Effects of Nitrogen addition on soil respiration
I am involved in a number of studies aimed at assessing the response of soil respiration to low dosages of N additions in order to better understand how future scenarios of N deposition will affect the terrestrial carbon cycle. This includes work in a coastal sage scrub community in Sardinia, a subtropical forest in eastern China, and boreal forests in northern Sweden.
Cascio ML, Morillas L, Ochoa-Hueso R, Munzi S, Roales J, Hasselquist NJ, Manrique E, Spano D, Jaoude RA, Mereu S. (2017) Contrasting effects of nitrogen deposition on soil respiration in two Mediterranean ecosystems. Environmental Science and Pollution Research 24: 26160-26171.
Maaroufi N, Nordin A, Hasselquist NJ, Holm Bach L, Palmqvist K, Gundale M. (2015)Anthropogenic nitrogen deposition enhances carbon sequestration in boreal soils. Global Change Biology 21: 3169-3180.
Gao Q, Hasselquist NJ, Palmroth S, Zheng Z, You W. (2014) Short-term response of soil respiration to nitrogen fertilization in a subtropical evergreen forest. Soil Biology and Biogeochemistry 76: 297-300.
Cascio ML, Morillas L, Ochoa-Hueso R, Munzi S, Roales J, Hasselquist NJ, Manrique E, Spano D, Jaoude RA, Mereu S. (2017) Contrasting effects of nitrogen deposition on soil respiration in two Mediterranean ecosystems. Environmental Science and Pollution Research 24: 26160-26171.
Maaroufi N, Nordin A, Hasselquist NJ, Holm Bach L, Palmqvist K, Gundale M. (2015)Anthropogenic nitrogen deposition enhances carbon sequestration in boreal soils. Global Change Biology 21: 3169-3180.
Gao Q, Hasselquist NJ, Palmroth S, Zheng Z, You W. (2014) Short-term response of soil respiration to nitrogen fertilization in a subtropical evergreen forest. Soil Biology and Biogeochemistry 76: 297-300.
CARBON Cycling IN UNDERSTORY VEGETATION
Ecological studies in boreal forests have primarily focused on larger organisms, such as trees and vertebrates, with little attention given to understory vegetation. However, understory vegetation in boreal forests has been identified as a key ecological driver in both above- and belowground processes and may also play an important role in the amount of C that is entering and leaving these forested ecosystems.
Hasselquist NJ, Metcalfe DB, Marshall JD, Lucas RW, Högberg P. Seasonality and nitrogen supply modify carbon partitioning in understory vegetation of a boreal coniferous forest. Ecology 97: 671-683.
Metcalfe DB, Eisele B, Hasselquist NJ. (2013) Effects of nitrogen fertilization on the forest floor carbon balance over the growing season in a boreal pine forest. Biogeosciences 10: 8223-8231.
Hasselquist NJ, Metcalfe DB, Marshall JD, Lucas RW, Högberg P. Seasonality and nitrogen supply modify carbon partitioning in understory vegetation of a boreal coniferous forest. Ecology 97: 671-683.
Metcalfe DB, Eisele B, Hasselquist NJ. (2013) Effects of nitrogen fertilization on the forest floor carbon balance over the growing season in a boreal pine forest. Biogeosciences 10: 8223-8231.
15N to assess in PATTERNS OF TERRESTRIAL NITROGEN CYCLING
I have been involved with a in numerous studies that have used stable isotopes to assess the key factors influencing the global pattern of N cycling as well as the recover of the nitrogen cycle after large-scale disturbances.
Hasselquist EM, Hasselquist NJ, Sparks JP, Nilsson C. (2016) Changes in nitrogen cycling in riparian zones along a chronosequence of restored streams in northern Sweden. Plant and Soil doi:10.1007/s11104-016-3038-3.
Craine JM, Elmore AJ, Wang L, Augusto L, Baisden WT, Brookshire ENJ, Cramer MD, Hasselquist NJ, Hobbie EA, Kahmen A, et al. (2015) Convergence of soil nitrogen isotopes across global climate gradients. Scientific Reports 5: 8280.
Hasselquist NJ, Santiago LS, Allen MF. (2010) Belowground nitrogen dynamics in relation to hurricane damage along a tropical dry forest chronosequence. Biogeochemistry 98: 89-100.
Hasselquist EM, Hasselquist NJ, Sparks JP, Nilsson C. (2016) Changes in nitrogen cycling in riparian zones along a chronosequence of restored streams in northern Sweden. Plant and Soil doi:10.1007/s11104-016-3038-3.
Craine JM, Elmore AJ, Wang L, Augusto L, Baisden WT, Brookshire ENJ, Cramer MD, Hasselquist NJ, Hobbie EA, Kahmen A, et al. (2015) Convergence of soil nitrogen isotopes across global climate gradients. Scientific Reports 5: 8280.
