Intermittent streams that regularly dry up constitute over half of the world's river network. They exhibit biogeochemical processes distinct from those of continuously flowing perennial rivers. In perennial rivers, discharge is often perceived as predominantly driving water chemistry, as demonstrated by the widespread use of concentration-discharge (CQ) relationships. Does discharge similarly drive water chemistry in intermittent streams? Given its extended periods of no flow, we hypothesized that stream chemistry depends less on discharge alone but more on the granularity of dry-wet transitions, including their direction (drying or rewetting), history (antecedent conditions), and intermittency. We tested this hypothesis by analyzing three decades of streamflow and solute chemistry data from an intermittent stream (N04D) in the Konza Prairie Biological Station, a Long-Term Ecological Research site in Kansas, USA. Results showed that concentrations are generally higher at no flow compared to flow conditions and depend on dry-wet transitions. Geogenic solutes were predominantly chemostatic (relatively constant C without Q dependence), contrasting primarily dilution patterns (decreasing C with Q) in perennial rivers. Biogenic solutes did not exhibit pronounced discharge-dependent patterns commonly observed in perennial rivers at decadal scale; at monthly scale, however, they exhibited a transition from highly variable CQ patterns at low flows to consistent flushing patterns (increasing C with Q) at flows higher than 2.5-5 mm/day. These observations support our hypothesis of weaker chemistry dependence on discharge in intermittent streams. We further hypothesize that the emerging discharge thresholds signal a tipping point at which intermittent streams switch from a dry state governed by intermittency-driven biogeochemistry to a wet, discharge-driven state resembling perennial rivers. The hypothesis calls for intensive data collection at dry-wet transitions to develop theories and models for intermittent streams that have become increasingly prevalent globally.

Nuanced characterizations of moisture source dynamics and local hydrometeorological processes are essential for interpreting long-term records of stable isotopes in precipitation. Here, we analyze over two decades of stable isotope records from a site in the Great Plains of United States, revealing a distinct seasonal contrast in δ18O variability between warm (March-November) and cold (December-February) periods. During the warm season, isotopic enrichment was largely driven by enhanced convective activity and sub-cloud evaporation under high VPD conditions. Back-trajectory diagnostics indicate that continental moisture sources dominate precipitation at the study site, while Gulf of Mexico transport via the Great Plains low-level jet exerts a disproportionate influence on δ18O and d-excess variability. During extreme precipitation years, isotopic signatures reflect the combined effects of atmospheric circulation anomalies and local aridity. The 2012 drought year exhibited elevated δ18O and reduced d-excess consistent with enhanced kinetic fractionation under dry conditions, whereas the wet year 2019 showed isotopic enrichment associated with intensified Gulf-sourced moisture transport under humid conditions. These findings demonstrate how precipitation δ18O in the Great Plains integrates both local evaporative demand and large-scale moisture transport processes. Given ongoing challenges in representing humidity trends and regional hydroclimate dynamics in climate models, improved characterization of moisture sources and isotope variability is critical for evaluating model projections and interpreting long-term climate change in semi-arid continental regions.

Woody encroachment threatens grassland ecosystems worldwide. Recovery options often aim for a return to an idealized, grassy state that is more vulnerable to future climate regimes and can no longer be maintained using historic management techniques. We argue for a fundamental rethinking of how to manage woody plant encroachment in the North American Great Plains that moves away from binary options (e.g., encroached versus pristine). This approach acknowledges that some grassland landscapes will contain mosaics of woody cover that, if managed effectively, can provide beneficial ecosystem services. The resist-accept-direct framework is one option to guide management efforts to maintain grasslands with high resilience and direct changes to avoid mono-specific communities and move toward heterogeneous communities of herbaceous and woody species. Shifting baseline conditions (e.g., climate and disturbances) and complex social views on grassland services render historic management options incomplete, requiring new perspectives and frameworks for grassland conservation.

