Forest productivity under elevated CO 2 and O 3 : positive feedbacks to soil N cycling sustain decade‐long net primary productivity enhancement by CO 2

The accumulation of anthropogenic CO 2 in the Earth’s atmosphere, and hence the rate of climate warming, is sensitive to stimulation of plant growth by higher concentrations of atmospheric CO 2 . Here, we synthesise data from a field experiment in which three developing northern forest communities have been exposed to factorial combinations of elevated CO 2 and O 3 . Enhanced net primary productivity (NPP) ( c. 26% increase) under elevated CO 2 was sustained by greater root exploration of soil for growth‐limiting N, as well as more rapid rates of litter decomposition and microbial N release during decay. Despite initial declines in forest productivity under elevated O 3 , compensatory growth of O 3 ‐tolerant individuals resulted in equivalent NPP under ambient and elevated O 3 . After a decade, NPP has remained enhanced under elevated CO 2 and has recovered under elevated O 3 by mechanisms that remain un‐calibrated or not considered in coupled climate–biogeochemical models simulating interactions between the global C cycle and climate warming.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/88002/1/j.1461-0248.2011.01692.x.pd

Species-specific responses to atmospheric carbon dioxide and tropospheric ozone mediate changes in soil carbon

We repeatedly sampled the surface mineral soil (0–20 cm depth) in three northern temperate forest communities over an 11-year experimental fumigation to understand the effects of elevated carbon dioxide (CO 2 ) and/or elevated phyto-toxic ozone (O 3 ) on soil carbon (C). After 11 years, there was no significant main effect of CO 2 or O 3 on soil C. However, within the community containing only aspen ( Populus tremuloides Michx.), elevated CO 2 caused a significant decrease in soil C content. Together with the observations of increased litter inputs, this result strongly suggests accelerated decomposition under elevated CO 2. In addition, an initial reduction in the formation of new (fumigation-derived) soil C by O 3 under elevated CO 2 proved to be only a temporary effect, mirroring trends in fine root biomass. Our results contradict predictions of increased soil C under elevated CO 2 and decreased soil C under elevated O 3 and should be considered in models simulating the effects of Earth’s altered atmosphere.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78639/1/j.1461-0248.2009.01380.x.pd

Soil respiration in northern forests exposed to elevated atmospheric carbon dioxide and ozone

The aspen free-air CO 2 and O 3 enrichment (FACTS II–FACE) study in Rhinelander, Wisconsin, USA, is designed to understand the mechanisms by which young northern deciduous forest ecosystems respond to elevated atmospheric carbon dioxide (CO 2 ) and elevated tropospheric ozone (O 3 ) in a replicated, factorial, field experiment. Soil respiration is the second largest flux of carbon (C) in these ecosystems, and the objective of this study was to understand how soil respiration responded to the experimental treatments as these fast-growing stands of pure aspen and birch + aspen approached maximum leaf area. Rates of soil respiration were typically lowest in the elevated O 3 treatment. Elevated CO 2 significantly stimulated soil respiration (8–26%) compared to the control treatment in both community types over all three growing seasons. In years 6–7 of the experiment, the greatest rates of soil respiration occurred in the interaction treatment (CO 2  + O 3 ), and rates of soil respiration were 15–25% greater in this treatment than in the elevated CO 2 treatment, depending on year and community type. Two of the treatments, elevated CO 2 and elevated CO 2  + O 3 , were fumigated with 13 C-depleted CO 2 , and in these two treatments we used standard isotope mixing models to understand the proportions of new and old C in soil respiration. During the peak of the growing season, C fixed since the initiation of the experiment in 1998 (new C) accounted for 60–80% of total soil respiration. The isotope measurements independently confirmed that more new C was respired from the interaction treatment compared to the elevated CO 2 treatment. A period of low soil moisture late in the 2003 growing season resulted in soil respiration with an isotopic signature 4–6‰ enriched in 13 C compared to sample dates when the percentage soil moisture was higher. In 2004, an extended period of low soil moisture during August and early September, punctuated by a significant rainfall event, resulted in soil respiration that was temporarily 4–6‰ more depleted in 13 C. Up to 50% of the Earth’s forests will see elevated concentrations of both CO 2 and O 3 in the coming decades and these interacting atmospheric trace gases stimulated soil respiration in this study.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45867/1/442_2006_Article_381.pd

