Studies on growth rate and grazing mortality rate by microzooplankton of size-fractionated phytoplankton in spring and summer in the Jiaozhou Bay,China

Dilution experiments were performed to examine the growth rate and grazing mortality rate of size-fractionated phytoplankton at three typical stations, inside and outside the bay, in the spring and summer of 2003 in the Jiaozhou Bay, China. In spring, the phytoplankton community structure was similar among the three stations, and was mainly composed of nanophytoplankton, such as, Skeletonema costatum and Cylindrotheca closterium. The structure became significantly different for the three stations in summer, when the dominant species at Stas A, B and C were Chaetoceros curvisetus, Pseudo-nitzschia delicatissima, C. affinis, C. debilis, Coscinodiscus oculus-iridis and Paralia sulcata respectively. Tintinnopsis beroidea and T. tsingtaoensis were the dominant species in spring, whereas the microzooplankton was apparently dominated by Strombidium sp. in summer. Pico- and nanophytoplankton had a relatively greater growth rate than microzooplankton both in spring and summer. The growth rate and grazing mortality rate were 0.18~0.44 and 0.12~1.47 d-1 for the total phytoplankton and 0.20~0.55 and 0.21~0.37 d-1 for nanophytoplankton in spring respectively. In summer, the growth rate and grazing mortality rate were 0.38~0.71 and 0.27~0.60 d-1 for the total phytoplankton and 0.11~1.18 and 0.41~0.72 d-1 for nano- and microphytoplankton respectively. The carbon flux consumed by microzooplankton per day was 7.68~39.81 mg/m3 in spring and 12.03~138.22 mg/m3 in summer respectively. Microzooplankton ingested 17.56%~92.19% of the phytoplankton standing stocks and 31.77%~467.88% of the potential primary productivity in spring; in contrast, they ingested 34.60%~83.04% of the phytoplankton standing stocks and 71.28%~98.80% of the potential primary productivity in summer. Pico- and nanophytoplankton appeared to have relatively greater rates of growth and grazing mortality than microphytoplankton during the experimental period. The grazing rate of microzooplankton in summer was a little bit greater than that in spring because of the relatively higher incubation temperature and different dominant microzooplankton species. Microzooplankton preferred ingesting nanophytoplankton to microphytoplankton in spring, while they preferred ingesting picophytoplankton to nanophytoplankton and microphytoplankton in summer. Compared with the results of dilution experiments performed in various waters worldwide, the results are in the middle range.

Grazing intensity effects on the vegetation in desert rangelands of Southern Tunisia

Although the effects of non-grazing and heavy grazing on vegetation structure have been extensively studied in a wide range of ecosystems, the effects of moderate grazing on desert land are still largely unknown. Many management opportunities exist for increasing forage intake. In order to determine an optimal management method of desert rangelands with high heritage value, we examined the respective effects of heavy grazing, moderate grazing and non-grazing on total vegetation cover, species richness, the Shannon-Wiener diversity index and rangeland productivity. Sampling was done from 2010 to 2012 （from the second year after treatments were imposed） using permanent transects under different grazing intensities. While total vegetation cover, species richness, Shan- non-Wiener diversity index, species composition and primary production were significantly greater on the ungrazed site and significantly weaker on the heavily grazed site, in contrast, moderate grazing had no significant effect on total vegetation cover, species richness, Shannon diversity index, species composition and primary production. These studies suggest that desert rangelands plant communities in general lack response to moderate grazing disturbance, and if managed properly they can provide a valuable source of feed for livestock.

Biological soil crust distribution in Artemisia ordosica communities along a grazing pressure gradient in Mu Us Sandy Land, Northern China

