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Restoration treatments in Bromus tectorum (cheatgrass)‐invaded sagebrush habitat have often produced poor results. This is perhaps due to multifaceted ecological changes associated with cheatgrass invasion like reduced water availability, altered nutrient availability, and shifts in soil microbial communities. We tested whether suppressing cheatgrass, altering nutrient availability, and inoculating with soil microbes improved restoration success. We conducted field experiments in Idaho, Utah, and Arizona where we transplanted seedlings of Artemisia tridentata ssp. tridentata (basin big sagebrush) and Elymus elymoides (squirreltail). Growth and survivorship of both species were higher in sites with greater precipitation and lower cheatgrass abundance. Significant nutrient modification effects were seen in Utah, where cheatgrass abundance was highest and soil nutrients were most limiting. In Utah, we observed an increase of 14% in survivorship for squirreltail in response to carbon addition, and 119% increase in growth of sagebrush with phosphorus addition. Inoculating plants with sagebrush rhizosphere soil or a commercial arbuscular mycorrhiza at the time of planting did not significantly affect growth, survivorship, arbuscular mycorrhizal fungi colonization, or extraradical mycorrhizal hyphae length for either plant species. The largest effects on seedling growth (+384%) and survivorship (+262%) were observed in response to the suppression of cheatgrass using a weed barrier cloth and associated with increased water availability. Interactions between suppressing cheatgrass, altering nutrient availability, and inoculating with soil microbes were not significant. Direct reduction of cheatgrass was shown to be more effective than targeting soil legacy effects associated with cheatgrass with regards to restoration outplanting success. [ABSTRACT FROM AUTHOR]

Global temperature increases and precipitation changes are both expected to alter ecosystem carbon (C) cycling. We tested responses of ecosystem C cycling to simulated climate change using field manipulations of temperature and precipitation across a range of grass-dominated ecosystems along an elevation gradient in northern Arizona. In 2002, we transplanted intact plant-soil mesocosms to simulate warming and used passive interceptors and collectors to manipulate precipitation. We measured daytime ecosystem respiration (ER) and net ecosystem C exchange throughout the growing season in 2008 and 2009. Warming generally stimulated ER and photosynthesis, but had variable effects on daytime net C exchange. Increased precipitation stimulated ecosystem C cycling only in the driest ecosystem at the lowest elevation, whereas decreased precipitation showed no effects on ecosystem C cycling across all ecosystems. No significant interaction between temperature and precipitation treatments was observed. Structural equation modeling revealed that in the wetter-than-average year of 2008, changes in ecosystem C cycling were more strongly affected by warming-induced reduction in soil moisture than by altered precipitation. In contrast, during the drier year of 2009, warming induced increase in soil temperature rather than changes in soil moisture determined ecosystem C cycling. Our findings suggest that warming exerted the strongest influence on ecosystem C cycling in both years, by modulating soil moisture in the wet year and soil temperature in the dry year. [ABSTRACT FROM AUTHOR]

Abstract: Soil microbial organisms are central to carbon (C) and nitrogen (N) transformations in soils, yet not much is known about the stable isotope composition of these essential regulators of element cycles. We investigated the relationship between C and N availability and stable C and N isotope composition of soil microbial biomass across a three million year old semiarid substrate age gradient in northern Arizona. The δ 15N of soil microbial biomass was on average 7.2‰ higher than that of soil total N for all substrate ages and 1.6‰ higher than that of extractable N, but not significantly different for the youngest and oldest sites. Microbial 15N enrichment relative to soil extractable and total N was low at the youngest site, increased to a maximum after 55,000 years, and then decreased slightly with age. The degree of 15N enrichment of microbial biomass correlated negatively with the C:N mass ratio of the soil extractable pool. The δ 13C signature of soil microbial biomass was 1.4‰ and 4.6‰ enriched relative to that of soil total and extractable pools respectively and showed significant differences between sites. However, microbial 13C enrichment was unrelated to measures of C and N availability. Our results confirm that 15N, but not 13C enrichment of soil microbial biomass reflects changes in C and N availability and N processing during long-term ecosystem development. [Copyright &y& Elsevier]

Abstract: We present a significant relationship between the natural abundance isotopic composition of ecosystem pools and the abundance of a microbial gene. Natural abundance 15N of soils and soil DNA were analysed and compared with archaeal ammonia oxidizer abundance along an elevation gradient in northern Arizona and along a substrate age gradient in Hawai'i. There was a significant positive correlation between the abundance of archaeal amoA genes and natural abundance δ15N of total soil or DNA suggesting that ammonia oxidizing archaea play an important role in ecosystem N release. [Copyright &y& Elsevier]

Leaf litter provides an important nutrient subsidy to headwater streams, but little is known about how tree genetics influence energy pathways from litter to higher trophic levels. Despite the charge to quantify carbon (C) and nitrogen (N) pathways from decomposing litter, the relationship between litter decomposition and aquatic consumers remains unresolved. We measured litter preference (attachments to litter), C and N assimilation rates, and growth rates of a shredding caddisfly (Hesperophylax magnus, Limnephilidae) in response to leaf litter of different chemical and physical phenotypes using Populus cross types (P. fremontii, P. angustifolia, and F 1 hybrids) and genotypes within P. angustifolia. We combined laboratory mesocosm studies using litter from a common garden with a field study using doubly labeled litter ( 13 C and 15 N) grown in a greenhouse and incubated in Oak Creek, Arizona, USA. We found that, in the lab, shredders initially chose relatively labile (low lignin and condensed tannin concentrations, rapidly decomposing) cross type litter, but preference changed within 4 d to relatively recalcitrant (high lignin and condensed tannin concentrations, slowly decomposing) litter types. Additionally, in the lab, shredder growth rates were higher on relatively recalcitrant compared to labile cross type litter. Over the course of a three-week field experiment, shredders also assimilated more C and N from relatively recalcitrant compared to labile cross type litter. Finally, among P. angustifolia genotypes, N assimilation by shredders was positively related to litter lignin and C:N, but negatively related to condensed tannins and decomposition rate. C assimilation was likewise positively related to litter C:N, and also to litter %N. C assimilation was not associated with condensed tannins or lignin. Collectively, these findings suggest that relatively recalcitrant litter of Populus cross types provides more nutritional benefit, in terms of N fluxes and growth, than labile litter, but among P. angustifolia genotypes the specific trait of litter recalcitrance (lignin or tannins) determines effects on C or N assimilation. As shredders provide nutrients and energy to higher trophic levels, the influence of these genetically based plant decomposition pathways on shredder preference and performance may affect community and food web structure., (© 2018 by the Ecological Society of America.)