Measurements of the bioelectrical potential of a Japanese oak (Quercus crispula Blume) sapling: Effect of the radial distribution of inorganic ingredients within a tree stem on the diurnal change in resting potential

This study investigated the relation between the resting potential of a 2-year-old Japanese oak (Quercus crispula Blume) sapling and its physiology, especially the radial transport of water containing inorganic ingredients in the stem using the scanning electron microscope-energy dispersive X-ray microanalyzer (SEM-EDXA) method. The resting potential of a sapling could be monitored continuously with our measuring apparatus. Changes in resting potential were due to the light. The hyperpolarization and depolarization peaks of the resting potential, whose absolute voltage was about 10mV, occurred right after lights-off and lights-on, respectively. The resting potential was found to show periodic responses for each day unit. At night (lights-off), the resting potential tended to depolarize with an increase in tangential strain. On the other hand, during the daytime (lights-on) the resting potential tended to hyperpolarize, depolarize, or show a nearly constant value for the tangential strain. The water containing inorganic ingredients was transported, via transpiration, in both directions between the mature xylem zone and the phloem zone through differentiating xylem cells. This water transport within a tree stem had a significant effect on the diurnal changes in resting potential.Part of this paper was presented at the 47th annual meeting of the Japan Wood Research Society, Kochi, April 3–5, 1997     

Nocturnal sap flow characteristics and stem water recharge of Acacia mangium

In this paper, we studied the nocturnal stem water recharge of Acacia mangium. It is helpful to improve the precision of canopy transpiration estimation and canopy stomatal conductance, and to further understand the lag time of canopy transpiration to stem sap flow. In this study, the whole-tree sap flow in an A. mangium forest was measured by using Granier’s thermal dissipation probe for over two years in the hilly land of South China. The environmental factors, including relative humidity (RH), precipitation, vapor pressure deficit (VPD), photosynthetically active radiation (PAR), and air temperature (T _a) were recorded simultaneously. The stem water recharge of A. mangium was analyzed on both daily and monthly scales. Sap flux density was lower at night than during the day. The time range of nighttime sap flux density was longer in the dry season than in the wet season. The water recharging mainly occurred from sunset to midnight. No significant differences were observed among inter-annual nighttime water recharges. Nighttime water recharge had no significant correlation with environmental factors, but was well correlated with the diameter at breast height, tree height, and crown size. In the dry season the contribution of nighttime water recharge to total transpiration had significant correlations with daytime transpiration, total transpiration, VPD, PAR and T _a, while in the wet season it was significantly correlated with daily transpiration and total transpiration. __________ Translated from Chinese Journal of Ecology, 2007, 26(4): 476–482 [译自: 生态学杂志]     

The ecological and functional correlates of nocturnal transpiration

Contrary to the conventional theory of optimal stomatal control, there is substantial transpiration at night in many tree species, but the functional significance of this phenomenon remains uncertain. To investigate the possible roles of nocturnal transpiration, we compared and contrasted the correlations of both nocturnal and diurnal sap flow with a range of traits in 21 temperate deciduous tree species. These traits included soil water affinity, shade tolerance, cold hardiness, nitrogen concentration of tissues, minimum transpiration rate of excised leaves, growth rate, photosynthetic capacity, stomatal length and density, and the water potential and relative water content of leaves at the wilting point. Nocturnal sap flow was higher in species with higher leaf nitrogen concentrations, higher rates of extension growth and lower shade tolerances. Diurnal sap flow was higher in species with higher leaf nitrogen concentrations and photosynthetic capacities on a leaf area basis. Because leaf metabolism and dark respiration, in particular, are strongly related to leaf nitrogen concentration, our findings suggest that nocturnal transpiration functions to sustain carbohydrate export and other processes driven by dark respiration, and that this function is most important in fast- growing shade-intolerant tree species.     