This study investigated the distribution pattern of biological soil crust （BSC） in Artemisia ordosica communities in Mu Us Sandy Land. Three experimental sites were selected according to grazing pressure gradient. In each experimental site, the total vegetation cover, A. ordosica cover, BSC cover, litter-fall cover, BSC degree of fragmentation, BSC thickness and soil properties were investigated in both fixed and semi-fixed sand dunes and simultaneously analyzed in the laboratory. The results showed that at the same grazing pressure, BSC cover and composition were significantly affected by the fixation degree of sand dunes. In addition, BSC cover in the fixed sand dunes was 83.74% on average, whereas it is proportionally dominated by 28% mosses, 21% lichens, and 51% algae. Meanwhile, BSC cover in the semi-fixed sand dunes was 23.54% on average, which is proportionally domi- nated by 6.3% mosses, 2.5% lichens, and 91.2% algae. Fine sand, organic matter, and total nitrogen （N） contents in the fixed sand dunes were all significantly higher than those in the semi-fixed sand dunes. Litter-fall cover de- creased along the grazing pressure gradient, whereas BSC fragmentation degree increased. Fine sand content decreased along with the increase of grazing pressure, whereas medium sand content increased in both fixed and semi-fixed dunes. The organic matter and total N contents in the no grazing site were significantly higher than those in light and normal grazing sites. However, there were no significant differences between the light and normal grazing sites. In addition, there were also no significant differences in BSC thickness between the light and normal grazing sites in the fixed sand dunes. However, a significant decrease was observed in both BSC cover and thick- ness in the normal grazing site. The BSC in the semi-fixed dunes was more sensitive to disturbance.

Effect of Vachellia tortilis on understory vegetation,herbaceous biomass and soil nutrients along a grazing gradient in a semi-arid African savanna

The spatial pattern and abundance of herbaceous vegetation in semi-arid savannas are dictated by a complex and dynamic interaction between trees and grasses. Scattered trees alter the composition and spatial distribution of herbaceous vegetation under their canopies. Therefore, we studied the effect of Vachellia tortilis on herbaceous vegetation composition, biomass and basal area, and soil nutrients on sites with varying grazing intensities in the central rift valley of Ethiopia. Data were collected on species composition, cover and biomass of herbs and grasses, and soil moisture and nutrient contents under light,medium, and heavy grazing pressures, both under the inside and outside of V. tortilis canopies. Species richness was similar in both locations but decreased with increased grazing. Only the overall biomass and herb cover were significantly greater under the canopy than outside, and overall biomass showed significant unchanging decline with increased grazing. However, vegetation cover was significantly greater on moderately grazed sites compared to low and heavily grazed sites. All soil variables were significantly higher under V. tortilis canopies than outside.Our findings suggest that V. tortilis has more effect on composition and diversity of herbaceous vegetation than on species richness, and that V. tortilis promotes the herbaceous layer biomass by reducing soil moisture loss and increasing soil fertility under the inside than outside the canopies. Therefore, we suggest that management practices should be directed on reducing pressure on V. tortilis by regulating grazing. Low to moderate grazing levels(i.e., a stocking rate less than 39.6 TLU ha-1yr-1) seems to be tolerable to ensure sustainable conservation of the species in the study area in particular and in semi-arid savannas in general.

Investigating factors driving phytoplankton growth and grazing loss rates in waters around Peninsular Malaysia

In tropical waters where temperatures are relatively stable,we investigated whether the relationship between phytoplankton growth and grazing loss rate across diff erent habitats around Peninsular Malaysia can be attributed to its eutrophication states.We measured phytoplankton growth(μ)and grazing loss(g)rates in waters off Bachok Marine Research Station(BMRS),located northeast of Peninsular Malaysia.Chlorophyll-a(chl-a)concentration ranged from 2.90 to 15.78μg/L and was dominated by nanoand micro-phytoplankton(>2μm in size).Using the Landry and Hassett dilution method,μat BMRS ranged from 1.02 to 1.58/d whereas g varied from 0.07 to 0.88/d.Grazing accounted for 35%of the primary production at BMRS.A systematic review of available data in waters around Peninsular Malaysia,revealed howμfl uctuated over a wide range(0.01–1.80/d)and correlated with chl a distribution(R 2=0.181,P<0.001).However,the relationship was only signifi cant at<9μg/L chl a for mesotrophic waters and<16μg/L chl a for eutrophic waters.In contrast,g ranged from 0.00 to 1.01/d,and correlated withμat all locations.The g/μslope ranged from 19%to 84%,and was generally similar for waters around Peninsular Malaysia.However,all the g/μslopes had a positive y-intercept except for BMRS,and this seemed to suggest the availability of alternative prey supporting grazing at the other stations.

