Tropical Greenhouse Research Articles

Sap flow measurements of Ceriops tagal and Rhizophora mucronata mangrove trees by deuterium tracing and lysimetry

Mangrove forest trees grow in severe conditions such as diurnal submersion and high salinity surface and subsurface waters. This study focuses on two species on Mayotte Island, i.e. Ceriops tagal and Rhizophora mucronata, living in the middle range of the coastal mangrove. The seedlings of these trees were planted in a tropical greenhouse with an original pump system built to reproduce the natural tidal effect. The water used by these saplings, in two contrasted salinity conditions, was measured by lysimetry. For adult species, the trees' water consumption was measured on the field side after being injected with heavy water (D(2)O). Our work shows that this isotopic technique also works in saline conditions, and a water consumption of around 1 ± 0.2 L per day and per centimeter of diameter was found. These values are discussed as follows: the techniques used, the distinctive features of the mangrove trees, and other factors affecting the water absorption.

Development of Control Program for Plant Growth Parameter Analysis in Lowland Tropical Greenhouse

The purpose of this project is to develop control system for environment parameter in the lowland tropical greenhouse using Microcontroller. The plant growth analysis covered both inside and outside greenhouse was presented. The controller was used to monitor the temperature, relative humidity and Vapor Pressure Deficit (VPD) in the planting of chili. The study of VPD is to show air moisture conditions for plant production while taking into account different temperature levels. The controller is used to maintain the ideal VPD inside the greenhouse where it has been done for an experimental greenhouse. The higher temperature inside greenhouse, during the day time, further proves the greenhouse effect. The ideal VPD is about to achieve at midnight where the temperature ranged between 19 and 23°C at relative humidity of 54 to 57%. PIC controller was successfully being used and interfacing with computer (read data). The ability of controlling the environment parameter such as temperature, relative humidity and VPD give great potential for the application of the greenhouse in agriculture plantation.

Arsenic hyperaccumulation by Pteris vittata and Pityrogramma calomelanos: a comparative study of uptake efficiency in arsenic-treated soils and waters

This work comprised of the comparative study of arsenic (As) uptake efficiency by Pteris vittata and Pityrogramma calomelanos grown in (i) As amended soils (0-600 ppm) and (ii) As tainted water (40 ppb) using a new compact continuous flow phytofiltration system in a tropical greenhouse. The As hyperaccumulation efficiency was dependent on the growth medium for the two fern species. The highest level of As detected in the fronds of P. vittata was 19,300+/-190 ppm (dry weight basis) and 11,600+/-230 ppm for Pityrogramma calomelanos, after growing for 78 days in soils amended with As. In the compact continuous flow As phytofiltration system experiments, Pityrogramma calomelanos was found to perform better than P. vittata in phytofiltrating As contaminated water under waterlogged conditions. During the 167 h of phytofiltration experiment, the removal efficiency was approximately 99% and 67% for Pityrogramma calomelanos and P. vittata systems respectively, based on an initial 40 ppb As. Pityrogramma calomelanos also required a shorter acclimatization time than P. vittata under waterlogged conditions.

Manipulation of Ultraviolet Light Affects Immigration Behavior of <I>Ceratothripoides claratris</I> (Thysanoptera: Thripidae)

Studies were conducted in tropical greenhouses to elucidate the role of UV light (UV) for the orientation and flight behavior of the thrips Ceratothripoides claratris (Shumsher) (Thysanoptera: Thripidae), an important pest on tomato (Lycopersicum spp.), in the hot and humid tropics of South-East Asia. Four greenhouse types characterized by different combinations of UV-absorbing or -transmitting plastic films and nets on the roof and sidewalls, respectively, were used in these studies. In choice experiments C. claratris always preferred the environment with higher UV intensity. Furthermore, natural thrips populations around the greenhouses were captured during the majority of control dates in lower numbers on sticky traps on the outer sidewalls of greenhouses clad with UV-absorbing materials compared with UV-transmitting materials. The immigration of thrips into the UV-absorbing greenhouses also was impeded, as measured by sticky traps on the inner side walls. UV-absorbing plastic roofs showed the most pronounced deterrent effect for thrips movement toward greenhouses, and the UV-absorbing net effectively reduced thrips numbers crossing the net barrier into the greenhouse. A simple extension of UV-absorbing plastic roof around conventional greenhouses clad with UV-transmitting plastic and net reduced thrips capture rates inside the greenhouse up to 77% when thrips was released at 1 m distance from the net walls. These results are discussed in the context of wavelength dependent insect vision and the dilemma of tropical greenhouse constructions, i.e., physical pest exclusion versus appropriate ventilation to ensure a conducive microclimate for plant growth.

