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Biodiversity Under Global Change
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Many common plant species, such as prairie grasses, have evolved traits for the efficient capture and use of two key resources that limit terrestrial productivity: nitrogen (N) and carbon dioxide (CO2). Over the past 60 years, human activity has vastly increased the availability of these resources. Atmospheric CO2 concentration has increased by 40%, and N availability has more than doubled. These changes are likely to have important consequences for species interactions, community structure, and ecosystem functioning. On
page 1399 of this issue, Reich investigates one important consequence, biodiversity loss, based on a long-term elevated CO2 and nitrogen fertilization experiment.
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Peatland Response to Global Change
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Peatlands can buffer the impact of external
perturbations, but can also rapidly shift to a
new ecosystem type, with large gains or losses
of stored carbon.
VOL 326 SCIENCE
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Amid Worrisome Signs of Warming, ‘Climate Fatigue’ Sets In
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As scientists debate whether climate is changing faster than anticipated, some worry that a
drumbeat of dire warnings may be helping to erode U.S. public concerns about global warming
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Biodiversity and Climate Change
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Efforts to elucidate the effect of climate change on biodiversity with detailed data sets and refined models reach novel conclusions.
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Drought Sensitivity of the Amazon Rainforest
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Amazon forests are a key but poorly understood component of the global carbon cycle. If, as
anticipated, they dry this century, they might accelerate climate change through carbon losses and
changed surface energy balances. We used records from multiple long-term monitoring plots across
Amazonia to assess forest responses to the intense 2005 drought, a possible analog of future events.
Affected forest lost biomass, reversing a large long-term carbon sink, with the greatest impacts
observed where the dry season was unusually intense. Relative to pre-2005 conditions, forest subjected
to a 100-millimeter increase in water deficit lost 5.3 megagrams of aboveground biomass of carbon per
hectare. The drought had a total biomass carbon impact of 1.2 to 1.6 petagrams (1.2 × 1015 to
1.6 × 1015 grams). Amazon forests therefore appear vulnerable to increasing moisture stress, with the
potential for large carbon losses to exert feedback on climate change.
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The Genetic Architecture of Maize Flowering Time
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Flowering time is a complex trait that controls adaptation of plants to their local environment in
the outcrossing species Zea mays (maize). We dissected variation for flowering time with a set of
5000 recombinant inbred lines (maize Nested Association Mapping population, NAM). Nearly a
million plants were assayed in eight environments but showed no evidence for any single largeeffect
quantitative trait loci (QTLs). Instead, we identified evidence for numerous small-effect QTLs
shared among families; however, allelic effects differ across founder lines. We identified no
individual QTLs at which allelic effects are determined by geographic origin or large effects for
epistasis or environmental interactions. Thus, a simple additive model accurately predicts flowering
time for maize, in contrast to the genetic architecture observed in the selfing plant species rice
and Arabidopsis.
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A-maize-ing Diversity
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Analysis of a new maize resource reveals that a large number of genetic loci with small effects may underlie the wide variation seen in traits such as flowering time.
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Phenology Feedbacks on Climate Change
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A longer growing season as a result of climate
change will in turn affect climate through
biogeochemical and biophysical effects.
SCIENCE VOL 324
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Risks of Climate Engineering
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Observations indicate that attempts to limit climate
warming by reducing incoming shortwave radiation risk
major precipitation changes.
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Seasons and Life Cycles
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A conceptual framework. This table is a guide to determining how individual species are responding to an extended growing
season by observing the duration of peak season. The life history of a species—from the onset of greening through the end of
senescence—is illustrated by the length of the solid lines. Each case represents a shift in the timing (columns) and duration
(rows) of one or more species in a hypothetical three-species community that includes an early-, mid-, and late-season species.
The growing season begins when the first species greens and ends when the last species senesces. The peak season (gray shaded
area) occurs when all species have started and none have completed their life history. Reproductive life history events likely
begin before the peak season and are completed before its end. The final row and column list changes that can be observed
through frequent observations of surface greenness.
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