Mathew E. Dornbush

QUANTIFYING FINE‐ROOT DECOMPOSITION: AN ALTERNATIVE TO BURIED LITTERBAGS

Our understanding of fine-root decay processes is derived almost exclusively from litterbag studies. However, preparation of roots for litterbag studies and their sub- sequent decay within litterbags represent major departures from in situ conditions. We hypothesized that litterbag studies misrepresent fine-root decay and nutrient release rates during decomposition. To test these hypotheses we developed a new intact-core technique that requires no a priori root processing, retains natural rhizosphere associations, and main- tains in situ decay conditions. Using both litterbags and intact cores, we measured annual decay rates and nitrogen release from newly senesced fine roots of silver maple, maize, and winter wheat. After one year, mass loss was 10-23% greater, and nitrogen release was 21-29% higher within intact cores. Differences appeared to result from litterbag-induced alterations to decomposer dynamics and from unavoidable changes to fine-root size-class composition within litterbags. Our results suggest that fine-root decay and nutrient turnover occur significantly faster than estimated from litterbag studies. By minimizing disturbances to roots, soil, and rhizosphere associates prior to root decay, the intact-core technique provides an improved alternative for measuring fine-root decomposition.

Exotic consumers interact with exotic plants to mediate native plant survival in a Midwestern forest herb layer

Consumer-facilitated invasions have been proposed as an alternative mechanism to direct competitive exclusion to explain the replacement of native plants by exotics. In a factorial field experiment manipulating competition from the exotic plant Alliaria petiolata and herbivory by exotic mollusks, we documented that mollusk herbivory significantly reduced the survival of two species of native palatable plants, but found minimal direct herbivore effects on less palatable species, including the invasive A. petiolata. These effects were evident after one growing season on younger juvenile plants of Aster cordifolius, but only after two growing seasons on older transplants of the same species, suggesting a greater vulnerability of young plants. In contrast to our expectations, A. petiolata competition alone had no effect on any of the six native species we tested. However, competition from A. petiolata did affect the survival of the most palatable native plant when mollusks were also present. While not significant for any other single species, this same pattern was observed for three of the five remaining native species tested. The selective grazing on palatable plants that we document provides novel evidence contributing to our understanding of observed shifts in the forest herbaceous layer towards the dominance of exotic plants and unpalatable species. More broadly, our results highlight the importance of the interactive effect of consumers and inter-specific competition in forest understories via its contribution to differential survival among regenerating species.

Intensified Agroecosystems and Their Effects on Soil Biodiversity and Soil Functions

Abstract This chapter defines agricultural intensification, its components, and ecosystem service delivery within row cropping systems. Particular attention is given to the homogenizing effects of intensive agriculture on vertical soil organic carbon distributions, soil structure, soil moisture and nutrient levels, and pesticide influences on ecosystem services and the soil communities responsible for their delivery. Comparisons are set along continuums spanning for intensive management to minimally managed perennial grasslands. The chapter ends by defining ecological intensification and the potential for its application to agroecosystems to meet a growing societal demand that agricultural systems supply both high yields and a broader delivery of ecological services tied to environmental quality.

Depth-Distributions of Belowground Production, Biomass, and Decomposition in Restored Tallgrass Prairie

Abstract Grasslands store large stocks of soil organic carbon (SOC) in the subsoil, but our knowledge of belowground processes becomes less robust with depth. Vertically explicit SOC models typically assume that the depth distribution of belowground production follows the depth distribution of belowground biomass, but this assumption has not been tested. In addition to the effects of soil temperature and moisture on decomposition, some vertically explicit SOC models implement an intrinsic decrease in belowground decomposition with depth, yet this effect has rarely been observed empirically. We simultaneously measured the depth distributions of belowground biomass, production, and litter decomposition to assess whether belowground biomass depth distributions were suitable predictors of belowground production and whether belowground decomposition decreased with soil profile depth. We found that live and total (live + dead) belowground biomass was distributed relatively more shallowly than total belowground production, and thus total belowground biomass was a biased predictor of the vertical distribution of belowground production. The depth distribution of live roots