Evidence plant phylogenetic dispersion increases soil respiration in a biodiversity manipulation experiment

While the relationship between biodiversity and aboveground productivity is well established, the role aboveground diversity and community composition plays in facilitating respiratory carbon losses from soil microbial communities remains less well understood. In a biodiversity manipulation experiment, we test the role of plant community composition and precipitation on soil respiration. Established spring 2018 at the University of Kansas field station (Jefferson Co., KS), we manipulated plant diversity, selecting 1, 2, 3, and 6 species, from 18 species in three families (Poacea, Asteracae, and Fabaceae). We manipulated phylogenetic dispersion in mixtures by randomly selecting species from the same or different families, totaling 240-2.25m² plots. Precipitation is altered to 50% and 150% of ambient conditions through rainfall manipulation shelters. Soils were harvested in fall 2018 for soil microbial analysis and sequenced for soil fungi, root bacteria, and root oomycetes. Soil respiration was measured from shallow collars with a Li-COR 8100A soil survey system monthly starting May 2020. Soil respiration significantly increases with precipitation in May, with both greater precipitation and richness in June, and with greater phylogenetic dispersion in July. Soil respiration likewise increases with plant cover, which is highly correlated with richness. We normalized soil respiration by total plant cover and included soil moisture as a covariate and found respiration decreased in all months with richness, though that relationship is leveraged by the large variation observed in lower diversity plots. Interestingly, cover normalized soil respiration did not correlate with soil moisture in any months, though its inclusion improved model fits. Accounting for both plant cover and soil moisture, in May and July greater plant phylogenetic dispersion increased soil respiration. In June greater precipitation increased cover normalized respiration. Soil microbial communities, specifically soil fungi, root bacteria, and root oomycetes, differentiate with plant family, some with dispersion, and some increasing in diversity with plant diversity. This suggests plant interactions with soil microbial communities may play a role in facilitating respiratory losses of carbon from soils.