Effects of soil water decline on diurnal and seasonal variations in sap flux density for differently aged Japanese cypress (Chamaecyparis obtusa) trees

Mediterranean type ecosystems such as cork oak (Quercus suber) woodlands are currently threatened by extreme drought events and shrub encroachment in the Iberian Peninsula. Recently, the frequency of extreme droughts has increased with negative effects on many ecosystems. Decreasing soil water availability reduces growth and fitness of trees, and may eventually induce tree mortality. Shrub encroachment may further increase the competition for soil water, impacting tree vulnerability and resilience negatively. Yet, the synergistic effects of extreme droughts and shrub encroachment on ecosystems have rarely been investigated.We established a precipitation manipulation and shrub encroachment experiment in a cork oak stand to study the combined effects of the two environmental pressures. The cork oak woodland is located in Southeast Portugal and partially invaded by the native shrub gum rockrose (Cistus ladanifer). In December 2017, we installed rainout shelters (30 to 45% of precipitation reduction) in replicated cork oak stands invaded and uninvaded by gum rockrose, complemented by control plots with natural precipitation. In each treatment, the trees (n = 9) and shrubs (n = 9) were measured for water and carbon fluxes to reveal species-specific responses and competition effects under recurrent extreme drought.The hydrological year 2018 was characterised by above-average precipitation mainly caused by large spring rainfall events. Probably due to sufficient water supply, no clear treatment effects were evident. For example, minimum leaf water potentials (&#936;PD) of the cork oak trees did not drop below &#8722;1.5 &#177; 0.1 MPa and maximum sap flux density was 2.1 &#177; 0.2 m3 m&#8722;2 day&#8722;1. Minimum &#936;PD of the shrubs was three times lower (&#8722;3.5 &#177; 0.1 MPa) and maximum sap flux density over four-fold higher (8.8 &#177; 0.8 m3 m&#8722;2 day&#8722;1) than those of the trees, suggesting distinct species-specific behaviour. Reduced winter and spring precipitation, combined with a late onset of autumn rainfalls in 2019, led to a decrease in water input down to 66% (control) and 44% (drought) compared to the long-term average of 585 mm. In this dry year, negative synergistic effects of drought and shrub encroachment were expressed during the dry-down and drought period by a lower minimum &#936;PD and an average sap flux density reduced by 50% (0.4 &#177; 0.1 m3 m&#8722;2 day&#8722;1) of invaded trees exposed to the experimental drought, compared to control trees (0.8 &#177; 0.1 m3 m&#8722;2 day&#8722;1). In sum, this resulted in a reduction of sap flux densities of the cork oaks by 25% (invaded), 23% (drought) and 34% (drought and invaded) over the course of the hydrological year 2019. The ongoing investigations aim to further determine the stress tolerance and critical physiological thresholds for both species and the entire ecosystem.

Download Full-text

Azimuthal variations of sap flux density within Japanese cypress xylem trunks and their effects on tree transpiration estimates

Journal of Forest Research ◽

10.1007/s10310-010-0202-0 ◽

2010 ◽

Vol 15 (6) ◽

pp. 398-403 ◽

Cited By ~ 28

Author(s):

Kenji Tsuruta ◽

Tomonori Kume ◽

Hikaru Komatsu ◽

Naoko Higashi ◽

Toshihiro Umebayashi ◽

...

Keyword(s):

Flux Density ◽

Sap Flux ◽

Sap Flux Density ◽

Japanese Cypress ◽

Tree Transpiration

Download Full-text

Assessing variation in the radial profile of sap flux density in Pinus species and its effect on daily water use

Tree Physiology ◽

10.1093/treephys/24.3.241 ◽

2004 ◽

Vol 24 (3) ◽

pp. 241-249 ◽

Cited By ~ 133

Author(s):

C. R. Ford ◽

M. A. McGuire ◽

R. J. Mitchell ◽

R. O. Teskey

Keyword(s):

Flux Density ◽

Water Use ◽

Radial Profile ◽

Sap Flux ◽

Sap Flux Density ◽

Pinus Species ◽

Daily Water

Download Full-text

Erratum to: Changes in stem water content influence sap flux density measurements with thermal dissipation probes

Trees ◽

10.1007/s00468-014-1098-7 ◽

2014 ◽

Vol 28 (6) ◽

pp. 1867-1868

Author(s):

Lidewei L. Vergeynst ◽

Maurits W. Vandegehuchte ◽

Mary Anne McGuire ◽

Robert O. Teskey ◽

Kathy Steppe

Keyword(s):

Water Content ◽

Flux Density ◽

Thermal Dissipation ◽

Sap Flux ◽

Sap Flux Density ◽

Density Measurements ◽

Stem Water

Download Full-text

A Direct Method for Estimating the Average Sap Flux Density Using a Modified Granier Measuring System

Functional Plant Biology ◽

10.1071/pp96099 ◽

1997 ◽

Vol 24 (5) ◽

pp. 701 ◽

Cited By ~ 11

Author(s):

Ping Lu

Keyword(s):

Flux Density ◽

Sap Flow ◽

Direct Method ◽

Estimation Error ◽

Original Method ◽

Measuring System ◽

Sap Flux ◽

Sap Flux Density ◽

Average Value ◽

Modified Method

The Granier sap flow measuring system that normally uses one analogue input channel of a datalogger for each sensor was modified to enable one channel to measure the average value of signals from two or more sensors. The sap flux density calculated from this average value of signals was very close (difference < 6.0%) to the arithmetic mean of the sap flux densities measured separately by means of individual sensors (using two or more input channels). The dynamics of the sap flux density measured by the modified method were similar to those measured by the original method. On a per-channel basis, the modified method reduced the ‘estimation error’ of sap flux density by 4–14-fold compared to the original method. By using the modified Granier system, the error in sap flow measurement that is usually associated with limited sampling can be substantially reduced without the need for extra dataloggers, the greatest item of expense.

