Nitrogen (N) fertilization causes long-term increases in biomass production in many N-limited forests around the world, but the mechanistic basis underlying the increase is often unclear. One possibility, especially in summer-dry climates, is that N fertilization increases the efficiency with which a finite water supply is consumed to support photosynthesis. This increase is achieved by a reduction in the canopy-integrated concentration of internal CO₂ and thus discrimination against ¹³C. We used stable isotopes of carbon (δ¹³C) in tree rings to experimentally test the physiological impact of N fertilization on mature Douglas-fir (Pseudotsuga menziesii Franco var. glauca) stands across the geographic extent of the Intermountain West, USA. The concentration and the stable isotopes of N (δ¹⁵N) in tree rings were also used to assess the presence and activity of fertilizer N. We hypothesized that N fertilization would (i) increase δ¹⁵N and N concentration of stemwood relative to non-fertilized stands and (ii) increase stemwood δ¹³C as photosynthetic gas exchange responded to the additional N. This experiment included two rates of urea addition, 178 kg ha⁻¹ (low) and 357 kg ha⁻¹ (high), which were applied twice over a 6-year interval bracketed by the 18 years of wood production measured in this study. Foliar N concentrations measured the year after each fertilization treatment suggest that the fertilizer N had been assimilated by the trees (P < 0.001). The N fertilization significantly enriched stemwood δ¹⁵N by 1.3‰ at the low fertilization rate and by 2.4‰ at the high rate (P < 0.001) despite variation in soil N between sites. However, we found no significant effect of the N fertilizer on δ¹³C of the annual rings (P = 0.76). These data lead us to suggest that alternative mechanisms underlie the growth response to fertilizer, i.e., increase in canopy area and shifts in biomass allocation.

Rain gardens are residential bioretention practices widely used to manage urban runoff, yet their design as plant-soil systems lacks understanding. We hypothesized that vegetative treatment (turfgrass, prairie, and shrubs, plus a non-vegetated control) would alter the volume and rate of drainage from 12 replicate mesocosms (i.e., rain gardens) through changes to the belowground system. Roof runoff was collected on-site and distributed equally among the mesocosms following natural rain events for two growing seasons. We monitored stormwater input, drainage output, and soil moisture to assess differences in hydrology by treatment, explained by indices of soil structural development (infiltration, saturated hydraulic conductivity, soil water retention). Drainage volume and response dynamics differed as predicted by vegetative treatment in support of our hypothesis. The greatest reductions in drainage volume were observed beneath shrubs and prairie following smaller stormwater inputs, and accelerated drainage responses were observed beneath turfgrass following larger stormwater inputs. Differences in infiltration, saturated hydraulic conductivity, and plant-induced changes in antecedent soil moisture among vegetative treatments help explain these plant-mediated drainage responses. This study shows that plants can alter the hydrologic dynamics of rain gardens and thus are a critical component of the design and intent of these plant-soil systems.

Data from 72 Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) plots across the Interior Northwest were used to determine whether (i) increased intercepted photosynthetically active radiation (%IPAR), effective leaf area index (LAI_e), and stemwood volume production (cubic metres stemwood per hectare per year) could still be detected 7 or 8 years after nitrogen fertilization and (ii) fertilization would increase the efficiency by which light is converted into stemwood volume. Projected LAI_e varied from 1.82 to 6.07 m²·m^-2 on the control plots. The fertilized plots intercepted 9-11% more light than the control plots (P < 0.001); they also had 22-25% higher LAI_e than the control plots (P < 0.001). Stemwood volume production increased by 25-29% relative to the control (P < 0.001) and increased exponentially with %IPAR across all study plots (R² = 0.57). Stemwood growth efficiency averaged 12.0 ± 0.4 (mean ± SE), 13.5 ± 0.4, and 13.7 ± 0.4 m³·ha^-1·a^-1 per IPAR for the control, low fertilization, and high fertilization plots, respectively (P < 0.01). Fertilization thus induced increases in both light interception and the efficiency with which intercepted light was converted to stemwood across the region.

Early-career faculty (ECF) are faced with maintaining excellence in teaching and research for tenure. However, many enter academia with little or no teaching experience. Madison Teaching and Learning Excellence, a year-long professional development program, was designed to mitigate these pressures and help faculty become fast, efficient, and effective teachers. The authors evaluated this program on participants’ use of learner-centered course designs and classroom practices compared with non-participants and also measured challenges encountered by ECF. Participants’ gains in effective course design were positive, stable, and transferable to other courses. Participants reported feeling more prepared for tenure review and possessed a heightened self-awareness and assessment of their teaching. Although participants scored moderately high on measures of learner-centered practices, their scores were similar to non-participants. The authors hope their evaluation will inform faculty development programs; they summarize challenges they encountered to spur development of better evaluation tools that balance practitioners’ needs and available resources.