Effects of plant competition on shoot versus root growth and soil microbial activity in brownfield versus allotment soils

Effects of plant competition on shoot versus root growth and soil microbial activity in

brownfield versus allotment soils

Abstract

Self/non-self discrimination has been studied as a below ground interaction in response to

both intraspecific competition and interspecific competition as resource control is established.

In this study, via the use of Timonen et al’s 1997 experimental design of testing root growth

responses to competition; the effects of two soil types were used to assess soil contamination

impacts and competition impacts on self/non-self discrimination. The findings of this study

were inconclusive and no significant impacts were recorded. Further testing and improvement

in experimental design is required.

Introduction

Optimal plant growth production is dependent on the availability of resources such as soil

nutrients and water. The abundance of root mass is dictated by the accessibility of resources,

as roots actively pursue these resources within the soil (Fitter & Hay 2002). As soil fertility

decreases, investment in root production is increased as the plant applies more surface area to

its search for resources (Nyakudya & Stroosnijder 2014). Investment in root production is

critical to the survival of plants faced with reduced access to resources which not only occurs

in low nutrient soils but also within environments where interspecific competition is abundant

(Craine & Dybzinski 2013). As all plants require the same fundamental resources, the

survival of a plant community is determined by the distribution of the available resources

either by partitioning or the establishment of a single dominant organism (Andrade et al

2014). Consequently belowground root interactions are critical not just for the success of a

plants production, but also for a plants establishment of its position within the community’s

hierarchy (Fort et al 2014). Self/non-self recognition in plants has been documented within

root interactions between both kin plants and interspecific plants (Chen et al 2012).

Observations have identified that belowground interactions are more sophisticated than

originally assumed in that plants increase root growth towards neighbours, consequently

increasing competition for resources; or invest in growth away from its neighbours to reduce

competition (Mahall & Callaway 1992). Interactions between kin plants also indicate plants

recognition of potential benefits of growing in close proximity to one another to mutually

benefit from the distribution of nutrients and soil microbes (Hamilton 1964). A study

performed by Mahall & Callaway in 1991 on desert shrubs found that shrubs of the same

species would reduce their root growth whenever the roots encountered the roots of another

shrub of the same species. However when roots of the same plant were encountered root

growth was not disrupted. It was determined that the reduction in root growth upon detection

of a same species neighbour, was an active trait used to reduce intraspecific competition for

water. Studies performed by the planting of same species and mixed species plants within

containers have also provided evidence that the presence of a non-self neighbour incurred a

response of increased root mass by up to 85% in contrast to containers which contained self

neighbours which only increased root mass by 30% (Gersani et al 2001).

In this study the hypotheses of self/non-self discrimination will be tested by the observation

of belowground interactions and biomass production of three species of plants, Lolium

perenne, Festuca ovina and Trifolium pratense; which will be exposed not only to

interspecific competition, but two different soil types. Soil microbial activity in both soil

types will also be tested to determine if activity is impacted by the soil type. The soils used in

this experiment were obtained from Abbey Hey allotments, Gorton, Manchester. Sample soils

were taken from a vegetable plot utilised in the production of produce for local residents and

a former scrap metal business plot which had discontinued over 40 years ago; with high

concentrations of soil metals considered harmful to human health and also of detriment to soil

quality.

Aims

To determine the interspecific competition impacts on plant productivity in two contrasting

soil types to test the hypothesis of self/non-self discrimination.

To measure the effects of soil type on species-specific plant production, determined by a total

plant fresh and a root versus shoot observation.

Plant species on soil microbial activity (FDA hydrolysis) responses in allotment and

contaminated brownfield soil

Method and materials

Lolium perenne, Festuca ovina and Trifolium pratense were selected for this investigation

due to the limitations of the study as to the time of year and time restrictions imposed to

conduct the study. Each species selected is relatively hardy with a quick growth rate and

ability to thrive in artificial growing conditions.

The experimental design used in this study mirrored that of the one used in Timonen et al’s

1997 of interactions between genets of Suillus spp and differen Pinus sylvestris genotype

combinations.

