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TURFGRASS SCIENCE

Atmospheric Composition under Impermeable Winter Golf Green Protections

^a Soils and Crops Research and Development Centre, Agriculture and Agri-Food Canada, 2560 Hochelaga Boulevard, Ste-Foy, Québec, Canada, G1V 2J3
^b Royal Canadian Golf Association, Golf House, 1333 Dorval Drive Suite 1, Oakville, Ontario, Canada, L6M 4X7; Département de phytologie, Université Laval, Sainte-Foy, Québec, Canada, G1K 7P4
^c Centre de recherche en horticulture, Département de phytologie, Université Laval, Sainte-Foy, Québec, Canada, G1K 7P4

^* Corresponding author (rochettep{at}agr.gc.ca)

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
The utilization of impermeable winter covers on annual bluegrass [Poa annua var. reptans (Hauskn.) Timm.] golf greens as a protection against excess water and ice is increasing rapidly in Canada and elsewhere in northern climates. A study was conducted to examine the impact of these covers on the atmospheric composition over golf green turfgrass during the 1997–1998 and 1998–1999 winters in Québec City and in Montréal, Canada. Winter protective covers tested included a commercial impermeable cover on top of either curled wood shavings mat (CW-CC), 15 cm of straw mulch (SM-CC) or a felt material (FM-CC), a clear polyethylene cover on top of a curled wood shavings mat (CW-PC), and an unprotected control. Oxygen was consumed at variable rates under impermeable winter protective covers. As a result, anoxic conditions were not reached during winter at the Québec City site but high respiration rates at the Montréal site resulted in anoxic conditions that lasted for periods as long as 50 d, without apparent damage to the annual bluegrass plants. Further tests were conducted on greens experiencing recurrent damages that could not be explained by freezing temperatures, snow mold pathogens, excess water, or ice. We showed that these problem greens had higher soil respiration rates than nonproblem greens indicating that the differences in O₂ consumption amongst golf greens are likely due to differences in soil biological activity rather than in plant respiration. We also established that the higher activity in soils of recurrently damaged greens was related to higher levels of soil organic C. Accordingly, sand-based golf greens built according to the USGA specifications had lower soil organic matter and lower respiration rates than greens built on native soils. We conclude that high rates of O₂ consumption by golf greens with high soil organic matter content results in potentially harmful anoxic conditions under impermeable covers during winter.

Abbreviations: CC, commercial impermeable cover • CTL, unprotected control • CW, curled wood shavings • DAT, days after treatment • FM, felt material • PC, polyethylene cover • SM, straw mulch

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
UNSEEDED annual bluegrass is an invasive species of putting surfaces of golf courses in many regions of Canada (Warwick, 1979) and the USA (Huff, 1996). A major weakness of annual bluegrass as a species for putting greens is its susceptibility to several environmental stresses including freezing temperatures (Beard, 1970). Winter damage to golf greens can disrupt play for several weeks in the spring and result in major economic losses associated to green repairs and lost revenues. In Eastern Canada, freezing temperatures and ice cover cause extensive winterkill to annual bluegrass golf greens and are a major concern for the golf industry (Dionne and Desjardins, 1996; Dionne, 2000).

The utilization of impermeable covers on annual bluegrass golf greens as an element of winter protection is increasing rapidly in Canada and elsewhere in cold regions. In combination with insulating materials, these covers are very efficient in preventing excess water and extreme freezing temperatures at the plant crown level, thereby increasing plant tolerance to winter stresses (Dionne et al., 1999). Winter protections can also be needed at the end of winter when rapid dehardening combined with lower vernalization requirements in some annual bluegrass genotypes (Johnson and White, 1997) can lead to increase susceptibility of annual bluegrass to late subfreezing temperatures (Tompkins et al., 2000). Yet, in spite of the presence of these covers, winter damages not directly linked to low temperatures, excess water, snow mold diseases, or ice are observed on some golf greens. Nearly all natural and synthetic materials that are impermeable to water are also impermeable to most atmospheric gases. Consequently, impermeable tarps can impede downward diffusion of ambient O₂ and hypoxic conditions may develop at the soil surface as O₂ is consumed by plant and soil respiration. Similarly, gases such as CO₂ that are produced by metabolic activity in the soil–plant system cannot escape to the atmosphere and accumulate under the covers. It was therefore hypothesized that unexplained winter damages to golf greens may result from the modification of the atmospheric composition at the plant level in presence of impermeable covers.

