Stephen A. Prior

Control of yellow and purple nutsedge in elevated CO2 environments with glyphosate and halosulfuron.

Atmospheric concentrations of carbon dioxide (CO2) have significantly increased over the past century and are expected to continue rising in the future. While elevated levels of CO2 will likely result in higher crop yields, weed growth is also highly likely to increase, which could increase the incidence of herbicide resistant biotypes. An experiment was conducted in 2012 to determine the effects of an elevated CO2 environment on glyphosate and halosulfuron efficacy for postemergence control of purple and yellow nutsedge (Cyperus rotundus L. and C. esculentus L.). Both species of nutsedge where grown in 3.0-L containers under either ambient or elevated (ambient + 200 μmol mol−1) CO2 in open-top field chambers and treated with either 0.5×, 1.0×, or 1.5× of the manufacturers labeled rate of halosulfuron, glyphosate, or a tank mix of the two herbicides. The growth of both nutsedge species responded positively to elevated CO2, purple nutsedge had increased shoot and root dry weights and yellow nutsedge had increased shoot, root, and tuber dry weights and counts. Few treatment differences were observed among the herbicides at any of the rates tested. At 3 weeks following herbicide application, both purple and yellow nutsedge were adequately controlled by both herbicides and combinations at all rates tested, regardless of CO2 concentration. Based on this study, it is likely that predicted future CO2 levels will have little impact on the efficacy of single applications of halosulfuron or glyphosate for control of purple and yellow nutsedge at the growth stages described here, although scenarios demanding more persistent control efforts remain a question.

Root to shoot ratio of crops as influenced by CO2

Crops of tomorrow are likely to grow under higher levels of atmospheric CO2. Fundamental crop growth processes will be affected and chief among these is carbon allocation. The root to shoot ratio (R:S, defined as dry weight of root biomass divided by dry weight of shoot biomass) depends upon the partitioning of photosynthate which may be influenced by environmental stimuli. Exposure of plant canopies to high CO2 concentration often stimulates the growth of both shoot and root, but the question remains whether elevated atmospheric CO2 concentration will affect roots and shoots of crop plants proportionally. Since elevated CO2 can induce changes in plant structure and function, there may be differences in allocation between root and shoot, at least under some conditions. The effect of elevated atmospheric CO2 on carbon allocation has yet to be fully elucidated, especially in the context of changing resource availability. Herein we review root to shoot allocation as affected by increased concentrations of atmospheric CO2 and provide recommendations for further research. Review of the available literature shows substantial variation in R:S response for crop plants. In many cases (59.5%) R:S increased, in a very few (3.0%) remained unchanged, and in others (37.5%) decreased. The explanation for these differences probably resides in crop type, resource supply, and other experimental factors. Efforts to understand allocation under CO2 enrichment will add substantially to the global change response data base.

Free-air CO2 enrichment effects on soil carbon and nitrogen

Since the onset of the industrial revolution, atmospheric CO2 concentration has increased exponentially to the current 370 #mol mo1-1 level, and continued increases are expected. Previous research has demonstrated that elevated atmospheric CO2 results in larger plants returning greater amounts of C to the soil. However, the effects of elevated CO 2 on C and N cycling and long-term storage of C in soil have not been examined. Soil samples (in 0-50, 50100, and 100-200 mm depth increments) were collected after 3 years of cotton (Gossypium hirsutum L.) production under free-air CO 2 enrichment (FACE, at 550 #tool CO 2 mol-l), in combination with 2 years of different soil moisture regimes (wet, 100% of evapotranspiration replaced, or dry, 75% and 67% of evapotranspiration replaced in 1990 and 1991, respectively) on a Trix clay loam (fine, loamy, mixed (calcareous), hyperthermic Typic Torrifluvent) at Maricopa, Arizona. Ambient plots (370 #mol CO2 mol -I (control)), in combination with the wet and dry soil moisture regimes, were also included in the study. Soil organic C and N concentrations, potential C and N mineralization, and C turnover were measured. Increased input of cotton plant residues under FACE resulted in treatment differences and trends toward increased organic C in all three soil depths. During the first 30 days of laboratory incubation, available N apparently limited potential C mineralization and C turnover in all treatments. Between 30 and 60 days of incubation, soils from FACE plots had greater potential C mineralization with both water regimes, but C turnover increased in soils from the dry treatment and decreased in soils where cotton was not water stressed. These data indicate that in high-CO 2 environments without water stress, increased C storage in soil is likely, but it is less likely where water stress is a factor. More research is needed before the ability of soil to store additional C in a high-CO 2 world can be determined.

