Performing Department
SCHOOL OF FORESTRY
Non Technical Summary
The primary objective of this research is to use the natural variation in strontium (Sr) isotope ratios to better understand nutrient cycling in pinon-juniper (PJ) woodlands during soil and ecosystem development from volcanic cinders. The analysis of the 87Sr/86Sr isotopic ratios in the vegetation, soil, and dust inputs across a gradient of sites with different soil ages will address two questions that will significantly enhance our understanding of the functioning of a dominant vegetation type in the American Southwest: 1) What is the importance of dust to the maintenance and sustainability of PJ woodlands as soils age; and 2) How will the soil depth at which nutrients are acquired by plants change as soils age This research is pivotal for improving the science and management of wildland ecosystems and their components in the American Southwest for several reasons. First, PJ woodlands are by far the most poorly studied forested ecosystem of the Southwest, even though they occupy more area than any other forest type in Arizona (over 3.5 million hectares or 46% of all forest land in the state). Second, plant communities developed on volcanic cinders are excellent barometers of climate change because these soils tend to be relatively droughty and nutrient poor compared to other parent materials from which soils develop in this region. Hence, short-term knowledge of the controlling factors of these environmentally sensitive ecosystems should provide valuable insight on how other, less stressed ecosystems of the Southwest may respond to changing climates over longer time periods. Finally, this research will allow comparisons of the structure and function of a major ecosystem of the Southwest with those of other ecosystems worldwide. Such comparisons of ecosystems across regions are vital for the development of adaptive strategies for the sound, scientifically based management of forests and other wildlands.
Animal Health Component
(N/A)
Research Effort Categories
Basic
80%
Applied
20%
Developmental
(N/A)
Goals / Objectives
The overarching objective of this research is to use the natural variation in strontium (Sr) isotope ratios to explore patterns of biogeochemical cycling of calcium (Ca) and other cation nutrients during soil and ecosystem development. The analysis of the 87Sr/86Sr isotopic ratios in the vegetation, soil, and dust inputs across a soil age gradient (the Substrate Age Gradient of Arizona, or SAGA) will address two hypotheses that will significantly enhance our current understanding of the function of a dominant vegetation type in the American Southwest: Hypothesis 1: The relative contribution of dust input to soil nutrient pools and nutrient uptake by vegetation will increase with ecosystem development. Hypothesis 2: The mean depth of nutrient uptake by vegetation will decrease with ecosystem development This research is pivotal for improving the science and management of wildland ecosystems and their components in the American Southwest for several reasons. First, PJ woodlands are by far the most poorly studied forested ecosystem of the Southwest, even though they occupy more area than any other forest type in Arizona (over 3.5 million hectares or 46% of all forest land in the state). Second, plant communities developed on volcanic cinders are excellent barometers of climate change because these soils tend to be relatively droughty and nutrient poor compared to other parent materials in this region. Hence, short-term knowledge of the controlling factors of these environmentally sensitive ecosystems should provide valuable insight on how other, less stressed ecosystems of the Southwest may respond to changing climates or increases in N deposition over longer time periods. Finally, this research will allow comparisons of the structure and function of a major ecosystem of the Southwest with those of other ecosystems worldwide. Such comparisons of ecosystems across regions are vital for the development of adaptive strategies for the sound, scientifically based management of forests and other wildlands.
Project Methods
At each of the four sites of contrasting ages across SAGA, we will measure the Sr isotopic ratio of the basalt cinder parent material and the dust input (via wet and dry deposition). Dust collection is inherently difficult, so we will use two different methods to sample dust. We will install three "dust traps" at each site. The dust traps consist of a Teflon-coated angel food cake pan containing glass marbles placed on galvanized mesh cloth, suspended at a 2 m height above the ground surface. Dust is sampled periodically by washing the pan and contents with deionized water and collecting the suspension in polyethylene bottles. We will also measure dust inputs by using 10 bulk precipitation and throughfall collectors (10 under pinon pine canopies and 10 under juniper canopies), similar to the design we have successfully employed at the youngest site. Tree canopies are known to be more efficient collectors of atmospheric dust than artificial dust traps because of the greater surface areas of trees. Previous work at Sunset Crater has shown that Ca inputs under pinon canopies (presumably the majority coming from dust) are two-fold greater than Ca inputs in the open (i.e., collected in bulk precipitation samplers). Both of these collectors will measure total deposition of Sr, which includes Sr contained in dust as well as Sr dissolved in solution; however, the vast majority of the atmospheric Sr input (as well as other cations) in these semi-arid ecosystems is likely dust-derived. At each of five soil pits within each site, we already have collected: one pinon pine foliage sample using a composite of needles of all age classes; a tree bole wood increment core; a composite (horizontally across the pit face) soil sample from each of three soil depths (upper: 0-10 cm, mid: 70-80 cm, and lower: 140-160 cm), and one composite soil sample from pedogenic soil carbonates (from calcic horizons > 70 cm). Additionally, as part of this research effort, we will sample the other two canopy types of these ecosystems, juniper and intercanopy bunch grasses, and the soil underneath them. Soil samples will be collected using a bucket auger at the same depths used for the soil pits, and juniper and intercanopy vegetation will be samples in a similar manner as done previously with pinon pine (intercanopy shrubs, mainly Fallugia paradoxa and Rhus trilobata, instead of bunchgrasses will be sampled at Sunset Crater because of the dominance of shrubs in the intercanopy spaces at this site). Strontium isotope analyses will be conducted by Dr. Michael Ketterer with a VG Axiom MC multiple collector ICPMS in the Department of Chemistry at Northern Arizona University. This method agrees favorably with TIMS-analyzed Sr isotopes (M. Ketterer, personal communication; comparative data on file). Sources of ecosystem and soil uptake strontium will be calculated using isotope mixing models.