| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
a Statewide Integrated Pest Management Program, Univ. of California, Kearney Agric. Center, 9240 South Riverbend Ave., Parlier, CA 93648
b Dep. of Botany and Plant Sciences, Univ. of California, Riverside, CA, and Kearney Agric. Center, 9240 South Riverbend Ave., Parlier, CA 93648
* Corresponding author (david{at}uckac.edu)
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Abbreviations: An, net carbon assimilation • CF, charcoal filtered air • gs, stomatal conductance • gfwt, grams fresh weight • hm, mean of hourly mean O3 concentrations over specified daylight period • HO3, high O3 concentration • LAR, leaf area ratio (total leaf area/total shoot dry weight) • LO3, low O3 concentration • LWR, leaf weight ratio (total leaf dry weight/total shoot dry weight) • MO3, medium O3 concentration • OTC, open-top chamber • SLW, specific leaf weight (leaf area/total leaf dry weight)
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Yield of tomato is moderately O3–sensitive (e.g., Clayberg, 1971), as demonstrated with a broad range of tomato cultivars in Spain (Gimeno et al., 1995), South Asia (Khan and Khan, 1994), the eastern USA (Ormrod, 1986; Reinert and Henderson, 1980), and in California (Brewer et al., 1986; Temple et al., 1985). Yield losses of 31% were found in the tomato cv. Tiny Tim in greenhouse chambers at 6 hourly mean (hm) concentrations of 80 nL/L (Reinert et al., 1997), and losses of 24.1% in cv. Murrietta in open top field exposure chambers at 7 hm concentrations of 53.1 nL/L in a typical SJV growing season (hot, dry, little cloud cover). In a subsequent cooler season in the SJV, O3 concentration and yields were less, but yield sensitivity was greater (Temple et al., 1985).
Ozone affects tomatoes through direct oxidant damage to physiological processes such as carbon assimilation in leaves and subsequently through altered biomass allocation (Clayberg, 1971; Gimeno et al., 1995; Tenga et al., 1990) and reduced root formation and colonization by mycorrhizae (McCool and Menge, 1983; Oshima et al., 1977).
In the SJV, economic production of tomatoes is also challenged by weed pressure. Weeds continue to account for substantial economic costs and crop yield losses globally, despite the extensive use of technology and human labor (Buhler, 2003). Vegetation management is a major cost, with herbicides applied to 99% of the tomatoes grown in California. This prevents an estimated 20% crop loss (NCFAP, 2002). Yellow nutsedge is a particularly difficult weed to control, particularly in irrigated row and vegetable crops (Holm et al., 1991; Mulligan and Junkins, 1976). Yellow nutsedge reduces yield of tomatoes through both above- and below-ground competition (Morales-Payan et al., 2003). Appropriate management of such weeds is threatened increasingly by restrictions on use of herbicides (Szmedra, 1997), appearance of herbicide-resistant weed biotypes (Heap, 1997), and indirectly by elements of global change (Fuhrer, 2003).
The interactive effect of O3 on crops and weeds need to be characterized for developing weed management strategies. However, little is known about such interactions (Fuhrer and Booker, 2003; Ziska, 2002). Any direct or indirect consequence of increasing O3 which differentially affects the growth and fitness of weeds and crops will alter crop–weed competitive interactions (Patterson, 1995). However, outcomes cannot be inferred from the relative O3 sensitivities of the individual species involved (Evans and Ashmore, 1992). For example, an early successional community dominated by sumac (Rhus copallina L.) was replaced during OTC fumigation by a community dominated by blackberry (Rubus cuneifolius Pursh.), even though blackberry is quite O3 sensitive (Evans and Ashmore, 1992). Ozone impacts on competitive interactions can be quite significant. Grass-legume mixtures (e.g., Lolium perenne L.–Trifolium repens L. and Medicago sativa L.–Phleum pratense L.) simplified toward pure grass in open air fumigation and OTC exposure systems (Nussbaum et al., 1995; Wilbourne et al., 1995; Johnson et al., 1996).