The American bison is often recognized as an ecological engineer because their grazing and wallowing behavior increases plant diversity and productivity. These disturbances increase spatial heterogeneity and can alter plant nutrient and water dynamics. We assessed how bison grazing and wallowing affect grass chemistry and physiology, and whether grass evolutionary legacies mediate species-specific responses. We measured grass drought tolerance, photosynthetic activity, and foliar and soil chemistry in four grass species at Konza Prairie Biological Station (Kansas, USA). Species included two dominant C4 panicoids, one C3 panicoid, and one C4 chloridoid species that becomes dominant in grazed areas. We sampled grasses in grazed areas near and away from bison wallows and adjacent fenced areas that have excluded bison for over 30 years. We assessed intra-annual changes in turgor loss point, maximum leaf electron transport rate, foliar δ13C, and C, N, P, and K content. Soil nutrient concentrations did not vary across locations, but foliar P, K, and N content was highest near bison wallows. Higher foliar N in bison grazed areas was correlated with higher electron transport rate. The chloridoid species showed the greatest response to bison wallows, with lower turgor loss point and higher foliar nutrients near wallows than in adjacent grazed prairie. Our results demonstrate that bison grazing creates fine-scale heterogeneity that alters plant nutrient dynamics, photosynthetic capacity, and drought tolerance. These findings suggest that bison engineer ecosystems not only through changes in plant communities but also through the physiological responses of dominant grass species.

Soil structure describes the repeating units of peds—aggregated soil particles bound by planes of weakness and formed from soil forming processes—and the corresponding network of interpedal pores. Processes forming soil structure can be altered in soils above shallow lithic contacts (SLCs), making the soil-rock interface potentially important to the development and maintenance of soil structure. Despite the widespread occurrence of SLCs, the mechanisms controlling soil structural development and water flow remain poorly understood. We used a unique long-term experiment at the Konza Prairie Biological Station where limestones were buried at ~20-25 cm depth to mimic a shallow bedrock and compared them to control plots without rocks. After 25 years, four soil pits (two control and two limestone treatments) were excavated to 40 cm to assess aggregate-size distribution, macroporosity, ped morphology, root biomass, micromorphology, and hydraulic properties. Larger aggregates (>0.5 mm) and greater macroporosity were observed above limestones compared to control. In the upper 0–5 cm, limestone plots exhibited larger, rougher, and less rounded peds, along with higher root biomass. Micromorphological analyses revealed distinct pore types and abundances, indicating structures that formed during the experiment as well as structural pores that can facilitate water and fine particle transport. Soil moisture data showed higher macropore flow and more macropore peaks in interspace (space b/w the rocks) than in control and rock plots. These findings provide a foundation for developing and testing hypotheses in experimental and natural settings for how lithic contacts influence soil structural formation and pore network development.

Ecosystems carry memory through the material remains of organisms. Foundation species-trees, grasses, corals, and oysters-while alive are central to ecosystem structure, and the remains of these organisms continue to influence ecological processes after death. We conducted, to our knowldge, the first continental-scale exploration of how dead foundation species influence living conspecifics, leveraging long-term experiments and observations (2 to 32 years) from 10 ecosystems (five terrestrial and five marine) across the US Long Term Ecological Research Network. We found that material legacies commonly alter demographic processes, ranging from a 50% reduction to a 12-fold increase. The ubiquity of these postmortem effects reveals an underappreciated dimension of ecological memory that shapes pathways of ecosystem resilience, reorganization, and collapse, providing a critical management tool in an era of increasing disturbance- and climate-driven mortality events.

Abstract Land surface models (LSMs), such as the Community Land Model version 5 (CLM5), represent complex vegetation processes; however, systematic biases persist between modeled and observed leaf area index (LAI) because of parameter uncertainties and knowledge gaps. The high computational cost of CLM5 is a barrier to extensive sensitivity analyses and ensemble simulations at the global scale. This study addresses these limitations by training an evidential deep neural network (EDNN) emulator on a 500‐member CLM5 perturbed parameter ensemble generated via Latin hypercube sampling of 32 key plant physiological parameters. The EDNN employs cyclic temporal encoding to preserve seasonal periodicity and to predict LAI anomalies, thereby emphasizing variability. It also quantifies predictive uncertainty by jointly learning aleatoric and epistemic components in a single forward pass, yielding well‐calibrated probabilistic outputs without requiring computationally intensive ensembles. Across the contiguous United States, the EDNN reproduces CLM5‐simulated LAI with a median R2≈0.8 on held‐out members and years while requiring substantially less computation. The EDNN emulator captures seasonal cycles, interannual variability in LAI, and uncertainties (aleatoric and epistemic) in a single pass. The sensitivity analysis highlights photosynthetic capacity and the leaf carbon‐to‐nitrogen ratio as dominant controls on LAI variability, with seasonal shifts in their influence reflecting phenological dynamics. These capabilities enable comprehensive parameter‐sensitivity studies and more efficient calibration and tuning of land surface models by supporting rapid probabilistic forecasting and adaptive model refinement, thereby paving the way for scalable Earth‐system modeling, robust parameter exploration, and uncertainty‐informed projections of land‐surface processes.