First records ofSpermophora kerinci,Nesticella mogeraandPseudanapis alohaon the European Mainland (Araneae: Pholcidae, Nesticidae, Anapidae)

The alien spider species Spermophora kerinci Huber, 2005, Nesticella mogera (Yaginuma, 1972) and Pseudanapis aloha Forster, 1959 are recorded from greenhouses in Germany. These are the first records from the European mainland. All these species have recently been found in the British Isles. The study of exotic spiders in greenhouses of the Botanic Garden in Berlin rendered interesting re- sults (KIELHORN 2008). Consequently, the spider fauna of other greenhouses in Berlin and Bran- denburg was examined. Spiders were collected in a hothouse of the Zoo-Aquarium Berlin (52°30'22N 13°20'29E, TK 3446, 37 m a.s.l.) and in the 'Tropical Islands' dome, a recreation facility with tropical plants in Brand, Brandenburg (52°2'20N 13°44'55E, TK 3948, 78 m a.s.l.). Several exotic spider species, which had been found in the Botanic Garden Berlin-Dahlem, were also present in the other greenhouses (KIELHORN 2009). Additionally, three species newly reported from the British Isles were caught: the pholcid Spermophora kerinci Huber, 2005, the nesticid Nesticella mogera (Yaginuma, 1972) and the anapid spider Pseudanapis aloha Forster, 1959. In Britain, these spiders were collected from leaf litter in the humid tropical greenhouse of the Eden project, a large greenhouse complex enclosing several artificial ecosystems (SNAZELL & SMITHERS 2007). Large tropical greenhouses, such as in the Eden project, have become popular attractions and have been built around the globe. It is nearly impossible to reconstruct the path by which exotic spider spe- cies may have reached these greenhouses (PAQUIN et al. 2008, SNAZELL & SMITHERS 2007). In the case presented here, a group of species has been imported to various countries in recent years. It is very likely that the institutions have acquired plants from the same common sources.

Effects of cover properties, ventilation rate, and crop leaf area on tropical greenhouse climate

Experimental results and validation of a simple greenhouse climate model are analysed according to data sets from six prototype greenhouses with three different plastics (reference N0, and two levels of near-infrared reflecting pigments N1 and N2); two ratios of ventilation openings to greenhouse covering area (0.223 and 0.427); a wide range of tomato leaf area index (0.01–4.97); and for three crop-growing periods that represent year-long tropical lowland climatic conditions in Purwakarta (107°30′E, 6°30′S, altitude 25 m), Indonesia. The model with a calibration factor for indirect absorbed solar radiation (indicating the part of the radiation absorbed by the greenhouse cover, structural elements, and soil surface released into the air) Λ of 0.1 satisfactorily calculated greenhouse air temperature TAir with less than 2% error and greenhouse air water vapour pressure deficits DAir with less than 10% error. The errors were higher at low values for the leaf area index. The model performance slightly improved by including the effect of leaf area index on Λ as an exponential term. Measurements and calculations demonstrated that TAir was affected more by variations of ventilation and leaf area index than by the applied cover properties. The leaf area index had the highest impact on greenhouse air temperature, implying that a large proportion of the cooling is achieved by the crop itself. The results enable the model to be used in the design of optimum greenhouse systems for tropical lowland Indonesia.

Modelling of tropical greenhouse temperature by auto regressive and neural network models

The variation of inside air temperature in a tropical greenhouse was investigated. The study included an auto regressive (AR) model with an external input (ARX), an auto regressive moving average model with an external input (ARMAX) and a neural network auto regressive model with an external input (NNARX). External and internal climatic data recorded over a year were used to build and validate models for simulating environmental conditions inside the greenhouse. The variables measured to estimate the greenhouse internal climate included external temperature, solar radiation, relative humidity and cloud cover. It was observed that models performed better when series tuning was done for fixed temperatures rather than fixed during time. Although ARX outperformed ARMAX, NNARX-predicted results were in close agreement with the measurements.