In many weedy species, short life cycles and prolific seed production and dispersal will accelerate adaptation to high ambient O3 concentrations. To our knowledge, O3–impacts on crop–weed competition and specifically on yellow nutsedge have not been reported. Nutsedge is of particular interest as a vegetatively propagated plant whose adaptation to O3 may be slower than that of sexually propagated weedy species. Therefore, the objective of this study was to determine the above- and below-ground effects of yellow nutsedge competition with tomato under varying levels of O3 concentration.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Yellow nutsedge juvenile plants with single tubers (approximately 6 cm tall; 2–3 leaf blades) were collected from agricultural fields around the experimental site (University of California, Kearney Research and Extension Center, Parlier, CA; 103 meters above sea level, 36.598 N 119.503 W). Soil was gently washed from the roots and tubers. Several nutsedge plants were transplanted into pots containing the tomato transplants on 8 May 2003, 26 June 2003, and 13 April 2004. Three days after transplanting, the nutsedge plants were thinned to desired populations of one, two, or three plants per pot. Additional pots were planted to single plants of nutsedge or tomato alone. Thus, there were five population ratios of nutsedge:tomato ranging from nutsedge alone (1:0) to tomato alone (0:1), and encompassing plantings of one nutsedge and one tomato (1:1), two nutsedge and one tomato (2:1), and three nutsedge and one tomato (3:1). There were four sample pots for each nutsedge:tomato ratio for a total of 60 pots. Each pot within each nutsedge:tomato ratio group was randomly assigned to an O3 treatment at this time, and O3 exposure was initiated immediately after moving the pots into OTCs in the field.
In the OTCs, the pots were automatically irrigated, to run-through, by automated drip emitters, one to three times daily as required by the weather. A complete fertilizer solution (Miracle Gro; Scotts Miracle-Gro Products Inc., Port Washington, NY; 1.3 g L–1) was applied to run-through weekly, with an automated fertigation system.
Ozone Exposure
In the OTCs (3.1-m diameter x 2.4-m height; Heagle et al., 1973), O3 was generated by corona discharge (Model G22; Pacific Ozone Technology, Brentwood, CA) from oxygen (Model AS-12; AirSep Corporation, Buffalo, NY).
The daily timecourse of O3 concentration was regulated in a single OTC by a dedicated O3 monitor (Model 49C, Thermo Environmental Instruments, Franklin, MA) interfaced to a computer for feedback control, as described previously (Grantz et al., 2003). The O3 concentration in each OTC was determined approximately every 15 min through samples obtained continuously from the center of each OTC through a Teflon dust filter and Teflon tubing attached to a multiport solenoid valve. The low O3 concentration treatment (LO3) was charcoal filtered (CF) and was nominally O3–free. The medium O3 (MO3) regime approximated the diurnal profile and maximal concentration observed on exceptionally polluted days at this location (see Grantz et al. (2003) for the shape of the diurnal timecourse). The high O3 (HO3) regime was approximately 1.8-fold greater than the MO3 at each time point. All O3 concentration data were archived electronically.
Experimental Design and Data Analysis
A group of three OTCs was selected randomly for each run and exposed to the three different O3 exposure concentrations. No individual OTC was used in more than one run, to avoid possible chamber effects. Exposure conditions were similar, with 12 hm O3 exposures for the low, medium and high O3 concentrations (LO3, MO3, HO3, respectively) of 19.3 ± 0.2 nL/L, 78.0 ± 8.5 nL/L, and 142.3 ± 11.2 nL/L averaged over the three replicate periods of growth.
The experiment was arranged as a split plot with three replications over time (the three independent runs). Ozone concentration (LO3, MO3, HO3; i.e., the OTC) was the main plot and nutsedge:tomato population ratio (0:1, 1:0, 1:1, 2:1, and 3:1) was the subplot. Each OTC contained four samples (pots) of the five nutsedge:tomato combinations. SPAD, gas exchange, root respiration were measured only on individual species, grown alone.
