B. García-Criado

Near infrared spectroscopy prediction of mineral content in botanical fractions from semi-arid grasslands

Near infrared reflectance spectroscopy (NIRS) was assessed for its capacity to estimate the mineral content of semi-arid grassland samples. NIRS calibrations were derived for P, K, Ca and Mg contents. Four populations of samples were used: total herbage, with a heterogeneous and complex botanical composition, and its botanical components (grasses, legumes and forbs). One set of samples from each population was selected to develop the specific calibration equations using three mathematical data treatments (log 1/R, first derivative, and second derivative). Reference values from the calibration sample set were regressed on the corresponding spectral data using stepwise multiple regression analysis. The equations were validated with samples from the same four populations that had not been included in the calibration. The NIRS method afforded acceptable accuracy in the prediction of P, K, Ca and Mg contents in the total herbage population and its botanical fractions. Botanical composition and mathematical treatment affected both the accuracy and precision of NIRS analyses; in this sense, the best fits were usually obtained using samples of simpler botanical composition (legumes and grasses), while the first derivative usually led to better results in the estimation of most parameters.

An Epichloë endophyte affects the competitive ability of Festuca rubra against other grassland species

Background and aimsFestuca rubra plants are asymptomatically infected by the systemic fungal endophyte Epichloë festucae and high infection rates have been found in natural grasslands. Our objective was to determine the effect of endophyte infection on the competitive ability of Festuca rubra in binary mixtures against other grassland species.MethodsIn two glasshouse experiments, endophyte-infected (E+) and non-infected (E−) plants of two half-sib lines (PEN, RAB) of Festuca rubra were grown in monocultures and in binary mixtures against five grassland species: Trifolium repens, Trifolium pratense, Trifolium subterraneum, Lotus corniculatus and Plantago lanceolata.ResultsBiomass production of F.rubra was affected by endophyte infection and plant line but not by competition with T.pratense. In the PEN line E+ plants produced less root biomass than E−; and in the RAB line E+ plants produced less shoot biomass than E−. In spite of these differences shoot and root biomass production of Trifolium pratense were more inhibited when growing with endophyte-infected plants of Festuca rubra than with E− plants, regardless of the plant line. In both F.rubra lines, the endophyte increased the phosphorus concentration in shoots. Regardless of F.rubra plant line, root biomass of the five target species was more inhibited when growing with endophyte-infected than with endophyte-free plants.ConclusionsIrrespective of F.rubra line, endophyte-infected plants had a better competitive ability than non-infected plants, as indicated by the lower relative yield of companion plants when growing in mixture with E+ plants. We suggest an allelopathic effect of E+ red fescue on other grassland species.

Fungal Endophyte (Epichloë festucae) Alters the Nutrient Content of Festuca rubra Regardless of Water Availability

Festuca rubra plants maintain associations with the vertically transmitted fungal endophyte Epichloë festucae. A high prevalence of infected host plants in semiarid grasslands suggests that this association could be mutualistic. We investigated if the Epichloë-endophyte affects the growth and nutrient content of F. rubra plants subjected to drought. Endophyte-infected (E+) and non-infected (E−) plants of two half-sib lines (PEN and RAB) were subjected to three water availability treatments. Shoot and root biomass, nutrient content, proline, phenolic compounds and fungal alkaloids were measured after the treatments. The effect of the endophyte on shoot and root biomass and dead leaves depended on the plant line. In the PEN line, E+ plants had a greater S:R ratio than E-, but the opposite occurred in RAB. In both plant lines and all water treatments, endophyte-infected plants had greater concentrations of N, P and Zn in shoots and Ca, Mg and Zn in roots than E- plants. On average, E+ plants contained in their shoots more P (62%), Zn (58%) and N (19%) than E- plants. While the proline in shoots increased in response to water stress, the endophyte did not affect this response. A multivariate analysis showed that endophyte status and plant line impose stronger differences in the performance of the plants than the water stress treatments. Furthermore, differences between PEN and RAB lines seemed to be greater in E- than in E+ plants, suggesting that E+ plants of both lines are more similar than those of their non-infected version. This is probably due to the endophyte producing a similar effect in both plant lines, such as the increase in N, P and Zn in shoots. The remarkable effect of the endophyte in the nutrient balance of the plants could help to explain the high prevalence of infected plants in natural grasslands.

