Simulating switchgrass biomass production across ecoregions using the DAYCENT model

The production potential of switchgrass (Panicum virgatum L.) has not been estimated in a Mediterranean climate on a regional basis and its economic and environmental contribution as a biofuel crop remains unknown. The objectives of the study were to calibrate and validate a biogeochemical model, DAYCENT, and to predict the biomass yield potential of switchgrass across the Central Valley of California. Six common cultivars were calibrated using published data across the US and validated with data generated from four field trials in California (2007–2009). After calibration, the modeled range of yields across the cultivars and various management practices in the US (excluding California) was 2.4–41.2 Mg ha^?1 yr^?1, generally compatible with the observed yield range of 1.3–33.7 Mg ha^?1 yr^?1. Overall, the model was successfully validated in California; the model explained 66–90% of observed yield variation in 2007–2009. The range of modeled yields was 2.0–41.4 Mg ha^?1 yr^?1, which corresponded to the observed range of 1.3–41.1 Mg ha^?1 yr^?1. The response to N fertilizer and harvest frequency on yields were also reasonably validated. The model estimated that Alamo (21–23 Mg ha^?1 yr^?1) and Kanlow (22–24 Mg ha^?1 yr^?1) had greatest yield potential during the years after establishment. The effects of soil texture on modeled yields tended to be consistent for all cultivars, but there were distinct climatic (e.g., annual mean maximum temperature) controls among the cultivars. Our modeled results suggest that early stand maintenance of irrigated switchgrass is strongly dependent on available soil N; estimated yields increased by 1.6–5.5 Mg ha^?1 yr^?1 when residual soil mineral N was sufficient for optimal re‐growth. Therefore, management options of switchgrass for regional biomass production should be ecotype‐specific and ensure available soil N maintenance.     

Avian body size changes and climate change: warming or increasing variability?

There has been a growing interest in whether established ecogeographical patterns, such as Bergmann's rule, explain changes in animal morphology related to climate change. Bergmann's rule has often been used to predict that body size will decrease as the climate warms, but the predictions about how body size will change are critically dependent on the mechanistic explanation behind the rule. To investigate change in avian body size in western North America, we used two long‐term banding data sets from central California, USA; the data spanned 40 years (1971–2010) at one site and 27 years (1983–2009) at the other. We found that wing length of birds captured at both sites has been steadily increasing at a rate of 0.024–0.084% per year. Although changes in body mass were not always significant, when they were, the trend was positive and the magnitudes of significant trends were similar to those for wing length (0.040–0.112% per year). There was no clear difference between the rates of change of long‐distance vs. short‐distance migrants or between birds that bred locally compared to those that bred to the north of the sites. Previous studies from other regions of the world have documented decreases in avian body size and have used Bergmann's rule and increases in mean temperature to explain these shifts. Because our results do not support this pattern, we propose that rather than responding to increasing mean temperatures, avian body size in central California may be influenced by changing climatic variability or changes in primary productivity. More information on regional variation in the rates of avian body size change will be needed to test these hypotheses.     

Sensitivity of leaf size and shape to climate within Acer rubrum and Quercus kelloggii

* Variation in the size and shape (physiognomy) of leaves has long been correlated to climate, and paleobotanists have used these correlations to reconstruct paleo-climate. Most studies focus on site-level means of largely nonoverlapping species sets. The sensitivity of leaf shape to climate within species is poorly known, which limits our general understanding of leaf-climate relationships and the value of intraspecific patterns for paleoclimate reconstructions. * The leaf physiognomy of two species whose native North American ranges span large climatic gradients (Acer rubrum and Quercus kelloggii) was quantified and correlated to mean annual temperature (MAT). Quercus kelloggii was sampled across a wide elevation range, but A. rubrum was sampled in strictly lowland areas. * Within A. rubrum, leaf shape correlates with MAT in a manner that is largely consistent with previous site-level studies; leaves from cold climates are toothier and more highly dissected. By contrast, Q. kelloggii is largely insensitive to MAT; instead, windy conditions with ample plant-available water may explain the preponderance of small teeth at high elevation sites, independent of MAT. * This study highlights the strong correspondence between leaf form and climate within some species, and demonstrates that intraspecific patterns may contribute useful information towards reconstructing paleoclimate.     

