Physiological and productive performance of forages Brachiaria brizantha cv Marandu and the hybrid Brachiaria Mavuno inoculated with Azospirillum brasilense and subjected to warming in a future climate simulation experiment

Abstract

Climate change and its effects are the biggest environmental challenges we face today. More frequent and more intense extreme weather events such as droughts, floods, and heat waves that significantly impact food production are recent evidence of climate change. To face climate change, there are two approaches: Adaptation, developing ways of living with climate change, with adjustments to the current and future climate scenario, and Mitigation, reducing the effects of climate change by reducing the emission of greenhouse gases into the atmosphere. Ecosystem-based adaptation is an important approach involving a wide range of strategies, from protecting, restoring, and sustainable management of ecosystems to more sustainable agricultural practices. In Brazil, around 90% of beef cattle are raised in pastures. Four of the seven programs of the Brazilian Low Carbon Agriculture Plan (ABC Plan), the recovery of degraded pastures, the biological nitrogen fixation, the Crop-Livestock-Forest integration, and the adaptation to climate change, are related to the pastures and their management. In this proposal, we intend to generate a scientific basis for better pasture management and contribute to the ABC plan. We will study the effects of warming (increase in plant temperature by +2°C) and of inoculation with two strains of nitrogen-fixing bacteria: Azospirrillum brasilense: CNPSo 2083 and CNPSo 2084, developed by EMBRAPA, on the physiological and productive performance of two forage types of grass: Brachiaria brizantha cv Marandu and the hybrid Brachiaria brizantha x Brachiaria ruziziensis, called Mavuno. Physiological, nutritional, biochemical, growth, plant productivity, and forage quality parameters will be evaluated. The T-FACE (Temperature-free air-controlled enhancement) system will be used to increase the plant canopy temperature by +2°C, in a future climate simulation experiment. We hypothesize that Brachiaria plants inoculated with N-fixing bacteria present a better physiological and productive performance than non-inoculated plants, during all-year seasons, including under high temperature in dry and wet seasons. The proposed hypothesis is plausible because there is strong evidence that in inoculated grasses, in addition to fixing the N from the air, Azospirillum bacteria also stimulate root growth, maintaining plant productivity, even in conditions of scarce water availability. The proposed research will continue the studies on the impacts of climate change on tropical forage species carried out at USP/RP, São Paulo, using the T-FACE system. This proposal has a relevant scientific and environmental impact because it will propose solutions regarding the use of nitrogen fixation for adaptation of C4 forage grasses to warming in dry and wet seasons. Solutions regarding mitigation aspects will be also considered because the use of biological N fixation through bacteria will allow a decrease in the use of N fertilizer and thus reducing the emission of N2O. This study will also have an important social and economic impact because we will study the performance of two forage types of Brachiarias, one of them older and widely used in Brazilian livestock (B. brizantha) and the other, younger (Brachiaria Mavuno), with apparent greater tolerance to drought, inoculated with A. brasiliense, for responding to warming conditions. The results could also support decision-makers for pasture management in future scenarios of global and regional climate change. The research results will be disseminated as scientific articles and lectures to the community, as well as to farmers using different media in an appropriate language, highlighting the relevance of the results for society. (AU)