[Radial growth dynamics of Chinese fir and its response to seasonal drought]. / æ‰æœ¨å¾„å‘ç”Ÿé•¿åŠ¨æ€åŠå ¶å¯¹å­£èŠ‚æ€§å¹²æ—±çš„å“åº”.

We explored the seasonal dynamics and climate responses of radial variation of Chinese fir, we continuously monitored intra-annual stem radial size changes with the automated dendrometers in central Jiangxi Province in 2016 and 2017. We analyzed daily and seasonal dynamics of radial variations, and their Spearman correlations with climatic factors. We found that the diurnal radial variations had a pattern of contraction during the day and expansion at night. The growth onset in 2017 was one month earlier than that in 2016, whereas the continuous tree water deficit in the dry season caused the cessation one month early. During the main growing season (from April to September), the radial increment was significantly positively correlated with precipitation and relative humidity but negatively correlated with photosynthetically active radiation and vapor pressure deficit in both wet and dry seasons. However, the correlation for tree water deficit was opposite to stem radial increment. Severe water deficit significantly enhanced the impacts of soil water content on stem radial variation in the dry season. Moisture condition was always the key factor affecting stem radial variation of Chinese fir. Appropriate measures such as increasing soil water content could promote stem radial growth during summer drought.

[Response of radial growth of Pinus sylvestriformis and Picea jezoensis to climate warming in the ecotone of Changbai Mountain, Northeast China]. / 长白山群落交错带长白松和鱼鳞云杉径向生长对气候变暖的响应.

Changbai Mountain is a typical distribution area of temperate coniferous and broad-leaved mixed forests, with significant influence of global climate change. In order to understand the responses of forest ecosystem to climate change, we examined the responses of dominant arbor species in the community ecotone of broad-leaved Korean pine forest and spruce-fir forest (also known as dark coniferous forest), Pinus sylvestriformis and Picea jezoensis. The standard chronologies were established by obtaining tree ring width data in order to identity the key climatic factors that confine the radial growth of both species. The responses of P. sylvestriformis and P. jezoensis to climate factors were different.P. sylvestriformis was more sensitive than P. jezoensis, indicating that P. sylvestriformis was more suitable for dendroclimatological analysis. The radial growth of P. sylvestriformis was consistent with the increases of mean temperature, while the radial growth of P. jezoensis showed a "divergence problem" which decreased with the increases of mean temperature. The radial growth of P. sylvestriformis was mainly limited by temperature, especially the mean temperature in last July and August and current September. However, there was a negative correlation between standard chronologies of P. jezoensis and mean temperature in most months, which was limited by both temperature and precipitation. The correlation between radial growth of both species and climate factors after sudden temperature rise, was weaker than that before sudden temperature rise. The correlation between radial growth and climate factors changed from positive to negative in some months. Current temperature rise might not exceed the critical threshold of the radial growth of P. sylvestriformis, which could promote the radial growth. In addition, the wavelet analysis showed that the radial growth of trees in this area might be affected by large-scale coupling effects of atmospheric-ocean-land changes. In conclusion, climate warming was beneficial to the radial growth of P. sylvestriformis, while drought stress caused by warming was the main factor limiting the radial growth of P. jezoensis. If the global temperature continues to increase in the future, it will have an adverse impact on P. jezoensis. The results would help improve our understanding of the responses of radial growth of P. sylvestriformis and P. jezoensis to future climate change, and provide some basic data for climate reconstruction using both species.

[Soil enzyme activities and their stoichiometry of typical plantations in mid-subtropical China].

