Dry Plots Research Articles

Tracing sources and turnover of soil organic matter in a long-term irrigated dry forest using a novel hydrogen isotope approach

The contribution from foliage, roots, and fungi to soil organic matter (SOM) represents a key unknown in SOM dynamics. Since stable hydrogen isotope ratios (δ2Hn) can greatly differ among these sources, we explored δ2Hn to elucidate sources contribution to SOM. Moreover, we assessed whether addition of 2H-depleted water – providing 2H-signal that gets incorporated into organic matter – allows tracing of new organic H and thus assessing SOM turnover.In a 17-year-long irrigation experiment in a dry pine forest, we measured δ2Hn and stable carbon and nitrogen isotope ratios (δ13C, δ15N) in SOM sources, bulk SOM and particle-size fractions. Relative source contribution to SOM was estimated by Bayesian mixing models including all three isotopes.The δ2Hn increased from foliar litter (−153‰) to fine roots (−118‰) and fungal mycelia (−81‰). Mixing models indicated that foliar litter dominated organic layers (69 ± 15%) and coarse particulate organic matter (POM) at 0–5 cm (65 ± 12%). In contrast, roots dominated fine POM at 2–5 cm (58 ± 12%). Fungal mycelia contributed only to 1–5% of coarse and fine POM, but to 5–25% of mineral associated organic matter (MOM) at 0–5 cm.The soil water 2H-depletion with irrigation (−76‰ vs −68‰ at 0–10 cm) was paralleled by lower δ2Hn in coarse POM of irrigated vs dry plots (−122‰ vs −111‰ at 0–5 cm), indicating organic H turnover of less than 17 years. In contrast, δ2Hn in fine POM and MOM decreased only by 3‰ with irrigation, implying mean residence times of approximately 30 years.While δ13C and δ15N differed by a maximum of 1‰ between plant sources, δ2Hn were 30–39‰ higher in roots than foliar litter, thus improving SOM sources differentiation. Long-term 2H-labelling by irrigation indicated higher organic H turnover in coarse vs fine soil fractions, offering a novel tool to identify SOM cycling and microbial H incorporation into SOM pools.

Cenostigma microphyllum seedlings in semiarid region grow faster under arbuscular mycorrhizal symbiosis, regardless of water availability

Reforestation dry tropical forests (DTF) has several challenges that need to be overcome. In this perspective, this study evaluated the performance of Cenostigma microphyllum seedlings inoculated with arbuscular mycorrhizal fungi (AMF plants) for 2 years after transplanting to the field with different rainfall intensity. AMF plants showed the highest gs values in both plots. These plants in wet plots stored more soluble sugars in their stems and roots, whereas root tissue was chosen under the dry plot. AMF plants had more phosphorus than Control plants in dry plots. Furthermore, AMF plants were 24% and 27% larger than Control plants in wet and dry plots, respectively. AMF plants root diameter was 25% and 18% greater in wet and dry plots, respectively, than in the control plants. Thus, the AMF plants showed higher main root biomass in both plots than the Control plants. The results of this study confirm that inoculation of C. microphyllum seedlings during germination confers a physiological advantage to these plants in field conditions after transplanting, regardless of water availability in the plot, even after two dry seasons. This can be a useful tool for recovering deforested areas in DTF.

Carbon and oxygen dual-isotopes in tree rings indicate alternative physiological responses opted by European beech trees to survive drought stress

ABSTRACT Poor drought tolerance of European beech trees raised concerns in Europe. We hypothesized that beech could show an opposite physiological response to the same level of climatic drought with change in edaphic drought. We performed a combined analysis of δ13C and δ18O in tree rings to reveal retrospective temporal physiological responses of trees to drought. The edaphic drought was assessed by quantifying the capacity of soil to store water in plots (classified as “dry” and “less-dry”) near the drought limit of the species in three near-natural oak-beech ecotones in Germany and Switzerland. Neighbourhood competition was quantified. A climatic drought index was calculated from meteorological records and related to the δ13C and δ18O values of the trees. Trees from dry plots showed a higher response to drought and climatic dependency than less-dry plots. Neighbourhood competetion increased δ18O values significantly. Dual isotope analysis shows a tendency of greater stomatal resistance in dry plots and higher stomatal conductance in less-dry plots. We conclude that beech trees belonging to the same population under changing soil water availability can show different physiological responses under climatic drought stress. Our finding indicates the high plasticity of the beech trees to survive drought stress with changing site conditions.