Partition of nocturnal sap flow in Acacia mangium and its implication for estimating the whole-tree transpiration

We analyzed the partition of nocturnal sap flow into refilling of internal water storage and transpiration in Acacia mangium. Sap flow of trees was monitored continuously with Granier’s sensors for estimating the whole-tree transpiration. Possible night transpiration and stomatal conductance at the leaf level in the canopy were measured with a LI-6400 photosynthesis measuring system. For nocturnal leaf transpiration and stomatal conductance were weak, nocturnal sap flow of mature A. mangium trees was mainly associated with water recharge in the trunk. No significant change in night water recharge of the trunk was found at both seasonal and inter-annual scales. Morphological features of trees including diameter at the breast height (DBH), tree height, and canopy size could explain variances of night water recharge. Furthermore, although the contribution of nocturnal sap flow to the total transpiration varied among seasons and DBH classes, the error caused by night water recharge on wholetree transpiration was negligible. __________ Translated from Journal of Plant Ecology (Chinese Version), 2007, 31 (5): 777–786 [译自: 植物生态学报]     

大青山油松人工林树干液流动态及其蒸腾耗水规律研究

应用TDP(Thermal Dissipation Probe)技术对大青山古路板林场的30a生油松人工林树干液流以及不同林分密度下的树木蒸腾耗水规律进行了研究。结果表明:1)在生长季内,树干径向断面形成层以下不同部位输水能力差异较大,最大流速位于形成层下3cm。2)油松树干液流的日进程呈现明显的昼夜变化规律。在11:00左右达到峰值,其值可达0.286 6~0.306 0cm3/s。3)树干液流量(Y)与树木的胸径(X)之间的关系可用Y=0.0053EXP(0.4823X)的指数函数模型表达。4)在相同立地条件下,随着阴坡林分密度从2 147株/hm2增加到4 463株/hm2,单株蒸腾耗水量从0.543 4cm3/s降低到0.319 7cm3/s,而林分蒸腾耗水量变化幅度较小,平均蒸腾耗水量为0.3710±0.0489(5)mm/h。结果指出,大青山30a生油松人工林经营密度应控制在3 307株/hm2左右。     

Xylem sap flow and drought stress of Fraxinus excelsior saplings

We report on diurnal and seasonal variations in sap flow rate and stem water potential of Fraxinus excelsior L. saplings growing at the edge of a Fraxino-Aceretum forest in western Germany. Because of shallow soil, the trees were subjected to drought in summer. When soil water availability was not limiting, sap flow rate was related to changes in solar radiation and vapor pressure deficit. Maximum transpiration rates per leaf area were 3.5-7.4 mmol m-2 s-1, and maximum daily totals were 1.7-3.3 kg m-2 day-1. Under drought conditions, stem water potential dropped to midday minima of -2.6 to -3.5 MPa and sap flow rate was strongly related to this parameter. After the drought period, reduced apparent (whole-plant) hydraulic conductance was observed, which was attributed to a continued reduction in stomatal conductance after the drought stress had ceased. A model was developed that linked sap flow rate directly to climatic variables and stem water potential. Good correlation between measured and simulated sap flow rates allowed the model to be used for data interpretation.     

Tree water storage and its diurnal dynamics related to sap flow and changes in stem volume in old-growth Douglas-fir trees

Diurnal and seasonal tree water storage was studied in three large Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) trees at the Wind River Canopy Crane Research site. Changes in water storage were based on measurements of sap flow and changes in stem volume and tissue water content at different heights in the stem and branches. We measured sap flow by two variants of the heat balance method (with internal heating in stems and external heating in branches), stem volume with electronic dendrometers, and tissue water content gravimetrically. Water storage was calculated from the differences in diurnal courses of sap flow at different heights and their integration. Old-growth Douglas-fir trees contained large amounts of free water: stem sapwood was the most important storage site, followed by stem phloem, branch sapwood, branch phloem and needles. There were significant time shifts (minutes to hours) between sap flow measured at different positions within the transport system (i.e., stem base to shoot tip), suggesting a highly elastic transport system. On selected fine days between late July and early October, when daily transpiration ranged from 150 to 300 liters, the quantity of stored water used daily ranged from 25 to 55 liters, i.e., about 20% of daily total sap flow. The greatest amount of this stored water came from the lower stem; however, proportionally more water was removed from the upper parts of the tree relative to their water storage capacity. In addition to lags in sap flow from one point in the hydrolic pathway to another, the withdrawal and replacement of stored water was reflected in changes in stem volume. When point-to-point lags in sap flow (minutes to hours near the top and stem base, respectively) were considered, there was a strong linear relationship between stem volume changes and transpiration. Volume changes of the whole tree were small (equivalent to 14% of the total daily use of stored water) indicating that most stored water came from the stem and from its inelastic (sapwood) tissues. Whole tree transpiration can be maintained with stored water for about a week, but it can be maintained with stored water from the upper crown alone for no more than a few hours.     

