Spatial,temporal, and environmental limits on xanthotoxin induction in wild parsnip foliage

Summary Although present constitutively in large amounts, furanocoumarins in leaves of wild parsnip,Pastinaca sativa, are inducible to even higher concentrations by mechanical and insect damage. We conducted several experiments in order to characterize the nature and extent of xanthotoxin inducibility inP. sativa foliage. In order to determine the extent to which induction is localized, we mechanically damaged a single leaflet of a compound leaf on seven plants. Xanthotoxin concentrations increased significantly only in the damaged leaflet and in the half of the terminal leaflet closest to the damaged leaflet; thus, xanthotoxin induction is localized to the immediate vicinity of damage. To determine whether xanthotoxin induction results fromin situ biosynthesis or translocation from other plant parts, we detached individual leaflets from ten plants, damaged half of these detached leaflets, and compared xanthotoxin concentrations after 6 h in damaged and intact leaflets. We found that xanthotoxin concentrations increased 41% in damaged leaflets compared to detached leaflets that were not damaged. We also determined the rapidity and duration of the induction response. In leaflets that were damaged and then harvested after 0, 3, 24, 72, 120 and 168 h, xanthotoxin concentrations increased rapidly compared to undamaged leaflets on the opposite side of the leaf, reaching maximum levels within 24 h. This response was of comparatively short duration; concentrations declined to preinduction levels after seven days. To determine whether availability of resources influences the induced response, we performed two experiments, one in which soil nutrients were manipulated and one in which light level was manipulated. The low nutrient treatment was sufficiently extreme to cause cessation of aboveground growth, and the low light treatment caused etiolation. Extremes of resource limitation notwithstanding, leaflets significantly increased xanthotoxin production (2 to 3-fold increase under nutrient limitation and 3-fold increase under light limitation) in response to damage in both experiments.     

Benefits of trenching behavior in the context of an inducible defense

Summary. Many species of insects sabotage the pressurized defense vessels of their host plants prior to feeding. This behavior, however, does not render leaves indefinitely suitable, as some species employing this behavior eventually abandon uneaten portions of sabotaged leaves. In this study, we examined whether and to what degree wild parsnip, Pastinaca sativa, is capable of restoring its pressurized defenses and whether cabbage loopers, Trichoplusa ni, which normally trench parsnip leaflets, benefit from their trenching behavior. The pressurized oil tubes of parsnip leaves are rich in toxic terpenoids and furanocoumarins. A disruption of the integrity of the tubes (via razor blade nicks) in leaflets revealed that that some of their contents were expelled at the break and that some movement of oil from outside the leaflet (i.e., the midvein) occurred, bolstering furanocoumarin levels in the leaflet within minutes. Pressure and chemical content in a leaflet’s oil tubes were also shown to be restored within 24 hours of depressurization. This recovery ability allowed parsnip leaflets to respond to daily depressurizations by mechanical damage for up to at least 5 assaults, cumulatively causing an approximate ten-fold increase in furanocoumarins. Cabbage loopers fed parsnip leaflets that were artificially trenched accumulated twice as much body mass as larvae fed leaflets augmented with furanocoumarins equivalent to the quantity that would be avoided through trenching, indicating that trenching does benefit the herbivore. Although parsnip recovers from trenching rapidly, it does not do so within the time that cabbage loopers consume trenched leaflets     

赤子爱胜蚓(Eisenia foetida)对三种土壤Zn、Pb有效态含量的影响

以褐土(Cinnamonsoil)、潮棕壤(Aquicbrownsoil)和酸性棕壤(Acidbrownsoil)为供试土壤,通过培养实验,研究了土壤中重金属Zn、Pb对赤子爱胜蚓(Eiseniafoetida)生长率的影响,赤子爱胜蚓(Eiseniafoetida)对不同土壤中有效态Zn、Pb含量的影响,并与野生环境中生长的灰暗异唇蚓(Allolobaphoracaliginosa)进行比较。结果表明:重金属的污染明显抑制了赤子爱胜蚓的生长;赤子爱胜蚓可以显著提高潮棕壤中DTPA-Pb的含量,对DTPA-Zn的含量影响不大;加赤子爱胜蚓,褐土中DTPA-Zn和Pb的含量显著高于加灰暗异唇蚓,潮棕壤中DTPA-Zn的含量和酸性棕壤中大DTPA-Pb的含量则相反。     

Urea Fluctuations in Stream Baseflow across Land Cover Gradients and Seasons in a Coastal Plain River System

Urea‐N is a component of bioavailable dissolved organic nitrogen (DON) that contributes to coastal eutrophication. In this study, we assessed urea‐N in baseflow across land cover gradients and seasons in the Manokin River Basin on the Delmarva Peninsula. From March 2010 to June 2011, we conducted monthly sampling of 11 streams (4 tidal and 7 nontidal), 2 wastewater treatment plants, an agricultural drainage ditch, and groundwater underlying a cropped field. At each site, we measured urea‐N, DON, dissolved organic carbon (DOC), total dissolved nitrogen (TDN), NO₃^?‐N, and NH₄⁺‐N. In general, urea‐N comprised between 1% and 6% of TDN, with the highest urea‐N levels in drainage ditches (0.054 mg N/L) and wetland‐dominated streams (0.035–0.045 mg N/L). While urea‐N did not vary seasonally in tidal rivers, nontidal streams saw distinct urea‐N peaks in summer (0.038 mg N/L) that occurred several months after cropland fertilization in spring. Notably, the proportion of wetlands explained 78% of the variance in baseflow urea‐N levels across the Manokin watershed. In wetland‐dominated basins, we found urea‐N was positively related to water temperature and negatively related to DOC:DON ratios, indicating short‐term urea‐N dynamics at baseflow were more likely influenced by instream and wetland‐driven processes than by recent agricultural urea‐N inputs. Findings demonstrate important controls of wetlands on baseflow urea‐N concentrations in mixed land‐use basins.     

