Stem Diameter Variations Research Articles

Tree Circumference Changes and Species-Specific Growth Recovery After Extreme Dry Events in a Montane Rainforest in Southern Ecuador.

Under drought conditions, even tropical rainforests might turn from carbon sinks to sources, and tree species composition might be altered by increased mortality. We monitored stem diameter variations of 40 tree individuals with stem diameters above 10 cm belonging to eleven different tree genera and three tree life forms with high-resolution dendrometers from July 2007 to November 2010 and additionally March 2015 to December 2017 in a tropical mountain rainforest in South Ecuador, a biodiversity hotspot with more than 300 different tree species belonging to different functional types. Although our study area receives around 2200 mm of annual rainfall, dry spells occur regularly during so-called “Veranillo del Niño” (VdN) periods in October-November. In climate change scenarios, droughts are expected with higher frequency and intensity as today. We selected dry intervals with a minimum of four consecutive days to examine how different tree species respond to drought stress, raising the question if some species are better adapted to a possible higher frequency and increasing duration of dry periods. We analyzed the averaged species-specific stem shrinkage rates and recovery times during and after dry periods. The two deciduous broadleaved species Cedrela montana and Handroanthus chrysanthus showed the biggest stem shrinkage of up to 2 mm after 10 consecutive dry days. A comparison of daily circumference changes over 600 consecutive days revealed different drought responses between the families concerning the percentage of days with stem shrinkage/increment, ranging from 27.5 to 72.5% for Graffenrieda emarginata to 45–55% for Podocarpus oleifolius under same climate conditions. Moreover, we found great difference of recovery times after longer-lasting (i.e., eight to ten days) VdN drought events between the two evergreen broadleaved species Vismia cavanillesiana and Tapirira guianensis. While Vismia replenished to pre-VdN stem circumference after only 5 days, Tapirira needed 52 days on average to restore its circumference. Hence, a higher frequency of droughts might increase inter-species competition and species-specific mortality and might finally alter the species composition of the ecosystem.

Coordination of stomatal control and stem water storage on plant water use in desert riparian trees

Populus euphratica Oliv. is a relatively ‘conservative’ water user even when growing in favourable water conditions, but the mechanistic understanding of this has received little attention. We undertook an experiment to determine trees water use by measuring stem and root sap flow (Fs), variation in stem diameter (Ds), leaf stomatal gas-exchange (e.g. conductance, gs and transpiration, Tr) and water potential $$\left( {{\psi _{\text{L}}}} \right)$$ during the growing season for P. euphratica. There was a hysteretic ‘apparent feedforward’ of stomatal response to increasing VPD. Mean of gs was not significantly different among months. $${\psi _{\text{L}}}$$ was negatively related to gs and Tr, but in contrast, stem Fs was positively associated to Tr but not to gs. There was no lag in the daily onset and cessation of Fs between the bottom and top of the trunk, possibly due to the short distance between measurement points (about 2 m), however, the lag time in Fs between the bottom of the trunk and roots, approximately 30 min, suggested that stored water was withdrawn first from the trunk and subsequently the roots. Daily contraction of Ds (− Ds) increased with increasing Fs during both day and night, and expansion of Ds (+ Ds) showed a logarithmic rise to a maximum with increasing Fs during the day. Day Fs and − Ds were also logarithmic with respect to VPD, with a correlation coefficient equal to 0.51 and 0.50, respectively (P < 0.001). This suggests that water use of P. euphratica was determined by the stomatal control and stem water storage together, which has great significance for the species buffers xylem water deficit, maintaining high leaf production, and water use efficiency.

Optical Flow-Based Analysis of the Relationships between Leaf Wilting and Stem Diameter Variations in Tomato Plants.