Interaction Between Iron Stress and Root-Zone Temperature on Physiological Aspects of Aeroponically Grown Chinese Broccoli

ABSTRACT Chinese broccoli (B. alboglabra), a subtropical vegetable was first grown at 25°C root-zone temperature (RZT) while its aerial portions were exposed to the hot, fluctuating temperatures for four weeks in the tropical greenhouse. Interaction between iron (Fe) stress and RZT were then studied by exposing the plant roots to 2 different RZTs: a constant cool 25°C-RZT (CRZT) and a fluctuating hot ambient RZT (ARZT). There were three different Fe levels [full Fe (FFe), 1/2Fe, and 0Fe] in the nutrient medium supplied to plants at each RZT. Compared to plant grown at CRZT, hot ARZT resulted in decreases in shoot and root productivities, photosynthetic CO2 assimilation rate (A), stomatal conductance (g s ), Fe and nitrate (NO3 −) uptake and transport and nitrate reductase activity (NRA). Hot ARZT also altered root morphology. Iron stress (1/2Fe and 0Fe) caused significant reductions in all the above parameters and changed root morphology when plants were grown at CRZT compared to those grown at FFe. However, most of the parameters studied had similar values at ARZT regardless of Fe levels. These results indicate that hot ARZT may mask the effects of Fe stress on certain physiological process which was clearly elucidated at RZT.

Design and Development of a Photovoltaic Power System for Tropical Greenhouse Cooling

Renewable energy sources like photovoltaic (PV) panels are used today in many applications. Natural ventilation in tropical greenhouse is common method for ventilation, which gives higher inside temperatures compared to the outside temperatures. In addition, this type of ventilation is not enough to reduce high temperature inside the structure in low land areas. Thus the requirement of cooling is increased. Use of the fossil fuel to run the cooling fans are not economically viable due to increasing of fuel cost and greenhouses are not always located near the electrical grid. This research presents a study on the installation and test of a complete photovoltaic hybrid system for cooling a tropical greenhouse. A hybrid photovoltaic system consisting of two photovoltaic sub-systems were connected to each other. This system includes 48 photovoltaic solar Panels with 18.75 watt each, one inverter, 1 charge controller and a battery bank (including 12 batteries). The PV system is located at University Putra Malaysia (UPM) Research Park. The national electricity grid was used as a backup unit. The load consisted of two misting fans for cooling greenhouse (during test period time) with 400 Watt electric power and five hours (11:00 am to 16:00 pm) daily operation. The results obtained showed that the maximum current drawn from the array was found to be 14.9 ampere at 13:00 pm (with load). The voltage of array was found to be 26.9 volt while the voltage and current of battery bank were found to be 26.2 volt and 23.0 ampere respectively. In conclusion, this study highlights the primary study of PV hybrid energy systems for tropical greenhouse cooling as an application of renewable energy in Selangor, Malaysia. The results showed that PV system would be suitable to supply electricity to cover the loads requirement demands without using energy from the grid.

Effects of Azadirachtin, Abamectin, and Spinosad on Sweetpotato Whitefly (Homoptera: Aleyrodidae) on Tomato Plants Under Laboratory and Greenhouse Conditions in the Humid Tropics

Direct and residual toxicity of NeemAzal-T/S (azadirachtin), Success (spinosad), and abamectin was tested against different life stages of sweetpotato whitefly, Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), under air-conditioned laboratory conditions and in a tropical net greenhouse. NeemAzal-T/S and abamectin deterred the settling of adults on tomato, Lycopersicon esculentum Mill (Solanaceae), plants and consequently reduced egg deposition. No such effect was detected for Success. All three pesticides influenced egg hatch. Effects of NeemAzal-T/ S were significantly altered if applied to different-aged eggs (1, 3, and 5 d old). In contrast, abamectin-treated eggs failed to hatch at any given age class. All three products caused heavy mortality of the three nymphal stages of B. tabaci, with the first instars being most susceptible, abamectin-treated nymphs died within 24 h postapplication. In contrast, 100% nymphal mortality with NeemAzal-T/S and Success was reached 6-9 d postapplication. abamectin caused 100% immature mortality at all residue ages (1, 5, 10, and 15 d) in the laboratory and greenhouse as well. Persistence of Success was comparably high in the laboratory, but in the greenhouse a faster decline of activity was evident by increased egg deposition, egg hatch, and reduced rates of immature mortality. Toxicity of NeemAzal-T/S however gradually declined under greenhouse conditions with time (5 d) postapplication. The findings are discussed within the context of integrated management of whitefly under protected cultivation in the humid tropics.

