Hydroclimate Variations in Central and Monsoonal Asia over the Past 700 Years

Peer reviewe

Silencing COI1 in Rice Increases Susceptibility to Chewing Insects and Impairs Inducible Defense

The jasmonic acid (JA) pathway plays a key role in plant defense responses against herbivorous insects. CORONATINE INSENSITIVE1 (COI1) is an F-box protein essential for all jasmonate responses. However, the precise defense function of COI1 in monocotyledonous plants, especially in rice (Oryza sativa L.) is largely unknown. We silenced OsCOI1 in rice plants via RNA interference (RNAi) to determine the role of OsCOI1 in rice defense against rice leaf folder (LF) Cnaphalocrocis medinalis, a chewing insect, and brown planthopper (BPH) Nilaparvata lugens, a phloem-feeding insect. In wild-type rice plants (WT), the transcripts of OsCOI1 were strongly and continuously up-regulated by LF infestation and methyl jasmonate (MeJA) treatment, but not by BPH infestation. The abundance of trypsin protease inhibitor (TrypPI), and the enzymatic activities of polyphenol oxidase (PPO) and peroxidase (POD) were enhanced in response to both LF and BPH infestation, but the activity of lipoxygenase (LOX) was only induced by LF. The RNAi lines with repressed expression of OsCOI1 showed reduced resistance against LF, but no change against BPH. Silencing OsCOI1 did not alter LF-induced LOX activity and JA content, but it led to a reduction in the TrypPI content, POD and PPO activity by 62.3%, 48.5% and 27.2%, respectively. In addition, MeJA-induced TrypPI and POD activity were reduced by 57.2% and 48.2% in OsCOI1 RNAi plants. These results suggest that OsCOI1 is an indispensable signaling component, controlling JA-regulated defense against chewing insect (LF) in rice plants, and COI1 is also required for induction of TrypPI, POD and PPO in rice defense response to LF infestation

Location of the PDSI grids and the central and eastern Asia is delimited according to Chen et al. (2010).

<p>Location of the PDSI grids and the central and eastern Asia is delimited according to Chen et al. (2010).</p

The drought area index (DAI) and the (red bold line) low-passed (lower than the cutoff frequency of 0.02) DAI for (a) central and (b) monsoonal Asia.

<p>The yellow shaded area indicates the in-phase decadal variations and the green shaded area indicates the anti-phase decadal variations between them.</p

Correlations between the reconstructed PDO series and the reconstructed PDSI for the periods (a) 1300–1450s, (b) 1460s–1550s, (c) 1560s–1640s, (d) 1650s–1710s, (e) 1720s–1850s and (f) 1860s–1996.

<p>Correlations between the reconstructed PDO series and the reconstructed PDSI for the periods (a) 1300–1450s, (b) 1460s–1550s, (c) 1560s–1640s, (d) 1650s–1710s, (e) 1720s–1850s and (f) 1860s–1996.</p

The cross wavelet transform (XWT) between PDO and DAI of (a) central and (b) monsoonal Asia, and the squared wavelet coherence (WTC) between PDO and DAI of (c) central and (d) monsoonal Asia.

<p>The significance level (<i>p</i><0.05) is indicated by thick contours. The left arrows indicate anti-phase relationship, and right arrows indicate in-phase relationship between PDO and DAI.</p

The multi-taper method (MTM) spectra of the drought area index (DAI) of the (a) central Asia and the (b) monsoonal Asia, as well as the wavelet spectra of the DAI of the (c) central Asia and the (d) monsoonal Asia.

<p>The multi-taper method (MTM) spectra of the drought area index (DAI) of the (a) central Asia and the (b) monsoonal Asia, as well as the wavelet spectra of the DAI of the (c) central Asia and the (d) monsoonal Asia.</p

Role of forest fires in Holocene stand-scale dynamics in the unmanaged taiga forest of northwestern Russia

Fossil pollen, conifer stomata, and charcoal records for the last 10,000 years were studied from three small hollow sites (Larix Hollow, Mosquito Hollow, and Olga Hollow) located at the modern western range limit of Siberian larch (Larix sibirica) in northwestern Russia to investigate the role of forest fires in stand-scale dynamics of taiga vegetation. Wavelet coherence analysis was utilized to reveal the significance of fire on the vegetation composition at different timescales by assessing the phase and strength of the relationship between forest fires and most common boreal tree taxa in a time–frequency window. Pollen and stomata data show that all of the modern-day common tree taxa, including Norway spruce (Picea abies) and Siberian larch, have been present in the study region since the early Holocene. The absence of charcoal layers at Mosquito Hollow suggests that this site has acted as a fire-free refugium with continuous dominance of spruce throughout the Holocene. Meanwhile, the Larix Hollow record indicates frequent local fire events and as a consequence, a more variable tree species composition. The wavelet coherence results show that the impact of forest fires on vegetation varies from short-term (<200-year periods) changes in individual tree taxa to long-term (400–800 years) changes in forest composition, such as the expansion of spruce population after local high-intensity fires around 7500–7000 cal. yr BP and the increase in abundance of birch and alder during periods of high fire frequency. Our results suggest that Holocene fire histories can be markedly different within a small geographical area, demonstrating the importance of site-specific factors in the local fire regime in the unmanaged taiga forest