Variation in soil communities across a heterogeneous habitat

Abstract only availableEnvironmental variation can impact the distribution of species in ecological communities. In alpine communities willows (Salix sp.) significantly affect the conditions experienced by soil biota in understory verses open meadow habitats. This study describes the distribution of collembola (springtails) and mycorrhizal fungi across the alpine willow-meadow ecotone. We surveyed the abundance of collembola and mycorrhizae in open meadow and willow understory habitats. We conducted the survey at three altitudinal sites on Pennsylvania Mountain (Park County, Colorado, USA) in June and July of 2008. We evaluated the abundance of ectomycorrhizae, endomycorrhizae, and collembola living in the leaf litter and soil. The distribution of these organisms differed between habitats. Overall, endomycorrhizae were more abundant in the open meadow, whereas ectomycorrhizae and collembola were more abundant in the willow understory. Within the collembola community most species were equally distributed between habitats. However, Folsomia candida was more abundant in the willow understory. We also found evidence that collembola may affect mycorrhizal colonization. In particular, the abundance of ectomycorrhizae and collembola was positively correlated in the open meadow, but not in the willow understory. To clarify whether leaf litter contributed to the distribution of these organisms we compared leaf litter biomass to collembola and mycorrhizal abundance. In the willow understory there was a negative relationship between the abundance of endomycorrhizae and leaf litter biomass. There were no correlations between the amount of leaf litter and the abundance of ectomycorrhizae or collembola. These results suggest that leaf litter can affect the soil community; however, other factors are also likely important. Future research should consider other effects of willows, such as shading and temperature, on the soil community.NSF Undergraduate Mentoring in Environmental Biolog

Evolutionary history underlies plant physiological responses to global change since the last glacial maximum

This is the author's accepted manuscript, also available here, http//dx.doi.org/10.1111/ele.12271.Assessing family- and species-level variation in physiological responses to global change across geologic time is critical for understanding factors that underlie changes in species distributions and community composition. Here, we used stable carbon isotopes, leaf nitrogen content and stomatal measurements to assess changes in leaf-level physiology in a mixed conifer community that underwent significant changes in composition since the last glacial maximum (LGM) (21 kyr BP). Our results indicate that most plant taxa decreased stomatal conductance and/or maximum photosynthetic capacity in response to changing conditions since the LGM. However, plant families and species differed in the timing and magnitude of these physiological responses, and responses were more similar within families than within co-occurring species assemblages. This suggests that adaptation at the level of leaf physiology may not be the main determinant of shifts in community composition, and that plant evolutionary history may drive physiological adaptation to global change over recent geologic time

Soil fungal effects on floral signals, rewards, and aboveground interactions in an alpine pollination web

This is the published version. The definitive version is available at www3.interscience.wiley.com.• Premise of the study: Plants interact with above- and belowground organisms; the combined effects of these interactions determine plant fitness and trait evolution. To better understand the ecological and evolutionary implications of multispecies interactions, we explored linkages between soil fungi, pollinators, and floral larcenists in Polemonium viscosum (Polemoniaceae). • Methods: Using a fungicide, we experimentally reduced fungal colonization of krummholz and tundra P. viscosum in 2008–2009. We monitored floral signals and rewards, interactions with pollinators and larcenists, and seed set for fungicide-treated and control plants. • Key results: Fungicide effects varied among traits, between interactions, and with environmental context. Treatment effects were negligible in 2008, but stronger in 2009, especially in the less-fertile krummholz habitat. There, fungicide increased nectar sugar content and damage by larcenist ants, but did not affect pollination. Surprisingly, fungicide also enhanced seed set, suggesting that direct resource costs of soil fungi exceed indirect benefits from reduced larceny. In the tundra, fungicide effects were negligible in both years. However, pooled across treatments, colonization by mycorrhizal fungi in 2009 correlated negatively with the intensity and diversity of floral volatile organic compounds, suggesting integrated above- and belowground signaling pathways. • Conclusions: Fungicide effects on floral rewards in P. viscosum link soil fungi to ecological costs of pollinator attraction. Trait-specific linkages to soil fungi should decouple expression of sensitive and buffered floral phenotypes in P. viscosum. Overall, this study demonstrates how multitrophic linkages may lead to shifting selection pressures on interaction traits, restricting the evolution of specialization.National Science Foundation (DBI-0603049 and DEB-0316110 to C.G. and DEB-0746106 to R.A.R.)

