Northern Temperate Grasslands Research Articles

Simulation of the nutritional requirements and energy balance of adult cows in a northern temperate grassland.

The forage-livestock balance is an important component of natural grassland management, and realizing a balance between the nutrient energy demand of domestic animals and the energy supply of grasslands is the core challenge in forage-livestock management. This study was performed at the Xieertala Ranch in Hulunbuir City, Inner Mongolia. Using the GRAZPLAN and GrazFeed models, we examined the forage-livestock energy balance during different grazing periods and physiological stages of livestock growth under natural grazing conditions. Data on pasture conditions, climatic factors, supplemental feeding, and livestock characteristics, were used to analyze the metabolizable energy (ME), metabolizable energy for maintenance (MEm), and total metabolizable energy intake (MEItotal) of grazing livestock. The results showed that the energy balance between forage and animals differed for adult cows at different physiological stages. In the early lactation period, although the MEItotal was greater than MEm, it did not meet the requirement for ME. MEItotal was greater than ME during mid-lactation, but there was still an energy imbalance in the early and late lactation periods. In the late lactation period, MEItotal could meet ME requirements from April-September. Adult gestational lactating cows with or without calves were unable to meet their ME requirement, especially in the dry period, even though MEItotal was greater than MEm. Adult cows at different physiological stages exhibited differences in daily forage intake and rumen microbial crude protein (MCP) metabolism, and the forage intake by nonpregnant cows decreased as follows: early lactation > mid-lactation > late lactation, pregnant cows' lactation > dry period. For the degradation, digestion and synthesis of rumen MCP, early-lactation cows were similar to those in the mid-lactation group, but both were higher than those in the late-lactation group, while pregnant cows had greater degradation, digestion, and synthesis of MCP in the lactation period relative to the dry period. For lactating cows, especially those with calves, grazing energy requirements, methane emission metabolism and heat production were highest in August, with increased energy expenditure in winter. Overall, grazing energy, methane emissions and heat production by dry cows were low. In the context of global climate change and grassland degradation, managers must adopt different strategies according to the physiological stages of livestock to ensure a forage-livestock balance and the sustainable utilization and development of grasslands.

Land use intensity controls the diversity-productivity relationship in northern temperate grasslands of China.

The diversity-productivity relationship is a central issue in maintaining the grassland ecosystem's multifunctionality and supporting its sustainable management. Currently, the mainstream opinion on the diversity-productivity relationship recognizes that increases in species diversity promote ecosystem productivity. Here, we challenge this opinion by developing a generalized additive model-based framework to quantify the response rate of grassland productivity to plant species diversity using vegetation survey data we collected along a land-use intensity gradient in northern China. Our results show that the grassland aboveground biomass responds significantly positively to the Shannon-Wiener diversity index at a rate of 46.8 g m-2 per unit increase of the Shannon-Wiener index in enclosure-managed grasslands, under the co-influence of climate and landscape factors. The aboveground biomass response rate stays positive at a magnitude of 47.1 g m-2 in forest understory grassland and 39.7 g m-2 in wetland grassland. Conversely, the response rate turns negative in heavily grazed grasslands at -55.8 g m-2, transiting via near-neutral rates of -7.0 and -7.3 g m-2 in mowing grassland and moderately grazed grassland, respectively. These results suggest that the diversity-productivity relationship in temperate grasslands not only varies by magnitude but also switches directions under varying levels of land use intensity. This highlights the need to consider land use intensity as a more important ecological integrity indicator for future ecological conservation programs in temperate grasslands.

