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AIM: Dead fine roots are crucial components of the carbon cycle in global forest ecosystems. Despite their importance, knowledge concerning geographical patterns of dead fine root pools (necromass) and factors influencing their dynamics remain scarce across the globe. LOCATION: Global. METHODS: We analysed 136 published case studies covering 169 forest sites located throughout the world to identify broad patterns of necromass and biomass (living fine root pools) and to determine the responses to climate, edaphic gradients and stand properties. RESULTS: W‐shaped pattern of forest necromass with latitude, from the Southern Hemisphere via the equator to the Northern Hemisphere, was observed. Specifically, more necromass was found at both low (tropical forests) and high latitudes (boreal forests), whereas less necromass was found at mid latitudes (temperate forests), which is in line with patterns of carbon stocks in soils at the global scale. Broad‐leaf forests had greater necromass than needle‐leaf forests, and fine root necromass of the two forest types showed opposing trends in response to shifts in mean annual precipitation and different sensitivities to changes in mean annual temperature and edaphic properties (e.g. soil carbon/nitrogen ratio and pH). Necromass increased with soil organic layer thickness and stand age for both forest types. MAIN CONCLUSIONS: The hemispheric symmetrical necromass distribution is likely determined by changes in environmental conditions across latitudes. Different responses of dead fine roots in broad‐leaf and needle‐leaf forests may be caused by their distinct allocation and accumulation of carbon in relation to climate and to edaphic and forest characteristics at the global scale. Our results have important implications for accurate quantification and modelling of forest ecosystem carbon stocks and cycles and for assessments of their sensitivity and stability in a changing climate.

Although much research has explored changes in ecosystem functions associated with global environmental changes, the mechanistic pathways behind the observed changes remain poorly understood. Using an 11‐year experiment that increased growing season precipitation and nitrogen deposition in a temperate steppe, we explored the relative importance of direct and indirect environmental change effects on plant primary productivity. We show that increases in water and nitrogen availability influenced plant productivity via both direct and indirect pathways. While both treatments stimulated plant productivity, changes in plant productivity cannot be explained by observed changes in species or phylogenetic diversity. Instead, the indirect effects of water and nitrogen addition were through their positive effects on plant functional diversity. Importantly, while the increase in one component of functional diversity (community‐level weighted mean of plant stature) resulted in increased productivity, the increase in another component of functional diversity (functional dispersion) resulted in decreased productivity. Synthesis. Our study provides the first evidence for the opposite effects of community‐weighted means and functional dispersion of plant functional traits on grassland productivity and highlights the importance of both traits of dominant species and trait distribution among species in modulating the effects of global changes on ecosystem functions.

Monitoring the soil microbial communities following forest management practices is vital since soil microorganism play a critical role in sustaining forest productivity, nutrient cycling and soil CO2 emission. Here, biomass and the structures of soil microbial communities in aerially seeded Pinus massoniana plantations across three growing and three non-growing seasons following canopy tree thinning and understory removal were investigated using PLFA method, and soil environmental factors were analyzed. Both overall microbial community structures and mean microbial biomass did not significantly differ among control (CK), heavily thinning (HT), light thinning (LT) and understory removal (UR), but were significantly affected by time following treatment. In spite of non-significant effects of treatment, thinning and UR tended to decrease soil microbial biomass in non-growing seasons, and to increase the microbial biomass in the 2nd and 3rd growing seasons following treatment. Soil moisture, carbon to nitrogen ratio and nitrogen (i.e. total N and mineral N) were the main drivers of soil microbial community changes. Lower soil moisture and higher soil nitrogen led to significant differences in soil microbial biomass in the 2nd year after treatment. Thinning significantly increased fungi to bacteria ratio (FB ratio), which was significantly positively correlated with soil heterotrophic respiration. Our study confirms that forest management practices such as thinning and understory removal exert strong effects on environmental conditions (i.e. microclimate and soil nutrient availability), which further influences FB ratio, and consequently might impact soil C cycling and forest productivity.

Soil extracellular enzyme activities (EEAs) and enzymatic acquisition ratios are significantly affected by both abiotic and biotic factors across various scales and ecosystems. However, what determines the soil EEAs and their acquisition ratios in planted forests remains poorly understood. In this study, we measured the activities of β-1,4-glucosidase (BG), β-1,4-N-acetylglucosaminidase (NAG) and acid phosphatase (AP) and explored their key controlling factors in Pinus massoniana plantations along a 1100 km latitudinal gradient in subtropical China. The three enzyme activities increased with an increase in latitude and were significantly and negatively affected by mean annual temperature (MAT) and mean annual precipitation (MAP), but were positively correlated with soil available P content. From south to north, the enzymatic C:N (ln(BG):ln(NAG)) acquisition ratio decreased significantly, while the enzymatic C:P (ln(BG):ln(AP)) and N:P (ln(NAG):ln(AP)) acquisition ratios increased significantly. The latitudinal patterns of the enzymatic C:P and N:P acquisition ratios were significantly and negatively affected by MAT and MAP, but were positively affected by soil available P content. In total, climatic factors (e.g., MAT and MAP) accounted for more (14.2% and 25.5%, respectively) of the latitudinal variations in soil EEAs and their acquisition ratios than soil (e.g., available P) and stand (e.g., diameter at breast height). Therefore, these results illustrate that planted forests are susceptible to variations in soil EEAs and their acquisition ratios along a latitudinal gradient and that such changes are mainly driven by climate. Moreover, the similar average enzymatic C:P and N:P acquisition ratios in this pine plantation with the literature values reported for tropical and subtropical natural forests indicate that the pine plantations in subtropical China may be strongly P limited.

