Temperate Grass Species Research Articles

Phleum pratense alone is sufficient for allergen‐specific immunotherapy against allergy to Pooideae grass pollens

Specific immunotherapy is the only causal treatment of allergy available today. Traditionally, therapeutic products based on either a single grass species or a mix of such extracts are used for grass pollen immunotherapy. Investigations comparing the immunological response to these allergen preparations are needed to ensure optimal treatment. The objective of this study was to investigate patterns of T and B cell cross-reactivity to Pooideae single-species extracts and to extract mixes. IgG4 induced by immunotherapy with Phleum pratense extract was investigated for cross-reactivity using nine single-species extracts and four mixes. For the mixes, studies of IgE cross-reactivity were also performed. T cell cross-reactivity was investigated in lines specific to nPhl p 1 or nPhl p 5 allergens, and the amounts of group 1 and 5 allergens in the extracts were quantified by a single radial immunodiffusion. The levels of treatment-induced IgG4 detected by all the extracts displayed a clear correlation to that detected by the P. pratense pollen extract. The IgE studies confirmed the cross-reactivity of P. pratense-specific B cells towards the allergens contained in the mixes, and the T cell studies demonstrated cross-reactivity towards group 1 and 5 major allergens in extracts of six temperate grass species. Extensive T and B cell cross-reactivity was observed towards the allergens of the Pooideae grasses, and the degree of B cell cross-reactivity was independent of the number of species included in the extract mixes. This implies that treatment with pollen extract of just one Pooideae species will affect the allergic responses caused by any of the temperate grasses in this subfamily.

Evolutionary diversification of satellite DNA sequences from Leymus (Poaceae: Triticeae)

The genus Leymus (lymegrass) comprises about 30 polyploid, perennial, temperate grass species in the tribe Triticeae (family Poaceae). Previous studies indicated a large diversity in the Leymus genome, and therefore, the aim of this study was to isolate new repetitive DNA sequences that can be used for differentiating Leymus species and elucidating their genomic relationships. A C0t-1 DNA plasmid library was generated from genomic DNA of American tetraploid species Leymus triticoides. A family of highly repetitive satellite DNA sequences, designated Lt1, was obtained from this library. The Lt1 family consisted of 380 bp SacI repeating units arranging in tandem arrays. A 120 bp MspI subfamily was discovered within this family, indicating that cytosine methylation may have played an important role in the evolution of satellite sequences. The Lt1 satellite was localized in the subtelomeric heterochromatic blocks of L. triticoides chromosomes, which are present on all chromosomes and often on both arms. The Lt1 sequences are abundant in L. triticoides but absent in its closely related species Leymus racemosus. Significant homology was found between the Lt1 family and numerous repetitive sequences from Poaceae species, indicating that the Lt1 is an ancient family of tandemly repeated sequences in grasses.

Quantifying the effect of nitrogen on productivity of cocksfoot ( Dactylis glomerata L.) pastures

Inorganic nitrogen fertilisers are commonly applied to crops and pastures to increase or maintain productivity. The benefits of N application must be balanced with the potential for environmental damage. At Lincoln University, Canterbury, New Zealand a split plot experiment with two irrigation levels (irrigated and dryland) and two N fertiliser application rates (0 and 800 kg N/ha/y (2003/2004) or 1600 kg N/ha/y (2004/2005) was established on a 9-year-old cocksfoot ( Dactylis glomerata L.) dominant pasture to validate the N dilution curve for temperate grass species. The extent of N deficiency of pastures which had suboptimal N was quantified by calculation of a ratio between measured N% of herbage and optimum N% from the N dilution curve. The N dilution curve had the form N% = 4.8 DM −0.35 ( R 2 = 0.65) and the NNI ranged from a maximum of 1.2, which indicated luxury uptake, to a minimum of 0.2, which has been proposed as the minimum NNI required to result in net growth. When moisture was adequate for growth, the main cause of yield differences between +N and −N pastures was radiation use efficiency with −N pastures producing 0.54 g DM/MJ PAR in spring or less than half that of +N pastures (1.16 g DM/MJ PAR). The intrinsic link between water availability and N uptake in dryland and irrigated pastures was explained ( R 2 = 0.88) by the relationship between the water use efficiency and N uptake ratio. Periods of low N uptake (N deficiency) were associated with low water use efficiency.