Microclimate and Air Exchange Rates in Greenhouses covered with Different Nets in the Humid Tropics

The effect of different mesh sizes of nets (40, 52 and 78 mesh) to cover ventilation openings of greenhouses located in the humid tropics on microclimate and air exchange rates was studied. Experiments were carried out in three identical greenhouses (each size of 10 m wide by 20 m long). These greenhouses were covered with a plastic film on the top, and different insect-proof nets on the roof and sidewalls, respectively. Water vapour, transpired from 300 tomato plants cultivated in each greenhouse, was used to determine air exchange rate. In addition, an energy balance method, based on solar radiation and daily microclimate in and outside the greenhouse, was used to predict the air exchange rate. A good agreement was achieved between the measured and predicted air exchange rates. Results show that the use of nets at different mesh sizes had a significant effect on microclimate and air exchange rate. Compared to the 40 mesh greenhouse, the reduction of air exchange rate of about 50% and 35% was obtained for the 78 and 52 mesh greenhouses, respectively. Consequently, the internal air temperature was also increased by 1–3 °C. Regarding air temperature rise, only minor differences have been observed due to very large ventilation openings. However, differences in absolute humidity were much more pronounced and statistically significant. Humidity in 78 mesh greenhouse was consistently approx. two times higher than 40 mesh greenhouse, while 50% increment was observed in the 52 mesh greenhouse. Based on internal microclimate and its ability to exclude some major insects, the 52 mesh net seems to be selected as a compromise size of nets appropriate for tropical greenhouse.

Water requirement of drip irrigated tomatoes grown in greenhouse in tropical environment

Four different levels of drip fertigated irrigation equivalent to 100, 75, 50 and 25% of crop evapotranspiration (ET c ), based on Penman–Monteith (PM) method, were tested for their effect on crop growth, crop yield, and water productivity. Tomato ( Lycopersicon esculentum , Troy 489 variety) plants were grown in a poly-net greenhouse. Results were compared with the open cultivation system as a control. Two modes of irrigation application namely continuous and intermittent were used. The distribution uniformity, emitter flow rate and pressure head were used to evaluate the performance of drip irrigation system with emitters of 2, 4, 6, and 8 l/h discharge. The results revealed that the optimum water requirement for the Troy 489 variety of tomato is around 75% of the ET c . Based on this, the actual irrigation water for tomato crop in tropical greenhouse could be recommended between 4.1 and 5.6 mm day −1 or equivalent to 0.3–0.4 l plant −1 day −1 . Statistically, the effect of depth of water application on the crop growth, yield and irrigation water productivity was significant, while the irrigation mode did not show any effect on the crop performance. Drip irrigation at 75% of ET c provided the maximum crop yields and irrigation water productivity. Based on the observed climatic data inside the greenhouse, the calculated ET c matched the 75–80% of the ET c computed with the climatic parameters observed in the open environment. The distribution uniformity dropped from 93.4 to 90.6%. The emitter flow rate was also dropped by about 5–10% over the experimental period. This is due to clogging caused by minerals of fertilizer and algae in the emitters. It was recommended that the cleaning of irrigation equipments (pipe and emitter) should be done at least once during the entire cultivation period.

Testing paleogeographic controls on a Neoproterozoic snowball Earth

The distribution of continents during the Neoproterozoic has been hypothesized to play an important role in the initiation of an ice‐covered Earth. In this study, the influence of paleogeography on the Neoproterozoic climate is evaluated using a fully coupled ocean‐atmosphere general circulation model (FOAM). Three simulations were completed with different continental distributions. Each simulation included a reduced solar luminosity (93% of present‐day) and low atmospheric CO2 (140 ppmv). Model results indicate that a low‐latitude concentration of continents leads to lower tropical temperatures, through reduced receipt of shortwave radiation and a smaller tropical greenhouse effect, but does not significantly affect high‐latitude temperatures or sea‐ice extent. In contrast, the presence of snow‐covered, mid‐ and high‐latitude continents increases the sensible heat transport over the ocean, giving rise to sea‐surface cooling, deep‐water formation, and an advanced sea‐ice margin. Nonetheless, an ice‐covered Earth is not simulated in these experiments.

