氮沉降对不同入侵程度加拿大一枝黄花化感作用的影响

为探究全球氮沉降影响外来植物入侵扩张的作用机制,该文通过受控模拟试验,以入侵植物加拿大一枝黄花(Solidago canadensis)为对象,研究了三种氮水平(N0、N5和N12)下五种不同入侵程度(种内及种间竞争)的加拿大一枝黄花凋落叶浸提液对本地植物莴苣(Lactuca sativa)种子萌发和幼苗生长化感作用的影响。结果表明:(1)N0、N5和N12处理下的不同入侵程度加拿大一枝黄花凋落叶浸提液均显著抑制莴苣的萌发和生长,其中N5土壤入侵初期(S1A3)处理浸提液的化感作用最显著,其发芽速度指数、发芽活力指数、根长、株高和叶长比对照分别降低了61%、79%、84%、68%和13%,此时凋落叶中的总酚和总黄酮含量最高,分别为0.48 mg·g^-1和1.50 mg·g^-1。(2)相同氮添加下,入侵程度对加拿大一枝黄花化感作用有显著影响,随着入侵程度的增加,加拿大一枝黄花化感作用显著减弱,入侵初期(S1A3)凋落叶化感作用显著高于入侵后期(S3A1)。(3)相同入侵程度下,氮添加对加拿大一枝黄花化感作用有显著影响,N5处理的加拿大一枝黄花化感作用比N0或N12处理显著增加。(4)氮添加与入侵程度有交互作用,两者共同作用显著影响了莴苣种子的综合化感作用。综上结果表明,氮沉降可能会增强入侵初期加拿大一枝黄花凋落叶对本地植物的化感抑制作用,进一步促进外来植物的成功入侵,为进一步研究加拿大一枝黄花的化感作用及生态防治提供了一定的理论参考。     

外来杂草加拿大一枝黄花对入侵地植物的化感效应

采用人工气候箱培养试验,初步研究了入侵杂草加拿大一枝黄花对本地植物的化感作用.测定了根系和根状茎的不同浓度浸提液对白三叶发芽率和幼苗生长的影响;不同播种密度下根系1:60提取浓度对白三叶种子萌发和幼苗生长的影响;根状茎1:60提取浓度对白三叶、红三叶、天蓝苜蓿、黑麦草、北美车前、鸡眼草、苇状羊茅、胜红蓟、马齿苋、碱蓬和刺苋的种子萌发和幼苗生长的影响.结果表明,加拿大一枝黄花根系和根状茎的化感抑制作用均随浓度的升高而增强,且根状茎提取物的抑制效应高于根系提取物的效应;在1:60低浓度根系浸提液作用下,不同密度的白三叶幼苗萌发率和幼根、幼芽长度差异不显著;1:60低浓度根状茎提取物对11个物种的种子萌发均有显著抑制作用,但对不同物种的抑制程度有差异,对禾本科植物的抑制作用大于非禾本科和豆科;1:60低浓度根状茎提取物对10个物种的幼根影响与对萌发率的影响相似,但在对幼芽的影响上,仅对鸡眼草、刺苋和苇状羊茅起抑制作用,而对其他植物无显著抑制(黑麦草、北美车前、胜红蓟、马齿苋和刺苋)或起促进作用(白三叶、红三叶、天蓝苜蓿).     

Relations between K+ uptake and photosynthetic uptake of inorganic carbon by aquatic plants

The uptake of K⁺ by the leafy shoots of four submersed higher aquatic plants (Elodea canadensis, Ranunculus aquatilis, R. trichophyllus, and Callitriche hamulata) with different HCO₃ ^- affinity was measured in successive 2-h periods under the conditions of high or low photosynthetic rates (i.e. at pH 7.5 or 10). At pH 7.5 the uptake of K⁺ by species with the higher HCO₃ ^- affinity (E. canadensis, R. trichophyllus) was significantly faster than that by species with a lower HCO₃ ^- affinity (R. aquatilis, C. hamulata). In the former group of species, the K⁺ uptake rate at pH 7.5 was 1.7 - 3.5 times higher than at pH 10. At pH 10, the soft-water species, R. aquatilis, had the lowest net photosynthetic rate (PN) of the three HCO₃ ^- users but, in contrast to the relative hard-water species, R. trichophyllus, showed a small K⁺ efflux (47 nmol kg^-1 s^-1). Thus, K⁺ uptake by shoots was not strictly correlated with PN. A significant K⁺ efflux (73 - 86 nmol kg^-1 s^-1) occurred from all HCO₃ ^- users in darkness. The relatively low K⁺ uptake by the strict CO₂ user, C. hamulata, was quite independent of PN and light or darkness. It may be suggested that uptake of K⁺ by shoots of submersed plants depends on their HCO₃ ^- affinity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Using Fecal Glucocorticoids to Assess Stress Levels in Captive River Otters

Abstract Reintroduction projects often expose animals to a series of acute stressors that may cause chronic stress and lead to the stress response. The stress response results in the release of glucocorticoids that, when excessive, can cause detrimental effects to the animal. Glucocorticoids can be extracted from feces and quantified as an effective method for assessing stress levels. We collected scats from 10 river otters (Lontra canadensis; 3 from MD and 7 from NY, USA) held captive for the Pennsylvania River Otter Reintroduction Project (PRORP). We used these scats to verify the use of the Correlate-EIA^TM Corticosterone Enzyme Immunoassay Kit (Assay Designs, Inc., Ann Arbor, MI) to evaluate stress levels in otters. We also determined trends in stress levels during the initial 10–12 days otters were in PRORP captivity, and compared glucocorticoid levels for 5 of the New York otters the morning before, the morning of, and the morning after veterinary examinations to determine if associated procedures (e.g., physical and chemical restraint) caused increased stress levels. Glucocorticoid concentrations declined from time 1 to time 2 for the 3 otters from Maryland (an average decline of about 6-fold) and for 5 of 7 otters from New York. Among otters evaluated for stress associated with veterinary examinations, average glucocorticoid concentrations were increased the morning of and the morning after veterinary examinations from the day before the veterinary examinations. We demonstrated that fecal glucocorticoids are an effective method for assessing stress levels in otters and that PRORP's captive management program did not contribute to increasing stress during the 10–12-day evaluation period. Fecal glucocorticoid assays could be used to evaluate stress levels of zoo or permanently captive otters, determine the most effective husbandry techniques for housing otters, and evaluate effects of both management practices and environmental conditions in the wild and in captivity.     

Response of Solidago canadensis clones to competition

Summary Transplants of ten Solidago canadensis clones were grown under high and low competition in the field to determine whether clones differed in survival, growth, and reproduction under natural conditions. Transplants had higher probability of survival and flowering and were larger in all measures of size when competition was experimentally reduced. Clones differed in almost all these measures of success, but only when variance among transplants within clones was reduced by excluding transplants that experienced heavy herbivore damage. Differences among clones were more apparent under low competition than under high competition, despite higher coefficients of variation within clones under low competition. Adjusting transplant size for initial size (parent ramet rhizome mass) did not change these results, although clones did differ in parent rhizome mass. All of these results suggest that there is little potential for selection to discriminate among these clones. Despite the strong differences in transplant performance between the competition treatments and among clones, the clones did not differ in competitive ability-almost none of the clone x competition interactions were significant. In addition, the measures of success of each clone were usually positively correlated between the high and low competition treatments, suggesting there were no tradeoffs between performance under high and low competition for these clones.