Changes In Sap Flow Research Articles

Quantifying Eucalyptus Transpiration Using the Dissipation Thermal Technique in Porto Seguro, Bahia

Granier’s sap flow method proved to be an important tool for estimating transpiration in woody plants. The present work aimed to estimate the transpiration of two clones (VCC0865 and CO1407) of a hybrid of the eucalyptus species Eucalyptus grandis × Eucalyptus urophylla, in order to understand the efficiency and patterns of water use in the forest ecosystem. The experiment was carried out on a eucalyptus farm in the municipality of Porto Seguro, located in the extreme south of Bahia. The spacing between trees was 3.60 m × 2.50 m. Sap flow measurements were performed daily, between February and December 2022, using 10 sensors installed in tree trunks, according to Granier’s thermal dissipation method. Data were recorded in the datalogger model CR10X system. For the systematization and analysis of the data, the R programming language was used. The results obtained indicated that the beginning of the transpiration period of the clones occurred around 07:00. On rainy days, less transpiration was observed in both clones. There were no significant changes in sap flow between dry and rainy seasons. It was also found for clone VCC0865 a transpiration rate of 43% higher in the daily average compared to clone CO1407. The present work is an important tool to contribute with information about transpiration in eucalyptus cultivation in the extreme south of Bahia, since there are few studies on the subject and given the importance of the activity in the region.

Sap flow characteristics and water demand prediction of cash crop in hyper-arid areas

Crop sap flow is a critical indicator of crop water demand, and predicting its variation trend is essential for adjusting agricultural planting structure and managing water resource in hyper-arid areas. Presently, research on crop sap flow in hyper-arid areas faces limitations due to inadequate meteorological data and restricted monitoring duration, leading to imprecise assessments of environmental impacts on future crop sap flow. Consequently, this hinders effective irrigation scheduling and oasis sustainable development policy. This study analyzed the sap flow changes characteristics of two economic crops (red jujube and walnut) at different time scales in the oasis in the south of Tarim Basin from 2017 to 2021 and the relationship between four environmental factors (solar radiation, temperature, relative humidity and vapor pressure deficit) and the sap flow of red jujube and walnut. By using the Random Forest (RF) model and the future climate data, the sap flow of the two economic crops from 2020 to 2100 was predicted. The results showed that: (1) walnut had a longer daily peak sap flow duration compared to red jujube, whereas red jujube showed a longer monthly peak sap flow duration; (2) in hyper-arid areas, the moisture and temperature directly influenced crop sap flow, while other environmental factor affected these two factors; (3) with the temperature increases, the water demand of red jujube and walnut in Cele Oasis will exceed local water resources carrying capacity. To achieve sustainable development of oasis, it is vital to consider future climatic changes in planning the expansion and crop structure.

Response of Typical Tree Species Sap Flow to Environmental Factors in the Hilly Areas of Haihe River Basin, China

Understanding developments in the trunk sap flow of prevalent tree species within the hilly areas of the Haihe River basin is imperative for ecosystem conservation. Nevertheless, the changes in sap flow of local trees and their response to environmental factors remain elusive. This study focuses on seven dominant tree species in the hilly area of the Haihe River basin and analyzed the relationship between tree sap flow rate and environmental factors at different time scales (hourly and daily). Our findings suggested: (1) Regardless of the time scale, total solar irradiance played a primary role in influencing sap flow rate. Conversely, as the time scale grew, the associations between most soil factors and sap flow rate enhanced, while those with meteorological factors declined. Notably, soil temperature exerted a more profound influence on sap flow rate than soil moisture and conductivity. (2) At the hourly scale, the sap flow rate of each species had a lag effect of 1–2 h with vapour pressure deficit, relative humidity and temperature, and 1 h or no lag effect with total solar irradiance and wind speed. (3) The response model of sap flow rate and environmental factors showed that, except for Pinus tabuliformis Carr., other tree species fit well at various time scales (R2 ≥ 0.59). As the time scale of most tree species increased from hourly scale to daily scale, the fit gradually weakened. Concurrently, considering the time-lag effect, the accuracy of the model has been improved, and the fitting accuracy of Koelreuteria paniculata Laxm. and Pinus tabuliformis Carr. has been significantly improved.

