LAUSR

Methane (CH4) emissions from plants have been shown to increase with stress factors. However, the effects of multiple environmental stressors on CH4 emissions from various shoot parts have not been studied. Peas (Pisum sativum L. cv. 237J Sundance) were used to determine CH4 emissions from the upper, middle and lower parts of shoot. Plants were grown in controlled-environment chambers under temperature regime of 22/18 or 28/24 °C (16-h light/8-h dark), ultraviolet-B (UVB) level of 0 or 5 kJ m−2 day−1, and watering to field capacity (well-watered) or at wilting point (water-stressed). Methane emission, photosynthetic parameters (AN, net CO2 assimilation; E, transpiration; gs, stomatal conductance; WUE, water use efficiency), chlorophyll fluorescence (ϕPSII, effective quantum yield of PSII; Fv/Fm, maximum quantum yield of PSII; qNP, non-photochemical quenching; qP, photochemical quenching), total chlorophyll and flavonoids were measured in shoots of 1-month-old plants. Higher temperatures and UVB increased CH4 emissions, which were higher from stem than leaf and from upper shoot than lower shoot. Lower leaves emitted more CH4 than upper leaves. Methane emissions were increased by higher temperatures with water stress from both shoot and stem, by UVB5 with water stress from stem, and by higher temperatures with UVB0 from leaf. Water stress decreased all photosynthetic parameters. Higher temperatures and UVB5 decreased WUE, whereas UVB5 increased E and gs. UVB5 and water stress decreased ϕPSII, but water stress increased qNP. AN, E, gs, ϕPSII and chlorophyll were highest in the upper leaves. All the main factors decreased chlorophyll. UVB5 decreased flavonoids, which were lowest in the lower leaves. Methane emission from the stem had a positive correlation with E and gs, but a negative correlation with WUE. Overall, stress factors increased CH4 emissions, which varied with shoot parts.