The experiment was initiated in October by the production of six plant pots to observe same

species interactions via the creation of pots containing one species per pot, per soil type. A

further two pots were created to observe belowground interspecific competition between the

three selected species by the creation of pots containing all three species per soil type. In

addition to this two control pots were produced separately containing only soil from the two

soil types. All experimental pots were then placed in a greenhouse under controlled

conditions to simulate climates ideal for growth. All pots were regularly watered and weeded

until the following January.

January harvest

In total 21 same species pots with vegetable plot soil were produced and 18 same species pots

with contaminated soil will produced. 12 competition pots with vegetable plot soil were

produced and 15 with contaminated soil were produced.

All the planted pots were then harvested by separation of each pots soil from its plants. From

the soil a 10 gram sample was taken from each pot for FDA hydrolysis activity.

Cutting and weighing

Following the techniques outlined by Timonen et al (1997) each plant was weighed to

determine its fresh shoot and root weight. Each plant was cut to separate its shoot and root,

which was then weighed and recorded to 4 decimal places. This process was repeated for the

roots and shoots for all pots in both soil types. After weighing all individual roots and all

individual shoots they were then dried at 80°C for 48 hours.

After 48 hours each root and shoot sample was then reweighed to determine its dry weight.

Results

Allotment ControlPlant variable T.pratense L. perenne F. ovina

Shoot Fresh wt (g)2.33 ± 1.02

P= 0.4160.33 ± 0.21

P= 0.0090.05 ± 0.02

P=0.958

Root Fresh (g)1.60 ± 0.83 P = 0.7446

0.51 ± 0.32 P= 0.060

0.12 ± 0.19 P= 0.000

Total Plant Fresh wt (g)3.93 ± 1.76

P= 0.8040.84 ± 0.45

P= 0.0290.18 ± 0.19

P= 0.00

Shoot Dry wt (g)0.73 ± 0.84 P = 0.000

0.08 ± 0.32 P= 0.000

0.00 ± 0.00 P= 0.803

Root Dry wt (g)0.54 ± 0.87

P= 0.0000.05 ± 0.03

P= 0.1120.01 ± 0.01

P= 0.098

Total Plant Dry wt (g)1.27 ± 1.71

P= 0.0000.14 ± 0.14

P= 0.0000.18 ± 0.01

P=0.508

Table 1. Allotment soil control sample analysis of mean ± SD and (Shapiro-Wilks) normality (P) per sample plant

species

Table 2. Contaminated soil control sample analysis of mean ± SD and (Shapiro-Wilks) normality (P) per sample plant

species

Analysis from table 1 (Allotment control samples) demonstrates a higher ratio of shoot

growth in T.pratense than root growth at approximately a shoot to root ratio (fresh weight) of

2:1. Whereas L. perenne and F. ovina both demonstrate a higher root growth ratio than shoot,

with L.perenne having a shoot to root ratios (fresh weight) of approx. 1.1 : 1.7 and F.ovina

1:2.4.

Contaminated ControlPlant variable T.pratense L. perenne F. ovina


P= 0.0770.40 ± 0.14

P= 0.7740.04 ± 0.02

P= 0.204

Root Fresh (g)0.95 ± 0.70

P=0.0330.65 ± 0.60

P= 0.0120.08 ± 0.10

P= 0.000


P= 0.1181.05 ± 0.62

P= 0.1010.12 ± 0.10

P= 0.024

Shoot Dry wt (g)0.23 ± 0.16

P= 0.1280.06 ± 0.03

P= 0.7990.01 ± 0.01

P=0.000

Root Dry wt (g)0.07 ± 0.05

P= 0.2410.04 ± 0.03 P = 0.010

0.01 ± 0.01 P=0.000


P= 0.4560.10 ± 0.51

P= 0.1580.01 ± 0.13

P= 0.001

Analysis from table 2 (Contaminated soil samples) demonstrates a similar observation of

shoot growth in T.pratense with a shoot to root ratio (fresh weight) of approximately 1.9 :

1.18. However there is a notable increase in root growth within the L. perenne with a shoot to

root ratio (fresh weight) of 2: 3.3. The shoot to root ratio of F. ovina has slightly decreased

with a ratio of 1:2.

