Quantifying soil organic carbon in complex landscapes: an example of grassland undergoing encroachment of woody plants

The invasion of woody plants into grass‐dominated ecosystems has occurred worldwide during the past century with potentially significant impacts on soil organic carbon (SOC) storage, ecosystem carbon sequestration and global climate warming. To date, most studies of tree and shrub encroachment impacts on SOC have been conducted at small scales and results are equivocal. To quantify the effects of woody plant proliferation on SOC at broad spatial scales and to potentially resolve inconsistencies reported from studies conducted at fine spatial scales, information regarding spatial variability and uncertainty of SOC is essential. We used sequential indicator simulation (SIS) to quantify spatial uncertainty of SOC in a grassland undergoing shrub encroachment in the Southern Great Plains, USA. Results showed that both SOC pool size and its spatial uncertainty increased with the development of woody communities in grasslands. Higher uncertainty of SOC in new shrub‐dominated communities may be the result of their relatively recent development, their more complex above‐ and belowground architecture, stronger within‐community gradients, and a greater degree of faunal disturbance. Simulations of alternative sampling designs demonstrated the effects of spatial uncertainty on the accuracy of SOC estimates and enabled us to evaluate the efficiency of sampling strategies aimed at quantifying landscape‐scale SOC pools. An approach combining stratified random sampling with unequal point densities and transect sampling of landscape elements exhibiting strong internal gradients yielded the best estimates. Complete random sampling was less effective and required much higher sampling densities. Results provide novel insights into spatial uncertainty of SOC and its effects on estimates of carbon sequestration in terrestrial ecosystem and suggest effective protocol for the estimating of soil attributes in landscapes with complex vegetation patterns.     

MEK�CERK-dependent multiple caspase activation by mitochondrial proapoptotic Bcl-2 family proteins is essential for heavy ion irradiation-induced glioma cell death

Recently developed heavy ion irradiation therapy using a carbon beam (CB) against systemic malignancy has numerous advantages. However, the clinical results of CB therapy against glioblastoma still have room for improvement. Therefore, we tried to clarify the molecular mechanism of CB-induced glioma cell death. T98G and U251 human glioblastoma cell lines were irradiated by CB, and caspase-dependent apoptosis was induced in both cell lines in a dose-dependent manner. Knockdown of Bax (BCL-2-associated X protein) and Bak (BCL-2-associated killer) and overexpression of Bcl-2 or Bcl-xl (B-cell lymphoma-extra large) showed the involvement of Bcl-2 family proteins upstream of caspase activation, including caspase-8, in CB-induced glioma cell death. We also detected the activation of extracellular signal-regulated kinase (ERK) and the knockdown of ERK regulator mitogen-activated protein kinase kinase (MEK)1/2 or overexpression of a dominant-negative (DN) ERK inhibited CB-induced glioma cell death upstream of the mitochondria. In addition, application of MEK-specific inhibitors for defined periods showed that the recovery of activation of ERK between 2 and 36 h after irradiation is essential for CB-induced glioma cell death. Furthermore, MEK inhibitors or overexpression of a DN ERK failed to significantly inhibit X-ray-induced T98G and U251 cell death. These results suggested that the MEK–ERK cascade has a crucial role in CB-induced glioma cell death, which is known to have a limited contribution to X-ray-induced glioma cell death.     

城市生态用地分类及其规划的一般原则

城市生态用地的规划布局是城市规划的难点之一,也是急待解决的问题.本文根据城市生态系统的特点,给出了城市生态用地定义,指出城市生态用地同时具有自然属性和社会属性,依据这个特点,将城市生态用地划分为服务型生态用地和功能型生态用地两大类型,并结合具体的城市生态规划对各种类型的生态用地规划进行了定性分析.     

