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Paul Dijkstra

Publications and source records attributed to Paul Dijkstra.

3 recordsLinked to original sources
PubMed2026

Reduced legacy precipitation decreases microbial community growth efficiency and alters soil organic carbon in a California grassland.

BACKGROUND: Changes in global patterns can leave a lasting legacy in semiarid grasslands by reshaping microbial growth dynamics and carbon cycling during the first wet-up in the autumn-a period known for intense microbial activity and significant carbon emissions. To study the lasting impacts of decreased winter rain, we implemented two precipitation regimes (100% vs. 50% mean annual precipitation) in California Mediterranean-climate grassland field plots. After the dry season, soils were rewetted in the laboratory with H218O and sampled at 0 h, 3 h, 24 h, 48 h, 72 h, and 168 h post rewet. We quantified CO2 efflux, measured microbial growth and mortality via quantitative 18O stable isotope probing and 16S rRNA gene amplicon sequencing, and characterized the soil organic carbon chemical composition, metagenomes, and metatranscriptomes. RESULTS: We found that reduced winter precipitation imposed a strong legacy effect on microbial turnover; despite maintaining similar respiration rates, microbial growth declined by ~1 order of magnitude, yielding decreased community growth efficiency (CGE = new biomass growth/respiration), and microbial mortality declined by ~2 orders of magnitude. Soil organic carbon also shifted from lipid-like, amino-sugar-like, and protein-like compounds (indicative of microbial necromass) to more oxidized lignin-like and tannin-like compounds (indicative of decomposing plant-derived compounds). Meta-omics revealed distinct metabolic strategies linked to CGE. At high-CGE, microbes appeared to consume more energetically favorable N-rich necromass (released via high microbial turnover); this allowed for increased amino acids and peptidoglycan biosynthesis and greater aromatic compound degradation, fueling further energy production and growth efficiency. At low CGE, communities had elevated carbohydrate metabolism and lipid turnover, consistent with increased investment in plant detritus degradation and membrane repair and maintenance rather than growth. CONCLUSIONS: Together, our findings demonstrate that reduced winter rainfall decreases microbial turnover following rewetting without a concurrent reduction in CO2 emissions. This shift results in persistently lower CGE, which has the potential to increase soil carbon loss as CO2. If such conditions are maintained over multiple years, these changes could reshape soil organic carbon stocks and alter the balance of grassland ecosystems under future climate scenarios. While our data suggest that sustained reductions in CGE may drive SOC decline, the magnitude and persistence of these effects depend on long-term environmental dynamics and warrant further investigation. Video Abstract.

Soil Microbiology↗
PubMed2006

Nitrogen cycling during seven years of atmospheric CO2 enrichment in a scrub oak woodland.

Experimentally increasing atmospheric CO2 often stimulates plant growth and ecosystem carbon (C) uptake. Biogeochemical theory predicts that these initial responses will immobilize nitrogen (N) in plant biomass and soil organic matter, causing N availability to plants to decline, and reducing the long-term CO2-stimulation of C storage in N limited ecosystems. While many experiments have examined changes in N cycling in response to elevated CO2, empirical tests of this theoretical prediction are scarce. During seven years of postfire recovery in a scrub oak ecosystem, elevated CO2 initially increased plant N accumulation and plant uptake of tracer 15N, peaking after four years of CO2 enrichment. Between years four and seven, these responses to CO2 declined. Elevated CO2 also increased N and tracer 15N accumulation in the O horizon, and reduced 15N recovery in underlying mineral soil. These responses are consistent with progressive N limitation: the initial CO2 stimulation of plant growth immobilized N in plant biomass and in the O horizon, progressively reducing N availability to plants. Litterfall production (one measure of aboveground primary productivity) increased initially in response to elevated CO2, but the CO2 stimulation declined during years five through seven, concurrent with the accumulation of N in the O horizon and the apparent restriction of plant N availability. Yet, at the level of aboveground plant biomass (estimated by allometry), progressive N limitation was less apparent, initially because of increased N acquisition from soil and later because of reduced N concentration in biomass as N availability declined. Over this seven-year period, elevated CO2 caused a redistribution of N within the ecosystem, from mineral soils, to plants, to surface organic matter. In N limited ecosystems, such changes in N cycling are likely to reduce the response of plant production to elevated CO2.

Atmosphere↗