Ecological genetics of Juglans nigra: Differences in early growth patterns of natural populations

Many boreal and temperate forest tree species distributed across large geographic ranges are composed of populations adapted to the climate they inhabit. Forestry provenance studies and common gardens provide evidence of local adaptation to climate when associations between fitness traits and the populations'' home climates are observed. Most studies that evaluate tree height as a fitness trait do so at a specific point in time. In this study, we elucidate differences in early growth patterns in black walnut (Juglans nigra L.) populations by modeling height growth from seed up to age 11. The data comprise tree height measurements between ages 2 and 11 for 52 natural populations of black walnut collected through its geographic range and planted in one or more of 3 common gardens. We use the Chapman–Richards growth model in a mixed effects framework and test whether populations differ in growth patterns by incorporating populations'' home climate into the model. In addition, we evaluate differences in populations'' absolute growth and relative growth based on the fitted model. Models indicated that populations from warmer climates had the highest cumulative growth through time, with differences in average tree height between populations from home climates with a mean annual temperature (MAT) of 13°C and of 7°C estimated to be as high as 80% at age 3. Populations from warmer climates were also estimated to have higher and earlier maximum absolute growth rate than populations from colder climates. In addition, populations from warm climates were predicted to have higher relative growth rates at any given tree size. Results indicate that natural selection may shape early growth patterns of populations within a tree species, suggesting that fast early growth rates are likely selected for in relatively mild environments where competition rather than tolerance to environmental stressors becomes the dominant selection pressure.     

Stability and synchrony across ecological hierarchies in heterogeneous metacommunities: linking theory to data

Understanding stability across ecological hierarchies is critical for landscape management in a changing world. Recent studies showed that synchrony among lower‐level components is key to scaling temporal stability across two hierarchical levels, whether spatial or organizational. But an extended framework that integrates both spatial scale and organizational level simultaneously is required to clarify the sources of ecosystem stability at large scales. However, such an extension is far from trivial when taking into account the spatial heterogeneities in real‐world ecosystems. In this paper, we develop a partitioning framework that bridges variability and synchrony measures across spatial scales and organizational levels in heterogeneous metacommunities. In this framework, metacommunity variability is expressed as the product of local‐scale population variability and two synchrony indices that capture the temporal coherence across species and space, respectively. We develop an R function ‘var.partition’ and apply it to five types of desert plant communities to illustrate our framework and test how diversity shapes synchrony and variability at different hierarchical levels. As the observation scale increased from local populations to metacommunities, the temporal variability of plant productivity was reduced mainly by factors that decreased species synchrony. Species synchrony decreased from local to regional scales, and spatial synchrony decreased from species to community levels. Local and regional species diversity were key factors that reduced species synchrony at the two scales. Moreover, beta diversity contributed to decreasing spatial synchrony among communities. We conclude that our new framework offers a valuable toolbox for future empirical studies to disentangle the mechanisms and pathways by which ecological factors influence stability at large scales.     

Global Biogeography and Quantitative Seasonal Dynamics of Gemmatimonadetes in Soil

Bacteria belonging to phylum Gemmatimonadetes comprise approximately 2% of soil bacterial communities. However, little is known of their ecology due to a lack of cultured representation. Here we present evidence from biogeographical analyses and seasonal quantification of Gemmatimonadetes in soils, which suggests an adaptation to low soil moisture.     

Effect of incubation temperature on zearalenone production by strains of Fusarium crookwellense.

After 6 weeks incubation on rice 2 strains of Fusarium crookwellense produced more zearalenone (6060-5010 mg/kg dry wt of culture) at ambient temperature (16-29 degrees C) in daylight than at ambient temperature (18-23 degrees C) in darkness or at controlled temperatures of 11 degrees C, 20 degrees C or 25 degrees C in darkness. Yields at 25 degrees C were low. Incubation at 11 degrees C during the second 3 weeks incubation increased yields only when preliminary incubation had been at 25 degrees C. After 6 weeks incubation at controlled temperatures in darkness, 4 strains produced most zearalenone at 20 degrees C (2460-21 360 mg/kg), 1 strain at 11 degrees C (6570 mg/kg). Yields at a temperature oscillating daily from 10-20 degrees C were less than at 15 degrees C. One of the 5 strains produced appreciable amounts of a-zearlaenol (1645 mg/kg at 20 degrees C) and 2 of nivalenol (340 and 499 mg/kg at 20 degrees C).