Laíse da Silveira Pontes

Habitat filtering and niche differentiation jointly explain species relative abundance within grassland communities along fertility and disturbance gradients

Deterministic niche-based processes have been proposed to explain species relative abundance within communities but lead to different predictions: habitat filtering (HF) predicts dominant species to exhibit similar traits while niche differentiation (ND) requires that species have dissimilar traits to coexist. Using a multiple trait-based approach, we evaluated the relative roles of HF and ND in determining species abundances in productive grasslands. Four dimensions of the functional niche of 12 co-occurring grass species were identified using 28 plant functional traits. Using this description of the species niche, we investigated patterns of functional similarity and dissimilarity and linked them to abundance in randomly assembled six-species communities subjected to fertilization/disturbance treatments. Our results suggest that HF and ND jointly determined species abundance by acting on contrasting niche dimensions. The effect of HF decreased relative to ND with increasing disturbance and decreasing fertilization. Dominant species exhibited similar traits in communities whereas dissimilarity favored the coexistence of rare species with dominants by decreasing inter-specific competition. This stabilizing effect on diversity was suggested by a negative relationship between species over-yielding and relative abundance. We discuss the importance of considering independent dimensions of functional niche to better understand species abundance and coexistence within communities.

Grass strategies and grassland community responses to environmental drivers: a review

Grassland covers about one quarter of the Earth’s land area and is currently estimated to contribute to the livelihoods of over 800 million people. Grassland provides ecosystem goods and services, mainly through the provisioning of milk and meat. Therefore, the proper use of grasslands will be essential for feeding the nine billion people that will inhabit planet Earth by 2050. In the context of a changing climate, we should better understand the interactions of environment, management and grass crop at individual, community and ecosystem levels. Functional ecology focuses on the roles and functions that species play in the community or ecosystem in which they occur. Functional ecology thus aims to understand how plant species adapt to environmental conditions and how management can alter this adaptation. Here, we review the latest advances in plant functional traits research and on species strategies to the main environmental factors occurring in grassland ecosystems: nutrient availability, grazing, cutting and shading. Functional ecology also provides a framework to better understand how species strategies interact with the species composition at the community level. Therefore, the literature on community assembling theories in relation to ecosystem processes most relevant to grassland management and services is also reviewed. Finally, future research questions and some new orientations for grassland experts are offered in order to meet the challenge of maintaining productivity and preservation of these semi-natural environments in the face of global change.

Definições e terminologias para Sistema Integrado de Produção Agropecuária

RESUMO - A pesquisa sobre Sistema Integrado de Producao Agropecuaria tem experimentado crescente importância no Brasil. Ha incremento no numero de publicacoes neste topico, refletindo seu renovado interesse. No entanto, a literatura brasileira que referencia esse sistema e confusa, por causa de diferentes termos, siglas e conceitos utilizados. Muitas publicacoes refletem caracteristicas regionais, sem aderencia a terminologia internacional. Ha necessidade de avancar no uso de terminologias e definicoes mais precisas, visando garantir clareza na comunicacao nacional e internacional. O objetivo deste artigo e desenvolver consenso para esclarecer definicoes e terminologias a serem adotadas na descricao do Sistema Integrado de Producao Agropecuaria. A regra proposta e usar a terminologia adotada pela Food and Agriculture Organization of the United Nations como referencia. Espera-se que os termos e definicoes discutidos tornem-se padrao para uso em publicacoes referentes a esse sistema, e auxiliem para uniformidade de uso na lingua portuguesa e de palavraschave usadas para indexacao internacional. Por fim, espera-se que essa padronizacao ajude na apropriada comunicacao em areas como ciencia, educacao e industria, a fim de promover essa tecnologia como caminho a seguir visando a intensificacao sustentavel na producao de alimentos. Palavras-chave: Integracao lavoura-pecuaria. Sistema misto de producao. Terminologia.

Desempenho de novilhas leiteiras em pastagens anuais de inverno sob sistema de integração lavoura-pecuária

The objective of this work was to assess the rearing viability of dairy heifers grazing single or intercropped winter pastures, under crop-livestock integration system. The experiment was carried out in Castro, Parana state, Brazil. A complete block design was used, in a factorial arrangement, with two animal categories - light-weight, with 192±40.9 kg, and heavy-weight animals, with 278±41.2 kg -, and two pasture types: annual ryegrass (Lolium multiflorum) intercropped with black oat (Avena strigosa), white clover (Trifolium repens) and red clover (Trifolium pratense); and single annual ryegrass pasture. A continuous grazing method with variable stocking was used, with 20-cm sward management height. Single annual ryegrass pasture provided an average daily gain (0.93±0.032 kg per day per animal) significantly higher than intercropped pastures (0.79±0.032 kg per day). Light animals had higher weight gain per hectare (3.54±0.163 kg ha-1 per day) than heavy animals (2.99±0.163 kg ha-1 per day), which was influenced by pasture type: light animals had best performance on single pasture, and heavy animals on intercropped pastures. Rearing dairy heifers is viable in the pasture phase of integrated crop-livestock systems.

Sward structure and relationship between canopy height and light interception for tropical C4 grasses growing under trees

Abstract. The canopy height (CH) at 95% light interception (LI) is a valuable defoliation frequency strategy used to handle variability in herbage accumulation throughout the year, mainly in C4 grasses. Such a strategy has been adopted as an open pasture management index, but defoliation frequency and intensity remain unsolved issues for shade-grown forages. A field experiment was conducted for 2 years to determine the influence of tree canopy (Eucalyptus dunnii) shading and nitrogen availability (0 and 300 kg N ha–1 year–1) on CH at 95% LI of six perennial tropical forage species. The plots were cut at 95% LI, and the height of the residual sward was kept at 50% of the corresponding CH at 95% LI. The shade level ranged from ∼40% at the beginning of the experiment to ∼60% at the end of summer 2013. Variations in CH at 95% LI occurred because of shading and across seasons. The range of these variations was species-dependent. Overall, species growing under trees showed higher CH, except for Paspalum notatum and Megathyrsus maximus in the first year. There was a significant increase in the length of the sheaths and leaves, as well as a decrease in tiller density and leaf : stem ratio in plants growing under trees. Nitrogen also had an impact on CH; however, its application did not compensate the shade effect on CH. Therefore, our results suggest that greater CH should be considered in case of defoliated, shade-grown plants and that such strategy might change throughout seasons.