Trade-offs between leaf stoichiometric characteristics and photosynthetic traits of Larix gmelinii and its differences among provenances.

Variations and trade-offs between leaf stoichiometric characteristics and photosynthetic traits are indicative of ecological adaptation strategies of plants and their responses to environment changes. In a common garden of Maoershan, we measured leaf stoichiometric characteristics (carbon content (C), nitrogen content (N), phosphorus content (P), C/N, C/P, N/P) and photosynthetic traits (maximum net photosynthetic rate (Amax), maximum electron transport rate (Jmax), maximum carboxylation rate (Vmax)) of Larix gmelinii from 17 geographical provenances. We examined the provenance differences in stoichiometric characteristics and photosynthetic traits, and analyzed their trade-offs and influencing factors. The results showed leaf stoichiometric characteristics and photosynthetic traits significantly differed among provenances. The climatic factors of seed-source sites explained 54.8% and 67.2% of the variation in stoichiometric characteristics and photosynthetic traits, respectively. Aridity index (AI) of seed-source sites was positively correlated with C, N, P, Amax, Jmax, Vmax, but negatively with C/N, C/P, and N/P. Results of redundancy analysis showed that stoichiometric characteristics accounted for 75.0% of the variation in photosynthetic traits. Amax, Jmax, Vmax were positively correlated with C, N, P, and negatively correlated with C/N, C/P, N/P. The provenance differences in stoichiometric characteristics, photosynthetic traits, and their synergistic relationship suggested the long-term adaptation of trees to the climate of seed-source sites. These findings were of great significance for understanding ecological adaptation strategies of trees in response to climate change.

Provenance variation of root C, N, P, and K stoichiometric characteristics under different diameter classes of Larix gmelinii.

For exploring the difference of root stoichiometric characteristics among diameter classes and provenances, we examined the contents and stoichiometric ratios of carbon (C), nitrogen (N), phosphorus (P), and potassium (K) in three diameter classes of roots (0-1, 1-2 and 2-5 mm, respectively) of 39-year-old Larix gmelinii grown in a common garden. The results showed that root element contents and their stoichiometric ratios had significant difference among three diameter classes of roots. C content, C:N, C:P, C:K were the lowest, and N, P, K contents, N:P, and N:K were the highest in 0-1 mm diameter class roots. Compared with the 1-2 and 2-5 mm diameter class roots, 0-1 mm diameter class roots had different seasonal dynamics, which might be caused by the fact that 0-1 mm diameter class roots are absorptive roots and the other diameter class roots are transport roots. There was no provenance difference in C content among all diameter class roots, while significant provenance differences were found in N, K contents, C:N, and C:K in 0-1 mm diameter class roots, and great provenance differences for in P content, C:P, N:P, and N:K in 0-1 and 1-2 mm diameter class roots. N content, K content, C:P, N:P, and N:K in 0-1 mm diameter class roots had positive correlation with the aridity index of seed-source sites, while the P content, C:N and C:K had negative correlations. The stoichiometric characteristics were related with the diameter (or function) of roots, and had significant provenance differences in 0-1 mm (absorptive root) and 1-2 mm diameter class roots, which might be attributed to their genotypic adaptation to the environment of seed-source sites.

[Temporal variation and influencing factors of albedo in a deciduous broad-leaved forest]. / è½å¶é˜”å¶æž—åç §çŽ‡çš„æ—¶é—´å˜åŒ–ä¸Žå½±å“å› ç´ .

In situ measurement of albedo is important for estimating ecosystem energy budget and its remote sensing application. However, the measurement method of albedo on sloping land is limited and the difference in temporal variation in albedo between visible and near-infrared bands remains unclear. Taking a deciduous broad-leaved forest at the Maoershan Forest Ecological Station in Northeast China as an example, we explored the temporal variation and influencing factors of albedo for three bands: incident and reflected solar radiation (SR, 300-2800 nm), photosynthetically active radiation (PAR, 400-700 nm), and near infrared radiation (NIR, 700-2800 nm). The temporal difference in albedo measurements between the two installation methods of radiometers was analyzed. The results showed that, in sunny days, the diurnal variation in SR and NIR albedo had an asymmetric U-shaped curve around the local noon, while PAR increased from sunrise to sunset. In cloudy days, the albedo decreased sharply and then tended to be stable. The measurement with parallel sensors to the slope increased the daily mean value of albedo, but reduced the daily asymmetry of SR and NIR. For the whole growing season, the maximum albedos of SR, NIR and PAR in horizontal measurement were 0.16, 0.27 and 0.11, respectively, and the minimums were 0.07, 0.11 and 0.03, respectively. Albedo in the SR and NIR wavebands increased first and then decreased (the peak value was in July), while PAR showed a contrasting pattern. SR albedo was mainly controlled by NIR rather than PAR. The contribution of the influencing factors was ranked in the order of normalized difference vegetation index (61.7%-78.5%, representing leaf area index) > solar altitude angle (15.4%-36.9%) > clearness index (0.4%-36.9%).

