Drought memory expression varies across ecologically contrasting forest tree species

Trees may exhibit long-lasting morpho-physiological acclimation in response to drought (i.e. drought memory) throughout their extensive life cycles. This acclimation might be particularly crucial for seedlings and saplings due to their limited access to water. We studied the development of drought stress memory in seedlings of black walnut (Juglans nigra L.), western larch (Larix occidentalis Nutt.), and Douglas-fir ((Pseudotsuga menziesii var. menziesii (Mirb.) Franco) in response to controlled drought exposure during their germination year (drought priming). We evaluated the effects of drought priming under a second-year drought, focusing on changes in water uptake capacity and transpiration demand, biomass allocation to new roots and foliage, root architecture, and photosynthesis. Drought priming led to significant morpho-physiological responses in the new leaves and roots developed during the subsequent growing season drought. Western larch showed increased biomass allocation to roots, higher specific root length and root tips, and enhanced water uptake, while Douglas-fir exhibited earlier bud break, greater net photosynthesis, and increased foliage growth. In contrast, black walnut seedlings displayed no notable changes in biomass allocation or physiology. Our results also show that biomass allocation to new roots plays a crucial role in enhancing water uptake capacity and gas exchange during seedling establishment. These findings underscore the importance of drought memory for stress resistance in trees, influencing the capacity of forests to regenerate and respond to recurrent droughts and climate change. The formation and expression of drought memory, however, varied across species, highlighting the complexity of adaptive responses across different forest ecosystems

Overstory and understory resource competition variably influences conversion of introduced conifer plantations to native hardwoods

Restoration of native hardwood forests through tree planting may provide significant ecological and economic benefits, but reforestation in natural forests and afforestation on open field sites is challenging. Conversion of existing plantations of introduced conifers to hardwoods may provide an alternative opportunity for restoration. In the Midwest US, large areas of mature, introduced pine (Pinus spp.) plantations exist that have little economic and ecological value. These stands may provide ideal sites for planting of native hardwood species that have similar site preferences to pine. We sought to determine optimal management strategies for converting pine plantations by manipulating overstory canopy density and understory competition. We underplanted American chestnut (Castanea dentata (Marsh.) Borkh.) and northern red oak (Quercus rubra L.) seedlings in three overstory canopy treatments: control, shelterwood, and clearcut. Understory competition was either controlled or not through two growing seasons. After three growing seasons, oak performed best in the clearcut and chestnut in the shelterwood, reflecting variation in the species' shade tolerance. Chestnut height and root collar diameter (RCD) were double that of oak, and chestnut leaf N content increased with light availability while oak did not, which can be explained by the species' different adaptive strategies in biomass allocation. Both species had highest photosynthesis in the clearcut. Chestnut seedlings had significantly higher RCD in weeded clearcut and shelterwood plots, and oak in weeded clearcut plots. Weeding in the uncut control plots was ineffective because shade limited competition. Our results indicate that pine plantations offer suitable habitat for these hardwood species and provide insight regarding their growth strategies. Pine shelterwoods and clearcuts are each viable silvicultural conversion options for chestnut and oak if understory competition is controlled

Influence of root architectural development on Douglas-fir seedling morphology and physiology