The estimation of water stress is critical for the reliable production of high-quality fruits cultivated using the tacit knowledge of expert farmers. Multimodal deep neural network has achieved success in the estimation of stem diameter variations as a water stress index, calculated from leaf wilting and environmental data. However, these studies have not addressed the specific role of leaf wilting in the estimation. Revealing the role of leaf wilting not only ensures the reliability of the estimation model but also provides an opportunity for improving the estimation method. In this paper, we investigated the relationships between leaf wilting and stem diameter variations without resorting to black-box approaches such as deep neural network. To clarify the role of leaf wilting, this study uses cross-correlation analysis to analyze the time lag correlation between leaf wilting, quantified by optical flow, and stem diameter variations as a water stress index. The analysis showed that leaf wilting had a significant time lag correlation with short-term stem diameter variations, which were water stress responses in plants. As the results were consistent with known plant water transport mechanisms, it was suggested that leaf wilting quantified by optical flow can explain short-term stem diameter variations.

Строение древостоев среднетаежных сосняков лишайниковых на европейском северо-востоке России

В статье представлены результаты, характеризующие строение древостоев среднетаежных сосняков лишайниковых на европейском северо-востоке России. Проведен статистический анализрядов распределения деревьев сосны по диаметру и высоте ствола. Установлено, что коэффициентвариации высоты в древостоях сосняков изменяется от 9 до 34 %, а асимметрия близка к нулевомузначению, что свидетельствует о почти нормальном распределении деревьев. Коэффициент вариации диаметра колеблется от 27 до 67 %, что говорит о растянутости распределения особей сосны в насаждениях по этому показателю. Показан вклад деревьев разных ступеней толщины в накопление запасов древесины древостоем. В средневозрастных и приспевающих насаждениях 41–55 % от числа деревьев и 32–41 % от объема древесины приходится на ступень толщины, соответствующую среднему диаметру дерева в древостое, и на две соседние ступени толщины. В спелых и перестойных сосняках эти величины составили 6–48 и 4–46 % соответственно, что отражает наличие нескольких поколений в древостоях на этих стадиях развития. Выявлена статистически достоверная взаимосвязь (положительная и отрицательная) между средним диаметром дерева и числом крупно- и тонкомерных деревьев, тогда как корреляции между средним диаметром дерева и запасом древесины в крупномерных и деревьях средних ступеней толщины не обнаружено. Выведено обобщенное регрессионное уравнение взаимосвязи высоты дерева от его диаметра, которое можно использовать для определения высоты деревьев среднетаежных сосняков лишайниковых на европейском северо-востоке России.

PENGARUH DOSIS PUPUK BIO SLURRY CAIR DAN JARAK TANAM TERHADAP PERTUMBUHAN DAN HASIL TANAMAN MENTIMUN (Cucumis sativus L.)

This study aims to determine the effect of liquid organic fertilizer on the growth andyield of cucumber plants, to determine the effect of applying spacing on the growth and yield ofcucumber plants, to determine the interaction of liquid bio slurry fertilizer and spacing ongrowth and yield of cucumber plants. The study was conducted using a randomized block designarranged in factorial (RAK) with 2 factors, the first factor was a liquid bio slurry fertilizer (P)dose consisting of 3 levels, 40 l / ha-1 (P1), 80 l / ha- 1 (P2), 120 l / ha-1 (P3). The second factoris the spacing (J) consisting of 3 levels: 30x60 cm (J1), 40x60 cm (J2), 50x60 cm (J3), 60x60 cm(J4). The variables observed included stem diameter, leaf area, and total weight. Data wereanalyzed using analysis of variance (ANOVA) level of 5% and further testing with Duncan 'sMultiple Range Test (DMRT). The results showed: By giving different liquid slurry bio fertilizerdoses gave a significant effect on the leaf area of cucumber plants at the age of 21 HSTobservations. The best treatment for organic fertilizer dosage is in the treatment of 120 L ha -1(P3). The application of spacing has a significant effect on the stem diameter variable at the ageof 28 HST observations, and on leaf area variables at all ages of observation. The best treatmentof spacing on the variable stem diameter and leaf area on the treatment spacing of 60x60 cm(J4). There were no significant interactions on the treatment of liquid bio slurry fertilizer dosesand the spacing of growth and yield of cucumber plants at all ages of observation.