Which plant traits promote growth in the low-light regimes of vegetation gaps?

Nine temperate grass species were screened for their potential to grow in the low-light conditions typical of gaps in dense vegetation. To this end, photosynthetic photon flux densities (PFD) were simulated in a growth chamber (PFD 100, 50 or 25 μmol photons m−2 s−1). Relative and absolute growth rates (RGR and AGR, respectively) of the species were regressed on ten different ecophysiological and morphogenetic plant attributes. No significant relationships were found between plant attributes and relative growth rate, while six attributes explained a significant proportion of the interspecific variance in absolute biomass growth: net photosynthetic rate at growth PFD (P net ) (75.5%), leaf apparent quantum yield of CO2 fixation (62.5%), leaf dark respiration rate (65.2%), leaf compensation PFD (71.0%), root: shoot ratio (66.4%) and plant nitrogen content on a mass basis (42.0%). Only species with extremely low allocation to roots and very high (relatively speaking) net photosynthetic rates were able to grow fast in low light. Specific leaf area (SLA), instantaneous photosynthetic nitrogen use efficiency (PNUE) and leaf nitrogen content on a mass basis as well as on an area basis were not significantly related to growth. The absence of effects of plant traits on RGR, unlike for AGR, could arise from a relationship that we observed between AGR and a fitted start value of the biomass-time course (i.e. seed mass or germination time). This suggests that interspecific differences in the very early growth stages of the plants were responsible for differences in successful development under low light, rather than differences in RGR. Based on its high explanatory power, its relative constancy with plant age and the lack of effect of growth PFD, P net would be the best candidate for characterizing potentially shade-tolerant species that are likely to establish in dense vegetation in the field.

Natural enemies act faster than endophytic fungi in population control of cereal aphids

1. Fast-growing populations of phytophagous insects can be limited by the presence of natural enemies and by alkaloids that are produced by symbiotic associations of many temperate grass species with endophytic fungi. It is unclear if and how acquired plant defences derived from endophytic fungi interact with natural enemies to affect phytophagous insect populations. 2. To assess the relative importance of endophytic fungi compared to that of natural enemies on the population dynamics of phytophagous insects, we carried out a fully factorial field experiment, in which the presence of natural enemies and the presence of endophytic fungi were manipulated simultaneously. Target colonies of aphids were monitored for 8 weeks starting from their natural appearance in the field to the end of the aphid season. 3. We show that on Lolium perenne increased natural enemy densities reduced the individual numbers of two common cereal aphids, Rhopalosiphum padi and Metopolophium festucae. 4. The presence of the endophytic fungi Neotyphodium lolii reduced the number of M. festucae but did not affect the number of R. padi. The reduction in R. padi numbers by predators and parasitoids was not influenced by the presence of endophytes. For adult M. festucae, however, the negative effects of natural enemies were significant only in the absence of endophytes. 5. Over the duration of the experiment, the effect of natural enemies on aphid colony growth was much stronger than the effect of the endophytic fungi N. lolii, presumably because predator and parasitoid action on aphid colonies is much faster than any effects of endophytes. 6. Our results demonstrate that with simultaneous action of acquired endosymbionts and natural enemies, both factors can control aphid colony growth but they generally act independently of each other.

Brachypodium Genomics

Brachypodium distachyon (L.) Beauv. is a temperate wild grass species; its morphological and genomic characteristics make it a model system when compared to many other grass species. It has a small genome, short growth cycle, self-fertility, many diploid accessions, and simple growth requirements. In addition, it is phylogenetically close to economically important crops, like wheat and barley, and several potential biofuel grasses. It exhibits agricultural traits similar to those of these target crops. For cereal genomes, it is a better model than Arabidopsis thaliana and Oryza sativa (rice), the former used as a model for all flowering plants and the latter hitherto used as model for genomes of all temperate grass species including major cereals like barley and wheat. Increasing interest in this species has resulted in the development of a series of genomics resources, including nuclear sequences and BAC/EST libraries, together with the collection and characterization of other genetic resources. It is expected that the use of this model will allow rapid advances in generation of genomics information for the improvement of all temperate crops, particularly the cereals.

