Assessing the N Cycling Ecosystem
Function-Processes and the Involved Functional
Guilds upon Plant Litter Amendment
in Lower Himalaya

Abstract Aims Classical theory predicts that herbivores impact herb assemblages and soil nitrogen (N) cycling through selective plant consumption and the deposition of N-rich waste, with effects dependent upon ecosystem N availability. Herbivores are predicted to accelerate N cycling when N availability is high and decelerate cycling when availability is low. However, experimental tests of these theories in natural systems are limited and have yielded contradictory results. California’s widespread chaparral shrublands provide a tractable system in which to test these theories. They are prone to periodic crown-fire, which temporarily removes living shrub cover, deposits mineral N on soils, and allows diverse herbaceous assemblages to dominate the landscape for 3-5 years. Chaparral is also increasingly vulnerable to herbaceous invasion; mammalian herbivory may limit the establishment of non-native herbs in the shrub understory. Methods We implemented a two-year herbivore-exclosure experiment (Hopland, California) to assess the impact of mammalian herbivory during early post-fire chaparral succession, both on herbaceous plant assemblages and soil N and C cycling. We predicted that, in high-N post-fire conditions, mammalian herbivory would not demonstrate a strong preference for N-fixing herbs, would accelerate N cycling, and would reduce the abundance of non-native herbs. Important Findings Excluding mammalian herbivores increased herb standing biomass by 54%, but changed neither the relative abundance of N-fixing vs. non-N-fixing herbs nor any measure of N or C cycling. Herbivore impacts on nutrient cycling may not be significant over the two-year time scale of the experiment and physical effects of herbivore activity could have counteracted the influence of plant litter and animal dung/urine inputs. Mammalian herbivores concentrated their feeding on typical non-native herbs, slightly decreasing their relative abundance; however, mammalian herbivory was not sufficient to stem the invasion of chaparral by invasive herbs or alter C and N cycling over the first two years after fire.

Download Full-text

ENDOGENOUS AND EXOGENOUS CONTROL OF ECOSYSTEM FUNCTION: N CYCLING IN HEADWATER STREAMS

Ecology ◽

10.1890/07-1003.1 ◽

2008 ◽

Vol 89 (12) ◽

pp. 3515-3527 ◽

Cited By ~ 64

Author(s):

H. M. Valett ◽

S. A. Thomas ◽

P. J. Mulholland ◽

J. R. Webster ◽

C. N. Dahm ◽

...

Keyword(s):

Ecosystem Function ◽

Headwater Streams ◽

N Cycling ◽

Exogenous Control

Download Full-text

Links between plant litter chemistry, species diversity, and below-ground ecosystem function

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.0805600105 ◽

2008 ◽

Vol 105 (50) ◽

pp. 19780-19785 ◽

Cited By ~ 196

Author(s):

C. L. Meier ◽

W. D. Bowman

Keyword(s):

Species Diversity ◽

Ecosystem Function ◽

Plant Litter ◽

Litter Chemistry ◽

Below Ground

Download Full-text

Biodiversity and Plant Litter: Experimental Evidence Which Does Not Support the View That Enhanced Species Richness Improves Ecosystem Function

Oikos ◽

10.2307/3546010 ◽

1997 ◽

Vol 79 (2) ◽

pp. 247 ◽

Cited By ~ 452

Author(s):

D. A. Wardle ◽

K. I. Bonner ◽

K. S. Nicholson

Keyword(s):

Species Richness ◽

Experimental Evidence ◽

Ecosystem Function ◽

Plant Litter

Download Full-text

Nitrogen Cycling Potential of a Grassland Litter Microbial Community

Applied and Environmental Microbiology ◽

10.1128/aem.02222-15 ◽

2015 ◽

Vol 81 (20) ◽

pp. 7012-7022 ◽

Cited By ~ 20

Author(s):

Michaeline B. Nelson ◽

Renaud Berlemont ◽

Adam C. Martiny ◽

Jennifer B. H. Martiny

Keyword(s):

Global Change ◽

Plant Litter ◽

N Cycling ◽

N Availability ◽

Microbial Composition ◽

Content Type ◽

Plant Litter Decomposition ◽

N Utilization ◽

Over Time ◽

Microbial N

ABSTRACTBecause microorganisms have different abilities to utilize nitrogen (N) through various assimilatory and dissimilatory pathways, microbial composition and diversity likely influence N cycling in an ecosystem. Terrestrial plant litter decomposition is often limited by N availability; however, little is known about the microorganisms involved in litter N cycling. In this study, we used metagenomics to characterize the potential N utilization of microbial communities in grassland plant litter. The frequencies of sequences associated with eight N cycling pathways differed by several orders of magnitude. Within a pathway, the distributions of these sequences among bacterial orders differed greatly. Many orders within theActinobacteriaandProteobacteriaappeared to be N cycling generalists, carrying genes from most (five or six) of the pathways. In contrast, orders from theBacteroideteswere more specialized and carried genes for fewer (two or three) pathways. We also investigated how the abundance and composition of microbial N cycling genes differed over time and in response to two global change manipulations (drought and N addition). For many pathways, the abundance and composition of N cycling taxa differed over time, apparently reflecting precipitation patterns. In contrast to temporal variability, simulated global change had minor effects on N cycling potential. Overall, this study provides a blueprint for the genetic potential of N cycle processes in plant litter and a baseline for comparisons to other ecosystems.

Download Full-text

Dominance determines fish community biomass in a temperate seagrass ecosystem

10.32942/osf.io/cqjvu ◽

2019 ◽

Author(s):

Aaron Matthius Eger ◽

Rebecca J. Best ◽

Julia Kathleen Baum

Keyword(s):

Species Richness ◽

Ecosystem Function ◽

Fish Community ◽

Prey Capture ◽

Fish Communities ◽

Functional Trait ◽

Ecosystem Functions ◽

Community Biomass ◽

Ecosystem Valuation ◽

Species Abundances

Biodiversity and ecosystem function are often correlated, but there are multiple hypotheses about the mechanisms underlying this relationship. Ecosystem functions such as primary or secondary production may be maximized by species richness, evenness in species abundances, or the presence or dominance of species with certain traits. Here, we combined surveys of natural fish communities (conducted in July and August, 2016) with morphological trait data to examine relationships between diversity and ecosystem function (quantified as fish community biomass) across 14 subtidal eelgrass meadows in the Northeast Pacific (54° N 130° W). We employed both taxonomic and functional trait measures of diversity to investigate if ecosystem function is driven by species diversity (complementarity hypothesis) or by the presence or dominance of species with particular trait values (selection or dominance hypotheses). After controlling for environmental variation, we found that fish community biomass is maximized when taxonomic richness and functional evenness is low, and in communities dominated by species with particular trait values – those associated with benthic habitats and prey capture. While previous work on fish communities has found that species richness is positively correlated with ecosystem function, our results instead highlight the capacity for regionally prevalent and locally dominant species to drive ecosystem function in moderately diverse communities. We discuss these alternate links between community composition and ecosystem function and consider their divergent implications for ecosystem valuation and conservation prioritization.

Download Full-text