Nitrogen Deposition Effects on Invasive and Native Plant Competition: Implications for Future Invasions.

Nitrogen (N) deposition has increased dramatically in recent decades, which is significantly affecting the invasion and growth of exotic plants. Whether N deposition leads to invasive alien species becoming competitively superior to native species remains to be investigated. In the present study, an invasive species (Oenothera biennis L.) and three co-occurring native species (Artemisia argyi Lévl. et Vant., Inula japonica Thunb., and Chenopodium album L.) were grown in a monoculture (two seedlings of the same species) or mixed culture (one seedling of O. biennis and one seedling of a native species) under three levels of N deposition (0, 6, and 12 g∙m-2∙year-1). Nitrogen deposition had no effect on soil N and P content. Nitrogen deposition enhanced the crown area, total biomass, leaf chlorophyll content, and leaf N to phosphorus ratio in both invasive and native plants. Oenothera biennis dominated competition with C. album and I. japonica due to its high resource acquisition and absorption capacity (greater height, canopy, leaf chlorophyll a to chlorophyll b ratio, leaf chlorophyll content, leaf N content, leaf mass fraction, and lower root-to-shoot ratio). However, the native species A. argyi exhibited competitive ability similar to O. biennis. Thus, invasive species are not always superior competitors of native species; this depends on the identities of the native species. High N deposition enhanced the competitive dominance of O. biennis over I. japonica by 15.45% but did not alter the competitive dominance of O. biennis over C. album. Furthermore, N deposition did not affect the dominance of O. biennis or A. argyi. Therefore, the species composition of the native community must be considered when preparing to resist future biological invasions. Our study contributes to a better understanding of the invasion mechanisms of alien species under N-loading conditions.

Effects of salt stress on interspecific competition between an invasive alien plant Oenothera biennis and three native species.

Biological invasions and soil salinization have become increasingly severe environmental problems under global change due to sea-level rise and poor soil management. Invasive species can often outcompete native species, but few studies focus on whether invasive alien species are always superior competitors under increasing stressors. We grew an invasive grass species, Oenothera biennis L., and three native grass species (Artemisia argyi Lévl. et Vant., Chenopodium album L., and Inula japonica Thunb.) as a monoculture (two seedlings of each species) or mixture (one seedling of O. biennis and one native species seedling) under three levels of salt treatments (0, 1, and 2 g/kg NaCl) in a greenhouse. We found that invasive O. biennis exhibited greater performance over native C. album and I. japonica, but lower performance compared to A. argyi, regardless of the soil salinity. However, salinity did not significantly affect the relative dominance of O. biennis. Interspecific competition enhanced the growth of O. biennis and inhibited the growth of I. japonica. Although O. biennis seedlings always had growth dominance over C. album seedlings, C. album was not affected by O. biennis at any salt level. At high salt levels, O. biennis inhibited the growth of A. argyi, while A. argyi did not affect the growth of O. biennis. Salt alleviated the competitive effect of O. biennis on I. japonica but did not mitigate the competition between O. biennis and the other two native species. Therefore, our study provides evidence for a better understanding of the invasive mechanisms of alien species under various salinity conditions.

[Ecophysiological responses of Camellia japonica (Naidong) to different light and water conditions]. / è€å†¬å±±èŒ¶å¯¹ä¸åŒå ‰ç §å’Œæ°´åˆ†çš„ç”Ÿç†ç”Ÿæ€å­¦å“åº”.