[Transcriptome analysis on responses of leaf photosynthesis and nitrogen metabolism of Larix gmelinii to environmental change]. / å ´å®‰è½å¶æ¾å¶å ‰åˆä¸Žæ°®ä»£è°¢å¯¹çŽ¯å¢ƒå˜åŒ–å“åº”çš„è½¬å½•ç»„åˆ†æž.

To reveal molecular mechanisms underlying photosynthesis responses of Dahurian larch (Larix gmelinii) to environmental changes, we used the high-throughput sequencing technology to sequence the transcriptome of larch leaves from four latitudinal sites with different environmental conditions, and compared differential expression genes (DEGs). The four sites from high- to low-latitude were Tahe (52°52' N), Songling (50°72' N), Heihe (49°22' N), and Dailing (47°08' N). A total of 282428811 clean reads were sequenced out, among which the abundace of DEGs were 16915, 18812, 28536, 20635, 29957 and 23617 for the Tahe-Songling, Tahe-Heihe, Tahe-Dailing, Songling-Heihe, Songling-Dailing, and Heihe-Dailing comparisons, respectively. The expression of nine Psb genes family (i.e., PsbB, PsbK, PsbO, PsbP, PsbQ, PsbS, PsbW, Psb27, and Psb28) encoding Photosystem Ⅱ and that of three genes (ATPF1A,atpA, ATPF1G, atpG, and ATPF1D, atpH) encoding F-type ATPase, which were involved in photosynthesis pathway, were significantly up-regulated with increasing environmental differences among the sites. A similar up-regulation pattern occurred for the expression of genes encoding glutamine synthetase (glnA, GLUL), nitrate reductase (NR), and carbonic anhydrase (cynT, can) that were involved in nitrogen metabolism pathway. The numbers of DEGs and up-regulated genes increased with the increases in environmental changes among the sites, resulting in inter-site divergence of photosynthetic capacity of larch trees.

[Drought tolerance traits of leaves of 20 tree species in temperate forest of Northeast China]. / 东北温带森林20ç§ä¹”æœ¨æ ‘ç§å¶ç‰‡å¹²æ—±å®¹å¿æ€§ç‰¹å¾.

The increases in frequency and intensity of drought worldwide has seriously affected tree growth, and even led to widespread forest mortality. Leaf traits estimated from pressure-volume (PV) curve provide key leaf physiological information that reflects the drought tolerance of trees. However, it is uncertain that which PV parameter performs the best at local scale. Here, we measured five PV traits (including TLP, π0, ε, Cleaf, and RWCtlp) and two leaf structural traits (specific leaf area and leaf density) in 20 tree species (16 angiosperms and 4 gymnosperms) in a temperate mixed forest at the Maoershan Forest Ecosystem Research Station, Northeast China. The objectives of this study were to search the best indicators of leaf drought tolerance at local scale, and to explore the correlation between PV traits and leaf structural traits. We found that angiosperms had significantly greater RWCtlp and lower Cleaf than gymnosperms, indicating that RWCtlp and Cleaf might be the good indicators of leaf drought tolerance in temperate mixed forest in Northeast China. Within angiosperm species, TLP and π0 were significantly and negatively correlated with leaf density, but positively correlated with specific leaf area; while ε was negatively correlated with specific leaf area. However, the opposite trends between PV traits and leaf structural traits were observed between gymnosperms and angiosperms, which might be attributed to their differences in drought response and adaptation strategies.

[Fine root biomass, production, and turnover rate in a temperate deciduous broadleaved forest in the Maoer Mountain, China]. / å¸½å„¿å±±æ¸©å¸¦è½å¶é˜”å¶æž—ç»†æ ¹ç”Ÿç‰©é‡ã€ç”Ÿäº§åŠ›å’Œå‘¨è½¬çŽ‡.

