Effect of competition and leaf age on visible and infrared reflectance in pine foliage

Abstract

Abstract. The effect of plant competition on spectral reflectance in the 400–2500 nm wavelength region was determined for 3‐month‐old and 15‐month‐old leaves of loblolly pine ( Pinus taeda L.). Strong competition decreased water potentials and Mg concentrations, and increased K in young and old leaves. Also, competition decreased Ca and total chlorophyll in young leaves. As measured with a scanning radiometer, reflectance in young leaves at 551 nm decreased from 20 to 14% as water potentials increased from ‐2.2 to ‐0.9 MPa (r 2 = 0.82). For young and old leaves reflectance at 551 nm decreased from 20 to 10% with increasing total chlorophyll (r 2 = 0.64). Reflectance decreased slightly with increasing K in young leaves (401 nm, r 2 = 0.55), and with increasing Mg in old leaves (470 nm, r 2 = 0.57). Increased visible reflectance under strong competition may have resulted primarily from decreased water potentials. Reflectances were much greater in young versus old leaves in the 750–1300 nm range, and were greater in old rather than young leaves from 1400–2500 nm. Infrared reflectances were not, however, significantly affected by competition.