Quantification of ozone uptake at the stand level in a Pinus canariensis forest in Tenerife, Canary Islands: An approach based on sap flow measurements [An article from: Environmental Pollution]

This digital document is a journal article from Environmental Pollution, published by Elsevier in 2006. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.

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Ozone uptake was studied in a pine forest in Tenerife, Canary Islands, an ecotone with strong seasonal changes in climate. Ambient ozone concentration showed a pronounced seasonal course with high concentrations during the dry and warm period and low concentrations during the wet and cold season. Ozone uptake by contrast showed no clear seasonal trend. This is because canopy conductance significantly decreased with soil water availability and vapour pressure deficit. Mean daily ozone uptake averaged 1.9nmolm^-^2s^-^1 during the wet and cold season, and 1.5nmolm^-^2s^-^1 during the warm and dry period. The corresponding daily mean ambient ozone concentrations were 42 and 51nll^-^1, respectively. Thus we conclude that in Mediterranean type forest ecosystems the flux based approach is more capable for risk assessment than an external, concentration based approach.

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Effects of xylem sap flow on carbon dioxide efflux from stems of birch (Betula pendula Roth) [An article from: Flora]

This digital document is a journal article from Flora, published by Elsevier in . The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.

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The effect of xylem sap flow in stems of mature Betula pendula Roth on radial CO"2 efflux was studied from April to October 2001. Temperature-controlled respiration cuvettes allowed measurements of CO"2 efflux without interference from temperature gradients between stem surface and sapwood. Variations of sap flow in different stem sectors, and in a given sector at different heights were analysed. Daytime reduction of CO"2 efflux caused by sap flow was expressed as the difference between gross and apparent CO"2 release. Gross CO"2 release was calculated from Arrhenius-equations derived from night-time data records of the same day, which were free from interference by sap flow. In mid-July, daytime reductions of CO"2 efflux reached 1.8-3.9@mmol CO"2m^-^2g^-^1 xylem sap transpired. Assuming tree-specific maximum transpiration rates of 30kg H"2Od^-^1 this is up to 40% of gross CO"2 release. In relation to photosynthetic CO"2 fixation the endogenous supply of dissolved CO"2 to the leaves acccounted for 0.5-3.7%. This study indicates a negative correlation between sap flow velocity and radial CO"2 efflux from B. pendula stems. Periods of unbalanced CO"2 partial pressures between aqueous and gaseous pathways during increase and decrease of sap flow seem to affect gaseous CO"2 release through lenticels. It is concluded that CO"2 efflux rates are not simply equivalent to respiration rates because of the interference of aqueous CO"2 transport by xylem sap flow in the wood-body of trees.

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Impact of soil drought on sap flow and water status of evergreen trees in a tropical monsoon forest in northern Thailand [An article from: Forest Ecology and Management]

This digital document is a journal article from Forest Ecology and Management, published by Elsevier in 2007. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.

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Hill evergreen forest is the dominant vegetation type in northern Thailand. In this region, there is higher atmospheric evaporative demand and lower soil moisture during the 5- to 7-month dry season than in the rainy season under influences from Asian monsoons. In an earlier study we revealed that canopy-scale transpiration is actively maintained even during the latter part of the dry season in hill evergreen forest. However, the impact of soil drought on tree water use was not investigated. To clarify the ecohydrological processes at this site, we used individual tree-scale measurements during a 2-year period to base our examination of whether limited water use in individual trees is caused by soil drought in the latter part of the dry season. Sap flow and water potential measurements were conducted in four evergreen trees, two large emergent trees 29.8 and 25.4m high, and two smaller understory trees 4.8 and 1.4m high. The amount of rainfall preceding the late dry season of 2004 was significantly less than that preceding the late dry season of 2003. Although a distinct decrease in sap-flow velocities in individual trees due to soil water stress was not found in the late dry season of 2003, it did become comparatively apparent in the late dry season of 2004; ranging from 10 to 40% for a given atmospheric evaporative demand. Furthermore, the reductions in sap-flow velocities and predawn stem-water potential were most significant in the smallest tree. The recovery of sap-flow velocities and water potential in the smallest tree after irrigation confirmed that the reductions in sap-flow velocity and predawn stem-water potential in the smallest tree were caused by soil drought. These results suggest that shallower roots could be reason for the significant decrease in water use in the smallest trees. The deeper roots of larger trees could be the reason for the reduced impact of soil drought on water use in larger trees, and canopy-scale transpiration might be maintained by larger trees, even in an unusually severe drought. These possibilities provide a new insight for management of evergreen forests under Asian monsoon influences.

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The Osmotic Pressure in the Cells of the Roots and Leaves and Its Relation to Sap Flow and Transpiration

This is an OCR edition without illustrations or index. It may have numerous typos or missing text. However, purchasers can download a free scanned copy of the original rare book from the publisher's website (GeneralBooksClub.com). You can also preview excerpts of the book there. Purchasers are also entitled to a free trial membership in the General Books Club where they can select from more than a million books without charge. Subjects: Encyclopedias and dictionaries; Reference / Encyclopedias;

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