Structural and Functional Grounds for Ephedra sinica Expansion in Mongolian Steppe Ecosystems

Morphological and structural characteristics of photosynthetic organs, diurnal changes in photosynthetic and transpiration rates, and the efficiency of water use were studied in three plant species from mountain-steppe ecosystems in Mongolia, Ephedra sinica Stapf, Stipa glareosa P. Smirn., and Allium polyrhizum Furcz. ex Regel. The species studied differed in the structural and functional mechanisms for the adaptation of photosynthetic apparatus to arid conditions. E. sinica has thick, vertical assimilating shoots, which are characterized by a high density (620 mg/cm³) and a small proportion of photosynthetic tissues (13%). The proportion of meso-phyll in the leaves of A. polyrhizum and S. glareosa was two and three times higher, respectively. The low content of phototrophic tissues in E. sinica shoot was compensated for by a high photosynthetic activity of single chloroplasts (25 mg CO₂/(10⁹ chloroplast h)), which was six times higher, than in two other species. Daily course of photosynthesis and transpiration inE. sinica differed from those of A. polyrhizum and S. glareosa by the absence of the midday depression. E. sinica had the highest efficiency of water use (45 mg CO₂/g H₂O) due to a low transpiration rate (0.25 g/g fr wt h). It is concluded that, in E. sinica, the main strategy for adaptation to arid stress is to develop in the shoot a few photosynthesizing cells of high assimilation activity. Such structural organization of photosynthetic organs in ephedra contributes to its higher efficiency of water use and stability of physiological characteristics under changing environmental conditions. These specific features of the structure of assimilating organs and their functional features contribute to a greater expansion of E. sinica with increasing climate aridization in Mongolia.     

The Effects of Fusicoccin,Abscisic Acid,and Benzyladenine on the Transport and Partitioning of Substances as Related to Cytokinin Sink Activity

We tested the possible cytokinin effect on the functioning of the active transport system involved in the assimilate loading into the phloem as a cause for the cytokinin sink and retention effect. This effect is manifested in the deceleration of substance export from and the stimulation of substance import to the sites of local phytohormone application to the mature detached leaf from untreated leaf areas. To affect the membrane mechanisms of the substance transport, we used leaf treatment with the phytotoxin fusicoccin, an enhancer of plasmalemmal H⁺-ATPase and a potential stimulator of assimilates export, and with the phytohormone ABA affecting transport, metabolism, and plant growth. However, fusicoccin did not enhance ¹⁴C-sucrose export from the leaf blade and did not interfere with the cytokinin-induced export deceleration. ABA reduced substantially ¹⁴C export from the leaf but eliminated the cytokinin effect on this process. Similar results were obtained for broad bean (Vicia faba L.) leaves with apoplastic phloem loading, involving H⁺-ATPase activity, and pumpkin (Cucurbita pepo L.) leaves with symplastic phloem loading, that is, occurring without sucrose transmembrane translocation and without H⁺-ATPase involvement. The conclusion is that the cytokinin-induced development of sink zones in source leaves is not related to the membrane mechanisms of the substance transport in the mesophyll–phloem system. The data obtained support the idea that the cause for the cytokinin sink and retention effect is the enhancement of elongation growth and total activation of metabolism in the mesophyll cells of the detached leaf.     

The effects of shredding invertebrates on the transfer of organic carbon from littoral leaf litter to water-column bacteria

