Steffen M. Noe

Elevated atmospheric CO2 concentration leads to increased whole‐plant isoprene emission in hybrid aspen (Populus tremula × Populus tremuloides)

Effects of elevated atmospheric [CO2] on plant isoprene emissions are controversial. Relying on leaf-scale measurements, most models simulating isoprene emissions in future higher [CO2] atmospheres suggest reduced emission fluxes. However, combined effects of elevated [CO2] on leaf area growth, net assimilation and isoprene emission rates have rarely been studied on the canopy scale, but stimulation of leaf area growth may largely compensate for possible [CO2] inhibition reported at the leaf scale. This study tests the hypothesis that stimulated leaf area growth leads to increased canopy isoprene emission rates. We studied the dynamics of canopy growth, and net assimilation and isoprene emission rates in hybrid aspen (Populus tremula × Populus tremuloides) grown under 380 and 780 μmol mol(-1) [CO2]. A theoretical framework based on the Chapman-Richards function to model canopy growth and numerically compare the growth dynamics among ambient and elevated atmospheric [CO2]-grown plants was developed. Plants grown under elevated [CO2] had higher C : N ratio, and greater total leaf area, and canopy net assimilation and isoprene emission rates. During ontogeny, these key canopy characteristics developed faster and stabilized earlier under elevated [CO2]. However, on a leaf area basis, foliage physiological traits remained in a transient state over the whole experiment. These results demonstrate that canopy-scale dynamics importantly complements the leaf-scale processes, and that isoprene emissions may actually increase under higher [CO2] as a result of enhanced leaf area production.

Scaling BVOC Emissions from Leaf to Canopy and Landscape: How Different Are Predictions Based on Contrasting Emission Algorithms?

A variety of leaf-level models has been embedded in a canopy model and used to predict monoterpene emissions from canopies and landscapes, but there is no objective basis of choice between different models. Here we analysed the capacity of four leaf-level models and their variations, yielding altogether eight models, for predicting diurnal and seasonal variations in canopy monoterpene emissions. The main models tested were Guenther et al. model with fixed light and temperature dependencies or with optimally adjusted dependencies, two models linking emissions to foliage photosynthetic rate, one to electron transport rate (ETR model) and the other to gross assimilation rate (C-ratio model), and a dynamic model considering non-specific monoterpene storage in leaves. Once parameterized in a consistent manner, all models showed similarly high performance, assessed by explained variance, modelling efficiency and average model deviations for homogeneous canopies. Simulations suggested potentially stronger deviations for landscapes with fragmented vegetation. This analysis indicates that the choice among the models cannot be based on model validation statistics alone, but depends on whether only BVOC emissions need to be simulated (Guenther et al. model) or both photosynthesis and BVOC fluxes are needed (ETR or C-ratio model) or whether one needs data on night atmospheric reactivity (dynamic model).

SMEAR Estonia: Perspectives of a large-scale forest ecosystem – atmosphere research infrastructure

Abstract Establishment of the SMEAR Estonia at a hemiboreal mixed deciduous broad-leaved-evergreen needle-leaved forest at Järvselja, South-Eastern Estonia, has strongly enhanced the possibilities for national and international cooperation in the fields of forest ecosystem – atmosphere research and impacts of climatic changes on forest ecosystems, atmospheric trace gases, aerosols and air ions. The station provides a multitude of comprehensive continuously measured data covering key climatic and atmospheric characteristics (state and dynamics of solar radiation, trace gases, aerosols and air ions, meteorological parameters) and forest ecosystem traits (net primary productivity, individual tree growth, gas-exchange characteristics, soil variables). The station follows a multidisciplinary and multiscale approach covering processes in spatial dimensions ranging from nanometres to several hundred square kilometres, being thus able to significantly contribute to worldwide measurement networks and the SMEAR network. Here we present an overview of the station, its data produced and we envision future developments towards sustainable research and development of the large-scale scientific infrastructure SMEAR Estonia.

In-Canopy Turbulence—State of the Art and Potential Improvements

The turbulence within and immediately above a vegetation canopy is the driver of the exchange processes of heat, trace gases and particles between the soil, the plants and the atmosphere above.