Responses of sap flow in Larix principis-rupprechtii to environment under different weather conditions.

This study was conducted in Liupanshan Forest Ecological Positioning Station of the National Forestry and Grassland Administration. We monitored sap flow of Larix principis-rupprechtii plantation in the Xiangshui River sub-basin throughout the 2019 growing season (from May 17 to October 12), as well as the meteorological conditions and soil environment (soil temperature and soil water content), to analyze the comprehensive environmental responses of sap flow in L. principis-rupprechtii under different weather conditions. The results showed that sap flow rate increased and then decreased on the daily scale, with the highest rate on sunny days, followed by overcast days and then rainy days. Sap flow rate had a single peak on sunny days and multiple peaks on overcast and rainy days. Sunny days had earlier and longer sap flow compared to overcast and rainy days. Dominant factors driving sap flow differed across different weather. Vapor pressure deficit was the dominant factor influencing sap flow in sunny and overcast days, while solar radiation was dominant one in rainy days. The contribution rates of main factors to sap flow on sunny, overcast and rainy days were 31.1%, 27.4% and 40.1%, respectively. Results of the principal component analysis showed the factors affecting sap flow on sunny days could be classified into hydrothermal complex factors (air temperature, soil temperature, and volumetric soil moisture), water vapor transpiration factors (relative humidity and vapor pressure deficit), and radiation factor (solar radiation). The factors affecting sap flow on overcast and rainy days were combined into transpiration (relative humidity, solar radiation, and vapor pressure deficit), heat (air temperature and soil temperature), and soil water factor volumetric (volumetric soil moisture). On sunny days, sap flow reached the peak value 110, 80, 70 min after the hydrothermal, water vapor transpiration, and radiation factors, respectively. On overcast and rainy days, sap flow reached its peak in 10, 20, 30 min and 140, 60, 150 min, respectively before the peaks of transpiration, heat, and soil water factors.

Response of leaf anatomical structure of Larix gmelinii to climate warming and provenance variation.

Exploring the response of leaf anatomical structure to climate warming is helpful for understanding the adaptive mechanisms of trees to climate change. We conducted a warming experiment by transplanting seedlings of Larix gmelinii from 11 provenances to two common gardens, and examined the response of leaf anatomical structure to climate warming. The results showed that warming significantly increased leaf thickness (TL), upper epidermal mesophyll thickness (TUEM), lower epidermal mesophyll thickness (TLEM), endodermal thickness (TE), vascular bundle diameter (DVB), transfer tissue thickness (TTT), and the percentage of mesophyll thickness to TL(PMT), and significantly decreased the upper epidermal thickness (TUE) and the percentage of epidermal thickness to TL (PE). The mesophyll thickness was positively associated with chlorophyll concentration and maximum net photosynthetic rate. The responses of TL, TUEM, TLEM, TE, DVB, TTT, TUE, PMT and PE to warming differed among all the provenances.As the aridity index of the original site increased, the magnitude of the warming treatment's effect decreased for TL, TUEM, TLEM, TTT and PMT, and increased for TUE and PE. Warming increased the thickness and proportion of profit tissue (e.g., mesophyll) and decreased the thickness and proportion of defensive tissue (e.g., epidermis), and those changes varied among provenances. L. gmelinii could adapt to climate warming by adjusting leaf anatomical structure, and this ability was weak for trees from provenance with high aridity index.

Function of MYB8 in larch under PEG simulated drought stress.