Effects of Elevated Carbon Dioxide and Increased Temperature on Methane and Nitrous Oxide Fluxes: Evidence from Field Experiments

Climate change could alter terrestrial ecosystems, which are important sources and sinks of the potent green-house gases (GHGs) nitrous oxide (N2O) and methane (CH4), in ways that either stimulate or decrease the magnitude and duration of global warming. Using manipulative field experiments, we assessed how N2O and CH4 soil fluxes responded to a rise in atmospheric carbon dioxide (CO2) concentration and to increased air temperature. Nitrous oxide and CH4 responses varied greatly among studied ecosystems. Elevated CO2 often stimulated N2O emissions in fertilized systems and CH4 emissions in wetlands, peatlands, and rice paddy fields; both effects were stronger in clayey soils than in sandy upland soils. Elevated temperature, however, impacted N2O and CH4 emissions inconsistently. Thus, the effects of elevated CO2 concentrations on N2O and CH4 emissions may further enhance global warming, but it remains unclear whether increased temperature generates positive or negative feedbacks on these GHGs in terrestri...

Effects of residue management and controlled traffic on carbon dioxide and water loss

Management of crop residues and soil organic matter is of primary importance in maintaining soil fertility and productivity and in minimizing agricultural impact on the environment. Our objective was to determine the effects of traffic and tillage on short-term carbon dioxide (CO2) and water (H2O) fluxes from a representative soil in the southeastern Coastal Plain (USA). The study was conducted on a Norfolk loamy sand (FAO classification, Luxic Ferralsols; USDA classification, fine-loamy siliceous, thermic Typic Kandiudults) cropped to a corn (Zea mays L.) — soybean (Glycine max (L.) Merr) rotation with a crimson clover (Trifolium incarnatum L.) winter cover crop for eight years. Experimental variables were with and without traffic under conventional tillage (CT) (disk harrow twice, chisel plow, field cultivator) and no tillage (NT) arranged in a splitplot design with four replicates. A wide-frame tractive vehicle enabled tillage without wheel traffic. Short-term CO2 and H2O fluxes were measured with a large portable chamber. Gas exchange measurements were made on both CT and NT at various times associated with tillage and irrigation events. Tillage-induced CO2 and H2O fluxes were larger than corresponding fluxes from untilled soil. Irrigation caused the CO2 fluxes to increase rapidly from both tillage systems, suggesting that soil gas fluxes were initially limited by lack of water. Tillage-induced CO2 and H2O fluxes were consistently higher than under NT. Cumulative CO2 flux from CT at the end of 80 h was nearly three times larger than from NT while the corresponding H2O loss was 1.6 times larger. Traffic had no significant effects on the magnitude of CO2 fluxes, possibly reflecting this soil’s natural tendency to reconsolidate. The immediate impact of intensive surface tillage of sandy soils on gaseous carbon loss was larger than traffic effects and suggests a need to develop new management practices for enhanced soil carbon and water management for these sensitive soils. # 1999 Elsevier Science B.V. All rights reserved.

