Dry Season Conditions Research Articles

Fertiliser timing and use of inhibitors to reduce N2O emissions of rainfed wheat in a semi-arid environment

Nitrogen (N) management is critical to the profitability of grain production systems, however careful management of fertiliser is needed to minimise environmental impacts. We investigated the effect of five N fertilisation strategies on nitrous oxide (N2O) emissions and nitrogen use efficiency (NUE) of rainfed wheat grown on a clay soil in a temperate, semi-arid environment of south eastern Australia during 2013 and 2014. Treatments included urea application (50 kg N/ha) at sowing with and without nitrification inhibitor (3,4–dimethylpyrazole phosphate) and surface broadcasting of urea with and without urease inhibitor (n-butyl thiophosphoric triamide) at the end of tillering plus an unfertilised control. Daily N2O emissions were low and responsive to in-season rainfall and fertiliser addition at sowing. Cumulative emissions from sowing until harvest were highest where N was applied at sowing in 2013; 160 g N2O-N/ha, while the 0 N control emitted 28 g N2O-N/ha (over 201 days). Emissions during 2014 were 77% lower than 2013 due to dry seasonal conditions; cumulative emissions were 49 g N2O-N/ha where N was applied at sowing, with background emissions of around 0 g N2O-N/ha (over 177 days). Inhibitors showed limited scope for reducing N2O emissions in this environment, however deferring N application until the end of tillering reduced N2O emissions. Grain yield responses to fertiliser were significant; increasing grain yield by 11–31% and NUE was generally high (recovery efficiency > 68%). However, deferring N application until the end of tillering in 2014 reduced yield (− 19%) and recovery of applied N (− 74%).

Physiological adjustments of an invasive tree species to extreme hydrological events in a tropical seasonal wetland

KEY MESSAGE: We analyzed the response of Vochysia divergens Pohl trees to hydrological variation over seasons in a Brazilian wetland-based 26 physiological parameters. Dry season conditions had a greater effect on the photosynthetic function than those in the wet season. Plants in seasonal wetlands are subject to large hydrological fluctuations and the physiological trade-offs that occur during these variations are still poorly understood. Within the Brazilian Pantanal, the largest tropical seasonal wetland in the world, the abundance of Vochysia divergens Pohl (Vochysiaceae) has been increasing and it forms mono-specific stands. The physiological performance of V. divergens trees to withstand seasonal variations in flooding and drought was evaluated to understand how the hydrological regime affects the species habitat and encourages new areas to be occupied. Individuals were evaluated for changes in their physiological parameters by means of CO₂ response curves, chlorophyll fluorescence, photosynthetic pigment and nitrogen (N) concentrations. Drought conditions caused reductions of 82, 64 and 80% of the maximum rate of CO₂-saturated photosynthesis (Aₘₐₓ ₘ), electron transport (Jₘₐₓ ₘ), and carboxylation (Vcₘₐₓ ₘ) per unit leaf mass, an increase in leaf fluorescence (F₀: 27%) and non-photochemical quenching (ΦNPQ: 18%), and a decrease in photochemical quantum yield of photosystem II (ΦPSII ᵢₙ: 29%). The dry season also caused a significant reduction in leaf photosynthetic pigments and an increase in leaf N concentration, but most of the N was allocated away from carboxylation and electron transport proteins and toward leaf structure. Our data indicate that dry season drought caused a significant decline in biochemical properties associated with leaf gas exchange and an increase in allocation to leaf structure. The ability to rapidly shift to high photosynthesis as soon as water levels rise in the wet season may be critical for the growth and expansion of this species in the Pantanal.

