Intercropping, which grows at least two crop species on the same pieces of land at the same time, can increase grain yields greatly. Legume-grass intercrops are known to overyield because of legume nitrogen fixation. However, many agricultural soils are deficient in phosphorus. Here we show that a new mechanism of overyielding, in which phosphorus mobilized by one crop species increases the growth of a second crop species grown in alternate rows, led to large yield increases on phosphorus-deficient soils. In 4 years of field experiments, maize (Zea mays L.) overyielded by 43% and faba bean (Vicia faba L.) overyielded by 26% when intercropped on a low-phosphorus but high-nitrogen soil. We found that overyielding of maize was attributable to belowground interactions between faba bean and maize in another field experiment. Intercropping with faba bean improved maize grain yield significantly and above-ground biomass marginally significantly, compared with maize grown with wheat, at lower rates of P fertilizer application (<75 kg of P2O5 per hectare), and not significantly at high rate of P application (>112.5 kg of P2O5 per hectare). By using permeable and impermeable root barriers, we found that maize overyielding resulted from its uptake of phosphorus mobilized by the acidification of the rhizosphere via faba bean root release of organic acids and protons. Faba bean overyielded because its growth season and rooting depth differed from maize. The large increase in yields from intercropping on lowphosphorus soils is likely to be especially important on heavily weathered soils.intercropping ͉ interspecific rhizosphere effect ͉ overyielding I ntercropping, which is the intermingled growth of two or more crops, with Ͼ28 million hectares of annually sown area in China (1), is also common in other parts of the world, such as in India, Southeast Asia, Latin America, and Africa (2). On nitrogen-deficient soils, legume-grass intercrops are known to overyield because of legume nitrogen fixation (2-5). About a third of terrestrial soils have insufficient available phosphorus (P) for optimum crop production, with many tropical acid soils being highly P-deficient (6, 7). Some pot experiments have suggested that legume/cereal mixtures can achieve greater P uptake on such soils (8-10) than can either species by itself. In field conditions, similar greater P uptake by intercropped maize with faba bean also was observed (11). However, both pot experiments and field experiments did not distinguish that the greater P uptake was derived from niche (rooting depth or seasonality) complementary or direct interspecific facilitation. We hypothesize that overyielding of intercropped species on P-deficient soil may result from a plant's chemical alteration of the rhizosphere that mobilizes P and thus enhances its own productivity and that of another species. We call this phenomenon the interspecific rhizosphere effect. Such chemical mobilization of a limiting nutrient would represent a mechanism of interspecific facilitation that, in concer...

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A novel Bayesian matrix factorization method for bounded support data is presented. Each entry in the observation matrix is assumed to be beta distributed. As the beta distribution has two parameters, two parameter matrices can be obtained, which matrices contain only nonnegative values. In order to provide low-rank matrix factorization, the nonnegative matrix factorization (NMF) technique is applied. Furthermore, each entry in the factorized matrices, i.e., the basis and excitation matrices, is assigned with gamma prior. Therefore, we name this method as beta-gamma NMF (BG-NMF). Due to the integral expression of the gamma function, estimation of the posterior distribution in the BG-NMF model can not be presented by an analytically tractable solution. With the variational inference framework and the relative convexity property of the log-inverse-beta function, we propose a new lower-bound to approximate the objective function. With this new lower-bound, we derive an analytically tractable solution to approximately calculate the posterior distributions. Each of the approximated posterior distributions is also gamma distributed, which retains the conjugacy of the Bayesian estimation. In addition, a sparse BG-NMF can be obtained by including a sparseness constraint to the gamma prior. Evaluations with synthetic data and real life data demonstrate the good performance of the proposed method.

Melatonin is the major secretory product of the pineal gland and is considered an important natural oncostatic agent. The anticancer activity of melatonin is due to its immunomodulatory, anti-proliferative and antioxidative effects. At present there are no direct data available as to melatonin's possible influence on angiogenesis, which is a major biological mechanism responsible for tumor growth and dissemination. The current study investigated the influence of melatonin on angiogenesis. Human umbilical vein endothelial cells (HUVECs) were cultured, identified, and purified. Cell growth and viability, DNA fragmentation and cell cycle analyses were determined. To elucidate the mechanism of action of melatonin, Western blot analyses for P53, Bax and Bcl-2 expression were carried out. The results demonstrate the anti-proliferative and apoptosis-inducing effects of melatonin; these changes were associated with cell cycle arrest, upregulation of P53 and Bax and downregulation of Bcl-2. Taken together, our data showed that melatonin in high concentrations markedly reduces HUVECs proliferation, induces cellular apoptosis, and modulates cell cycle length. P53 and Bax/Bcl-2 expression changes may be involved in these actions of melatonin.