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31 results for “semiarid grassland”
Data on: Dynamics of short-term ecosystem carbon fluxes induced by precipitation events in a semiarid grassland
<p>Data correspond to mean daytime net ecosystem carbon exchange (NEE) obtained through the eddy covariance method along six years from 2011 to 2016 (For more details of data see <a href="https://doi.org/10.1029/2018JG004799">https://doi.org/10.1029/2018JG004799</a>).</p> <p>Database contain changes of daytime NEE after a precipitation event (difference between previous day and the day after a precipitation event). Moreover, environmental and soil variables are included: 1) daily mean, previous and the change of soil water content at 2.5 and 15 cm depth, 2) previous NEE rate, 3) change of photosynthetic photon flux density, and 4) air temperature.</p> <p>Data was used to test the effect of environmental and soil variables on the daytime net ecosystem exchange. We was interested in short-term effects, i.e. the priming effect or the Birch effect.</p> <p>Manuscript where this database was used is under review.</p> <p> </p>
Gross primary production responses to warming, elevated CO2 , and irrigation: quantifying the drivers of ecosystem physiology in a semiarid grassland
<p>Determining whether the terrestrial biosphere will be a source or sink of carbon (C) under a future climate of elevated CO<sub>2</sub> (eCO<sub>2</sub>) and warming requires accurate quantification of gross primary production (GPP), the largest flux of C in the global C cycle. We evaluated 6 years (2007–2012) of flux‐derived GPP data from the Prairie Heating and CO<sub>2</sub> Enrichment (PHACE) experiment, situated in a grassland in Wyoming, USA. The GPP data were used to calibrate a light response model whose basic formulation has been successfully used in a variety of ecosystems. The model was extended by modeling maximum photosynthetic rate (<i>A</i><sub>max</sub>) and light‐use efficiency (<i>Q</i>) as functions of soil water, air temperature, vapor pressure deficit, vegetation greenness, and nitrogen at current and antecedent (past) timescales. The model fits the observed GPP well (<i>R</i><sup>2</sup> = 0.79), which was confirmed by other model performance checks that compared different variants of the model (e.g. with and without antecedent effects). Stimulation of cumulative 6‐year GPP by warming (29%, <i>P</i> = 0.02) and eCO<sub>2</sub> (26%, <i>P</i> = 0.07) was primarily driven by enhanced C uptake during spring (129%, <i>P</i> = 0.001) and fall (124%, <i>P</i> = 0.001), respectively, which was consistent across years. Antecedent air temperature (Tair<sub>ant</sub>) and vapor pressure deficit (VPD<sub>ant</sub>) effects on <i>A</i><sub>max</sub> (over the past 3–4 days and 1–3 days, respectively) were the most significant predictors of temporal variability in GPP among most treatments. The importance of VPD<sub>ant</sub> suggests that atmospheric drought is important for predicting GPP under current and future climate; we highlight the need for experimental studies to identify the mechanisms underlying such antecedent effects. Finally, posterior estimates of cumulative GPP under control and eCO<sub>2</sub> treatments were tested as a benchmark against 12 terrestrial biosphere models (TBMs). The narrow uncertainties of these data‐driven GPP estimates suggest that they could be useful semi‐independent data streams for validating TBMs.</p>
Data from: Trading water for carbon in the future: effects of elevated CO2 and warming on leaf hydraulic traits in a semiarid grassland
<p class="MsoNormal"><a name="_Hlk96844723"></a><span>The effects of climate change on plants and ecosystems are mediated by plant hydraulic traits, including interspecific and intraspecific variability of trait phenotypes. Yet, integrative and realistic studies of hydraulic traits and climate change are rare. In a semiarid grassland, we assessed the response of several plant hydraulic traits to elevated CO<sub>2</sub> (+200 ppm) and warming (+1.5</span><span><span> to </span></span><span><span>3</span></span><span><span>℃;</span></span><span><span> day to night). For leaves of five dominant species (three graminoids, two forbs), and in replicated plots exposed to seven years of elevated CO<sub>2</sub>, warming, or ambient climate, we measured: stomatal density and size, xylem vessel size, turgor loss point, and water potential (pre-dawn). Interspecific differences in hydraulic traits were larger than intraspecific shifts induced by elevated CO<sub>2</sub> and/or warming. Effects of elevated CO<sub>2</sub> were greater than effects of warming, and interactions between treatments were weak or not detected. The forbs showed little phenotypic plasticity. The graminoids had leaf water potentials and turgor loss points that were 10 to 50% less negative under elevated CO<sub>2</sub>; thus, climate change might cause these species to adjust their drought resistance strategy away from tolerance and toward avoidance. The C4 grass also reduced allocation of leaf area to stomata under elevated CO<sub>2</sub>, which helps explain observations of higher soil moisture. The shifts in hydraulic traits under elevated CO<sub>2</sub> were not, however, simply due to higher soil moisture. Integration of our results with others' indicates that common species in this grassland are more likely to adjust stomatal aperture in response to near-term climate change, rather than anatomical traits; this contrasts with apparent effects of changing CO<sub>2</sub> on plant anatomy over evolutionary time. Future studies should assess how plant responses to drought may be constrained by the apparent shift from tolerance (via low turgor loss point) to avoidance (via stomatal regulation and/or access to deeper soil moisture).</span></span></p>
