佛山城市典型森林群落土壤重金属分布、流通及枯落物富集特征

富集重金属的枯落物分解可能提高重金属暴露率,增加人体接触健康风险。为了解南方城市土壤重金属在森林生态系统中的分布及流转情况,通过调查研究了佛山市8个典型森林群落土壤及枯落物重金属含量,分析了各森林群落枯落物对不同重金属的富集效应及重金属随枯落物回归土壤流通量。结果表明：1）城市森林各土壤重金属含量在不同典型群落间差异显著（P<0.05）,差异最大为Pb、Cr、Zn,As、Cu、Ni次之,Hg、Cd最小;土层深度（0-20,20-40,40-60 cm）对重金属含量影响显著（P<0.05）,差异最大为Cd、Hg,其次为As、Cu,最小为Zn、Ni、Pb、Cr。整体上,Cd、Hg、As、Pb、Zn在0-20 cm最高,表层富集特征明显,Cr和Ni在40-60 cm最高。2）8个森林群落中阴香-白楸-醉香含笑群落（CMMC）枯落物对8种重金属的综合富集系数（TBCF,66.76）最高,其中以Cd的富集效果最突出,富集系数为44.45,且对Pb、Cu、Zn也相对富集;最低的为黧蒴锥-香椿-樟树群落（CTCC）,综合富集系数（TBCF）为8.09,仅对Cd、Cr、Cu相对富集,对其余重金属富集效应不明显。3）相关分析显示,群落重金属枯落物流通量与0-60 cm土壤重金属平均含量（Cr和Ni除外）无显著相关性。本研究对城市森林建设管理及筛选重金属富集植物及群落具有较强理论及实践意义。     

西沙永兴岛抗风桐与海岸桐群落凋落叶分解及中型土壤动物的贡献

我国南海诸岛主要是珊瑚岛。植物凋落物分解是生态系统元素循环的关键环节,但目前关于南海珊瑚岛生态系统凋落物分解的研究还是空白。以我国西沙群岛的优势树种抗风桐（Pisonia grandis）和海岸桐（Guettarda speciosa）为研究对象,采用凋落物袋法,分别于分解期间的第3、6、9、13和15个月取样,探究中型土壤动物对两种植物群落中凋落物分解过程中质量损失和养分释放的影响。结果表明：与没有中型土壤动物存在的情况（0.1 mm凋落物袋）相比,分解开始后的6个月内,中型土壤动物存在（2 mm凋落物袋）使抗风桐和海岸桐凋落叶分解速率分别提高了12.3%和4.8%（P<0.05）;分解6-15个月期间,中型土壤动物存在使抗风桐和海岸桐凋落叶分解速率分别提高了33.0%和12.3%（P<0.05）。中型土壤动物排除显著影响了不同分解阶段凋落叶总碳（Total carbon,TC）、总氮（Total nitrogen,TN）、纤维素、木质素和半纤维素的残留率变化。中型土壤动物群落组成受土壤温度显著影响（P<0.05）,它们对凋落叶分解的贡献可能主要受优势类群如真螨目和寄螨目的影响。相较海岸桐,抗风桐凋落叶的分解周期更短,中型土壤动物对其的贡献更大;选用抗风桐作为南海珊瑚岛退化植被恢复或新建的先锋种对促进生态系统元素循环更有利。     

不同地下水位灰化薹草分解过程中木质素降解与碳、氮、磷释放的关系

为研究湿地植物分解过程中木质素分解与碳、氮、磷元素释放之间的关系及其对不同地下水位环境梯度的响应,在鄱阳湖典型碟形湖泊-白沙湖设置了200 m×300 m分解试验样地,沿地下水位梯度划分4个试验样带(从湖岸到湖心依次为GT-A, GT-B, GT-C, GT-D),采用分解袋法模拟了典型湿地植物灰化薹草在不同地下水位环境的分解过程。结果表明,分解15 d后,地下水位的升高促进了木质素的分解和碳、氮、磷元素的释放;在分解第60—90天,碳、氮、磷元素的相对归还指数随着木质素分解速率的升高而显著增大,并且相关性程度随着分解时间先增强,后减弱;分解过程中土壤pH、含水量和微生物量碳、氮对木质素的分解和碳、氮、磷元素的归还具有显著的促进作用。研究结果将有助于深化对湿地植物分解和生物地球化学循环过程的认识,为湿地自然保护区的科学有效管理提供理论依据。     

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.     

