The effect of nitrogen fertilization on nitrogen use efficiency of irrigated and non-irrigated tobacco (Nicotiana tabacum L.).

Burley tobacco (Nicotiana tabacum L.) plants were grown in the field with or without irrigation and fertilized with 0, 120, 240 or 360 kg N ha^–1 over two growing seasons to assess nitrogen use under Mediterranean climate conditions. Kjeldahl-N and NO₃-N in leaves and stems and NO₃-N and NH₄-N in the soil at two depths (0–0.3 and 0.3–0.6 m) were determined. The effect of N fertilization on total N accumulated in the canopy biomass was markedly different between irrigated and non-irrigated plants. Under non-irrigated conditions N accumulated in the plant did not depend on the amount of N applied. In both years, the amount of N in irrigated plants increased in response to the amount of N applied, starting from 49 to 56 days after transplanting (DAT). The average amount of total N in the canopy of irrigated plants, measured across all sampling dates of both years, ranged from 30 kg ha^–1 of the unfertilized control to 88 kg ha^–1 of the 360 kg ha^–1 of N applied. The average amount of plant NO₃-N was 2.6 and 4.4 kg ha^–1 for non-irrigated and irrigated plots across all N treatments (means of 1996 and 1997). Nitrogen uptake rate (NUR) of non-irrigated plants was high between seedling establishment and the period of rapid stem elongation in 1996 (from 36 to 50 DAT) and until flowering in 1997 (from 42 to 71 DAT), but much less or negligible at later stages of plant development. Irrigation increased NUR dramatically in the second part of the growing season. Maximum NUR was estimated for plants receiving 240 or 360 kg N ha^–1 in both years. The year of study did not affect the recovery fraction (RF), physiological efficiency (PE) or agronomic efficiency (AE). Irrigation and N fertilization had significant effects on both RF and AE, but not on PE. Maximum values of RF were 45 and 22% for irrigated and non-irrigated treatments, respectively. In irrigated plots there was a negative relationship between RF and increasing N levels at all sampling dates.     

Soil organic C sequestration and stabilization in karstic soils of Yucatan

The tropical semiarid soils of northwestern Yucatan, Mexico, haveexceptionally high organic matter (OM) contents, between 50 and 150 g Ckg^–1. The soils are formed on limestone and form amosaic of shallow black lithosols surrounding rock outcrops and deeper redrendzinas at slightly lower relief. Traditionally, these soils were managedunder shifting cultivation with an uncommonly short cultivation period of only2years followed by a long bush fallow. We examined OM mineral associationsusing size and density fractionations of two soils after 1 and 12 years offallow in a search for factors responsible for the high OM stability, shortcultivation period and poor productivity. Light-fraction OM accounted for up to38% of total soil OM and was responsible for almost all the OM accretion duringfallow. Red soils contained half as much OM as black soils. Lower average OMcontents of silt-size aggregates of red soils were due to a lower proportion ofOC-rich agregates, not to differences in composition of individual aggregateclasses. Expandable clays were practically absent in both soil types andsesquioxides were not related to OM contents or stability. Fine-sized secondarycarbonates, undetectable to X-ray, impreganted light fraction OM and stabilizedaggregates, and may be the principal cause of the OM accumulation.Mineralisation of coarse OM accumulated during fallow was impeded in bothsoils,but to a greater extent in the more calcareous black soils, so that relativelyundecomposed OM accumulates to well above the levels that are typical for othersemiarid tropical soils. Limited OM turnover will limit nutrient release, whichmay limit the agricultural productivity.     

耕作对黄土高原和北美大草原三种典型农业土壤有机碳的影响

耕作对黄绵土(Calclaric Cambisols,FAO)、灰褐土(Haplic Greyxems,FAO)和典型褐灰钙土(Orthic Brown Chernozem)的土壤有机碳(SOC)动态的影响存在明显差异,黄绵土在开垦5年内O～20cm土壤有机碳损失了77％,损失速率为2．15t·hm^-2·yr^-1,其主要原因为水蚀和耕作侵蚀,灰褐土在开垦后的42年里耕层土壤的有机碳损失了70％,损失速率为0．96～1．06t·hm^-2·yr^-1,主要为水蚀和有机碳的矿化分解,1960以后开垦的典型褐灰钙土0～20cm耕层土壤有机碳损失了11％,损失速率为0．17t·hm^-2·yr^-1。1920年开垦的典型褐灰钙土有机碳损失了44％,损失速率为0．45t·hm^-2·yr^-1,造成这一差异的主要原因是耕作和轮作体制的改善有效地阻止了风蚀的危害,并增加了进入土壤系统的有机物的量,3种土壤轻组有机碳(LFOC)的变化趋势与总有机碳的变化趋势相似：黄绵土和灰褐土在相应的时间内LFOC损失了73％和90％,1920年和1960年开垦的典型褐灰钙土LFOC分别损失了74％和70％,3种土壤间LFOC和HFOC的分配比例不同也可能是造成黄绵土和灰褐土有机碳下降快的原因。     