Light to moderate long-term grazing enhances ecosystem carbon across a broad climatic gradient in northern temperate grasslands

Grasslands are globally abundant and provide many ecosystem services, including carbon (C) storage. While grasslands are widely subject to livestock grazing, the influence of grazing on grassland ecosystem C remains unclear. We studied the effect of long-term livestock grazing on C densities of different ecosystem components in 110 northern temperate grasslands across a broad agroclimatic gradient in Alberta, Canada. These grasslands stored 50 to 180 t ha−1C in live and dead vegetation, as well as soil C to 30 cm depth, with the majority as soil organic C (SOC). The mulch layer comprised a large amount of C (~18 t ha−1C) especially within humid grasslands. Although grazing reduced C densities in litter mass, total ecosystem C was 8.5 % greater under grazing (127.8 t ha−1) compared to those non-grazed (117.8 t ha−1), primarily due to increases in SOC and roots. Increases in SOC were consistently observed in the 0–15 cm layer across all climatic conditions, with changes in SOC of the 15–30 cm layer inversely related to aridity. A structural equation model revealed that increased SOC under grazing was indirectly attributed to increases in eudicot rather than graminoid biomass. In addition, SOC increased with graminoid quality (i.e., a reduced carbon to nitrogen ratio), which together with elevated eudicots, increased litter and mulch C, and ultimately enhanced SOC densities. When applied to spatial maps of habitat type and land use (livestock grazing) activity across the region, an area of ~3.8 M ha of grassland was projected to contain an additional 17.1 M t of C under grazing, primarily in mesic grasslands, worth an estimated $3.1 B (Cdn.) under current C valuation guidelines in Canada. Overall, these results highlight the importance of grasslands for C storage and establishing policies that maintain and promote their sustainable use, including light to moderate grazing.

Legume re-establishment in northern temperate grasslands following application of aminocyclopyrachlor and aminopyralid

Herbicides with residual properties are often used for broadleaf weed control in pastures but can remove desirable legumes such as alfalfa (Medicago sativa L.) and white clover (Trifolium repens L.). Field trials at five sites within central Alberta, Canada were used to assess legume population dynamics during recovery after spraying. Medicago sativa and T. repens populations were monitored for three years following application of aminopyralid (AMP) at 120 g a.i. ha−1, or aminocyclopyrachlor (AMCP) at 60 g a.i. ha−1, in combination with repeated mowing and legume over-seeding. Bioassays were performed twice a year (spring and fall) using M. sativa and T. repens seeded into soil sourced from each plot up until 26 months-after-spraying (MAS) and grown in a greenhouse. Medicago sativa and T. repens densities in the field remained below non-sprayed control levels throughout the study (26 MAS). In contrast, bioassay results indicated a shorter time than the field trial for legume recovery, with recovery occurring in soil from treated grassland as soon as 14 MAS. There were no differences between AMCP and AMP in the time required to facilitate legume establishment. Critically, legume establishment in the field depended on intermittent mowing, particularly for T. repens, which failed to persist in the absence of mowing at 22 MAS regardless of herbicide application. Medicago sativa had a high potential to establish from the natural seed bank, while T. repens depended on over-seeding. These findings indicate it may be possible to reintroduce legumes to temperate pastures as early as the second growing season after herbicide application, though field trials indicate legume population recovery will depend on seeding and secondary disturbances to reduce competition.

Estimation of Heat Released from Fire Based on Combustible Load in Inner Mongolian Grasslands

The grasslands of Inner Mongolia are prone to wildfires, which can endanger the grassland ecosystem, as well as people’s lives and property. The amount of heat released by grassland fires must be determined for the quantitative evaluation of grassland fires. On the basis of a field survey of combustible load and an indoor heat release experiment, together with the acquisition of NDVI and fire area data, this study evaluated the amount of combustible load, plant heat release, potential heat release, and fire-caused heat release in Inner Mongolia grasslands. The following results were obtained: (1) The models for determining Inner Mongolia’s combustible load (Y) per unit area throughout the growing and nongrowing seasons were Yi = 412.74NDVIi1.5917 and Yj = −7.21tj + Y10 (i represents May–October of the growing season; j represents November–April of the following year). In the northern temperate zones, grasslands and meadows showed a decline in combustible load per unit area. The interannual combustible load variance increased between 2001 and 2016; (2) the per square meter average heat release of Stipa capillata, Cleistogenes squarrosa, Carex doniana, Leymus chinensis, and other plants was 0.51, 0.18, 0.17, 0.3, and 1.42 MJ/g, respectively. Unit weights were released at 2.13, 1.77, 2.06, 1.9, and 3.99 MJ/m2; (3) from 2001 to 2016, Inner Mongolia’s grassland fires predominantly occurred in northern temperate grasslands and meadows. Over the 16 year period, the total heat emission was 1.01 × 1012 MJ, with variable decreasing trends noted in spring and fall. The main practical objectives of this paper were to provide basic data for fire spread modeling and suggest more scientific and effective fire management methods for the future.