Given the rapid pace of global change, determining if our past understanding of the controls of ecosystem structure and function remains robust today is essential for managing and conserving ecosystems. Here, we revisit a foundational study that evaluated patterns and controls of aboveground net primary productivity (ANPP) across topographic gradients and in response to fire frequency treatments from 1975 to 1993 in tallgrass prairie (Konza Prairie). We replicated this 30-year-old study for a contemporary period (2005–2023) and found that overall patterns of ANPP across fire treatments and topographic gradients remained consistent. However, the magnitude of ANPP responses to fire increased substantially (> twofold) in lowlands, resulting in greater landscape-scale divergence in ANPP. Differences in temporal variability among topographic positions and fire regimes also increased ( fourfold). Annual precipitation remained a primary determinant of ANPP, but atmospheric vapor pressure deficit (VPD) has emerged as a new driver in contemporary times. Furthermore, air temperature and deep soil moisture have now become significant controls of ANPP in unburned grassland. We conclude that despite myriad global changes, the primary controls of ANPP have not changed dramatically over three decades, but additional drivers have emerged (notably VPD), and the magnitude of responses to fire have been altered. Increased spatial variation in ANPP as well as interannual variability in ANPP differing more strongly among sites will be particularly challenging for managing this rare grassland. As temperatures and VPD continue to increase, additional revision to our understanding of the functioning of this and other ecosystems will likely be necessary.

Root distributions are typically based on root mass per soil volume. This plant‐focused approach masks the biogeochemical influence of fine roots, which weigh little. We assert that centimeter‐scale root presence‐absence data from soil profiles provide a more soil‐focused approach for probing depth distributions of root‐regolith interfaces, where microsite‐scale processes drive whole‐ecosystem functioning. In 75 soil pits across the continental USA, Puerto Rico, and the Alps, we quantified fine and coarse root presence as deep as 2 m. In 70 of these pits we estimated root mass and created standardized metrics of both data sets to compare their depth distributions. We addressed whether: (a) depth distributions of root presence‐absence data differ from root mass data, thus implying different degrees of root‐regolith interactions with depth; and (b) if root presence or any depth‐dependent differences between these data sets vary predictably with environmental conditions. Presence of fine roots exhibited diverse depth‐dependent patterns; root mass generally declined with depth. In B and C horizons, standardized root presence was greater than standardized root mass; random forest analyses suggest these discrepancies are greater in B horizons with increasing mean annual precipitation and in C horizons with increasing mean annual temperature. Our work suggests that deep in the subsurface, biogeochemical and reactive transport processes result from more numerous root‐regolith interfaces than mass data suggest. We present a new paradigm for discerning patterns in depth distributions of root‐regolith interfaces across multiple biomes and land uses that promotes understanding of the roles of those interfaces in driving key critical zone processes.

Plant species can modify the phosphorus (P) sorption in soils through the release of low molecular weight organic acids (LMWOA) in their root exudates. These LMWOAs compete with P for adsorption sites on soil minerals and induce dissolution of Fe and Al oxyhydroxides via complexation or ligand promoted dissolution, which could affect P availability for crops and P loss. This study examined the effect of plant species and P input on the P sorption dynamics with respect to LMWOA. A greenhouse study was conducted with ten different plant species, two P fertilizer treatments (0 and 70 kg P ha− 1), and two-time intervals (35 and 70 days). All treatments were structured in a 10 × 2 × 2 complete factorial with two controls arranged in a randomized complete block design with five replicates (210 experimental units). Species from Poaceae and Fabaceae exhibited a consistent trend of increased LMWOA release in low P compared to high P conditions whereas Brassicaceae species consistently released higher concentrations of LMWOAs regardless of P. On average, LMWOA release followed the order: Brassicaceae > Fabaceae > Poaceae. In certain circumstances, P availability may be more closely related to specific LMWOAs, particularly oxalic and citric acids, rather than total LMWOA concentration. Their influence on P sorption and water-extractable P is dependent on plant species, growth stage and P status. Our findings suggest that certain cover crop species rye, triticale and crimson clover may have potential to enhance P availability as well as minimize P loss.

