The temperature dependence of shoot hydraulic resistance: implications for stomatal behaviour and hydraulic limitation

Recent soil pressurization experiments have shown that stomatal closure in response to high leaf–air humidity gradients can be explained by direct feedback from leaf water potential. The more complex temperature‐by‐humidity interactive effects on stomatal conductance have not yet been explained fully. Measurements of the change in shoot conductance with temperature were made on Phaseolus vulgaris (common bean) to test whether temperature‐induced changes in the liquid‐phase transport capacity could explain these temperature‐ by‐humidity effects. In addition, shoot hydraulic resistances were partitioned within the stem and leaves to determine whether or not leaves exhibit a greater resistance. Changes in hydraulic conductance were calculated based on an Ohm’s law analogy. Whole‐plant gas exchange was used to determine steady‐ state transpiration rates. A combination of in situ psychrometer measurements, Scholander pressure chamber measurements and psychrometric measurements of leaf punches was used to determine water potential differences within the shoot. Hydraulic conductance for each portion of the pathway was estimated as the total flow divided by the water potential difference. Temperature‐induced changes in stomatal conductance were correlated linearly with temperature‐induced changes in hydraulic conductance. The magnitude of the temperature‐induced changes in whole‐plant hydraulic conductance was sufficient to account for the interactive effects of temperature and humidity on stomatal conductance.     

IncrementR: Analysing height growth of trees and shrubs in R

Dendrochronology mostly deals with secondary (radial) growth and attention to primary (height) growth has so far been limited. However, tree-ring widths might not adequately represent stem volume increments, net primary productivity and the size of the tree stem carbon sink. The main reason for the prevailing focus on radial growth is that establishing height growth chronologies requires time-consuming and destructive methods. However, for certain ecological applications, less laboriously acquired data on height growth averaged over several successive years are satisfactory. Here we present an R package that contains a set of tools for the analysis of height growth. The tools have been developed for input data of tree-ring widths extracted from series of successive stem height levels. Tree-ring widths ideally represent four directions in each cross section to capture potential changes in stem eccentricity between various height levels. The main computed parameters provided by the package include height growth along the stem, changes of stem eccentricity and stem taper. Accurate determination of average height growth depends on the correct estimation of the number of tree rings at different stem height levels, which might be complicated by missing rings in off-pith cores. The presented package therefore also contains functions implementing common procedures for the estimation of the number of missing tree rings near to the pith. Most outputs can be visualized graphically. The package is useful for estimating height growth in ecological and dendrogeomorphological studies, especially in situations where both primary and secondary growth is influenced by different environmental factors. It is also useful for analysing tree-ring chronologies assembled using serial sectioning, which typically applies to shrubs.     

Phenology, growth and physiological adjustments of oil palm (Elaeis guineensis) to sink limitation induced by fruit pruning

Background and Aims

Despite its simple architecture and small phenotypic plasticity, oil palm has complex phenology and source–sink interactions. Phytomers appear in regular succession but their development takes years, involving long lag periods between environmental influences and their effects on sinks. Plant adjustments to resulting source–sink imbalances are poorly understood. This study investigated oil palm adjustments to imbalances caused by severe fruit pruning.

Methods

An experiment with two treatments (control and complete fruit pruning) during 22 months in 2006–2008) and six replications per treatment was conducted in Indonesia. Phenology, growth of above-ground vegetative and reproductive organs, leaf morphology, inflorescence sex differentiation, dynamics of non-structural carbohydrate reserves and light-saturated net photosynthesis (A_max) were monitored.

Key Results

Artificial sink limitation by complete fruit pruning accelerated development rate, resulting in higher phytomer, leaf and inflorescence numbers. Leaf size and morphology remained unchanged. Complete fruit pruning also suppressed the abortion of male inflorescences, estimated to be triggered at about 16 months before bunch maturity. The number of female inflorescences increased after an estimated lag of 24–26 months, corresponding to time from sex differentiation to bunch maturity. The most important adjustment process was increased assimilate storage in the stem, attaining nearly 50 % of dry weight in the stem top, mainly as starch, whereas glucose, which in controls was the most abundant non-structural carbohydrate stored in oil palm, decreased.

