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Soil labile organic carbon (LOC) responds rapidly to environmental changes and plays an important role in carbon cycle. In this study, the seasonal fluctuations in LOC, the activities of carbon-cycle related enzymes, and the bacterial and fungal communities were analyzed for soils collected from two forests, namely Betula albosinensis (Ba) and Picea asperata Mast. (Pa), in the Qinling Mountains of China. Results revealed that the seasonal average contents of microbial biomass carbon (MBC), easily oxidized organic carbon (EOC), and dissolved organic carbon (DOC) of Pa forest soil were 13.5%, 30.0% and 15.7% less than those in Ba soil. The seasonal average enzyme activities of β-1,4-glucosidase (βG), and β-1,4-xylosidase (βX) of Ba forest soils were 30.0% and 32.3% higher than those of Pa soil while the enzyme activity of cellobiohydrolase (CBH) was 19.7% lower. Furthermore, the relative abundance of Acidobacteria was significantly higher in summer than in winter, whereas the relative abundance of Bacteroidetes was higher in winter. Regarding the fungal communities, the relative abundance of Basidiomycota was lowest in winter, whereas Ascomycota predominated in the same season. In addition, the soil LOC was significantly positively correlated with the CBH, βG and βX activities. Changes in LOC were significantly correlated with Acidobacteria, Bacteroidetes and Basidiomycota. We conclude that the seasonal fluctuations in forest soil LOC fractions relied on carbon cycle-associated enzymatic activities and microorganisms, which in turn were affected by climatic conditions.

Aims Competition, temperature and nutrient are the most important determinants of tree growth in the cold climate on the eastern Tibetan Plateau. Although many studies have reported their individual effects on tree growth, little is known about how the interactions of competition with fertilization and temperature affect root growth. We aim to test whether climate warming and fertilization promote competition and to explore the functional strategies of Picea asperata in response to the interactions of these factors. Methods We conducted a paired experiment including competition and non-competition treatments under elevated temperature (ET) and fertilization. We measured root traits, including the root tip number over the root surface (RTRS), the root branching events over the root surface (RBRS), the specific root length (SRL), the specific root area (SRA), the total fine root length and area (RL and RA), the root tips (RTs) and root branching (RB) events. These root traits are considered to be indicators of plant resource uptake capacity and root growth. The root biomass and the nutrient concentrations in the roots were also determined. Important Findings The results indicated that ET, fertilization and competition individually enhanced the nitrogen (N) and potassium (K) concentrations in fine roots, but they did not affect fine root biomass or root traits, including RL, RT, RA and RB. However, both temperature and fertilization, as well as their interaction, interacting with competition increased RL, RA, RT, RB and nutrient uptake. In addition, the SRL, SRA, RTRS and RBRS decreased under fertilization, the interaction between temperature and competition decreased SRL and SRA, while the other parameters were not affected by temperature or competition. These results indicate that P. asperata maintains a conservative nutrient strategy in response to competition, climate warming, fertilization and their interactions. Our results improve our understanding of the physiological and ecological adaptability of trees to global change.

Background The terminal branch orders of plant root systems are increasingly known as an ephemeral module. This concept is crucial to recognize belowground processes. However, it is unknown if root modules still exist after they die? Methods The decomposition patterns of the first five root orders were observed for 3 years using a branch-order classification, a litter-bag method and sequential sampling in a common subalpine tree species (Picea asperata) of southwestern China. Results Two root modules were observed during the 3-year incubation. Among the first five branch orders, the first three order roots exhibited temporal patterns of mass loss, nutrients and stoichiometry distinct from their woody mother roots throughout the experimental period. This study, for the first time, reported the decomposition pattern of each individual root order and found a similar decomposition dynamic among ephemeral root branches in a forest tree species. Conclusions Results from this study suggest that root modules may also exist after death, while more data are needed for confirmation. The findings may further advance our understanding of architecture-associated functional heterogeneity in the fine-root system and also improve our ability to predict belowground processes.

According to the forest resources inventory data for different periods and the latest estimation parameters of forest carbon reserves in China, the carbon reserves and carbon density of forest biomass in the Tibet Autonomous Region from 1999 to 2019 were estimated using the IPCC international carbon reserves estimation model. The results showed that, during the past 20 years, the forest area, forest stock, and biomass carbon storage in Tibet have been steadily increasing, with an average annual increase of 1.85×104 hm2, 0.033×107 m3, and 0.22×107 t, respectively. Influenced by geographical conditions and the natural environment, the forest area and biomass carbon storage gradually increased from the northwest to the southeast, particularly in Linzhi and Changdu, where there are many primitive forests, which serve as important carbon sinks in Tibet. In terms of the composition of tree species, coniferous forests are dominant in Tibet, particularly those containing Abies fabri, Picea asperata, and Pinus densata, which comprise approximately 45% of the total forest area in Tibet. The ecological location of Tibet has resulted in the area being dominated by shelter forest, comprising 68.76% of the total area, 64.72% of the total forest stock, and 66.34% of the total biomass carbon reserves. The biomass carbon storage was observed to first increase and then decrease with increasing forest age, which is primarily caused by tree growth characteristics. In over-mature forests, trees’ photosynthesis decreases along with their accumulation of organic matter, and the trees can die. In addition, this study also observed that the proportion of mature and over-mature forest in Tibet is excessively large, which is not conducive to the sustainable development of forestry in the region. This problem should be addressed in future management and utilization activities.

Forests are essential biomes for global biochemical cycles, and soil microorganisms play a key role in providing and maintaining forest ecosystem services. A comprehensive understanding of how biotic and abiotic factors drive soil microbial community composition can help predict the effects of environmental changes on forest ecosystem service functions. Therefore, this study was conducted in a subalpine coniferous forest (Picea asperata forests and Sabina chinensis forests) in the Sanjiangyuan National Natural Reserve of Qinghai Province, China, to investigate the effects of understorey vegetation on soil microbial communities by measuring shrub roots, herbaceous roots, litter and soil physicochemical properties and soil microbial communities (16S, ITS). The results showed the following: (1) In both the P. asperata and S. chinensis forests, the dominant phyla in the soil bacterial communities were Acidobacteria, Proteobacteria and Verrucomicrobia, and the dominant phyla in the fungal communities were Ascomycota and Basidiomycota. In different forest types, the soil microbial communities contained differences that were significant in beta diversity (P 0.05). (2) Results from the structural equation model showed that in different forest types, bacterial community composition was significantly influenced by herbaceous roots, while fungal community composition was significantly influenced by shrub roots (P

Litter chemical quality regulates the distinct composition of the main microbial groups and ecoenzymatic stoichiometry. Microbes in spruce ( Picea asperata Mast.) and fir ( Abies faxoniana Rehd.) rather than birch ( Betula platyphylla Suk.) and rhododendron ( Rhododendron lapponicum (L.) Wahl.) can more easily adjust their physiological metabolism to acclimate to low N resources. Litter decomposition is the main pathway of nutrient cycling that bridges aboveground and underground material circulation and energy flow. Microorganisms are essential for the regulation of organic carbon decomposition and nutrient cycling. We sought to reveal whether litter chemical quality predominates forest floor microbial structure and function in different species and how their characteristics vary with litter decomposition stages. We measured litter substrate quality, microbial community structure, microbial biomass carbon (MBC) and nitrogen (MBN), extracellular enzyme activities and stoichiometric homeostasis of fresh litter (L), and fermentative (F) and humus (H) layers for these tree species. Overall, the enzyme activities and microbial biomass of birch and rhododendron were greater than those of spruce and fir. The microbial abundances of birch and rhododendron decreased with decomposition. Forest floor microbial nutrient limitation is generally restricted by N in subalpine forests, and ecoenzymatic stoichiometry is affected mainly by dissolved C/N/P stoichiometry. Stronger microbial C:N homeostasis (H′) was observed for spruce (5.56) and fir (4.17) than that for birch (1.82) and rhododendron (1.33). We conclude that litter chemical quality led to the disparity in forest floor microbial groups and ecoenzymatic stoichiometry for different tree species.