Trees at temperature-limited alpine treeline are highly sensitive to temperature fluctuations. However, few studies have directly linked the recruitment and growth of juvenile trees to climate warming to investigate the processes underlying climate-induced alpine treeline shift. On the cold-humid Changbai Mountain of northeastern China, almost no tree recruitment occurred above the current treeline on the west side before 1985, whereas considerable recruitment has occurred since 1985. To investigate whether this recent recruitment was caused by warming temperatures, we established a 450 m × 50 m permanent plot above the current alpine treeline. We used dendrochronology to reconstruct the time series of recruitment of Betula ermanii juveniles. In addition, we used open top chambers (OTCs) to increase the growing season day-time temperature by c. 2.8°C and thereby to study the growth responses of juvenile trees to future warmer conditions beyond the current treeline. We found that tree recruitment increased substantially during a period of warmer summer temperatures since 1985, showing a high sensitivity of tree recruitment to temperature above the alpine treeline. The daily stem radial increment recorded by dendrometers was significantly (p ≤ 0.05) positively correlated with temperature but negatively correlated with soil water content, indicating no water limitation. Correspondingly, the increase in radial growth in OTCs was primarily a consequence of higher temperatures, especially in July. The regression slope between stem radial growth and temperature in the OTCs did not differ from that in ambient controls, indicating that the sensitivity of stem radial growth to temperature was not altered by warming. These suggest that future climate warming will induce increases in tree recruitment and growth above the alpine treeline. Our results revealed a direct link between temperature and recruitment and growth of juvenile trees, and that climate warming will likely cause forests to advance beyond the alpine treeline.

Treeline responses to environmental changes describe an important phenomenon in global change research. Often conflicting results and generally too short observations are, however, still challenging our understanding of climate-induced treeline dynamics. Here, we use a state-of-the-art dendroecological approach to reconstruct long-term changes in the position of the alpine treeline in relation to air temperature at two sides in the Changbai Mountains in northeast China. Over the past 160 years, the treeline increased by around 80 m, a process that can be divided into three phases of different rates and drives. The first phase was mainly influenced by vegetation recovery after an eruption of the Tianchi volcano in 1702. The slowly upward shift in the second phase was consistent with the slowly increasing temperature. The last phase coincided with rapid warming since 1985, and shows with 33 m per 1°C, the most intense upward shift. The spatial distribution and age structure of trees beyond the current treeline confirm the latest, warming-induced upward shift. Our results suggest that the alpine treeline will continue to rise, and that the alpine tundra may disappear if temperatures will increase further. This study not only enhances mechanistic understanding of long-term treeline dynamics, but also highlights the effects of rising temperatures on high-elevation vegetation dynamics.

Defoliation by herbivores commonly imposes negative effects on plants, and physiological integration (resource sharing) can enhance the ability of guerilla clonal plants to tolerate stresses. Here we examined whether physiological integration can increase the ability of phalanx clonal plants to withstand defoliation. On a high mountain grassland in southwestern China, we subjected the phalanx clonal plant Iris delavayi within 10 cm × 10 cm plots to three levels of defoliation intensity, i.e., control (no defoliation), moderate (50% shoot removal to simulate moderate herbivory) and heavy defoliation (100% shoot removal to simulate heavy herbivory), and kept rhizomes at the plot edges connected (allowing physiological integration) or disconnected (preventing integration) with intact ramets outside the plots. Defoliation significantly reduced leaf biomass, root biomass and ramet number of I. delavayi . Clonal integration did not affect the growth of I. delavayi under control, but significantly increased total biomass, rhizome and root biomass under heavy defoliation, and leaf biomass and ramet number under moderate defoliation. We conclude that clonal integration associated with resource reallocation plays an important role in maintaining the productivity of the alpine and subalpine grassland ecosystems in SW China where clonal plants are a dominant component of the grasslands and are commonly extensively managed with moderate grazing intensity. Our results also help to better understand the adaption and tolerance of phalanx clonal plants subjected to long-term grazing in the high mountain environment.

Precipitation and nitrogen (N) deposition are predicted to increase in northern China. The present paper aimed to better understand how different dominant species in semi-arid grasslands in this region vary in their litter decomposition and nutrient release responses to increases in precipitation and N deposition. Above-ground litter of three dominant species (two grasses, Agropyron cristatum and Stipa krylovii, and one forb, Artemisia frigida) was collected from areas without experimental treatments in a semi-arid grassland in Inner Mongolia. Litter decomposition was studied over three years to determine the effects of water and N addition on litter decomposition rate and nutrient dynamics. Litter mass loss and nutrient release were faster for the forb species than for the two grasses during decomposition. Both water and N addition increased litter mass loss of the grass A. cristatum, while the treatments showed no impacts on that of the forb A. frigida. Supplemental N had time-dependent, positive effects on litter mass loss of the grass S. krylovii. During the three-year decomposition study, the release of N from litter was inhibited by N addition for the three species, and it was promoted by water addition for the two grasses. Across all treatments, N and potassium (K) were released from the litter of all three species, whereas calcium (Ca) was accumulated. Phosphorus (P) and magnesium (Mg) were released from the forb litter but accumulated in the grass litter after three years of decomposition. Our findings revealed that the litter decomposition response to water and N supplementation differed among dominant plant species in a semi-arid grassland, indicating that changes in dominant plant species induced by projected increases in precipitation and N deposition are likely to affect litter decomposition, nutrient cycling, and further biogeochemical cycles in this grassland. The asynchronous nutrient release of different species’ litter found in the present study highlights the complexity of nutrient replenishment from litter decomposition in the temperate steppe under scenarios of enhancing precipitation and N deposition.