Leaf litter can be of great importance for the productivity of small oligotrophic lakes surrounded by deciduous forests. Feeding invertebrate shredders produce particulate organic leftovers, but their feeding also enhances the release of dissolved organic carbon (DOC). We tested whether invertebrate-mediated DOC release affects the production of heterotrophic water-column bacteria. Submersed leaves were incubated in microcosms with and without shredders; and DOC, absorbance, bacterial abundance and bacterial production in the water column were monitored. We also measured dry weight of the organic particles (FPOC, fine particulate organic carbon, leaf residues and shredders). Total leaf-litter carbon decreased by nearly 80% in the presence of shredders, and on average 56% of the initial leaf carbon ended up as FPOC after 126 days of incubation. Without shredders FPOC production was almost zero, and 72% of the added leaf carbon could be retrieved as leaves when the experiment ended. Both these figures include the rapid release of DOC during the first week of leaf incubation in the lake water (equivalent to 16–19% of total added leaf carbon). Although bacterial production in the water was several times higher in treatments with shredders, bacterial consumption of leaf-derived DOC from shredding was obviously of minor importance in the total carbon budget. This result suggests, although shredders have a strong impact on transformation of leaves to FPOC, they do not greatly enhance the initial rate of mineralization of the leaf-derived detritus.     

Impact of fire on leaf nutrients,arthropod fauna and herbivory of native and exotic eucalypts in Kings Park,Perth, Western Australia

The vegetation of Kings Park, near the centre of Perth, Western Australia, once had an overstorey of Eucalyptus marginata (jarrah) or Eucalyptus gomphocephala (tuart), and many trees still remain in the bushland parts of the Park. Avenues and roadsides have been planted with eastern Australian species, including Eucalyptus cladocalyx (sugar gum) and Eucalyptus botryoides (southern mahogany), both of which have become invasive. The present study examined the effect of a recent burn on the level of herbivory on these native and exotic eucalypts. Leaf damage, shoot extension and number of new leaves were measured on tagged shoots of saplings of each tree species in unburnt and burnt areas over an 8‐month period. Leaf macronutrient levels were quantified and the number of arthropods on saplings was measured at the end of the recording period by chemical knockdown. Leaf macronutrients were mostly higher in all four species in the burnt area, and this was associated with generally higher numbers of canopy arthropods and greater levels of leaf damage. It is suggested that the pulse of soil nutrients after the fire resulted in more nutrient‐rich foliage, which in turn was more palatable to arthropods. The resulting high levels of herbivory possibly led to reduced shoot extension of E. gomphocephala, E. botryoides and, to a lesser extent, E. cladocalyx. This acts as a negative feedback mechanism that lessens the tendency for lush, post‐fire regrowth to outcompete other species of plants. There was no consistent difference in the levels of the various types of leaf damage or of arthropods on the native and the exotic eucalypts, suggesting that freedom from herbivory is not contributing to the invasiveness of the two exotic species.     

The influence of leaf age on the oviposition preference of Chrysophtharta bimaculata (Olivier) and the establishment of neonates

1 The degree of discrimination shown by a herbivore when selecting oviposition sites has been suggested as a key factor to understanding herbivore population dynamics. Chrysophtharta bimaculata (Coleoptera: Chrysomelidae) is a primary pest of Tasmanian eucalypt forests and can cause severe defoliation. Previous work suggests that females show discrimination when selecting oviposition sites. Our aim was to test the degree of oviposition discrimination exhibited by C. bimaculata with regards to leaf toughness, a character that is critical to neonate survival. 2 We conducted an experiment examining the leaf toughness critical for neonate survival and found that significant larval mortality occurs above a toughness of 46.9 g. We also determined that the maximum toughness of leaves upon which larvae established in the field was 48.2 g, supporting the laboratory result. 3 Field surveys showed that although the majority of eggs were laid on leaves suitable for larval establishment, many eggs were laid on unsuitable, tougher leaves. However, all eggs were normally placed within 20 cm of suitable leaves and glasshouse trials demonstrated the neonates could move this distance without mortality occurring. 4 We conclude that egg batch distribution and larval performance of C. bimaculata will influence the population dynamics of C. bimaculata in two ways. Firstly, the availability of expanding/newly expanding leaves of eucalypt hosts will determine larval carrying capacity. Secondly, at a more localized level, the deposition of large numbers of egg batches on both suitable and unsuitable leaves followed by successful neonate migration increases the risk of resource depletion and poor larval development.     

