Summary• Specific orchid-fungal associations are known for nonphotosynthetic orchids but fungal diversity in photosynthetic orchids is thought to be quite broad. Specific fungal associations will figure prominently in conservation efforts, while diverse associations may require less attention. We combined culture techniques with ITS and mtLSU sequences and phylogenetic analysis to determine the genetic diversity of mycorrhizal fungi associated with an evergreen, a spring-green, and a winter-green orchid and compared this diversity with that published for a nonphotosynthetic orchid.• Mycorrhizal diversity in two of the three photosynthetic orchids was lower than for the nonphotosynthetic orchid. Mycorrhizal diversity in protocorms of the third species was also equal to, or less than, the fungal diversity associated with the nonphotosynthetic species, but adult fungal diversity was greater.• We found that photosynthetic orchids do not necessarily have more diverse mycorrhizal associations than nonphotosynthetic orchids. Similarly, evergreen orchids do not necessarily have greater mycorrhizal diversity than seasonally green orchids. Thus, orchid mycorrhizal diversity may not be determined by adult photosynthetic capacity.

Within-stand nutrient cycling is dependent on many factors, including primary productivity, nutrient-use efficiency, nutrient resorption, sclerophylly, decomposition, nutritional quality of plant tissue, and allocation to defense. The efficiency of these plantmediated processes depends on nutrient availability in the environment and inherent functional properties of plants. However, little is known about how nutrient availability will affect these processes in forested wetlands in the tropics. In a factorial experiment we fertilized 48 dwarfed Rhizophora mangle (red mangrove) trees along tidal-elevation and water-depth gradients at Twin Cays, a range of intertidal, peat-based offshore mangrove islands in Belize, Central America. Initial results indicated that phosphorus (P) deficiency is a major factor limiting primary productivity. Phosphorus-fertilized trees had a significant decrease in P-use efficiency and P-resorption efficiency, but a significant increase in nitrogen (N)-use efficiency and N-resorption efficiency in their leaves compared with controls and N-fertilized trees. Sclerophylly decreased dramatically in P-fertilized trees, while the nutritional quality of the plant tissue increased. Phosphorus fertilization did not affect P leaching from green leaves. We found no fertilizer effect on the decomposition rates of leaf tissue, possibly due to higher phenolic concentrations in the P-fertilized trees compared with controls and N-fertilized trees. However, belowground decomposition of cotton strips increased in the substrate associated with P-fertilized trees. Environmental conditions related to position along a tidal gradient may be as important as nutrients in controlling belowground decomposition.

Mycorrhizal fungi have substantial potential to influence plant distribution, especially in specialized orchids and mycoheterotrophic plants. However, little is known about environmental factors that influence the distribution of mycorrhizal fungi. Previous studies using seed packets have been unable to distinguish whether germination patterns resulted from the distribution of appropriate edaphic conditions or the distribution of host fungi, as these cannot be separated using seed packets alone. We used a combination of organic amendments, seed packets and molecular assessment of soil fungi required by three terrestrial orchid species to separate direct and indirect effects of fungi and environmental conditions on both seed germination and subsequent protocorm development. We found that locations with abundant mycorrhizal fungi were most likely to support seed germination and greater growth for all three orchids. Organic amendments affected germination primarily by affecting the abundance of appropriate mycorrhizal fungi. However, fungi associated with the three orchid species were affected differently by the organic amendments and by forest successional stage. The results of this study help contextualize the importance of fungal distribution and abundance to the population dynamics of plants with specific mycorrhizal requirements. Such phenomena may also be important for plants with more general mycorrhizal associations.

This study evaluated whether the development of immune-related adverse events in non-melanoma patients treated with programmed cell death 1 checkpoint inhibitors correlates with improved clinical outcomes. The results indicate that for a subset of patients, in particular those with low-grade immune-related adverse events, immune-related adverse events predicted for an improved response rate and longer time to next therapy or death.

The abundance and reproductive activity of orchids have been linked to variations in weather conditions, but few investigators have examined the relationships between orchid flowering dynamics and the distribution and abundance of mycorrhizal fungi. We quantified the abundance of flowering individuals of Corallorhiza odontorhiza, a mycoheterotrophic orchid, over a 14-year period and mapped the distribution of individuals in six of the 14 years. For two seasons, we conducted intensive and extensive studies of the mycorrhizal fungi that were associated with C. odontorhiza. The annual abundance of flowering plants was statistically related to growing-season precipitation and winter temperature, and the distribution of individuals within the study plot was related to the abundance and distribution of appropriate host fungi. We used DNA sequencing to identify ectomycorrhizal root tips that hosted Tomentella fungi that could potentially support C. odontorhiza. We found that Tomentella spp. were distributed throughout the study plot and on all ectomycorrhizal tree species, including in areas that have historically supported few or no orchids. However, there were fewer ectomycorrhizal trees, total ectomycorrhizal root tips, and root tips hosting Tomentella spp. in areas with few or no orchids compared to areas with abundant orchids. Furthermore, one Tomentella taxon dominated in C. odontorhiza rhizomes but was never found except immediately adjacent to C. odontorhiza plants. This suggests that abundance of flowering C. odontorhiza reflects both the presence of ''preferred'' taxa and abundance of appropriate host fungi associated with ectomycorrhizal roots. Results of this research provide the first indication that the relationship between plants and mycorrhizal fungi may be influenced by both the relative abundance of fungi that are sufficient to support orchid growth and by the presence of particular fungal types that are especially good at supporting orchid growth.

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