Excess energy and photosynthesis: responses to seasonal water limitations in co-occurring woody encroachers of the semi-arid Southern Great Plains

Abstract

Woody plant areal encroachment is pervasive throughout the Southern Great Plains, USA. The ability of woody plants to dissipate excess solar radiation - dynamically over the day and sustained periods without recovery overnight -is key for maintaining photosynthetic performance during dry stretches, but our understanding of these processes remains incomplete. Photosynthetic performance and energy dissipation were assessed for co-occurring encroachers on the karst Edwards Plateau (<i>Juniperus ashei</i>, <i>Prosopis glandulosa</i>, and <i>Quercus fusiformis</i>) under seasonal changes in water status. Only <i>J. ashei </i>experienced mild photoinhibition from sustained energy dissipation overnight while experiencing the lowest photochemical yields, minimal photosynthetic rates, and the highest dynamic energy dissipation rates at midday during the dry period - indicating susceptibility to photosynthetic downregulation and increased dissipation under future drought regimes. Neither other encroacher experienced sustained energy dissipation in the dry period, though <i>P. glandulosa</i> did experience marked reductions in photosynthesis, photochemical yields, and increased regulatory dynamic energy dissipation.