PENGARUH DOSIS PUPUK BIO SLURRY CAIR DAN JARAK TANAM TERHADAP PERTUMBUHAN DAN HASIL TANAMAN MENTIMUN (Cucumis sativus L.)

This study aims to determine the effect of liquid organic fertilizer on the growth andyield of cucumber plants, to determine the effect of applying spacing on the growth and yield ofcucumber plants, to determine the interaction of liquid bio slurry fertilizer and spacing ongrowth and yield of cucumber plants. The study was conducted using a randomized block designarranged in factorial (RAK) with 2 factors, the first factor was a liquid bio slurry fertilizer (P)dose consisting of 3 levels, 40 l / ha-1 (P1), 80 l / ha- 1 (P2), 120 l / ha-1 (P3). The second factoris the spacing (J) consisting of 3 levels: 30x60 cm (J1), 40x60 cm (J2), 50x60 cm (J3), 60x60 cm(J4). The variables observed included stem diameter, leaf area, and total weight. Data wereanalyzed using analysis of variance (ANOVA) level of 5% and further testing with Duncan 'sMultiple Range Test (DMRT). The results showed: By giving different liquid slurry bio fertilizerdoses gave a significant effect on the leaf area of cucumber plants at the age of 21 HSTobservations. The best treatment for organic fertilizer dosage is in the treatment of 120 L ha -1(P3). The application of spacing has a significant effect on the stem diameter variable at the ageof 28 HST observations, and on leaf area variables at all ages of observation. The best treatmentof spacing on the variable stem diameter and leaf area on the treatment spacing of 60x60 cm(J4). There were no significant interactions on the treatment of liquid bio slurry fertilizer dosesand the spacing of growth and yield of cucumber plants at all ages of observation.

Classifying development stages of primeval European beech forests: is clustering a useful tool?

BackgroundOld-growth and primeval forests are passing through a natural development cycle with recurring stages of forest development. Several methods for assigning patches of different structure and size to forest development stages or phases do exist. All currently existing classification methods have in common that a priori assumptions about the characteristics of certain stand structural attributes such as deadwood amount are made. We tested the hypothesis that multivariate datasets of primeval beech forest stand structure possess an inherent, aggregated configuration of data points with individual clusters representing forest development stages. From two completely mapped primeval beech forests in Albania, seven ecologically important stand structural attributes characterizing stand density, regeneration, stem diameter variation and amount of deadwood are derived at 8216 and 9666 virtual sampling points (moving window, focal filtering). K-means clustering is used to detect clusters in the datasets (number of clusters (k) between 2 and 5). The quality of the single clustering solutions is analyzed with average silhouette width as a measure for clustering quality. In a sensitivity analysis, clustering is done with datasets of four different spatial scales of observation (200, 500, 1000 and 1500 m2, circular virtual plot area around sampling points) and with two different kernels (equal weighting of all objects within a plot vs. weighting by distance to the virtual plot center).ResultsThe clustering solutions succeeded in detecting and mapping areas with homogeneous stand structure. The areas had extensions of more than 200 m2, but differences between clusters were very small with average silhouette widths of less than 0.28. The obtained datasets had a homogeneous configuration with only very weak trends for clustering.ConclusionsOur results imply that forest development takes place on a continuous scale and that discrimination between development stages in primeval beech forests is splitting continuous datasets at selected thresholds. For the analysis of the forest development cycle, direct quantification of relevant structural features or processes might be more appropriate than classification. If, however, the study design demands classification, our results can justify the application of conventional forest development stage classification schemes rather than clustering.