Altered precipitation rather than warming and defoliation regulate short-term soil carbon and nitrogen fluxes in a northern temperate grassland

Grasslands store large quantities of organic carbon (C) and thus can markedly impact global climate change if they are disturbed. How practices such as grazing intensity and climate change interact to affect soil greenhouse gas (GHG) fluxes within native northern temperate grasslands is unclear. We investigated the responses of three major GHGs (CO2, N2O and CH4) to temperature (ambient vs. warmed), precipitation (ambient vs. reduced or increased) and defoliation (no defoliation vs. low- or high-intensity defoliation) treatments in a factorial experiment over a two-year period in a native northern temperate grassland in Alberta, Canada. Growing season mean soil gas fluxes across all treatments were 93.8 mg CO2 m−2 h−1, −0.025 mg CH4 m−2 h−1, and 0.003 mg N2O m−2 h−1, suggesting that this grassland was a source for CO2 and N2O, but a sink for CH4 over the study period. Structural equation modeling showed that increased precipitation, rather than warming or defoliation, was the primary driver directly regulating fluxes of CO2 and N2O. While increased precipitation also increased microbial biomass C (MBC), the latter had little impact on GHG fluxes, suggesting that MBC was not a critical factor regulating the precipitation-GHG flux relationship. Warming and precipitation effects on CH4 fluxes depended on the month of sampling during the growing season. Warming decreased CH4 uptake but only in mid-July, while increased precipitation reduced CH4 uptake across all sampling dates except early August, at which time increased precipitation increased CH4 uptake. Our study shows that short-term soil GHG fluxes in this native grassland are relatively resilient to moderate warming and defoliation, but sensitive to altered precipitation. Increased precipitation was the main contributor to short-term GHG fluxes in this temperate grassland via changes in CO2 efflux.

Effect of shrub encroachment on land surface temperature in semi-arid areas of temperate regions of the Northern Hemisphere

Under the influences of climate change and human activities, grassland ecosystems are being invaded by shrubs around the world, especially in temperate semi-arid regions of the Northern Hemisphere. Shrub encroachment can not only affect the properties of grassland ecosystem, but also have an important impact on regional or global climate by affecting biogeochemical and biophysical processes. Although shrub encroachment has become a serious ecological problem in the northern temperate region during the past decades, the possible effects of shrub encroachment on regional climate in northern temperate grasslands remain unclear due to a lack of in situ and long-term environmental records. Based on the satellite-derived land use data, land surface temperature (LST), evapotranspiration, leaf area index, and albedo data, this study quantified, for the first time, the biophysical effects of shrub encroachment on regional climate in semi-arid areas of temperate regions of the Northern Hemisphere. The results indicate that shrub encroachment tends to increase the average annual daytime and mean LST in most of the northern temperate semi-arid region due to increased bare soil fraction. In contrast, shrub encroachment could decrease the daytime LST in relatively humid region of southwest of North America by increasing evapotranspiration (vegetation coverage) and decreasing bare soil fraction. In the arid center region of Central Asia, grassland conversion to shrubland slightly decreases the surface temperature during both daytime and nighttime due to increased albedo caused by decreasing soil water content. Our findings imply that the biophysical effects of shrub encroachment on regional climate should be considered in climate models if they are to accurately simulate climate change in temperate regions of the Northern Hemisphere. More attention should be paid to the climate feedbacks of shrub encroachment, especially considering the distinct effects in different regions and how these climate feedbacks are likely to further impact ecosystem properties.