Absence of O₂ is a serious hazard for overwintering crops (Andrews, 1996) and accumulation of CO₂ has been shown to have potential phytotoxic effects (Freyman and Brink, 1967; Andrews and Pomeroy, 1989; McKersie and Leshem, 1994). Reduction in O₂ concentration and concomitant rise in CO₂ observed in sealed enclosures during winter were attributed to slow but significant respiration rates by both soil microflora and plants at low temperatures (Bertrand et al., 2001). Consequently, temperature, soil water content, plant dormancy level, soil organic matter, and other factors controlling autotrophic and heterotrophic respiration underneath impermeable covers are bound to affect the atmospheric composition at the soil–plant interface.

Very little is known regarding the gaseous composition of the atmosphere underneath impermeable covers (ice, plastic sheet, etc.) during winter. There are few reports of the temporal variation of the concentrations of gases such as CO₂ and N₂O in the soil profile of natural (Sommerfeld et al., 1993) and agricultural (Burton and Beauchamp, 1994) ecosystems covered by snow. Relatively low CO₂ concentrations (<0.01 mol mol^–1) have been observed in forests but concentrations as high as 0.05 mol mol^–1 for CO₂ and 20 µmol mol^–1 for N₂O have been reported in agricultural fields. However, we are unaware of in situ experiments that studied the influence of impermeable barriers on soil gas concentrations during winter in either forest, agricultural fields or golf greens. The objectives of this experiment were to: (i) assess the impact of impermeable protection covers on the atmospheric composition at the surface of golf greens during the winter; (ii) relate atmospheric composition under impermeable covers to winter damage to turfgrass; and (iii) identify factors controlling O₂ consumption by golf greens during winter.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
The study was conducted at the Royal Québec (Québec City, QC, Canada; 46°48' N, 71°23' W, 70 m) and Royal Montréal (Montréal, QC, Canada; 45°28' N, 73°45' W, 26 m) golf clubs. Winters in Québec City are characterized by lower air temperature and greater snowfall than in Montréal (Dionne et al., 1999). A total of three experiments were carried out between December 1997 and May 2000: (i) Atmospheric composition was monitored during two consecutive winters under several types of impermeable protections applied on one golf green at the Québec City and Montréal sites; (ii) At the Québec site, atmospheric composition was monitored during one winter at the surface of two golf greens with known contrasted frequencies of damage when protected using straw mulch under an impermeable cover; and (iii) Incubations and analyses of golf green soils were made to investigate relationships between variations in O₂ consumption and soil characteristics.

Experiment 1
The experiment was carried out during the 1997–1998 and 1998–1999 winters on one golf green at the Royal Québec and one golf green at the Royal Montréal. Greens at both sites were predominantly annual bluegrass and made of native soil but the green in Montréal had higher soil organic matter content and more creeping bentgrass (Agrostis palustris Huds.) (Table 1). Treatments consisted of the following winter protective covers: (i) curled wood shavings mat (American Excelsior Company, Arlington, TX) protected with an impermeable commercial cover (Hinspergers Poly Industries Ltd., Mississauga, ON) (CW-CC); (ii) curled wood shavings mat protected with an impermeable clear polyethylene cover (0.15 mm thick) (CW-PC); (iii) straw mulch (15 cm) protected with an impermeable commercial cover (SM-CC); (iv) felt material (Golftex pro, Texel Inc., St-Élzéar, QC) protected with an impermeable commercial cover (FM-CC); (v) unprotected control (CTL). The treatments were replicated three times and plots were arranged in a randomized complete blocks design.