Impacts of stump harvesting on carbon dioxide, methane and nitrous oxide fluxes

During 2010-2013, we investigated the effects of stump harvesting on greenhouse gas (GHG) fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) with the flux-gradient technique at four experimental plots in a hemiboreal forest in Sweden. All plots were clear-cut and soil scarified and two of the plots were additionally stump harvested. The two clear-cut plots served as control plots. Due to differences in topography, we had one wetter and one drier plot of each treatment. All plots exhibited substantial emissions of GHGs and we noted significant effects of wetness on CO2, CH4 and N2O fluxes within treatments and significant effects of stump harvesting on CO2 and N2O fluxes at the dry plots. The CO2 emissions were lower at the dry stump harvested plot than at the dry control, but when estimated emissions from the removed stumps were added, total CO2 emissions were higher at the stump harvested plot, indicating a small enhancement of soil respiration. In addition, we noted significant emissions of N2O at this plot. At the wet plots, CO2 emissions were higher at the stump harvested plot, also suggesting a treatment effect but differences in wetness and vegetation cover at these plots make this effect more uncertain. At the wet plots, we noted sustained periods (weeks to months) of net N2O uptake. During the year with simultaneous measurements of the abovementioned GHGs, GHG budgets were 1.224×103 and 1.442×103 gm-2 of CO2-equivalents at the wet and dry stump harvested plots, respectively, and 1.070×103 and 1.696×103 gm-2 of CO2-equivalents at the wet and dry control plots, respectively. CO2 fluxes dominated GHG budgets at all plots but N2O contributed with 17% at the dry stump harvested plot. For the full period 2010-2013, total carbon (CO2+CH4) budgets were 4.301×103 and 4.114×103 g m-2 of CO2-eqvivalents at the wet and dry stump harvest plots, respectively and 4.107×103 and 5.274×103 gm-2 of CO2-equivalents at the wet and dry control plots, respectively. Our results support recent studies suggesting that stump harvesting does not result in substantial increase in CO2 emissions but uncertainties regarding GHG fluxes (especially N2O) remain and more long-term measurements are needed before robust conclusions can be drawn.

Comparative Analysis of Bacterial Genera in Seasonally Inundated and Permanently Submerged Sediments of Sultanpur Lake – Ramsar Site, Haryana, India

Sultanpur Lake is a shallow waterbody, within Sultanpur National Park, a Ramsar Site in Gurugram, Haryana. This area is home to a wide variety of plants and animals, and it is a crucial eating, resting, and nesting ground for local and migratory birds. The lake is under severe threat from rising pollution and summertime water shortage. The current study was undertaken to characterize the shifts in bacterial genera in the sediments of Sultanpur Lake brought on by intermittent drying and wetting. Next-generation sequencing of 16S rRNA amplicon was used to characterize the bacterial communities in Dry and Wet sediments of this lake and analyze the changes in them. There was a change in the community structure at the phylum as well as the genus level. The top bacterial genera in Wet sediments were Clostridium sensusstricto (23%), Sunxiuqinia (17%), Clostridium_XIVa (12%), Geobacter (12%), Bifidobacterium (6%), Caldilinea (6%), Decholoromonas (6%), Carboxylicivirga (6%), Desulfomonile (6%) and Bacillus (6%) whereas the top ten genera in Dry sediments were Clostridium sensus- stricto (19%), GPl (17%), Parcubacteria genera increate (14%), Lactobacillus (12%), Sunxiuqinia (9%), Alkaliflexus (7%), Methanobacterium (7%), Bacillariophyta (5%), Clostridium_III (5%) and Methanothrix (5%).This compositional shift in the sediment bacterial communities in the Dry plots is towards communities that do not play a major role in the biogeochemical processes.

