We investigated whether root grafts between lodgepole pine (Pinus contorta var. latifolia Dougl. ex. Loud.) trees can transfer sufficient carbohydrate reserves from a source tree to a grafted sink tree to affect the vigor of trees growing in a light-limited environment. Eleven plots were established in early spring and two grafted tree pairs and two independent non-grafted trees were selected at each plot. One tree in a grafted pair and one non-grafted tree were shaded at each plot, whereas the remaining trees were non-shaded during the experimental period. Shaded trees had significantly lower carbohydrate reserves and smaller crowns than non-shaded trees following one growing season. Grafted shaded trees had significantly higher root total nonstructural carbohydrate concentrations than non-grafted shaded trees, indicating that root grafts partially offset the effects of shading. Also, large root grafts transferred proportionately more carbohydrates to the shaded trees than small root grafts. Carbohydrates transferred through root grafts could allow grafted trees to persist under conditions where non-grafted trees would be removed by competition.
S ARS-CoV-2 originated in horseshoe bats and probably reached humans through an unidentified intermediary host (1). The virus is aerosolized and highly transmissible among humans; new variants have arisen and spread in successive waves across the world since late 2019. Since a report of SARS-CoV-2 infection in a dog in March 2020 (2), an ever-increasing range of species has been shown to be susceptible to infection, including household cats, dogs, ferrets, and hamsters (3-10).Companion animals have closest contact with humans, creating ample opportunity for exposure. Experimental infections have suggested that most companion animals are infected only transiently, as indicated by PCR positivity or virus isolation (11,12). Conversely, detection of antibodies by ELISA or neutralizing antibody assay suggests infection rates of 0.2%-43.9% related to factors such as the likelihood and frequency of interaction with infected humans (13-16). Infections in animals are typically subclinical or associated with transient respiratory or gastrointestinal disease (17,18). In rare cases, death has been attributed to SARS-CoV-2 infection; however, defining the contribution of SARS-CoV-2 to death in animals with underlying conditions such as cancer, bacterial pneumonia, or obesity is challenging. On the other hand, minks are highly susceptible to infection and pneumonia, and mortality rates of 35%-55% caused by SARS-CoV-2 infection were reported from outbreaks among farmed mink in Utah ( 19). Captive minks also contracted viruses with a unique amino acid substitution in the spike (S) protein that were subsequently retransmitted to humans and to community cats and dogs, around mink farms in the Netherlands (5,20). Similarly, infected pet Syrian hamsters may also retransmit SARS-CoV-2 to humans (21). More than 30% of free-ranging white-tailed deer tested in Ohio were SARS-CoV-2 positive by PCR, and a similarly high proportion of white-tailed deer in Texas and other North America locations had neutralizing antibodies (22,23). Experimentally, white-tailed deer transmitted SARS-CoV-2 to other deer vertically and horizontally by direct contact (24). It has not yet been determined if infected deer experience illness or have increased illness and death rates or if transmission is sustained among wild deer populations. However, such high
This study investigated stand factors associated with the rate of root graft formation in lodgepole pine stands. Forty plot areas, each containing 10 trees, were excavated in pure, even-aged pine stands in western Alberta. Exposed root systems were examined for grafts and various stand measurements were recorded at each plot. Results indicate that the number of grafts per square metre is controlled by plot tree density and tree diameter. Also, the percentage of grafted trees increased with both increasing tree age and decreasing distance between trees. Grafts also appear to form relatively early in stand development; the majority of grafts in the present study had formed by the time roots were 20 years old and 50 mm in diameter. These results suggest that grafting is a common occurrence in lodgepole pine stands where trees are <109 cm apart, which translates to a density of approximately 8500 stems/ha (based on even tree distribution). However, even clumps within relatively low density stands are likely to be grafted from a relatively early stage of development.Key words: Pinus contorta, graft formation, stand dynamics.
In two separate studies, the suckering of trembling aspen (Populus tremuloides Michx.) roots was assessed in response to different daily maximum soil temperatures and in relation to available nutrients (CaSO4 and NH4NO3). In the first study, aspen root sections were incubated under high:low temperature regimes of 12:8, 14:8, 16:8, 18:8, or 20:8°C until 124 degree-days above 8°C had been reached. Daily maximum temperature did not affect the number of suckers produced per square centimetre of root surface area or per root section. However, more time was required to initiate suckers on root sections grown under the 12:8°C temperature regime compared with those grown at 20:8°C. Furthermore, when calculated from a base temperature of 5°C, the number of degree-days needed to initiate aspen suckers was not different across the temperature regimes. In the second study, CaSO4, NH4NO3, or distilled water was added to aspen root sections. While nutrients did not affect the number of suckers produced, the addition of CaSO4 or NH4NO3 significantly increased sucker dry mass. Nutrient addition appeared to stimulate sucker growth and mobilization of stored reserves to support this growth.
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