Grasslands exhibit high taxonomic and functional diversity, particularly at fine spatial scales, posing challenges for remote sensing due to patchiness and species turnover. The spatial resolution of most remote sensing platforms often exceeds the size of homogeneous grassland patches, resulting in mixed pixels that hinder vegetation mapping. To address this, we applied Multiple Endmember Spectral Mixture Analysis (MESMA) to high-resolution (1 m(2)) hyperspectral imagery from the NEON Airborne Observatory Platform (AOP) to assess the predictive accuracies of fractional cover and dominance of four major grass evolutionary lineages, Andropogoneae, Panicoideae, Chloridoideae, and Pooideae, across four U.S. Great Plains grasslands. MESMA performance was evaluated using different endmember selection strategies, including leaf- vs. plot-level spectral endmembers and site-specific vs. multiple-site endmembers. Overall classification accuracy reached similar to 90% (Matthews Correlation Coefficient similar to 0.84) using optimal endmember combinations. While no single approach was universally superior, in general, leaf-level endmembers from focal sites and plot-level endmembers aggregated across all sites yielded higher overall accuracies. These results demonstrate that plot-level endmembers are more transferable across sites compared to leaf-level endmembers. Our results furthermore demonstrate that incorporating information about evolutionary relatedness can improve spectral unmixing results. This study advances sub-pixel mapping of grassland composition, offering insights for ecological modelling, land change prediction, and assessing grassland responses to environmental change and community composition.

Displacement of grasses by woody plants (woody encroachment) is occurring in grasslands worldwide. Previous studies indicate that encroachment can alter subsurface carbon dioxide (CO2) concentrations and mineral weathering, though these impacts are still poorly understood. To address this knowledge gap, we sampled groundwater and stream water every three weeks during the 2022 water year from two watersheds at Konza Prairie Biological Station, a native tallgrass prairie underlain by limestone and mudrock units in Kansas, USA. Amounts of woody encroachment differ between the watersheds primarily because of differences in fire frequency. One watershed is burned annually and contains 6 % and 45 % woody plant coverage in its upland and riparian areas, respectively, whereas the other is burned every four years and contains 28 % and 74 % woody plant coverage, respectively. We expected to find higher CO2 levels in the more encroached watershed, assuming the deep roots of woody plants increase inputs of CO2 to bedrock. However, we found the opposite. Our results indicate that groundwater from a single limestone aquifer contained an average of 1.4 mM CO2 in the less encroached watershed and 1.0 mM CO2 in the more encroached watershed. Similarly, stream water CO2 concentrations at the outlet of the less encroached watershed (0.25 mM) were more than twice that of the more encroached watershed (0.12 mM) on average. Despite these differences in CO2 concentration, amounts of mineral weathering per liter of groundwater differed little between watersheds. We hypothesize that encroachment is causing differences in CO2 concentrations between watersheds by decreasing the proportion of mineral weathering that occurs under conditions that are open with respect to CO2 exchange. During open- system weathering, dissolved CO2 consumed by weathering reactions can be replaced from an adjacent gas phase, allowing CO2 concentrations to remain elevated as weathering progresses. In contrast, during closed- system weathering, CO2 is not replaced and decreases in concentration as weathering progresses. If weathering primarily occurs under open-system conditions within the study area soils, which are unsaturated, and closed-system conditions within the underlying bedrock, where pores are more commonly saturated, then woody encroachment has the potential to decrease the proportion of open-system weathering by increasing soil permeability and thus decreasing soil water residence times. This hypothesis is consistent with our findings and implies that a shortening of soil water residence time with woody encroachment lowers the proportion of CO2 delivered from the soil to the subsurface and creates a more aggressive weathering engine at depth and along deeper flow paths. Encroachment may also be altering soil CO2 production and/or venting, though these possibilities require further investigation.

The conversion of grasslands to shrublands, known as woody encroachment, has increased vegetation water use, particularly in mesic systems. However, declines in soil moisture due to woody encroachment have not been extensively explored. This study examines the impacts of woody encroachment on the depth and degree of soil drying in a mesic tallgrass prairie in Kansas, USA. We compared soil drying beneath roughleaf dogwood (Cornus drummondii) and non-encroached tallgrass prairie using half-hourly measurements of soil moisture from 2021 to 2024 (event scale), electrical resistivity in June and October of 2022 (seasonal scale), and neutron probe measurements collected monthly between 1984 and 2021(decadal scale). Across all time scales, we found increased soil drying beneath shrubs compared to grasses, particularly in deeper layers. Soil moisture declined up to 20