We measured the activities of six kinds of enzyme, including ß-glucosidase (BG), ß-N-acetyl-glucosaminidase (NAG), leucine aminopeptidase (LAP), acid phosphatase (AP), polyphenol oxidase (POX), peroxidase (POD), as well as enzyme stoichiometric ratios and soil physical and chemical properties at 0-10 and 10-20 cm layers across typical Pinus massoniana plantation, Pinus elliottii plantation and mixed plantation of P. massoniana and Schima superba (broadleaved-conifer mixed plantation) in mid-subtropical China. Key factors driving the variation in soil enzyme activity and stoichiometry among different stand types were investigated. The results showed that the activities of soil BG and LAP were significantly affected by stand type. Soil BG activity at 10-20 cm soil layer was significantly higher in P. elliottii plantation than in P. massoniana plantation, while the activity of LAP was highest in the P. massoniana plantation. Soil BG/(NAG+LAP) and BG/AP at 10-20 cm layer of P. elliottii plantation were significantly higher than those of P. massoniana plantation, while (NAG+LAP)/AP of P. massoniana plantation was significantly higher than those of P. elliottii plantation and mixed plantation. The vector length of enzyme stoichiometry at 10-20 cm soil layer was significantly different among stand type, with an order of P. elliottii plantation > broadleaved-conifer mixed plantation > P. massoniana. The vector angles of enzyme stoichiometry in the three plantations were greater than 45°, with the vector angle in the P. elliottii plantation at 10-20 cm soil layer being significantly greater than that of the P. massoniana plantation. Results from redundancy analysis showed that soil carbon quality index and the ratio of soil organic carbon to total phosphorus (C/P), soil water content and C/P were the key factors affecting soil enzyme activity and stoichiometry at 0-10 and 10-20 cm soil layers, respectively. The quantity and quality of soil carbon and phosphorus, and soil water content played a key role in regulating nutrient cycling in mid-subtropical plantation ecosystem.

Long-term monitoring of tree population dynamics of broad-leaved Korean pine forest in Changbai Mountains, China.

Based on four investigations of a one-hectare permanent plot in Changbai Mountains from 1981 to 2016, the changes of tree species composition and structure of broad-leaved Korean pine forest were examined, and diameter distribution, spatial pattern distribution, and quantitative changes of each tree species were analyzed. The results showed that there were little changes in tree species composition and an overall decreasing trend in total density in 35 years. Both basal area and stand volume were 43-45 m2·hm-2 and 474-496 m3·hm-2, respectively. Pinus koraiensis was the most dominant species, whose basal area and volume accounted for 57.8%-59.7% and 62.5%-65.4% of the total in the community, respectively. All dominant species showed random distribution and changed little in 35 years. The DBH distribution of P. koraiensis was in a near-to-normal form. Total species showed a reversed "J" shape. The number of dead trees was the largest in small DBH class (10-26 cm) with the percentage of 30%. The percentage of dead trees was the largest in intermediate class (30-50 cm) with 30%-50%. Except Acer mono, all species in the tree layer showed little recruitment, with mortality rate being higher than recruiting rate. Specially, P. koraiensis had no saplings or recruitment, and the population was in decline. The regeneration of dominant species such as P. koraiensis and Tilia amurensis was hindered in the original broad-leaved Korean pine forest, the population maintenance of which might need natural disturbance.

[Response of radial growth of Pinus koraiensis and Picea jezoensis to climate change in Xiao-xing'anling Mountains, Northeast China]. / å°å ´å®‰å²­çº¢æ¾å’Œé±¼é³žäº‘æ‰å¾„å‘ç”Ÿé•¿å¯¹æ°”å€™å˜åŒ–çš„å“åº”.

Based on dendrochronological methods, we established residual chronologies of Pinus koraiensis and Picea jezoensis, with the dominant species of broadleaved Korean pine mixed forest at low altitudes chosen as the research object, to identify the key climatic factors affecting the radial growth of the two species in Xiaoxing'anling Mountains, Northeast China. The results showed that the responses of the two species to climate factors were different, and P. koraiensis was more sensitive, and hence more suitable for dendroclimatological analysis. Response function coefficients indicated that the radial growth of P. koraiensis negatively correlated with June mean temperature of current year, while positively correlated with precipitation in June of current year. There was no significant correlation between P. jezoensis and all climate variables. Spatial correlation analysis revealed that variations in chronology of P. koraiensis contained strong regional signals, and the highest correlation occurred in the vicinity of the study area. Warming caused drought stress, which was the main factor that limited the growth of P. koraiensis, and it might have adverse effects on the Korean pine if global temperature continues to increase. The coupling effects of large-scale atmospheric-oceanic variability may affect the radial growth of P. koraiensis in Xiaoxing'anling Mountains.