Canopies in evergreen coniferous plantations often consist of various-aged needles. However, the effect of needle age on the photosynthetic responses to thinning remains ambiguous. Photosynthetic responses of different-aged needles to thinning were investigated in a Chinese fir (Cunninghamia lanceolata) plantation. A dual isotope approach [simultaneous measurements of stable carbon (δ13C) and oxygen (δ18O) isotopes] was employed to distinguish between biochemical and stomatal limitations to photosynthesis. Our results showed that increases in net photosynthesis rates upon thinning only occurred in the current-year and one-year-old needles, and not in the two- to four-year-old needles. The increased δ13C and declined δ18O in current year needles of trees from thinned stands indicated that both the photosynthetic capacity and stomatal conductance resulted in increasing photosynthesis. In one-year-old needles of trees from thinned stands, an increased needle δ13C and a constant needle δ18O were observed, indicating the photosynthetic capacity rather than stomatal conductance contributed to the increasing photosynthesis. The higher water-soluble nitrogen content in current-year and one-year-old needles in thinned trees also supported that the photosynthetic capacity plays an important role in the enhancement of photosynthesis. In contrast, the δ13C, δ18O and water-soluble nitrogen in the two- to four-year-old needles were not significantly different between the control and thinned trees. Thus, the thinning effect on photosynthesis depends on needle age in a Chinese fir plantation. Our results highlight that the different responses of different-aged needles to thinning have to be taken into account for understanding and modelling ecosystem responses to management, especially under the expected environmental changes in future.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Research Highlights: Extraradical mycorrhizal fungal mycelium (MFM) plays critical roles in nutrient absorption and carbon cycling in forest ecosystems. However, it is often ignored or treated as a root uptake apparatus in existing biogeochemical models. Methods: We conducted a meta-analysis to reveal how MFM responds to various, coinciding environmental factors and their interactions. Results: Nitrogen (N) addition and N-phosphorus (P)-potassium (K) combination significantly decreased MFM. However, elevated CO2, organic matter addition, P addition, and CO2-N combination significantly increased MFM. In contrast, warming, K addition, N-P combination, and P-K combination did not affect MFM. Mycorrhizal fungal levels (individual vs. community), mycorrhizal type (ectomycorrhizal fungi vs. arbuscular mycorrhizal fungi), treatment time (&lt, 1 year vs. &gt, 1 year), and mycelium estimation/sampling method (biomarker vs. non-biomarker, ingrowth mesh bag vs. soil core) significantly affected the responses of MFM to elevated CO2 and N addition. The effect sizes of N addition significantly increased with mean annual precipitation, but decreased with soil pH and host tree age. The effect sizes of P addition significantly increased with N concentration in host plant leaves. Conclusions: The differential responses revealed emphasize the importance of incorporating MFM in existing biogeochemical models to precisely assess and predict the impacts of global changes on forest ecosystem functions.

Research Highlights: A detailed picture of the seasonality in fine root biomass (FRB), necromass (FRN), and the biomass/necromass ratio (FRBN) throughout the whole year is crucial to uncover profound effects of long-term environmental changes on fine root dynamics. Materials and Methods: We used meta-analysis to characterize the variability of FRB, FRN and FRBN, and determined their relations with climatic (monthly versus annual), edaphic and geomorphic factors for tropical, temperate and boreal forest biomes across the Northern Hemisphere. Results: Boreal forests exhibited the highest FRB and FRN, while tropical forests yielded the lowest FRN, and thus the greatest FRBN. FRB and FRN significantly decreased with sampling depth, but increased with soil organic carbon content and elevation, while an opposite pattern was found for FRBN. Temperature and precipitation at different time scales (monthly versus annual) and latitude had varying influences on fine roots. High FRB and FRN were observed during dry season for tropical forests, but in the late growing season for temperate forests. The three forest biomes exhibited the high root activity (measured as FRBN) in June or July. Conclusions: It is crucial to realize the universal and specific responses of fine roots to multiple environmental factors when attempting to incorporate these parameters into fine root monthly dynamic models in forest ecosystems. The biome-specific fluctuation of fine roots contributes to identify the influence factors on fine root seasonal patterns throughout the whole year. Our analysis is expected to improve the understanding of the key role of fine roots at monthly level in modeling and predicting carbon budget of various forest biomes under future climate change.

