ABSTRACT Evaluations of biomass and nutrient contents in teak stands are necessary alternatives for avoiding early cutting to provide supplemental data for the plant module of fertilization recommendation systems. This study aimed to adjust allometric equations to estimate the accumulation of biomass and nutrient contents in teak plantations in the central region of Brazil. Plots in seminal and clonal stands contained 81 trees aged 75 months, that had not received previous fertilization or thinning. Additional clonal stands aged 15, 51 and 63 months and a seminal stand aged 63 months had been previously fertilized during implantation. Allometric equations for biomass and macronutrient contents were obtained for components of the aerial parts of trees as a function of diameter at 1.3 m height (DBH), and the possibility of using an equation or the need for specific equations was evaluated for genetic material (seminal or clonal) and the fertilization scheme (not fertilized or fertilized). The equations adjusted to the four sets of stands, all with elevated predictive capacity, did not differ among each other based on an identity test. Thus, the use of a robust equation adjusted with data from all stands is recommended to obtain estimates with a high degree of accuracy. The biomass and accumulation of macronutrients in components of the aerial parts of teak trees should be considered to obtain the nutrient contents in both the exportable components in thinned trees and the components maintained in the area and available for biogeochemical cycling.

ABSTRACT The adoption of more productive and nutrient-demanding genotypes, in addition soils with low availability of nutrients of soils under forest plantations, lead high fertilizer demand and justify research that seeks to rationalize the use of these inputs. Therefore, we aimed with this research to determine classes of interpretation of soil fertility using boundary line (BL) and estimate macronutrient sufficiency ranges for eucalyptus. Fertility classes and sufficiency ranges were obtained using a database of areas cultivated with eucalyptus in the Central-East region of Minas Gerais, Brazil, totaling 689 plots, containing information on yield, leaf contents, and soil chemical properties. Scatter plots were drawn relating the mean annual increment (MAI) in trunk volume (relative) with soil organic matter (OM), phosphorus (P), potassium (K+), calcium (Ca2+), and magnesium (Mg2+) of the 0.00-0.20 m layer. Those graphs and equations were used to estimate soil fertility classes. Leaf contents of N, P, K, Ca, and Mg were plotted with soil contents of OM, P, K+, Ca2+, and Mg2+. Using the Quadrant Diagram of the plant-soil Relationship (QDpsR) method, horizontal and vertical lines were drawn separating the cloud of points in four quadrants. With the points at the quadrants III and I, regression equations were fitted. To obtain foliar sufficiency ranges, soil values of critical and optimal levels of OM, P, K+, Ca2+, and Mg2+, obtained by BL, were substituted in the equations generated by the QDpsR method. The appropriate soil content ranges determined by BL for productivity of 47.7 m3 ha-1 yr-1 were: 24.75-38.28 g kg-1 of OM, 8.5-14.6 mg dm-3 of P, 100.0-150.35 mg dm-3 of K+, 0.77-1.47 cmolc dm-3 of Ca2+, and 0.25-0.43 cmolc dm-3 of Mg2+. Leaf content ranges determined by QDpsR are: 19.4-21.3 g kg-1 of N, 1.0-1.2 g kg-1 of P, 8.5-10.6 g kg-1 of K, 4.8-6.1 g kg-1 of Ca, and 1.9-2.4 g kg-1 of Mg. The critical levels of nutrients in the soil, obtained by the BL method, and the leaf sufficiency ranges, obtained using the QDpsR method, are similar to those existing in the literature. This indicates that this methodology is reliable in establishing standards and that the critical levels obtained can be used to improve the recommendation of fertilizers for eucalyptus.

ABSTRACT: The mineral nutrient uptake of plants in the field occurs in pulses, due to variations in the substance concentrations at the root surface. The fluctuations in nutrient supply probably induce changes in the plant, which are to date unknown for Eucalyptus. This study evaluated these changes in plant growth, nutritional status, photosynthesis, and gene expression, which can serve as biomarkers of the nitrogen status, of four eucalypt clones exposed to N omission and resupply. A greenhouse experiment with four Eucalyptus clones was installed, and after initial growth exposed to N omission for 21 d, followed by N resupply in nutrient solution for 14 d. Nitrogen omission decreased the total N and photosynthetic pigments, net photosynthesis and photochemical dissipation, and increased enzyme activity especially in leaves and the gene expression in leaves and roots. Nitrogen resupply decreased these variations, indicating recovery. The total N concentration was highly and significantly correlated with net photosynthesis, enzyme activity, expression of genes GS2;1 and Gln1;3 in the leaves and AMT1;2 in the roots, contents of chlorophyll a and b, and photochemical energy dissipation. The enzymes GS and NR in the leaves and the genes AMT1;2, GS2;1 and Gln1;3 proved to be sensitive N indicators.

