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Increasing atmospheric [CO₂] and temperature are expected to affect the productivity, species composition, biogeochemistry, and therefore the quantity and quality of forage available to herbivores in rangeland ecosystems. Both elevated CO₂ (eCO₂) and warming affect plant tissue chemistry through multiple direct and indirect pathways, such that the cumulative outcomes of these effects are difficult to predict. Here, we report on a 7-yr study examining effects of CO₂ enrichment (to 600 ppm) and infrared warming (+1.5°C day/3°C night) under realistic field conditions on forage quality and quantity in a semiarid, mixedgrass prairie. For the three dominant forage grasses, warming effects on in vitro dry matter digestibility (IVDMD) and tissue [N] were detected only in certain years, varied from negative to positive, and were relatively minor. In contrast, eCO₂ substantially reduced IVDMD (two most abundant grasses) and [N] (all three dominant grass species) in most years, except the two wettest years. Furthermore, eCO₂ reduced IVDMD and [N] independent of warming effects. Reduced IVDMD with eCO₂ was related both to reduced [N] and increased acid detergent fiber (ADF) content of grass tissues. For the six most abundant forage species (representing 96% of total forage production), combined warming and eCO₂ increased forage production by 38% and reduced forage [N] by 13% relative to ambient climate. Although the absolute magnitude of the decline in IVDMD and [N] due to combined warming and eCO₂ may seem small (e.g., from 63.3 to 61.1% IVDMD and 1.25 to 1.04% [N] for Pascopyrum smithii), such shifts could have substantial consequences for the rate at which ruminants gain weight during the primary growing season in the largest remaining rangeland ecosystem in North America. With forage production increases, declining forage quality could potentially be mitigated by adaptively increasing stocking rates, and through management such as prescribed burning, fertilization at low rates, and legume interseeding to enhance forage quality

The intermountain grasslands of North America reach their most northern geographic extent in interior British Columbia’s Cariboo-Chilcotin region. Here, this study examined the long-term effects of livestock grazing exclusion and reductions in grazing severity on plant community characteristics including plant and litter cover, species richness and abundance of leading species of 33 grassland sites across a broad aridity and soil property gradient. Across the aridity gradient, grazing reduced species richness, plant cover, and litter cover. However, the effects of grazing on dominant species varied across the gradient. In more arid grasslands, historical grazing substantially reduced cover of late-seral native bunchgrass Psuedoroegnaria spicata, and repeated measurements indicate that very long time periods are necessary for successional processes associated with recovery of native bunchgrasses. At the cool-wet end of the aridity gradient, successional processes are more rapid but dominated by exotic species Poa pratensis and Tragopogon pratensis. Recent (past 20 years) light grazing and rest-rotation have favored Poa pratensis at the expense of native needlegrasses (Achnatherum spp. and Hesperostipa spp.). We suggest that absence of a dominant large-stature native bunchgrass for mesic grasslands was a key factor in the invasion and dominance of Poa pratensis.

1. Temporal changes in semi-arid ecosystems can include transitions between alternative stable states, involving thresholds and multiple domains of attraction, but can also include relatively continuous, symmetric and reversible shifts within a single stable state. Conceptual state-and-transition models (STMs) describe both types of ecosystem dynamics by including state transitions (plant community changes difficult-to-reverse without substantial input or effort) and phase shifts (easily reversible community changes) as consequences of management practices and environmental variability. Grazing management is purported to be the primary driver of state transitions in current STMs for North American grasslands, but there is limited empirical evidence from these grasslands showing that grazing can cause difficult-toreverse transitions between alternate stable states. 2. In a northern mixed-grass prairie in Wyoming, USA, we examined plant community responses to (i) long-term (33-year) grazing intensity treatments (none, light, moderate and heavy stocking rates) and (ii) 8 years of light or no grazing in pastures that were grazed heavily for the previous 25 years. 3. Long-term grazing treatments were associated with distinct, but not stable, plant communities. From year 22 to 33, heavier stocking rates decreased cover of dominant C₃ grasses and increased cover of the dominant C₄ grass Bouteloua gracilis. 4. Reversing stocking rates from heavy to light or no grazing resulted in reversal of changes induced by prior heavy stocking for dominant C₃ grasses, but not for B. gracilis. For both groups, rates of change following grazing treatment reversals were consistent with rates of change during the initial years of the experiment (1982-1990). 5. Synthesis and applications. In a semi-arid rangeland with a long evolutionary history of grazing, different long-term grazing intensity treatments caused slow, continuous and directional changes with important management implications, but did not appear to induce alternative stable states. For this and similar ecosystems, quantifying the time-scales and compositional gradients associated with key phase shifts may be more important than identifying thresholds between alternative stable states.

