Diel plant water use and competitive soil cation exchange interact to enhance NH4+ and K+ availability in the rhizosphere

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Plant and Soil 414 (2017): 33-51, doi:10.1007/s11104-016-3089-5.Hydro-biogeochemical processes in the rhizosphere regulate nutrient and water availability, and thus ecosystem productivity. We hypothesized that two such processes often neglected in rhizosphere models — diel plant water use and competitive cation exchange — could interact to enhance availability of K+ and NH4+, both high-demand nutrients. A rhizosphere model with competitive cation exchange was used to investigate how diel plant water use (i.e., daytime transpiration coupled with no nighttime water use, with nighttime root water release, and with nighttime transpiration) affects competitive ion interactions and availability of K+ and NH4+. Competitive cation exchange enabled low-demand cations that accumulate against roots (Ca2+, Mg2+, Na+) to desorb NH4+ and K+ from soil, generating non-monotonic dissolved concentration profiles (i.e. ‘hotspots’ 0.1–1 cm from the root). Cation accumulation and competitive desorption increased with net root water uptake. Daytime transpiration rate controlled diel variation in NH4+ and K+ aqueous mass, nighttime water use controlled spatial locations of ‘hotspots’, and day-to-night differences in water use controlled diel differences in ‘hotspot’ concentrations. Diel plant water use and competitive cation exchange enhanced NH4+ and K+ availability and influenced rhizosphere concentration dynamics. Demonstrated responses have implications for understanding rhizosphere nutrient cycling and plant nutrient uptake.This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Biological & Environmental Research Terrestrial Ecosystem Science program under Award Number DE-SC0008182 to Z.G.C. and R.B.N

Improving the Efficacy of Web-Based Educational Outreach in Ecology

Scientists are increasingly engaging the web to provide formal and informal science education opportunities. Despite the prolific growth of web-based resources, systematic evaluation and assessment of their efficacy remains limited. We used clickstream analytics, a widely available method for tracking website visitors and their behavior, to evaluate 60,000 visits over three years to an educational website focused on ecology. Visits originating from search engine queries were a small proportion of the traffic, suggesting the need to actively promote websites to drive visitation. However, the number of visits referred to the website per social media post varied depending on the social media platform and the quality of those visits (e.g., time on site and number of pages viewed) was significantly lower than visits originating from other referring websites. In particular, visitors referred to the website through targeted promotion (e.g., inclusion in a website listing classroom teaching resources) had higher quality visits. Once engaged in the site’s core content, visitor retention was high; however, visitors rarely used the tutorial resources that serve to explain the site’s use. Our results demonstrate that simple changes in website design, content and promotion are likely to increase the number of visitors and their engagement. While there is a growing emphasis on using the web to broaden the impacts of biological research, time and resources remain limited. Clickstream analytics provides an easily accessible, relatively fast and quantitative means by which those engaging in educational outreach can improve upon their efforts

Hysteresis of soil moisture spatial heterogeneity and the “homogenizing” effect of vegetation

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94935/1/wrcr12475.pd

Overcoming the barriers to teaching teamwork to undergraduates in STEM.

There is widespread recognition that undergraduate students in the life sciences must learn how to work in teams. However, instructors who wish to incorporate teamwork into their classrooms rarely have formal training in how to teach teamwork. This is further complicated by the application of synonymous and often ambiguous terminology regarding teamwork that is found in literature spread among many different disciplines. There are significant barriers for instructors wishing to identify and implement best practices. We synthesize key concepts in teamwork by considering the knowledge, skills, and attitudes (KSAs) necessary for success, the pedagogies and curricula for teaching those KSAs, and the instruments available for evaluating and assessing success. There are only a limited number of studies on teamwork in higher education that present an intervention with a control group and a formal evaluation or assessment. Moreover, these studies are almost exclusively outside STEM disciplines, raising questions about their extensibility. We conclude by considering how to build an evidence base for instruction that will empower students with the KSAs necessary for participating in a lifetime of equitable and inclusive teamwork