Multi‐year drought alters plant species composition more than productivity across northern temperate grasslands

Abstract The occurrence of multi‐year drought is predicted to increase globally with climate change. However, it is unclear whether drought effects on ecosystems are progressive through time. Here, we experimentally reduced growing season precipitation (GSP) by 45% at seven North American temperate grasslands for four consecutive years to determine the following: (a) whether the effects of reduced precipitation on plant community structure and biomass components (shoot, root, litter) are compounding over time; (b) whether prior year climatic and soil conditions influence subsequent drought impacts on plant community structure and biomass components; and (c) whether the effects of reduced precipitation on individual ecosystem components are related to one another. Across the seven field sites, we observed neither consistent nor progressive effects of reduced precipitation on any biomass component during the experiment, despite having extreme drought conditions imposed for four consecutive years. Relative to the ambient treatment, above‐ground net primary productivity (ANPP) declined in response to drought during the early years of the experiment but increased above the ambient treatment in the fourth year, while root and litter biomass were stable across the sites throughout the study. Similarly, graminoid cover decreased initially but recovered by the final year of the experiment, contributing to observed differences in species composition between treatments across sites. Compositional changes were not associated with any declines in species richness or evenness. Divergent responses among years were not driven by lag effects based on prior year climatic and soil conditions. Furthermore, precipitation effects on ecosystem components were largely independent as we found only two positive links: between ANPP and plant species richness, and between species evenness and composition. Synthesis. Overall, our results suggest that these northern grasslands are relatively resistant to short‐term multi‐year drought in the context of supporting plant diversity and biomass production.

Effects of grazing on plant communities and successional processes vary along an aridity gradient at a northern temperate grassland

Effects of grazing on plant communities and successional processes vary along an aridity gradient at a northern temperate grassland

Increasing impact of warm droughts on northern ecosystem productivity over recent decades

Climate extremes such as droughts and heatwaves have a large impact on terrestrial carbon uptake by reducing gross primary production (GPP). While the evidence for increasing frequency and intensity of climate extremes over the last decades is growing, potential systematic adverse shifts in GPP have not been assessed. Using observationally-constrained and process-based model data, we estimate that particularly northern midlatitude ecosystems experienced a +10.6% increase in negative GPP extremes in the period 2000–2016 compared to 1982–1998. We attribute this increase predominantly to a greater impact of warm droughts, in particular over northern temperate grasslands (+95.0% corresponding mean increase) and croplands (+84.0%), in and after the peak growing season. These results highlight the growing vulnerability of ecosystem productivity to warm droughts, implying increased adverse impacts of these climate extremes on terrestrial carbon sinks as well as a rising pressure on global food security.

Soil greenhouse gas emissions and grazing management in northern temperate grasslands

Adaptive multi-paddock (AMP) grazing, a grazing system in which individual paddocks are grazed for a short duration at a high stock density and followed by a long rest period, is claimed to be an effective tool to sustainably manage and improve grasslands and enhance their ecosystem services. However, whether AMP grazing is superior to conventional grazing (n-AMP) in reducing soil greenhouse gas (GHG) emissions is unclear. Here, we measured CO2, CH4, and N2O fluxes between August 2017 and August 2019 in 12 pairs of AMP vs. n-AMP ranches distributed across an agro-climatic gradient in Alberta, Canada. We found that field GHG fluxes did not differ between AMP and n-AMP grazing systems, but instead were regulated by specific management attributes, environmental conditions, and soil properties, including cattle stocking rate, cultivation history, soil moisture content, and soil bulk density. Specifically, we found that seasonal mean CO2 emissions increased with increasing cattle stocking rates, while CH4 uptake was lower in grasslands with a history of cultivation. Seasonal mean CO2 emissions increased while CH4 uptake decreased with increasing soil moisture content. In addition, CH4 uptake decreased with increasing soil bulk density. Observed N2O emissions were poorly predicted by the management, environmental conditions, and soil properties investigated in our study. We conclude that AMP grazing does not have an advantage over n-AMP grazing in reducing GHG fluxes from grasslands. Future efforts to develop optimal management strategies (e.g., the use of sustainable stocking rates and avoided cultivation) that reduce GHG emissions should also consider the environmental conditions and soil properties unique to every grassland ecosystem.

