Diversity and seasonal phenology of aboveground arthropods in conventional and transgenic maize crops in Central Spain

One of the major concerns regarding the release of Bt maize is its potential negative impact on non-target organisms present in this crop. In this paper, we compare the temporal phenology and community structure of the aboveground arthropods in commercial Bt maize fields in Central Spain with those of conventional maize crops, with or without an insecticide (imidacloprid) seed treatment, over a period of three years. Spiders, harvestmen, centipedes, ground beetles, rove beetles, carrion beetles, click beetles, earwigs and damsel bugs were captured in pitfall traps every year in sufficient number to provide meaningful phenological data. One predator spider and three omnivorous species of ground beetles have been consistently present in the maize fields: Pardosa occidentalis, Poecilus cupreus, Pseudophonus rufipes and Pseudophonus griseus, respectively. Rove beetles were caught to a lesser extent, with three dominant species: Acrotona aterrima, Philonthus varians and Platystethus nitens. The variability in activity–density patterns of the aboveground fauna was mainly influenced by the year, but no detrimental effects could be attributed to Bt maize. The only exception being the changes detected in rove beetles, although these differences were transitory and varied from year to year. No changes in species richness and diversity indices for spiders and ground beetles resulted from treatments. However, imidacloprid-treated maize caused a reduction in species richness of rove beetles, even though the abundance of the main species was not reduced. Our results suggest that Bt maize could be compatible with natural enemies that are common in maize fields in Spain.     

基因型与环境对小麦品种粉质参数的影响

用陕西省关中小麦品种区域试验所选用的20个小麦品种(品系)在12个试点1996～1997、1997～1998两年度的数据资料,分析了品种、环境及品种×环境互作(GEI)对粉质参数的影响。结果表明:品种与环境对所有粉质参数指标均有显著影响,但由品种决定的粉质参数的变异程度远大于环境引起的变异。基因型×环境互作效应对形成时间、稳定时间、软化度与评价值影响较大,而对吸水率影响较小。品种稳定性分析的回归系数(b值)表明基因型对不同环境的反应存在着显著差异。对每一粉质参数指标大部分品种都具有平均稳定性,只有1至2个品种稳定性显著较好或较差。     

Plant diversity effects on pollinating and herbivorous insects can be linked to plant stoichiometry

Changes in plant diversity have consequences for higher trophic levels, e.g., higher plant diversity can enhance the reproduction and fitness of plant-associated insects. This response of higher trophic levels potentially depends on diversity-related changes in both resource quantity (abundance) and quality (nutritional content). The availability of elemental nutrients in plant resources is one aspect of nutritional quality, but has rarely been addressed as a pathway relating plant diversity to associated insects. Using the experimental plant diversity gradient of a large biodiversity grassland project, the Jena-Experiment, we analysed the %C, %N and %P and the molar ratios of those elements (C:N, C:P and N:P) in a pollinating bee, Chelostoma distinctum, and an herbivorous grasshopper, Chorthippus parallelus, reared on plots of different plant diversity. Insects showed higher content of C, N and P (% dry mass), and lower C:N and C:P ratios than plants. C:N ratios were significantly higher in grasshoppers than in bees and higher in females than in males of both species. Increasing plant species richness increased the C:N ratio of male bees and female grasshoppers. In both groups, stoichiometry was positively related to plant stoichiometry (male bees: C:P and N:P; grasshoppers: C:N and N:P). Path analysis revealed that diversity-driven changes in plant elemental composition can have consequences for abundance and chemical composition of higher trophic levels, with different responses of the two functional groups.     

Soil legacy effects of plants and drought on aboveground insects in native and range-expanding plant communities

Soils contain biotic and abiotic legacies of previous conditions that may influence plant community biomass and associated aboveground biodiversity. However, little is known about the relative strengths and interactions of the various belowground legacies on aboveground plant–insect interactions. We used an outdoor mesocosm experiment to investigate the belowground legacy effects of range-expanding versus native plants, extreme drought and their interactions on plants, aphids and pollinators. We show that plant biomass was influenced more strongly by the previous plant community than by the previous summer drought. Plant communities consisted of four congeneric pairs of natives and range expanders, and their responses were not unanimous. Legacy effects affected the abundance of aphids more strongly than pollinators. We conclude that legacies can be contained as soil ‘memories’ that influence aboveground plant community interactions in the next growing season. These soil-borne ‘memories’ can be altered by climate warming-induced plant range shifts and extreme drought.     

Conflicting management objectives on the Colorado Plateau: Understanding the effects of bison and cattle grazing on plant community composition

The American Bison (Bison bison Linnaeus) in the Henry Mountains are one of the last free-roaming, genetically pure herds of bison remaining in North America. Anecdotal evidence indicates that this herd is utilising a cattle winter range during the summer and fall, creating a conflict between the state agency that manages the bison, and the Bureau of Land Management (BLM) and local ranchers. In theory, the addition of bison grazing pressure could reduce forage availability in the short term and lead to undesired changes in the plant community in the long term. Our objective was to determine whether bison have altered the plant species composition of the cattle winter range. We characterised plant species composition, percent cover, and grazing intensity on three adjacent, geomorphologically similar mesas. Grazing regimes were different on the three mesas, one with bison and cattle present, one with cattle only present, and the third with neither cattle nor bison present. Vegetation surveys were accompanied by a 28-year remote sensing time series to test for temporal shifts in an index of primary productivity. We found a higher grazing intensity on two dominant forage species on the bison plus cattle grazed mesa in fall, before the cattle were turned out to winter pasture. Despite this difference in grazing intensity, we found few differences in species composition, percent cover, or NDVI across the three grazing regimes. Our results suggest that high intensity summer bison grazing, while likely creating short-term reductions in forage availability, has not caused differences in plant community composition or productive potential. Shifts in community composition can take years to unfold and just as long to correct; therefore, continued monitoring of the combined effects of cattle and bison is needed.     

不同施肥水平对不同品种小麦籽粒蛋白质和地上器官游离氨基酸含量的影响

研究了小麦不同品种开花后各地上器官游离氨基酸含量的变化动态及其与籽粒蛋白质含量的关系,以及氮素营养的调节作用。结果表明,小麦叶片和颖壳十穗轴游离氨基酸含量均在开花后持续增加,至花后14d达到最大值,之后开始下降。茎和叶鞘游离氨基酸含量则在开花后上升较缓慢,至花后21d达最大值。籽粒游离氨基酸含量一般在开花后就持续降低。各地上器官游离氨基酸含量与成熟期籽粒蛋白质含量均呈显著或极显著正相关,说明源器宫中游离氨基酸供应充足,有利于籽粒蛋白质积累。增施氮肥能够提高各地上器官中的游离氨基酸含量,进而促进籽粒蛋白质的合成,提高籽粒蛋白质含量。品种之间籽粒蛋白质含量的差异,是由各地上营养器官向籽粒运输氨基酸的综合作用所造成的。