Richard L. Jasoni

Prolonged suppression of ecosystem carbon dioxide uptake after an anomalously warm year

Terrestrial ecosystems control carbon dioxide fluxes to and from the atmosphere through photosynthesis and respiration, a balance between net primary productivity and heterotrophic respiration, that determines whether an ecosystem is sequestering carbon or releasing it to the atmosphere. Global and site-specific data sets have demonstrated that climate and climate variability influence biogeochemical processes that determine net ecosystem carbon dioxide exchange (NEE) at multiple timescales. Experimental data necessary to quantify impacts of a single climate variable, such as temperature anomalies, on NEE and carbon sequestration of ecosystems at interannual timescales have been lacking. This derives from an inability of field studies to avoid the confounding effects of natural intra-annual and interannual variability in temperature and precipitation. Here we present results from a four-year study using replicate 12,000-kg intact tallgrass prairie monoliths located in four 184-m3 enclosed lysimeters. We exposed 6 of 12 monoliths to an anomalously warm year in the second year of the study and continuously quantified rates of ecosystem processes, including NEE. We find that warming decreases NEE in both the extreme year and the following year by inducing drought that suppresses net primary productivity in the extreme year and by stimulating heterotrophic respiration of soil biota in the subsequent year. Our data indicate that two years are required for NEE in the previously warmed experimental ecosystems to recover to levels measured in the control ecosystems. This time lag caused net ecosystem carbon sequestration in previously warmed ecosystems to be decreased threefold over the study period, compared with control ecosystems. Our findings suggest that more frequent anomalously warm years, a possible consequence of increasing anthropogenic carbon dioxide levels, may lead to a sustained decrease in carbon dioxide uptake by terrestrial ecosystems.

Plant-water relations of NaCl and calcium-treated sunflower plants

Abstract Salinity has been shown to alter a number of physiological processes, including the plant–water relations of some crop species. We examined the initial effects of NaCl salinity on the plant–water relations of sunflower (Helianthus annuus L.) and the potential of calcium supplements to ameliorate those effects. Sunflower plants were grown in a controlled-environment and treated solely with 0, 50, 100, or 150 mM of NaCl or the same rates of NaCl plus 10 mM Ca+2. Increasing salinity levels significantly decreased stomatal conductance in the 100 and 150 mM treatments compared to the control and 50 mM treatments, produced significantly more negative water potentials in the 100 and 150 mM treatments compared to the control, and significantly decreased root hydraulic conductance in all treatments compared to the control. Calcium supplements did not ameliorate the adverse effects of NaCl. Our experiments indicated that short-term NaCl stress can alter the plant–water relations of sunflower and that calcium supplements of 10 mM do not ameliorate these effects.

Circadian ethylene production in cotton

Light strongly influences plant processes and is instrumental inestablishing patterns in photosynthetic responses, enzymatic activity, andlevels of some plant hormones. At this time, it is unclear how the biosynthesisof the plant hormone ethylene is influenced by light in cotton cotyledonarytissue. To answer this question, the cotton (Gossypiumhirsutum L.) cultivar ‘DPL50’ was exposed to thefollowing light and/or dark treatments over a 72-h period: a12-h photoperiod, continuous light, or continuous dark. Ethylene,1-aminocyclopropane-1-carboxylic acid (ACC), andN-malonyl-1-aminocyclopropane-1-carboxylic acid (MACC) were assayed from wholeplant samples. Cotton plants exhibited a pattern of ethylene evolution thatappears to be controlled by a circadian clock. This circadian pattern wassuggested by the lack of change in ethylene evolution rate under continuouslight. The pattern of ethylene evolution was disrupted during a continuous darktreatment, indicating that light in some way is responsible for setting thecircadian clock for ethylene evolution and that light-sensing molecules such asphytochrome may be involved. Patterns of ACC and MACC concentration were notcircadian.

Nutrient Solution and Solution pH Influences on Onion Growth and Mineral Content

ABSTRACT The effects of hydroponic nutrient solution composition and pH on growth and mineral content of green onions was evaluated. Three onion varieties [Allium cepa L. (‘Deep Purple’ and ‘Purplette’) and A. fistulosum L. (‘Kinka’)] were propagated in three nutrient solutions (Peters Hydro-Sol, modified Hoaglands, and half-strength modified Hoaglands) at two pH levels (5.8 and 6.5) in a three-by-two factorial design applied in a randomized block with three replications. Seeds were germinated in Cropkings Oasis Horticubes under greenhouse conditions and irrigated with tap water. Once the seedlings reached the flag stage, the plants were placed into hydroponic units within the greenhouse and grown under ambient conditions. Plants were harvested 30 d after transplanting to the hydroponic units. The results indicated nutrient solution, pH, and variety significantly affected several plant physiological variables. Total biomass and edible biomass production was as high for plants grown in half-strength Hoaglands nutrient solution as for those grown in the other solutions. Total biomass was greatest for plants grown at a solution pH of 6.5. ‘Deep Purple’ produced a significantly greater overall total biomass than did ‘Purplette’ or ‘Kinka.’ Hydro-Sol tended to produce onions with highest mineral content. Due to the fact that biomass production was as great in the half-strength Hoaglands as in the more concentrated solution and that a pH of 6.5 produced greater total biomass, the half-strength Hoaglands solution at pH 6.5 was the preferred nutrient solution evaluated in this research. Selection of an appropriate nutrient solution must consider both edible biomass production and mineral content. In the research reported here, the solution that produced the greatest biomass did not produce plant material with the highest mineral content.

Elevated Carbon Dioxide Alters Hydrocarbon Emissions and Flavor in Onion

Bulb onion (Allium cepa), non-bulbing Japanese bunching onion (A. fistulosum), common chives (A. schoenoprasum) and garlic chives (A. tuberosum) have markedly different harvest indices. With the onset of bulbing, leaf production ceases, photosynthates are reallocated to the bulb, lowering production of new shoots and crop canopy. Successive harvests from the same planting allow for a cumulative harvest index. In testing the influence of growing plants under different CO2 conditions, a set of volatile methyl-ketones have been identified from onion that are emitted at higher levels when plants are grown at elevated CO2 compared to controls grown at ambient CO2 levels. Sensory panel taste testing has indicated differences in flavor for some cultivars when comparisons were made between plants grown at ambient and elevated CO2 conditions. In future studies we will examine if thiosulfinates generated from the enzymatic conversion of alk(en)yl cysteine sulphoxides contribute to flavor differences detected between ambient and elevated CO2 grown plants.