Grazing alters the sensitivity of plant productivity to precipitation in northern temperate grasslands

AbstractQuestionsInter‐annual variability in precipitation is expected to increase in grasslands, potentially causing additional stress to systems already impacted by anthropogenic activities such as livestock grazing, which can induce changes to grassland vegetation. Yet, the sensitivity of key ecosystem functions to these co‐occurring factors is often overlooked. Here, we determine: (a) the effects of grazing on the sensitivity of above‐ground net primary productivity (ANPP sensitivity) to inter‐annual variation in water‐year precipitation (the sum of precipitation from September through to the following August); (b) whether ANPP sensitivity to precipitation is associated with shifts induced by grazing in functional group biomass (grass vs forb) contribution to total ANPP, litter, and species richness, and mean annual water‐year precipitation; and (c) whether the impacts of grazing on ANPP vary between dry and wet years.LocationNative grasslands in Alberta, Canada.MethodsWe used long‐term (14–28 years) ANPP and precipitation data from 31 grazed grasslands, each with a paired non‐grazed livestock exclosure. ANPP was sampled annually within exclosures and adjacent grazed locations at each site.ResultsWe found that grazing increased ANPP sensitivity to inter‐annual changes in precipitation. Increased ANPP sensitivity to precipitation in grazed, relative to non‐grazed locations was associated with both an increase in the contribution of forbs to total ANPP and a decrease in the contribution of grasses to total ANPP; reduced litter also increased ANPP sensitivity to precipitation. Species richness was not associated with ANPP sensitivity in both grazed and non‐grazed locations. Arid grasslands were more sensitive to inter‐annual variation in precipitation when grazed than were mesic grasslands. Similarly, grazing reduced ANPP during dry years but had no effect during wet years.ConclusionsOverall, these findings suggest that grazed grasslands are more vulnerable to reductions in primary productivity in dry years, which may present a challenge for maintaining ecosystem services in an era of increasing precipitation variability.

Adaptive Multi-Paddock Grazing Lowers Soil Greenhouse Gas Emission Potential by Altering Extracellular Enzyme Activity

Adaptive multi-paddock (AMP) grazing is a form of rotational grazing in which small paddocks are grazed with high densities of livestock for short periods, with long recovery periods prior to regrazing. We compared the fluxes of greenhouse gases (GHGs), including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), from soils of AMP-grazed grasslands to paired neighboring non-AMP-grazed grasslands across a climatic gradient in Alberta, Canada. We further tested GHG responses to changes in temperature (5 °C vs. 25 °C) and moisture levels (permanent wilting point (PWP), 40% of field capacity (0.4FC), or field capacity (FC)) in a 102-day laboratory incubation experiment. Extracellular enzyme activities (EEA), microbial biomass C (MBC) and N (MBN), and available-N were also measured on days 1, 13, and 102 of the incubation to evaluate biological associations with GHGs. The 102-day cumulative fluxes of CO2, N2O, and CH4 were affected by both temperature and moisture content (p < 0.001). While cumulative fluxes of N2O were independent of the grazing system, CH4 uptake was 1.5 times greater in soils from AMP-grazed than non-AMP-grazed grasslands (p < 0.001). There was an interaction of the grazing system by temperature (p < 0.05) on CO2 flux, with AMP soils emitting 17% more CO2 than non-AMP soils at 5 °C, but 18% less at 25 °C. The temperature sensitivity (Q10) of CO2 fluxes increased with soil moisture level (i.e., PWP < 0.4FC ≤ FC). Structural equation modelling indicated that the grazing system had no direct effect on CO2 or N2O fluxes, but had an effect on CH4 fluxes on days 1 and 13, indicating that CH4 uptake increased in association with AMP grazing. Increasing soil moisture level increased fluxes of GHGs—directly and indirectly—by influencing EEAs. Irrespective of the grazing system, the MBC was an indirect driver of CO2 emissions and CH4 uptake through its effects on soil EEAs. The relationships of N-acetyl-β glucosaminidase and β-glucosidase to N2O fluxes were subtle on day 1, and independent thereafter. AMP grazing indirectly affected N2O fluxes by influencing N-acetyl-β glucosaminidase on day 13. We conclude that AMP grazing has the potential to mitigate the impact of a warmer soil on GHG emissions by consuming more CH4 compared to non-AMP grazing in northern temperate grasslands, presumably by altering biogeochemical properties and processes.