Distinct transpiration characteristics of black locust plantations acclimated to semiarid and subhumid sites in the Loess Plateau, China

Black locust (Robinia pseudoacacia) is widely planted throughout semiarid and subhumid regions of the Loess Plateau of China. Determining the changes in transpiration of this species in different climatic areas is important for revealing the acclimation mechanism of black locust and developing suitable forest management practices, particularly in the context of global climate change. Here, sap flow and canopy conductance of black locust plantation trees in semiarid (Yan’an) and subhumid (Yongshou) sites were quantified using Granier-type thermal dissipation probes and concurrent environmental observations from 2012 to 2017. Several physiological parameters were measured throughout the growing season. The results showed that sap flow was correlated with phenological factors across seasons within a year. However, interannual changes in sap flow were affected mainly by the reference evapotranspiration (ET0) at the Yongshou site, and jointly by precipitation (P), soil water content, and P/ET0 at the Yan’an site. Sap flow response to meteorological factors showed less discrepancy between pre- and post-rainfall periods at the Yan’an site. Moreover, canopy conductance fluctuated less with a wider range of vapor pressure deficit (VPD) and the slope of canopy resistance as a function of VPD was lower, indicating relatively lower sensitivity of stomatal conductance to environmental factors in Yan’an site. Physiological parameters, except for predawn leaf water potential, were significantly different between the two sites. The results suggested that black locust tended to reduce transpiration, modify leaf morphology, and improve water use efficiency to enhance its adaptability to the dryer site. The species changes stomatal regulation characteristics and general growth rate to acclimatize to distinct water habitats.

Precipitation dominates the transpiration of both the economic forest (Malus pumila) and ecological forest (Robinia pseudoacacia) on the Loess Plateau after about 15 years of water depletion in deep soil

Understanding how different tree species consume soil water is critical for land management, especially in areas with limited water resources. This study examined the soil water consumption characteristics of two exotic tree species—economic forest apple tree (Malus pumila) and ecological forest black locust (Robinia pseudoacacia)—and the effect of soil desiccation on plant transpiration in the 2018 growing season in a semi-arid region of the Loess Plateau. We investigated root distribution and deep soil water content in the vertical soil profile and used hydrogen and oxygen stable isotopes to identify the contribution of water to transpiration in shallow (0–2 m) and deep (>2 m) soil. We also measured sap flow changes using thermal dissipation probes during the growing season. The apple orchard had a maximum rooting depth of about 16 m, with a deep soil water deficit of about 771 mm. The corresponding figures for the black locust forest were about 25 m and 1926 mm. In previous years, the apple trees consumed 51.4 mm yr–1 of deep soil water and black locust consumed 120.4 mm yr–1. In the 2018 growing season, soil water content varied from 0–200 cm depth, with no significant changes beyond 200 cm in either species. Shallow soil water contributed, on average, 68.1% and 80.9% to transpiration in the apple orchard and black locust forest, respectively, and both they had a similar amount of transpiration during the growing season. These results indicate that rapid deep soil desiccation leads to a lack of sustainable root water uptake in deep soil, and the dominance of transpiration by precipitation in this region. This study increased our understanding on how intensive water extraction from deep soil affects tree transpiration, which is significant for sustainable afforestation in the Loess Plateau and other regions with similar hydrogeology.

Sap flow changes and climatic responses over multiple-year treatment of rainfall exclusion in a sub-humid black locust plantation

Black locust (Robinia pseudoacacia) plantations have been widely established in the semiarid and sub-humid areas of central China. Under the condition of global climate change, which is introducing much uncertainty of precipitation patterns in this region, it is of special significance to investigate their responses to precipitation. Here, we investigated sap flow response to reduced throughfall. Stem sap flow was measured from 2011 to 2017 using Granier-type sensors. By placing waterproof panels within tree rows, about 47.5% precipitation was excluded from treated plots since April 2015. Differences in soil water content gradually increased to 4.3% between treated and control plots with continued throughfall exclusion. Decreased precipitation input significantly reduced the average sap flux density in treated plots by 9.1%–45.3%. The extent of this reduction depended on precipitation in the previous and current years. Transpiration and forest growth were negatively affected by the treatment. Furthermore, sap flow response to environmental factors became insensitive, with the discrepancy increasing with increasing drought duration, but was regained by rainfall recharge to soil water in the first two treatment years. However, prolonged drought might damage transpiration resilience capacity, as the saturated sap flux after soil water recharging during the wet period was still lower than that in the control plot in the latter year. Predawn leaf water potential was significantly lower in the treated plot compared to the control plot, whereas midday leaf water potential was similar. Whole tree hydraulic conductance (GP) was also similar between the two plots, except in extreme drought months when GP was much lower in the treated plot. In addition, the specific leaf area and stomatal density decreased in the treated plot. Therefore, decreases in precipitation would cause a transpiration reduction, weakening the tree’s response to meteorological variables and lowering growth and productivity, potentially damaging transpiration resilience. These results suggest that black locust is sensitive to water changes, its capacity of drought tolerant is restrained by the drought time scale or drought severity, the use of such species in reforestation in semiarid regions should be implemented with caution.

