scholarly journals Environmental Control on Transpiration: A Case Study of a Desert Ecosystem in Northwest China

Water ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 1211 ◽  
Author(s):  
Shiqin Xu ◽  
Zhongbo Yu
Keyword(s):  
Sap Flow ◽  
Environmental Control ◽  
Arid Ecosystems ◽  
Desert Ecosystem ◽  
Time Lags ◽  
Evaporative Demand ◽  
Threshold Control ◽  
Stand Transpiration ◽  
Semi Arid

Arid and semi-arid ecosystems represent a crucial but poorly understood component of the global water cycle. Taking a desert ecosystem as a case study, we measured sap flow in three dominant shrub species and concurrent environmental variables over two mean growing seasons. Commercially available gauges (Flow32 meters) based on the constant power stem heat balance (SHB) method were used. Stem-level sap flow rates were scaled up to stand level to estimate stand transpiration using the species-specific frequency distribution of stem diameter. We found that variations in stand transpiration were closely related to changes in solar radiation (Rs), air temperature (T), and vapor pressure deficit (VPD) at the hourly scale. Three factors together explained 84% and 77% variations in hourly stand transpiration in 2014 and 2015, respectively, with Rs being the primary driving force. We observed a threshold control of VPD (~2 kPa) on stand transpiration in two-year study periods, suggesting a strong stomatal regulation of transpiration under high evaporative demand conditions. Clockwise hysteresis loops between diurnal transpiration and T and VPD were observed and exhibited seasonal variations. Both the time lags and refill and release of stem water storage from nocturnal sap flow were possible causes for the hysteresis. These findings improve the understanding of environmental control on water flux of the arid and semi-arid ecosystems and have important implications for diurnal hydrology modelling.

scholarly journals Sap flow in response to rainfall pulses for two shrub species in the semiarid Chinese Loess Plateau

2016 ◽  
Vol 64 (2) ◽  
pp. 121-132 ◽  
Author(s):  
Shengqi Jian ◽  
Zening Wu ◽  
Caihong Hu ◽  
Xueli Zhang
Keyword(s):  
Loess Plateau ◽  
Sap Flow ◽  
Arid Ecosystems ◽  
Interactive Effects ◽  
Chinese Loess Plateau ◽  
Flow Density ◽  
Delay Model ◽  
Chinese Loess ◽  
Caragana Korshinskii ◽  
Semi Arid

Abstract Rainfall pulses can significantly drive the evolution of the structure and function of semiarid ecosystems, and understanding the mechanisms that underlie the response of semiarid plants to rainfall is the key to understanding the responses of semi–arid ecosystems to global climatic change. We measured sap flow in the branches and stems of shrubs (Caragana korshinskii Kom. and Hippophae rhamnoides Linn.) using sap flow gauges, and studied the response of sap flow density to rainfall pulses using the “threshold–delay” model in the Chinese Loess Plateau. The results showed that the sap flow began about 1 h earlier, and increased twofold after rainfall, compared to its pre-rainfall value. The sap flow increased significantly with increasing rainfall classes, then gradually decreased. The response of sap flow was different among rainfall, species, position (branch and stem) during the pulse period, and the interactive effects also differed significantly (P < 0.0001). The response pattern followed the threshold–delay model, with lower rainfall thresholds of 5.2, 5.5 mm and 0.7, 0.8 mm of stem and branch for C. korshinskii and H. rhamnoides, demonstrating the importance of small rainfall events for plant growth and survival in semi–arid regions.

scholarly journals Climate change adaptation in Semi-Arid Ecosystems: A case study from Ghana

2020 ◽  
Vol 27 ◽  
pp. 100206 ◽  
Author(s):  
Mawulolo Yomo ◽  
Grace B. Villamor ◽  
Mawuli Aziadekey ◽  
Felix Olorunfemi ◽  
Khaldoon A. Mourad
Keyword(s):  
Climate Change ◽  
Climate Change Adaptation ◽  
Arid Ecosystems ◽  
Semi Arid

scholarly journals Assessment of Downscaling Planetary Boundaries to Semi-Arid Ecosystems with a Local Perception: A Case Study in the Middle Reaches of Heihe River

