New England Wild Flower Society

The consequences of initial variability in reproductive effort on later pollination and fruit development have frequently been investigated with flower removal experiments. Often, plants produce many fewer fruits than flowers, so flower removal might not be expected to alter subsequent growth or development patterns all that much. Yet, many studies have demonstrated such changes even for species with low average fruit set, which begs for an explanation. Many (at least seven, by our count) such explanations have been reported in the literature, but experimental support for most is limited. In summer 2014, we conducted a field experiment on a lowbush blueberry (Vaccinium angustifolium) farm in Maine. In this experiment, we coupled flower removal with three other treatments, each designed to assess the validity of one of three often-cited hypotheses invoked to explain why growth and development changes occur following flower removal: 1) “Short-term nutrient shortages;” 2) “spatiotemporal limitations;” and 3) “the compound interest effect.” The three respective treatments—foliar nitrogen fertilization, positionally biased flower removal, and defoliation—were designed to either intensify or weaken the apparent effects of flower removal if the corresponding hypothesis had merit. As in a 2013 preliminary experiment, flower removal elicited several statistically significant growth and development changes in blueberry, including increases in final leaf area, ripe fruit weight, fruit ripening rate, and relative fruit production. The additional treatments also elicited several significant plant responses, though not always with concomitant flower removal effects as well. For example, fertilization generally increased fruit cluster mass by harvest, but flower removal itself had no such effect on cluster mass. Most observed interactive effects between flower removal and the additional treatments either ran counter to expectations, were limited in scope, or couldn't be unambiguously interpreted. For at least a few observed changes, none of the additional treatments significantly altered the effects of flower removal. We conclude that current hypotheses for the mechanistic basis for changes induced by flower removal are inadequate, at least for blueberry, a species with frequently low fruit set even when managed commercially. However, strong intellectual and economic imperatives exist to encourage further investigation into this open question.Plants grown in horticulture or occurring as adventives outside their native range can provide insight into species’ fundamental niche requirements that might not be evident from the native range, or realized niche, alone. Such occurrences can also identify conditions that support individual survival, but do not currently sustain positive population growth (i.e., a species’ ‘tolerance niche’). Further, in the context of rapid climate change, horticultural and adventive occurrences beyond current range edges might circumvent natural dispersal limitations and facilitate species range shifts. To explore these concepts in the field, we investigated the history and structure of five newly discovered populations of naturalized Magnolia tripetala near horticultural sites in western Massachusetts, USA. This tree species is native to the southeastern US, but has been grown horticulturally in the Northeast since the 1800s. However, naturalized populations had not been well documented in the region previously, raising the possibility that the species’ escape has been triggered by recent climate change. With tree coring and life stage surveys, we asked whether the naturalized populations exhibited synchronous patterns of establishment and expansion, suggestive of climatic release and a shift from tolerance niche to fundamental niche conditions in the region. Across the five sites, we documented 660 individuals, with populations ranging in size from 46 to 396 individuals, including seedlings, saplings, and reproduct

This is the second year of a comparative study examining soil and plant characteristics between mine sites that had not actively been reclaimed and early seral natural sites that had experienced some type of disturbance. Results from this study describe native plant species and communities potentially suitable for establishment on ecologically comparable mine sites, and long-term experiments will test their applications in mine reclamation. Thirty-four field plots were established in 2010, 14 of which were located on areas that had experienced some form of mining activity, and 20 on selected natural areas. A total of 239 plant species were recorded in 2010 field work, including 92 new species not seen in 2009. The total number of plant species recorded from 2009 and 2010 field work is 256, including 222 native species, 11 introduced species, 13 invasive species and eight agronomic species. This study has identified 88 species with high potential for use in reclamation, based on occurrence in reference plots, native versus non-native, and ease of seed collection and propagation. Native plant species were observed on a wide range of elevations, slopes and aspects, and mean biomass production ranged between 560–1,360 kg/ha. Soil sampling revealed a mean of 8.4 kg/ha N in non-reclaimed mine sites, and 13.8 kg/ha N on natural reference sites, which were closer than expected for the two site types. No relationships were found between either pH, EC or coarse fragment content and total cover, species distribution or species richness, confirming null hypotheses. Recommendations include the establishment of long-term trials that will investigate native plant installation techniques, native plant successional plantings, fungal inoculation, fertilisation, and specific seed collection efforts and or seed increase projects to facilitate these trials.

Introduction: Phytohormones, molecular biology, and the “real world” of early seedling ecology The seedling stage is arguably the busiest phase in a plant's lifetime. A miniscule individual, possessing only a rudimentary cotyledon and radicle, must quickly make its way in the world before a host of environmental challenges and larger competitors bully it out of existence. The maternal reserves from the seed must be mobilized to provide the fuel for producing the first pair of photosynthetically competent leaves and proliferating roots that will assimilate nutrients and firmly secure the seedling to its new home in the soil. These critical activities are initiated within minutes of germination, requiring a flurry of rapid signal transduction, protein synthesis, and tissue differentiation. To grasp how the seedling accomplishes all this demands an examination of physiological mechanisms that govern life after germination. Studies at the molecular level are making great headway in understanding the complex and fascinating physiological events that mark the early infancy of plants. Phytohormones (a broad term that encompasses a range of organic and polypeptide compounds) are increasingly recognized as the primary integrators of environmental signals that enable the nascent seedling to evaluate and adjust to existing conditions. Biologists working across the spectrum of organizational levels – from cells to trees, from genes to populations – are now in an exciting position to elucidate how phytohormones modulate phenotype, and seedlings from a variety of taxa are natural model systems for study and synthesis (Table 7.1).