Toxicity of Cipadessa fruticosa to the leaf-cutting ants Atta sexdens rubropilosa (Hymenoptera: Formicidae) and their symbiotic fungus

Crude extracts from fruits, branches and leaves of Cipadessa fruticosa were assayed on Atta sexdens rubropilosa workers and their symbiotic fungus Leucoagaricus gongylophorus. The results showed that the majority of the extract tested reduced significantly (p < 0.05) the survival of the workers comparable to the neem oil. In addition, the dichloromethane extract from fruits and the hexane extract from branches of C. fruticosa inhibited in 80% the development of the symbiotic fungus. The hexane and dichloromethane extracts from fruits of C. fruticosa were fractionated and their fractions were subjected to new bioassays. Several fractions showed relevant activity on ants, but none of them inhibited significantly the fungal growth. The possibility of controlling leaf-cutting ants in the future using C. fruticosa is discussed.

Limonoids from Cipadessa fruticosa and Cedrela fissilis and their insecticidal activity

The chemical investigation of the fruits of Cipadessa fruticosa (Meliaceae) afforded the new limonoid cipadesin B and the known swietemahonolide. From the roots of Cedrela fissilis (Meliaceae) were isolated the limonoid 3β-acetoxycarapin, new as natural product, along with the triterpenes oleanolic and oleanonic acid. These compounds and other six mexicanolide limonoids previously isolated from C. fruticosa showed insecticidal activity against the leaf-cutting ants Atta sexdens rubropilosa. ©2005 Sociedade Brasileira de Química.

Salix aurita-viminalis Wimmer (S. fruticosa Döll)

Von Dr. Schatz

A new species of gall midge (Diptera: Cecidomyiidae) feeding on ornamental Cordyline fruticosa(Asparagaceae) in Australia

Larvae of an undescribed gall midge were found feeding on leaves and stems within leaf sheaths and between leaf blades of potted plants of Cordyline fruticosa (Asparagaceae) in a production nursery in Queensland. The following varieties of the host plant were infested: Apple Blossom', Glauca', Kilauea', Negra', Pink Diamond, 'Purple Prince' and Willy's Gold'. The new species, Dasineura cordylineaeKolesik sp. nov., is described and its cytochrome oxidase unit I mitochondrial gene segment is sequenced. The new species is the first known gall midge feeding on a plant species of the genus Cordyline. Orange larvae induce oval shallow swellings on the leaf and stem tissue, which becomes necrotised during the later stage of larval feeding. Necrotic areas remain visible to the end of leaves' lives and decrease the market value of the plants. In the production nursery investigated, the lesions caused by the gall midge provided an entry for a fungal infection by Fusarium sp. inflicting further injury to plants. Larvae of the new species were preyed on by larvae of Gaurax sp. (Diptera: Chloropidae). This is the first worldwide record of Chloropidae preying on Cecidomyiidae.

围封对退化矮嵩草草甸群落结构和主要种群空间分布格局的影响

通过研究围栏封育1年后中度退化的矮嵩草草甸（夏季牧场）群落结构的变化,探讨主要植物种群在小尺度（50 cm×50 cm）上的空间分布格局,并从生活史特征和生态适应对策等角度探讨产生和维持这些格局的机理。结果表明,围封1年显著降低了群落中主要种群矮嵩草（Kobresia humilis）、高山唐松草（Thalictrum alpinum）和雪白委陵菜（Potentilla nivea）的重要值,而增加了线叶龙胆（Gentiana farreri）的重要值;显著增加了群落的地上生物量和总生物量,但对地下生物量和群落多样性的影响不显著。围封使退化矮嵩草草甸主要种群矮嵩草、高山唐松草、珠芽蓼（Polygonum viviparum）、线叶嵩草（Kobresia capillifolia）和金露梅（Potentilla fruticosa）等空间分布格局从放牧后的随机分布向聚集分布发展,而雪白委陵菜、重齿风毛菊（S.katochaeteMaxim）、矮火绒草（Leonto-podium nanum）和美丽风毛菊（Saussurea pulchra）等种群的空间分布格局没有发生改变;但黑褐苔草（Carex atro-fusca）的空间格局从放牧后的聚集分布转向随机分布。因此,退化的矮嵩草草甸在围封的初始阶段,由于避免了家畜的选择性采食及其践踏作用,首先可能是使主要种群的空间分布格局有从随机分布向聚集分布变化的趋势,从而使小尺度的种间隔离来降低种间的竞争强度,从而改变了不同物种对资源和空间的竞争能力,进而推动群落物种组成和结构的恢复演替。

青藏高原3种主要植被类型的表观量子效率和最大光合速率的比较

以海北高寒草甸生态系统定位站的涡度相关系统连续观测的CO_2通量数据为基础,分析了青藏高原的高寒矮嵩草(Kobresia humilis)草甸、高寒金露梅(Potentilla fruticosa)灌丛草甸和高寒藏嵩草(Kobresia tibetica)沼泽化草甸等3种主要植被类型在2005年植物生长季(6-9月)的表观量子产额(a)、最大光合速率(Pmax)和呼吸速率(Reco)的变化特征.结果表明:3种植被类型白天的净生态系统CO_2交换量(NEE)和光量子通量密度(PPFD)存在明显的直角双曲线关系(P＜0.05),其a、Pmax和Reco呈现出相似的季节变化趋势,在生长季初期(6月)最小,在7月或8月份达到最大;高寒矮嵩草草甸的a、Pmax和Reco大于灌丛草甸和沼泽化草甸,而后两者差别不大.

