北京东灵山暖温带典型植被类型物种构成及物种多样性对氮素转化过程的影响

通过调查东灵山地区7个典型植被类型的物种多样性，并测定各林型中植物叶片养分特征，凋落物品质，土壤理化特性，豆科植物的生物固氮作用以及土壤有机质的净N矿化与硝化作用，研究了不同林型及其物种多样性对氮素转化过程的可能影响。结果表明： 1) 各林型乔灌草三层13个物种多样性指数之间都不同程度存在差异，且都表现基本一致的大小顺序，各样地乔灌草三层3个丰富度指数和5个多样性指数之间大都表现草本层>灌木层>乔木层的大小顺序。 2) 林型对植物叶片养分特征、叶片凋落物品质指标、土壤的大多数理化特性都有显著影响，其中，落叶阔叶林与针叶林之间的差异最为明显，优势种不同的针叶林之间也不同程度地存在差异。各林型物种多样性对植物叶片养分特征，凋落物品质和土壤理化特性也都不同程度存在显著影响，且乔灌草三层的物种多样性的影响不同。我们的结果支持物种多样性对生态系统过程存在显著影响的观点。 3) 胡枝子(Lespedeza bicolor)％FNDA值较低，在0～53.3％之间，与国外学者对某些木本豆科固氮植物的研究结果接近，但低于三叶草、野豌豆等草本豆科固氮植物。胡枝子生物固氮具有明显的季节差异，不同样地生境对胡枝子％FNDA值也存在显著影响，大都都表现铁塔辽东栎样地>重力点样地>站下灌丛样地>垭口样地的趋势。除胡枝子之外的其他豆科植物的％FNDA都高于胡枝子，且存在种间差异，以三籽两型豆(Amphicarpaea capillipes)最高(100％)，歪头菜(Vicia unijuga)最低(平均66.4％)，这些结果与国外相关研究接近。不同林型之间和同一林型不同样地之间也影响豆科植物的％FNDA。东灵山地区有相当数量的植物种具有和固氮植物相近的δ15N值和全N含量，具有潜在的生物固氮能力。6个林型中所有豆科植物的％FNDA平均值主要受乔木层和草本层物种多样性的影响，乔木层和草本层物种多样性提高，豆科植物的％FNDA将随之显著降低。 4) 气温、土壤温度和降水量显著影响各林型净氮硝化速率的季节动态，都表现为温度升高，降水量增加，净氮硝化速率也随之增大。 5) 在不同取样时间，不同林型在土壤NH4+、N03-含量，矿化、硝化速率以及年度总净矿化、硝化量之间均不同程度存在显著差异，其中，以辽东栎落叶阔叶林与针叶林之间，常绿针叶林与落叶针叶林之间，纯林与混交林之间的差异最为明显。 6) 土壤初始N0_3含量与年度总净硝化量，年度总净矿化量及其占TKN的百分比呈显著正相关关系;植物叶片全N浓度与净氮矿化、硝化作用呈显著负相关：植物叶片凋落物的品质指标与净氮矿化、硝化作用没有显著相关。 7) 胡枝子固氮作用(％FNDA值)越强，土壤有机氮的净硝化量就越大，胡枝子在从大气中获取大量N，的同时，很可能会增加氮素的淋溶损失量。胡枝子固氮作用(％FNDA值)与净氮矿化量不存在显著相关关系。 8) 只有乔木层和草本层部分种多样性指数对净氮矿化、硝化量存在显著影响。乔木层均匀度提高，土壤净氮碳化量将随之增大;而草本层物种多样性提高，均匀度提高，净氮矿化、硝化作用将随之降低，草本层植物对土壤氮素矿化作用具有显著抑制作用。 9) 落叶阔叶林与针叶林的供氮能力和维持无机氮素的能力之间存在比较明显的差异，而不同针叶林的矿化／硝化作用也有所差别。其中，辽东栎落叶阔叶林的供氮能力和维持氮素能力均高于针叶林和山杏灌丛;油松林的供氮能力与防止氮素损失的能力显然要强于落叶松林和山杏灌丛。 10) 尽管箭叶锦鸡儿灌丛植物叶片与凋落物中全N、全P浓度在大多数取样点上都低于硕桦(高于草甸)，但表层土中全N浓度高于硕桦和草甸，且其土壤有机质的供氮能力以及维持氮素能力都高于硕桦林和草甸，表明，锦鸡儿灌丛为侵入草甸和硕桦入侵提供了良好的养分条件，在该演替序列的发展过程中起了一定的推动作用。

Drivers of soil net nitrogen mineralization in the temperate grasslands in Inner Mongolia, China

