Dendrometer and intra-annual tree growth : what kind of information can be inferred?

Dendrometer measurements provide time series composed of the rhythm of water storage fluctuations over the year and seasonal tree growth. For slow-growing trees, however, difficulties have been found in the identification of crucial events such as growth onset, stem growth period and cessation, rendering it necessary to define what can be measured and at which time scale. Time scale means the time interval (from one day to one month) at which stem radius variation is extracted. In this study, two conifer species were monitored by an automatic band dendrometer to assess several time scales and analysis approaches. Data were collected from 8 trees of Picea abies (L.) Karst and Larix decidua L., growing at 1020 and 2080 m a.s.l. in the eastern Italian Alps, from 2000 to 2003. Time series of stem radius variation were extracted with different approaches, such as the stem cycle, daily mean and daily maximum. Several approaches can be used, as very similar time series of stem radius variations were produced with high coefficients of correlation among the series. At lower altitude, the approximate onset was identified at the beginning of May with a 10-day time scale, when the distribution of stem radius variation differed from zero. The main growth period, from May to June-July, corresponded mainly with earlywood cell formation. At higher altitude, a time scale of at least 15 days facilitated identification of the main period of stem growth only, corresponding with earlywood cell formation. Even if latewood cells were produced in August at both altitudes, the variability in stem radius changes was higher than the amount of growth in terms of cell-wood production. For a slow-growing species in a cold environment, an understanding of the growth period, assessed with several time scales, is necessary when using time series of stem radius variation to assess growth and climate relationships. The period used for growth and climate analysis should correspond only with the main period of stem growth

Allometric Trajectories and \u201cStress\u201d: A Quantitative Approach

The term \u201cstress\u201d is an important but vague term in plant biology. We show situations in which thinking in terms of \u201cstress\u201d is profitably replaced by quantifying distance from functionally optimal scaling relationships between plant parts. These relationships include, for example, the often-cited one between leaf area and sapwood area, which presumably reflects mutual dependence between source and sink tissues and which scales positively within individuals and across species. These relationships seem to be so basic to plant functioning that they are favored by selection across nearly all plant lineages. Within a species or population, individuals that are far from the common scaling patterns are thus expected to perform negatively. For instance, \u201ctoo little\u201d leaf area (e.g. due to herbivory or disease) per unit of active stem mass would be expected to incur to low carbon income per respiratory cost and thus lead to lower growth. We present a framework that allows quantitative study of phenomena traditionally assigned to \u201cstress,\u201d without need for recourse to this term. Our approach contrasts with traditional approaches for studying \u201cstress,\u201d e.g. revealing that small \u201cstressed\u201d plants likely are in fact well suited to local conditions. We thus offer a quantitative perspective to the study of phenomena often referred to under such terms as \u201cstress,\u201d plasticity, adaptation, and acclimation

Stable allometric trajectories in picea abies (L.) karst. trees along an elevational gradient

The effect of temperature on tree phenology and growth has gained particular attention in relation to climate change. While a number of reports indicate that warming can extend the length of the growing season and enhance tree growth rates, it is still debated whether temperature also affects biomass partitioning. Addressing the question of whether trees grown at different elevations invest similarly in various organs, we established four sites along an elevational gradient (320 to 595 m a.s.l.) in managed Norway spruce (Picea abies (L.) Karts) stands regenerating after clearcuts in central Norway. There, differences in temperature, bud break, tree growth, and allometric scaling were measured in small spruce trees (up to 3 m height). The results showed that bud break and shoot growth are affected by temperature, as lower sites completed the bud break process 5 days earlier than the higher sites did. There was some evidence indicating that the summer drought of 2018 affected tree growth during the season, and the implications of this are discussed. The allometric scaling coefficients did not change for the crown volume (slope value range 2.66–2.84), crown radius (0.77–0.89), and tree diameter (0.89–0.96) against tree height. A slight difference was found in the scaling coefficients of crown length against tree height (slope value range 1.04–1.12), but this did not affect the general scaling of the crown volume with tree height. Our results showed that different local environmental conditions affect both the growth rate and phenology in Norway spruce trees but, on the contrary, that the biomass partitioning among different parts of the tree remains essentially unchanged. This demonstrates that the allometric approach is an important tool for unraveling true vs. apparent plant plasticity, which in turn is an essential awareness for predicting plant responses to environmental changes.publishedVersio

