The century experiment: the first twenty years of UC Davis' Mediterranean agroecological experiment.

The Century Experiment at the Russell Ranch Sustainable Agriculture Facility at the University of California, Davis provides long-term agroecological data from row crop systems in California's Central Valley starting in 1993. The Century Experiment was initially designed to study the effects of a gradient of water and nitrogen availability on soil properties and crop performance in ten different cropping systems to measure tradeoffs and synergies between agricultural productivity and sustainability. Currently systems include 11 different cropping systems-consisting of four different crops and a cover crop mixture-and one native grass system. This paper describes the long-term core data from the Century Experiment from 1993-2014, including crop yields and biomass, crop elemental contents, aerial-photo-based Normalized Difference Vegetation Index data, soil properties, weather, chemical constituents in irrigation water, winter weed populations, and operational data including fertilizer and pesticide application amounts and dates, planting dates, planting quantity and crop variety, and harvest dates. This data set represents the only known long-term set of data characterizing food production and sustainability in irrigated and rainfed Mediterranean annual cropping systems. There are no copyright restrictions associated with the use of this dataset.

Outside the envelope: rare events disrupt the relationshipbetween climate factors and species interactions.

The order in which species arrive during community assembly can be an important driver of community composition and function. However, the strength of these priority effects can be variable, in part because of strong site and year effects. To understand how priority effects vary in importance with abiotic conditions, we initiated identical community assembly experiments in which we varied the timing of arrival of native and exotic grass species in each of 4 yr across three grassland sites in northern California. This uniquely replicated experiment tested the power of priority to determine initial community structure in a restoration context across a natural range of conditions. There were large and significant differences in both total seeded cover and the strength of priority across sites and years of initiation, confirming the suspicion that most ecological experiments may lack spatial and temporal generality. On the other hand, much of the variation in strength of priority could be related to climate. Strikingly, however, the model fit across the three sites and the first 3 yr of the study (the first nine experiments) was radically altered when we included the fourth year, which was characterized by an unusual weather pattern with higher temporal variability in rainfall (a rainfall pattern predicted to increase with climate change). This year produced relatively low strength of priority, supporting the suggestion that highly variable climates may be associated with lower strength of priority effects. Experiments that examine community assembly over a range of naturally occurring abiotic conditions enhance our ability to predict when priority effects will be important, allowing us to explore shifting patterns of community assembly in the face of climate change and optimize restoration strategies based on environmental conditions.

Bioelectric impedance predicts total body water, blood pressure, and heart rate during hemodialysis in children and adolescents.

OBJECTIVE: The purposes of our study were to: (1) assess if changes in the volemic status of children and adolescents over the course of standard dialysis could be observed using bioelectric impedance (BIA); and (2) evaluate whether the variability of blood pressure (systolic blood pressure, SBP; diastolic blood pressure, DBP) and heart rate (HR) could be explained by independent variables from BIA data. DESIGN: We used a randomized, single-blinded treatment and repeated-measures design. SETTING: This study took place at the DaVita Children's Dialysis Center (Chicago, IL). PATIENTS: There were 7 subjects, aged 10 to 16 years. INTERVENTION: Two identical standard hemodialysis (HD) sessions were completed, with data collected five times during each HD session: pre-HD, intra-HD (hours 1, 2, and 3), and post-HD. Endpoints included total body water (TBW), resistance (R), reactance (Xc), bioimpedance vector |Z|, supine and sitting SBP, DBP, and HR. Standing SBP, DBP, and HR were collected pre-HD and post-HD. RESULTS: No differences were observed in TBW between HD sessions for all subjects. However, TBW decreased throughout the HD sessions for all subjects (although no significant differences were seen between hour 3 and post-HD). Reactance (representative of extracellular water) correlated with supine, sitting, and standing SBP (r = 0.55, 0.59, and 0.51, respectively; P < or = .008). The bioimpedance vector increased beginning at hour 1 (P < .001), reflective of a decline in tissue hydration over the course of HD. CONCLUSIONS: Weight gain in end-stage kidney disease patients is largely fluid. Thus, the use of BIA during HD may aid in the prediction of cardiovascular instability before the development of symptoms, because intravascular hypovolemia and hypotension can result from excessive ultrafiltration below the critical dry weight. In addition, BIA explains, in part, the variability of SBP, DBP, and HR during HD. We suggest that our data also demonstrates the delay in mobilization of fluid from the interstitial space for plasma refill, as evidenced by the delayed change in |Z| over HD. Bioelectric impedance is useful for explaining changes in volemic status and, in part, the variability of SBP, DBP, and HR during HD.

Plant communities in harsh sites are less invaded: a summary of observations and proposed explanations.

Plant communities in abiotically stressful, or 'harsh', habitats have been reported to be less invaded by non-native species than those in more moderate habitats. Here, we synthesize descriptive and experimental evidence for low levels of invasion in habitats characterized by a variety of environmental stressors: low nitrogen; low phosphorus; saline, sodic or alkaline soils; serpentine soils; low soil moisture; shallow/rocky soils; temporary inundation; high shade; high elevation; and high latitude. We then discuss major categories of hypotheses to explain this pattern: the propagule limitation mechanism suggests invasion of harsh sites is limited by relatively low arrival rates of propagules compared with more moderate habitats, while invasion resistance mechanisms suggest that harsh habitats are inherently less invasible due to stressful abiotic conditions and/or increased effects of biotic resistance from resident organisms. Both propagule limitation and invasion resistance may simultaneously contribute to low invadedness of harsh sites, but the management implications of these mechanisms differ. If propagule limitation is more important, managers should focus on reducing the likelihood of propagule introductions. If invasion resistance mechanisms are in play, managers should focus on restoring or maintaining harsh conditions at a site to reduce invasibility.