Amount Of Transpiration Research Articles

Analysis of Bell Pepper (Capsicum annuum L.) Leaf Spectral Properties and Photosynthesis According to Growth Period

This study analyzed the leaf spectral properties and photosynthesis rates of greenhouse-grown bell pepper leaves according to the growth period and leaf position to investigate the changes in carbon assimilation function according to leaf aging. Photosynthesis, growth, transpiration, stomatal conductance, light transmittance, and light reflectance were measured. As the plants’ growth progressed, the number of leaves, fresh weight, and dry weight increased, but the specific leaf area decreased, likely due to the increased distribution of assimilates to reproductive organs. The average photosynthesis rate, according to the measured dates, exhibited a high value despite a large standard error, which was likely influenced by measurement errors caused by external environmental factors. The reflectance and transmittance increased from the upper to the middle and bottom leaves, and the absorption ratio decreased in the same order. The green light spectrum (500–580 nm) had a lower absorption ratio than other spectra because the green coloration of the leaves increased the light reflectance of this spectrum. As the PPFD increased where the leaf was positioned higher, the photosynthesis rate, transpiration amount, and stomatal conductance also increased. The higher the leaf position, the higher the photosynthesis rate, the amount of transpiration, and the stomatal conductance. As the CO2 concentration increased, the photosynthesis rate increased, but the transpiration and stomatal conductance changed little, indicating that the gas exchange within leaves was hardly affected by CO2, but the light levels promoted photosynthesis. From the results of this study, the optical properties of the leaves indicate that they are consistent with Lambert–Beer’s law, which implies that the length of the optical path is linearly proportional to the number of molecules in the absorption layer. We obtained the light saturation point and CO2 saturation point of bell peppers grown in a greenhouse and were able to determine the physiological changes in the leaves with increasing leaf age. Therefore, based on this information, it appears that a leaf removal model based on the productivity of bell pepper leaves could be developed.

Influence of irrigation on root zone storage capacity estimation

Abstract. Vegetation plays a crucial role in regulating the water cycle through transpiration, which is the water flux from the subsurface to the atmosphere via roots. The amount and timing of transpiration is controlled by the interplay of seasonal energy and water supply. The latter strongly depends on the size of the root zone storage capacity (Sr), which represents the maximum accessible volume of water that vegetation can use for transpiration. Sr is primarily influenced by hydroclimatic conditions, as vegetation optimizes its root system in such a way that it guarantees water uptake and overcomes dry periods. Sr estimates are commonly derived from root zone water deficits that result from the phase shift between the seasonal signals of root zone water inflow (i.e., precipitation) and outflow (i.e., evaporation). In irrigated croplands, irrigation water serves as an additional input into the root zone. However, this aspect has been ignored in many studies, and the extent to which irrigation influences Sr estimates has never been comprehensively quantified. In this study, our objective is to quantify the influence of irrigation on Sr and identify the regional differences therein. To this end, we integrated two irrigation methods, based on the respective irrigation water use and irrigated area fractions, into the Sr estimation. We evaluated the effects compared with Sr estimates that do not consider irrigation for a sample of 4856 catchments globally with varying degrees of irrigation activity. Our results show that Sr consistently decreased when considering irrigation, with a larger effect in catchments with a larger irrigated area. For catchments with an irrigated area fraction exceeding 10 %, the median decrease in Sr was 19 and 23 mm for the two methods, corresponding to decreases of 12 % and 15 %, respectively. Sr decreased the most for catchments in tropical climates. However, the relative decrease was the largest in catchments in temperate climates. Our results demonstrate, for the first time, that irrigation has a considerable influence on Sr estimates over irrigated croplands. This effect is as strong as the effects of snowmelt that have previously been documented in catchments that have a considerable amount of precipitation falling as snow.

