Diurnal, seasonal and annual variation in net ecosystem CO₂ exchange of an alpine shrubland on Qinghai‐Tibetan plateau

Abstract

Thus far, grassland ecosystem research has mainly been focused on low-lying grassland areas, whereas research on high-altitude grassland areas, especially on the carbon budget of remote areas like the Qinghai-Tibetan plateau is insufficient. To address this issue, flux of CO 2 were measured over an alpine shrubland ecosystem (37136 0 N, 101118 0 E; 3250 m above sea level [a. s. l.]) on the Qinghai-Tibetan Plateau, China, for 2 years (2003 and 2004) with the eddy covariance method. The vegetation is dominated by formation Potentilla fruticosa L. The soil is Mol-Cryic Cambisols. To interpret the biotic and abiotic factors that modulate CO 2 flux over the course of a year we decomposed net ecosystem CO 2 exchange (NEE) into its constituent components, and ecosystem respiration (R eco ). Results showed that seasonal trends of annual total biomass and NEE followed closely the change in leaf area index. Integrated NEE were À58.5 and À75.5 g C m À2 , respectively, for the 2003 and 2004 years. Carbon uptake was mainly attributed from June, July, August, and September of the growing season. In July, NEE reached seasonal peaks of similar magnitude (4-5 g C m À2 day À1 ) each of the 2 years. Also, the integrated night-time NEE reached comparable peak values (1.5-2 g C m À2 day À1) in the 2 years of study. Despite the large difference in time between carbon uptake and release (carbon uptake time o release time), the alpine shrubland was carbon sink. This is probably because the ecosystem respiration at our site was confined significantly by low temperature and small biomass and large day/night temperature difference and usually soil moisture was not limiting factor for carbon uptake. In general, R eco was an exponential function of soil temperature, but with season-dependent values of Q 10 . The temperature-dependent respiration model failed immediately after rain events, when large pulses of R eco were observed. Thus, for this alpine shrubland in Qinghai-Tibetan plateau, the timing of rain events had more impact than the total amount of precipitation on ecosystem R eco and NEE.

Assessing MODIS GPP in Non-Forested Biomes in Water Limited Areas Using EC Tower Data

“…For the two sites located in shrublands (USSO4 and USKS2) water limitation might have played a role, since the overestimation was much larger for the site located in a water-limited area (USSO4) compared to non-water limited areas. This overestimation by GPPm could be attributed to the fact that the DAO meteorology used by the MOD17 algorithm underestimates local VPD in many waterlimited sites during the summer, and therefore photosynthesis is not sufficiently constrained when calculating GPPm for dry periods in North America [13,42]. This result agrees with [13], who found a similar overestimation of 67% for an open shrubland site in a dry area.…”

A study of soil-dynamics based on a simulated drought in an alpine meadow on the Tibetan Plateau

“…Some studies have revealed the stability of soil processes underground in a drought experiment, semiarid soil microbiological parameters including microbial biomass and extracellular enzyme activities showing a sufficient resistance and a rapid recovery after soil rewetting (Hueso et al 2011). So far, most studies that simulated drought events have been done in semiarid and Mediterranean region (De Boeck et al 2011;Godfree et al 2011;Jentsch et al 2011;Jimenez et al 2011;Penuelas et al 2007;Rich et al 2008), but not on the Tibetan Plateau , where the unique geography yields relatively high vegetation growth with concentrated rainfall during the growing season, but overall very slow soil organic matter decomposition rates during dry cold winters (Kato et al 2006;Zhao et al 2006).…”

Application of a mass consistent flow model to study the CO2 mass balance of forests

“…Goulden et al, 1996;Suyker et al, 2005;Moureaux et al, 2006;Zhao et al, 2006); and (ii) the "correction approach", based on a direct estimation of all the CO 2 balance terms, including the advection terms (e.g. Aubinet et al, 2003Aubinet et al, , 2005Feigenwinter et al, 2004;Staebler and Fitzjarrald, 2004;Marcolla et al, 2005;Sun et al, 2007;Yi et al, 2008;Montagnani et al, 2009).…”