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1. Belowground responses to altered precipitation regimes in two semi-arid grasslands

   https://doi.org/10.6073/pasta/2d233f4ba9af3a13b564a1c6364704c7  

   Holguin, Jennifer; Collins, Scott L; McLaren, Jennie R (January 2022, Environmental Data Initiative)

   Predicted climate change extremes, such as severe and prolonged drought, may profoundly impact biogeochemical processes like carbon and nitrogen cycling in water-limited ecosystems. To increase our understanding of how extreme climate events impact belowground ecosystem processes, we investigated the effects of five years of severe growing season drought and two-month delay in monsoon precipitation on belowground productivity and biogeochemical processes in two semi-arid grasslands. This experiment takes place during the fifth year of the Extreme Drought in Grassland Experiment (EDGE) at the Sevilleta National Wildlife Refuge (SNWR), a Long-Term Ecological Research in central New Mexico, USA. The two grassland sites a Chihuahuan Desert grassland dominated by Bouteloua eriopoda and Great Plains grassland dominated by B. gracilis are ~5km apart in the SWNR. The EDGE platform was established in the spring of 2012 (pre-treatment). Each site contains three treatments (ten replicates): ambient rainfall, extreme growing season drought, and delayed monsoon. The extreme drought treatment reduces growing season rainfall (April through September) each year by 66%, which equates to a 50% reduction of annual precipitation while maintaining natural precipitation patterns. There are 10 replicates per treatment within each site. All plots are 3 x 4 m in size and are paired spatially into blocks with treatments assigned randomly within a block. We measured an array of belowground and biogeochemical variables. Each variable was measured either once, twice, or three times (specific information on sampling scheme for each measured variable in methods section). Belowground net primary productivity, standing crop root biomass, total organic carbon, and total nitrogen were measured once. Extractable organic carbon, extractable total nitrogen, microbial biomass carbon, microbial biomass nitrogen and extracellular enzymes were measured twice. Available soil nitrate, available soil ammonium, and available soil phosphate were measured three times. 

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2. Small rainfall events increase belowground production in Chihuahuan Desert grassland

   https://doi.org/10.1002/ecy.70206  

   Collins, Scott L; Brown, Renée F (September 2025, Ecology)

   Abstract Dryland productivity is highly sensitive to precipitation variability, and models predict that rainfall variability will increase in the future. Numerous studies have documented the relationship between productivity and precipitation, but most focus on aboveground production (ANPP), while the effects on belowground production (BNPP) remain poorly understood. Furthermore, previous research suggests that ANPP and BNPP are uncoupled within ecosystems, but the degree to which rainfall variability affects the interplay between aboveground and belowground production is unknown. We conducted a long‐term rainfall manipulation experiment in Chihuahuan Desert grassland to investigate how the size and frequency of growing season rain events affected BNPP and its relationship to ANPP. Experimental plots received either 12 small‐frequent rain events or 3 large‐infrequent events during the monsoon season for a total of 60 mm of added rainfall per treatment per year. All plots, including three controls, received ambient rainfall throughout the year. Total BNPP ranged from a low of 94.7 ± 38.2 g m²year⁻¹under ambient conditions to a high of 183.7 ± 44.6 g m²year⁻¹under the small‐frequent rainfall treatment. Total BNPP was highest under small‐frequent rain events, and there was no difference in BNPP between 0–15 and 15–30 cm soil depths in either rainfall treatment. ANPP and BNPP were uncorrelated within rainfall treatments, but weakly positively correlated across all plots and years. Our results contribute to a growing body of research on the importance of small rain events in drylands and provide further evidence regarding the weak coupling between aboveground and belowground processes. 

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3. Extreme Drought Decreases the Stability of Above‐ but Not Below‐Ground Productivity Across Eurasian Steppes

   https://doi.org/10.1111/gcb.70303  

   Yan, Yingjie; Xu, Chong; Hautier, Yann; Wang, Hongqiang; Ke, Yuguang; Wu, Honghui; Wang, Jinsong; Cheng, Changjin; Zuo, Xiaoan; Luo, Wentao; et al (June 2025, Global Change Biology)

