The interior climate and its microclimatic variation of temperate forests in Northern Patagonia, Argentina.

Knowledge on mesoclimatic zonation and microclimatic variations within mountain forest ecosystems is crucial for understanding regional species turnover and effects of climate change on these systems. The temperate mountain forests in the Andean region of South America are among the largest and contiguous natural deciduous forest areas in the world. Due to their pronounced disturbance regime and different successional stages, a climatic zonation combined with the characterisation of its microclimatic variation is important to identify thresholds of species occurrences.We used micro-loggers to measure air temperature and relative humidity for one year at 40 measurement locations along longitudinal and elevation gradients in mountain forests in Northern Patagonia, Argentina. Our results unveil mesoclimatic patterns within these forests characterised by variations in temperature and vapour pressure deficit along the elevational gradient in general, but also at different times of the year. For example, Austrocedrus chilensis and Nothofagus dombeyi forests differed mainly by temperature and its diurnal range in the warmest months of the year. Also, differences between forest stands and gaps were more pronounced in the warmest months of the year and at lower elevations, with up to 2.5 K higher temperatures in the second half of the day in gaps. We found clear indications that shrubland of Nothofagus antarctica representing a successional stage after disturbances alters the mesoclimatic pattern, favouring forest fire ignition. Such mesoclimatic variations have a major influence on tree species turnover and ecological processes within these forest ecosystems.The findings contribute to our understanding of the complex interplay between topography, climate, and vegetation in shaping the spatial patterns of species occurrences.

Detection of swainsonine-producing endophytes in Patagonian Astragalus species.

Swainsonine has been identified as the toxin in legumes belonging to the genera Astragalus and Oxytropis throughout the world including China, North America, and South America. Several South American Astragalus species have been reported to contain swainsonine; however, data is lacking to support the presence of a fungal symbiont in South American Astragalus species as has been shown for North American and Chinese Astragalus and Oxytropis species. The objective of this study was to investigate several South American species that have been reported to contain swainsonine for the presence of the fungal symbiont using culturing and PCR. Swainsonine was detected in field collections of A. pehuenches, A. illinii and A. chamissonis but not A. moyanoi, which is consistent with reports of toxicity regarding these species. The symbiont Alternaria section Undifilum was detected by PCR in all three species that contained swainsonine but not in A. moyanoi. A fungal symbiont was isolated from seeds of Astragalus pehuenches and A. illinii. The isolated symbiont from both respective species produced swainsonine in vitro, and was demonstrated to belong to the genus Alternaria section Undifilum by analysis of the nuclear ribosomal DNA. It is highly likely that Alternaria section Undifilum isolates will be associated with other South American Astragalus species that are reported to contain swainsonine.