沙地柏对除叶干扰的生理和生长响应

为了研究沙地柏对模拟自然干扰的生理和生长响应,在毛乌素沙地对它进行了人为除叶为处理的模拟山羊啃食,虫害实验,结果表明,除叶干扰通过改变生理指标峰值出现的时间影响日动态,并显著影响生理指标的日平均值,除叶干扰对当年生枝生物量分配的影响不明显,但显著影响其生长特征。除叶干扰的最终效应受干扰方式和强度的双重制约,不同生理,生长指标对除叶干扰的敏感性存在差异,如净光合速率和腾速率,除干扰具有补偿效应,尤其是除老叶,因此适度剪除2年生以下枝条上的叶可促进当年生枝的生长和生物量积累。     

不同肥料对黄山药根茎产量和薯蓣皂甙元含量的影响

通过对施用硝酸钾肥和复合肥的比较试验,表明硝酸钾肥对促进黄山药(Dioscrea panthaica)地上、地下部分生长,提高次生根茎产量有显著效果.栽培32个月的次生根茎平均生长量达405.9±254.0g/株,产量58.5t/ha,比施用复合肥的增产37.5%和20.5%,比对照增产29.9%和17.9%.施用复合肥的次生根茎平均生长量253.6±148.6g/株,产量46.3t/ha,比对照低10.8%和3.1%.三者的薯蓣皂甙元含量无明显差异.     

番木瓜环斑病毒畸叶株系的CP基因克隆和序列分析

采用RT－PCR方法合成了本研究室保存的番木瓜畸叶病毒（PMaLV）的外壳蛋白（CP）基因,将其CP基因克隆进Promega公司的pGEM-T and pGEM-T Easy Vector System（简称T－载体）,并进行了序列分析。结果表明,PMaLV CP基因核苷酸序列全长为861nt,推导其编码287个氨基酸。与番木瓜环斑病毒（PRSV）美国夏威HA株系和澳大利亚W株系的CP基因相比,在第66nt处开始连续缺失3个核苷酸。与PRSV的华南Ys、Sm和G株系以及夏威夷的HA和澳大利亚的W株系相比,其CP基因序列同源率分别为96％、98％、95％、89％和89％。其的氨基酸序列同源率分别为98％、97％、97％、96％和95％。此结果表明,PMaLV属于PRSV的一个株系,不是一种新病毒。因此,我们称其为番木瓜环斑病毒畸叶株系（ML株系）。     

施用EM堆肥对土壤螨群落结构的影响

对不同施肥条件下农田中的土壤螨进行调查,结果表明：（1）EM堆肥区土壤有机层加深,土壤螨垂直分布下限下移;（2）施用EM堆肥土壤螨数量多,物种丰富,分布均匀,长期施用EM堆肥可以形成多层次的食物网络,传统堆肥区土壤螨数量和种类较化肥区多,单纯施用化肥的农田,土壤螨数量和种类呈减少趋势,群落结构稳定性差,土壤生物间的联系向单一化方向发展。     

Comparative sensitivity of larval mosquitoes to vegetable polyphenols versus conventional insecticides

The larvicidal effects of polyphenols of natural crude decomposed alder leaf litter and commercially available tannic acid were experimentally compared with those of two common conventional insecticides (Bacillus thuringiensis ssp. israelensis: microbial insecticide; temephos: organophosphate insecticide). Comparative standard bioassays using third instar larval Aedes aegypti, A. albopictus, Culex pipiens and Coquillettidia richiardii as references indicated that Aedes and Culex taxa are far more sensitive to alder leaf litter than to tannic acid and conventional insecticides. C. richiardii is far more resistant to conventional insecticides than Aedes and Culex taxa, but its sensitivity to tannic acid is close to that of those taxa. Dietary vegetable polyphenols are thus proposed as new, practical, alternative chemicals for mosquito control when conventional insecticides are difficult and costly to be used (e.g., in the management of Aedes and Culex populations in man-made breeding sites and Coquillettidia control strategy).