@conference {JRN55247, title = {Effects of contrasting rooting distribution patterns on plant transpiration along a precipitation gradient}, booktitle = {Ecological Society of America}, year = {2020}, month = {08/2020}, address = {Virtual Conference}, abstract = {Understanding and predicting ecosystem responses to projected increases in climate extremes in water limited ecosystems requires a thorough assessment of the role plant root systems. Land-use change and shrub encroachment may drastically change root distribution in the soil profile affecting water and nutrient uptake. However, the relationship among plant rooting distribution patterns, climate change and ecosystem functioning has been understudied. Our objective was to study the effect of rooting distribution patterns ranging from very shallow to very deep on plant transpiration across sites along precipitation gradient. We used SOILWAT, a multi-layer, daily time-step model that simulates soil water content by depth in the soil profile. Processes simulated in SOILWAT include water interception and subsequent evaporation from the plant canopy and litter, water infiltration into the soil, vertical water flow among soil layers, evaporation and transpiration from each soil layer, and soil water content by layer. We hypothesized that (1) plant-root distribution has a significant effect on plan transpiration. (2) The effect of rooting depth pattern changes from arid to mesic ecosystems. In order to test these hypotheses, we modeled water losses and soil-water availability at 100 dryland locations with virtual root distributions that simulate shallow and deep root systems. We evaluated the effect of contrasting rooting distribution on maximum plant transpiration, a proxy for plant growth and primary productivity. Our results showed that plant rooting depth has a significant effect on plant transpiration, soil evaporation and deep percolation. The rooting depth profile that maximized plant transpiration changed along a precipitation gradient. Arid ecosystems maximized transpiration with significantly shallower roots than more mesic ecosystems. Differences along the precipitation gradient are related to the relative contribution of water fluxes to the overall water balance. In arid ecosystems, soil water losses occur predominantly through soil evaporation while in mesic ecosystems the main water loss path is deep percolation. Therefore, shallow roots minimized water losses in arid sites (Evap = -1.12 + 8.94 * rooting depth, R2 = 0.3, P = 0.006) and deep roots minimized water losses in mesic sites (Percol = 60.4 {\textendash} 18 * rooting depth, R2 = 0.4, P = 0.008). The effect of biotic exchange and land-use change resulting in novel plant communities with different root traits will affect the water-use efficiency of water limited ecosystems. Changes in rooting distribution patterns will impact primary productivity because plant transpiration is tightly related to photosynthesis. Poster $\#$84160.}, author = {Laureano A. Gherardi and O. E. Sala and Debra C. Peters} } @conference {JRN54648, title = {Effects of contrasting rooting distribution patterns on plant transpiration along a precipitation gradient}, booktitle = {Ecological Society of America}, year = {2016}, month = {08/2016}, publisher = {Ecological Society of America Abstracts}, organization = {Ecological Society of America Abstracts}, address = {Ft Lauderdale, FL}, abstract = {

Understanding and predicting ecosystem functioning in water limited ecosystems requires a thorough assessment of the role plant root systems. Widespread ecological phenomena such as shrub encroachment may drastically change root distribution in the soil profile affecting the uptake of water and nutrients. However, the relationship between plant rooting distribution patterns and ecosystem functioning has been largely overlooked. Our objective was to assess the role of a range of rooting distribution patterns on plant transpiration across sites along precipitation gradient. We used SOILWAT, a multi-layer, daily time-step model that simulates soil water content by depth in the soil profile. Processes simulated in SOILWAT include water interception and subsequent evaporation from the plant canopy and litter, water infiltration into the soil, vertical water flow among soil layers, evaporation and transpiration from each soil layer, and soil water content by layer. We hypothesized that (1) plant root distribution would have a significant effect on plan transpiration. (2) The effect of rooting pattern changes along a precipitation gradient. In order to test these hypotheses, we modeled water losses and soil-water availability at 55 grassland locations with virtual root distributions that simulate shallow and deep root systems. We evaluated the effect of contrasting rooting distribution on plant transpiration, a variable tightly correlated with plant growth and primary productivity. Our results show that plan rooting distribution patterns have a significant effect on plant transpiration. Shallow root distribution showed significantly lower transpiration than deep root distributions, a mean difference of 8.2 cm/yr. Such effect changed along a precipitation gradient showing smaller effects of root distribution in arid sites than in mesic sites. Locally, plant transpiration increased with rooting depth up to a point where transpiration reached a plateau. The shape of such relationship and the maximum transpiration rate changed among sites. Arid ecosystems showed shallower transpiration rate increases as root depth increased and smaller maximum transpiration rates than mesic ecosystems. The effect of species invasions or changes in the relative abundance of plan types with different root traits will affect ecosystem functioning. Given the tight relationship that exists between transpiration and photosynthesis, we expect that changes in rooting distribution patterns will impact primary productivity with greater effects in mesic.

