Abstract. Droughts reduce gross primary production (GPP) and ecosystem respiration (Reco), contributing to most of the inter-annual variability in terrestrial carbon sequestration. In seasonally dry climates (Mediterranean), droughts result from reductions in annual rainfall and changes in rain seasonality. We compared carbon fluxes measured by the eddy covariance technique in three contrasting ecosystems in southern Portugal: an evergreen oak woodland (savannah-like) with ca. 21% tree crown cover, a grassland dominated by herbaceous annuals and a coppiced short-rotation eucalyptus plantation. During the experimental period (2003)(2004)(2005)(2006)) the eucalyptus plantation was always the strongest sink for carbon: net ecosystem exchange rate (NEE) between −861 and −399 g C m −2 year −1 . The oak woodland and the grassland were much weaker sinks for carbon: NEE varied in the oak woodland between −140 and −28 g C m −2 year −1 and in the grassland between −190 and +49 g C m −2 year −1 . The eucalyptus stand had higher GPP and a lower proportion of GPP spent in respiration than the other systems. The higher GPP resulted from high leaf area duration (LAD), as a surrogate for the photosynthetic photon flux density absorbed by the canopy. The eucalyptus had also higher rain use efficiency (GPP per unit of rain volume) and light use efficiency (the daily GPP per unit incident photosynthetic photon flux density) than the other two ecosystems. The effects of a severe drought could be evaluated during the hydrological-year (i. oak woodland a large proportion of GPP resulted from carbon assimilated by its annual vegetation component, which was strongly affected by the shortage of rain in winter. Overall, severe drought affected more GPP than Reco leading to the deterioration of NEE. Although the rain-use efficiency of the eucalyptus plantation increased in the dry year, this was not the case of evergreen oak woodland, which rainuse efficiency was not influenced by drought. Recovery after drought alleviation, i.e., beginning with heavy rain in October 2005, was fully accomplished in 2006 in the oak woodland and grassland, but slow in the eucalyptus plantation.

The objective of this study was to evaluate the litterfall deposition, the decomposition rate (K L ) and the water holding capacity (WHC) of litter stored in the soil in two areas degraded by mining submitted to different methods of forest restoration: induction of natural regeneration (NR) and planting seedlings of native forest species (PS) with a forest fragment (FF) used as reference. The litterfall deposition was collected monthly over 12 months in collectors of 0.25 m 2 . The KL was estimated by the relation between annual litter production and litter stock in the soil surface. WHC was determined in the rainy and dry period. The litterfall deposition was lower in PS with values of 6.61 ± 0.20, 10.75 ± 0.52 and 11.83 ± 0.72 Mg ha -1 yr -1 for PS, NR and FF respectively. The K L and WHC were significantly lower in PS when compared to NR and FF, and WHC decreased significantly from the rainy season to the dry season. The induction of natural regeneration was the more effective restoration method for degraded areas regarding litterfall deposition, decomposition and water retention capacity, surpassing planting native tree species and approaching a native forest fragment.Fluxo, estoque e capacidade de retenção hídrica de serapilheira em ecossistemas de restauração florestal pós mineração, Amazônia Oriental RESUMO: O objetivo deste estudo foi avaliar a deposição da serapilheira, a taxa de decomposição (K L ) e a capacidade de retenção hídrica (CRH) da serapilheira estocada no solo em duas áreas degradadas por mineração submetidas a diferentes métodos de restauração florestal: indução de regeneração natural (RN) e plantio de mudas de espécies florestais nativas (PM) e um fragmento de floresta (FF) usado como referência. A deposição de serapilheira foi coletada mensalmente ao longo de 12 meses em coletores de 0,25 m 2 . O KL foi estimado pela relação entre a produção anual de serapilheira e o estoque de serapilheira na superfície do solo. A CRH foi determinada no período chuvoso e seco. A deposição de serapilheira foi menor no PM, com valores de 6,61 ± 0,20, 10,75 ± 0,52 e 11,83 ± 0,72 Mg ha -1 ano -1 para o PM, RN e FF respectivamente. O K L e CRH foram significativamente menores no PM quando em comparação com RN e FF, sendo que, a CRH diminuiu significativamente da estação chuvosa para à estação seca. A indução da regeneração natural foi o método mais eficaz de restauração de áreas degradadas quanto à deposição, decomposição e capacidade de retenção de água da serapilheira, superando o plantio de espécies arbóreas nativas e se aproximando de um fragmento de floresta nativa.Palavras-chave: mineração de bauxita; recuperação ambiental; indicadores de restauração florestal; regeneração natural; plantio de mudas nativas Litterfall, litter stock and water holding capacity in post-mining forest restoration ecosystems, Eastern Amazon Rev. Bras.

