John R. Seiler

Growth and physiological responses of yellow-poplar seedlings exposed to ozone and simulated acidic rain

Nine-week-old, yellow-poplar (Liriodendron tulipifera L.) seedlings were exposed to ozone (O(3)) 4 h day(-1), 5 days week(-1), in combination with simulated rain (pH 3.0, 4.3, or 5.6, 1 h day(-1), 2 days week(-1), at 0.75 cm h(-1)) for 6 weeks, under controlled laboratory conditions. There was no main treatment effect of O(3) (<0.02, 0.05, 0.10, or 0.15 microlitre(-1)) on height growth or total plant biomass. However, specific leaf area increased linearly (P=0.05) with exposure of plants to increasing O(3) concentrations. Exposure of seedlings to 0.10 microl litre(-1) O(3) reduced the leaf area ratio and the stomatal conductance (S(c)), but increased the mean unit leaf rate compared to control plants. This O(3) concentration also caused S(c) to decrease more rapidly, relative to non-fumigated plants, in response to increasing vapor pressure deficit. The only main treatment effect caused by simulated rain was a linear decrease in S(c) with increasing acidity. For combined pollutant effects, O(3) applied at 0.05 or 0.10 microl litre(-1) resulted in significant (P=0.05) linear decreases in dry weights and relative growth rates (RGR) of stems and leaves, and in cumulative leaf area (LAI), as the solution pH decreased. Root to shoot ratio (RSR) decreased linearly, whereas stem RGR and LAI increased linearly in response to decreasing pH for seedlings exposed to 0.15 microl litre(-1) O(3). Seedlings treated with a pH 5.6 solution exhibited a linear decrease (P=0.05) in leaf dry weight and RGR and a linear increase (P=0.05) in RSR as O(3) concentrations increased.

Effects of ozone and water stress on greenhouse-grown fraser fir seedling growth and physiology

Abstract Three-year-old Fraser fir (Abies fraseri (Pursh) Poir.) seedlings were exposed to ozone (

Carbon efflux rates of fine roots of three tree species decline shortly after excision

Abstract Fine roots (diameter ≦2 mm) of Acer rubrum, Quercus rubra and Pinus strobus were used to determine whether respiration rates (measured as CO 2 efflux rates) remain sufficiently stable for the 1 min to 10 h interval after excision to allow reliable measurements to be taken. Roots of five individuals of each species were excavated from the upper 10 cm of the soil. From each tree, two samples of roots (dry weights between 0.21 and 1.18 g) were excised and immediately subjected to one of two treatments. The attached soil was removed mechanically with (wet treatment) or without (dry treatment) the further removal of soil by submersion in and rinsing with water. Within 1 min of excision, roots were placed in a gas exchange system and their respiration was measured. The measurements were repeated 5, 15, 30 min and 1, 2 ( Acer and Pinus ), 3 ( Quercus ), 6 and 10 h after excision. For all species, carbon efflux rates showed a marked decline over time, dropping significantly ( p ≤ 0.05) over 5 min for Acer and Pinus and over 15 min for Quercus (by 37, 52 and 33%, respectively). The initial rates (12.9, 9.2 and 8.7 nmol CO 2 g −1 s −1 at 25 °C for Acer, Quercus and Pinus , respectively) declined to a minimum (4.2, 2.9 and 4.4 nmol CO 2 g −1 s −1 ) in 30 ( Pinus ) or 60 ( Acer and Quercus ) min then levelled off ( Acer and Quercus ) or started to increase ( Pinus ). Possible mechanisms causing the decline are discussed.

