Timeline of Leaf and Cambial Phenology in Relation to Development of Initial Conduits in Xylem and Phloem in Three Coexisting Sub-Mediterranean Deciduous Tree Species

Andreja Vedenik,Peter Prislan,Gregor Skoberne,Polona Hafner,Jožica Gričar

doi:10.3390/f11101104

Abstract

It is unclear how the anticipated climate change will affect the timing of phenology of different tree organs/tissues and thus the whole-tree functioning. We examined the timing of leaf phenology and secondary growth in three coexisting deciduous tree species (Quercus pubescens Willd., Fraxinus ornus L. and Ostrya carpinifolia Scop) from a sub-Mediterranean region in 2019. In addition, we investigated the relationship between leaf and cambial phenology and the onset of the potential functioning of initial conduits, as determined by the completed differentiation process (vessels) or final size (sieve tubes). For this purpose, leaf development was monitored and the microcores of cambium and the youngest phloem and xylem increments were repeatedly collected at 7–10-day intervals during the growing season. The results revealed differences in the timing of leaf development and seasonal radial growth patterns in spring among the studied tree species, depending on wood porosity. We found that cambial cell production started in all cases in the first half of March. However, in ring-porous Q. pubescens and F. ornus, radial growth in the stem occurred more than a month before buds were swollen, whereas in diffuse-porous O. carpinifolia, these two events were detected at almost the same time. The end of cambial cell production occurred earliest in F. ornus (mid-July) and two weeks later also in the other two species. The widest initial earlywood vessels and early phloem sieve tubes were found in Q. pubescens, the narrowest initial earlywood vessels in O. carpinifolia and the narrowest early phloem sieve tubes in F. ornus. This indicates differences in the efficiency of conducting systems among the studied species. This novel approach of studying phloem phenology and anatomy in relation to leaf and xylem development contributes to a better understanding of how different tree species adapt their structure of secondary vascular tissues in response to environmental change.

Highlights

Global warming and the increased frequency and severity of weather events will greatly impact the radial growth patterns of tree species, which adjust their phenology to given environmental cues [1,2].Phenology, the timing of plant seasonal events, ranging from an individual to an ecosystem level, plays a fundamental role in the functioning and productivity of terrestrial ecosystems [3,4]
We examined the timing of leaf phenology and secondary growth in three tree species (Quercus pubescens Willd, Fraxinus ornus L. and Ostrya carpinifolia Scop.) in the 2019 growing season
AlmostAlmost simultaneously with cambial reactivation, buds were half of March in alldeciduous three deciduous simultaneously with cambial reactivation, buds swollen in diffuse-porous carpinifolia, while this happened more than a month later in ring-porous were swollen in diffuse-porous O. carpinifolia, while this happened more than a month later in ringF

Summary

Introduction

The timing of plant seasonal events (e.g., leaf bud burst, flowering, fruiting, cambial activity), ranging from an individual to an ecosystem level, plays a fundamental role in the functioning and productivity of terrestrial ecosystems [3,4]. Since the phenology of different organs/tissues does not necessarily coincide and is under different biotic and abiotic constraints [5,7], it is unclear how climate change will affect phenological events and the whole-tree functioning. Vegetation indices can be used, for example, to scale up ground measurements on individual trees to assess the effect of climate extremes on future forest growth [8]. Since vegetation indices are sensitive to the green biomass of the canopy, the link between the timing of leaf and cambial phenology needs to be provided at individual tree and species levels. Species may have almost synchronous phenologies among individuals or show high levels of intraspecific variation [9]

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Discussion

Conclusion