Sunflecks and Photosynthesis in Plant Canopies

INTRODUCTION .. . . . . .... ......... . . . . . . . . ....... ........ . ... .. ......... 421 LIGHT DYNAMICS IN CANOPIES 422 Theory . . . . . . . . . .. . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . ... . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422 Empirical Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . ....... . . . . . . . 424 PHOTOSYNTHESIS IN TRANSIENT LIGHT .. . ..... . . . . . . .. ........ .. . . . . . . . ...... .. . . ...... 425 Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425 Measurement of Transient Photosynthesis ...... . . . . . . ......... .. . .. . . . . . . . . . . . . . . . 427 Dynamics of CO2 Assimilation during Sunj1ecks . . . ... . .. ... . . .. . . . . . . . . .. .. ... 429 Limitation of Sunj1eck Use by the P hotosynthetic Induction Requirement ........ ..... 436 Modulation of Induction State in Natural Light Regimes . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . 440 ENVIRONMENTAL CONSTRAINTS ON SUNFLECK UTILIZATION . . . . . . ........ . . . 442 Temperature and Water Stress ..... .. . . . . . . . . . . . ..... . . ........ . . . . . . . . .... .... ... . .. 442 Ph otoinhibition during Sunflecks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . .. . ........ .... . . . . .. 443 CONCLUDING REMARKS 444