Precipitation Exclusion Research Articles

Responses of soil respiration and its temperature/moisture sensitivity to precipitation in three subtropical forests in southern China

Abstract. Both long-term observation data and model simulations suggest an increasing chance of serious drought in the dry season and extreme flood in the wet season in southern China, yet little is known about how changes in precipitation pattern will affect soil respiration in the region. We conducted a field experiment to study the responses of soil respiration to precipitation manipulations – precipitation exclusion to mimic drought, double precipitation to simulate flood, and ambient precipitation as control (abbr. EP, DP and AP, respectively) – in three subtropical forests in southern China. The three forest sites include Masson pine forest (PF), coniferous and broad-leaved mixed forest (MF) and monsoon evergreen broad-leaved forest (BF). Our observations showed that altered precipitation strongly influenced soil respiration, not only through the well-known direct effects of soil moisture on plant and microbial activities, but also by modification of both moisture and temperature sensitivity of soil respiration. In the dry season, soil respiration and its temperature sensitivity, as well as fine root and soil microbial biomass, showed rising trends with precipitation increases in the three forest sites. Contrarily, the moisture sensitivity of soil respiration decreased with precipitation increases. In the wet season, different treatments showed different effects in three forest sites. The EP treatment decreased fine root biomass, soil microbial biomass, soil respiration and its temperature sensitivity, but enhanced soil moisture sensitivity in all three forest sites. The DP treatment significantly increased soil respiration, fine root and soil microbial biomass in the PF only, and no significant change was found for the soil temperature sensitivity. However, the DP treatment in the MF and BF reduced soil temperature sensitivity significantly in the wet season. Our results indicated that soil respiration would decrease in the three subtropical forests if soil moisture continues to decrease in the future. More rainfall in the wet season could have limited effect on the response of soil respiration to the rising of temperature in the BF and MF.

Effects of free air carbon dioxide enrichment and drought stress on the feed value of maize silage fed to sheep at different thermal regimes

Information about the effects of rising atmospheric CO2 concentration and drought on the feed value of maize silage and interactions with the thermal environment during feeding is limited. A free air carbon dioxide enrichment facility was operated in a maize field to generate an elevated CO2 concentration of 550 ppm. Drought was induced by the exclusion of precipitation in one half of all experimental plots. Plants were harvested, chopped and ensiled. In a balance experiment on sheep, the nutrient digestibility was determined for three climatic treatments (temperate, temperature humidity index (THI) 57–63; mild heat, THI 68–71; severe heat, THI 75–80). The CO2 concentration and drought did not alter the crude nutrient content of silage dry matter (DM) or nutrient and organic matter (OM) digestibility. Drought increased the concentration of deoxynivalenol (DON, p < 0.001). The drought-associated increase of DON was reduced by CO2 enrichment (p = 0.003). The lowest digestibility of acid detergent fibre (p = 0.024) and neutral detergent fibre (p = 0.005) was observed during the coldest climate. OM digestibility increased during mild heat (p = 0.023). This study did not indicate considerable alterations of the feed value of maize silage due to increased atmospheric CO2 and drought. Enriched CO2 may decrease DON contaminations during drought. The thermal environment during the balance experiment did not interact with feeding maize silage grown under elevated CO2, but may affect cell wall and OM digestibility.

Consequences of exclusion of precipitation on microorganisms and microbial consumers in montane tropical rainforests

The structure and functioning of decomposer systems heavily relies on soil moisture. However, this has been primarily studied in temperate ecosystems; little is known about how soil moisture affects the microfaunal food web in tropical regions. This lack of knowledge is surprising, since the microfaunal food web controls major ecosystem processes. To evaluate the role of precipitation in the structure of soil food web components (i.e., microorganisms and testate amoebae), we excluded water input by rain in montane rainforests at different altitudes in Ecuador. Rain exclusion strongly reduced microbial biomass and respiration by about 50 %, and fungal biomass by 23 %. In testate amoebae, rain exclusion decreased the density of live cells by 91 % and caused a shift in species composition at each of the altitudes studied, with ergosterol concentrations, microbial biomass, and water content explaining 25 % of the variation in species data. The results document that reduced precipitation negatively affects soil microorganisms, but that the response of testate amoebae markedly exceeds that of bacteria and fungi. This suggests that, in addition to food, low precipitation directly affects the community structure of testate amoebae, with the effect being more pronounced at lower altitudes. Overall, the results show that microorganisms and testate amoebae rapidly respond to a reduction in precipitation, with testate amoebae—representatives of higher trophic levels—being more sensitive. The results imply that precipitation and soil moisture in tropical rainforests are the main factors regulating decomposition and nutrient turnover.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-012-2360-6) contains supplementary material, which is available to authorized users.