Variation of natural characteristics of Tanjero Basin in Sulaymaniyah Governorate using GIS

Objective: The research aims to clarify the natural factors of the Tanjero River Basin. The Tanjero River Basin is located within the complex region in terms of topography in northeastern Iraq, eastern Iraqi Kurdistan region, and southwest of Sulaymaniyah Governorate. It is bordered on the eastern side by the Shahrazur Plain, the Sourin Mountains, and the Kweiza and Azmar Heights. On the western side, it is bordered by the Bernan mountain range, and on the northern side it is adjacent to the starting point of the Doula Rut Heights and Birah Mah Karun Mountain, and it is surrounded from the south by Darbandikhan Lake administratively. Methodology: The current research relied on the descriptive and analytical approach in describing the phenomenon and analyzing it spatially, and the systematic approach in revealing the geographical factors causing the variation in water volume in the Tanjero River Basin and diagnosing the factors affecting it positively or negatively. Results: By presenting the problem, reviewing the data, as well as linking it to the results, it becomes clear to us the clear influence of natural factors on the variation and diversity in the natural characteristics of the Tanjiro Basin in Sulaymaniyah Governorate, and this proves the validity of the study’s hypothesis. Conclusion: The results show that the hydro-climatic budget in the Tanjiro Valley Basin is represented by the Khanaqin and Sulaymaniyah stations, which express the hydro-climatic characteristics in the Tanjiro Valley Basin, as the results of the water budget appear. According to table (1), the basin region is witnessing a water surplus because the effective amounts of rainfall exceed the amounts of evaporation and transpiration in the months “October, December, January, and February.” This surplus is within the Sulaymaniyah station, which represents the feeding area of the Tanjiro Basin. In the north, it was recorded the highest in January at (39.8) mm, while Khanaqin station witnesses a water deficit for all months and does not record any water surplus in its monthly characteristics, which represents the southern region of the basin’s extension range, and for this reason the water flow was described as the northern region in Sulaymaniyah is the recharge area and the southern area with a climate similar to Khanaqin station is the water drainage area of the basin.

Allometric Model of Crown Length for Pinus sylvestris L. Stands in South-Western Poland

The growth of a tree depends on the size, shape, and functioning of the crown. The length of the crown is a somewhat subjective value because the base of the crown is often difficult to determine. The aim of this study was to develop an allometric model to calculate the crown length of Pinus sylvestris L., which might serve as an alternative to the current equations used especially for stands of variable density. The model used three predictive variables, i.e., diameter at breast height, tree height, and density. The developed crown length model showed high compatibility with empirical data within the studied stands differing in diameter at breast height, height, age, biosocial position, and, above all, density (SD = 1.786). The correlation coefficient between the empirical crown length for the stand (Hemp*) and the calculated model (Hcal*) was r = 0.974, with a discrepancy of (±) 3.17%. The derived crown length model can be one of the components used to estimate the mass of needles or leaf area index (LAI) and, consequently, the amount of transpiration or the amount of carbon dioxide bound, which is crucial in the context of climate change.

Transpiration Efficiency of Some Potato Genotypes under Drought

Potato (Solanum tuberosum L.) is the third most consumed food crop after rice and wheat in the world. It is a short-duration crop, suitable for growing in a wide range of environments, but abiotic factors can limit potato production, and drought is the main one. Therefore, managing drought stress is of utmost importance under climate change conditions. Potato as a drought-sensitive crop needs choice of suitable genotypes for dry environments. In this study, transpiration efficiency (TE), soil water conservation and drought tolerance were analysed for potato genotypes from different origins. Three glasshouse experiments under different Vapor Pressure Deficit (VPD) conditions with water-stressed (WS) and well-watered (WW) plants resulted in significantly different total amounts of transpiration among the genotypes and water supply levels. Transpiration in WS plants was the same as with WW plants up to a specific threshold “Fraction of Transpirable Soil Water” (FTSW) and then sharply decreased in response to soil drying. Genotypes showed a substantial variation in FTSW thresholds (0.19 to 0.36 FTSW) under low VPD condition, which narrowed down (0.19 to 0.29) when air humidity was lower. Furthermore, we observed hardly any relationships between TE and FTSW threshold (r = 0.125) or TE and water saving (r = 0.031). Our results provide insights into genotypic interactions with VPD on FTSW threshold and TE under dry-down conditions in potato.