Enhanced canopy growth precedes senescence in 2005 and 2010 Amazonian droughts

Unprecedented droughts hit southern Amazonia in 2005 and 2010, causing a sharp increase in tree mortality and carbon loss. To better predict the rainforest's response to future droughts, it is necessary to understand its behavior during past events. Satellite observations provide a practical source of continuous observations of Amazonian forest. Here we used a passive microwave-based vegetation water content record (i.e., vegetation optical depth, VOD), together with multiple hydrometeorological observations as well as conventional satellite vegetation measures, to investigate the rainforest canopy dynamics during the 2005 and 2010 droughts. During the onset of droughts in the wet-to-dry season (May–July) of both years, we found large-scale positive anomalies in VOD, leaf area index (LAI) and enhanced vegetation index (EVI) over the southern Amazonia. These observations are very likely caused by enhanced canopy growth. Concurrent below-average rainfall and above-average radiation during the wet-to-dry season can be interpreted as an early arrival of normal dry season conditions, leading to enhanced new leaf development and ecosystem photosynthesis, as supported by field observations. Our results suggest that further rainfall deficit into the subsequent dry season caused water and heat stress during the peak of 2005 and 2010 droughts (August–October) that exceeded the tolerance limits of the rainforest, leading to widespread negative VOD anomalies over the southern Amazonia. Significant VOD anomalies were observed mainly over the western part in 2005 and mainly over central and eastern parts in 2010. The total area with significant negative VOD anomalies was comparable between these two drought years, though the average magnitude of significant negative VOD anomalies was greater in 2005. This finding broadly agrees with the field observations indicating that the reduction in biomass carbon uptake was stronger in 2005 than 2010. The enhanced canopy growth preceding drought-induced senescence should be taken into account when interpreting the ecological impacts of Amazonian droughts.

Potential impact of climate change on peanut yield in Senegal, West Africa

Crop models are useful tools to investigate climate change impacts and suitable adaptations strategies on crops. In order to evaluate the impact of climate change on peanut yield in Senegal, a solution of the SIMPLACE crop modelling framework using the Lintul5 crop model together with a Tc model and FAO-56 based approach to simulate evapotranspiration was used with consideration of Tc versus Ta in driving heat stress with output from four regional climate models (RCMs) and two climate change scenarios (RCP4.5 and RCP8.5). Results from six field experiments at two sites (Bambey and Nioro) in Senegal in the dry seasons of 2014 and 2015 and the rainy season of 2014, were used for calibration and evaluation for two peanut varieties. Our calibration and evaluation exercise revealed that simulation skill was markedly improved when Tc was considered under irrigated, dry season conditions during which time the plants were subject to periodic heat stress. Under future climatic conditions, positive changes of up to 2.4% for RCP4.5 and 8.3% for RCP8.5 for seed yield were found when increasing [CO2] is taken into account for the period 2016–2045 in dry season. While, in rainy season seed yield increased by 11.0% for RCP4.5 and 19.0% for RCP8.5. The effect of climate change on seed yield was negative in the dry season where maximum Ta is often higher than 38 °C compared to the rainy season in particular when Ta is used for simulating heat stress effects. It is concluded that climate change could have limited negative impacts on peanut yield in Senegal due to the effect of elevated [CO2]. However, simulated Tc should be used instead of Ta to accurately account for heat stress impact on peanut especially during the dry season.

Distinct physiological, biochemical and morphometric adjustments in the malaria vectors Anopheles gambiae and A. coluzzii as means to survive dry season conditions in Burkina Faso.

Aestivation and dispersive migration are the two strategies evoked in the literature to explain the way in which malaria vectors Anopheles coluzzii and A. gambiae survive the harsh climatic conditions of the dry season in sub-Saharan Africa. However, the physiological mechanisms regulating these two strategies are unknown. In the present study, mosquito species were exposed to controlled environmental conditions mimicking the rainy and dry seasons of south western Burkina Faso. Survival strategies were studied through morphometric (wing length), ecophysiological (respiratory gas exchanges), biochemical (cuticular hydrocarbons composition) and molecular (AKH mRNA expression levels) parameters, variations of which are usually considered to be hallmarks of aestivation and dispersion mechanisms in various insects. Our results showed that ecophysiological and morphometric adjustments are made in both species to prevent water losses during the dry season. However, the usual metabolic rate modifications expected as signatures of aestivation and migration were not observed, highlighting specific and original physiological mechanisms sustaining survival in malaria mosquitoes during the dry season. Differences in epicuticular hydrocarbon composition and AKH levels of expression were found between the permanent and temporary A. coluzzii populations, illustrating the great phenotypic plasticity of this mosquito species. Altogether, our work underlines the diverse and complex pattern of changes occurring in the two mosquito species and at the population level to cope with the dry season and highlights potential targets of future control tools.