Data were analyzed by PROC GLM (SAS Institute, 1990). Appropriate transformations were made before analysis on data that failed to pass the homogeneity of variance test (Shapiro-Wilk; P > 0.05). The data were back-transformed for presentation. Variances were not back-transformed and are not presented. An additional, single degree of freedom, contrast was performed to compare biomass parameters in tomato grown with and without nutsedge (all population ratios combined) and in nutsedge grown with and without tomato. Means separation was performed in cases of significant overall F test, by Fisher's Protected Least Significant Difference (LSD).
Gas Exchange and Leaf Pigmentation
Net carbon assimilation (An) and stomatal conductance (gs) were measured on the youngest fully expanded leaf of tomato and on a young, fully exposed leaf of nutsedge. Measurements were obtained with a steady state gas exchange system (LI-6400; LI-COR Inc., Lincoln, NE), in situ in the OTC. Net carbon assimilation and gs were expressed relative to projected leaf area. The measurements were taken on 12 June 2003, 11 Aug. 2003, and 9 June 2004, in the three runs, respectively.
A relative measure of chlorophyll content was obtained as greenness of individual leaves in experiments 2 and 3, using a portable Chlorophyll Meter (Minolta SPAD-502; Spectrum Technologies, Plainfield, IL) on 4 Aug. 2003, and 7 June 2004, respectively. In tomato, measurements were made on the youngest fully expanded leaf (upper-canopy), a medium-aged leaf (mid-canopy), and an older leaf with visible symptoms of incipient senescence (lower-canopy). In nutsedge, insertion level was more difficult to determine and measurements were made on representative exposed leaves.
Root Respiration
Fine root samples were obtained from distal portions of the intact root system of nutsedge and tomato plants growing alone (1:0 and 0:1), at the time of plant harvest. The terminal 3 to 4 cm of fine root were excised, washed in cold water to remove sintered clay potting medium, and immediately transferred to a respirometer chamber.
Fine root respiration (Rr) was determined in liquid phase with a Clark-type oxygen electrode (Delieu and Walker, 1972). Four respirometer chambers (Oxygraph Oxygen Electrode System; PP Systems, Haverhill, MA) were run in parallel, interfaced with a computer for data acquisition and analysis. A magnetic stir bar was placed in each chamber, separated from the root material by a laboratory-designed porous metal screen. Temperature control (25°C) was maintained by circulation of water through a precision water bath (Model 9100, Isotemp, Pittsburgh, PA) and through the plastic housing of each respirometer chamber.
Electrodes were calibrated by means of air-saturated water and oxygen-free water obtained by adding a small amount of sodium dithioinite to each chamber. Two milliliters water was placed in each chamber after several rinsings. When output had become stable (about 10 min), fine root samples were introduced. Root respiration was expressed relative to the blotted wet mass of root in each chamber, obtained following the measurement.
Growth Measurements
Growth of tomato was measured nondestructively on a weekly basis as plant height (length of mainstem). Tomato and nutsedge plants were destructively harvested at 4, 7, and 8 wk after transplanting, in the three runs, respectively. Aboveground biomass was placed directly in plastic bags for storage at 4°C until further processing (maximum 1–2 d). The root mass in each pot was washed to remove the sintered clay growth media. Tubers were separated from the roots and counted. Roots and tubers were placed in separate paper bags. The tomato and nutsedge roots were intertwined in those pots containing both species, so the total mass of the combined root system was determined.
Roots and tubers were immediately dried to constant weight in a forced-air oven at 70°C. The dry weight of the root mass and tubers was recorded and each sample was combusted (Thermolyne Corp., Dubuque, IA) at 800°C, leaving only the sintered clay medium. Total root weight was then determined as the difference between the root dry weight and the ash weight.
