POM. We concluded that heterotrophic processes did not fractionate stable carbon isotopes but caused an increase in the variability of stable nitrogen ratios and a change in the C/N ratios in our experimental system. Therefore, it was not possible to distinguish fresh and senescent material or even POM when used as a food source. The ¹³C values of the aquatic larvae were closely coupled to those of the carbon source provided.     

Nitrogen availability affects saprotrophic basidiomycetes decomposing pine needles in a long term laboratory study

Fungi, especially basidiomycetous litter decomposers, are pivotal to the turnover of soil organic matter in forest soils. Many litter decomposing fungi have a well-developed capacity to translocate resources in their mycelia, a feature that may significantly affect carbon (C) and nitrogen (N) dynamics in decomposing litter. In an eight-month long laboratory study we investigated how the external availability of N affected the decomposition of Scots pine needles, fungal biomass production, N retention and N-mineralization by two litter decomposing fungi – Marasmius androsaceus and Mycena epipterygia. Glycine additions had a general, positive effect on fungal biomass production and increased accumulated needle mass loss after 8 months, suggesting that low N availability may limit fungal growth and activity in decomposing pine litter. Changes in the needle N pool reflected the dynamics of the fungal mycelium. During late decomposition stages, redistribution of mycelium and N out from the decomposed needles was observed for M. epipterygia, suggesting autophagous self degradation.     

Nutrient release from decomposing leaf litter of Banksia ornata,Dark Island heathland,South Australia

Distinct O₁ and O₂ layers, representing annual litter fall, enabled the sequential loss of biomass and nutrients (phosphorus and nitrogen) to be reconstructed in undisturbed litter layers of Banksia ornata in the Dark Island heathland, South Australia. Apart from an initial loss in biomass and nitrogen, the dry weight and nutrient content of the O₁ layer, exposed to the desiccating influence of the atmosphere, remained relatively constant until covered by the following year's leaf fall. Under the blanket of newly fallen leaves, biomass decomposition proceeded continuously through autumn, winter, spring, into the dry summer season. Even though the biomass of the decomposing leaf (O₂) layer decreased continuously, its nutrient content remained relatively constant until the summer season was reached when total decomposition and nutrient loss occurred. During spring, fine rootlets invaded the decomposing litter layer (O₂) and, together with decomposer fungi, bacteria and soil fauna, maintained the total nutrient content of the decomposing leaf at a constant level. By late spring-early summer shoot growth of the dominant heath species was initiated, inducing the mobilization of the nutrients stored in the decomposing litter layer.     

EFFECT OF AN AMMONIUM NITRATE PULSE ON THE GROWTH AND ELEMENTAL COMPOSITION OF NATURAL STANDS OF SPARTINA ALTERNIFLORA AND JUNCUS ROEMERIANUS

A nitrogen (ammonium nitrate) pulse of 200 kg ha“¹ was added to stands of tall (1.0–1.5 m) Spartina alterniflora, short (< 0.5 m) Spartina alterniflora, and Juncus roemerianus in a Georgia salt marsh in July. The major response ten weeks later was an increase in the aerial biomass and a sharp reduction in the C/N ratio in short Spartina alterniflora. One year after the treatment the difference between the biomass in enriched and control plots was greater than ten weeks after treatment, but the C/N ratio in the plants in the treated plots had risen to that of the controls. The availability of nitrogen appears to limit growth in the middle elevation Georgia salt marsh (short S. alterniflora), but not in the lower (tall S. alterniflora) or higher (J. roemerianus) portions.     

氮输入对滨海盐沼湿地碳循环关键过程的影响及机制

滨海盐沼湿地是缓解全球变暖的有效蓝色碳汇, 但是近岸海域富营养化导致的大量氮输入对盐沼湿地稳定性和碳汇功能构成严重威胁。潮汐作用下大量氮输入对盐沼湿地植物光合碳输入、植物-土壤碳分配和土壤碳输出等碳循环关键过程产生深刻影响, 进而影响盐沼湿地碳汇功能评估的准确性。该文从植物光合固碳、植物-土壤系统碳分配、土壤有机碳分解、土壤可溶性有机碳释放、盐沼湿地土壤碳库5个方面综述了氮输入对盐沼湿地碳循环关键过程的影响。在此基础上, 针对当前研究的不足, 提出今后的研究中, 需要进一步探究氮输入对盐沼湿地植物光合固碳及碳分配过程的影响、盐沼湿地土壤有机碳分解的微生物机制、盐沼湿地土壤可溶性有机碳产生和横向流动的影响、以及氮类型对盐沼湿地土壤碳库的影响。以期为揭示氮输入对盐沼湿地碳汇形成过程与机制提供基础资料和理论依据, 为评估未来近岸海域水体富营养化影响下滨海盐沼湿地碳库的潜在变化提供新思路。     

