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Made available in DSpace on 2022-04-28T19:40:25Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 Cunninghamia lanceolata has been indicated for cultivation on the highlands of southern Brazil, but in spite of its high potential it is not commercially cultivated. This study aimed to characterize the wood of C. lanceolata and evaluate the effects of meteorological variables on the 21-years of wood formation and, therefore, expand the understanding and commercial use possibilities of the species. Results indicate that apparent density was 0.364 g cm-3, similar on trees with smaller and bigger diameter. There were no substantial differences between the wood formed close to the pith (juvenile) band the one close to the bark (mature). Growth was significantly and positively affected by the minimum temperature in June previous to the beginning of the vegetative growth period, and by the air relative humidity of March, April and May. Aside from the negative effects of frosts on the growth during the whole period studied, the absence of 4-7 annual growth rings at tree's base indicates that frosts are probably the main limiting factor for plantation establishment of this species in the studied region. Universidade Federal de Santa Catarina - UFSC Universidade Federal do Acre - UFAC Universidade Tecnológica Federal do Paraná - UTFPR Universidade Estadual Paulista Júlio de Mesquita Filho - UNESP Universidade de São Paulo - USP Universidade Estadual Paulista Júlio de Mesquita Filho - UNESP

Belowground interactions in mixed forest plantations remain poorly understood as that of short-tenn nitrogen (N) transfer from N-fixing trees to non-N-fixing trees (Non-NFT) depending on nutrient availability. We investigated in this facilitation process met the Stress Gradient Hypothesis. which predicts that under stressful environmental conditions competition decreases and facilitation increases. A 15N pulse-labelling study was conducted in a five-year-old mixture of 50% Eucalyptus grandis x E. urophylla and 50% Acacia mangium with the hypothesis of higher transfer from acacia when no fertilization was applied. A complete randomized block design was set up with three replicates of fertilized and non-fertilized mixture. In each treatment of each block, a labeled solution of potassium nitrate (98 atom% 15N-N03) was injected into the stem of an Acacia tree with the same basal area as the average of the stand. The x (15N) was monitored over two months in each labeled acacia and four neighboring eucalypts. For both species, young leaves and tine roots were sampled at 7.14 and 30 days after injection. After 60 days. the x (15N) was determined in the wood, bark, branches, total foliage and fine roots of the 6 labeled acacias and 12 eucalypts trees The preliminary results showed that complete absorption of the labeled solution occurred between 28 and 60 days after labeling depending on Acacia trees and treatments. The dynamics in the proportion of Eucalyptus N derived from transfer will give insights into how this process may promote N nutrition of non-NFTs growing in unfertile tropical soils.

The association of Acacia could increase Eucalyptus plantations productivity through a positive balance between facilitative effects and competition between species. In Brazil, the development of mono-specific stands of Acacia mangium (100A) and Eucalyptus sp. (100E) was compared with nitrogen (N) fertilisation treatment (100E + N) and mixed-species plantations in a 1:1 ratio (50A:50E). The study was conducted in Itatinga-SP, Sinop-MT and Colinas-TO with mean annual temperature of 19.4, 25.0 and 27.5 °C, mean annual rainfall of 1320, 2640, and 1850 mm, and dry season duration of 3, 5 and 7 months, respectively. The soils are sandy to sandy-clay. At 36 months, Eucalyptus height in 100E was 18.9, 10.9 and 13.7 m, in SP, MT and TO, respectively. For Acacia the corresponding values in 100A were 14.2, 13.5 and 10.8 m, respectively. This pattern, also observed for diameter at breast height, showed that Eucalyptus was proportionally more adapted to the ecological conditions than Acacia in SP, the opposite being found in MT. Stand basal area (SBA) was 2, 10 and 3 % higher in 100E+N than in 100E in SP, MT and TO, respectively. SBA was 7 and 1 % higher in 100E (8.33 and 3.70 m2 ha-1) than in 100A (7.77 and 3.66 m2 ha-1) in SP and TO, respectively. By contrast, SBA was 69 % higher in 100A (7.54 m2 ha-1) than in 100E (4.47 m2 ha-1) in MT. SBA was 6 and 4 % higher in 100E than in 50A:50E in SP and TO, respectively. By contrast, SBA was 21 % higher in 50A:50E than in 100E in SP. The occurrence of higher stand production in mixed species plantations of Eucalyptus and A. mangium than Eucalyptus monocultures depends on ecological conditions. When conditions permit high eucalypt stand yield as observed in SP, the potential N facilitation by Acacia cannot balance the lower potential of growth of Acacia trees, which are also deeply competed by Eucalyptus trees. By contrast, as observed in MT mixed plantations are likely more productive than Eucalyptus monoculture when the environmental conditions (hot and humid climate) are more favourable for acacia than eucalyptus and when the soils are deficient in N. Adverse conditions for both Eucalyptus and Acacia (e.g. extreme high temperatures, marked dry season) as found in TO are likely to prevent any efficient facilitation processes between species.

Little is still known about the role of deep roots in the nutrition of forest. We then studied the potential uptake of N, K and Ca by Eucalyptus grandis trees (2 years of age), in Brazil, as a function of soil depth and fertilization. Our hypotheses were: i) deep roots are more efficient than the shallow roots in potassium and calcium uptake compared to nitrogen ii) the specialization of the eucalyptus roots in nutrient absorption decreases when soil fertility is improved by fertilization. We injected NO3 -15N, Rb+ (analog of K+) and Sr 2+ (analog of Ca 2+) tracers simultaneously in a solution at 10, 50, 150 and 300 cm in depth. A complete randomized design was set up with three replicates of paired trees per injection depth and soil fertility. Recently expanded leaves were sampled at 70 days after tracer injection. Determination of foliar Rb, Sr concentrations and 15N atom% makes it possible to estimate the relative uptake potential (RUP) from the 4 soil depths and the Specific RUP, defined as RUP, per unit of fine root length density in the corresponding soil layer. The results being analysed will give insights into the functional specialization of roots in forests.