Pairing Bouteloua gracilis with its "home-team" soil organisms enhances plant growth regardless of environmental conditions
Monday, August 10, 2015: 4:20 PM
327, Baltimore Convention Center
Michael Remke, Forestry, Northern Arizona University, Flagstaff, AZ, USA
Matthew A. Bowker, School of Forestry, Northern Arizona University, Flagstaff, AZ, USA
Nancy C. Johnson, Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ, USA
On the Colorado Plateau, land use changes and prolonged drought are negatively impacting native plants. Bouteloua gracilis is a native perennial grass on the Colorado Plateau that is obligate to soil organisms, such as mycorrhizal fungi. Plants and soil organisms may be locally adapted to one another suggesting that benefits from soil organisms are site specific. Some evidence exists that soil organisms from a dry environment are more efficient in mitigating plant responses to drought stress. It is unclear whether soil organisms and plants are co-adapted, or if soil organisms from novel environments facilitate plant adaptations to novel environments. In this experiment, we conducted a greenhouse study to examine whether novel soil organisms would provide equal benefits to B. gracilis populations as natal soil organisms. We also examined the lasting effects of exotic plant invasion on soil organism communities, and how these altered soil communities affect native grass growth. We used soil inocula and B. gracilis individuals from two different sites to determine the benefits received from novel versus natal soil organisms. We used live soil inoculum from an area invaded by Bromus tectorum to examine how altered soil organism communities alter plant growth.
We found that plants grown in association with soil organisms from their natal site were the tallest and grew fastest (p=0.0184). We also found that plants grown in association with B. tectorum invaded soil had the lowest establishment rates and were the shortest (p=0.0022). In addition, plant roots were more colonized by arbuscular mycorrhizal fungi when paired with their home team soil organisms. These data suggests the symbiosis that occurs between B. gracilis and its soil organisms likely co-evolved and is site specific. Land managers should then be interested in preparing soil inoculum from seed collection sites to enhance performance of restoration projects in disturbed or invaded sites. In addition, B. tectorum appears to manipulate soil organism communities in a way that inhibits establishment of B. gracilis. This could be due to a reduction of mycorrhizal densities, or due to an accumulation of parasitic organisms. This negative plant-soil feedback has major implications for land managers interested in restoring landscapes invaded by B. tectorum. Matching plant populations with their natal, un-invaded soil organism communities could be the missing link in restoration following exotic species invasion.
Biological soil crusts and global change: Spectrally monitoring moss responses to future climate change scenarios
Wednesday, August 12, 2015: 9:00 AM
318, Baltimore Convention Center
Kristina E. Young, School of Forestry, Northern Arizona University, Flagstaff, AZ, USA
Sasha C. Reed, Southwest Biological Science Center, U.S. Geological Survey, Moab, UT, USA
Dryland biological soil crusts - a community of mosses, lichens, cyanobacteria, and heterotrophs living at the soil surface - are a fundamental component of the structure and function of arid and semiarid ecosystems. These soil communities play critical roles in dryand carbon fixation, nitrogen fixation, and soil stabilization, and existing data suggest biocrusts are sensitive to seemingly subtle changes in climate. For example, previous research on the Colorado Plateau showed dramatic mortality of the common moss Syntrichia caninervis in response to an increase in the frequency of small monsoonal rainfall events. Yet, despite the importance of these biocrust organisms, our ability to monitor biocrust responses to altered climate remains limited. Spectral imaging represents an under-exploited tool for documenting change within biological soil crust communities. Here, we induced stress within Syntrichia caninervis samples by increasing the frequency (twice weekly) of small (1.2mm) rainfall events, and used spectral analyses to monitor the moss’s progression towards eventual mortality. We focused on a number of indices as potential tools for assessing change, including the Normalized Difference Vegetative Index (NDVI). In addition, we concurrently examined shifts in nitrogen cycling within the soil matrix of stressed mosses to link moss stress, spectral imaging, and biogeochemical consequences.
As expected, mosses were strongly, negatively affected by the increased frequency of small rainfall events, and exhibited clear signs of chlorisis - a yellowing and reddening of moss leaves. Belowground changes to biogeochemical cycling occurred in the form of decreasing NH4+ concentrations, and concurrently increasing NO3- concentrations, alluding to a steady progression towards NO3- dominance in the soil. These changes to soil N cycling occurred before significant moss stress became visibly apparent, implying that even early stress to moss has large implications for soil fertility. We found spectral analyses an effective tool for quantify the progression towards chlorosis within this moss species, however, the NDVI wide band index that is widely used for remote sensing of vascular plants was an unexpectedly poor indicator of stress. Instead, narrow band hyperspectral indices were much more effective at quantifying chlorosis. These findings suggest that the correctly employed hyperspectral images could be a valuable tool for documenting change within biological soil crust communities. Tools such as these, which can document stress, will become increasingly important to dryland ecosystem assessment in light of the dramatic biogeochemical changes associated with moss mortality.