Data from: Trading water for carbon in the future: effects of elevated CO2 and warming on leaf hydraulic traits in a semiarid grassland
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Scale dependence and mechanisms of grazing-induced biodiversity changes depend on herbivore type in semiarid grasslands
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Gross primary production responses to warming, elevated CO2 , and irrigation: quantifying the drivers of ecosystem physiology in a semiarid grassland
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Data from: Sensitivity of plant species to warming and altered precipitation dominates the community productivity in a semiarid grassland on the Loess Plateau
Global warming and changes in precipitation patterns can critically influence the structure and productivity of terrestrial ecosystems. However, the underlying mechanisms are not fully understood. We conducted two independent but complementary experiments (one with warming and precipitation manipulation (+ or – 30%) and another with selective plant removal) in a semi-arid grassland on the Loess Plateau, northwestern China to assess how warming and altered precipitation affect plant community. Our results showed that warming and altered precipitation affected community aboveground net primary productivity (ANPP) through impacting soil moisture. Results of the removal experiment showed competitive relationships among dominant grasses, dominant semi-shrub and non-dominant species, which played a more important role than soil moisture in the response of plant community to warming and altered precipitation. Precipitation addition intensified the competition but primarily benefited dominant semi-shrubs. Warming and precipitation reduction enhanced water stresses but increased ANPP of dominant semi-shrubs and grasses, indicating that plant tolerance to drought critically meditated the community responses. These findings suggest that specie competitivity for water resources as well as tolerance to environmental stresses may dominate the responses of plant communities on the Loess Plateaus to future climate change factors.
Data from: Changes in ecosystem carbon stocks following grazing exclusion in arid and semiarid grasslands
<ol> <li>Grazing exclusion (GE) is widely considered to be an important strategy for restoring overgrazed grasslands and promoting carbon (C) storage. However, the changes in the components of ecosystem C with GE and their related drivers remain largely unexplored.</li> <li>Here, we investigated the effects of GE on the ecosystem C components (plant and soil C) and their key driving factors through sampling inside and outside 15 grazing exclosures across the Inner Mongolia arid and semiarid grasslands in northern China.</li> <li>Our results showed that, except for dead root C, GE significantly promoted plant C stocks. The increase in AGB and litter C stocks resulted from the accumulation of both biomass and C concentration, while the increase in live root C stock was mainly attributed to biomass accumulation. In contrast, although the topsoil soil C concentration (0-20 cm) showed a marginal increase following GE, its bulk density greatly declined, which resulted in little change in the soil C stocks. Overall, GE had no significant effect on total ecosystem C stocks. Our results further indicated that across the grasslands, GE likely enhanced C accumulation in live roots in humid and fertile sites, while it caused losses of dead root C in relatively humid and fertile sites and increases in arid and infertile sites.</li> <li>We also found that the increases in AGB C, litter C and live root C stocks were driven by the direct effects of GE and its indirect effects mediated by soil water content. The marginal increases in soil C concentration with GE were linked to only high soil water contents. Meta-analysis further revealed that across the grasslands of China, the responses of ecosystem C components to GE were associated with changes in soil water conditions, suggesting the generality of soil water effects at the national scale.</li> <li>Overall, our results showed that across arid and semiarid grasslands, GE is generally beneficial for plant C accumulation but has little effect on soil C stocks. Importantly, our study highlighted the important role of soil water in regulating ecosystem C dynamics with GE across the grasslands of China.</li> </ol>
Effects of different functional structure parameters of plant communities on slope runoff in different periods of the year in semiarid grasslands
