Phytochemical changes in leaves of subtropical grasses and fynbos shrubs at elevated atmospheric CO2 concentrations (original) (raw)
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Elevated CO2 concentrations and extreme climate events, are two increasing components of the ongoing global climatic change factors, may alter plant chemical composition and thereby their economic and ecological characteristics, e.g. nutritional quality and decomposition rates. To investigate the impact of climate extremes on tissue quality, four temperate grassland species: the fructan accumulating grasses Lolium perenne, Poa pratensis, and the nitrogen (N) fixing legumes Medicago lupulina and Lotus corniculatus were subjected to water deficit at elevated temperature (+3uC), under ambient CO2 (392 ppm) and elevated CO2 (620 ppm). As a general observation, the effects of the climate extreme were larger and more ubiquitous in combination with elevated CO2. The imposed climate extreme increased non-structural carbohydrate and phenolics in all species, whereas it increased lignin in legumes and decreased tannins in grasses. However, there was no significant effect of climate extreme on structural carbohydrates, proteins, lipids and mineral contents and stoichiometric ratios. In combination with elevated CO2, climate extreme elicited larger increases in fructan and sucrose content in the grasses without affecting the total carbohydrate content, while it significantly increased total carbohydrates in legumes. The accumulation of carbohydrates in legumes was accompanied by higher activity of sucrose phosphate synthase, sucrose synthase and ADP-Glc pyrophosphorylase. In the legumes, elevated CO2 in combination with climate extreme reduced protein, phosphorus (P) and magnesium (Mg) contents and the total element:N ratio and it increased phenol, lignin, tannin, carbon (C), nitrogen (N) contents and C:N, C:P and N:P ratios. On the other hand, the tissue composition of the fructan accumulating grasses was not affected at this level, in line with recent views that fructans contribute to cellular homeostasis under stress. It is speculated that quality losses will be less prominent in grasses (fructan accumulators) than legumes under climate extreme and its combination with elevated CO2 conditions.
European Journal of Agronomy, 2004
Monoliths of a fertile, although N limited, C 3 grassland community were subjected (or not) to an atmospheric CO 2 enrichment (600 mol mol −1 ), owing to the Mini-FACE system from August 1998 to June 2001, at two contrasting cutting frequencies (3 and 6 cuts per year). The present study reports the effects of elevated CO 2 on the above-ground productivity and on the herbage quality. Elevated CO 2 did not affect the dry matter (DM) yield of the swards in 1999. In 2000, the second year, there was a positive CO 2 effect (+26%) both on the DM and on the nitrogen yields (+30%). With the frequently cut monoliths, the DM of the legume component of the sward was strongly increased by elevated CO 2 . This effect became also significant in July 2000 for the low cutting frequency treatment. These results are in good agreement with the concept of an increased legume development and symbiotic N 2 fixation triggered by an increased ecosystem scale demand of N under elevated CO 2 . At a low cutting frequency, the DM of the forbs was strongly increased in elevated compared with ambient CO 2 . This increased development of the forbs apparently led to a competitive decline of the grasses. Therefore, the total DM yield response to CO 2 was smaller at a low (+15%) compared with a high (+36%) cutting frequency in 2000. An increase in the water soluble sugar content of the bulk forage under elevated CO 2 and a corresponding decline in cell wall contents (NDF) were observed. In June 1999, the decline in NDF was correlated with an increased in-vitro DM digestibility. The forage quality was also indirectly affected by elevated CO 2 through changes in leaf:stem ratio and in botanical composition. At a low cutting frequency, the increased forb content favoured the herbage quality because of a higher digestibility of the forb shoots and, indirectly, through the reduction in the mass of the grass stems. These results emphasise the role of species dynamics for elevated CO 2 impacts on semi-natural grassland productivity and herbage quality.
Nutrient relations in calcareous grassland under elevated CO 2
Oecologia, 1998
Plant nutrient responses to 4 years of CO 2 enrichment were investigated in situ in calcareous grassland. Beginning in year 2, plant aboveground C:N ratios were increased by 9% to 22% at elevated CO 2 (P < 0.01), depending on year. Total amounts of N removed in biomass harvests during the ®rst 4 years were not aected by elevated CO 2 (19.9 1.3 and 21.1 1.3 g N m A2 at ambient and elevated CO 2), indicating that the observed plant biomass increases were solely attained by dilution of nutrients. Total aboveground P and tissue N:P ratios also were not altered by CO 2 enrichment (12.5 2 g N g A1 P in both treatments). In contrast to non-legumes (>98% of community aboveground biomass), legume C/N was not reduced at elevated CO 2 and legume N:P was slightly increased. We attribute the less reduced N concentration in legumes at elevated CO 2 to the fact that virtually all legume N originated from symbiotic N 2 ®xation (%N dfa % 90%), and thus legume growth was not limited by soil N. While total plant N was not aected by elevated CO 2 , microbial N pools increased by +18% under CO 2 enrichment (P 0.04) and plant available soil N decreased. Hence, there was a net increase in the overall biotic N pool, largely due increases in the microbial N pool. In order to assess the eects of legumes for ecosystem CO 2 responses and to estimate the degree to which plant growth was P-limited, two greenhouse experiments were conducted, using ®rstly undisturbed grassland monoliths from the ®eld site, and secondly designed`microcosm' communities on natural soil. Half the microcosms were planted with legumes and half were planted without. Both monoliths and microcosms were exposed to elevated CO 2 and P fertilization in a factored design. After two seasons, plant N pools in both unfertilized monoliths and microcosm communities were unaected by CO 2 enrichment, similar to what was found in the ®eld. However, when P was added total plant N pools increased at elevated CO 2. This community-level eect originated almost solely from legume stimulation. The results suggest a complex interaction between atmospheric CO 2 concentrations, N and P supply. Overall ecosystem productivity is N-limited, whereas CO 2 eects on legume growth and their N 2 ®xation are limited by P.
