Text by Lauri Laanisto
Together with Spanish colleagues, Ülo has published a study about how Scots pine´s primary and secondary metabolism in the needles changes when the tree is experiencing water deficit in soil. Frome the methodoligical point of view it is a rather run-of-the-mill small-scale study concentrating on a single stress factor in one species. Pretty self-explanatory stuff. Though, note the fact that the authors are also describing different phases of the response process, which is something that is not so common.
Such studies could be (or rather will be) vital for eventually drawing more comprehensive conclusions about how plants react to different stress factors. If you could put together 100+ of such studies, it could result in a pretty seminal meta-analysis (I am after all a macroecologist…). However, conducting such meta-analysis is currently not possible. Because such studies are actually not very abundant. We do not yet know the fundamentals in this fundamental area of research! Which for me is a quite convincing argument for publishing this kind of research.
Citation: Sancho-Knapik, D., Sanz, M. Á., Peguero-Pina, J. J., Niinemets, Ü., & Gil-Pelegrín, E. (2017). Changes of secondary metabolites in Pinus sylvestris L. needles under increasing soil water deficit. Annals of Forest Science, 74(1), 24. (link to full text)
A multiphasic response to water deficit was found in Scots pine primary and secondary metabolism. First, an increase of terpenoids coincided with the stomatal closure. Second, an accumulation of proline, ABA, and shikimic acid was detected when photosynthesis was negligible.
Drought-induced mortality is characterized by a major needle yellowing followed by severe defoliation and whole branch death. Before these external visual symptoms of drought stress take place, different alterations occur in plant metabolism.
This study aims to detect changes in primary and secondary metabolism of Pinus sylvestris L. in response to a decrease in soil water availability.
We analyzed needle water potential, photosynthetic characteristics, and concentrations of proline, terpenoids, shikimic acid, total polyphenols, and abscisic acid (ABA) in P. sylvestris through a 55-day soil water deficit period.
Concentrations of most metabolites varied with the decrease in soil water availability, but changes in different compounds were triggered at different times, highlighting a multiphasic response. Increases in monoterpene and sesquiterpenoid content at moderate water deficit coincided with stomatal closure which preceded the accumulation of proline, ABA, and shikimic acid under severe water deficit when net photosynthesis was negligible.
This work confirms that most of the secondary metabolites under investigation in Pinus sylvestris did not increase until a moderate to severe water deficit was experienced, when photosynthesis was limited by stomatal closure.