Eric S. Fabio

The Geography of Demography: Long-Term Demographic Studies and Species Distribution Models Reveal a Species Border Limited by Adaptation

Potential causes of species’ geographic distribution limits fall into two broad classes: (1) limited adaptation across spatially variable environments and (2) limited opportunities to colonize unoccupied areas. Combining demographic studies, analyses of demographic responses to environmental variation, and species distribution models, we investigated the causes of range limits in a model system, the eastern border of the California annual plant Clarkia xantiana ssp. xantiana. Vital rates of 20 populations varied with growing season temperature and precipitation: fruit number and overwinter survival of 1-year-old seeds declined steeply, while current-year seed germination increased modestly along west-to-east gradients in decreasing temperature, decreasing mean precipitation, and increasing variation in precipitation. Long-term stochastic finite rate of increase, λs, exhibited a fourfold range and varied among geologic surface materials as well as with temperature and precipitation. Growth rate declined significantly toward the eastern border, falling below 1 in three of the five easternmost populations. Distribution models employing demographically important environmental variables predicted low habitat favorability beyond the eastern border. Models that filtered or weighted population presences by λs predicted steeper eastward declines in favorability and assigned greater roles in setting the distribution to among-year variation in precipitation and to geologic surface material. These analyses reveal a species border likely set by limited adaptation to declining environmental quality.

Genotype × environment interaction analysis of North American shrub willow yield trials confirms superior performance of triploid hybrids

Development of dedicated bioenergy crop production systems will require accurate yield estimates, which will be important for determining many of the associated environmental and economic impacts of their production. Shrub willow (Salix spp) is being promoted in areas of the USA and Canada due to its adaption to cool climates and wide genetic diversity available for breeding improvement. Willow breeding in North America is in an early stage, and selection of elite genotypes for commercialization will require testing across broad geographic regions to gain an understanding of how shrub willow interacts with the environment. We analyzed a dataset of first‐rotation shrub willow yields of 16 genotypes across 10 trial environments in the USA and Canada for genotype‐by‐environment interactions using the additive main effects and multiplicative interactions (AMMI) model. Mean genotype yields ranged from 5.22 to 8.58 oven‐dry Mg ha−1 yr−1. Analysis of the main effect of genotype showed that one round of breeding improved yields by as much as 20% over check cultivars and that triploid hybrids, most notably Salix viminalis × S. miyabeana, exhibited superior yields. We also found important variability in genotypic response to environments, which suggests specific adaptability could be exploited among 16 genotypes for yield gains. Strong positive correlations were found between environment main effects and AMMI parameters and growing environment temperatures. These findings demonstrate yield improvements are possible in one generation and will be important for developing cultivar recommendations and for future breeding efforts.

Whole-Genome Sequences of 13 Endophytic Bacteria Isolated from Shrub Willow (Salix) Grown in Geneva, New York

ABSTRACT Shrub willow, Salix spp. and hybrids, is an important bioenergy crop. Here we report the whole-genome sequences and annotation of 13 endophytic bacteria from stem tissues of Salix purpurea grown in nature and from commercial cultivars and Salix viminalis × Salix miyabeana grown in bioenergy fields in Geneva, New York.

Poplar and shrub willow energy crops in the United States: field trial results from the multiyear regional feedstock partnership and yield potential maps based on the PRISM-ELM model

To increase the understanding of poplar and willow perennial woody crops and facilitate their deployment for the production of biofuels, bioproducts, and bioenergy, there is a need for broadscale yield maps. For national analysis of woody and herbaceous crops production potential, biomass feedstock yield maps should be developed using a common framework. This study developed willow and poplar potential yield maps by combining data from a network of willow and poplar field trials and the modeling power of PRISM‐ELM. Yields of the top three willow cultivars across 17 sites ranged from 3.60 to 14.6 Mg ha−1 yr−1 dry weight, while the yields from 17 poplar trials ranged from 7.5 to 15.2 Mg ha−1 yr−1. Relationships between the environmental suitability estimates from the PRISM‐ELM model and results from field trials had an R2 of 0.60 for poplar and 0.81 for willow. The resulting potential yield maps reflected the range of poplar and willow yields that have been reported in the literature. Poplar covered a larger geographic range than willow, which likely reflects the poplar breeding efforts that have occurred for many more decades using genotypes from a broader range of environments than willow. While the field trial data sets used to develop these models represent the most complete information at the time, there is a need to expand and improve the model by monitoring trials over multiple cutting cycles and across a broader range of environmental gradients. Despite some limitations, the results of these models represent a dramatic improvement in projections of potential yield of poplar and willow crops across the United States.

