Grass invasion causes rapid increases in ecosystem carbon and nitrogen storage in a semiarid shrubland

Accurately predicting terrestrial carbon (C) and nitrogen (N) storage requires understanding how plant invasions alter cycling and storage. A common, highly successful type of plant invasion occurs when the invasive species is of a distinctly different functional type than the native dominant plant, such as shrub encroachment throughout the western United States and annual grass invasions in Mediterranean shrublands, as studied here. Such invasions can dramatically transform landscapes and have large potential to alter C and N cycling by influencing storage in multiple pools. We used a manipulation of non‐native annual grass litter within a shrub‐dominated habitat in southern California (coastal sage scrub, CSS) to study how grass invasion alters ecosystem C and N storage. We added, removed, or left unchanged grass litter in areas of high and low invasion, then followed soil and vegetation changes. Grass litter greatly increased C and N storage in soil, aboveground native and non‐native biomass. Aboveground litter storage increased due to the greater inputs and slower decomposition of grass litter relative to shrub litter; shading by grass litter further reduced decomposition of both non‐native and native litter, which may be due to reduced photodegradation. Soil C and N pools in areas of high litter increased ～20% relative to low litter areas in the two years following manipulation and were generally sinks for C and N, while areas with low litter were sources. We synthesize our results into a C cycle of invaded and uninvaded areas of CSS and link changes in storage to increases in the soil fungi : bacteria ratio, increased plant inputs, and decreased litter loss. Overall, we show that grasses, especially through their litter, control important abiotic and biotic mechanisms governing C and N storage, with widespread implications for C sequestration and N storage in semiarid systems undergoing grass or shrub invasions.     

Microhabitat selection by a stream-dwelling amphipod: a muitivariate analysis approach

SUMMARY. 1. Colonization of microhabitat implants by the amphipod Gammarus pseudolimmnaeus in a small southern Ontario stream was studied in order to analyses the factors controlling habitat selection. The variables substrate particle size, current speed, presence of food and light were used in an analysis of covariance, with percentage weight of organic matter of silt and percentage interstitial space occluded by silt as the covariates.
2. Greatest numbers of amphipods settled on microhabitats featuring large substrate particles, no current and presence of food. There was also a positive relationship between total numbers and the volume of silt deposited on the microhabitats by the stream; small quantities of silt had a beneficial effect on colonization but larger quantities became detrimental.
3. The change from a positive effect occurred at approximately 25% occlusion of the interstitial space in large gravel ( diameter=3.2 cm) and at approximately 55% occlusion in small gravel ( diameter = 0.34 cm).
4. Large animals (6–16.0 mm long) were found predominantly in microhabitats featuring food and large substrate. Medium-sized animals (3–6.0 mm) were most commonly associated with no current and presence of food, and were positively affected by the amount of silt but, at the same time, were negatively affected by increasing occlusion of interstitial spaces by silt. Numbers of small Gammarus (<3.0 mm) were affected only by silt and in a similar manner to medium-sized animals.
5. Amphipod biomass was greatest in microhabitats featuring food and no current. Previous data on the behaviour of this species in laboratory stream-tanks are compared with the microhabitat selections seen.     

Patterns of Testa-imposed Seed Dormancy in Native Australian Legumes

The testa-imposed seed dormancy of 34 native Australian speciesof Faboideae and Mimosoideae was examined immediately afterthe seeds matured and again after 3.5 years of dry storage inthe laboratory. Three groups of dormancy patterns are recognized:17 species (of the Mirbelieae and Acacieae) that have a relativelysmall nondormant fraction (0–10%) of their ripe seedsand that maintain this fraction through time; ten species (ofthe Mirbelieae) that have a relatively large non-dormant fraction(10–40%) of their ripe seeds and that maintain this fractionthrough time; and seven species (of the Bossiaeeae and Phaseoleae)that have a relatively small non-dormant fraction when the seedsripen, and have this fraction increase significantly throughtime. The species in the second group have smaller seeds thando those of the first and third groups, while the species inthe third group have a different testa construction from thosein the first and second groups. For all of the non-dormant seedstested, the water permeability is not localized only at thelens. Leguminosae, Fabaceae, Mimosoideae, Papilionoideae, Faboideae, legume seeds, seed dormancy, hard-seededness, dormancy loss, germination     

Extreme cyclomorphosis in Daphnia lumholtzi

1. Daphnia lumholtzi, not previously reported in North America, was found in a small reservoir in East Texas in January, 1991, This species possesses extremely long spines and large fornices; an allometric study was performed to detect any temporal differences in specific growth rates of the spines relative to the body. 2. In nature, mature females attained 1.8mm body length, excluding spines, but when the head and tail spines are included, the total length reached a maximum of 5.6mm. 3. Differences in the growth patterns of the head spine and the tail spine relative to the body existed for D. lumholtzi from January to March 1991. Both the head and the tail spines grew at a faster rate than the body during all 3 months although the rates varied between them. The results contradict the invertebrate predation hypothesis (Dodson, 1974) in that D. lumholtzi's head and tail spines continue to grow during adulthood instead of stopping after the juvenile instars. 4. The head spines grew at a constant allometric rate over time while the tail spine grew faster as the temperature increased. Both varied significantly in length over the 3 months, with animals having the shortest spines in February and the longest in March.     