Sap flow of Salix psammophila and its principal influencing factors at different slope positions in the Mu Us desert.

The changes in sap flow of Salix psammophila growing on a gentle slope (lower slope, P1), a middle slope (P2), and an upper slope (P3), and the response of sap flow to meteorological factors at the different slope positions were studied using the continuous and synchronized observations, the instrument were wrapped stem flowmeter EMS 62 sap-flow heat-balance-based system and the LSI-LASTEM automatic weather station. The results revealed that the soil moisture content was the highest and the growth conditions of Salix psammophila were the best at P1, followed by P2. At P3, however, although good apical dominance was observed, the proportion of dead branches was the highest. Furthermore, the daily variation patterns of sap flow on the three slopes presented as multi-peak bell-shaped curves. The daily accumulation changes in sap flow showed a trend of P1 > P3 > P2, and within the same diameter range, the sap flow at P1 was significantly different from that at P2 and P3, whereas the sap flow at P2 and P3 did not vary significantly. All the three slopes showed a significant and positive correlation with photosynthetically active radiation, atmospheric temperature, and vapor pressure difference, and a significant and negative correlation with relative humidity; however, the degrees of correlation varied slightly. The stepwise regression analysis showed that, at different slopes, different variables were selected for different branch diameters, but photosynthetically active radiation and atmospheric temperature played dominant roles on all slopes. This study reveals the sap flow pattern of Salix psammophila on different slopes and its response mechanism to meteorological factors, which was essential for understanding the restoration ability, physiological adaptability, and ecosystem stability of Salix psammophila communities.

The Relationship between Stem Diameter Shrinkage and Tree Bole Moisture Loss Due to Transpiration

The responsiveness of four types of stem diameter shrinkage indicators to sap flow changes was compared under four air temperature and cloudiness conditions: above 0 °C below 80% cloud cover days; above 0 °C large percentage cloud cover days; low temperature below 80% cloud cover days; and low temperature large percentage cloud cover days. In this study, we investigated the effects of indicative functions of relatively easy-to-access stem diameter shrinkage on variation characteristics of sap flow. High-resolution-based stem diameter shrinkage is related to changes in tree moisture content. Stem diameter shrinkage indicators are adopted to confirm sap flow changes resulting from transpiration pull, which may enhance the power of stem diameter shrinkage as an index for tree bole moisture loss. After measuring stem diameter variations, the following stem diameter shrinkage indicators were calculated: maximum daily shrinkage, daily stem diameter increment, daily stem diameter variation, and tree water deficit-induced stem shrinkage (TWD). Sap flow was measured synchronously, and stem diameter shrinkage indicators were analyzed to confirm their responses to sap flow. TWD was positively correlated (r ≥ 0.317) with daily variations in sap flow and reached extremely significant levels (p ≤ 0.001) under all conditions. TWD and maximum daily shrinkage were able to better reflect the correlation between changes in stem diameter and sap flow on a daily scale, except large percentage cloud cover days with low temperatures. Changes in stem diameter had no correlation with sap flow during low temperature and large percentage cloud cover days. Among all stem diameter shrinkage indicators, TWD showed the highest correlation (r ≥ 0.601 and p ≤ 0.001) with sap flow under all conditions, except during large percentage cloud cover days with low temperatures. The stem diameter shrinkage indicators did not reflect sap flow changes during large percentage cloud cover days with low temperatures. The indicator that best reflected moisture loss of trees was TWD.

Are Dracaena nebulophytes able to drink atmospheric water?