Bioclimatological Measurements and Turfgrass Quality Rating
Daily climatological data, including air temperature, thickness of snow cover, rainfall, and snowfall, were obtained from Environment Canada weather stations (Québec City, Jean-Lesage international airport; Montréal, Pierre-Elliot-Trudeau international airport) located within 20 km of each experimental site. Soil temperature at plant crown level under protective covers was recorded on two of the three replications using copper–constantan thermocouples (Omega Engineering Inc., Stanford, CA). Thermocouples were connected to a data acquisition system (AM416 multiplexer and CR10 datalogger, Campbell Scientific, Logan, UT). Temperature was measured every hour and averaged over 10-d periods.

Turfgrass visual quality was evaluated after cover removal based on a hedonic scale of 1 to 9, where 1 = dead grass, 9 = best visual quality, and 5 = lowest acceptable quality rating. Statistical analysis was performed on turfgrass visual quality.

Gaseous Composition under Impermeable Covers
Gas concentration was monitored at the surface of the green under protective covers from five to seven times during the winter. At the time of sampling, air was removed from under the covers via a plastic tube (Bev-A-Line IV, Labcor, Anjou, QC) using pre-evacuated 250-mL glass sampling bulbs (Kontes, Vineland, NJ). Before collecting the soil air sample, 10 mL of air was removed from the tube and discarded to account for the dead volume of the tube. After collecting the air sample, the bulbs were brought to the laboratory and analyzed for O₂, CO₂, and N₂O concentrations using a gas chromatograph (Varian 3800, Varian Canada, Mississauga, ON) fitted to electron capture, flame ionization and thermal conductivity detectors (Rochette and Hutchinson, 2005).

Statistical analysis was performed on gas concentrations and on turfgrass visual quality. Data were analyzed for statistical significance using the General Linear Model Procedure and means were separated with Duncan's Multiple Range Analysis of the Statistical Analysis System (SAS Institute, 1990). Values were considered different from each other at P < 0.05.

Experiment 2
Information obtained in Experiment 1 during the first winter indicated that the impact of impermeable covers on atmospheric composition at the golf green surface may differ between greens. Consequently, we instrumented two additional annual bluegrass golf greens at the Royal Québec golf club during the 1998–1999 winter for monitoring gaseous composition under the impermeable winter protections. Both greens had been protected by impermeable covers (10 cm straw + impermeable cover [Model: RB 26-6 HEAVY DUTY, Covertech Fabricating Inc, Toronto.]) for many consecutive winters. The turfgrass of the first one always overwintered well while the second one had a history of recurrent winter damage despite protection. Gas sampling probes made of plastic tube (Bev-A-Line IV, Labcor, Anjou, QC) were installed on 30 Nov. 1998 when the golf club field crew deployed the winter protections. Measurements were made at seven dates until protections were removed on 5 Apr. 1999. The evolution of gas composition underneath the impermeable covers was monitored as described previously and visual assessment of green quality was made in the following spring.

Experiment 3
To assess whether variations in atmospheric composition induced by impermeable covers were related to variations in soil characteristics, nine greens protected using straw and an impermeable cover (Model RB 26-6 Heavy Duty, Covertech Fabricating Inc., Toronto) were selected at the Royal Québec golf club: five of them showing excellent winter survival of annual bluegrass and the other four showing recurrent damage. Five independent soil samples (cores of 5.3-cm cross-section, 10-cm height) collected from the 10- to 20-cm soil layer of each of the 10 greens were incubated under controlled conditions and analyzed for their physical and chemical properties. For their incubation, intact soil cores were placed in sealed glass jars kept at 22°C. Air samples were drawn from the jars headspace at incubation time 0 and 24 h and analyzed for CO₂ concentration using a gas chromatograph (Rochette and Hutchinson, 2005). Respiration rates (R, µg CO₂–C g^–1 soil d^–1) were calculated as follows:

where C₂₄ and C₀ are the CO₂ concentration (µmol mol^–1) at time 24 and 0 h after jars sealing, respectively, M_v is the molecular volume at 22°C (24000 cm³ mol^–1), M_m is the mass of C in a molecule of CO₂ (12 g mol^–1), V is the headspace of the jars (779 cm³) and m_s is the mass of the soil cores (320 g). Three additional soil samples were taken from each green and analyzed for particle size distribution (sieving method), total organic C (dry combustion method), total N (dry combustion method), bulk density (core method), and total porosity (core method) (Carter, 1993).