Soil respiration is stimulated by elevated CO2 and reduced by summer drought: three years of measurements in a multifactor ecosystem manipulation experiment in a temperate heathland (CLIMAITE)

AbstractThis study investigated the impact of predicted future climatic and atmospheric conditions on soil respiration (RS) in a Danish Calluna‐Deschampsia‐heathland. A fully factorial in situ experiment with treatments of elevated atmospheric CO2 (+130 ppm), raised soil temperature (+0.4 °C) and extended summer drought (5–8% precipitation exclusion) was established in 2005. The average RS, observed in the control over 3 years of measurements (1.7 μmol CO2 m−2 sec−1), increased 38% under elevated CO2, irrespective of combination with the drought or temperature treatments. In contrast, extended summer drought decreased RS by 14%, while elevated soil temperature did not affect RS overall. A significant interaction between elevated temperature and drought resulted in further reduction of RS when these treatments were combined. A detailed analysis of short‐term RS dynamics associated with drought periods showed that RS was reduced by ~50% and was strongly correlated with soil moisture during these events. Recovery of RS to pre‐drought levels occurred within 2 weeks of rewetting; however, unexpected drought effects were observed several months after summer drought treatment in 2 of the 3 years, possibly due to reduced plant growth or changes in soil water holding capacity. An empirical model that predicts RS from soil temperature, soil moisture and plant biomass was developed and accounted for 55% of the observed variability in RS. The model predicted annual sums of RS in 2006 and 2007, in the control, were 672 and 719 g C m−2 y−1, respectively. For the full treatment combination, i.e. the future climate scenario, the model predicted that soil respiratory C losses would increase by ~21% (140–150 g C m−2 y−1). Therefore, in the future climate, stimulation of C storage in plant biomass and litter must be in excess of 21% for this ecosystem to not suffer a reduction in net ecosystem exchange.

Evapotranspiration (ET) Covers

Evapotranspiration (ET) cover systems are increasingly being used at municipal solid waste (MSW) landfills, hazardous waste landfills, at industrial monofills, and at mine sites. Conventional cover systems use materials with low hydraulic permeability (barrier layers) to minimize the downward migration of water from the surface to the waste (percolation), ET cover systems use water balance components to minimize percolation. These cover systems rely on soil to capture and store precipitation until it is either transpired through vegetation or evaporated from the soil surface. Compared to conventional membrane or compacted clay cover systems, ET cover systems are expected to cost less to construct. They are often aesthetic because they employ naturalized vegetation, require less maintenance once the vegetative system is established, including eliminating mowing, and may require fewer repairs than a barrier system. All cover systems should consider the goals of the cover in terms of protectiveness, including the pathways of risk from contained material, the lifecycle of the containment system. The containment system needs to be protective of direct contact of people and animals with the waste, prevent surface and groundwater water pollution, and minimize release of airborne contaminants. While most containment strategies have been based on the dry tomb strategy of keeping waste dry, there are some sites where adding or allowing moisture to help decompose organic waste is the current plan. ET covers may work well in places where complete exclusion of precipitation is not needed. The U.S. EPA Alternative Cover Assessment Program (ACAP), USDOE, the Nuclear Regulatory Commission, and others have researched ET cover design and efficacy, including the history of their use, general considerations in their design, performance, monitoring, cost, current status, limitations on their use, and project specific examples. An on-line database has been developed with information about specific projects using ET covers. There are three general approaches for non-conventional cover systems to achieve approval for installation; the first is when equivalent performance to conventional final cover systems can be demonstrated directly on site. This is the approach used by the Sandia study, by most ACAP sites, and the Rocky Mountain Arsenal. A second approach is used when there are data from a site specific study such as an ACAP installation at a site that has analogous soil and climate conditions. Several sites in Colorado and Southern California have achieved approval based on data from similar sites. The third most common approach for regulatory approval is by installation of data collection systems with the agreement that the permanence of the ET cover installation is contingent on success of the cover in meeting certain performance goals. This article is intended as an introduction to the topic and is not intended to serve as guidance for design or construction, nor indicate the appropriateness of using an ET cover systems at a particular site.

