The ectomycorrhizal fungal communities associated with Quercus liaotungensis in different habitats across northern China.

Quercus liaotungensis is a major tree species in deciduous broad-leaved forests in northern China. In this study, we investigated ectomycorrhizal (ECM) communities associated with Q. liaotungensis from five typical habitats across northern China. We used internal transcribed spacer-polymerase chain reaction and DNA sequencing to identify ECM fungi, and we detected 220 operational taxonomic units. In general, at the regional scale, the dominant ECM lineages were /tomentella-thelephora, /cenococcum, /russula-lactarius, and /inocybe. Analysis of variance demonstrated significant differences in alpha diversity among these ECM communities, and the ECM fungal richness was positively correlated with elevation and soil organic matter. Analysis of similarity and a nonmetric multidimensional scaling analysis revealed that there were significant differences in community composition, and the geographical distance was correlated with the ECM fungal communities. Among the environmental factors we studied, soil parameters and climate factors were the primary direct driving factors of the ECM fungal communities. Our study primarily advances our understanding of environmental factors affecting ECM fungal communities at regional scale.

Unraveling the genetic diversity and structure of Quercus liaotungensis population through analysis of microsatellite markers.

BACKGROUND: Quercus liaotungensis Koidz. is an ecologically and economically important tree species widely distributed in Northern China. However, the effective assessment, utilization, and protection of Q. liaotungensis resources remain unexplored. METHODS: In total, 120 samples obtained from 12 Q. liaotungensis populations of Northern China were investigated for genetic diversity and structure using 19 simple sequence repeat (SSR) primer pairs. RESULTS: The total number of alleles detected was 293, the average number of effective allele (Ne) was 6.084, the genetic differentiation coefficient (Fst) was 0.033, and the mean observed heterozygosity (Ho) and expected heterozygosity (He) were 0.690 and 0.801, respectively. Moreover, analysis of molecular variance (AMOVA) showed a 5.5% genetic variation among 12 Q. liaotungensis populations, indicating that a high level of genetic diversity and a low degree of genetic differentiation among Q. liaotungensis populations. STRUCTURE and cluster analysis divided the 12 Q. liaotungensis populations into the following three subpopulations: Bashang Plateau subpopulation (SH), Liaodong Peninsula subpopulation (NC), and Loess Plateau subpopulation (other 10 populations). The cluster analysis based on 19 climatic factors was consistent with the genetic structure. A positive correlation was found between genetic distance and geographical distance (r = 0.638, p = 0.028) by the Mantel test, and two boundaries were found among the 12 Q. liaotungensis populations by the Barrier analysis, indicating that Q. liaotungensis populations existed isolated by geographical distance and physical barrier. CONCLUSION: This study suggests that geographical isolation, physical barrier, climatic types, and natural hybridization promote the formation of genetic structures, which can contribute to future protection and genetic improvement of Q. liaotungensis.

[Dynamics and influencing factors of stem diameter micro-variations during the growing season in two typical forestation species in the loess hilly region, China.] / é»„åœŸä¸˜é™µåŒºä¸¤å ¸åž‹é€ æž—æ ‘ç§ç”Ÿé•¿å­£æ ‘å¹²ç›´å¾„å¾®å˜åŒ–åŠ¨æ€åŠå ¶å½±å“å› ç´ .

Using DC3 high-resolution dendrometer and Granier-type thermal dissipation probes, we measured stem diameter micro-variations and xylem sap flow of two typical forestation species, Quercus liaotungensis and Robinia pseudoacacia, for a growing season in the loess hilly region of China. The main environmental factors (soil water content, solar radiation, air temperature and relative humidity) were monitored. The linkage between diameter micro-variations and transpiration water use were analyzed with respect to their responses to environmental factors. The results showed that the variations in stem diameter and sap flux density of both species had obvious diurnal rhythms. The maximum daily shrinkage was positively correlated with daily sap flux density. The micro-variation of stem diameter at the daily scale was affected by transpiration during the day. The maximum daily shrinkage of stem diameter was positively correlated and well fitted with transpiration driving factors (solar radiation, vapor pressure deficit, and the integrated variable VT). The difference in slopes of regression curves suggested that the daily variation of stem diameter in Q. liaotungensis was greater and more sensitive to meteorological factors than that in R. pseudoacacia. The sap flux densities of both tree species were higher during the period with relatively higher soil water content than that with lower soil water content. The difference of maximum daily diameter shrinkage between different soil water conditions was statistically significant in Q. liaotungensis, but not in R. pseudoacacia. These differences may be related to water use strategies, including transpiration regulation and stem water replenishment.