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Winter Climate and Turfgrass Temperature
Climatic conditions that prevailed at the Québec City and Montréal sites during the study are described in Fig. 1 and 2 and in Table 2. The combination of slightly warmer temperatures (+2.5°C) and less abundant snowfall (–55 cm) resulted in more frequent thawing events and a thinner snow cover in Montréal than in Québec City. During both winters, snow cover reached a maximum depth of 100 cm at the Québec site and 50 cm at the Montréal site. Moreover, snowcover was <15 cm during three months from December 1998 to March 1999, providing limited protection against low freezing air temperatures. These results are in agreement with estimates by Bélanger et al. (2002) that perennial forage crops in the Montréal region can be exposed to damaging air temperatures (less than –15°C) in absence of protective snow cover (<10 cm) during an average period of 12 d annually.

View larger version (49K): [in this window] [in a new window]   Fig. 1. (a) Air temperature and snow cover (shaded area) at the Québec Jean-Lesage International airport. Vertical bars indicate measured values of snow cover at the Royal Québec experimental golf green. (b) Crown-level soil temperature in an unprotected control (CTL) and under winter protective covers: a commercial impermeable cover on top of either curled wood shavings mat (CW-CC), 15 cm of straw mulch (SM-CC) or a felt material (FM-CC), a clear polyethylene cover on top of a curled wood shavings mat (CW-PC) at the Royal Québec experimental golf green.

View larger version (40K): [in this window] [in a new window]   Fig. 2. (a) Air temperature and snow cover (shaded area) at the Montréal Pierre-Elliot Trudeau International airport. Vertical bars indicate measured values of snow cover at the Royal Montréal experimental golf green. (b) Crown-level soil temperature in an unprotected control (CTL) and under winter protective covers: a commercial impermeable cover on top of either curled wood shavings mat (CW-CC), 15 cm of straw mulch (SM-CC) or a felt material (FM-CC), a clear polyethylene cover on top of a curled wood shavings mat (CW-PC) at the Royal Montréal experimental golf green.

View this table: [in this window] [in a new window]   Table 2. Climatic conditions during the 1997–1998 and 1998–1999 winters at the Québec and Montréal experimental sites.

Periods of simultaneous occurrence of freezing air temperatures with no or thin (<5 cm) snow covers occurred between 20 to 40 days after treatment application (DAT) and 80 and 90 DAT at the Montréal site during the 1998–1999 winter (Fig. 2). During these periods, ranking of the cover types in relation to their soil temperature was the same as in the presence of a snow cover but differences between protected and control plots were greater: temperature under SM remained close to 0°C and was up to 6°C warmer than in the control, CW maintained temperature close to that under straw (1°C lower), and FM provided less insulation with temperatures closer to that of the control. During cold spells and in absence of snow cover, temperature under FM (–4°C) was only slightly higher than in the control while SM and CW maintained temperature –2°C.

