Jane C. Marks

Bio: Jane C. Marks is an academic researcher from Northern Arizona University. The author has contributed to research in topics: Plant litter & Ecosystem. The author has an hindex of 32, co-authored 85 publications receiving 3877 citations. Previous affiliations of Jane C. Marks include Royal Victoria Infirmary & Bowling Green State University.

Genetic and environmental controls of microbial communities on leaf litter in streams

Abstract: Summary 1. Despite the importance of microorganisms for leaf litter decomposition in streams, little is known about which factors affect community composition of bacterial and fungal communities. Standard morphological techniques probably underestimate microbial diversity. 2. We used terminal restriction fragment length polymorphisms of the ITS regions for fungi, and the 16S region for bacteria, to compare fungal and bacterial communities on four cross types of cottonwood leaves (Populus fremontii, P. angustifolia, and their naturally occurring F1 and backcross hybrids). Decomposing leaves were studied in two Arizona rivers that differ in water chemistry and macroinvertebrates. 3. Hybridising cottonwoods are an ideal model system to test how genetic differences in leaf litter chemistry affect microbial communities because cross types have different decomposition rates and leaf litter chemistry. Leaves were incubated in litter bags for 2 weeks and brought to the laboratory for genetic analysis. Communities were analysed using non-metric multi dimensional scaling (NMDS) and diversity indices. 4. Fungal and bacterial communities differed between the two rivers, even when growing on identical substrates. There were also significant differences in microbial communities among the four cross types, indicating that genetically based differences in leaf litter translate to differences in microbial communities. 5. Diversity increased along the hybridising complex from P. fremontii to P. angustifolia, with hybrids showing intermediate values. Fungal and bacterial diversity were significantly higher on cross types with higher tannin concentrations and slower decomposition rates. 6. Environmental conditions most strongly structured microbial communities, but within an environment, genetic-based differences in leaf litter quality yielded differences in diversity and community structure. 7. Molecular tools are making it possible to understand patterns of microbial diversity in river ecosystems, paving the way for a better understanding of how differences in microbial species affect ecosystem processes and higher trophic levels.

Leaf litter quality affects aquatic insect emergence: contrasting patterns from two foundation trees

Abstract: Reciprocal subsidies between rivers and terrestrial habitats are common where terrestrial leaf litter provides energy to aquatic invertebrates while emerging aquatic insects provide energy to terrestrial predators (e.g., birds, lizards, spiders). We examined how aquatic insect emergence changed seasonally with litter from two foundation riparian trees, whose litter often dominates riparian streams of the southwestern United States: Fremont (Populus fremontii) and narrowleaf (Populus angustifolia) cottonwood. P. fremontii litter is fast-decomposing and lower in defensive phytochemicals (i.e., condensed tannins, lignin) relative to P. angustifolia. We experimentally manipulated leaf litter from these two species by placing them in leaf enclosures with emergence traps attached in order to determine how leaf type influenced insect emergence. Contrary to our initial predictions, we found that packs with slow-decomposing leaves tended to support more emergent insects relative to packs with fast-decomposing leaves. Three findings emerged. Firstly, abundance (number of emerging insects m(-2) day(-1)) was 25% higher on narrowleaf compared to Fremont leaves for the spring but did not differ in the fall, demonstrating that leaf quality from two dominant trees of the same genus yielded different emergence patterns and that these patterns changed seasonally. Secondly, functional feeding groups of emerging insects differed between treatments and seasons. Specifically, in the spring collector-gatherer abundance and biomass were higher on narrowleaf leaves, whereas collector-filterer abundance and biomass were higher on Fremont leaves. Shredder abundance and biomass were higher on narrowleaf leaves in the fall. Thirdly, diversity (Shannon's H') was higher on Fremont leaves in the spring, but no differences were found in the fall, showing that fast-decomposing leaves can support a more diverse, complex emergent insect assemblage during certain times of the year. Collectively, these results challenge the notion that leaf quality is a simple function of decomposition, suggesting instead that aquatic insects benefit differentially from different leaf types, such that some use slow-decomposing litter for habitat and its temporal longevity and others utilize fast-decomposing litter with more immediate nutrient release.