Larch, a prominent afforestation, and timber species in northeastern China, faces growth limitations due to drought. To further investigate the mechanism of larch's drought resistance, we conducted full-length sequencing on embryonic callus subjected to PEG-simulated drought stress. The sequencing results revealed that the differentially expressed genes (DEGs) primarily played roles in cellular activities and cell components, with molecular functions such as binding, catalytic activity, and transport activity. Furthermore, the DEGs showed significant enrichment in pathways related to protein processing, starch and sucrose metabolism, benzose-glucuronic acid interconversion, phenylpropyl biology, flavonoid biosynthesis, as well as nitrogen metabolism and alanine, aspartic acid, and glutamic acid metabolism. Consequently, the transcription factor T_transcript_77027, which is involved in multiple pathways, was selected as a candidate gene for subsequent drought stress resistance tests. Under PEG-simulated drought stress, the LoMYB8 gene was induced and showed significantly upregulated expression compared to the control. Physiological indices demonstrated an improved drought resistance in the transgenic plants. After 48 h of PEG stress, the transcriptome sequencing results of the transiently transformed LoMYB8 plants and control plants exhibited that genes were significantly enriched in biological process, cellular component and molecular function. Function analyses indicated for the enrichment of multiple KEGG pathways, including energy synthesis, metabolic pathways, antioxidant pathways, and other relevant processes. The pathways annotated by the differential metabolites mainly encompassed signal transduction, carbohydrate metabolism, amino acid metabolism, and flavonoid metabolism.

Different drought recovery strategy between Larix spp. and Quercus mongolica in temperate forests.

Forests are experiencing increasingly severe drought stress worldwide. Although most studies have quantified how tree growth was affected by extreme droughts, how trees recover from different drought intensities are still poorly understood for different species. We used a network of tree-ring data comprising 731 Quercus mongolica trees across 29 sites, 312 Larix olgensis Henry trees from 13 sites, and 818 Larix principis-rupprechtii trees from 34 sites, covering most of their distribution range in northern China, to compare the influences of drought intensity on post-drought recovery. The results showed that summer droughts had strong negative influences on tree growth. Post-drought growth varied with drought intensity for the three species. Larix species exhibited strong legacy effects after severe droughts, which is related to the lack of compensatory growth. In contrast, the compensatory growth of Q. mongolica reduced drought legacy effect. However, the compensatory growth of Q. mongolica gradually weaken with increasing drought intensity and disappeared during severe drought. Our findings indicated that influence of drought on Q. mongolica growth mainly shown in drought years, but Larix species suffered from long-term drought legacy effects, implying Q. mongolica rapidly recovered from droughts but Larix species need several years to recover from droughts, thus the two genera have different recovery strategy.

Contrasting water-use strategies to climate warming in white birch and larch in a boreal permafrost region.

The effects of rising atmospheric CO2 concentrations (Ca) with climate warming on intrinsic water-use efficiency and radial growth in boreal forests are still poorly understood. We measured tree-ring cellulose δ13C, δ18O, and tree-ring width in Larix dahurica (larch) and Betula platyphylla (white birch), and analyzed their relationships with climate variables in a boreal permafrost region of northeast China over past 68 years covering a pre-warming period (1951-1984; base period) and a warm period (1985-2018; warm period). We found that white birch but not larch significantly increased their radial growth over the warm period. The increased intrinsic water-use efficiency in both species was mainly driven by elevated Ca but not climate warming. White birch but not larch showed significantly positive correlations between tree-ring δ13C, δ18O and summer maximum temperature as well as vapor pressure deficit in the warm period, suggesting a strong stomatal response in the broad-leaved birch to temperature changes. The climate warming-induced radial growth enhancement in white birch is primarily associated with a conservative water-use strategy. In contrast, larch exhibits a profligate water-use strategy. It implies an advantage for white birch over larch in the warming permafrost regions.

Rapid migration of Mongolian oak into the southern Asian boreal forest.