The effect of aqueous transport of CO(2) in xylem sap on gas exchange in woody plants

The influence of CO(2) transported in the transpiration stream on measurements of leaf photosynthesis and stem respiration was investigated. Measurements were made on trees in a temperate forest in Scotland and in a tropical rain forest in Cameroon, and on shrubs in the Sahelian zone in Niger. A chamber was designed to measure the CO(2) partial pressure in the gas phase within the woody stems of trees. High CO(2) partial pressures were found, ranging from 3000 to 9200 Pa. Henry's Law was used to estimate the CO(2) concentration of xylem sap, assuming that it was in equilibrium with the measured gas phase partial pressures. The transport of CO(2) in the xylem sap was calculated by multiplying sap CO(2) concentration by transpiration rate. The magnitude of aqueous transport in the studied species ranged from 0.03 to 0.35 &mgr;mol CO(2) m(-2) s(-1), representing 0.5 to 7.1% of typical leaf photosynthetic rates. These values strongly depend on sap pH. To examine the influence of aqueous transport of CO(2) on stem gas exchange, we made simultaneous measurements of stem CO(2) efflux and sap flow on the same stem. After removing the effect of temperature, stem CO(2) efflux was positively related to sap flow. The apparent effect on measurements of stem respiration was up to 0.7 &mgr;mol m(-2) s(-1), representing ~12% of peak stem respiration rates.     

Sap flow of the major tree species in the eastern mountainous region in northeast China

This study is based on Quercus mongolica, Fraxinus mandshurica, Phellodendron amurense, Juglans mandshurica, Tilia amurensis, and Pinus koraiensis trees of the same age (12 years) and seedling origin under the same site conditions. The sap flow density, water consumption, and related environmental factors were also measured using thermal dissipation method and ICT-2000TE (Transpiration-Environment) automatic measuring system for tree transpiration and environmental factors. On clear days during the growing season, the sap flow density exhibited mono-peak diurnal patterns, mostly between 10:00 and 14:00, except for Phellodendron amurense, whose sap flow showed two peaks during the daytime three times. The photosynthetically active radiation (PAR) and vapour pressure deficit (VPD) were the major factors influencing diurnal changes in sap flow, which explained 60%–74% variations in sap flow density for all species except Phellodendron amurense. Maximum sap flow densities for F. mandshurica, Phellodendron amurense, Q. mongolica, J. mandshurica, T. amurensis, and Pinus koraiensis were 516.36, 234.00, 625.93, 945.83, 507.93, and 286.21 cm³/(cm²·h), in July, June, September, August, August, and July, respectively. Water consumption during the whole growing season for J. mandshurica, T. amurensis, F. mandshurica, Pinus koraiensis, Phellodendron amurense, and Q. mongolica was 3,840, 2,820, 2,710, 2,120, 1,470, and 1,390 kg/sapling, respectively. __________ Translated from Scientia Silvae Sinicae, 2005, 41(3): 36–42 [译自: 林业科学, 2005, 41(3): 36–42]     

不同黑杨无性系叶片及单木水平蒸腾特性研究

以廊坊地区杨树胶合板用材林主要造林树种中林46杨和廊坊杨为研究对象,应用快速称重法和热扩散茎流计分别观测了不同杨树叶片蒸腾速率和树干液流变化特征,旨在为该地区更精确地估计生态用水定额提供科学依据,而且也可为该区域杨树胶合板材林的造林、营林及流域综合管理提供理论基础。结果表明:无论晴天还是阴天,林木叶片蒸腾速率日变化都呈现有规律的单峰曲线,晴天表现为单峰宽峰曲线,阴天为单峰窄峰曲线;树干边材液流的日变化均表现出明显的昼夜规律;树干的测定方位不同,其液流速率存在着一定差异,白天均表现出一致的规律:树干南侧液流速率>树干北侧液流速率,而夜间树干南北液流速率大小相差不大,维持在0～2cm/h上下波动。     

刺槐春夏季树干液流变化规律

用热扩散式树干茎流计(TDP)于4-8月对刺槐树干液流进行连续观测,结果表明:刺槐边材液流速率日变化呈宽峰曲线,每日6:50左右启动,13:00左右达到峰值,19:30左右开始迅速下降,没有明显的液流停止界限,夜间有较高的液流存在;夏季液流每天启动的时间早于春季10min左右,达到峰值的时间早于春季1h左右,迅速下降的时间晚于春季1h左右,即夏季液流高峰维持的时间长于春季,但是夏季的峰值、日平均液流速率和液流通量小于春季;树干液流速率与直径关系不大,但日周期单木耗水量随树干直径的增大而增加,与树干直径和边材面积相关显著,相关系数分别为0.983和0.999.     

