The response of inorganic carbon distributions and dynamics to upwelling-favorable winds on the northern Gulf of Mexico during summer

Upwelling-favorable winds and an offshore-distributed Mississippi and Atchafalaya River plume trajectory were observed in summer 2009 in contrast to the mean conditions from 2002 to 2010 (upwelling-unfavorable winds and an alongshore river plume trajectory), a set of conditions which was also observed in summer 2007. The responses of dissolved inorganic carbon (DIC) distributions and dynamics to upwelling-favorable winds are studied by comparing the contrasting conditions between summer 2009 and summer 2007 on the northern Gulf of Mexico. Patterns of surface water partial pressure of CO2 (pCO2), DIC, δ13C in DIC, and total alkalinity (TA) determined in July 2009 and August 2007 were strongly related to river plume trajectories, and differed between the two summers. The slope of the relationship between dissolved oxygen (DO) and DIC in summer 2007 was comparable to the Redfield O/C ratio of 1.3, which was attributed to respiration of organic matter in the bottom water. The slope of the DO and DIC relationship and δ13CDIC values in bottom waters during July 2009 were clearly affected by mixing since their salinities were <35. A three end-member mixing model was used to remove mixing effects in (1) δ13CDIC, to estimate the organic source of respiration, and (2) in DIC concentrations, to calculate DIC removal and release. δ13CDIC results in both summers were consistent with an apparent release of DIC in hypoxic waters (DO less than 2 mg L−1) associated with respiration of surface organic matter. The area-weighted surface DIC removal (i.e., biological production) was lower in 2009 than in 2007 on the shelf, as the plume was distributed offshore. The release of DIC in bottom waters was higher over the shelf in 2009 and was surmised to be related to stronger mixing, which was favorable for the DO supply for respiration. Overall, surface waters on the continental shelf in the region of study in July 2009 acted as a weak CO2 source to the atmosphere, but a weak CO2 sink in August 2007. We contend that the inorganic carbon distribution and concentrations on the shelf were related to regional wind forcing, through its influence on the distribution of coastal currents and plume trajectories and their subsequent impact on biogeochemical processes.This work was supported by the National Science Foundation (OCE-0752110 and OCE-0752254), the National Aeronautics and Space Administration (NNX10AU06G, NX10AU78G, NNH14AY07I, and NNX14AO73G), and the BP-funded Gulf of Mexico Research Initiative RFP-II award (GoMRI-020)

Cucumber seedling dependence on cotyledonary leaves for early growth Dependência das folhas cotiledonares para o crescimento inicial de pepino

The objective of this work was to evaluate the dependence of cucumber (Cucumis sativus L.) seedlings on cotyledonary leaves for early growth and establishment. Sets of two uniform emerging seedlings were used to quantify the initial growth and dry matter accumulation, as well as the intensity and stage of cotyledon damage in seedling establishment and to determine cotyledon protein, amino acid and carbohydrate contributions to the growing seedling. Cucumber seedling establishment was found to be highly dependent on cotyledonary leaves. Root system establishment was highly dependent on the health of the aerial part. One cotyledon was enough to maintain aerial growth of seedlings after unfolding the first true leaf. Cucumber seedlings depended on both cotyledons to keep root system growth at least until leaf area was equivalent to cotyledon area. Covering one or both cotyledons of seedlings with one unfolded leaf increased carbohydrate content of uncovered cotyledon and leaves compared with control seedlings. Cucumber seedlings are highly dependent on cotyledonary leaves and aerial parts are less dependent than root system. Cotyledon damage at early stages of plant establishment would adversely impact crop yield by reducing plant density, an important yield component, or slowing down seedling growth and establishment.<br>O objetivo deste trabalho foi estudar o desempenho das folhas cotiledonares no crescimento inicial e estabelecimento de plântulas de pepino (Cucumis sativus L.). Grupos de duas plântulas uniformemente emergidas foram utilizados para quantificar o crescimento inicial e acúmulo de matéria seca, o efeito da intensidade e época de remoção dos cotilédones sobre o estabelecimento da plântula, e a contribuição de proteínas, aminoácidos e carboidratos dos cotilédones para o crescimento inicial. O estabelecimento das plântulas de pepino foi altamente dependente das folhas cotiledonares. As folhas cotiledonares foram fundamentais para o estabelecimento do sistema radicular. A presença de um cotilédone após a emissão da primeira folha verdadeira foi suficiente para manter o crescimento da parte aérea da plântula. Plântulas de pepino foram dependentes de ambas as folhas cotiledonares para sustentar o crescimento do sistema radicular, pelo menos até a equivalência entre área foliar e cotiledonar. A cobertura de uma ou ambas folhas cotiledonares antes da emissão da primeira folha verdadeira aumentou o conteúdo de carboidratos no cotilédone descoberto e nas folhas, comparado com a testemunha. O crescimento inicial de plântulas de pepino é altamente dependente das folhas cotiledonares, sendo a parte aérea menos dependente do que o sistema radicular. Danos nos cotilédones durante o crescimento inicial podem afetar o rendimento pela redução da densidade de plantas, um importante componente do rendimento, ou da taxa de crescimento e estabelecimento da plântula, que afeta a uniformidade da cultura