Extremely low fine root biomass in Larix sibirica forests at the southern drought limit of the boreal forest

Mongolia's Larix sibirica forests at the southern fringe of the Eurosiberian boreal forest belt are exposed not only to very low winter temperatures, but also to frequent summer droughts. It is not completely known how Siberian larch adapts to these stressors. We examined whether (i) these forests differ in their fine root bio- and necromass from more humid boreal forests further in the North and (ii) inter-annual fluctuations in fine root biomass are related to tree vitality. In two exceptionally dry summers, we found only 4–5 g DM m^?2 of fine root biomass (in 0–20 cm depth), which is far less than typical conifer fine root biomass figures from boreal forests (c. 200–400 g m^?2) and the lowest forest fine root biomass reported worldwide; in a moist summer, fine root biomass was 20 fold higher. In contrast to fine root biomass, both necromass and non-tree root mass were high in all three years. From the large increase of fine root biomass in the moist summer and the generally high root necromass, we conclude that drought-induced fine root dieback was the likely cause of the very small amount of live root mass in the dry summers. Larch fine roots seem to be more drought-sensitive than shoots, since marked needle loss did not occur under the extreme conditions.     

Effects of invasive alien kahili ginger (Hedychium gardnerianum) on native plant species regeneration in a Hawaiian rainforest

Questions: Does the invasive alien Hedychium gardnerianum (1) replace native understory species, (2) suppress natural regeneration of native plant species, (3) increase the invasiveness of other non‐native plants and (4) are native forests are able to recover after removal of H. gardnerianum. Location: A mature rainforest in Hawai'i Volcanoes National Park on the island of Hawai'i (about 1200 m a.s.l.; precipitation approximately 2770 mm yr^?1). Study sites included natural plots without effects of alien plants, ginger plots with a H. gardnerianum‐dominated herb layer and cleared plots treated with herbicide to remove alien plants. Methods: Counting mature trees, saplings and seedlings of native and alien plant species. Using non‐parametric H‐tests to compare impact of H. gardnerianum on the structure of different sites. Results: Results confirmed the hypothesis that H. gardnerianum has negative effects on natural forest dynamics. Lower numbers of native tree seedlings and saplings were found on ginger‐dominated plots. Furthermore, H. gardnerianum did not show negative effects on the invasive alien tree species Psidium cattleianum. Conclusions: This study reveals that where dominance of H. gardnerianum persists, regeneration of the forest by native species will be inhibited. Furthermore, these areas might experience invasion by P. cattleianum, resulting in displacement of native canopy species in the future, leading to a change in forest structure and loss of other species dependent on natural rainforest, such as endemic birds. However, if H. gardnerianum is removed the native Hawaiian forest is likely to regenerate and regain its natural structure.     

Is Mundulla Yellows really a threat to undisturbed native vegetation? A comment

The term Mundulla Yellows (MY) was coined in 1997 to refer to a dieback disorder involving leaf chlorosis which affects Eucalyptus and other native southern Australian vascular plants. It was thought to be a new, spreading, contagious biotic disease with the potential to devastate native vegetation. Since then, research has found no evidence to confirm any role of biotic agents and generally the disorder has been more convincingly attributed to abiotic soil factors. It has now been suggested that most or all of the reported cases of MY are simply the very well‐known nutrient disorder of alkaline soils, lime‐induced chlorosis. All of the well‐documented records of MY are from sites where acidic soils have become more alkaline because of the use of crushed limestone in road‐making or to the use of alkaline irrigation water; none are from undisturbed native vegetation. Despite this research and much circumstantial evidence, the view that MY poses a grave risk to undisturbed vegetation still persists and needs to be corrected accordingly.     

Antifungal and Insecticidal Activities of Selected Plant Species from Cloud Forest of Veracruz,Mexico: A Contribution to the Search of Novel Control Agents against Ambrosia Pest Complexes

The antifungal and insecticidal activities of 34 extracts from 27 plant species were evaluated against fungal phytopathogens of the genus Fusarium and Xyleborus Scolytine ambrosia beetles involved in Fusarium dieback (FD) and laurel wilt (LW) diseases. Sixteen extracts caused mycelial growth inhibition (MGI) above 23 % at 2 mg mL⁻¹ against F. solani, those from S. nudum and M. argyrophylla exhibited the highest MGI (57 % and 49 %, respectively). Thirteen extracts displayed significant antifungal activity against F. kuroshium, those from C. nocturnum and M. argyrophylla exhibited the highest MGI (100 % and 54.9 %, respectively). Additionally, ten plants extracts caused mortality in at least one of the beetle species tested, mainly from Solanaceae species. In the most active species, 39 phenolics were identified that may have contributed to their biological effects. This study is one of the first to report the potential of plant-derived natural products against the causative agents of FD and LW.     

Defining the twig fungal communities of Fraxinus species and Fraxinus excelsior genotypes with differences in susceptibility to ash dieback

Ash dieback disease (caused by Hymenoscyphus fraxineus) has affected European ash species (Fraxinus spp.) in recent decades. However, some Asian and American species of Fraxinus and certain genotypes of Fraxinus excelsior are less affected by the disease. We used ITS1-metabacoding to explore the drivers influencing diversity and composition of the twig fungal communities of Fraxinus species and F. excelsior genotypes. Our results revealed that fungi in the classes Eurotiomycetes and Dothideomycetes were among the most prevalent taxa in both Fraxinus species and F. excelsior genotypes. The diversity of the fungal communities differed significantly among Fraxinus species and could be explained by seed origin. Neither host genotype nor season had a significant effect on the community diversity of F. excelsior genotypes. On the other hand, the composition of twig fungal communities differed significantly among host species and among F. excelsior genotypes, and in F. excelsior there was also a significant effect of season on the composition of the fungal community. We did not find a clear effect of ash dieback susceptibility on either diversity or composition of fungal communities in twigs of Fraxinus species, although the effect was significant on the composition of fungal communities among F. excelsior genotypes. Our results demonstrated differences in fungal communities among species of Fraxinus and of F. excelsior genotypes, suggesting specific relationship between individual host genotypes and endophytic fungi.