Habitat matters – Strong genetic and epigenetic differentiation in Linum catharticum from dry and wet grasslands

Plant species differ in their ecological amplitude, with some species occurring in very different habitats under strongly differentiated environmental conditions. We were interested in to what extent the occurrence of Linum catharticum in dry calcareous grasslands (Bromion) and wet litter meadows (Molinion), two habitats on opposing ends concerning, for example, moisture level, is reflected on the genetic and epigenetic level. Using AFLP (amplified fragment length polymorphisms) and MSAP (methylation sensitive amplification polymorphisms) analyses, we studied the genetic and epigenetic variation of L. catharticum from calcareous grasslands and litter meadows. From each habitat, we included five study sites with 16 individuals per sampling location. We observed lower genetic than epigenetic diversity, but considerable differentiation among habitats, which was stronger on the genetic than the epigenetic level. Additionally, we observed a strong correlation of genetic and epigenetic distance, irrespective of geographic distance. The dataset included a large portion of fragments exclusively found in individuals from one or the other habitat. Some epigenetic fragments even occurred in different methylation states depending on the habitat. We conclude that environmental effects act on both the genetic and epigenetic level, producing the clear differentiation among plant individuals from calcareous grasslands and litter meadows. These results may also point into the direction of ecotype formation in this species.     

Drought conditions alter litter decomposition and nutrient release of litter types in an agroforestry system of China

Evaluating how decomposition rates and litter nutrient release of different litter types respond to changes in water conditions is crucial for understanding global carbon and nutrient cycling. However, it is unclear how decreasing water affects litter mixture interactions for the maize–poplar system in arid regions. Here, the responses of the litter decomposition process and litter mixture interactions in the agroforestry system to changes in water conditions (control, light drought, and moderate drought) were tested. Moderate drought significantly decreased the decomposition rate for poplar leaf and mixed litters, and decomposition rate was significantly reduced for maize straw litter in light and moderate drought stress. The mass loss rates of maize straw and mixed litters were significantly higher than that of the poplar leaf litter under drought conditions, but there was no significant difference among the three litter types in the control. There was no interaction between mass loss of the mixed litter in the control and light drought conditions, and the litter mixture interaction showed nonadditive synergistic interactions under moderate drought. In terms of nutrient release, there was also no interaction between litter mixture with nitrogen and carbon, but there was antagonistic interaction with potassium release under the light drought condition. Our results demonstrate that drought conditions can lead to decreasing decomposition rate and strong changes in the litter mixture interactions from additive effects to nonadditive synergistic effects in moderate drought. Moreover, light drought changed the mixture interaction from an additive effect to an antagonistic interaction for potassium release.     

Influence of culinary treatment on the concentration and on the bioavailability of cadmium,chromium, copper,and lead in seafood

BackgroundSeafood present important advantages for human nutrition, but it can also accumulate high levels of toxic and potentially toxic elements. Culinary treatments could influence seafood chemical element content and element bioavailability. In this study, the influence of culinary treatments on the total concentration and on the bioavailability of Cd, Cr, Cu and Pb in shark, shrimp, squid, oyster, and scallop was assessed.MethodsBoiling, frying, and sautéing with or without seasonings (salt, lemon juice and garlic) were evaluated. Total concentration and bioavailability of Cd, Cr, Cu and Pb in seafood after all these culinary treatments were compared with those in uncooked samples. Analytes were determined by triple-quadrupole inductively coupled plasma mass spectrometry (ICP-MS/MS). An alternative to express the results avoiding underestimated or overestimated values was proposed.ResultsThe analytes concentration in seafood without culinary treatment varied from 0.0030 μg g⁻¹ (shrimp) to 0.338 μg g⁻¹ (oyster) for Cd; 0.010 μg g⁻¹ (squid) to 0.036 μg g⁻¹ (oyster) for Cr; 0.088 μg g⁻¹ (scallop) to 8.63 μg g⁻¹ (oyster) for Cu, and < 0.005 μg g⁻¹ (shrimp, squid and oyster) to 0.020 μg g⁻¹ (shark) for Pb. Only Cd (in scallop) was influenced by culinary treatments (reduction from 37 to 53 % after boiling, frying, and sautéing). Bioavailability percentage varied from 11% (oyster) for Cd; 18% (oyster) to 41% (shark) for Cr; 6% (shark) for Cu, and 8% (oyster) for Pb. Bioavailability percentage was not influenced by culinary treatments.ConclusionCadmium concentration was reduced in scallop after some culinary treatments (reduction o 37-53% after boiling, frying, and sautéing), but bioavailability percentage was not influenced. The employed analytical method was adequate for the purpose, presenting import results for food safety assessment about the influence of culinary treatments on metals concentration and bioavailability in seafood.     