Physiological changes of sweet pepper under low irrigation regimes applied in three phenological stages of vegetative growth, reproductive growth, and fruit set

ABSTRACT A factorial experiment based on a completely randomised design (CRD) with 10 replicates was planned to evaluate if commercially low irrigation reduced output and how physiologically low irrigation influenced yield at different plant growth stages. In three phonological phases of the vegetative stage (VG), reproductive stage (RP), and fruit set (FS), two irrigation regimes of 100% of field capacity (FC) and 80% field capacity (low irrigation = LI) were employed. The results demonstrated that the shoot's fresh weight did not vary between the VG and RP phases, but rose during the FC stage. In FS, both photosynthesis and transpiration were reduced. VG had the highest amounts of photosynthesis and transpiration. Nevertheless, fruit yield rose during the second and third weeks of FS. As starch dropped and glucose, sucrose, and fructose increased, plasma membrane aquaporins (PIP) gene expression and abscisic acid (ABA) levels climbed. In conclusion, it was proved that lowering water consumption to 80% FC did not impact yield at any development stage, including FS, due to the larger sink of fruit rather than maintaining ideal photosynthetic conditions. ABA and PIP expression increased, which may serve as a signal for the plant to overcome the moderate stress generated by LI.

Evaluating the vegetation–atmosphere coupling strength of ORCHIDEE land surface model (v7266)

Abstract. Plant transpiration dominates terrestrial latent heat fluxes (LE) and plays a central role in regulating the water cycle and land surface energy budget. However, Earth system models (ESMs) currently disagree strongly on the amount of transpiration, and thus LE, leading to large uncertainties in simulating future climate. Therefore, it is crucial to correctly represent the mechanisms controlling the transpiration in models. At the leaf scale, transpiration is controlled by stomatal regulation, and at the canopy scale, through turbulence, which is a function of canopy structure and wind. The coupling of vegetation to the atmosphere can be characterized by the coefficient Ω. A value of Ω→0 implies a strong coupling of vegetation and the atmosphere, leaving a dominant role to stomatal conductance in regulating water (H2O) and carbon dioxide (CO2) fluxes, while Ω→1 implies a complete decoupling of leaves from the atmosphere, i.e., the transfer of H2O and CO2 is limited by aerodynamic transport. In this study, we investigated how well the land surface model (LSM) Organising Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE) (v7266) simulates the coupling of vegetation to the atmosphere by using empirical daily estimates of Ω derived from flux measurements from 90 FLUXNET sites. Our results show that ORCHIDEE generally captures the Ω in forest vegetation types (0.27 ± 0.12) compared with observation (0.26 ± 0.09) but underestimates Ω in grasslands (GRA) and croplands (CRO) (0.25 ± 0.15 for model, 0.33 ± 0.17 for observation). The good model performance in forests is due to compensation of biases in surface conductance (Gs) and aerodynamic conductance (Ga). Calibration of key parameters controlling the dependence of the stomatal conductance to the water vapor deficit (VPD) improves the simulated Gs and Ω estimates in grasslands and croplands (0.28 ± 0.20). To assess the underlying controls of Ω, we applied random forest (RF) models to both simulated and observation-based Ω. We found that large observed Ω are associated with periods of low wind speed, high temperature and low VPD; it is also related to sites with large leaf area index (LAI) and/or short vegetation. The RF models applied to ORCHIDEE output generally agree with this pattern. However, we found that the ORCHIDEE underestimated the sensitivity of Ω to VPD when the VPD is high, overestimated the impact of the LAI on Ω, and did not correctly simulate the temperature dependence of Ω when temperature is high. Our results highlight the importance of observational constraints on simulating the vegetation–atmosphere coupling strength, which can help to improve predictive accuracy of water fluxes in Earth system models.