A Mann-Whitney U test concludes that the null hypothesis of “fresh root weight is the same

across both soil types” should be rejected with a P value of 0.049 occurring; identifying that

soil type has a significant impact on root growth of same species plant pots.

Overall comparisons between the two soil types indicate a notable decline in biomass per

species, with the allotment soil producing the greater amount of biomass. This is not true in

the case of L. perenne however which indicated an increase in growth within the

contaminated soil in comparison to the allotment soil.

Allotment CompetitionPlant variable T.pratense L. perenne F. ovina


P= 0.5600.50 ± 0.30

P= 0.1390.03 ± 0.02 P = 0.512

Root Fresh (g)1.66 ± 1.32 P = 0.282

0.92 ± 0.92 P= 0.040

0.03 ± 0.03 P= 0.024


P= 0.5491.43 ± 1.20

P= 0.0590.06 ± 0.46

P= 0.022

Shoot Dry wt (g)

0.41 ± 0.26 P =

0.3810.08 ± 0.06

P= 0.0670.01 ± 0.01

P= 0.114

Root Dry wt (g)0.14 ± 0.08

P= 0.9260.05 ± 0.03 P = 0.100

0.01 ± 0.01 P=0.003

Total Plant Dry wt (g)

0.54 ± 0.33 P= 0.132

0.13 ± 0.09 P= 0.234

0.02 ± 0.02 P= 0.004

Table 3. Allotment soil competition sample analysis of mean ± SD and (Shapiro-Wilks) normality (P) per sample

plant species

Table 4. Contaminated soil competition sample analysis of mean ± SD and (Shapiro-Wilks) normality (P) per sample

plant species

Comparisons between table 1 and table 3 demonstrate that in both T.pratense and L.perenne

there is a notable increase in biomass with L.perenne almost doubling in total fresh weight

when planted in competition with the two other plant species. F. ovina however demonstrated

notable decline in biomass between table 1 and table 3, indicating reduction in productivity

when planted with the two other plant species. The shoot to root ratio of L.perenne

demonstrated a notable increase in root production within the allotment competition pots. F.

ovina indicated a reduction in root production within competition pots in comparison to root

production in the control pot.

Comparatively, table 2 and table 4 demonstrate an increase in biomass production between

T.pratense and L.perenne with the highest amount of biomass recorded in the competition

pots. However even in contaminated soil F. ovina demonstrates decline in biomass

production when placed in competition pots.

T.pratense has P value of 0.531 when a Mann-Whitney U test is performed indicating that

null hypothesis that “soil type does not influence self/non-self discrimination” should be

accepted and there is no difference in self/non-self discrimination between soil types for this

species.

L.perenne has a P value of 0.664 when a Mann-Whitney U test is performed indicating that


Contaminated CompetitionPlant variable T.pratense L. perenne F. ovina


P= 0.0810.65 ± 0.49

P= 0.2100.07 ± 0.06

P= 0.144

Root Fresh (g)1.14 ± 0.54

P= 0.0190.83 ± 0.81

P= 0.0240.08 ± 0.12

P= 0.000


P= 0.0011.48 ± 1.19

P= 0.2180.16 ± 0.15

P=0.031

Shoot Dry wt (g)0.28 ± 0.14

P= 0.0290.10 ± 0.11

P= 0.0530.01 ± 0.01

P= 0.008

Root Dry wt (g)0.11 ± 0.20

P= 0.0000.05 ± 0.05

P= 0.0260.06 ± 0.05

P= 0.048


P= 0.4280.15 ± 0.12

P= 0.0080.07 ± 0.51

P= 0.044

accepted and there is no difference in self/non-self discrimination between soil types for this

species.

F. ovina has a P value of 0.130 when a Mann-Whitney U test is performed indicating that


rejected and there is a difference in self/non-self discrimination between soil types for this

species.