Fine roots play an important role in energy flow and substance cycling in forests. How-ever, the estimates of biomass, production and turnover of fine roots remain large uncertainties, and the mechanism underlying local-scale spatial variation in fine roots is still unclear. In a temperate secondary forest in the Maoer Mountain in Northeast China, we investigated the vertical distribution of fine root biomass and necromass at the 0-100 cm profile and the dynamics, production and turnover rate of fine root in 0-20 cm soil layer. The sequential coring (including the Decision Matrix and the Maximum-Minimum formula) and the ingrowth core (3 cm diameter and 5 cm diameter) were compared in estimating production and turnover rate of fine roots. Forest stand variables that might affect fine roots were also explored. The results showed that 76.8% of fine root biomass and 62.9% of necromass concentrated in the 0-20 cm soil layer, and that both decreased exponentially with increa-sing soil depth. The seasonal variation in both fine root biomass and necromass was not significant in 0-20 cm soil layer, which might be related to the negligible snowfall in winter and the extremely high precipitation in summer. There was no significant difference in the results of the estimated fine root production between two diameter ingrowth cores. After log-transformed, fine root production and turnover rate estimated by the Decision Matrix, the Maximum-Minimum formula and ingrowth cores were significantly different among methods. With the increases of soil nutrient concentrations, fine root biomass/fine root necromass ratio significantly increased, fine root necromass significantly decreased, whereas fine root biomass, productivity, and turnover rate were not related to soil nutrient. There was a significant positive correlation between fine root production and aboveground woody biomass increment in the previous-year but not current-year.

[Carbon budget estimation based on different methods of CO2 storage flux in forest ecosystems]. / CO2储存通量估算方法对森林生态系统碳收支估测的影响.

Accurate measurement of CO2 storage flux (Fs) in forest ecosystems is of great significance for estimating ecosystem carbon budget by eddy covariance (EC). The errors in the estimation of ecosystem carbon budget caused by different methods for calculating Fs has yet not been comprehensively assessed. Using data from an open-path EC system and an eight-level CO2/H2O profile system (AP100, Campbell Scientific Inc., USA) in a broadleaved deciduous forest at the Maoer-shan in 2018, we evaluated the methodological effect of Fs[2-min mean profile (P2 min), 30-min mean profile (P30 min) and 30-min mean EC single point (Ps)] on the estimation of net ecosystem exchange (NEE), ecosystem respiration (Re), and gross primary productivity (GPP). The results showed that the impact of Fs methods on forest carbon flux generally increased with the increases of time scale, indicating that gap-filling of flux data would further amplify the impacts of Fs estimation methods. At the annual scale, NEE based on P2 min and Ps methods were 36.3% and 29.4% lower than that based on P30 min, while Re based on P2 min was higher than that based on P30 min and Ps by 8.7%. The GPP based on P2 min was 5.4% higher, while that based on Ps was 2.1% lower than that based on P30 min. The traditional P30 min ignored the instantaneous changes in CO2 concentration, Ps missed the changes of CO2 concentration within canopy, and thus both underestimated the actual Re. The approximately instantaneous profile (2-min mean profile) had higher temporal and spatial resolution and could more accurately estimate forest carbon budget with non-flat terrain and complex canopy structure. Our findings had great implications for solving the underestimation of forest Re and GPP as well as the overestimation of net carbon sink on complex conditions with the EC method.

[Effects of Simulated Acid Rain on Soil Fungi Diversity in the Transition Zone of Moso Bamboo and Broadleaf Forest].