Prediction of sap flow with historical environmental factors based on deep learning technology

Sap flow is an important intermediate link that reflects the continuous soil–plant-atmosphere cycle. Therefore, it is important to predict the sap flow to analyze the amount of tree transpiration for assessing of water consumption. In this paper, we propose a new sap flow assessment using environmental factors based on a convolutional neural network-gated recurrent unit (CGRU) hybrid deep learning method. The model was trained and tested with the sap flow and environmental factors from 17,568 group observations from public SAPFLUXNET dataset. These group observations measured from January 1, 2012 to December 31, 2012, with acquisition interval of 30 min for one tree of New Zealand Agathis australis. After designed the CGRU structure by integrated a convolutional neural network (CNN) and a gated recurrent unit (GRU) neural network, the input variables were selected with a correlation analysis between sap flow and environmental factors. Additionally, the number of previous conditions were introduced into the input of the model. Results showed that when the number of previous conditions set to 16, the learning rate set to 0.01 with Adam optimization algorithm, the mean squared error, mean absolute percentage error, and coefficient of determination of the CGRU model were 0.00231, 22.31 and 0.948 respectively. Comparing results showed that the CGRU-based sap flow prediction model has more accuracy than other eight models participating in the test including the independent CNN, GRU, CNN-Long short-term memory (LSTM) and five traditional machine learning based models. The least time spent on training is also the CGRU model. The CGRU-based sap flow prediction model proposed in this paper can capture complex nonlinear dependencies and yield accurate assessments of sap flow. Our model we established in this paper can be useful for research on forest stand transpiration, water consumption and the soil–plant-atmosphere cycle.

Spatial Variation in Catchment Response to Climate Change Depends on Lateral Moisture Transport and Nutrient Dynamics

AbstractFuture shifts in rainfall, temperature and carbon dioxide (CO2) will impact hydrologic and ecosystem behavior. These changes are expected to vary in space because water and nutrient availability vary with terrain and soil properties, with feedbacks on vegetation and canopy adjustment. However, within‐basin patterns and spatial dependencies of ecohydrologic dynamics have often been ignored in future scenario modeling. We used a distributed process‐based ecohydrologic model, the Regional Hydro‐Ecological Simulation System, as a virtual catchment to examine spatial and temporal variability in climate change response. We found spatial heterogeneity in Leaf Area Index, transpiration and soil saturation trends, with some scenarios even showing opposite trends in different locations. For example, in a drying scenario, decreased vegetation productivity in water‐limited upslope areas enhanced downslope nutrient subsidies so that productivity increased in the nutrient‐limited riparian zone. In scenarios with both warming and rising CO2, amplifying feedbacks between mineralization, vegetation water use efficiency and litter fall led to large increases in growth that were often strongest in the riparian area (depending on the coincident rainfall change). Modeled transpiration trends were determined by the competing effects of vegetation growth and changing water use efficiency. Overall, the riparian zone experienced substantially different (and even opposing) ecohydrologic trends compared to the rest of the catchment, which is important because productive riparian areas often contribute a disproportionate amount of vegetation growth, transpiration and nutrient consumption to catchment totals. Models that are spatially lumped, lack key ecosystem‐driving dynamics, or ignore lateral transport could misrepresent the complex ecohydrologic changes catchments could experience in the future.

Land Development and Role of Evapotranspiration in Climate Change

Analyses of underground temperatures have been used to obtain ground surface temperature (GST) histories. At individual sites, changes in the GST over time are synchronous with development which altered the evapotranspiration. At different, closely spaced sites, measured differences in GST between sites depend on the relative amounts of evaporation and transpiration at each site. These observations prove that a significant portion of the climate change observed on land is caused by changes in the amounts of evapotranspiration at each location. The magnitudes of GST changes vary from 0.6 to 2.6 C, for developments occurring from 8 to 52 years ago. In the temperate zone of Canada, these differences occur primarily in the summer. Our development, including urbanization and development of agricultural land, has produced a significant warming. It is best defined from underground temperature data.

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.

Intensity of spring wheat transpiration due to weather factors and methods of basic tillage

The paper presents the study of daily course transpiration of the three upper leaves of cultivars of spring hard wheat of different origin, grown against the background of two methods of primary tillage in different conditions of the vegetation period according to weather factors. The studies were carried out according to the method of rapid weighing using the torsion scales VT-500 three times during the day (9:00, 12:00 and 15:00 hours) in the phases of stem elongation and wheat earing. The paper identifies cultivar specificity of the course of daytime transpiration, the influence of soil tillage methods on the amount of transpiration, as well as a significant dependence on weather factors over the years of study. The results can be used in practical breeding with the perspective assessment of varieties according to the transpiration activity of the leaves in the most important phases of the spring wheat growing season. In connection with changes in the climatic factor in the direction of increasing aridity, it is important to know the patterns of the response of the plant organism to the extreme conditions and the possibility of its use in breeding practice. The results obtained can substantiate the needs to use various methods of basic processing to reduce negative weather factors.

