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Picea schrenkiana is the dominant tree species in Ili River Basin located in the western Tianshan Mountains of Xinjiang. We investigated the growth decline characteristics of P. schrenkiana at different altitudes (1800, 2300 and 2800 m) based on tree-ring index (TRI) and percentage growth change (GC), aiming to understand the growth response of P. schrenkiana to drought events at different altitudes and the impacts of altitude on tree growth decline in this region. The results showed that P. schrenkiana experienced multiple decline events at low-altitude (1800 m). TRI and GC identified inconsistent occurrence time of the decline events. The variations of TRI indicated that P. schrenkiana at low-altitude experienced two large-scale declines during 1927-1933 and 2017-2014, respectively. The variations of GC identified four decline events, including 1891-1893, 1924-1926, 1973-1975, and 2004-2009. The radial growth of P. schrenkiana across altitudes from low to high was significantly affected by the Palmer drought severity index (PDSI) of the previous growing season. The impact of current PDSI on P. schrenkiana during the growing season initially enhanced but later decreased with increasing altitude. In the extreme drought year 1917, the magnitude of growth decline increased with altitude. At low-altitude (1800 m), the TRI was 0.65, which was 35% lower than the normal level. At mid-altitude (2300 m) and high-altitude (2800 m), it was 0.56 and 0.54, respectively, being 40% lower than the average level. The drought event in 1917 had a 2-year legacy effect on the growth of P. schrenkiana at all the altitudes, with the TRI in 1920 recovered to exceeding 0.9, being close to the normal level. The impact of altitude on drought-induced forest decline was significant. Tree growth in low-altitude areas was more vulnerable to drought events due to the relatively poorer water and temperature conditions at low-altitude, which could lead to multiple large-scale decline events. In mid- and high-altitude areas, where hydrothermal conditions were more favorable, trees could experience even more severe decline during extreme droughts.

A key objective for herbicide research is to develop new compounds with improved bioactivity. Protoporphyrinogen IX oxidase (PPO) is an essential target for herbicide discovery. Here, we report using an in silico structure-guided optimization approach of our previous lead compound 1 and designed and synthesized a new series of compounds 2 - 6 . Systematic bioassays led to the discovery of a highly potent compound 6g , 1-methyl-3-(2,2,7-trifluoro-3-oxo-4-(prop-2-yn-1-yl)-3,4-dihydro-2 H -benzo[ b ][1,4]oxazin-6-yl)thieno[2,3- d ]pyrimidine-2,4(1 H ,3 H )-dione, which exhibited an excellent and wide spectrum of weed control at the rates of 30-75 g ai/ha by the postemergence application and is relatively safe on maize at 75 g ai/ha. Additionally, the K i value of 6g to Nicotiana tabacum PPO (NtPPO) was found to be 2.5 nM, showing 3-, 12-, and 18-fold higher potency relative to compound 1 ( K i = 7.4 nM), trifludimoxazin ( K i = 31 nM), and flumioxazin ( K i = 46 nM), respectively. Furthermore, molecular simulations further suggested that the thieno[2,3- d ]pyrimidine-2,4-dione moiety of 6g could form a more favorable π-π stacking interaction with the Phe392 of NtPPO than the heterocyclic moiety of compound 1 . This study provides an effective strategy to obtain enzyme inhibitors with improved performance through molecular simulation and structure-guided optimization.

Based on the standard method of dendrochronology, we examined the tree-ring width index of two dominant tree species in the Altay Mountains, China, including Picea obovata and Larix sibirica . We analyzed the basal area increments (BAI) of those two species and the relationships between their radial growth and the climatic factors, which were compared in similar habitats. The results showed that the BAI of P. obovata was greater than L. sibirica , but the radial growth rate of L. sibirica was greater. In recent 60 years, the radial growth of P. obovata negatively correlated with high temperature in the fast growing stage of previous year, while the high temperature in June of current year promoted the radial growth of L. sibirica. There was a significantly negative correlation between radial growth of L. sibirica with temperature in January of current year. The sensitivity of tree growth to climate showed an obvious increase after an abrupt climate change under the background of recent warming and wetting trend in mid-1980s. Results of the moving correlation analysis showed that the response of the radial growth of P. obovata and L. sibirica to temperature and precipitation were enhanced under the background of climate change in the study area.

Taking windfall woods of Picea schrenkiana in the southern mountainous area of the Ili Prefecture as the research object, tree-ring density chronologies were developed from the discs for maximum density (MXD), minimum density (MID), mean earlywood density (EWD), and mean latewood density (LWD) at five different stem heights (1.3, 5, 10, 15 and 20 m) to examine the climatic responses of tree-ring density by correlation analysis with local meteorological data. The results showed that there was a good coherence among the four types of tree-ring density chronologies for the same stem height, which was relatively significant for the data from 10, 15 and 20 m. The LWD had good coherence among different stem heights, while the climatic responses of tree-ring density at different stem heights varied. The MXD and LWD at 15 m were sensitive to mean tempera-ture from July to September in the previous year and from May to September in the current year. It might underestimate the response of P. schrenkiana to temperature if we sample tree-ring at 1.3 m.

Protoporphyrinogen oxidase (PPO, EC 1.3.3.4) is an important target for green agrochemical discovery. Herein, a novel N -phenylisoxazoline-thiadiazolo[3,4- a ]pyridazine herbicidal active scaffold was designed by the scaffold hybridization strategy. Systematic structural optimization enabled the discovery of a series of derivatives with excellent weed control at 9.375-150 g ai/ha by the post-emergent application. Some derivatives exhibited improved Nicotiana tabacum PPO (NtPPO)-inhibitory activity than fluthiacet-methyl. Of these, 2b , with K i = 21.8 nM, displayed higher weed control than fluthiacet-methyl at the rate of 12-75 g ai/ha, and selective to maize at 75 g ai/ha. In planta , 2b was converted into a bioactive metabolite 5 ( K i = 4.6 nM), which exhibited 4.6-fold more potency than 2b in inhibiting the activity of NtPPO. Molecular dynamics simulation explained that 5 formed stronger π-π interaction with Phe392 than that of 2b . This work not only provides a promising lead compound for weed control in maize fields but is also helpful to understand the molecular mechanism and basis of the designed hybrids.

In continuation of our search for potent protoporphyrinogen IX oxidase (PPO, EC 1.3.3.4) inhibitors, we designed and synthesized a series of novel herbicidal cycloalka[ d ]quinazoline-2,4-dione-benzoxazinones. The bioassay results of these synthesized compounds indicated that most of the compounds exhibited very strong Nicotiana tabacum PPO (NtPPO) inhibition activity. More than half of the 37 synthesized compounds displayed over 80% control of all three tested broadleaf weeds at 37.5-150 g ai/ha by postemergent application, and a majority of them showed no phytotoxicity toward at least one kind of crop at 150 g ai/ha. Promisingly, 17i ( K i = 6.7 nM) was 6 and 4 times more potent than flumioxazin ( K i = 46 nM) and trifludimoxazin ( K i = 31 nM), respectively. Moreover, 17i displayed excellent, broad-spectrum herbicidal activity, even at levels as low as 37.5 g ai/ha, and it was determined to be safe for wheat at 150 g ai/ha in postemergent application, indicating the great potential for 17i development as a herbicide for weed control in wheat fields.