Topography is more important than forest type as a determinant for functional trait composition of Collembola community

The relative importance of topography and vegetation in shaping local soil invertebrate communities is poorly understood. We investigated changes in the species and trait compositions of Collembola communities associated with different topography and forest types. Our study sites encompassed various topographies with different slope aspects and forest types; specifically, natural deciduous broad-leaved forests and deciduous coniferous plantations in Japan. The body length and edaphic adaptation score, which are representative of a certain life-form, were used as Collembola traits. Across a topographic gradient from south to north-facing slopes, the total biomass of Collembola was higher in dry plots than in humid plots, and the forest types did not affect either abundance, biomass, or species diversity. Variation partitioning analysis revealed that topography played an important role in determining species composition and functional traits, whereas forest types and spatial distance had minor roles. The responses of community weighted mean traits (CWMs) to environmental change were more pronounced than those of species composition. The CWM and functional diversity of body length were higher in the dry plots than in the humid plots. These changes in traits might be explained by food supply or habitat structure increasing large individuals via topography, rather than by physical stress filtering out intolerant small individuals. These results suggest that slope topography is an important determinant of the Collembola community structure in cool-temperate forest ecosystems.

Plant-soil feedbacks depend on drought stress, functional group, and evolutionary relatedness in a semiarid grassland.

Plant-soil feedback (PSF) occurs when plants change the biota and physicochemical properties of the soil, and these changes affect future survival or growth of plants. PSF depends on several factors such as plant functional attributes (e.g., life cycle or photosynthetic metabolism) and the environment. PSF often turn positive under dry conditions because soil biota confers drought tolerance. Conspecifics and close relatives share pathogens and consume similar resources, exerting negative PSF on each other. These ideas have mostly been tested under controlled conditions, while field studies remain scarce. To reevaluate these findings in nature, we analyzed plant-soil feedbacks over a drought-stress gradient in a phosphorus-limited semiarid grassland. We planted seedlings of 17 species in plots where community composition had been monitored for six years. To determine PSF intensity, we measured how seedling longevity was affected by previous occupancy of conspecifics and heterospecifics. The previous occupancy-survival relationship (OSR) was used as a proxy for PSF. Evidence for OSRs was found in one-third of the species pairs, with inconclusive evidence for the rest suggesting weak feedbacks. This is in line with the expectation that PSFs in the field are weaker than under controlled conditions. As expected, positive PSFs were more frequent as drought stress increased. The strongest OSRs were caused in dry plots by C4 perennial grasses, which had very positive OSRs on several C3 annual forbs, but negative effects on each other. Well-documented differences between these two functional groups may explain this result: C3 plants are more sensitive to drought, and thus may be favored by tolerance-conferring microbiota; in contrast, water-efficient C4 perennial grasses compete for phosphorus strongly, perhaps driving strong negative PSFs between them. Finally, close relatives had more negative OSRs on each other than on distant relatives as expected, although only in dry plots. This pattern was mostly due to the negative effects of closely related C4 grasses under dry conditions, and their positive effects on distantly related dicots. Our results highlight the importance of plant traits and of the environmental context in determining the direction and strength of PSFs under field conditions.