Significant replacement of shrub species by herbaceous species has been observed in the Changbai alpine tundra zone, China, since the 1990s. This study used plot surveys to analyze variations in the spatial distribution of dominant plants and to ascertain the changing mechanisms of dominant species in the alpine tundra zone. We found that the two previously dominant shrubs, Rhododendron chrysanthum and Vaccinium uliginosum, differed markedly in their distribution characteristics. The former had the highest abundance and the lowest coefficient of variation, skewness, and kurtosis, and the latter showed the opposite results, while the six herb species invaded had intermediate values. R. chrysanthum still had a relatively uniform distribution, while the herbaceous species and V. uliginosum had a patch distribution deviating from the normal distribution in the tundra zone. Micro-topography and slope grade had stronger effects on the spatial distribution of the eight plant species than elevation. Herbs tended to easily replace the shrubs on a semi-sunny slope aspect, steep slope, and depression. Overall, the dominance of dwarf shrubs declined, while the herbaceous species have encroached and expanded on the alpine tundra zone and have become co-dominant plant species. Our results suggest that various micro-topographic factors associated with variations in climatic and edaphic conditions determine the spatial distribution of plants in the alpine tundra zone. Future climate warming may cause decreased snow thickness, increased growing season length, and drought stress, which may further promote replacement of the shrubs by herbs, which shows retrogressive vegetation successions in the Changbai alpine tundra zone. Further studies need to focus on the physio-ecological mechanisms underlying the vegetation change and species replacement in the alpine tundra area under global climate change.

The natural abundance of stable nitrogen (N) isotope (&delta, 15N) in plants and soils can reflect N cycling processes in ecosystems. However, we still do not fully understand patterns of plant and soil &delta, 15N at alpine treelines and shrublines in different climate zones. We measured &delta, 15N and N concentration in leaves of trees and shrubs and also in soils along elevational gradients from lower altitudes to the upper limits of treelines and shrublines in subtropical, dry- and wet-temperate regions in China. The patterns of leaf &delta, 15N in trees and shrubs in response to altitude changes were consistent, with lower values occurring at higher altitude in all three climate zones, but such patterns did not exist for leaf &Delta, &delta, 15N and soil &delta, 15N. Average &delta, 15N values of leaves (&minus, 1.2&permil, ) and soils (5.6&permil, ) in the subtropical region were significantly higher than those in the two temperate regions (&minus, 3.4&permil, and 3.2&permil, respectively). Significant higher &delta, 15N values in subtro4pical forest compared with temperate forests prove that N cycles are more open in warm regions. The different responses of leaf and soil &delta, 15N to altitude indicate complex mechanisms of soil biogeochemical process and N sources uptake with environmental variations.

Most of our knowledge about forest responses to global environmental changes is based on experiments with seedlings/saplings grown in artificially controlled conditions. We do not know whether this knowledge will allow us to upscale to larger and mature trees growing in situ. In the present study, we used elevation as a proxy of various environmental factors, to examine whether there are ontogenetic differences in carbon and nutrient allocation of two major treeline species (Pinus cembra L. and Larix decidua Mill.) along elevational gradients (i.e., environmental gradient) in the Swiss alpine treeline ecotone (~300 m interval). Young and adult trees grown at the same elevation had similar levels of non-structural carbohydrates (NSCs), total nitrogen (TN), and phosphorus (TP), except for August leaf sugars and August leaf TP in P. cembra at the treeline. We did not detect any interaction between tree age and elevation on tissue concentration of NSCs, TN, and TP across leaf, shoot, and root tissues for both species, indicating that saplings and mature trees did not differ in their carbon and nutrient responses to elevation (i.e., no ontogenetic differences). With respect to carbon and nutrient allocation strategies, our results show that young and adult trees of both deciduous and evergreen tree species respond similarly to environmental changes, suggesting that knowledge gained from controlled experiments with saplings can be upscaled to adult trees, at least if the light is not limited. This finding advances our understanding of plants&rsquo, adaptation strategies and has considerable implications for future model-developments.

The alpine treeline demarcates the temperature-limited upper elevational boundary of the tree life form. However, this treeline does not always occur exclusively as a sharp &ldquo, line&rdquo, outposts of tree groups (OTG) with a height of at least 3 m are often observed in microsites up to several hundred meters beyond the line of continuous forest on some mountains. This suggests that other factors such as microenvironment may play a significant role in compensating for the alpine tree facing growth-limiting low temperature conditions. To test the microenvironment effects, this study compared the differences in growing conditions (climate and soil properties) and ecophysiological performance of Erman&rsquo, s birch (Betula ermanii Cham.) trees growing in a continuous treeline site (CTL, ~1950 m above sea level, a.s.l.) and OTGs (~2050 m a.s.l.) on Changbai Mountain in northeastern China. The results show the average 2-m air temperature for OTG was slightly lower in the non-growing season than which at the CTL (&minus, 10.2 &deg, C &lt, &minus, 8.4 &deg, C), there was no difference in growing season air temperature and soil temperature at 10 cm depth between CTL and OTG. The contents of focal soil nutrients in CTL and OTG were similar. Difference in K and Mn contents between sites were detected in leaves, difference in K, Mn, and Zn in shoots. However, comparing similarity of ecophysiological performances at an individual level, trees at CTL and OTG show no significant difference. Our study reveals that mature trees at the CTL and OTG experience generally similar environmental conditions (climate and soil properties) and exhibit similar overall ecophysiological performance (reflected in carbon reserves and nutrients). This might provide insight into how mature trees might be able to survive in areas higher than the continuous treeline, as well as the importance of microclimatic amelioration provided by protective microsites and the trees themselves.