青藏高原两种草甸地表通量季节变化特征

2003年1月-2004年7月运用涡度相关法技术研究青藏高原金露梅(Potentilla fruticosa)灌丛草甸(SWM)和藏嵩草(Kobresia humilis)沼泽化草甸(SRM)的地表通量。结果表明：二者地表湍流通量都具有明显的季节变化和日变化，其中感热通量以4月最大，1月最小，而潜热通量则以5月最大；感热通量随着季节的变动而显著变化，在相同月份中沼泽化草甸白天最大值大于灌丛草甸，日变化振幅比灌丛草甸强；白天潜热通量达到最大值的时间和波动强度因季节不同而各异，在非生长季节白天最大值在13～15 h，日波动较弱，生长季节最大值在12 h，日波动较强；高寒草甸地表湍流通量与温度间存在着线性关系；不同季节感热通量：沼泽化草甸>灌丛革甸，而潜热通量与感热通量各异，在1月沼泽化革匈>灌丛草甸，在4和10月，沼泽化草甸<灌丛草甸，在7月二者基本一致。

青藏高原矮嵩草草甸和金露梅灌丛草甸CO2通量变化与环境因子的关系

利用涡度相关技术观测了青藏高原两个典型的生态系统即矮嵩草（Kobresia humilis）草甸和金露梅（Potentilla fruticosa）灌丛草甸的CO2通量，并就2003年8月份的数据，分析了生态系统通量变化与环境因子的关系。8月份是这两个生态系统的叶面积指数达到最高也是相对稳定的时期，在此期间矮嵩草草甸和金露梅灌丛草甸净碳吸收量分别达56．2和32．6g C•m^-2，日CO2吸收量最大值分别为12．7μmol•m^-2•s^-1和9．3μmol•m^-2•s^-1，排放量最大值分别为5．1μmol•m^-2•s^-1和5．7μmol•m^-2•s^-1。在相同光合有效光量子通量密度（PPFD）条件下，矮嵩草草甸CO2吸收速度大于金露梅灌丛草甸；在PPFD高于1200μmol•m^-2•s^-1。的条件下，随气温增加，两生态系统的CO2吸收速度都下降，但矮嵩草草甸的下降速度（-0．086）比金露梅灌丛草甸（-0．016）快。土壤水分影响土壤呼吸，并且影响差异因植被类型不同而不同。生态系统日CO2吸收量随昼夜温差增加而增大；较大的昼夜温差导致较高的净CO2交换量；植物反射率与CO2通量之间存在负相关关系。

高寒金露梅灌丛生物量及年周转量

采用样方调查与挖掘相结合的方法，以金露梅（Potentilla fruticosa）灌丛多年累积枝干、地下生物量和当年新生枝叶量及6-9月冠面长度、宽度和高度为参数进行线性回归分析，结合金露梅灌丛与草本植物在样地所占比例，估算其年净初级生产量及年净固碳量。结果表明：2004年金露梅灌丛地下实际周转量为53．7g／m^2，周转率为26％；当年新生枝叶量为41．0g／m^2，年净初级生产量94．7g／m^2；以草本植物与金露梅灌丛在样地所占比例为60％和40％进行估算，2004年金露梅灌丛草甸总净初级生产量为858．3g／m^2，固碳量481．9g／m^2。

高寒灌丛草甸生态系统CO2释放的初步研究

以金露梅(Potentilla fruticosa)灌丛草甸生态系统为对象，应用静态密闭箱-气相色谱法对高寒灌丛(GG)、丛内草甸(GC)和裸地(GL)的CO2释放进行了初步研究。结果表明：GG、GC和GL CO2的释放速率均呈明显的单峰型日变化进程，最大释放速率出现在15：00～17：00之间，最小值在7：00前后出现，白天释放速率大于夜晚；CO2释放速率具有明显的季节性变化特征，生长期CO2释放速率明显高于枯黄期，且均表现为正排放，8月为CO2释放高峰期，释放速率GG>GC>GL(P<0．01)；2003年6月30日至2004年2月28日，高寒灌丛植被-土壤系统CO2释放量为3088．458±287．02g／m^2，丛内草甸植被-土壤系统CO2释放量为2239．685±183．68g／m^2，其中基础土壤呼吸CO2的释放量约为1346．748±176．24g／m^2，分别占GG和GC释放量的43．61％和60．13％；CO2释放速率的日变化主要受地表和5cm地温制约，而季节动态与5cm地温呈显著正相关关系(P<0．01)。