Soil net nitrogen mineralization (NNM) of four grasslands across the elevation and precipitation gradients was studied in situ in the upper 0-10 cm soil layer using the resin-core technique in Xilin River basin, Inner Mongolia, China during the growing season of 2006. The primary objectives were to examine variations of NNM among grassland types and the main influencing factors. These grasslands included Stipa baicalensis (SB), Aneulolepidum Chinense (AC), Stipa grandis (SG), and Stipa krylovii (SK) grassland. The results showed that the seasonal variation patterns of NNM were similar among the four grasslands, the rates of NNM and nitrification were highest from June to August, and lowest in September and October during the growing season. The rates of NNM and nitrification were affected significantly by the incubation time, and they were positively correlated with soil organic carbon content, total soil nitrogen (TN) content, soil temperature, and soil water content, but the rates of NNM and nitrification were negatively correlated with available N, and weakly correlated with soil pH and C:N ratio. The sequences of the daily mean rates of NNM and nitrification in the four grasslands during the growing season were AC > SG > SB > SK, and TN content maybe the main affecting factors which can be attributed to the land use type.

In vivo mineralization and osteogenesis of nanocomposite scaffold of poly (lactide-co-glycolide) and hydroxyapatite surface-grafted with poly(L-lactide)

Nanocomposite of hydroxyapatite (HAP) surface-grafted with poly(L-lactide) (PLLA) (g-HAP) shows a wide application for bone fixation materials due to its improved interface compatibility, mechanical property and biocompatibility in our previous study. In this paper, a 3-D porous scaffold of g-HAP/poly (lactide-co-glycolide) (PLGA) was fabricated using the solvent casting/particulate leaching method to investigate its applications in bone replacement and tissue engineering. The composite of un-grafted HAP/PLGA and neat PLGA were used as controls. Their in vivo mineralization and osteogenesis were investigated by intramuscular implantation and replacement for repairing radius defects of rabbits. After surface modification, more uniform distribution of g-HAP particles but a lower calcium exposure on the surface of g-HAP/PLGA was observed. Intramuscular implantation study showed that the scaffold of g-HAP/PLGA was more stable than that of PLGA, and exhibited similar mineralization and biodegradability to HAP/PLGA at the 12-20 weeks post-surgery.

Autumn net copepod abundance and assemblages in relation to water masses on the continental shelf of the Yellow Sea and East China Sea

Copepod species diversity, abundance and assemblages in relation to water masses over the continental shelf of the Yellow Sea (YS) and East China Sea (ECS) were studied extensively based on the net plankton samples in autumn 2000. Multivariate analysis based on copepod assemblage resulted in recognition of five groups (Groups 1-5) corresponding to the water masses. Groups 1 and 2 delineated from inshore stations with low salinity YS Surface Water, and offshore stations with YS Cold Water in the YS. Group 3 located in the joint area of YS and ECS mainly with Mixed Water. Groups 4 and 5 in the ECS delineated two assemblages mainly from inshore and shallow stations with ECS Mixed Water in the southeastern ECS, and offshore stations along the ECS shelf edge controlled by saline Kuroshio Water. Salinity and temperature were more important in characterizing copepod assemblage of the continental shelf than chlorophyll a. (c) 2005 Elsevier B.V. All rights reserved.

Net primary productivity and spatial distribution of vegetation in an alpine wetland, Qinghai-Tibetan Plateau

To initially describe vegetation structure and spatial variation in plant biomass in a typical alpine wetland of the Qinghai-Tibetan Plateau, net primary productivity and vegetation in relationship to environmental factors were investigated. In 2002, the wetland remained flooded to an average water depth of 25 cm during the growing season, from July to mid-September. We mapped the floodline and vegetation distribution using GPS (global positioning system). Coverage of vegetation in the wetland was 100%, and the vegetation was zonally distributed along a water depth gradient, with three emergent plant zones (Hippuris vulgaris-dominated zone, Scirpus distigmaticus-dominated zone, and Carex allivescers-dominated zone) and one submerged plant zone (Potamogeton pectinatus-dominated zone). Both aboveground and belowground biomass varied temporally within and among the vegetation zones. Further, net primary productivity (NPP) as estimated by peak biomass also differed among the vegetation zones; aboveground NPP was highest in the Carex-dominated zone with shallowest water and lowest in the Potamogeton zone with deepest water. The area occupied by each zone was 73.5% for P. pectinatus, 2.6% for H. vulgaris, 20.5% for S. distigmaticus, and 3.4% for C. allivescers. Morphological features in relationship to gas-transport efficiency of the aerial part differed among the emergent plants. Of the three emergent plants, H. vulgaris, which dominated in the deeper water, showed greater morphological adaptability to deep water than the other two emergent plants.