Allotment ControlPlant variable No Plants T.pratense L. perenne F. ovinaSoil Microbial FDA hydrolysis activity (µg fluorescein g-1 30 min-1)

0.29 ± 0.35 P= 0.084

0.36 ± 0.46 P= 0.167

0.54 ± 0.58 P= 0.109

1.11 ± 1.00 P= 0.498

Table 5. FDA hydrolysis of soil microbial activity in allotment soil control sample analysis of mean ± SD and

(Shapiro-Wilks) normality (P) per sample plant species and non-planted soil

Contaminated ControlPlant variable No Plants T.pratense L. perenne F. ovinaSoil Microbial FDA hydrolysis activity (µg fluorescein g-1 30 min-1)

0.21 ± 0.15 P= 0.079

0.61 ± 0.94 P= 0.002

0.55 ± 0.36 P= 0.725

0.14 ± 0.11 P= 0.076

Table 6. FDA hydrolysis of soil microbial activity in contaminated soil control sample analysis of mean ± SD and

(Shapiro-Wilks) normality (P) per sample plant species and non-planted soil

Allotment CompetitionPlant variable All PlantsSoil Microbial FDA hydrolysis activity (µg fluorescein g-1 30 min-1)

0.68 ± 0.77 P= 0.008

Contaminated CompetitionPlant variable All PlantsSoil Microbial FDA hydrolysis activity (µg fluorescein g-1 30 min-1)

0.40 ± 0.22 P= 0.189

Table 7. FDA hydrolysis of soil microbial activity in contaminated and allotment soil competition sample analysis of

mean ± SD and (Shapiro-Wilks) normality (P) for all plants

A Kruskal-Wallis test was performed on the data from table 5 and found that there was no

significant difference between planted and non-planted allotment pots, per species; producing

a P value of 0.389 concluding that the null hypothesis that there is a difference between in

microbial activity in planted and non-planted soil, should be rejected.

Another Kruskal-Wallis test was run on the table 6 data and the same conclusions were found

in contaminated soil with a P value of 0.174 and rejecting the same null hypothesis.

A Mann-Whitney U test was then performed on the table 7 data and soil type did not produce

any significant difference in microbial activity, producing a P value of 0.962 and rejecting the

null hypothesis that microbial activity is different per soil type.

Discussion

The findings from this study cannot extensively test the aims of the investigation due to the

high volume of standard error in the data collect and the large degree of operator and

instrumental error. Comparatively to previous attempts at this investigation, previous datasets

was substantially more comprehensive and more substantial in quantity than the dataset used

in this study. Subsequently operator error in the handling and preparation of the specimens

for testing, had a greater impact on the data analysis as the resulting dataset means were

notably skewed and the standard deviation per data variable significantly fluctuated due to

the high amount of standard error.

The findings from this study would indicate that the contaminates in the contaminated soil

had no impact on plant growth production, root growth or soil microbial activity. This is in

direct contradiction to findings observed by Kim et al (2012) who found the presence of Pb

changed microbial activity and Lin et al (2014) who found Cu and Pb impact on root growth

and metal uptake in plants.

With regards to self/non-self discrimination, mild differences per species between the two

soil types could be observed in root growth. In both soil type T.pratense had the greater

biomass and could be considered the dominant species, with L.perenne indicating mild

competition root growth in the allotment soil; however statistical analysis of this data

determined the growth was not significant enough to support self/non-self discrimination. F.

ovina continued to be relatively indifferent in both soil type and treatment, consistently

producing the lowest biomass and failing to support any hypothesis. This directly contradicts

findings that F. ovina can survive in soils low in nutrients and has notable symbiotic relations

with mycorrhizal fungi which aids the plants establishment by extracting minerals,

phosphates and nitrogen (Granath et al 2007). This could indicate that the presence of the two

other plant species could have impacted on the growth production of F. ovina and caused the

consistently poor biomass production, however this would require further testing to

determine.

Overall the findings from this study are inconclusive due to a same dataset and high amount

of operator error. Weights produced by some operators were clearly taken incorrectly and

preparation of the specimens for testing was not consistent throughout all operators taking

place in the study. Future improvements to this study could be the standardisation of

specimen preparation by a single operator to ensure greater control over all measured

variables. In addition to this, a larger dataset to provide more validity to the statistical

analysis is required. Potentially the production of more specimens/pots, produced over a

greater length of time could be of benefit to the test species to allow for greater opportunity

for self/non-self below ground competition to be established.

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Effects of plant competition on shoot versus root growth and soil microbial activity in brownfield versus allotment soils