Plant history and soil history jointly influence the selection environment for plant species in a long‐term grassland biodiversity experiment

Long‐term biodiversity experiments have shown increasing strengths of biodiversity effects on plant productivity over time. However, little is known about rapid evolutionary processes in response to plant community diversity, which could contribute to explaining the strengthening positive relationship. To address this issue, we performed a transplant experiment with offspring of seeds collected from four grass species in a 14‐year‐old biodiversity experiment (Jena Experiment). We used two‐ and six‐species communities and removed the vegetation of the study plots to exclude plant–plant interactions. In a reciprocal design, we transplanted five “home” phytometers (same origin and actual environment), five “away‐same” phytometers (same species richness of origin and actual environment, but different plant composition), and five “away‐different” phytometers (different species richness of origin and actual environment) of the same species in the study plots. In the establishment year, plants transplanted in home soil produced more shoots than plants in away soil indicating that plant populations at low and high diversity developed differently over time depending on their associated soil community and/or conditions. In the second year, offspring of individuals selected at high diversity generally had a higher performance (biomass production and fitness) than offspring of individuals selected at low diversity, regardless of the transplant environment. This suggests that plants at low and high diversity showed rapid evolutionary responses measurable in their phenotype. Our findings provide first empirical evidence that loss of productivity at low diversity is not only caused by changes in abiotic and biotic conditions but also that plants respond to this by a change in their micro‐evolution. Thus, we conclude that eco‐evolutionary feedbacks of plants at low and high diversity are critical to fully understand why the positive influence of diversity on plant productivity is strengthening through time.     

Competition for safe real estate,not food,drives density‐dependent juvenile survival in a large herbivore

Density‐dependent competition for food reduces vital rates, with juvenile survival often the first to decline. A clear prediction of food‐based, density‐dependent competition for large herbivores is decreasing juvenile survival with increasing density. However, competition for enemy‐free space could also be a significant mechanism for density dependence in territorial species. How juvenile survival is predicted to change across density depends critically on the nature of predator–prey dynamics and spatial overlap among predator and prey, especially in multiple‐predator systems. Here, we used a management experiment that reduced densities of a generalist predator, coyotes, and specialist predator, mountain lions, over a 5‐year period to test for spatial density dependence mediated by predation on juvenile mule deer in Idaho, USA. We tested the spatial density‐dependence hypothesis by tracking the fate of 251 juvenile mule deer, estimating cause‐specific mortality, and testing responses to changes in deer density and predator abundance. Overall juvenile mortality did not increase with deer density, but generalist coyote‐caused mortality did, but not when coyote density was reduced experimentally. Mountain lion‐caused mortality did not change with deer density in the reference area in contradiction of the food‐based competition hypothesis, but declined in the treatment area, opposite to the pattern of coyotes. These observations clearly reject the food‐based density‐dependence hypothesis for juvenile mule deer. Instead, our results provide support for the spatial density‐dependence hypothesis that competition for enemy‐free space increases predation by generalist predators on juvenile large herbivores.     

Diet estimation based on an integrated mixed prey feeding experiment using Arctocephalus seals

Food web models depend on identifying which taxa are eaten and in what proportion they are consumed. Arctocephalus seals are generalist foragers and are an ongoing focus of Southern Hemisphere marine ecosystem research. This is the first feeding experiment to use Arctocephalus spp. to assess the utility of hard part scat analysis for diet estimation, based on mixed prey diets integrated over several days. Recovery rates of otoliths were extremely low for all taxa (0-9%). Although we could not collect scats produced during a 90 min period each day, during which the seals had access to a large pool, this result could not be attributed to otolith robustness, pinniped species or class, activity level, meal size or frequency, or fat content of the diet. We conclude that the unusually low recovery rates in this study may be due to unaccounted scats produced during 90 min of each day, if they contained otolith numbers an order of magnitude greater than all otoliths retrieved from scats produced during the other 22.5 h of each day, and/or may be related to the digestive processing of a mixed prey diet. Our study demonstrates the inadequacy of using otoliths in field collected scats for diet estimation due to the high level of unexplained variability of otolith occurrence in scats. We also identify two new potential sources of this variability. These are variability in numbers of otoliths per scat depending on activity level when a scat is excreted, and variability in recovery rates of otoliths as a function of the complexity of the diet.     

