Nitrogen and Carbon Isotopic Dynamics of Subarctic Soils and Plants in Southern Yukon Territory and its Implications for Paleoecological and Paleodietary Studies

We examine here the carbon and nitrogen isotopic compositions of bulk soils (8 topsoil and 7 subsoils, including two soil profiles) and five different plant parts of 79 C3 plants from two main functional groups: herbs and shrubs/subshrubs, from 18 different locations in grasslands of southern Yukon Territory, Canada (eastern shoreline of Kluane Lake and Whitehorse area). The Kluane Lake region in particular has been identified previously as an analogue for Late Pleistocene eastern Beringia. All topsoils have higher average total nitrogen δ15N and organic carbon δ13C than plants from the same sites with a positive shift occurring with depth in two soil profiles analyzed. All plants analyzed have an average whole plant δ13C of −27.5 ± 1.2 ‰ and foliar δ13C of ±28.0 ± 1.3 ‰, and average whole plant δ15N of −0.3 ± 2.2 ‰ and foliar δ15N of ±0.6 ± 2.7 ‰. Plants analyzed here showed relatively smaller variability in δ13C than δ15N. Their average δ13C after suitable corrections for the Suess effect should be suitable as baseline for interpreting diets of Late Pleistocene herbivores that lived in eastern Beringia. Water availability, nitrogen availability, spacial differences and intra-plant variability are important controls on δ15N of herbaceous plants in the study area. The wider range of δ15N, the more numerous factors that affect nitrogen isotopic composition and their likely differences in the past, however, limit use of the modern N isotopic baseline for vegetation in paleodietary models for such ecosystems. That said, the positive correlation between foliar δ15N and N content shown for the modern plants could support use of plant δ15N as an index for plant N content and therefore forage quality. The modern N isotopic baseline cannot be applied directly to the past, but it is prerequisite to future efforts to detect shifts in N cycling and forage quality since the Late Pleistocene through comparison with fossil plants from the same region

Grazing and plant growth interactions in a semiarid Festuca pallescens grassland (Patagonia)

The effects of grazing on relative (g g-1 d-1) and absolute (g m-2 d-1) aboveground net primary productivity and senescence of coirón blanco (Festuca pallescens (St. Yves) Parodi) were investigated in northwestern Patagonia. Aboveground net primary productivity under ungrazed and grazed conditions was estimated by means of a simulation model fitted to biomass data. Relative and absolute aboveground net primary productivity was greater for grazed than ungrazed plants during the early growing season while the inverse occurred during the late growing season (reproductive period). Grazing reduced the relative and absolute aboveground senescence during the late growing season. Relative and absolute effective primary productivity, expressed as the difference between the corresponding primary productivity and senescence, were greater for grazed than ungrazed plants. This increase is in accordance with the grazing optimization hypothesis. However, the increase was not of sufficient magnitude to compensate for losses of green biomass caused by grazing. Results imply that current grazing intensities in this region reduce aboveground productivity of coirón blanco. It follows that a reduction in stocking rates would be necessary to increase aboveground primary productivity.This material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

Comparison of four methods of grassland productivity assessment based on Festuca pallescens phytomass data

The relative utility of 4 methods for grasslands above-ground net primary productivity (ANPP) assessment were evaluated. These methods, applied to a set of phytomass and litter data collected at about bimonthly intervals for 2 years in a Festuca pallescens (St. Yves) Parodi grassland steppe of southwestern Chubut, Argentina, were: (1) summation of positive increments of green (live) biomass between harvests, (2) summation of positive increments of total phytomass between harvests, (3) summation of positive increments of green biomass between harvests plus correction factors which accounted for the concomitant increases in dry, old dead, and litter, respectively, and (4) mathematical model of simultaneous differential equations which fitted the values of phytomass data obtained in the field. Method 1 gave consistently (p less than or equal to 0.05) the lowest ANPP values in both years. Productivity values obtained with methods 2, 3, and 4 were highly correlated and did not differ significantly (p less than or equal to 0.05) with each other. Their estimates varied from 94.9 to 105.3 g of dry matter per m2 for the first year and from 73.0 to 149.4 g of dry matter per m2 for the second year. These values are within the range of productivity given for other climatologically and physiognomically similar semiarid grasslands of North America. Each method except 1 provided reliable estimations of ANPP for the grassland studied. Methods 2, 3, and 4 can also be used to assess ANPP in any other grassland with similar characteristics. Each one, however, might have particular applications according to the specific objectives pursued.This material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

