Biochar and compost effects on soil microbial communities and nitrogen induced respiration in turfgrass soils

Abstract

We examined the effect of a labile soil amendment, compost, and recalcitrant biochar on soil microbial community structure, diversity, and activity during turfgrass establishment. Two application rates of biochar (B1 at 12.5 t ha-1and B2 at 25 t ha-1), a 5 centimeter (cm) green waste compost treatment (CM) in top soil, a treatment with 12.5 t ha-1 biochar and 5 cm compost (B1+CM), and an unamended control (CK) treatment were prepared and seeded with tall fescue. Overall, results of phospholipid fatty acid analysis (PLFA) profiling and Illumina high-throughput sequencing of 16S rRNA genes amplified from soil DNA revealed significant shifts in microbial community structures in the compost amended soils whereas in biochar amended soils communities were more similar to the control, unamended soil. Similarly, increases in enzymatic rates (6-56%) and nitrogen-induced respiration (94%) were all largest in compost amended soils, with biochar amended soils exhibiting similar patterns to the control soils. Both biochar and compost amendments impacted microbial community structures and functions, but compost amendment, whether applied alone or co-applied with biochar, exhibited the strongest shifts in the microbial community metrics examined. Our results suggest application of compost to soils in need of microbiome change (reclamation projects) or biochar when the microbiome is functioning and long-term goals such as carbon sequestration are more desirable.

Fig 1. Nonmetric multidimensional scaling (NMDS) based on Bray-Curtis community dissimilarity revealed that bacterial/ archaeal community compositions in compost amended soils were most dissimilar to the unamended CK soil.

Treatments include unamended control (CK), 12.5 t ha^-1 biochar (B1), 25 t ha^-1 biochar (B2), 5 centimeter (cm) green waste compost (CM), and 12.5 t ha^-1 biochar and 5 cm compost (B1+CM).

Fig 2. Bacterial/ archaeal community α-diversity based on Shannon indices indicated that the low biochar treatment (B1) significantly reduced community diversity compared to the control (Holm-Sidak, P < 0.05).

Treatments include unamended control (CK), 12.5 t ha^-1 biochar (B1), 25 t ha^-1 biochar (B2), 5 centimeter (cm) green waste compost (CM), and 12.5 t ha^-1 biochar and 5 cm compost (B1+CM).

Fig 3. Heatmap depicting the dominant bacterial phyla (A) and classes (B) in the turfgrass plot soils.

♦ symbols identify classes that were important in delineating the soil treatments (presence or absence of biochar or compost) based on Random Forest analyses (%MSE in upper 25% range). Treatments include unamended control (CK), 12.5 t ha^-1 biochar (B1), 25 t ha^-1 biochar (B2), 5 centimeter (cm) green waste compost (CM), and 12.5 t ha^-1 biochar and 5 cm compost (B1+CM).

Fig 4. Urease (UA), dehydrogenase (DHA) and β-glucosidase activity (BGA) in soils was influenced by biochar and compost application (P < 0.05).

Treatments include unamended control (CK), 12.5 t ha^-1 biochar (B1), 25 t ha^-1 biochar (B2), 5 centimeter (cm) green waste compost (CM), and 12.5 t ha^-1 biochar and 5 cm compost (B1+CM).

Fig 5. Nitrogen enhanced substrate induced respiration in soils from turfgrass plots with 0N, 50N, and 100N added via urea.

Soil treatments included unamended control (CK), 12.5 t ha^-1 biochar (B1), 25 t ha^-1 biochar (B2), compost (CM), and 12.5 t ha^-1 biochar with compost (B1+CM).

Fig 6. Canonical correspondence analyses revealed associations between soil physical, chemical, and biological properties in turfgrass soils with and without compost and biochar amendments.

(a) compares soil properties, PLFA-based microbial groups and enzyme activities (b) compares PLFA-based microbial groups, enzyme activity and nitrogen stimulated-substrate induced respiration (SIR).