Conclusions

The development rate of oil palm is in part controlled by source–sink relationships. Although increased rate of development and proportion of female inflorescences constituted observed adjustments to sink limitation, the low plasticity of plant architecture (constant leaf size, absence of branching) limited compensatory growth. Non-structural carbohydrate storage was thus the main adjustment process.Key words: Carbon allocation, non-structural carbohydrates, source–sink relationships, Elaeis guineensis, phenotypic plasticity, photosynthesis     

Identification of phosphate granules occurring in seedling tissue of two palm species (Phoenix dactylifera and Washingtonia filifera)

Haustoria of two palm species, Phoenix dactylifera L. (date) and Washingtonia filifera (Lindl.) Wendl were carefully dissected from seeds, and the ultrastructural characteristics of the large, electron-opaque granules present in the cells of this tissue were compared using standard aldehyde and OsO₄ fixations. In Washingtonia, the granules were smaller than those in date and were more variable in size and presence of non-opaque inclusions. All granules appeared to be membrane bounded although they often filled the bounded space. No protein, lipid, carbohydrate or tannins were found in the granules by standard staining procedures. The granules stained positively with two different metallic-phosphate stains which contained either bismuth or lead. Energy dispersive X-ray microprobe analysis, done on aldehyde-fixed granules and those stained with both phosphate stains, confirmed the fact that phosphorus and calcium were present in the granules. The granules also bound the metallic stains as expected. All procedures consistently confirmed the presence of phosphate in the granules. The data are most consistent with the hypothesis that the granules are composed of polyphosphate.Abbreviations and symbols EDAX energy-dispersive X-ray microanalysis - K K shell peak - K K shell peak - L L shell peak - L L shell peak - M M shell peak     

Species of Lachesilla (Psocoptera) associated with palm trees in central Brazil

Three new species of Lachesilla are described from material collected from palm trees in central Brazil. Notes on their early stages and association with palm trees are given.     

Intrinsic and extrinsic hydraulic factors in varying sizes of two Amazonian palm species (Iriartea deltoidea and Mauritia flexuosa) differing in development and growing environment

? Premise of the study: This study seeks to determine how hydraulic factors vary with ontogeny and whether they begin to limit further height growth in palms. Palms are an attractive group for physiological research because their columnar trunks and simple leaf habit allow key intrinsic and extrinsic hydraulic variables to be estimated more easily than in complex arborescent dicotyledons. ? Methods: We measured various biometric and physiological factors including sap flux, leaf areas, turnover rates, and internode lengths in two Amazonian rainforest species: terra firme Iriartea deltoidea and swamp-adapted Mauritia flexuosa. These two palm species differ markedly in edaphic conditions, leaf type (pinnately compound vs. palmate), and bole development, making physiological comparisons between them important as well. ? Key results: The species exhibited differing patterns in height growth rate along boles, which appear to relate to their differences in bole development. Growth rates ultimately slowed at the tops of tall palms in both species. We also found a high degree of convergence in total leaf area with height in both species even though they exhibited contrasting patterns in both live frond number and leaf area per frond with height. Sap flux density from leaves was constant with height but four times greater in M. flexuosa than in I. deltoidea. ? Conclusions: Although height growth rates slow considerably in tall palms, neither species shows evidence that hydraulic factors become limiting because they are able to support much greater leaf areas with similar sap flux densities as shorter palms.     

