Partitioning of ecosystem respiration in winter wheat and silage maize—modeling seasonal temperature effects

Publication Type

Journal contribution (peer reviewed)

Authors

Demyan, M.S., Ingwersen, J., Nkwain Funkuin, Y., Ali, R.S., Mirzaeitalarposhti, R., Rasche, F., Poll, C., Müller, T., Streck, T., Kandeler, E., Cadisch, G.

Year of publication

2016

Published in

Agriculture, Ecosystems and Environment

Band/Volume

224/

DOI

10.1016/j.agee.2016.03.039

Page (from - to)

131-144

The response of agroecosystem carbon (C) respiration fluxes to environmental changes needs to be better understood as respiration subcomponents may respond differently to management and seasonal weather dynamics, which is important for soil organic matter (SOM) modeling. Respiration measurements at two different spatial and temporal scales (eddy covariance (EC) and soil chambers) were used to ascertain the relationship between temperature and CO₂ flux of different ecosystem respiration components (ecosystem (R_eco), soil and root combined, and soil). Further, different model approaches (static versus dynamic reference CO₂ rate (r_b) and activation energy type parameter (E₀) with an Arrhenius-like function) in order to partition R_eco into above- and belowground autotrophic (R_{A_above}, R_{A_below}) and heterotrophic respiration (R_{H_SOM}) were tested. Canopy level CO₂ fluxes in winter wheat and silage maize were measured by EC stations and soil surface CO₂ flux by a handheld chamber analyzer in arable fields in Southwest Germany over a period of three growing seasons (2009, 2010, and 2012). Additionally, successive bare fallow plots were installed at the beginning of each growing season to partition soil respiration between autotrophic and heterotrophic sources (including “labile” soil C (newest bare fallow) as the difference to the oldest bare fallow). Stepwise model building was tested with keeping r_b and E₀ constant (static method) and then by varying r_b and E₀ each individually or together by time period (dynamic method) over the whole growing season (15, 10 or 7 days for R_eco, measurement periods for soil chamber measurements). The dynamic models were superior as measured by Aaike Information Criteria (AIC) and coefficient of determination (average R², 0.15 for the static model and 0.50 for the dynamic model). In the best fitting model for each crop-year (lowest AIC), r_b was successfully estimated in each time period (relative standard error E₀ estimates were found in half of the crop years. Estimated Q₁₀ values were between 1 to 6.01 between different components and seasons. Estimated R_eco components during 2012, autotrophic above ground respiration accounted for the largest component during the intense measurement periods under both winter wheat (50%) and maize (60%), with root respiration accounting for 19% and 21%, respectively. Additionally under winter wheat 31% of R_eco was estimated as heterotrophic respiration, with 15% from labile soil C. The results highlight the need to apply individual temperature response functions when using temperature as a driving force for ecosystem respiration components (autotrophic and soil heterotrophic).