In arid and semi-arid environments, fog interception as a water acquisition mechanism has been long recognized as an important factor for plant survival. The “narrow-leaf syndrome” increases water absorption from horizontal precipitation and is typical of nebulophytes characterized by dense rosette type crowns, to which also Dracaena species belong. In this paper, we demonstrate that Dracaena nebulophytes are able to direct water intercepted from fog through the leaf axils into their succulent woody organs to be stored for later use. We conducted leaf axil watering (LAW) experiments in four young Dracaena plants (two Dracaena cinnabari and two Dracaena draco) while simultaneously measuring sap flow in plant stems using the heat field deformation method. It was assumed that inducing water potential within stems closed to zero would initiate simultaneous bidirectional water transport from the stem to the crown and roots, and that this moment would be reflected in corresponding sap flow. Three hypothetical scenarios of induced water transport imbalance were confirmed by analyzing measured temperature gradients around heated probes and calculating sap flow. Sap flow responses to LAW clearly appeared to be dependent on flow direction prior to water treatments, on the strength of forces driving upward and downward water movement and the quantity of water applied. Intrinsic sap flow changes depicted in the results confirm the hypothesis that the Dracaena species are able to direct atmospheric water through the axils of their leaves to stem tissues. This mechanism of bypassing soil water represents an alternative means of water uptake in plants and is especially important in foggy areas of arid and semi-arid climates.

基于热扩散技术的梭梭树干液流特征研究

PDF HTML阅读 XML下载 导出引用 引用提醒 基于热扩散技术的梭梭树干液流特征研究 DOI: 10.5846/stxb201608301764 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点基础研究发展计划（2013CB429902）；国家自然科学基金面上项目（41671032） Characterization of stem sapflow Haloxylon ammodendron by using thermal dissipation technology Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:利用TDP热扩散式茎流计，结合自动气象站，对古尔班通古特沙漠南缘原生梭梭的树干液流及环境因子进行连续监测，分析了梭梭树干液流对环境要素的响应，建立了生长季梭梭树干液流与环境因子的关系，估算出梭梭群落的日、季耗水量。结果表明：（1）液流速率日变化主要为单峰曲线，夏季偶有出现双峰曲线，不同季节间的液流速率大小差异显著，夏季树干液流启动早，峰值出现早，夜间持续有微弱的液流；（2）梭梭树干瞬时液流速率与风速、净辐射、空气温度、饱和水汽压亏缺值等因素呈显著正相关，与实际水汽压和空气湿度呈极显著负相关，影响梭梭树干瞬时液流速率变化的关键因子是净辐射和饱和水汽压亏缺值是导致树干液流速率瞬时变化的关键因子；（3）梭梭树干日均液流速率与净辐射、空气温度、实际水汽压、土壤含水率和土壤温度等呈极显著正相关，与空气湿度等呈极显著负相关，与风速相关性不显著，影响梭梭日均液流速率变化的关键因子是净辐射、饱和水汽压亏缺和空气温度。 Abstract:The transpiration water consumption of Haloxylon ammodendron is an important physiological index, which is greatly influenced by many environmental factors. We accurately measured the transpiration water consumption of the individual trees by investigating their sap-flow characteristics in response to various environmental factors. We predicted the transpiration of a single tree with the help of the environmental indicators by building a sap-flow model and environmental factors. Combined with the automatic weather stations, a thermal dissipation probe (TDP) was used to continuously measure the sap-flow dynamics and environmental factors of H. ammodendron in the southern marginal zone of the Gurbantunggut Desert, China. The response of sap-flow velocity to the environmental factors was analyzed, and a relationship was established between the stem sap flow and environmental factors during the growing season of H. ammodendron. The results showed that: (1) the change of sap-flow velocity mainly presented a single-peak curve, or occasionally, a double-peak curve in summer. The amplitudes of daily variation and sap-flow peak were relatively greater in summer than in spring and autumn, and presented a significant difference with the sap-flow velocity during different seasons. In summer, the initial and peak sap-flows were observed earlier in the day, but a weak sap-flow was observed at night. (2) In the growingseason, the net radiation, air temperature, and saturated vapor pressure deficit were the key factors leading to the instantaneous changes in sap flow. The instantaneous sap-flow of H. ammodendron was positively correlated with wind speed, net radiation, saturated vapor pressure deficit, and air temperature, and negatively correlated with actual water vapor pressure and air humidity. (3) The key factors affecting the seasonal change in sap-flow velocity included net radiation, saturated vapor pressure deficit, and air temperature. The daily average flow rate was positively correlated with net radiation, air temperature, saturated vapor pressure deficit, actual water vapor pressure, soil water content, and soil temperature, and negatively correlated with air humidity. (4) The daily transpiration first showed an increasing trend, and then decreased during the whole growing season. In early May, the daily transpiration was 0.21 mm/d, and in the middle of June, it showed a peak-value, which lasted for forty days. The daily transpiration began to decline in late July until it reached a value of 0.10 mm/d. In H.ammodendron study samples, the daily transpiration was 0.35 mm/d and the total transpiration during the entire study period was 53.35 mm, suggesting strong ecological adaptability of H. ammodendron to drought conditions. In the study area, where the ecological environment was harsh because of high temperature and little rain, the water consumption of H. ammodendron was very low, making it the first choice to be used as the ecological restoration and reconstruction shrub in an arid land. 参考文献 相似文献 引证文献

