Effects of elevated pCO2 and/or pO3 on C-, N-, and S-metabolites in the leaves of juvenile beech and spruce differ between trees grown in monoculture and mixed culture

Three and four-year-old saplings of beech (Fagus sylvatica L.) and spruce (Picea abies (L.) Karst.) grown in monoculture and mixed culture were exposed in phytotrons to (1) ambient air, (2) elevated pO3, (3) elevated pCO2, or (4) elevated pCO2 plus elevated pO3. After 5 months, the contents of soluble sugars, starch, soluble amino compounds, non-structural proteins (NSP), as well as reduced (GSH) and oxidized (GSSG) glutathione were determined in the leaves of both species in order to assess the effects of the gaseous regimes on primary metabolism. Elevated pO3 did not affect sugar and starch levels in beech leaves in monoculture, but significantly increased sugar levels in beech leaves grown in mixed culture. In spruce needles, sugar levels tended to be enhanced in both culture types. Individual and combined exposure of elevated pCO2 led to an increase in non-structural carbohydrate (soluble sugars plus starch) levels in beech and spruce leaves of both culture types. Differences in the responses of non-structural carbohydrate levels to elevated pCO2 between beech and spruce were apparent from different contributions of sugars and starch to the increase in carbohydrate levels. Exposure to elevated pCO2 and/or elevated pO3 did not affect the levels of soluble amino compounds and NSP in beech leaves, but reduced amino compound levels in spruce needles of both culture types. Elevated pO3 increased GSH levels in the leaves of both tree species in both culture types, while GSSG levels in monoculture were reduced in beech leaves, but significantly enhanced in spruce needles. Elevated pCO2 reduced GSSG levels in beech and spruce leaves in monoculture, and GSH levels in spruce needles of both culture types. The combination of elevated pCO2 and pO3 increased GSSG levels in beech leaves of both culture types and in spruce needles in monoculture, but reduced GSH levels in spruce needles of both culture types. Apparently, under each gaseous regime, the culture type significantly altered primary metabolism of the leaves of beech and spruce.