Cochlodinium heterolobatum n.sp.: Structure and Some Cytophysiological Aspects*

SYNOPSIS. Structure and morphogenesis, and cytochemical data on Cochlodinium heterolobatum, a new species of unarmored dinoflagellate, were derived from living and fixed material from culture. C. heterolobatum is characterized by the torsion of the girdle which descends in a left-hand spiral 1.8 turns; the sulcus having a torsion of 0.8 turn; a sulcus loop in the epicone; a tongue-shaped lobe in the right hypocone; nucleus in the epicone; and a stigma in the left epicone. Trichocysts and behavior of the nucleus during typical and atypical divisions are described in cells from cultures of different ages. A small form with the specific characters was found. Intracellular bacteria were seen and their growth followed in individuals from cultures of different ages. A possible relationship between those bacteria and the accumulation of metabolites inside old cells is discussed.     

Proline Accumulation as a Symptom of Drought Stress in Maize: A Tissue Differentiation Requirement

Ibarra-Caballero, J., Villanueva-Verduzco, C., Molina-Galan,J. and Sanchez-de-Jimenez, E. 1988. Proline accumulation asa symptom of drought stress in maize: a tissue differentiationrequirement.—J. exp. Bot. 39: 889–897. Seedlings and callus tissue of maize (Zea mays L.) were testedfor proline accumulation under drought stress. A variety froma tropical humid region, a semi-desertic variety and its improvedpopulation selected for drought stress resistance, were usedfor this study. Proline accumulation was found in green leaves of maize seedlingsunder drought stress; no correlation was found between prolineaccumulation in leaves and the variety or population tested.White tissue, callus and leaves of etiolated seedlings did notshow this response to drought stress, nor did green callus ordetached leaves (green or etiolated), even when stress causeda loss of water from leaves similar to that observed when wholeseedlings were drought-stressed. Addition of abscisic acid togreen or white tissue did not result in proline accumulation.The above data indicate that proline accumulation caused bydrought stress does not seem to be an indication of droughtstress resistance, but rather a symptom of it. For this accumulationto take place it seems that fully organized chloroplasts arerequired as well as the systemic development of the plant. Key words: Proline, maize, drought-stress     

Effect of soil water stress on soil respiration and its temperature sensitivity in an 18-year-old temperate Douglas-fir stand

We analyzed 17 months (August 2005 to December 2006) of continuous measurements of soil CO₂ efflux or soil respiration (R_S) in an 18‐year‐old west‐coast temperate Douglas‐fir stand that experienced somewhat greater than normal summertime water deficit. For soil water content at the 4 cm depth (θ) > 0.11 m³ m^?3 (corresponding to a soil water matric potential of ?2 MPa), R_S was positively correlated to soil temperature at the 2 cm depth (T_S). Below this value of θ, however, R_S was largely decoupled from T_S, and evapotranspiration, ecosystem respiration and gross primary productivity (GPP) began to decrease, dropping to about half of their maximum values when θ reached 0.07 m³ m^?3. Soil water deficit substantially reduced R_S sensitivity to temperature resulting in a Q₁₀ significantly < 2. The absolute temperature sensitivity of R_S (i.e. dR_S/dT_S) increased with θ up to 0.15 m³ m^?3, above which it slowly declined. The value of dR_S/dT_S was nearly 0 for θ < 0.08 m³ m^?3, thereby confirming that R_S was largely unaffected by temperature under soil water stress conditions. Despite the possible effects of seasonality of photosynthesis, root activity and litterfall on R_S, the observed decrease in its temperature sensitivity at low θ was consistent with the reduction in substrate availability due to a decrease in (a) microbial mobility, and diffusion of substrates and extracellular enzymes, and (b) the fraction of substrate that can react at high T_S, which is associated with low θ. We found that an exponential (van't Hoff type) model with Q₁₀ and R₁₀ dependent on only θ explained 92% of the variance in half‐hourly values of R_S, including the period with soil water stress conditions. We hypothesize that relating Q₁₀ and R₁₀ to θ not only accounted for the effects of T_S on R_S and its temperature sensitivity but also accounted for the seasonality of biotic (photosynthesis, root activity, and litterfall) and abiotic (soil moisture and temperature) controls and their interactions.     

Annual cycles of water vapour and carbon dioxide fluxes in and above a boreal aspen forest

Water vapour and CO₂ fluxes were measured using the eddy correlation method above and below the overstorey of a 21-m tall aspen stand in the boreal forest of central Saskatchewan as part of the Boreal Ecosystem-Atmosphere Study (BOREAS). Measurements were made at the 39.5-m and 4-m heights using 3-dimensional sonic anemometers (Kaijo-Denki and Solent, respectively) and closed-path gas analysers (LI-COR 6262) with 6-m and 4.7-m long heated sampling tubing, respectively. Continuous measurements were made from early October to mid-November 1993 and from early February to late-September 1994. Soil CO₂ flux (respiration) was measured using a LI-COR 6000-09 soil chamber and soil evaporation was measured using Iysimetry. The leaf area index of the aspen and hazelnut understorey reached 1.8 and 3.3, respectively. The maximum daily evapotranspiration (E) rate was 5–6 mm d^?1. Following leaf-out the hazelnut and soil accounted for 22% of the forest E. The estimated total E was 403 mm for 1994. About 88% of the precipitation in 1994 was lost as evapotranspiration. During the growing season, the magnitude of half-hourly eddy fluxes of CO₂ from the atmosphere into the forest reached 1.2 mg CO₂ m^?2 s^?1 (33 μmol C m^?2 s^?1) during the daytime. Downward eddy fluxes at the 4-m height were observed when the hazelnut was growing rapidly in June and July. Under well-ventilated night-time conditions, the eddy fluxes of CO₂ above the aspen and hazelnut, corrected for canopy storage, increased exponentially with soil temperature at the 2-cm depth. Estimates of daytime respiration rates using these relationships agreed well with soil chamber measurements. During the 1994 growing season, the cumulative net ecosystem exchange (NEE) was -3.5 t C ha^?1 y^?1 (a net gain by the system). For 1994, cumulative NEE, ecosystem respiration (R) and gross ecosystem photosynthesis (GEP = R - NEE) were estimated to be -1.3, 8.9 and 10.2 t C ha^?1 y^?1 respectively. Gross photosynthesis of the hazelnut was 32% of GEP.