Data from: Improving the efficacy of web-based educational outreach in ecology

Scientists are increasingly engaging the web to provide formal and informal science education opportunities. Despite the prolific growth of web-based resources, systematic evaluation and assessment of their efficacy remains limited. We used clickstream analytics, a widely available method for tracking website visitors and their behavior, to evaluate >60,000 visits over three years to an educational website focused on ecology. Visits originating from search engine queries were a small proportion of the traffic, suggesting the need to actively promote websites to drive visitation. However, the number of visits referred to the website per social media post varied depending on the social media platform and the quality of those visits (e.g., time on site and number of pages viewed) was significantly lower than visits originating from other referring websites. In particular, visitors referred to the website through targeted promotion (e.g., inclusion in a website listing classroom teaching resources) had higher quality visits. Once engaged in the site's core content, visitor retention was high; however, visitors rarely used the tutorial resources that serve to explain the site's use. Our results demonstrate that simple changes in website design, content and promotion are likely to increase the number of visitors and their engagement. While there is a growing emphasis on using the web to broaden the impacts of biological research, time and resources remain limited. Clickstream analytics provides an easily accessible, relatively fast and quantitative means by which those engaging in educational outreach can improve upon their efforts

Modeled profiles of NH4+ and K+ in the rhizosphere resulting from diel plant water use and competitive soil cation exchange, Links to model results

Aims: Hydro-biogeochemical processes in the rhizosphere regulate nutrient and water availability, and thus ecosystem productivity. We hypothesized that two such processes often neglected in rhizosphere models - diel plant water use and competitive cation exchange - could interact to enhance availability of K+ and NH4+, both high-demand nutrients. Methods: A rhizosphere model with competitive cation exchange was used to investigate how diel plant water use (i.e., daytime transpiration coupled with no nighttime water use, with nighttime root water release, and with nighttime transpiration) affects competitive ion interactions and availability of K+ and NH4+. Results: Competitive cation exchange enabled low-demand cations that accumulate against roots (Ca2+, Mg2+, Na+) to desorb NH4+ and K+ from soil, generating non-monotonic dissolved concentration profiles (i.e. 'hotspots' 0.1-1 cm from the root). Cation accumulation and competitive desorption increased with net root water uptake. Daytime transpiration rate controlled diel variation in NH4+ and K+ aqueous mass, nighttime water use controlled spatial locations of 'hotspots', and day-to-night differences in water use controlled diel differences in 'hotspot' concentrations. Conclusions: Diel plant water use and competitive cation exchange enhanced NH4+ and K+ availability and influenced rhizosphere concentration dynamics. Demonstrated responses have implications for understanding rhizosphere nutrient cycling and plant nutrient uptake

Appendix G. Results of the proportional hazards regression for root survivorship data (species and root branching order effects).

Results of the proportional hazards regression for root survivorship data (species and root branching order effects)

Limited potential for terrestrial carbon sequestration to offset fossil-fuel emissions in the upper midwestern US

Many carbon dioxide (CO2) emission-reduction strategies currently under consideration rely on terrestrial carbon (C) sequestration to offset substantial proportions of CO2 emissions. We estimated C sequestration rates and potential land areas for a diverse array of land-cover changes in the Upper Midwest of the US, a “best case” region for this study because of its relatively modest CO2 emissions and the large areas of cropland potentially available for conversion. We then developed scenarios that apply some of the most widespread mitigation strategies to the region: the first, which aimed to offset 29% of regional CO2 emissions, required the unrealistic loss of two-thirds of working cropland; the second, which estimated the emission offset attainable by conversion of 10% of harvested croplands (5.8% of the US total), resulted in < 5% CO2 emissions reduction for the region (<1.1% of total US emissions). There is limited capacity for terrestrial C sequestration, so strategies should aim to directly reduce CO2 emissions to mitigate rising atmospheric CO2 concentrations

Appendix H. A figure showing the species-specific time courses of the number of living roots pertaining to each seasonal cohort.

A figure showing the species-specific time courses of the number of living roots pertaining to each seasonal cohort