Yaling Qian

Carbon Dynamics and Sequestration in Urban Turfgrass Ecosystems

Urbanization is a global trend. Turfgrass covers 1.9% of land in the continental US, occupying about 16 million ha. In this article, we review existing literature associated with carbon (C) pools, sequestration, and nitrous oxide emission of urban turfgrass ecosystems. Turfgrasses exhibit significant carbon sequestration (0.34–1.4 Mg ha−1 year−1) during the first 25–30 years after turf establishment. Several studies have reported that residential turfgrass soil can store up to twofold higher soil organic carbon (SOC) content than agricultural soils. Published research suggests that the dynamics of nitrogen (N) is controlled by C transformation. Turfgrass areas have high levels of SOC and microbial biomass creating a carbon-based “sink” for inorganic N. Therefore, lower than “expected” nitrate leaching and N2O emissions have been measured in the majority of the experiments carried out for turfgrass ecosystems. Increased SOC in turfgrass soil can result from: (1) returning and recycling clippings, (2) appropriate and efficient-fertilizer use, and (3) irrigation based on turfgrass needs. Some turfgrass management practices (such as fertilization, mowing, and irrigation) carry a carbon “cost”. Therefore turfgrass’s contribution to a sink for carbon in soils must be discounted by fuel and energy expenses and fertilizer uses in maintaining turf, and the flux of N2O. More work is needed to evaluate the carbon sequestration, total carbon budget, and fluxes of the other greenhouse gases in turfgrass systems.

Leachability of chemical constituents in soil–plant systems irrigated with synthetic graywater.

Over recent years, reuse of graywater for irrigation has become increasingly widespread internationally. While this practice is rapidly growing, there remain unanswered questions with respect to impacts to environmental quality and human health. The objective of this research was to determine the leachability of graywater constituents after applied to soil through a set of controlled greenhouse experiments. Four plant species including bermudagrass, tall fescue, Meyer Lemon and Emerald Gaiety Euonymus were included in the study. Three replicate columns for each species were set up and irrigated either with synthetic graywater or potable water for a 17 month duration. Leachate quality was assessed for dissolved organic carbon, nitrate, ammonium, total phosphorous, boron, sodium adsorption ratio, conductivity, surfactants, and total dissolved solids. The same constituents and also organic matter were measured in soil samples collected at the end of experiments. Phosphorus did not leach through the 50 cm deep soil columns. Salts, including boron, showed potential to leach through graywater irrigated soil. A portion of the applied nitrogen was assimilated by plants, but leaching of nitrogen was still observed as documented by statistically higher nitrogen in leachate collected from graywater-irrigated columns compared to potable water-irrigated columns (P ≤ 0.05). A low percentage of surfactants added to columns leached through (7 ± 6% on average) and a mass balance on surfactant parent compounds showed that 92–96% of added surfactants were biodegraded.

First Report of Brown Stripe of Saltgrass Caused by Bipolaris heveae in Colorado

Inland saltgrass (Distichlis spicata var. stricta (L.) Greene) is indigenous to western North America and Australia and is a dioecious, rhizomatous, perennial, warm-season grass. It is commonly found in areas where salinity, alkalinity, and drought have eliminated many other types of vegetation (1). It has potential for revegetation of mine spoils or use along roadsides (2). During September 2004, multiple lenticular, brown lesions were observed on leaves of saltgrass accession no. 1023 at the Horticulture Field Research Center, Colorado State University, Fort Collins. Segments of symptomatic leaf tissue were surface sterilized in 0.5% sodium hypochlorite and placed on one-quarter-strength potato dextrose agar and incubated at 25°C in the dark. Dark green fungal colonies with aerial mycelium consistently grew on the medium. Slightly curved, ellipsoidal, pale-to-golden brown, smooth conidia 46 to 80 μm long and 13 to 17 μm wide (average 64.5 × 14.7 μm) with 6 to 9 septations formed after 7 days in cultures grown on V8 juice agar. The morphology and bipolar germination of conidia was consistent with the genus Bipolaris, however, conidia were often shorter than previously reported (3). The rDNA internal transcribed spacer (ITS) regions of one isolate were amplified using polymerase chain reaction (PCR) with universal fungal rDNA primers ITS1 and ITS4. PCR products were sequenced (555 bp) and exhibited 99% nucleotide identity to Bipolaris heveae isolates collected from zoysiagrass and bermudagrass in Japan (3) and rubber in Nigeria (4). To confirm pathogenicity, a suspension of 104 conidia per ml of water containing 0.1% Tween 20 was sprayed on saltgrass leaves to runoff. Plants were covered with transparent plastic bags and incubated at 25°C in the dark. After 72 h, the bags were removed and plants were placed in the greenhouse. Brown stripe symptoms were observed on all plants after 7 days, and B. heveae was consistently isolated from symptomatic tissue. To our knowledge, this is the first report of brown stripe on inland saltgrass caused by B. heveae. References: (1) D. J. Hansen et al. Am. J. Bot. 63:635, 1976. (2) K. A. Pavlicek et al. J. Range Manag. 30:377, 1977. (3) T. Tsukiboshi et al. Mycoscience 46:17, 2005. (4) G. Zhang and M. L. Berbee. Mycologia 93:1048, 2001.