The response of carbon dioxide exchange to manipulations of Sphagnum water content in an ombrotrophic bog

AbstractSphagnum mosses contribute to the long‐term carbon sequestration of many northern peatlands. Variability in both Sphagnum and peatland CO2 exchange is strongly influenced by water availability, but there is limited work examining the links between these relationships, particularly in a field setting. In this study, the effects of varying moss water content (WC), through precipitation exclusion (PE) and water addition (WA) treatments, on net ecosystem CO2 exchange (NEE) and component fluxes were assessed during a single growing season at Mer Bleue bog, a temperate ombrotrophic peatland. CO2 exchange by Sphagnum, vascular plants, and the total ecosystem were measured in situ using chambers. On average, the hummock species of Sphagnum dominant at the site maintained WCs within the optimal range for photosynthesis in all treatments and no treatment effect on CO2 exchange was observed. However, in a few samples associated with below optimal WCs, Sphagnum photosynthesis was reduced. Water table (WT) depth and direct precipitation were both important controls on Sphagnum WC, suggesting that frequent small rain events may be important in maintaining Sphagnum WC. This study only explored one variable associated with drought conditions (i.e. water availability through intercepted precipitation). Consequently, further study is necessary to assess the relative importance of deep WT positions and high temperatures on moss WC. Nevertheless, the results of this study suggest that decreased Sphagnum photosynthesis has the potential to influence peatland CO2 uptake at Mer Bleue in drought years, but only if moss WC is reduced below the optimal range. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Comparison of Two Methods for the Quantitation of β-Glucans from Shiitake Mushrooms

ABSTRACT Fungal polysaccharides and glucans, including lentinan from shiitakes, have been identified as promoting human health, and consequently, the sale of mushroom-based health products has increased significantly in recent years. Reliable methods for the quantitation of lentinan must be available if shiitakes or shiitake-derived products are to be promoted as health-promoting food. The objective of this study was to characterize two methods for the quantitation of β-glucans from aqueous extracts of shiitake mushrooms. The first method utilized ethanol precipitation and batch size exclusion chromatography to isolate a fraction enriched in lentinan, called high molecular weight polysaccharides, HMWP. Gel filtration chromatography characterization of HMWP fraction indicated that the size distribution of carbohydrates was similar to that of a lentinan standard. Analyses for total starch and glycogen, to a lesser extent, indicate these polysaccharides are less than 10% of the total carbohydrates in HMWP. These results suggest that the HMWP fraction had a high level of lentinan. The second method measured the production of glucose by enzymes that specifically hydrolyze plant β-glucans. The amount of carbohydrate detected by the enzymatic β-glucan assay was significantly less than the carbohydrate found in the HMWP fraction. The low content of β-glucan was not due to a failure of the assay's enzymes to unction. In addition, no glucose was produced when a lentinan standard was subjected to the β-glucan assay. These results indicate that the carbohydrate content of HMWP fraction was a better indicator of lentinan content of shiitakes compared to the mushroom's β-glucan content.

Climatic determinants of the northern range limit of Fagus crenata forests in Japan

AbstractWe sought to identify the factors that determine the current northern range limit of Fagus crenata (Fagaceae) forests in Japan. Four climatic factors (warmth index, minimum temperature of the coldest month, summer precipitation and winter precipitation) can potentially explain the distribution. Five classification tree models were developed: one based on all four factors, the others based on the four permutations of three of the four climatic factors (i.e. each excluded one of the four factors). The performance and the distributions of F. crenata forests predicted by these models were then compared, with particular reference to the distributions in Hokkaido. The distribution predicted by the model developed without summer precipitation extended continuously northwards along the Sea of Japan coast beyond the current northern range limits, but the distributions predicted by the other three models showed gaps around the current limit. When the warmth index, minimum temperature of the coldest month or winter precipitation were excluded the contribution to the resulting models of the other three variables increased, thereby compensating for the exclusion. However, the exclusion of summer precipitation was not compensated by increases in the contributions of the other variables in the model developed without this factor. These results suggest that summer precipitation is the most influential factor explaining the absence of F. crenata forests in the areas immediately to the north‐east of the current northern range limit.

