The 2008 Joint Meeting of the Society for Range Management and the America Forage and Grassland Council. |
Tuesday, January 29, 2008
28
Plant Root Biomass and Respiration on Rangelands of South-Central North Dakota: Impact from 18 Years of Cattle Grazing
Xuejun Dong1, Jinzhi Wang2, Guojie Wang3, Danjun Wang2, Jinhui Wang4, Xueyan Zhao2, Bob Patton1, Shiping Wang4, and Paul Nyren1. (1) Central Grasslands Research Extension Center, North Dakota State University, Streeter, ND 58483, (2) Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, China, (3) Department of Animal and Range Sciences, North Dakota State University, Fargo, ND 58105, (4) Institute of Plateau Biology, Chinese Academy of Sciences, Xining, 810008, China
Quantifying belowground plant biomass and respiration is important for the evaluation of grassland carbon sequestration. Three moderately grazed (MG) (2.7 AUM ha-1 since 1989 with cattle) and three heavily grazed (HG) (6.9 AUM ha-1) pastures were used. In Aug. 2006, 48 soil samples, each from 0-15 cm deep and 25×25 cm2 in area, were collected. A computer re-sampling technique was used for significance test. Grazing had no effect on fine root (FR) density (p = 0.5), with 104 ± 10 g FR per m2 in 0-15 cm soil depth for the two treatments combined. However, HG marginally reduced the densities of coarse roots (CR) (p = 0.098) and rhizomes (RH) (p = 0.11). The CR density was 43 ± 10 g and 17 ± 4 g, and RH density was 20 ± 2 g and 11 ± 2 g for the MG and HG pastures, respectively. The 2006 drought might have resulted in similar FR density for the two treatments; the higher densities of CR and RH in the MG pastures could come from previous years’ growth and provide a potential for fast re-growth under favorable environments. Belowground plant biomass (0-2 m) was estimated as 3110 ± 404 kg ha-1 for MG and 2460 ± 295 kg ha-1 for HG in Aug. 2006. FR respiration for both the field-collected and barrel-grown roots of six species was measured using a gas exchange system in 2006 and 2007. The six species had similar respiration (without temperature acclimation), with a Q10 of 1.6 ± 0.1. The majority of the field roots had similar temperature response with a Q10 of 2.16 ± 0.26, however, 25% of the samples from the MG sites had a high Q10 (5 ± 1.57) and low nitrogen content (0.95%), suggesting a physiological vigor even during the 2006 summer drought.