Site-level soil moisture controls water-use efficiency improvement and climate response in sugar maple: a dual dendroisotopic study

Given the large contribution of forests to terrestrial carbon storage, there is a need to resolve the environmental and physiological drivers of tree-level response to rising atmospheric CO2. This study examines how site-level soil moisture influences growth and intrinsic water-use efficiency in sugar maple (Acer saccharum Marsh.). We construct tree-ring, δ18O, and Δ13C chronologies for trees across a soil moisture gradient in Ontario, Canada, and employ a structural equation modelling approach to ascertain their climatic, ontogenetic, and environmental drivers. Our results support previous evidence for the presence of strong developmental effects in tree-ring isotopic chronologies — in the range of −4.7‰ for Δ13C and +0.8‰ for δ18O — across the tree life span. Additionally, we show that the physiological response of sugar maple to increasing atmospheric CO2 depends on site-level soil moisture variability, with trees only in relatively wet plots exhibiting temporal increases in intrinsic water-use efficiency. These results suggest that trees in wet and mesic plots have experienced temporal increases in stomatal conductance and photosynthetic capacity, whereas trees in dry plots have experienced decreases in photosynthetic capacity. This study is the first to examine sugar maple physiology using a dendroisotopic approach and broadens our understanding of carbon–water interactions in temperate forests.

How Does Radial Growth of Water-Stressed Populations of European Beech (Fagus sylvatica L.) Trees Vary under Multiple Drought Events?

European beech (Fagus sylvatica L.) trees are becoming vulnerable to drought, with a warming climate. Existing studies disagree on how radial growth varies in European beech in response to droughts. We aimed to find the impact of multiple droughts on beech trees’ annual radial growth at their ecological drought limit created by soil water availability in the forest. Besides, we quantified the influence of competition and canopy openness on the mean basal area growth of beech trees. We carried out this study in five near-natural temperate forests in three localities of Germany and Switzerland. We quantified available soil water storage capacity (AWC) in plots laid in the transition zone from oak to beech dominated forests. The plots were classified as ‘dry’ (AWC < 60 mL) and ‘less-dry’ (AWC > 60 mL). We performed dendroecological analyses starting from 1951 in continuous and discontinuous series to study the influence of climatic drought (i.e., precipitation-potential evapotranspiration) on the radial growth of beech trees in dry and less-dry plots. We used observed values for this analysis and did not use interpolated values from interpolated historical records in this study. We selected six drought events to study the resistance, recovery, and resilience of beech trees to drought at a discontinuous level. The radial growth was significantly higher in less-dry plots than dry plots. The increase in drought had reduced tree growth. Frequent climatic drought events resulted in more significant correlations, hence, increased the dependency of tree growth on AWC. We showed that the recovery and resilience to climatic drought were higher in trees in less-dry plots than dry plots, but it was the opposite for resistance. The resistance, recovery, and resilience of the trees were heterogeneous between the events of drought. Mean growth of beech trees (basal area increment) were negatively impacted by neighborhood competition and positively influenced by canopy openness. We emphasized that beech trees growing on soil with low AWC are at higher risk of growth decline. We concluded that changes in soil water conditions even at the microsite level could influence beech trees’ growth in their drought limit under the changing climate. Along with drought, neighborhood competition and lack of light can also reduce beech trees’ growth. This study will enrich the state of knowledge about the ongoing debate on the vulnerability of beech trees to drought in Europe.

Development of Fertility-Restoring Lines for 9E Type CMS of Sorghum Using Environmentally Induced Fertility Revertants

Development of reliable fertility-restoring lines is the most important prerequisite for using cytoplasmic male sterility (CMS) in plant breeding. Sorghum 9E type CMS is characterized by unstable expression of fertility-restoring genes, which require high levels of water availability for plants during microsporogenesis and flowering. In order to create reliable male-fertility-restoring lines for 9E type CMS, the progeny of test crosses of fertile revertant lines in 9E cytoplasm, which were obtained as a result of reversions in sterile F1 hybrids induced by conditions of high water availability, with CMS lines in this cytoplasm were grown in selective backgrounds: in the dry plots and in the plots with additional watering as well as in the field under natural moisture supply. In the majority of hybrid combinations, fertile plants were observed only when additionally watered during the flowering period. F1 hybrids with different CMS lines with 9E cytoplasm significantly differed in terms of the degree of restored fertility and the response to water availability conditions. Fertile plants predominated in the F2 families; in different hybrid combinations, the ratio of restored and sterile plants corresponded to 3 : 1 or 13 : 3 segregation. After selection in the drought conditions of the fertile plants from the offspring of hybrids from the cross of the CMS line 9E Pishchevoe 614 and male-fertile revertants, two lines were obtained that were able to restore fertility of F1 hybrids in field conditions.

