Geology topics

Timothy M. Wertin

Publications and source records attributed to Timothy M. Wertin.

4 recordsLinked to original sources

USGS2018

Spatially explicit patterns in a dryland's soil respiration and relationships with climate, whole plant photosynthesis and soil fertility

Arid and semiarid ecosystems play a significant role in regulating global carbon cycling, yet our understanding of the controls over the dominant pathways of dryland CO 2 exchange remains poor. Substantial amounts of dryland soil are not covered by vascular plants and this patchiness in cover has important implications for spatial patterns and controls of carbon cycling. Spatial variation in soil respiration has been attributed to variation in soil moisture, temperature, nutrients and rhizodeposition, while seasonal patterns have been attributed to changes in moisture, temperature and photosynthetic inputs belowground. To characterize how controls over respiration vary spatially and temporally in a dryland ecosystem and to concurrently explore multiple potential controls, we estimated whole plant net photosynthesis (A net ) and soil respiration at four distances from the plant base, as well as corresponding fine root biomass and soil carbon and nitrogen pools, four times during a growing season. To determine if the controls vary between different plant functional types for Colorado Plateau species, measurements were made on the C 4 shrub, Atriplex confertifolia , and C 3 grass, Achnatherum hymenoides . Soil respiration declined throughout the growing season and diminished with distance from the plant base, though variations in both were much smaller than expected. The strongest relationship was between soil respiration and soil moisture. Soil respiration was correlated with whole plant A net , although the relationship varied between species and distance from plant base. In the especially dry year of this study we did not observe any consistent correlations between soil respiration and soil carbon or nitrogen pools. Our findings suggest that abiotic factors, especially soil moisture, strongly regulate the response of soil respiration to biotic factors and soil carbon and nitrogen pools in dryland communities and, at least in dry years, may override expected spatial and seasonal patterns.

Oikos↗

USGS2016

Experimental warming in a dryland community reduced plant photosynthesis and soil CO 2 efflux although the relationship between the fluxes remained unchanged

1. Drylands represent our planet's largest terrestrial biome and, due to their extensive area, maintain large stocks of carbon (C). Accordingly, understanding how dryland C cycling will respond to climate change is imperative for accurately forecasting global C cycling and future climate. However, it remains difficult to predict how increased temperature will affect dryland C cycling, as substantial uncertainties surround the potential responses of the two main C fluxes: plant photosynthesis and soil CO 2 efflux. In addition to a need for an improved understanding of climate effects on individual dryland C fluxes, there is also notable uncertainty regarding how climate change may influence the relationship between these fluxes. 2. To address this important knowledge gap, we measured a growing season's in situ photosynthesis, plant biomass accumulation, and soil CO 2 efflux of mature Achnatherum hymenoides (a common and ecologically important C 3 bunchgrass growing throughout western North America) exposed to ambient or elevated temperature (+2°C above ambient, warmed via infrared lamps) for three years. 3. The 2°C increase in temperature caused a significant reduction in photosynthesis, plant growth, and soil CO 2 efflux. Of important note, photosynthesis and soil respiration appeared tightly coupled and the relationship between these fluxes was not altered by the elevated temperature treatment, suggesting C fixation's strong control of both above-ground and below-ground dryland C cycling. Leaf water use efficiency was substantially increased in the elevated temperature treatment compared to the control treatment. 4. Taken together, our results suggest notable declines in photosynthesis with relatively subtle warming, reveal strong coupling between above- and below-ground C fluxes in this dryland, and highlight temperature's strong effect on fundamental components of dryland C and water cycles.

Functional Ecology↗

USGS2015

C 3 and C 4 plant responses to increased temperatures and altered monsoonal precipitation in a cool desert on the Colorado Plateau, USA

Dryland ecosystems represent >40 % of the terrestrial landscape and support over two billion people; consequently, it is vital to understand how drylands will respond to climatic change. However, while arid and semiarid ecosystems commonly experience extremely hot and dry conditions, our understanding of how further temperature increases or altered precipitation will affect dryland plant communities remains poor. To address this question, we assessed plant physiology and growth at a long-term (7-year) climate experiment on the Colorado Plateau , USA, where the community is a mix of shallow-rooted C 3 and C 4 grasses and deep-rooted C 4 shrubs. The experiment maintained elevated-temperature treatments (+2 or +4 °C) in combination with altered summer monsoonal precipitation (+small frequent precipitation events or +large infrequent events). Increased temperature negatively affected photosynthesis and growth of the C 3 and C 4 grasses, but effects varied in their timing: +4 °C treatments negatively affected the C 3 grass early in the growing season of both years, while the negative effects of temperature on the C 4 grass were seen in the +2 and +4 °C treatments, but only during the late growing season of the drier year. Increased summer precipitation did not affect photosynthesis or biomass for any species, either in the year the precipitation was applied or the following year. Although previous research suggests dryland plants, and C 4 grasses in particular, may respond positively to elevated temperature, our findings from a cool desert show marked declines in C 3 and C 4 photosynthesis and growth, with temperature effects dependent on the degree of warming and growing-season precipitation.

Utah↗

USGS2013

Eco-evolutionary responses of Bromus tectorum to climate change: implications for biological invasions

How plant populations, communities, and ecosystems respond to climate change is a critical focus in ecology today. The responses of introduced species may be especially rapid. Current models that incorporate temperature and precipitation suggest that future Bromus tectorum invasion risk is low for the Colorado Plateau. With a field warming experiment at two sites in southeastern Utah, we tested this prediction over 4 years, measuring B. tectorum phenology, biomass, and reproduction. In a complimentary greenhouse study, we assessed whether changes in field B. tectorum biomass and reproductive output influence offspring performance. We found that following a wet winter and early spring, the timing of spring growth initiation, flowering, and summer senescence all advanced in warmed plots at both field sites and the shift in phenology was progressively larger with greater warming. Earlier green-up and development was associated with increases in B. tectorum biomass and reproductive output, likely due early spring growth, when soil moisture was not limiting, and a lengthened growing season. Seeds collected from plants grown in warmed plots had higher biomass and germination rates and lower mortality than seeds from ambient plots. However, in the following two dry years, we observed no differences in phenology between warmed and ambient plots. In addition, warming had a generally negative effect on B. tectorum biomass and reproduction in dry years and this negative effect was significant in the plots that received the highest warming treatment. In contrast to models that predict negative responses of B. tectorum to warmer climate on the Colorado Plateau, the effects of warming were more nuanced, relied on background climate, and differed between the two field sites. Our results highlight the importance of considering the interacting effects of temperature, precipitation, and site-specific characteristics such as soil texture, on plant demography and have direct implications for B. tectorum invasion dynamics on the Colorado Plateau.

Utah↗