This study provides a novel desiccation indicator for somatic embryos and an efficient system for somatic seedling production in Picea asperata Mast. Picea asperata Mast. is a widely distributed native spruce in China with outstanding wood properties and adaptability. In this study, we established an effective system to propagate plantlets through somatic embryogenesis in P. asperata. The effects of cone collection date, seed family, and plant growth regulators on the initiation of embryonal masses (EM) were analyzed. Besides the significant effects of seed family and cone collection date on EM initiation, the highest induction frequency was obtained with modified Litvay medium (MLV) containing 10 µM 2,4-dichlorophenoxyacetic acid and 5 µM 6-benzylaminopurine. The best tissue proliferation in suspension cultures was obtained with an inoculum density of 1:7 (v/v, sedimented cells:liquid medium) after 9 days in culture. The best medium for somatic embryo (SE) maturation was MLV supplemented with 105 µM (±)-abscisic acid, 5% polyethylene glycol 4000, 3% sucrose, 0.1% activated charcoal (AC), 0.05% l-glutamine, 0.1% casein acid hydrolysate, and 0.4% gellan gum. In this medium, 415 ± 103 SEs with well-developed cotyledons were obtained per gram (fresh weight) of EM. After partial desiccation treatment under low light intensity, somatic embryos, depending on their color change, were divided into green cotyledonary embryos (GCEs) and non-green cotyledonary embryos (NGCEs). These embryos, along with non-desiccated SEs as controls, were germinated on 1/2 MLV supplemented with 2% sucrose, 0.2% AC, 0.05% l-glutamine, and 0.6% gellan gum. Only GCEs, with red radicles, produced plantlets at the highest rates (>74.5%) among all of the treatments. This efficient system of somatic seedling production in P. asperata includes screened culture factors and a novel desiccation indicator to ensure SE quality before germination.

Previous studies about the effects of experimental warming on tree species have focused primarily on response of morphology and physiology in leaf and biomass allocation in the growing season, and a few studies considered the importance of roots. Based on the available evidence, it is unclear whether photosynthesis rate is enhanced by night warming in late autumn an issue that deserves further investigation. Thus, we exposed two coniferous species, Picea asperata and Abies faxoniana , to night warming continued throughout the year to investigate morphological and physiological responses of roots and leaves in the autumn. The results showed that night warming caused significant increases in net influxes of NH 4 + and NO 3 − in P. asperata seedlings corresponding well with net H + efflux and net influx of O 2 . Meanwhile, night warming had a positive effect on foliar gas exchange such as net photosynthesis rate, apparent quantum efficiency, dark respiration rate and maximum quantum efficiency of PS II, and nitrate reductase activity of roots. Additionally, root morphology such as total roots length, surface area, specific root area and specific root length was also stimulated by night warming. In contrast, night warming decreased concentrations of non-structural carbohydrate in leaves and roots of both species in autumn. The present study demonstrates that night warming would enhance late autumn leaf photosynthetic rate, and increase N uptake capacity of roots.

Aims Plant roots play a critical role in the uptake of nutrients, and nitrogen (N) absorption is considered as the first step and a pivotal process in N metabolism of plants. Our objective was to better understand the absorption of two major inorganic N forms (NH4 and NO3) in subalpine coniferous forests under global warming. Methods Experimental warming using infrared heater was applied to two dominant species in subalpine coniferous forests of Sichuan, China, Picea asperata and Abies fargesii var. faxoniana. The non-invasive micromeasurement technology was used to investigate the effects of warming on the uptake rates of NH4 and NO3 and the potential interactions between these two ions. Important findings Results showed that the maximal net root uptake of NH4 and NO3 occurred at a distance of 17–18 mm and 17 mm from root tips, respectively for P. asperata. and at a distance of 11 mm and 11.5 mm from root tips respectively for A. fargesii var. faxoniana. Experimental warming elevated the uptake rates of NH4 and NO3 in both species, but the interactions between NH4 and NO3 differed between the two species. While NO3 uptake was inhibited in the presence of NH4 for both P. asperata and A. fargesii var. faxoniana, net NH4 uptake was promoted by NO3 supply only in P. asperata roots under experimental warming.

Temperature and freeze-thaw events are two key factors controlling litter decomposition in cold biomes. Predicted global warming and changes in freeze-thaw cycles therefore may directly or indirectly impact litter decomposition in those ecosystems. Here, we conducted a 2-year-long litter decomposition experiment along an elevational gradient from 3000 to 3600 m to determine the potential effects of litter quality, climate warming and freeze-thaw on the mass losses of three litter types [dragon spruce (Picea asperata Mast.), red birch (Betula albosinensis Burk.), and minjiang fir (Abies faxoniana Rehd. et Wild)]. Marked differences in mass loss were observed among the litter types and sampling dates. Decay constant (k) values of red birch were significantly higher than those of the needle litters. However, mass losses between elevations did not differ significantly for any litter type. During the winter, lost mass contributed 18.3–28.8 % of the net loss rates of the first year. Statistical analysis showed that the relationships between mass loss and litter chemistry or their ratios varied with decomposition periods. Our results indicated that short-term field incubations could overestimate the k value of litter decomposition. Considerable mass was lost from subalpine forest litters during the wintertime. Potential future warming may not affect the litter decomposition in the subalpine forest ecosystems of eastern Tibetan Plateau.

Rust diseases of spruce and rhododendrons caused by Chrysomyxa succinea are commonly observed in forests of northern and eastern Asia. The heteroecious life cycle of this species alternating between spermogonial and aecial stages on Picea jezoensis and uredinial and telial stages on Rhododendron aureum is confirmed for the first time in China by inoculations and phylogenetic analyses. Morphological characters of all stages are described based on specimens obtained from the field and from inoculations. Based on morphological similarities and phylogenetic analyses, Ch. zhouniensis reported on Picea asperata is treated as a synonym of Ch. succinea. Four Caeoma species on Rhododendron are included in the same phylogenetic group as species of Chrysomyxa. Therefore, these species are treated as Chrysomyxa, and four new combinations in Chrysomyxa are proposed.

Water retained on tree leaves after rainfall, dew, or fog impacts transpiration. To determine the impact of leaf retained water (LRW) on the transpiration of trees, the difference between transpiration rates of different species with and without water sprayed on the leaves was measured. Results show that transpiration was inhibited by LRW. Both the inhibition extent and duration of LRW were higher on broadleaf species than on coniferous species. Under conditions of saturated LRW of the tree crown, mean transpiration inhibition rates of the test species were 0.32 (Quercus mongolica Fisch. ex Ledeb.), 0.25 (Acer mono), 0.37 (Tilia amurensis Rupr.), 0.31 (Fraxinus mandshurica Rupr.), 0.22 (Pinus koraiensis Siebold & Zucc.), 0.22 (Abies nephrolepis (Trautv. ex Maxim.) Maxim.), and 0.23 (Picea asperata Mast.). Mean inhibition rate and inhibition time for broadleaf species were 0.31 and 115 min, which were 40% higher and 27 min longer than those for coniferous species, respectively. The transpiration inhibition rate of LRW increased linearly with the LRW amount, and there was a higher transpiration inhibition rate in broadleaf species than in coniferous species for the same amount of LRW. Mean rising velocity of the inhibition with LRW amount for broadleaf species was 0.53%, whereas it was only 0.15% for the coniferous species.