Climate change and defoliation interact to affect root length across northern temperate grasslands

Abstract Grassland plants, especially their root systems, are dynamic and can buffer changes resulting from exposure to multiple stressors; however, the interactive stressor effects on root dynamics and associated above‐ground growth are poorly understood. Here, we examine the effects of changed precipitation and air temperature, and defoliation intensity on root length dynamics and above‐ground biomass using the third year data from a multifactor experiment conducted across three northern temperate grasslands. We found that root length was more sensitive to the changes in environmental and management conditions than root mass, demonstrating the importance of root length as an indicator of rapid root system changes. Across all sites, warming, altered precipitation and defoliation intensity interacted to affect root length while above‐ground biomass was only affected by defoliation intensity, indicating that the root system was more responsive than above‐ground biomass when climatic conditions change. Overall, drought reduced root length, particularly under low defoliation intensity, as well as in combination with warming and heavy defoliation, highlighting the risk of additive effects of such environmental stresses. Across unclipped plots, above‐ground biomass was positively associated with total root length, the latter of which further interacted with precipitation, to affect above‐ground biomass. Compared to defoliated communities, non‐defoliated plant communities exhibited a greater ability to maintain above‐ground biomass under drought conditions via increases in root system efficiency (the amount of above‐ground biomass produced per unit of root length invested). Our results highlight the rapid change of root length in the face of interactive stressors. We postulate that the degree of stability in above‐ground biomass is driven by the altered root system dynamics or species turnover. Future studies are warranted that more directly assess how root length responses under climate change impact other important plant traits in grasslands. A free Plain Language Summary can be found within the Supporting Information of this article.

Assessing variation in range health across grazed northern temperate grasslands

Contemporary methods of rangeland health (RH) assessment evaluate indicators designed to assess land use impacts on ecosystem function. These methods have not been tested relative to variation in specific grazing practices, including grazing period length and stocking rates during the growing season. We report on RH outcomes for three habitat types (native grassland, tame pasture, and forested pasture) across 97 pastures on 28 beef cattle ranches in Alberta, Canada. Pastures were distributed along a climatic gradient encompassing the grassland, parkland/foothill, and boreal regions. Surveys of ranchers were used to quantify typical grazing period length (1 May–31 October) and, if applicable, rotation length, along with corresponding stocking rates for each pasture over the previous 5 yr. Pastures were assessed for RH using indicators of vegetation composition and structure, litter abundance, soil stability, weed presence, and within tame pastures, woody plant encroachment. An Akaike Information Criterion analysis compared the influence of aridity, grazing period length, and stocking rate on total range health scores (RHS) and ordination used to identify associations between indicator scores and grazing metrics. Total RHS varied among habitat types, being greater in forests than native and tame grasslands (P < 0.05), and declined with increasing forage utilization, particularly in forests. Within tame pastures, total RHS varied primarily in response to regional climate, with RHS decreasing as moisture deficits increased and declining with longer grazing periods during summer. Native grasslands also decreased in RHS in response to longer grazing periods, with stocking rates having little impact on RHS. Select RH indicators were associated with improved health in native grasslands grazed for shorter periods including low weed abundance and greater litter. Further studies are recommended to understand how, over and above climatic influences, variation in grazing practices alter the health of northern temperate grasslands.