Review of elevated atmospheric CO2 effects on agro-ecosystems: residue decomposition processes and soil C storage

A series of studies using major crops (cotton [Gossypium hirsutum L.], wheat [Triticum aestivum L.], grain sorghum [Sorghum bicolor (L.) Moench.] and soybean [Glycine max (L.) Merr.]) were reviewed to examine the impact of elevated atmospheric CO2 on crop residue decomposition within agro-ecosystems. Experiments evaluated utilized plant and soil material collected from CO2 study sites using Free Air CO2 Enrichment (FACE) and open top chambers (OTC). A incubation study of FACE residue revealed that CO2-induced changes in cotton residue composition could alter decomposition processes, with a decrease in N mineralization observed with FACE, which was dependent on plant organ and soil series. Incubation studies utilizing plant material grown in OTC considered CO2-induced changes in relation to quantity and quality of crop residue for two species, soybean and grain sorghum. As with cotton, N mineralization was reduced with elevated CO2 in both species, however, difference in both quantity and quality of residue impacted patterns of C mineralization. Over the short-term (14 d), little difference was observed for CO2 treatments in soybean, but C mineralization was reduced with elevated CO2 in grain sorghum. For longer incubation periods (60 d), a significant reduction in CO2-C mineralized per g of residue added was observed with the elevated atmospheric CO2 treatment in both crop species. Results from incubation studies agreed with those from the OTC field observations for both measurements of short-term CO2 efflux following spring tillage and the cumulative effect of elevated CO2 (> 2 years) in this study. Observations from field and laboratory studies indicate that with elevated atmospheric CO2, the rate of plant residue decomposition may be limited by N and the release of N from decomposing plant material may be slowed. This indicates that understanding N cycling as affected by elevated CO2 is fundamental to understanding the potential for soil C storage on a global scale.

Effects of free-air CO2 enrichment on cotton root growth

The rise in atmospheric CO2 concentration is predicted to have a positive effect on agroecosystem productivity. However, an area which requires further investigation centers on responses of crop root systems to elevated atmospheric CO2 under field conditions. The advent of free-air CO2 enrichment (FACE) technology provides a new method of CO2 exposure with minimal alteration of plant microclimate. In 1990 and 1991, cotton (Gossypium hirsutum (L.) ‘Deltapine 77’) was grown under two atmospheric CO2 levels (370 and 550 γmol mol−1) and two water regimes (wet (100% of ET replaced) and dry (75% of ET replaced in 1990 and 67% in 1991)). Plant root samples were collected at early vegetative and mid-reproductive growth. Taproots of CO2-enriched plants displayed greater volume, dry weight, length, and tissue density. Water treatment effects were noted for length, volume and dry weight of roots at the second sampling in 1991. In general, whole soil profile root densities (both length and dry weight densities) and root weight per unit length at the initial sampling were increased under CO2 enrichment at each of three positions (0.00, 0.25, and 0.50 m) from row center to the middle of the inter-row space. At the second sampling, root length density and root dry weight density were generally unaffected by water stress, whereas root weight per unit length was somewhat higher. In addition, extra CO2 increased whole profile root length density only at the 0.50 m inter-row position, whereas whole profile root dry weight density and root weight per unit length were generally higher under elevated CO2 at all three positions. The results from this field experiment strongly indicated that increased atmospheric CO2 level would enhance plant root growth.

8 – Response of Plants to Elevated Atmospheric CO2: Root Growth, Mineral Nutrition, and Soil Carbon

Publisher Summary This chapter focuses on the effects of elevated atmospheric carbon dioxide in plants. Elevated CO2 enhances plant growth . Carbon dioxide is the substrate for photosynthesis and, when elevated, both carbon assimilation and water use efficiency generally increase. Stimulation of root system development associated with increased growth implies more rooting, which, in turn, implies the possibility of increased water and nutrient capture. Microbes mediate carbon and nutrient flows within the soil, and CO2-induced changes in the structure and function of plant root systems may lead to changes in the microbiology of both rhizosphere and soil. Enhanced plant growth further suggests greater delivery of carbon to soil, and thus, potentially greater soil carbon storage. Soil is a vital reservoir in the global carbon cycle. Sequestration of soil carbon is closely linked to nutrient cycling. Root growth, rhizosphere microbiology, nutrient cycling and availability, and carbon storage in soils are integrally linked and have important implications for plant health. Predicting how belowground processes respond to rising CO2 will be necessary for the management of future crop and forest systems.