Controls on decomposition and soil nitrogen availability at high latitudes

At high latitudes, decomposition rates and soil nitrogen (N) availability are pivotal in determining ecosystem responses to climate change. The effects of temperature, soil moisture content, resource quality, and saprotrophic fungi as an example of soil organisms, on carbon (C) and N mineralisation are reviewed. The controls on N availability are less well characterised than those on decomposition, and C and net N mineralisation sometimes do not respond to these controls in a parallel manner. Increases in mean summer temperatures of 2–4°C predicted for high latitudes may not necessarily cause greater rates of decomposition and N mineralisation because of concomitant small rises in soil temperature together with interactions between the controls, including interactions of the temperature and moisture content of the substrata with the diversity and function of decomposer fungi. Research on decomposition and soil N availability has been carried out at several scales, at all of which future research remains necessary. It is not clear whether species diversity of decomposer fungi influences decomposition and C and N release above the microscale.     

Characteristics of culm structure and carbon and nitrogen concentrations in dead bamboo culms of two Phyllostachys species

The tissue structure of a bamboo stem (culm) differs from that of woody species, exhibiting a large cavity in the internode surrounded by a cortex with high silica concentration. Thus, to obtain an accurate estimation of the necromass, as well as carbon (C) and nitrogen (N) stocks in dead bamboo culms, we examined the basic characteristics of culm structure as well as the C and N concentrations of decomposing culms of Phyllostachys bambusoides and P. heterocycla. We collected dead culms of the two bamboo species from 15 bamboo stands in central and southwestern Japan, and analyzed the relationship between the ratio of wall volume to culm disk volume and culm diameter, as well as the changes of C and N concentrations in dead culms with wall density, which can be used as an indicator of the degree of decomposition. The ratio of wall volume to culm volume tended to decrease with increasing culm diameter for both species. The C concentration did not change, but the N concentration increased with decreasing wall density. The wall density was related to the C/N ratio, which is a chemical parameter of the degree of decomposition. The culm structure should be considered when estimating culm density. The mean C concentration can be used for estimating the C stock of decomposing culms irrespective of decomposition level. N concentration, however, should be determined according to decomposition level for N stock estimation.     

人工调控措施下马尾松凋落叶化学质量变化及与分解速率的关系

马尾松凋落叶分解缓慢,促进其凋落物分解,提高养分归还速度,维持地力稳定,已成为马尾松人工林可持续经营中的关键问题。基于此,采用正交试验L_9(3~4)设计,选择菌剂、表面活性剂、不同碳氮营养液和有机肥料4种人工调控因素,在马尾松林下开展凋落叶分解调控试验,以掌握不同调控组合对凋落叶分解速率和化学质量的影响及作用效果等。结果表明:有机肥料和菌剂显著影响马尾松凋落叶分解速率,腐解剂2和鸡粪联合作用更利于分解。马尾松凋落叶在林下自然分解过程中,化学质量参数向着利于分解的方向变化,N、P以积累为主,C/N、C/P、L/N和L/P呈降低态势,人为调控措施加速了这一变化进程;不同调控措施对凋落叶化学质量参数的影响不尽相同,添加有机肥料有利于剩余凋落叶N、P含量升高,C/N、C/P、L/N和L/P的降低;菌剂腐解剂2有利于L/P、C/P的降低;表面活性剂OP-10有利于凋落叶L/N的降低。人工调控下,调控因素可通过改变凋落物化学质量影响其分解速率,N含量和C/N是影响马尾松凋落叶分解速率的主要因素;而P浓度、L/N、C/P、L/P对分解速率的影响不规律或不显著。