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LI-6400XT Literature: Customer Application Articles

Global climate change research at the University of Michigan Biological Station

Global Climate Change research is a collaborative effort between scientists from all around the world. A number of networks(i.e., Ameriflux, Asiaflux, Carboeurope) have been established to coordinate data gathering and interpretation. An increasing number of research sites have emerged in all continents. Dr. Peter S. Curtis of The Ohio State University and colleagues from various other universities conduct their research at such sites.

6400 Custom Chamber 6400-09 in the snow 6400-09 in use

At the University of Michigan Biological Station, located in northern Lower Michigan, Dr. Curtis and colleagues use a variety of LI-COR instruments. Since 1998, a 46 m tower has been used for micrometeorological studies and, among other, direct measurements of the concentration and fluxes of carbon dioxide and water vapor at two levels above the canopy using the LI-6262 CO2/H2O Gas Analyzer. Carbon budget is also studied with a combination of tree growth and gas exchange measurements. The LAI-2000 Plant Canopy Analyzer is used to measure leaf area index in 60 m plots and the LI-6400 Portable Photosynthesis System for stem and leaf respiration studies using standard leaf or custom stem cuvettes (below).

The 6400-09 Soil CO2 Flux Chamber has also been used with the LI-6400 System for soil CO2 respiration studies. Periodic measurements were made within a defined flux area. Linear interpolation was used between measurement points to yield annual flux estimates.

In addition, since the beginning of the 1999 growing season, the 6400-09 Soil CO2 Flux Chamber and the LI-6400 System were used to conduct a soil trenching study to partition soil respiration into CO2 lost via the rhizosphere (live roots and soil affected by live roots) versus the non-rhizosphere. Two treatment groups were established: 'control' (rhizosphere + non-rhizosphere respiration) and 'no-roots' (non-rhizosphere respiration). Treatments were achieved by inserting 10 cm diameter polyvinyl chloride tubes into the forest soil. The 'control' tubes were inserted 1 cm into the soil so that living roots were not severed. The 'no-roots' tubes (1 m in length) were inserted 100 cm into the soil to sever all roots within the soil column. Following tube insertion, respiration rates from each soil column were measured weekly during the 1999 growing season. Dr. Curtis and his colleagues calculated the relative contributions of the rhizosphere and non-rhizosphere to total soil respiration by mass balance as, pRnr = Rnr/Rtotal, and pRr = 1- pRnr, where pRnr is the proportion of non-rhizosphere respired CO2, Rnr is the respiratory flux from the no-roots collars, Rtotal is the respiratory flux from the control roots collars, and pRr is the proportion of rhizosphere respired CO2. In addition, empirical models were developed for predicting daily-integrated soil, rhizosphere and non-rhizosphere respiratory carbon losses.

Dr. Curtis and his colleagues concluded that seasonal patterns in rhizosphere and non-rhizosphere fluxes are similar to total soil CO2 fluxes. During the growing season, the non-rhizosphere contributes ~55-60% of total soil respiration. In the fall, non-rhizosphere contributions increase to ~90%, as rhizosphere fluxes become minimal during the winter. As a result of root severing from the trenching, enhanced respiration in the non-rhizosphere tubes occurs mainly within 28 days following insertion.

References

  1. Curtis, P.S., P.J. Hanson, P. Bolstad, C. Barford, J.C. Randolph, H.P. Schmid, K.B. Wilson. Biometric and eddy-covariance based estimates of ecosystem carbon storage in five eastern North American deciduous forests. Agricultural and Forest Meteorology (in press).

  2. Davidson, E.A., K. Savage, P. Bolstad, D.A. Clark, P.S. Curtis, D.S. Ellsworth, P.J. Hanson, B.E. Law, Y. Luo, K.S. Pregitzer, J.C. Randolph, D. Zak. Belowground carbon allocation in forests estimated from litter fall and IRGA-based soil respiration measurements. Agricultural and Forest Meteorology (in press).


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