Evaluation of sap flow density of <Emphasis Type="Italic">Acacia melanoxylon</Emphasis> R. Br. (blackwood) trees in overstocked stands in north-western Iberian Peninsula

Sap flow density and meteorological variables were monitored in a very dense Acacia melanoxylon stand (about 9,000 trees/ha) in north-western Iberian Peninsula during the growing season of 2006 (from 8 June to 24 August). Evidences of an increment of stomatal control on transpiration were observed during the study period, probably as a consequence of higher evaporative demand of the atmosphere. However, high sap flow density values observed for the whole study period (from 1.14 to 52.73 dm³ dm⁻² day⁻¹) were similar than those found for other fast-growing species. Mean transpiration for the whole study period was 2.21 mm day⁻¹, with a maximum value of 3.17 mm day⁻¹ and a minimum of 1.23 mm day⁻¹. Mean sap flow density values were correlated with crown length and crown ratio, relationships being fairly weak with other dendrometric parameters such as tree diameter or height. Mean transpiration values were correlated with main dendrometric parameters (diameter at breast height, total height, crown length, sapwood area and leaf biomass). It was found that the degree of competition per tree could be used as a good index for sap flow density. Taking into account the high tree density of the stand and the sap flow density values, water consumptions of A. melanoxylon can be very high, playing a relevant role in the hydrological balances of the watersheds where it grows.     

Change of trunk sap flow of Ginkgo biloba L. and its response to inhibiting transpiration treatment

For this paper, GREENSPAN sap flow system was used to monitor the dynamics of trunk sap flow of Gingkgo biloba. Results indicate that sap flow velocity is significantly different among different heights, depths, and directions of the trunk. Sap flow velocity at the upper position of the trunk is higher than that of the middle and lower position, but cumulative flux is not significantly different among the upper, middle and lower sections. Sap flow velocity at 10 mm reached the most and that at 20 mm the least. However, sap flow velocity at 5 mm and 15 mm was similar and was second among the four depths. Results also showed that sap flow velocity of the south was the highest, and that of the west was next. An Automatic Weather Station of HOBO was synchronously applied to measure these meteorological parameters, and the relationship between these parameters and the changes of trunk sap flow velocity were analyzed. We found that the change of sap flow velocity was a single-crest curve on clear days and multi-crest curve on cloudy and rainy days. In addition, it is also revealed that by stepwise regression analyses photosynthetical active radiation (PAR), temperature and wind speed are the main environmental factors affecting sap flow velocity. The efficient methods of reducing water transpiration of trees, including leaf pruning, overshadowing and antitranspirant spraying, were found by investigating the effects on inhibiting transpiration, which indicated that spraying of antitranspirants, leaf pruning and overshadowing could significantly reduce transpiration but the effects of leaf pruning and overshadowing were far better than that of antitranspirant spraying. Translated from Scientia Silvae Sinicae, 2006, 42(5): 22–28 [译自: 林业科学]     

热平衡茎流计在荒漠灌木植物耗水研究中的应用

首先对茎流热平衡技术测定植株茎流的基本原理进行了介绍。在此基础上,探讨了4种干旱沙区常见造林灌木的日耗水变化规律。并通过对同时观测的气象因子的分析,揭示植物耗水与太阳辐射、气温和大气湿度等因子的相关关系,建立了在西北干旱沙区,预测这4种植物蒸腾耗水的方程。     

Evaluation of the sap flow using heat pulse method to determine transpiration of the Populus euphratica canopy

