Increasing biodiversity is an important issue in more secure and sustainable agriculture. Diversified systems are more resilient to climate change, environmental stresses and enhance soil health, nutrient cycling and nutrient use efficiency. In tropical agroecosystems, cover crops and intercrops are an alternative toward a more diverse and sustainable production. Urochloa spp. (syn. Brachiaria spp.) are perennial grasses, known for their high biomass production. They are commonly used as cover and companion crops in conservation agriculture in the tropics and the residues left in the field after cutting protect the soil and provide nutrient to the next crop cycle or intercropped culture. Urochloa species roots are vigorous, abundant and deep, as opposed to the more shallow and scarce roots of common crops. These traits contribute to carbon sequestration, soil organic matter stabilization and nutrient cycling. Urochloa roots also improve soil physical characteristics and influence soil nutrient dynamics, reducing nutrient losses and enhancing cycling, what is key to achieve greater nutrient use efficiency in agriculture. For instance, Urochloa root exudates can reduce nitrogen losses by denitrification and leaching through a process called biological nitrification inhibition; root exudates can mobilize recalcitrant phosphorus from soils and make it available for plant uptake; the deep roots of these grasses have the potential to recover nutrients that are virtually lost away from the root zone of other crops. This review compiles scientific progress regarding the introduction of Urochloa in agroecosystems, mainly on the aspects related to the contribution to more secure and sustainable agriculture.

Plant biostimulants have been increasingly used in agriculture. Plant biostimulants have been mostly investigated regarding their stress attenuation and only a few reports have brought information on their effects on fruit quality, which is related to appearance, chemical and physical attributes. Due to their organic nature, they have a sustainable appeal, attending the demand of consumers worried about the beneficial effects of healthier foods. This review turns evident the little information available on this matter. As fruits have differentiated metabolism, from pollination to harvest and after-harvesting, it is suggested that further research should focus separately on each stage. Thus, research should aim at quality formation, when the fruits are still attached to the plant, and shelf life extension, after harvesting.

Urochloa (syn. Brachiaria spp.) is the most cultivated forage species in the tropics and is being introduced to agroecosystems as it can provide multiple services, such as nutrient cycling. In this regard, phosphorus (P) cycling has received particular attention for its little availability in soils and the fact that Urochloa has mechanisms to cope with its low availability. However, there are interspecific differences regarding adaptation to low fertility and P requirements among Urochloa species. This study aimed to evaluate the responses of three Urochloa species—Urochloa brizantha, Urochloa decumbens and Urochloa ruziziensis—to low P availability, as well as their mechanisms to grow on these conditions. We conducted a hydroponic experiment with three levels of P availability—10% (6.2 mg P dm−3), 25% (15.5 mg P dm−3) and 100% (62 mg P dm−3)—and evaluated plant biomass production, P tissue concentration, root acid phosphatase activity, root exudation and P transporter expression on roots. We identified several metabolites in root exudates including amino acids, non‐protein amino acids, polyamides, organic acids and phenolic acids. Although all metabolites were found in all the species, metabolite exudation varied among species and P level. Overall, U. brizantha and U. ruziziensis plants exudated more metabolites when growing under P limitation (10 and 25% P), which can be a response to low P availability and stress. We identified three P transporters in roots from the PHT1 family—UPHT1;1a, UPHT1;1b and UPHT1;1c. We did not find an explicit expression pattern for UPHT1;1a, but the expression of UPHT1;1b and UPHT1;1c increased at low P availability. U. ruziziensis accumulated more biomass than the other species at all levels of P availability, possibly because of the greater expression of these P transporters. Urochloa species differ regarding nutrient availability requirements, including P, which may explain the P transporters expression and metabolite exudation results. Thus, to cope with low P in the soil, the species developed different metabolic strategies to improve the uptake of this nutrient.

Background Plant biostimulants are organic products primarily based on algae, microorganisms, fulvic and humic acids, proteins, and amino acids, which improve physiological plant performance, leading to increased crop productivity. In this work, commercial algae extract of Ascophyllum nodosum were sprayed on Sweet Heaven mini tomato variety [algae extract 0.5 L ha−1 (AE1) and 2 L ha−1 (AE2); aqueous solution prepared with A. nodosum powder at 1% (w/v) (DA1) and 3% (w/v) (DA2)] growing under greenhouse conditions. Results Algae treatment significantly affected the yield, diameter, length, color, and Brix degree of the fruits. Fruit volume and weight and the number of cracked fruits did not change. The treatment of mini tomato plants with DA1 led to a higher fruit yield compared to other treatments and untreated plants. Conclusion Therefore, A. nodosum extract can be an interesting sustainable practice to increase the productivity of mini tomatoes growing under protected conditions.