}, author = {Laureano A. Gherardi and O. E. Sala and Debra C. Peters} } @article {JRN54386, title = {Enhanced interannual precipitation variability increases plant functional diversity that in turn ameliorates negative impact on productivity}, journal = {Ecology Letters}, volume = {18}, year = {2015}, pages = {1293-1300}, abstract = {

Although precipitation interannual variability is projected to increase due to climate change, effects of changes in precipitation variance have received considerable less attention than effects of changes in the mean state of climate. Interannual precipitation variability effects on functional diversity and its consequences for ecosystem functioning are assessed here using a 6-year rainfall manipulation experiment. Five precipitation treatments were switched annually resulting in increased levels of precipitation variability while maintaining average precipitation constant. Functional diversity showed a positive response to increased variability due to increased evenness. Dominant grasses decreased and rare plant functional types increased in abundance because grasses showed a hump-shaped response to precipitation with a maximum around modal precipitation, whereas rare species peaked at high precipitation values. Increased functional diversity ameliorated negative effects of precipitation variability on primary production. Rare species buffered the effect of precipitation variability on the variability in total productivity because their variance decreases with increasing precipitation variance.

}, keywords = {arid zones, climate change, ecosystem functioning, functional diversity, grassland, interannual, precipitation variability, productivity, stability}, doi = {10.1111/ele.12523}, url = {/files/bibliography/15-028.pdf}, author = {Laureano A. Gherardi and O. E. Sala} } @article {JRN54387, title = {Enhanced precipitation variability decreases grass- and increases shrub-productivity}, journal = {Proceedings of the National Academy of Sciences}, volume = {112}, year = {2015}, pages = {12735-12740}, abstract = {

Although projections of precipitation change indicate increases in variability, most studies of impacts of climate change on ecosystems focused on effects of changes in amount of precipitation, overlooking precipitation variability effects, especially at the interannual scale. Here, we present results from a 6-y field experiment, where we applied sequences of wet and dry years, increasing interannual precipitation coefficient of variation while maintaining a precipitation amount constant. Increased precipitation variability significantly reduced ecosystem primary production. Dominant plantfunctional types showed opposite responses: perennial-grass productivity decreased by 81\%, whereas shrub productivity increased by 67\%. This pattern was explained by different nonlinear responses to precipitation. Grass productivity presented a saturating response to precipitation where dry years had a larger negative effect than the positive effects of wet years. In contrast, shrubs showed an increasing response to precipitation that resulted in an increase in average productivity with increasing precipitation variability. In addition, the effects of precipitation variation increased through time. We argue that the differential responses of grasses and shrubs to precipitation variability and the amplification of this phenomenon through time result from contrasting root distributions of grasses and shrubs and competitive interactions among plant types, confirmed by structural equation analysis. Under drought conditions, grasses reduce their abundance and their ability to absorb water that then is transferred to deep soil layers that are exclusively explored by shrubs. Our work addresses an understudied dimension of climate change that might lead to widespread shrub encroachment reducing the provisioning of ecosystem services to society.\ 

}, keywords = {ANPP, interannual variability, nonlinear response, plant-functional types, precipitation}, doi = {10.1073/pnas.1506433112}, url = {/files/bibliography/15-027.pdf}, author = {Laureano A. Gherardi and O. E. Sala} }