Development of near Infrared Analysis of Faeces to Estimate Non-Grass Proportions in Diets Selected by Cattle Grazing Tropical Pastures

Grass (monocots) and non-grass (dicots) proportions in ruminant diets are important nutritionally because the non-grasses are usually higher in nutritive value, particularly protein, than the grasses, especially in tropical pastures. For ruminants grazing tropical pastures where the grasses are C4 species and most non-grasses are C3 species, the ratio of 13C/12C in diet and faeces, measured as δ13C‰, is proportional to dietary non-grass%. This paper describes the development of a faecal near infrared (NIR) spectroscopy calibration equation for predicting faecal δ13C from which dietary grass and non-grass proportions can be calculated. Calibration development used cattle faeces derived from diets containing only C3 non-grass and C4 grass components, and a series of expansion and validation steps was employed to develop robustness and predictive reliability. The final calibration equation contained 1637 samples and faecal δ13C range (‰) of [12.27]–[27.65]. Calibration statistics were: standard error of calibration (SEC) of 0.78, standard error of cross-validation (SECV) of 0.80, standard deviation ( SD) of reference values of 3.11 and R2 of 0.94. Validation statistics for the final calibration equation applied to 60 samples were: standard error of prediction ( SEP) of 0.87, bias of −0.15, R2 of 0.92 and RPD of 3.16. The calibration equation was also tested on faeces from diets containing C4 non-grass species or temperate C3 grass species. Faecal δ13C predictions indicated that the spectral basis of the calibration was not related to 13C/12C ratios per se but to consistent differences between grasses and non-grasses in chemical composition and that the differences were modified by photosynthetic pathway. Thus, although the calibration equation could not be used to make valid faecal δ13C predictions when the diet contained either C3 grass or C4 non-grass, it could be used to make useful estimates of dietary non-grass proportions. It could also be used to make useful estimates of non-grass in mixed C3 grass/non-grass diets by applying a modified formula to calculate non-grass from predicted faecal δ13C. The development of a robust faecal-NIR calibration equation for estimating non-grass proportions in the diets of grazing cattle demonstrated a novel and useful application of NIR spectroscopy in agriculture.

The effects of growth temperature on digestibility and fibre concentration of seven temperate grass species

The effects of growth temperature on digestibility and fibre concentration of seven grass species: Kentucky bluegrass (Poa pratensis L), timothy (Phleum pratense L), meadow foxtail (Alopecurus pratensis L), perennial ryegrass (Lolium perenne L), red fescue (Festuca rubra L), tufted hair-grass (Deschampsia caespitosa L (PB)) and meadow fescue (Festuca pratensis Huds) were investigated in growth chamber and greenhouse experiments. Seedlings from each grass species were established in a greenhouse and then transferred at five weeks of age to three growth chambers with day/night temperatures of 9/5, 13/9 and 17/13°C, respectively. Three pots of each species from each temperature treatment, and from the greenhouse control, were harvested weekly for three weeks. The rate of decline of in vitro true digestibility (IVTD) and in vitro cell wall digestibility (IVCWD) increased with increasing temperature for all species. Each degree of increase in temperature decreased the IVTD by an average of 0.22 g kg−1 dry matter (DM) day−1 between 9 and 13°C, and by 0.35 g kg−1 DM day−1 between 13 and 17°C. On average, the neutral detergent fibre (NDF) increased at a rate of 0.78 g kg−1 DM day−1 for each degree increase in temperature between 9 and 17°C. The effects of temperature were less for perennial ryegrass and meadow fescue than for the other species. Perennial ryegrass was consistently ranked as highest in digestibility, followed by meadow fescue; tufted hair-grass had the lowest digestibility. The rate of decline in digestibility was slower for perennial ryegrass and meadow fescue than for the other species.

Can you dig it? Use of excavation, a risky foraging tactic, by dugongs is sensitive to predation danger