Emerging Water Quality Issues along Rio de la Sabana, Mexico

The basin of Rio de la Sabana is the largest tributary of the Tres Palos coastal lagoon in Southwest Mexico, east of Acapulco. This lagoon and its upstream basin areas have become a high priority area for the preservation of coastal and marine environments. To obtain information about water quality as affected by urban expansion since 2002, fourteen physicochemical parameters (temperature, pH, electrical conductivity, dissolved oxygen, ammonium, nitrate, nitrite, sulphate, phosphate), biochemical (biological and chemical oxygen demand, methylene blue active substances) and bacteriological parameters (total and fecal coliforms) were determined. This sampling was done for dry and rainy season conditions at seven locations (S1, S2, S3, …, S7) along the river, spaced 3 to 6 km apart to a total of 30.4 km. The results were grouped into four zones: (Z1) reference, (Z2) transition, (Z3) polluted, (Z4) recovery. The Alborada (S5) and Tunzingo (S6) sites, adjacent to dense high-class residential areas (Z3), had the greatest pollution charges in both seasons, while the La Poza (S7) site near the Tres Palos lagoon (Z4) showed a decrease in pollution. All parameters correlated with increasing head- to down-river sampling distance by following linear (pH, DO) or curvilinear patterns (all other parameters). Using sampling location and dry versus rainy sampling season as multivariate regression (predictor) variables led to least-squares capturing: 1) 66% to 95% of the T(°C), pH, DO, and PO3-4 variations, and 2) 57% to 96% of the log-linear variations of the other parameters. Among the parameters, T(°C), DO, and PO3-4 were not significantly affected by sampling season, while pH became so after deleting two higher than usual pH values at the S5 and S6 locations during the dry season.

Tree legumes-temperate grass agroforestry system effects on inorganic soil nitrogen as ecosystem services provision for smallholder farming systems in South Africa

ABSTRACTNitrogen is an essential macro-nutrient for plant growth and is indispensable for high agricultural food productivity and quality. Shortage of good quality forage under the dry winter season and low soil fertility conditions are the major constraints in rural farming systems in the Moist Tall Grassveld of the Upper Thukela, South Africa. The effect of legumes on inorganic soil nitrogen was assessed in an agroforestry trial (Leucaena leucocephala (Lam.) De Wit, Acacia karroo Hayne, Dactylis glomerata L., Festuca arundinacea Schreb.), by soil sampling method. In the agroforestry trial, total inorganic soil nitrogen accumulation was significantly greater under intercropping than under sole crop treatments and, irrespective of the treatments, significantly more nitrate than ammonium nitrogen was measured. The study demonstrated that intercropping grasses with tree legumes could provide important ecosystem services of nitrogen supply in the soil. The results suggested that introducing legume intercrops might constitute a relevant cropping strategy to improve the soil fertility status with regard to nitrogen while at the same time providing forage in smallholder farming systems in South Africa’s Moist Tall Grassveld regions.

Photoperiodic responses of Sahelian malaria mosquitoes Anopheles coluzzii and An. arabiensis