Water repellency of agricultural crop residues may affect the hydrologic balance and increase runoff loss of pesticides by greater wash off from hydrophobic residue. We conducted a laboratory study to measure water repellency and hydrophobicity of 30 major agricultural crops (grass, legume, cereal, oilseed, pulse, and specialty crops). Crop samples were collected in southern Alberta, Canada in 2017 and 2018. Water repellency (WR) of oven‐dried (60°C) and ground (<2 mm) crop residues was measured using the water drop penetration time (WDPT) and molarity of ethanol (MED) tests. Hydrophobicity was evaluated using the ratio of hydrophobic CH– to hydrophilic CO–functional groups using Fourier Transform Infrared (FTIR) spectroscopy. The WDPTs of the 30 agricultural crops ranged from 8.3 to 2438 s, suggesting that crop species influenced WR of the dried and undecomposed residues. Needle‐and‐thread grass (Stipa comata Trin. and Rupr.), blue grama (Bouteloua gracilis [Kunth] Lag. ex Griffiths), and western wheatgrass (Agropyron smithii Rydb.) were the most WR crops based on WDPT. Fababean (Vicia faba), mustard (Sinapis alba L.), and sweet clover (Melilotus officinalis) were the least WR crops. Mean WDPTs were significantly (P ≤ 0.05) greater for grass than the other four crop types by 23 to 44 times. Significant differences in WDPT occurred among crop species within each of the six crop types. A significant positive correlation occurred between WDPT and hydrophobicity (r = 0.54), but not between WDPT and organic carbon. Overall, crop type and species may influence WR of crop residues and could affect the hydrologic balance. Core Ideas Agricultural crop species residue influenced water repellency and hydrophobicity Grass was the most water repellent and hydrophobic crop type A positive correlation occurred between water repellency and hydrophobicity The physical morphology of leaves may contribute to water repellency Water repellency differences also occurred for species within the six crop types

PREMISE OF THE STUDY: Tiller recruitment from the belowground bud bank of caespitose grasses influences their ability to monopolize local resources and, hence, their genet fitness. Differences in bud production and outgrowth among tiller types within a genet and among species may explain co-occurrence of caespitose grasses. This study aimed to characterize genet bud-bank and tiller production and dynamics in two co-occurring species and compare their vegetative reproductive strategies. METHODS: Bud-bank and tiller dynamics of Hesperostipa cornata and Nassella viridula, dominant C₃ caespitose grasses in the northern mixed-grass prairie of North America, were assessed throughout an annual cycle. KEY RESULTS: The two species showed similar strategies, maintaining polycyclic tillers and thus creating mixed-age genet bud banks comprising multiple bud cohorts produced in different years. Vegetative tillers produced the majority of buds, whereas flowering tillers contributed little to the bud bank. Buds lived for at least 2 yr and were maintained in multiple developmental stages throughout the year. Because bud longevity rarely exceeded tiller longevity, tiller longevity drove turnover within the bud bank. Tiller population dynamics, more than bud production per tiller, determined the differential contribution of tiller types to the bud bank. Nassella viridula had higher bud production per tiller, a consistent annual tiller recruitment density, and greater longevity of buds on senesced and flowering tillers than H. comata. CONCLUSIONS: Co-occurring C₃ caespitose grasses had similar bud-bank and tiller dynamics contributing to genet persistence but differed in bud characteristics that could affect genet longevity and species coexistence.