有机碳质量对黄河三角洲芦苇凋落物分解及其温度敏感性的影响

凋落物分解速率及其温度敏感性Q_(10)能够影响凋落物对土壤的碳归还及其对全球变暖的响应。然而,凋落物有机碳质量对凋落物分解及其温度敏感性的影响研究仍不充分。以黄河三角洲芦苇(Phragmites australi)为例,通过凋落物袋法、室内模拟实验及固态~(13)C核磁共振技术,研究有机碳质量对凋落物分解及其温度敏感性的影响,探讨预测凋落物分解及其温度敏感性的指标。结果表明:(1)随着凋落物分解,易分解碳组分(烷氧碳、双烷氧碳)相对含量逐渐降低,而难分解碳组分(芳香碳)相对含量显著增加,疏水碳/亲水碳、芳香碳/烷氧碳比值逐渐增大,凋落物有机碳更加稳定,凋落物呼吸速率及失重率呈下降趋势。(2)凋落物失重主要受烷基碳、烷氧碳相对含量及C/N的影响,凋落物CO_2累积释放量主要受烷氧碳及双烷氧碳相对含量的影响。羰基碳相对含量可以用来解释Q_(10)的变异。因此,相对于生态化学计量比,烷基碳、烷氧碳、双烷氧碳、羰基碳相对含量是预测凋落物分解及其温度敏感性的敏感性指标。     

森林生态系统服务功能及其生态经济价值评估初探——以海南岛尖峰岭热带森林为例

以尖峰岭地区为研究区域,探讨了森林生态系统服务功能的内涵,并使用市场价值、影子工程、机会成本和替代花费等方法评价了海南岛尖峰岭地区热带森林生态系统服务功能的生态经济价值.结果表明,在尖峰岭地区,面积为44667.00hm²的热带森林生态系统服务功能价值平均每年66438.49万元,其中林产品价值为7164.11万元,涵养水源价值为39429.21万元,保持土壤减少侵蚀价值为247.26万元,固定CO₂减轻温室效应的价值为1316.24万元,营养物循环价值为428.55万元,净化空气的价值为17853.12万元.     

亚热带几种典型稻田与旱作土壤中外源输入秸秆的分解与转化差异

选取亚热带四种典型母质(花岗岩风化物、第四纪红色粘土、板页岩风化物、近代河流沉积物)发育的稻田土壤,以毗邻的旱作土壤为对比,通过室内模拟培养试验研究45%田间持水量(WHC)条件下稻田和旱作土壤中外源输入秸秆矿化和转化的特征与差异。结果表明:在180 d的培养期内,所选4种稻田土壤中外源输入秸秆的累积矿化率(18%—21%)均显著低于对应的旱作土壤(21%—28%),外源秸秆的输入对土壤原有有机碳矿化的激发效应也是以稻田土壤(5%—30%)明显低于对应的旱作土壤(17%—65%)。外源秸秆在土壤中的分解产物主要向颗粒有机碳(POC)和铁铝结合态有机碳(Fe/Al-OC)分配,分配比例分别为9%—21%和12%—24%,其次为腐殖质碳(HMC)(11%—15%),而向微生物生物量碳(MBC)和溶解性有机碳(DOC)分配的比例极小,分别仅为2%—7%和0.1%-0.7%。与旱作土壤相比,稻田土壤中外源秸秆的分解产物向POC、Fe/Al-OC和MBC分配的比例较高,分别为15%—21%、17%—24%和6%—7%,而旱作土壤为9%—17%、13%—18%和2%—4%。此外,外源秸秆分解产物向2000—250μm水稳性粗团聚体分配的比例也以稻田土壤(10%—13%)高于旱作土壤(6%—7%),其它粒径中稻田与对应的旱作土壤之间并无显著差异。本研究结果说明,稻田土壤中外源输入秸秆的矿化率低于旱作土壤的现象在不同母质类型的土壤中可能普遍存在,这可能与稻田土壤中外源秸秆分解产物受水稳性团聚体的物理保护、与氧化铁铝的化学键合以及向有机碳稳定组分的分配作用较强有关,从而贡献于稻田土壤较高的有机碳积累。     

Factors Influencing Formation of Sclerotia in Grifola umbellate （Pers.） Pilaet Under Artificial Conditions

The effects of substrate composition and temperature on myceilal growth and sclerotium production in Grlfola umbellate （Pers.） Pilaet were Investigated In the present study. The Induction of sclerotla of G. umbellate was affected greatly by the type of medium, as well as the type of carbon source. Malt-extract agar was able to induce the production of sclerotia. The production of sclerotia was also observed when the carbon source in the GPC agar medium （glucose 20 g/L, peptone 6 g/L, corn steep liquor 10 g/L, and agar 15 g/L） was replaced with glycerol or mannitol. Altering the composition of the GPC medium with milk powder, thiamine hydrochlorlde, extract of Armlllarla mellea, active clay, dlatomite, kaolin, or arginlne did not induce the production of sclerotla. A temperature range of 18-25 ℃ was suitable for both mycellai growth and sclerotium formation. Glycerol significantly Induced slerotium formation on nutrient supplemented with sawdust substrates In bottle culture. 24S-Polyporusterone A and polyporusterone B were assayed In samples of natural and cultured sclerotla. Both natural and cultured sclerotla contained 24S- polyporusterone A and polyporusterone B.     