A NATURALLY VENTILATED GREENHOUSE FOR TEMPERATE VEGETABLE PRODUCTION IN THE TROPICS

A naturally ventilated tropical greenhouse (NVTGS) has been developed for high value temperate vegetable production in the lowlands of Malaysia. The structure has a simple frame, transparent roof and insect screen sides. Several NVTGS have been designed, constructed and their performance evaluated. The design criteria, material selection, construction cost, maintenance and in-house environments were developed and evaluated. The structure was found to be stable, durable, reliable and required minimal maintenance, while providing an environment conducive for good vegetable production, with high quality, early harvests and higher yields compared to open field crops. Proper design and choice of covering material could control problems of extreme solar radiation, high rainfall, insects, diseases, weeds, high temperature, high humidity and reduce labor requirements. Studies on covering materials and natural ventilation inside a full scale NVTGS were conducted. Natural ventilation models were developed and verified. The ventilation was by the stack effect (temperature difference), wind effect or a combination of both effects. The natural ventilation rates that could reduce in-house air temperature, humidity and maintain carbon dioxide concentration are discussed. The importance of the physical properties of covering materials is also discussed.

Relationship among photosynthesis, ribulose-1,5-bisphosphate carboxylase (Rubisco) and water relations of the subtropical vegetable Chinese broccoli grown in the tropics by manipulation of root-zone temperature

Photosynthesis, initial Rubisco activity, Rubisco protein, total soluble protein and water relations were studied in subtropical Chinese broccoli ( Brassica alboglabra) grown aeroponically in a tropical (Singapore) greenhouse. Aerial parts of the plant were maintained at hot ambient (A) temperature, but with their roots exposed to two different root-zone temperatures (RZTs): a constant 25°C-RZT and a diurnally fluctuating ambient temperature (25–40°C). Plants grown at 25°C-RZT exhibited greater non-stomatal and stomatal limitation of photosynthetic rates (light- and CO 2-saturated O 2 evolution, P max and light-saturated CO 2 assimilation, A sat). Light saturated stomatal conductance ( g s sat) was higher in 25°C-RZT than A-RZT plants. Initial Rubisco activity and Rubisco protein was significantly lower in A-RZT plants than 25°C-RZT. The total soluble protein per unit leaf area showed a marked decrease in plants grown at A-RZT compared to those grown at 25°C-RZT. Predawn and midday leaf water potential ( Ψ leaf) were higher in 25°C-RZT than A-RZT plants. Reciprocal RZT transfer experiments were also conducted to study the relationship among photosynthesis, Rubisco and water relations. Immediate parallel decreases were observed in A sat, g s sat and Ψ leaf when plants were transferred from 25°C-RZT to A-RZT. However, significant increases in these parameters were observed after only 3 days of RZT transfer from ambient to 25°C. Decreases in non-stomatal limitation of photosynthesis, P max, initial Rubisco activity, Rubisco and total leaf soluble proteins were not detected until 4 or 5 days post-transfer, while decreases in total leaf soluble protein was observed 2 or 3 days after RZT transfer from 25°C to ambient temperature. When plants were transferred from A-RZT to 25°C-RZT, no significant changes in P max, initial Rubisco activity, Rubisco and total leaf soluble proteins were observed during the first 4 days of RZT transfer. These results indicate that the direction of RZT transfer determined the relative contributions of stomatal and non-stomatal limitations to photosynthesis and the importance of water stress.

The Compounding Effects of Tropical Deforestation and Greenhouse Warming on Climate