Impacts of Clear-Cutting of a Boreal Forest on Carbon Dioxide, Methane and Nitrous Oxide Fluxes

The 2015 Paris Agreement encourages stakeholders to implement sustainable forest management policies to mitigate anthropogenic emissions of greenhouse gases (GHG). The net effects of forest management on the climate and the environment are, however, still not completely understood, partially as a result of a lack of long-term measurements of GHG fluxes in managed forests. During the period 2010–2013, we simultaneously measured carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes using the flux-gradient technique at two clear-cut plots of different degrees of wetness, located in central Sweden. The measurements started approx. one year after clear-cutting, directly following soil scarification and planting. The study focused on robust inter-plot comparisons, spatial and temporal dynamics of GHG fluxes, and the determination of the global warming potential of a clear-cut boreal forest. The clear-cutting resulted in significant emissions of GHGs at both the wet and the dry plot. The degree of wetness determined, directly or indirectly, the relative contribution of each GHG to the total budgets. Faster establishment of vegetation on the wet plot reduced total emissions of CO2 as compared to the dry plot but this was partially offset by higher CH4 emissions. Waterlogging following clear-cutting likely caused both plots to switch from sinks to sources of CH4. In addition, there were periods with N2O uptake at the wet plot, although both plots were net sources of N2O on an annual basis. We observed clear diel patters in CO2, CH4 and N2O fluxes during the growing season at both plots, with the exception of CH4 at the dry plot. The total three-year carbon budgets were 4107 gCO2-equivalent m−2 and 5274 gCO2-equivalent m−2 at the wet and the dry plots, respectively. CO2 contributed 91.8% to the total carbon budget at the wet plot and 98.2% at the dry plot. For the only full year with N2O measurements, the total GHG budgets were 1069.9 gCO2-eqvivalents m−2 and 1695.7 gCO2-eqvivalents m−2 at the wet and dry plot, respectively. At the wet plot, CH4 contributed 3.7%, while N2O contributed 7.3%. At the dry plot, CH4 and N2O contributed 1.5% and 7.6%, respectively. Our results emphasize the importance of considering the effects of the three GHGs on the climate for any forest management policy aiming at enhancing the mitigation potential of forests.

Modelling Toxin-Producing Algae in the Coastal Waters of Nigeria

This research describes the development and application of an empirical model for toxin-producing algae developed from time series of cell abundance coupled with concurrent measurements of environmental variables in Nigerian coast, Gulf of Guinea. A Generalized Linear Model was formulated to predict the population size of Cyanophyta, Oscillatoria, Dinophyta, total phytoplankton abundance and toxic algae, for four different months in a year, namely March (dry-wet period), July (wet period), October (wet-dry period) and January (dry period), using 12 input variables, namely pH, salinity, PO4, NO3, Fe, water temperature, DO, turbidity, Si, SO4 and location determined by Latitude and Longitude coordinates, with data collected from 53 locations. The interactive effects of silicate and iron were also modeled to elicit effect of these nutrients on the density and occurrence of toxic algae/phytoplankton and total phytoplankton abundance. The model gives a very good fit for the data and the results reveal the influence of season, location and nutrients on the variation in the abundance of total phytoplankton abundance and the toxic form abundance. In the wet season and dry seasons, surface and stem plots for total phytoplankton abundance and toxic algae abundance were noticeably dissimilar, with the Lagos axis of the Atlantic Ocean having significantly high total phytoplankton abundance in the wet season and abundant toxic algae in the south-south locations of Cross River and Akwa Ibom. Ondo and Ogun axes of the Atlantic Ocean had significantly high abundance of the toxic algae in the dry season. In the dry-wet and wet-dry seasons, the surface and stem plots for total phytoplankton abundance and toxic algae abundance were similar. There was significant abundance of toxic algae in the south-west locations. Specifically, Ondo and Ogun in the south-west had significantly high total phytoplankton and toxic algae abundance in the dry-wet season.