Tandem repeat markers for population genetic studies of the protected California tiger salamander (<Emphasis Type="Italic">Ambystoma californiense</Emphasis>)

Habitat loss is the single greatest threat to persistence of the critically threatened California tiger salamander (Ambystoma californiense). To aid management plans that designate critical habitat for this species, I developed and characterized 21 tetranucleotide microsatellite markers using two native populations in Santa Barbara and Alameda Counties. Allelic variation and average heterozygosities were lower in the endangered Santa Barbara population (allele range 1–4, mean 2.4; H _O = 0.308 H _E = 0.288) compared with the threatened Alameda population (allele range 2–10, mean 6.7; H _O = 0.712, H _E = 0.722). In-depth population studies using these markers will provide vital information for plans to assign critical habitat that optimize gene flow among breeding populations, as well as for identifying non-native hybrid genotypes that threaten native A. californiense stocks. Beyond the conservation goals for A. californiense, the close phylogenetic relationships within the tiger salamander complex also suggest a broad utility for population studies using these markers.     

The emergence of Cochlodinium along the California Coast (USA)

A sudden and nearly synchronous emergence of the red tide forming dinoflagellate Cochlodinium along more than 800 km of California coastline was initially observed in late summer 2004. Thereafter high cell concentrations have been detected on an annual basis. Here, we present quantitative and semi-quantitative data indicating that Cochlodinium was uncommon in the phytoplankton community in California prior to 2004 and is now persisting as a more regular component and one that seasonally can cause red tides. The quantitative portion of this study was primarily conducted in Monterey Bay, where cell densities reached at least 6 × 10⁴ cells L⁻¹ during the initial outbreak. A semi-quantitative comparison of California coastal counties by the California Department of Health Services (CDHS) was also made: of the 15 counties surveyed (most with multiple sites per county), cells were detected only from Los Angeles County in the south to San Mateo County in the central region (seven counties), but not in the northern part of the state (six counties). Two counties in the central region of the state, San Luis Obispo and Santa Cruz, displayed intense and frequent periods of elevated Cochlodinium cell abundances. Although not observed in the state-wide CDHS survey, we occasionally found cells in San Diego County with densities up to 2.7 × 10⁴ cells L⁻¹. Though these colonial dinoflagellates have been recognized in California for over 80 years, with several “blooms” recorded prior to 2004, the species’ geographic range and abundance in recent years suggest significant shifts in the nearshore phytoplankton community of this region of the eastern Pacific.     

DNA damage and biliary PAH metabolites in flatfish from Southern California bays and harbors, and the Channel Islands

Southern California bays and harbors have been shown to contain high concentrations of a variety of contaminants, including polycyclic aromatic hydrocarbons (PAHs), metals, and pesticides. Conventional monitoring tools do not assess exposure to PAHs in fish, or sublethal effects, which can be more sensitive indicators of stress than traditional methods. This study was conducted to evaluate DNA damage (a sublethal effect) and PAH exposure in flatfish from southern California bays and harbors, and the Channel Islands. California halibut (Paralichthys californicus) were collected from eight bays and harbors (Ventura Harbor, Channel Islands Harbor, Marina del Rey, King Harbor, Alamitos Bay, Long Beach Harbor, Newport Bay, San Diego Bay), and a reference site off Camp Pendleton. Pacific sanddab (Citharichthys sordidus) were collected near four of the Channel Islands (San Miguel Island, Santa Cruz Island, Anacapa Island, Santa Barbara Island). Metabolites of high molecular weight PAHs in fish bile were characterized using a semi-quantitative technique that measures fluorescent aromatic compounds (FACs) in fish bile. DNA damage in fish blood cells was assessed by measuring the amount of single-strand breaks in stained DNA using the Comet assay. The concentration of FACs in fish from all bays and harbors was elevated, with average concentrations ranging from three to ten times greater than FACs in reference fish. FAC levels were elevated in Pacific sanddabs from a Channel Islands station located between Santa Cruz Island and Anacapa Island. DNA damage varied by a factor of five among California halibut from bays and harbors, with significant damage occurring in fish from Alamitos Bay. There was a significant association between FAC concentrations and DNA damage in California halibut at Marina del Rey and Ventura Harbor, but not at other locations, presumably due to contaminants other than PAHs.     

