Ecosystem respiration and its components from a Carex meadow of Poyang Lake during the drawdown period

Abstract

h i g h l i g h t sEcosystem respiration and its components were mainly controlled by temperature. Q 10 values varied widely with time and among ecosystem respiratory components. Summer flood duration could largely alter drawdown period carbon sink intensity. a r t i c l e i n f o a b s t r a c tLittle is known about the components of ecosystem respiration from a subtropical littoral wetland with dramatic annual inundation dynamics. In this study, we investigated ecosystem respiration and its components in a Poyang lake Carex meadow during the drawdown periods from May 2009 to June 2011. Both ecosystem respiration and its components showed clear temporal variation pattern, with temperature being the dominant control. Ecosystem respiration ranged from 98.01 to 1359.25 mg CO 2 m À2 h À1. Shoot and root respiration contributed approximately 36% and 26% to the ecosystem respiration, respectively, whereas microbial respiration accounted for 38% of the ecosystem respiration. The ratio of total soil respiration to ecosystem respiration varied from 0.45 to 0.90, depending on growing season stages. Their Q 10 values ranged from 1.72 to 2.51, with the maximum for shoot respiration and the minimum for microbial respiration. In addition, the Q 10 values varied with time and among ecosystem respiratory components and hence could not be treated as a constant. None of the respiration measurements was significantly related to soil moisture, suggesting that soil moisture was not a limiting environmental factor for respiratory activity during the drawdown periods in this meadow. The Carex meadow acted as strong carbon sink during the drawdown periods due to double growing seasons, but the previous summer flood duration could substantially alter carbon sink intensity in the following drawdown period. The total carbon sink of the littoral zone of Poyang Lake during drawdown periods was estimated to be 0.17e0.59 Tg C yr À1.

Plant-mediated methane and nitrous oxide fluxes from a carex meadow in Poyang Lake during drawdown periods

“…Therefore, we used CH 4 and N 2 O flux data from the RE treatment measured after February 2010 to determine the effects of root exclusion on the fluxes, because we found the effects of decomposing roots could be negligible after about 9 months when the trenching plots were completed. The CO 2 efflux rate ratio of the RE treatment to the SC treatment declined substantially from the previous average of 0.86 to 0.60 in March 2010, and the latter ratio (i.e., the contribution of soil microbial respiration to total soil respiration) was consistent with previous studies and was maintained in the following flux measurement days (Hu et al 2015). …”

“…NPP was estimated as the sum of the above-ground and below-ground NPP, and NEP was calculated as the difference between NPP and the total soil C emission as heterotrophic respiration, which was published in Hu et al (2015) ( Table 1). To correlate with plant biomass, GHG fluxes measured at the dates of plant samplings (n = 18) were used.…”

“…The long dash, dotted and solid regression lines were used for IP, SC and RE treatments, respectively decomposing roots may not be eliminated, it should be less important with time (Ewel et al 1987;Bowden et al 1993;Hanson et al 2000;Zhou et al 2007). According to our previous study (Hu et al 2015), the effects of decomposing roots on soil CO 2 efflux are almost negligible after 9 months when the trenching plots were completed. Thus, root exclusion significantly decreased the CH 4 flux rate compared to the control treatment (t = 3.0, P < 0.01) when flux data measured after February 2010 was used for the comparison.…”

“…Annual drawdown periods are largely dependent on both local precipitation and the hydrologic regime of the Yangtze River, ranging from 165 to 271 days (Liu et al 2006;Hu et al 2010 (Hu et al 2010). More details of this Carex meadow are described in Hu et al (2015).…”

“…Quantifying GHG fluxes from Carex meadows during drawdown periods will help to advance the understanding of biogeochemical processes in response to ongoing climate warming and hydrological change in this large subtropical lake. We have reported ecosystem respiration and its components in a Carex meadow during the drawdown period in a recent study (Hu et al 2015). In this study, we evaluated CH 4 and N 2 O emissions during drawdown periods, and aimed to determine the effects of above-ground and below-ground compartments of Carex on CH 4 and N 2 O fluxes through shoot clipping and root exclusion.…”