At both sites, the 1997–1998 and 1998–1999 winters were relatively warmer than normal with a snow cover that protected the turfgrass for most of the cold season (Table 2). Lack of prolonged periods of cold temperatures combined with adequate snow cover allowed temperature at the surface of control plots to safely remained above the –10°C threshold below which annual bluegrass can die from freezing injuries (Dionne et al., 1999) (Fig. 1, 2). Therefore, these conditions, did not allow us to discriminate winter covers for their protective efficiency in terms of plant damage or winterkill attributable to subfreezing temperatures. However, our results suggest that all covers may not perform equally well in providing a physical environment favoring winter survival of annual bluegrass. For example, use of straw mulch maintained crown-level temperatures above freezing point during both winters at the Royal Québec and during the 1997–1998 winter at the Royal Montréal site. Above-freezing temperatures prevent plants from reaching optimum levels of freezing tolerance while promoting respiration of autotrophic and heterotrophic organisms and the development of psychrophillic pathogens (Hsiang et al., 1999; Tompkins et al., 2000). Strategies for golf green winter protection should aim at maintaining temperature slightly below freezing point when a cover is present while preventing exposure of damaging freezing temperatures (–10°C) when snow cover is thin or absent. In this study, CW met these criteria at both sites and during both years while the use of a thick SM resulted in potentially harmful warm temperatures. Temperatures close (differences 1°C) to those on the control plots under FM indicate that the insulation provided by the felt material was small and suggest that this type of protection may not fully protect against freezing damage in absence of snow cover.

Winters in Québec City and Montréal are characterized by very cold weather with mean annual low temperature of –28 and –25°C, respectively (Rochette et al., 2004b). These temperatures are considerably below the lower limits that annual bluegrass can tolerate (Dionne et al., 1999). Therefore annual bluegrass golf greens can survive these harsh conditions only if an adequate snow cover or artificial protections insulate them from low air temperatures. Our results agree with previous studies on winter protective covers conducted from 1993 to 1996 in Québec City and Montréal that showed evidence that local winter conditions, mostly snow cover, and winter protective covers characteristics are two major factors influencing golf green soil temperatures and consequent winter damages (Dionne and Desjardins, 1996; Dionne et al., 1999). A thick (>20 cm) and stable dry snow cover represents the best protection against freezing temperatures for golf greens. However, golf green protective covers are invaluable tools for reducing and mitigating cold stress in most northern climate region experiencing thin or unstable snow covers.

Atmospheric Composition under Covers
Oxygen and Carbon Dioxide
Sampling air at the surface of the control plots during winter could not be made at several dates because of nonfunctional sampling probes. Sampling probes were blocked by ice that was likely formed at the soil surface when water from rainfall and snowmelt froze because of subsequent heat loss through the snowpack. Absence of such problems in plots protected by an impermeable cover confirms the efficiency of these protections to prevent the formation of an ice layer in direct contact with the green surface. Sampling made on eight dates at the Québec site and on seven dates at the Montréal site during the experiment indicated well-aerated conditions (O₂ concentration 0.19 mol mol^–1) in the control plots except on day 120 at Québec city in 1998–1999 when O₂ concentration decreased to 0.09 mol mol^–1 (Fig. 3 and 4) .

View larger version (31K): [in this window] [in a new window]   Fig. 3. Oxygen (a) and CO2 (b) concentrations in an unprotected control (CTL) and under winter protective covers: a commercial impermeable cover on top of either curled wood shavings mat (CW-CC), 15 cm of straw mulch (SM-CC) or a felt material (FM-CC), a clear polyethylene cover on top of a curled wood shavings mat (CW-PC) at the Royal Québec experimental golf green.

View larger version (26K): [in this window] [in a new window]   Fig. 4. Oxygen (a) and CO2 (b) concentrations in an unprotected control (CTL) and under winter protective covers: a commercial impermeable cover on top of either curled wood shavings mat (CW-CC), 15 cm of straw mulch (SM-CC) or a felt material (FM-CC), a clear polyethylene cover on top of a curled wood shavings mat (CW-PC) at the Royal Montréal experimental golf green.