Acid rain is an important phenomenon in the context of global climate change, and can strongly influence forest ecology. There have been many studies on the response of plants to acid rain. However, the effect of acid rain on soil microbial communities is still largely unknown. Studying the effects of acid rain on soil microbial community structure is of great significance for predicting the interactive effects of multiple climate factors on forest ecosystems in the future. Moso bamboo (Phyllostachys edulis) is often cultivated not only for its delicious shoots and versatile culms, but also as an important biomass resource in southern China. However, with its robust growth and strong rhizomes, Moso bamboo populations have been expanding rapidly into adjacent forests. Different perturbation regimes, including disturbance caused by simulated acid rain, can have significant effects on a soil fungal community in response to Moso bamboo invasion into native broadleaf forest. To explore the effect of acid rain on a mixed forest of Moso bamboo and broadleaf soil fungi diversity, and to understand the relationship between fungal community structure and acid rain stress, a mixed forest of Moso bamboo and broadleaf (transition forest) in Zhejiang Tianmu Mountain Nature Reserve was taken as the study site, and simulated acid rain was set at different acidity according to the acid rain component of Linan in recent years. The experiment consisted of three different treatments. Three gradients of simulated acid rain treatment[pH 2.5, 4.0, and CK (lake water)] were designed to determine the effects of simulated acid rain on soil bacterial community diversity in transition forest. Soil DNA was extracted from the soils for polymerase chain reaction amplification and high-throughput sequencing to study the effects of acid rain on the fungal communities of the mixed forest of Moso bamboo and broadleaf soil. We obtained 601 287 sequences across the three types of sampling sites. Sequences were affiliated to 13 different phyla throughout the dataset. The dominant fungal groups were Ascomycota, Basidiomycota, Mortierellomycota, and Mucoromycota. Simulated acid significantly increased the number of operational taxonomic units, Ace index, and Chao1 index of fungal communities (P<0.05). The results of principal coordinates analysis (PCoA) also revealed that acid rain significantly modified the structure. The changes in soil fungal community structure were mainly related to the abundance of genera Bifiguratu, Geminibasidium, Purpureocillium, and Oidiodendron, which could be utilized as indicator species to determine changes in soil fungal community structure. Redundancy and correlation analysis showed that changes in basic physicochemical factors in the soil, such as soil pH and total nitrogen, can significantly influence the composition of the fungal community (P<0.05).

[Diurnal variation and light response of net ecosystem carbon exchange in a temperate broadleaved deciduous forest at Maoershan, Northeast China]. / å¸½å„¿å±±æ¸©å¸¦è½å¶é˜”å¶æž—å‡€ç”Ÿæ€ç³»ç»Ÿç¢³äº¤æ¢çš„æ—¥å˜åŒ–åŠå ‰å“åº”ç‰¹å¾.

Photosynthetically active radiation (PAR) is a key environmental factor affecting the change of net ecosystem exchange (NEE) during the daytime. However, the coordinate system of PAR measured by horizontal radiometers over sloping terrain does not match that of NEE after tilt-corrected of the ultrasonic anemometer. Using the temperate deciduous broad-leaved forest at the Maoershan site with an average slope of 9° and a azimuth of 296° as a case, we investigated the diurnal variations in NEE and its driving factors in the growing season (May to September) of 2016. We assessed the differences in estimating light response parameters and the explanations of NEE by other environmental factors between the PAR measured by horizontal and slope-parallel radiometers. The results showed that the diurnal change of NEE in each month of the growing season presented a morning-afternoon asymmetrically unimodal curve: the value was negative (net carbon absorption) about 2.5 h after sunrise, reached the peak around 12:00, then approached zero again at two hours before sunset. The daily net uptake maximized in July and minimized in May. During the whole growing season, the time-lag and difference in the PAR measured by the horizontal versus slope-parallel radiometers led to that the PAR values measured by the horizontal radiometer increased photosynthetic quantum yield (α) and daytime respiration rate (Rd) by 13.3% and 11.5%, respectively, and decreased the maximum photosynthetic efficiency (Amax) by 7.7%. The light response curves of NEE were asymmetrical in the morning and afternoon, with Rd and Amax in the afternoon being greater than that in the morning. Weather conditions affected light response parameters: on cloudy days, Amax was higher than that in sunny days, the α and Rd were lower versus those in sunny days for most conditions. However, the monthly Amax and Rd were generally higher for horizontally measured PAR than for slope-parallelly measured PAR, especially for Amax in the cloudy afternoon. The radiometer-orientation affected the explanation of daytime NEE by air temperature (Ta) and vapor pressure deficit (VPD). The correlation of NEE residual based on the slope-parallel radiometer with Ta and VPD (r ranged: 0.013 to 0.197, 0.098 to 0.224) was tighter than that based on the horizontal radiometer (r ranged: 0.082 to 0.219, 0.162 to 0.282) when the negative correlations with Ta for September was excluded. Our results indicated that the measurements of PAR on the inclined terrains could cause errors in the environmental interpretations of NEE. Such findings had implications for the radiometric measurement of mountain vegetation and the reasonable interpretation of carbon exchange in terrestrial ecosystems.