Shoots of tomato were separated into leaves (leaf blades and petioles) and stems. A few tomato plants in LO3 had developed small, immature fruits, which were included with the stem biomass. Total leaf area was determined with an area meter (LI-3000; LI-COR Inc.). Leaves and stems were placed in separate paper bags and dried to constant weight in a forced-air oven at 70°C and weighed. Dry weight of nutsedge was determined as above, but leaf area was not determined.
Specific leaf weight (SLW; g m–2) and leaf area ratio (LAR; m2 kg–1) of the tomato plants were calculated as total leaf dry weight/total leaf area and total leaf area/total above-ground dry weight, respectively. Similarly, leaf weight ratio (LWR; kg kg–1) was calculated as total leaf dry weight/total shoot dry weight.
The root:shoot biomass ratios (R:S) for nutsedge alone (1:0) and for tomato alone (0:1) were determined. For nutsedge this was actually the below- to above-ground biomass ratio, because tuber biomass (a shoot tissue) was pooled with root biomass.
|
RESULTS AND DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
|
Leaf morphology of tomato was not altered by exposure to O3 as the SLW of the tomato plants was similar under all O3 concentrations (Table 1). However, the allometric relationships between leaf area and plant development responded to O3 with a greater investment in leaf area and biomass per unit shoot biomass (Table 1) compared with the LO3 treatment. Both LAR and LWR increased with increasing O3 concentration (Table 1). Competition from nutsedge had no effect on tomato leaf morphology or on leaf allometric parameters (data not shown).
|
|
Net carbon assimilation declined by about 16 and 26% at MO3 and HO3, respectively (Fig. 2A; squares), similar to the decline in photosynthetic pigments (cf. Fig. 1B). This contrasts with the nearly complete absence of response in tomato, though with the possible caveat that tomato may have been represented by a more homogeneous leaf sample across the O3 treatments. In general, An declines with increasing exposure to O3, associated with reductions in gs, activities of Calvin-Benson Cycle enzymes, and eventually electron transport (Calatayud and Barreno, 2001; Hill and Littlefield, 1969). Stomatal conductance was similarly reduced (data not shown).
Gas exchange of nutsedge reflected its C4 photosynthetic pathway, with approximately a 75% lower gs, reduced intercellular CO2 concentration, and an approximately threefold greater intrinsic water use efficiency (An:gs) than in tomato (data not shown). Because O3 uptake is strongly coupled to gs, the responses of these two species to the same external conditions may actually be due to vastly different internal doses of O3 (amount absorbed into leaf tissues). The photosynthetic sensitivity of nutsedge to O3 may be considerably greater than that of tomato, when expressed in appropriate toxicological units of absorbed O3 dose.
Root Respiration
Respiration of fine roots (Rr; averaged over all O3 concentrations) was greater in tomato (91.4 nmol gfwt–1 min–1) than in nutsedge (65.6 nmol O2 gfwt–1 min–1), but the Rr in both species was unaffected by increasing O3 (Fig. 2A). However, Grantz et al. (2003) observed an increase in Rr previously over this range of O3 concentrations in both Pima cotton (Gossypium hirsutum L.) and in muskmelon (Cucumis melo L.). A putative balance between increased Rr in response to O3–induced damage repair in roots and decreased Rr because of inhibited substrate translocation from source leaves to the roots (Grantz and Farrar, 1999; Grantz et al., 2003) could vary between species and experiments, yielding variability in responses of Rr to O3.
Above-Ground Productivity
Tomato
Plant height (mainstem length) was reduced by exposure to O3 (Table 2), particularly at HO3 (Fig. 3A), by approximately 12%. Competition from nutsedge had no density-specific nor overall effect on plant height of tomato (Table 2; see population ratio, contrast).
|
|
Shoot biomass is a growth indicator that is closely associated with total biological productivity. Presence of nutsedge (averaged across all population ratios) caused a decline (Table 2) in tomato shoot biomass over all O3 concentrations imposed (Fig. 4A). Increasing O3 concentrations also reduced shoot biomass of tomato, whether grown with or without nutsedge. In tomato grown alone (0:1), shoot biomass was reduced by O3 (Table 2), declining substantially (31%) between LO3 and MO3, with little further reduction in HO3 (Fig. 4A, open circles). There was no interaction between O3 concentration and nutsedge population ratio for tomato shoot biomass (Table 2).