Radial growth responses of gap-edge trees to GT intensity greatly depends on microclimate condition (soil temperature and PAR) within gaps and their abilities in competing and utilizing the limited resources. Gap-model thinning (GT) is an effective management technique to improve the productivity of dense monoculture plantation. However, how GT intensity influence inter- and intra-annual radial growth of the gap-edge trees remains an open question. In order to explore this question, we implemented an experiment with four treatments (control and gap sizes of 74, 109, and 196 m2) in a 30-year-old spruce (Picea asperata) plantation in 2008. We used dendrochronological method to explore dynamic of the basal area increment (BAI) of gap-edge trees (n = 127) from 2009 to 2012 after GT treatments. We found that effects of GT on the BAI of gap-edge trees highly depended on GT intensity and their crown classes. The large gaps significantly increased the BAI of gap-edge trees and further the latewood growth responded more sensitively than the earlywood, whereas the influences of the small and intermediate gaps were weak; the large gaps effectively improved the BAI of the dominant trees, following by the intermediate, but not for the suppressed trees. Our results also displayed that the earlywood increment was strongly related to the soil temperature in spring and the latewood formation was influenced by the photosynthetically active radiation in autumn. It was eventually concluded that dynamic radial growth of gap-edge trees were driven by the improved microclimate caused by GT and their abilities in competing and utilizing resources. The present study highlights the importance of setting appropriate GT intensity and choosing the felled trees in GT operation.

To understand the effects of reforestation on soil carbon (C) dynamics, we measured soil carbon dioxide (CO2) effluxes and soil C pools in dragon spruce (Picea asperata Mast.) stands of various ages (22-, 47- and 68-year-old dragon spruce plantations, and a 150-year-old primeval coniferous forest) in the eastern Tibet Plateau. The soil respiration rate of all the stands increased from March, followed by a peak in late July to August with temporal fluctuations, and then dramatically declined in September. The annual total soil CO2 effluxes (Rtot), soil heterotrophic CO2 effluxes (Rh), and soil autotrophic CO2 effluxes (Ra) were higher in the 22- (1004, 656 and 348 g C m−2 year−1, respectively) and 150-year-old stands (1070, 712 and 358 g C m−2 year−1, respectively), and lower in the 47- (792, 543 and 249 g C m−2 year−1, respectively) and 68-year-old stands (952, 607 and 345 g C m−2 year−1, respectively). The soil total organic carbon (TOC), easily oxidizable organic C (EOC), microbial biomass C (MB...

Increased rates of litter decomposition due to climatic warming have great potential to modify the carbon balance in forest soils, with consequent feedbacks to climate change. Reforestation could affect responses of litter decomposition to warming by altering litter type and soil conditions. However, less is known about the interactive impacts of forest management and climate change on litter decomposition. Here, we conducted a 4-year field experiment to investigate the effects of experimental warming on the decomposition of dragon spruce ( Picea asperata Mast.) and red birch ( Betula albo-sinensis Burk.) foliar litter in two contrasting sites (a dragon spruce plantation and a natural forest) using litter-bag method on the eastern Tibetan Plateau of China. During the four years of decomposition in the field, a clear pattern of faster mass loss was observed in red birch litter compared to dragon spruce needle. Additionally, regardless of warming regimes and litter types, mass loss rates were higher in the natural forest site than in the plantation site. Warming did not affect mass loss of dragon spruce litter during the early decomposition stage, but increased it over the later decomposition stage. In contrast, warming had enhanced mass loss of red birch litter on most sampling days. Red birch litter was more sensitive to warming compared with dragon spruce needle. Our results clearly indicated that reforestation can alter litter quality and soil conditions, and further affect the litter decomposition of subalpine forest ecosystem to projected climatic warming. This calls for incorporating forest management practice in climate–carbon models to better understand carbon dynamics of forest ecosystems under climate change.

Investigating the responses of trees to the heterogeneous distribution of nutrients in soil and simultaneous presence of neighboring roots could strengthen the understanding of an influential mechanism on tree growth and provide a scientific basis for forest management. Here, we conducted two split-pot experiments to investigate the effects of nutrient heterogeneity and intraspecific competition on the fine root morphology and nutrient capture of Picea asperata. The results showed that P. asperata efficiently captured nutrients by increasing the specific root length (SRL) and specific root area (SRA) of first-and second-order roots and decreasing the tissue density of first-order roots to avoid competition for resources and space with neighboring roots. The nutrient heterogeneity and addition of fertilization did not affect the fine root morphology, but enhanced the P and K concentrations in the fine roots in the absence of a competitor. On the interaction between nutrient heterogeneity and competition, competition decreased the SRL and SRA but enhanced the capture of K under heterogeneous soil compared with under homogeneous soil. Additionally, the P concentration, but not the K concentration, was linearly correlated to root morphology in heterogeneous soil, even when competition was present. The results suggested that root morphological features were only stimulated when the soil nutrients were insufficient for plant growth and the nutrients accumulations by root were mainly affected by the soil nutrients more than the root morphology.

This study aimed at predicting how sub-alpine coniferous ecosystems respond to global changes in the Eastern Tibetan Plateau by understanding soil microbial communities and activities, as well as variation in the quality and quantity of soil organic matter. An experiment was conducted to examine soil microbial communities and their related soil processes in rhizospheric soil of two coniferous species that were exposed to two levels of temperature (unwarmed and infrared heater warming) and two levels of nitrogen (unfertilized and 25 g N m−2 a−1) from April 2007. Four-year night warming alone slightly affected the phospholipid fatty acid contents of the microbial community. However, the combination of nitrogen addition and soil warming significantly affected soil microbial composition while reducing the biomass of major microbial groups and the activities of most enzymes, especially in Abies faxoniana plots. The combination of warming and nitrogen addition increased soil labile C and N pools in Picea asperata plots and was beneficial for soil recalcitrant C, as well as for labile and total C and N pools in A. faxoniana plots. Results indicated that future warming will slightly affect soil microbial communities and their related soil processes. However, warming combined with high nitrogen deposition will significantly constrain soil microbial biomass and enzyme activities, consequently increasing soil C and N pools in sub-alpine coniferous forests of this region.

