Regeneration patterns and persistence of the fog-dependent Fray Jorge forest in semiarid Chile during the past two centuries

The persistence of rainforest patches at Fray Jorge National Park (FJNP) in semiarid Chile (30°40′S), a region receiving approximately 147 mm of annual rainfall, has been a source of concern among forest managers. These forests are likely dependent on water inputs from oceanic fog and their persistence seems uncertain in the face of climate change. Here, we assessed tree radial growth and establishment during the last two centuries and their relation to trends in climate and canopy disturbance. Such evaluation is critical to understanding the dynamics of these semiarid ecosystems in response to climate change. We analyzed forest structure of six forest patches (0.2–22 ha) in FJNP based on sampling within 0.1 ha permanent plots. For the main canopy species, the endemic Aextoxicon punctatum (Aextoxicaceae), we used tree‐ring analysis to assess establishment periods, tree ages, growing trends and their relation to El Niño Southern Oscillation (ENSO), rainfall, and disturbance. The population dynamics of A. punctatum can be described by a continuous regeneration mode. Regeneration of A. punctatum was sensitive to different canopy structures. Growth release patterns suggest the absence of large scale human impact. Radial growth and establishment of A. punctatum were weakly correlated with rainfall and ENSO. If water limits forests patch persistence, patches are likely dependent on the combination of fog and rain water inputs. Forest patches have regenerated continuously for at least 250 years, despite large fluctuations in rainfall driven by ENSO and a regional decline in rainfall during the last century. Because of the positive influence on fog interception, forest structure should be preserved under any future climate scenario. Future research in FJNP should prioritize quantifying the long‐term trends of fog water deposition on forests patches. Fog modeling is crucial for understanding the interplay among physical drivers of water inputs under climate change.     

Root cortical aerenchyma improves the drought tolerance of maize (Zea mays L.)

Root cortical aerenchyma (RCA) reduces root respiration in maize by converting living cortical tissue to air volume. We hypothesized that RCA increases drought tolerance by reducing root metabolic costs, permitting greater root growth and water acquisition from drying soil. To test this hypothesis, recombinant inbred lines with high and low RCA were observed under water stress in the field and in soil mesocosms in a greenhouse. In the field, lines with high RCA had 30% more shoot biomass at flowering compared with lines with low RCA under water stress. Root length density in deep soil was significantly greater in the high RCA lines compared with the low RCA lines. Mid‐day leaf relative water content in the high RCA lines was 10% greater than in the low RCA lines under water stress. The high RCA lines averaged eight times the yield of the low RCA lines under water stress. In mesocosms, high RCA lines had less seminal root respiration, deeper rooting, and greater shoot biomass compared with low RCA lines under water stress. These results support the hypothesis that RCA is beneficial for drought tolerance in maize by reducing the metabolic cost of soil exploration.     

Decolonizing Time Regimes: Lakota Conceptions of Work, Economy, and Society

One of the hegemonic forces associated with the spread of capitalism is a shift in the time sense of production from task orientation to labor timed by the clock. On the periphery of the global economy, Lakota households on the Pine Ridge reservation must make fragmentary allocations of time between clock-based wage jobs and task-oriented forms of production governed by social relationships. Despite a long and ongoing history of state policies designed to enforce the discipline of the clock, task orientation continues to dominate Lakota time-sense. Rather than active resistance to or internalization of clock time, Lakota practices flout time-values that interfere with the task-oriented demands of more materially certain, socially embedded economic activities. Lakota conceptions of time, born of their contemporary material conditions, are better understood when theoretical concepts of work and time are decolonized to remove the assumptions that emulating or opposing Euro-Americans is of central concern.     

Morphogenetic Responses to Gibberellic Acid of a Radiation-induced Mutant Dwarf in Groundsel, Senecio vulgaris L.

A dwarf mutant of Senecio vulgaris L. induced by gamma radiation,which differs from the wild-type by a single recessive gene,grew as tall as the wild-type plant, and almost five times astall as dwarf control plants when treated at weekly intervalsfrom the seedling stage with 10 p.p.m. gibberellic acid. Thewild-type groundsel responded only slightly to similar treatment.Some evidence was obtained that the response to GA was relativilygreater when plants were grown during the late autumn. Dwarfnessin the mutant is due to fewer as well as to shorter internodes;the rate of leaf initiation is reduced, but the onset of thereproductive phase and the duration of the life-cycle are notaffected by the mutation. Gibberellic acid leads to a conspicuouselongation of the internodes intreated dwarf plants, but notalways to a significant increase in their number. An increasein the dry weight of treated plants was observed, and this wasshown to be due to an increase in photosynthetic area and notto increased photosynthetic efficiency. Comparative observationsof shoot morphogenesis in wild-type and dwarf groundsel. andin dwarf treated with gibberellic acid, have shown that thetype of shoot development induced by gibberellic acid in dwarfplants does not correspond exactly to the normal mode of developmentin wild-type plants. Increased mitotic activity in the subapicaltissue of the mutant following gibberellic acid treatment resultedin greater and earlier elongation of the internodes. However,the typical form and dimensions of the wild-type plant werenot wholly restored.     