Cambial phenology, wood formation and temperature thresholds in two contrasting years at high altitude in Southern Italy

Xylogenesis was monitored during 2003 and 2004 in a timberline environment in southern Italy to assess links between temperature, cambial phenology and wood formation on a short-time scale. Wood microcores were collected weekly from May to October from 10 trees of Pinus leucodermis Ant., histological sections were cut with a rotary microtome and anatomical features of the developing and mature tracheids were observed and measured along the growing tree ring. Spring 2003 was hotter than spring 2004, with temperatures up to 2.6°C above historical means. The hotter conditions resulted in an earlier onset of cambial activity and all differentiation phases of about 20 days, resulting in an increased duration of xylogenesis of about 23 days. Air and stem temperatures at which xylogenesis had a 0.5 probability of being active were calculated with logistic regressions fitted on binary responses. In both years, similar thresholds were estimated with daily mean values of 8.2 and 9.5°C for air and stem temperatures, respectively. The observed convergent responses of cambium phenology to temperature during the two contrasting springs confirm the key role of this environmental factor in determining the onset and duration of wood formation in timberline areas. The intra-annual dynamics of ring-width increase differed between years, with significantly narrower rings formed in 2004 than in 2003. These differences were mainly related to cell size because larger early wood tracheids were produced in 2003. This study demonstrates the plasticity of tree-ring formation in response to high temperatures as a result of modifications in the onset and duration of differentiation

An allometry-based approach for understanding forest structure, predicting tree-size distribution and assessing the degree of disturbance

Tree-size distribution is one of the most investigated subjects in plant population biology. The forestry literature reports that tree-size distribution trajectories vary across different stands and/or species, while the metabolic scaling theory suggests that the tree number scales universally as -2 power of diameter. Here, we propose a simple functional scaling model in which these two opposing results are reconciled. Basic principles related to crown shape, energy optimization and the finite size scaling approach were used to define a set of relationships based on a single parameter, which allows us to predict the slope of the tree-size distributions in a steady state condition. We tested the model predictions on four temperate mountain forests. Plots (4 ha each, fully mapped) were selected with different degrees of human disturbance (semi-natural stands vs. formerly managed). Results showed that the size distribution range successfully fitted by the model is related to the degree of forest disturbance: in semi-natural forests the range is wide, while in formerly managed forests, the agreement with the model is confined to a very restricted range. We argue that simple allometric relationships, at individual level, shape the structure of the whole forest community.Comment: 22 pages, 4 figure

Axial anatomy of the leaf midrib provides new insights into the hydraulic architecture and cavitation patterns of Acer pseudoplatanus leaves

The structure of leaf veins is typically described with a hierarchical scheme (e.g. midrib, 1st order, 2nd order), that is used to predict variation in conduit diameter from one order to another overlooking possible variation within the same order. We tested whether xylem conduit diameter changes within the same vein order, with consequences on resistance to embolism. We measured the hydraulic diameter (Dh), and number of vessels (VNo) along the midrib and petioles of Acer pseudoplatanus leaves. We estimated the leaf area supplied (LAsup) at different points of the midrib and how variation in anatomical traits affected embolism resistance. Our results showed that Dh scales with distance from the midrib tip (L) with a power of 0.42, and that VNo scales with LAsup with a power of 0.66. Total conductive area scales isometrically with the LAsup. Embolism events along the midrib occurred first in the basipetal part and afterwards at the leaf tip where vessels are narrower. The distance from the midrib tip well predicts the variations in vessels diameter along the 1st order vein in sycamore maple leaves and this anatomical pattern seems to have an effect on hydraulic safety since wider vessels at the leaf base embolize first