Download Full-text

Partitioning the causes of spatiotemporal variation in the sunny day sap flux density of a larch plantation on a hillslope in northwest China

Journal of Hydrology ◽

10.1016/j.jhydrol.2019.02.004 ◽

2019 ◽

Vol 571 ◽

pp. 503-515 ◽

Cited By ~ 5

Author(s):

Ao Tian ◽

Yanhui Wang ◽

Ashley A. Webb ◽

Zebin Liu ◽

PengtaoYu ◽

...

Keyword(s):

Flux Density ◽

Northwest China ◽

Spatiotemporal Variation ◽

Sap Flux ◽

Sap Flux Density ◽

Larch Plantation

Download Full-text

The importance of conduction versus convection in heat pulse sap flow methods

Tree Physiology ◽

10.1093/treephys/tpaa009 ◽

2020 ◽

Vol 40 (5) ◽

pp. 683-694

Author(s):

Michael A Forster

Keyword(s):

Flux Density ◽

Sap Flow ◽

Peclet Number ◽

Velocity Measurement ◽

Measurement Range ◽

Heat Pulse ◽

Sap Flux ◽

Sap Flux Density ◽

Péclet Number ◽

Fast Methods

Abstract Heat pulse methods are a popular approach for estimating sap flow and transpiration. Yet, many methods are unable to resolve the entire heat velocity measurement range observable in plants. Specifically, the Heat Ratio (HRM) and Tmax heat pulse methods can only resolve slow and fast velocities, respectively. The Dual Method Approach (DMA) combines optimal data from HRM and Tmax to output the entire range of heat velocity. However, the transition between slow and fast methods in the DMA currently does not have a theoretical solution. A re-consideration of the conduction/convection equation demonstrated that the HRM equation is equivalent to the Péclet equation which is the ratio of conduction to convection. This study tested the hypothesis that the transition between slow and fast methods occurs when conduction/convection, or the Péclet number, equals one, and the DMA would be improved via the inclusion of this transition value. Sap flux density was estimated via the HRM, Tmax and DMA methods and compared with gravimetric sap flux density measured via a water pressure system on 113 stems from 15 woody angiosperm species. When the Péclet number ≤ 1, the HRM yielded accurate results and the Tmax was out of range. When the Péclet number > 1, the HRM reached a maximum heat velocity at approximately 15 cm hr −1 and was no longer accurate, whereas the Tmax yielded accurate results. The DMA was able to output accurate data for the entire measurement range observed in this study. The linear regression analysis with gravimetric sap flux showed an r2 of 0.541 for HRM, 0.879 for Tmax and 0.940 for DMA. With the inclusion of the Péclet equation, the DMA resolved the entire heat velocity measurement range observed across 15 taxonomically diverse woody species. Consequently, the HRM and Tmax are redundant sap flow methods and have been superseded by the DMA.

Download Full-text

Contribution of Advanced Regeneration of Pinus radiata D. Don. to Transpiration by a Fragment of Native Forest in Central Chile Is out of Proportion with the Contribution to Sapwood Area

Forests ◽

10.3390/f11020187 ◽

2020 ◽

Vol 11 (2) ◽

pp. 187

Author(s):

Don A. White ◽

Richard P. Silberstein ◽

Francisco Balocchi-Contreras ◽

Juan Jose Quiroga ◽

Pablo Ramírez de Arellano

Keyword(s):

Climate Change ◽

Leaf Area ◽

Flux Density ◽

Pinus Radiata ◽

Native Forest ◽

Sap Flux ◽

Sap Flux Density ◽

Sapwood Area ◽

Central Chile ◽

Potential Index

The transpiration of Nothofagus glauca (Phil.) Krasser and advanced Pinus radiata D. Don. regeneration was measured in a fragment of native N. glauca forest. Over the eight months of this study, P. radiata contributed approximately 60% of the total stand transpiration. This was out of proportion with the approximately 34% of the stand sapwood area contributed by P. radiata. This was due to the significantly greater sap flux density of the P. radiata compared to the N. glauca between May and October. Though the results are from a small study conducted as part of a larger experiment, it is argued that they suggest that invasion by P. radiata may substantially increase the risk from climate change to reserves of N. glauca forest in the Maule region of central Chile. In some reserves of N. glauca forest, Forestal Arauco S.A. manually removed P. radiata that regenerated after the wildfire of January 2017. This was a costly operation and there is a need for indices to assess competition. The ratio of sapwood area to leaf area is suggested as a potential index for assessing competition to identify stands at risk.

Download Full-text