Climate change could alter the population growth of dominant species, leading to profound effects on community structure and ecosystem dynamics. Understanding the links between historical variation in climate and population vital rates (survival, growth, recruitment) is one way to predict the impact of future climate change. Using a unique, long-term data set from eastern Idaho, USA, we parameterized integral projection models (IPMs) for Pseudoroegneria spicata , Hesperostipa comata , and Artemisia tripartita to identify the demographic rates and climate variables most important for population growth. We described survival, growth, and recruitment as a function of genet size using mixed-effect regression models that incorporated climate variables. Elasticites for the survival ++ growth portion of the kernel were larger than the recruitment portion for all three species, with survival ++ growth accounting for 87-–95%% of the total elasticity. The genet sizes with the highest elasticity values in each species were very close to the genet size threshold where survival approached 100%%. We found strong effects of climate on the population growth rate of two of our three species. In H. comata , a 1%% decrease in previous year's precipitation would lead to a 0.6%% decrease in population growth. In A. tripartita , a 1%% increase in summer temperature would result in a 1.3%% increase in population growth. In both H. comata and A. tripartita , climate influenced population growth by affecting genet growth more than survival or recruitment. Late-winter snow was the most important climate variable for P. spicata , but its effect on population growth was smaller than the climate effects we found in H. comata or A. tripartita . For all three species, demographic responses lagged climate by at least one year. Our analysis indicates that understanding climate effects on genet growth may be crucial for anticipating future changes in the structure and function of sagebrush steppe vegetation.

In perennial grassland dominated systems, belowground bud banks regulate plant community dynamics. Plant community responses to disturbance are largely driven by the ability to generate future aboveground growth originating from belowground axillary buds. This study examined bud bank dynamics for Bouteloua gracilis, Hesperostipa comata, and Pascopyrum smithii following fire in northwestern mixed-grass prairie in eastern Montana, USA. Belowground axillary buds were counted and classified for three growing seasons to determine immediate and short-term effects of summer, fall, and spring prescribed burns on patterns of bud bank activity, dormancy, and mortality. Prescribed burns did not result in immediate mortality of B. gracilis, H. comata, or P. smithii buds. Surprisingly, spring prescribed burns immediately increased the number of active B. gracilis buds. Summer fire, however, reduced B. gracilis active bud numbers. Fall burns immediately activated P. smithii buds, whereas fire did not influence any immediate bud dynamics for H. comata. Reduced bud numbers of H. comata may limit the ability to respond to fire. Season of fire directly manipulated bud activity, dormancy, and mortality for these species throughout the growing and dormant seasons following fire. Using season of fire to manipulate bud bank dynamics illustrates potential to improve post-fire management strategies based on known bud development trajectories and bud dynamics following fire.

Climate change is expected to alter precipitation patterns. Droughts may become longer and more frequent, and the timing and intensity of precipitation may change. We tested how shifting precipitation patterns, both seasonally and by frequency of events, affects soil nitrogen availability, plant biomass and diversity in a shrub-steppe temperate grassland along a natural productivity gradient in Lac du Bois Grasslands Protected Area near Kamloops, British Columbia, Canada. We manipulated seasonal watering patterns by either exclusively watering in the spring or the fall. To simulate spring precipitation we restricted precipitation inputs in the fall, then added 50% more water than the long term average in the spring, and vice-versa for the fall precipitation treatment. Overall, the amount of precipitation remained roughly the same. We manipulated the frequency of rainfall events by either applying water weekly (frequent) or monthly (intensive). After 2 years, changes in the seasonality of watering had greater effects on plant biomass and diversity than changes in the frequency of watering. Fall watering reduced biomass and increased species diversity, while spring watering had little effect. The reduction in biomass in fall watered treatments was due to a decline in grasses, but not forbs. Plant available N, measured by Plant Root Simulator (PRS)-probes, increased from spring to summer to fall, and was higher in fall watered treatments compared to spring watered treatments when measured in the fall. The only effect observed due to frequency of watering events was greater extractable soil N in monthly applied treatments compared to weekly watering treatments. Understanding the effects of changing precipitation patterns on grasslands will allow improved grassland conservation and management in the face of global climatic change, and here we show that if precipitation is more abundant in the fall, compared to the spring, grassland primary productivity will likely be negatively affected.

