Decreasing Soil Moisture Content Research Articles

Context-dependent effects of a reintroduced ungulate on soil properties are driven by soil texture, moisture, and herbivore activity.

Although there is considerable evidence that large mammalian herbivores influence ecosystem‐level processes, studies have reported such widely varying results that generalizations have remained elusive. Here, we use an 18‐year‐old exclosure experiment—stratified across a landscape heterogeneous with respect to soil texture, moisture and herbivore activity—to understand the variable effects of tule elk (Cervus canadensis nannodes), a native reintroduced herbivore, on soil properties along the coast of northern California. Elk significantly increased soil bulk density and created a compacted layer at shallow soil depth, while decreasing infiltration rate and pH. The effects of elk on bulk density, penetration resistance, and pH varied with soil type, being least pronounced in coarse, sandy loams, and greatest in loose sand. The effects of elk on nutrient availability varied along gradients of soil texture and moisture. In coarser soils, elk decreased ammonium availability, but increased it in finer soils. Elk also decreased soil moisture content, in part through their positive effect on bulk density, and this effect was most pronounced in coarser soils. Through decreasing soil moisture content, elk also decreased nitrate availability in coarser soils. At greater levels of elk activity (as measured by dung deposition), the elk effect on bulk density was amplified, and this had a corresponding negative effect on nitrate and phosphate availability. Our study has demonstrated that a better understanding of spatial variation in the effects of herbivores on ecosystems can emerge by evaluating their influences across gradients of soil texture, soil moisture, and herbivore activity. These data enabled us to evaluate several frameworks that have been developed to understand the variable effects of herbivores on ecosystems, which is a significant step in reconciling the many competing ideas put forth to explain the context‐dependent effects of large herbivores on grazed ecosystems.

Seed dormancy release of Halenia elliptica in response to stratification temperature, duration and soil moisture content

BackgroundAlthough the effect of cold stratification on seed dormancy release has been extensively studied for many species, knowledge of the role of stratifying temperature, soil moisture content and duration of stratification on seed dormancy release at the population level is limited. Here, we aimed to determine the response of seed dormancy release to these factors in six populations of Halenia elliptica.ResultsSeed dormancy release was more responsive to low than high temperatures, and no dormancy break occurred at 8 °C. Seed germination percentage increased first and then remained unchanged as stratifying soil moisture content increased from 0 to 24%. Seed dormancy release of populations from low altitude was more sensitive to increased stratifying temperature and decreased soil moisture content than those from high altitudes.ConclusionsTemperature and soil moisture changes resulting from global warming could affect seed dormancy release and consequently seedling establishment. Thus, incorporating data on seed dormancy release involving temperature, soil moisture content and stratification duration is beneficial for predicting plant species regeneration, migration and coexistence in a scenario of climate change.

The Impact of Human Activities on Flood Trends in the Semi-Arid Climate of Cheliff Basin, Algeria

Algeria shares similarities with other countries of the world facing destructive floods. The need to understand changes in the intensity, frequency and severity of floods is critical for reducing significant social, economic, and environmental implications. In this study, flood indicators derived from annual maximum series and peak over threshold series were analyzed using Mann−Kendall trend analysis and linear regression analysis. Several studies in northern Algeria found decreasing trends of annual precipitation. However, precipitation could not explain most flood indicator trends found in our study. A general decreasing annual and seasonal trends of flood indicators were detected in the wadi Cheliff Basin. This result is partly due to decreasing precipitation and partly due to the construction of dams which have significantly altered flood processes. Increasing trends were found in the Mina Basin, which could be explained as the result of increases in urban area and decrease in soil moisture content before the occurrence of floods. Conversely, there was no dependency demonstrated between significant changes and spatial scales for these flood indicators. That is to say, human impacts and climate variability likely constitute the main factors causing increasing or decreasing flood trends.