Salmonella Survival in Soil and Transfer Onto Produce via Splash Events

Nearly one-half of foodborne illnesses in the United States can be attributed to fresh produce consumption. The preharvest stage of production presents a critical opportunity to prevent produce contamination in the field from contaminating postharvest operations and exposing consumers to foodborne pathogens. One produce-contamination route that is not often explored is the transfer of pathogens in the soil to edible portions of crops via splash water. We report here on the results from multiple field and microcosm experiments examining the potential for Salmonella contamination of produce crops via splash water, and the effect of soil moisture content on Salmonella survival in soil and concentration in splash water. In field and microcosm experiments, we detected Salmonella for up to 8 to 10 days after inoculation in soil and on produce. Salmonella and suspended solids were detected in splash water at heights of up to 80 cm from the soil surface. Soil-moisture conditions before the splash event influenced the detection of Salmonella on crops after the splash events-Salmonella concentrations on produce after rainfall were significantly higher in wet plots than in dry plots (geometric mean difference = 0.43 CFU/g; P = 0.03). Similarly, concentrations of Salmonella in splash water in wet plots trended higher than concentrations from dry plots (geometric mean difference = 0.67 CFU/100 mL; P = 0.04). These results indicate that splash transfer of Salmonella from soil onto crops can occur and that antecedent soil-moisture content may mediate the efficiency of microbial transfer. Splash transfer of Salmonella may, therefore, pose a hazard to produce safety. The potential for the risk of splash should be further explored in agricultural regions in which Salmonella and other pathogens are present in soil. These results will help inform the assessment of produce safety risk and the development of management practices for the mitigation of produce contamination.

Respon Pertumbuhan Dan Produksi Kacang Tanah (Arachis Hypogaea L.) Terhadap Pemberian Pupuk Kandang Kambing Dan Pupuk Organik Cair Bonggol Pisang

The study aimed to determine the response of growth and production of peanuts to the provision of goat manure and banana hump liquid organic fertilizer. This study used a Randomized Block Design (RBD) with 3 replications. Factorial consisting of II treatment factors, Factor I treatment of giving goat manure and Factor II, the treatment of Hump Banana POC treatment The parameters observed in this study; Plant height (cm), number of branches (branches), number of pods per sample (fruit), wet weight of production per sample (g), wet weight of production per plot (g), production dry weight per sample (g), and dry weight Production Per Plot (g). The results showed that goat manure had an effect on growth but did not affect the production of peanut plants, liquid organic fertilizer of banana humps had an influence on the growth and production of peanut plants, Combination of goat manure and banana hump liquid organic fertilizer had no significant effect on growth and production of peanut plants.

Building Variable Productivity Ratios for Improving Large Scale Spatially Explicit Pruning Biomass Assessments

