Changes in climate and land use that interact synergistically to increase fire frequencies and intensities in tropical regions are predicted to drive forests to new grass-dominated stable states. To ...reveal the mechanisms for such a transition, we established 50 ha plots in a transitional forest in the southwestern Brazilian Amazon to different fire treatments (unburned, burned annually (B1yr) or at 3-year intervals (B3yr)). Over an 8-year period since the commencement of these treatments, we documented: (i) the annual rate of pasture and native grass invasion in response to increasing fire frequency; (ii) the establishment of Brachiaria decumbens (an African C4 grass) as a function of decreasing canopy cover and (iii) the effects of grass fine fuel on fire intensity. Grasses invaded approximately 200 m from the edge into the interiors of burned plots (B1yr: 4.31 ha; B3yr: 4.96 ha) but invaded less than 10 m into the unburned plot (0.33 ha). The probability of B. decumbens establishment increased with seed availability and decreased with leaf area index. Fine fuel loads along the forest edge were more than three times higher in grass-dominated areas, which resulted in especially intense fires. Our results indicate that synergies between fires and invasive C4 grasses jeopardize the future of tropical forests.
Induced mutagenesis through gamma radiation generates structural and chemical changes in plants. This study evaluated the morphological and nutritional variability of natal grass Melinis repens ...(Willd.) Zizka plants produced from seed irradiated with gamma radiation. Natal grass seed was collected from wild populations in the state of Chihuahua, Mexico. The seed was exposed to a source of Co.sup.60 . The radiation doses were: 0, 10, 50, 100, 150, 200, 250, 300 and 350 Gray (Gy). Sixty-six first generation mutant genotypes (M1), produced from irradiated seed, and nine non-mutant genotypes (M0), developed from non-irradiated seed (0 Gy), were evaluated. For the morphological characterization, 18 variables were measured on the plants when they were at the reproductive stage. The nutritional analysis was performed on the M0, as well as on a group of plants from the M1, which resulted morphologically different (p <0.005) from the rest. The differenced M1 plants were classified as promising mutant genotypes (M1p). Results showed that variability was induced in the M1p. These individuals presented morphological differences in leaf weight-tillering weight ratio and foliage height, compared to the rest of the plants (p <0.001). The M1p 250-10 genotype presented the highest (p <0.001) crude protein and the lowest (p <0.001) lignin contents. Gamma radiation in the seed of natal grass induced morphological and nutritional variability. With that, promising mutant genotypes, with desirable morphological and nutritional attributes, were identified.
The morphogenetic characteristics of eight native grasses of South Brazil were evaluated during autumn. They were classified in a functional typology, according to dry matter content and specific ...leaf area (A, B, C, D): Axonopus affinis (A), Andropogon lateralis (B), Paspalum notatum (B), Paspalum plicatulum (C), Piptochaetium montevidense (C) Aristida laevis (D), Saccharum angustifolius (D) and Sorghastrum pellitum (D), under two nitrogen (N) fertilization levels (zero and 200kg ha.sup.-1 N). Experimental design was completely randomized in a factorial arrangement: eight (species) x two (N levels) with three replicates or four (functional types) x two (N levels) both with three replicates. Plants were submitted to cuts according to different leaf lamina elongation, defined by means of species classified by functional type. The variables were statistically analyzed using randomization tests with software MULTIV. There was no significant difference between N levels, but there was among species and among functional types. Morphogenic variables are consistent according to the functional typology used as reference, based on leaf traits. Nitrogen fertilization does not change morphogenetic characteristics of evaluated species during autumn, and its use is discouraged during this season. Key words: pampa biome, phyllochron, plant functional types. Este estudo teve como objetivo avaliar, no outono, as caracteristicas morfogenicas de oito gramineas nativas da regiao central do Rio Grande do Sul, classificadas sob uma tipologia funcional, segundo o teor de materia seca e a area foliar especifica em A, B, C, D: Axonopus affinis (A), Andropogon lateralis (B), Paspalum notatum (B), Paspalum plicatulum (C), Piptochaetium montevidense (C) Aristida laevis (D), Saccharum angustifolius (D) e Sorghastrumpellitum (D); submetidas a dois niveis de nitrogenio (zero e 200kg ha.sup.-1 de N). O delineamento experimental foi o inteiramente casualizado com arranjo fatorial 8 (especies) x 2 (niveis de N) ou 4 (tipos funcionais) x 2 (niveis de N), ambos com tres repeticoes. As plantas foram submetidas a cortes segundo diferentes duracoes de elongacao foliar, definidas por medias das especies por tipo funcional. As variaveis foram analisadas estatisticamente usando testes de aleatorizacao com o softwareMULTIVNao houve diferenca significativa entre os niveis de N, porem houve entre as especies e entre os tipos funcionais. As variaveis morfogenicas sao coerentes com a tipologia funcional utilizada como referencia, baseada em atributos foliares. Os niveis de nitrogenio nao alteram a morfogenese das especies na estacao do outono, sendo seu uso desaconselhado nesse periodo. Palavras-chave: bioma pampa, filocrono, tipos funcionais de plantas.
The morphogenetic characteristics of eight native grasses of South Brazil were evaluated during autumn. They were classified in a functional typology, according to dry matter content and specific ...leaf area (A, B, C, D): Axonopus affinis (A), Andropogon lateralis (B), Paspalum notatum (B), Paspalum plicatulum (C), Piptochaetium montevidense (C) Aristida laevis (D), Saccharum angustifolius (D) and Sorghastrum pellitum (D), under two nitrogen (N) fertilization levels (zero and 200kg ha.sup.-1 N). Experimental design was completely randomized in a factorial arrangement: eight (species) x two (N levels) with three replicates or four (functional types) x two (N levels) both with three replicates. Plants were submitted to cuts according to different leaf lamina elongation, defined by means of species classified by functional type. The variables were statistically analyzed using randomization tests with software MULTIV. There was no significant difference between N levels, but there was among species and among functional types. Morphogenic variables are consistent according to the functional typology used as reference, based on leaf traits. Nitrogen fertilization does not change morphogenetic characteristics of evaluated species during autumn, and its use is discouraged during this season.
The Iowa sedges Cratty, Robert Irvin, 1853-1940
Bull. lab. nat. hist, University of Iowa, Iowa City, 1898, 24 cm. v. 4, no. 4, p. 313-375. X pl
Journal
50 & 100 years ago
Nature (London),
01/2010, Letnik:
463, Številka:
7278
Journal Article
Recenzirano
Odprti dostop
50 YEARS AGO Under New Zealand conditions of sheep-farming, incisors of grazing sheep wear much more rapidly on improved pasture, chiefly ryegrass (Lolium perenne) and white clover (Trifolium ...repens), than on the finer native pastures of low carrying capacity.
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