Research paperThe importance of plants to development and maintenance of soil structure, microbial communities and ecosystem functions

- Plants shaped the microbial community structure independent of tillage systems.
- Tillage changed the dynamics and quantity of the carbon input.
- Increased microbial biomass and metabolism was related to long-term system stability.

Soil ecosystem functions depend on the development, activity and maintenance of soil biology which in turn depends on plants because they add important carbon resources through litter fall, root exudates, mucilage and root remnants, and root activity for the aggregates formation. Correspondingly, our hypothesis was that maintaining high inputs of plant-derived carbon is important to the formation and stabilisation of soil structure, and this in-turn may support a greater diversity of habitats for microbial communities thereby ensuring more robust soil ecosystem function. To test this hypothesis we measured the physical, chemical and biological characteristics of soil from a long-term field trial. The trail was initiated in Spring 2000 on a silt loam soil (Udic Dystocrept, USDA) in Canterbury, New Zealand and includes a combination of crop and tillage treatments: permanent pasture [PP], permanent fallow [PF], rotation of barley, wheat and peas under intensive [Ii], minimum [Mm] and no tillage [Nn]. Soil aggregate profiles (size class, distribution, mean weight diameter - MWD), total organic carbon and nitrogen (TOC, and TN), along with metabolic and PLFA data were analysed using a multi-phase experimental design to investigate the effect of different plants and soil management practices on soil structure, microbial metabolic diversity and activity. The PP treatment had the most complex soil structure (MWD between 3.6 and 2.8 depending on depth) with 61% of aggregates in the 8.000 2.000 mm size class compared with PF (MDW between 1.8 and 0.5) that had only 14% of aggregates in this size class. There was strong evidence for maintenance of good soil structure within the no tillage treatment (Nn) which had higher proportions of the 8.000 2.000 mm aggregates (45%) compared to Mm (40%) and Ii (35%). Similar relationships were observed in TOC and TN data. PP had superior metabolic activity with approximately 5 μg CO2-C g−1 soil (dry weight) produced in the 0-7.5 cm depth for all C-source groups. These superior indicators of soil ecosystem function for PP was attributed to the lack of soil disturbance, continual supply of carbon and a stable microbial community with an enrichment of bacteria compared to fungi at the surface. We conclude that continuous growth of plants in combination with low soil disturbance promoted greater macroaggregate scale structure, added more carbon and promoted greater microbial biomass, metabolic diversity and capacity to execute soil ecosystem function.