Kelly D. McConnaughay

Interpreting phenotypic variation in plants

Plant ecologists and evolutionary biologists frequently examine patterns of phenotypic variation across variable environments or genetic identities. Too often, we ignore the fact that most phenotypic traits change throughout growth and development of individual plants, and that rates of growth and development are highly variable. Plants growing in different environments are likely to grow at different rates, and will be of different sizes and stages of development at a particular age. When we compare plants as a function of plant size or developmental stage, as well as a function of age, we broaden our understanding of phenotypic variation between plants.

BIOMASS ALLOCATION IN PLANTS: ONTOGENY OR OPTIMALITY? A TEST ALONG THREE RESOURCE GRADIENTS

We examined biomass allocation patterns throughout the entire vegetative growth phase for three species of annual plants along three separate gradients of resource availability to determine whether observed patterns of allocational plasticity are consistent with optimal partitioning theory. Individuals of the annual plant species Abutilon theophrasti, Chenopodium album, and Polygonum pensylvanicum were grown from locally field-gathered seed in controlled greenhouse conditions across gradients of light, nutrients, and water. Frequent harvests were used to determine the growth and allocation (root vs. shoot, and leaf area vs. biomass) responses of these plants over a 57-d period. Growth analysis revealed that each species displayed significant plasticity in growth rates and substantial amounts of ontogenetic drift in root:shoot biomass ratios and ratios of leaf area to biomass across each of the three resource gradients. Ontogenetically controlled comparisons of root:shoot and leaf area ratios across light ...

Can plants track changes in nutrient availability via changes in biomass partitioning

Can old-field annuals exposed to temporally varying nutrient regimes adjust biomass partitioning programs in order to maximize growth? We grew three species of old-field annuals, Abutilon theophrasti, Chenopodium album, and Polygonum pensylvanicum, at low or high nutrient levels, and switched a subset of plants to the alternate nutrient regime after one or two weeks of growth. If plants were able to partition biomass in an optimal fashion, it would be predicted that changes in growth would be accompanied by changes in biomass partitioning programs. We found that when nutrient availability changes (e.g., from low to high) early in ontogeny, growth and partitioning to leaf area development are adjusted to be indistinguishable from those of plants grown at constant nutrient availabilities (e.g., always high). Root shoot partitioning, however, was developmentally fixed in two of the three species such that nutrient environment had no effect on root/shoot partitioning. Thus, although fluctuations in nutrient availability altered plant growth, the observed changes in growth occurred without concomitant adjustments to the root/ shoot partitioning program. These results imply that adjustments in allocation of biomass resources, at least between roots and shoots, are not necessary to effect alterations in plant growth in variable environments.

Impacts of elevated CO2 concentration on the productivity and surface energy budget of the soybean and maize agroecosystem in the Midwest USA

The physiological response of vegetation to increasing atmospheric carbon dioxide concentration ([CO2 ]) modifies productivity and surface energy and water fluxes. Quantifying this response is required for assessments of future climate change. Many global climate models account for this response; however, significant uncertainty remains in model simulations of this vegetation response and its impacts. Data from in situ field experiments provide evidence that previous modeling studies may have overestimated the increase in productivity at elevated [CO2 ], and the impact on large-scale water cycling is largely unknown. We parameterized the Agro-IBIS dynamic global vegetation model with observations from the SoyFACE experiment to simulate the response of soybean and maize to an increase in [CO2 ] from 375 ppm to 550 ppm. The two key model parameters that were found to vary with [CO2 ] were the maximum carboxylation rate of photosynthesis and specific leaf area. Tests of the model that used SoyFACE parameter values showed a good fit to site-level data for all variables except latent heat flux over soybean and sensible heat flux over both crops. Simulations driven with historic climate data over the central USA showed that increased [CO2 ] resulted in decreased latent heat flux and increased sensible heat flux from both crops when averaged over 30 years. Thirty-year average soybean yield increased everywhere (ca. 10%); however, there was no increase in maize yield except during dry years. Without accounting for CO2 effects on the maximum carboxylation rate of photosynthesis and specific leaf area, soybean simulations at 550 ppm overestimated leaf area and yield. Our results highlight important model parameter values that, if not modified in other models, could result in biases when projecting future crop-climate-water relationships.

Patterns of defensive chemical production in wild parsnip seedlings (Apiaceae: Pastinaca sativa L.).

Summary. To ascertain patterns of allocation between growth and defense in seedlings, we measured plant biomass and the amount of six furanocoumarin defensive chemicals in wild parsnip roots and shoots (Apiaceae: Pastinaca sativa L.) in sequential harvests for sixty days following emergence and compared them to previous studies on mature plants. Furanocoumarins were present from the first day of emergence and were actively synthesized from the onset of seedling growth. Although initial amounts of each furanocoumarin species differed, they were produced at the same rate. Furanocoumarin production was not commensurate with biomass accretion, and fluctuations in concentration varied dramatically between roots and shoots. Concentrations of furanocoumarins in seedlings are far lower than in adult plants, perhaps because the selective regime of seedlings differs from that of mature plants, and inter-seedling competition favors investment in growth rather than defense.

Confident Voices: How Professional Development for Teachers by Teachers Using Video Promotes Inquiry-Based Practice

Abstract This study examined educators’ self-perception as practitioners of inquiry-based math and science instruction, their motivation to produce videos to share that practice, and the impact of video production on their use of inquiry and role in the professional development community. Semi-structured interviews were used to address the research questions. Participant responses indicated a high level of self-reflection and a keen understanding of the nature of inquiry-based math and science teaching. Participants were motivated to share their practice largely by their desire to help other educators develop as inquiry practitioners. Articulating how and why they used inquiry-based techniques for the videos deepened their already reflective teaching. The positive aspects of participation also increased their confidence in their ability to engage in professional development as teacher-leaders. Overall this study indicated that videos created for the purposes of professional development had a transforming effect on those who produced them in addition to their benefit for others.