The sap flow of the sampled Populus euphratica stems at different radial depths and directions had been studied in Ejina Oasis, in the lower reaches of the Heihe River. Based on sap flow measurements, the transpiration of the entire canopy was calculated. Results showed a linear correlation between the sap flow and the sapwood area of the P. euphratica. Through the analysis of the diameter at breast height in the sample plot, it was found that the distribution of the diameters and the corresponding sapwood area was exponentially correlated, with the coefficient of correlation being 0.976,7. The calculated transpiration of the Populus euphratica canopy was 214.9 mm based on the specific conductivity method. Translated from Scientia Silvae Sinicae, 2006, 42(7): 28–32 [译自: 林业科学]     

Sap flow of irrigated <Emphasis Type="Italic">Populus alba</Emphasis> var. <Emphasis Type="Italic">pyramidalis</Emphasis> and its relationship with environmental factors and leaf area index in an arid region of Northwest China

Populus alba L. var. pyramidalis Bge. (Populus) is a main tree of the farmland shelter-belt system in the arid region of Northwest China. However, soil moisture cannot satisfy the water requirements of normal Populus growth under local natural conditions, thus studying the transpiration characteristics of irrigated Populus and its relationship with the environmental factors and growth parameters is very important to the growth of the trees in this region. In this study, the sap flow of two irrigated Populus trees was measured during May to September from 2005 to 2008 using the heat-pulse technique. The results show that the maximum and minimum daily sap fluxes in Populus were 15.7–24.0 and 3.0–4.0 L day⁻¹, respectively. And the sum of sap fluxes from June to August accounted for approximately 63–69% of the total sap flux during May to September (almost the whole growing season). The order of the meteorological factors affecting the daily sap flux of Populus was: vapor pressure deficit > solar radiation > mean air temperature > wind speed. Furthermore, a highly linear relationship between the ratio of daily sap flux to the reference evapotranspiration (SF/ET₀) and the amount of soil water in the 0–2.0 m layer was found, indicating that the amount of soil water at this layer was quite important to the growth of Populus in this region. Especially, the amount of soil water in the 0.5–1.0 m soil layer contributed to most of the plant transpiration as the highest coefficient of determination at this layer. Based on the environmental factors and leaf area index influencing sap flux, an empirical transpiration model was constructed to estimate daily transpiration.     

Tree stem diameter variations and transpiration in Scots pine: an analysis using a dynamic sap flow model

A dynamic model for simulating water flow in a Scots pine (Pinus sylvestris L.) tree was developed. The model is based on the cohesion theory and the assumption that fluctuating water tension driven by transpiration, together with the elasticity of wood tissue, causes variations in the diameter of a tree stem and branches. The change in xylem diameter can be linked to water tension in accordance with Hookea s law. The model was tested against field measurements of the diurnal xylem diameter change at different heights in a 37-year-old Scots pine at Hyyti?l?, southern Finland (61 degrees 51' N, 24 degrees 17' E, 181 m a.s.l.). Shoot transpiration and soil water potential were input data for the model. The biomechanical and hydraulic properties of wood and fine root hydraulic conductance were estimated from simulated and measured stem diameter changes during the course of 1 day. The estimated parameters attained values similar to literature values. The ratios of estimated parameters to literature values ranged from 0.5 to 0.9. The model predictions (stem diameters at several heights) were in close agreement with the measurements for a period of 6 days. The time lag between changes in transpiration rate and in sap flow rate at the base of the tree was about half an hour. The analysis showed that 40% of the resistance between the soil and the top of the tree was located in the rhizosphere. Modeling the water tension gradient and consequent woody diameter changes offer a convenient means of studying the link between wood hydraulic conductivity and control of transpiration.     

Estimating sap flux densities in date palm trees using the heat dissipation method and weighing lysimeters