BackgroundThroughout large parts of sub-Saharan Africa, seasonal malaria transmission follows mosquito density, approaching zero during the dry season and peaking during the wet season. The mechanisms by which malaria mosquitoes survive the long dry season, when no larval sites are available remain largely unknown, despite being long recognized as a critical target for vector control. Previous work in the West African Sahel has led to the hypothesis that Anopheles coluzzii (formerly M-form Anopheles gambiae) undergoes aestivation (dry-season diapause), while Anopheles gambiae (s.s.) (formerly S-form An. gambiae) and Anopheles arabiensis repopulate each wet season via long-distance migration. The environmental cues used by these species to signal the oncoming dry season have not been determined; however, studies, mostly addressing mosquitoes from temperate zones, have highlighted photoperiod and temperature as the most common token stimuli for diapause initiation. We subjected newly established colonies of An. coluzzii and An. arabiensis from the Sahel to changes in photoperiod to assess and compare their responses in terms of longevity and other relevant phenotypes.ResultsOur results showed that short photoperiod alone and to a lesser extent, lower nightly temperature (representing the early dry season), significantly increased longevity of An. coluzzii (by ~30%, P < 0.001) but not of An. arabiensis. Further, dry season conditions increased body size but not relative lipid content of An. coluzzii, whereas body size of An. arabiensis decreased under these conditions.ConclusionsThese species-specific responses underscore the capacity of tropical anophelines to detect mild changes (~1 h) in photoperiod and thus support the role of photoperiod as a token stimulus for An. coluzzii in induction of aestivation, although, these responses fall short of a complete recapitulation of aestivation under laboratory conditions.

Ina

Land and forest fires in Indonesia occur almost every year since 1997. The main causes of fires are due to human activities, driven by El Nino during dry season and biophysical conditions of degraded land. In Indonesia land and forest fires have an impact on socio-cultural, economic and political aspects. Therefore, Indonesian government involves multi institutions to control land and forest fire. Thus, to manage fire, coordination among institutions is absolutely necessary. This study using qualitative approach to analyze coordination among government agencies in term of land and forest fire control with case in South Sumatera Province. The results showed that coordination among government agencies occured in the context of fire suppression and the performance was less than optimal when viewed from the achievement of fire fighting targets. Factors influenced the coordination of fire management were authority, communication, controlling and leadership. Therefore, need to be improved by considering that fire suppression in peatlands is relatively difficult.

Mechanisms of desiccation tolerance in the bromeliad Pitcairnia burchellii Mez: biochemical adjustments and structural changes

Rocky outcrops represent the diversity center of vascular desiccation tolerant (DT) plants. Vegetation in this environment is exposed to an extended dry season and extreme conditions due to rocky soils and high sun exposure. In this study, we demonstrated that Pitcairnia burchellii, a bromeliad from rocky outcrops, tolerates intense desiccation for about 90 days due to strategies as accumulation of compatible osmolytes and antioxidant substances together with leaf morphological changes. In dehydrated plants, an increase in antioxidant activity was observed and the vacuolization of parenchyma cells was accompanied by proline accumulation in leaves and rhizomes. Precursors related to phenylpropanoid pathway increased significantly during plant dehydration. Accordingly, increases in anthocyanin and phenolic contents as well as lignin deposition were observed in leaves of dehydrated plants. Cell divisions and a decrease in stored starch were observed in the rhizomes indicating starch mobilization. Anatomical analyses revealed the presence of a more developed water-storage tissue in dehydrated leaves. During desiccation, leaves curl upwards and the adaxial V deep water-storage tissue is supported by two larger lateral vascular bundles. Cell wall folding and an increased proportion of arabinose-containing polymers was observed in leaves under dehydration, suggesting increasing of cell wall flexibility during desiccation. Such biochemical and morphological changes are consistent with the ability of P. burchellii to tolerate intense desiccation and behave as a resurrection species.

Long‐Lead Prediction of the 2015 Fire and Haze Episode in Indonesia

We conducted a case study of NCEP CFSv2 seasonal model forecast performance over Indonesia in predicting the dry conditions in 2015 that led to severe fire, in comparison to the non-El Niño dry season conditions of 2016. Forecasts of the Drought Code (DC) component of Indonesia's Fire Danger Rating System were examined across the entire Equatorial Asia region and for the primary burning regions within it. Our results show that early warning lead times of high observed DC in September and October 2015 varied considerably for different regions. High DC over Southern Kalimantan and Southern New Guinea were predicted with 180-day lead times, whereas Southern Sumatra had lead times of up to only 60 days, which we attribute to the absence in the forecasts of an eastward decrease in Indian Ocean SSTs. This case study provides the starting point for longer-term evaluation of seasonal fire danger rating forecasts over Indonesia.

