Acid Rain Increases Impact of Rice Blast on Crop Health via Inhibition of Resistance Enzymes.

Worldwide, rice blast (Pyricularia oryzae) causes more rice crop loss than other diseases. Acid rain has reduced crop yields globally for nearly a century. However, the effects of acid rain on rice-Pyricularia oryzae systems are still far from fully understood. In this study, we conducted a lab cultivation experiment of P. oryzae under a series of acidity conditions as well as a glasshouse cultivation experiment of rice that was inoculated with P. oryzae either before (P. + SAR) or after (SAR + P.) simulated acid rain (SAR) at pH 5.0, 4.0, 3.0 and 2.0. Our results showed that the growth and pathogenicity of P. oryzae was significantly inhibited with decreasing pH treatments in vitro culture. The SAR + P. treatment with a pH of 4.0 was associated with the highest inhibition of P. oryzae expansion. However, regardless of the inoculation time, higher-acidity rain treatments showed a decreased inhibition of P. oryzae via disease-resistance related enzymes and metabolites in rice leaves, thus increasing disease index. The combined effects of high acidity and fungal inoculation were more serious than that of either alone. This study provides novel insights into the effects of acid rain on the plant-pathogen interaction and may also serve as a guide for evaluating disease control and crop health in the context of acid rain.

Invasive Chromolaena odorata species specifically affects growth of its co-occurring weeds.

Plant-plant interaction is essential to weed invasion success and is related to impacts on the environment. To understand interactions of the well-known invasive plant siamweed (Chromolaena odorata) and its neighbors (exotic Praxelis clematidea and native cadillo) in South China, and their competitive mechanisms above- and belowground, a multicultivation experiment was conducted. Competitive indices, plant morphological traits, soil nutrient contents, enzyme activities, and microbial biomass were measured. Competitive balance index and morphological traits revealed balanced competition between P. clematidea and siamweed, and suppressive effect of siamweed on cadillo. In coculture of siamweed and P. clematidea, the branch length of siamweed slightly lengthened, while the branch number of P. clematidea increased compared with their respective monocultures accordingly. Overall impacts of the two invaders on soil properties were near averages of their single impacts. In coculture of siamweed and cadillo, siamweed was more competitive in both light and nutrient capture; soil urease activity and acid phosphatase activity were magnified and mitigated compared with the averages of those in their respective monocultures, respectively. The species-specific results of siamweed competing with its co-occurring weeds would contribute to a better understanding of mechanism in synergistic effect of siamweed with the other invasive plants.

Different water relations between flowering and leaf periods: a case study in flower-before-leaf-emergence Magnolia species.

The differing water relations between flowers and leaves on a plant reflect the lack of co-ordination between reproductive and vegetative organs during the evolution of angiosperm species. The amount of water that flowers consume has been reported to vary across species, and compared with studies of leaves, accurate measurements of flower water relations at the branch level are lacking. Further, the mechanisms by which flowers regulate their hydraulic function and structure to maintain water balance remain unclear. To explore the ecophysiological basis underpinning the differences between flowers and leaves, we measured hydraulic and morphological traits and monitored sap flow in flowers and leaves from the same branches of two Magnoliaceae species that flower before leaf emergence (Magnolia denudata Desr. and Magnolia soulangeana Soul.-Bod.). Sap flux density (JS) of flowers was 22% and 55% of that predicted for leaves in M. denudata and M. soulangeana respectively. JS of flowers commenced before predawn and ceased early in the afternoon, reflecting their night-time flowering pattern and a dramatic decrease of JS with increasing vapour pressure deficit (D) under the high light of midday. Relative to leaves, tepals were thicker and more hydrated, and had bigger but scarcer stomata, leading to lower stomatal conductance (gs) and transpiration rate (E), less negative water potential (Ψtepal) and lower hydraulic conductance. This study revealed different hydraulic patterns in the flowers and leaves of the two Magnolia species. Although flowers consumed less than half the water that leaves did, they used different strategies to maintain sufficiently high Ψ to sustain hydraulic safety. Magnolia flowers retained more hydrated tepals by exhibiting less water loss than leaves via lower hydraulic conductance. In contrast, Magnolia leaves maintained high transpiration rates through efficient stomatal responses to environmental changes compared with flowers.