2016 ◽  
Vol 8 (12) ◽  
pp. 1233 ◽  
Author(s):  
Heng Teah ◽  
Tomohiro Akiyama ◽  
Ricardo San Carlos ◽  
Orlando Rayo ◽  
Yu Khew ◽  
...  
Keyword(s):  
Arid Ecosystems ◽  
Heihe River ◽  
Planetary Boundaries ◽  
Local Perception ◽  
Semi Arid

Interannual variation in stand transpiration estimated by sap flow measurement in a semi-arid black locust plantation, Loess Plateau, China

Ecohydrology ◽  
2014 ◽  
Vol 8 (1) ◽  
pp. 137-147 ◽  
Author(s):  
Jian-Guo Zhang ◽  
Jin-Hong Guan ◽  
Wei-Yu Shi ◽  
Norikazu Yamanaka ◽  
Sheng Du
Keyword(s):  
Loess Plateau ◽  
Sap Flow ◽  
Flow Measurement ◽  
Interannual Variation ◽  
Black Locust ◽  
Stand Transpiration ◽  
Semi Arid

scholarly journals The Future of Semi-Arid Regions: A Weak Fabric Unravels

Climate ◽  
2020 ◽  
Vol 8 (3) ◽  
pp. 43 ◽  
Author(s):  
Robert J Scholes
Keyword(s):  
Land Surface ◽  
Arid Regions ◽  
Arid Ecosystems ◽  
Plant Production ◽  
Climate Trends ◽  
Evaporative Demand ◽  
Social Ecological ◽  
Global Atmospheric Circulation ◽  
Global Mean ◽  
Semi Arid

The regions of the world where average precipitation is between one fifth and half of the potential plant water demand are termed ‘semi-arid’. They make up 15.2% of the global land surface, and the approximately 1.1 billion people who live there are among the world’s poorest. The inter-annual variability of rainfall in semi-arid regions is exceptionally high, due to intrinsic features of the global atmospheric circulation. The observed and projected climate trends for most semi-arid regions indicate warming at rates above the global mean rate over land, increasing evaporative demand, and reduced and more variable rainfall. Historically, the ecosystems and people coped with the challenges of semi-arid climates using a range of strategies that are now less viable. Semi-arid ecosystems are by definition water limited, generally only suitable for extensive pastoralism and opportunistic cropping, unless irrigation supplementation is available. The characteristics of dryland plant production in semi-arid ecosystems, as they interact with climate change and human systems, provide a conceptual framework for why land degradation is so conspicuous in semi-arid regions. The coupled social-ecological failures are contagious, both within the landscape and at regional and global scales. Thus, semi-arid lands are a likely flashpoint for Earth system changes in the 21st century.

Xylem sap flow, growth and flower production of cultivated Geraldton wax with different vigour under semi-arid conditions

1995 ◽  
Vol 46 (3) ◽  
pp. 581
Author(s):  
K Akilan ◽  
JA Considine ◽  
JK Marshall
Keyword(s):  
Water Use ◽  
Sap Flow ◽  
Xylem Sap ◽  
Root Systems ◽  
Stem Length ◽  
Growth Responses ◽  
Evaporative Demand ◽  
Flower Production ◽  
Arid Conditions ◽  
Semi Arid

Diurnal and seasonal water use and the effects of different levels of irrigation on growth and flower production were studied using commercially cultivated Geraldton wax (Chamelaucium uncinatum Schauer cv. Purple Pride) under semi-arid conditions. Water use and growth responses to increased irrigation differed widely with vigour. Vigorous plants had extensive root systems and used more water than less vigorous plants whether irrigated or unirrigated and responded to increased irrigation by producing more shoots, secondary stems and flowers. In vigorous plants, marketable stem length and flower number were increased from 63 to 89 cm and 61 to 226 when irrigation was increased from 25 to 75% of pan replacement respectively. Less vigorous plants had distorted root systems (i.e. curling and circling) and showed no significant growth response to increased irrigation. Increase of stem length to a desirable length of 90 cm in less vigorous plants, which are wide-spread in commercial plantings, was unlikely. The results highlight the significance of good propagation and establishment techniques to aid vigorous growth. The sap flow study shows that Geraldton wax is a high water using species. A single plant can use in excess of 20 L per day under high evaporative demand when root growth is not limiting.

scholarly journals The Role of Hillshade, Aspect, and Toposhape in the Woodland Dieback of Arid and Semi-Arid Ecosystems: A Case Study in Zagros Woodlands of Ilam Province, Iran