<p>Research on sustainable use of water resources is needed to ensure food security, limit erosion, and prevent land degradation. Owing to the importance of water conservation to ecosystems, further research on the water conservation functions of different ecosystems is needed. Given the influence on water conservation functions, it is critical to identify environmental factors mediating slope runoff. In this study, the focal study area was the Yangjuangou catchment (36°42' N, 109°31' E) of the Loess Plateau in Shaanxi Province, China. Using a trait-based approach, a quantitative analysis was conducted to research effects of the functional structure parameters of plant communities on runoff of grass slopes for different periods of the year under differing rainfall intensity conditions. Results show that in mid-June, which represents the start of the growing season, effects of root traits on slope runoff decrease with increasing rainfall intensity. Slope runoff was found to be mainly affected by various plant functional traits in late July and aboveground parts of plants in early September. Given that few studies have focused on runoff processes using a trait-based approach at the community scale, this research can serve as a new reference for investigating the relationship between slope runoff and vegetation.</p>
Data from: Aridity Modulates N Availability in Arid and Semiarid Mediterranean Grasslands
While much is known about the factors that control each component of the terrestrial nitrogen (N) cycle, it is less clear how these factors affect total N availability, the sum of organic and inorganic forms potentially available to microorganisms and plants. This is particularly true for N-poor ecosystems such as drylands, which are highly sensitive to climate change and desertification processes that can lead to the loss of soil nutrients such as N. We evaluated how different climatic, abiotic, plant and nutrient related factors correlate with N availability in semiarid Stipa tenacissima grasslands along a broad aridity gradient from Spain to Tunisia. Aridity had the strongest relationship with N availability, suggesting the importance of abiotic controls on the N cycle in drylands. Aridity appeared to modulate the effects of pH, plant cover and organic C (OC) on N availability. Our results suggest that N transformation rates, which are largely driven by variations in soil moisture, are not the direct drivers of N availability in the studied grasslands. Rather, the strong relationship between aridity and N availability could be driven by indirect effects that operate over long time scales (decades to millennia), including both biotic (e.g. plant cover) and abiotic (e.g. soil OC and pH). If these factors are in fact more important than short-term effects of precipitation on N transformation rates, then we might expect to observe a lagged decrease in N availability in response to increasing aridity. Nevertheless, our results suggest that the increase in aridity predicted with ongoing climate change will reduce N availability in the Mediterranean basin, impacting plant nutrient uptake and net primary production in semiarid grasslands throughout this region.
The effect of plant invasion on soil microbial carbon-use efficiency in semiarid grasslands of the Rocky Mountain West
<p>1. Grassland ecosystems invaded by exotic plant species often exhibit substantially higher aboveground productivity and soil nitrogen (N) than the native communities they replace. These shifts are likely associated with altered microbial carbon (C) and N cycling, but we know surprisingly little about how these processes change with plant invasion.</p> <p>2. Targeting four invasive plant species common in the Rocky Mountain West, we collected soils from invaded and adjacent uninvaded grassland field plots, as well as from an experimental garden. We used a laboratory incubation of soils with <sup>13</sup>C- and <sup>15</sup>N-labelled substrates to examine how microbial C respiration, C assimilation, and N cycling differed among plant communities. To assess how these rates corresponded with plant productivity and microbial communities, we measured aboveground plant biomass and characterized bacterial and fungal communities using Illumina sequencing.</p> <p>3. In the paired observational plots, soil microbial communities associated with invaders generally had higher respiration rates and lower growth rates than those associated with the native plant communities, leading to a lower microbial carbon-use efficiency (CUE). Overall, soil substrate with a lower C:N was related to decreased CUE, and lower CUE was related to increased gross and net N mineralization. In turn, faster gross N mineralization was related to greater aboveground biomass. These patterns coincided with significant differences in fungal communities, whereas bacterial communities varied by site. Invasive plants also altered microbial communities in the experimental plots, but this was not associated with shifts in microbial CUE, which was low overall.</p> <p>4. <i>Synthesis.</i> Our results provide evidence that invasive plants alter bacterial and fungal communities. These shifts were not associated with changes in microbial CUE and, thus, the often-assumed link between compositional and functional shifts was not apparent in this study. However, lower CUE was associated with elevated rates of N cycling and productivity, which, in low-productivity systems, could help explain the increased growth and success of exotic plant invaders.</p>
Increased interannual precipitation variability enhances the carbon sink in a semiarid grassland
