Short-term effects of fertilization on photosynthesis and leaf morphology of field-grown loblolly pine following long-term exposure to elevated CO2 concentration
We examined effects of a first nitrogen (N) fertilizer application on upper-canopy needle morphology and gas exchange in ~20-m-tall loblolly pine (Pinus taeda L.) exposed to elevated carbon dioxide concentration ([CO2]) for 9 years. Duke Forest free-air CO2 enrichment (FACE) plots were split and half of each ring fertilized with 112 kg ha–1 elemental N applied in two applications in March and April 2005. Measurements of needle length (L), mass per unit area (LMA), N concentration (Nl) on a mass and an area basis, light-saturated net photosynthesis per unit leaf area (Aa) and per unit mass (A>sub>m), and leaf conductance (gL) began after the second fertilizer application in existing 1-year-old foliage (FO) and later in developing current-year first-flush (FC1) and current-year second- flush (FC2) foliage. Elevated [CO2] increased Aa by 43 and 52% in FO and FC1 foliage, respectively, but generally had no significant effect on any other parameter. Fertilization had little or no significant effect on L, LMA, A or gL in FO foliage; although Nl was significantly higher in fertilized trees by midsummer. In contrast, fertilization resulted in large increases in L, Nl, and A in FC1 and FC2 foliage, increasing a by about 20%. These results suggest that, although both needle age classes accumulate N following fertilization, they use it differently— current-year foliage incorporates N into photosynthetic machinery, whereas 1-year-old foliage serves as an N store. There were no significant interaction effects of elevated [CO2] and fertilization on A. Elevated [CO2] increased the intercept of the A:Nl relationship but did not significantly affect the slope of the relationship in either foliage age class.
Requesting Print Publications
Publication requests are subject to availability. Fiscal responsibility limits the hardcopies of publications we produce and distribute. Electronic versions of publications may be downloaded, distributed and printed.
Please make any requests at email@example.com.
- This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.
- Our online publications are scanned and captured using Adobe Acrobat. During the capture process some typographical errors may occur. Please contact the SRS webmaster if you notice any errors which make this publication unusable.
- To view this article, download the latest version of Adobe Acrobat Reader.