Effects of Water Stress on Fluorescence Parameters and Photosynthetic Characteristics of Drip Irrigation in Rice

To study the effects of water stress on the fluorescence parameters and photosynthetic characteristics of rice under drip irrigation and mulching, so as to determine the response mechanisms to water stress during the tillering stage. A two-year trial was carried out at Shihezi University, China. Three water gradients were investigated. The results showed that the chlorophyll content (a + b), photosynthetic rate (Pn), and leaf area index (LAI) decreased with decreasing soil moisture content at the tillering stage. The chlorophyll content (a + b) and Pn in the flooding irrigation (CK) treatment were significantly higher than those in the stress treatments, and the chlorophyll content (a + b) and Pn in the W1 and W2 treatments were significantly lower than those in the other treatments. The maximum LAI of the CK, W1, and W2 treatments were similar, while the W3 produced lower values; stress treatment improved the ability of tillering in the early and middle stages, while the decrease in soil water content in the tillering stage resulted in a decrease in the final tillering rate; drought stress in the tillering stage resulted in decreased rice yields. The yield of the W1 and W2 treatments were similar, while that of the W3 treatment was seriously reduced. The main reasons for the reduction in yield was the significant decrease in the number of effective panicles, the seed setting rate, and a decrease in the 1000-grains weight. Water consumption in the stress treatments decreased by 51.69%–58.78% compared to the CK treatment; water-use efficiency in the CK treatment was only 0.25 kg·m−3, and the water-use efficiency of the stress treatments increased by 40%–72%. We should make full use of the compensation effect of drought stress in the water regulation of drip irrigation in covered rice and adopt the water control measure of the W2 treatment in the tillering stage. These measures are conducive to improving water-use efficiency and achieving the goal of high quality, high yield, and high efficiency.

Predicted Climate Change Impact on Groundwater Flow for the Upper Zone of Iraqi Aquifers

A 3D groundwater steady-state flow conceptual model was built for all of Iraq using a MODFLOW package integrated with the Groundwater Modeling System to simulate the groundwater movement and flow direction for the upper zone of Iraq as well as to compute the water budget for all aquifer systems in Iraq. This model was run for seven scenarios of climate change conditions for the period of 2020–2050. A Representative Concentration Pathway model (RCP4.5) was used for the prediction of future rainfall over the next 31 years. The results showed that the decline in rainfall will be 6.247% due to climate change impacts. The decline in rainfall will cover two-thirds of the area of Iraq. Seven scenarios simulating groundwater flow behavior showed that decreased soil moisture content will significantly reduce groundwater recharge and increase runoff. A decline in groundwater levels by an average of 1.8–4.8 m will occur for the upper zone of Iraqi aquifers over the next 31 years. These results will help Iraqi decision-makers improve water resource management.

The influence of soil matric pressure on the acidity and cation composition of soil solutions extracted by different methods

From the samples of gradually drying (beginning from the field moisture capacity, FMC) soddy-podzolic sandy loam soil (Albic Retisol (Loamic, Ochric)) contaminated with Zn were isolated the soil solutions (SS) by centrifugation, while from the other samples of the soil, moistened to FMC, various energy fractions of the SS were pressed using a hydraulic press. The acidity of the centrifuge solutions extracted from the soil of the experiment variant with the cultivation of plants (“barley”) was, on average, 1 pH higher than on “bare fallow”, and decreased with decreasing soil moisture content. The acidity of the solutions extracted from the soils of the “bare fallow” variant in the same range of soil moisture content practically did not change. It was also found that in more acidic solutions from the “bare fallow” variant the content of Ca, Mg, Mn, Zn and K was 2.4 – 6.9 times higher than the content of these metals in solutions from the “barley” variant. The positive correlation between pF and pH was clearly observed for the pressed solutions from the soils of both variants. Concentrations of Ca, Mg, Sr, Ba,Zn, K and Na in successively pressed fractions of SSs from more acidic soil of the “bare fallow” variant, on average, 3.0 – 8.4 times exceeded their concentrations in similar fractions of solutions of the “barley” variant and showed an inverse correlation with soil moisture (pF value).

