Nitrogen fertilization has minimal influence on rhizosphere effects of smooth crabgrass (Digitaria ischaemum) and bermudagrass (Cynodon dactylon)

doi:10.1093/jpe/rtu034

Abstract

Abstract: Aims Plants generally respond to nitrogen (N) fertilization with increased growth, but N addition can also suppress rhizosphere effects, which consequently alters soil processes. We quantified the influence of N addition on rhizosphere effects of two C₄ grasses: smooth crabgrass (Digitaria ischaemum) and bermudagrass (Cynodon dactylon).
Methods Plants were grown in nutrient-poor soil for 80 days with either 20 or 120 μg NH 4 NO 3 -N g dry soil^-1. N mineralization rates, microbial biomass, extracellular enzyme activities and bacterial community structure were measured on both rhizosphere and bulk (unplanted) soils after plant harvest.
Important findings Fertilization showed nominal differences in net N mineralization, extracellular enzyme activity and microbial biomass between the rhizosphere and bulk soils, indicating minimal influence of N on rhizosphere effects. Instead, the presence of plant roots showed the strongest impact (up to 80%) on rates of net N mineralization and activities of three soil enzymes indicative of N release from organic matter. Principal component analysis of terminal restriction fragment length polymorphism (T-RFLP) also reflected these trends by highlighting the importance of plant roots in structuring the soil bacterial community, followed by plant species and N fertilization (to a minor extent). Overall, the results indicate minor contributions of short-term N fertilization to changes in the magnitude of rhizosphere effects for both grass species.

Key words: rhizosphere effect, N fertilization, belowground carbon allocation, microbial biomass, extracellular enzyme, net N mineralization, microbial community composition

摘要：
Aims Plants generally respond to nitrogen (N) fertilization with increased growth, but N addition can also suppress rhizosphere effects, which consequently alters soil processes. We quantified the influence of N addition on rhizosphere effects of two C₄ grasses: smooth crabgrass (Digitaria ischaemum) and bermudagrass (Cynodon dactylon).
Methods Plants were grown in nutrient-poor soil for 80 days with either 20 or 120 μg NH 4 NO 3 -N g dry soil^-1. N mineralization rates, microbial biomass, extracellular enzyme activities and bacterial community structure were measured on both rhizosphere and bulk (unplanted) soils after plant harvest.
Important findings Fertilization showed nominal differences in net N mineralization, extracellular enzyme activity and microbial biomass between the rhizosphere and bulk soils, indicating minimal influence of N on rhizosphere effects. Instead, the presence of plant roots showed the strongest impact (up to 80%) on rates of net N mineralization and activities of three soil enzymes indicative of N release from organic matter. Principal component analysis of terminal restriction fragment length polymorphism (T-RFLP) also reflected these trends by highlighting the importance of plant roots in structuring the soil bacterial community, followed by plant species and N fertilization (to a minor extent). Overall, the results indicate minor contributions of short-term N fertilization to changes in the magnitude of rhizosphere effects for both grass species.

Biao Zhu, Kevin Panke-Buisse, Jenny Kao-Kniffin. Nitrogen fertilization has minimal influence on rhizosphere effects of smooth crabgrass (Digitaria ischaemum) and bermudagrass (Cynodon dactylon)[J]. J Plant Ecol, 2015, 8(4): 390-400.

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