Hasselquist NJ, Santiago LS, Allen MF. (2010) Belowground nitrogen dynamics in relation to hurricane damage along a tropical dry forest chronosequence. Biogeochemistry 98: 89-100.
Sensing the soil environment
I am involved in an interdisciplinary project that includes engineers, computer scientists and ecologists working together to develop novel environmental sensing technologies to monitor belowground ecological processes. I am particularly interested in incorporating high-frequency in situ observations of belowground processes into models to better predict how changes in abiotic conditions affects soil organisms and the cycling of C and N in natural ecosystems.
Hasselquist NJ, Vargas R, Allen MF. (2010) Using soil sensing technology to examine interactions and controls between ectomycorrhizal growth and environmental factors on soil CO2 dynamics. Plant and Soil 331: 17-29.
Hasselquist NJ, Vargas R, Allen MF. (2010) Using soil sensing technology to examine interactions and controls between ectomycorrhizal growth and environmental factors on soil CO2 dynamics. Plant and Soil 331: 17-29.
ALPINE TREELINE
As a Master student I examined how abiotic and biotic factors influence conifer seedling establishment in the alpine-treeline ecotone. Using a combination of observational and manipulative field experiments, I found evidence that successful seedling establishment is not only related to favorable microclimatic conditions, but also to the availability of mycorrhizal inoculum.
Hasselquist NJ, Germino MJ, McGonigle TC, Smith WK. (2005) Variability of Cenococcum infection and its ecophysiological significance for young conifers at alpine-treeline. New Phytologist 165: 867-873.
Maher EL, Germino MJ, Hasselquist NJ. (2005) Interactive effects of tree and herb cover on survivorship, physiology, and microclimate of conifer seedlings at the alpine-treeline ecotone. Canadian Journal of Forest Research 35: 567-574.
Hasselquist NJ, Germino MJ, McGonigle TC, Smith WK. (2005) Variability of Cenococcum infection and its ecophysiological significance for young conifers at alpine-treeline. New Phytologist 165: 867-873.
Maher EL, Germino MJ, Hasselquist NJ. (2005) Interactive effects of tree and herb cover on survivorship, physiology, and microclimate of conifer seedlings at the alpine-treeline ecotone. Canadian Journal of Forest Research 35: 567-574.
EXTREME EVENTS
During my PhD, I was involved with a number of studies that examined the immediate effects and short-term recovery of aboveground forest structure and belowground processes to Hurricane Wilma, one of the strongest hurricanes to make landfall on the northern Yucatan Peninsula. I have also examined the effects of large wildfires on soil biogeochemistry, namely quantifying the losses of soil carbon and nitrogen during episodic pulses of wind erosion following a wildfire.
Hasselquist NJ, Germino MJ, Sankey JB, Ingram LJ, Glenn NF. (2011) Aeolian nutrient fluxes following wildfire in sagebrush steppe: implications for soil carbon storage. Biogeosciences 8: 3649-3659.
Vargas R, Hasselquist NJ, Allen EB, Allen MF. (2010) Effects of a hurricane disturbance on aboveground forest structure, arbuscular mycorrhizae and belowground carbon in a restored tropical forest. Ecosystems 13: 118-128.
Hasselquist NJ, Germino MJ, Sankey JB, Ingram LJ, Glenn NF. (2011) Aeolian nutrient fluxes following wildfire in sagebrush steppe: implications for soil carbon storage. Biogeosciences 8: 3649-3659.
Vargas R, Hasselquist NJ, Allen EB, Allen MF. (2010) Effects of a hurricane disturbance on aboveground forest structure, arbuscular mycorrhizae and belowground carbon in a restored tropical forest. Ecosystems 13: 118-128.
CONSERVATION BIOLOGY
I have also been involved in a few applied studies with natural resource management implications. In one, I worked with the U.S. Fish and Wildlife Department to examine the potential consequences of groundwater pumping in Las Vegas on two federally protected plant species near Death Valley. In another study, I worked with a private non-profit land management organization (Center for Natural Lands Management) to study effective management practices of non-native plant species growing with an endangered forb.
Hasselquist NJ, Allen MF. (2009) Increasing demands on limited water resources: consequences for two endangered plants in Amargosa Valley, USA. AmericanJournal of Botany 96: 620-626.
Hasselquist EM, Hasselquist NJ, Roger DL. (2013) Management of non-native annual plants to support recovery of the endangered perennial forb, Ambrosia pumila. Restoration Ecology 21: 224-231.
Hasselquist NJ, Allen MF. (2009) Increasing demands on limited water resources: consequences for two endangered plants in Amargosa Valley, USA. AmericanJournal of Botany 96: 620-626.
Hasselquist EM, Hasselquist NJ, Roger DL. (2013) Management of non-native annual plants to support recovery of the endangered perennial forb, Ambrosia pumila. Restoration Ecology 21: 224-231.