Differential Responses of Age-related Leaf Photosynthetic Characteristics of Pinus armandii and Pinus tabuliformis to Gap-model Thinning

Objective To study the responses of age-related leaf morphology, photosynthetic rate, photosynthetic pigments, and leaf nitrogen of Pinus armandii and P. tabuliformis to gap-model thinning, intending to explore the influences of gap size, leaf age, and species on leaf characteristics after thinning.

Method The small gaps (80 m²), intermediate gaps (110 m²) and a control were set in a 30-year-old mixed P. tabuliformis and P. armandii plantation in 2008. The P. armandii and P. tabuliformis in control plots and gap-edged pines were chosen as test materials, and the leaf mass per area (LMA), area-based chlorophyll a, chlorophyll b, nitrogen content (N), maximum photosynthetic rate (A_max), and photosynthetic nitrogen use efficiency (PNUE) of current year, one-year-old, and two-year-old leaves were measured in 2013.

Result Small and intermediate gaps had no significant influences on current-year leaves of P. armandii and P. tabuliformis, while significantly altered chlorophyll, N content, and PNUE, enhanced A_max of one-year-old and two-year-old leaves. P. armandii had lower LMA, chlorophyll content, N, and A_max. Moreover, older leaves of P. armandii and P. tabuliformis showed differentiated responses to gap-model thinning:gap-edged P. armandii showed lower chlorophyll content, higher A_max and PNUE than the control, while the LMA and N were no significantly different with the control; gap-edged P. tabuliformis had higher A_max and N than the control, while LMA and PNUE had no obvious difference with the control.

Conclusion Gaps in size of 80-110m² can alter the leaf characteristics and improve its photosynthetic capacity. Gap-model thinning has significant influences on the older leaves, while has no influence on current leaves. P. armandii and P. tabuliformis have different responding strategies to gap-model thinning.