To predict ecological responses at broad environmental scales, grass species are commonly grouped into two broad functional types based on photosynthetic pathway. However, closely related species may have distinctive anatomical and physiological attributes that influence ecological responses, beyond those related to photosynthetic pathway alone. Hyperspectral leaf reflectance can provide an integrated measure of covarying leaf traits that may result from phylogenetic trait conservatism and/or environmental conditions. Understanding whether spectra‐trait relationships are lineage specific or reflect environmental variation across sites is necessary for using hyperspectral reflectance to predict plant responses to environmental changes across spatial scales. We measured hyperspectral leaf reflectance (400–2400 nm) and 12 structural, biochemical, and physiological leaf traits from five grass‐dominated sites spanning the Great Plains of North America. We assessed if variation in leaf reflectance spectra among grass species is explained more by evolutionary lineage (as captured by tribes or subfamilies), photosynthetic pathway (C 3 or C 4 ), or site differences. We then determined whether leaf spectra can be used to predict leaf traits within and across lineages. Our results using redundancy analysis ordination (RDA) show that grass tribe identity explained more variation in leaf spectra (adjusted R 2 = 0.12) than photosynthetic pathway, which explained little variation in leaf spectra (adjusted R 2 = 0.00). Furthermore, leaf reflectance from the same tribe across multiple sites was more similar than leaf reflectance from the same site across tribes (adjusted R 2 = 0.12 and 0.08, respectively). Across all sites and species, trait predictions based on spectra ranged considerably in predictive accuracies ( R 2 = 0.65 to <0.01), but R 2 was >0.80 for certain lineages and sites. The relationship between Vc max , a measure of photosynthetic capacity, and spectra was particularly promising. Chloridoideae, a lineage more common at drier sites, appears to have distinct spectra‐trait relationships compared with other lineages. Overall, our results show that evolutionary relatedness explains more variation in grass leaf spectra than photosynthetic pathway or site, but consideration of lineage‐ and site‐specific trait relationships is needed to interpret spectral variation across large environmental gradients.

Woody encroachment-the expansion of woody shrubs into grasslands-is a widely documented phenomenon with global significance for the water cycle. However, its effects on watershed hydrology, including streamflow and groundwater recharge, remain poorly understood. A key challenge is the limited understanding of how changes to root abundance, size and distribution across soil depths influence infiltration and preferential flow. We hypothesised that woody shrubs would increase and deepen coarse-root abundance and effective soil porosity, thus promoting deeper soil water infiltration and increasing soil water flow velocities. To test this hypothesis, we conducted a study at the Konza Prairie Biological Station in Kansas, where roughleaf dogwood (Cornus drummondii) is the predominant woody shrub encroaching into native tallgrass prairie. We quantified the distribution of coarse and fine roots and leveraged soil moisture time series and electrical resistivity imaging to analyse soil water flow beneath shrubs and grasses. We observed a greater fraction of coarse roots beneath shrubs compared to grasses, which was concurrent with greater saturated hydraulic conductivity and effective porosity. Half-hourly rainfall and soil moisture data show that the average soil water flow through macropores was 135% greater beneath shrubs than grasses at the deepest B horizon, consistent with greater saturated hydraulic conductivity. Soil-moisture time series and electrical resistivity imaging also indicated that large rainfall events and greater antecedent wetness promoted more flow in the deeper layers beneath shrubs than beneath grasses. These findings suggest that woody encroachment alters soil hydrologic processes with cascading consequences for ecohydrological processes, including increased vertical connectivity and potential groundwater recharge.

Grasses are cosmopolitan, existing in many biome and climate types from xeric to tropical. Traits that control physiological responses to drought vary strongly among grass lineages, suggesting that tolerance strategies may differ with evolutionary history. Here, we withheld water from 12 species representing 6 tribes of grasses to compare how tolerant and intolerant species respond to drought in different grass lineages. We measured physiological, morphological, and microanatomical traits. Dominant lineages from tropical savannas, like Andropogoneae, tolerated drought due to above and belowground morphological traits, while temperate grasses utilized conservative leaf physiology (gas exchange) and microanatomy. Increased intrinsic water-use efficiency (iWUE) coincided with a larger number of stomata, resulting in greater water loss (with inherently greater carbon gain) and increased drought sensitivity. Inherent leaf and root economic strategies impacting drought response were observed in all species, resulting in either high SLA or SRL, but not both. Our results indicate that grasses subjected to severe drought were influenced by microanatomical traits (e.g., number of stomata and xylem area) which were shared within lineages. In addition, grasses recovered at least 50% of physiological functioning across all lineages and 92% within Andropogoneae species, illustrating how drought can influence functional responses across diverse grass lineages.