[Stomatal regulation of plants in response to drought stress]. / 植物应对干旱胁迫的气孔调节.

The regulation on carbon acquisition and water loss plays a critical role in plant growth and survival. Stomata are important portals for plants to control the exchanges of carbon and water between leaves and the atmosphere. Therefore, understanding stomatal control mechanisms and modelling stomatal conductivity are indispensable to accurately simulate carbon and water cycling in terrestrial ecosystems. As global climate change is accelerating in recent years, drought events have become more and more frequent and thus profoundly affect the survival, growth and distribution of plants. In order to deeply understand the underlying mechanism of carbon-water coupling of plants and predict the dynamics of plants and communities under global changes, it is crucial to explore responses of stomatal regulation of plants to drought stress. In this review, we synthesized recent research progress on mechanisms and modeling of plant stomatal regulation under drought stress. First, this review described the active and passive regulation of plant stomatal control in response to drought stress, and discussed the evolution of plant stomatal regulation, including the passive hydraulic regulation of ferns and lycophytes, the active regulation of angiosperms, and the dual-control mechanism of gymnosperms that was proposed as an important transitional type during evolution from ferns to angiosperms. Then, we analyzed the relationship between stomatal and hydraulic regulations, and discussed the debates on the decoupling of plant water potential from stomatal conductivity. The application of stomatal-conductivity optimization models was introduced based on the water use efficiency hypothesis and the maximum carbon gain hypothesis. The model based on the latter had a greater potential of prediction and practical application. Finally, we proposed two issues that should be urgently addressed: 1) to scale up the research of plant stomatal regulation from leaf or individual to ecosystem or even larger scales so as to improve the mechanistic models of carbon and water cycling in terrestrial ecosystems; and 2) to quantify the hydroactive feedback processes of plant stomatal regulation so as to modify current hydraulics models of plant stomatal function.

[Temporal dynamics and influencing factors of soil microbes in Larix gmelinii forest soil during spring freezing-thawing period]. / æ˜¥å­£å†»èžæœŸå ´å®‰è½å¶æ¾æž—åœŸå£¤å¾®ç”Ÿç‰©çš„æ—¶é—´åŠ¨æ€åŠå ¶å½±å“å› å­.

Soil microbial community dynamics during the spring freezing-thawing period could affect carbon and nutrient cycling in the subsequent growing season. During spring soil freezing-thawing period, we monitored temporal dynamics of soil microbial community in different soil substrates for Larix gmelinii forest using phospholipid fatty acids (PLFAs) as biomarkers every 3-7 days. The results were as followed: 1) the total PLFAs content, the PLFAs content and relative abundance of each soil microbial group, the ratio of Gram-positive bacteria to Gram-negative bacteria (G+/G-), the ratio of saturated PLFAs to unsaturated PLFAs (S/NS) and the ratio of bacteria to total fungi (fungi + arbuscular mycorrhizal fungi) (B/F) all varied among sampling times; 2) soil total organic carbon (TOC) and nitrogen (TN) were the main factors affecting soil microbial community in the early stage of soil freezing-thawing period; soil moisture, TOC and TN were the main driving factors in the middle stage of soil freezing-thawing period; soil microbes were affected by soil tempera-ture, moisture, TOC, TN and C/N in the late stage of soil freezing-thawing period; 3) the total PLFAs content, the PLFAs content and relative abundance of each soil microbial group (except the relative abundance of bacteria), B/F, G+/G- and S/NS all showed significant difference between soil substrates, and soil TOC, TN and C/N were the key determination factors. Soil temperature, moisture, and nutrient availability were the main factors affecting soil microbial community during the spring soil freezing-thawing period, but the degree of influence varied with the freezing-thawing stages and microbial groups.

[Variations in topsoil carbon and nitrogen contents of five temperate plantations in Northeast China.] / 东北5种温带人工林表层土壤碳氮含量的分异.