Examining diel patterns of soil and xylem moisture using electrical resistivity imaging

Summary The feedbacks among forest transpiration, soil moisture, and subsurface flowpaths are poorly understood. We investigate how soil moisture is affected by daily transpiration using time-lapse electrical resistivity imaging (ERI) on a highly instrumented ponderosa pine and the surrounding soil throughout the growing season. By comparing sap flow measurements to the ERI data, we find that periods of high sap flow within the diel cycle are aligned with decreases in ground electrical conductivity and soil moisture due to drying of the soil during moisture uptake. As sap flow decreases during the night, the ground conductivity increases as the soil moisture is replenished. The mean and variance of the ground conductivity decreases into the summer dry season, indicating drier soil and smaller diel fluctuations in soil moisture as the summer progresses. Sap flow did not significantly decrease through the summer suggesting use of a water source deeper than 60 cm to maintain transpiration during times of shallow soil moisture depletion. ERI captured spatiotemporal variability of soil moisture on daily and seasonal timescales. ERI data on the tree showed a diel cycle of conductivity, interpreted as changes in water content due to transpiration, but changes in sap flow throughout the season could not be interpreted from ERI inversions alone due to daily temperature changes.

Sap flow responses to seasonal thaw and permafrost degradation in a subarctic boreal peatland

Key message We demonstrate the negative impacts of ground thaw on sap flow in black spruce. Climate warming is accelerating permafrost thaw; our study may inform observed warming-related productivity declines in subarctic forests. Abstract Many of Canada's northern boreal peatlands are situated on discontinuous permafrost. Here, permafrost provides the physical foundation on which forests persist. However, climate warming is leading to increased rates of permafrost thaw resulting in both increased active layer thickness (ALT) as well as shrinkage of the area underlain by permafrost due to lateral thaw at plateau margins. Such changes to the substrate likely impact growth and physio- logical processes of the trees. Despite this, little is known about the role of active layer development, and changes to it, including thaw of the underlying permafrost on tree water relations. Here, we measured sap flow in black spruce from a peatland experiencing rapid permafrost thaw and quantified drivers of changes in sap flow. Time series analyses revealed that of the environmental drivers exam- ined, vapour pressure deficit was the strongest predictor of diurnal sap flow, while seasonal patterns were driven lar- gely by energy inputs; however, the environmental drivers of importance did not change as a function of ground thaw conditions. To understand the implications of changing permafrost and active layer conditions, we quantified dif- ferences in sap flow between trees in interior positions of permafrost plateaus and trees on degrading plateau edges. We found (65 % reductions in sap flow in edge trees, attributable to reduced root function at waterlogged edges. Seasonal thaw processes also influenced sap flow. Paired measures of ALT indicated a negative linear relationship with sap flow that was stronger for interior trees. Greater ALT, which corresponds with deeper frost and water tables reduced sap flow by up to 60 % and is likely attributable to drying in surface soil layers where rooting occurs. Climate warming will accelerate permafrost thaw, which our data suggests will drive decreases in the productivity of black spruce-dominated subarctic forests. These findings may thus enhance our understanding of widespread reductions in productivity in boreal forests in northwestern North America.

Do Hummocks Provide a Physiological Advantage to Even the Most Flood Tolerant of Tidal Freshwater Trees?