Determination of nitrogen and ash contents in total herbage and botanical components of grassland systems with near infra-red spectroscopy

Near infra-red reflectance spectroscopy (NIRS) was used to develop calibration equations to measure nitrogen and ash contents in grassland samples. Four populations of samples were collected or prepared: total herbage, with a heterogeneous and complex botanical composition, and its botanical components (grasses, legumes and forbs). A set of samples from each population was selected to develop the specific calibration equations using three mathematical data treatments (log 1/R, first and second derivative). Six and seven wavelengths were selected by multiple regression to predict nitrogen and ash contents, respectively. Calibration equations were evaluated by comparing the values obtained by reference methods (Kjeldahl test and dry ashing measurements) with those predicted by NIRS. The three data treatments generally provided similar results as regards estimations of nitrogen contents. The correlation coefficients varied from 0.94 to 0.98, and the standard errors of prediction ranged from 1.10 to 1.49 g kg -1 (total herbage), from 0.73 to 0.98 g kg -1 (grasses), from 0.99 to 1.30 g kg -1 (legumes) and from 0.76 to 0.80 g kg -1 (forbs). The most suitable treatments to predict ash contents were log 1/R and the first derivative. The best performance was obtained for legumes, using log 1/R, with a correlation coefficient of 0.95 and a standard error of prediction of 3.54 g kg -1 . The calibration equations became more accurate as the components of the sets of samples became botanically simpler. Prediction accuracy was greater when the specific calibration equations for each population of samples were used.

Interannual variations of above-ground biomass and nutritional quality of Mediterranean grasslands in Western Spain over a 20-year period

The ‘dehesas’ are savannah-like semi-arid grasslands typical of western Spain, which are subject to strong inter-annual variations in biomass production. Over a 20-year period, from 1986 to 2005, above-ground biomass and the nutritional quality of these grasslands in the province of Salamanca (western Spain) were evaluated to determine the relationships between interannual variations in grassland parameters and climate variables (precipitation and temperature). Herbage samples were collected from several sites, along a topographic gradient that differentiated two types of herbaceous communities on the upper and lower part of the slope. Nutritional quality was assessed on the basis of protein, acid detergent fibre, neutral detergent fibre, lignin and digestibility. On both the upper and lower zones, total biomass and biomass of grasses were correlated with annual precipitation calculated from the previous October to the current June. Biomass of legumes and forbs, on the upper zones, was correlated with spring precipitation. Step-wise multiple regression analysis provided different models for grasses, legumes, forbs, and total biomass for the upper and lower zones. Protein concentration was negatively correlated with annual precipitation in both zones of the slope. The number of days in spring with precipitation (≥1 mm or ≥10 mm) was a good predictor of the lignin content and digestibility in both zones of the slope, and of the acid detergent fibre content on the upper zones and the neutral detergent fibre content on the lower zones.

Interannual variations of nutrient concentrations in botanical fractions from extensively managed grasslands

Abstract We studied interannual variations in the concentrations of N, P, K, Ca, Mg, Na, Mn, Fe, Cu, and Zn in botanical fractions from semi-natural grassland in central-western Spain. Herbage samples were collected at the ripening stage at the end of May over a 4-year period (1987, 1988, 1989 and 1991) and classified into: grasses, legumes and forbs. There was an increase in N, P and K contents from 1987 until 1991. The interannual differences in Ca, Mn, Cu and Zn concentrations showed no clear trends. However, the sampling year had no significant effect on Mg and Na contents. Grasses generally exhibited significant lower nutrient contents than legumes and forbs. Forbs had N, Ca, Mg and Cu concentrations midway between those of grasses and legumes, and higher P, K, Fe and Zn contents than legumes. The P, Mg, and Na contents in the three botanical fractions were inadequate for feeding livestock. However, the K, Mn, and Fe contents in the three botanical groups and the Ca, Cu, and Zn contents in legumes and forbs were within recommended ranges for cattle. The N contents were only adequate in legumes. These and forbs appear to be most suitable for cattle feeding on account of their mineral contents.

