Matching Items (3)
Filtering by
- All Subjects: Drylands
- All Subjects: carbon cycling
- All Subjects: Carbon Isotope
- Genre: Masters Thesis
- Creators: Hultine, Kevin
- Creators: Monus, Brittney
- Creators: Munson, Seth M
Climate Sensitivity in Mature Versus Pre-Reproductive Saguaro Determined from Spine Isotopic Signals
Description
The saguaro cactus is vital to the unique biodiversity of the Sonoran Desert. Many animals rely on it for survival and shelter. Due to its thick waxy exterior, it is able to retain a massive amount of water in its succulent stems, making it an ideal habitat for many birds that are native to the region. It also holds a large cultural significance for many native tribes of this region. Thus, it is important to understand how these magnificent plants are affected by changing environmental conditions in order to protect them in the future. Measurements of carbon isotope (13C) signals in saguaros spine tissues have been shown to be a robust approach for evaluating plant responses to climate variation over multiple seasons and years. This study investigated growth and 13C signals in young saguaros (< 2.5 m tall) at a location north of Phoenix to compare with large saguaros (> 4 m tall) that actively flower in the spring. Adolescent saguaros were examined to determine how they responded to variation in moisture between the years 2012 through 2016. As with a previous study by Hultine et al. (2018), this research demonstrated a strong relationship between height growth and precipitation. Stem growth was also highly correlated with the number of areoles produced across both young and old plants. Winter and late summer moisture from the previous year had a significant effect on stem growth, and a legacy effect could be seen in the low growth rates in 2014 which may be a result of low precipitation during the previous fall and winter. This study also established that the adolescent saguaro may be less sensitive to seasonal changes than the mature saguaro. When comparing the large plants with the adolescent plants, spine 13C values were similar between mature and adolescent plants, indicating that perhaps flower does not impose a significant added cost to saguaro water budgets. However, identifying the cost of flowering requires more investigation than that from only spine carbon isotope measurements and coarse measurements of plant productivity.
ContributorsDe Leon, Isabella (Author) / Hultine, Kevin (Thesis advisor) / Pigg, Kathleen (Thesis advisor) / Maienschein, Jane (Committee member) / Arizona State University (Publisher)
Created2021
Description
Soil organic carbon (SOC) is a critical component of the global carbon (C) cycle, accounting for more C than the biotic and atmospheric pools combined. Microbes play an important role in soil C cycling, with abiotic conditions such as soil moisture and temperature governing microbial activity and subsequent soil C processes. Predictions for future climate include warmer temperatures and altered precipitation regimes, suggesting impacts on future soil C cycling. However, it is uncertain how soil microbial communities and subsequent soil organic carbon pools will respond to these changes, particularly in dryland ecosystems. A knowledge gap exists in soil microbial community responses to short- versus long-term precipitation alteration in dryland systems. Assessing soil C cycle processes and microbial community responses under current and altered precipitation patterns will aid in understanding how C pools and cycling might be altered by climate change. This study investigates how soil microbial communities are influenced by established climate regimes and extreme changes in short-term precipitation patterns across a 1000 m elevation gradient in northern Arizona, where precipitation increases with elevation. Precipitation was manipulated (50% addition and 50% exclusion of ambient rainfall) for two summer rainy seasons at five sites across the elevation gradient. In situ and ex situ soil CO2 flux, microbial biomass C, extracellular enzyme activity, and SOC were measured in precipitation treatments in all sites. Soil CO2 flux, microbial biomass C, extracellular enzyme activity, and SOC were highest at the three highest elevation sites compared to the two lowest elevation sites. Within sites, precipitation treatments did not change microbial biomass C, extracellular enzyme activity, and SOC. Soil CO2 flux was greater under precipitation addition treatments than exclusion treatments at both the highest elevation site and second lowest elevation site. Ex situ respiration differed among the precipitation treatments only at the lowest elevation site, where respiration was enhanced in the precipitation addition plots. These results suggest soil C cycling will respond to long-term changes in precipitation, but pools and fluxes of carbon will likely show site-specific sensitivities to short-term precipitation patterns that are also expected with climate change.
ContributorsMonus, Brittney (Author) / Throop, Heather L (Thesis advisor) / Ball, Becky A (Committee member) / Hultine, Kevin R (Committee member) / Munson, Seth M (Committee member) / Arizona State University (Publisher)
Created2019
Description
Climate change is increasing global surface temperatures, intensifying droughts and increasing rainfall variation, particularly in drylands. Understanding how dryland plant communities respond to climate change-induced rainfall changes is crucial for implementing effective conservation strategies. Concurrent with climate change impacts on drylands is woody encroachment: an increase in abundance of woody plant species in areas formerly dominated by grasslands or savannahs. For example, the woody plant, Prosopis velutina (velvet mesquite), has encroached into grasslands regionally over the past century. From an agricultural perspective, P. velutina is an invasive weed that hinders cattle forage. Understanding how P. velutina will respond to climate change-induced rainfall changes can be useful for management and conservation efforts. Prosopis velutina was used to answer the following question: Is there a significant interactive effect of mean soil water moisture content and pulse frequency on woody seedling survival and growth in dryland ecosystems? There were 256 P. velutina seedlings sourced from the Santa Rita Experimental Range in southern Arizona grown under four watering treatments where mean and pulse frequency were manipulated over two months. Data were collected on mortality, stem height, number of leaves, instantaneous gas exchange, chlorophyll fluorescence, biomass, and the leaf carbon to nitrogen (C:N) ratio. Mortality was low across treatments. Pulse frequency had less impact across response variables than the mean amount of water received. This may indicate that P. velutina seedlings are relatively insensitive to rainfall timing and are more responsive to rainfall amount. Prosopis velutina in the low mean soil moisture treatments lost a majority of their leaves and had greater biomass allocation to roots. Prosopis velutina’s ability to survive in low soil moisture conditions and invest in root biomass can allow it to persist as drylands are further affected by climate change. Prosopis velutina could benefit ecosystems where native plants are at risk due to rainfall variation if P. velutina occupies a similar niche space. Due to conflicting viewpoints of P. velutina as an invasive species, it’s important to examine P. velutina from both agricultural and conservation perspectives. Further analysis on the benefits to P. velutina in these ecosystems is recommended.
ContributorsDavis, Ashley R. (Author) / Throop, Heather (Thesis advisor) / Hultine, Kevin (Committee member) / Sala, Osvaldo (Committee member) / Arizona State University (Publisher)
Created2020