Journal of Geophysical Research: Biogeosciences, 2018
Water relations in plant communities are influenced both by contrasting functional groups (grasse... more Water relations in plant communities are influenced both by contrasting functional groups (grasses and shrubs) and by climate change via complex effects on interception, uptake, and transpiration. We modeled the effects of functional group replacement and biomass increase, both of which can be outcomes of invasion and vegetation management, and climate change on ecological drought (soil water potential below which photosynthesis stops) in 340 semiarid grassland sites over 30 year periods. Relative to control vegetation (climate and site‐determined mixes of functional groups), the frequency and duration of drought were increased by shrubs and decreased by annual grasses. The rankings of shrubs, control vegetation, and annual grasses in terms of drought effects were generally consistent in current and future climates, suggesting that current differences among functional groups on drought effects predict future differences. Climate change accompanied by experimentally increased biomass...
Summary Atmospheric nitrogen (N) deposition has become one of the most important agents of vegeta... more Summary Atmospheric nitrogen (N) deposition has become one of the most important agents of vegetation change in densely populated regions. It may also contribute to forest expansion into grasslands at the northern edge of the North American Great Plains. We measured N deposition and available soil N with ion‐exchange resin over 2 years in six national parks in areas varying in population density and industrialization. N deposition was significantly higher in four parks in densely populated regions than in two remote parks. Available soil N increased significantly with N deposition across all parks. We measured N mass and 15N abundance (δ15N) in vegetation and soil in two parks: Elk Island, receiving 22 kg N ha−1 year−1, and Jasper, receiving 8 kg N ha−1 year−1. Differences between parks in tissue N concentrations were small, but forest expansion over five decades resulted in the mass of N in vegetation increasing by 74% in Elk Island but by only 26% in Jasper. δ15N in forest vegetat...
Numerous studies have suggested a role for ubiquitin–proteasome-mediated protein degradation in l... more Numerous studies have suggested a role for ubiquitin–proteasome-mediated protein degradation in learning-dependent synaptic plasticity; however, very little is known about how protein degradation is regulated at the level of the proteasome during memory formation. The ubiquitin-specific protease 14 (USP14) is a proteasomal deubiquitinating enzyme that is thought to regulate protein degradation in neurons; however, it is unknown if USP14 is involved in learning-dependent synaptic plasticity. We found that infusion of a USP14 inhibitor into the amygdala impaired long-term memory for a fear conditioning task, suggesting that USP14 is a critical regulator of long-term memory formation in the amygdala.
Homozygous ataxic mice ( ax J) express reduced levels of the deubiquitinating enzyme Usp14. They ... more Homozygous ataxic mice ( ax J) express reduced levels of the deubiquitinating enzyme Usp14. They develop severe tremors by 2–3 wk of age, followed by hindlimb paralysis, and death by 6–8 wk. While changes in the ubiquitin proteasome system often result in the accumulation of ubiquitin protein aggregates and neuronal loss, these pathological markers are not observed in the ax J mice. Instead, defects in neurotransmission were observed in both the central and peripheral nervous systems of ax J mice. We have now identified several new alterations in peripheral neurotransmission in the ax J mice. Using the two-microelectrode voltage clamp technique on diaphragm muscles of ax J mice, we observed that under normal neurotransmitter release conditions ax J mice lacked paired-pulse facilitation and exhibited a frequency-dependent increase in rundown of the end plate current at high-frequency stimulation (HFS). Combined electrophysiology and styryl dye staining revealed a significant reductio...
Journal of Geophysical Research: Biogeosciences, 2018
Water relations in plant communities are influenced both by contrasting functional groups (grasse... more Water relations in plant communities are influenced both by contrasting functional groups (grasses and shrubs) and by climate change via complex effects on interception, uptake, and transpiration. We modeled the effects of functional group replacement and biomass increase, both of which can be outcomes of invasion and vegetation management, and climate change on ecological drought (soil water potential below which photosynthesis stops) in 340 semiarid grassland sites over 30 year periods. Relative to control vegetation (climate and site‐determined mixes of functional groups), the frequency and duration of drought were increased by shrubs and decreased by annual grasses. The rankings of shrubs, control vegetation, and annual grasses in terms of drought effects were generally consistent in current and future climates, suggesting that current differences among functional groups on drought effects predict future differences. Climate change accompanied by experimentally increased biomass...
Summary Atmospheric nitrogen (N) deposition has become one of the most important agents of vegeta... more Summary Atmospheric nitrogen (N) deposition has become one of the most important agents of vegetation change in densely populated regions. It may also contribute to forest expansion into grasslands at the northern edge of the North American Great Plains. We measured N deposition and available soil N with ion‐exchange resin over 2 years in six national parks in areas varying in population density and industrialization. N deposition was significantly higher in four parks in densely populated regions than in two remote parks. Available soil N increased significantly with N deposition across all parks. We measured N mass and 15N abundance (δ15N) in vegetation and soil in two parks: Elk Island, receiving 22 kg N ha−1 year−1, and Jasper, receiving 8 kg N ha−1 year−1. Differences between parks in tissue N concentrations were small, but forest expansion over five decades resulted in the mass of N in vegetation increasing by 74% in Elk Island but by only 26% in Jasper. δ15N in forest vegetat...
Numerous studies have suggested a role for ubiquitin–proteasome-mediated protein degradation in l... more Numerous studies have suggested a role for ubiquitin–proteasome-mediated protein degradation in learning-dependent synaptic plasticity; however, very little is known about how protein degradation is regulated at the level of the proteasome during memory formation. The ubiquitin-specific protease 14 (USP14) is a proteasomal deubiquitinating enzyme that is thought to regulate protein degradation in neurons; however, it is unknown if USP14 is involved in learning-dependent synaptic plasticity. We found that infusion of a USP14 inhibitor into the amygdala impaired long-term memory for a fear conditioning task, suggesting that USP14 is a critical regulator of long-term memory formation in the amygdala.
Homozygous ataxic mice ( ax J) express reduced levels of the deubiquitinating enzyme Usp14. They ... more Homozygous ataxic mice ( ax J) express reduced levels of the deubiquitinating enzyme Usp14. They develop severe tremors by 2–3 wk of age, followed by hindlimb paralysis, and death by 6–8 wk. While changes in the ubiquitin proteasome system often result in the accumulation of ubiquitin protein aggregates and neuronal loss, these pathological markers are not observed in the ax J mice. Instead, defects in neurotransmission were observed in both the central and peripheral nervous systems of ax J mice. We have now identified several new alterations in peripheral neurotransmission in the ax J mice. Using the two-microelectrode voltage clamp technique on diaphragm muscles of ax J mice, we observed that under normal neurotransmitter release conditions ax J mice lacked paired-pulse facilitation and exhibited a frequency-dependent increase in rundown of the end plate current at high-frequency stimulation (HFS). Combined electrophysiology and styryl dye staining revealed a significant reductio...
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