ABSTRACT
Increased drought frequency and intensity and agricultural intensification have been key stressors to ecological systems over the past century. Biological proxies (e.g., pollen, tree rings) have been used to track this environmental change; however, linking these changes to the ecology of organisms remains challenging. Here, we link historical drought records to conditions of high water-stress in grassland habitats through the stable isotope analysis of California vole museum specimens (Microtus californicus). Using museum collections spanning 118-years (1891-2009), isotope values of dated hair tissues were associated with statewide drought metrics on the Palmer Drought Severity Index. We observed a positive correlation between δ15N and δ18O values and drought severity. The range in δ15N values (~ 18) is greater than what would be expected as a result of dietary shifts across the landscape (~ 3), and is likely attributed to the combined effects of physiological responses of M. californicus and isotopic shifts in plant resources with increased water-stress. Geospatial patterns in δ34S values of hair tissues reflect higher baseline isotope values in coastal habitats. However, comparably high δ34S values in the southern-most inland localities suggest sulfur fertilization of croplands and subsequent transfer to surrounding grassland habitats in 34S enriched forms. A broad δ13C range (- 28.7 to - 14.3) further suggests the consumption of C3 and C4 plant-based dietary proteins. As shown here, stable isotope analysis of museum collections can provide a climate and land use record based on the physiological performance and ecology of a study species in a region affected intensely by anthropogenic activities.
Subject(s)
Droughts , Hair , Animals , Arvicolinae , California , Carbon IsotopesABSTRACT
Exotic earthworm introductions can alter above- and belowground properties of temperate forests, but the net impacts on forest soil carbon (C) dynamics are poorly understood. We used a mesocosm experiment to examine the impacts of earthworm species belonging to three different ecological groups (Lumbricus terrestris [anecic], Aporrectodea trapezoides [endogeic], and Eisenia fetida [epigeic]) on C distributions and storage in reconstructed soil profiles from a sandy temperate forest soil by measuring CO2 and dissolved organic carbon (DOC) losses, litter C incorporation into soil, and soil C storage with monospecific and species combinations as treatments. Soil CO2 loss was 30% greater from the Endogeic x Epigeic treatment than from controls (no earthworms) over the first 45 days; CO2 losses from monospecific treatments did not differ from controls. DOC losses were three orders of magnitude lower than CO2 losses, and were similar across earthworm community treatments. Communities with the anecic species accelerated litter C mass loss by 31-39% with differential mass loss of litter types (Acer rubrum > Populus grandidentata > Fagus grandifolia > Quercus rubra > or = Pinus strobus) indicative of leaf litter preference. Burrow system volume, continuity, and size distribution differed across earthworm treatments but did not affect cumulative CO2 or DOC losses. However, burrow system structure controlled vertical C redistribution by mediating the contributions of leaf litter to A-horizon C and N pools, as indicated by strong correlations between (1) subsurface vertical burrows made by anecic species, and accelerated leaf litter mass losses (with the exception of P. strobus); and (2) dense burrow networks in the A-horizon and the C and N properties of these pools. Final soil C storage was slightly lower in earthworm treatments, indicating that increased leaf litter C inputs into soil were more than offset by losses as CO2 and DOC across earthworm community treatments.