Elevated growth temperatures alter hydraulic characteristics in trembling aspen (Populus tremuloides) seedlings: implications for tree drought tolerance

Although climate change will alter both soil water availability and evaporative demand, our understanding of how future climate conditions will alter tree hydraulic architecture is limited. Here, we demonstrate that growth at elevated temperatures (ambient +5 °C) affects hydraulic traits in seedlings of the deciduous boreal tree species Populus tremuloides, with the strength of the effect varying with the plant organ studied. Temperature altered the partitioning of hydraulic resistance, with greater resistance attributed to stems and less to roots in warm‐grown seedlings (P < 0.02), and a 46% (but marginally significant, P = 0.08) increase in whole plant conductance at elevated temperature. Vulnerability to cavitation was greater in leaves grown at high than at ambient temperatures, but vulnerability in stems was similar between treatments. A soil–plant–atmosphere (SPA) model suggests that these coordinated changes in hydraulic physiology would lead to more frequent drought stress and reduced water‐use efficiency in aspen that develop at warmer temperatures. Tissue‐specific trade‐offs in hydraulic traits in response to high growth temperatures would be difficult to detect when relying solely on whole plant measurements, but may have large‐scale ecological implications for plant water use, carbon cycling and, possibly, plant drought survival.     

Intra-annual radial growth and water relations of trees: implications towards a growth mechanism

There is a missing link between tree physiological and wood-anatomical knowledge which makes it impossible mechanistically to explain and predict the radial growth of individual trees from climate data. Empirical data of microclimatic factors, intra-annual growth rates, and tree-specific ratios between actual and potential transpiration (T PET(-1)) of trees of three species (Quercus pubescens, Pinus sylvestris, and Picea abies) at two dry sites in the central Wallis, Switzerland, were recorded from 2002 to 2004 at a 10 min resolution. This included the exceptionally hot and dry summer of 2003. These data were analysed in terms of direct (current conditions) and indirect impacts (predispositions of the past year) on growth. Rain was found to be the only factor which, to a large extent, consistently explained the radial increment for all three tree species at both sites and in the short term as well. Other factors had some explanatory power on the seasonal time-scale only. Quercus pubescens built up much of its tree ring before bud break. Pinus sylvestris and Picea abies started radial growth 1-2 weeks after Quercus pubescens and this was despite the fact that they had a high T PET(-1) before budburst and radial growth started. A high T PET(-1) was assumed to be related to open stomata, a very high net CO2 assimilation rate, and thus a potential carbon (C)-income for the tree. The main period of radial growth covered about 30-70% of the productive days of a year. In terms of C-allocation, these results mean that Quercus pubescens depended entirely on internal C-stores in the early phase of radial growth and that for all three species there was a long time period of C-assimilation which was not used for radial growth in above-ground wood. The results further suggest a strong dependence of radial growth on the current tree water relations and only secondarily on the C-balance. A concept is discussed which links radial growth over a feedback loop to actual tree water-relations and long-term affected C-storage to microclimate.     

Tapering of xylem conduits and hydraulic limitations in sycamore (Acer pseudoplatanus) trees

Vertical conduit tapering is proposed as an effective mechanism to almost eliminate the increase in hydraulic resistance with increased height. Despite this potential role, very little is known about its changes during ontogeny. Here, conduit tapering and stem morphology of young/small and old/tall individuals of Acer pseudoplatanus in the field, as well as 3-yr-old grafted trees from both age classes, were analysed. The distribution of hydraulic resistance along stems was also determined in a subsample of trees. Substantial conduit tapering was found in small trees (field-grown and grafted from both age classes), whereas values were lower in tall trees, indicating that tapering was a size-related, not an age-related process. Apical conduit diameters were larger in tall trees and were inversely correlated with the degree of tapering. Hydraulic resistance increased less than linearly with distance from the apex. Its scaling against distance was indistinguishable from that predicted from anatomical measurements. Conduit tapering was an effective but partial mechanism of compensation for the increase in hydraulic resistance with tree height. Size-related changes in tapering and in apical conduit diameters may be explained by the combined need to reduce the build-up of hydraulic resistance while minimizing the carbon costs of building vessel walls.     