Effects of Straw Returning and Residue Cleaner on the Soil Moisture Content, Soil Temperature, and Maize Emergence Rate in China’s Three Major Maize Producing Areas

Straw returning is of significant value for the sustainable development of agriculture, but it can easily cause the decrease of soil moisture content (SMC) and soil temperature (ST), leading to the serious reduction of maize emergence rate (MER). This paper focuses on the influence law and influence principle of straw returning amounts and residue cleaner on SMC, ST, and MER. This paper selected representative areas of China’s three major maize-producing areas as test sites to take two-factor tests. Four levels were selected with straw returning amounts of 30%, 50%, 70%, and 100%. Three types of residue cleaners were selected: corrugated disc (CD), profiling residue cleaner (PRC), and rotary blade (RB). The test results show that the test factors have significant effects on the test indicators, and there is an interaction between the test factors. However, due to the large difference in annual average temperature, the influence of test factors on ST in different major maize producing areas is not the same. In order to obtain the optimal combination of factors in the three major maize producing areas, the nine regression models and the combination of factors corresponding to the extreme values were obtained through MATLAB. The following conclusions are drawn from the regression models: The maize emergence rate reached 91.7% when using PRC, and the amount of straw returning was 52% at the Jilin Maize Production Area. The maize emergence rate reached 94.7% when using CD, and the amount of straw returning was 67% at the Heilongjiang Maize Production Area. The maize emergence rate reached 91.4% when using CD, and the amount of straw returning was 68% at the Inner Mongolia Maize Production Area. This paper discussed the principle that test factors have a significant impact on test indicators. It is believed that, because the test factors can change the residual cover thickness (RCT) and soil compactness (SC), they have a significant impact on SMC and ST. In addition, it is believed because the test factors can change SMC, ST and the difficulty of cleaning operations, they have a significant impact on MER. At the same time, the basis for selecting straw returning amounts and rescue cleaner under different conditions is discussed. This paper can provide theoretical support and data reference for the sustainable development of agriculture in China’s three major maize producing areas.

Hydrogeochemical and microbiological effects of simulated recharge and drying within a 2D meso-scale aquifer.

Oscillating cycles of dewatering (termed drying) and rewetting during managed aquifer recharge (MAR) are used to maintain infiltration rates and could also exert an influence on subsurface microbial structure and respiratory processes. Despite this practice, little knowledge is available about changes to microbial community structure and trace organic chemical biodegradation potential in MAR systems under these conditions. A biologically active two-dimensional (2D) synthetic MAR system equipped with automated sensors (temperature, water pressure, conductivity, soil moisture, oxidation-reduction potential) and embedded water and soil sampling ports was used to test and model these important subsurface processes at the meso-scale. The fate and transport of the antiepileptic drug carbamazepine, the antibiotics sulfamethoxazole and trimethoprim, and the flame retardant tris (2-chloroethyl) phosphate were simulated using the finite element analysis model, FEFLOW. All of these compounds exhibit moderate to poor biodegradability in MAR systems. Within the operational MAR scenario tested, three episodic drying cycles spanning between 18 and 24 days were conducted over a period of 184 days. Notably, cessation of flow and partial dewatering of the 2D synthetic aquifer during dry cycles caused no measurable decrease in soil moisture content beyond the near-surface layer. The episodic flow introduction and dewatering cycles in turn had little impact on overall trace organic chemical biotransformation behavior and soil microbial community structure. However, spatial differences in oxidation-reduction potential and soil moisture were both identified as significant environmental predictors for microbial community structure in the 2D synthetic aquifer.

Effect of Soil Moisture Content and End-Effector Speed on Pick-up Force and Lump Damage for Seedling Transplanting

Efficient transplanting has been identified as one of the essential steps towards achieving an increased yield in the farm. However, many factors are affecting these processes such as soil moisture content and the speed of pickup. This study was carried out to investigate the effect of different soil moisture content and pickup speeds on pickup force, balance, resistance, and lump damage during transplanting of seedlings. The results showed that penetration resistance was inversely proportional to the speed and soil moisture content. The highest penetration resistance (38 N) values were recorded under the lowest speed (0.5 mm/s) at the low moisture content; whereas, the lowest penetration resistance was obtained at highest speed (10 mm/s) under high moisture content. The highest pick-up force resistance values were recorded under the lowest speed (0.5 mm/s) at low moisture content than the lowest pick-up force resistance of 1.4 N at (10 mm/s) under the high moisture content. On the other hand, an increase of pick-up force led to a decrease in the pick-up force resistance. The pick-up damage and the pick-up speed are directly proportional—nevertheless, the former increased with a decreasing soil moisture content. The highest pick-up damage values (82%) were observed under the top-most speed (10 mm/s) at high moisture content. It can be concluded that for successful auto-transplanting of seedling the soil condition, the force applied and speed should be taken into consideration. This work will implement an effective seedling-picking performance and basis for the optimal design of end-effectors.