Global air temperature has increased and continues to increase, especially in high latitude and high altitude areas, which may affect plant resource physiology and thus plant growth and productivity. The resource remobilization efficiency of plants in response to global warming is, however, still poorly understood. We thus assessed end-season resource remobilization from leaves to woody tissues in deciduous Betula ermanii Cham. trees grown along an elevational gradient ranging from 1700 m to 2187 m a.s.l. on Changbai Mountain, northeastern China. We hypothesized that end-season resource remobilization efficiency from leaves to storage tissues increases with increasing elevation or decreasing temperature. To test this hypothesis, concentrations of non-structural carbohydrates (NSCs), nitrogen (N), phosphorus (P), and potassium (K) during peak shoot growth (July) were compared with those at the end of growing season (September on Changbai Mt.) for each tissue type. To avoid leaf phenological effects on parameters, fallen leaves were collected at the end-season. Except for July-shoot NSC and July-leaf K, tissue concentrations of NSC, N, P, and K did not decrease with increasing elevation for both July and September. We found that the end-season leaf-to-wood reallocation efficiency decreased with increasing elevation. This lower reallocation efficiency may result in resource limitation in high-elevation trees. Future warming may promote leaf-to-wood resource reallocation, leading to upward shift of forests to higher elevations. The NSC, N, P, and K accumulated in stems and roots but not in shoots, especially in trees grown close to or at their upper limit, indicating that stems and roots of deciduous trees are the most important storage tissues over winter. Our results contribute to better understand the resource-related ecophysiological mechanisms for treeline formation, and vice versa, to better predict forest dynamics at high elevations in response to global warming. Our study provides resource-related ecophysiological knowledge for developing management strategies for high elevation forests in a rapidly warming world.

This study was designed to test the hypothesis that nitrogen (N) addition leads to enhanced soil respiration (SR) in nitrogen deficient marsh. Here, we report the response of SR to simulated N deposition in a temperate marsh of northeastern China from June 2009 to September 2011. The experiment included three-levels of N treatment (control: no N addition, Low-N: 4g N m-2 y-1, and High-N: 8 g N m-2 y-1). Our study showed various responses of SR to level and duration of N addition. Yearly SR was increased by 11.8%-15.2% (P0.05) and 15.4% (P

Knowledge on the ecology of tree species in both their native and introduced range can increase the understanding of their successful establishment and spread outside the native range. Here, we analysed radial growth patterns of Ailanthus altissima (Mill.) Swingle in two sites in its native range in eastern China and in two sites in the introduced range in southern Switzerland, where it started to disperse into forests in the 1950s. Growth rates were similar despite lower amounts of growing season precipitation in China. Furthermore, we found negative correlations between annual radial growth and average temperatures in the growing season at the warmest of the four sites, which suggest that radial growth of A. altissima starts to be limited by average growing season temperatures above 21 °C. Regarding wood anatomy, we did not find clear correlations between vessel lumen area and monthly temperature or precipitation at the time of tissue formation in spring. Overall, our results demonstrate that A. altissima has the potential to grow in drier conditions than currently found in Switzerland, which is in line with previous studies.

Globally, chronic nitrogen (N) deposition into terrestrial ecosystems has resulted in changes in community composition, depending on the responses of co-existing species to increasing soil N availability. The levels of plant non-structural carbohydrates (NSCs) produced by photosynthesis are associated with leaf N content, and together they represent the capital of a plant for its life including competitive ability. However, the specific ways that concentrations of plant NSCs, and also N, influence the growth of plants, and thus their productivity, are still abscue. Here, we explored the effect of variations in plant leaf NSCs (starch and soluble sugars) and N concentrations on the growth of plants with different soil N uptake capacities, i.e. two grasses (Leymus chinensis and Stipa baicalensis), two forbs (Potentilla tanacetifolia and Galium verum), and one legume (Thermopsis lanceolate) in Inner Mongolian grasslands subjected to three N addition rates (i.e., 0, 10, or 20 g N m−2 yr−1) and three N forms [i.e., NH4NO3, (NH4)2SO4, or CO(NH2)2] for four years. Irrespective of N addition rate and N form, N addition significantly increased aboveground biomass of the grasses, but not that of the forbs or the legume. The grasses had higher increase in N concentrations than the forbs and the legume. N addition increased the starch concentrations of grasses, but decreased that of forbs and the legume. Changes in the aboveground biomass of all tested plant species were significantly positively correlated with changes in concentrations of both NSCs and N. Our results indicate that, irrespective of the N addition rates and N forms, greater increase in NSCs and N concentrations contributed to higher aboveground productivity in grasses, but not in forbs and legumes. These results imply that future nitrogen deposition will benefit grasses over other plant forms, and thus the former may become more dominant in grasslands in northern China.

In most defoliation experiments with evergreen trees, leaves are removed proportionally across all leaf age classes or only the younger ones are removed. However, it remains unclear how the ecophysiological functions of older foliage potentially differ from those of younger leaves. Hence, we conducted a field experiment with five intensities of artificial defoliation (0%, 11% needle biomass loss = all ≥ 5-year-old needles removed, 27% loss = all ≥ 4-year-old needles removed, 46% loss = all ≥ 3-year-old needles removed, and 71% loss = all ≥ 2-year-old needles removed) of Abies alba trees grown under low-light (LL, 28% of full sunlight) and high-light conditions (HL, 70%). Photosynthesis of the remaining one-year-old needles; concentrations of non-structural carbohydrates (NSCs = soluble sugars + starch), total nitrogen (N), and soluble protein (SP) in stem sapwood and one-year-old needles; and tree height and stem radial growth rates were measured. We found that growth light conditions, rather than old needle defoliation up to a needle biomass loss of 70%, significantly affected growth, photosynthetic capacity and concentrations of tissue N, SP, and NSCs, with levels of all parameters greater in HL trees than in LL tress. Defoliation-induced compensatory growth was found in HL trees only, whereas tree height growth rates tended to decrease with increasing defoliation intensity in LL trees. Our results indicate that light availability, rather than damage to older foliage, plays an important role in determining plant physiology and growth. These results from A. alba trees suggest that the resource uptake by older foliage almost balances their resource consumption, leading to the conclusion that the older needles from evergreen trees physiologically contribute less to the whole-tree carbon and nitrogen balance. Our findings also suggest that the effects of older foliage defoliation on forest survival and productivity may have been overestimated in past forest ecosystem management practices, while the physiological functions of the youngest foliage may have been underestimated.

