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Forest fragmentation is the main cause of biodiversity loss in the Anthropocene and it is triggering a top-down cascade effect that may influence leaf litter decomposition. However, the link between biodiversity loss and changes in ecosystem processes is not fully understood. We conducted an experiment to evaluate whether the exclusion of vertebrates affects the decomposition rates of different litter types (grass, a pioneer species and a mix of litters from a well preserved secondary forest). To answer this question, we placed litter bags inside artificial exclusion plots that were built in two types of vegetation coverage (abandoned pastureland and preserved forest) in the Atlantic forest of southeast Brazil. Our hypothesis is that vertebrate exclusion will change decomposition rates of different litter types due to the top-down cascade effect on soil invertebrates. We found out that vertebrate exclusion did not affect decomposition rates, possibly due to the overlap of ecological functions in the soil fauna responsible for the decomposition process. Furthermore, grass litter was decomposed faster (k value), possibly due to its initial nutrient content and hence litter quality which plays a significant role on decomposition rates.

By analyzing 6,480 tree leaf samples from 57 sites within Brazilian biomes, we considered whether vegetation types in terrestrial ecosystems reflect biogeochemical diversity and whether they fit into a leaf economics spectrum (LES). To achieve this, we investigated the relations among leaf carbon (C) and nitrogen (N) concentrations, their isotope natural abundance and C:N ratio. In addition, we tested their correlations with mean annual temperature (MAT) and precipitation (MAP), as climatic factors. We found consistent differences in the C and N concentrations and their isotopic composition among the vegetation types. MAP is the main climatic driver of changes in N, C:N ratio, δ15N, and δ13C, correlating negatively with N and positively with C:N ratio. These relations show that these biomes follow an LES. The Caatinga had the highest δ15N values, suggesting that N residence time in soil is longer due to low leaching and plant uptake. We observed that MAP is not the only factor influencing δ13C values in different biomes; instead canopy effect probably explains the highest values observed in the Cerrado. Our results reinforce earlier findings that life diversity in the tropics reflects biogeochemistry diversity and leaf δ15N opens the possibility for investigating plant trade-offs dictated by the LES. Finally, we expect our findings to contribute to a better understanding of the tropics in global climate models.

Exploiting native soil phosphorus (P) and the large reservoirs of residual P accumulated over decades of cultivation, namely “legacy P”, has great potential to overcome the high demand of P fertilisers in Brazilian cropping systems. Long-term field experiments have shown that a large proportion (> 70%) of the surplus P added via fertilisers remains in the soil, mainly in forms not readily available to crops. An important issue is if the amount of legacy P mobilized from soil is sufficient for the crop nutritional demand and over how long this stored soil P can be effectively ‘mined’ by crops in a profitable way. Here we mapped the spatial–temporal distribution of legacy P over the past 50 years, and discussed possible agricultural practices that could increase soil legacy P usage by plants in Brazil. Mineral fertiliser and manure applications have resulted in ~ 33.4 Tg of legacy P accumulated in the agricultural soils from 1967 to 2016, with a current annual surplus rate of 1.6 Tg. Following this same rate, soil legacy P may reach up to 106.5 Tg by 2050. Agricultural management practices to enhance soil legacy P usage by crops includes increasing soil pH by liming, crop rotation, double-cropping, inter-season cover crops, no-tillage system and use of modern fertilisers, in addition to more efficient crop varieties and inoculation with P solubilising microorganisms. The adoption of these practices could increase the use efficiency of P, substantially reducing the new input of fertilisers and thus save up to 31.8 Tg of P fertiliser use (US$ 20.8 billion) in the coming decades. Therefore, exploring soil legacy P is imperative to reduce the demand for mineral fertilisers while promoting long-term P sustainability in Brazil.

Made available in DSpace on 2018-12-11T16:51:48Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-12-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Brazil's large land base is important for global food security but its high dependency on inorganic phosphorus (P) fertilizer for crop production (2.2 Tg rising up to 4.6 Tg in 2050) is not a sustainable use of a critical and price-volatile resource. A new strategic analysis of current and future P demand/supply concluded that the nation's secondary P resources which are produced annually (e.g. livestock manures, sugarcane processing residues) could potentially provide up to 20% of crop P demand by 2050 with further investment in P recovery technologies. However, the much larger legacy stores of secondary P in the soil (30 Tg in 2016 worth over $40 billion and rising to 105 Tg by 2050) could provide a more important buffer against future P scarcity or sudden P price fluctuations, and enable a transition to more sustainable P input strategies that could reduce current annual P surpluses by 65%. In the longer-term, farming systems in Brazil should be redesigned to operate profitably but more sustainably under lower soil P fertility thresholds. School of Environment Natural Resources and Geography Bangor University, Thoday Building College of Agriculture 'Luiz de Queiroz' University of São Paulo - ESALQ-USP, Av. Pádua Dias, 11. CEP Federal University of Lavras - UFLA Campus Universitário, PO Box 3037 Brazilian Agricultural Research Corporation Embrapa Soils, Rua Jardim Botânico, 1024 Santa Catarina State University UDESC., Av. Luís de Camões 2090 Brazilian Agricultural Research Corporation Embrapa Cerrados. BR 020, Km 18 Planaltina. PO Box 08223 São Paulo State University FCA/UNESP. Rua José Barbosa de Barros 1780, CEP 186010-307 Brazilian Agricultural Research Corporation Embrapa Soybean, PO Box 231 São Paulo State University FCAV/UNESP. Via de Acesso Prof, Paulo Donato Castellane, s/n. km 5 São Paulo State University FCA/UNESP. Rua José Barbosa de Barros 1780, CEP 186010-307 São Paulo State University FCAV/UNESP. Via de Acesso Prof, Paulo Donato Castellane, s/n. km 5