In a world of diminishing water reservoirs and a rising demand for food, the practice and development of water stress indicators and sensors are in rapid progress. The heat dissipation method, originally established by Granier, is herein applied and modified to enable sap flow measurements in date palm trees in the southern Arava desert of Israel. A long and tough sensor was constructed to withstand insertion into the date palm's hard exterior stem. This stem is wide and fibrous, surrounded by an even tougher external non-conducting layer of dead leaf bases. Furthermore, being a monocot species, water flow does not necessarily occur through the outer part of the palm's stem, as in most trees. Therefore, it is highly important to investigate the variations of the sap flux densities and determine the preferable location for sap flow sensing within the stem. Once installed into fully grown date palm trees stationed on weighing lysimeters, sap flow as measured by the modified sensors was compared with the actual transpiration. Sap flow was found to be well correlated with transpiration, especially when using a recent calibration equation rather than the original Granier equation. Furthermore, inducing the axial variability of the sap flux densities was found to be highly important for accurate assessments of transpiration by sap flow measurements. The sensors indicated no transpiration at night, a high increase of transpiration from 06:00 to 09:00, maximum transpiration at 12:00, followed by a moderate reduction until 08:00; when transpiration ceased. These results were reinforced by the lysimeters' output. Reduced sap flux densities were detected at the stem's mantle when compared with its center. These results were reinforced by mechanistic measurements of the stem's specific hydraulic conductivity. Variance on the vertical axis was also observed, indicating an accelerated flow towards the upper parts of the tree and raising a hypothesis concerning dehydrating mechanisms of the date palm tree. Finally, the sensors indicated reduction in flow almost immediately after irrigation of field-grown trees was withheld, at a time when no climatic or phenological conditions could have led to reduction in transpiration.     

Processes preventing nocturnal equilibration between leaf and soil water potential in tropical savanna woody species

The impact of nocturnal water loss and recharge of stem water storage on predawn disequilibrium between leaf (psiL) and soil (psiS) water potentials was studied in three dominant tropical savanna woody species in central Brazil (Cerrado). Sap flow continued throughout the night during the dry season and contributed from 13 to 28% of total daily transpiration. During the dry season, psiL was substantially less negative in covered transpiring leaves, throughout the day and night, than in exposed leaves. Before dawn, differences in psiL between covered and exposed leaves were about 0.4 MPa. When relationships between sap flow and psiL of exposed leaves were extrapolated to zero flow, the resulting values of psiL (a proxy of weighted mean soil water potential) in two of the species were similar to predawn values of covered leaves. Consistent with substantial nocturnal sap flow, stomatal conductance (gs) never dropped below 40 mmol m(-2) s(-1) at night, and in some cases, rose to as much as 100 mmol m(-2) s(-1) before the end of the dark period. Nocturnal gs decreased linearly with increasing air saturation deficit (D), but there were species-specific differences in the slopes of the relationships between nocturnal gs and D. Withdrawal and recharge of water from stem storage compartments were assessed by monitoring diel fluctuations of stem diameter with electronic dendrometers. Stem water storage compartments tended to recharge faster when nocturnal transpiration was reduced by covering the entire plant. Water potential of covered leaves did not stabilize in any of the plants before the end of the dark period, suggesting that, even in covered plants, water storage tissues were not fully rehydrated by dawn. Patterns of sap flow and expansion and contraction of stems reflected the dynamics of water movement during utilization and recharge of stem water storage tissues. This study showed that nighttime transpiration and recharge of internal water storage contribute to predawn disequilibrium in water potential between leaves and soil in neotropical savanna woody plants.     

Relationship between effective solar radiation and sap flow process during an entire growing season in Western Mountains of Beijing

In order to explore the relationship between the time processes of solar radiation and sap flow, sap flow velocity (SFV) of Platycladus orientalis and Pinus tabulaeformis, effective solar radiation (ESR) and other environmental factors were synchronously monitored for one year in the Beijing Western Mountains by using a thermal dissipation probe (TDP) system and an automatic weather station. Results showed significant differences between changes in diurnal characteristics of ESR and sap flow in sunny days during three seasons. Starting times of sap flow occurred generally 1.5–3 hours later than those of solar radiation and there were small differences between Platycladus orientalis and Pinus tabulaeformis. But peak times and stopping times of sap flow varied con-siderably with large contrasts in ESR. The duration of sap flow showed clear differences among the seasons owing to the variable rhythms of climate factors in Beijing. Fluctuation amplitude in the duration of sap flow remained relatively stable during the autumn but changed greatly during spring and summer. Changes in diurnal sap flow velocity of both Platycladus orientalis and Pinus tabu-laeformis were about 0–3 hours later than those of ESR but with the same configuration. The start of sap flow was mainly induced by the sudden intensification of ESR (sunrise effect). Seasonal models of SFV indicated that a cubic equation had the best fit. It was more practical to simulate seasonal water consumption models of trees with ESR. In further investigations, these models should be optimized.