Importance of Different Volatile Petroleum Hydrocarbon Fractions in Human Health Risk Assessment

Soil vapor data for benzene and four aliphatic and aromatic hydrocarbon fractions from five volatile petroleum hydrocarbon (VPH)-contaminated sites in western Canada were used together with the Canadian Council of Ministers of the Environment (CCME) Canada-Wide Standard for petroleum hydrocarbons to investigate the relative importance of benzene and the different fractions in human health risk assessment. VPH concentrations in soil vapor samples ranged from 4.0 to 4200?mg/m³, of which 0 to 4.6% was BTEX and 90 to 95% was hydrocarbons of the C_5–8 aliphatic fraction. VPH inhalation exposure by an adult receptor in a hypothetical, commercial building was modelled deterministically assuming 16- and 70 year occupational tenures. The magnitude of hazard quotients varied widely between sites, but their hydrocarbon fraction signatures were consistent, and characterized by higher hazard quotients in the C_5–8 and C_9–10 aliphatic and C_9–10 aromatic fractions relative to benzene and the TEX aromatic fraction. This work has shown that the C_5– and C_9–10 aliphatic fractions yield greater relative risk than the commonlyregulated TEX compounds, and that benzene becomes the primary chemical of potential concern only when an occupational tenure approaching 70 years is assumed.     

Transient releases of acetaldehyde from tree leaves − products of a pyruvate overflow mechanism?

Emissions of acetaldehyde from tree leaves were investigated by proton‐transfer‐reaction mass spectrometry (PTR‐MS), a technique that allows simultaneous monitoring of different leaf volatiles, and confirmed by derivatization and high‐performance liquid chromatography analysis. Bursts of acetaldehyde were released by sycamore, aspen, cottonwood and maple leaves following light–dark transitions; isoprene emission served as a measure of chloroplastic processes. Acetaldehyde bursts were not accompanied by ethanol, but exposure of leaves to inhibitors of pyruvate transport or respiration, or anoxia, led to much larger releases of acetaldehyde, accompanied by ethanol under anoxic conditions. These same leaves have an oxidative pathway for ethanol present in the transpiration stream, resulting in acetaldehyde emissions that are inhibited in vivo by 4‐methylpyrazole, an alcohol dehydrogenase (Adh) inhibitor. Labelling of leaf volatiles with ¹³CO₂ suggested that the pools of cytosolic pyruvate, the proposed precursor of acetaldehyde bursts, were derived from both recent photosynthesis and cytosolic carbon sources. We hypothesize that releases of acetaldehyde during light–dark transitions result from a pyruvate overflow mechanism controlled by cytosolic pyruvate levels and pyruvate decarboxylase activity. These results suggest that leaves of woody plants contribute reactive acetaldehyde to the atmosphere under different conditions: (1) metabolic states that promote the accumulation of cytosolic pyruvate, triggering the pyruvate decarboxylase reaction; and (2) leaf ethanol oxidation resulting from ethanol transported from anoxic tissues.     

Variability in the diet of New Zealand sea lion (Phocarctos hookeri) at the Auckland Islands, New Zealand

We examined the stomach contents of 121 New Zealand (NZ) sea lions ( Phocarctos hookeri ) caught by the squid fishery during the summer/autumn 1997–2006 around the Auckland Islands (51°S, 166°E). Dietary variation was assessed among juveniles, lactating females, nonlactating females and males, and between areas on the Auckland Islands shelf. The digested fraction of the contents consisted mostly of opalfish ( Hemerocoetes spp.) (50.1% by number [ N ], 4.7% by mass [ M ]), rattail ( Coelorinchus spp.) (12.0% N , 2.4% M ), arrow squid ( Nototodarus sloani ) (14.1% N , 17.9% M ), octopus ( Enteroctopus zealandicus ) (2.1% N , 27.8% M ), and red cod ( Pseudophycis bachus ) (3.8% N , 4.3% M ). Opalfish was found in greater proportions in the stomachs of females (lactating: 58.1% N , nonlactating: 62.4% N ) and juveniles (56.9% N ) than males (14.5% N ). Juveniles caught smaller opalfish and rattail than adults did. Over all classes, sea lions ate larger prey in the east than in the north of the Auckland Islands shelf. The common prey—arrow squid and rattail—constitute an abundant resource at the edges of the Auckland Islands shelf, where lactating NZ sea lions forage. Although these key areas are far from the rookeries and impacted by the squid fishery, they may provide the only reliable resource able to support the cost of benthic foraging behavior in the deepest diver of all otariids.     

