Cavaleri, M. A. | Search bioRxiv

bioRxiv2024

Experimental Warming Alters Nitrogen Cycle in a Humid Tropical Forest

O_LIHumid tropical forests typically contain high soil nitrogen (N), supporting rapid rates of primary productivity and recovery from disturbances. Nitrogen fixation is regulated by microbial communities, which can be free-living in the soil and leaf litter (asymbiotic) or in symbioses with plants. C_LIO_LITo investigate how warming affects asymbiotic and symbiotic components of the N cycle, we analyzed soil and leaf litter samples as well as annual seedling census data from an experimental warming field site in Puerto Rico. C_LIO_LI16S and nifH sequencing revealed that warming significantly altered bacterial composition. Asymbiotic N fixation rates were 55% greater in soil (0.004 nmol N2/g/hr) and 525% greater (0.217 nmol N2/g/hr) in leaf litter from warmed compared to ambient plots. This increase in fixation was associated with changes in the N-fixing bacterial community. Under warming, N fixers experienced a 4.4-fold increase in growth rate compared to non-fixers, yet competition with neighboring N fixers eventually reduced N fixer growth. Seedling growth, especially of N fixers, initially increased following hurricane disturbances before declining. C_LIO_LITogether, our findings suggest that warming increases the flux of N from the atmosphere into this tropical forest, driving changes in both microbial and tree dynamics. C_LI

ecology↗

bioRxiv2024

Tropical Forest Soil Microbiome Modulates Leaf Heat Tolerance More Strongly Under Warming than Ambient Conditions

Tropical forests are increasingly threatened by climate change. Yet, it is still unclear how tropical plants respond to increasing temperatures. Leaf heat tolerance (LHT) in tropical plants is often at its upper limit, suggesting that climate change might negatively impact tropical forests. We hypothesized that intraspecific variation in this leaf trait might be associated with changes in the soil microbiome, which might also respond to climate. Specifically, we hypothesized that warming would increase LHT through changes in the soil microbiome: this study combined an in-situ tropical warming experiment with a shade house experiment in Puerto Rico. The shade house experiment consisted of growing seedlings of Guarea guidonia, a dominant forest species, under different soil microbiome treatments (reduced arbuscular mycorrhizal fungi, reduced plant pathogens, reduced microbes, and unaltered) and soil inoculum from the field experiment. Heat tolerance was determined using chlorophyll fluorescence (FV/Fm) on individual seedlings in the field and on pooled seedlings by pot in the shade house. We sequenced soil fungal DNA to analyze the impacts of the field and shade house treatments on the soil microbiome. In the field, seedlings from ambient temperature plots showed higher FV/Fm values under high temperatures (0.648 at 46 {degrees}C and 0.067 at 52 {degrees}C) than seedlings from the warming plots (0.535 at 46 {degrees}C and 0.031 at 52 {degrees}C). In the shade house, the soil microbiome treatments, which significantly influenced the fungal community composition, significantly influenced LHT. Reduction in fungal pathogen abundance and diversity altered FV/Fm before T50 for seedlings grown with soil inoculum from the warming plots but after T50 for seedlings grown with soil inoculum from the ambient plots. Our findings emphasize that the soil microbiome might play an important role in modulating the impacts of climate change on plants. Understanding and harnessing this relationship might be vital for mitigating the effects of warming on tropical forests, emphasizing the need for further research on microbial responses to climate change.

ecology↗