A series of experiments were established to gain a better understanding of the extent to which Douglas-fir seeding root architecture may be manipulated and subsequent influences on seedling morphological and physiological development. The incorporation of amendments into nursery soils changed root architecture to some degree, but did not produce large differences in morphology at lifting or following two growing seasons under field-fertilized and non-fertilized conditions. The application of controlled-release fertilizers (CRF) to the planting hole, however, produced an interesting response in which aboveground growth was enhanced during the first field season but negatively affected thereafter. The resulting hypothesis was that drought stress was responsible for the growth reduction. To investigate rooting response to locally-applied CRF, two greenhouse experiments were established. In the first experiment, differences in seedling morphological and physiological development over time were observed under two comparable CRF types and this was attributed to variations in nutrient release. Roots proliferated in the soil zone above the locally-applied CRF, though root penetration into lower soil zones was not restricted. With increasing CRF rates in the second greenhouse experiment, however, root penetration into soil zones below the CRF decreased with increasing CRF rate six months following transplant (R2 = 0.72), likely due to the creation of a toxic osmotic gradient between rhizosphere and root. It was hypothesized that this response might intensify seedling drought stress following field fertilization. A field study investigated the influence of initial root volume and field fertilization at a relatively high rate on seedling drought resistance. Regardless of initial root volume, fertilized seedlings became more drought stressed during summer and had lower rates of stomatal conductance near the end of summer. An increase in shoot:root dry weight, which was greater for fertilized seedlings, was inversely correlated with xylem pressure potential (R2 = 0.54). There was no distinct proliferation of roots near the CRF layer as root growth in all vertical soil zones was negatively affected for fertilized seedlings

2009 Focused Updates: ACC/AHA Guidelines for the Management of Patients With ST-Elevation Myocardial Infarction (Updating the 2004 Guideline and 2007 Focused Update) and ACC/AHA/SCAI Guidelines on Percutaneous Coronary Intervention (Updating the 2005 Guideline and 2007 Focused Update)

Late-breaking clinical trials presented at the 2007 and 2008 annual scientific meetings of the ACC, AHA, Transcatheter Cardiovascular Therapeutics, the European Society of Cardiology, and the 2009 annual scientific sessions of the ACC were reviewed by the standing guideline writing committee along with the parent Task Force and other experts to identify those trials and other key data that may impact guideline recommendations. On the basis of the criteria/considerations noted above, recent trial data and other clinical information were considered important enough to prompt a focused update of the ACC/AHA 2004 Guidelines for the Management of Patients With ST-Elevation Myocardial Infarction and the ACC/AHA 2005 Guidelines for Percutaneous Coronary Intervention, inclusive of their respective 2007 focused updates (2–5)

Development of Douglas-fir seedling root architecture in response to localized nutrient supply

Three months following sowing, Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were transplanted into pots with controlled-release fertilizer (CRF) applied at rates of 0, 8, 16, and 24 g/2200 cm3 soil as a single uniform layer beneath the root system. Seedlings were destructively harvested periodically, and roots were divided into vertical segments above (S1), within (S2), and below (S3) the fertilizer layer. Two months following transplant, the number of active root tips was positively correlated with CRF rate in S1 and negatively correlated with rate in S2 and S3. At 6 months, root penetration into S3 was severely restricted at 16 and 24 g. This was attributed to detrimental changes in soil osmotic potential in S2. Fertilizer improved seedling growth at 8 g after 6 months compared with controls but was inhibitory at 24 g. Photochemical quantum yield was higher in all CRF treatments compared with controls 3 months following transplant, which corresponded with rapid initial CRF nutrient release. Despite improvements in nutrient release technology with CRF, high application rates may result in excessive concentrations of fertilizer nutrients in media, which can restrict root penetration and negatively affect seedling growth. Conservative application rates and improvements in CRF technology will help reduce the potential for adverse effects on seedling development

Effect of ethephon on hardening of Pachystroma longifolium seedlings

Immediately after planting, tree seedlings face adverse environmental and biotic stresses that must be overcome to ensure survival and to yield a desirable growth. Hardening practices in the nursery may help improve seedling stress resistance through reduction of aboveground plant tissues and increased root volume and biomass. We conducted an assay to quantify changes in the morphogenesis following application of ethephon on seedlings of Pachystroma longifolium (Ness) I. M. Johnst.during hardening. The results showed no effect of the ethephon treatments on the number of leaves but a reduction of up to 50% in seedling height increment, and an increase in stem diameter increment of up to 44% with the 600 mg L-1 ethephon treatment, which consequently altered seedling Dickson Quality Index. Our results indicate that ethephon may help to promote desired morphological changes that occur during seedling hardening in nurseries