Species-specific reactions to elevated CO2 and nutrient availability in four grass species
Basic and Applied Ecology, 2002
The objective of this study was to determine effects of elevated CO 2 and soil nutrient availability on growth and plant tissue quality in four grass species, Agrostis stolonifera, Anthoxanthum odoratum, Festuca rubra and Poa pratensis, native in Western European calcareous grassland. Plants were grown for 65 days in the greenhouse in pots with untreated soil from calcareous grassland under ambient (350 ppm) and elevated (700 ppm) CO 2 either with or without fertilisation. In general, elevated CO 2 increased plant height, total biomass, starch and sugar concentrations, and decreased water and nitrogen concentrations. However, the response to CO 2 -enrichment depended strongly on the grass species investigated. Fertilisation enhanced most effects of elevated CO 2 . Biomass production in fertilised plants increased more under elevated CO 2 than in unfertilised plants whereas leaf nitrogen concentration of fertilised plants decreased more at elevated CO 2 than it did in unfertilised plants. Furthermore, a species-specific response to elevated CO 2 , depending on soil nutrient availability was detected in starch and sugar concentrations (three-way interaction). The data from this study indicate that grass species vary in their response to elevated CO 2 in biomass production and tissue quality. Furthermore, increasing nutrient availability can substantially alter effects of elevated CO 2 . Since the investigated grass species are important larval food-plants of insect herbivores on calcareous grassland, the observed species-specific reactions to CO 2 -enrichment and high nutrient availability in tissue quantity and quality are discussed with respect to their effects on insect performance and thus abundance and biodiversity of these insects.
Crop Science, 2001
CO 2 . Repeated defoliation decreased CO 2 -in-Little work has been done to assess the impact of elevated CO 2 duced growth enhancements in grasses (Hunt et al., on responses of forages to defoliation. This study examines regrowth, 1995) and in Lolium perenne L. (Hebeisen et al., 1997) biomass partitioning, and labile C and N metabolites in three functional plant-types: a C 3 grass [Pascopyrum smithii (Rydb.) A. Love], under nutrient-limited conditions. However, when nua C 4 grass [Bouteloua gracilis (H.B.K.) Lag.], and a forage legume trients were abundant, positive CO 2 -induced growth en-(Medicago sativa L.). Plants were grown from seed, defoliated twice, hancements were maintained under defoliation. These and grown in a controlled environment under a factorial arrangement results indicate the importance of soil nutrients in susof two CO 2 [low CO 2 (LC), 355 mol mol Ϫ1 , and high CO 2 (HC), 700 taining CO 2 -induced growth responses of forages, espemol mol Ϫ1 ] and two N nutrition regimes [low N (LN), watered twice cially when subject to defoliation. weekly with half-strength Hoagland's containing 0 N, and high N The partitioning of biomass between above-and be-(HN), half-strength Hoagland's containing 14 mM N]. High N enlow-ground organs in response to environmental perturhanced regrowth in all three species, while high CO 2 enhanced rebations like CO 2 is another important plant trait that growth only in the two C 3 species. In M. sativa, CO 2 and N treatments has been studied extensively, but little information exists had no significant effect on k, the allometric growth coefficient. In contrast, k was reduced in P. smithii plants grown under LN (0.63) on how defoliation might interact with CO 2 and affect compared with HN (0.99). In B. gracilis, low N also reduced k, but partitioning. The enhanced plant growth that generally it interacted with CO 2 so that k was greatest for plants grown at HN/ occurs under elevated CO 2 concentrations is often ac-HC (0.95) and HN/LC (0.89), intermediate at LN/LC (0.58), and least companied by shifts in biomass partitioning, often (alat LN/HC (0.44). These results indicate greater partitioning to belowthough not always) with increased partitioning of bioground organs (reduced k ) when N is limiting, particularly under mass to belowground organs (Bazzaz, 1990; Rogers et elevated CO 2 . Significant correlations were established between k and al. , 1994, 1996). Several researchers (Campagna and several measures of plant N status, suggesting that the effects of CO 2
Plant and Soil, 1995
In previous experiments systematic differences have been found in the morphology, carbon economy and chemical composition of seedlings of inherently fast-and slow-growing plant species, grown at a non-limiting nutrient supply. In the present experiment it was investigated whether these differences persist when plants are grown at suboptimal nutrient supply rates. To this end, plants of the inherently fast-growing Holcus lanatus L. and the inherently slow-growing Deschampsia flexuosa (L.) Trin. were grown in sand at two levels of nitrate supply. Growth, photosynthesis, respiration and carbon and nitrogen content were studied over a period of 4 to 7 weeks.
