Responses of plant traits of four grasses from contrasting habitats to defoliation and N supply

Abstract

The objective of the study was to identify specific plant traits determining adaptation of grass species to defoliation and N availability, and thus having a major impact on species dynamics, primary productivity, and on nutrient cycling in grassland ecosystems. It was specifically examined whether the response of species to defoliation is related to their plasticity in leaf growth and in leaf growth zone components, and whether the response of species to nitrogen is related to their plasticity in root morphology and subsequent N acquisition, and to N losses through leaf senescence. The study was conducted on L. perenne and D. glomerata, two grazing tolerant species from fertile habitats, and on F. arundinacea and F. rubra, two less grazing tolerant species from less fertile habitats. Plants were subjected to repeated defoliation at three cutting heights under both high N and low N supply. Biomass allocation, leaf elongation, characteristics of the leaf growth zone (height and relative growth rate), and root morphology, N uptake and N losses through leaf senescence were evaluated. Under high N supply, L. perenne and D. glomerata showed the greatest tolerance to defoliation, due to a large plasticity in the height of the leaf growth zone and due to compensatory growth, either within the leaf growth zone or between growing leaves. Under low N supply, F. rubra was the only species with the ability to develop a more branched root system and a greater length of tertiary roots than under high N. As a consequence, under low N supply F. rubra had a higher specific N uptake and a higher growth rate than the other species. This slow growing species also showed a higher nitrogen allocation to dead leaves and subsequently a higher potential N loss to leaf litter.

Effects of leaf zeatin and zeatin riboside induced by different clipping heights on the regrowth capacity of ryegrass

“…Increasing the clipping height from 5 to 8 cm above the soil surface caused an increase in dry weight per plant of 85.2, 308.3, 393.3, and 51.85 % in Galium aparine L., Galeopsis tetrahit L., Polygonum convolvulus L., and Avena fatua L., respectively (Andreasen et al 2002). Other studies have also reported that clipping height is an important influencing factor for grass regrowth (Conn and Seefeldt 2009;Gastal et al 2010;Regmi and Devkota 2009;Zhang et al 2011). However, the mechanism by which clipping height affects forage grass regrowth remains unknown.…”

Índice de nutrição nitrogenada em pastagens de Trachypogon plumosus nos cerrados de Roraima

“…A adubação nitrogenada ao reduzir a respiração de manutenção e estimular a de crescimento -diretamente proporcional ao conteúdo proteico da planta e responsável pela produção de novos compostos orgânicos -contribui positivamente para maior acúmulo de biomassa (Plénet and Lemaire, 1999, Gastal et al, 2010, Lemaire et al, 2015. A aplicação de N estimula o desenvolvimento dos primórdios foliares, diminui o intervalo de tempo para o aparecimento de folhas, redução da senescência foliar, promoção do perfilhamento e produção de lâminas foliares, as quais proporcionam maiores taxas fotossintéticas das plantas e o maior fornecimento de fotoassimilados para os tecidos em crescimento (Paciullo et al, 1998, Lemaire et al, 2008, Teixeira et al, 2011.…”

Fertilización nitrogenada y mezcla de Trachypogon plumosus con Stylosanthes capitata cv. Lavradeiro bajo diferentes densidades de siembra

“…A adubação nitrogenada ao reduzir a respiração de manutenção e estimular a de crescimento -diretamente proporcional ao conteúdo proteico da planta e responsável pela produção de novos compostos orgânicos -contribui positivamente para o maior acúmulo de biomassa (Gastal et al, 2010 A participação da leguminosa na composição botânica da pastagem foi diretamente proporcional às densidades de semeadura (30,4; 36,7; 37,8 e 45,3%, respectivamente para 1,0; 2,0; 3,0 e 4,0 kg ha -1 ). Visando potencializar os benefícios decorrentes da introdução de leguminosas em pastagens monoespecíficas de gramíneas, em termos de fixação biológica de nitrogênio, reciclagem de nutrientes, valor nutritivo da forragem em oferta e maior eficiência de pastejo, recomenda-se como proporção adequada 20 a 40% da leguminosa (Townsend et al, 1999).…”