Presenter: Reuben HilliardFaculty Advisors: Dr. Paula Jackson & Dr. Brad Barney

Undergraduate Research Assistants: Chelsea Harris, Josh Hashemi & Gage Allred

Introduction

Surviving Climate ChangeComparing drought & fungicide response in two riparian tree species for use in ecological restoration

Riparian zones fulfill many ecosystem functions and occur at all elevations near rivers, streams, and in floodplains. They function as a natural buffer against erosion in river and stream banks, filter downstream pollution, and provide increased habitat complexity (Wildlife, 2006). Due to development, logging, and expanding agriculture, many riparian zones have been destroyed or depleted. This has a profound ecological effect that leads to increased sedimentation and pollution in natural water systems (Hernandez-Santana, 2011). These zones often undergo rehabilitation to restore health back into the surrounding environment. Salix nigra (Black Willow) and Platanus occidentalis (American Sycamore) are two common riparian species of trees (Conger, 1996). Of these, Salix nigra is frequently used to restore these areas, however not much information exists on the ability to use Platanus occidentalis for this purpose. This research is part of a larger study looking at the ecology and physiology of both of these species, with the overarching aim of comparing the behavior of Platanus occidentalis to the more widely studied Salix nigra, and determining the feasibility of using Platanus occidentalis in restoration processes. Of additional importance is the fungal biota which inhabit the soil beneath these trees. Mycorrhizal fungi have been reported to improve plant growth in many crops through enhanced root growth and function (Westphat et al, 2008). It also improves early plant establishment and increased the most valuable early fruit yield under some environmental stress conditions. This is of ecological importance and will be incorporated in this study.

Objectives1) Determine whether there is a different response in Salix nigra and Platanus occidentalis to drought.2) Determine if the fungal biota, Mycorrhizae, modified the drought response among species.

One cause for data errors in greenhouse experiments can be due to microclimate differences, such as light, airflow and heat among saplings, within different planters. As stated by Brien et al. (2003), sound statistical design and analysis is better than rearranging the position of plants during the experiment itself. In our experiment, Platanus occidentalis and Salix nigra saplings were planted using a Randomized Complete Block Design, as seen in Table I. It involved a complete experimental treatment within each planter series, allowing for homogenous growing conditions within a single tray, regardless of differences among planters themselves. To account for variability in sapling size, each tray had a similar distribution of size classes. All the saplings were tagged with unique identifiers, such as PO-01 or SN-02. 15-17 individuals of each species were subjected to a control, inundation, or drought condition; and drought with and without the addition of mycorrhizal spores, a fungal biota, which was controlled with the addition of a fungicide, Benomyl. In total, 31 Platanus and 34 Salix cuttings received sufficient nutrients in the form of a slow-release fertilizer and after taking baseline measurements, were allowed to grow in planters through the spring of 2015. From May 18th until August 23rd, a team of myself and 3 undergraduate research assistants, took anatomical and physiological measurements. For the anatomical measures, an indicator of growth rate, both the circumference and the height were taken for each plant on a weekly basis. For the physiological data, a LICOR LI-6400 Infrared Gas Analyzer (IRGA) was used to measure photosynthetic rate from leaves repeatedly over the period of weeks, systematically moving through the plants, selecting a predefined leaf from a randomly selected plant from each treatment and block. This was a tedious process, with each leaf taking up to 16min for a full measurement run. The results were used to build light response curves. Net Photosynthetic rate, or CO2 assimilation (µmol CO2 m-2 leaf area s-1) from several trials were plotted against light intensity, or Absorbed Photosynthetically Active Radiation (αPAR, µmol photons m-2 leaf area s-1). The slope of the linear phase of the response curve is a measure of "photosynthetic efficiency" of the plant, or how efficiently solar energy is converted into chemical energy. Different plants show differences in the shape of their light response curves, which reveals characteristics of the underlying photosynthesis processes, including the efficiency at which light is utilized by photosynthesis and the rate of O2 uptake.In this longitudinal study, both the anatomical and the physiological data were analyzed using SAS 9.4 with the MIXED Procedure, which models mixed effects over time.