Mean respiration rates (R) of the soil–plant system under the impermeable covers can be approximated using the early winter rate of change in O₂ or CO₂ concentration and considering an air-filled soil porosity of 0.25 m³ m^–3 down to the 0.6-m depth [R = (dC/dt) (M_m/M_v)(V/A), where dC/dt is the rate of change in gas concentration, M_m and M_v are the molecular mass and volume, respectively, V is the volume occupied by air, and A is the turfgrass area]. Such calculations for the first 50 DAT yielded rates of –79 mg O₂ m^–2 d^–1 (216 mg CO₂ m^–2 d^–1) in 1997–1998 and of –156 mg O₂ m^–2 d^–1 (428 mg CO₂ m^–2 d^–1) in 1998–1999 at the Québec city site, and –216 mg O₂ m^–2 d^–1 (594 mg CO₂ m^–2 d^–1) in 1997–1998 and –268 mg O₂ m^–2 d^–1 (737 mg CO₂ m^–2 d^–1) in 1998–1999 at the Montréal site. Compared to agricultural soils in Eastern Canada, these rates are much lower than those reported during the growing season (Rochette et al., 1991) but are similar to those observed on perennial grasses in late fall at the onset of winter (Rochette et al., 2004a). Significant soil respiration rates near freezing point under the protective covers are in agreement with other reports of biological activity at low temperatures during winter. Respiration was shown to occur at measurable rates at temperatures as low as –2°C in tundra and taiga soils (Clein and Schimel, 1995), and N₂O production was measured at –6°C (Röver et al., 1998). Furthermore, significant levels of microbial activity were measured in frozen soils at temperatures down to –5°C (Brooks et al., 1997) and microbial activity was detected at temperatures as low as –20°C (Bremner and Zantua, 1975). These observations provide growing evidence that the soil microflora can play a major role in the modification of the atmosphere composition at low temperatures under impermeable covers.

The CO₂ concentration under covers increased as a result of O₂ consumption. During aerobic respiration, one molecule of CO₂ is produced for every molecule of O₂ consumed and the increase in CO₂ concentration is directly proportional to the decrease in O₂. Such direct relationship was not observed under winter covers where CO₂ concentration increase was only 50% of the O₂ decrease in Montréal and 75% in Québec. Assuming that aerobic respiration was the only fate for lost O₂, the slower increase in CO₂ concentration indicates that some of the respired CO₂ did not accumulate in the gas phase. Carbon dioxide solubility in water is approximately 80 times higher than that of O₂ (Taiz and Zeiger, 1998) and gas solubility increases as temperature decreases. Consequently, large quantities of CO₂ have likely been dissolved in soil water. Also, CO₂–consuming anaerobic microbiological reactions such as methanogenesis have been found to occur during winter in cold environments (Avery et al., 1999) and may have contributed to the slower increase in CO₂ under the covers. These phenomena can be of crucial importance for the survival of the annual bluegrass since high CO₂ concentrations can be more harmful for the plants than low O₂ conditions. Indeed, Freyman (1967) has shown that, under laboratory conditions, alfalfa can tolerate O₂–free air for 21 d but that exposure to pure CO₂ for 21 d killed the plants.

Anoxic conditions were not reached in Québec city in either winters but were attained 90 DAT in 1997–1998 and 70 DAT in 1998–1999 in Montréal because of higher respiration rates. Considering the date when covers were removed, the potential duration of plant exposure to anoxic conditions was therefore 10 d in 1997–1998 and 50 d in 1998–1999. Respiration rates were not only different between sites for a given year but were also greater during the 1998–1999 than the 1997–1998 winter at both sites. In golf greens, O₂ is consumed by autotrophic respiration of the grasses and by heterotrophic respiration of the soil microbes during the decomposition of organic substrates. Differences in O₂ use between Montréal and Québec sites and between years were therefore the result of differences in plant or soil respiration, or both. Plant and soil respiration has been shown to increase exponentially with temperature at temperature < 30°C (Fang and Moncrieff, 2001). Higher early winter soil temperatures in 1998–1999 than in 1997–1998 are in agreement with interannual differences in respiration rates at both sites. However, soil temperature was colder in Montréal than in Québec city and factors other than temperature must therefore be considered to explain the differences in respiration rates between the two sites. Such factors may include: (i) dormancy levels of turfgrass at the onset of winter that can be affected by several factors such as fall climatic conditions (Bélanger et al., 2002), genetics, and management factors (mowing regimes, fertilization) (Rossi, 1996); (ii) availability of substrates for decomposers which can be affected by the quality and amounts of organic materials (Kilham, 1994) such as native soil organic matter, topdressing, thatch, and organic fertilizers; and (iii) soil temperature (Fang and Moncrieff, 2001), aeration (Schjønning et al., 2003), and soil moisture content (Davidson et al., 1998) that modulate the biological activity in soils.

