@article {JRN54629, title = {Global-change drivers of ecosystem functioning modulated by natural variability and saturating responses}, journal = {Global Change Biology}, volume = {23}, year = {2017}, pages = {503-511}, abstract = {

Humans are altering global environment at an unprecedented rate through changes in biodiversity, climate, nitrogen cycle, and land use. To address their effects on ecosystem functioning, experiments most frequently explore one driver at a time and control as many confounding factors as possible. Yet, which driver exerts the largest influence on ecosystem functioning and whether their relative importance changes among systems remain unclear. We analyzed experiments in the Patagonian steppe that evaluated the aboveground net primary production (ANPP) response to manipulated gradients of species richness, precipitation, temperature, nitrogen fertilization (N), and grazing intensity. We compared the effect on ANPP relative to ambient conditions considering intensity and direction of manipulations for each driver. The ranking of responses to drivers with comparable manipulation intensity was as follows: biodiversity\>grazing\>precipitation\>N. For a similar intensity of manipulation, the effect of biodiversity loss was 4.0, 3.6, and 1.5, times larger than N deposition, decreased precipitation, and increased grazing intensity. We interpreted our results considering two hypotheses. First, the response of ANPP to changes in precipitation and biodiversity is saturating, so we expected larger effects when the driver was reduced, relative to ambient conditions, than when it was increased. Experimental manipulations that reduced ambient levels had larger effects than those that increased them. Second, the sensitivity of ANPP to each driver is inversely related to the natural variability of the driver. In Patagonia, the ranking of natural variability of drivers is as follows: precipitation\>grazing\>temperature\>biodiversity\> N. So, in general, the ecosystem was most sensitive to drivers that varied the least. Comparable results from Cedar Creek (MN) support both hypotheses and suggest that sensitivity to drivers varies among ecosystem types. Given the importance of understanding ecosystem sensitivity to predict global-change impacts, it is necessary to design new experiments located in regions with contrasting natural variability and that include the full range of drivers.

}, keywords = {ANPP, biodiversity loss, climate change, ecosystem sensitivity, land-use change, nitrogen deposition}, doi = {10.1111/gcb.13441}, url = {files/bibliography/JRN00656.pdf}, author = {P. Flombaum and Laura Yahdjian and O. E. Sala} } @article {JRN52695, title = {Interactions among resource partitioning, sampling effect, and facilitation on the biodiversity effect: a modeling approach}, journal = {Oecologia}, volume = {174}, year = {2014}, pages = {559-566}, abstract = {

Resource partitioning, facilitation, and sampling effect are the three mechanisms behind the biodiversity effect, which is depicted usually as the effect of plantspecies richness on aboveground net primary production. These mechanisms operate simultaneously but their relative importance and interactions are difficult to unravel experimentally. Thus, niche differentiation and facilitation have been lumped together and separated from the sampling effect. Here, we propose three hypotheses about interactions among the three mechanisms and test them using a simulation model. The model simulated water movement through soil and vegetation, and net primary production mimicking the Patagonian steppe. Using the model, we created grass and shrub monocultures and mixtures, controlled root overlap and grass water-use efficiency (WUE) to simulate gradients of biodiversity, resource partitioning and facilitation. The presence of shrubs facilitated grass growth by increasing its WUE and in turn increased the sampling effect, whereas root overlap (resource partitioning) had, on average, no effect on sampling effect. Interestingly, resource partitioning and facilitation interacted so the effect of facilitation on sampling effect decreased as resource partitioning increased. Sampling effect was enhanced by the difference between the two functional groups in their efficiency in using resources. Morphological and physiological differences make one group outperform the other; once these differences were established further differences did not enhance the sampling effect. In addition, grass WUE and root overlap positively influence the biodiversity effect but showed no interactions.

}, keywords = {biodiversity and ecosystem functioning, facilitation, model, net primary production model, NPP model, Patagonian steppe, resource partitioning, sampling effect, water movement}, issn = {0029-8549}, doi = {10.1007/s00442-013-2775-8 }, url = {files/bibliography/JRN00627.pdf}, author = {P. Flombaum and O. E. Sala and E. B. Rastetter} } @article {50206, title = {Higher effect of plant species diversity on productivity in natural than artificial ecosystems}, journal = {Proceedings of the National Academy of Sciences}, volume = {105}, year = {2008}, note = {//OTHER//OTHER//entered 06/02/2008 per DEP}, month = {2008}, pages = {6087-6090}, keywords = {article, biodiversity, plant, carbon cycle, ecosystem, artificial, ecosystem, natural, journal, Patagonian steppe, resource partitioning}, author = {P. Flombaum and O. E. Sala} } @article {50328, title = {A non-destructive and rapid method to estimate biomass and aboveground net primary production in arid environments}, journal = {Journal of Arid Environments}, volume = {69}, year = {2007}, note = {//Other//LTER-V//entered 08/15/2007}, month = {2007}, pages = {352-358}, abstract = {

We present the calibration of a fast and non-destructive method to estimate aboveground plant biomass measuring vegetation cover. We double-sampled vegetation cover and aboveground biomass in the Patagonian steppe using 150 plots for shrubs and 50 plots for grasses. We performed simple linear regressions between vegetation cover and biomass for the dominant species and life forms (shrubs: Mulinum spinosum, Senecio filaginoides, and Adesmia campestris; grasses: Poa ligularis, Stipa speciosa, and Stipa humilis). All regressions were significant (po:01) for green and total biomass. Whereas all grass species had similar slopes, shrub slopes differed among each other with S. filaginoides and A. campestris having the steepest slopes for green and total biomass, respectively (po:05). Life-form calibrations showed steeper slopes for shrubs than for grasses (po:05). Our regressions are a basis for a non-destructive, rapid, and inexpensive way of estimating green biomass, aboveground net primary production (ANPP), and forage availability. Our life-form equations very likely could be used to estimate biomass and ANPP in other arid ecosystems dominated by tussock grasses and shrubs. {\textcopyright}2006 Elsevier Ltd. All rights reserved.

}, keywords = {article, journal, method, aboveground net primary production, method, ANPP, method, calibration, method, double sampling, method, vegetation cover, Patagonian steppe}, doi = {10.1016/j.jaridenv.2006.09.008}, url = {files/bibliography/JRN00466.pdf}, author = {P. Flombaum and O. E. Sala} }