Aims There is an obvious seasonal freezing and thawing process (early winter freezing-thawing, late winter freezing, and early spring freezing-thawing) in the subalpine coniferous forests, where there is also a strong effect of climate change in winter. Hence, global warming will likely affect the seasonal freezing and thawing process in this area. Our objective was to determine the ecophysiological characteristics of leaves and fine roots in dominant tree species in a subalpine coniferous forest of western Sichuan during seasonal frozen soil period, in order to improve our understanding of the ecological processes in subalpine coniferous forests. Methods We analyzed the changes in malondialdehyde (MDA) content, osmoregulation substance content, tissue water content, peroxidase (POD) activity, and nitrate reductase (NR) activity in leaves and fine roots of Picea asperata and Abies fargesii var. faxoniana seedlings, and measured specific root length, specific surface area, diameter and tissue density of fine roots over the course of the seasonal frozen soil period. Important findings The POD activity and the contents of proline and soluble proteins in leaves were significantly lower than in fine roots, despite that the daily fluctuations of soil temperature was less than that of air temperature during the seasonal frozen soil period, suggesting that fine roots were more susceptible to the seasonal frozen soil than leaves. In comparison with the soil freezing period, a greater daily fluctuations of air and soil temperature resulted in an increase in the soluble sugar content in leaves of P. asperata and the POD activity and 344 植物生态学报 Chinese Journal of Plant Ecology 2014, 38 (4): 343–354 www.plant-ecology.com proline content in leaves of the two species during the soil freezing-thawing period, whereas the tissue water content was significantly decreased and the contents of proline, soluble proteins and soluble sugars were significantly increased in fine roots, indicating that the effects of soil freezing-thawing on plants were stronger than soil freezing. In soil freezing-thawing period, the POD activity and osmolyte contents were significantly increased in both A. fargesii var. faxoniana and P. asperata, but changes in the MDA content and the NR activity in the fine roots and leaves were not consistent in the two species. In A. fargesii var. faxoniana, the MDA content was significantly increased in fine roots and the NR activity was significantly reduced in both leaves and fine roots. A change in the MDA content was only observed in leaves of P. asperata, which was significantly decreased, indicating that P. asperata had more tolerance to soil freeze-thaw cycles. Moreover, no significant changes in fine root morphology and growth were observed during the seasonal frozen soil period.

Divergence during the early stage of speciation can be driven by a population bottleneck via reduced gene flow and enhanced lineage sorting. In this study, we aimed to examine whether such bottlenecks occurred during the initial speciation of two closely related spruce species Picea asperata and P. crassifolia occurring on the Qinghai–Tibet Plateau (QTP). We analyzed sequences of three chloroplast, two mitochondrial DNA fragments and a further 13 nuclear loci from 216 individuals of the two species. Both species showed a low level of genetic diversity in contrast to other congeners occurring in the QTP and adjacent regions. The estimated population sizes of P. asperata and P. crassifolia are less than the ancestral population size before splitting. These results together with multiple statistical tests (Tajima's D, Fu and Li's D* and F*) suggest that these two species underwent recent bottlenecks. Based on approximate Bayesian computation (ABC), we also determined that the period of the population shrinkage was consistent with the interspecific divergence during the late Pleistocene. The reduced population sizes and the divergent selection may together have triggered the initial divergence under high gene flow between these two species. Our results therefore highlight the importance of climatic oscillations during the late Pleistocene in promoting speciation through changing demographic sizes of the ancestral species on the QTP and in adjacent regions.

Tree species can exert a strong influence on rhizosphere nutrient cycling through root and rhizosphere processes and create feedback in the patterns of nutrient cycling in forest ecosystems. In this study, we conducted an experiment to compare the rhizosphere effects of two coniferous species on N transformation as well as their responses to experimental warming using infrared heaters in the Eastern Tibetan Plateau. We examined the potential net N mineralization and nitrification rates. N availability, and microbial biomass C (MBC) and N (MBN) in rhizosphere soils of Picea asperata and Abies faxoniana plots and compared them to bulk soils. The infrared heater increased both the mean air and the soil temperatures by 1.5 degrees C and 2.1 degrees C respectively. Potential net N mineralization and net nitrification rates were generally greater in rhizosphere soils for the two conifers than in bulk soil, especially in the warmed plots. This led to higher NH4+ and NO3- concentrations in the rhizosphere soils. MBC and MBN were markedly higher in the rhizosphere soils relative to bulk soil in the study plots. In the control subplots of P. asperata, MBC, MBN, potential net N mineralization and net nitrification rates in the rhizosphere were 9.6%, 21.7%, 33.3% and 20.1% greater than in the bulk soil, respectively. MBC, MBN, potential net N mineralization and net nitrification rates in the control subplots of A. faxoniana, however, were 2.0%, 7.7%, 22.0% and 11.8% higher, respectively, in the rhizosphere than in the bulk soil; all of the variables were significantly lower than those of P. asperata subplots. Warming significantly promoted N transformation and nutrient availability by enhancing the rhizosphere priming effects for the two conifers, but the magnitudes of the rhizosphere effects on soil N transformation stimulated by warming were generally greater in P. asperata than in A. faxoniana subplots. Differences in the altered morphological and functional characteristics of the roots between the two species under experimental warming could be largely responsible for this variation. Taken together, the results indicated that the two species exhibited similar patterns but with considerably different magnitudes of rhizosphere effects on N transformations in response to experimental warming, implying different capacities of the two conifers to acquire nutrients and thereby altered the competitive and adaptive relationships between the tree species under climate change. (c) 2012 Elsevier B.V. All rights reserved.

Temperature and litter quality are two of the key factors controlling litter decomposition. Predicted global warming and vegetation succession will therefore have profound impacts. This study was conducted to assess effects of experimental warming on litter decomposition and nutrient dynamics of two contrasting tree species (red birch, Betula albosinensis Burk., and dragon spruce, Picea asperata Mast.) and a mixture of the two with the heating cable method in the eastern Tibetan Plateau of China. This treatment raised surface soil temperature by 3.2 degrees C and resulted in a 5.2% decline in soil moisture 10 cm below the soil surface. The water content of dragon spruce, red birch and mixed litter was decreased by 18, 11 and 13%, respectively. Marked differences between the two species in the decomposition rates and nutrient remaining percentages were detected. Moreover, we found positive, non-additive effects of litter mixture. Experimental warming did not affect mass loss and nutrient release of dragon spruce litter but significantly increased mass loss and affected nutrient release of red birch and mixed litter during the early decomposition period. Overall, inter-specific (red birch and dragon spruce) differences in decomposability were substantially larger than warming-induced responses. Thus, a warming-induced community succession towards dragon spruce forests in the Tibetan Plateau region could have a greater impact on early litter decomposition than warming itself.

Low temperatures are generally limiting factors in alpine ecosystems. Predicted global warming therefore could have profound impacts on these ecosystems in the future. This study was conducted to compare effects of experimental warming on the phenology, growth and photosynthesis of dragon spruce seedlings of two age classes (2- and 8-year-old seedlings) grown in two contrasting subalpine forest ecosystems (dragon spruce plantation versus spruce-fir dominated natural forest) using the open top chamber (OTC) method in the Eastern Tibetan Plateau of China. The OTCs enhanced daily mean air (30 cm above the soil surface) and soil temperatures (5 cm below the soil surface) by 1.2 °C and by 0.6 °C in two experimental sites, respectively, throughout the growing season. Conversely, soil volumetric moisture declined by 3.8% and 2.8% in the plantation and natural forest. Experimental warming markedly extended the growing season of two age classes in both sites. However, there were no clear differences in phenology between ages or sites. Warming often increased the growth and photosynthesis of dragon spruce seedlings. There were pronounced differences in the morphological and physiological performances between ages or sites. Nevertheless, there were no significant interactions of warming, age and site on phenology, growth and photosynthesis. Irrespective of seedling ages or experimental sites, artificial warming had significant increases in component biomass except the root. The size of warming effect on biomass depended strongly on seedling age and experimental site. Elevated temperatures remarkably increased net N mineralization rates and extractable inorganic N pools in both sites. Both net N mineralization and extractable inorganic N pool were pronouncedly greater in the natural forest than in the plantation. Taken together, our results indicate that warming generally has positive effects on the phenology, growth and photosynthesis for both seedling age classes in any site. Younger seedlings are more sensitive to warming as compared with the older seedlings. Reforestation dramatically affects the responses of soil N turnover and availability to warming. We conclude that both direct and indirect warming effects synchronously modify the seedling responses.