CO2 enrichment increases element concentrations in grass mixtures by changing species abundances
Plant Ecology, 2010
Atmospheric carbon dioxide (CO 2) enrichment may increase plant growth more than the uptake of chemical elements from soil. Increased CO 2 also may alter element levels in biomass from multi-species vegetation by changing plant species abundances. We measured concentrations of ten elements in aboveground tissues of three C 4 grasses that had been exposed for 2-3 growing seasons to a continuous gradient in CO 2 from 250 to 500 lmol mol-1. The grasses, Bouteloua curtipendula, Schizachyrium scoparium, and Sorghastrum nutans, are competitive dominants in assemblages of tallgrass prairie vegetation growing on each of three soil types along a field CO 2 gradient in central Texas, USA. Our objective was to determine whether CO 2 influences element concentrations in grass mixtures by changing concentrations in individual species or shifting species abundances. Increased CO 2 had little effect on element concentrations in grasses compared to differences observed among grass species and soils. Increasing CO 2 from the pre-Industrial to elevated levels reduced the phosphorus concentration in grasses grown on a clay and sandy loam soil. Concentrations of most other elements did not respond to CO 2 treatment. Cover of the mid-grass Bouteloua declined at higher CO 2 levels as cover of the taller grass Sorghastrum increased. Concentrations of several elements were lower in Bouteloua than Sorghastrum; hence, this exchange of species at higher CO 2 increased element concentrations in grass assemblages. Potential consequences include an improvement in the nutritional quality of plants for herbivores. Results highlight the underappreciated impact that CO 2 enrichment may have on ecosystem functioning by changing plant composition. Keywords Bouteloua curtipendula Á C 4 grasses Á Soil type Á Sorghastrum nutans Á Subambient CO 2 concentration Á Tallgrass prairie Electronic supplementary material The online version of this article (
New Phytologist, 2001
To evaluate whether functional groups have a similar response to global change, the responses to CO 2 concentration and N availability of grassland species from several functional groups are reported here. • Sixteen perennial grassland species from four trait-based functional groups (C 3 grasses, C 4 grasses, non-leguminous forbs, legumes) were grown in field monocultures under ambient or elevated (560 µ mol mol -1 ) CO 2 using free-air CO 2 enrichment (FACE), in low N (unamended field soil) or high N (field soil + 4 g N m -2 years -1 ) treatments. • There were no CO 2 × N interactions. Functional groups responded differently to CO 2 and N in terms of biomass, tissue N concentration and soil solution N. Under elevated CO 2 , forbs, legumes and C 3 grasses increased total biomass by 31%, 18%, and 9%, respectively, whereas biomass was reduced in C 4 -grass monocultures. Two of the four legume species increased biomass and total plant N pools under elevated CO 2 , probably due to stimulated N-fixation. Only one species markedly shifted the proportional distribution of below-vs aboveground biomass in response to CO 2 or N.
Ecophysiological aspects of herbage production in grazed and cut grassland
1996
Grasslands account for about 20% of the terrestrial CO 2 fluxes of the global carbon cycle and may therefore contribute to a global biotic carbon sequestration, reducing the rate of increase of atmospheric CO 2 , At a fertilizer N input higher than 100 kg N ha'l year'] the annual gross crop CO 2 assimilation on loam and clay perennial ryegrass swards in the Netherlands is between 20 and 22 t C ha'l under cutting or grazing management. irrespective of grazing system. The absence of an effect of N fertilization on crop CO 2 assimilation could be explained from a 'down-regulation' in the relationship between leaf N concentration and maximum leaf CO 2 assimilation rate from low to high N input levels. The main effect of low N was a marked reduction in leaf area development. reflected in lower herbage intake levels under grazing and a reduced light-use effiCiency (LUE) under cutting with respect to the harvested yield. This reduction in LUE at decreasing N supply was associated with an increased allocation of assimilates to unharvested plant parts (roots and stubble). The latter phenomenon was also observed in a seminatural grassland ecosystem in Slovakia. In a study of short-term grassland ecosystem processes at the field scale (1 km length) in the Netherlands, a net CO 2 uptake was measured in spring whereas in the autumn a net emission occurred. After correction for soil and vegetation respiration, the relationship between short-wave irradiance and gross photosynthetic CO 2 flux was not different for the two parts of the growing season and was in accordance with measurements at much smaller spatial scales (l or 2 m 2 of canopy).