Soil carbon increases with long‐term cattle stocking in northern temperate grasslands

AbstractGrassland management aimed at enhancing carbon (C) in soil is an important tool in mitigation of rising atmospheric CO2, yet little is known of how grassland soil C changes with livestock stocking rate (SR). We relate soil organic and inorganic C mass (t ha−1 to 60 cm depth) with cattle stocking over periods of 7–27 year for 32 paddocks distributed across nine community pastures in the mixed‐grass prairie of Saskatchewan, Canada. Initial analysis comparing Akaike information criterion models showed that cattle SR explained a greater proportion of variance in soil C, particularly soil organic C, than rainfall. Soil organic C mass increased with cattle SR (R2 = .293; p = .001), even when the latter was normalized to account for differences in vegetation composition and growing conditions among pastures. Normalized SR varied from 0.49 to 2.30 times recommended levels, over which SOC increased from 24.7 to 57.4 t ha−1. Increases in soil organic C under greater stocking coincided with increased abundance of introduced vegetation, particularly the rhizomatous grass Poa pratensis. Inorganic soil C accounted for 34.6% of total soil C, being particularly large below 30 cm soil depth, but did not vary with stocking rate. These findings indicate that both organic and inorganic C are important pools of C in northern temperate grassland soils, with soil organic C positively associated with long‐term cattle SR. Further studies are recommended to understand more fully the mechanisms regulating grazing impacts on soil C mass in northern temperate grasslands.

Herbage biomass and its relationship to soil carbon under long-term grazing in northern temperate grasslands

While northern temperate grasslands are important for supporting beef production, it remains unclear how grassland above- and belowground biomass responds to long-term cattle grazing. Here, we use a comprehensive dataset from 73 grasslands distributed across a broad agro-climatic gradient to quantify grassland shoot, litter, and shallow (top 30 cm) root biomass in areas with and without grazing. Additionally, we relate biomass to soil carbon (C) concentrations. Forb biomass was greater (p &lt; 0.05) in grazed areas, particularly those receiving more rainfall. In contrast, grass and total aboveground herbage biomass did not differ with grazing (total: 2320 kg ha−1 for grazed vs. 2210 kg ha−1 for non-grazed; p &gt; 0.05). Forb crude protein concentrations were lower (p &lt; 0.05) in grazed communities compared with those that were non-grazed. Grasslands subjected to grazing had 56% less litter mass. Root biomass down to 30 cm remained similar between areas with (9090 kg ha−1) and without (7130 kg ha−1) grazing (p &gt; 0.05). Surface mineral soil C concentrations were positively related to peak grassland biomass, particularly total (above + belowground) biomass, and with increasing forb biomass in grazed areas. Finally, total aboveground shoot biomass and soil C concentrations in the top 15 cm of soil were both positively related to the proportion of introduced plant diversity in grazed and non-grazed grasslands. Overall, cattle grazing at moderate stocking rates had minimal impact on peak grassland biomass, including above- and belowground, and a positive contribution exists from introduced plant species to maintaining herbage productivity and soil C.

Soil properties in northern temperate pastures do not vary with management practices and are independent of rangeland health

Studies examining the influence of disturbance and management history on pasture soils across a large sampling area are uncommon. We report on the soil properties found in 102 northern temperate pastures sampled in central Alberta, Canada, and relate these attributes to ongoing pasture management practices compiled from producer surveys and aboveground measures of rangeland health (RH). Tame pastures, typically seeded to introduced forages, were associated with higher soil fertility (total carbon, nitrogen, and organic matter) than semi-native grasslands, which were associated with coarse-textured soils. Soil properties remained independent of most grazing and pasture management practices, including the grazing systems, class of livestock, fertilization, and stocking rate. However, manure application, often combined with harrowing, was associated with improved soil fertility and increased electrical conductivity (salinity). Soils with a fire history reported by land managers, largely in the Boreal natural region, were characterized by a greater soil C:N ratio. Soil surface properties (litter cover, litter depth, and bare soil) were responsive to grazing management, with growing season and year-round grazing associated with a thinner litter layer having less cover, and bare ground twice as high under continuous grazing compared with pastures rotationally grazed. Further, variation in soil surface cover was associated with contrasting RH classes (healthy, healthy with problems, and unhealthy), whereas soil attributes remained unrelated to RH. This study demonstrates that soils within these northern temperate grasslands are relatively insensitive to many pasture management practices, and highlights that existing RH assessments may provide limited insight into differences in mineral soil properties.