Factors controlling spatio‐temporal variation in carbon dioxide efflux from surface litter, roots, and soil organic matter at four rain forest sites in the eastern Amazon

This study explored biotic and abiotic causes for spatio‐temporal variation in soil respiration from surface litter, roots, and soil organic matter over one year at four rain forest sites with different vegetation structures and soil types in the eastern Amazon, Brazil. Estimated mean annual soil respiration varied between 13–17 t C ha−1 yr−1, which was partitioned into 0–2 t C ha−1 yr−1 from litter, 6–9 t C ha−1 yr−1 from roots, and 5–6 t C ha−1 yr−1 from soil organic matter. Litter contribution showed no clear seasonal change, though experimental precipitation exclusion over a one‐hectare area was associated with a ten‐fold reduction in litter respiration relative to unmodified sites. The estimated mean contribution of soil organic matter respiration fell from 49% during the wet season to 32% in the dry season, while root respiration contribution increased from 42% in the wet season to 61% during the dry season. Spatial variation in respiration from soil, litter, roots, and soil organic matter was not explained by volumetric soil moisture or temperature. Instead, spatial heterogeneity in litter and root mass accounted for 44% of observed spatial variation in soil respiration (p &lt; 0.001). In particular, variation in litter respiration per unit mass and root mass accounted for much of the observed variation in respiration from litter and roots, respectively, and hence total soil respiration. This information about patterns of, and underlying controls on, respiration from different soil components should assist attempts to accurately model soil carbon dioxide fluxes over space and time.

Identification and semi-quantitative determination of gum Arabic in wines by GC-MS and size exclusion chromatography.

A method for the identification and the semi-quantitative determination of the food additive gum Arabic in wines is described. Tests carried out on solutions spiked with known amounts of wine and gum Arabic polysaccharides allowed to define the suitable conditions for their quantitative precipitation and size exclusion analysis. CG-MS analyses of the different recovered fractions allowed to discriminate between gum Arabic and wine polysaccharides through the identification of glucose and mannose present only in wine polysaccharides. The proposed method was based on the wine polysaccharides free peak area obtained by size exclusion chromatography. The same cut-off time was always used both in the preparation of the calibration plot and in the analysis of the real samples. Gum Arabic was determined in a ratio of 1/10 w/w with wine polysaccharides with a detection limit of 0.074 mg ml(-1) which is lower than the lowest gum Arabic amount usually added into wines. Owing to the moderately low natural variability of the gum Arabic standards the described procedure is suitable for a semi-quantitative analysis even if its accuracy allowed a quite reliable determination of the gum Arabic amount usually added to wine.

Acute seasonal drought does not permanently alter mass loss and nitrogen dynamics during decomposition of red maple (Acer rubrum L.) litter

AbstractLitter decomposition is a major component of nutrient cycling in forest ecosystems and is known to be sensitive to both temperature and moisture. A drought during periods of the year when moisture is normally abundant may impact decomposition more than moisture limitation during seasons that are routinely dry. We excluded precipitation for a 3‐month period during each of four seasons and measured mass loss and nitrogen (N) dynamics in Acer rubrum leaf litter by using a litterbag approach. We hypothesized that rainfall exclusion would retard mass loss during the exclusion period, with the maximum effect occurring during the spring and summer months when moisture was normally adequate and temperatures optimum for decomposition, and that exclusion during these two periods would have the greatest impact on subsequent timing of decomposition events, particularly N mineralization. Mass loss in litterbags was initially reduced by precipitation exclusion in the spring treatment only. For each season, a set of bags exposed to drying in the same way and allowed to remain in the field under ambient conditions for an additional 9 months no longer showed a difference in mass loss relative to control bags. Nitrogen accumulation was immediately and significantly reduced in the exclusion treatments in all seasons; however, like mass loss, there was no difference 9 months later. We conclude that short‐term effects of drought do occur, especially with regard to N accumulation, and that these effects do not persist and are unlikely to have any substantial effect on nutrient cycling.