Effects of rhizosphere inundation on the growth and physiology of wet and dry-site Acer rubrum (red maple) populations

-Six-wk-old Acer rubrum L. (red maple) seedlings, grown from fruits collected on paired wet and dry sites on the Coastal Plain, Piedmont, and Ridge and Valley physiographic regions of Virginia, were flooded to determine whether there are ecotypic differences in growth and physiology between seedlings from wet and dry sites. Periodic harvests were conducted over 3 mo to measure growth of flooded and unflooded seedlings derived from three trees per site. Shoot water potential and gas exchange were measured for 2 wk to determine if the physiology of seedlings from wet and dry sites were affected differently by flooding. Flooding adversely affected seedling growth and physiology resulting in shorter (18%) and lighter (30% less leaf mass, 14% less stem mass and 68% less root mass) seedlings that had higher water potentials (20%) and reduced photosynthetic rates (50%). Significant differences developed between seedlings from wet and dry sites with the wet site seedlings having lower water potentials and taller, heavier shoots. However, no significant interactions between flooding and maternal hydrologic conditions were found that would indicate genetic differences in flood response between wet and dry site seedlings. This lack of a differential growth or physiological response to waterlogging by the distinct populations strongly suggests that young Acer rubrum seedlings do not exhibit ecotypic differences in flood tolerance.

Fraser fir seedling gas exchange and growth in response to elevated CO2

Abstract Growth and gas exchange characteristics were examined in Fraser fir ( Abies fraseri (Pursh.) Poir.) seedlings grown from seed in elevated (713 ppm) or ambient (374 ppm) CO 2 for 1 year (two artificial growing seasons) to determine the potential influence of a twice-ambient CO 2 concentration on this species. A subset of seedlings was transplanted from 172 cm 3 pots into 1000 cm 3 pots at 7 months to determine if CO 2 effects were dependent on rooting volume. At 5 and 12 months, net photosynthesis ( P net ) and leaf conductance ( g l ) were lower in elevated CO 2 -grown seedlings grown in 172 cm 3 pots than in ambient CO 2 -grown seedlings when measured at either 346 or 796 ppm CO 2 . For 12-month-old seedlings grown in 1000 cm 3 pots, P net was reduced by an elevated CO 2 growth environment only when measured at 346 ppm CO 2 , although g l was lower in these seedlings when measured at either CO 2 measurement level. Seedlings grown in both pot sizes and in elevated CO 2 for 1 year had greater height, diameter, and leaf, stem, root and total dry weights than seedlings grown in ambient CO 2 . Specific leaf weight ( SLW ) was greater in elevated than in ambient CO 2 -grown needles only in the large pot size treatment. These results suggest that Fraser fir seedling growth will increase in a future elevated CO 2 environment despite changes in gas exchange characteristics.

Gas exchange and canopy structure of 9-year-old loblolly pine, pitch pine and pitch x loblolly hybrids

SummarySeasonal gas exchange and canopy structure were compared among 9-year-old loblolly pine (Pinus taeda L.), pitch pine (Pinus rigida Mill.), and pitch x loblolly hybrids (Pinus rigida x taeda) growing in an F2 plantation located in Critz, Va., USA. Leaf net photosynthesis, conductance, internal CO2 concentration (ci), water use efficiency (WUE; photosynthesis/conductance), dark respiration and the ratio of net photosynthesis/respiration did not vary among or within the three taxa. Significant differences in volume production, crown length, total crown leaf surface area and the silhouette area of shade shoots among the taxa were observed. The loblolly-South Carolina source had greater volume and crown surface area than the pitch pine, and the hybrid taxa were intermediate between the two. Although the silhouette area ratio of shade foliage varied among taxa, it was not related to volume. A strong relationship between total leaf surface area and volume was observed. Leaf conductance, ci, WUE and leaf water potential were the physiological parameters significantly and positively correlated with volume. This study suggests that the amount of needle surface in the canopy is more important in early stand volume growth than the leaf carbon exchange rate and the degree of needle self-shading in the lower canopy.

Growth and gas exchange of loblolly pine seedlings as influenced by drought and air pollutants.