Spatial and temporal hydrochemistry variations of karst water in Gunung Sewu, Java, Indonesia

A hydrogeochemical study was conducted in the Gunung Sewu Karst, Java Island, Indonesia. The main objective of this study is to describe the spatial and temporal variations of hydrochemistry that occur in the central and western parts of Gunung Sewu. Discharge measurements for a one-year period are taken in some karst springs or underground rivers to define their discharge hydrograph. Furthermore, baseflow separation analysis was conducted to determine the base flow percentage throughout the year. Water sampling for hydrogeochemical analysis was taken every month to represent the dry and rainy season conditions. To describe the hydrogeochemical processes, a scatter plot analysis with a small sample size was conducted. The results showed that the hydrochemistry of karst water in the study area has different characteristics spatially and temporally. Within the dry season, the dominant hydrogeochemical process is water–rock interaction (precipitation of calcite mineral), indicated by achieving the maximum level of Ca2+, HCO3 −, electrical conductivity, base flow percentage, and SI calcite, with the lowest level of log $$P_{{{\text{CO}}_{2} }}$$ in the water. In addition, the dry season hydrochemistry is characterized by a strong relationship between electrical conductivity–calcium/bicarbonate, base flow percentage-discharge, base flow percentage-SI calcite, and SI calcite-log $$P_{{{\text{CO}}_{2} }}$$ . Spatially, the different level of correlations between these parameters depended on the sampling location, flow recharge, and the conduit development. Conversely, in the rainy season, the hydrogeochemical process shifted from water–rock interaction to dilution of rainwater as a result of rain water supply through a conduit system channel, which is characterized by declining Ca2+, HCO3 −, electrical conductivity, base flow percentage, and SI calcite, with the highest level of log $$P_{{{\text{CO}}_{2} }}$$ in the water. The dilution of rainwater process also caused a decline in the correlation of some hydrogeochemical parameters.

Spatial heterogeneity and long-term dynamics of cladoceran ephippia in a monsoonal reservoir, driven by hydrology and eutrophication

Most freshwater Cladocera produce ephippia to survive harsh episodes in their life cycle. Ephippia represent the dormant community in sediments and allow tracing population dynamics and community succession with environmental change in water bodies in time. As reservoirs are created by damming rivers, the species composition and structure of a dormant cladoceran community are expected to depend on trophic state as well as on hydrological conditions. We collected ephippia from sediments in the transition and lacustrine zones of Liuxihe reservoir, a warm-water impoundment in southern China. High species richness with low abundance was found in the transitional zone, while high abundance was found at the lacustrine zone. Ephippia identified Daphnia galeata as the first Cladocera colonizer of the newly created water body, but littoral or small sized species—Scapholeberis sp. and Bosmina sp. fast increased and became dominated from damming till the end of 1970s. Medium-sized pelagic species—Moina micrura and D. galeata—increased from 1975 onwards, corresponding to an increase in diatom abundance with slight eutrophication and hydrological shift due to the construction of two small dams in the upstream zone of the feeding rivers. A two-way stepwise linear regression analysis showed that spatial variables explained 33% of ephippial total abundance while diatom abundance explained 5.2%. Hydrological conditions in the dry season (October to next March) were unrelated to total ephippial abundance but explained 37.5% in the wet season (April to September). We conclude the distinct longitudinal gradient and vertical variation of the dormant community provide useful information for understanding of long-term dynamics of site-specific hydrological processes, primary productivity and hydrologic events.