Global climate change has great effects on ecosystems via changes in air and soil temperature. While the effects of temperature have been extensively studied, relatively few studies have truly separated the impact of soil temperature from that of air temperature. Furthermore, little is known about how removal of older ramets may affect the performance of their interconnected younger ramets of bamboos. By maintaining air temperature constantly (at 17 °C) in growth chambers and manipulating soil temperature (2, 7, 12, 17 and 22 °C) using thermostatic water bath systems, we tested the effects of soil temperature and removal of the older ramets on survival, growth and physiology of its interconnected young ramet of a bamboo Indocalamus decorus. Soil temperature significantly affected the survival of the young ramet of I. decorus and also the growth and photosynthetic rate of the surviving young ramet when the shoots of its connected older ramets were not removed. Removing shoots of the older ramets greatly enhanced the survival of the young ramet at the two highest soil temperatures (17 and 22 °C) and the growth of the surviving ramet at 7 and 12 °C. We conclude that shoot removal of older ramets can interact with soil temperature to affect survival and growth of young ramets of the bamboo, and that resource sharing (translocation of photosynthates) from older ramets to young ramets of the bamboo is rather limited. Instead, newly emerged, interconnected ramets of bamboos may compete fiercely for resources stored in rhizomes. These results suggest that bamboo forest management should consider the balance between resource sharing and competition for resources stored in rhizomes under ongoing global climate change.

The ability of plants to tolerate freezing limits their geographical distribution. Therefore, winter warming may shift a species’ occurrence northwards and/or to higher altitudes. In Europe, the hemiparasitic vascular plant Viscum album (mistletoe) has two common and widespread subspecies: V. a. ssp. album and V. a. ssp. austriacum. The former has a more northern geographic distribution than the latter. Therefore we hypothesised that seeds of V. a. ssp. album are more tolerant to freezing than those of V. a. ssp. austriacum. From these two mistletoe subspecies V. a. ssp. austriacum is, in some managed forest areas, considered a novel threat to tree growth and forest health. Berries of V. a. ssp. album were collected from Sweden, Poland and Switzerland and berries of V. a. ssp. austriacum were collected from Poland, Switzerland and Spain. After storage at −3 °C, seeds were extracted from the pulp of berries and exposed to eight different temperatures between −8 °C and −30 °C, with the storage temperature serving as the control. After freezing treatments, germination of seeds was monitored. In addition, differential thermal analysis was used to measure freeze tolerance of seeds. The seeds of V. a. ssp. album tolerated lower temperatures than seeds of V. a. ssp. austriacum. The temperature at which 50% of seeds lost their ability to germinate (LT50) was −15 °C in V. a. ssp. austriacum and between −15 °C and −19 °C in V. a. ssp. album. The results of differential thermal analysis to determine the freezing point of seeds supported these findings. The freezing tolerance of mistletoe seeds was relatively well coupled with the winter climate at the edge of their current geographic distribution. Based on our results, the warming of winters may eliminate the abiotic barrier that has thus far limited mistletoes’ expansion, opening a window of opportunity for these parasites to increase their abundance and shift their distribution range towards higher latitudes and altitudes. Although mistletoes play important ecological roles in forest ecosystems, their recent increase has raised concern among forest managers, because they may cause a substantial reduction in tree growth in single species dominated stands. Increasing tree species diversity might be an effective method for limiting future mass infestations in homogeneous managed forests.

In the cold temperate zone of the western and southern slopes of the Changbai Mountain, Betula ermanii Cham. forest, Picea jezoensis (Siebold & Zucc.) Carriere forest, and mixed forests of B. ermanii and P. jezoensis are heterogeneously distributed in a mosaic of patches, and the reason for this formation is still unclear. In August 1986, a typhoon disturbed the forests on the western and southern slopes of Changbai Mountain, forming a large number of forest gaps. After more than 30 years of vegetation succession, vegetation patches in wind-stricken areas are obvious. To reveal the effects of catastrophic wind on the patch mosaic structure of these forests, a study was carried out in the cold temperate wind-stricken areas of the western and southern slopes of Changbai Mountain. Vegetation differences were classified according to the degree of vegetation damage by the catastrophic wind and the status of vegetation restoration was investigated, as well as the soil fertility was determined. The results show that the degree of forest damage caused by the catastrophic wind is not homogeneous, and there are significant differences in community composition and structure in the wind-stricken areas. After 30 years of restoration, some of the differences in damaged forests have been enhanced. The heterogeneity of vegetation in wind-stricken areas is due to both the difference in the degree of catastrophic wind damage and the differences in the succession of the damaged vegetation. There is a strong correlation between vegetation and soil fertility, and the variation in soil fertility strengthens the heterogeneity of vegetation in wind-stricken areas. Therefore, it can be inferred that several catastrophic wind disasters may occur in the history, which resulted in succession from shrub and herb to B. ermanii forest and then from B. ermanii forest to P. jezoensis forest on the western and southern slopes. This pattern of disturbance and succession formed the patch mosaic distribution pattern of the forests on Changbai Mountain.