Foraging and vigilance are mutually exclusive for some foraging tactics but not others. Thus, in response to changes in predation danger, prey species with multiple foraging tactics may switch facultatively between them, allowing for differential levels of vigilance. Using data from focal observations collected over 4 years (2002–2004, 2006) in Shark Bay, Western Australia, we explored the use of two tactics, cropping and excavation, by dugongs, Dugong dugon, foraging under risk of predation by tiger sharks, Galeocerdo cuvier. Overall, dugongs predominantly used the cropping tactic, which allows for regular visual scans, to harvest temperate sea grass species. Dugongs only used the excavation tactic, which precludes regular visual scans but allows individuals to access the nutritious rhizomes of preferred tropical sea grass species, in months when tropical species were most available (February–May). However, during these months the time dugongs allocated to excavation was inversely related to shark abundance rather than the availability of these sea grass species. We conclude that use of foraging tactics by dugongs is sensitive to predation danger, and that individuals manage their risk of mortality via reduced use of a profitable but potentially hazardous tactic when the likelihood of encountering predators is high. Excavating dugongs are more likely to disrupt sea grass meadow structure and promote succession than are those engaged in cropping. Thus, by altering the time dugongs devote to these alternative tactics, tiger sharks may exert an indirect effect on sea grass patch composition and structure and, ultimately, benthic communities.

Association of Candidate Genes With Flowering Time and Water-Soluble Carbohydrate Content in Lolium perenne (L.)

We describe a candidate gene approach for associating SNPs with variation in flowering time and water-soluble carbohydrate (WSC) content and other quality traits in the temperate forage grass species Lolium perenne. Three analysis methods were used, which took the significant population structure into account. First, a linear mixed model was used enabling a structured association analysis to be incorporated with the nine populations identified in the structure analysis as random variables. Second, a within-population analysis of variance was performed. Third, a tree-scanning method was used, in which haplotype trees were associated with phenotypes on the basis of inferred haplotypes. Analysis of variance within populations identified several associations between WSC, nitrogen (N), and dry matter digestibility with allelic variants within an alkaline invertase candidate gene LpcAI. These associations were only detected in material harvested in one of the two years. By contrast, consistent associations between the L. perenne homolog (LpHD1) of the rice photoperiod control gene HD1 and flowering time were identified. One SNP, in the immediate upstream region of the LpHD1 coding sequence (C-4443-A), was significant in the linear mixed model. Within-population analysis of variance and tree-scanning analysis confirmed and extended this result to the 2118 polymorphisms in some of the populations. The merits of the tree-scanning method are compared to the single SNP analysis. The potential usefulness of the 4443 SNP in marker-assisted selection is currently being evaluated in test crosses of genotypes from this work with turf-grass varieties.

Plant-based manipulation of nitrification in soil: a new approach to managing N loss?

Much work has gone into the management of nitrification through applications of chemicals known to inhibit enzyme function in nitrifiers with indifferent outcomes when tested in the field. Much less attention has been focused on the capacity of plants to modify nitrification in situ. Subbarao and coworkers in a series of neat and elegant studies have confirmed that a tropical grass species, Brachiaria humidicola, produces chemicals that inhibit nitrification in soil. Critical to the work was the use of a Nitrosomonas europaea strain (nitrifying bacteria) that had been specifically constructed to produce bioluminescence due to the expression of “luxAB’ genes during nitrification. This application led to the development of an assay that enabled the suppression of nitrification to be assessed directly. They produce evidence that the production of chemicals by Brachiaria humidicola roots, described as biological nitrification inhibitors (BNIs), is under plant control. However, the triggers or molecular controls for BNI production have yet to be ascertained. Examination of the capacity of major crops to produce BNIs, including wheat (Triticum aestivum), barley (Hordeum vulgare), rice (Oryza sativa) and maize (Zea mays) indicate that these do not have this capacity. Work is needed on wild relatives of these crops and the major temperate grass species such as Lolium perenne to determine whether these have the capacity to produce BNIs with an aim to introduce this capacity into domesticated lines. The work of Subbarao et al. highlights how molecular biology can be used to introduce traits into micro-organisms responsible for key soil N transformations in a way that facilitates analysis of the interaction between plants and the soil environment so crucial to their growth and survival.

The response of four perennial grass species to sodium chloride salinity when irrigated with saline waters