林下植被和凋落物对寒温带森林生长季土壤CH4通量的影响

为进一步探究林下植被和凋落物管理对我国寒温带森林生长季土壤CH₄通量的影响,采用静态箱-气相色谱法对大兴安岭北部4种林型（白桦林、山杨林、樟子松林和兴安落叶松林）4种处理（自然状态、去除凋落物、去除林下植被以及去除林下植被和凋落物）的土壤CH₄通量排放特征进行观测研究。结果表明：该地区森林生长季土壤均表现为CH₄的汇,4种林型不同处理后土壤CH₄通量表现为单峰变化趋势,吸收峰值出现在7月或8月。自然状态4种林型土壤CH₄平均吸收通量表现为白桦林（-79.23±14.92）μg m^-2 h^-1>山杨林（-64.27±9.60）μg m^-2 h^-1>樟子松林（-62.54±15.48）μg m^-2 h^-1>兴安落叶松林（-48.73±12.26）μg m^-2 h^-1,兴安落叶松土壤CH₄平均吸收通量显著小于其他三种林型（P<0.05）。相比于自然状态,4种林型在去除凋落物后土壤CH₄吸收通量提高了2.12%-12.15%,但变化幅度均没有达到显著水平（P>0.05）。去除林下植被后4种林型CH₄吸收通量提高了0.84%-20.55%,且只有山杨林吸收增加达到显著水平（P<0.05）。同时去除林下植被和凋落物后,对白桦林和樟子松土壤CH₄通量影响不显著（P>0.05）,但对山杨林和兴安落叶松林影响显著（P<0.05）。总之,去除凋落物或林下植被均会提高土壤对CH₄吸收,去除林下植被对土壤CH₄通量的影响要大于去除凋落物的影响,但不同林型不同处理之间还存在差异。     

模拟冻融环境下亚高山森林凋落物分解速率及有机碳动态

森林凋落物分解是森林生态系统物质循环的重要环节,季节性冻融交替是影响凋落物分解的重要环境因素之一,但不同林型的凋落物对冻融响应的差异性很少被量化。为了解冻融环境对森林凋落物分解进程的影响,以川西亚高山森林地区阔叶林、针叶林和针阔混交林3种典型林型的凋落物为实验材料,从凋落物基质质量、冻融环境等影响凋落分解的因素着手,采用模拟冻融循环过程（-5-5℃）,研究了冻融循环中3种林型凋落物分解速率和有机碳含量的动态变化。结果发现,3中典型林型凋落物经过不同冻融处理后,其质量损失、质量损失速率均存在显著差异（P<0.05）。混交林凋落物和针叶林凋落物的分解速率呈慢-快-慢的趋势,而阔叶林凋落物的分解速率逐渐减小。在冻融循环处理下,3种林型的凋落物碳绝对含量呈波动下降的趋势,说明微生物固定外源碳和凋落物释放碳间存在动态平衡。相同林型的凋落物在不同冻融处理下,有机碳释放有显著差异（P<0.05）。其中,冻融环境显著（P<0.05）促进了混交林凋落物和针叶林凋落物有机碳的释放,但是对阔叶林凋落物有机碳的释放没有起到促进作用。这表明全球气候变暖情景下,亚高山森林土壤冻融事件频发将加快凋落物的分解,但变化程度受到凋落物质量控制。     

改变碳输入对沂蒙山区典型次生林土壤微生物碳源代谢功能的影响

凋落物和根系向土壤的碳输入是森林生态系统的关键过程,输入量及组分的变化直接影响森林土壤碳汇功能和生产力。在沂蒙山区栎类天然次生林中,开展添加/去除凋落物及去除根系的定位控制试验。于控制试验开展21个月后,采用Biolog Eco微平板培养法,研究凋落物和根系对土壤微生物碳源代谢功能的影响。结果表明,凋落物倍增处理增加了土壤微生物碳源代谢功能,增加了对糖类和胺类的代谢能力。去除凋落物处理、去除根系处理和无输入处理都降低了土壤微生物碳源代谢功能。去除凋落物处理降低土壤微生物碳源代谢功能的幅度大于去除根系处理,表明当前条件下凋落物对土壤微生物碳源代谢功能的影响大于根系,但如果抛除掉去除根系处理中残留根系的影响,凋落物和根系对土壤微生物碳源代谢功能的相对大小可能会发生变化。土壤有机碳含量、铵态氮含量显著影响微生物碳源代谢多样性（P<0.05）,并与碳源代谢功能正相关。凋落物倍增处理通过增加土壤铵态氮和有机碳含量,增加微生物碳源代谢功能,去除凋落物处理和无输入处理通过降低土壤铵态氮和有机碳含量,降低微生物碳源代谢功能。结果深化了碳输入途径（地上凋落物与地下根系）和数量（凋落物倍增、凋落物去除与对照）对温带栎类天然次生林土壤碳代谢过程的认识。