Leaf Photosynthesis Response to Change of Soil Moisture Content in Sugarcane

It is necessary to practice efficient irrigation in any agricultural development strategy under the context of climate change and competition from other economic sectors. Irrigation based on the relationship between photosynthetic activity and change of soil moisture could be an effective practice. Herein, we investigated the response of sugarcane photosynthetic parameters on drought stress at yield formation stage. The experiment was carried out by withholding water for 3 weeks from 190 days after transplanting and then re-watering until the end of experimental period. Data were collected for photosynthetic parameters including potential photosynthetic rate, stomatal conductance, transpiration rate, internal CO2 concentration, SPAD, and soil physical parameters. The results showed that sugarcane photosynthetic parameters decreased with decreasing soil moisture content to certain extent and the stayed static before dropping off again. Internal CO2 concentration increased when soil moisture reached the most severe, and it caused a standstill in photosynthesis. However, photosynthesis also recovered with soil moisture recovery. Photosynthetic parameters could be used as indicators to evaluate drought stress’s effect as well as to determine the time to re-irrigate to maintain normal growth of the plants. Soil volume moisture content of 15% (recorded by the 5TE sensor) or at pF of 2.8 (recorded by the MPS-6 sensor) seems to be the initial time to start irrigation to keep standard growth. Soil moistures at 10% and 3.8 pF, respectively, could be the critical points beyond which irrigation was found to result in photosynthetic disorders.

Physiological responses to drought of Cnidoscolus quercifolius Pohl in semi-arid conditions

This study aimed to evaluate the physiological behavior of faveleira (Cnidoscolus quercifolius Pohl) plants grown in the field, in Caatinga, during wet and dry seasons. Adult plants were selected for evaluation in March and April (wet season) and May and June (dry season), during 2016. We evaluated the soil water content, water potential (Ψw), osmotic potential (Ψπ), relative water content (RWC), stomatal conductance (gs), transpiration rate (E), photosynthetic rate (A), intercellular CO2 concentration (Ci), instantaneous water use efficiency (A/E) and carboxylation efficiency (A/Ci). The reduction in water availability in the soil promoted a marked decrease in soil water potential, which was more affected than the relative water content. The opening of the stomata was affected by the decrease in soil moisture content, reducing the stomatal conductance, transpiration rate, photosynthesis rate, instantaneous water use efficiency and carboxylation efficiency. The photosynthesis was more affected than transpiration by the reduction in soil moisture content.

Organic and Biodynamic Viticulture Affect Biodiversity and Properties of Vine and Wine: A Systematic Quantitative Review

Demand for organically grown crops has increased exponentially in the last few decades. Particularly in the wine sector, organic and biodynamic management systems are gaining more and more importance, with some of the most prestigious wineries converting to organic or biodynamic viticulture. The purpose of this study was to review evidence comparing effects of conventional, organic, and biodynamic viticulture on soil properties, biodiversity, vine growth and yield, disease incidence, grape composition, sensory characteristics, and wine quality. Only studies with representative field replicates or studies with a representative number of samples were included. Soil nutrient cycling was enhanced under organic viticulture, especially after conversion was completed. Cover crop mixtures used, compost application, and the absence of herbicides might be factors that account for higher biological activity in organically and biodynamically managed soils. Seventeen out of 24 studies observed a clear increase in biodiversity under organic viticulture on different trophic levels. Plant protection regime and cover crop mixtures mainly determine higher biodiversity in organic and biodynamic viticulture. Organic and biodynamic treatments showed 21% lower growth and 18% lower yield compared to conventional viticulture. The decrease of growth and yield under organic and biodynamic viticulture was not correlated to the growth or yield level under conventional viticulture. A decrease in soil moisture content and physiological performance (assimilation rate, transpiration rate, and stomatal conductance) under organic and biodynamic viticulture is likely to be responsible for the lower growth and yield in the respective management systems. Juice total soluble solids concentration did not differ among the different management systems. No overall differences in berry composition or juice and wine quality among management systems could be observed. By describing different hypotheses concerning the effects of organic and biodynamic viticulture, this review and meta-analysis provides helpful guidance for defining further research in organic agriculture on perennial, but also on annual, crops.