Willows indirectly reduce arbuscular mycorrhizal colonization of understorey plants

1. Understanding mechanisms underlying species distributions is a central theme in ecology. This study identifies factors driving spatial variation in arbuscular mycorrhizal fungi (AMF). We conducted two experiments to test whether heterogeneity in AMF colonization of alpine perennial plants across a willow-meadow ecotone is due to variation in (i) above-ground competition with willows for light (experiment 1), (ii) below-ground interactions with willows and their ectomycorrhizal fungi (EMF; experiment 1) or (iii) leaf litter deposition (experiment 2). 2. In experiment 1, we tested the above-ground interactions hypothesis by covering open meadow plots with 80% shade cloth to simulate willow shading (S). To test the below-ground interactions hypothesis we transplanted ectomycorrhizal (MW) and nonmycorrhizal willows (NW) into open meadow plots. AMF colonization of herbaceous plants in the S, MW and NW treatments was compared to colonization of plants growing in unmanipulated open meadow (OC) and willow understorey (WC) control plots. In experiment 2, we tested the leaf litter hypothesis by manipulating leaf litter deposition in open meadow and willow understorey plots. AMF and EMF colonization was compared in plots with and without leaf litter. 3. In experiment 1, AMF colonization was reduced in MW willow and WC plots compared to the other three treatments, suggesting that below-ground interactions with EMF suppressed AMF colonization of herbaceous hosts. In experiment 2, the presence of leaf litter increased EMF colonization in the open meadow and reduced AMF colonization in both open meadow and willow understorey habitats, suggesting that willow-derived leaf litter indirectly affected AMF colonization by promoting EMF colonisation. 4. Synthesis. Our results indicate that willows indirectly reduce AMF colonization of neighbouring herbaceous plants via feedbacks with leaf litter and EMF. These willow-mediated effects could alter the distribution of mycorrhizal fungi in alpine communities, which could in turn impact the fitness and distribution of closely associated host species. Ultimately, this study demonstrates the potential for below-ground interactions to drive variation in species associations across ecotonal boundaries

Aquilegia, Vol. 33 No. 2, Summer 2009, Newsletter of the Colorado Native Plant Society

https://epublications.regis.edu/aquilegia/1128/thumbnail.jp

A dynamic leaf gas-exchange strategy is conserved in woody plants under changing ambient CO2: evidence from carbon isotope discrimination in paleo and CO2 enrichment studies