|
Nutsedge
Plant height and leaf area were not determined in nutsedge. Shoot biomass (above ground excluding rhizomes and tubers) of nutsedge grown alone (1:0) was affected by O3 concentration (P = 0.08; Table 3). An increase was observed at moderate exposure (MO3; Fig. 4B), with a significant subsequent reduction (42%) at HO3 compared with MO3 (Fig. 4B).
|
There was no interaction of nutsedge:tomato population ratio and O3 concentration for shoot biomass in nutsedge (Table 3). However, the nutsedge shoots exhibited a more erect growth habit in the LO3 and MO3 treatments than in the HO3 treatment. This would likely affect competitiveness under many field conditions.
Below-Ground Productivity
Tomato
Inhibited root development is a common plant response to O3 exposure (Andersen, 2003; Grantz, 2003). In tomato, root biomass productivity was sensitive to O3 (Table 2), declining nearly linearly with O3 concentration (Fig. 5; open circles). Root biomass was approximately 25% lower at MO3 and 44% lower at HO3, relative to LO3.
|
The root:shoot biomass ratio (R:S) of tomato was reduced by O3 concentration (P = 0.059; Table 2), particularly at HO3 relative to LO3 (Fig. 6C; open circles). This reflected the nearly balanced decline in both root and shoot biomass as O3 exposure increased (Fig. 4A, 5; open circles). In previous studies, O3 also induced increased leaf number and reduced shoot and root biomass of tomatoes (Olszyk and Wise, 1997; Varshney and Rout, 1998). Ambient O3 exposure in India (up to 120 nL/L hourly maxima) increased leaf number in tomato by about 15% (mean of three cultivars; Varshney and Rout, 1998) while reducing shoot and root length, relative to chemically (ethylene diurea)-protected controls. In these studies, shoot biomass declined by 26.6%, while root biomass declined by only 18.0%, resulting in an unusual increase in R:S with increasing O3, in contrast to the modest decline observed in the present study.
|
The number of tubers produced by the nutsedge plants increased with the number of seedlings initially planted in each pot (Table 3; Fig. 7). However, the presence of a tomato plant reduced the number of tubers relative to nutsedge grown alone (Fig. 7). In the study of Morales-Payan et al. (2003), the number of tubers was reduced by 50% when yellow nutsedge plants were grown with tomato. In the present study, the number of tubers were reduced by about 70, 55, and 55%, in LO3, MO3, and HO3, respectively, when one nutsedge plant was grown with or without one tomato plant.
|
Below-ground productivity was also more sensitive in tomato compared with nutsedge (Fig. 6B) as below-ground biomass of tomato declined with increasing O3, whereas nutsedge increased slightly due to stimulated allocation to reproductive tubers. Overall, nutsedge was more tolerant to moderate O3 concentrations than was tomato, with a substantial shoot response and enhanced allocation to tubers observed only at HO3, whereas tomato responded substantially and monotonically to O3 at MO3 and HO3 (Fig. 6A; 6B).
|
CONCLUSIONS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
|
ACKNOWLEDGMENTS |
|---|
Received for publication October 22, 2004.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Related articles in Crop Science:
This article has been cited by other articles:
|
|
 |
|
  D. A. Grantz and A. Shrestha Tropospheric Ozone and Interspecific Competition between Yellow Nutsedge and Pima Cotton Crop Sci., July 25, 2006; 46(5): 1879 - 1889. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Agronomy Journal | Vadose Zone Journal | |||
| Journal of Natural Resources and Life Sciences Education |
Soil Science Society of America Journal | ||||
| Journal of Plant Registrations | Journal of Environmental Quality |
The Plant Genome | |||
0.05.