Before the spatial analysis of Beg-er-Vil: A journey through the multiple archaeological dimensions of a Mesolithic dwelling in Atlantic France

The Beg-er-Vil coastal site (Quiberon, Morbihan, France), initially excavated in the 1980s, and more extensively since 2012, is exposed to strong marine and anthropic erosion. At the present time, the main challenge is to define the status of the site by describing its formation dynamics. This necessitates investigating the taphonomic and erosive mechanisms using a combined method adapted to the shell midden levels, before undertaking spatial analysis. The archaeological level is protected by a thick dune and is subdivided into several stratigraphic units (SU), which record several changes in the function of the site. It is made up of accumulations of shell pockets covered in sandy sediments. The micromorphological analysis shows that this waste area seems to develop into an area of activities and movement. These surfaces also record alternating dry and wet seasonal conditions, but with no phase of abandonment. Systematic pH measurements show variations of 7.7 to 9.0 depending on the layers, corresponding to a slightly alkaline to alkaline acid-basic status. The mapping of measurements can be correlated to structures and archaeological remains of organic origin. The excavation shows that the division of the dwelling area was guided by topographic factors, with a circular dwelling 3.50m in diameter installed on a flat zone and a shell waste zone on a slope towards the sea. Numerous fire-related activities were also carried out in this zone (pits, hearths). Spatial analysis by GIS shows a high concentration of recorded objects (lithics, bones, shells) to the west of the excavated area, in the shell level. Marine erosion is the main erosive factor limiting our knowledge of the site. The distance to the coastline was estimated after reconstruction of the relative sea level during the Holocene using the “Sea-Level Index Points” (SLIPs) methodology. Three SLIPs indicate a relative sea-level position between −15.5m and −11m and a foreshore area at a depth between −7.15 and −14.02m around 6200BCE. This paleogeographic reconstruction approach indicates that the site of Beg-er-Vil was located a few hundred to a few kilometres from the coastline.

Assessing hydrologic changes across the Lower Mekong Basin

Study regionIn this study, 33 catchments across the Lower Mekong Basin in Southeast Asia are examined to detect historical changes in their hydrological response via a model-based methodology. Study focusIntensive development over the past half century across Southeast Asia’s Lower Mekong Basin has inevitably affected natural resources. Large areas have been converted from forests for subsistence and commercial agriculture, and urban development. We implement an innovative approach to screen hydrologic data for detecting impacts of such large-scale changes on hydrological response. In a first step, temporal changes in the rainfall-runoff relationship were assessed using the parsimonious, two-parameter GR2M hydrological model. In a second step, a distribution-free statistical test was applied to detect whether significant changes have occurred in the wet season (high flow) and dry season (low flow) conditions. New hydrological insights for the regionOur results indicate that the majority of catchments (64% of those considered) with sufficiently long data records exhibited no discernable trends in hydrological response. Those catchments that did exhibit significant trends in hydrological response were fairly evenly split between increasing trends (between 21% and 24%) and decreasing trends (between 15% and 12%) with time. There was a lack of evidence that these changes where brought about by shifts in precipitation or potential evapotranspiration; however, catchments exhibiting significant increasing trends in hydrological behavior were found to have different land cover compositions (lower percentage of forest coverage and subsequently higher paddy rice coverage) than those exhibiting significant decreasing trends. The approach presented here provides a potentially valuable screening method to highlight regions for further investigation of improved mechanistic understanding. Without this connection, we might be blind to future hydrological shifts that can have significant impact on development.

Bio-Optical Properties of Two Neigboring Coastal Regions of Tropical Northern Australia: The Van Diemen Gulf and Darwin Harbour

