Seasonal and individual event-responsiveness are key determinants of carbon exchange across plant functional types

Authors: WINKLER, DANIEL - Us Geological Survey (USGS); BELNAP, JAYNE - Us Geological Survey (USGS); DUNIWAY, MICHAEL - Us Geological Survey (USGS); Hoover, David; REED, SASHA - Us Geological Survey (USGS); YOKUM, HANNAH - Brigham Young University; GILL, RICHARD - Brigham Young University

Submitted to: Oecologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/19/2020
Publication Date: N/A
Citation: N/A

Interpretive Summary: In drylands, plant community composition is driven largely by how plants and plant functional types respond to changes in water availability. In cold deserts, such as the Colorado Plateau, warming associated with climate change may provide plants with more opportunities to be photosynthetically active throughout the year. However, not all plants are are able to respond to rapidly changing conditions the same way. In this study, we examined the seasonal physiological responses of 13 common plant species of this region, representing perennial shrubs, cool- and warm-season grasses, and annual forbs. Our results suggest that the plant functional types differed in their seasonal physiological strategies with shrubs likely to increase in abundance with warming conditions.

Technical Abstract: Differentiation in physiological activity is a critical component of resource partitioning in resource-limited environments. It is crucial to understand how physiological performance varies through time for different functional groups to forecast how terrestrial ecosystems will respond to change. Here, we tracked the seasonal progress of 13 species representing perennial C3 shrubs, C3 grasses, C4 grasses, and annual forb functional groups of the Colorado Plateau. We tested for differences in carbon assimilation strategies across functional groups and related photosynthetic rates to recent, seasonal, and annual precipitation and temperature variables. Despite seasonal shifts in species presence and activity, we found relatively small differences in seasonally weighted annual photosynthetic rates among groups. However, differences in the timing of maximum assimilation (Anet) was strongly functional group-dependent. Importantly, we found C3 shrubs employed a relatively consistent, low carbon capture strategy that enabled them to maintain photosynthetic activity year-round, but switched to a rapid growth strategy by responding to recent environmental conditions. C4 grasses, on the other hand, maintained higher Anet rates than C3 grasses late in the spring growing season by decreasing gs when temperatures were higher, thereby increasing water-use efficiency under conditions stressful for C3 grasses. Further, perennial grass Anet rates were explained in part by precipitation accumulated since the beginning of the current water year, a result opposite to shrubs that responded primarily to precipitation totals in the 48 hours prior to sampling. These results lend important insight into physiological growth strategies and potential for shrubs to increase in abundance in drylands given the group’s ability to respond rapidly to changing conditions.