Estimating the heights and diameters at breast height of trees in an urban park and along a street using mobile LiDAR

Because trees can positively influence local environments in urban ecosystems, it is important to measure their morphological characteristics, such as height and diameter at breast height (DBH). However, measuring these data for each individual tree is a time-consuming process that requires a great deal of manpower. In this study, we investigated the feasibility of using mobile LiDAR to estimate tree height and DBH along urban streets and in urban parks. We compared measurements from a mobile LiDAR unit with field measurements of tree height and DBH in urban parks and streets. The height-above-ground and Pratt circle fit methods were applied to calculate tree height and DBH, respectively. The LiDAR-estimated tree heights were highly accurate albeit slightly underestimated, with a root mean square error of 0.359 m for the street trees and 0.462 m for the park trees. On the other hand, the estimated DBHs were moderately accurate and overestimated, with a root mean square error of 3.77 cm for the street trees and 8.95 cm for the park trees. Densely planted trees in the park and obstacles in urban areas result in “shadows” (areas with no data), reducing accuracy. Irregular trunk shapes and scanned data that did not include full data point coverage of every trunk were the reasons for the errors. Despite these errors, this study highlights the potential of tree measurements obtained with mobile terrestrial LiDAR platforms to be scaled up from point-based locations to neighborhood-scale and city-scale inventories.

     

Reproductive implications of combined and separate sexes in a trioecious population of Opuntia robusta (Cactaceae)

Opuntia robusta has hermaphroditic, dioecious, and trioecious populations. To enhance our understanding of this breeding system diversity, we compared the reproductive output of males, females, and hermaphrodites in a trioecious population using field evaluations, controlled crosses, and progeny tests. Unisexuals were fully sterile in one sex function. Hermaphrodites were fully fertile for both functions. Consistent with the sex-allocation theory, unisexuality increased the quality and quantity (in males) of the gametes of the functional sex, relative to those of hermaphrodites, probably explained by maternal and paternal effects. The increase was higher in males than in females, suggesting a more expensive female function. Theoretically, this disproportional increase is required for unisexuals to invade a hermaphroditic population with prior selfing, negligible pollen discounting, and undetectable inbreeding depression, features found in O. robusta, therefore helping to explain dioecious populations. However, in the study population, the actual seed output of females was lower and had a higher variance than that of hermaphrodites, which also reproduce through pollen. Unisexuals are unlikely to be maintained by their actual reproductive output in this pollen-limited environment. Hermaphrodites may persist in this population by producing their seeds autonomously and by reducing interspecific fertilization by prior selfing and ovule discounting.     

"Secondary stem lengthening" in the palm Iriartea deltoidea (Arecaceae) provides an efficient and novel method for height growth in a tree form

? Premise of the study: Although traditionally assumed that all height growth in trees occurs at apical meristems, sequential measurement of internode lengths in the palm Iriartea deltoidea suggested that stems were lengthening long after the differentiation of tissues and far below the apical meristem. This observation is difficult to reconcile with the fact that neither the water-conducting vessels nor the sugar-transporting sieve tube cells are capable of lengthening after differentiation. However, the vascular bundles in palms form a spiral within the stem and could theoretically lengthen if the spiral "straightened". ? Methods: We marked stretches of internodes on small and medium-sized palms and measured their lengths over 2 years. Additionally, we collected material from small palms with short internodes and large palms with long internodes and made cross sections to determine the angle of vascular bundles within stems. ? Key results: We found that stems lengthened (up to 12% over 2 years) below the apical meristem in small and medium-sized palms and that the spiral angle in vascular bundles of small palms was significantly larger than at the base of large palms indicating a straightening of the spiral. ? Conclusions: These results represent the first determination of "secondary lengthening" in tree stems as well as the most efficient method for height growth in terms of carbon investment. Likewise, elongation of stems allows palms to exhibit plasticity in height growth rates for more rapid growth when short-lived canopy gaps are present than they would have with apical growth alone.     