Reduction of Disulphide Bonds at Acid pH and Quantitative Estimation of Prolamins from Rye, Wheat and Barley following Separation by Electrophoresis

Storage proteins from three cereal species were reduced at acidpH in the presence or absence of urea. Reactions were usuallycarried out at 100°C and pH 3.2, using dithiothreitol asthe reductant. Changes in electrophoretic mobility of prolaminsin polyacrylamide gels were taken as evidence of protein reduction.One-dimensional polyacrylamide gel electrophoresis, densitometricanalyses and computerized evaluation of data were used to quantifyreactions. Parameters tested include the influence of time,heat, reductant concentration and the presence or absence ofurea. More than 45% of secalin, the alcohol-soluble proteinfrom rye, readily underwent reductive cleavage to yield bandsof substantially different mobilities. Results suggest thatat least 35% of the alcohol-soluble rye components contain intermoleculardisulphide bonds and that at least 12% consist of intramoleculardisulphides; other components appear to be already fully reducedor devoid of disulphide linkages. Analogous measurements forgliadins and hordeins showed that at least 10% of these prolaminsunderwent similar reductions; mobilities of the products suggestthat intramolecular linkages are involved. The method employedprovides a convenient measure of both the qualitative and quantitativechanges associated with the reduction of protein disulphidebonds and the results are important to an understanding of themolecular reactions responsible for the properties of glutenproteins. Key words: Rye proteins, Wheat proteins, Barley proteins, Reduction, Quantitative PAGE, Densitometry     

Impact of Clutch Relocation on Green Turtle Offspring

ABSTRACT For species with temperature-dependent sex determination, such as marine turtles, global climate change poses numerous threats. At the nesting beach, rising temperatures are predicted to further skew already female-biased sex ratios and increase embryonic mortality; sea-level rise and resultant coastal squeeze may leave few alternative breeding habitats in developed regions. As a result, clutch relocation, a commonly used management tool to reduce egg loss, may become necessary for safeguarding populations. Although studies have examined the impact of relocation on clutch success, few have examined the impact of this practice on the sex or phenotypic characteristics of hatchlings produced. We used a randomized block design experiment to examine effects of relocation on green turtle (Chelonia mydas) clutches. We compared hatching success, thermal conditions, and size (length and mass) of hatchlings from in situ control clutches with those subjected to 2 relocation methods, while controlling for maternal and other environmental effects. Relocated clutches did not vary significantly from control clutches in incubation temperature or inferred sex ratios during the critical middle third of incubation when sex is thought to be determined. Hatchling size was also unaffected by relocation. Both relocation methods, however, resulted in a 20% reduction in hatching success in comparison to in situ clutches. Clutch relocation is, however, likely to affect the population primary sex ratio, when clutches are relocated from sites in proximity to the sea where tidal inundation is a threat. Here, cooler conditions are likely to produce more males than are the warmer female-producing temperatures higher up the beach. For clutches at risk, relocation is a viable process and does not appear to affect hatchling size or predicted sex ratios if relocation sites are selected in areas utilized by other females. We urge caution, however, when moving clutches from potentially male-producing sites, particularly given predicted impacts of climate change on already female-biased sex ratios.     

Impact of an invasive alien ant,Wasmannia auropunctata Roger., on a specialised plant–ant mutualism,Barteria fistulosa Mast. and Tetraponera aethiops F. Smith., in a Gabon forest

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The ecology and phylogeny of oomycete infections in Asplanchna rotifers

1. Recently, the potential for parasites to influence the ecology and evolution of their zooplankton hosts has been the subject of increasing study. However, most research to date has focussed on Daphnia hosts, and the potential for parasites to influence other zooplankton taxa remains largely unstudied. 2. During routine sampling of zooplankton in a eutrophic lake, we observed that the rotifer Asplanchna girodi was often infected with a parasitic oomycete. Epidemics of this parasite occurred frequently, with three separate events in a single year. Prevalence at peak infection ranged from 29 to 41% and epidemics lasted from 17 to 56 days. Our data indicate that high densities of the host population are required for epidemics to occur. 3. Our morphological and molecular analyses suggest that this parasite is in the genus Pythium. Most Pythium spp. are plant pathogens, but our study supports recent work on Daphnia, suggesting that Pythium spp. are also important parasites of zooplankton. 4. As the parasite in this study was recalcitrant to cultivation, we developed an alternative method to verify its identity. Our approach used quantitative PCR to show that the ribosomal sequences identified increased with increasing density of infected hosts and, thus, were associated with the parasite. This approach should be generally applicable to other plankton parasites that are difficult to cultivate outside their hosts. 5. Infections significantly reduced host fecundity, lifespan and population growth rate. As a result of the virulence of this parasite, it is likely to influence the population ecology and evolution of its Asplanchna host, and may be a useful model system for studies on host–parasite coevolutionary dynamics.     

Specialist pollinating seed predator exhibits oviposition strategy consistent with optimal oviposition theory

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