Seedlings dynamics of Festuca spp. in a grassland of Patagonia, Argentina, as affected by competition, microsites, and grazing

The effects of competition, grazing, and microsites on seedling dynamics of Festuca spp. were investigated in a semiarid steppe of Patagonia, Argentina. In an exclosure and an adjacent grazed area, the level of root competition for seedlings was controlled through root exclusion tubes (0.1 m diameter, 0.4 m long) installed adjacent to 7 similarly-sized Festuca pallescens plants and in the interspace between F. pallescens plants. Seedling dynamics at the phenological stages of a) recently emerged and up to 4 leaves and b) 5 leaves and up to 1 tiller were followed inside the tube area (no competition) and in paired circles (competition) for approximately 3 growing seasons. Peak density of Festuca spp. seedlings occurred in fall and early spring, when water content in the first 0 to 5 cm of the soil was above 8%. Seedling densities of Festuca spp. at the 2 phenological stages were significantly reduced by grazing. At the phenological stage of 1 to 4 leaves, seedlings were not affected by root competition, although their densities were significantly higher for seedlings adjacent to F. pallescens plants than in the interspace between plants. This was due to higher soil water content in these areas throughout the season in the 0 to 5 cm of the soil. Seedling densities at the phenological stage of 5 leaves and up to 1 tiller were significantly higher when there was no competition from neighboring grass plants as compared to seedlings exposed to competition. In regard to microsite differences, seedling density was significantly greater in the interspaces than adjacent to mature plants. These results suggest that although higher seedling densities can be obtained by excluding the area from grazing, intraspecific competition for soil water during the summer drought period can act as a barrier for further Festuca spp. seedling establishment.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

Plant phenology, leaf traits and leaf litterfall of contrasting life forms in the arid Patagonian Monte, Argentina

Question: Do coexisting plant life forms differ in overall phenology, leaf traits and patterns of leaf litterfall? Location: Patagonian Monte, Chubut Province, Argentina. Methods: We assessed phenology, traits of green and senesced leaves and the pattern of leaf litterfall in 12 species of coexisting life forms (perennial grasses, deciduous shrubs, evergreen shrubs). Results: We did not identify differences in phenology, leaf traits and patterns of leaf litterfall among life forms but these attributes contrasted among species. Independent of the life form, the maintenance of green leaves or vegetative growth during the dry season was mostly associated with leaves with high leaf mass per area (LMA) and high concentration of secondary compounds. Low LMA species produced low litterfall mass with low concentration of secondary compounds, and high N concentration. High LMA species produced the largest mass of leaf litterfall. Accordingly, species were distributed along two main dimensions of ecological variation, the dimension secondary compounds in leaves - length and timing of the vegetative growth period (SC - VGP) and the dimension leaf mass per area - leaf litterfall mass (LMA - LLM). Conclusions: Phenology, leaf traits and leaf litterfall varied among species and overlapped among life forms. The two dimensions of ecological variation among species (SC - VGP, LMA - LLM) represent distinct combinations of plant traits or strategies related to resource acquisition and drought tolerance which are reflected in the patterns of leaf litterfall.Fil: Campanella, María Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Bertiller, Monica Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentin

Above-ground phytomass dynamics in a grassland steppe of Patagonia, Argentina

Aerial phytomass and litter dynamics of a grassland steppe in Patagonia, Argentina, were studied at either monthly or bimonthly intervals for 2 years. This area is characterized by a cold and wet winter (June to September) and a warm and dry summer (December to March). The growing season extends from September to April, with moist spring and fall periods interrupted by a midsummer drought. Festuca pallescens (St. Yves) Parodi produced about 95% of the total annual phytomass. Peaks of green phytomass were recorded in spring-summer of the first growing season (33.6 +/- 2.9 g m-2) and in early spring (35.0 +/- 2.4 g m-2) and fall (32.7 +/- 2.7 g m-2) of the second growing season. Less abundant forage grasses were Poa ligularis Nees ap Steudel, Bromus setifolius Presl., Hordeum comosum Presl., and Rytidosperma virescens (Desvaux) Nicors. Shrubs and forbs represented less than 2% of the total annual phytomass of this grassland. The relationships between phytomass production of the main species and some environmental variables are discussed. These results contribute to the knowledge of above-ground phytomass dynamics and forage availability throughout seasons of this grassland in Patagonia, and are part of the data necessary for proper range management planning. This information will permit the designing of appropriate grazing schedules by balancing the number of grazing animals to the forage resources available.This material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202