Changes in the pH of paddy soils after flooding and drainage: Modeling and validation

The precise determination and characterization of soil acidity was the basis for a robust and realistic assessment of many biogeochemical processes. Samples of twenty paddy soils with varying soil properties were subjected to a successive flooding and drainage period in this work. The soil pH was measured in situ at intervals, and soil samples were collected after each pH measurement during drainage for an analysis of the moisture content. During the flooding period, the pH for soils with an initial pH < 6.5 increased to approximately 7.0, and for soils with an initial pH > 6.5, the pH first decreased and then increased to approximately 7.0. The changes were reversed during the drainage period, as the pH of acidic soils decreased linearly with the decreasing soil moisture content, while neutral-to-alkaline soils showed the opposite pattern. The developed predictive models indicated that the initial soil pH, cation exchange capacity, content of organic matter and flooding or drainage time were the main factors that controlled the change of soil pH after flooding and drainage. The models explained 82% and 67% of the soil pH variability after flooding and drainage, respectively. The predictive model of the soil pH change after flooding was further validated and was found to be reliable on the basis of a number of independent data points for which the predicted soil pH after flooding was within the 95% prediction intervals of the observations. The results suggested that the soil pH, which was determined in the laboratory using air-dried samples, could be corrected to the in situ pH through the developed predictive models.

Change in soil microbial biomass along a rural-urban gradient in Varanasi (U.P., India)

Soil microbial biomass has been used as an early indicator of change in soil properties resulting from urbanization. We analyzed the effect of urbanization along a rural–urban gradient on soil microbial biomass and physico-chemical properties of the soil. The mean microbial biomass carbon (MBC) value were 107.4, 121.3, and 134.2 μg g−1 of soil, respectively, for urban, sub-urban and rural sections of the gradient. Whereas, the mean microbial biomass nitrogen (MBN) was 10.2, 11.5, and 12.5 μg g−1 of soil for urban, sub-urban, and rural gradient. Similarly, the mean values of microbial biomass phosphorus (MBP) were 5.1, 5.8, and 6.3 μg g−1 of soil, for urban, sub-urban, and rural gradient, respectively. ANOVA and Tukey’s Honest Significant Difference (HSD) analyses showed significant difference (P ≤ 0.05) in microbial biomass with physico-chemical characteristics of soils. Maximal soil microbial biomass was reported for rural soils followed by sub-urban and urban soil. Disturbance in soil texture, increased in BD and decrease in soil moisture content as major factors responsible for depletion in soil microbial biomass in urban soils. . Thus, suggesting that the urbanization adversely effected soil microbial biomass by altering natural soil characteristics.

Survival of root-lesion nematode Pratylenchus neglectus during progressive soil desiccation after growth of wheat in a vertisol

Whether soil desiccation causes a fall in peak population abundances of Pratylenchus neglectus after wheat growth was investigated by drying a vertisol through a range of moisture contents (MC) by both fast and slow drying methods. Live nematodes were then extracted for 2 and 7 days and counted in four life stages (adult and juvenile stages J2, J3 and J4). The population of P. neglectus declined more steeply with decreasing soil moisture content from fast drying than from slow drying. These trends were modelled by regression equations. Upon desiccation of the soil from an initial 64.4% MC to the plant permanent wilting point (31.5% MC), 48% of the nematodes survived after fast drying, but 86% survived after slow drying. With further desiccation to 21% MC only 23% of the P. neglectus population survived after fast drying, whereas 81% of the population survived after slow drying. On continued drying, the fast dried soil was at 11.9% MC after 7 days with virtually no surviving P. neglectus, whereas the slowly dried soil reached 16.5% MC after 8 days with 79% surviving. The P. neglectus population declined by 2.2 and 0.5% per 1% loss of soil moisture for fast and slow drying, respectively. With fast drying, all life stages declined; however, with slow drying, only the J2 stage declined with 44% surviving at 16.5% MC. This information can be applied to crop growth modelling, to extraction techniques for soil from the glasshouse and field, and to consideration of whether molecular methods measure DNA from recently dead nematodes killed by soil desiccation in the field giving an overestimation of the number of live nematodes.