Biomass assessments of agro–residues performed at large geographical scales generally base calculations on single constant pruning productivity ratios (RSRs). Reliability of biomass assessments shall be improved if RSRs respond to prevailing regional crop growing conditions. The present paper describes the methodology applied to create geographically varying pruning RSR ratios–tons of dry matter per hectare—for five crop groups: vineyard, olive, fruit species, citrus and dry fruits. A newly created database containing 230 records–from seven EU28 countries—is submitted to statistical analysis. Results reveal that agro-climatic conditions are able to explain a not negligible share of the pruning productivity as dependent variable. Subsequent regression analysis provides two equations—for vineyard and citrus—achieving a reasonable good fitting (R2 0.18 and 0.42 respectively) between RSR and the agroclimatic variables. Analysis of olive, fruit species and dry fruits scatter and whisker plots were useful for zoning and inducing ramp functions. A Geographical Information System (GIS) was utilised to apply the functions to the agroclimatic raster coverages in order to obtain RSR raster grids. Zonal statistic procedures applied by European regional units (NUTs0, NUTs2, NUTs3) provide a specific crop RSR ratio per administrative unit as a principal output of the present work.

Response of moorland vegetation to 20 years of conservation management in two Cairngorm glens

The response of vegetation to a large reduction in red deer numbers was assessed over a 20 year period in two contrasting glens in the Eastern Cairngorms. Monitoring was done in spring when the annual maximum herbivore impact accumulates on the heather. We estimated deer presence from pellet-group counts, and for heather we measured cover, height and shoot browsing. Deer numbers declined earlier in Glen Derry, and correspondingly heather height increased sooner. Trends in Glen Lui were related to plot wetness and distance from places where the deer were fed in winter; dry plots received much heavier usage from deer and rabbits initially, keeping the heather short and cover stable, whereas on wet plots usage was much lower and heather increased both in cover and height. Subsequently, as deer densities fell, the Lui heather thrived, and by 2013 heather height on dry plots had surpassed height on wet plots. Colonisation by pine saplings was very patchy, being virtually confined to plots within 50 m of mature trees and having heather swards less than 25 cm tall. Despite deer numbers falling, saplings still suffered browsing by black grouse, lagomorphs and voles. Annual increments were greatest on dry plots in Glen Lui. However, we estimate that another eight years of negligible deer numbers are needed for the present sapling crop to become safe from deer damage. A limited regime of burning near mature pines may assist regeneration.

The Effect of Contrasting Moistening Regimes on CO2 Emission from the Gray Forest Soil under a Grass Vegetation and Bare Fallow

The effect of contrasting moisture regimes on the CO2 emission from the gray forest soils (Haplic Luvisols (Loamic, Cutanic, Humic)) under a grass vegetation and bare fallow was studied in a field simulation experiment in June–September, 2015 (Moscow region). Two short soil droughts (53 and 34 days) and a long one (94 days) were simulated on plots isolated from precipitation. A variant with regular irrigation, where the soil moisture was maintained 60–70% of their water holding capacity, was used as a control. Over the whole observation period, the CO2 emissions from the soils studied decreased by a factor of 1.8 compared to the control only in the variant with the grass vegetation under prolonged drought. During the first hours after irrigation of the dry plots, the soil respiration intensified due to the “Birch effect”. The magnitude of this effect was 84–104% in the soils under the grass vegetation and 114–133% in the fallow areas. Owing to this phenomenon, the total CO2 emission from the soils subjected to two short droughts was equal to the CO2 flux under regular moistening for the grass plots and exceeded it by almost 1.3 times for the fallow plots as compared to the control. However, the share of extra CO2 flux induced by moistening of the dry soils did not exceed 8–10% of the total CO2 emission over the whole observation period.

Early dynamics in plant community trait responses to a novel, more extreme hydrological gradient