<p>1. The amplifying interannual precipitation variability has been observed globally and is projected to intensify under climate change scenarios. However, its impacts on terrestrial vegetation and carbon (C) sink have not been well investigated.</p> <p>2. As part of a field manipulative experiment with three precipitation variabilities (20%, 40%, and 60%) in a semiarid grassland, this study was conducted to examine the responses of ecosystem C cycling to increased precipitation variability.</p> <p>3. Across the 3 experimental years from 2010 to 2012, amplified precipitation variability enhances gross primary productivity (GPP) and ecosystem respiration (ER) as both GPP and ER were more sensitive to above- than below-average precipitation. In addition, the larger responses of GPP than ER to precipitation variability resulted in an enhancement of net ecosystem productivity (NEP), and the magnitudes of NEP increased with the increasing precipitation variability. More species with higher sensitivity to increased precipitation under wet condition and the insensitive response of root growth to decreased precipitation could largely be responsible for the above observations, which suggest that the semiarid grassland was more sensitive to wet treatment yet strongly resistant to drought.</p> <p>4. Our results provide empirical evidence that intensified precipitation variability could stimulate grassland C sink. The findings revealed in this study could facilitate the mechanistic understanding and imply the potential positive feedback of climate variability-terrestrial C sink.</p>
Responses of a semiarid grassland to recurrent drought is linked to community functional composition
<p>Climate change-driven increases in the frequency of extreme droughts could negatively impact the functioning of grassland ecosystems. While several studies have documented the impact of individual droughts on grassland function, less is known about how grasslands will respond to recurrent drought. We conducted a repeated extreme drought experiment in a semiarid grassland that consisted of three stages: (1) initial drought, (2) recovery, and (3) subsequent drought. We measured aboveground net primary productivity (ANPP), species richness, plant functional traits, and functional diversity. Using structural equation modeling (SEM), we investigated the causal mechanisms of ANPP response to recurrent drought. The initial drought led to reduced ANPP, although this was driven by a differential reduction in the growth of grasses and forbs. Total ANPP completely recovered as the rapid recovery of grass productivity compensated for the slow recovery of forb productivity. The magnitude of ANPP responses to the subsequent drought was greater than the initial drought. The SEMs revealed that soil moisture influenced ANPP responses directly during the initial drought, and indirectly during the subsequent drought by altering community functional trait means and diversity during the subsequent drought. These differential mechanisms alter our fundamental understanding of ecosystem drought sensitivity, which is primarily based on single drought studies.</p>
Data from: Grassland management regimes alter the coordination of plant functional traits and nutrient resorption in semiarid grasslands
<p>Grazing and enclosure (grazing exclusion) are the main grassland management regimes that affect nutrient cycling and ecosystem function by altering plant traits. However, the coordination among plant functional traits and nutrient resorption under different grassland management regimes remains unclear. We examined the coordination of eight root and four leaf traits along with the nitrogen (N) and phosphorus (P) resorption efficiencies under four grazing intensities and two enclosure chronosequences in a semiarid steppe ecosystem in China. The principal components analysis (PCA) of root traits and multiple factors analysis of root and leaf traits showed two-dimensional economic spaces at the individual level. Increasing grazing intensity shifts species and community trait composition from conservative to acquisitive with increases in specific root length, specific root area, root alkaline phosphatase activity, and specific leaf area, accelerating nutrient cycling and coordination among traits. Increasing grazing intensity promoted nutrient resorption efficiency. Such adaptations optimize plant nutrient acquisition and nutrient conservation under nutrient-poor conditions. Conversely, long-term enclosure increases plant nutrient and light acquisition by promoting root tissue density, mycorrhizal colonization, and specific leaf area. The conservative (e.g., <em>Stipa grandis</em>) and acquisitive species (e.g., <em>Carex korshinskyi</em>) dominated under grazing, whereas the mid-acquisitive species, including <em>Leymus chinensis</em> and <em>Agropyron cristatum</em>,<em> </em>dominated under enclosure. The observed N and P resorption efficiencies decrease with increasing PC1 score (increase in nutrient acquisition by itself) in root PCA, indicating the trade-off between nutrient-conservative and nutrient-acquisitive strategies. Community-weighted mean traits were primarily driven by intraspecific trait variation, enhancing the adaptability of plants and communities to environmental changes and external stressors. Our study highlights the coordination among above- and below-ground traits, as well as the trade-off between root nutrient acquisition and leaf nutrient resorption under different grassland management regimes in semi-arid grassland ecosystems. From these findings, we conclude that enhancing soil nutrient availability is the most effective approach to the solution to grazing-induced grassland degradation. This knowledge is crucial for devising more effective strategies for sustainable land use and biodiversity conservation in grassland ecosystems.</p>
Data from: Native lagomorphs suppress grass establishment in a shrub‐encroached, semiarid grassland
