Understanding Plant Responses to Drought: How Important Is Woody Tissue Photosynthesis?

Abstract

Within trees, it is known that a part of the respired CO 2 is assimilated in chlorophyll-containing stem and branch tissues. However the role of this woody tissue photosynthesis in tree functioning remains unclear, in particular under drought stress conditions. In this study, stem diameter and leaf photosynthesis were measured for one-year-old cutting-derived plants of Populus nigra "Monviso" under both well-watered and drought stress conditions. Half of the plants were subjected to a stem and branch light-exclusion treatment to prevent woody tissue photosynthesis to occur, while the other trees served as controls. Drought stress was induced in both treatments by limiting the water supply. We found that under wellwatered conditions, light-exclusion resulted in reduced stem radial daily growth rate (DG) relative to DG observed for control trees. In response to drought, stem shrinkage of the light-excluded trees was more pronounced as compared to the control trees. Maximum leaf net photosynthesis (A max ) decreased more rapidly in light-excluded trees compared to the controls during drought stress. Our results are the first to report on the potentially significant role of woody tissue photosynthesis in tree drought stress tolerance. Moreover, our study implies that the impact of assimilation of respired CO 2 on tree functioning extends beyond local stem processes and indicates that woody tissue photosynthesis is potentially a key factor in understanding plant responses to drought stress.

Woody tissue photosynthesis in trees: salve on the wounds of drought?

“…Finally, in plants inhabiting arid environments, recycling of carbon by woody tissue photosynthesis is an integral part of the plant carbon balance (Nilsen, 1995;Bloemen et al, 2013a). Nevertheless, woody tissue photosynthesis has been almost never accounted for in tree drought experiments (Bloemen et al, 2013c(Bloemen et al, , 2014.…”

“…Additionally, locally produced carbohydrates can help regulate the osmotic potential of living tissues under drought, facilitating for instance turgor maintenance and phloem functioning and, hence, plant hydraulic integrity (Woodruff, 2013;Sevanto, 2014;Sevanto et al, 2014). Moreover, these carbohydrates might aid in xylem refilling after embolism (Zwieniecki & Holbrook, 2009;Schmitz et al, 2012;Secchi & Zwieniecki, 2012) and therefore potentially play a role in the tree's resistance to hydraulic failure (Bloemen et al, 2013c(Bloemen et al, , 2014.…”

“…Besides recycling of internal carbon (stem recycling photosynthesis), the stems of some species, typically desert species, contain stomata, which allow for a photosynthetic process very similar to leaf photosynthesis (stem net photosynthesis) (Ávila et al ., ). Because of its role in carbon fixation, woody tissue photosynthesis has been associated with stem growth (estimated contribution between 11% and 24%; Saveyn et al ., ; Cernusak & Hutley, ; Bloemen et al ., ; Steppe et al ., ) and bud development (Saveyn et al ., ), and suggested to play a role in wound callus formation, re‐foliation after fungal or insect defoliation (Pfanz, ; Eyles et al ., ), flowering, cold adaptation, as energy source for local exudate synthesis (Pfanz et al ., ) and to reduce winter respiratory carbon drain in temperate species (Nilsen, ).…”

The benefits of recycling: how photosynthetic bark can increase drought tolerance

“…Stem recycling photosynthesis, however, can produce locally available carbohydrate resources in close proximity to xylem parenchyma cells, where they can be used for maintenance processes, osmotic adjustment, and xylem embolism refilling (Vandegehuchte et al .). Although in its infancy as a research topic, there is evidence to suggest that light exclusion from bark leads to reduced hydraulic function in the underlying sapwood (Schmitz et al ., ; Bloemen et al ., ; Gao et al ., ), suggesting that stem recycling photosynthesis plays an important role in supporting stem hydraulic function.…”

Contrasting patterns of hot spell effects on morbidity and mortality for cardiovascular diseases in the Czech Republic, 1994–2009

“…Stem recycling photosynthesis, however, can produce locally available carbohydrate resources in close proximity to xylem parenchyma cells, where they can be used for maintenance processes, osmotic adjustment, and xylem embolism refilling (Vandegehuchte et al). Although in its infancy as a research topic, there is evidence to suggest that light exclusion from bark leads to reduced hydraulic function in the underlying sapwood (Schmitz et al, 2012;Bloemen et al, 2013;Gao et al, 2015), suggesting that stem recycling photosynthesis plays an important role in supporting stem hydraulic function.…”