Arctic and Boreal terrestrial ecosystems are important components of the climate system because they contain vast amounts of soil carbon (C). Evidence suggests that deciduous shrubs are increasing in abundance, but the implications for ecosystem C budgets remain uncertain. Using midsummer CO2 flux data from 21 sites spanning 16° of latitude in the Arctic and Boreal biomes, we show that air temperature explains c. one‐half of the variation in ecosystem respiration (ER) and that ER drives the pattern in net ecosystem CO2 exchange across ecosystems. Woody sites were slightly stronger C sinks compared with herbaceous communities. However, woody sites with warm soils (> 10 °C) were net sources of CO2, whereas woody sites with cold soils (< 10 °C) were strong sinks. Our results indicate that transition to a shrub‐dominated Arctic will increase the rate of C cycling, and may lead to net C loss if soil temperatures rise. 相似文献
Mosquitoes, which evade contact with long-lasting insecticidal nets and indoor residual sprays, by feeding outdoors or upon animals, are primary malaria vectors in many tropical countries. They can also dominate residual transmission where high coverage of these front-line vector control measures is achieved. Complementary strategies, which extend insecticide coverage beyond houses and humans, are required to eliminate malaria transmission in most settings. The overwhelming diversity of the world's malaria transmission systems and optimal strategies for controlling them can be simply conceptualized and mapped across two-dimensional scenario space defined by the proportion of blood meals that vectors obtain from humans and the proportion of human exposure to them which occurs indoors. 相似文献
A sowing experiment was carried out using three endemic secondary successional species that commonly co‐occur with Pinus halepensis in afforestations in southeast Spain. The experiment simulated the natural arrangement of needle litter over soil to test the litter's effect on seedling emergence and early growth of dwarf‐shrubs and annual species, the main components of some European Habitats of Community Interest in Spain. Three sowing treatments were compared in a growth chamber: (1) soil without litter taken from clearings in a pine plantation (BARE); (2) intact soil and litter forming two distinct layers as in the field (PINE); and (3) soil and pine litter mixed in the laboratory (PINEMX). Seedling emergence of Diplotaxis harra and Thymus zygis were seven and two times higher, respectively, on BARE than on the pine litter treatments. Pine litter significantly decreased seedling biomass, length, and number of leaves of D. harra and T. zygis. Thymus capitatum was weakly affected by the presence of pine litter. We suggest that plant recruitment in the understory of P. halepensis is partially controlled by interference of pine litter, which might affect dynamics of the studied species. We propose that management practices counteract this negative effect by manipulating the pine litter layer to achieve successful ecological restoration and conservation of endemic‐rich secondary communities in Natura 2000 sites in semiarid western Mediterranean areas. 相似文献
Background: Climate warming has been causing an increase in tall shrub cover around the Arctic, however, mammalian herbivory has been shown to inhibit shrub expansion. Though the effect of reindeer (Rangifer tarandus) and many other mammals has been widely studied in this context, the role of the mountain hare (Lepus timidus) in subarctic Scandinavia remains unknown.
Aims: To quantify browsing from mountain hare and reindeer on tall shrubs in different vegetation types and to investigate differences in shrub preference between the two.
Methods: In the summers of 2013 and 2014, we counted signs of browsing by hare and reindeer on tall shrub species in 31 study plots at three alpine locations in the Scandes range, Sweden.
Results: Hare browsing was significantly more frequent than that by reindeer in two (dry-mesic heath and dry meadow) out of seven vegetation types studied. Reindeer browsing was significantly higher in the low herb meadow and Långfjället shrub heath. Two shrub species, Betula nana and Salix hastata, were significantly more browsed by hare, while reindeer browsing was significantly higher on S. phylicifolia and S. lapponum.
Conclusions: Our results show that mountain hares can cause extensive damage to tall shrubs in the subarctic and may have a stronger impact on shrub communities than previously recognised. 相似文献
Sample pretreatment was optimized to obtain high sequence coverage for human serum albumin (HSA, 66.5 kDa) when using nano-electrospray ionization quadrupole time-of-flight mass spectrometry (nESI–Q-TOF–MS). Use of the final method with trypsin, Lys-C, and Glu-C digests gave a combined coverage of 98.8%. The addition of peptide fractionation resulted in 99.7% coverage. These results were comparable to those obtained previously with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI–TOF–MS). The sample pretreatment/nESI–Q-TOF–MS method was also used with collision-induced dissociation to analyze HSA digests and to identify peptides that could be employed as internal mass calibrants in future studies of modifications to HSA. 相似文献
Abstract
To interpret broad-scale erosion and accretion patterns and the expansion and contraction of shrub thickets in response to
sea level rise for a coastal barrier system, we examined the fine-scale processes of shrub recruitment and mortality within
the context of the influence of ocean current and sediment transport processes on variations in island size and location.
We focused on Myrica cerifera shrub thickets, the dominant woody community on most barrier islands along the coastline of the southeastern USA. Observations
suggest that M. cerifera, a salt-intolerant species, is increasing in cover throughout the Virginia barrier islands, yet rising sea level in response
to climate change is increasing erosion and reducing island area. Our objective was to explain this apparent paradox using
pattern–process relationships across a range of scales with a focus on ocean currents and sediment transport interacting with
island characteristics at intermediate scales. Multi-decadal comparisons across scales showed a complex pattern. At the scale
of the entire Virginia barrier complex, modest decreases in upland area were accompanied by large increases in shrub area.
Responses were more variable for individual islands, reflecting inter-island variations in erosion and accretion due to differences
in sediment transport via ocean currents. Several islands underwent dramatic shrub expansion. Only for within-island responses
were there similarities in the pattern of change, with a lag-phase after initial shrub colonization followed by development
of linear, closed canopy thickets. Understanding the fine-scale processes of shrub seedling establishment and thicket development,
in conjunction with the influence of ocean currents and sediment transport, provides a framework for interpreting island accretion
and erosion patterns and subsequent effects on shrub thicket expansion or contraction across scales of time and space. 相似文献