Soil moisture decline due to afforestation across the Loess Plateau, China

The Loess Plateau of China is a region with one of the most severe cases of soil erosion in the world. Since the 1950s, there has been afforestation measure to control soil erosion and improve ecosystem services on the plateau. However, the introduction of exotic tree species (e.g., R. pseudoacacia, P. tabulaeformis and C. korshinskii) and high-density planting has had a negative effect on soil moisture content (SMC) in the region. Any decrease in SMC could worsen soil water shortage in both the top and deep soil layers, further endangering the sustainability of the fragile ecosystem. This study analyzed the variations in SMC following the conversion of croplands into forests in the Loess Plateau. SMC data within the 5-m soil profile were collected at 50 sites in the plateau region via field survey, long-term in-situ observations and documented literature. The study showed that for the 50 sites, the depth-averaged SMC was much lower under forest than under cropland. Based on in-situ measurements of SMC in agricultural plots and C. korshinskii plots in 2004–2014, SMC in the 0–4m soil profile in both plots declined significantly (p<0.01) during the growing season. The rate of decline in SMC in various soil layers under C. korshinskii plots (−0.008 to −0.016cm3cm−3yr−1) was much higher than those under agricultural plots (−0.004 to −0.005 cm3cm−3yr−1). This suggested that planting C. korshinskii intensified soil moisture decline in China’s Loess Plateau. In the first 20–25yr of growth, the depth-averaged SMC gradually decreased with stand age in R. pseudoacacia plantation, but SMC somehow recovered with increasing tree age over the 25-year period. Irrespectively, artificial forests consumed more deep soil moisture than cultivated crops in the study area, inducing soil desiccation and dry soil layer formation. Thus future afforestation should consider those species that use less water and require less thinning for sustainable soil conservation without compromising future water resources demands in the Loess Plateau.

Physiological and biochemical responses of Festuca sinensis seedlings to temperature and soil moisture stress.

The interaction effects between temperature and soil moisture on Festuca sinensis Keng ex E.B.Alexeev were analysed to determine how F. sinensis responds to these environmental conditions. A pot experiment was conducted in a greenhouse under simulated growth conditions with four soil moisture contents (80, 65, 50 and 35% relative saturation moisture content) and three temperature conditions (15, 20 and 25°C). Physiological (relative water content and root activity) and biochemical parameters (chlorophyll, peroxidase (POD), malondialdehyde (MDA), soluble protein, soluble sugar and free proline) were evaluated at the seedling stage. Results showed that with a decrease in soil water content, the POD activities, MDA content, soluble protein content, soluble sugar content and free proline content of plants under the 15°C and 20°C treatments initially decreased and then increased, whereas they increased with a decrease of soil water content at 25°C. The relative water contents of plants under the three temperature treatments decreased with a decreasing soil moisture content, but then increased temperature significantly reduced the relative water content of the seedlings under low soil water content. The chlorophyll contents of plants under the 25°C treatment decreased with a decrease of soil moisture content, but those of plants under the 15°C and 20°C treatments initially increased and then decreased. The root activities of plants under the 15°C and 20°C treatments increased with a decreasing soil moisture content; however, those of plants under the 25°C treatment initially increased and then decreased. Thus, results indicated that changes of temperature and soil moisture content had significant and complicated effects on the physiological-biochemical characteristics of F. sinensis; the conditions of 20°C and 65% RSMC had positive effects on F. sinensis seedling growth and the appropriate drought stress could promote the growth of seedling roots under the three different temperature conditions. In conclusion, F. sinensis seedlings could adapt to certain changes in the ecological environment by regulating their physiological and biochemical reactions.

Toxicity of a metal(loid)-polluted agricultural soil to Enchytraeus crypticus changes under a global warming perspective: Variations in air temperature and soil moisture content