Use of palm trees as a sleeping site for hamadryas baboons (Papio hamadryas hamadryas) in Ethiopia

Hamadryas baboons sleep on cliffs throughout their range, and this can be attributed to the safety cliffs provide against predators in the absence of tall trees. In this paper, we report the first documented occurrence of hamadryas baboons sleeping in doum palm trees rather than on cliffs. Data derive from a study of hamadryas baboons at the Filoha site in lowland Ethiopia. During all-day follows, data were collected on travel patterns, band activity, and location. Variation in the baboons' home range was characterized using vegetation transects. We discovered that one band in this population, Band 3, occasionally slept in doum palm trees (Hyphaene thebaica). The palm tree sleeping site differed from other palm fragments in the baboons' home range in that it contained a higher density of palm trees. Possible factors influencing this unique use of palm trees as a sleeping site include access to palm fruit, avoiding contact with Afar nomads, avoiding sharing sleeping cliffs with other bands, protection from predators, and the lack of cliffs in a section of the baboons' home range. Evidence from this study suggests that the palm tree sleeping site is used because it affords better protection from predators than other palm fragments in an area of the band's home range that does not contain cliffs.     

The role of Palmyra palm trees (Borassus flabellifer) and sand fly distribution in northeastern India

Visceral leishmaniasis (VL), known as Kala-azar in India, is a parasite transmitted by the bite of the sand fly vector Phlebotomus argentipes. Published information on the species indicates it is a poor flyer, mainly hopping and gliding. This study describes the vector as more arboreal than previously documented. Data collected indicate the ability of P. argentipes and Sergentomyia spp to attain vertical heights in Palmyra palm trees Borassus flabellifer up to 18.4 m above ground level. To determine if sand flies were either climbing the tree trunk to rest in the canopy or flying, sticky traps were set around the tree trunk and checked for captures overnight. CDC traps set in the palm tree canopy resulted in the capture of 5,067 sand flies, 3,990 of which were P. argentipes. Traps were set during daylight hours to determine if sand flies remained and rested in the canopy. A total of 128 sand flies were trapped over 29 trap days in the palm trees. With the CDC traps, 130 P. argentipes and no Sergentomyia spp were captured. The converse was true for the sticky traps set around tree trunks 3 m below the CDC traps. Of the 105 sand flies collected, only one was P. argentipes and 104 were Sergentomyia spp. As reported elsewhere, this indicates Sergentomyia spp tend to climb and hop, wheareas P. argentipes are capable of longer and more sustained flight. Data presented herein suggest that P. argentipes is more exophylic and exophagic than previously reported. These findings have implications for sand fly control.     

Allozyme variation and structure of the Canarian endemic palm tree Phoenix canariensis (Arecaceae): implications for conservation

Electrophoretic analysis of 18 allozyme loci was used to estimate the levels and structuring of genetic variation within and among natural populations of the protected endemic palm species from the Canary Islands (Phoenix canariensis) to evaluate its genetic relationship with the widespread congener P. dactylifera, and to assess comparatively the genetic variation in the populations where the two species coexist with morphologically intermediate plants (mixed populations). Our survey revealed that the within-population component explains roughly 75% of the genetic variation levels detected in P. canariensis (A=1.59; P=41.8; He=0.158), which rank higher than those reported for other species of the Arecaceae. A Principal Component analysis (PCA) based on allele frequencies consistently separates populations of P. canariensis and P. dactylifera, and reveals a close genetic relationship between P. canariensis and the mixed populations. Reduced levels of genetic variation in P. canariensis with respect to P. dactylifera, the fact that the genetic makeup of the Canarian endemic (with no unique alleles) is a subset of that found in P. dactylifera, and the high genetic identity between both species strongly suggest that P. canariensis is recently derived from a common ancestor closely related to P. dactylifera.