Xylem and Phloem Formation Dynamics in Quercus ilex L. at a Dry Site in Southern Italy

Abstract

Quercus ilex L. dieback has been recently reported at numerous Mediterranean sites. Wood and phloem formation dynamics and tree-ring series of anatomical traits can be used to evaluate growth conditions of trees. We monitored cambial activity in Q. ilex trees growing at a site in southern Italy in order to assess how xylem and phloem production are affected by harsh seasonal climatic variation during a dry year. We followed xylogenesis by counting the number of cambial cells and detecting the occurrence of post-cambial cells throughout the year. As phloem did not show clear growth rings and boundaries between them, we followed the development of phloem fibres—their morphological traits during development and the distance from the cambium served as a reference point to evaluate the phloem production during the year. We detected a multimodal pattern in cambial activity, with wood production in three periods of the year and consequent formation of intra-annual density fluctuations (IADFs). The lowest production of xylem cells was observed in the dry late spring and summer period (likely due to the low water availability), while the highest occurred in autumn (the wettest period). Although we could not differentiate between early and late phloem, the analysis of phloem traits was useful to follow the dynamics of phloem production, which is generally difficult in Mediterranean tree species. We found cambial production of phloem throughout the year, even in the periods without xylem production. The results showed that if tree growth was constrained by environmental limitations, the ratio between xylem to phloem cells decreased and, in the most severely affected trees, more cells were formed preferentially in the phloem compared to xylem. We also briefly report the way in which to solve technical problems with tissue preparation due to extreme hardness and to the peculiar structure of Q. ilex wood and outer bark.

Wood Density and Ring Width in Quercus rotundifolia Trees in Southern Portugal

“…In diffuse or semi-ring porous species this explanation does not apply, and other ring structural features may be important. However, some of the year-to-year fluctuations found in Q. rotundifolia could be explained as reported for Q. ilex, i.e., the narrow rings may be a result of the drought summer conditions [14,33,65,66], while the wider rings may be a result of a second or multi growth during the year [35,67,68]. Nevertheless, the ring width variation in Q. ilex was found as less climate-sensitive compared, for example, to vessel-related features [44].…”

“…Lower ring density was explained by a smaller proportion of dense thick-walled cells and a larger number of pores in diffuse-porous species [64]. These ring structural changes, called by some authors inter-annual density fluctuations, will affect the within-ring density variation and may occur in Q. rotundifolia as reported in Q. ilex in Spain and Italy as growth and vessel climate responses, related mainly to Mediterranean summer drought conditions [35,44,67,68].…”

Critical steps and troubleshooting in sample preparation for wood and phloem formation: from sampling to microscopic observation

“…Balzano, A., Čufar, K., Krže, L., & Merela, M.: Critical steps and troubleshooting in sample preparation for wood and phloem formation: from sampling to microscopic observation > 2 mm) would help to obtain wider tissue sections for analyses. This is especially important when studying species with wider rays such as beech (Fagus) and oaks (Quercus) (Balzano et al, 2021b). Too narrow sections and large rays hinder the analyses, as in the case of Quercus ilex (Figure 3a).…”

Effects of growing site parameters on vessel elements of Quercus ilex through Turkey and evaluating in respect of forestry

“…The formation of IADF increased the hydraulic conductivity late in the growing season, due to larger lumen area of vessels in comparison to "true latewood" (Balzano et al (2020). The lowest cambial activity was seen during dry late spring and summer months (driest period) while the highest occurred in autumn (the wettest period) (Balzano et al, 2021).…”