This study aimed to assess how the current global warming perspective, with increasing air temperature (20°C vs. 25°C) and decreasing soil moisture content (50% vs. 30% of the soil water holding capacity, WHC), affected the toxicity of a metal(loid)-polluted agricultural soil to Enchytraeus crypticus. Enchytraeids were exposed for 21d to a dilution series of the agricultural soil with Lufa 2.2 control soil under four climate situations: 20°C+50% WHC (standard conditions), 20°C+30% WHC, 25°C+50% WHC, and 25°C+30% WHC. Survival, reproduction and bioaccumulation of As, Cd, Co, Cu, Fe, Mn, Ni, Pb and Zn were obtained as endpoints. Reproduction was more sensitive to both climate factors and metal(loid) pollution. High soil salinity (electrical conductivity~3dSm−1) and clay texture, even without the presence of high metal(loid) concentrations, affected enchytraeid performance especially at drier conditions (≥80% reduction in reproduction). The toxicity of the agricultural soil increased at drier conditions (10% reduction in EC10 and EC50 values for the effect on enchytraeid reproduction). Changes in enchytraeid performance were accompanied by changes in As, Fe, Mn, Pb and Zn bioaccumulation, with lower body concentrations at drier conditions probably due to greater competition with soluble salts in the case of Fe, Mn, Pb and Zn. This study shows that apart from high metal(loid) concentrations other soil properties (e.g. salinity and texture) may be partially responsible for the toxicity of metal(loid)-polluted soils to soil invertebrates, especially under changing climate conditions.

Metal/metalloid (As, Cd and Zn) bioaccumulation in the earthworm Eisenia andrei under different scenarios of climate change

This study aimed at assessing the effects of global warming (increasing air temperature and decreasing soil moisture content) on the bioaccumulation kinetics of As, Cd and Zn in the earthworm Eisenia andrei in two polluted soils (mine tailing and watercourse soil). Earthworms were exposed for up to 21 d under four climate conditions: 20 °C + 50% soil water holding capacity (WHC) (standard conditions), 20 °C + 30% WHC, 25 °C + 50% WHC and 25 °C + 30% WHC. Porewater metal/metalloid availability did not change in the mine tailing soil after the incubation period under the different climate conditions tested. However, in the watercourse soil, porewater Cd concentrations decreased from ∼63 to ∼32–41 μg L−1 after 21 d and Zn concentrations from ∼3761 to ∼1613–2170 μg L−1, especially at 20 °C and 50% WHC. In both soils, As and Zn showed similar bioaccumulation patterns in the earthworms, without major differences among climate conditions. Earthworm concentrations peaked after 1–3 d of exposure (in μg g−1 dry weight: As∼32.5–108, Zn∼704–1172) and then remained constant (typical pattern of essential elements even for As). For Cd the bioaccumulation pattern changed when changing the climate conditions. Under standard conditions, earthworm Cd concentrations increased to ∼12.6–18.5 μg g−1 dry weight without reaching equilibrium (typical pattern of non-essential elements). However when increasing temperature and/or decreasing soil moisture content the bioaccumulation pattern changed towards that more typical of essential elements due to increased Cd elimination rates (from ∼0.11 to ∼0.24–1.27 d−1 in the mine tailing soil, from ∼0.07 to ∼0.11–0.35 d−1 in the watercourse soil) and faster achievement of a steady state. This study shows that metal/metalloid bioaccumulation pattern in earthworms may change dependent on climate conditions.

Water Use Patterns of Four Tropical Bamboo Species Assessed with Sap Flux Measurements.

Bamboos are grasses (Poaceae) that are widespread in tropical and subtropical regions. We aimed at exploring water use patterns of four tropical bamboo species (Bambusa vulgaris, Dendrocalamus asper, Gigantochloa atroviolacea, and G. apus) with sap flux measurement techniques. Our approach included three experimental steps: (1) a pot experiment with a comparison of thermal dissipation probes (TDPs), the stem heat balance (SHB) method and gravimetric readings using potted B. vulgaris culms, (2) an in situ calibration of TDPs with the SHB method for the four bamboo species, and (3) field monitoring of sap flux of the four bamboo species along with three tropical tree species (Gmelina arborea, Shorea leprosula, and Hevea brasiliensis) during a dry and a wet period. In the pot experiment, it was confirmed that the SHB method is well suited for bamboos but that TDPs need to be calibrated. In situ, species-specific parameters for such calibration formulas were derived. During field monitoring we found that some bamboo species reached high maximum sap flux densities. Across bamboo species, maximal sap flux density increased with decreasing culm diameter. In the diurnal course, sap flux densities in bamboos peaked much earlier than radiation and vapor pressure deficit (VPD), and also much earlier than sap flux densities in trees. There was a pronounced hysteresis between sap flux density and VPD in bamboos, which was less pronounced in trees. Three of the four bamboo species showed reduced sap flux densities at high VPD values during the dry period, which was associated with a decrease in soil moisture content. Possible roles of internal water storage, root pressure and stomatal sensitivity are discussed.