The migration of trees induced by climatic warming has been observed at many alpine treelines and boreal-tundra ecotones, but the migration of temperate trees into southern boreal forest remains less well documented. We conducted a field investigation across an ecotone of temperate and boreal forests in northern Greater Khingan Mountains of northeast China. Our analysis demonstrates that Mongolian oak (Quercus mongolica), an important temperate tree species, has migrated rapidly into southern boreal forest in synchrony with significant climatic warming over the past century. The average rate of migration is estimated to be 12.0 ± 1.0 km decade-1 , being slightly slower than the movement of isotherms (14.7 ± 6.4 km decade-1 ). The migration rate of Mongolian oak is the highest observed among migratory temperate trees (average rate 4.0 ± 1.0 km decade-1 ) and significantly higher than the rates of tree migration at boreal-tundra ecotones (0.9 ± 0.4 km decade-1 ) and alpine treelines (0.004 ± 0.003 km decade-1 ). Compared with the coexisting dominant boreal tree species, Dahurian larch (Larix gmelinii), temperate Mongolian oak is observed to have significantly lower capacity for light acquisition, comparable water-use efficiency but stronger capacity to utilize nutrients especially the most limiting nutrient, nitrogen. In the context of climatic warming, and in addition to a high seed dispersal capacity and potential thermal niche differences, the advantage of nutrient utilization, reflected by foliar elementomes and stable nitrogen isotope ratios, is also likely a key mechanism for Mongolian oak to coexist with Dahurian larch and facilitate its migration toward boreal forest. These findings highlight a rapid deborealization of southern Asian boreal forest in response to climatic warming.

[Responses of radial growth of Larix principis-rupprechtii to abrupt warming]. / 华北落叶松径向生长对升温突变的响应.

To investigate the impacts of abrupt warming on tree growth, we collected tree ring cores from larch (Larix principis-rupprechtii) in three different sites, including Saihanba National Nature Reserve, Pangquangou National Nature Reserve, and Fengning Qiansongba National Forest Park. Based on the tree ring method, Mann-Kendall test was used to examine the occurrence time of temperature rise mutation. We further analyzed the radial growth law of larch before and after the temperature mutation and its correlation with the monthly climate data. The results showed that the sudden temperature rise occurred in the Saihanba area in 1987, the Fengning area in 1989, and the Pangquangou area 1994. Before the sudden warming, there was no significant trend for the radial growth in all the three regions. After the sudden warming, however, it decreased significantly (with a decrease rate of 0.08·10 a-1) in Saihanba area. The radial growth of larch increased significantly in Pangquangou area (with an increase rate of 0.10·10 a-1), while no significant change was observed in the Fengning area. Before the sudden warming, there was a significant positive correlation between the radial growth of larch in the Saihanba area and the highest temperature in May and June. After the sudden warming, there was a significant positive correlation with precipita-tion in July, and a highly significant positive correlation with the standardized precipitation evapotranspiration index(SPEI) from September of the previous year to July. Prior to the sudden warming, there was no significant relationship between the radial growth of larch in the Pangquangou area and monthly climate factors. However, after the sudden warming, a significant positive correlation was found with the lowest temperature in September of the pre-vious year. Before the sudden warming, the radial growth of larch in Fengning area was significantly negatively correlated with the lowest average temperature in July. After the sudden warming, it showed a significant negative correlation with the average and highest temperatures in June. Accordingly, the radial growth of larch in the Saihanba area experienced drought stress following a sudden temperature change. If temperature continues to rise in the future, larch in the Fengning area would also face drought stress. Conversely, warming conditions would be beneficial for the radial growth of larch in the Pangquangou area.

Do epiphytic lichens negatively impact their hosts through allelopathy? The effect of Evernia esorediosa on growth and biochemical processes of Larix gmelinii.

The question of the nature of the interaction between epiphytic lichens and their host trees remains highly debated. Some authors showed cases of allelopathy, but this needs further investigation. Our study covers the effects caused by the epiphytic lichen Evernia esorediosa (Müll. Arg.) Du Rietz on growth and biochemical processes in Larix gmelinii (Rupr.) Rupr. ex Kuzen trees in cryolithozone boreal forests. Usnic acid (UA) is shown to migrate from the thalli of E. esorediosa in the bark and phloem of L. gmelinii, from which it is transported to the root system of the tree, and then UA is moved upward through the xylem into tree needles. Accumulation of UA in L. gmelinii needles causes the following effects: inhibition of photosynthesis, cellular respiration and oxidative phosphorylation. These disruptions could reflect on the tree growth processes. The L. gmelinii trees inhabited by the epiphytic lichen E. esorediosa were found to show lower radial and apical growth parameters. Our results show that E. esorediosa exhibits an allelopathic effect toward L. gmelinii through the migration of UA from the lichen thalli to the tissues of the tree, which led to inhibition of energetic processes in cells. This caused the tree growth to slow down and could ultimately lead to its death.