Dissertação apresentada para obtenção do título de Mestre em Ciências. Área de concentração: Fitotecnia

Summary Phosphorus (P) is a limiting resource for agricultural production in the tropics. Urochloa spp. is commonly used as a cover crop and has mechanisms to mobilize partially the nonavailable P forms from the soil. The use of Urochloa intercropped with Arabica coffee (Coffea arabica L.) is increasing in Brazil, but P cycling has been overlooked in this system. Here, we proposed two experiments to test the hypothesis that Urochloa decumbens could mobilize and absorb P from deep soil layers and increase overall P cycling of the intercrop system. We measured U. decumbens root and shoot dry mass (SDM), root morphology and activity, nutrient uptake, soil nutrient availability, and soil P fractionation in both experiments. To better understand P cycling by Urochloa alone, in the first experiment, U. decumbens was cultivated in rhizotrons where adequate P was supplied in distinct soil layers – 0.0 to 0.3 m, 0.3 to 0.8 m, 0.8 to 1.3 m, and 1.3 to 2 m. Root dry mass (RDM) and morphology were not affected by P availability. Moreover, total biomass production (root plus shoot) and P uptake were higher when P was available in the superficial top soil layer compared to P availability in more than one layer or only in the bottom layer. Nevertheless, U. decumbens was able to reach and acquire P from depth. Correlation analysis showed that P cycling was strongly dependent on SDM, labile, and moderately labile fractions of soil P and was not significantly correlated with RDM. The second experiment aimed at verifying P uptake and mobilization from different soil depths in field conditions. P was supplied in different depths of the soil profile – 0.3 m, 0.6 m, and 0.9 m – in the field with preestablished U. decumbens intercropped with Arabica coffee plants. Shoot P content was higher at the first sample date when P was supplied at 0.3 m, compared to 0.6 m, 0.9 m, and control with no P. Soil P fractionation showed that there was no P mobilization of less labile forms by U. decumbens during the evaluated time. Our results showed that P fertilization in the top layer rather than suppling P trough the soil profile can maximize U. decumbens growth. Also, Urochloa P accumulation was enough to support coffee demand even in high yields and can be an alternative to increase P use efficiency in coffee production systems, being an effective recycler of P.

Algae extract biostimulants increase nutrient uptake, stress tolerance, and productivity in several crops. However, there is still a gap in the knowledge of the mechanisms of action of algae extracts on nitrogen plant metabolism. This study aimed to evaluate the effect of a commercial Ascophyllum nodosum algae extract on nitrogen metabolism in nodulating soybean plants and their productivity. Two concentrations of algae extract (0.25% and 0.50%) were used, which were applied via seeds and leaf spray. Seeds were treated at sowing, and plants were sprayed twice at two vegetative phenological stages. Plants were harvested at the R5 phenological stage for leaf biochemical and enzyme activity analyses and leaf and root gene expression analyses. The experiment was carried out a second time to evaluate productivity. There was an increase in leaf and stem biomass, number of pods and seeds, weight of pods and seeds, and productivity in plants treated with both concentrations. Biochemical analysis showed increased amino acid content in leaves after extract application. No marked differences were found regarding the parameters related to nitrogen metabolism when the data were analysed individually. However, principal component analysis and gene expression heatmaps supported the conclusion that N metabolism was affected by algae extract application, leading to higher seed production.

Research on the accumulation and partitioning of biomass in the tobacco cycle is scarce, particularly those comparing different varieties. The objective of this work was to study the partition of biomass in air-cured burley - ACB (BAT2101) and flue-cured virginia - FCV (CSC4704) varieties. In a greenhouse experiment, the two varieties were transplanted into pots containing a mixture of fine sand and substrate (1:1). Samples were taken for a period of 98 days, with 7 day intervals. In each harvest, dry mass and leaf area were measured, and specific leaf mass, leaf area ratio, relative growth rate, net assimilation rate, and root to shoot ratios were estimated. The data showed that carbon partitioning in plants of both varieties is influenced by root growth, which was 50% higher in ACB by the end of the experiment. The higher accumulation of mass in the roots of this variety may be related to the fact that it requires more nitrogen than virginia and, therefore, it could be a mechanism for increased uptake of this element. ACB also had higher specific leaf mass than FCV, which may be related to the body of ACB. This information is important for choosing varieties adapted for field conditions, as well as for the genetic improvement of tobacco. Furthermore, from the point of view of crop management, this knowledge may provide useful information for maximizing leaf growth.