Spatial Salinity Heterogeneity in Soil: Evaluating Compensatory Growth in Hordeum Vulgare

Transcript

By 2050, the world’s population will reach nearly 10 billion but at the same time, increasing soil salinization is quietly reducing how much cropland we have left to grow food for future generations.

Hi, my name is Akshayha, and I explored how salinity affects plant growth and whether plants can cope when only part of their roots are exposed to salt.

To test this, I used barley, Hordeum vulgare, in a split-root system with three conditions: non saline, fully saline (the controls), and partially saline (the treatment: spatial salinity heterogeneity). I measured growth over 28 days using height, biomass, and tiller number.

Plants in fully saline soil grew the worst, while non-saline plants grew the best. But partially saline plants performed much closer to the control, maintaining higher biomass and steadier growth.

This shows that root-zone variability can reduce salinity stress, offering a simpler and more cost-effective alternative to traditional treatments.

As soil degradation increases, this approach could help farmers protect crop yields and support future food security.

Why Agriculture/Soil Science?

Agriculture and soil science are essential for sustainable food production and ecosystem health. Studying soil helps address issues like erosion, salinity, and land degradation, ensuring long-term agricultural productivity for a growing population.

Problem

Soil salinization is a growing threat to agriculture because it reduces farmland productivity by disrupting water uptake, nutrient balance, and plant function. However, when only part of a plant’s roots are exposed to salt (spatial salinity heterogeneity), roots in healthier soil can still absorb water and nutrients, helping reduce stress. This approach could be more efficient and cost-effective than traditional methods like soil washing, easing the burden on farmers.

Objectives

The objective of this experiment is to investigate how saline stress affects the response of barley (Hordeum vulgare) to spatial salinity heterogeneity using a split-root system by evaluating:

The impact of salinity stress on early plant development compared to a non-salinized control.

The ability of the plant to remain productive due to access to a non-salinized portion of soil despite high salinity in the adjacent compartment.

Whether Hordeum vulgare responds differently to uniform and spatially heterogeneous salinity conditions.

Hypothesis

Hordeum vulgare is expected to show compensatory growth in the partially saline (SN) condition.

Growth should rank from highest to lowest: NN > SN > SS.

SN plants should maintain greater biomass and tiller numbers than fully saline (SS) plants despite partial salt stress.

SS plants will likely grow slower and more gradually, while SN plants should show faster, more linear growth closer to NN.

Variables

Independent Variables:

Soil configuration (SN, NN, SS)

Sampling time (7, 14, 21, 28 days post emergence)

Dependent Variables:

Shoot height

Shoot FW (fresh weight)

Shoot DW (dry weight)

Leaf number

Tiller number

Experimental Procedure

Phase 1: Setting Up

Key Materials:

Growth Chamber

Barley seeds

Soil

AVV (acrylic) split containers

Process:

Gather materials and set up 36 containers with three soil treatments (NN, SN, SS), including replicates and sampling dates.

Fill containers with the correct saline and non-saline soil amounts, then place the seed at the interface between both soil types.

Label each container clearly with treatment, date, and replicate.

Place containers in a growth chamber, randomize layout, and maintain proper watering and soil conditions during germination and growth.

Phase 2: Recording Data

Key Materials:

Lab Scale

Ruler

Aluminum Plates

Process:

At weekly intervals, remove 3 containers from each treatment (SN, SS, NN) and maintain proper watering for the remaining plants.

Record growth data: tiller number, leaf number, shoot height, and fresh shoot weight.

Bag and label shoots, then dry them and record dry weight.

Prepare a clean, sterile workspace and gather materials for root washing following lab safety procedures.

Separate soils carefully, wash roots without damage, and store roots in ethanol and soil in labeled bags.

Repeat the process at 14, 21, and 28 days.

Phase 3: Analyzing Data

Key Materials:

Excel

SAS computer software

Process:

Record all values on excel, include date, type of soil configuration, and replicate on sheet.

Plug values into SAS using ANOVA one way with repeated measures testing, evaluate statistical significance, comparative analysis and averages for each growth parameter (ex. tiller #, fresh weight of shoots, dry weight of shoots, height, etc.)

Graph values and averages.

Analyze data.

*Root data was not analyzed due to machine delays, all data is based on previously stated growth parameters*

Statistical Significance

According to ANOVA one way with repeated measures testing, 3 out of the 5 growth parameters shows statistical significance (shoot length, shoot fresh weight, and shoot dry weight), since the p value is < 0.05 the results are statistically significant. Null hypothesis is rejected.

Comparative Analysis

Using the Tukey-Kramer multiple comparisons test, it is found that SN is statistically different from SS in shoot length in the later stages of time periods (21, 28) performing better than SS. SN is statistically different from SS in dry weight in the latest stage of time periods (28) performing better than SS, SN is not however statically different from NN in fresh weight for all time periods but still performing better than SS. SN is relativity similar to NN in shoot length and fresh weight there is no statistical difference, however SN performed better in dry weight than NN and after careful observation there is a statistical difference between SN and NN in period 28.