Axial variation of xylem conduits in giant cacti

Giant columnar cacti store massive amounts of water in their parenchymous storage tissues in order to persist under conditions of extreme aridity. Nevertheless, the relationship between stem water storage capacity and the maximum efficiency to deliver water from the roots to stem storage tissues via xylem vessels remains largely unknown. Indeed, the relationship between the axial water flow in xylem and the lateral flow through the storage tissue may affect the xylem structure and, therefore, the plant water conduction strategies. Since the axial structure of vascular conduits has been demonstrated to be universal (i.e. in a broad spectrum of plant species xylem conduits widen basipetally at the same rate), we wanted to determine if both the vessel size and wall thickness in giant cactae follow the same general rule in spite of the buffer action of water storage tissue. To address these hypotheses, we are investigating anatomical variation in xylem structural traits and storage volume in the stems of giant cacti species belonging to different phylogenetic lineages that are native to both the Northern and Southern hemisphere (e.g.Pachycereus weberi, Echinopsis terschekii, Carnegiea gigantea). We collected cross-sections from 6 to 13 samples along the stem of each plant. We found that vessel lumina increased basipetally following a widening rate similar to what has been documented by the theoretical model (WBE model) and from existing surveys on a wide range of tree species. The conduits double wall thickness (t) and its span (s) ratio decrease basipetally and interplay to reduce the risk of cell collapse. We concluded that the xylem architecture of columnar cacti in this study was not influenced by the buffering action of the surrounding storage tissue, and that axial water transport efficiency is maintained for the length of the path as in many other plant species

Constant theoretical conductance, changes in vessel diameter and number, with height growth in Moringaoleifera

As trees grow taller, hydraulic resistance can be expected to increase, causing photosynthetic productivity to decline. Yet leaves maintain productivity over vast height increases; this maintenance of productivity suggests that leaf-specific conductance remains constant as trees grow taller. Here we test the assumption of constant leaf-specific conductance with height growth and document the anatomical adjustments involved. We measured the scaling of total leaf area, mean vessel diameter at terminal twigs and at the stem base, and total vessel number in 139 individuals of Moringaoleifera of different heights, and estimated a whole-plant conductance index from these measurements. Whole-plant conductance and total leaf area scaled at the same rate with height. Congruently, whole-plant conductance and total leaf area scaled isometrically. Constant conductance is made possible by a complex adjustment in anatomy, with conduit diameters in terminal twigs becoming wider, lowering per-vessel resistance, with a concomitant decrease in vessel number per unit leaf area with height growth. Selection maintaining constant conductance per unit leaf area with height growth (or at least minimizing drops in conductance) is likely a potent selective pressure shaping plant hydraulics, and is crucially involved in the maintenance of photosynthetic productivity per leaf area across the terrestrial landscape

Widening of xylem conduits in a conifer tree depends on the longer time of cell expansion downwards along the stem

The diameter of vascular conduits increases towards the stem base. It has been suggested that this profile is an efficient anatomical feature for reducing the hydraulic resistance when trees grow taller. However, the mechanism that controls the cell diameter along the plant is not fully understood. The timing of cell differentiation along the stem was investigated. Cambial activity and cell differentiation were investigated in a Picea abies tree (11.5 m in height) collecting microsamples at nine different heights (from 1 to 9 m) along the stem with a 4 d time interval. Wood sections (8-12 μm thick) were stained and observed under a light microscope with polarized light to differentiate the developing xylem cells. Cell wall lignification was detected using cresyl violet acetate. The first enlarging cells appeared almost simultaneously along the tree axis indicating that cambium activation is not height-dependent. A significant increase in the duration of the cell expansion phase was observed towards the tree base: at 9 m from the ground, xylem cells expanded for 7 d, at 6 m for 14 d, and at 3 m for 19 d. The duration of the expansion phase is positively correlated with the lumen area of the tracheids (r2=0.68, P < 0.01) at the same height. By contrast, thickness of the cell wall of the earlywood did not show any trend with height. The lumen area of the conduits down the stem appeared linearly dependent on time during which differentiating cells remained in the expansion phase. However, the inductive signal of such long-distance patterned differentiation remains to be identified