Reassessment of growth-climate relations indicates the potential for decline across Eurasian boreal larch forests.

Larch, a widely distributed tree in boreal Eurasia, is experiencing rapid warming across much of its distribution. A comprehensive assessment of growth on warming is needed to comprehend the potential impact of climate change. Most studies, relying on rigid calendar-based temperature series, have detected monotonic responses at the margins of boreal Eurasia, but not across the region. Here, we developed a method for constructing temporally flexible and physiologically relevant temperature series to reassess growth-temperature relations of larch across boreal Eurasia. Our method appears more effective in assessing the impact of warming on growth than previous methods. Our approach indicates widespread and spatially heterogeneous growth-temperature responses that are driven by local climate. Models quantifying these results project that the negative responses of growth to temperature will spread northward and upward throughout this century. If true, the risks of warming to boreal Eurasia could be more widespread than conveyed from previous works.

Precipitation regulates the responses of xylem phenology of two dominant tree species to temperature in arid and semi-arid forest of the southern Altai Mountains.

Arid and semi-arid forests are important carbon sinks, with implications for the global carbon balance. However, the impacts of climate warming on the growth of arid and semi-arid forest tree species and ecosystem carbon sink dynamics remain uncertain because the effects of the complex interactions between precipitation and temperature on xylem phenology are not clearly understood. Here, we monitored xylem formation over two years in two dominant tree species (Siberian larch, Larix sibirica Ledeb.; Siberian spruce, Picea obovata Ledeb.) along the arid and semi-arid southern Altai Mountains of Central Asia. We determined that temperature interaction with precipitation plays a key role in regulating xylem phenology of these two species, with differences between species. Under rising mean annual temperatures, the growth of L. sibirica advanced as the onset of xylem formation was not limited by early season water availability. However, the earlier cessation of cell enlargement, likely due to legacy effects, compensated for such advancement. In contrast, water stress constrained the advancement of xylem formation under rising temperatures in P. obovata. Nevertheless, water stress was seemingly relieved later in the growing season and consequently did not lead to the earlier cessation of xylem formation. Our results demonstrate that precipitation drives species-specific response to rising temperatures and thus is a key driver of growing season length and carbon sink dynamics in arid and semi-arid forests under climate warming. Integrating the effects of temperature and precipitation on xylem phenology in climate models may improve estimates of climate-carbon feedback in arid and semi-arid forests under future warming scenarios.

Stable isotopes in tree rings record physiological trends in Larix gmelinii after fires.

Fire is an important regulator of ecosystem dynamics in boreal forests, and in particular has a complicated association with growth and physiological processes of fire-tolerant tree species. Stable isotope ratios in tree rings are used extensively in eco-physiological studies for evaluating the impact of past environmental (e.g., drought and air pollution) factors on tree growth and physiological processes. Yet, such studies based on carbon (δ13C) and oxygen (δ18O) isotope ratios in tree rings are rarely conducted on fire effect, and are especially not well explored for fire-tolerant trees. In this study, we investigated variations in basal area increment and isotopes of Larix gmelinii (Rupr.) Rupr. before and after three moderate fires (different fire years) at three sites across the Great Xing'an Mountains, Northeastern China. We found that the radial growth of L. gmelinii trees has significantly declined after the fires across study sites. Following the fires, a simultaneous increase in δ13C and δ18O has strengthened the link between the two isotopes. Further, fires have significantly enhanced the 13C-derived intrinsic water-use efficiency (iWUE) and largely altered the relationships between δ13C, δ18O, iWUE and climate (temperature and precipitation). A dual-isotope conceptual model revealed that an initial co-increase in δ13C and δ18O in the fire year can be mainly attributed to a reduction in stomatal conductance with a constant photosynthetic rate. However, this physiological response would shift to different patterns over post-fire time between sites, which might be partly related to spring temperature. This study is beneficial to better understand, from a physiological perspective, how fire-tolerant tree species adapt to a fire-prone environment. It should also be remembered that the limitation of model assumptions and constraints may challenge model applicability and further inferred physiological response.