Atmospheric warming and increasing tropospheric ozone (O3) concentrations often co-occur in many cities of the world including China, adversely affecting the health status of urban trees. However, little information is known about the combined and interactive effects from increased air temperature (IT) and elevated O3 (EO) exposures on urban tree species. Here, Ginkgo biloba and Populus alba ‘Berolinensis’ seedlings were subjected to IT (+2 °C of ambient air temperature) and/or EO (+2-fold ambient air O3 concentrations) for one growing season by using open-top chambers. IT alone had no significant effect on physiological metabolisms at the early growing stage, but significantly increased photosynthetic parameters, antioxidative enzyme activities (P

The root of Moso bamboo (Phyllostachys edulis (Carrière) J. Houz.) develops extremely rapidly at seedling phase and is highly sensitive to water content in soil, but its response patterns and adaptation strategies of its root to drought are little known. The aim of this study was to investigate the response of root morphology and architecture of Moso bamboo to drought at seedling phase and then to explore the drought adaptation strategies of its root. One-year-old potted seedlings of Moso bamboo were planted under three drought treatments (control, moderate drought and severe drought) for three months. Seedling growth, specific root length (SRL), root architecture (fractal dimension (FD), root branching angle (RBA) and root topological index (TI)) and non-structural carbohydrate (NSC) concentrations in roots were measured every month. The results are as follows: (i) The dry weight of root and shoot decreased significantly under drought stress. (ii) The SRL decreased under drought stress in the early duration (the first month), and then increased in the late duration (the third month). Both FD and RBA decreased, while TI and the concentrations of NSCs increased under drought stress. (iii) The NSC concentrations were positively correlated with SRL and TI, but exhibited an inverse relationship to FD and RBA. Our results indicated that Moso bamboo seedlings formed a “steeper, simpler, expensive (low SRL and high TI)” root architecture to adapt to a short-term drought (one month), and formed a “cheaper (high SRL)” root to adapt to a long-term drought (three months). Increase of NSC concentrations supported the root architecture plasticity to some extent.

Enzyme activities in decomposing litter are directly related to the rate of litter mass loss and have been widely accepted as indicators of changes in belowground processes. Studies of variation in enzyme activities of soil–litter interface and its effects on decomposition are lacking. Evaluating enzyme activities in this layer is important to better understand energy flow and nutrient cycling in forest ecosystems. Litter decomposition and the seasonal dynamics of soil–litter enzyme activities were investigated in situ in 20- (younger) and 46-year-old (older) Pinus massoniana stands for 540 days from August 2010 to March 2012 by litterbag method. We measured potential activities of invertase, cellulase, urease, polyphenol oxidase, and peroxidase in litter and the upper mineral soils, and evaluated their relationships with the main environment factors. Remaining litter mass was 57.6 % of the initial weights in the younger stands and 61.3 % in the older stands after 540-day decomposition. Levels of enzyme activity were higher in the litter layer than in the soil layer. Soil temperature, litter moisture, and litter nitrogen (N) concentration were the most important factors affecting the enzyme activities. The enzyme activity showed significantly seasonal dynamics in association with the seasonal variations in temperature, water, and decomposition stages. Remaining litter dry mass was found to be significantly linearly correlated with enzyme activities (except for litter peroxidase), which indicates an important role of enzyme activity in the litter decomposition process. Our results indicated the important effects of biotic (litter N) and abiotic factors (soil temperature and litter moisture) on soil–litter interface enzyme activities. Overall significant linear relationship between remaining dry mass and enzyme activities highlighted the important role of enzyme activity in affecting litter decomposition processes, which will further influence nutrient cycling in forest ecosystems. Our results contributed to the better understanding of the mechanistic link between upper soil–litter extracellular enzyme production and litter decomposition in forest ecosystems.

Evidence for impacts of environmental changes on belowground net primary production (BNPP) from long-term experiments is rather scarce. We aimed to understand how long-term changes in water and nitrogen availability affect production and vertical allocation of roots in semi-arid grasslands and its consequence on carbon (C) and nitrogen (N) cycles. We investigated changes of BNPP and its vertical allocation along the soil profile to 40 cm in depth in response to simultaneous increases in water and N availability over 11 years in an old-field grassland in northern China. Water addition increased BNPP in all soil layers (0–10 cm, 10–20 cm, and 20–40 cm), and enhanced the percentage BNPP in the upper soils but decreased that in 10–20 cm soil layer. Nitrogen addition decreased BNPP in 10–20 cm and 20–40 cm soil layers as well as total BNPP in 0–40 cm, and increased the percentage BNPP in the upper soil layer but decreased that in 10–20 cm soil layer. Water addition increased soil total C and N concentrations in 0–10 cm and 10–20 cm soil layers, while N addition only marginally decreased soil C:N ratio in 0–10 cm and 20–40 cm soil layers. Both soil total N concentration and soil C:N ratio were closely related to BNPP. Our results highlight the importance of environmental factors, especially water availability, in determining BNPP, and in turn controlling soil nutrient accumulation in semi-arid grasslands, although the specific mechanisms remain unclear. The projected increase in precipitation in those semi-arid grasslands would enhance soil C and N sequestration. The increased allocation of BNPP in upper soils with long-term precipitation increment and N deposition may accelerate the cycles of C and N in these ecosystems, and thus increase the risk of soil C and N loss.

