Jennifer Carson. Profile

Transcription

1 Jennifer Carson Profile Jennifer grew up spending time on her uncle and aunt s market garden in Spearwood but never considered a career in. The possibility was first brought to her attention in first year uni when she saw Soil Science on the list of majors right above Wool Science and wondered who in earth majored in such obscure subjects. Four years later she graduated from the University of Western Australia with a Bachelor of Science majoring in Soil Biology. During university, Jennifer became interested in the challenge of increasing the sustainability of agriculture and in the possibility that organic farming might offer some solutions to this challenge. After university, she worked at Rick and Annie Dunn s organic market garden in Perth for 18 months before working as a laboratory assistant at UWA and then travelling overseas. On returning to Perth, Jennifer commenced a PhD at UWA with the Soil Biology Group which she has recently completed.

2 Influence of rock fertilisers on soil microorganisms in an organic pasture Jennifer Carson Prof Lynette Abbott & Dr Deirdre Gleeson

3 Outline Introduction: Soil microorganisms and rock fertilisers in organic farming Evidence that rock fertilisers may influence soil bacteria Experiments Rock fertilisers influence bacteria because of their: Composition Particle size Implications: Organic farming Rock fertilisers can alter structure of bacterial communities Soil biology Influence of soil minerals on bacterial communities underestimated

4 Introduction Microorganisms & rock fertilisers in organic farming Microbial processes improve soil fertility, but uncertain response to management Particularly important in organic farming Field trials in Australia Identify practices that improve soil conditions for microbial processes Potential of rock fertilisers Rock fertilisers Rock phosphate, basalt, mica, lime Often poorly effective due to slow dissolution Exception sandy soils with ph<5

5 Introduction Evidence rock fertilisers affect microorganisms Increase biomass & activity when increase plant biomass & soil ph In other habitats, composition of minerals affects microbes Rock fertilisers can alter particle & pore size distribution, but not linked to effect on microorganisms Hypothesise rock fertilisers affect microbial communities due to: Effect on plant growth & ph Composition Particle size

6 Composition Composition of rock fertilisers Soil is spatial heterogeneous: Microbes affected by properties of microhabitats Microhabitats differ in mineral composition & size Mineral composition affects bacteria in other habitats Different minerals colonised by distinct microbial communities Preferential colonisation of minerals containing nutrients hotspots of activity D Role of soil minerals overlooked Microbial community on stones different from soil stonesphere c

7 Composition Hypothesis: The microhabitats of different rock fertilisers in soil select distinct bacterial communities. Experimental design: 3 rock fertiliser treatments: mica, basalt and rock phosphate. 2 fraction treatments: rock fertilisers (>1 mm) & soil (<1 mm) 3 pasture treatments: T. subterraneum (clover), L. rigidum (ryegrass) and unplanted.

8 Composition Composition of soil & rock fertiliser differed % Composition of soil & rock fertilisers (XRF). P2O5 CaO K2O MgO SiO2 Soil Mica Basalt Rock P cm Picture mica grains here mica basalt rock phosphate With organic Organic matter matter removed

9 Composition Microcosm experiment mm grains rock fertilisers added to soil. 2. Incubate in soil 10 w. 3. Sieve 1 mm. 4. Total DNA extracted from fractions & region amplified by PCR. Community structure (composition & relative abundance) >1 mm: Rock fertiliser fraction <1 mm: Soil fraction

10 Composition Statistics PCO (ordination): Samples plotted in 2-D space. Distance between samples shows difference. PERMANOVA Permutational multivariate analysis of variance. Treatment effects and pairwise comparisons. DISTLM (multivariate multiple regression): Model variation in bacterial communities using soil properties Modelled values for samples can plotted in 2-D space (RDA)

11 Composition Unplanted Fraction treatments Bacterial communities in rock fertiliser and soil fractions Formed separate clusters All pairwise comparisons were significant Microhabitats of rock fertilisers selected bacterial communities with different structure to surrounding soil. L. rigidum Mica Basalt Rock phosphate

12 Composition Unplanted Rock fertiliser fraction Bacterial communities in microhabitats of different rock fertilisers Formed separate clusters All pairwise comparisons were significant L. rigidum Microhabitats of mica, basalt & rock phosphate selected bacterial community with distinct structure. Mica Basalt Rock phosphate

13 Composition Unplanted Soil fraction Bacterial communities in soil with different rock fertilisers applied Formed clusters Fewer pairwise comparisons were significant Applying different rock fertilisers to soil also influenced bacterial community in bulk soil. L. rigidum Mica Basalt Rock phosphate

14 Composition Element composition Composition of rock fertilisers & soil minerals explained variance in structure of bacterial communities: Unplanted: 44% by P, Mg & Na L. rigidum: 35% by P, K & Mg Bacterial community structure partly determined by nutrient content of rock fertilisers and soil minerals.

15 Composition Implications Soil microorganisms in organic farming: Rock fertilisers create new microhabitats in soil that select bacterial communities with distinct structure Partly due to their elemental content Effect of soil minerals on microorganisms: Mineral types in microhabitats may affect bacterial community structure Mineral heterogeneity may contribute to spatial variation in soil bacteria

16 Particle size Particle size & spatial isolation Rock fertilisers can alter particle & pore size distribution but not linked to change in bacterial communities Theory predicting texture affects diversity of microbial communities When not connected by water, diversity increases Theory predicts: Evidence: Texture Water content

17 Particle size Hypothesis: Texture & water content affect structure and diversity of bacterial community. Experimental design: 2 texture treatments: 100% sand & 10% silt+clay Ground quartz (<10 μm) so altered particle size not composition 6 water potential treatments: Between -15 cm and -55 cm Potential so knew size saturated pores

18 Particle size Column experiment Soil column connected to water reservoir Added 5 cm segments, packing to constant bulk density Soil columns saturated & adjusted to water potential of -10 cm at column base Incubated for 1 w at 25 C. Analysed structure & diversity bacterial communities Potential (cm) Largest water-filled pores (μm)

19 Particle size Texture treatments 10% silt+clay 100% sand Bacterial communities from different textures: Plotted in separate regions of graph All pairwise comparisons significant Bacterial diversity was not affected by texture % silt+clay 100% sand Texture affected bacterial communities due to changes in physical properties of soil Supports theory

20 Particle size Water content treatments 10% silt+clay 100% sand Bacterial communities from wet and dry soil: Plotted in separate regions of graph All pairwise comparisons significant, except at 56% WFPS Bacterial diversity was higher in dry soil. Water content influences diversity of complex bacterial community in field soil Dry Wet

21 Particle size Texture Difference in physical properties of soil explained 38% variance in structure of bacterial communities Silt+clay content 13% Water content 15% Water in pores: μm 3.2% μm 3.8% μm 2.6% Variation in bacterial communities statistically related to changes in physical properties of soil.

22 Particle size Implications Soil microorganisms in organic farming: Applying rock fertilisers with small particle size may alter the structure of bacterial communities Partly due to their effect on physical properties of soil Effect of soil minerals on microorganisms: Texture influences bacterial community structure (not only by altering chemical properties) by altering physical properties Texture influences spatial isolation of bacterial communities in soil

23 Influence of rock fertilisers on soil microorganisms Implications and future research Rock fertilisers have potential to influence soil bacterial communities Future research examine if changes benefit production Nutrient content of rock fertilisers may create hotspots of microbial activity Future research examine if also hotspot of nutrient availability Rock fertilisers may increase microbial activity by improving physical conditions in soil