Tree-ring isotopes from the Swiss Alps reveal non-climatic fingerprints of cyclic insect population outbreaks over the past 700 years.

Recent experiments have underlined the potential of δ2H in tree-ring cellulose as a physiological indicator of shifts in autotrophic versus heterotrophic processes (i.e., the use of fresh versus stored non-structural carbohydrates). However, the impact of these processes has not yet been quantified under natural conditions. Defoliator outbreaks disrupt tree functioning and carbon assimilation, stimulating remobilization, therefore providing a unique opportunity to improve our understanding of changes in δ2H. By exploring a 700-year tree-ring isotope chronology from Switzerland, we assessed the impact of 79 larch budmoth (LBM, Zeiraphera griseana [Hübner]) outbreaks on the growth of its host tree species, Larix decidua [Mill]. The LBM outbreaks significantly altered the tree-ring isotopic signature, creating a 2H-enrichment and an 18O- and 13C-depletion. Changes in tree physiological functioning in outbreak years are shown by the decoupling of δ2H and δ18O (O-H relationship), in contrast to the positive correlation in non-outbreak years. Across the centuries, the O-H relationship in outbreak years was not significantly affected by temperature, indicating that non-climatic physiological processes dominate over climate in determining δ2H. We conclude that the combination of these isotopic parameters can serve as a metric for assessing changes in physiological mechanisms over time.

Anatomical observation and transcriptome analysis of buds reveal the association between the AP2 gene family and reproductive induction in hybrid larch (Larix kaempferi × Larix olgensis).

Hybrid larch is an excellent afforestation species in northern China. The instability of seed yield is an urgent problem to be solved. The biological characteristics related to seed setting in larch are different from those in angiosperms and other gymnosperms. Studying the developmental mechanism of the larch sporophyll can deepen our understanding of conifer reproductive development and help to ensure an adequate supply of seeds in the seed orchard. The results showed that the formation of microstrobilus primordia in hybrid larch could be observed in anatomical sections collected in the middle of July. The contents of endogenous gibberellin 3 (GA3) and abscisic acid (ABA) were higher and the contents of GA4, GA7, jasmonic acid and salicylic acid were lower in multiseeded larch. Transcriptome analysis showed that transcription factors were significantly enriched in the AP2 family. There were 23 differentially expressed genes in the buds of the multiseeded and less-seeded types, and the expression of most of these genes was higher in the buds than in the needles. We conclude that mid-July is the early stage of reproductive organ development in hybrid larch and is suitable for the study of reproductive development. GA3 and ABA may be helpful for improving seed setting in larch, and 23 AP2/EREBP family genes are involved in the regulation of reproductive development in larch.

[Intra-annual radial growth of Abies georgei and Larix potaninii and its responses to environmental factors in the Baima Snow Mountain, Northwest Yunnan, China.] / æ»‡è¥¿åŒ—ç™½é©¬é›ªå±±é•¿è‹žå†·æ‰å’Œå¤§æžœçº¢æ‰å¹´å† å¾„å‘ç”Ÿé•¿åŠ¨æ€åŠå ¶å¯¹çŽ¯å¢ƒå› å­çš„å“åº”.