[Time lag of stem sap flow and its relationships with transpiration characteristics in Quercus liaotungensis and Robina pseudoacacia in the loess hilly region, China]. / é»„åœŸä¸˜é™µåŒºè¾½ä¸œæ Žå’Œåˆºæ§æ ‘å¹²æ¶²æµæ—¶æ»žæ•ˆåº”ä¸Žè’¸è ¾ç‰¹å¾çš„å ³è”æ€§.

Using Granier-type thermal dissipation probes (TDP), we measured stem xylem sap flow of the natural dominant species Quercus liaotungensis and a reforestation species Robinia pseudoacacia from July to September in 2016 in the semiarid loess hilly region. Meteorological factors and soil water content were simultaneously monitored during the study period. Using cross-correlation analysis, time lag between diurnal patterns of sap flux density and vapor pressure deficit (VPD) was quantitatively estimated. Differences in the time lag between the two species and possible influence by different diameter classes and soil water contents were analyzed. The results showed that the diurnal courses of sap flux density were similar to those of meteorological factors, with daily peaks ear-lier than VPD. The peak of VPD lagged behind the sap flux densities of Q. liaotungensis and R. pseudoacacia 118.2 min and 39.5 min, respectively. The peak of PAR lagged behind the sap flux density of Q. liaotungensis 12.4 min, but was 68.5 min ahead of that for R. pseudoacacia. Time lag between sap flux density and VPD significantly varied between tree species and was affected by soil water content. Those during higher soil water content period were about 32.2 min and 68.2 min longer than those during the period with lower soil water content for the two species, respectively. There was no correlation between time lag and tree diameter classes. The time lag between VPD and sap flux density for R. pseudoacacia was about 21.4 min longer in smaller diameter trees than in larger trees, which was significantly different under the lower soil water content. Our results suggested that the time lag effect between VPD and sap flux densities in the two species reflected their sensitivities to driving factors of transpiration, and that higher soil water content was favorable to sap flux density reaching its peak early. The lower soil water content might lead to lower sensitivity of the trees to meteorological factors. R. pseudoacacia was more sensitive to changes of soil water content.

Climatic and Soil Factors Shape the Demographical History and Genetic Diversity of a Deciduous Oak (Quercus liaotungensis) in Northern China.

Past and current climatic changes have affected the demography, patterns of genetic diversity, and genetic structure of extant species. The study of these processes provides valuable information to forecast evolutionary changes and to identify conservation priorities. Here, we sequenced two functional nuclear genes and four chloroplast DNA regions for 105 samples from 21 populations of Quercus liaotungensis across its distribution range. Coalescent-based Bayesian analysis, approximate Bayesian computation (ABC), and ecological niche modeling (ENM) were integrated to investigate the genetic patterns and demographical history of this species. Association estimates including Mantel tests and multiple linear regressions were used to infer the effects of geographical and ecological factors on temporal genetic variation and diversity of this oak species. Based on multiple loci, Q. liaotungensis populations clustered into two phylogenetic groups; this grouping pattern could be the result of adaptation to habitats with different temperature and precipitation seasonality conditions. Demographical reconstructions and ENMs suggest an expansion decline trend of this species during the Quaternary climatic oscillations. Association analyses based on nuclear data indicated that intraspecific genetic differentiation of Q. liaotungensis was clearly correlated with ecological distance; specifically, the genetic diversity of this species was significantly correlated with temperature seasonality and soil pH, but negatively correlated with precipitation. Our study highlights the impact of Pleistocene climate oscillations on the demographic history of a tree species in Northern China, and suggests that climatic and soil conditions are the major factors shaping the genetic diversity and population structure of Q. liaotungensis.