Influence of CO2 enrichment and nitrogen fertilization on tissue chemistry and carbon allocation in longleaf pine seedlings.

One-year old, nursery-grown longleaf pine (Pinus palustris Mill.) seedlings were grown in 45-L pots containing a coarse sandy medium and were exposed to two concentrations of atmospheric CO2 (365 or 720 μmol-1) and two levels of nitrogen (N) fertility (40 or 400 kg N ha-1 yr-1) within open top chambers for 20 months. At harvest, needles, stems, coarse roots, and fine roots were separated and weighed. Subsamples of each tissue were frozen in liquid N, lyophilized at -50°C, and ground to pass a 0.2 mm sieve. Tissue samples were analyzed for carbon (C), N, nonpolar extractives (fats, waxes, and oils = FWO), nonstructural carbohydrates (total sugars and starch), and structural carbohydrates (cellulose, lignin, and tannins). Increased dry weights of each tissue were observed under elevated CO2 and with high N; however, main effects of CO2 were significant only on belowground tissues. The high N fertility tended to result in increased partitioning of biomass aboveground, resulting in significantly lower root to shoot ratios. Elevated CO2 did not affect biomass allocation among tissues. Both atmospheric CO2 and N fertility tended to affect concentration of C compounds in belowground, more than aboveground, tissues. Elevated CO2 resulted in lower concentrations of starch, cellulose, and lignin, but increased concentrations of FWO in root tissues. High N fertility increased the concentration of starch, cellulose, and tannins, but resulted in lower concentrations of lignin and FWO in roots. Differences between CO2 concentrations tended to occur only with high N fertility. Atmospheric CO2 did not affect allocation patterns for any compound; however the high N treatment tended to result in a lower percentage of sugars, cellulose, and lignin belowground.

Wheel-traffic effects on corn as influenced by tillage system

Surface and subsoil compaction limit crop productivity on many soils of the southeastern Coastal Plain of the United States. Deep tillage, and to a lesser extent, controlled traffic have been utilized to manage soil compaction on these soils, but there is a need to develop tillage systems that integrate conservation tillage practices with deep tillage and controlled traffic. In 1988, a study was initiated with a wide-frame (6.3 m) vehicle to determine the interactive effects of traffic, deep tillage, and surface residues on corn (Zea mays L.) grown on a Norfolk loamy sand (fine-loamy, siliceous, thermic, Typic Kandiudults). Corn was planted into a winter cover crop of ‘Cahaba White’ vetch (Vicia sativa L.) Treatments included: traffic (conventional equipment or no traffic); deep tillage (no deep tillage, in-row subsoiling, or complete disruption); surface tillage (no surface tillage or disk and field cultivate). Complete disruption was accomplished by subsoiling at a depth of 43 cm on 25-cm centers. Although tillage × traffic interactions significantly affected soil strength and soil water, the only grain yield response both years was due to a surface tillage × deep tillage interaction. In a drought year (1988), with surface tillage, yields averaged 3.54, 2.75, and 1.41 t ha−1 with complete disruption, in-row subsoiling, and no deep tillage, respectively. Without surface tillage, respective yields averaged 3.77, 3.14, and 1.12 t ha−1. In 1989 when rainfall amount and distribution were excellent, yields with complete disruption, in-row subsoiling, and no deep tillage averaged 7.79 t ha−1, 7.08 t ha−1, and 6.44 t ha−1, respectively, with surface tillage; and 7.40 t ha−1, 6.91 t ha−1, and 4.70 t ha−1 respectively, without surface tillage. Soil strength and soil water measurements confirmed the detrimental effect of traffic after disking and field cultivation; however, soil water measurements and the lack of any yield response to applied traffic suggest that corn compensated for reduced rooting capacity in wheeled interrows by increased rooting in non-wheeled interrows.