Biology subjects

Estera-Molina, K.

Publications and source records attributed to Estera-Molina, K..

3 recordsLinked to original sources

bioRxiv2022

Divergent microbial traits influence the transformation of living versus dead root inputs to soil carbon

Soil microorganisms influence the global carbon cycle by transforming plant inputs into soil organic carbon (SOC), but the microbial traits that facilitate this process are unresolved. While current theory and biogeochemical models suggest microbial carbon-use efficiency and growth rate are positive predictors of SOC, recent observations demonstrate these relationships can be positive, negative, or neutral. To parse these contradictory effects, we used a 13C-labeling experiment to test whether different microbial traits influenced the transformation of plant C into SOC within the microbial habitats surrounding living root inputs (rhizosphere) versus decaying root litter (detritusphere), under both normal soil moisture and droughted conditions. In the rhizosphere, bacterial-dominated communities with fast growth, high carbon-use efficiency, and high production of extracellular polymeric substances formed microbial-derived SOC under normal moisture conditions. However, in the detritusphere - and the rhizosphere under drought - more fungal-dominated communities with slower growth but higher exoenzyme activity formed plant-derived SOC. These findings emphasize that microbial traits linked with SOC accrual are not universal, but contingent on how microorganisms allocate carbon under different resource conditions and environmental stressors.

ecology↗

bioRxiv2022

Spatial turnover of soil viral populations and genotypes overlain by cohesive responses to moisture in grasslands

Although soil viral abundance, diversity, and potential roles in microbial community dynamics and biogeochemical cycling are beginning to be appreciated1-5, little is known about the patterns and drivers of soil viral community composition that underlie their contributions to terrestrial ecology. Here, we analyzed 43 soil viromes from a precipitation manipulation experiment in a Mediterranean grassland in California, USA. We recovered 5,315 viral population sequences (vOTUs), and viral community composition exhibited a highly significant distance-decay relationship within the 18 m long field. This pattern was recapitulated in the microheterogeneity of 130 prevalent vOTUs (detected in >=90% of the viromes), which tended to exhibit significant negative correlations between genomic similarity of their predominant allelic variants and distance. Although spatial turnover was also observed in the bacterial and archaeal communities from the same soils, the signal was dampened relative to the viromes, suggesting differences in assembly drivers at local scales for viruses and their microbial hosts and/or differences in the temporal scales captured by viromes and total DNA. Despite the overwhelming spatial signal, vOTUs responsive to a decrease in soil moisture were significantly enriched in a predicted protein-sharing subnetwork of 326 vOTUs linked to 191 known actinobacteriophages, suggesting a genomically cohesive viral response to soil moisture evocative of environmental filtering, potentially by way of actinobacterial hosts. Overall, soil viral ecological processes appear to be highly constrained in space and tightly coupled to the heterogeneous, dynamic soil environment and thus fundamentally different from those of their well-mixed and more thoroughly studied marine counterparts.

microbiology↗

bioRxiv2021

Belowground allocation and dynamics of recently fixed plant carbon in a California annual grassland soil

Plant roots and the organisms that surround them are a primary source for stabilized organic C, particularly in grassland soils, which have a large capacity to store organic carbon belowground. To quantify the flow and fate of plant fixed carbon (C) in a Northern California annual grassland, we tracked plant carbon from a five-day 13CO2 pulse field labeling for the following two years. Soil and plant samples were collected immediately after the pulse labeling, and again at three days, four weeks, six months, one year, and two years. Soil organic matter was fractionated using a sodium polytungstate density gradient to separate the free-light fraction (FLF), occluded-light fraction (OLF), and heavy fraction (HF). Using isotope ratio mass spectrometry, we measured 13C enrichment and total C content for plant shoots, roots, soil, soil dissolved organic carbon (DOC), and the FLF, OLF, and HF. The HF was further analyzed by solid state 13C NMR spectroscopy. At the end of the labeling period, the largest amount of 13C was recovered in plant shoots (60%), but a substantial amount (40%) was already found belowground in roots, soil, and soil DOC. Density fractionation of 4-week soil samples (from which living roots were removed) indicated that the highest isotope enrichment was in the mineral-rich heavy fraction, with similar enrichment of the FLF and OLF. At the 6-month sampling, after the dry summer period during which plants senesced and died, the amount of label in the FLF increased such that it was equal to that in the HF. By the 1-year sampling, 13C in the FLF had declined substantially and continued to decline by the 2-year sampling. 13C recovery in the OLF and HF, however, was qualitatively stable between sampling times. By the end of the 2-year experiment, 69% of remaining label was in the HF, 18% in the FLF and 13% in the OLF. While the total 13C content of the HF did not change significantly from the 4-week to the 2-year sample time, 13C NMR spectroscopic analysis of spring HF samples from 2018, 2019, and 2020 suggests that the relative proportion of aliphatic/alkyl functional groups declined in the newly formed SOC over the 2-year period. Simultaneously, aromatic and carbonyl functional groups increased, and the proportion of carbohydrate groups remained relatively constant. In summary, our results indicate that initial associations between minerals and root-derived organic matter are significant and form rapidly; by 4 weeks, a substantial amount (17%) of the total plant-derived 13C had become associated with the heavy fraction (HF) of soil. While the majority of annual C input cycles rapidly (<2-year timescale), a sizeable proportion ([~]12% of the original inputs) persisted for 2 years.

biochemistry↗