Intrashoot variation in aerobic methane emissions from pea plants exposed to multiple abiotic stresses

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 (A_N, net CO₂ assimilation; E, transpiration; g_s, stomatal conductance; WUE, water use efficiency), chlorophyll fluorescence (ϕPSII, effective quantum yield of PSII; F_v/F_m, 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 g_s. UVB5 and water stress decreased ϕPSII, but water stress increased qNP. A_N, E, g_s, 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 g_s, but a negative correlation with WUE. Overall, stress factors increased CH₄ emissions, which varied with shoot parts.