Effect of Different Stocking Rates on Deyeuxia angustifolia Bog Meadow in Sanjiang Plain of China

This paper investigated the effects of cattle grazing on herbage production and its nutrient and soil characteristics over the grazing season. The grazing experiment was conducted on Deyeuxia angustifolia Bog meadow grassland established in 2010 in Sanjiang Plain. Four grazing treatments were light grazing （LG）, moderate grazing （MG）, heavy grazing （HG）, and a non-grazed exclosure （CK） with corresponding stocking rates of 0.6, 1.0, 1.4, and 0 AU·hm2. month-1, selected as three replications. And then found out the optimum carrying capacity after analyzed the nutrition balance between livestock and grassland. Heavy grazing led to a decline in grassland productivity and soil nutrients. The SOM and the TN content in the soil layer of 0-10 cm were much higher than that in the soil layer of 20-30 cm. More attention should be paid to the nutrient changes in the soil layer of 20-30 cm. Currently, studies showed that the reliable carrying capacity in this type of grassland was 1.0 AU·hm-2. month-l. Inclusion of rangeland health monitoring and optimum stocking rate into grassland management model could facilitate the sustainable development of the grassland.

Land use and dingo baiting are correlated with the density of kangaroos in rangeland systems

Rangelands worldwide have been subject to broadscale modification,such as widespread predator control,intro-duction of permanent livestock water and altered vegetation to improve grazing.In Australia,these landscape changes have resulted in kangaroos(i.e.large macropods)populations increasing over the past 200 years.Kan-garoos are a key contributor to total grazing pressure and in conjunction with livestock and feral herbivores have been linked to land degradation.We used 22 years of aerial survey data to investigate whether the density of 3 macropod species in the southern rangelands of Western Australia was associated with:(i)land use,including type of livestock,total livestock,density of feral goats,type of land tenure,and kangaroo commercial harvest effort;(ii)predator management,including permitted dingo control effort,estimated dingo abundance,and presence of the State Barrier Fence(a dingo exclusion fence);and(iii)environmental variables:ruggedness,rainfall,fractional cover,and total standing dry matter.Red kangaroos(Osphranter rufus)were most abundant inflat,open vegetation,on pastoral land,where area permitted for dingo control was high,and numbers were positively associated with antecedent rainfall with a 12-month delay.Western grey kangaroos(Macropus fuliginosus)were most abundant onflat,agricultural land,but less abundant in areas with high permitted dingo control.Euros(Osphranter robustus)were most abundant in rugged pastoral land with open vegetation,where permitted dingo control was high.While environmental variables are key drivers of landscape productivity and kangaroo populations,anthropogenic factors such as land use and permitted dingo control are strongly associated with kangaroo abundance.

Effect of piospheres on physio-chemical soil properties in the Southern Rangelands of Kenya

Introduction:Water-based interventions haphazardly introduced in the drylands of Kenya have led to the introduction of piospheres used as concentration mounts.Not much is known about the effect of these piospheres on soil physio-chemical properties,especially in the Kenyan rangelands where the government and other development agencies have created piospheres aimed at curbing water shortages and sustaining livestock production.The study assessed the effect of piospheres on soil physio-chemical characteristics in the southern rangelands of Kajiado,Kenya,in order to provide evidence-based insights that will be useful in guiding future water interventions.Methods:Soil samples were collected within 0.25-m2 plots at 20-m intervals along 100-m transects from three piospheres(a dam,a trough,and a seasonal river).Two-way ANOVA was used to determine if there were significant differences in soil parameters between piospheric distances.Results:Soil bulk density significantly different between piospheric distances(F=22.25,P=0.001)and piospheres(F=13.10,P=0.002),being highest at 20 m from the trough(1.1–1.21 gcm−3)relative to a similar distance from the dam(1.01–1.20 gcm−3)and the river(1.1–1.17 gcm−3).On the other hand,mean soil aggregate stability significantly increased(F=66.89,P=0.001)with piospheric distance,being lowest at 20 m from the trough(43.9–46.2%),the dam(43.1–48.9%),and the river(46.6–47.5%).Conclusions:High soil bulk density and consequent low soil porosity,hydraulic conductivity,and moisture content demonstrated that grazing was high near the piospheres.It is recommended that livestock should be herded away from the piospheres after drinking water to ensure that grazing livestock spend less time near the piospheres if reduced soil compaction is to be realized.Piospheres should also be better planned and placed at landscape level to exploit landscape heterogeneity.