Using high-resolution dendrometers, we monitored the intra-annual stem radial variations of Abies georgei and Larix potaninii in the subalpine coniferous forest in Baima Snow Mountain, Northwest Yunnan Province. The seasonal dynamics of stem radial growth of both species and their responses to environmental factors were analyzed. The results showed that the stem radial growth of A. georgei and L. potaninii mainly occurred during April to August, with the maximum growth rate in June. Compared with A. georgei, L. potaninii showed an earlier start but later cessation of stem radial growth, resulting in longer growth duration. Annual radial growth and maximum radial growth rates of L. potaninii were slightly higher than those of A. georgei. Daily growth rate of A. georgei was positively correlated with precipitation, but negatively correlated with vapor pressure deficit and air temperature. Daily growth rate of L. potaninii was positively correlated with precipitation, but negatively correlated with soil volume water content and vapor pressure deficit. Radial growth of A. georgei and L. potaninii was limited by water availability, with L. potaninii being more sensitive to moisture. Under the background of global warming, the increase of plant transpiration and soil evaporation might further aggravate soil water loss and reduce water availability for plants, which would make A. georgei and L. potaninii more vulnerable to drought stress.

Genetic transformation of LoHDZ2 and analysis of its function to enhance stress resistance in Larix olgensis.

To study the function of LoHDZ2 in larch, we first constructed a VB191103-LoHDZ2::GUS overexpression vector. Through Agrobacterium-mediated infection, the expression vector was transferred into a larch embryogenic cell line. A stable resistant cell line was subsequently screened, and mature embryos were induced to grow until they developed into seedlings. Antagonistic cell lines were identified at both the DNA and RNA levels. The transgenic cell lines were then subjected to GUS staining, and transgenic cell lines were ultimately identified and obtained. These transgenic cell lines were sequenced to identify differentially expressed genes, and a cluster analysis was performed. The resistant cell lines were cultured under stress conditions involving 20% PEG6000 and 200 mM NaCl proliferation media (1/10-BM). After the stress treatment, the contents of peroxidase (POD), malondialdehyde (MDA) and superoxide dismutase (SOD) in both wild-type and transgenic cell lines were measured. The results are summarized below: (1) When the specific fragment of the target gene in the genome of the resistant cell line was amplified. At the RNA level, the expression of the fragment in four resistant lines increased. In addition, GUS staining showed a blue reaction, indicating that LoHDZ2 was successfully integrated into the larch embryonic cell lines. (2) To verify the accuracy and reliability of the transcriptome data, 10 differentially expressed genes (5 upregulated and 5 down regulated genes) were subjected to qRT-PCR verification. The results showed that the expression trend of the 10 differentially expressed genes was the same as that revealed by RNA-Seq, indicating that the transcriptome data were reliable. (3) The transcriptome sequencing showed that 176 genes were upregulated and that 140 genes were down regulated. Through GO enrichment analysis and KEGG metabolic pathway analysis, the screened differentially expressed genes were related to biological processes such as larch metabolism and response to stimuli, indicating that these genes may be closely involved in the regulation of the larch response to external stimuli, including heat stress, drought stress, metal ion stress and bacterial infection, and may participate in the growth process. (4) After 20% PEG6000 treatment, the POD enzyme activity of the transgenic cell line was greater than that of the wild-type; this activity could effectively remove the amount of peroxide produced. The MDA content of the transgenic cell lines was lower than that of the wild-type cell lines, and the accumulation degree of harmful substances was low, indicating that the degree of oxidative damage of the transgenic cell lines was lower than that of the wild-type cell lines. The SOD content of the transgenic cell lines was lower than that of the wild-type cell lines, indicating that the drought resistance of the transgenic cell lines was enhanced. After 200 mM NaCl treatment, although the increase in SOD content was not obvious, the same trend was detected, indicating that the resistance of the transgenic cell lines was indeed stronger than that of the wild-type cell lines. According to the results of previous experiments, after this gene was overexpressed in tobacco, the transformed plants showed obvious dwarfing, which may indicate that the stress resistance of the plant was enhanced. In conclusion, a transgenic larch cell line was successfully obtained, and transgenic larch seedlings were successfully induced. LoHDZ2 may participate in the response of plants to the external environment, and may participate in the growth and development of Larix olgensis by affecting plant metabolic pathways.

Effects of photosynthetic models on the calculation results of photosynthetic response parameters in young Larix principis-rupprechtii Mayr. plantation.