Nitrous Oxide
Although N₂O is not a direct threat for overwintering plants, its concentration level provides a indication of the redox potential of the soil–plant environment. Nitrous oxide is produced when NO₃^– is used as an alternative electron acceptor to O₂ during oxidation processes when O₂ becomes less available (Kilham, 1994). Production of N₂O in soils is therefore associated to low-O₂ conditions that can be potentially harmful to higher plants. Concentration in N₂O remained low and close to ambient in the control plots (Fig. 5 ). Under impermeable covers, N₂O concentrations generally increased during winter, reaching higher values at the Montréal than at the Québec site. In Montréal, concentration peaks of 20 to 35 µmol mol^–1 (100 times greater than ambient concentration), occurred approximately at 70 DAT when O₂ levels decreased below 0.05 mol mol^–1 indicating an active NO₃^– reduction. The late winter decrease in N₂O concentration indicates that N₂O itself was used as an electron acceptor in place of NO₃^–, as a result of a further reduction in redox potential. Therefore, temporal evolution of N₂O concentrations under the impermeable covers provides additional evidence that the turfgrass plants were exposed to more severe anaerobic conditions at the Montréal than at the Québec City site.

View larger version (25K): [in this window] [in a new window]   Fig. 5. Nitrous oxide concentrations in an unprotected control (CTL) and under winter protective covers: a commercial impermeable cover on top of either curled wood shavings mat (CW-CC), 15 cm of straw mulch (SM-CC) or a felt material (FM-CC), a clear polyethylene cover on top of a curled wood shavings mat (CW-PC) at the Royal Québec (a) and Royal Montréal (b) experimental golf greens.

View this table: [in this window] [in a new window]   Table 3. Mean visual quality rating of golf green turfgrass immediately after winter protection removal in April 1998 and 1999 at the Royal Québec and Royal Montréal experimental sites.

The lethal temperature for 50% of the annual bluegrass plants (LT₅₀) was found to be as low as –20 to –25°C depending on the ecotypes (Dionne et al., 2001). These thresholds are considerably lower than the minimum temperatures observed in this study. LT₅₀ determination is an arbitrary test based on short-term exposures (few hours) of plants to progressively declining temperatures. However, Paquin et al. (1987) reported that damage to winterhardy plants can occur at temperatures markedly higher than their LT₅₀ when they were exposed to cold stress for periods of several days. This duration factor is likely responsible for the apparent discrepancy that exists between Dionne et al. (1999) observation of –10°C threshold for damage observed under field conditions and the significantly lower LT₅₀ that was subsequently documented (Dionne et al. 2001). Temperatures that were measured under winter protections in the current study did not reach the –10°C critical threshold and it is thus more likely that the slight reduction in visual quality observed on protected plots in the spring was caused by factors other than freezing temperatures.

