Effects of carbon dioxide, fertilization, and irrigation on photosynthetic capacity of loblolly pine trees

• Published in: Tree physiology Vol. 16; no. 6; pp. 537 - 546
• Main Authors: Murthy, R, Dougherty, P.M, Zarnoch, S.J, Allen, H.L
• Format: Journal Article
• Language: English
• Published: Canada 01.06.1996
• Subjects: carbon dioxide; fertilizers; irrigation; leaf conductance; leaves; light intensity; net assimilation rate; nitrogen content; nutrient availability; photosynthesis; Pinus taeda; seasonal variation; soil water; stomata; temperature; North Carolina
• ISSN: 0829-318X; 1758-4469
• DOI: 10.1093/treephys/16.6.537

Branches of nine-year-old loblolly pine trees grown in a 2 X 2 factorial combination of fertilization and irrigation were exposed for 11 months to ambient, ambient + 175, or ambient + 350 micromoles mol-1 CO2. Rates of light-saturated net photosynthesis (Amax), maximum stomata! conductance to water vapor (gmax), and foliar nitrogen concentration (% dry mass) were assessed monthly from April 1993 until September 1993 on 1992 foliage (one-year-old) and from July 1993 to March 1994 on 1993 foliage (current-year). Rates of Amax of foliage in the ambient + 175 CO2 treatment and ambient + 350 were 32-47 and 83-91% greater, respectively, than that of foliage in the ambient CO2 treatment. There was a statistically significant interaction between CO2 treatment and fertilization or irrigation treatment on Amax on only one measurement date for each age class of foliage. Light-saturated stomatal conductance to water vapor (gmax) was significantly affected by CO2 treatment on only four measurement dates. Light-saturated gmax in winter was only 42% of summer gmax even though soil water during winter was near field capacity and evaporative demand was low. Fertilization increased foliar N concentration by 30% over the study period when averaged across CO2 treatments. During the study period, the ambient + 350 CO2 treatment decreased average foliar N concentration of one-year-old foliage in the control, irrigated, fertilized and irrigated + fertilized plots by 5,6 4,9.6 and 11% respectively, compared with one-year-old foliage in the corresponding ambient CO2 treatments. The percent increase in Amax due to CO2 enrichment was similar in all irrigation and fertilization treatments and the effect persisted throughout the 11-month study period for both one-year-old and current-year foliage.