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Methanol is the second most abundant volatile organic compound in the troposphereand plays a significant role in atmospheric chemistry. While there is consensus aboutthe dominant role of living plants as the major source and the reaction with OH asthe major sink of methanol, global methanol budgets diverge considerably in terms of source/sink estimates reflecting uncertainties in the approaches used to model,and the empirical data used to separately constrain these terms. Here we compiledmicrometeorological methanol flux data from eight different study sites and reviewedthe corresponding literature in order to provide a first cross-site synthesis of the ter-restrial ecosystem-scale methanol exchange and present an independent data-driven view of the land–atmosphere methanol exchange. Our study shows that the controls ofplant growth on the production, and thus the methanol emission magnitude, and stom-atal conductance on the hourly methanol emission variability, established at the leaflevel, hold across sites at the ecosystem-level. Unequivocal evidence for bi-directionalmethanol exchange at the ecosystem scale is presented. Deposition, which at some sites even exceeds methanol emissions, represents an emerging feature of ecosystem-scale measurements and is likely related to environmental factors favouring the forma-tion of surface wetness. Methanol may adsorb to or dissolve in this surface water andeventually be chemically or biologically removed from it. Management activities in agri-culture and forestry are shown to increase local methanol emission by orders of magnitude; they are however neglected at present in global budgets. While contemporarynet land methanol budgets are overall consistent with the grand mean of the microm-eteorological methanol flux measurements, we caution that the present approach ofsimulating methanol emission and deposition separately is prone to opposing system-atic errors and does not allow taking full advantage of the rich information content of micrometeorological flux measurements. ISSN:1680-7375 ISSN:1680-7367

We investigated the possibility of interspecific water transfer in an alfalfa (Medicago sativa L.) and maize (Zea mays L.) association. An alfalfa plant was grown through two vertically stacked plastic tubes. A 5 centimeter air gap between tubes was bridged by alfalfa roots. Five-week old maize plants with roots confined to the top tube were not watered, while associated alfalfa roots had free access to water in the bottom tube (the -/+ treatment). Additional treatments included: top and bottom tubes watered (+/+), top and bottom tubes droughted (-/-), and top tube droughted after removal of alfalfa root bridges and routine removal of alfalfa tillers (-(*)). Predawn leaf water potential of maize in the -/+ treatment fell to -1.5 megapascals 13 days after the start of drought; thereafter, predawn and midday potentials were maintained near -1.9 megapascals. Leaf water potentials of maize in the -/- and -(*) treatments declined steadily; all plants in these treatments were completely desiccated before day 50. High levels of tritium activity were detected in water extracted from both alfalfa and maize leaves after (3)H(2)O was injected into the bottom -/+ tube at day 70 or later. Maize in the -/+ treatment was able to survive an otherwise lethal period of drought by utilizing water lost by alfalfa roots.

Methanol is the second most abundant volatile organic compound in the troposphereand plays a significant role in atmospheric chemistry. While there is consensus aboutthe dominant role of living plants as the major source and the reaction with OH asthe major sink of methanol, global methanol budgets diverge considerably in terms of source/sink estimates reflecting uncertainties in the approaches used to model,and the empirical data used to separately constrain these terms. Here we compiledmicrometeorological methanol flux data from eight different study sites and reviewedthe corresponding literature in order to provide a first cross-site synthesis of the ter-restrial ecosystem-scale methanol exchange and present an independent data-driven view of the land–atmosphere methanol exchange. Our study shows that the controls ofplant growth on the production, and thus the methanol emission magnitude, and stom-atal conductance on the hourly methanol emission variability, established at the leaflevel, hold across sites at the ecosystem-level. Unequivocal evidence for bi-directionalmethanol exchange at the ecosystem scale is presented. Deposition, which at some sites even exceeds methanol emissions, represents an emerging feature of ecosystem-scale measurements and is likely related to environmental factors favouring the forma-tion of surface wetness. Methanol may adsorb to or dissolve in this surface water andeventually be chemically or biologically removed from it. Management activities in agri-culture and forestry are shown to increase local methanol emission by orders of magnitude; they are however neglected at present in global budgets. While contemporarynet land methanol budgets are overall consistent with the grand mean of the microm-eteorological methanol flux measurements, we caution that the present approach ofsimulating methanol emission and deposition separately is prone to opposing system-atic errors and does not allow taking full advantage of the rich information content of micrometeorological flux measurements., Atmospheric Chemistry and Physics Discussions, 15, ISSN:1680-7375, ISSN:1680-7367

Methanol is the second most abundant volatile organic compound in the troposphere and plays a significant role in atmospheric chemistry. While there is consensus about the dominant role of living plants as the major source and the reaction with OH as the major sink of methanol, global methanol budgets diverge considerably in terms of source/sink estimates, reflecting uncertainties in the approaches used to model and the empirical data used to separately constrain these terms. Here we compiled micrometeorological methanol flux data from eight different study sites and reviewed the corresponding literature in order to provide a first cross-site synthesis of the terrestrial ecosystem-scale methanol exchange and present an independent data-driven view of the land–atmosphere methanol exchange. Our study shows that the controls of plant growth on production, and thus the methanol emission magnitude, as well as stomatal conductance on the hourly methanol emission variability, established at the leaf level, hold across sites at the ecosystem level. Unequivocal evidence for bi-directional methanol exchange at the ecosystem scale is presented. Deposition, which at some sites even exceeds methanol emissions, represents an emerging feature of ecosystem-scale measurements and is likely related to environmental factors favouring the formation of surface wetness. Methanol may adsorb to or dissolve in this surface water and eventually be chemically or biologically removed from it. Management activities in agriculture and forestry are shown to increase local methanol emission by orders of magnitude; however, they are neglected at present in global budgets. While contemporary net land methanol budgets are overall consistent with the grand mean of the micrometeorological methanol flux measurements, we caution that the present approach of simulating methanol emission and deposition separately is prone to opposing systematic errors and does not allow for full advantage to be taken of the rich information content of micrometeorological flux measurements., Atmospheric Chemistry and Physics, 15 (13), ISSN:1680-7375, ISSN:1680-7367