Hummock and hollow microtopography is pervasive in tidal freshwater swamps. Many tree species grow atop hummocks significantly more than in hollows, leading to the hypothesis that hummocks provide preferred locations for maximizing physiological proficiency of inhabiting trees that experience repeated flooding. We used thermal dissipation probes to measure the ecophysiological proficiency of a very flood-tolerant tree, Taxodium distichum, as manifested through in-situ changes in sapflow (a proxy for transpiration) in 11 trees on hummocks and 11 trees in hollows. Overall, sapflow increased significantly by 3.3 g H2O m−2 s−1 (11 %) in trees on both hummocks and hollows during flooding, contrary to our expectations. We found no significant differences in sapflow rates between T. distichum trees positioned on hummocks versus hollows in relation to discrete flood events. Coincidentally, hummock elevations were equivalent to the flood depths that promoted greatest physiological proficiency in T. distichum, suggesting a physiological role for the maintenance of hummock height in tidal swamps. While we reject our original hypotheses that flooding and positioning in hollows will reduce sapflow in T. distichum, this research reveals a potentially important feedback between hummock height, flood depth, and maximum tree physiological response.

Sap flow changes in relation to permafrost degradation under increasing precipitation in an eastern Siberian larch forest

ABSTRACTContinuous observation over the last decade has revealed evidence of abrupt land surface moistening as well as rapid soil warming within the active layer and upper part of permafrost within the central Lena River basin in eastern Siberia. The present study examined the relationship between permafrost degradation and ecohydrological change in this region. Increases in the depth of the active layer recorded since the winter of 2004 resulting from increases in moisture saturation within the soil have resulted in thawing the upper permafrost causing thermokarst subsidence, which has negatively impacted the growth of boreal (larch) forests in the region. According to multi‐year sap flow measurements taken between 2006 and 2009, transpiration from larch trees (Larix cajanderi Mayr.) was significantly reduced as a result of the region's concave micro‐topography, which, in conjunction with the deepening and moistening of the active layer, created perennially waterlogged conditions that left mature trees withered and dead. Several trees with reduced amounts of foliage showed a remarkable reduction in seasonal average canopy stomatal conductance during the 2009 growing season. The reduction ratio of canopy stomatal conductance within emergent trees of heights greater than 15 m between 2006 and 2009 had a significant positive correlation with the increase in thickness of the active layer over that same period. These findings indicated that wetting trends in a permafrost region caused by arctic climate change may lead to unexpected ecohydrological responses with respect to permafrost degradation in eastern Siberia. Copyright © 2013 John Wiley & Sons, Ltd.

Implications of twenty-first century climate change on Northeastern United States maple syrup production: impacts and adaptations

Previous research on the impacts of maple syrup production in the Northeastern United States has been based on correlative relationships between syrup production and average temperature. Here a simple biologically and physically-based model of sapflow potential is used to assess observed changes in sapflow across the Northeastern US from 1980 to 2006; document the correspondence between these observations and independent downscaled atmosphere ocean general circulation model (AOGCM) simulations of conditions during this period; and quantify changes in sapflow potential through 2100. The sapflow model is able to capture the spatial and temporal (in terms of the start date of sapflow) variations of sapflow that are observed across the Northeast. Likewise the AOGCM simulations reflect the mean number of sapflow days and the timing of sapflow during the 1980–2006 overlap period. Through the twenty-first century, warming winter temperatures will result in a decline in the number of sapflow days if traditional sap collection schedules are maintained. Under the A1fi emissions scenario the number of sapflow days decreases by up to 14 days. However, the changes in climate also translate the optimal timing of sap collection to earlier in the year. Across the region, the time period that maximizes the number of sapflows days becomes as much as 30 days earlier by 2100 under the A1fi emissions scenario. Provided this change is accounted for by modifying the start of the traditional sap collection schedule, there is essentially no net loss of sapflow days across the majority of the region, with a net increase of sapflow days indicated in the extreme north.