The response of 4 temperate grass species (Lolium perenne cv. Victorian, Thinopyrum ponticum cv. Tyrell, Austrodanthonia richardsonii cv. Taranna, A. bipartita cv. Bunderra) to saline irrigated conditions was evaluated over 4 seasons at Tatura in northern Victoria. This experiment followed earlier research where the salt tolerance of ~20 species of grasses was evaluated in the greenhouse. Field plots were established under non-saline conditions and were irrigated with saline water at 1.6, 2.5, and 4.5 dS/m. Measurements made on these plots included dry-matter production, tissue ion (Na+, Cl–, K+, Mg2+, Ca2+) concentrations, in vitro dry-matter digestibility, root distribution, and soil chemistry. Soil salinity (EC1 : 5) and sodicity (SAR1 : 5) levels peaked at 0.30–0.60 m depth and reached 1.3 dS/m and 9.8, respectively, for the highest saline irrigation treatment. Cumulative plant dry-matter production was lower in T. ponticum compared with the Austrodanthonia species and L. perenne at all salinity levels, but in relative terms there was no difference in the salt tolerance among any of the 4 species (the reduction in dry weight at 4.5 dS/m was 10–15% for all species). Leaf tissue concentrations of Na+ and Cl– were significantly lower in A. richardsonii and A. bipartita compared with T. ponticum and L. perenne, and in vitro dry-matter digestibility tended to be greater in L. perenne under saline conditions than in the other 3 species. This research suggests that the 2 native Austrodanthonia species can be grown under moderately saline conditions—either under saline irrigation or in a dryland discharge area—in environments where perennial ryegrass may also be grown.

Late heading of perennial ryegrass caused by introducing an Arabidopsis homeobox gene

AbstractPerennial ryegrass (Lolium perenne L.) is the most important temperate forage grass species. Unfortunately, the nutritional value of perennial ryegrass declines as maturity progresses, mainly because of a high concentration of poorly digestible compounds in inflorescences. Therefore, the development of forage‐type ryegrass varieties with extended vegetative growth is of interest for agriculture. To delay floral transition in perennial ryegrass the Arabidopsis ATH1 gene driven by the maize ubiquitin promoter, the rice actin promoter or the rice OSH1 promoter, respectively was introduced. In ATH1‐expressing plants heading was delayed, and in a number of cases the plants never flowered at all. Such non‐ or late‐heading was accompanied by the outgrowth of normally quiescent lateral meristems into extra leaves, resulting in a leafy growth habit. When eventually heading, these plants generally produced a reduced number of inflorescences. These observations suggest that ATH1‐mediated delay of heading may be useful to improve fodder quality of perennial ryegrass.

Use of the hydrothermal time model to analyse interacting effects of water and temperature on germination of three grass species

The temperate grass species, red fescue (Festuca rubrassp.litoralis), perennial ryegrass (Lolium perenne) and Kentucky bluegrass (Poa pratensis), are often sown in mixtures for turfgrass. Differences in germination response to environmental conditions often result in different establishment success. The three species were compared in a study of imbibition at reduced water potential (Ψ) and in a study of the effects of Ψ and temperature on germination. In all three species, imbibition rate and extent were reduced with decreasing Ψ, causing a prolonged lag-phase before germination, particularly in Kentucky bluegrass. In perennial ryegrass and Kentucky bluegrass, water content at radicle emergence decreased non-linearly with decreasing Ψ, with a lower asymptote expressing the critical water content for germination. Seeds were germinated in factorial combinations of two temperatures (10 and 25°C) and nine Ψ levels (–2 to 0 MPa). Kentucky bluegrass required a longer thermal time to germinate than the other species and exhibited conditional dormancy at 25°C, which affected the use of the thermal time model. The effects of Ψ were described by a hydrotime model. Kentucky bluegrass had higher base water potential (Ψb) and required a longer hydrotime for germination than the other species. However, Ψbincreased with temperature in Kentucky bluegrass and red fescue, but decreased in perennial ryegrass, and the base temperatures also changed with Ψ. The interacting effects of Ψ and temperature affected the ability of the hydrothermal time model to predict germination performance across all temperature and Ψ conditions.

Laying the cytotaxonomic foundations of a new model grass, Brachypodium distachyon (L.) Beauv.

Brachypodium distachyon is a ubiquitous, temperate grass species which is being developed and exploited as an alternative model to rice, in order to gain access to important syntenic regions of the genomes of less tractable relatives such as wheat. As part of this initiative, this paper describes for the first time the cytotaxonomy of members of the polyploid series of this species, and challenges the assumption that the series evolved simply by chromosome doubling. In situ hybridization using genomic DNA probes and rDNA markers uncovers a hybrid origin of several of the polyploid ecotypes, and sheds light upon the complex evolution of this species and its close relatives.