Stomatal sensitivity inCorylus avellana(L.): first analysis from a global dataset

The cultivated area planted with hazelnut is rapidly increasing. The species is now being planted in areas where precipitation is scarce and irrigation is needed for ensuring profitable orchards. Moreover hazelnut is known to be sensitive to water shortage as it responds quickly to the increase of vapor pressure deficit by reducing stomatal aperture and consequently carbon assimilation. However modeling stomatal responses in different climatic conditions is still a challenging task. The general aim of the research was to predict stomatal responses by collecting data in different climatic conditions and soil water availability. We installed five measurement sites with different cultivars (‘Tonda Gentile delle Langhe’, ‘Tonda di Giffoni’, ‘Ennis’) in different countries (France, Georgia, Australia, Chile) and under different irrigation regimes. In each site we measured the sap flow in six trees, the soil water content, the stem diameter variations and the meteorological parameters. In two sites (Australia and France) we measured the stomatal conductance and the carbon assimilation by using a portable gas analyzer. Results showed that in all sites and cultivars, hazelnut trees strongly reduce the stomatal aperture when the vapor pressure deficit exceeds 10 hPa, which leads to a decrease in the assimilation rate. The daily course of stomatal aperture showed that the maximum is reached very early in the morning (about 9 AM) and then it drops abruptly. Furthermore, the species responses at leaf level were coherent with those at the tree canopy level, establishing a crucial basis for the future modelling of the water use at the orchard level. We showed that the carbon assimilation is mainly controlled by stomatal sensitivity to vapor pressure deficit and that, even in conditions of high soil water content, the photosynthetic capacity of the species is clearly reduced.

Transpiration at leaf and tree level in a poplar short-rotation coppice culture: seasonal and genotypic differences

Poplar (Populus spp.) is one of the most commonly cultivated genera in experimental and commercial short-rotation coppice (SRC) plantations. The genus is among the fastest growing in temperate latitudes, but the success of highly productive poplar SRC plantations strongly depends on soil water availability. We examined the transpiration at the leaf and the individual tree levels of four different poplar genotypes under an SRC regime. Measurements were performed for the entire growing season of 2016, during the seventh growth year of the plantation and before the third coppice on four poplar genotypes (three individual multiple-stem trees per genotype) belonging to different species and from a different genetic background. The experimental site was a commercial scale multi-genotype SRC plantation, established in Flanders (Belgium). Measurements at the leaf level were performed on specific days of the growing season that differed in evaporative demand, temperature and incoming radiation. To determine the transpiration at the stem level, we measured single-stem sap flow using the stem heat balance (SHB) method and daily stem diameter variation measurements. The whole-tree transpiration was estimated by summing the sap flow rates from all stems. Measurements at the stem level were continuously monitored during the entire growing season. Sap flow was tightly connected to the phenological stage of the trees, thus onset of spring (leaf area development) and late autumn (leaf fall) were easily identifiable from sap flow measurements, showing differences among the four genotypes. The dynamics of transpiration at the leaf and tree level were driven by photosynthetic photon flux density (PPFD), but the sap flow intensity was controlled by vapour pressure deficit (VPD). The four poplar genotypes showed different water use strategies, based on determination of transpiration and other plant water status indicators.

The potential of the tree water potential.

Non-invasive quantification of tree water potential is one of the grand challenges for assessing the fate of trees and forests in the coming decades. Tree water potential is a robust and direct indicator of tree water status and is preferably used to track how trees, forests and vegetation in general respond to changes in climate and drought. In this issue of Tree Physiology, Dietrich et al. (2018) predict the daily canopy water potential of mature temperate trees from tree water deficit derived from stem diameter variation measurements.

Genotypic variation in transpiration of coppiced poplar during the third rotation of a short-rotation bio-energy culture.

The productivity of short‐rotation coppice (SRC) plantations with poplar (Populus spp.) strongly depends on soil water availability, which limits the future development of its cultivation, and makes the study of the transpirational water loss particularly timely under the ongoing climate change (more frequent drought and floods). This study assesses the transpiration at different scales (leaf, tree and stand) of four poplar genotypes belonging to different species and from a different genetic background grown under an SRC regime. Measurements were performed for an entire growing season during the third year of the third rotation in a commercial scale multigenotype SRC plantation in Flanders (Belgium). Measurements at leaf level were performed on specific days with a contrasted evaporative demand, temperature and incoming shortwave radiation and included stomatal conductance, stem and leaf water potential. Leaf transpiration and leaf hydraulic conductance were obtained from these measurements. To determine the transpiration at the tree level, single‐stem sap flow using the stem heat balance (SHB) method and daily stem diameter variations were measured during the entire growing season. Sap flow‐based canopy transpiration (E c), seasonal dry biomass yield, and water use efficiency (WUE; g aboveground dry matter/kg water transpired) of the four poplar genotypes were also calculated. The genotypes had contrasting physiological responses to environmental drivers and to soil conditions. Sap flow was tightly linked to the phenological stage of the trees and to the environmental variables (photosynthetically active radiation and vapor pressure deficit). The total E c for the 2016 growing season was of 334, 350, 483 and 618 mm for the four poplar genotypes, Bakan, Koster, Oudenberg and Grimminge, respectively. The differences in physiological traits and in transpiration of the four genotypes resulted in different responses of WUE.