[Sap flow characteristics of Quercus liaotungensis in response to sapwood area and soil moisture in the loess hilly region, China]. / é»„åœŸä¸˜é™µåŒºè¾½ä¸œæ Žæ ‘å¹²æ¶²æµç‰¹å¾å¯¹è¾¹æé¢ç§¯å’ŒåœŸå£¤æ°´åˆ†çš„å“åº”.

To examine the characteristics of sap flow in Quercus liaotungensis and their response to environmental factors under different soil moisture conditions, Granier-type thermal dissipation probes were used to measure xylem sap flow of trees with different sapwood area in a natural Q. liaotungensis forest in the loess hilly region. Solar radiation, air temperature, relative air humidity, precipitation, and soil moisture were monitored during the study period. The results showed that sap flux of Q. liaotungensis reached daily peaks earlier than solar radiation and vapor pressure deficit. The diurnal dynamics of sap flux showed a similar pattern to those of the environmental factors. Trees had larger sap flux during the period with higher soil moisture. Under the same soil moisture conditions, trees with larger diameter and sapwood areas had significantly higher sap flux than those with smaller diameter and sapwood areas. Sap flux could be fitted with vapor pressure deficit, solar radiation, and the integrated index of the two factors using exponential saturation function. Differences in the fitted curves and parameters suggested that sap flux tended to reach saturation faster under higher soil moisture. Furthermore, trees in the smaller diameter class were more sensitive to the changes of soil moisture. The ratio of daily sap flux per unit vapor pressure deficit under lower soil moisture condition to that under higher soil moisture condition was linearly correlated to sapwood area. The regressive slope in smaller diameter class was larger than that in bigger diameter class, which further indicated the higher sensitivity of trees with smaller diameter class to soil moisture. These results indicated that wider sapwood of larger diameter class provided a buffer against drought stress.

[Effects of thinning intensities on reproductive modules of Quercus liaotungensis in Huanglong and Qiaoshan Mountains, Northwest China]. / é—´ä¼å¼ºåº¦å¯¹é»„æ¡¥æž—åŒºè¾½ä¸œæ Žç”Ÿæ®–æž„ä»¶çš„å½±å“.

Taking the Quercus liaotungensis middle-aged forests in Huanglong and Qiaoshan Mountains as study objects, the average size of individual trees of Q. liaotungensis, yield and rate of its reproductive modules, as well as their spatial distribution characteristics were investigated in five years after thinning at different intensities (CK, 10%, 20% and 30%), in order to demonstrate the impact of thinning intensity on reproductive modules of Q. liaotungensis. Thinning intensity had no significant effect on average height and average DBH, while it had significant positive correlation with crown area and crown volume. The yield of generative shoots, young fruits and mature fruits increased with thinning intensity, but vegetative shoots, staminate inflorescence, staminate flowers and pistillate flowers of Q. liaotungensis had little change. The yield of generative shoots, young fruits and mature fruits had raised significantly under 20% thinning, and reached the maximum under 30% thinning intensity. The rate of generative shoots and fruit setting rate increased with thinning intensity, and reached significant level under 20% or 30% thinning compared with the control. About three-quarters of the generative shoots, female and male flowers centered in the upper canopy, and the rest were in the lower part. Numbers of reproductive modules at sunny side accounted for about 65% of the total. The lower crown, shaded generative shoots, pistillate flowers and staminate inflorescence increased with the increasing thinning intensity, and the upper crown, sunny generative shoots, pistillate flowers and staminate inflorescence showed a decreasing trend with the increasing thinning intensity. Thinning at the intensity of 30% (canopy density 0.6) was the best, which could greatly improve the fruit set percentage of Q. liaotungensis and its mature rate, so as to improve the seed yield and quality, providing the guarantee for the seed collection and natural regeneration of Q. liaotungensis forests.