Accurately predicting the crown photosynthesis of trees is necessary for better understanding the C circle in terrestrial ecosystem. However, modeling crown for individual tree is still challenging with the complex crown structure and changeable environmental conditions. This study was conducted to explore model in modeling the photosynthesis light response curve of the tree crown of young Larix principis-rupprechtii Mayr. Plantation. The rectangular hyperbolic model (RHM), non-rectangular hyperbolic model (NRHM), exponential model (EM) and modified rectangular hyperbolic model (MRHM) were used to model the photosynthetic light response curves. The fitting accuracy of these models was tested by comparing determinants coefficients (R2), mean square errors (MSE) and Akaike information criterion (AIC). The results showed that the mean value of R2 of MRHM (R2 = 0.9687) was the highest, whereas MSE value (MSE = 0.0748) and AIC value (AIC = -39.21) were the lowest. The order of fitting accuracy of the four models for Pn-PAR response curve was as follows: MRHM > EM > NRHM > RHM. In addition, the light saturation point (LSP) obtained by MRHM was slightly lower than the observed values, whereas the maximum net photosynthetic rates (Pmax) modeled by the four models were close to the measured values. Therefore, MRHM was superior to other three models in describing the photosynthetic response curve, the accurate values were that the quantum efficiency (α), maximum net photosynthetic rate (Pmax), light saturation point (LSP), light compensation point (LCP) and respiration rate (Rd) were 0.06, 6.06 µmol·m-2s-1, 802.68 µmol·m-2s-1, 10.76 µmol·m-2s-1 and 0.60 µmol·m-2s-1. Moreover, the photosynthetic response parameters values among different layers were also significant. Our findings have critical implications for parameter calibration of photosynthetic models and thus robust prediction of photosynthetic response in forests.

Functional Characteristics Analysis of Dehydrins in Larix kaempferi under Osmotic Stress.

Dehydrins (DHN) belong to the late embryogenesis abundant II family and have been found to enhance plant tolerance to abiotic stress. In the present study, we reported four DHNs in Larix kaempferi (LkDHN) which were identified from the published transcriptome. Alignment analysis showed that these four LkDHNs shared close relationships and belonged to SK3-type DHNs. The electrophoretic mobility shift assay indicated that these four LkDHNs all possess sequence-independent binding capacity for double-strands DNAs. The subcellular localizations of the four LkDHNs were in both the nucleus and cytoplasm, indicating that these LkDHNs enter the nucleus to exert the ability to bind DNA. The preparation of tobacco protoplasts with different concentrations of mannitol showed that LkDHNs enhanced the tolerance of plant cells under osmotic stress. The overexpression of LkDHNs in yeasts enhanced their tolerance to osmotic stress and helped the yeasts to survive severe stress. In addition, LkDHNs in the nucleus of salt treated tobacco increased. All of these results indicated that the four LkDHNs help plants survive from heavy stress by participating in DNA protection. These four LKDHNs played similar roles in the response to osmotic stress and assisted in the adaptation of L. kaempferi to the arid and cold winter of northern China.

Determination of the most effective design for the measurement of photosynthetic light-response curves for planted Larix olgensis trees.

A photosynthetic light-response (PLR) curve is a mathematical description of a single biochemical process and has been widely applied in many eco-physiological models. To date, many PLR measurement designs have been suggested, although their differences have rarely been explored, and the most effective design has not been determined. In this study, we measured three types of PLR curves (High, Middle and Low) from planted Larix olgensis trees by setting 31 photosynthetically active radiation (PAR) gradients. More than 530 million designs with different combinations of PAR gradients from 5 to 30 measured points were conducted to fit each of the three types of PLR curves. The influence of different PLR measurement designs on the goodness of fit of the PLR curves and the accuracy of the estimated photosynthetic indicators were analysed, and the optimal design was determined. The results showed that the measurement designs with fewer PAR gradients generally resulted in worse predicted accuracy for the photosynthetic indicators. However, the accuracy increased and remained stable when more than ten measurement points were used for the PAR gradients. The mean percent error (M%E) of the estimated maximum net photosynthetic rate (Pmax) and dark respiratory rate (Rd) for the designs with less than ten measurement points were, on average, 16.4 times and 20.1 times greater than those for the designs with more than ten measurement points. For a single tree, a unique PLR curve design generally reduced the accuracy of the predicted photosynthetic indicators. Thus, three optimal measurement designs were provided for the three PLR curve types, in which the root mean square error (RMSE) values reduced by an average of 8.3% and the coefficient of determination (R2) values increased by 0.3%. The optimal design for the High PLR curve type should shift more towards high-intensity PAR values, which is in contrast to the optimal design for the Low PLR curve type, which should shift more towards low-intensity PAR values.