Extracellular enzyme activity in grass litter varies with grazing history, environment and plant species in temperate grasslands

Long-term livestock grazing (here after ‘grazing’) affects carbon (C) and nutrient cycling in grassland ecosystems, in part by altering the quantity and quality of litter inputs. Despite their spatial extent and size of carbon and nutrient stocks, the effect of grazing on grassland biogeochemical cycling through the mediation of microbial activity remains poorly understood. To better understand the relationship between grazing and C and nutrient cycling in litter, we conducted an 18-month long study in paired grasslands previously grazed and nongrazed by cattle for 25 years, measuring extracellular enzyme activity (EEA) in various plant litter samples. Litter sources, including seven grass species dominant in one or more subregions and possessing divergent responses to grazing, as well as a community mix of litter sourced from each site, were tested at 15 sites spanning three grassland subregions in Alberta, Canada. We quantified EEAs associated with C cycling (β-glucosidase, β-Cellobiosidase and β-xylosidase), nitrogen (N) cycling (N-acetyl-glucosaminidase) and phosphorus (P) cycling (phosphatase). In general, litter in grasslands exposed to grazing had greater activity of C-liberating and P-liberating enzyme (β-xylosidase and phosphatase) in the mesic grasslands of the Foothills Fescue subregion (P ≤ 0.10). Observed EEAs were strongly mediated by litter type, with greater EEAs in litter of grass species known to increase in abundance under long-term grazing, including Poa pratensis in the Foothills Fescue subregion, and Bouteloua gracilis in arid grasslands of the Mixedgrass Prairie. In contrast, Pascopyrum smithii litter had the lowest enzyme activities in all subregions. We also found that EEAs changed through time (0–18 months) with consistently high levels detected at 1 (June 2014), 6 (October 2014) and 18 months (October 2015) after placement. Overall, these findings indicate grazing enhances EEA, and thus C and N-cycling, in northern temperate grasslands.

Soil Nitrogen and Greenhouse Gas Dynamics in a Temperate Grassland under Experimental Warming and Defoliation

Core Ideas Warming but not defoliation increased short‐term N mineralization. The CO2 efflux initially increased with warming and defoliation but promptly stabilized. Warming and defoliation reduced N2O emissions but not when combined. Soil responses to warming were complex and transient in this temperate grassland. Grasslands are important for C storage and supporting livestock production, yet little is understood about how warming interacts with defoliation to alter soil C and N dynamics. We examined how increased growing season temperature and defoliation influenced soil microbial biomass C (MBC) and N (MBN), N mineral dynamics, and greenhouse gas (GHG) flux within the top 15 cm of mineral soil in a northern temperate grassland of Alberta, Canada. We performed a 2‐yr experiment with open‐top chambers to increase soil temperatures, with warming assessed alone and combined with a single intense midsummer defoliation treatment. Soil MBC and MBN did not respond to warming or defoliation (P &gt; 0.05). Warming increased soil nitrification and net N mineralization in the spring of the second growing season (P &lt; 0.05) but did not persist beyond May. Although warming and defoliation both increased CO2 efflux separately during the first growing season (P &lt; 0.05), the combination of these treatments reduced CO2 efflux to levels similar to the controls, with no lasting effects into the following growing season. Warming also interacted with defoliation to increase N2O flux in the second growing season relative to plots under either warming or defoliation treatment, whereas CH4 uptake was not influenced by our treatments. These results show the complex but transient impacts of warming and defoliation on soil C and N, particularly GHGs. Further research is needed to understand how these northern temperate grasslands respond to long‐term factorial experiments involving warming, defoliation, and variation in other factors (e.g., precipitation).