Rising atmospheric [CO2 ], ca , is expected to affect stomatal regulation of leaf gas-exchange of woody plants, thus influencing energy fluxes as well as carbon (C), water and nutrient cycling of forests. Researchers have proposed various strategies for stomatal regulation of leaf gas-exchange that include maintaining a constant leaf internal [CO2 ], ci , a constant drawdown in CO2 (ca - ci ), and a constant ci /ca . These strategies can result in drastically different consequences for leaf gas-exchange. The accuracy of Earth systems models depends in part on assumptions about generalizable patterns in leaf gas-exchange responses to varying ca . The concept of optimal stomatal behavior, exemplified by woody plants shifting along a continuum of these strategies, provides a unifying framework for understanding leaf gas-exchange responses to ca . To assess leaf gas-exchange regulation strategies, we analyzed patterns in ci inferred from studies reporting C stable isotope ratios (δ(13) C) or photosynthetic discrimination (∆) in woody angiosperms and gymnosperms that grew across a range of ca spanning at least 100 ppm. Our results suggest that much of the ca -induced changes in ci /ca occurred across ca spanning 200 to 400 ppm. These patterns imply that ca - ci will eventually approach a constant level at high ca because assimilation rates will reach a maximum and stomatal conductance of each species should be constrained to some minimum level. These analyses are not consistent with canalization towards any single strategy, particularly maintaining a constant ci . Rather, the results are consistent with the existence of a broadly conserved pattern of stomatal optimization in woody angiosperms and gymnosperms. This results in trees being profligate water users at low ca , when additional water loss is small for each unit of C gain, and increasingly water-conservative at high ca , when photosystems are saturated and water loss is large for each unit C gain. This article is protected by copyright. All rights reserved.Rising atmospheric [CO2], c(a), is expected to affect stomatal regulation of leaf gas-exchange of woody plants, thus influencing energy fluxes as well as carbon (C), water, and nutrient cycling of forests. Researchers have proposed various strategies for stomatal regulation of leaf gas-exchange that include maintaining a constant leaf internal [CO2], c(i), a constant drawdown in CO2 (c(a)-c(i)), and a constant c(i)/c(a). These strategies can result in drastically different consequences for leaf gas-exchange. The accuracy of Earth systems models depends in part on assumptions about generalizable patterns in leaf gas-exchange responses to varying c(a). The concept of optimal stomatal behavior, exemplified by woody plants shifting along a continuum of these strategies, provides a unifying framework for understanding leaf gas-exchange responses to c(a). To assess leaf gas-exchange regulation strategies, we analyzed patterns in c(i) inferred from studies reporting C stable isotope ratios (C-13) or photosynthetic discrimination () in woody angiosperms and gymnosperms that grew across a range of c(a) spanning at least 100ppm. Our results suggest that much of the c(a)-induced changes in c(i)/c(a) occurred across c(a) spanning 200 to 400ppm. These patterns imply that c(a)-c(i) will eventually approach a constant level at high c(a) because assimilation rates will reach a maximum and stomatal conductance of each species should be constrained to some minimum level. These analyses are not consistent with canalization toward any single strategy, particularly maintaining a constant c(i). Rather, the results are consistent with the existence of a broadly conserved pattern of stomatal optimization in woody angiosperms and gymnosperms. This results in trees being profligate water users at low c(a), when additional water loss is small for each unit of C gain, and increasingly water-conservative at high c(a), when photosystems are saturated and water loss is large for each unit C gain

A dynamic leaf gas-exchange strategy is conserved in woody plants under changing ambient CO₂: evidence from carbon isotope discrimination in paleo and CO₂ enrichment studies

Rising atmospheric [CO₂], cₐ, is expected to affect stomatal regulation of leaf gas-exchange of woody plants, thus influencing energy fluxes as well as carbon (C), water, and nutrient cycling of forests. Researchers have proposed various strategies for stomatal regulation of leaf gas-exchange that include maintaining a constant leaf internal [CO₂], cᵢ, a constant drawdown in CO₂ (cₐ - cᵢ), and a constant cᵢ/cₐ. These strategies can result in drastically different consequences for leaf gas-exchange. The accuracy of Earth systems models depends in part on assumptions about generalizable patterns in leaf gas-exchange responses to varying cₐ. The concept of optimal stomatal behavior, exemplified by woody plants shifting along a continuum of these strategies, provides a unifying framework for understanding leaf gas-exchange responses to cₐ. To assess leaf gas-exchange regulation strategies, we analyzed patterns in cᵢ inferred from studies reporting C stable isotope ratios (δ¹³C) or photosynthetic discrimination (Δ) in woody angiosperms and gymnosperms that grew across a range of cₐ spanning at least 100 ppm. Our results suggest that much of the cₐ-induced changes in cᵢ/cₐ occurred across cₐ spanning 200 to 400 ppm. These patterns imply that cₐ - cᵢ will eventually approach a constant level at high ca because assimilation rates will reach a maximum and stomatal conductance of each species should be constrained to some minimum level. These analyses are not consistent with canalization toward any single strategy, particularly maintaining a constant cᵢ. Rather, the results are consistent with the existence of a broadly conserved pattern of stomatal optimization in woody angiosperms and gymnosperms. This results in trees being profligate water users at low cₐ, when additional water loss is small for each unit of C gain, and increasingly water-conservative at high cₐ, when photosystems are saturated and water loss is large for each unit C gain

Friends in high places: Ecology of mycorrhizal associations in alpine plant communities