Results

The results support the hypothesis that Hordeum vulgare exhibits compensatory growth under spatially heterogeneous salinity conditions. Significant differences in growth were observed among treatments, with overall performance following the predicted order of NN > SN > SS. Plants in the SN treatment maintained higher biomass numbers compared to those in the SS treatment, despite exposure to 11.8 dS/m salinity on one side, although tiller number was the same. Additionally, growth trajectories differed among treatments, with SN plants displaying a more linear and faster growth pattern relative to SS, and more closely resembling the NN control. In contrast, SS plants showed reduced and more gradual growth, consistent with sustained high salinity stress.

Discussion

This study shows how spatial salinity variability shapes early growth in Hordeum vulgare. Plants in heterogeneous conditions (SN) maintained biomass and growth patterns closer to non-saline controls, suggesting compensatory growth through resource allocation to less saline zones. Some traits, like fresh weight and tiller number, were less affected by localized stress, while uniform salinity (SS) consistently reduced growth. These findings highlight that salinity impacts are not uniform across plant functions and emphasize the importance of root-zone heterogeneity in influencing plant tolerance and improving performance in salt-affected environments.

Conclusion

The purpose of this experiment was to investigate how saline stress affects the response of barley and to see if the plant would still be able to be productive due to access of a non-salinized portion of soil despite the influence of high salinity in the adjacent compartment. This experiment proves the hypothesis correct and follows the purpose that Hordeum vulgare responds differently to uniform and spatially heterogeneous salinity conditions, with clear evidence of compensatory growth under partial stress. Barley plants exposed to spatial salinity heterogeneity (SN) maintained greater tiller production and biomass than those grown under uniformly high salinity (SS). Growth patterns followed the predicted trend of NN > SN > SS, indicating that while salinity negatively impacts overall development, the presence of a non-saline zone allows plants to partially offset stress effects. Overall, this project contributes to a better understanding of how crop species may tolerate and adapt to saline conditions, with potential implications for agricultural management in salt-affected soils.

Limitations

Possible sources of variation could include slight differences in watering, salinity distribution, root handling, & measurements. Future trials could refine consistency, increase sample size, and further standardize methods.

Future Applications

A key next step is to investigate the root systems in more detail, particularly the chemical interactions occurring in the roots and surrounding soil. Additionally, studying root signaling compounds and hormone responses may reveal how plants coordinate growth between stressed & non-stressed zones.

Further research could examine microbial activity in the rhizosphere. Expanding this work to field conditions would help determine how these interactions function in real agricultural systems.

Acknowledgements

I would firstly like to express my gratitude towards Dr. Francis Zvomuya (Professor, Department of Soil Science, University of Manitoba), for being my mentor making this experiment possible, and also with permitting me to use the lab space in the University of Manitoba, allowing me to conduct this experiment.

I would also like to express gratitude towards Lanmin Liu (phD student, Department of Soil Science, University of Manitoba) for also assisting me with this project and being my mentor. Providing me with the samples, data collection tools, explanations on certain topics regarding soil sciences and providing me with encouragement throughout this experiment.

Additionally, I'd like to thank my family and friends for supporting me always, my older sister for looking over any errors and providing technical support, my parents for cheering me on, and my late grandfather who was a farmer, inspiring me to do a project on agriculture.

Works Cited:

Images:

All graphics (not including photos) courtesy of Canva.

Project photo in title courtesy of of the International Center for Biosaline Agriculture.

Webpages:

Food and Agriculture Organization of the United Nations. Arable Land. Wikipedia, 2023, https://en.wikipedia.org/wiki/Arable_land.

Isayenkov, Stanislav V., and Frans J. M. Maathuis. “Plant Salinity Stress: Many Unanswered Questions Remain.” Frontiers in Plant Science, vol. 10, 2009, https://pmc.ncbi.nlm.nih.gov/articles/PMC2755029/.

Shabala, Sergey, et al. “Salinity Tolerance in Hordeum vulgare: Ion Concentrations in Root Cells of Cultivars Differing in Salt Tolerance.” Figshare, 2023, https://sussex.figshare.com/articles/journal_contribution/Salinity_tolerance_in_Hordeum_vulgare_ion_concentrations_in_root_cells_of_cultivars_differing_in_salt_tolerance/23346113.

United Nations. (2021, October 20). 1.5 billion people, living with soil too salty to be fertile | UN news. United Nations. https://news.un.org/en/story/2021/10/1103532

Zhang, Ming, et al. “Salinity Stress Responses and Tolerance Mechanisms in Plants.” International Journal of Molecular Sciences, vol. 23, no. 3, 2022, article 1149, https://www.mdpi.com/1422-0067/23/3/1149.