HR: 10:50h
AN: B32B-03    [Abstracts]
TI: Productivity, Respiration, CO2 Sink Potential, and Light-Response Parameters of World Grasslands Derived From Flux-Tower Data Partitioning
AU: * Gilmanov, T G
EM: tagir.gilmanov@sdstate.edu
AF: South Dakota State University, SAG 304, Box 2207B, Brookings, SD 57007, United States
AU: contributors, W d
EM: tagir.gilmanov@sdstate.edu
AF: WORLDGRASSFLUX data set contributors, SAG 304, Box 2207B, Brookings, SD 57007, United States
AB: Net CO2 flux (Fc) data from 52 grassland flux tower sites in North America, Europe, and Asia representing 101 years of measurements were partitioned into gross primary productivity (Pg) and ecosystem respiration (Re) components using light-temperature-response functions method (Bas. Appl. Ecol. 2003, 4:167-183). This sample of sites encompasses a wide climatic range (mean annual temperatures 0.5 to 20° C and precipitation 190 to 1500 mm/yr) and includes unmanaged and extensively or intensively managed grasslands. Highest values of daily gross primary productivity (Pg,max = 64 g CO2/m2/d) were found in intensively managed grasslands of W. Europe with Atlantic climate, while lowest Pg,max (<10 g CO2/m2/d) were recorded in mixed prairies and shortgragss steppes of the Great Plains, shrubsteppes of the Intermountain West, and dry steppes of Mongolia. Maximum values of gross primary production (GPP) were achieved in intensively managed European grasslands with Atlantic climate (GPP=6900 g CO2/m2/yr), and lowest GPP values (<500 g CO2/m2/yr) were estimated for grazed mixed prairies under drought. Highest annual ecosystem respiration (RE) were recorded for warm-temperate and low montane W.European grasslands (RE > 5000 g CO2/m2/yr), and lowest RE were characteristic for shrubsteppes and grazed dry steppes (RE < 1000 g CO2/m2/yr). In 62 out of 101 site-years, the grasslands were net CO2 sinks, with average net annual CO2 exchange NEE = 250, maximum NEE = 2400 (uptake), and minimum NEE = –1350 g CO2/m2/yr (release). Maximum mean weekly values of the apparent quantum yield (α >70 mmol CO2/mol photons) were recorded in intensively managed Atlantic grasslands, the lowest weekly quantum efficiencies were observed in grazed mixed prairies of N.America and dry steppes of Central Asia (α <10 mmol/mol). The maximum values of the gross photosynthesis parameter (mean weekly Amax>2 mg CO2/m2/s) were estimated for intensively managed C3 grasslands of W.Europe and for unmanaged tallgrass (C3/C4) prairies. Maximum daytime respiration (rDay) were determined in intensively managed warm-temperate grasslands of W.Europe and E.North America (mean weekly rDay > 0.4 mg CO2/m2/s), while lowest rDay values are characteristic for semiarid mixed prairies and shrubsteppes (rDay<0.1 mg CO2/m2/s). Gross ecological light-use efficiency (ε=daily gross photosynthesis/daily income of photosynthetically active radiation) achieves maximum in intensively managed European grasslands with Atlantic climate (mean weekly ε >35 mmol/mol), and has lowest values in semiarid short- and mixed prairies and shrubsteppes of N. America and dry steppes of Central Asia (mean weekly ε <5 mmol/mol). Our data show significant allometric relationships between light-response parameters: α(Amax) and rDay(Amax), with allometry exponent <1 in both cases. Both the CO2 exchange characteristics (Pg,max, Re,max, GPP, RE, NEE), and the light-response parameters (α, Amax, rDay, ε) demonstrate significant relationships to climate (growing season length, sum of temperatures above 5° C, hydrologic year precipitation). These relationships become even stronger after stratification with respect to management (e.g., unmanaged vs. managed grasslands).
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0430 Computational methods and data processing
DE: 0434 Data sets
SC: Biogeosciences [B]
MN: 2007 Fall Meeting