One-year-old loblolly pine seedlings were exposed to 03(≤0.025 or 0.10 μ L L−1, 4 hr d−1, 3 d wk−1) in combination with simulated rain (pH 5.6 or 3.0, 1 hr d−1, 2 d wk−1, 0.75 cm hr−1) for 10 wk. After the 10-wk treatment, the seedlings were submitted to two drought cycles, and water potential, net photosynthesis (Pn), and transpiration (Tr) were measured. Whole-plant fresh weight increment and relative growth rate were significantly increased in seedlings exposed to simulated rain at pH 3.0 compared to pH 5.6. An interaction between 03 and simulated rain occurred in height growth. Shoot height elongation was significantly less in seedlings exposed to 0.10 μL L−1 03 + pH 5.6 than in any other pollutant combination after the 10-wk treatment period. There were no significant effects of 03 on Pn and Tr prior to the drought cycles; however, after the first drought cycle, Pn was significantly higher in seedlings pre-exposed to 0.10 μL L−1 03 compared to the low 03 concentration. The 10-wk treatment with simulated rain at pH 3.0 significantly increased Pn and Tr. The relationship between gas exchange rates and needle water potential during the moisture stress period was affected by preexposure to pollutants. In general, Pn and Tr were more sensitive to decreasing needle water potential in seedlings exposed to pH 3.0 during the first drought cycle and to 0.10 μL L−1 03 during second drought cycle.

Early growth promotion and leaf level physiology changes in Burkholderia phytofirmans strain PsJN inoculated switchgrass

Switchgrass (SG) is one of the most promising next generation biofuel crops in North America. Inoculation with bacterial endophytes has improved growth of several plant species. Our study demonstrated that Burkholderia phytofirmans strain PsJN, a well-studied plant growth promoting rhizo-bacterium (PGPR) significantly increased both aboveground and belowground biomass (DW) and promoted elongation of root, stem and leaf within 17 days following inoculation. Furthermore, the enhanced root growth in PsJN inoculated plants lagged behind the shoot response, resulting in greater allocation to aboveground growth (p = 0.0041). Lower specific root length (SRL, p = 0.0158) and higher specific leaf weight (SLW, p = 0.0029) were also observed in PsJN inoculated seedlings, indicating changes in development. Photosynthetic rates (Ps) were also significantly higher in PsJN inoculated seedlings after 17 days (54%, p = 0.0016), and this occurred initially without increases in stomatal conductance resulting in significantly greater water use efficiency (WUE, 37.7%, p = 0.0467) and lower non-stomatal limitation (LNS, 29.6%, p = 0.0222). These rapid changes in leaf level physiology are at least partially responsible for the growth enhancement due to PsJN.

Growth and water potential of j-rooted loblolly and eastern white pine seedlings over three growing seasons

The effects of j-rooting on water stress and growth of loblolly (Pious taeda L.) and eastern white pine (Pious strobus L.) were examined over three growing seasons in the field. Seedlings were planted in an area with severe herbaceous competition with either their roots planted straight or bent into a j shape. All seedlings were planted with their root collars placed at the soil surface. During the first year j-rooted seedlings consistently had lower water potentials but never statistically significant. Since both treatments were planted with the root collar at the soil surface, this trend was likely due to an initial shallower root system in j-rooted seedlings. In year three no differences in water potential were significant and no trends were evident. Growth did not differ significantly by treatment at any time but, by year three, j-rooted plants were consistently larger for both species.

The influence of elevated carbon dioxide and water availability on herbaceous weed development and growth of transplanted loblolly pine (Pinus taeda)

Loblolly pine (Pinus taeda L.) seedlings were grown in competition with native weeds using soil and seed bank collected from recently chopped and burned areas near Appomattox, Virginia. One-year-old seedlings were planted and weeds allowed to germinate from the native seed bank while being exposed to CO(2) (ambient and elevated - approximately 700 ppm) and water (water stressed and well watered) treatments for approximately one growing season in a greenhouse. Elevated CO(2) did not influence total weed biomass; however, C(3) weed community development was favored over C(4) weed community development in elevated CO(2) regardless of water availability. This suggests that weed community composition may shift toward C(3) plants in a future elevated CO(2) atmosphere. Pine growth was significantly greater in the well watered and elevated CO(2) treatments compared to the water stressed and ambient treatments, respectively, even though they were competing with native herbaceous weeds for resources. There was a significant water and CO(2) interaction for pine root:shoot ratio. Under elevated CO(2), root:shoot ratio was significantly greater in the water stressed treatment than the well watered treatment. In contrast, there was no significant difference in the root:shoot ratio under the ambient CO(2) treatment for either water treatment. These results suggest that loblolly pine seedlings will respond favorably in an elevated CO(2) atmosphere, even under dry conditions and competing with herbaceous weeds.