Mycorrhizal responses to nitrogen fertilization in boreal ecosystems: potential consequences for soil carbon storage

Mycorrhizal fungi can contribute to soil carbon sequestration by immobilizing carbon in living fungal tissues and by producing recalcitrant compounds that remain in the soil following fungal senescence. We hypothesized that nitrogen (N) fertilization would decrease these carbon stocks, because plants should reduce investment of carbon in mycorrhizal fungi when N availability is high. We measured the abundance of two major groups of mycorrhizal fungi, arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi, in the top 10 cm of soil in control and N-fertilized plots within three Alaskan boreal ecosystems that represented different recovery stages following severe fire. Pools of mycorrhizal carbon included root-associated AM and ECM structures; soil-associated AM hyphae; and glomalin, a glycoprotein produced by AM fungi. Total mycorrhizal carbon pools decreased by approximately 50 g C m⁻² in the youngest site under N fertilization, and this reduction was driven mostly by glomalin. Total mycorrhizal carbon did not change significantly in the other sites. Root-associated AM structures were more abundant under N fertilization across all sites, and root-associated ECM structures increased marginally significantly. We found no significant N effects on AM hyphae. Carbon sequestered within living mycorrhizal structures (0.051–0.21 g m⁻²) was modest compared with that of glomalin (33–203 g m⁻²). We conclude that our hypothesis was only supported in relation to glomalin stocks within one of the three study sites. As N effects on glomalin were inconsistent among sites, an understanding of the mechanisms underlying this variation would improve our ability to predict ecosystem feedbacks to global change.     

Salt Tolerance in Cell Suspension Cultures of the Halophyte Kosteletzkya virginica

Tolerance to NaCl was studied in cell suspension cultures ofKosteletzkya virginica (L.) Presl. (Malvaceae), a dicotyledonoushalophyte that grows in tidal marshes of the eastern UnitedStates. Growth of salinized cultures was significantly inhibitedat high (255 mol m^–3 NaCl), but not at lower externalsalinities. Adjustment of cell suspensions to Nacl was rapid,with the duration of the normal growth cycle unaffected by salinity.Maximum biomass was attained when cultures were exposed to NaClduring early log growth. Patterns of inorganic ion accumulationreflected the utilization of both Na⁺ and K⁺ as osmotica, withNa⁺ content substantially increasing when cells were grown atan external salinity sufficient to reduce growth. K⁺ uptakeselectivity was high and Na⁺/K⁺ ratios were low in salt-treatedcultures even though K⁺ content was somewhat lower comparedto unsalinized cultures. Free proline and microsomal lipid contentincreased in salt-treated cell cultures. Key words: Kosteletzkya virginica, halophyte, salt tolerance, cell suspension culture     

Did incumbency play a role in maintaining boundaries between Late Ordovician brachiopod realms?

Studies of ecosystem level changes in the geological record have found that the major extinction events eliminated many incumbent clades that had been ecologically dominant for long intervals. Surviving clades that had not been able to compete with the extinct incumbents were then able to evolve adaptations that allowed them to move into the niches vacated by the incumbents. Underlying this pattern is the inability of clades that do not occupy a particular niche to evolve adaptations that would permit them to compete with incumbent clades that are already successfully occupying that niche. The zoogeographic distributions of brachiopods in the Late Ordovician of Laurentia may also have been maintained by incumbency, which was disrupted by the end-Ordovician extinction event. Following the extinction event, an Early Silurian zoogeographic reorganization occurred, during which surviving clades evolved into the vacated epeiric sea niches in the Early Silurian. Just as incumbency plays a role in long-term evolutionary patterns, zoogeographic realms and provinces are also partially maintained by incumbency.     

Particle-Based Axenic Media for Tetrahymenids*

SYNOPSIS. Autoclavable, natural particulate media simplify axenic cultivation of tetrahymenid ciliates and presumably favor selection for phagotrophy. Viability is at least 2 months at room temperature (24–26 C) for the lipid-sensitive tetrahymenids Tetrahymena setosa, T. corlissi, T. paravorax, T. limacis, and T. patula, also for T. rostrata and (at 12 C), for strains of the T. pyriformis complex and Glaucoma chattoni. A typical medium consists of crude soy “lecithin”+ skim milk powder +Saccharomyces cerevisiae cells. Other useful particules readily available commercially are: whole liver powder, cells of Micrococcus lysodeikticus and Escherichia coli, and powdered residue of liver which had been extracted with 70% ethanol (liver #2). Preliminary experiments indicate that some of these media are suitable for the maintenance of Paramecium octaurelia stock 299S and Colpidium campylum. Such mixtures may serve as points of departure for devising media for more fastidious phagotrophs.