海北高寒灌丛草甸生态系统CO2释放速率的季节变化规律

在中国科学院海北高寒草甸生态系统定位站干柴滩地区以金露梅Potentilla fruticosa灌丛草甸生态系统为研究对象,应用静态密闭箱-气相色谱法对高寒灌丛(GG)、丛内草甸(GC)和次生裸地(GL)的CO2释放速率进行了长期观测,并对年释放量作了初步估测.结果表明,GG,GC和GL CO2的释放速率在一年内有明显的季节变化.植物生长季CO2释放量明显高于枯黄期,释放速率GG>GC>GL(P＜0.01),且均表现为正排放.不同季节CO2释放存在明显差异,表现为夏季＞秋季＞春季＞冬季.2003年6月30日至2004年6月28日,高寒灌丛植被-土壤系统CO2释放量为4 293.63±955.75 g/m2,丛内草甸植被-土壤系统CO2释放量为3 319.68±806.19 g/m2,裸地CO2的释放量为1 724.14±444.14 g/m2.CO2释放速率的季节变化与土壤5 cm温度呈显著正相关关系(P＜0.01).

Carbon Dioxide Exchange Between the Atmosphere and an Alpine Shrubland Meadow During the Growing Season on the Qinghai-Tibetan Plateau

In the present study, we used the eddy covariance method to measure CO2 exchange between the atmosphere and an alpine shrubland meadow ecosystem (37°36'N, 101°18'E; 3 250 m a.s.l.) on the Qinghai-Tibetan Plateau, China, during the growing season in 2003, from 20 April to 30 September. This meadow is dominated by formations of Potentilla fruticosa L. The soil is Mol-Cryic Cambisols. During the study period, the meadow was not grazed. The maximum rates of CO2 uptake and release derived from the diurnal course of CO2 flux were -9.38 and 5.02 μmol•m-2•s-1, respectively. The largest daily CO2 uptake was 1.7 g C•m-2•d-1 on 14 July, which is less than half that of an alpine Kobresia meadow ecosystem at similar latitudes. Daily CO2 uptake during the measurement period indicated that the alpine shrubland meadow ecosystem may behave as a sink of atmospheric CO2 during the growing season. The daytime CO2 uptake was correlated exponentially or linearly with the daily photo synthetic photon flux density each month. The daytime average water use efficiency of the ecosystem was 6.47 mg CO2/g H2O. The efficiency of the ecosystem increased with a decrease in vapor pressure deficit.

Comparative study on CO2 emissions from different types of alpine meadows during grass exuberance period

Potentilla fruticosa scrub, Kobresia humilis meadow and Kobresia tibetica meadow are widely distributed on the Qinghai-Tibet Plateau. During the grass exuberance period from 3 July to 4September, based on close chamber-GC method, a study on CO2 emissions from different treatments was conducted in these meadows at Haibei research station, CAS. Results indicated that mean CO2emission rates from various treatments were 672.09+152.37 mgm-2h-1 for FC (grass treatment); 425.41+191.99 mgrn-2h-1 for FJ (grass exclusion treatment); 280.36+174.83 mgrn-2h-1 for FL (grass and roots exclusion treatment); 838.95+237.02 mgm-2h-1 for GG (scrub+grass treatment); 528.48+205.67 mgm-2h-1for GC (grass treatment); 268.97 ±99.72 mgm-2h-1 for GL (grass and roots exclusion treatment); and 659.20±94.83 mgm-2h-1 for LC (grass treatment), respectively (FC, FJ, FL, GG, GC, GL, LC were the Chinese abbreviation for various treatments). Furthermore, Kobresia humilis meadow, Potentilla fruticosa scrub meadow and Kobresia tibetica meadow differed greatly in average CO2 emission rate of soil-plant system, in the order of GG＞FC＞LC＞GC. Moreover, in Kobresia humilis meadow,heterotrophic and autotrophic respiration accounted for 42% and 58% of the total respiration of soil-plant system respectively, whereas, in Potentilla fruticosa scrub meadow, heterotrophic and autotrophic respiration accounted for 32% and 68% of total system respiration from G-G; 49% and 51%from GC. In addition, root respiration from Kobresia humilis meadow approximated 145 mgCO2m-2h-1,contributed 34% to soil respiration. During the experiment period, Kobresia humilis meadow and Potentilla fruticosa scrub meadow had a net carbon fixation of 111.11 grn-2 and 243.89 grn-2,respectively. Results also showed that soil temperature was the main factor which influenced CO2 emission from alpine meadow ecosystem, significant correlations were found between soil temperature at 5 cm depth and CO2 emission from GG, GC, FC and FJ treatments. In addition, soil moisture may be the inhibitory factor of CO2 emission from Kobresia tibetica meadow, and more detailed analyses should be done in further research.