Influence of phenology and land management on biosphere-atmosphere isotopic CO2 exchange

Abstract

Stable isotope and micrometeorological techniques have long been used to study carbon cycle dynamics at a variety of spatial and temporal scales. Combination of these techniques provide a powerful tool for gaining greater process information at the ecosystem and regional scales and can provide a meaningful way to scale processes from leaf to region. In this chapter we review the recent literature and examine the key processes influencing biosphere-atmosphere 13CO2 exchange. These processes are examined from the perspective of agricultural land management and rapid seasonal changes in phenology. Novel measurement techniques are introduced that can be used to better quantify the 13CO2 exchange between the biosphere and atmosphere to determine how ecosystem processes, land use modifications, and phenology impact the isotopic composition of the atmosphere (i.e. The atmospheric isotopic forcing associated with land surface processes). High temporal resolution isotope mixing ratio and flux measurements, based on tunable diode laser absorption spectroscopy, are presented. The results demonstrate that the isotopic composition of respiration at the ecosystem scale is strongly linked to plant assimilated carbon, which is dependent on plant metabolic physiology and growth phase. We review how this strong isotopic coupling between ecosystem respiration and photosynthesis can impact isotope-based flux partitioning of net ecosystem CO2 exchange, the variation in the canopy isotopic discrimination parameter, and the resulting isotopic forcing on the atmosphere. © 2009 Springer-Verlag New York.