PREMISE OF THE STUDY: Vegetative reproduction from belowground bud banks is the primary driver of grassland systems. Despite the importance of bud banks, the timing of recruitment and the crucial link between formation and maintenance is unknown. METHODS: We assessed patterns of belowground bud development, dormancy, and mortality associated with three perennial native grasses in the northern Great Plains. Temperature and soil moisture were measured below the soil surface to determine relationships with belowground bud development. KEY RESULTS: Blue grama (Bouteloua gracilis) generated more buds over winter that remained dormant; whereas, C3 species needle‐and‐thread (Hesperostipa comata) and western wheatgrass (Pascopyrum smithii), maintained limited dormant buds throughout winter. Soil temperature was a good predictor for C4 species bud production; whereas, soil moisture was a reliable predictor for C3 buds. Distinct differences existed between C4 species blue grama and C3 species needle‐and‐thread, whereas C3 species western wheatgrass (Pascopyrum smithii) was intermediate, indicating there is likely a species‐specific continuum between the C3 and C4 extremes rather than a stark difference. CONCLUSIONS: The ability to predict belowground bud development is a novel insight to native perennial grasses. Native grass species’ strategies and adaptability regarding belowground bud bank size and bud phenology are important factors optimizing tiller recruitment given the variable growing conditions. Patterns of bud dormancy and development will provide insight to the underlying mechanisms by which management practices and fluctuations in precipitation amount and growing season length can alter mixed‐grass prairie plant community dynamics.

A majority of soil carbon (C) is either directly or indirectly derived from fine roots, yet roots remain the least understood component of the terrestrial carbon cycle. The decomposability of fine roots and their potential to contribute to soil C is partly regulated by their tissue chemical composition. Roots rely heavily on heteropolymers such as suberins, lignins and tannins to adapt to various environmental pressures and to maximize their resource uptake functions. Since the chemical construction of roots is partly shaped by their immediate biotic/abiotic soil environments, global changes that perturb soil resource availability and plant growth could potentially alter root chemistry, and hence the decomposability of roots. However, the effect of global change on the quantity and composition of root heteropolymers are seldom investigated. We examined the effects of elevated CO2 and warming on the quantity and composition of suberin in roots of Bouteloua gracilis (C4) and Hesperostipa comata (C3) grass species at the Prairie Heating and CO2 Enrichment (PHACE) experiment at Wyoming, USA. Roots of B. gracilis exposed to elevated CO2 and warming had higher abundances of suberin and lignin than those exposed to ambient climate treatments. In addition to changes in their abundance, roots exposed to warming and elevated CO2 had higher ω-hydroxy acids compared to plants grown under ambient conditions. The suberin content and composition in roots of H. comata was less responsive to climate treatments. In H. comata, α,ω-dioic acids increased with the main effect of elevated CO2, whereas the total quantity of suberin exhibited an increasing trend with the main effect of warming and elevated CO2. The increase in suberin content and altered composition could lower root decomposition rates with implications for root-derived soil carbon under global change. Our study also suggests that the climate change induced alterations in species composition will further mediate potential suberin contributions to soil carbon pools.