Water balance and tree water use dynamics in remnant urban reserves

During the expansion of urban areas, small natural reserves have often been left intact within the built environment as central elements of biodiversity conservation, ecological connectivity, landscape sustainability, and quality of life of urban dwellers. Consequently, the surrounding urbanized landscape may impact the environmental conditions of these reserves (e.g., high temperatures, low moisture conditions), resulting in the need for extensive maintenance. This study presents an estimation of the water balance over two years (2017–2018) in three small urban reserves (between 2 and 30 ha) within the Greater Melbourne metropolitan area in Australia, for the purpose of understanding tree water use. Measurements of micrometeorological variables, soil moisture content profiles, water-table levels, sap flow velocities, and stem diameter variations were used to quantify the water sources of tree transpiration in these reserves. Results revealed that, despite the urban surroundings and the climate variations, these reserves have enough water to sustain tree transpiration. In two of the three reserves, groundwater was pivotal in sustaining transpiration rates; specifically, groundwater was estimated to contribute about 30–40% of the total transpiration amount during the driest periods of the year. Groundwater also played an essential role during nights with temperatures above 25 °C, helping trees to maintain night-time water use from 3 to 16% of the daily water use. In the third reserve, the presence of a shallow layer of heavy clay supplied water to the trees, which were able to maintain relatively constant transpiration rates throughout the year. These results demonstrate the importance of understanding the water regime of each urban reserve in order to support government authorities in preserving these ecosystems.

Luxury transpiration of winter wheat and its responses to deficit irrigation in North China Plain

Reducing crop luxury transpiration is an important step in improving water productivity; water shortage regions are potential hotspots for studying physiological water conservation. This study investigated the amount of luxury transpiration in winter wheat and its responses to different irrigation treatments in North China Plain. The results showed that luxury transpiration existed and increased with growth of winter wheat and after rainfall. In each sampling day, the amount of luxury transpiration under full irrigation was significantly higher than that under deficit irrigation. The average amount of luxury transpiration was 258.87 g/m<sup>2</sup> under full irrigation, and 125.18 g/m<sup>2</sup> under deficit irrigation during the experimental period. Although the amount of luxury transpiration was 2.09-fold higher under full irrigation than that in deficit irrigation, the water loss ratio due to luxury transpiration in deficit irrigation (8.13%) was significantly higher than that in full irrigation (6.75%). Furthermore, the ratio between luxury transpiration amount and crop daily transpiration was revealed in all sampling dates. Therefore, deficit irrigation should be generalized in the water shortage area, because it can save irrigation water and reduce the amount of luxury transpiration. Full irrigation should be carried out in the water abundant region mainly for higher production.

Extrapolation of Leaf Measurements to Obtain the Whole-Canopy Transpiration of C3 and C4 Xerophytic Shrubs

Quantifying the water balance within areas with sparse vegetation requires frequent measurement of transpiration in water-limited, arid, desert ecosystems. Field experiments were conducted in Shapotou, northwestern China, to examine the feasibility of up-scaling the transpiration of C3 and C4 xerophytic shrubs (Reaumuria soongorica and Salsola passerina, respectively) from the leaf to the canopy level throughout the growing season in 2015. The large weighing lysimeter method and LI-6400XT portable photosynthesis system were used to make relatively long-term measurements of transpiration. The results indicated that meteorological factors coupled with stomatal conductance affected the transpiration rate of the two shrubs at the leaf level, and that the vapor pressure deficit other than net radiation and the air temperature affected the transpiration rate of S. passerina at the canopy level. Precipitation and vegetation characteristics determined the transpiration amount of the C3 and C4 xerophytic shrubs. The leaf gas exchange measurements were arithmetically scaled up to the canopy level based on the leaf area. The validity of the extrapolation was evaluated by comparing the upscale values of transpiration with the calculated values obtained from lysimeter measurement. The up-scaling approach accurately (±0.005 mm h−1, RMSE = 35%) obtained canopy transpiration from the leaf measurements. Our study suggests that the up-scaling method based on leaf area can be adopted to determine the canopy transpiration of C3 and C4 xerophytic shrubs in arid desert environments.

