R Inouye

Exotic plants increase and native plants decrease with loss of foundation species in sagebrush steppe

Dominant plant species, or foundation species, are recognized to have a disproportionate control over resources in ecosystems, but few studies have evaluated their relationship to exotic invasions. Loss of foundation species could increase resource availability to the benefit of exotic plants, and could thereby facilitate invasion. The success of exotic plant invasions in sagebrush steppe was hypothesized to benefit from increased available soil water following removal of sagebrush (Artemisia tridentata), a foundation species. We examined the effects of sagebrush removal, with and without the extra soil water made available by exclusion of sagebrush, on abundance of exotic and native plants in the shrub steppe of southern Idaho, USA. We compared plant responses in three treatments: undisturbed sagebrush steppe; sagebrush removed; and sagebrush removed plus plots covered with “rainout” shelters that blocked winter-spring recharge of soil water. The third treatment allowed us to examine effects of sagebrush removal alone, without the associated increase in deep-soil water that is expected to accompany removal of sagebrush. Overall, exotic herbs (the grass Bromus tectorum and four forbs) were 3–4 times more abundant in shrub-removal and 2xa0times more abundant in shrub-removalxa0+xa0rainout-shelter treatments than in the control treatment, where sagebrush was undisturbed. Conversely, native forbs were only about half as abundant in shrub removal compared to control plots. These results indicate that removal of sagebrush facilitates invasion of exotic plants, and that increased soil water is one of the causes. Our findings suggest that sagebrush plays an important role in reducing invasions by exotic plants and maintaining native plant communities, in the cold desert we evaluated.

Evaluation of four grasses for use in phytoremediation of Cs-contaminated arid land soil

We used greenhouse experiments to evaluate cesium (Cs) uptake by four grasses, Agropyron spicatum (Pursh) Scribn & Smith, Leymus cinereus Scribn & Merr., Agropyron cristatum (L.) Gaertn. and Bromus tectorum L., to determine their potential as phytoremediation agents for Cs-contaminated soils. These four species grow well in the Intermountain region of western North America primarily on moderately coarse to coarsely textured soils where annual precipitation ranges from 20 to 50xa0cm. Whereas A. cristatum and B. tectorum are introduced species from Asia and the Mediterranean region of Europe, respectively, A. spicatum and L. cinereus are native to the Great Plains and Intermountain regions of North America. Plants were grown under two treatments each of: (1) soil Cs (ambient and 50xa0mg kg−1 + ambient), (2) soil fertility (ambient and ambient + 40xa0mg N kg−1 and 60xa0mg P kg−1), and 3) soil moisture (35% and 70% water holding capacity of the potted soils). Shoot Cs concentration in high soil Cs treatments was approximately ten times greater than in low soil Cs treatments. Even though shoot Cs concentrations tended to be lower in high soil Cs-high fertility-high soil moisture treatments than in high soil Cs-ambient fertility-low soil moisture treatments, total Cs uptake was greater because shoot biomass was approximately ten-fold greater. Shoots did not show signs of Cs toxicity in the high soil Cs treatments. We concluded, however, based on the low transfer factors (∼1.0) for all these grasses, that none were strong candidates as phytoremediation agents for Cs-contaminated soils.

Effects of temperature and concentration on nutrient release rates from nutrient diffusing substrates

Abstract Nutrient diffusing substrates (NDS) are an important tool for evaluating periphyton nutrient limitation. The rate at which nutrients are released from NDS depends on both the initial nutrient concentration and the length of time that NDS are in place. Whether temperature also affects nutrient release rates from NDS is unclear. However, this information is important because temperature effects on release rates could confound experimental results for NDS-based experiments testing rates of accumulation of periphyton biomass when stream water temperature is variable. We measured N and P release rates from NDS vials with 3 initial concentrations (0.05, 0.1, and 0.5 mol/L) of nutrients at 3 temperatures (4, 15, and 21°C) for 21 d. Release rates of both nutrients were greater for vials with higher nutrient concentrations and for vials at warmer temperatures. For all concentrations, release rates decreased log linearly with time, a result that might have important implications for patterns of colonization and subsequent interspecific interactions within the periphyton community. In our opinion, temperature-caused differences in release rates are not biologically important because the differences were much smaller (3%) than expected changes in periphyton maximum growth rates over similar temperature ranges (∼300%). Our results suggest that seasonal and site-related differences in temperature will not significantly affect nutrient release rates within the range of temperatures we tested, but researchers should consider nutrient concentration carefully when planning studies using NDS.

Nutrient limitation of biofilm biomass and metabolism in the Upper Snake River basin, southeast Idaho, USA

It is essential to know the nutrient limitation status of biofilms to understand how they may buffer uptake and export of nutrients from polluted watersheds. We tested the effects of nutrient additions on biofilm biomass (chlorophyll a, ash free dry mass (AFDM), and autotrophic index (AI, AFDM/chl a)) and metabolism via nutrient-diffusing substrate bioassays (control, nitrogen (N), phosphorus (P), and Nxa0+xa0P treatments) at 11 sites in the Upper Snake River basin (southeast Idaho, USA) that differed in the magnitude and extent of human-caused impacts. Water temperature, turbidity, and dissolved inorganic N concentrations all changed seasonally at the study sites, while turbidity and dissolved inorganic N and P also varied with impact level. Chl a and AI on control treatments suggested that the most heavily impacted sites supported more autotrophic biofilms than less-impacted sites, and that across all sites biofilms were more heterotrophic in autumn than in summer. Nutrient stimulation or suppression of biofilm biomass was observed for chl a in 59% of the experiments and for AFDM in 33%, and the most frequent response noted across all study sites was N limitation. P suppression of chl a was observed only at the most-impacted sites, while AFDM was never suppressed by nutrients. When nutrient additions did have significant effects on metabolism, they were driven by differences in biomass rather than by changes in metabolic rates. Our study demonstrated that biofilms in southeast Idaho rivers were primarily limited by N, but nutrient limitation was more frequent at sites with good water quality than at those with poor water quality. Additionally, heterotrophic and autotrophic biofilm components may respond differently to nutrient enrichment, and nutrient limitation of biofilm biomass should not be considered a surrogate for metabolism in these rivers.

Outcomes of Co-Review in the National Science Foundation's Ecosystem Studies Program

Most core programs in the Biological Sciences Directorate in the National Science Foundation (NSF) reflect academic disciplines that are common in the higher education system in the United States. This facilitates review of discipline-specific proposals. Proposals that integrate topics that are relevant to more than one core program may be handled by co-review, a process by which more than one program evaluates the merits of a proposal.