Effects of supercritical CO2 exposure and depressurization on immobilized lipase activity

Lipozyme IM20 from Novo Nordisk (Denmark) was examined after various treatments. Conditions were chosen to reflect those that would be considered in the design of an industrial process. A two-level factorial design was employed to assess the effects of pressurization/depressurization cycles, rate of depressurization and exposure length. A significant three-factor interaction was observed. Lowest residual activity was observed for runs in which the depressurization rate was 86–89 bar min^–1. Incubation for 12 h also yielded low residual activity but only when exposing the immobilized enzyme to one cycle. The highest residual activity was obtained for immobilized enzymes repeatedly exposed for periods of 12 h (5 times) with a depressurization rate of 4.3 to 4.45 bar min^–1. This effect may be due to the extraction of an inhibiting compound. Tuning process parameters can lead to a seven-fold change in residual activity.     

A protein with an inactive pterin‐4a‐carbinolamine dehydratase domain is required for Rubisco biogenesis in plants

Ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) plays a critical role in sustaining life by catalysis of carbon fixation in the Calvin–Benson pathway. Incomplete knowledge of the assembly pathway of chloroplast Rubisco has hampered efforts to fully delineate the enzyme's properties, or seek improved catalytic characteristics via directed evolution. Here we report that a Mu transposon insertion in the Zea mays (maize) gene encoding a chloroplast dimerization co‐factor of hepatocyte nuclear factor 1 (DCoH)/pterin‐4α‐carbinolamine dehydratases (PCD)‐like protein is the causative mutation in a seedling‐lethal, Rubisco‐deficient mutant named Rubisco accumulation factor 2 (raf2‐1). In raf2 mutants newly synthesized Rubisco large subunit accumulates in a high‐molecular weight complex, the formation of which requires a specific chaperonin 60‐kDa isoform. Analogous observations had been made previously with maize mutants lacking the Rubisco biogenesis proteins RAF1 and BSD2. Chemical cross‐linking of maize leaves followed by immunoprecipitation with antibodies to RAF2, RAF1 or BSD2 demonstrated co‐immunoprecipitation of each with Rubisco small subunit, and to a lesser extent, co‐immunoprecipitation with Rubisco large subunit. We propose that RAF2, RAF1 and BSD2 form transient complexes with the Rubisco small subunit, which in turn assembles with the large subunit as it is released from chaperonins.     

A global study of relationships between leaf traits, climate and soil measures of nutrient fertility

Aim This first global quantification of the relationship between leaf traits and soil nutrient fertility reflects the trade‐off between growth and nutrient conservation. The power of soils versus climate in predicting leaf trait values is assessed in bivariate and multivariate analyses and is compared with the distribution of growth forms (as a discrete classification of vegetation) across gradients of soil fertility and climate. Location All continents except for Antarctica. Methods Data on specific leaf area (SLA), leaf N concentration (LNC), leaf P concentration (LPC) and leaf N:P were collected for 474 species distributed across 99 sites (809 records), together with abiotic information from each study site. Individual and combined effects of soils and climate on leaf traits were quantified using maximum likelihood methods. Differences in occurrence of growth form across soil fertility and climate were determined by one‐way ANOVA. Results There was a consistent increase in SLA, LNC and LPC with increasing soil fertility. SLA was related to proxies of N supply, LNC to both soil total N and P and LPC was only related to proxies of P supply. Soil nutrient measures explained more variance in leaf traits among sites than climate in bivariate analysis. Multivariate analysis showed that climate interacted with soil nutrients for SLA and area‐based LNC. Mass‐based LNC and LPC were determined mostly by soil fertility, but soil P was highly correlated to precipitation. Relationships of leaf traits to soil nutrients were stronger than those of growth form versus soil nutrients. In contrast, climate determined distribution of growth form more strongly than it did leaf traits. Main conclusions We provide the first global quantification of the trade‐off between traits associated with growth and resource conservation ‘strategies’ in relation to soil fertility. Precipitation but not temperature affected this trade‐off. Continuous leaf traits might be better predictors of plant responses to nutrient supply than growth form, but growth forms reflect important aspects of plant species distribution with climate.