Short-term effects of fertilization on photosynthesis and leaf morphology of field-grown loblolly pine following long-term exposure to elevated CO(2) concentration.
We examined effects of a first nitrogen (N) fertilizer application on upper-canopy needle morphology and gas exchange in approximately 20-m-tall loblolly pine (Pinus taeda L.) exposed to elevated carbon dioxide concentration ([CO(2)]) for 9 years. Duke Forest free-air CO(2) 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 (N(l)) on a mass and an area basis, light-saturated net photosynthesis per unit leaf area (A(a)) and per unit mass (A(m)), and leaf conductance (g(L)) began after the second fertilizer application in existing 1-year-old foliage (F(O)) and later in developing current-year first-flush (F(C1)) and current-year second-flush (F(C2)) foliage. Elevated [CO(2)] increased A(a) by 43 and 52% in F(O) and F(C1) foliage, respectively, but generally had no significant effect on any other parameter. Fertilization had little or no significant effect on L, LMA, A or g(L) in F(O) foliage; although N(l) was significantly higher in fertilized trees by midsummer. In contrast, fertilization resulted in large increases in L, N(l), and A in F(C1) and F(C2) foliage, increasing A(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 [CO(2)] and fertilization on A. Elevated [CO(2)] increased the intercept of the A:N(l) relationship but did not significantly affect the slope of the relationship in either foliage age class.
Maier
Chris A
CA
Southern Research Station, USDA Forest Service, Research Triangle Park, NC 27709, USA. cmaier@fs.fed.us
Palmroth
Sari
S
Ward
Eric
E
D000704:Analysis of Variance; D002245:Carbon Dioxide / Q000378:metabolism*; D005308:Fertilizers; D016018:Least-Squares Analysis; D008027:Light; D009584:Nitrogen / Q000378:metabolism; D010788:Photosynthesis / Q000502:physiology* / Q000528:radiation effects; D041603:Pinus taeda / Q000502:physiology* / Q000528:radiation effects; D018515:Plant Leaves / Q000033:anatomy & histology* / Q000528:radiation effects; D012621:Seasons; D013997:Time Factors
D005308:Fertilizers; D002245:Carbon Dioxide; D009584:Nitrogen