Design, fabrication and testing of a low cost Trunk Diameter Variation (TDV) measurement system based on an ATmega 328/P microcontroller

A fast-responding inexpensive dendrometer is needed for measuring daily or hourly plant growth responses to water stress. This study reports on a low-cost microcontroller driven Trunk Diameter Variations (TDV) measurement system that was designed and constructed for automating the measurement and recording of plant stem diameter. The TDV system comprises of an ATmega 328/P microcontroller, which forms the heart of the controlling circuit, a real time clock for time stamping measurements, liquid crystal display for displaying purposes and an external secure digital card and shield for storing measured data. The stem diameter variations are measured by a caliper-type sensor based on a full bridge strain gauge that is attached to a flexible arm of mild steel. When bearing bending strain, the excited full bridge strain gauge outputs a voltage directly proportional to the bending strain, hence linear displacement. The TDV sensor displacement calibration procedure was carried out using an inside micrometer from a calibration kit. The calibration of the sensor indicated a linear relationship between the displacement and the sensor’s output voltage with a high coefficient of determination value of 0.998, calibration multiplier of 0.426 mm V−1 and an offset output voltage of 0.688 V. The TDV sensor was mounted on a smooth cylindrical dried wood away from direct sunlight and rain while air temperature was measured close to the TDV installation. Temperature sensitivity test results show that the accuracy of the sensor above 20 °C is 0.031 mm and for temperatures below 20 °C the accuracy is above 0.050 mm. The TDV system was tested on a tomato plant for 42 days, Fountain tree for three weeks and on a Citrus tree for one week under greenhouse and open-field conditions in order to evaluate its performance and suitability under different plant species and climatic conditions. The TDV system proved to be robust and produced valid results on the plant’s physiological measurements, with a good storage of the measured data over the experimental period. We concluded that the TDV system is suitable for stem diameter variations measurements and water and fertilizer stress monitoring on herbaceous and woody stem plants due to its fast response (hourly or less), ease of construction and installation, and low cost (<US$60).

Direct uptake of canopy rainwater causes turgor-driven growth spurts in the mangrove Avicennia marina.

Mangrove forests depend on a dense structure of sufficiently large trees to fulfil their essential functions as providers of food and wood for animals and people, CO2 sinks and protection from storms. Growth of these forests is known to be dependent on the salinity of soil water, but the influence of foliar uptake of rainwater as a freshwater source, additional to soil water, has hardly been investigated. Under field conditions in Australia, stem diameter variation, sap flow and stem water potential of the grey mangrove (Avicennia marina (Forssk.) Vierh.) were simultaneously measured during alternating dry and rainy periods. We found that sap flow in A. marina was reversed, from canopy to roots, during and shortly after rainfall events. Simultaneously, stem diameters rapidly increased with growth rates up to 70 μm h-1, which is about 25-75 times the normal growth rate reported in temperate trees. A mechanistic tree model was applied to provide evidence that A. marina trees take up water through their leaves, and that this water contributes to turgor-driven stem growth. Our results indicate that direct uptake of freshwater by the canopy during rainfall supports mangrove tree growth and serve as a call to consider this water uptake pathway if we aspire to correctly assess influences of changing rainfall patterns on mangrove tree growth.

