Curt M. Peterson

Anatomical and Morphological Alterations in Longleaf Pine Needles Resulting from Growth in Elevated CO2: Interactions with Soil Resource Availability

Studies of anatomical changes in longleaf pine (Pinus palustris Mill.) needles for plants exposed to elevated atmospheric CO2 may provide insight into the potential influences of global CO2 increases on plant productivity. Longleaf pine seedlings were grown in open‐top field chambers supplied with either ambient (∼365 μmol mol−1) or elevated (∼720 μmol mol−1) atmospheric CO2 for 20 mo. Two levels of soil nitrogen (40 and 400 g ha−1 yr−1) and two soil moisture regimes (−0.5 or −1.5 MPa predawn xylem pressure potential) were used in combination with CO2 treatments. Needle tissue was collected 12 and 20 mo after treatment initiation and subjected to light and scanning electron microscopy. There was no effect of elevated CO2 on stomatal distribution or the proportion of internal leaf area allocated to a given tissue type at either sampling date. Although the relationships between vascular, transfusion, mesophyll, and epidermal tissue cross‐sectional areas to total leaf cross‐sectional areas appear nonplastic, leaves grown in elevated CO2 with low N availability exhibit anatomical characteristics suggestive of reduced capacity to assimilate carbon, including decreased mesophyll cell surface area per unit needle volume (in low‐N soil). Significantly greater (8%) needle fascicle volume as a result of growth in elevated CO2 was observed after 12 mo because of thicker needles. After 20 mo of exposure, there was a trend indicating smaller fascicle volume (8%) in plants grown with elevated CO2 compared with those grown in ambient conditions, resulting from shorter needles and smaller mesophyll, vascular tissue, and epidermal cell cross‐sectional areas. These results indicate short‐term stimulation and long‐term inhibition of needle growth in longleaf pine as a result of exposure to elevated CO2 and suggest at the leaf level that pine species are less responsive to elevated CO2 than are dicotyledons, including other tree species.

Calcium Sulfate Deposits Associated with Needle Substomatal Cavities of Container‐Grown Longleaf Pine (Pinus palustris) Seedlings

Extracellular calcium sulfate (CaSO4) formations associated with substomatal cavities of longleaf pine (Pinus palustris Mill.) are described. Longleaf pine seedlings were grown with two levels of soil nitrogen (N) (40 or 400 kg N ha−1 yr−1) and water stress (−0.5 or −1.5 MPa xylem pressure potential) in open‐top field chambers under two levels of atmospheric CO2 (365 or 720 &mgr;mol mol−1). Needles were subjected to scanning electron microscopy after 12 mo exposure to experimental conditions. Crystalline to fibrillar formations, appressed to surfaces of guard cells facing the interior of the needle, were observed in all treatments. In some cases, both crystalline and fibrillar formations were observed to occur within the same needle cross section. Formations were characterized as calcium sulfate using energy‐dispersive spectrometry. Crystal‐like CaSO4 appeared to originate from guard cells in the vicinity of the stomatal aperture. Formations may arise from evaporation of plant water at the interface between stomatal antechambers and substomatal cavities, leaving Ca and SO4 behind to precipitate. Many questions remain regarding their ecological and physiological significance as well as their occurrence and prevalence in both time and space.

Thidiazuron-induced adventitious shoot regeneration of sweetpotato (Ipomoea batatas)

Adventitious shoots of sweetpotato (Ipomoea batatas L. Lam.) were produced in vitro using a two-stage culture method. Petiole explants were incubated on Murashige and Skoog (MS) medium supplemented with 2,4-dichlorophenoxy acetic acid (0.2 mg·liter−1) for 3 d, and transferred to MS medium with thidiazuron (0 to 0.4 mg·liter−1). Shoot regeneration was observed in most explants (78.2%) of genotype PI 318846-3 within 28 days when cultured on thidiazuron at 0.2 mg·liter−1. Histological studies of cultured petiole explants showed meristematic activity within cells of vascular bundles and throughout the ground tissue. Explants isolated from apical leaves exhibited higher shoot regeneration frequency than those isolated from the basal portion of the shoot. Leaf lamina explants exhibited lower frequency of regeneration than petiole explants. In contrast to thidiazuron, the use of zeatin riboside, and kinetin resulted in a lower frequency of shoot regeneration although more sweetpotato genotypes could be regenerated using either of these two cytokinins. The sweetpotato plants regenerated using thidiazuron grew vigorously and rooted easily when transferred to the greenhouse.

Predicting root growth and water uptake under different soil water regimes

Abstract The model ROOTSIMU version 4.0 was used to predict soybean ( Glycine max [L.] Merr. ) root growth and water uptake under actual weather conditions. A comparison was made between simulated results from this model and measured data from companion rhizotron experiments. The experimental data were taken from rhizotron studies where ‘Braxton’ soybean plants were grown under irrigated (IR) and non-irrigated (NI) water regimes in a Marvyn loamy sand (fine-loamy, siliceous, thermic Plinthic Paleudult). Detailed measurements of shoot and root growth and soil water content and potential were made. The environmental conditions used as forcing functions in the simulation model were identical to the physical ones measured in the actual field experiments. In ROOTSIMU version 4.0, no dry matter was partitioned into reproductile structures (e.g., flowers, pods, and seeds). Therefore, each simulation run was terminated after full pod development (R4) and the beginning of seed fill (R5), i.e. about 100 days after emergence. During the first 25 days of the simulation period, simulated plants showed only a gradual increase in dry matter; during the next 30-day growth period dry matter increased exponentially. Simulated vegetative growth plateaued at the time when pod and seed development began in the rhizotron-grown plants. As in the rhizotron experiments, predicted total shoot dry matter in the simulation model was greater for IR than for NI plants. Simulated soil water potential ( ψ soil ) at the 0·4 m depth declined for the NI treatment during periods of drought, similar to measured ψ soil with experimental plants. The model predicted an increase in ψ soil following periods of rain. Simulated ψ soil stayed fairly constant in the IR treatment during two drought periods, although a slight decrease in ψ soil was predicted by the model at the beginning of a dry period. No differences were indicated between the root systems of NI and IR simulated plants when early season growth was predicted in the model. During a drought period later in the season, however, the model showed that simulated NI plants had a much larger increase in total root length than IR plants. The difference between total root length of IR and NI plants was greater for the experimental data than for the simulated data. One reason for the discrepancy may be that the model used a constant factor to convert root dry matter into root length. The model does not consider changes in size of the taproot and, therefore, may have overestimated total root length for the IR treatment. The model was able to predict trends with the IR and NI treatments which were similar to those observed in the rhizotron grown plants during the 1981 growing season. Additional modifications may make the model predictions more accurate and are essential if growth responses during reproductive development are to be simulated.