Tiller size/density compensation in grazed Tifton 85 bermudagrass swards

The objective of this study was to evaluate the occurrence of the tiller size/density compensation mechanism in Tifton 85 bermudagrass swards grazed by sheep under continuous stocking. Treatments corresponded to four sward steady state conditions (5, 10, 15, and 20 cm of sward surface height), maintained by sheep grazing. The experimental design was a complete randomized block with four replicates. Pasture responses evaluated include: tiller population density, tiller mass, leaf mass and leaf area per tiller, and herbage mass. Tiller volume, leaf area index, tiller leaf/stem ratio, and tiller leaf area/volume ratio were calculated and simple regression analyses between tiller population density and tiller mass were performed. Measurements were made in December, 1998, and January, April, and July, 1999. The swards showed a tiller size/density compensation mechanism in which high tiller population densities were associated with small tillers and vice-versa, except in July, 1999. Regression analyses revealed that linear coefficients were steeper than the theoretical expectation of -3/2. Increments in herbage mass were attributable to increases in tiller mass in December and January. Leaf area/volume ratio values of Tifton 85 tillers were much lower than those commonly found for temperate grass species.

Growth and photosynthetic responses to elevated [C02] in grasses from Tasmanian native pasture

Six species of grass (four C 3 and two C4) from southeastern Australian native pastures were grown in controlled environment cabinets at current (~370 !!mol CO2 mol-I) and twice current (~750 !!mol CO2 mol-I) cabinet [C02l. Photosynthetic gas exchange and above­ ground biomass were estimated after seven weeks. Cabinet [C02l had a highly significant impact on above-ground biomass (P<0.0003) with plants exposed to elevated [C02l having on average 78% greater above-ground biomass than the controls. The relative increase of above-ground biomass caused by elevated [C02] varied among species. [C02] during gas exchange measurements and species had highly significant impacts on carbon assimilation and evapotranspiration rates, stomatal conductance and water-use efficiency. Cabinet [C02l had a significant impact on carbon assimilation rate only, for which there was a significant cabinet [C02l x species interaction. Carbon assimilation rate was influenced by cabinet [C02l only for Poa labillardierei, but this may well be related to pot conditions. Three-factor analysis of variance found no interaction between cabinet [C02l and [C02l during photosynthetic measurements, further supporting a lack of photosynthetic acclimation to elevated [C02l in young plants of these temperate Australian grass species.

Root structure and function in an ecological context.

Ecological theories concerning the relationship of suites of traits with resource supply and plant potential growth rate have concentrated primarily on leaf structure and physiology - much less is known about interspecific patterns of variation in root structure and physiology. In this issue, Wahl & Ryser reduce this knowledge gap by demonstrating important correlations of root structure with potential growth rate and height among a range of perennial temperate grass species adapted to sites of a wide range of fertility (see pp. 459-471).

Changes in Dry Matter, Carbohydrate and Seed Yield Resulting from Lodging in Three Temperate Grass Species

The adverse effect of lodging on grass seed yield may be attributed, in part, to assimilate limitation during the seed filling period. This investigation examined plant dry matter assimilate partitioning and seed yield as affected by lodging in three species that are closely related but phenotypically different: tall fescue (Festuca arundinacea Schreber.), Italian ryegrass (Lolium multiflorum Lam.), and perennial ryegrass (L. perenne L.). Studies were performed in field plots at Corvallis, Oregon, USA. Seed yield components (seed number per inflorescence, seed yield per inflorescence, and single seed mass) and leaf, stem (lower, middle, and peduncle) and seed inflorescence dry mass were measured just prior to anthesis to seed maturity. Dry mass and water soluble carbohydrates (WSC) were determined for shoot components. The reduction in dry mass and WSC in leaves and stem components following anthesis was often greater in lodged plants compared to upright plants. The relatively low seed yield depression in lodged tall fescue suggested a higher compensation potential for partitioning reserve assimilate from leaves and stems to support seed growth and development. This potential does not appear to be present to the same degree in Italian ryegrass and to an even lesser extent in perennial ryegrass. These findings suggest that the potential to compensate for reduced assimilate supply during the period of high assimilate demand by seeds may be attributed, in part, to the total assimilate reserve accumulated prior to photoassimilate reduction caused by the lodged condition.

Differences among Temperate Grass Species in Growth Response to Nitrogen Nutrition during the Second Growing Period

Differences among Temperate Grass Species in Growth Response to Nitrogen Nutrition during the Second Growing Period