Daily stem diameter variations can predict the canopy water status of mature temperate trees

Direct evidence for the link between stem diameter variations (SDV) and the daily canopy water status, i.e., daily water potentials (Ψ), is rare, particularly for tall trees. It thus remains unclear up to what degree SDV readings are useful to estimate daily canopy Ψ. We measured SDV with point dendrometers at the stem base of tall, mature individuals of six European forest tree species in a near-natural temperate forest and compared them with daily canopy Ψ during the growing seasons of 2014 (wet) and 2015 (dry). Stem diameter variations were de-trended for growth with two different approaches leading to the so-called tree water deficit (TWD). We found that midday Ψ can be predicted from TWD, independent of the growth-de-trending procedure to obtain TWD from SDV. Further, daily TWD was a better indicator for daily midday Ψ, particularly under dry conditions, than maximum daily shrinkage, another common quantity derived from SDV. Based on data from six temperate tree species, we conclude that TWD measured at the stem base is a consistent proxy for daily canopy midday Ψ of tall trees over the entire range of measured conditions.

Are there tides within trees?

Tree stem diameters and electrical stem potentials exhibit rhythmic variations with periodicities of 24-25 h. Under free-running conditions of constant light or darkness these rhythms were suggested to be mediated by the lunisolar gravitational force. To further unravel the regulation of tree stem diameter dilatations, many of the published time courses of diameter variations were re-evaluated in conjunction with the contemporaneous time courses of the lunisolar tidal acceleration. This was accomplished by application of the Etide program, which estimates, with high temporal resolution, local gravitational changes as a consequence of the diurnal variations of the lunisolar gravitational force due to the orbits and relative positions of Earth, Moon and Sun. In all instances investigated, it was evident that a synchronism exists between the times of the turning points of both the lunisolar tide and stem diameter variations when the direction of extension changes. This finding of synchrony documents that the lunisolar tide is a regulator of the tree stem diameter dilatations. Under the described experimental conditions, rhythms in tree stem diameter dilations and electrical stem potentials are controlled by the lunisolar gravitational acceleration.

Post-veraison irreversible stem shrinkage in grapevine (Vitis vinifera) is caused by periderm formation.

Grapevines are characterized by a period of irreversible stem shrinkage around the onset of ripening of the grape berries. Since this shrinkage is unrelated to meteorological conditions or drought, it is often suggested that it is caused by the increased sink strength of the grape berries during this period. However, no studies so far have experimentally investigated the mechanisms underlying this irreversible stem shrinkage. We therefore combined continuous measurements of stem diameter variations and histology of potted 2-year-old grapevines (Vitis vinifera L. 'Boskoop Glory'). Sink strength was altered by pruning all grape clusters (treatment P), while non-pruned grapevines served as control (treatment C). Unexpectedly, our results showed irreversible post-veraison stem shrinkage in both treatments, suggesting that the shrinkage is not linked to grape berry sink strength. Anatomical analysis indicated that the shrinkage is the result of the formation of successive concentric periderm layers, and the subsequent dehydration and compression of the older bark tissues, an anatomical feature that is characteristic of Vitis stems. Stem shrinkage is hence unrelated to grape berry development, in contrast to what has been previously suggested.

Cambial pinning relates wood anatomy to ecophysiology in the African tropical tree Maesopsis eminii.

A better understanding and prediction of the impact of changing climate on tree stem growth could greatly benefit from the combination of anatomical and ecophysiological knowledge, yet the majority of studies focus on one research field only. We propose an approach that combines the method of pinning (cambial wounding) to timestamp anatomical X-ray computed microtomography images with continuous measurements of sap flow and stem diameter variations. By pinning the cambium of well-watered and drought-treated young African tropical trees of the species Maesopsis eminii Engl. we could quantify wood formation during a specific period of time and relate it to tree physiology and prevailing microclimate. Integrating continuous plant measurements and high-frequency pinning proved very useful to visualize and quantify the effects on stem growth of drought in M. eminii. Wood formation completely stopped during drought, and was associated with a strong shrinkage in stem diameter. Next, an unexpected increase in stem diameter was observed during drought, probably caused by root pressure, but not accompanied by wood formation. Our proposed approach of combining continuous plant measurements with cambial pinning is very promising to relate ecophysiology to stem anatomy and to understand the mechanisms underlying tree stem growth and bridge the gaps between the two research fields.