Afforestation is an effective way for carbon (C) sequestration, which also profoundly influences soil nitrogen (N) dynamics in the forest ecosystem. The impacts of tree species on soil C and N budgets and the underlying mechanism remain uncertain. In this study, we used a common garden experiment and measured the soil organic C (Csoil) and total N contents (Nsoil) of the topsoil (0-10 cm) and related vegetative and soil microbial properties in 2007 and 2015 (3 and 11 years after afforestation), respectively. Our aim was to explore the effects of five major tree species (i.e., Fraxinus mandshurica, Juglans mandshurica, Betula platyphylla, Larix gmelinii and Pinus sylvestris var. mongolica) in the temperate forests in Northeast China on soil C and N contents and their dri-vers. The results showed that both Csoil and Nsoil of the five stands decreased as the stand ages increased, the change rates of which were significantly correlated with each other. The rate of change in Csoil(2.6%·a-1-4.8%·a-1) was significantly greater than that in Nsoil(0.8%·a-1-2.8%·a-1). The decrements of the Csoil and Nsoil for the broadleaved stands were significantly lower than those of the coniferous stands. The tree-species traits and microbial properties together explained 68.5% and 90.9% of the variability of the change rates of Csoil and Nsoil, respectively. The change rates of Csoil and Nsoil decreased with the increases in leaf litter C/N and microbial biomass C/N, but increased with the increases of fine root biomass, microbial biomass C, and the ratio of the C-acquisition to the N-acquisition enzyme activity. Additionally, the change rate of Nsoil decreased with the increases of the leaf litter production and the microbial metabolic activity. Our findings indicated that C and N contents in the topsoil of these temperate plantations decreased significantly 11 years after afforestation, while the different change rates mainly resulted from different properties of tree species and soil microbes.

[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.

[Effects of latitudinal transplanting on temperature sensitivity of leaf dark respiration for Larix gmelinii.] / çº¬åº¦æ¢¯åº¦ç§»æ ½å¯¹å ´å®‰è½å¶æ¾é’ˆå¶æš—å‘¼å¸æ¸©åº¦æ•æ„Ÿæ€§çš„å½±å“.

Exploring the temperature sensitivity of leaf dark respiration is of significance for understanding forest carbon cycling and its response to climate change. However, its intra-specific variability and seasonality are not clear yet. In this study, we measured the temperature sensitivity coefficient (Q10) of leaf dark respiration for Dahurian larch (Larix gmelinii) that were transplanted from four latitudinal sites (i.e., Tahe, Songling, Heihe, and Dailing) in a common garden. Our specific aims were to explore the seasonal dynamics of Q10 and compare differences in Q10 among the indivi-duals from the four latitudinal sites. The results showed that the Q10 for the four sites exhibited similar seasonal trend, with the maximum Q10 in the middle growing season. The inter-site difference in Q10 was significant, ranging from (1.48±0.01) to (2.15±0.03). Furthermore, the inter-site difference showed the same pattern across the whole growing season, i.e., the warmer and lower latitudinal sites, the higher Q10. The Q10 was significantly and positively correlated with foliar nitrogen concentration and soluble sugar concentration, and mean annual temperature and mean annual precipitation in the transplanting sites. These findings suggested that the inter-site variation in Q10 and its seasonality could be mainly attributed to the foliar nutrient concentration and adaptation of trees to the climatic conditions of the transplanting sites, which should be considered in modeling and predicting responses of forest carbon cycling to climate change.

[Influence of snow depth changes on leaf litter decomposition of Fraxinus mandshurica and Larix gmelinii]. / æ¨¡æ‹Ÿé›ªè¢«å˜åŒ–å¯¹æ°´æ›²æŸ³å’Œå ´å®‰è½å¶æ¾å‡‹è½å¶åˆ†è§£çš„å½±å“.

Changes in snowpack induced by climate change can profoundly affect forest litter decomposition. A snow depth manipulation experiment with three treatments (i.e.,control,snow addition, and snow removal) was conducted to assess the effects of snow depth changes on leaf litter decomposition of two temperate tree species [Manchurian ash (Fraxinus mandshurica) and Dahurian larch (Larix gmelinii)]. The annual loss of the litter mass after one year decomposition varied between 51.3% and 57.4% for the ash and between 21.7% and 31.4% for the larch. The decomposition constants (k) ranged from 0.048 to 0.057 and from 0.022 to 0.030 for these two species respectively.The greatest k value occurred under the snow addition treatment, while the least occurred under the snow removal treatment.Snow addition treatment shortened the 50% and 95% decomposition time by 1.1 months and 4.2 months for the ash, respectively, and by 3.7 months and 15.5 months for the larch, respectively. The snow removal treatment lengthened those decomposition time by 1.8 months and 6.4 months for the ash,and by 5.0 months and 21.1 months for the larch, respectively. Litter decomposition rate was significantly correlated with tree species, snow depth, decomposition time, and soil temperature, but its major influencing factors varied with decomposition stage. Soil temperature and the initial litter quality were the major factors affecting decomposition rates during the snow covered and following snow free periods, respectively. Our findings highlight that changes in snow depth exert significantly instantaneous and prolonged effects on forest litter decomposition.

