Importance of changing CO₂, temperature, precipitation, and ozone on carbon and water cycles of an upland‐oak forest: incorporating experimental results into model simulations

Abstract

Observed responses of upland-oak vegetation of the eastern deciduous hardwood forest to changing CO 2 , temperature, precipitation and tropospheric ozone (O 3 ) were derived from field studies and interpreted with a stand-level model for an 11-year range of environmental variation upon which scenarios of future environmental change were imposed. Scenarios for the year 2100 included elevated [CO 2 ] and [O 3 ] ( 1 385 ppm and 1 20 ppb, respectively), warming ( 1 4 1C), and increased winter precipitation ( 1 20% November-March). Simulations were run with and without adjustments for experimentally observed physiological and biomass adjustments.Initial simplistic model runs for single-factor changes in CO 2 and temperature predicted substantial increases ( 1 191% or 508 g C m À2 yr À1 ) or decreases (À206% or À549 g C m À2 yr À1 ), respectively, in mean annual net ecosystem carbon exchange (NEE a % 266 AE 23 g C m À2 yr À1 from 1993 to 2003). Conversely, single-factor changes in precipitation or O 3 had comparatively small effects on NEE a (0% and À35%, respectively). The combined influence of all four environmental changes yielded a 29% reduction in mean annual NEE a . These results suggested that future CO 2 -induced enhancements of gross photosynthesis would be largely offset by temperature-induced increases in respiration, exacerbation of water deficits, and O 3 -induced reductions in photosynthesis. However, when experimentally observed physiological adjustments were included in the simulations (e.g. acclimation of leaf respiration to warming), the combined influence of the year 2100 scenario resulted in a 20% increase in NEE a not a decrease. Consistent with the annual model's predictions, simulations with a forest succession model run for gradually changing conditions from 2000 to 2100 indicated an 11% increase in stand wood biomass in the future compared with current conditions. These model-based analyses identify critical areas of uncertainty for multivariate predictions of future ecosystem response, and underscore the importance of long term field experiments for the evaluation of acclimation and growth under complex environmental scenarios.

Timing of climate variability and grassland productivity

“…The majority of the grass biomass in watershed 1D at Konza is produced by a few C 4 grass species (44); future research would need to compare the physiology of a range of grass species with different evolutionary histories to test this possibility. Likewise, although other studies have quantified the seasonal sensitivity of aspects of plant productivity to precipitation (14,15,45), more research in other sites will be necessary to understand the geographic patterns of seasonal sensitivity to climate.…”

“…However, most climate variability would not be considered extreme and occurs on much shorter time scales throughout the growing season with temperature and precipitation frequently disassociated. The response of ecosystems to short-term climate variability at different times of year is thought to vary (11)(12)(13)(14)(15)(16)), but we know little about how the timing of short-duration climate variability impacts key ecosystem dynamics such as plant productivity.…”

Consequences of Climate Warming and Altered Precipitation Patterns for Plant-Insect and Multitrophic Interactions

“…respiration and photosynthesis) influencing plant growth are also temperature sensitive, but differentially so, both among species and plant functional groups (Tjoelker et al, 1999;Hanson et al, 2005;Rennenberg et al, 2006;Wang et al, 2012). Net photosynthesis (primary production) typically peaks within the range of normally experienced temperatures (Kirschbaum, 2000;Berggren et al, 2009), which as described in the following section, is a key difference with respect to insect herbivores.…”

The effect of climate on the net primary productivity (NPP) of Pinus koraiensis in the Changbai Mountains over the past 50 years

“…Controlled experiments and long-term observations can be helpful for understanding the responses of plants to global change. A 14-year controlled multifactor experiment was carried out in a temperate deciduous forest in the eastern part of the U.S. state of Tennessee (Hanson et al 2005). These authors found that a change in precipitation considerably influenced the physiological adjustments of trees and resulted in a change in leaf biomass.…”