Comparative Transpiration Studies on the Invasive Eastern Redcedar (Juniperus virginiana L.) and Adjacent Woody Trees

Fire suppression and grazing on the Great Plains have resulted in alteration of the grassland ecosystem, including an increase in woody trees. Eastern redcedar ( Juniperus virginiana L.) is a native but invasive conifer that is rapidly expanding its range in Oklahoma due to human and ecological factors and the ability to tolerate aridity. It is known to reduce soil moisture due to high rates of water uptake compared to neighboring grasses and herbaceous species. The objectives of this study were to compare average amounts of water transpired between eastern redcedar and adjacent woody trees in central Oklahoma to determine how water loss in the conifer compares with other trees in the same locality. Average amounts of transpiration in eastern redcedar were compared with those of loblolly pine ( Pinus taeda L.) , white mulberry ( Morus alba L.) , eastern cottonwood ( Populus deltoides W. Bartram ex Marshall) and bur oak ( Quercus macrocarpa Michx.). Three to six branch tips per tree were securely bagged over 24-hour periods, and water collected in each bag was weighed and analyzed. Three to five sampling months spanning two or three seasons were conducted for each comparative study. Results indicated that for winter, spring, and fall, transpiration from eastern redcedar exceeded that from the other tree species. Weather variables such as day length and temperature were found to have strong to moderate effects on transpiration in eastern redcedar. Day length and temperature also had strong effects on transpiration in white mulberry and bur oak, respectively, and humidity had an effect on transpiration in loblolly pine. No reliable or significant effect of weather variables was detected in eastern cottonwood.

Nocturnal transpiration in 18 broadleaf timber species under a tropical seasonal climate

Global increase in night time as compared to day time temperatures results in an increased nocturnal VPD, which possibly increases nocturnal transpiration of plants. However, there are few studies on nocturnal transpiration of plantations in the tropics. Here, we investigated the ratio of nocturnal to daily transpiration and its seasonal differences in timber plantations of tropical angiosperm tree species in low land seasonal tropical botanical garden in southwest China. We measured sap flow in 18 tree, comprising of nine evergreen and nine deciduous species, during three months in the wet season and three months in the dry season between 2012 and 2013. We partitioned the nocturnal sap flux density (SFD) into nocturnal transpiration and trunk water recharge. We also measured wood density to investigate its relationship with nocturnal sap flux density. Our results showed that the mean nocturnal (whole night-time) VPD was linearly correlated with mean nocturnal SFD (R2 > 0.41–0.73 across species) in both the wet and dry seasons. During the wet season, the ratio of nocturnal SFD to daily SFD was 0.12–0.19 and 0.15–0.2 among evergreen and deciduous species, respectively. During the dry season, this ratio increased to 0.18–0.28 for evergreen species. For evergreen species, the nocturnal trunk water recharge and nocturnal transpiration in the wet season were between 11.37–59.80% and 40.20–88.62% of nocturnal SFD, respectively. For deciduous species, these values were 18.10–66.26% and 81.90–33.73%, respectively. We found an inverse relationship between nocturnal SFD and wood density (R2 = 0.24, P = ≤0.05) across the 18 studied species. In conclusion, this study demonstrates a substantia amount of nocturnal transpiration in a number of tropical tree species, even in the wet season and increased nocturnal transpiration in evergreen species in dry season. However, there was not any significant difference of the nocturnal SFD between evergreen and deciduous species during the wet season. Nocturnal transpiration is constrained by wood density across species. High nocturnal air temperature will result in increased transpirational demand and hence water loss at night. Our findings revealed important implications for nocturnal transpiration on soil-plant equilibrium and hydrology of forest ecosystems in the seasonal tropics.