Camellia japonica (Naidong), a Tertiary relict species with abundant morphological characteristics and special genetic characteristics, is the northernmost distributed population of C. japonica. The seedlings of Naidong were subjected to two light regimes (65%, 15% of full sunlight, respectively) and three water supply regimes (75%, 50% and 25% of field capacity, respectively). Our objectives were to reveal the ecophysiological responses of Naidong under different drought and shade conditions and to examine the four existing hypotheses explaining the responses of Naidong seedlings to the interactions of shade and drought. The results showed that 15% of full sunlight reduced the growth of seedlings. Compared with those under 65% of full sunlight condition, the net photosynthetic rate, transpiration rate and chlorophyll content of seedlings under 15% of full sunlight condition were decreased by 63.3%, 82.9% and 17.5%, respectively. In contrast, the specific leaf area, leaf water content and maximal quantum yield under 15% of full sunlight condition were enhanced by 60.3%, 8.3% and 6.4%, respectively. Drought limited the growth of seedlings,decreased their height and basal diameter. The net photosynthetic rate, transpiration rate and stomatal conductance of seedlings significantly decreased with the increases of drought stress, with their minimum values being 0.83 µmol·m-2·s-1, 0.30 µmol·m-2·s-1 and 11.56 mmol·m-2·s-1, respectively. With the increases of drought stress, the contents of peroxidase and catalase showed a general declining trend, but the contents of malondialdehyde and proline significantly increased. The treatment 15% of full sunlight alleviated the negative effects of drought on Naidong seedlings, which supported the above-ground facilitation hypothesis. Our results indicated that Naidong seedlings could respond and acclimate to environmental changes through various mechanisms, and the seedlings might normally grow under broad ranges of light and water stresses. In addition, providing ideal light and water conditions for the Naidong seedlings could facilitate its application in gardening.

[Adaptability of Camellia sasanqua leaf morphology during natural changes in temperature.] / èŒ¶æ¢ å¶ç‰‡ç»“æž„å¯¹è‡ªç„¶å˜æ¸©çš„é€‚åº”.

In this study, the adaptability of leaf shape, structure and stomata characteristics of Camellia sasanqua to temperature variation in natural process was investigated by field morphological observation, conventional paraffin section and scanning electron microscopy methods. The results showed that, as the temperature decreased, the leaf color changed from green to dark green, toge-ther with white and purple spots on the leaves. The relative conductivity and the percentage of wi-thered leaves increased initially and then decreased during this period. The highest percentages of relative conductivity and withered leaves in March 2015 were 56.0% and 25.4%, respectively. Different leaf tissue structure indexes, including middle vein thickness, leaf thickness, upper and lower epidermis thickness, upper and lower cuticle thickness, palisade tissue thickness, spongy tissue thickness, ratio of palisade tissue to spongy tissue, cell tense ratio and vein protuberant degree were also determined during the natural temperature change from September 2014 to April 2015. Gradually, these parameters increased initially and then decreased with the decrease of temperature except spongy ratio, which showed the opposite trend. These indicators above changed significantly in different months. Stomata length and width were not significantly changed in October 2014, December 2014 and March 2015, while the percentage of completely closed stomata was higher in March 2015, compared with other months. Taken together, we proposed that the improved adaptability of cold tolerance of C. sasanqua relies on the changes of leaf structure and stomatal closure.

The checkpoint 1 kinase inhibitor LY2603618 induces cell cycle arrest, DNA damage response and autophagy in cancer cells.

Chemotherapy- or radiotherapy-induced DNA damage activates the Chk1-dependent DNA damage response (DDR) and cell cycle checkpoints to facilitate cell survival. Numerous attempts have been made to identify specific Chk1 inhibitors to enhance the efficiency of chemotherapy or radiotherapy. In this study, we investigated the molecular mechanisms underlying the antitumor activity of LY2603618, a potent and selective small molecule inhibitor of Chk1 protein kinase, in human lung cancer cells. Treatment of cancer cells with LY2603618 caused cell cycle arrest in the G2/M phase. A marked induction of DDR, including the phosphorylation of ATM, Chk2, p53 and histone H2AX, was observed after LY2603618 treatment. LY2603618 inhibited Chk1 autophosphorylation (S296 Chk1) and increased DNA damage-mediated Chk1 phosphorylation (S345 Chk1). In addition, LY2603618-treated lung cancer cells transitioned from LC3-I to LC3-II, a hallmark of autophagy. Blocking autophagy with chloroquine (CQ) further enhanced LY2603618's inhibitory effect on cell viability/proliferation. LY2603618 also significantly increased p38 and c-Jun N-terminal kinase (JNK) phosphorylation. Pretreatment with the JNK inhibitor reduced cleavage of caspase-3 and PARP levels in LY2603618-treated cells. These results suggest the following: (i) the biological consequences of LY2603618 in lung cancer cells is associated with both inhibition of Chk1 phosphorylation on S296 and activation of the DNA damage response network; and (ii) the anticancer property of LY2603618 might be increased by inhibiting autophagy.