The aim of this study was to analyze the composition and spatio-temporal variation of soil macroinvertebrate communities in the northern Hengduanshan Mountains, Southwest China. The soil macroinvertebrates were investigated in April, August and November of 2008 in two deciduous broad-leaved forests: secondary shrub forest (SSF) and Betula albosinensis forest (BSF), two coniferous forests: Picea asperata plantation (PAP) and Abies fabri and Larix kaempferi mixed forest (ALF), a coniferous (A. fabri) and broad leaf (B. albosinensis) mixed forest (ABF) and a subalpine meadow (SM) at elevations of 2659 to 3845 m. The soil macroinvertebrate community showed typical zonal characteristics compared with other localities in China. It comprised at least 113 taxa and was dominated by Insects (43.33%, mainly Coleoptera and Diptera), followed by Diplopoda (16.37%), Malacostraca (14.31%), Oligochaeta (12.71%) and Chilopoda (6.67%). Abundances of each taxa showed clear differences among habitats. Community abundance ranged from 71.56 individuals/m2 in the PAP to 148.00 individuals/m2 in the SM. The composition and structure of the soil macroinvertebrate communities varied among the six habitats and changed with the sampling periods. The richness, abundance and Shannon index of soil macroinvertebrate communities were significantly different among habitats, but not between sampling periods. Significant temporal responses in abundance were recorded in the SSF and BSF and the Shannon index for the SM. Further analysis showed that the abundance of the seven taxonomic groups also differed significantly among habitats, but that sampling period only had significant effects on a few taxonomic groups. Patterns of temporal variation in abundance differed among the seven taxonomic groups, even when the same taxa also differed markedly among habitat types. On the whole, these temporal variations in abundance on community and taxa group levels were greater in the SSF and BSF than in the PAP, ABF, ALF and the SM. However, the habitat had a stronger effect on soil macroinvertebrates than the sampling period. Moreover, a significant correlation was found between the abundance, richness and Shannon index of soil macroinvertebrate community and plant species richness, but not with soil properties or elevation. Additionally, more taxonomic groups were significantly influenced by the litter mass and plant coverage, but few with soil properties. Plant community was the main environmental determinant influencing macroinvertebrate distribution in ecosystem of the northern Hengduanshan Mountains and presented a greater effect on the soil macroinvertebrates than soil properties or elevation. The temporal effects on soil macroinvertebrates were stronger in the deciduous broad-leaved forests than in the coniferous forests.

Microorganism plays an essential role in the decomposition of litter and senesced fine root,as a consequence of which more and more attentions have been paid to the microbial biomass dynamics in litter and soil in the past two decades.Moreover,increasingly studies have also demonstrated that lots of litter mass lost in cold winter in the seasonal freeze-thaw area.However,little information has been available on the dynamics of microbial biomass during litter decomposition in wintertime,far less for fine roots decomposition.In order to character the dynamics of microbial biomass during fine roots decomposition in a alpine forest over the growing season and freeze-thaw season,microbial biomass carbon(MBC),nitrogen(MBN) and phosphorus(MBP) were measured using the litterbag method from November 11,2009 to November 11,2010.The fine roots of Picea asperata,Abies faxoniana and Betula albosinensi were selected which are three representative tree species in the alpine and subalpine forest of Western China.Microbial biomass C(MBC) displayed a sharp decline tendency before the soil frozen as soil temperature decreased,and significantly increased utile to soil thawing,but continually declined as temperature increased after the middle stage of soil thawing,and then a increased tendency was observed.However,the changed time of MBC was different in the fine root decomposition of different species.The peak values of MBC during the decomposition of spruce and fir fine roots were observed in the late stage of growing season,but which of birch was detected in the early stage of soil frozen.MBN displayed the similar dynamics pattern during the fine roots decomposition for all three species,which rapidly decreased until soil completely frozen,and showed little changes during the whole freeze-thaw season,but obviously increased to a peak value in the later stage of growing season.In addition,MBP during the decomposition of spruce and fir fine roots were increased as the decomposition proceeded,although which of birch displayed its maximum value in the later stage of soil thawing,another peak value in the middle stage of growing season,and then obviously declined in the later stage of growing season.The results indicated that large quantities microorganisms could be available even in winter,which could do great contributions to the litter decomposition.Nevertheless,the microbial biomass could be significantly affected by fine root quality,temperature and other climate conditions.

The annual and seasonal variations in the temperature sensitivity of soil respiration (Rs) were assessed through continuous measurements during the 2004–2006 growing seasons using chamber-based techniques in two sub-alpine forest ecosystems in the Eastern Qinghai-Tibet Plateau, China. The study sites were 40-year-old spruce plantations ( Picea asperata ) (FSPF) and Faxon Fir Primary Forest (FPF). Our results showed that Q 10, regardless of site origin, exhibited a strong seasonal and annual variation pattern, and decreased with soil temperature increase. Estimated Q 10 values ranged between 1.16 and 24.3. The maximum, annual, mean Q 10 values remained consistent over 3 years, while the highest Q 10 values (7.01 in FSPF and 6.39 in FPF) occurred in 2005 (for all sites). There was no significant difference observed among Q 10 values between the two forest types in each year (2004–2006) ( p = 0.07). Q 10 values were fitted well with data of soil temperature using linear regression models, while the correlation between Q 10 and soil moisture was not significant ( p > 0.1). This study suggested that soil temperature was the dominant factor influencing Q 10 values, while soil moisture was a potential contributor to the annual and seasonal variations of Q 10 in a sub-alpine forest. Due to the complexity of correlation between Rs and soil moisture, Q 10 values derived from annual and seasonal patterns of R S should be used with caution when predicting future soil CO 2 emissions under conditions of global warming.

Summary Naturally regenerated seedlings or saplings in post-harvest forest stands are expected to contribute to population regeneration and the restoration and maintenance of genetic diversity in forest trees. In this study, we used intact old-growth stands of dragon spruce ( Picea asperata Mast.) as a benchmark to compare genetic diversity between mature and progeny cohorts sampled from post-harvest planted and post-harvest naturally regenerated stands in western Sichuan, China. Mature cohorts in the intact stands exhibited the highest levels of genetic diversity among the three types of stands. Genetic diversity within the progeny cohorts in the intact stands was significantly lower than their parent cohorts for all five measures of diversity. The progeny cohorts of the intact stands had lower genetic diversity than progeny cohorts from two types of post-harvest stands, but only for two measures of diversity. There were no significant differences in diversity between the mature or progeny cohorts of the planted and naturally regenerated stands. When mature and progeny cohorts were pooled, genetic variation within the united sample was enriched and close to that of the mature cohort in the intact stands. High genetic similarity and low genetic differentiation between progeny cohorts in the post-harvest stands and mature cohorts in the intact stands indicated a sufficient seed or pollen migration from the surrounding intact stands into the regenerated area. These findings illustrate the important role of the mature cohorts in the intact stands as reservoirs of genetic diversity.