Influence of bacterivorous nematodes on the decomposition of cordgrass

The influence of bacterivorous nematodes (Diplolaimelloides meyli, Diplolaimelloides oschei, Diplolaimella dievengatensis, Panagrolaimus paetzoldi) on the decomposition of a macrophyte (Spartina anglica) in an aquatic environment was investigated by using laboratory microcosm experiments. Several earlier studies have shown enhancement of the decomposition process in the presence of nematodes, but nematode species-specific effects were never tested. In this study four bacterivorous nematode species were applied separately to microcosms to investigate such species-specific influences.No stimulation of the decomposition process nor of the microbial community was observed in the presence of the nematodes, both were highest in the absence of nematodes. However, clear differences were found between nematode treatments. P. paetzoldi reached much higher numbers than the other species, causing a decrease in microbial activity, probably due to (over)grazing. Remarkably this low microbial activity did not result in a slow-down of the decomposition process compared to the other nematode treatments, raising the question whether P. paetzoldi might be able to directly assimilate detrital compounds. Other nematode species reached much lower densities, but nevertheless an influence on the decomposition process was observed. However, this experiment does not support the view that bacterivorous nematodes enhance decomposition rate.The experimental results show that in nematode communities the use of functional groups is inadequate for biodiversity studies. The four nematode species used in this study belong to the same functional group, but are clearly not functionally redundant since they all have a different influence on the cordgrass decomposition. This suggests that the relationship between nematode species diversity and ecosystem functioning may be idiosyncratic.     

Simulating trends in crop yield and soil carbon in a long-term experiment—effects of rising CO2, N deposition and improved cultivation

Measurements of crop yield and soil carbon in the Bad Lauchstädt long-term fertiliser experiment were analysed with the FASSET model. The model satisfactorily predicted yield and soil carbon development in four treatments: no fertiliser, mineral fertiliser, farmyard manure and farmyard manure plus mineral fertiliser. However, there was a residual between the observed and simulated yield, which was correlated with year. This could be attributed to an increase in observed yields during the last six decades. Scenario analysis showed that the most probable explanation for this yield increase was the use of new crop varieties and/or pesticides, while the increase in atmospheric CO₂ and changes in local N deposition were of lesser importance. The rise in CO₂ thus only explained 9–37% of the yield increase. The observed and simulated developments in soil carbon were quite different in the four treatments. However, the changes within each treatment for different scenarios were much smaller than the substantial difference between treatments. Thus, it was concluded that the type of nutrient applied was more important than development in CO₂ concentration or N deposition in determining soil carbon.     

In Vivo Accumulation of Plastic-Derived Chemicals into Seabird Tissues

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Relative importance of drought,soil quality,and plant species in determining the strength of plant–herbivore interactions

1. Although studies on plant–herbivore interactions comparing different plant species are common, little is known about the importance of environmental conditions in determining variation in herbivory within single plant species. 2. This study assessed the effects of experimentally manipulated nutrient and water availability on plant palatability, and compared these differences with differences among species. The extent to which these patterns can be explained by leaf toughness and specific leaf area was also investigated. Six plant species from the subfamily Carduoideae and four free‐living leaf chewing invertebrates were used in the study. 3. Herbivore preferences were significantly affected by soil nutrients and water regime and varied among plant as well as herbivore species. Generally, herbivores preferred watered plants and plants from nutrient‐poor soil. The effects of soil nutrients and water regime differed between the plant and herbivore species. The differences between the plant species were greater than those between the environmental treatments. Differences at both levels could be partly explained by leaf toughness and specific leaf area. Leaf toughness, in particular, turned to be an important predictor indicating that herbivores preferred species with softer leaves, and species from wetter conditions with reduced leaf toughness. 4. The environmental conditions in which plants are growing have significant effects on plant palatability. Between‐species comparisons thus need to pay attention to this variation. Future studies may consider how the effects of current conditions interact with conditions of plant origin to predict possible effects of changes in environmental conditions on the intensity of plant–herbivore interactions.     

Optimization of Recombinant Cytochrome P450 2C9 Protein Production in Escherichia coli DH5α by Statistically-Based Experimental Design

Cytochrome P450 (CYP) 2C9 is of major importance in drug metabolism. However, the low yield of recombinant CYP2C9 protein in E. coli strains prevents its extensive use in the study of in vitro drug metabolism. In the present study, Taguchi design and desirability function were first used to investigate the effect of medium components (glycerol, δ-ALA, IPTG, ampicillin, chloramphenicol, inoculum density, peptone, thiamine, trace elements, NH₄Cl, and MgSO₄) on recombinant human CYP2C9 production by E. coli DH5α. An L₁₂ (2¹¹) orthogonal array was used to design the experiments to screen out the most influential factors. The CYP concentration and the specific content of CYP were considered as two product quality variables. A desirability function was applied to combine these two qualities as a single objective function. Optimization via central composite design (CCD) was then undertaken to yield the best performance. The confirmation experiments indicated that the expression performance under the optimized conditions was better than those obtained under other conditions. A compromise between conflicting goals, such as achievement of good yield of recombinant CYP2C9 and facility of the following purification, was found by means of the desirability function D. This is the first report that combined Taguchi design and CCD, and performed experiments in a multiresponse framework to optimize the production of human CYP in a recombinant E. coli strain.