Estimating near-infrared leaf reflectance from leaf structural characteristics

The relationship between near-infrared reflectance at 800 nm (NIRR) from le aves and characteristics of leaf structure known to affect photosynthesis w as investigated in 48 species of alpine angiosperms. This wavelength was se lected to discriminate the effects of leaf structure vs. chemical or water content on leaf reflectance. A quantitative model was first constructed cor relating NIRR with leaf structural characteristics for six species, and the n validated using ail 48 species. Among the structural characteristic teste d in the reflectance model were leaf trichome density, the presence or abse nce of both leaf bicoloration and a thick leaf cuticle (> 1 mum). leaf thic kness. the ratio of palisade mesophyll to spongy mesophyll thickness (PM/SM ). the proportion of the mesophyll occupied by intercellular air spaces (%I AS). and the ratio of mesophyll cell surface area exposed to IAS (A(mes)) p er unit leaf surface area (A). or A(mes)/A. Multiple regression analysis sh owed that measured NIRR was highly correlated with A(mes)/A, leaf bicolorat ion. and the presence of a thick leaf cuticle (r(2) = 0.93). In contrast. c orrelations between NIRR and leaf trichome density. leaf thickness, the PM/ SM ratio, or %IAS were relatively weak (r(2) < 0.25). A model incorporating A(mes)/A, leaf bicoloration. and cuticle thickness predicted NIRR accurate ly for 48 species (r(2) = 0.43: P < 0.01) and may be useful for linking rem otely sensed data to plant structure and function.