Influences of travertine dam formation on leaf litter decomposition and algal accrual

Abstract: At the time of this study Fossil Creek was being considered as a site for the restoration of a native fish assemblage, however there was concern amongst fisheries managers about the stream being food limited due to calcium carbonate (travertine) deposition. To evaluate the effects of travertine deposition on the aquatic food base we used leaf litterbags to compare decomposition rates and nutrient diffusing artificial substrates to compare algal accrual rates and nutrient limitation between two distinct reaches in Fossil creek: a travertine dam forming reach and a reach without travertine dam formation (riffle-pool reach). Decomposition was significantly faster in the travertine dam forming reach than in the riffle-pool reach. Macroinvertebrates in the leaf packs were more diverse in the travertine reach but more abundant in the riffle-pool reach. Algae accrued more quickly in the travertine reach than in the riffle-pool reach and only responded to nutrient enrichment in the travertine reach. This study was conducted prior to a hydroelectric dam decommissioning project in Fossil Creek where full flows were reintroduced back into the stream after a century of diversion. Our results suggest concurrent increases in algal productivity, decomposition, and macroinvertebrate diversity in the next decade as travertine dams rebuild, providing a richer food base for fish and other aquatic organisms.

Linking tree genetics and stream consumers: isotopic tracers elucidate controls on carbon and nitrogen assimilation.

Abstract: Leaf litter provides an important nutrient subsidy to headwater streams, but little is known about how tree genetics influence energy pathways from litter to higher trophic levels. Despite the charge to quantify carbon (C) and nitrogen (N) pathways from decomposing litter, the relationship between litter decomposition and aquatic consumers remains unresolved. We measured litter preference (attachments to litter), C and N assimilation rates, and growth rates of a shredding caddisfly (Hesperophylax magnus, Limnephilidae) in response to leaf litter of different chemical and physical phenotypes using Populus cross types (P. fremontii, P. angustifolia, and F1 hybrids) and genotypes within P. angustifolia. We combined laboratory mesocosm studies using litter from a common garden with a field study using doubly labeled litter (13 C and 15 N) grown in a greenhouse and incubated in Oak Creek, Arizona, USA. We found that, in the lab, shredders initially chose relatively labile (low lignin and condensed tannin concentrations, rapidly decomposing) cross type litter, but preference changed within 4 d to relatively recalcitrant (high lignin and condensed tannin concentrations, slowly decomposing) litter types. Additionally, in the lab, shredder growth rates were higher on relatively recalcitrant compared to labile cross type litter. Over the course of a three-week field experiment, shredders also assimilated more C and N from relatively recalcitrant compared to labile cross type litter. Finally, among P. angustifolia genotypes, N assimilation by shredders was positively related to litter lignin and C:N, but negatively related to condensed tannins and decomposition rate. C assimilation was likewise positively related to litter C:N, and also to litter %N. C assimilation was not associated with condensed tannins or lignin. Collectively, these findings suggest that relatively recalcitrant litter of Populus cross types provides more nutritional benefit, in terms of N fluxes and growth, than labile litter, but among P. angustifolia genotypes the specific trait of litter recalcitrance (lignin or tannins) determines effects on C or N assimilation. As shredders provide nutrients and energy to higher trophic levels, the influence of these genetically based plant decomposition pathways on shredder preference and performance may affect community and food web structure.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Abstract: The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Biofilms: an emergent form of bacterial life.

Abstract: Bacterial biofilms are formed by communities that are embedded in a self-produced matrix of extracellular polymeric substances (EPS). Importantly, bacteria in biofilms exhibit a set of 'emergent properties' that differ substantially from free-living bacterial cells. In this Review, we consider the fundamental role of the biofilm matrix in establishing the emergent properties of biofilms, describing how the characteristic features of biofilms - such as social cooperation, resource capture and enhanced survival of exposure to antimicrobials - all rely on the structural and functional properties of the matrix. Finally, we highlight the value of an ecological perspective in the study of the emergent properties of biofilms, which enables an appreciation of the ecological success of biofilms as habitat formers and, more generally, as a bacterial lifestyle.

Going back to the roots: the microbial ecology of the rhizosphere.

Abstract: The rhizosphere is the interface between plant roots and soil where interactions among a myriad of microorganisms and invertebrates affect biogeochemical cycling, plant growth and tolerance to biotic and abiotic stress. The rhizosphere is intriguingly complex and dynamic, and understanding its ecology and evolution is key to enhancing plant productivity and ecosystem functioning. Novel insights into key factors and evolutionary processes shaping the rhizosphere microbiome will greatly benefit from integrating reductionist and systems-based approaches in both agricultural and natural ecosystems. Here, we discuss recent developments in rhizosphere research in relation to assessing the contribution of the micro- and macroflora to sustainable agriculture, nature conservation, the development of bio-energy crops and the mitigation of climate change.