Warming and drought effects on leaf light absorptance in three subtropical tree species

This is the authors' abstract. We don't add key points for this paper.

Leaf light absorptance quantifies foliar capacity to absorb solar radiation and is important for photosynthesis, energy balance, and growth. In the photosynthetically active radiation (PAR; 400–700 nm) region, leaf absorptance (α PAR ) is commonly assumed as 85%. However, how absorptance responds to warming and drought remains unclear. Potted seedlings of three functionally distinct subtropical tree species ( Castanopsis carlesii , Schima superba , Cunninghamia lanceolata ) were subjected to ambient, simulated warming, and drought treatments, and leaf light absorptance (350–2500 nm) and key traits in both young and old leaves were continuously monitored. Across all three species, α PAR continuously decreased as drought proceeded, falling below 85% after three weeks of drought in C. carlesii , and after four weeks in C. lanceolata and S. superba . Warming-treated C. carlesii leaves exhibited slower reductions in near-infrared absorptance during the drought than their control counterparts. Variation in α PAR was associated with a relative leaf chlorophyll content index (SPAD index) in S. superba , with LWC and specific leaf area in C. carlesii , and with lamina thickness in C. lanceolata. Changes in LWC and leaf structure rendered SPAD index ineffective for estimating α PAR under drought. Furthermore, normalized difference indices incorporating leaf structure-sensitive wavelengths (e.g., 565 nm) outperformed conventional spectral indices (e.g., normalized difference vegetation index) in predicting α PAR across species and treatments. Our findings demonstrate that drought reduces absorptance by altering the content of light-absorbing compounds and leaf structure. This study provides implications for modeling leaf light absorptance and productivity under drought stress.