Quantitative trait locus mapping of Populus bark features and stem diameter

BackgroundBark plays important roles in photosynthate transport and storage, along with physical and chemical protection. Bark texture varies extensively among species, from smooth to fissured to deeply furrowed, but its genetic control is unknown. This study sought to determine the main genomic regions associated with natural variation in bark features and stem diameter. Quantitative trait loci (QTL) were mapped using an interspecific pseudo-backcross pedigree (Populus trichocarpa x P. deltoides and P. deltoides) for bark texture, bark thickness and diameter collected across three years, two sites and three biological replicates per site.ResultsQTL specific to bark texture were highly reproducible in shared intervals across sites, years and replicates. Significant positive correlations and co-localization between trait QTL suggest pleiotropic regulators or closely linked genes. A list of candidate genes with related putative function, location close to QTL maxima and with the highest expression level in the phloem, xylem and cambium was identified.ConclusionCandidate genes for bark texture included an ortholog of Arabidopsis ANAC104 (PopNAC128), which plays a role in lignified fiber cell and ray development, as well as Pinin and Fasciclin (PopFLA) genes with a role in cell adhesion, cell shape and migration. The results presented in this study provide a basis for future genomic characterization of genes found within the QTL for bark texture, bark thickness and diameter in order to better understand stem and bark development in Populus and other woody perennial plants. The QTL mapping approach identified a list of prime candidate genes for further validation using functional genomics or forward genetics approaches.

Simulation of long-term stem diameter variation of Ficus benjamina based on simulated transpiration

Greenhouse microclimate (light, temperature, relative humidity and CO2) and irrigation are important factors for plant growth, development and quality in ornamental horticulture. To optimize plant growth, actual stem diameter growth can be measured and compared with a desired growth pattern. Using the deviation between measured and simulated stem diameter growth, growers can decide whether and in which way the microclimate or irrigation needs to be adjusted. Together with this decision, costs associated with climate control and irrigation must also be taken into account. This will help growers to find a proper balance between cultivation costs and plant growth. In this study, Ficus benjamina was grown from cutting to mature plant in a controlled greenhouse environment. Growing conditions, microclimate as well as plant spacing, closely resembled the ones used in commercial greenhouses. Microclimate, soil water content, leaf temperature, sap flow, stem diameter variation and leaf thickness were continuously measured on three plants. In addition, discrete measurements of leaf area, projected crown surface area, stem water potential, photosynthesis, transpiration and stomatal conductance were performed. These measurements were used to further extend a mechanistic plant model, which allows simulation of long-term stem diameter variation.

Daytime depression in temperature-normalised stem CO2 efflux in young poplar trees is dominated by low turgor pressure rather than by internal transport of respired CO2.

Daytime decreases in temperature-normalised stem CO2 efflux (EA_D ) are commonly ascribed to internal transport of respired CO2 (FT ) or to an attenuated respiratory activity due to lowered turgor pressure. The two are difficult to separate as they are simultaneously driven by sap flow dynamics. To achieve combined gradients in turgor pressure and FT , sap flow rates in poplar trees were manipulated through severe defoliation, severe drought, moderate defoliation and moderate drought. Turgor pressure was mechanistically modelled using measurements of sap flow, stem diameter variation, and soil and stem water potential. A mass balance approach considering internal and external CO2 fluxes was applied to estimate FT . Under well-watered control conditions, both turgor pressure and sap flow, as a proxy of FT , were reliable predictors of EA_D . After tree manipulation, only turgor pressure was a robust predictor of EA_D . Moreover, FT accounted for <15% of EA_D . Our results suggest that daytime reductions in turgor pressure and associated constrained growth are the main cause of EA_D in young poplar trees. Turgor pressure is determined by both carbohydrate supply and water availability, and should be considered to improve our widely used but inaccurate temperature-based predictions of woody tissue respiration in global models.