Mutualisms are ubiquitous in nature, yet these interactions often vary in strength and persistence over space and time. This variation raises the questions of what determines whether mutualisms persist or vanish, and how does variation in the strength of mutualisms affect populations, communities, and ecosystems. I addressed these questions using mycorrhizal associations, symbiotic interactions between plants and root-colonizing fungi. An estimated 80% of plant species associate with mycorrhizae, providing their fungal partners with carbon in return for soil resources. Mycorrhizal associations are generally viewed as mutualisms; however, mycorrhizal effects often depend on the biotic and abiotic context. To better understand mechanisms underlying the strength and distribution of mutualisms I compared mycorrhizal associations in co-occurring alpine host species and along natural gradients in environmental conditions. First, I examined the distribution of arbuscular mycorrhizae (AM) across the willow-meadow ecotone at treeline on Pennsylvania Mountain (Park County, CO, USA). Specifically, I compared AM colonization, richness, diversity, and composition in Taraxacum ceratophorum, T. officinale, Polemonium delicatum , and P. viscosum in open meadow and willow understory habitats. Results indicate that AM associations are more abundant and more species-rich in the open meadow, and that host species differ in their associations with AM fungi. These results highlight the context-dependent nature of mutualisms, and suggest that both biotic and abiotic factors determine the strength of these associations. Next, I identified environmental factors that contribute to variation in mycorrhizal associations across the willow-meadow ecotone. Field experiments indicate that alpine willows indirectly influence AM colonization through feedbacks with ectomycorrhizae (ECM) and leaf litter deposition. Greenhouse experiments further suggest that resource availability influences net mycorrhizal effects in Taraxacum hosts. Together these studies suggest that biotic and abiotic factors alter partner benefits, thereby generating variation in these mutualisms. Finally, I evaluated implications of variation in mycorrhizal associations by examining the role of mycorrhizae in plant invasions, aboveground interaction webs, and the evolution of plant traits. Results from one study indicate that mycorrhizae influence the distribution and performance of T. officinale , an invasive species in North American alpine communities. In a second study, mycorrhizae influenced the behavior of floral visitors to P. viscosum and the potential for insect-mediated selection on floral traits. Both studies demonstrate the potential for mutualisms to impact the broader ecological community and evolutionary processes. Overall, this research advances our understanding of mutualism, highlighting the inherent complexity of these interactions and their importance to ecological and evolutionary processes. Furthermore, comparisons between native and exotic congeners establish a model system for answering questions about the ecology and evolution of mycorrhizae. Finally, my research supports the prediction that mycorrhizal associations are important in alpine plant communities and suggests that factors disrupting these interactions may have significant consequences for alpine ecosystems

Host identity impacts rhizosphere fungal communities associated with three alpine plant species

Fungal diversity and composition are still relatively unknown in many ecosystems; however, host identity and environmental conditions are hypothesized to influence fungal community assembly. To test these hypotheses we characterized the richness, diversity, and composition of rhizosphere fungi colonizing three alpine plant species, Taraxacum ceratophorum, Taraxacum officinale, and Polemonium viscosum. Roots were collected from open meadow and willow understory habitats at treeline on Pennsylvania Mountain, Colorado, USA. Fungal small subunit ribosomal DNA was sequenced using fungal-specific primers, sample-specific DNA tags, and 454 pyrosequencing. We classified operational taxonomic units (OTUs) as arbuscular mycorrhizal (AMF) or non-arbuscular mycorrhizal (non-AMF) fungi, then tested whether habitat or host identity influenced these fungal communities. Approximately 14% of the sequences represented AMF taxa (44 OTUs) with the majority belonging to Glomus group A and B. NONAMF sequences represented 186 OTUs belonging to Ascomycota (58%), Basidiomycota (26%), Zygomycota (14%), and Chytridiomycota (2%) phyla. Total AMF and non-AMF richness were similar between habitats, but varied among host species. AMF richness and diversity per root sample also varied among host species and were highest in T. ceratophorum compared to T. officinale and P. viscosum. In contrast, non-AMF richness and diversity per root sample were similar among host species except in the willow understory where diversity was reduced in T. officinale. Fungal community composition was influenced by host identity, but not habitat. Specifically, T. officinale hosted a different AMF community than T. ceratophorum and P. viscosum, while P. viscosum hosted a different non-AMF community than T. ceratophorum and T. officinale. Our results suggest that host identity has a stronger effect on rhizosphere fungi than habitat. Furthermore, although host identity influenced both AMF and non-AMF this effect was stronger for the mutualistic AMF community