The ventilationjet system as a step towards controlled ventilation and adapted properties of insulation screens in greenhouses

Moisture control in a greenhouse based on the creation of screen gaps has many disadvantages. This study describes a new approach where screen gaps are avoided by installing a Ventilationjet system. A speed controlled fan creates an airflow through a small opening in the fully closed screens. A second fan under the screen mixes the cold, dry air with greenhouse air. This system is controlled based on the difference in absolute humidity of the air under and above the screen. This difference, multiplied by the volume of air that is exchanged equals the amount of transpiration produced by the plants. This system was tested in multiple crops including gerbera and roses. This resulted in a 16-23% lower gas consumption in a situation where the screen system was not changed. The reduction was a result of more controlled ventilation and the reduction of horizontal and vertical temperature differences within the greenhouse. Based on these positive results, the development of new screen systems that can be combined with the Ventilationjet system has started. A first test with a cucumber crop resulted in a 63% reduction of energy consumption compared to a standard greenhouse with a single energy screen.

Roles of forest bioproductivity, transpiration and fire in a nine-year record of cave dripwater chemistry from southwest Australia

Forest biomass has the potential to significantly impact the chemistry and volume of diffuse recharge to cave dripwater via the processes of nutrient uptake, transpiration and forest fire. Yet to-date, this role has been under-appreciated in the interpretation of speleothem trace element records from forested catchments. In this study, the impact of vegetation is examined and quantified in a long-term monitoring program from Golgotha Cave, SW Australia. The contribution of salts from rain and dry-deposition of aerosols and dissolved elements from soil mineral and bedrock dissolution to dripwater chemistry are also examined. This study is an essential pre-requisite for the future interpretation of trace element data from SW Australian stalagmite records, whose record of past environmental change will include alterations in these biogeochemical fluxes. Solute concentrations in dripwater vary spatially, supporting the existence of distinct flow paths governed by varying amounts of transpiration as well as nutrient uptake by deeply-rooted biomass. Applying principal components analysis, we identify a common pattern of variation in dripwater Cl, Mg, K, Ca, Sr and Si, interpreted as reflecting increasing transpiration, due to forest growth. Mass-balance calculations show that increasing elemental sequestration into biomass has the largest impact on SO4, providing an explanation for the overall falling dripwater SO4 concentrations through time, in contrast to the transpiration-driven rising trend dominating other ions. The long-term rise in transpiration and nutrient uptake driven by increased forest bioproductivity and its impact on our dripwater chemistry is attributed to (i) the post-fire recovery of the forest understorey after fire impacted the site in 2006 CE; (ii) and/or increased water and nutrient demand as trees in the overlying forest mature. The impact of climate-driven changes on the water balance is also examined. Finally, the implications for interpreting SW Australian speleothem trace element records are discussed.

Penman's sink-strength model as an improved approach to estimating plant canopy transpiration

The Penman energy balance equation has become a common approach to estimating the evaporation of plant canopies. Unfortunately, implementation of the energy balance equation requires various assumptions and empiricisms, including “crop coefficients”, so that in practice the Penman equation is used as a framework in which to apply empirical approximations. These limitations are reviewed in this paper. An alternative to the energy balance approach suggested by Penman was a “sink strength” model in which the gradient in vapor pressure was considered the prime driver of plant water loss. In this paper, the sink strength model is developed for determining plant canopy transpiration based on explicitly defined properties of the plants. The key variables are the carbon assimilation pathway of photosynthesis and the biochemical composition of the plant material being synthesized. These two parameters define the transpiration efficiency coefficient and radiation use efficiency that are required in the calculation of transpiration. Also, it is necessary to define a weighted vapor pressure gradient for transpiration when making estimates of the amount of transpiration on a daily basis. The derived expression of the sink strength model was used to compare predicted transpiration with measured values of four turf grass species measured over three years. A close linear correlation was observed for all grasses (P<0.0001). However, there was an indication that the grasses may vary slightly in their radiation use efficiencies, which with measurement of photosynthetic capacity would further improve the predicted transpiration rates. The ability to directly compute transpiration from explicitly defined variables based on plant traits offers an attractive alternative to the Penman energy balance approach.