Intergolf Greens Variations in Respiration Rate
Field observations during the 1997–1998 winter suggested that the rate of O₂ consumption by the golf greens under impermeable covers was not primarily controlled by soil temperature but was more likely affected by the nature of the turf and/or soil. Bertrand et al. (2001) estimated the relative contribution of plant and soil respiration under simulated winter conditions in Eastern Canada. They reported that soil microflora respiration near freezing point was two times greater than autotrophic respiration of several perennial plants in sealed enclosures. These results suggest that differences in atmospheric composition under impermeable covers may be linked to differences in soil characteristics between the Québec and Montréal sites. On golf courses, they also imply that certain greens could exhibit respiration rates greater than those that we observed at the Montréal site with associated higher risks of anoxic stress for the turfgrasses under impermeable covers. Consequently, we hypothesized that the impact of impermeable covers on O₂ consumption rates and associated anoxia-related damage, may vary from green to green, and that respiration on some greens could be greater than those observed at the Québec and Montréal sites. To test this hypothesis, two additional annual bluegrass greens were instrumented at the Royal Québec golf club during the 1998–1999 winter. Both greens had been protected by impermeable covers over straw mulch for more than 10 consecutive winters. The turfgrass of the first one always overwintered well (no damage, ND) while the second one had a history of recurrent winter damage (RD) that could not be related to freezing stress, excess water, or snow mold diseases. Several indices pointed towards anoxia as the main cause of damage on the RD green: extended affected surface not limited to poorly drained areas and strong odors typical of anoxic environments at the time of cover removal.

The differences in the evolution of gas concentrations between the two greens were striking (Fig. 6a ). The initial respiration rate (0–13 DAT) of the RD green (977 mg O₂ m^–2 d^–1) was more than four times greater than that of the ND green (224 mg O₂ m^–2 d^–1). As a result, the RD green consumed as much O₂ during the first 13 d following installation of covers as the ND green did during all winter. The occurrence of the N₂O peak only 20 DAT (Fig. 6b) indicates that anoxia conditions developed more rapidly than in 1997–1998 and 1998–1999 winters at the Montréal site (Fig. 5). Consequently, it can be assumed that the RD green was exposed to anoxic conditions for a much longer period than the ND and other greens previously tested in this study. When covers were removed at the end of winter, the ND green was healthy while the RD green was nearly completely dead with a strong smell typical of the volatile fatty acids produced during fermentation processes. The turfgrass on the RD green could have been killed by exposure to low redox potential induced by the rapid O₂ consumption. Under such conditions, volatile fatty acids are produced by anaerobic Clostridium bacteria and have been shown to be antagonistic of plant growth (Biwas et al., 2001; Brandsaeter et al., 2005). Accordingly, the accumulation of butyrate was shown to occur after ice encasement (Brandsaeter et al. 2005).

View larger version (23K): [in this window] [in a new window]   Fig. 6. Oxygen and CO2 (a) and N2O (b) concentrations under 15 cm of straw mulch covered by an impermeable commercial cover (SM-CC) installed on a green with a history of no winter damage (ND) and another green with history of recurrent damage (RD) at the Royal Québec golf club.

View larger version (25K): [in this window] [in a new window]   Fig. 7. Soil respiration rate and organic C content of five sand-based USGA and five native soil golf greens from the Royal Montréal golf club. Top soil mix (U-TS) used to build the USGA golf greens was also included as a comparison. Mean organic C content and respiration rates were significantly different (P < 0.001) between USGA-based and native soils.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

Golf course superintendents face a difficult situation when selecting the best management practices to ensure winter survival of recurrently damaged greens: Either they protect the greens with impermeable covers and expose the turfgrass to anoxia problems or they do not use covers and increase the risk of damage related to extreme subfreezing temperatures, excess water, and ice formation. Options to mitigate the negative impact of higher soil respiration rates on recurrently damaged greens include the rebuilding of the greens using sand-based USGA methodology and ventilating under protective covers during winter. Future research should aim at developing passive or active ventilation methods that could efficiently supply O₂ under the cover and withdraw CO₂ and other metabolic gases.

	ACKNOWLEDGMENTS

 
The authors thank Normand Bertrand, Marcellin Duval, Michel Tardif, Patrice Jolicoeur, and Guillaume Thibault for their excellent technical assistance. We also acknowledge the generous collaboration of the Royal Québec and Royal Montréal Golf Clubs and their superintendents, MM. Michel Tardif and Blake McMaster. This research was conducted through a collaborative research agreement between the Canadian Turfgrass Research Foundation and Agriculture and Agri-Food Canada Matching Investment Initiative program.

Received for publication May 17, 2005.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

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