Kudzu Leaf Energy Budget and Calculated Transpiration: The Influence of Leaflet Orientation

Leaflet orientation in exposed and shaded leaves of Pueraria lobata, kudzu, was measured during four phenological periods in central Maryland. Exposed leaflets had random azimuths but showed a strong diurnal orientation away from direct solar radiation. Shaded leaflets oriented towards diffuse light sources and did not change angle or azimuth diurnally. Energy budget simulations and field manipulations revealed that the orientation response reduced incident midday irradiance by one—half, leaf temperature by 5°—6°C, and calculated transpirational water loss by 18—26% under midsummer conditions, compared to horizontal leaves. We hypothesize that these movements may also play a role in improving water use efficiency and in avoiding thermal and photoinhibitory damage to the photosynthetic apparatus. Preliminary evidence suggests that kudzu may represent a widespread group of perennial, canopy—developing species in subtropical and temperate biomes that share this particular suite of leaf movement responses.