[Whole-tree sap flow of Quercus liaotungensis and Populus davidiana in response to environmental factors in the loess plateau area of western Shanxi Province, northern China.] / æ™‹è¥¿é»„åœŸåŒºè¾½ä¸œæ Žå’Œå±±æ¨æ ‘å¹²æ¶²æµå¯¹çŽ¯å¢ƒå› å­çš„å“åº”.

Sap flow velocity (SFV) of Quercus liaotungensis and Populus davidiana, which are two main tree species of secondary forests in the Loess Plateau area of western Shanxi Pro-vince, was measured using a thermal dissipation probe during the growing season from April to October 2012. The responses of SFV to vapor pressure deficit (VPD), photosynthetically active radiation (PAR), air temperature (T) and soil water content (θ) were investigated. The results showed that the diurnal changes of SFV of Q. liaotungensis and P. davidiana were mainly influenced by VPD and PAR in May and June, whereas VPD and T were the determining meteorological factors for the diurnal changes of SFV in July and August. Besides the meteorological factors, θ also had an important effect on SFV. The increases in θ during rainfall events resulted in the increases in SFV of both the two tree species. The average SFV of Q. liaotungensis after rainfall events was 28.3％, 48.6％, 16.9％ and 11.5％ higher than that before rainfall events in May, June, July and August, respectively. The average SFV of P. davidiana only increased, respectively, 0.6％, 4.5％ and 2.3％ after rainfall events in June, July and August. It showed that Q. liaotungensis had a higher water demand and was more sensitive to soil water condition than P. davidiana, while the latter could mana-ge its water consumption more conservatively after raining. The relationship between SFV and VPD could be approximately expressed using an exponential saturation function. The change of the parameters of the fitted exponential saturation function indicated that the SFV could quickly reach its maximum value as soil moisture increased.

[Effect of thinning intensities on fruiting regularities of Quercus liaotungensis forests in Huang-long and Qiaoshan mountains.] / é—´ä¼å¼ºåº¦å¯¹é»„æ¡¥æž—åŒºè¾½ä¸œæ Žæž—ç»“å®žè§„å¾‹çš„å½±å“.

In order to clarify the impact of thinning intensities on fruiting regularity of Quercus liaotungensis forests, we took the Q. liaotungensis half-mature forests in Huanglong and Qiaoshan mountains on south of the Loess Plateau as the object of study, which were under close-to-natural management of different thinning intensities (CK, 10%, 20% and 30%). An analysis was made on stand density and percent of seed trees, seed number of sample tree and unit area, seed spatial distributions, seed characteristics of the Q. liaotungensis forests after 5 years of thinning. The results showed that, percent of seed trees, seed number per sample tree and percent of developed seeds of Q. liaotungensis forests increased with the increasing intensity, and showed a pattern of 30%>20%>10%>CK. Seed number per area reached the maximum number under 20% thinning, and showed a pattern of 20%>30%>CK>10%. From the seed spatial distribution in the canopy, the upper accounted for 73.6%, while the lower had 26.4%. The sunny side of canopy layer set relatively the most fruits of 65.8%, shady side only had 34.2%. Under thinning, further improving was geater under lower canopy than under upper canopy and so was on shady side than on sunny side. The seed long diameter, seed short diameter and 1000-seed mass of Q. liaotungensis forests increased with the increasing intensity, which reached the maximum under 30% thinning. 10% thinning did not significantly impact Q. liaotungensis fruiting, the thinning intensity of 20% was most conducive to the seed quantity and quality improvement of Q. liaotungensis, while the thinning intensity of 30% did not improve the fruiting, and lowered the total number of seeds. It was proposed that 20% thinning should be chosen (canopy density of 0.7) to effectively improve fruiting and quality of Q. liaotungensis.