[Interspecific difference of relationship between radial growth and climate factor for Larix olgensis and Picea jezoensis var. komarovii in Changbai Mountain, Northeast China.] / 长白山落叶松与鱼鳞云杉生长-æ°”å€™å ³ç³»çš„ç§é—´å·®å¼‚.

To clarify the responses of radial growth of different tree species to climate change and its stability, we explored the relationships between radial growth and climate factors of larch (Larix olgensis) and spruce (Picea jezoensis var. komarovii) distributed at high altitude (1600-1750 m) on the northern slope of Changbai Mountain, using the chronological method. The results showed that the growth of larch was significantly positively correlated with the maximum temperature in June and negatively correlated with the precipitation in June. The radial growth of spruce was significantly positively correlated with the maximum temperature in May. Results from redundancy analysis showed that larch growth was mainly affected by summer temperature, while spruce growth was significantly restricted by spring temperature. During 1959-2014, the relationship between larch growth and summer temperature was relatively stable. For spruce, the correlation between radial growth and spring temperatures had gradually weakened since 1986, mainly due to the growth slowdown because of decreased maximum air temperature. Our results provide theoretical references for predicting the growth response of conifers at Changbai Mountain region in the context of climate change.

[Effects of thinning on soil carbon and nitrogen fractions in a Larix olgensis plantation.] / æŠšè‚²é—´ä¼å¯¹é•¿ç™½è½å¶æ¾äººå·¥æž—åœŸå£¤ç¢³ã€æ°®åŠå ¶ç»„åˆ†çš„å½±å“.

Thinning, an important forest management strategy, can alter forest structure and stability, and consequently affect ecosystem biogeochemical cycles. The effects of thinning on soil carbon and nitrogen is far from conclusive especially due to the lack of long-term experiments. Here, we investigated soil carbon and nitrogen in Larix olgensis plantations in Mengjiagang Forest Farm, Heilongjiang Province, with four thinning treatments (i.e., 4 times low-intensity thinning, LT4; 3 times medium-intensity thinning, MT3; 2 times high-intensity thinning, HT2; and un-thinned control). The effects of thinning on soil total organic carbon and total nitrogen were examined from the perspective of the composition of labile and recalcitrant pools (labile carbon or nitrogen pool I; labile carbon or nitrogen pool II; and recalcitrant carbon or nitrogen pool) by an acid hydrolysis approach. The results showed that thinning significantly increased soil total organic carbon and nitrogen by 48.7%-50.3% and 28.9%-42.7%, respectively. The carbon and nitrogen contents in all the labile I, labile II, and recalcitrant pools were increased by thinning, with the magnitudes varying across different pools and thinning types. LT4, MT3, and HT2 improved the recalcitrant carbon by 71%, 69% and 75%, respectively, which was significantly higher than the increment of two labile carbon pools. In addition, the percentage of recalcitrant carbon in total organic carbon was increased by thinning. LT4 significantly increased microbial biomass and microbial quotient, but no significant change was found in MT3 and HT2 treatments. Overall, our results indicated that thinning might increase the input of soil recalcitrant carbon components such as suberin and lignin by producing more coarse woody residues, thus leading to decline of organic matter decomposition and ultimately enhancement of soil organic carbon.