Apesar da grande quantidade de N acumulada em plantações de eucalipto de alta produtividade, o aumento em volume do tronco em resposta à aplicação de N não tem sido expressivo nem consistente. O objetivo deste trabalho foi verificar o efeito de doses e fontes de N sobre o crescimento e o acúmulo de N em plantas de eucalipto, na serapilheira, além do impacto nas frações da matéria orgânica do solo (MOS). O experimento foi instalado em campo, no município de Itamarandiba-MG, em blocos ao acaso com três repetições, consistindo da aplicação em cobertura de doses (0, 60, 120 e 240 kg ha-1) e fontes de N distintas (sulfato de amônio e nitrato de amônio) em clone de eucalipto (AEC1528®). O efeito dos tratamentos sobre o crescimento e acúmulo de N nas plantas foi avaliado aos 30 meses de idade, abatendo-se árvores com DAP médio e separando-as em lenho, casca, galhos e folhas, para determinação da produção de matéria seca e dos teores e conteúdos de nutrientes das plantas. Amostras de solo e de serapilheira foram coletadas para análises de nutrientes. Os teores de C e N total da matéria orgânica particulada (MOP) e da matéria orgânica associada à fração mineral (MOAM) foram determinados por espectrometria de massa de razão isotópica, após separação física da MOS. As análises estatísticas consistiram de análise de variância e de regressão. A aplicação de adubos nitrogenados promoveu aumento no crescimento volumétrico do tronco e na matéria seca da parte aérea. A dose de N como sulfato de amônio para obter 90 % da produção máxima foi de 74 kg ha-1, a qual resultou em incremento de 42,3 % no volume de tronco em relação à testemunha sem adubação nitrogenada. Na dose de 120 kg ha-1 de N, não houve diferença de resposta à aplicação de sulfato de amônio e nitrato de amônio. Não foram detectadas alterações nos estoques de C e N da MOS com a adubação nitrogenada. No entanto, houve aumento da absorção de Ca, Mg e S. A taxa de recuperação aparente de N no campo foi maior na dose de 120 kg ha-1 de N, atingindo 34,4 %.

In spite of the high amount of N accumulated in high-yielding, short-rotation eucalyptus plantations, no significant or consistent increases in trunk volume have been observed in response to N fertilization. This experiment evaluated the effect of N fertilization on the growth and chemical composition of eucalyptus as well as its role in soil organic matter (SOM) mineralization. The field experiment was carried out in a randomized block design with three replications, in Itamarandiba- MG. Two N sources (ammonium sulphate and ammonium nitrate) of increasing N rates (0, 60, 120, 240 kg ha-1) were tested on the eucalyptus clones AEC1528®. The effect of the treatments on tree growth and N accumulation were evaluated in 30 month-old trees with average DBH, which were harvested and separated in stem, bark, branches, and leaves to determine dry matter production and nutrient contents. Soil and forest litter samples were collected for chemical analyses. Total C and N content of particulate organic matter (POM) and organic matter associated to the mineral fraction (OMAM) were quantified by mass spectrometry (IRMS) after physical separation of SOM. The statistical analyses consisted of variance analysis and regression. Nitrogen fertilization increased trunk volume and aerial dry matter. The estimated N rate to obtain 90 % of the maximum trunk volume was 74 kg ha-1 in the form of ammonium sulfate, and increased the yield by 42.3 % in comparison to the control plot without N fertilization. In response to N rates of 120 kg ha-1, no difference was observed between ammonium sulfate and ammonium nitrate. No alterations in SOM C and N stocks were detected due to N application. However, there was an increase in Ca, Mg and S absorption. The apparent N recovery rate in the field was highest at the N rate of 120 kg ha-1, reaching 34.4%.

Este estudo teve como objetivo caracterizar o banco de sementes sob vegetação secundária em uma área degradada por mineração de caulim em Brás Pires, MG. Foram coletadas 40 amostras de solo de 0,5 x 0,5 m até a profundidade de 5,0 cm. As amostras foram mantidas em viveiro por quatro meses, sendo metade em sombreamento de 11,5% (luz) e metade em sombreamento de 60% (sombra). A germinação das sementes foi comparada nas duas condições de sombra (11,5% e 60%), utilizando-se o teste t para amostras independentes. Foram amostradas 36 espécies pertencentes a 17 famílias botânicas. As famílias com maior riqueza específica foram Asteraceae, com nove espécies, Rubiaceae com cinco e Poaceae com quatro. A maioria das espécies (66,7%) e dos indivíduos (82,2%) amostrados no banco foi de herbácea. As espécies com maior número de indivíduos germinados do banco foram as herbáceas Urochloa decumbens (Stapf) R.D. Webster, Cenchrus sp. e Eragrostis sp. e a arbustiva Leandra niangaeformis Cogn. Entre as arbóreas, destacaram-se em número de indivíduos Luehea grandiflora Mart. e Trema micranta (L.) Blume. A maior densidade de ervas daninhas oriundas de áreas antropizadas do entorno indicou baixa resiliência da vegetação presente na área degradada em caso de ocorrer alguma perturbação severa.

This study aimed to characterize the soil seed bank under secondary vegetation in an area degraded by kaolin mining in Brás Pires, MG, Brazil. Forty soil samples of 0.5 x 0.5 m were collected to the depth of 5.0 cm. The soil samples were maintained in nursery for four months, half in shading of 11.5% (light), and half in shading of 60% (shade). Seed germination was compared under the two shade conditions (11.5% and 60%), utilizing the t test for independent samples. Thirty-six species belonging to 17 botanical families were sampled. The families with the largest number of species were Asteraceae with 9, Rubiaceae with 5, and Poaceae with 4. Most of the species sampled (66.7%) were herbaceous. The most abundant species were the herbaceous Urochloa decumbens (Stapf) R.D. Webster, Cenchrus sp. and Eragrostis sp., and the shrub Leandra niangaeformis Cogn. Among the tree species, Luehea grandiflora Mart. and Trema micranta (L.) Blume presented the largest number of individuals. The largest density of the herbs originating from the disturbed surrounding areas indicates a low resilience of the vegetation in the degraded area, in case a severe disturbance occurs.