This study focuses on the seasonal and spatial characterization of inherent optical properties and biogeochemical concentrations in the Van Diemen Gulf and Darwin Harbour, two neighboring tropical coastal environments of Northern Australia that exhibit shallow depths (~20 m), large (> 3 m) semi-diurnal tides and a monsoonal climate. To gain insight in the functioning of these optically complex coastal ecosystems, a total of 23 physical, biogeochemical and optical parameters were sampled at 63 stations during three field campaigns covering the 2012 wet and dry seasons, and the 2013 dry season. The total light absorption budget in the Van Diemen Gulf was dominated by non-algal particles (aNAP; >45%) during the dry season (May-October) and colored dissolved organic matter (aCDOM; 60%) during the wet season (November-April). The combined absorption by aNAP and aCDOM generally exceeded 70% of the total absorption budget from 400 to 620 nm, with phytoplankton, aPhy, accounting for less than 20%. In Darwin Harbour, where only the dry season conditions were sampled, the total absorption budget was dominated by an equivalent contribution of aCDOM, aNAP and phytoplankton. The major processes explaining the seasonal variability observed in the Van Diemen Gulf are resuspension from seasonal south-easterly trade winds in combination with the tidal energy and shallow bathymetry during the dry season months, and mostly terrestrial river runoff during the monsoon which discharge terrestrial CDOM from the surrounding wetlands. Due to light-limited conditions all year round, the particulate scattering coefficient (bp(555)) contributed significantly (90%) to the beam attenuation coefficient c(555), thus strongly limiting phytoplankton growth (Chlorophyll a~1 mg.m-3). Spatially, the Van Diemen Gulf had higher total suspended solids and nutrient concentrations than Darwin Harbour, with dissolved organic carbon and aCDOM subjected to photobleaching during the dry season. Key bio-optical relationships derived from this comprehensive set of parameters, the first ever to be collected in this tropical coastal environment, were successfully used for a region-specific seasonal parameterization of a Linear Matrix Inversion-based ocean color algorithm. Challenges related to the parameterization, and the use, of ocean color remote sensing algorithms for these optically complex waters are discussed.

Tropical Montane Cloud Forests in the Orinoco river basin: The role of soil organic layers in water storage and release

The Tropical Montane Cloud Forest (TMCF) is a hydrologically unique and highly vulnerable ecosystem to changes in land-use and climate. Assessing the impacts of these changes needs to consider soil-water dynamics. In particular, the organic layer and its functioning requires attention because its difference in water retention characteristics and root density compared to the underlying mineral soils. A higher root density and a higher water storage capacity of the organic layer compared to the mineral soils suggests that most nutrient and water uptake occurs in this layer. However, hydraulic properties of mineral soils and their impact on hydrology of TMCFs have been poorly studied. Here we provide organic layer water retention curves for TMCF soils that were measured in the laboratory. With these data we assessed the potential land-use and climate change impacts on TMCF soil moisture dynamics. From the land-use change perspective, we estimated the water storage capacity loss by slash-and-burn deforestation practices. These estimates show that the storage loss ranges from 35 to 59mm when TMCFs are converted to pastures. This is several times higher than the estimated TMCF canopy storage capacity (2 to 5mm). Therefore, the higher peak flow observations in deforested catchments might not only be explained by a decreasing canopy water storage but also likely due to a decreasing soil water storage. From the climate change perspective, we evaluated the effect of contrasting dry season conditions on soil moisture and transpiration using a 1-D water-flow model, and assessed the sensitivity of these hydrological variables to uncertainties in saturated hydraulic conductivity. Although transpiration was not limited by soil moisture during the mild dry season, it was affected during the severe dry season and continued to decline under expected climate change with the prolongation of dry spells. Our results show that the organic layer is a key element in TMCF's hydrological functioning and call for an increased focus on the role of organic soils when evaluating effects of land-use change.

Ecophysiological responses of two closely related Magnoliaceae genera to seasonal changes in subtropical China

