Substrate age and tree islands influence carbon and nitrogen dynamics across a retrogressive semiarid chronosequence

The long-term dynamics of carbon (C) and nitrogen (N) in semiarid ecosystems remain poorly understood. We measured pools and fluxes of surface soil C and N, as well as other soil properties, under tree canopies and in intercanopy spaces at four sites that form a volcanic substrate age gradient in semiarid piñon-juniper woodlands of northern Arizona, United States. Clay content and soil water-holding capacity increased consistently with substrate age, but both soil organic C and N increased only up to the 750,000 year site and then declined at the oldest (3,000,000 year) site. Measures of soil C and N flux displayed a similar pattern to total C and N pools. Pools and fluxes of C and N among the three canopy types became more homogeneous with substrate age up to the 750,000 year site, but disparity between tree and intercanopy microsites widened again at the oldest site. The δ15N of both tree leaves and surface soils became progressively more enriched across the substrate age gradient, consistent with a N cycle increasingly dominated by isotope fractionating losses. Our results point to consistencies in patterns of ecosystem development between semiarid and more humid ecosystems and suggest that pedogenic development may be an important factor controlling the spatial distribution of soil resources in semiarid ecosystems. These data should help both unify and broaden current theory of terrestrial ecosystem development

Christmas Card from Joseph F. Padien to the Bryant College Service Club

[Transcription begins] [inside card] This is a nice Season~And mostly, that’s trueBecause it reminds meOf people like YOU~And that’s why I’m wishing,As always before,The joys of this SeasonTo bless you once more! Joe PADIEN ‘35 [Transcription ends

Plant Establishment in Masticated Utah Juniper Woodlands

Juniper (Juniperus spp.) encroachment into sagebrush (Artemisia spp.)-bunchgrass communities has reduced understory cover on millions of hectares of semiarid rangelands. Mechanical masticators shred trees to restore desirable vegetation and reduce the potential for catastrophic wildfire. Mechanical mastication where juniper density is high and perennial grass cover is low brings a risk of invasive weed dominance unless perennial species are established. To determine whether juniper mastication favors annual- or perennial-grass establishment, we compared seedling emergence, tillers, and aboveground biomass of cheatgrass (Bromus tectorum L.) and Anatone bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Löve). Comparisons were made among hand-planted rows between and under juniper canopies of masticated and adjacent untreated control areas at three locations in Utah. Bluebunch wheatgrass had 16% (95% CI: 11-21) and cheatgrass had 10% (95% CI: 5-15) fewer seedlings emerge per row in masticated than untreated areas (P<0.001). However, bluebunch wheatgrass had 3.2 (95% CI: 2.0-5.2) times more tillers and 1.9 (95% CI: 1.6-2.2) times more aboveground biomass per row in masticated than untreated areas (P<0.001). Similarly, cheatgrass had 2.3 (95% CI: 1.5-3.8) times more tillers, 2.0 (95% CI: 1.7-2.4) times more aboveground biomass, and 11.4 (95% CI: 6.3-20.7) times more spikelets per row in masticated than untreated areas (P<0.001). This increased seedling growth in masticated areas was associated with increased inorganic nitrogen and soil water compared to untreated areas. Because mastication improves the growth of both cheatgrass and bluebunch wheatgrass seedlings, it could support dominance by either annual- or perennial-life forms. To avoid cheatgrass dominance where perennial understory cover is limited and cheatgrass propagule pressure is high, mastication should be accompanied by seeding desirable perennial species such as Anatone bluebunch wheatgrass.The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202