Dragon spruce (Mast) is a conifer endemic to western China and a popular species for reforestation programs of this region. We used inter simple sequence repeats (ISSRs) molecular markers to conduct a population genetic study of nine geographically close stands from three types of dragon spruce forests: (1) intact, (2) plantation, and (3) natural regenerated following clearcut. Our main objective was to investigate the genetic structure of these populations and our expectation was that gene flow was an important evolutionary force among them. We were unable to sample a large number of individuals in each cohort. However, when young and mature cohorts from a particular stand were interpreted as a single unit, then sample size increased significantly. The highest levels of genetic diversity were found in mature cohorts of the intact forests, the lowest in young cohorts of these stands. Contrary to our expectations, low levels of gene flow existed between mature and young cohorts of different forest types; and most gene flow occurred between cohorts belonging to the same stand. There were major differences in the genetic structure of the three types of stands. Our results have conservation implications as the majority of wild populations of dragon spruce are small and fragmented. Low gene flow among populations will lead to high levels of genetic drift and a decline of genetic diversity within populations.

The endemic Chinese Grouse (Tetrastes sewerzowi) inhabits subalpine coniferous forests. Little is known about its diet in the breeding season, especially while birds feed on the ground. Analysis of crop contents indicated that willow (Salix spp.) was the primary food of males (>98% wet weight, n = 4), whereas Dragon spruce (Picea asperata) seeds and willow were the primary foods of females (both >40% wet weight, n = 2). Dragon spruce seeds, invertebrates (mainly ants), and forbs were frequently consumed by females, but seldom by males, possibly to meet the nutrient constraints of egg formation. We suggest the different diets of males and females of this monogamous species may be the result of females allocating more time to searching for scarce, nutritious food, whereas males spend more time in vigilance behavior.

In the subalpine zone of the Qinghai-Tibetan Plateau of China, Dragon spruce (Picea asperata Mast.) is com- monly used for reforestation. The aim of the present work was to study the effects of seasonally frozen soil on the germi- nation of P. asperata seeds and to investigate whether these effects were associated with resumption of the antioxidant defense system. The nonfrozen treatment resulted in near failure of germination (1%) and was associated with relatively high levels of hydrogen peroxide (H2O2) and low activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxide (APX). Germination of P. asperata seeds at 10 cm under the seasonally frozen soil was higher than that at 5 cm by 26%; this higher germination rate was associated with the recovery of SOD, CAT, and APX activities. The levels of malondialdehyde (MDA) in seeds from seasonally frozen treatments were higher than those in the nonfrozen treatment, implying greater lipid peroxidation and that frozen seeds might have suffered from oxidative stress. The results indicate that seasonally frozen soil facilitated the germination of P. asperata seeds and that germination was closely related to the resumption of antioxidant enzymes activity. Overall, these findings suggest that the disappearance of seasonally frozen ground caused by global warming might result in failure of regeneration of P. asperata. Resume´ : L'epicea de Chine (Picea asperata Mast.) est couramment utilisepour le reboisement dans la zone subalpine du plateau Qinghai-Tibet en Chine. Le but des travaux presentes dans cet article consistait aetudier les effets d'un gel saison- nier dans le sol sur la germination des graines de P. asperata et a determiner si ces effets etaient associesa u retablisse- ment du systeme de defense antioxydant. Un traitement sans gel a empechepresque toute germination (1 %) et etait associea un niveau relativement elevede peroxyde d'hydrogene (H2O2 )e t aune faible activitede la superoxyde dismutase (SOD), de la catalase (CAT) et de l'ascorbate peroxydase (APx). Aune profondeur de 10 cm dans un sol soumis a un gel

The morphological and physiological plasticity to 6 light conditions was investigated for seedlings of 4 tree species dominating at different successional serals in subalpine coniferous forests in eastern Qinghai-Tibet Plateau, China. Abies faxoniana is a late successional species, while Betula albo-sinensis is a pioneer tree species, with Picea asperata and Acer davidii among other mid-late successional species. To compare the responses of photosynthetic characters to different growth light conditions, the seedlings were potted and placed in artificially shaded chambers with gradients of 100%, 55%, 40%, 25%, 15% and 7% of the full sunlight, respectively. During two and a half years' cultivation, various morphological and photosynthetic parameters were measured and analyzed. The results were: 1) all seedlings of the four species under the low growth light conditions showed decrease in root collar diameter, relative growth rate, leaf thickness, root mass ratio, leaf area-based photosynthetic capacity, dark respiration rate, light saturation point and light compensation point, while showed increase in specific leaf area, above-ground to under-ground mass ratio, specific stem length, leaf mass ratio and stem mass ratio; 2) under most light conditions, A. faxoniana of the two conifers revealed lower values in both leaf area-based photosynthetic capacity and respiration rates than P. asperata ; the same fact held true for the two broad-leaved trees with lower values observed in B. albo-sinensis ; 3) under higher light conditions, relative growth rates of P . asperata and B . albo-sinensis got higher values than those of A . faxoniana and A . davidii , while contrary results were obtained under lower light regimes; 4) the means of phenotypic plastic indices of the eleven morphological and physiological parameters of P . asperata and B . albo-sinensis were higher than those of A . faxoniana and A . davidii , respectively. The findings indicate that A . faxoniana has better adaptation to low light regimes, but as a shade-tolerant species, it is not so adapted to low light regimes as the trees of earlier successional serals, especially P . asperata and B . albo-sinensis . Of the four tree species, physiological plastic indices were higher than morphological plastic indices, suggesting that morphological plasticity plays an important role in their adaptation to different growth light conditions. The results also support the hypothesis that ecophysiological traits of tree species determine their successional status and associate habitats of their seedlings.

The responses of two Picea asperata Mast. populations to enhanced ultraviolet B (UV-B) radiation under well-watered and drought conditions were investigated to further elucidate the effect of UV-B radiation on drought tolerance. Two P. asperata populations originating from wet- and dry-climate regions in China were employed. Drought significantly decreased the CO2assimilation rate, stomatal conductance, and effective photosystem II quantum yield, while it significantly increased nonphotochemical quenching and the activity of superoxide dismutase in both populations. Compared with the wet-climate population, the dry-climate population was more acclimated to drought stress and showed much higher superoxide dismutase and ascorbate peroxidase activities and much lower levels of malondialdehyde and electrolyte leakage. Enhanced UV-B radiation also induced a significant decrease in chlorophyll content in both populations under well-watered conditions and a significant increase in UV-absorbing compounds in the wet-climate population. After exposure to different UV-B radiation levels and watering regimes over one growing season, the increases in malondialdehyde and electrolyte leakage, which are indicators of damage to the cellular membrane induced by drought, were less pronounced under the combination of enhanced UV-B radiation and drought than they were under well-watered conditions without enhanced UV-B radiation. In addition, an additive effect of drought and UV-B radiation on the CO2assimilation rate and stomatal conductance was observed in the wet-climate population and on the activity of ascorbate peroxidase and nonphotochemical quenching in the dry-climate population. These results suggest that the UV-B exposure may have alleviated some of the damage induced by drought.

