Observations and modeling of aboveground tree carbon stocks and fluxes following a bark beetle outbreak in the western United States

Bark beetle epidemics result in tree mortality across millions of hectares in North America. However, few studies have quantified impacts on carbon (C) cycling. In this study, we quantified the immediate response and subsequent trajectories of stand‐level aboveground tree C stocks and fluxes using field measurements and modeling for a location in central Idaho, USA that experienced an outbreak of mountain pine beetle (Dendroctonus ponderosae Hopkins). We measured tree characteristics in lodgepole pine (Pinus contorta) plots spanning a range of structure and mortality conditions. We then initialized the forest vegetation simulator, an individual tree‐based model, with these measurements and simulated the response of aboveground production of C fluxes as well as trajectories of C stocks and fluxes in the coming decades. Mountain pine beetles killed up to 52% of the trees within plots, with more larger trees killed. C stocks in lodgepole pine were reduced by 31–83% following the outbreak, and plot‐level C fluxes decreased 28–73%. Modeled C stocks increased nearly continuously following the infestation, recovering to preoutbreak levels in 25 years or less. Simulated aboveground tree C fluxes increased following the immediate postoutbreak decrease, then subsequently declined. Substantial variability of C stocks and fluxes among plots resulted from the number and size of killed and surviving trees. Our study illustrates that bark beetle epidemics alter forest C cycling unlike stand‐replacement wildfires or clear‐cut harvests, due in part to incomplete mortality coupled with the preference by beetles for larger trees. The dependency of postoutbreak C stocks and fluxes on stand structure suggests that C budget models and studies in areas experiencing mountain pine beetle disturbances need to include size distribution of trees for the most accurate results.     

II gruppo Aristolochia pallida nell'Italia nordorientale

Abstract

The Aristolochia pallida group in the north-eastern Italy. The Aristolochia pallida group includes two closely related species: A. pallida Willd. and A. lutea Desf. For each species, a biometrical-morphological analysis on selected characters and critical notes are given. The distribution of both species in the north-eastern Italy is also defined.     

变色马兜铃化学成分的研究

从变色马兜铃块根乙醇提取物的石油醚溶解部分中分得一个倍半萜内酯(B_2),分子式C_(15)H_(20)O_2,熔点94—95℃,[α]_D~(36)-49°(C=1.8,EtOH)。通过光谱分析和化学反应测定了结构,并证明它与异马兜铃内酯(isoaristolactone)为同一化合物,从而使异马兜铃内酯的结构得以明确。B_2系首次从植物中分到。另从石油醚不溶部分中分得12个成分(D_1—D_3,D_(4f),D_(4y),D,—D_(10)和 C_2)。其中7个分别鉴定为6-甲氧基去硝基马兜铃酸甲酯(D_1)、去硝基马兜铃酸(D_3)、6-甲氧基去硝基马兜铃酸(D_(4f))、6-甲氧基马兜铃酸甲酯(D_(4y))、马兜铃酸A(D_5)、β-谷甾醇-D-葡萄糖甙(D_(10))和尿囊素(C_2)。D_(4f)亦系首次从植物中分到。动物试验表明,D_1、D_3和 D,均有明显的抗生育活性。     

Antitoxin activity of plants used in Mexican traditional medicine against scorpion poisoning

Scorpions, especially in urban areas of tropical and subtropical regions, present a common risk of poisoning. In Mexico, scorpion envenomation is considered a public health problem. Despite the frequency of scorpion sting cases, there are to date no uniform criteria for their treatment. In Mexican traditional medicine, different plant species have been widely used as a remedy for treating scorpion poisoning. The aim of this work was to evaluate the effect of Bouvardia ternifolia, Aristolochia elegans and Vitex mollis extracts on Centruroides limpidus limpidus venom lethality in mice, and to determine their antagonist activity on guinea pig ileum. The hexane and methanol extract from B. ternifolia modified the LD50 of C. limpidus limpidus venom from 0.750 +/- 0.08 to 1.64 +/- 0.19 and 1.16 +/- 0.14 mg/kg, respectively. The extracts of A. elegans produced lower antitoxic activity, while extracts of V. mollis did not show any protection. On in vitro test, addition of B. ternifolia and A. elegans extracts strongly inhibited, in a concentration-dependent manner, the ileum contractions induced by venom. In general, the results demonstrated the effectiveness of these two plant species in modifying the lethality of C. limpidus limpidus venom in mice.     

