Grassland restoration reveals the importance of ecotypic variation on community assembly along a longitudinal aridity gradient

Two dominant species, Andropogon gerardii and Sorghastrum nutans, have a wide distribution across the Great Plains (USA) and are widely used in restorations. We ask: Do dominant species' ecotypes influence community diversity and structure evenly across a longitudinal aridity gradient? We established reciprocal common gardens at four sites across the gradient. Ecotypes of the two dominant species were seeded along with a prairie seed mix according to a randomized complete block design. Species composition was measured after 3 and 10 years. We used linear mixed models to analyze the effect of the ecotype and year on community diversity. NMDS and PERMANOVA were applied to examine the contribution of ecotype to community structure. Results showed that ecotype significantly affected species richness and shaped taxonomic, phylogenetic, and functional diversity. Accordingly, restorations should consider ecotypic variation as a critical biological filter to community assembly in grassland ecosystems.

87 Evaluation of two stocking rates for grazing heifers on mixed sward native warm-season grass pastures in the Black Belt Prairie region

Optimal use of native warm-season grasses in pasture systems involves stocking grazing livestock at suitable rates. The study objective was to evaluate forage nutritive value and heifer ADG at two stocking rates on mixed-sward pastures of big bluestem (Andropogon gerardi Vitman), little bluestem (Andropogon scoparius), and indiangrass (Sorghastrum nutans L.). Pastures (3 replications) were stocked for 56 d during June and July in 2 yr with crossbred (Bos taurus) heifers (n = 24 heifers/year) stratified by initial BW (288.3 ± 1.7 kg) to one of two continuous stocking rates: 1.9 heifers/ha (HIGH) and 1.2 heifers/ha (LOW). Mean forage nutritive values on a DM basis were not different between HIGH and LOW stocking rates, respectively, for CP (7.0 ± 0.2% vs 6.7 ± 0.2%; P = 0.27), ADF (41.0 ± 0.6 vs. 41.4 ± 0.6; P = 0.64), NDF (69.9 ± 0.5 vs. 68.7 ± 0.5; P = 0.09), or relative feed value (RFV) (76.0 ± 1.0 vs. 76.9 ± 1.0; P = 0.53). There was a year effect (P < 0.01) and stocking rate x day effect (P < 0.01) for TDN. At LOW, TDN decreased from day 0 to day 28 (P = 0.02) and day 28 to day 56 (P = 0.02). At HIGH, TDN decreased (P < 0.01) from day 0 to day 28 but remained steady until day 56 (P = 0.21). There was a stocking rate x day interaction (P < 0.01) with ADG: LOW day 28 to 56 (1.20 ± 0.08 kg/day), HIGH day 0 to 28 (0.89 ± 0.08 kg/day), HIGH day 28 to 56 (0.44 ± 0.08 kg/day), and LOW day 0 to 28 (0.30 ± 0.08 kg/day). Further assessment of cattle ADG using more divergent stocking rates and plant persistence measures is warranted to inform ideal native grass stocking rate recommendations.

Tolerance of Native and Ornamental Grasses to Over-the-top Applications of Topramezone Herbicide

Research was conducted to determine the tolerance of multiple native and ornamental grass species and one ornamental sedge species to over-the-top applications of the postemergence herbicide topramezone at three locations in the southeastern United States in 2016 and 2017. Fully rooted liners of selected grass species were outplanted into research plots in Apopka, FL; Dallas, TX; and Knoxville, TN in late spring, allowed time to establish (≈1–2 months) and then treated with two applications of topramezone at either 0.05 or 0.10 kg a.i./ha at 6–8 weeks intervals. Results showed that species including Andropogon virginicus (broomsedge), Schizachyrium scoparium ‘The Blues’ (little bluestem), Tripsacum dactyloides (eastern gamagrass), and Tripsacum floridanum (florida gamagrass) exhibited the greatest tolerance to topramezone with <10% injury to no injury being evident after each application of both herbicide rates tested. Chasmanthium latifolium (wild oats), Eragrostis elliottii ‘Wind Dancer’, Muhlenbergia capillaris (pink muhly), and Spartina bakeri (sandcord grass) were significantly injured (50% injury or greater) at both herbicide rates. Average injury observed on Panicum virgatum ‘Shenandoah’ (red switchgrass) (ranging from 39% to 100% injury) and Sorghastrum nutans (indian grass) (ranging from 0% to 40% injury) was higher in Florida than in Tennessee (injury ranging from 23% to 43% on red switchgrass and 0% to 10% on indian grass). Similarly, Pennisetum alopecuroides (dwarf fountain grass) showed higher tolerance in Texas (ranging from 0% to 34% injury) compared with those observed in Tennessee (ranging from 0% to 53% injury). Topramezone injury to Carex appalachica (appalachian sedge) was ≤18% following two applications at both rates tested. Although no injury was observed in appalachian sedge following a single application up to 0.1 kg a.i. in Florida, plants succumbed to heat stress and accurate ratings could not be taken following the second application. Because of variability observed, tolerance of red switchgrass, indian grass, dwarf fountain grass, and appalachian sedge to applications of topramezone deserves further investigation. There is potential for future use of topramezone for control of certain grass and broadleaf weeds growing in and around certain ornamental grass species. However, as there was significant variability in tolerance based on species and differences in cultivars, testing a small group of plants before large-scale application would be recommended.