Oregon Department of Fish and Wildlife. 2006. Oregon Conservation Strategy. Oregon Department of Fish and Wildlife, Salem, Oregon.  Hernandez-Santana, V., Asbjornsen, H., Sauer, T., Isenhart, T., Schilling, K., & Schultz, R. 2011. Enhanced transpiration by riparian buffer trees in response to advection in a humid temperate agricultural landscape. Forest Ecology and Management, 261(8), 1415-1427.  Conger, RM. 1996. Black willow (Salix nigra ) use in phytoremediation techniques to remove the herbicide bentazon from shallow groundwater. Master’s thesis, Louisiana State University  Brien, C. J., Berger, B., Rabie, H., & Tester, M. 2013. Accounting for variation in designing greenhouse experiments with special reference to greenhouses containing plants on conveyor systems. Plant Methods, 9(5), 1746-4811

Westphal, A., Snyder, N., Xing, L. 2008. Effects of Inoculations with Mycorrhizal Fungi of Soilless Potting Mixes During Transplant Production on Watermelon Growth and Early Fruit Yield. HortScience, 43(2), 354-360 

References

(Image: bioimages.vanderbilt.edu/baskauf/15370.htm)

Table I: A Randomized Complete Block Design(Image: bioimages.vanderbilt.edu/baskauf/23004.htm)

(Image: bioimages.vanderbilt.edu/baskauf/29666.htm)

(Image: http://bioimages.vanderbilt.edu/baskauf/13574.htm)

Salix nigra and Platanus occidentalis saplings planted and set up in greenhouse.

Salix nigra leaves (left) and Salix nigra tree (right)

Platanus occidentalis leaves (left) and Platanus occidentalis tree (right)

Height measurements for Salix nigra sapling and mature plant (above) and LICOR LI-6400 IRGA (below).

Block 1 Block 2A B B AD C C D

ConclusionsMethods ResultsAnatomical Results: Linear Rate of Growth among Species & Drought Conditions

Physiological Results: Photosynthetic Light Response Curve & Mean Maxima Bar Chart

** p < .0001

Statistical ModelsRandomized Complete Block Design

yij = µ + αi + bj + εij

Autoregressive Heterogeneous Covariance Matrix

Unstructured Covariance Matrix

Mixed Effects Modely = Xβ + Zu + ε

Relevant Code

Graphs and Bar Chart designed in Tableau 9.2

*Coding the explanatory variables;DATA research.anatomical_data;

SET together;daysc = date - mdy(5,18,2015);dayscat = daysc;tag = species;species = substr(tag,1,2);fungicide = scan(treatment,1,"/"); drought = substr(scan(treatment,2,"/"),1,1);tmt=1;if species="PO" then tmt=tmt+4;if drought="D" then tmt=tmt+2;if fungicide="Fungicide" then tmt=tmt+1; RUN;

*Optimal Anatomical model. Unstructured Cov Matrix;PROC MIXED data = research.anatomical_data;CLASS species drought fungicide tag blocknum dayscat;MODEL height = species drought species|daysc drought|daysc

/solution ddfm = kr;REPEATED dayscat/ subject = tag(blocknum) type = un R RCORR ; RUN;*Optimal Physiological model, stratified by species. Autoregressive Heterogeneous Cov Matrix;PROC SORT data = research.master_photo; BY Species Tag PAR; run;PROC MIXED data = research.master_photo;BY Species;CLASS tag treatment blocknum PAR;MODEL photo = treatment PAR ;RANDOM blocknum;REPEATED PAR /subject = tag type = arh(1) ;LSMEANS treatment /pdiff tdiff ; RUN;*Data output for Mean Maxima Photosynthetic Rate and Std Errors;

ODS GRAPHICS ON;PROC MIXED data = research.master_photo;WHERE PAR = 800;CLASS Tag blocknum fungicide drought species PAR period;MODEL photo = species*fungicide*drought

/ noint solution ddfm=kr;RANDOM blocknum;RANDOM int / subject=tag; RUN; ODS GRAPHICS OFF;

The results indicate that Salix nigra and Platanus occidentalis do respond differently to drought conditions. In fact, the interaction of the days count and the drought condition was highly significant (p < .0001). This meant that as the experiment proceeded the drought condition became more pronounced. As seen in the anatomical results, for the drought condition, Platanus was able to outperform Salix in the linear rate of growth (corrected for errors), 0.86cm/Day and 0.74cm/Day, respectively. The fungicide treatment did not have a significant effect in either species.The physiological results indicated that the PAR level, or light intensity given to the leaf, was significant (p < 0.05). This analysis had to be stratified by species, as none of the other factors were significant initially. When this was done, Platanus was right on the cusp of being significant in the drought condition during period 2 (last 5 weeks of the experiment). Even though Salix didn’t respond to the drought or fungicide treatments, this information is still of biological interest to researchers, as it indicates that Salix can be stressed and still perform unhindered, with minimal interruptions.Of particular note is how well Platanus performed in the ‘No Fungicide/Drought’ treatment, which can be observed in both the light curve and the mean maxima photosynthetic output figures (left). This could indicate that the fungal biota which remained in the soil, had a beneficial effect on the outcome of Platanus growth, as well as its solar energy conversion efficiency. This will require future research to isolate these outcomes.These results were quite positive and allow future research to focus specifically on Platanus as a species to use in restoration of Georgia’s riparian ecosystems.