Effects of delayed first feeding on the nutritional condition and mortality of California halibut larvae

The effect of the timing of first feeding (3, 4, 5, 6, 7 and 8 days post‐hatch, dph) on laboratory‐reared California halibut Paralichthys californicus larvae was evaluated by means of morphologic, morphometric and histological criteria. Larvae began to feed exogenously at 3 dph (2·7 ± 0·01 mm standard length, L _S) at 18° C. Eye pigmentation, rather than mouth opening was the most distinctive trait of California halibut larvae at first feeding. Larval growth was significantly affected by the time of first exogenous feeding. At notochord flexion (21 dph), the L _S of larvae fed for the first time at 3 dph was significantly larger (5·1 ± 0·1 mm) than that of those fed at 4 and 5 dph (4·9 ± 0·1 mm), although the latter fish had a more uniform size distribution. The point of no return was reached at 7 dph. Survival of larvae initially fed at 3, 4 and 5 dph was similar (58·4–60%), while no larvae were able to survive when food was offered for the first time between 6 and 8 dph. Food deprivation resulted in a progressive deterioration of the larval digestive system and atrophy of skeletal muscle fibres. Significant changes in the anterior and posterior enterocyte height were detected after 2 days of food deprivation. Similarly, tail height: L _S and trunk length: L _S ratios were the most sensitive morphometric indices to detect the effect of fasting on larval condition. Present results show that a combination of morphometric and histological variables can be used to evaluate the nutritional condition of California halibut larvae.     

Two new Marina (Leguminosae) from the southern Baja California peninsula, Mexico

Marina victoriae andM. brevis are newly described species from the southern Baja California peninsula, Mexico. The former is a perennial herb locally abundant in the eroded hillsides at the foothills of Sierra de la Victoria, where an oak woodland and a dry tropical forest meet. The latter is an elusive ephemeral inhabiting a narrow strip of land between the mangroves and the desert scrub on an island in the Gulf of California. These two new species belong to the seriesChrysorrhizae, a group native to the Gulf of California basin.     

The diatom flora of the Salton Sea, California

We report on diatom species of the Salton Sea, a highly saline (43 g l^–1) inland lake in California. We identified and photographed all diatom taxa encountered in the phytoplankton and benthos of the Salton Sea and its immediate tributaries. Ninety-four taxa were distinguished based on their morphological features using light- and electron microscopy. In the Salton Sea, there are four general categories of diatom assemblages related to their habitats: (1) A planktonic assemblage composed of Chaetoceros muelleri var. subsalsum, Cyclotella choctawhatcheeana, Cyclotella sp., Cylindrotheca closterium, Pleurosigma ambrosianum, Thalassionema sp.; (2) a benthic assemblage with diatoms that live on the bottom (e.g. genera Caloneis, Diploneis, Entomoneis, Gyrosigma, Plagiotropis, Pleurosigma, Surirella and Tryblionella), or in algal mats (Proschkinia bulnheimii, several species of Navicula and Seminavis gracilenta); (3) an epiphytic community attached to the macroscopic green algae which grow on the rocks and other hard surfaces near shore (e.g. Achnanthes brevipes, Licmophora ehrenbergii, Tabularia parva); and (4) a freshwater assemblage composed of species that get washed in by the rivers and other inflows discharging into the Sea (e.g. Achnanthidium minutissimum, Cocconeis pediculus, Cyclotella atomus, C. scaldensis, Nitzschia elegantula, T. weissflogii). The most striking feature of the phytoplankton is the abundance of species formerly known only from marine environments; this is not surprising given the high salinity and the peculiar history of the lake.