2019 ◽  
Vol 12 (2) ◽  
pp. 79-91
Author(s):  
Ali Najafifar ◽  
Jaafar Hosseinzadeh ◽  
Abdolali Karamshahi
Keyword(s):  
Soil Moisture ◽  
Risk Model ◽  
Quadratic Equation ◽  
The Other ◽  
Arid Ecosystems ◽  
Strongly Correlated ◽  
Ecological Processes ◽  
Forest Dieback ◽  
Semi Arid

Abstract Soil moisture plays a key role in the ecological capability of arid and semi-arid woodland. Reducing soil moisture due to frequent droughts causes pest prevalence and disease outbreak and the consequence of forest dieback. On the other hand, soil moisture is strongly correlated with the amount of radiation received on the Earth’s surface. The sun’s radiation is traditionally described often by aspect and sometimes by toposhape. The use of the hillshade map for estimating solar radiation is possible through developing GIS. The present study aimed to compare the relationship and the ability of these indices to describe the phenomenon of arid and semi-arid woodland decline better and more accurately in a case study in the west of Iran. To this aim, the aspect and toposhape layers were generated in 5 and 12 classes, respectively. Then, the hillshade map in range of 0-255 was made during the peak of summer heat. The comparison of the dieback ratio in the three characteristic histograms showed that the shade index, unlike the other two indicators, had a significant effect on forest drought (R2=0.91 for linear equation and R2=0.94 for quadratic equation). The results indicated that the application of hillshade in describing and analysing ecological processes by relying on soil moisture such as woodland dieback is superior to the other two indicators. It is suggested that this index be used to obtain a risk model to predict woodlands dieback which are under the pressure of frequent droughts due to climate change or other mortal factors.

scholarly journals Effects of heat and drought on carbon and water dynamics in a regenerating semi-arid pine forest: a combined experimental and modeling approach

2014 ◽  
Vol 11 (1) ◽  
pp. 551-591 ◽  
Author(s):  
N. K. Ruehr ◽  
B. E. Law ◽  
D. Quandt ◽  
M. Williams
Keyword(s):  
Ponderosa Pine ◽  
Pine Forest ◽  
Water Dynamics ◽  
Arid Ecosystems ◽  
Soil Drought ◽  
Field Observations ◽  
Evaporative Demand ◽  
Early Season ◽  
Spa Model ◽  
Semi Arid

Abstract. Increasing summer temperatures and a reduction in precipitation will enhance drought stress in Mediterranean and semi-arid ecosystems. Predicting the net effects on forests' carbon and water balance will depend on our ability to disentangle the sensitivity of component fluxes responding to increasing soil and atmospheric drought. Here we studied carbon and water dynamics in a semi-arid regenerating ponderosa pine forest using field observations and process based modeling. Field observations of two summer dry seasons were used to calibrate a soil-plant-atmosphere (SPA) model. In addition, the ecosystem's response to reduced soil drought was quantified based on a field watering experiment and evaluated with the model. Further, the SPA model was used to estimate the relative effects of increasing soil and atmospheric drought over time, by simulating temperature and precipitation scenarios for 2040 and 2080. The seasonality and drought response of ecosystem fluxes was well captured by the calibrated SPA model. Dramatic increases in summer water availability during seasonal drought had a small effect on pine physiology in both the watering experiment and the model. This clearly demonstrates that atmospheric drought induced a strong limitation on carbon uptake in young ponderosa pine due to tight regulation of stomatal conductance. Moreover, simulations showed that net ecosystem exchange (NEE) and gross primary productivity (GPP) were about three times more affected by summer heat and increased evaporative demand than by reductions in summer precipitation. Annual NEE decreased by 38% in response to extreme summer conditions as predicted to occur in 2080 (June–August: +4.5 °C), because of a strong decline in GPP (−17%) while heterotrophic respiration was relatively unaffected (−1%). Considering warming trends across all seasons (September–May: +3 °C and June–August: +4.5 °C), the negative drought effects were largely compensated by an earlier initiation of favorable growing conditions and bud break, enhancing early season GPP and needle biomass. An adverse effect, triggered by changes in early season allocation patterns, was the decline of wood and root biomass. This imbalance may increase water stress over the long-term to a threshold at which ponderosa pine may not survive, and highlights the need for an integrated process understanding of the combined effects of trends and extremes.

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