Determinants of brominated flame retardants in breast milk from a large scale Norwegian study

Brominated flame retardants (BFRs), particularly polybrominated diphenyl ethers (PBDEs), are widely present in human populations. In order to investigate human exposure pathways and associations with socioeconomic and lifestyle factors, 393 breast milk samples from mothers living in various regions throughout Norway were analyzed. Up to ten PBDE congeners were measured in all the samples, hexabromocyclododecane (HBCD) and BDE-209 in subsets of 310 and 46, respectively. The median concentrations of the sum of the seven most prominent PBDEs (BDE-28, 47, 99, 100, 153, 154 and 183), BDE-209 and HBCD were 2.1, 0.32 and 0.86 ng/g lipids, respectively. These concentrations are comparable to the levels generally observed in human populations in Europe. The frequency distributions were quite skewed with long tails towards higher concentrations. Maternal age, parity, education, having a cohabitant employed as electrician, and ventilation were factors significantly associated with some of the BFRs, although these factors only explained a small amount of the variability (R² 0.04–0.16). The mothers' diet was not found to influence the breast milk PBDE and HBCD levels. Our results show that sources other than the diet are important for the variability seen in breast milk BFR concentrations and that exposure from the indoor atmosphere should be emphasized in future studies.     

城市路口差异对行道树叶片叶绿素含量的影响研究

为明确城市道路路口差异对行道树叶片叶绿素的影响,研究选取太原市平阳路和长风街2条城市主干道为采样点,采摘春、秋季大十字路口、小十字路口、丁字路口和非路口绿化植株叶片,测定叶片叶绿素a含量、叶绿素b含量及叶绿素总量。结果表明:(1)城市交通对行道树叶片叶绿素总量影响为冬青卫矛(EuonymusjaponicusThunb)国槐(Sophora japonica)毛白杨(Populusto mentosa)。冬青卫矛适宜作指示物种。(2)与清洁对照区相比,污染区国槐和毛白杨叶片的叶绿素a、叶绿素b的含量及两者比值总体呈增加态势,冬青卫矛叶片叶绿素a、叶绿素b含量则以减少为主。(3)冬青卫矛叶片的叶绿素a含量相对叶绿素b含量影响明显,表现出了较好的相关性,建议用叶绿素a含量作为污染指示指标。(4)路口差异对不同种类行道树叶片叶绿素影响未显现一致性,表明路口差异受街道走向、交通流量、扩散能力、植株株高等多因素影响。在道路不畅、车流量大的区域,应在吸尘抑毒和降低绿化高度、增加扩散能力间寻求一种最佳平衡。     

Proposal for new best estimates for the soil solid–liquid distribution coefficient and soil-to-plant transfer of nickel

The objective of this study was to compile data, based on an extensive literature survey, for the soil solid–liquid distribution coefficient (K_d) and soil-to-plant transfer factor (TF) for nickel. The K_d best estimates were calculated for soils grouped according to texture and organic matter content (sand, loam, clay and organic) and soil cofactors affecting soil–nickel interaction, such as pH, organic matter, and clay content. Variability in K_d was better explained by pH than by soil texture.     

Interaction of bisphenol A with dissolved organic matter in extractive and adsorptive removal processes

The fate of endocrine disrupting chemicals (EDCs) in natural and engineered systems is complicated due to their interactions with various water constituents. This study investigated the interaction of bisphenol A (BPA) with dissolved organic matter (DOM) and colloids present in surface water and secondary effluent as well as its adsorptive removal by powdered activated carbons. The solid phase micro-extraction (SPME) method followed by thermal desorption and gas chromatography-mass spectrometry (GC-MS) was utilized for determining the distribution of BPA molecules in water. The BPA removal by SPME decreased with the increased DOM content, where the formation of BPA-DOM complexes in an aqueous matrix was responsible for the reduced extraction of BPA. Colloidal particles in water samples sorbed BPA leading to the marked reduction of liquid phase BPA. BPA-DOM complexes had a negative impact on the adsorptive removal of BPA by powered activated carbons. The complex formation was characterized based on Fourier transform infrared (FTIR) and ultraviolet-visible (UV-Vis) spectroscopy, along with the calculation of molecular interactions between BPA and functional groups in DOM. It was found that the hydrogen bonding between DOM and BPA would be preferred over aromatic interactions. A pseudo-equilibrium molecular coordination model for the complexation between a BPA molecule and a hydroxyl group of the DOM was developed, which enabled estimation of the maximum sorption site and complex formation constant as well as prediction of organic complexes at various DOM levels.