[Effects of detritus removal on soil carbon, nitrogen and phosphorus stoichiometry and related factors in a temperate deciduous forest in the Maoershan Mountain, China.] / æ¤ç‰©æ®‹ä½“åŽ»é™¤å¯¹å¸½å„¿å±±æ¸©å¸¦è½å¶æž—åœŸå£¤ç¢³ã€æ°®ã€ç£·åŒ–å­¦è®¡é‡ç‰¹å¾åŠå ¶ç›¸å ³å› å­çš„å½±å“.

A detritus-removal experiment was conducted in a temperate deciduous broad-leaved forest in 2007 at the Maoershan Ecological Station in Northeast China, including two treatments: Litterfall removal (NL), root removal (NR). Soil water content, bulk density and the concentrations of soil C, N and P were measured in 2016. The results showed that the C concentration at the surface soil layer (0-10 cm) was reduced by 15.6% and 10.7% for the NL and NR treatments, respectively, while the weighted-mean soil C concentration in 0-30 cm depth was reduced by 7.9% and 4.6%, respectively. The N concentration of the surface layer in the NL treatment decreased by 10.2%, whereas the surface-soil P concentration in the NR treatment increased by 6.6%, resulting in reduced C:P and N:P for both treatments. The standardized major axis regressions showed that the regression slopes between the C, N and P at each layer of 0-30 cm soil depth differed significantly among the treatments. The intercepts of the regressions between soil C concentration and bulk density or soil water content had significant differences among the treatments. The results suggested that detritus-removal caused a coordinated variation in soil C, N and P stoichiometry and physical properties. Therefore, we recommend taking the effect on soil ecological stoichiometry into account in future detritus-removal experiments.

[Effects of changes in seasonal snow-cover on litter decomposition and soil nitrogen dynamics in forests.] / 季节性雪被变化对森林凋落物分解及土壤氮动态的影响.

Changes in snow-cover patterns induced by global climate change profoundly influence ecological processes in terrestrial ecosystems, including litter decomposition and soil nutrient cycling. Forest, a major terrestrial ecosystem, plays a crucial role in global biogeochemical cycling. Here, we reviewed the effects of changes in seasonal snow-cover on litter decomposition and soil nitrogen (N) cycling in forests. Global climate change would result in increasing or decreasing seasonal snow-cover depending on local conditions, with direct and indirect effects on forest litter decomposition. The changes in seasonal snow-cover would directly affect decomposition process by changing environmental temperature and moisture, litter quality, and decomposer dynamics, and would indirectly influence decomposition via altering community structure, vegetation phenology, and soil nutrients. Meanwhile, the changes in seasonal snow-cover would modify forest soil N dynamics through changing N enrichment, soil temperature and moisture, freeze-thaw cycle, forest community, subnivean fauna and microorganisms. Further studies in this field should focus on: 1) employing experiments with divergent protocols to simulate diverse changing patterns of seasonal snow-cover under the global climate change scenarios; 2) the effects of the seasonal snowmelt leaching on forest litter decomposition and soil N dynamics; 3) elucidating mechanisms underlying forest litter decomposition and soil N dynamics driven by changes in seasonal snow-cover patterns in different ecosystems and climate zones; and 4) quantifying the instantaneous and prolonged effects of changes in seasonal snow-cover on forest litter decomposition and soil N dynamics in the snow-covered and snow-free seasons, respectively. These studies will provide theoretical basis and solid data support for the understanding and model-prediction of the responses of the biogeochemical cycle in terrestrial ecosystems to global climate change.

[Application of near-surface remote sensing in monitoring the dynamics of forest canopy phenology.] / è¿‘åœ°é¥æ„Ÿåœ¨æ£®æž—å† å±‚ç‰©å€™åŠ¨æ€ç›‘æµ‹ä¸­çš„åº”ç”¨.

