Plant species and nitrogen effects on soil biological properties of temperate upland grasslands

Abstract

Summary 1.The aim was to assess the extent to which the microbial biomass and activity, and community structure of fertilized upland grasslands are directly related to changes in soil N availability or indirectly related to individual plant species effects caused by changes in plant species composition and dominance. We investigated the short-term interactive effects of dominant plant species (Lolium perenne, Agrostis capillaris, Holcus lanatus and Festuca rubra) and nitrogen (N) amendment using an N-limited upland grassland soil. 2. In soils planted with different grass species, soil microbial biomass, and to some extent microbial activity, were determined by temporal changes in plant productivity. Variations in the way that individual plants influenced soil microbial biomass and activity were highly inconsistent over time, and largely independent of N-additions and differences in plant productivity. At the final sample date, those grass species which co-dominate the total plant biomass of intermediate fertility (H. lanatus) and semi-improved grasslands (A. capillaris and F. rubra) had a beneficial effect on the soil microbial biomass. In contrast, the dominant plant species of improved grasslands, L. perenne, had zero or a negative effect on soil microbial biomass. Two plant species (A. capillaris and H. lanatus) increased the proportion of fungi relative to bacteria in the soil microbial community, relative to the unplanted control soil and the other plant species. Lolium perenne and A. capillaris reduced the evenness of microbial PLFAs, suggesting negative effects of these plant species on the diversity of the soil microbial community. 3. The addition of N had no consistent effect on measures of soil microbial biomass or activity, but significantly altered the structure of the microbial community in favour of fungi. The lack of effects of N-addition on microbial biomass and activity were despite the finding that nitrogen addition reduced root biomass in all plant species and increased rhizosphere acidity. 4. The results suggest that in the short term, the abundance and activity of soil microorganisms in upland grasslands are regulated more by plant species traits than by a direct effect of nitrogen. These effects are likely to be related to variations amongst plant species in root exudation patterns and/or efficiency of nutrient aquisition. 5. Our study provides evidence that the functional characteristics of dominant plant species are important determinants of soil biological properties, and hence ecosystem functioning in temperate upland grasslands.

Effect of nitrogen fertilizer on nitrogen pools and soil communities under grazed pastures

“…The bacterial community structure (and nitrifier activity) can respond rapidly to changes in management, such as increased grazing and additions of animal urine (Le Roux et al 2008;Rooney & Clipson 2008;Singh et al 2009;Di et al 2010). The actinomycetes (a group of gram' bacteria) measured by PLFA were higher at HFC (P 00.01) and this is generally consistent with other studies showing that gram' bacteria often increase with increased intensity of grazing (Bardgett et al 1999;Klumpp et al 2009). Di et al (2009), however, suggested that AOA do not increase with N, but in our study there were significantly higher numbers of both AOA and AOB at HFC compared with LFC.…”

“…This is higher than with other studies showing that fungi and fungal-feeding organisms are often reduced when soil N fertility and recycling increases (Coleman et al 1983;Bardgett et al 1999;De Vries et al 2006, 2007Lauber et al 2008;Krumins et al 2009). The mechanism is unknown but both are direct effects of fertilizer itself, and changes in the plant community and litter associated with fertilizers could be involved (Donnison et al 2000;Manning et al 2006).…”

“…Email: parfittr@landcareresearch.co.nz substrates that lead to a high diversity of soil biota (Bardgett et al 1999;Wardle 2006;Parfitt et al 2010). Although pasture production and quality improve with N fertilizer, below-ground diversity may decrease as the quantity and quality of litter entering the soil food web changes (Donnison et al 2000).…”

“…In grassland soils, both the bacterial and fungal communities may experience a reduction in diversity in response to N fertilizer (Kennedy et al 2004(Kennedy et al , 2005. Further, both soil microbial biomass and the soil fungal:bacterial ratio generally decrease with N fertilizer, (Bardgett et al 1999Grayston et al 2001).…”

Soil Microbial Community Changes in Wooded Mountain Pastures due to Simulated Effects of Cattle Grazing

“…Cattle have, for example, preferred resting and dunging areas, which may be different from their preferred grazing areas (Bokdam and Gleichman, 2000). In addition, the field studies compared existing situations with little control over the fields and independent variables (pseudoexperiment) (e.g., Bardgett et al, 2001;Donnison et al, 2000;Grayston et al, 2004) and microcosms were usually used in experiments (e.g., Bardgett et al, 1999;Jordan et al, 2003). Only a few studies used controlled field experiments (Clegg et al, 2003;Harrison and Bardgett, 2004;Wardle et al, 1999;Williams et al, 2000).…”