丁烯羟酸内酯对公鸡花种子萌发和赤霉素含量的影响

从植物燃烟中提取的丁烯羟酸内酯（buten01ide）能提高公鸡花种子的萌发率,并促进其萌发后的生长。光可以增强丁烯羟酸内酯的作用。公鸡花对外源GA的响应与对丁烯羟酸内酯的响应类似,二者有协同效应。酶联免疫法测定结果显示,在种子尚未萌发时,经丁烯羟酸内酯处理的种子中内源赤霉素含量低于不做处理的;萌发生长后,其赤霉素含量则高于不做处理的。因此认为,丁烯羟酸内酯可能是通过增加种子对GA的敏感性而起作用的。     

Plants as concept generators for biomimetic light-weight structures with variable stiffness and self-repair mechanisms

1 Introduction Over the last few years, plants have proved to be areal treasure trove as models for the construction of bio-logically inspired technical structures and materials [1–5].One ongoing project of the Competence Network ‘Plantsas Concept Generators for Biomimetic Materials andTechnologies’deals with the construction of light-weightstructures with variable stiffness and rapid self-repairmechanisms based on plant structures [6, 7] …     

The discovery of three genetic races of the dwarf mistletoe Arceuthobium americanum (Viscaceae) provides insight into the evolution of parasitic angiosperms

A population genetic approach was used to explore the evolutionary biology of the parasitic angiosperm Arceuthobium americanum Nutt. ex Engelm. (Viscaceae). Arceuthobium americanum infects three principal hosts and has the most extensive geographical range of any North American dwarf mistletoe. Based on the lack of apparent morphological and phenological differences between populations of A. americanum, past researchers have found no evidence for recognizing infraspecific taxa. In this study, molecular analysis using amplified fragment length polymorphism (AFLP) analysis indicated that A. americanum is divided into three distinct genetic races, each associated with a different host taxon in regions of allopatry: (i) Pinus banksiana in western Canada; (ii) Pinus contorta var. murrayana in the Sierra Nevada and Cascade Mountain ranges in the western US; and (iii) Pinus contorta var. latifolia in the western US and Canada. These observations suggest that host identity, geographical isolation and environmental factors have contributed to race formation in A. americanum. The lack of fine-scale patterning within each of the A. americanum races is attributed to random dispersal of seeds over long distances by animal vectors. Historical factors such as glaciations and founder events have also influenced structuring and genetic diversity in A. americanum populations. Given sufficient time, it is possible that these races will become reproductively isolated and undergo speciation.     

Nitrogen fixation associated with Suillus tomentosus tuberculate ectomycorrhizae on Pinus contorta var. latifolia

BACKGROUND AND AIMS: Tuberculate ectomycorrhizae are a unique form of ectomycorrhiza where densely packed clusters of mycorrhizal root tips are enveloped by a thick hyphal sheath to form a tubercle. The functional significance of such a unique structure has not previously been established. The purpose of the present study was to investigate and measure the potential nitrogenase activity associated with Suillus tomentosus/Pinus contorta tuberculate ectomycorrhizae in two stand ages, young and old, and across a range of nitrogen-poor soil conditions. METHODS: Short roots were compared with other mycorrhizae and non-mycorrhizal secondary roots using tuberculate ectomycorrhizae. Assessment of nitrogenase activity was determined and quantitative measurements were taken on tuberculate ectomycorrhizae in situ in a variety of different circumstances, by using an adaptation of the acetylene reduction assay. KEY RESULTS: Significant nitrogenase activity was measured associated with S. tomentosus/P. contorta tuberculate ectomycorrhizae whereas no nitrogenase activity was measured with non-tuberculate mycorrhizae or secondary roots without mycorrhizae. Average nitrogenase activity ranged from undetectable to 5696.7 nmol C2H4 g(-1) tubercle 24 h(-1). Maximum nitrogenase activity was 25,098.8 nmol C2H4 g(-1) tubercle 24 h(-1). Nitrogenase activity was significantly higher in young stands than in old stands of P. contorta. Season or some covariate also seemed to affect nitrogenase activity and there was suggestion of a site effect. CONCLUSIONS: Suillus tomentosus/P. contorta tuberculate ectomycorrhizae are sites of significant nitrogenase activity. The nitrogenase activity measured could be an important contribution to the nitrogen budget of P. contorta stands. Season and stand age affect levels of nitrogenase activity.