The response of an Eastern Amazonian rain forest to drought stress: results and modelling analyses from a throughfall exclusion experiment

AbstractWarmer and drier climates over Eastern Amazonia have been predicted as a component of climate change during the next 50–100 years. It remains unclear what effect such changes will have on forest–atmosphere exchange of carbon dioxide (CO2) and water, but the cumulative effect is anticipated to produce climatic feedback at both regional and global scales. To allow more detailed study of forest responses to soil drying, a simulated soil drought or ‘throughfall exclusion’ (TFE) experiment was established at a rain forest site in Eastern Amazonia, Brazil, for which time‐series sap flow and soil moisture data were obtained. The experiment excluded 50% of the throughfall from the soil. Sap flow data from the forest plot experiencing normal rainfall showed no limitation of transpiration throughout the two monitored dry seasons. Conversely, data from the TFE showed large dry season declines in transpiration, with tree water use restricted to 20% of that in the control plot at the peak of both dry seasons. The results were examined to evaluate the paradigm that the restriction on transpiration in the dry season was caused by limitation of soil‐to‐root water transport, driven by low soil water potential and high soil‐to‐root hydraulic resistance. This paradigm, embedded in the soil–plant–atmosphere (SPA) model and driven using on‐site measurements, provided a good explanation (R2 > 0.69) of the magnitude and timing of changes in sap flow and soil moisture. This model‐data correspondence represents a substantial improvement compared with other ecosystem models of drought stress tested in Amazonia. Inclusion of deeper rooting should lead to lower sensitivity to drought than the majority of existing models. Modelled annual GPP declined by 13–14% in response to the treatment, compared with estimated declines in transpiration of 30–40%.

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.

Sap flow and water transfer in the Garonne River riparian woodland, France: first results on poplar and willow

This work is the first attempt at using Granier sap sensors on Populus nigra, Populus x euramericanacv I45/51 and Salix alba for the monitoring of sap flows in an active floodplain over two consecutive years. The main characteristic of these diffuse porous trees is their capacity to use several tree rings for xylem sap transfer. Results showed that the sap flux densities remained homogeneous on the external 4 cm of the trunk, then decreased with depth. For young trees, the active sapwood can represent half of the trunk. Results indicated that in the same environment and at the same age, daily differences existed between the two major native riparian tree species, the black poplar and the white willow. Their maximal sap flux density (2.6-3.6 dm 3 dm -2 h -1 ) was similar to other fast growing trees. The influence of age was the third important screened factor. Sap flow measurements over several months indicated that water uptake was variable throughout the season, depending on water availability, and was more pronounced for older trees. The sap flux densities for the planted poplar (I45/51) ranged from 2.2-2.6 dm 3 dm -2 h -1 (about 90 dm 3 day -1 ) in the wetter spring conditions and dropped to 1.6-1.7 dm 3 dm -2 h -1 (about 60 dm 3 day -1 ) in less favourable conditions. Under the worst conditions, e.g., the especially long drought in the summer of 1998, these values dropped to 1.0-1.2 (about 40 dm 3 day -1 ), and even to 0.35 dm 3 dm -2 h -1 (about 12 dm 3 day -1 ) for a few days. Complementary long-term studies are needed to better understand the complex sap flow changes and to be able to relate them to si- gnificant environmental factors. Priority should be given to the long-term monitoring of sap flows at different depths for a correct esti- mation of actual daily water uptakes by riparian softwood trees. sap flow / riparian forest / water cycle / poplar / willow

Measurements of Sap Flow in the Roots, Trunk and Shoots of an Apple Tree Using Heat Pulse and Heat Balance Methods.

To understand more deeply water dynamics in an apple tree, we examined diurnal changes in sap flow in the shoots, trunk and roots of a 10-year old apple tree (cv. Splendor), using to advantage both the heat balance and heat pulse methods. There was little time lag between sap flow in the trunk and the root, suggesting a high hydraulic conductivity between them. The time lag between the start of shoot sap flow, and that of trunk and root, after sunrise was estimated to be about 30min. Considering the finding of Schulze et al. (1985) that the main water store is located in the tree crown, it appeared here in our experiment that the main storage element of the apple tree was also the crown.

Measurement of Mass Flow Rate of Sap in Ligustrum japonicum

The heat balance method of measuring mass flow of sap was tested on wax leaf ligustrum (Ligustrum japonicum Thunb.) to evaluate its usefulness for measuring water use in shrubs. Sap flow measurements were compared with gravimetric estimates of transpiration in growth chamber and field environments. Sap flow measurements in both environments were within 10% of transpiration, which compared favorably with results reported for herbaceous plants by other researchers. Sizable differences in sap flow, due mainly to differences in leaf area, were found among five plants tested in the field. When flow was expressed on a unit leaf-area basis, differences among plants were greatly reduced. Measurements under partly cloudy skies with fluctuating irradiance showed that changes in sap flow matched those occurring in irradiance.