This study reports the first assessment of the compounding effects of land-use change and greenhouse gas warming effects on our understanding of projections of future climate. An AGCM simulation of the potential impacts of tropical deforestation and greenhouse warming on climate, employing a version of NCAR Community Climate Model (CCM1-Oz), is presented. The joint impacts of tropical deforestation and greenhouse warming are assessed by an experiment in which removal of tropical rainforests is imposed into a greenhouse-warmed climate. Results show that the joint climate changes over tropical rainforest regions comprise large reductions in surface evapotranspiration (by about −180 mm yr−1) andprecipitation (by about −312 mm yr−1) over the Amazon Basin, along with anincrease of surface temperature by +3.0 K. Over Southeast Asia, similar but weaker changes are found in this study. Precipitation is decreased by −172 mmyr−1, together with the surface warming of 2.1 K. Over tropical Africa, changes in regional climate is much weaker and with some different features, such as the increase of precipitation by 25 mm yr−1. Energy budgetanalyses demonstrates that the large increase of surface temperature in the joint experiment is not solely produced by the increase of CO2concentration, but is a joint effect of the reduction of surface evaporation (due to deforestation) and the increase of downward atmospheric longwave radiation (due to the doubling of CO2 concentration). Furthermore, impactsof tropical deforestation on the greenhouse-warmed climate are estimated by comparing a pair of tropical deforestation simulations. It is found that in CCM1-Oz, deforestation has very similar impacts on greenhouse-warmed regional climates as on current climates over tropical rainforest regions. The extra-tropical climatic response to tropical deforestation is identified in both sets of tropical deforestation experiments. Statistically significant responses are seen in the large-scale atmospheric circulation such as changes in the velocity potential and vertically integrated kinetic and potential energy fields. Wave propagation patterns are identified in the large-scale circulation anomalies, which provides a mechanism for interpreting the model responses in the extra-tropics. In addition, this study suggests that land-use change such as tropical deforestation may affect projections of future climate.

A long-term study on interactions between the Adh and αGpdh allozyme polymorphisms and the chromosomal inversion In(2L)t in a seminatural population of D. melanogaster

Abstract The Adh and αGpdh allozyme loci (both located on the second chromosome) showed considerable fluctuations in allele frequencies in a seminatural population of Drosophila melanogaster during 1972–97. Both long-term and short-term fluctuations were observed. The short-term fluctuations occurred within almost all years and comparison of allele frequencies between winters and summers showed significantly higher AdhS (P < 0.001) and αGpdhF (P < 0.01) allele frequencies in summers. Frequencies of these alleles were significantly positively correlated with environmental temperature, suggesting the adaptive significance of these allozyme polymorphisms. Frequency changes of the Odh locus (located on the third chromosome) showed no seasonal pattern and were not correlated with environmental temperature. Almost all short-term and long-term increases in AdhS frequency were accompanied by a corresponding decrease in αGpdhS frequency (r = –0.82, P < 0.001) and vice versa. Further analysis showed that gametic disequilibria between the Adh and αGpdh loci, which frequently occurred, were due to the presence of inversion In(2L)t located on the same chromosome arm and In(2L)t frequencies were positively correlated with environmental temperature. Gametic disequilibria between Adh and Odh and between Odh and αGpdh were hardly observed. Because In(2L)t is exclusively associated with the AdhS/αGpdhF allele combination, the observed correlated response in Adh/αGpdh allele frequencies is (at least partly) explained by hitchhiking effects with In(2L)t. This means that the adaptive value of the allozyme polymorphisms has been overestimated by ignoring In(2L)t polymorphism. Fluctuations in Adh allele frequencies are fully explained by selection on In(2L)t polymorphism, whereas we have shown that αGpdh frequency fluctuations are only partly explained by chromosomal hitchhiking, indicating the presence of selective differences among αGpdh genotypes in relation with temperature and independent of In(2L)t. Frequency fluctuations of αGpdh and In(2L)t are consistent with their latitudinal distributions, assuming that temperature is the main environmental factor varying with latitude that causes directly or indirectly these frequency distributions. However, the results of the tropical greenhouse population show no correlation of Adh (independent of In(2L)t) and Odh allele frequencies with environmental temperature, which may indicate that the latitudinal distribution in allele frequencies for these loci is not the result of selection on the F/S polymorphism in a direct way.

Diurnal changes in xylem pressure and mesophyll cell turgor pressure of the lianaTetrastigma voinierianum: The role of cell turgor in long-distance water transport