Plants use a variety of hydraulic strategies to adapt to seasonal drought that differ by species and environmental conditions. The early-diverging Magnoliaceae family includes two closely related genera with contrasting leaf habits, Yulania (deciduous) andMichelia (evergreen), which naturally inhabit temperate and tropical regions, respectively. Here, we evaluate the hydraulic strategy of species from both genera that have beenex situ conserved in a subtropical region to determine how they respond to the novel cool-dry season climatic pattern. We measured ecophysiological traits in fiveMichelia and fiveYulania species conserved in the South China Botanical Garden in both wet and dry season conditions and monitored the whole-year sap flow for four of these species. We found that Magnoliaceae species that have beenex situ conserved in a subtropical climate did not suffer from excessive water stress due to the mild drought conditions of the dry season and the ecophysiological adjustments the species made to avoid this stress, which differed by leaf habit. Specifically, deciduous species completely shed their leaves during the dry season, while evergreen species decreased their turgor loss points, dry mass based photosynthetic rates, stomatal conductance and specific leaf areas (SLAs) compared to wet season measurements. In comparing the two distinct leaf habits during the wet season, the leathery-leaved evergreen species had higher leaf hydraulic conductance and leaf to sapwood area ratios than the papery-leaved deciduous species, while the deciduous species had greater hydraulic conductivity calculated on both a stem and leaf area basis, dry mass based photosynthetic rates, leaf nutrients, SLAs and stomatal sizes than the evergreen species. Interestingly, species from both genera maintained similar sap flow in the wet season. Both photosynthetically active radiation and vapour pressure deficit affected the diurnal patterns of sap flow in the wet season, while only vapour pressure deficit played a dominant role in the dry season. This study reveals contrasting hydraulic strategies inYulania andMichelia species under subtropical seasonal conditions, and suggests that these ecophysiological adjustments might be affected more by leaf habit than seasonality, thus reflecting the divergent evolution of the two closely related genera. Furthermore, we show that Magnoliaceae species that areex situ conserved in a subtropical climate are hydraulically sound, a finding that will inform future conservation efforts of this ancient family under the threat of climatic change.

Integration of Optical and X-Band Radar Data for Pasture Biomass Estimation in an Open Savannah Woodland

Pasture biomass is an important quantity globally in livestock industries, carbon balances, and bushfire management. Quantitative estimates of pasture biomass or total standing dry matter (TSDM) at the field scale are much desired by land managers for land-resource management, forage budgeting, and conservation purposes. Estimates from optical satellite imagery alone tend to saturate in the cover-to-mass relationship and fail to differentiate standing dry matter from litter. X-band radar imagery was added to complement optical imagery with a structural component to improve TSDM estimates in rangelands. High quality paddock-scale field data from a northeastern Australian cattle grazing trial were used to establish a statistical TSDM model by integrating optical satellite image data from the Landsat sensor with observations from the TerraSAR-X (TSX) radar satellite. Data from the dry season of 2014 and the wet season of 2015 resulted in models with adjusted r2 of 0.81 in the dry season and 0.74 in the wet season. The respective models had a mean standard error of 332 kg/ha and 240 kg/ha. The wet and dry season conditions were different, largely due to changed overstorey vegetation conditions, but not greatly in a pasture ‘growth’ sense. A more robust combined-season model was established with an adjusted r2 of 0.76 and a mean standard error of 358 kg/ha. A clear improvement in the model performance could be demonstrated when integrating HH polarised TSX imagery with optical satellite image products.

Convective cloud vertical velocity and mass‐flux characteristics from radar wind profiler observations during GoAmazon2014/5

AbstractA radar wind profiler data set collected during the 2 year Department of Energy Atmospheric Radiation Measurement Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) campaign is used to estimate convective cloud vertical velocity, area fraction, and mass flux profiles. Vertical velocity observations are presented using cumulative frequency histograms and weighted mean profiles to provide insights in a manner suitable for global climate model scale comparisons (spatial domains from 20 km to 60 km). Convective profile sensitivity to changes in environmental conditions and seasonal regime controls is also considered. Aggregate and ensemble average vertical velocity, convective area fraction, and mass flux profiles, as well as magnitudes and relative profile behaviors, are found consistent with previous studies. Updrafts and downdrafts increase in magnitude with height to midlevels (6 to 10 km), with updraft area also increasing with height. Updraft mass flux profiles similarly increase with height, showing a peak in magnitude near 8 km. Downdrafts are observed to be most frequent below the freezing level, with downdraft area monotonically decreasing with height. Updraft and downdraft profile behaviors are further stratified according to environmental controls. These results indicate stronger vertical velocity profile behaviors under higher convective available potential energy and lower low‐level moisture conditions. Sharp contrasts in convective area fraction and mass flux profiles are most pronounced when retrievals are segregated according to Amazonian wet and dry season conditions. During this deployment, wet season regimes favored higher domain mass flux profiles, attributed to more frequent convection that offsets weaker average convective cell vertical velocities.