A survey of allozymic alleles and genetic diversity was conducted for ten natural populations of Picea asperata Mast. originating from the mountains of Southwest China. A total of twenty-seven alleles at seventeen loci were observed. Ten of the loci were found monomorphic. Our results showed that the populations sampled were characterized by low genetic diversity (mean He = 0.096) and a low level of inbreeding (mean Fis = 0.005). The UPGMA tree of genetic relationships indicated that there was significant differentiation among populations. The coefficient of genetic differentiation among populations, based on Fst, equaled 0.311. Such extensive inter-populational differentiation detected in P. asperata could have resulted from allele frequency divergence among populations, particularly, in one population. Introgression from another species, variation in environmental conditions, and differing selection pressures could be some of the factors attributing to significant differences among populations. In addition, our results showed that the geographic and genetic distances were not correlated in the populations of P. asperata. Based on the genetic information obtained, we concluded that monitoring appropriate genetic markers may be an effective means of identifying potential genetic changes occurring during forest tree evolution.

This study represents a geographical approach to morphological variation of cones, needles and seeds in natural dragon spruce (Picea asperata Mast.) populations across western China and the relationship between morphological traits and weather variation for the origins of populations. Significant differences were found for all cone, needle and seed traits among populations and trees within populations. The coefficients of variation in 2 higher latitude populations were higher than those in other populations in all traits except for needle width and seed width. Fairly high within-population variability was also detected for cone dry weight, seed dry weight and needle traits in this study. Cone length, cone width, cone dry weight, seed scale length, seed scale width and seed wing length were strongly positively intercorrelated. Seed length and seed dry weight showed a significantly positive correlation with seed wing length. And needle width showed a significant negative correlation with cone traits, seed scale length, seed wing length and seed length. The higher the annual mean temperature, the higher the average cone length. This study also revealed a negative linear dependence on latitude: the higher the latitude, the lower the population average seed length. Seed dry weight was positively and linearly related with altitude.

From 2002 to 2003, based on the investigation of sample plots and stem analysis of remained plantation communities in the areas of returning farmland to forest in the 1980s in Datong County, Qinghai Province, this paper studies tree productivity and moisture potential productivity of six types of plantations on the land of returning farmland to forest, such as green poplar (Populus cathayana Rehd.) and shrub mixed forest, Asia white birch (Betula platyphylla) and China spruce (Picea asperata) mixed forest, Dahurian larch (Larix gmelinii) pure forest, China spruce pure forest and Asia white birch pure forest and so on. The results show that: in sub-humid region of Loess Plateau, 3 000 trees per hm2 is a proper standard of planting density. Under current condition, the productivity index of green poplar and shrub mixed forest, Asia white birch pure forest, China spruce pure forest, and Asia white birch and China spruce mixed forest with the density of 2 100-3 333 trees per hm2 can serve as potential productivity standard of actual biomass of arbor established forest. In sub-humid area, Thornthwaite Model is adopted to estimate plant climate potential productivity, which is about 8 462 kg·hm−2·a−1. The actual potential water productive efficiency of Purplecone spruce (Picea purpurea) and Asia white birch pure established forest are 17.22 and 22.14 kg·mm−1·hm−2·a−1 respectively, and that of green poplar and shrub mixed established forest, and Asia white birch and China spruce mixed established forest are 21.14 and 19.09 kg·mm−1·hm−2·a−1 respectively. The potential productivity of green poplar and shrub mixed forest, Asia white birch and China spruce mixed forest, China spruce pure forest and Asia white birch pure forest which have grown into forest with the density of 3 000 trees per hm2 have attained or been close to that of local climax community, which is local maximum tree productivity at present. These types of forestation models are the developing direction of the returning farmland to forest project.

We measured plant structural and physiological responses of two sympatric Picea species, Picea likiangensis (Franchet) E. Pritzel var. balfouriana and Picea asperata Masters var. retroflexa to altitude close to the treeline in the eastern Himalaya. Most measured tree characteristics differed between different altitudes, between different ages, and between shaded and un-shaded treatments. Both P. likiangensis and P. asperata had lower foliage area/stem cross-sectional area ratios, smaller specific leaf areas, higher root mass/foliage area ratios, and less negative δ13C at 3,900 m than at 3,600 m altitude, and in the un-shaded treatment than in the shaded treatment. The 7- and 9-year-old seedlings also showed lower foliage area/stem cross-sectional area ratios, higher root mass/foliage area ratios and less negative δ13C than younger seedlings. Shading resulted in an increase of biomass accumulation at all altitudes. A close relationship, independent of altitude, was observed between δ13C and specific leaf area, suggesting that internal resistance could limit CO2 diffusion to the site of carboxylation. The results indicate that, in spite of greater water availability, trees at higher altitudes show quite a number of apparent acclimations to drought.

Summary In this paper we describe the pollen developmental processes in Picea asperata Mast. by means of cytochemical and ultrastructural methods, with an emphasis on starch grains, callose dynamics and the ultrastructure of prothallial cells. It was observed that microsporogenesis and pollen development of Picea asperata proceeded from early March to late April. The meiosis of pollen mother cells (PMC) was of the simultaneous type and the arrangement of microspores in the tetrad was tetrahedral. A mature pollen grain consisted of four cells. Therefore, the pollen development of this species should be categorized into the Keteleeria type. During meiosis, starch grains and callose had a regular dynamic distribution. At the four-celled stage, the organelles were asymmetrically distributed. The degenerated prothallial cells had some remarkable characteristics that are typical to cells involved in programmed cell death (PCD), a phenomenon observed in some plants and animals. In comparison with other taxa of the Pinaceae, the synchronized development from meiosis of the pollen mother cell to mature pollen together with frequent insect damage to the pollen cones might be a possible cause of frequent low pollen production in this species.

In this study, spruce tree rings from the southern slope of mid-Qinling Mountains were adopted to investigate the characteristics of average minimum temperatures during the past 138 years. Analysis showed that the interannual variability in radial growth of trees was positively correlated with the interannual variability of average minimum temperatures from previous December to current September (VTM DS) in the study area during 1955–2010 ad. Based on the correlation analysis, the VTM DS were reconstructed for 1876–2013 ad with an explained variance of 42.5 % for the calibration period. Among the 22 dramatic changing years, extreme changes occurred more times when it was cooling, while the warming was comparatively gentle. Both the 10-year filtering of VTM DS series and the frequency of occurrences for those dramatic changing years showed a relatively stationary variation after the early 1950s. Over the last five decades, the accumulated VTM DS series showed an obvious warming trend, and the increase of the minimum temperature had contributed to the regional warming. The comparison of VTM DS and the dryness/wetness indices generally reflected cold-wet and warm-dry climate conditions in the study area. Significant positive correlations between the reconstructed VTM DS and the gridded minimum temperature indicated a regional representative of the temperature reconstruction, and positive correlations between VTM DS and sea surface temperature (SST) of the Indian Ocean and western Pacific regions suggested a possible linkage between the VTM DS variations and the Asian summer monsoon. Synchronous fluctuations in three tree-ring study series and connections of VTM DS with Arctic oscillation (AO) and El Nino-Southern Oscillation (ENSO) activities suggested that the minimum temperature variations in the TTH area responded sensitively to large-scale climate fluctuations and were the results of atmosphere-ocean interactions.