Soil CO2 effluxes, temporal and spatial variations, and root respiration in shrub willow biomass crops fields along a 19-year chronosequence as affected by regrowth and removal treatments.

In shrub willow biomass crop (SWBC) production systems, the soil CO2 efflux (Fc) component in the carbon cycle remains poorly understood. This study assesses (i) differences of Fc rates among the 5‐, 12‐, 14‐, and 19‐year‐old SWBCs with two treatments: continuous production (regrowth) willow fields that were harvested and allowed to regrow, and willow fields that were harvested, killed, and then stools and roots were ground into the soil (removal); (ii) temporal and spatial variations of Fc rates; (iii) root respiration contributions to total Fc; and (iv) climatic variables affecting Fc. During the growing season (May to September), Fc rates showed no statistically significant differences across different ages (P = 0.664), and between treatments (P = 0.351); however, there was an interaction between age and treatment (P = 0.001). Similarly, during the dormant season (October to April), Fc rates revealed no statistically significant differences across different ages (P = 0.305) and treatment interaction with age (P = 0.097). Fc rates differed significantly (P < 0.001) among different times of the day and times of the year. Fc rates, between 00 and 1059 h, between 1100 and 1659 h, and between 1700 and 2400 h displayed consistency from May to November; however, Fc rates in these three time intervals showed significant differences (P < 0.0001). In December, Fc rates remained constant over 24 h. Fc rates demonstrated higher temporal and spatial variations among willow age classes than between regrowth and removal treatments. Temporal and spatial variations of Fc were higher during the dormant season than during the growing season. The proportion of root respiration to total Fc ranged from 18 to 33% across age classes. Fc rates showed strong association with soil and air temperatures, and relative humidity.

Effects of nitrogen fertilization in shrub willow short rotation coppice production - a quantitative review

Sustained interest in producing renewable energy from dedicated woody biomass crops, such as shrub willow (Salix spp.), through short rotation coppice (SRC) has resulted in a substantial amount of published research on SRC over the past few decades. One area of constant focus has been the nutritional requirements for optimal growth and yield. Inconsistency in the results of individual research trials has likely been a driver of repeated experimentation. This review is intended to provide a quantitative examination of the effect of fertilization treatments on willow biomass yield in field conditions. Data from the literature were collected and summarized to test for significant sources of variation in willow biomass nitrogen (N) pools of common SRC genotypes used in North American and European research programs. A meta‐analysis was conducted on studies comparing synthetic or organic sources of N willow fertilization to an unfertilized control treatment to test for yield response. Overall, the majority of responses to fertilization were positive, although variation by species, N source material, and crop age were found. While no clear pattern in N dosage response was observed, the level of yield response was correlated with geographic and climatic variables. Nitrogen export levels were fairly predictable, and the synthesis presented here can be used to refine current guidelines. Environmental and economic aspects are also considered.

Differential growth response to fertilization of ten elite shrub willow ( Salix spp.) bioenergy cultivars

Key MessageShrub willow triploid hybrid cultivars obtained the greatest aboveground biomass compared to diploid and tetraploid cultivars, and greater biomass was highly correlated with leaf traits and rapid early stem elongation.AbstractShrub willow (Salix L. spp.) is a strong candidate for use as a dedicated bioenergy crop in moist, temperate climates due to high growth rates, excellent regenerative properties and relatively low nutrient demand. Large discrepancies exist in the literature as to the benefits of fertilization for improving biomass production. Controlled environment fertilization studies can remove some confounding edaphic and climatic factors present in field studies. Ten top-performing commercial or pre-commercial cultivars, mostly bred in the US, were assessed for response to five fertilization levels by measuring 20 biomass and growth traits. Triploid hybrid Salix viminalis × S. miyabeana cultivars had the greatest total aboveground biomass, as well as high stem biomass. There was a strong relationship between early stem growth and final aboveground biomass, but only under adequate fertilization. Different strategies for high biomass production among cultivars are discussed in the context of nitrogen investment in leaves. Comparing field trial results and this greenhouse experiment indicates that while the yield ranking is generally preserved, the greenhouse results diverged greatly for two cultivars.