RESUMOO objetivo deste estudo foi avaliar o efeito da remoção e sazonalidade da precipitação na deposição de serapilheira e teor dos nutrientes P e K em uma floresta em estágio sucessional no município de Castanhal-PA. Foram estabelecidos dois sistemas: 1) Remoção: retirada da serapilheira do solo e; 2) Controle ou testemunha: sem a retirada de serapilheira. Com isso, foram instalados 12 coletores de 1 m² em cada sistema para quantificação mensal da massa seca e obtenção dos teores de P e K. A deposição total de serapilheira foi de 6,65 e 6,24 Mg ha -1 ano -1 para os sistemas controle e remoção respectivamente, não diferindo entre si (p < 0,05). A remoção da serapilheira não alterou o teor de P e K, no entanto, houve variação ao longo dos meses, com maiores valores de P no período de maior precipitação pluviométrica, com o K apresentando padrão inverso. Portanto a produção de serapilheira apresentou-se sazonal durante o ano de e a remoção da serapilheira não causou alteração no teor de P e K, sendo que, a precipitação pluviométrica foi a variável climática que influenciou no teor desses elementos.Palavras-chave: Amazônia brasileira; ciclagem de nutrientes; floresta secundária Influence of litter removal in the content of phosphorus and potassium in Eastern Amazon ABSTRACTThe aim of this study was to evaluate the effect of removing and seasonality of precipitation on litter deposition and content of nutrients P and K in a forest successional stage in the city of Castanhal-PA. Two systems were established: 1) removal: removal of soil and litter: 2) Control or witness, without the removal of litter. With this, 12 collectors of 1 m² were installed in each system for monthly quantification of the dry mass and obtain the contents of P and K. The total litter deposition was 6.65 and 6.24 Mg ha -1 yr -1 for control systems and removal respectively, did not differ from each other (p < 0.05). The removal of litter did not change the content of P and K, however, there was change over the months, with higher P values in the period of increased rainfall, with the K featuring reverse pattern. Therefore, litter production has performed seasonal during the year and the removal of litter caused no change in P and K content, and the rainfall was the climate variable that influenced the content of these elements.

Abstract. Droughts cause reductions in gross primary production (GPP) and also in net ecosystem exchange (NEE), contributing to most of the inter-annual variability in terrestrial carbon sequestration. In seasonally dry climates (Mediterranean) droughts result from reductions in annual rainfall and from changes in rain seasonality. In western Iberia, the hydrological-year (i.e., from October to September) of 2004–2005 was extremely dry, with precipitation 50% below the long-term mean (691 mm in 1961–1990), but 2005–2006 was normal. We compared the carbon fluxes measured by the eddy covariance technique from three contrasting ecosystems in southern Portugal: an evergreen oak woodland (savannah-like) with ca. 21% tree cover; a Mediterranean C3/C4 grassland; and a coppiced eucalyptus plantation. During the dry hydrological-year of 2004–2005, NEE was lowest, the highest sink strength was in the eucalypt plantation (NEE = –399 g C m −2 year−1) as compared to the oak woodland (NEE = –88 g C m −2 year−1), and the grassland (NEE = +49 g C m −2 year −1). The latter was a source of carbon dioxide. The NEE values of the dry year were, however, much lower than those for wetter years, e.g. NEE = –861 g C m−2 year −1 in 2002–2003 in the eucalypt plantation. The NEE of the grassland and the oak savannah in the 2005–2006 hydrological-year, with annual precipitation above the long term mean, were –190 and –120 g C m −2 year−1, respectively. All ecosystems studied increased their rain-use efficiency (GPP per unit of rain volume) increased in dry years. In the case of annual vegetation – grassland and low tree density woodland, however &amp;ndash, rain-use efficiency decreased with severe drought. However, this was more pronounced in the eucalypt plantation due to greater GPP and the use of deep soil water resources. Although both calendar years of 2004 and 2005 had equally low rainfall, the effect of drought on the eucalypt plantation was delayed until the second dry year. This suggests that the effects of water deficits on Mediterranean forests are exacerbated by prolonged droughts when long-term soil water reserves are depleted. The grassland, however, was more vulnerable and responded faster to water deficits. This effect of drought was less pronounced in the oak woodland due to the sparse tree cover.

Corn sowing time in Sete Lagoas region, Minas Gerais State, based on the probability of occurrence of dry and rainy spellsThe objective of this study was to determine the probability of dry and rainy occurrence periods in Sete Lagoas, Minas Gerais State, Brazil, from a historical series of 66-year-long daily rainfall data to establish the best sowing date for corn crop. Dry days were considered as those that had precipitation below corn evapotranspiration, ET corn . This study was carried out for the stages of flowering and grain filling, starting from seven sowing times ST (10/01, 10/16, 10/31, 11/15, 12/01, 12/16 e 12/31). The probabilities of occurring dry and rainy spells were estimated by the Markov´s chain. The probability of occurring dry days was always higher than rainy days. The highest probability of dry days were found between ST 15/11 and DS 31/12. The highest probability of occurring rainy days was recorded at ST 01/10. Considering the studied average cycle (for the most critical stage of corn development), the combination of the lowest probability of dry spells with the highest probability of rainy days indicates that the best dates to initiate non-irrigated sowing should be ST 01/10 and 16/10.