Analysis of peptidogalactomannans from the mycelial surface of Aspergillus fumigatus

Peptidogalactomannans (pGMs) from mycelium of two strains of Aspergillus fumigatus were fractionated by Cetavlon precipitation and size exclusion chromatography and their carbohydrate structures analysed using methylation-fragmentation analysis, partial acetolysis and 13C-nuclear magnetic resonance spectroscopy. The most significant difference between the pGMs of the two strains was the degree of branching and the proportion of non-reducing ends of alpha-D-Manp and beta-D-Galf units. Methylation data showed that the pGM from AF 2109 contained alpha-D-Manp and beta-D-Galf non-reducing end units in a proportion of 3:1 while, in contrast, the proportion of these structures in pGM from AF 2140 was 7:1, resulting in a highly branched structure. The immunoreactivity of the pGM fractions was tested by indirect immunofluorescence. The fractions were also tested in an ELISA system with rabbit antiserum raised to whole cells of A. fumigatus NCPF 2140 and with serum from patients with either proven aspergilloma or ABPA. The carbohydrate moiety of the pGM appears to be responsible for the antigenicity. Periodate treatment, partial acid hydrolysis and beta-elimination removed most of the antibody binding capacity.

Reversing Acidification in a Forested Catchment in Southwestern Sweden: Effects on Soil Solution Chemistry

AbstractThe exclusion of acid precipitation in whole‐catchment experiments can provide valuable information to further our understanding of recovery processes of acidified soils. In this study, we focused on the reversibility of acidification‐induced changes in different soil horizons when anthropogenic deposition was excluded. A small forested catchment in the Gårdsjön area in southwest Sweden was covered with a transparent roof in April 1991 and sprinkled with water that simulated preindustrial deposition levels. Within the roofed catchment and a reference catchment the soil solution was studied using a centrifugation drainage technique. Sulfate concentrations in the O and E horizons decreased by 75 and 65%, respectively, within 3 mo after treatment. In the Bs horizon, the sulfate concentration decreased more gradually, reaching about 52% of the pretreatment level in 1993 after 2.5 yr of treatment. The decline in sulfate concentrations in the runoff followed the pattern observed in the Bs horizon. The net loss from the catchment during the first 2.5 yr of the treatment period represents approximately 9% of the phosphate‐extractable sulfate pool. No increase in soil solution pH occurred until 1994. In 1993, Al concentrations were lower compared with those found in earlier samplings of the soil solution and runoff. Fluctuations in Al concentrations were correlated most strongly with changes in ionic strength in the soil solution and runoff. Nitrate concentrations remained unchanged in the soil solution and runoff. Concentrations of NO−3 were, however, already low (&lt;30 µmol L−1) before the exclusion.

Field simulation of wet and dry years in the Chihuahuan desert: soil moisture, N mineralization and ion-exchange resin bags

Irrigation and rain-out shelters were used to simulate precipitation patterns of wet and dry years in the northern Chihuahuan Desert. Irrigation provided approximately double the long-term average monthly precipitation. Rain was excluded during the wet season, July-October, to simulate a dry year. N net mineralization in laboratory incubations was undectable at calculated water potentials less than -1 MPa. Witb increasing moisture, mineralization gradually rose to the highest observed rates near field capacity. There was no mineralization maximum at moisture contents below field capacity. Irrigation significantly increased the water potential and rainfall exclusion reduced water potentials to less than-8 MPa. The general absence of important irrigation effects may have resulted from the high natural precipitation during the experiment or because irrigation inputs were insufficient to increase microbial activity during very dry periods. Precipitation exclusion reduced ion capture during the warm-wet season. After allowing precipitation inputs to resume, NH4+-N capture was increased in the cool-dry seasons of both 1987–1988 and 1988–1989. NH4+-N capture more than doubled that predicted from the overall covariance of moisture input and ion capture, suggesting increased availability of N. An unusually hot, dry period in May and June 1989 was followed by a threeto fourfold increase in the warm-wet season NO3−+NO2−N capture compared to 1988. These data suggest that short droughts of about 3 months in length (both simulated and natural) increased N availability relative to moisture availability.