Codominant grasses differ in gene expression under experimental climate extremes in native tallgrass prairie

Extremes in climate, such as heat waves and drought, are expected to become more frequent and intense with forecasted climate change. Plant species will almost certainly differ in their responses to these stressors. We experimentally imposed a heat wave and drought in the tallgrass prairie ecosystem near Manhattan, Kansas, USA to assess transcriptional responses of two ecologically important C4 grass species, Andropogon gerardii and Sorghastrum nutans. Based on previous research, we expected that S. nutans would regulate more genes, particularly those related to stress response, under high heat and drought. Across all treatments, S. nutans showed greater expression of negative regulatory and catabolism genes while A. gerardii upregulated cellular and protein metabolism. As predicted, S. nutans showed greater sensitivity to water stress, particularly with downregulation of non-coding RNAs and upregulation of water stress and catabolism genes. A. gerardii was less sensitive to drought, although A. gerardii tended to respond with upregulation in response to drought versus S. nutans which downregulated more genes under drier conditions. Surprisingly, A. gerardii only showed minimal gene expression response to increased temperature, while S. nutans showed no response. Gene functional annotation suggested that these two species may respond to stress via different mechanisms. Specifically, A. gerardii tends to maintain molecular function while S. nutans prioritizes avoidance. Sorghastrum nutans may strategize abscisic acid response and catabolism to respond rapidly to stress. These results have important implications for success of these two important grass species under a more variable and extreme climate forecast for the future.

Growth of Ornamental Grasses Under Salinity Stress

The aim of this study was to determine the effect of substrate salinity caused by increasing NaCl doses on growth and development of ornamental grasses: Briza media L., Deschampsia cespitosa (L.) P. Beauv., Koeleria glauca (Spreng.) DC., Sesleria caerulea (L.) Ard. and Sorghastrum nutans (L.) Nash. Results provide the basis for the preliminary classification of analyzed grasses in terms of their tolerance to substrate salinity. Grasses, responding negatively to substrate salinity caused by small doses of 5 and 10 g·NaCl·dm−3, may be considered to be sensitive species. Within the studied genotypes, B. media showed a negative response to salt stress in most of the analyzed traits. Genotypes responded differently to salinity but all had a decreased tolerance index even at the lowest concentration of NaCl. The lowest percentages of dry leaves at 5 and 10 g NaCl·dm−3 were in K. glauca and S. caerulea. The percentage of dry matter and leaf greenness were least affected.

Effects of Root-trimming and Cutting-heights on Growth Performance of Potted Native Warm-season Grasses

Mechanized transplanting of native warm-season grass (NWSG) seedlings raised in biodegradable strip-cups may require trimming outgrown and entwined roots to facilitate individual placement and complete root covering. During establishment, mowing is often used to reduce weed competition and promote tillering. In two randomized complete block split-split-plot design experiments, effects of root-trimming and cutting-height on growth and biomass production of potted NWSGs [big bluestem (BB, <em>Andropogon gerardii</em> Vitman), eastern gamagrass (GG, <em>Tripsacum dactyloides</em> L.), indiangrass (IG, <em>Sorghastrum nutans</em> L.), and switchgrass (SG, <em>Panicum virgatum</em> L.)] were assessed. Six-week old seedlings were transplanted, with or without root-trimming, and four of each type and species, assigned to 10-, 15-, or 20-cm cutting-height. All plants were fertilized uniformly and watered sufficiently. After a 7-d adjustment period, plants were clipped to 10 cm which promoted tillering. A three-week regrowth was then allowed before the first of three forage harvests, at assigned cutting-heights. Plant heights were recorded every two weeks after transplanting and on each harvest date. Data were analyzed for effects of root-trimming, cutting-height, and species. Root-trimming had no effect on the parameters. Cutting-height had no effect on plant heights except for second GG and SG regrowths, and/or the third BB and SG. Cutting-height affected only SG forage biomass significantly (<em>P</em> &lt; 0.05) during year1 and every species during year2 with 100%+ greater values at the 20- than the 10-cm. All 20-cm average growth rates and belowground biomass in year2 were greater (<em>P</em> &lt; 0.001) than the 10-cm by &gt; 100%, but with similar root:total biomass ratios. Overall, species yield increased in the order; IG&lt;BB&lt;GG&lt;SG. With adequate soil moisture and fertility, results indicate that root-trimming may not affect growth or forage biomass of NWSGs during establishment. Mowing NWSGs, during establishment, for up to three 20-cm cuts at ≥ 3-week intervals, may not impact recovery growth or belowground biomass, negatively. Results from field studies are required ahead of practical establishment management recommendations.

Rotation with Cover Crops Suppresses Weeds and Increases Plant Density and Yield of Strawberry

Yield of strawberry grown continuously on the same site often declines over time as a result of proliferation of weed seeds and pathogenic organisms in the soil. Plots were established and maintained in seven different cover crops and as continuous strawberry or continuous tillage for 10 years (1996 to 2005) in a site that was previously in strawberry production for 10 years (1986 to 1995). Cover crops included blackeyed Susan (Rudbeckia hirta L.), sorghum Sudangrass [Sorghum bicolor (L.) Moench], marigold (Tagetes erecta L.), big bluestem (Andropogon gerardii Vitman), perennial ryegrass (Lolium perenne L.), switchgrass (Panicum virgatum L.), and Indiangrass [Sorghastrum nutans (L.) Nash]. Treatments were ended in 2005 and plots were planted with ‘Honeoye’ strawberry in a matted row. Effectiveness of soil pretreatments in reducing weed populations and enhancing strawberry production was evaluated for four growing seasons by quantifying weed growth by type and biomass and strawberry plant density and yield. The results indicate that matted-row strawberry production plots that were either in continuous tillage or established in S. bicolor, P. virgatum, or A. gerardii before planting strawberry had lower weed biomass and greater strawberry plant establishment and yield than plots established in L. perenne or R. hirta or that had supported continuous strawberry production.