Despite the perceived importance of exudation to forest ecosystem function, few studies have attempted to examine the effects of elevated temperature and nutrition availability on the rates of root exudation and associated microbial processes. In this study, we performed an experiment in which in situ exudates were collected from Picea asperata seedlings that were transplanted in disturbed soils exposed to two levels of temperature (ambient temperature and infrared heater warming) and two nitrogen levels (unfertilized and 25 g N m(-2) a(-1) ). Here, we show that the trees exposed to an elevated temperature increased their exudation rates I (μg C g(-1) root biomass h(-1) ), II (μg C cm(-1) root length h(-1) ) and III (μg C cm(-2) root area h(-1) ) in the unfertilized plots. The altered morphological and physiological traits of the roots exposed to experimental warming could be responsible for this variation in root exudation. Moreover, these increases in root-derived C were positively correlated with the microbial release of extracellular enzymes involved in the breakdown of organic N (R(2) = 0.790; P = 0.038), which was coupled with stimulated microbial activity and accelerated N transformations in the unfertilized soils. In contrast, the trees exposed to both experimental warming and N fertilization did not show increased exudation rates or soil enzyme activity, indicating that the stimulatory effects of experimental warming on root exudation depend on soil fertility. Collectively, our results provide preliminary evidence that an increase in the release of root exudates into the soil may be an important physiological adjustment by which the sustained growth responses of plants to experimental warming may be maintained via enhanced soil microbial activity and soil N transformation. Accordingly, the underlying mechanisms by which plant root-microbe interactions influence soil organic matter decomposition and N cycling should be incorporated into climate-carbon cycle models to determine reliable estimates of long-term C storage in forests.

Background: We have limited understanding of root foraging responses when plants were simultaneously exposed to nutrient heterogeneity and competition, and our goal was to determine whether and how plants integrate information about nutrients and neighbors in root foraging processes. Methodology/Principal Findings: The experiment was conducted in split-containers, wherein half of the roots of spruce (Picea asperata) seedlings were subjected to intraspecific root competition (the vegetated half), while the other half experienced no competition (the non-vegetated half). Experimental treatments included fertilization in the vegetated half (FV), the non-vegetated half (FNV), and both compartments (F), as well as no fertilization (NF). The root architecture indicators consisted of the number of root tips over the root surface (RTRS), the length percentage of diameter-based fine root subclasses to total fine root (SRLP), and the length percentage of each root order to total fine root (ROLP). The target plants used novel root foraging behaviors under different combinations of neighboring plant and localized fertilization. In addition, the significant increase in the RTRS of 0-0.2 mm fine roots after fertilization of the vegetated half alone and its significant decrease in fertilizer was applied throughout the plant clearly showed that plant root foraging behavior was regulated by local responses coupled with systemic control mechanisms. Conclusions/Significance: We measured the root foraging ability for woody plants by means of root architecture indicators constructed by the roots possessing essential nutrient uptake ability (i.e., the first three root orders), and provided new evidence that plants integrate multiple forms of environmental information, such as nutrient status and neighboring competitors, in a non-additive manner during the root foraging process. The interplay between the responses of individual root modules (repetitive root units) to localized environmental signals and the systemic control of these responses may well account for the non-additive features of the root foraging process.

A survey of allozymic alleles and genetic diversity was conducted for ten natural populations of Picea asperata Mast. originating from the mountains of Southwest China. AÂ total of twenty-seven alleles at seventeen loci were observed. Ten of the loci were found monomorphic. Our results showed that the populations sampled were characterized by low genetic diversity (mean He = 0.096) and a low level of inbreeding (mean Fis = 0.005). The UPGMA tree of genetic relationships indicated that there was significant differentiation among populations. The coefficient of genetic differentiation among populations, based on Fst, equaled 0.311. Such extensive inter-populational differentiation detected in P. asperata could have resulted from allele frequency divergence among populations, particularly, in one population. Introgression from another species, variation in environmental conditions, and differing selection pressures could be some of the factors attributing to significant differences among populations. In addition, our results showed that the geographic and genetic distances were not correlated in the populations of P. asperata. Based on the genetic information obtained, we concluded that monitoring appropriate genetic markers may be an effective means of identifying potential genetic changes occurring during forest tree evolution.

SummaryPicea asperata Mast., which occurs in a restricted habitat in western China, has a wide ecological amplitude. In the present study, ten natural populations of P. asperata were studied using AFLP markers to investigate the population genetic structure and the level of genetic diversity. Of the 210 loci identified with two EcoRI/MseI primer combinations, 142 loci were found to be polymorphic. Yet, the level of genetic diversity observed within populations was quite low. The averages of NEI’s gene diversities (h) and Shannon's indices of diversity (I) calculated across populations equaled 0.156 and 0.227, respectively. The coefficient of gene differentiation among populations, based on the estimate GSTand the unbiased estimate Φst, equaled 0.340 and 0.231, respectively. The mean genetic distance (D) between population pairs was 0.119 (range 0.050-0.156). Such high values indicate that there is significant differentiation among populations of P. asperata. Several factors could have contributed to the strong population differentiation, including relatively limited gene flow between populations (Nm= 0.968). Variation in environmental conditions and consequent selection pressures may be other factors attributing to the high level of genetic differentiation among populations. In addition, it was discovered that the geographic distances are not correlated with the genetic distances between the populations of P. asperata.

Microsatellite variation of Picea asperata Mast. originating from the mountains of China was investigated by analyzing variation at seven SSR loci in 250 individuals representing ten populations. A fair degree of genetic diversity and considerable population subdivision occurred with the mean gene diversity (H) of 0.707, and genetic distances among populations varying between 0.121 and 0.224 (F) and between 0.100 and 0.537 (R). However, inter-population genetic distances showed no correlation with geographic distances between the population sites. This ruled out a simple isolation by distance model and suggested that migration does not have a great impact. In fact, the amount of gene flow, detected using private alleles, was very low, equaling only 0.753. Allele permutation tests revealed that stepwise-like mutations, coupled with genetic drift, could contribute to population differentiation. Moreover, significant genetic differences between populations were detected at most loci. The results indicate that natural selection, presumably through environmental stress, may be one of the main factors causing micro-geographical differentiation in the genetic structure of P. asperata. Based on SSR genotypes, 70% of the 250 individuals were correctly classified into their sites of origin. This suggests that microsatellites (SSRs) are effective in distinguishing genotypes of P. asperata originating from diverse eco-geographical sites in China.STST

With the planted forest ecosystems of Cercidiphyllum japonicum, Betula utilis, Pinus yunnansinsis, and Picea asperata in subalpine area of west Sichuan as test objects, their total biomass and the C and N contents in soils and tree organs were determined. The results showed that the allocation of C in tree organs had less correlation with the age of the organs, while that of N and C/N ratio had closer relationship with the age. The N content in young organs was higher than that in aged ones, whereas the C/N ratio was higher in aged organs than in young organs, and higher in the leaf litters of needle-leaved forests than in those of broad-leaved forests. There was an obvious enrichment of C and N in the topsoil of test forests. The accumulated amounts of C and N in the whole planted forest ecosystem, including tree, litter, and 0-40 cm soil layer, were 176.75-228.05 t x hm(-2) and 11.06-16.54 t x hm(-2), respectively, and the nutrients allocation ratio between soil-litter and tree was (1.9-3.3):1 for C and (15.6-41.5):1 for N. Needle-leaved forests functioned as a stronger "C-sink" than broad-leaved forests. The decomposition rate of the leaf litters in needle-leaved forests was larger than that in broad-leaved forests, with the turnover rate being 2.2-3.7 years and 3.9-4.2 years, respectively. During the decomposition of leaf litter, the C in all of the four forests released at super-speed, with the turnover rate being 1.9-3.4 years. As for N, it also released at super-speed in C. japonicum and B. utilis forests, with the turnover rate being 1.9-3.2 years, but released at low speed in P. yunnansinsis and P. asperata forests, with the turnover rate being 6.7-8.5 years.