   ABSTRACT Ecological stability plays a crucial role in determining the sustainability of ecosystem functioning and nature's contribution to people. Although the disruptive effects of extreme drought on ecosystem structure and functions are widely recognized, their effect on the stability of above‐ and belowground productivity remains understudied. We assessed the effects of drought on ecosystem stability using a 3‐year drought experiment established in six Eurasian steppe grasslands. The treatments imposed included ambient precipitation, chronic drought (66% reduction in precipitation throughout the growing season), and intense drought (complete exclusion of precipitation for two months during the growing season). We found that drought, irrespective of how it was imposed, reduced the stability of aboveground net primary productivity (ANPP) but had little impact on belowground net primary productivity (BNPP) stability. Reduced ANPP stability under drought was primarily attributed to changes in subordinate species stability, with mean annual precipitation (MAP) and its variability, historical drought frequency, and the aridity index (AI) also influencing responses to extreme drought. In contrast, BNPP stability was not related to any community factor investigated, but it was influenced by MAP variability and AI. Our findings that above‐ and belowground productivity stability in grasslands are differentially sensitive to multi‐year extreme drought under both common (MAP and AI) as well as unique drivers (plant community changes) highlight the complexity of predicting carbon cycle dynamics as hydrological extremes become more severe. 

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4. Limited legacy effects of extreme multiyear drought on carbon and nitrogen cycling in a mesic grassland

   https://doi.org/10.1525/elementa.2021.000093  

   Vilonen, Leena L.; Blair, John; Trivedi, Pankaj; Zeglin, Lydia; Smith, Melinda D. (January 2022, Elementa: Science of the Anthropocene)

   The intensification of drought throughout the U.S. Great Plains has the potential to have large impacts on grassland functioning, as has been shown with dramatic losses of plant productivity annually. Yet, we have a poor understanding of how grassland functioning responds after drought ends. This study examined how belowground nutrient cycling responds after drought and whether legacy effects persist postdrought. We assessed the 2-year recovery of nutrient cycling processes following a 4-year experimental drought in a mesic grassland by comparing two different growing season drought treatments—chronic (each rainfall event reduced by 66%) and intense (all rain eliminated until 45% of annual rainfall was achieved)—to the control (ambient precipitation) treatment. At the beginning of the first growing season postdrought, we found that in situ soil CO2 efflux and laboratory-based soil microbial respiration were reduced by 42% and 22%, respectively, in the intense drought treatment compared to the control, but both measures had recovered by midseason (July) and remained similar to the control treatment in the second postdrought year. We also found that extractable soil ammonium and total inorganic N were elevated throughout the growing season in the first year after drought in the intense treatment. However, these differences in inorganic N pools did not persist during the growing season of the second year postdrought. The remaining measures of C and N cycling in both drought treatments showed no postdrought treatment effects. Thus, although we observed short-term legacy effects following the intense drought, C and N cycling returned to levels comparable to nondroughted grassland within a single growing season regardless of whether the drought was intense or chronic in nature. Overall, these results suggest that the key aspects of C and N cycling in mesic tallgrass prairie do not exhibit persistent legacies from 4 years of experimentally induced drought. 

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5. Soil seedbank analysis under experimental drought and delayed monsoon treatments in blue grama and black grama grassland at Sevilleta

   https://doi.org/10.6073/pasta/0c1cfdf74faae96dd4d489f8b6c49c24  

   Loydi, Alejandro; Collins, Scott L (January 2021, Environmental Data Initiative)

   {"Abstract":["This study investigated the question, "Does climate change\n affect vegetation and seed bank composition in desert\n grasslands?" The work was done in the Sevilleta National\n Wildlife Refuge, New Mexico, USA, in in the Extreme Drought in\n Grassland Experiment (EDGE). Vegetation and seed bank species\n composition were recorded in black grama (Bouteloua eriopoda) and\n blue grama (B. gracilis) grasslands at Sevilleta. At each site, two\n rainfall manipulations and ambient controls were established in 2013\n (n=10). Treatments included extreme drought (-66% rainfall\n reduction) and delayed monsoon (precipitation captured during\n July-August and reapplied during September-October). Aboveground\n species composition was assessed and composite soil samples were\n collected in 2017, five years after the experiment started. Seed\n bank composition was evaluated using the seedling emergence method.\n Rainfall treatments increased aboveground species richness at both\n sites, and seed bank richness only in the blue grama community.\n Vegetation cover was reduced by both rainfall manipulations, but\n seed bank density increased or remained the same compared with\n controls. In aboveground vegetation, cover of annual and perennial\n forbs increased, and dominant perennial grasses decreased. In the\n soil seed bank, species composition was similar among all treatments\n and was dominated by annual and perennial forbs. The seed bank was\n more resistant to drought than aboveground vegetation. Because seed\n banks enhance long-term community stability, their drought\n resistance plays an important role in maintaining ecosystem\n processes during and following drought in these grassland\n communities."]} 

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