For temperate regions such as Northern Europe, predicted climate change patterns include an increase in winter precipitation causing increased risk of flooding, whereas periods of droughts will become more frequent in summer. The aim of this study is to explore variations in plant functional trait distributions along a hydrological gradient spanning from recurrent drought events to recurrent flooding—mimicking future precipitation patterns. The experiment was conducted in a controlled grassland experiment over a period of 3 years. A novel and more extreme hydrological regime was achieved by manipulating the flow of a nearby stream thereby creating a continuous hydrological gradient from flooding during winter to drought during summer. Plant community responses were recorded along this hydrological gradient. Community-weighted trait distribution changes along the gradient were described using null models. Six functional traits were considered: seed mass, leaf dry matter content (LDMC), leaf area, leaf thickness, specific leaf area (SLA) and height. Over time, responses in plant functional traits changed at the community level. Over the study period consistent changes occurred in the mean trait value of several traits. Communities in relatively dry plots became dominated by species with water-conserving life strategies, represented by high seed mass and thick leaves. In contrast, disturbance-resistant species (high leaf dry matter content) became dominant in flooded plots, indicating that persistence to flooding was the most important factor controlling the functional structure in those communities. Furthermore, a high abundance of small-seeded species in flooded plots likely indicates higher frequency of species with higher dispersal ability through hydrochory. In conclusion, plant traits are useful for predicting responses to climate change, but abrupt and extreme climate event may cause unexpected responses because they have no analog to previously more stable conditions. We suggest that traits related to dispersal and resistance to disturbance are useful in describing responses to flooding and that these traits should be included in future investigations of plant community responses to extreme hydrological events.

Effect of UV-B radiation on the content of UV-B absorbing compounds and photosynthetic parameters in Parmotrema austrosinense from two contrasting habitats.

We studied the resistance of Parmotrema austrosinense to UV-B stress. We focused on the effects of a high dose UV-B radiation on the content of chlorophylls, carotenoids and UV-B screening compounds. Photosynthetic parameters were measured by chlorophyll fluorescence (potential and effective quantum yields, photochemical and non-photochemical quenching) and evaluated in control and UV-B-treated lichens. Lichens from two different locations in Cordoba, Argentina, were selected: (i) high altitude and dry plots at (Los Gigantes) and (ii) lowland high salinity plots (Salinas Grandes). UV-B treatment led to a decrease in the content of photosynthetic pigments and UV-B screens (absorbance decrease in 220-350nm) in the samples from Salinas Grandes, while in Los Gigantes samples, an increase in UV-B screen content was observed. Chlorophyll fluorescence parameters showed a UV-B-induced decline in FV /FM , ΦPSII and qP indicating limitation of primary photosynthetic processes in photosystem II (PSII) of symbiotic alga, more pronounced in Salinas Grandes samples. Protective mechanism of PSII were activated by the UV-B treatment to a higher extent in samples from Salinas Grandes (NPQ 0.48) than in Los Gigantes samples (NPQ 0.26). We concluded that site-related characteristics, and in particular different UV-B radiation regimen, had a strong effect on resistance of the photosynthetic apparatus of P.austrosinense to UV-B radiation.

The contribution of shelter from rain to the success of pit-building predators in urban habitats

Trap-building predators are sit-and-wait predators that construct a trap and wait for other arthropods to be captured in their trap. The abiotic features of their microhabitat play a significant role in their foraging success, and trap relocation can be costly and risky. Wormlions are fly larvae that construct pits in loose soil to catch prey that fall into their pit-traps and serve as a fine example of a trap-building predator. Wormlions flourish in cities and often occur under buildings that provide shelter from direct sunlight and rain. Here, we studied in the laboratory and in the field the effect of simulated rain and soil moisture on wormlion (Vermileo sp.) habitat choice, response to prey and prey escape success. Wet soil had a strong negative effect on the wormlion pit size and its response to prey, and a positive effect on the probability of ant prey escaping the pit-trap. All these limitations led to a strong avoidance by wormlions of wet soil both before and after a pit was constructed, even at the cost of pit relocation. A field experiment comparing wet and dry plots nevertheless failed to show the expected directional relocation from wet to dry plots, and we provide several explanations as to why the patterns detected in the laboratory were less clear in the field. We suggest that rain presents a considerable limiting factor for wormlion hunting success, and that rain-shielding artificial structures could be responsible for the success of these predators in urban environments. It remains to be tested whether our results hold true for other trap-building predators and whether their preference for dry habitats is as strong as that of wormlions.