Shrub encroachment into arid grasslands has been associated with reduced grass abundance, increased soil erosion, and local declines in biodiversity. Livestock overgrazing and the associated reduction of fine fuels has been a primary driver of shrub encroachment in the southwestern United States, but shrublands continue to persist despite livestock removal and grassland restoration efforts. We hypothesized that herbivory feedbacks from native mammals may contribute to continued suppression of grasses after the removal of livestock. Our herbivore exclusion experiment in southeastern Arizona included five treatment levels and allowed access to native mammals based on their relative body size, separating the effects of rodents, lagomorphs, and mule deer. We included two control treatments and replicated each treatment 10 times (n = 50). We introduced uniform divisions of lawn sod (Cynodon dactylon) into each exclosure for 24-hour periods prior to (n = 2) and following (n = 2) the monsoon rains and used motion-activated cameras to document herbivore visitations. In the pre-monsoon trials, treatments that allowed lagomorph access had less sod biomass relative to other treatments (p < 0.001), averaging 44% ( 36%) and 29% ( 45%) remaining biomass after the 24-hour trial periods. Following the onset of monsoons, differences in remaining biomass among treatments disappeared. Desert cottontails (Sylvilagus audubonii) were detected more frequently than any of the other 11 herbivore species present at the site, accounting for 83% of detections during the pre-monsoon trials. Significantly more (p < 0.001) desert cottontails were detected during the pre-monsoon trials (2,077) compared to the post-monsoon trials (174), which coincided with biomass removal from lagomorph accessible treatments. We conclude that desert cottontails are significant consumers of herbaceous vegetation in shrub-encroached arid grasslands and they, along with other native herbivores, may act as a biotic feedback contributing to the competitive advantage and persistence of shrubs.
Data from: Shrub encroachment does not reduce the activity of some soil enzymes in Mediterranean semiarid grasslands
Shrub encroachment is a worldwide phenomenon with implications for desertification and global change. We evaluated its effects on the activities of urease, phosphatase and b-glucosidase in Mediterranean semiarid grasslands dominated by Stipa tenacissima by sampling 12 sites with and without resprouting shrubs along a climatic gradient. The presence of shrubs affected the evaluated enzymes at different spatial scales. Soils under S. tenacissima tussocks and in bare ground areas devoid of vascular plants had higher values of phosphatase and urease when the shrubs were present. For the b-glucosidase, this effect was site-specific. At the scale of whole plots (30 m 30 m), shrubs increased soil enzyme activities between 2% (b-glucosidase) and 22% (urease), albeit these differences were significant only in the later case. Our results indicate that shrub encroachment does not reduce the activity of extracellular soil enzymes in S. tenacissima grasslands.
Overcompensation of ecosystem productivity following sustained extreme drought in a semiarid grassland
<p>Drought events are projected to be more extreme and frequent in the future and have profound influences on the structure and functions of terrestrial ecosystems. Thus, better understanding the mechanisms of recovery is critical for predicting the future dynamics of terrestrial ecosystems. We performed a seven-year field precipitation experiment to examine recovery of a grassland ecosystem from different magnitudes of sustained drought, from slight to extreme. The ecosystem was exposed to precipitation treatments in the first three years (2010-2012) and recovered during the last four years (2013-2016) without precipitation treatments. Overall, large reductions of aboveground net primary productivity (ANPP, -43.3%) and perennial forb biomass (-83.1%) were observed in the 3rd year (2012) of extreme drought only. Nevertheless, ANPP fully recovered within one year after the drought treatments were terminated, and the rapid recovery was mainly due to increased soil total nitrogen and root biomass allocation after drought. Surprisingly, large increases of ANPP under the extreme drought treatment occurred during the recovery periods from 2013-2015 (+74.1, +88.5, and +119.8 g m-2 yr-1) compared to the control. The overcompensation offset the extreme drought-induced reduction of ANPP in the treatment years and was primarily ascribed to the enhanced biomass of perennial grasses. Higher resistance to drought and fast resource acquisition strategy might drive the rapid recovery and expansion of perennial grasses. Our findings revealed the rapid recovery of grasslands and the critical role of community overcompensation in maintaining grassland ecosystem function and stability under future climate change scenarios.</p>
Data from: Native lagomorphs suppress grass establishment in a shrub‐encroached, semiarid grassland
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Increased interannual precipitation variability enhances the carbon sink in a semiarid grassland
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Data from: Sensitivity of plant species to warming and altered precipitation dominates the community productivity in a semiarid grassland on the Loess Plateau
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