Functional trait differences between native bunchgrasses and the invasive grass Bromus tectorum

We conducted 30-and 60-d greenhouse experiments to compare functional traits of Bromus tectorum(invasive annual grass) and four perennial bunchgrasses under well-watered or drought conditions.Even under drought, B. tectorum experienced significantly less stress(i.e., higher xylem pressure potential and greater shoot water content, water use per day and water-use efficiency) and biomass production than the perennial grasses after 30 d. However, after 60 d, its superiority was reduced under infrequent watering. Differences among perennial grasses were more pronounced for physiological traits under infrequent watering and for morphological traits under frequent watering. Elymus multisetus(fastgrowing species) had a higher transpiration rate, lower leaf temperature, and lower water-use efficiency than the other grasses after 30 d. In contrast, Pseudoroegneria spicata(slow-growing) had lower xylem pressure potential and higher leaf temperature than all other grasses under infrequent watering. Under frequent watering, shoot dry mass and specific leaf area of B. tectorum was matched by Elymus wawawaiensis(moderate-growing species). Our results indicate that multiple-species plantings or seedings are necessary to foster greater weed resistance against B. tectorum. We also emphasize that when choosing plant material for restoration, performance during both pulse(resource-rich) and inter-pulse(resource-poor) periods should be considered.

Forage production and persistence characteristics of grazed native warm-season grass mixtures with or without nitrogen fertilizer

Background:Native warm-season grass(NWSG)mixtures may provide a lownitrogen(N)-input summer perennial forage option to extensively managed forage-livestock systems.Methods:Mixed pastures of big bluestem(Andropogon gerardii Vitman),little bluestem(Schizachyrium scoparium Michx.),and indiangrass(Sorghastrum nutans L.)fertilized with 0 or 67 kgNha−1 were continuously stocked with beef heifers and cows.Forage mass,nutritive value,and canopy heights were determined every 2 weeks during the grazing season.Stand persistence measures included the canopy cover and leaf area index(LAI)and plant crown density at spring emergence following 3 years of grazing management.Results:Forage mass,canopy height,and stocking densities were greater for N-fertilized NWSG than unfertilized NWSG for the first 30 days of the growing season across the 3-year study.Forage NWSG fertilized with N had a greater decrease in LAI during the growing season(51%decrease)than unfertilized NWSG.Spring NWSG plant density estimates following 3 years of grazing did not differ across N management strategies.Conclusions:Forage NWSG mixtures supported superior forage attributes and greater stocking densities early in the grazing season under low-level N than zero-N-input systems and may provide a low-N-input alternative for improved species use in southeastern US forage-livestock systems.

Endophyte infection of Festuca eskia enhances seedling survival to drought and cutting at the expense of clonal expansion

Symbiotic relationships between fungal endophytes and grass species are known to increase stress resistance in the grass host;however,there is little evidence to suggest that the positive effects occur early in the grass life cycle.In this study,we explored the effects of the endophyte Epichloe¨festucae on the growth and survival of Festuca eskia seedlings under drought and frequent cutting stress.Methods Festuca eskia seedlings were collected from the western part of the plant repartition area in a non-symbiotic population located in a mesic and heavily grazed site(W-NS)and from the eastern part in a symbiotic population from a xeric and lightly grazed site(E-S).The E-S population was experimentally freed from its endophyte(E-F).Two greenhouse experiments were conducted to compare growth and survival between the three seedling types under drought stress and frequent cutting.In the first experiment,126 seedlings per seedling type(n=378)were grown for 6 weeks under non-limiting conditions before the cessation of watering.After 3 weeks without irrigation,full irrigation was restored for 10 days to measure the survival rate.Leaf length,leaf elongation rate and survival rate were assessed per population.In the second experiment,156 seedlings per seedling type(n=468)were grown under non-limiting conditions.All seedlings were cut to 3 cmhigh,twice a week,during the first month of growth.Leaf elongation and tillering were monitored on 52 seedlings per seedling type.For each type,seedling survival rate was determined by the number of plants alive after 10 days of regrowth,without cutting.Important Findings The drought experiment revealed a phenotypic differentiation to drought in 30 F.eskia populations,suggesting adaptive differentiation:the eastern seedlings showed the highest survival rate.A tradeoff between growth and survival was highlighted:the highest drought survival rate was associated with the lowest leaf elongation rate under non-limiting water conditions.Endophyte presence in the eastern population increased seedling drought survival.In contrast,cutting survival rate was similar between W-NS and E-S because the presence of the endophyte increased seedling survival to frequent cutting.However,this positive effect came with a cost:the endophyte reduced seedling tillering rate.

Effects of endophyte infection on the competitive ability of Achnatherum sibiricum depend on endophyte species and nitrogen availability

Aims the leaves of almost all terrestrial plant species are colonized by endophytic fungi.compared to agronomic grasses,which usually harbor few endophytes,native grasses generally possess greater endophyte species diversity.Existing studies examining endophyte effects on natural grasses under competition normally considered the infection status(infected or uninfected),and rarely considered endophyte species.Methods We examined the effects of endophyte infection and of endophyte species on the interspecific competitive ability of a subdominant species,Achnatherum sibiricum,at two nitrogen levels(high ni-trogen and low nitrogen).Achnatherum sibiricum plants infected by two different species of endophyte(Epichloësibirica and E.gansuensis)and uninfected plants were grown in monoculture and binary mixtures with a dominant species,Stipa grandis(six individuals per species for monocultures and three+three in-dividuals of each species in mixtures).Shoot and root biomass,tiller number and total phenolic concentration were measured after 3 months.Moreover,the aggressivity index was calculated to compare the competitive ability of A.sibiricum relative to S.grandis.Important Findings Both E.gansuensis(Eg)-and E.sibirica(Es)-infected A.sibiricum plants showed a greater competitive ability than the uninfected plants under high nitrogen supply,while the opposite result oc-curred under low nitrogen supply.At high nitrogen levels,Eg plants had a higher tiller number and a greater shoot biomass in-hibitory effect on S.grandis than Es plants had when growing in mixture,while Es plants showed better root growth performance than Eg and uninfected plants under mixture conditions at all ni-trogen levels.A higher concentration of phenolic compounds in Eg plants than in Es plants might contribute to the higher inhibi-tory effect of Eg plants on competing plants.Our study indicates that the interaction between endophyte infection and nitrogen availability can alter the competitive ability of the host plant A.sibiricum but that these two endophyte species work in different ways,which may influence the coexistence of A.sibiricum with the dominant species.