• Energy Research

AbstractIncreased human activity and climate change are driving numerous tree species to endangered status, and in the worst cases extinction. Here we examine the genomic signatures of the critically endangered ironwood treeOstrya rehderianaand its widespread congenerO. chinensis. Both species have similar demographic histories prior to the Last Glacial Maximum (LGM); however, the effective population size ofO. rehderianacontinued to decrease through the last 10,000 years, whereasO. chinensisrecovered to Pre-LGM numbers.O. rehderianaaccumulated more deleterious mutations, but purged more severely deleterious recessive variations than inO. chinensis. This purging and the gradually reduced inbreeding depression together may have mitigated extinction and contributed to the possible future survival of the outcrossingO. rehderiana. Our findings provide critical insights into the evolutionary history of population collapse and the potential for future recovery of the endangered trees.

AbstractAlthough genetic diversity is very important for alien species, which have to cope with new environments, little is known about the role that genetic diversity plays in their invasive success. In this study, we set up a manipulation experiment including three levels of genotypic diversity to test whether genotypic diversity can enhance the invasive ability of alien species, in our case the invasive Spartina alterniflora in China, and to infer the underlying mechanisms. There was no significant relationship between genotypic diversity and parameters of performance in the first year; however, from the summer of the second year onwards, genotypic diversity enhanced four of the six parameters of performance. After two growing seasons, there were significant positive relationships between genotypic diversity and maximum spread distance, patch size, shoot number per patch, and aboveground biomass. Moreover, abundance of the native dominant species Scirpus mariqueter was marginally significantly decreased with genotypic diversity of S. alterniflora, suggesting that enhanced invasive ability of S. alterniflora may have depressed the growth of the native species. There was no significant difference in most measures of performance among six genotypes, but we observed a transgressive over performance in four measures in multiple‐genotype patches. At the end of the experiment, there were significant nonadditive effects of genotypic diversity according to Monte Carlo permutations, in six‐genotype, but not three‐genotype plots. Our results indicated that both additive and nonadditive effects played roles in the positive relationship between genetic diversity and invasion success, and nonadditive effects were stronger as duration increased.

Summary At local spatial scales, loss of genetic diversity within species can lead to species loss. Few studies, however, have examined plant genotypic diversity effects across trophic levels. We investigated genotypic diversity effects of Phragmites australis on belowground biomass and soil nematode communities. Our results revealed that belowground plant biomass and nematode abundance responses to plant genotypic diversity were uncoupled. Decreasing plant genotypic diversity decreased the abundance of lower, but not higher trophic level nematodes. Low plant genotypic diversity also decreased the structural footprint and functional indices of nematodes, indicating lowered metabolic functioning of higher trophic level nematodes and decreased soil food web stability. Our study suggests that plant genotypic diversity effects differ across trophic levels, taxonomic groups and ecosystem functions and that decreasing plant genotypic diversity could destabilise belowground food webs. This highlights the importance of conserving intraspecific plant diversity.

Tree diversity improves forest productivity Experimental studies in grasslands have shown that the loss of species has negative consequences for ecosystem functioning. Is the same true for forests? Huang et al. report the first results from a large biodiversity experiment in a subtropical forest in China. The study combines many replicates, realistic tree densities, and large plot sizes with a wide range of species richness levels. After 8 years of the experiment, the findings suggest strong positive effects of tree diversity on forest productivity and carbon accumulation. Thus, changing from monocultures to more mixed forests could benefit both restoration of biodiversity and mitigation of climate change. Science , this issue p. 80