Fungal community composition and metabolism under elevated CO 2 and O 3

Atmospheric CO 2 and O 3 concentrations are increasing due to human activity and both trace gases have the potential to alter C cycling in forest ecosystems. Because soil microorganisms depend on plant litter as a source of energy for metabolism, changes in the amount or the biochemistry of plant litter produced under elevated CO 2 and O 3 could alter microbial community function and composition. Previously, we have observed that elevated CO 2 increased the microbial metabolism of cellulose and chitin, whereas elevated O 3 dampened this response. We hypothesized that this change in metabolism under CO 2 and O 3 enrichment would be accompanied by a concomitant change in fungal community composition. We tested our hypothesis at the free-air CO 2 and O 3 enrichment (FACE) experiment at Rhinelander, Wisconsin, in which Populus tremuloides , Betula papyrifera , and Acer saccharum were grown under factorial CO 2 and O 3 treatments. We employed extracellular enzyme analysis to assay microbial metabolism, phospholipid fatty acid (PLFA) analysis to determine changes in microbial community composition, and polymerase chain reaction–denaturing gradient gel electrophoresis (PCR–DGGE) to analyze the fungal community composition. The activities of 1,4-β-glucosidase (+37%) and 1,4,-β- N -acetylglucosaminidase (+84%) were significantly increased under elevated CO 2 , whereas 1,4-β-glucosidase activity (−25%) was significantly suppressed by elevated O 3 . There was no significant main effect of elevated CO 2 or O 3 on fungal relative abundance, as measured by PLFA. We identified 39 fungal taxonomic units from soil using DGGE, and found that O 3 enrichment significantly altered fungal community composition. We conclude that fungal metabolism is altered under elevated CO 2 and O 3 , and that there was a concomitant change in fungal community composition under elevated O 3 . Thus, changes in plant inputs to soil under elevated CO 2 and O 3 can propagate through the microbial food web to alter the cycling of C in soil.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47711/1/442_2005_Article_249.pd

Assessing the impacts of climate change and nitrogen deposition on Norway spruce (Picea abies L. Karst) growth in Austria with BIOME-BGC

The aim of this paper is to determine whether a detectable impact of climate change is apparent in Austrian forests. In regions of complex terrain such as most of Austria, climatic trends over the past 50 years show marked geographic variability. As climate is one of the key drivers of forest growth, a comparison of growth characteristics between regions with different trends in temperature and precipitation can give insights into the impact of climatic change on forests. This study uses data from several hundred climate recording stations, interpolated to measurement sites of the Austrian National Forest Inventory (NFI). Austria as a whole shows a warming trend over the past 50 years and little overall change in precipitation. The warming trends, however, vary considerably across certain regions and regional precipitation trends vary widely in both directions, which cancel out on the national scale These differences allow the delineation of \u27climatic change zones\u27 with internally consistent climatic trends that differ from other zones. This study applies the species-specific adaptation of the biogeochemical model BIOME-BGC to Norway spruce (Picea abies (L.) Karst) across a range of Austrian climatic change zones, using input data from a number of national databases. The relative influence of extant climate change on forest growth is quantified, and compared with the far greater impact of non-climatic factors. At the national scale, climate change is found to have negligible effect on Norway spruce productivity, due in part to opposing effects at the regional level. The magnitudes of the modeled non-climatic influences on aboveground woody biomass increment increases are consistent with previously reported values of 20-40kg of added stem carbon sequestration per kilogram of additional nitrogen deposition, while climate responses are of a magnitude difficult to detect in NFI data

Molecular analysis of the improvement in rachis quality by high CO2 levels in table grapes stored at low temperature

Rachis browning is one of the main factors reducing the quality of table grapes during storage at low temperature. To better understand the effect of a 3-day CO2 pretreatment (20% CO2 plus 20% O2) on maintaining the rachis quality of table grapes (Vitis vinifera cv. Cardinal) at 0°C, we analyzed the expression of genes codifying enzymes related to the synthesis and oxidation of phenolic compounds (phenylalanine ammonia-lyase, VcPAL; and polyphenol oxidase, GPO) and the detoxification of reactive oxygen species (catalase, GCAT; and ascorbate peroxidase, VcAPX) in rachis of treated and non-treated bunches. Furthermore, due to their role in senescence, the implication of ethylene and abscisic acid (ABA) was also investigated by studying the expression pattern of key regulatory genes for these hormones such as ACC synthase (ACS1) and oxidase (ACO1), VvNCED1 and 2. To determine whether these changes in gene expression were specifically related to rachis deterioration, their expression pattern in pulp and skin of treated and non-treated grapes were evaluated. The appearance of browning in non-treated rachis was associated with an increase in GPO and VcPAL mRNA levels, whereas high CO2 levels arrested this accumulation. In pulp, even though browning was not evident, a slight increase in GPO1 mRNA accumulation in non-treated bunches was detected. Moreover, lipid peroxidation level revealed lower oxidative stress in rachis of CO2-treated bunches than in non-treated ones, which seemed to be regulated by VcAPX and GCAT gene expression induction. This regulation was specific to rachis, showing a different pattern in pulp and skin. Regarding phytohormones, the effect of high CO2 levels reducing rachis browning seems to be linked to the modulation of ethylene biosynthesis genes. On the other hand, neither VvNCED1 nor VvNCED2 expression levels were altered in rachis, but NCED1 was induced specifically by low temperature in pulp. Overall, our results suggest a specific response of rachis to high levels of CO2 that could be related to the mitigation of rachis browning. © 2012 Elsevier B.V.Peer Reviewe

Key Indicators of Air Pollution and Climate Change Impacts at Forest Supersites

Untangling the complex effects that different air pollution and climate change factors cause to forest ecosystems is challenging. Supersites, that is, comprehensive measurement sites where research and monitoring of the whole soil–plant–atmosphere system can be carried out, are suggested as a refinement of the current monitoring and research efforts in Europe. This chapter identifies and discusses key measurements to be carried out at such supersites, with a focus on four topical subjects: the carbon, nitrogen, ozone and water budgets. This kind of holistic approach is vital to a realistic translation of the ongoing changes in climate and air quality into research on the impacts on forest ecosystems. Such an integrated effort requires a considerable use of resources at highly instrumented measurement sites and can only be achieved by building on existing infrastructures