Non‐destructive method for determining ash content in pasture samples: Application of near infrared reflectance spectroscopy

Abstract Ash content is a useful parameter in forage and grass quality studies, but the traditional methods used to quantify this parameter are tedious and sample processing time‐consumig is. Near infrared reflectance spectroscopy (MRS) overcomes some drawbacks of the traditional methods. Measurement of a samples diffuse reflectance is rapid and non‐destructive and chemical reagents are not necessary, which is environmentally friendly. We predicted the ash content of herbage samples from semiarid grassland communities by NIRS. The samples were collected on different sites, over four consecutive years. The calibration equations generated from log 1/reflectance to predict ash content had a standard error of calibration (SEC) of 4.6 g kg‐1 and R2 of 0.88. The standard error of prediction (SEP) was 5.1 g kg‐1 and r was 0.94.

Influence of fungal endophyte infection on nutrient element content of tall fescue

Abstract Fungal endophytes infect several grass species. The fungus can alter the growth, and physiological and morphological characteristics of the infected plant. A greenhouse experiment was designed to determine the effect of the fungal endophyte Neotyphodium coenophialum on the nutrient element content of a selected ecotype of tall fescue (Festuca arundinacea), when growing at two nutrient element supply levels. Stem dry matter, averaged over all harvests and nutrient element supply treatments, was higher in non‐infected (E‐) than in endophyte infected (E+) plants. We found a significant interaction between endophyte infection and nutrient element supply level and/or harvest date on the nitrogen (N), phosphorus (P), calcium (Ca), and magnesium (Mg) plant tissue concentrations. Only for Ca leaf concentrations the effect of infection status was not influenced by harvest date or nutrient element supply treatment and Ca concentration was higher in E‐ than in E+ plants. Differences between E+ and E‐ plants...

Ash and Mineral Contents in Leaves of Woody Species: Analysis by Near‐Infrared Reflectance Spectroscopy

Abstract Near‐infrared reflectance spectroscopy (NIRS) was evaluated for its effectiveness to determine ash and mineral concentrations [potassium (K), magnesium (Mg), copper (Cu), iron (Fe), and zinc (Zn)], in a total of 182 leaf samples of 17 woody species located in the central‐western region of the Iberian Peninsula. Chemical analysis revealed great variability in all leaf mineral elements. This variability was mainly related to differences in leaf habit (deciduous versus evergreen) and to differences in mean leaf longevity and among leaf age classes within evergreen species. A set of samples including all 17 species and leaf age classes was used to develop the calibration equations using multiple linear regression (MLR) and partial‐least squares regression (PLSR). The set of samples that did not enter in the calibration was used for external validation. In general, the most satisfactory results were obtained using PLSR and derivative transformations. Despite the strong heterogeneity of the samples included in the study, the results showed that NIRS can be employed as an effective tool, alternative to the more time‐consuming standard methods. The best predictive model was obtained for ash content. Models with acceptable accuracy were obtained in the prediction of K and Mg contents. However, their applicability for the determination of trace elements was more limited.

Effect of topographic and temporal (maturity) gradients on the nutritive quality of semiarid herbaceous communities.

Abstract Five slopes representative of the “dehesa”; grassland communities in the semi‐arid zones of Central‐Western Spain (province of Salamanca) were studied. Above‐ground biomass production was recorded from April to June and the NDF (neutral detergent fibre), ADF (acid detergent fibre), hemicellulose, cellulose, lignin, and digestibility were determined in the dry matter. Principal component analysis was applied to the data. The changes with time along the growth period show a parallel effect on the three positions of the slope, although the effect tended to be greater on the middle and upper zones. There were decreases in the levels of protein, cellular content, and digestibility, and an increase in cell wall components. The variability in nutritive characteristics induced by the phenology and time changes in the communities was reflected in the first factor of analysis, whereas the topographic gradient was related to the second component.