Golf Course Management

DEC 2012

Golf Course Management magazine is dedicated to advancing the golf course superintendent profession and helping GCSAA members achieve career success.

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research Managing thatch with fungal laccase In greenhouse studies, nine months of laccase applications significantly reduced thatch in creeping bentgrass maintained at putting green height. High organic matter accumulation in the form This research was funded in part by the Environmental Institute for Golf. of thatch or mat is one of the major problems in modern turfgrass greens. Thatch is a layer of organic matter containing tightly intermingled living and dead plant tissue that accumulates between the soil and green turfgrass. It con- sists of stolons, rhizomes, roots, leaf sheaths and blades (5). Thatch accumulation causes problems like decreased movement of oxygen through the thatch or mat zone, decreased saturated hydraulic conductivity and increased water retention (3,6). These primary problems may lead to secondary problems like wet wilt, a soft surface, black layer, limited rooting and extra-and intra-cellular freez- ing damage (4,8). The major problems in the thatch or mat layer are excessive accumulation of organic matter over time and the rapid change from the nature of the structured organic matter seen in live plant root tissues to the unstructured organic matter in dead root tissues. A high density of living roots near the soil surface may adversely affect the soil's physi- cal properties. However, a more serious problem is rapid root death in summer, which creates dead gelatinous organic matter that swells in the pres- ence of water during decomposition and plugs the soil macropores (air-filled pores), causing low oxy- gen levels in the root zones (4,8). High organic matter accumulation occurs Sudeep S. Sidhu, Ph.D. Qingguo Huang, Ph.D. Robert N. Carrow, Ph.D. Paul L. Raymer, Ph.D. 84 GCM December 2012 when organic matter degrades more slowly than it accumulates. It is believed that rate of degrada- tion of organic matter is related to the presence of lignin content in the organic residue. Lignin is an abundant source of carbon second only to cel- lulose and acts as a protective physical matrix that makes readily decomposable cellulosic and hemi- cellulosic sugars unavailable for microbial degra- dation. Lignin is extremely resistant to degrada- tion because it has a complex structure derived from oxidative coupling of lignin monomers that limits microbial degradation of organic matter (7). For this reason, turfgrass species high in lig- nin content are resistant to decomposition (2). We studied the use of fungal laccase, a ligno- lytic enzyme, for enhancing the rate of organic matter degradation in thatch layer. Oxidative enzymes such as laccases produced by white rot fungi are recognized for their ability to attack the aromatic components of lignin and lead to its effective degradation (1). Materials and methods A greenhouse experiment was established at the University of Georgia's Griffin Campus using Crenshaw creeping bentgrass (Agrostis stolonifera) acquired from East Lake Country Club, Atlanta. The sod, which was approximately 1.18 inch (3 centimeters) thick and consisted of existing thatch and mat but not the underlying soil, was cut to fit the pots and placed on the 85:15 sand and organic matter mix. All the pots were irrigated daily, fertil- ized monthly with a 1.7-fluid-ounce (50-milliliter) solution of 0.4% (w/v) Macron water-soluble 28-7- 14 fertilizer, and maintained at a height of 0.24 inch (0.6 centimeter). The refrigerated air-condi- tioned greenhouse was maintained at 77±4/64± 4 F (25±2/18 ±2 C) day/night temperature. The experimental design was a randomized complete block design with five replications. The treatment design was a 4 × 2 factorial with all combinations of four levels of laccase and two levels of guaiacol, a compound that may enhance laccase activity. The four levels of laccase were 0 (control), 0.206, 2.06 and 20.6 units/square cen- timeter and the two levels of guaiacol were 0 (con- trol) and 0.1 Molar solution. After two months,

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