Near-surface remote sensing is an important technique for in-situ monitoring of forest phenology and a robust tool for scaling of the phenology with a high temporal resolution and mode-rate spatial coverage. Here, we first reviewed the methods of near-surface remote sensing with three major optical sensors (i.e., radiometer, spectrometer, and digital camera) for monitoring forest phenology. Second, we analyzed sources of uncertainties from distinguishing the phenophases by using the data obtained at the Maoershan flux site in the temperate forest. We found that the error was mainly attributed to the extracting method. Third, we analyzed the linkage of near-surface remote sensing with other methods and its intrinsic problems. Finally, we proposed four priorities in the research of this field: 1) linking optical (or canopy structural) phenology with functional phenology (physiological and ecological processes); 2) integrating the regional networks of canopy phenology for global networking observation and data sharing of canopy phenology; 3) integrating multi-source and multi-scale phenological data with the help of near-surface remote sensing; 4) developing phenology models based on near-surface remote sensing in order to improve the phenology simulation in the dynamic global vegetation models.

[Vertical variation in stoichiometric relationships of soil carbon, nitrogen and phosphorus in five forest types in the Maoershan region, Northeast China.] / 帽儿山5ç§æž—åž‹åœŸå£¤ç¢³æ°®ç£·åŒ–å­¦è®¡é‡å ³ç³»çš„åž‚ç›´å˜åŒ–.

Five forests under diverse site conditions but under identical climate in the Maoershan region of Northeast China were sampled for measuring contents of soil carbon (C), nitrogen (N), and phosphorus (P), soil bulk density, and soil thickness by soil profile horizons. The stands included two plantations (i.e., Pinus koraiensis and Larix gmelinii plantations) and three broadleaved forests (i.e., Quercus mongolica stand, Populus davidiana Betula platyphylla mixed stand, and hardwood stand). Our aim was to examine vertical distribution of the content, density, and stoichio metry of soil C, N and P for the five forest types. The results showed that the contents and densities of soil C, N and P differed significantly among the forest types, with the maxima of the soil C and N at both O and A horizons occurring in the hardwood stand. The contents of C and N decreased significantly with increasing soil depth in all the stands. P content decreased significantly only in the broadleaved stands, and P content had no significant difference among different soil layers in the coniferous stands. The soil C/N at the A horizon, N/P at the O horizon, and the C/P at A and B horizons were significantly different among the forest types. The soil C and N linearly correlated significantly across all the forest types without significant differences in the slopes and intercepts, and the soil N and P, or the soil C and P correlated significantly only in the broadleaved stands. This result suggested that the C-N coupling relationship tended to converge across the forest types, and the N-P and C-P relationships varied with forest types.

[Spatial variation in diurnal courses of stem temperature of Betula platyphylla and Fraxinus mandshurica and its influencing factors]. / ç™½æ¡¦å’Œæ°´æ›²æŸ³æ ‘å¹²æ¸©åº¦æ—¥å˜åŒ–çš„ç©ºé—´å˜å¼‚åŠå ¶å½±å“å› å­.

Plant temperature is an important parameter for estimating energy balance and vegetation respiration of forest ecosystem. To examine spatial variation in diurnal courses of stem temperatures (Ts) and its influencing factors, we measured the Ts with copper constantan thermocouples at different depths, heights and azimuths within the stems of two broadleaved tree species with contrasting bark and wood properties, Betula platyphylla and Fraxinus mandshurica. The results showed that the monthly mean diurnal courses of the Ts largely followed that of air temperature with a 'sinusoi dal' pattern, but the Ts lagged behind the air temperature by 0 h at the stem surface to 4 h at 6 cm depth. The daily maximal values and ranges of the diurnal course of Ts decreased gradually with increasing measuring depth across the stem and decreasing measuring height along the stem. The circumferential variation in Ts was marginal, with slightly higher daily maximal values in the south and west directions during the daytime of the dormant season. Differences in thermal properties (i.e. , specific heat capacity and thermal conductivity) of both bark and wood tissue between the two species contributed to the inter specific variations in the radial variation in Ts through influencing the heat exchange between the stem surface and ambient air as well as heat diffusion within the stem. The higher reflectance of the bark of B. platyphylla decreased the influence of solar radiation on Ts. The stepwise regression showed that the diurnal courses of Ts could be well predicted by the environmental factors (R2 > 0.85) with an order of influence ranking as air temperature > water vapor pressure > net radiation > wind speed. It is necessary to take the radial, vertical and inter specific varia-tions in Ts into account when estimating biomass heat storage and stem CO2 efflux.