Long-term xylem pressure measurements were performed on the lianaTetrastigma voinierianum (grown in a tropical greenhouse) between heights of 1 m and 9.5 m during the summer and autumn seasons with the xylem pressure probe. Simultaneously, the light intensity, the temperature, and the relative humidity were recorded at the measuring points. Parallel to the xylem pressure measurements, the diurnal changes in the cell turgor and the osmotic pressure of leaf cells at heights of 1 m and 5 m (partly also at a height of 9.5 m) were recorded. The results showed that tensions (and height-varying tension gradients) developed during the day time in the vessels mainly due to an increase in the local light intensity (at a maximum 0.4 MPa). The decrease of the local xylem pressure from positive, subatmospheric or slightly above-atmospheric values (established during the night) to negative values after daybreak was associated with an almost 1 ∶ 1 decrease in the cell turgor pressure of the mesophyll cells (on average from about 0.4 to 0.5 MPa down to 0.08 MPa). Similarly, in the afternoon the increase of the xylem pressure towards more positive values correlated with an increase in the cell turgor pressure (ratio of about 1 ∶ 1). The cell osmotic pressure remained nearly constant during the day and was about 0.75–0.85 MPa between 1 m and 9.5 m (within the limits of accuracy). These findings indicate that the turgor pressure primarily determines the corresponding pressure in the vessels (and vice versa) due to the tight hydraulic connection and thus due to the water equilibrium between both compartments. An increase in the transpiration rate (due to an increase in light intensity) results in very rapid establishment of a new equilibrium state by an equivalent decrease in the xylem and cell turgor pressure. From the xylem, cell turgor, and cell osmotic pressure data the osmotic pressure (or more accurately the water activity) of the xylem sap was calculated to be about 0.35–0.45 MPa; this value was apparently not subject to diurnal changes. Considering that the xylem pressure is determined by the turgor pressure (and vice versa), the xylem pressure of the liana could not drop to — in agreement with the experimental results — less than -0.4 MPa, because this pressure corresponds to zero turgor pressure.

Provenance variation in morphology and leaflet anatomy of Parkia biglobosa and its relation to drought tolerance

Measurements of morphological and anatomical characteristics made on 4-month-old seedlings from five provenances of Parkia biglobosa (Jacq.) Benth., grown in a tropical greenhouse under controlled conditions, showed significant differences between the northern provenances, which represented the Sudan savanna zone, and the southern provenances which represented the forest zone of the species distribution. Seedlings of provenances from the savanna zone showed more xerophytic characteristics than those from the forest zone. They were smaller in height, with a greater number of smaller leaflets per pinnae, a lower specific leaflet mass, smaller palisade and guard cells and a lower ratio of palisade:non-palisade tissue. There were also significant differences in the same characteristics, except palisade cell length, between provenances from the easterly and westerly extremes of the species range. Stomatal conductance measured after 2 weeks of droughting also showed that provenances from the savanna zone had higher values, indicating greater physiological activity and reduced stress, compared with provenances from the forest zone. Multivariate discriminant analysis of the morphological and anatomical characteristics showed that 98% of the seedlings were classified correctly with respect to provenance. The squared distances between provenances were closely related to the geographical distances between locations. Yet, not all variation in leaf anatomy could be explained by the difference in climatic conditions from north to south. Also drought tolerance was not always related to morphological and anatomical features. It is possible that clinal variation within the species from east to west may be interacting with climatic differences from north to south.

Large‐scale coupling between the tropical greenhouse effect and latent heat flux via atmospheric dynamics

The clear‐sky greenhouse effect (GE) is determined primarily by the amount and vertical distribution of water vapor in the atmospheric column. GE hampers surface radiative cooling and is maintained through surface evaporative cooling. This paper examines the intimate space‐time relationships between the patterns of radiative heating of the atmosphere and surface evaporative cooling. We use data derived from satellite and in situ observations to show that tropical maritime GE is decoupled in space and time from latent heat flux (LHF), its source of water vapor. Large scale transport of atmospheric water vapor responsible for the observed relationships between GE and LHF is discussed. The spatial patterns of average GE and LHF are imbedded in the Walker and Hadley circulations and reinforce these circulations with strong evaporative cooling in the subtropical highs and greenhouse warming in the equatorial trough zones. Throughout tropical areas characterized by strong seasonality, the seasonal cycles of GE and LHF are out of phase. Much of the moisture that feeds GE in these off‐equatorial regions is advected by the Hadley circulation from tropical moisture source regions of the opposite hemisphere. An out‐of‐phase relationship between GE and LHF also turns up on El Niño ‐ Southern Oscillation timescales, most notably in the central tropical Pacific. The “super” greenhouse effect (SGE), a situation when GE absorption increases more than colocated surface longwave emission, is a seasonal feature of extensive tropical off‐equatorial areas where it is maintained by moisture convergence and convection. On interannual timescales, the same dynamical processes appear to assert the SGE in the central equatorial Pacific. GE and LHF regimes are also described for the equatorial cold tongue and warm pool regions.