Jim Elser talks with
ScienceWatch.com and answers a few questions about
this month's Emerging Research Front Paper in the field of
Multidisciplinary. The author has also sent along
images of their work.
Article: Global analysis of nitrogen and phosphorus
limitation of primary producers in freshwater, marine and
JJ;Bracken, MES;Cleland, EE;Gruner, DS;Harpole,
WS;Hillebrand, H;Ngai, JT;Seabloom, EW;Shurin, JB;Smith,
Journal: ECOL LETT, 10 (12): 1135-1142 DEC 2007
Addresses: Arizona State Univ, Sch Life Sci, Tempe, AZ
Arizona State Univ, Sch Life Sci, Tempe, AZ 85287
Univ Calif Davis, Bodega Marine Lab, Bodega Bay, CA 94923
(addresses have been truncated.)
The paper involves a meta-analysis of more than 1,000 nutrient enrichment
experiments testing for nitrogen (N) or phosphorus (P) limitation (and
interactions) of primary production in all of Earth's ecosystems (marine,
freshwater, terrestrial). It is likely highly cited because nutrient
limitation is a fundamentally important phenomenon in ecosystems, because
the paper addresses both N and P limitation, and because the paper involves
ALL kinds of ecosystems. Thus, there seems to be something for everyone in
Does it describe a new discovery, methodology, or
synthesis of knowledge?
Yes. It provides data challenging some existing paradigms in ecosystem
ecology, such as the generalizations that phosphorus is predominantly
limiting in freshwaters (our data show an equal role for nitrogen ), that N
is predominantly limiting in terrestrial systems (our data show an equal
role for P), and that N is predominant in marine systems (our data show
that, yes, N enrichment results in stronger response than P, but P is also
important). Our data also show quite clearly that there are strong N x P
synergistic interactions in all ecosystems.
Would you summarize the significance of your paper in
Our study shows that plant production is generally equally limited by
available nitrogen and phosphorus in all of Earth's ecosystems, from lakes
to forests to grasslands to oceans. Thus, proper management of human
sources of nitrogen and phosphorus (fertilizer, sewage,
air pollution) is important in order to preserve
ecosystems from over-enrichment.
How did you become involved in this research and were
any particular problems encountered along the way?
I became involved in nutrient limitation research at the beginning of my
career in the early 1980s, studying N and P limitation in reservoirs. It
has been a major theme of my work since then. To do this study, however,
was well beyond the capacity of a single person. Instead, a large number of
colleagues, working together in a group at the
National Center for Ecological Analysis and
Synthesis at the University of California, Santa Barbara, was able
to put together all available knowledge about nutrient enrichment
effects from previous studies to obtain this broad view.
The problems are those always encountered in meta-analysis: finding all the
studies, extracting the data from graphs or incomplete data tables,
correcting for possible differences in methodology, quality control, etc.
It required a group of dedicated and outstanding colleagues in order to
complete this study.
Where do you see your research leading in the future?
We need better information about both the external and internal factors
that control N and P availability in ecosystems. Especially important will
be to understand how anthropogenic influences, such as atmospheric N
deposition to ecosystems, may have impacted patterns of nutrient limitation
Do you foresee any social or political implications for your
Yes, this study implies that ecosystem managers and environmental
regulators need to pay attention to inputs of both N and P in protecting
ecosystems from anthropogenic perturbations. And they need to do this for
ALL kinds of ecosystems, freshwater, marine, or terrestrial.
James J. Elser
Professor and Associate Director
School of Life Sciences
Arizona State University
Tempe, AZ, USA
Average Relative Response (biomass in enriched treatment / control
treatment) to N enrichment alone, P enrichment alone, or combined N&P
enrichment in more than 1000 experiments in freshwater (lake, stream),
terrestrial (forest, grassland, tundra, etc) Note that relative response is
log-transformed on the y-axis.
Related:listen to a Science Studio interview with Jim Elser.
Keywords: nutrient enrichment experiments testing for nitrogen
or phosphorus limitation, meta-analysis, earth's ecosystems, existing
paradigms in ecosystem ecology, synergistic interactions in all
ecosystems, anthropogenic influences, patterns of nutrient limitation,