Differences in the abilities of human tau isoforms to promote microtubule assembly

Three isoforms of human tau protein were compared for their abilities to induce microtubule assembly. The three isoforms, tau 3 (tau containing three microtubule-binding domains), tau 4 (tau containing four microtubule-binding domains) and tau 4L (tau containing four microtubule binding domains plus a 58-amino-acid insert near the N-terminus) were expressed in E. coli and purified using ammonium sulfate precipitation, ion exchange, and size exclusion chromatography. All three isoforms induced microtubule assembly at micromolar concentrations and showed similar critical concentrations for assembly of 0.4-0.45 microM. However, tau 4 induced microtubule formation at a rate five- to tenfold faster than either tau 3 or tau 4L. The rate of microtubule elongation seen with tau 4 was twofold greater than with tau 3 or tau 4L, suggesting that the faster rate of microtubule assembly seen with tau 4 was due, at least in part, to faster elongation. Tau 4 induced a greater number of microtubules to form at steady state than did tau 3 or tau 4L. The microtubules generated with each tau isoform had similar steady-state length distributions and were equally susceptible to cold-induced disassembly. These results indicate that the additional microtubule-binding domain in tau 4 enhances microtubule assembly, while the 58-amino-acid insert negates the stimulatory effect of the fourth microtubule-binding domain.

Field Study of the Interaction between Solar Ultraviolet-B Radiation and Drought on Photosynthesis and Growth in Soybean

Soybean, Glycine max (L.) Merr. cv Essex, plants were grown in the field in a 2 x 2 factorial design, under ambient and supplemental levels of ultraviolet-B (UV-B) radiation (supplemental daily dose of 5.1 effective kilojoules per square meter) and were either well-watered or subjected to drought. Soil water potentials were reduced to -2.0 megapascals by the exclusion of natural precipitation in the drought plots and were maintained at approximately -0.5 megapascal by supplemental irrigation in well-watered plots. Plant growth and gas exchange characteristics were affected under both drought and supplemental UV-B radiation. Whole-leaf gas exchange analysis indicated that stomatal limitations on photosynthesis were only significantly affected by the combination of UV-B radiation and drought but substrate (ribulose bisphosphate) regeneration limitations were observed under either stress. The combined effect of both drought and UV-B radiation on photosynthetic gas exchange was a reduction in apparent quantum efficiency and the rapid appearance of biochemical limitations to photosynthesis concomitant with reduced diffusional limitations. However, the combination of stresses did not result in additive effects on total plant growth or seed yield compared to reductions under either stress independently.

Liquid Chromatographic Determination of 4-Amino-N-(2,6-dimethylphenyl)-benzamide in Rat Serum and Urine

Abstract The compound 4-amino-N-(2,6-dimethylphenyl)-benzamide has shown potential as a new anticonvulsant. A method for the liquid chromatographic determination of serum and urine concentrations of the compound and its N-acetylated metabolite was developed for pharmacokinetic studies. Quantitation was achieved via UV detection at 275 nm following isocratic reversed phase (C18) separation using a ternary solvent system of water:acetonitrile:acetic acid (60:39:1) at a flow rate of 1.5 mL/min. The compounds were isolated from a 50 μL sample of serum using solid phase extraction with prior protein precipitation. The compounds and internal standard were eluted from the extraction column with acetonitrile. Isolation from urine was achieved similarly with the exclusion of protein precipitation. The assay procedure is useful for the determination of concentrations of parent compound from 0.68 to 204.6 μg/mL.

A one year study on the viability of Cryptococcus neoformans in nature.

Using four different assat procedures we found a 50 to 86% decrease in viability of Cryptococcus neoformans over a one year period after two towers in the Oklahoma City area were modified to exclude pigeons and weather elements, especially rain. In homogeneous pigeon dropping samples a sharp decrease in viability occurred after 7 to 9 months of storage. The decrease occurred in pigeon dropping samples maintained at the natural sites and at ambient temperature in the laboratory in the laboratory but not in droppings stored at -4 degrees C. Air sampling studies done at the natural sites before and after tower modifications also showed a decrease in C. neoformans viability. The decrease in viability cannot be explained by seasonal temperature variations that occurred at natural sites. Our findings suggest that death of C. neoformans occurred because of lack of available intracellular water exacerbated by low humidity, exclusion of precipitation and moisture from fresh pigeon droppings. In light of our experiences, at one site in south central United States, the feasibility of controlling C. neoformans at heavily contaminated sites, other than by the use of noxious or potentially dangerous chemicals, is discussed.