We studied regional variation in growth-limiting factors and responses to climatic variability in subalpine forests by analyzing growth patterns for 28 tree-ring growth chronologies from subalpine fir (Abies lasiocarpa (Hook.) Nutt.) stands in the Cascade and Olympic Mountains (Washington and Oregon, U.S.A.). Factor analysis identified four distinct time series of common growth patterns; the dominant growth pattern at any site varied with annual precipitation and temperature (elevation). Throughout much of the region, growth is negatively correlated with winter precipitation and spring snowpack depth, indicating that growth is limited primarily by short growing seasons. On the driest and warmest sites, growth is negatively correlated with previous summer temperature, suggesting that low summer soil moisture limits growth. Growth patterns in two regions were sensitive to climatic variability associated with the Pacific Decadal Oscillation, apparently responding to low-frequency variation in spring snowpack and summer soil moisture (one negatively, one positively). This regional-scale analysis shows that subalpine fir growth in the Cascades and Olympics is limited by different climatic factors in different subregional climates. Climate-growth relationships are similar to those for a co-occurring species, mountain hemlock (Tsuga mertensiana (Bong.) Carrière), suggesting broad biogeographic patterns of response to climatic variability and change by subalpine forest ecosystems in the Pacific Northwest.Résumé : Les auteurs ont étudié la variation régionale des facteurs qui limitent la croissance et les réponses à la variabilité climatique de forêts subalpines en analysant les patrons de croissance de 28 séries dendrochronologiques établies à partir de peuplements de sapin subalpin (Abies lasiocarpa (Hook.) Nutt.) situés dans les Cascades et les monts Olympic (Washington et Oregon, États-Unis). Une analyse factorielle a identifié quatre séries temporelles distinctes de patrons de croissance communs; le patron de croissance dominant dans tous les sites varie en fonction de la précipitation annuelle et de la température (altitude). Dans la plus grande partie de la région, la croissance est négativement corrélée à la précipitation hivernale et à la hauteur de neige accumulée au printemps, ce qui indique que la croissance est surtout limitée par de courtes saisons de croissance. Dans les sites les plus chauds et les plus secs, la croissance est néga-tivement corrélée à la température de l'été précédent, indiquant qu'une faible quantité d'humidité dans le sol en été limite la croissance. Les patrons de croissance de deux régions sont sensibles aux variations climatiques associées à l'Oscillation Décennale du Pacifique, en répondant apparemment à la variation de basse fréquence de la couverture nivale au printemps et de l'humidité du sol en été (négativement dans un cas et positivement dans l'autre). Cette analyse à l'échelle régionale montre que la croissance du sapin subalpin dans les Cascades et les monts Olympic est limit...
SummarySustainable production of biomass for bioenergy relies on low-input crop production. Inoculation of bioenergy crops with plant growth-promoting endophytes has the potential to reduce fertilizer inputs through the enhancement of biological nitrogen fixation (BNF).Endophytes isolated from native poplar growing in nutrient-poor conditions were selected for a series of glasshouse and field trials designed to test the overall hypothesis that naturally occurring diazotrophic endophytes impart growth promotion of the host plants.Endophyte inoculations contributed to increased biomass over uninoculated control plants. This growth promotion was more pronounced with multi-strain consortia than with singlestrain inocula. Biological nitrogen fixation was estimated through 15 N isotope dilution to be 65% nitrogen derived from air (Ndfa). Phenotypic plasticity in biomass allocation and branch production observed as a result of endophyte inoculations may be useful in bioenergy crop breeding and engineering programs.
Growth response of subalpine fir {Abies lasiocarpa) to climate was studied across its local geographical and elevation range in the Olympic Mountains, Washington. A dendroecological analysis of subalpine fir across a range of elevations (1350-1850 m) and annual precipitation (125-350 cm y"^), was used to compare environmental factors affecting growth. Climate-growth relationships were explored using Pearson productmoment correlation coefficients; partial correlation analysis was used to assess relationships among site chronologies and climatic variables. Radial growth is negatively correlated with winter precipitation at high elevation and wet sites, but not at low and middle elevation dry sites. Growth is positively correlated with current growing season temperature at all sites; however, growth is negatively correlated with previous year August temperature, indicating that climate affects growth in subsequent years. Positive correlations between growth and summer precipitation during the growing season at low and middle elevation dry sites suggest that soil moisture is partially limiting to growth on these sites. If the climate of the Pacific Northwest becomes warmer and drier, then subalpine fir growth may increase at high elevation and wet sites, but may decrease at lower elevation dry sites in the Olympic Mountains. However, the growth response of subalpine fir to potentially rapid climate change will not be uniform because subalpine fir grows over a wide range of topographic features, habitats, and local climates at different geographical scales. A comparison of growth response to current growing season temperature suggests that the temperature-related growth response of subalpine fir is not adequately described by the parabolic curve used in JABOWAbased models.
Plants that grow and thrive under abiotic stress often do so with the help of endophytic microorganisms. Although nitrogen-fixing (diazotrophic) endophytes colonize many wild plants, these natural relationships may be disrupted in cultivated crop species where breeding and genotype selection often occur under conditions of intensive fertilization and irrigation. Many energy crops including corn may still benefit from diazotrophic endophyte inoculations allowing for more efficient biomass production with less input of petroleum-derived fertilizer. A selection of diazotrophic endophytes isolated from willow (Salix sitchensis, Sitka willow) and poplar (Populus trichocarpa, black cottonwood) growing in nutrient-poor river sides were used as inoculum in three experiments testing the effect on plant growth and leaf level physiology of a sweet corn variety under various levels of applied nitrogen fertilizer. We report substantial growth promotion with improved leaf physiology of corn plants in response to diazotrophic endophyte inoculations. Significant gains of early biomass with a greater root : shoot ratio were found for plants receiving endophytic inocula over the uninoculated control groups regardless of the nitrogen level. Furthermore, inoculated plants exhibited consistently higher rates of net CO 2 assimilation than did those without endophytic inoculation. These results have beneficial implications for enhanced plant growth in a low-input system on nutrient-poor sites. The immediate increase of root mass observed in endophyte inoculated plants has the potential to provide better establishment and early growth in resource-limited environments. The initial results of this study also indicate that the beneficial effect from endophytes isolated from poplar and willow species is not restricted to the species from which they were initially isolated.
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