3D—HoVAIF模型用于八角茴香油成分色谱保留时间研究

本文采用GC/MS测定了八角茴香油中各组分,应用本实验室新近提出的三维原子场全息作用矢量(3D-HoVAIF)对鉴定的48个挥发性有机物的结构进行了表征,并分别采用了偏最小二乘回归(PLS)与多元线性回归(MLR)进行了建模研究.结果表明,3D-HoVAIF能够较好地表征茴香油中各组分的化学结构,所建模型具有良好的估计能力与稳定性.     

虎榛子叶片挥发性成分HS-SPME & GC-MS分析

为探明虎榛子Ostryopsis davidiana叶片挥发物的组成及其相对含量,以长势优植株为研究对象,利用固相微萃取-气相色谱质谱法(HS-SPME & GC-MS)分析其叶片挥发性物质,通过面积归一法计算各成分的相对含量。结果表明,从虎榛子叶片中共鉴定出39种化学成分,其中5种绿叶气味物质,占75.61%;6种芳香化合物,占1.30%;9种萜烯类化合物,占5.04%;19种脂肪族化合物,占17.76%。该结果可为其寄生昆虫栎黄枯叶蛾的植物源引诱剂开发奠定基础。     

内蒙古植被降水利用效率的时空格局及其驱动因素

植被降水利用效率(precipitation-use efficiency, PUE)是评价干旱、半干旱地区植被生产力对降水量时空动态响应特征的重要指标。该研究利用光能利用率CASA (Carnegie-Ames-Stanford Approach)模型估算了2001-2010年内蒙古地区植被净初级生产力(net primary productivity, NPP), 结合降水量的空间插值数据, 分析了近10年内蒙古地区植被PUE的空间分布、主要植被类型的PUE,及其时空格局的驱动因素。结果表明: 2001-2010年内蒙古地区所有植被的平均PUE为0.94 g C·m^-2·mm^-1, 且在105-120° E地带性规律明显,PUE上升速率为每10° 0.55 g C·m^-2·mm^-1。各植被类型间PUE差别较大, 其中灌丛PUE最高, 荒漠PUE最低。在不同的降水量区域, 植被PUE的空间分布与气候因子的关系有较大差别, 0-75 mm降水量区间内, PUE随降水量、气温的升高显著下降(R² = 0.226, p < 0.05); 175-300 mm降水量区间内, 植被 PUE的空间变化与降水量和气温呈极显著相关关系(R² = 0.878, p < 0.001), 且随降水量的增加显著上升( R² = 0.94, p < 0.001), 变化速率约为每100 mm降水0.57 g C·m ^-2·mm^-1; 在降水量大于475 mm的区域, 植被PUE的空间分布与降水量、气温的相关性显著(R² = 0.19, p < 0.05), 且随着气温的上升、降水量的下降而增加, 其中气温的贡献是降水量的8.61倍。在不同的降水量区域, 植被 PUE的年际波动与气候因子的关系也有较大差别, 对于年降水量0-220 mm的地区, PUE的年际波动与降水量呈正相关性、与气温呈负相关性; 在年降水量为220-310 mm的地区, PUE的年际波动主要受降水量的控制, 受气温影响较小; 在年降水量>310 mm的地区,PUE的年际波动与降水量、气温均呈正相关关系, 但在降水量越高的地区, PUE的年际波动与降水量的相关性越弱, 与气温的相关性越强。植被覆盖度与PUE的空间分布极显著相关(R² = 0.73, p < 0.001), 且与 PUE的年际波动也存在线性相关关系(R² = 0.11, p < 0.001); 叶面积指数( LAI)与PUE的年际波动呈线性相关关系(R² = 0.42, p < 0.001), 而当 LAI < 3.15时, PUE的空间分布随LAI增加而呈线性增加。