Photosynthetic responses of loblolly pine (Pinus taeda) needles to experimental reduction in sink demand

Abstract

Sink strength in loblolly pine (Pinus taeda L.) was experimentally manipulated on two sun-exposed branches on each of two neighboring trees by excising the emerging terminal cohort (second flush of 1996) during a period of rapid needle expansion. In addition, export of photosynthate was restricted on one of these branches from each tree by removal of bark and phloem just below the second flush of 1995. Treatment-induced changes in needle biochemistry were measured in 3-month-old (first flush of 1996) and 1-year-old (final flush of 1995) needles collected 1, 5 and 8 days after treatment. In 3-month-old needles, sugar concentration increased by 24% one day after leader excision, and increased by 86% on Day 8 after leader excision and girdling. Starch concentration increased by 33% in 3-month-old needles on Day 1 after leader excision, and by 400% in 1-year-old needles on Day 8 after leader excision and girdling. Physiological changes in 3-month-old and 1-year-old needles were measured by open-flow gas exchange and chlorophyll fluorescence on Day 8 after leader excision and girdling. Light- and CO(2)-saturated net photosynthesis decreased following treatment in both 3-month-old and 1-year-old needles (23 and 17%, respectively). Maximum rate of carboxylation (V(cmax)) decreased by 25% in 3-month-old needles and by 31% in 1-year-old needles in response to leader excision and girdling. The combined treatment resulted in a 38% decrease in maximum rate of electron transport (J(max)) in 3-month-old needles and a 37% decrease in J(max) in 1-year-old needles. Before leader excision and girdling, 2% oxygen in air stimulated photosynthesis by 17 to 19%, but this stimulation was only 3 to 4% at 9 days after treatment. These physiological responses indicate that experimentally lowered sink strength resulted in rapid feedback inhibition of leaf-level photosynthetic capacity in loblolly pine.

Tree Girdling: A Tool to Improve Our Understanding of Coupled Sugar and Water Transport

“…3). This increased starch content is consistent with previous girdling studies (Myers et al, 1999;Li et al, 2003;Daudet et al, 2005). In comparison with the sample taken at 0.5 cm above the upper-girdled-zone (Uwound), the wound tissue displayed a different storage behaviour (Fig.…”

“…Several girdling studies (Iglesias et al, 2002;Bondada and Syvertsen, 2005;Johnsen et al, 2007;Cheng et al, 2008;Rivas et al, 2008) have reported this P n inhibition which they attributed to the decreased sink demand in girdled trees. In literature two processes are described which might trigger inhibition of P n : stomatal closure (Williams et al, 2000;Cheng et al, 2008;Domec and Pruyn, 2008) and damage to the photosynthesis system (Myers et al, 1999;Bondada and Syvertsen, 2005;Rivas et al, 2008). Cheng et al (2008) observed that these two processes occur simultaneously.…”

Long-term effects of stem girdling on needle structure in Scots pine

“…In this study, we observed several changes in needle structure in response to stem girdling 227 and 411 DAG, similarly to several previous investigations which measured physiological changes after stem girdling (Myers et al 1999, Rivas et al 2007, Urban & Alphonsout 2007, Murakami et al 2008. While the morphological and anatomical structures of needles 227 DAG were very similar to those of the control trees (the only marked difference was an increase of 9% in LMA, that is, the first hypothesis was not confirmed), seven of the eleven studied needle parameters were significantly different 411 DAG (in part, supporting our second hypothesis).…”

Multiple feedbacks between chloroplast and whole plant in the context of plant adaptation and acclimation to the environment

“…girdling of branches or trees (e.g. [7][8][9]) or cold-girdling of stems [1,5]; the negative feedback from limiting sink strength was demonstrated e.g. via photosynthetic repression in response to removal of fruit and other sinks (e.g.…”