How climatic factors influence the balance of sulfur (S) with carbon (C) and nitrogen (N) in soils is not well understood. Here we report the results of S, C and N concentrations in 550 soil samples along a 3500-km aridity gradient across arid and semi-arid grasslands in northern China. Our results showed that soil available S (AS) concentrations decreased with increasing aridity index (AI, calculated as '1—the ratio of mean annual precipitation to potential evapotranspiration') when AI\0.91 (90-450 mm rainfall year -1 ), but increased when AI(0.91 (30-90 mm rainfall year -1 ), having a threshold at AI = 0.91 (90 mm rainfall year -1 ). Soil AS concen- trations were positively related to soil organic C (OC), soil total N (TN), microbial biomass C and N con- centrations, and arylsulphatase activities when AI\0.91, but were not positively related to these variableswhenAI(0.91.TopsoilAS:OCandAS:TN ratios mainly depended on OC and TN concentrations when AI\0.91, but mainly depended on AS con- centrations when AI(0.91. The decreased (AI\0.91) and increased total S concentrations (AI(0.91) with increasing AI along the gradient provided further evidence for the existence of this fundamental threshold. High concentrations of sulfate in drier soils were associated with long-term atmo- sphere inputs and groundwater-derived salts with minimal leaching rates. Overall, our findings imply that aridity asymmetrically controls the relationships of soil AS with OC and TN on the two sides of the threshold, i.e. biological processes exerted stronger controls in wetter sites, while geochemical processes played more significant roles in drier sites. These results should be incorporated into predictive models of global biogeochemical cycling under various global climate change scenarios.

Soil pH buffering capacity (pHBC) plays a crucial role in predicting acidification rates, yet its large-scale patterns and controls are poorly understood, especially for neutral-alkaline soils. Here, we evaluated the spatial patterns and drivers of pHBC along a 3600 km long transect (1900 km sub-transect with carbonate-containing soils and 1700 km sub-transect with non-carbonate-containing soils) across northern China. Soil pHBC was greater in the carbonate-containing soils than in the non-carbonate-containing soils. Acid addition decreased soil pH in the non-carbonate-containing soils more markedly than in the carbonate-containing soils. Within the carbonate soil sub-transect, soil pHBC was positively correlated with cation exchange capacity (CEC), carbonate content and exchangeable sodium (Na) concentration, but negatively correlated with initial pH and clay content, and not correlated with soil organic carbon (SOC) content. Within the non-carbonate sub-transect, soil pHBC was positively related to initial pH, clay content, CEC and exchangeable Na concentration, but not related to SOC content. Carbonate content was the primary determinant of pHBC in the carbonate-containing soils and CEC was the main determinant of buffering capacity in the non-carbonate-containing soils. Along the transect, soil pHBC was different in regions with different aridity index. Soil pHBC was positively related to aridity index and carbonate content across the carbonate-containing soil sub-transect. Our results indicated that mechanisms controlling pHBC differ among neutral-alkaline soils of northern China, especially between carbonate- and non-carbonate-containing soils. This understanding should be incorporated into the acidification risk assessment and landscape management in a changing world.

Altered drying-rewetting patterns due to climate change may affect soil nitrogen (N) and phosphorus (P) cycling in terrestrial ecosystems. The responses of soil N and P cycling to drying and rewetting cycles can vary with drying-rewetting patterns, experimental methods, ecosystems, and soil types, thus making a synthesis of these studies necessary for understanding mechanisms and predicting future responses to climate change. Here, we compiled data of 1882 observations from 79 studies for a meta-analysis of the responses of soil N and P pools and fluxes to drying and rewetting and how these responses are modified by experimental conditions. Results showed that 1) experimental drying increased NH4+, extractable organic nitrogen (EON), and available P in the soil significantly by 22, 27, and 72%, respectively. In contrast, soil NO3−, enzymatic activities, microbial biomass, net nitrification, and N2O emissions significantly decreased by 37, 13–21, 21–28, 39, and 93%, respectively. 2) Upon rewetting of dried soil, soil EON, extractable organic phosphorus (EOP), net N mineralization, nitrification, phosphatase activity, dissolved organic N leaching, dissolved inorganic P leaching, and N2O emissions significantly increased by 59, 27, 19, 15, 12, 60, 116, and 218%, respectively, while soil NO3− and NO3− leaching significantly decreased by 9 and 74%, respectively. Soil microbial N and P as well as enzymatic activities recovered from drought during the rewetting phase. The mean effect sizes of drying and rewetting generally increased with drying intensity, which was probably also the main reason for greater effect sizes observed in laboratory than in field experiments. Our meta-analysis showed stronger positive responses of available P to drying and rewetting than mineral N, which agreed with greater effect sizes on P than on N leaching. This suggests that drying and rewetting induce an imbalance between N and P, which was more pronounced in soils from forests than from agricultural systems. Overall, these results imply that the expected increase in the frequency and intensity of droughts potentially decouples the cycling of P and N, with consequences for nutrient leaching and the supply of plants and microorganisms with these nutrients.

Biochar addition to soil is increasing worldwide, the effect of combined application of biochar and nitrogen (N) fertilizer on soil respiration is still unknown. Understanding of the interactive effects of biochar and N fertilizer addition on temperature sensitivity of soil respiration and temporal dynamics of soil CO2 emissions in forest ecosystems remains limited. We conducted a full factorial experiment with biochar (B0, B1 and B2 with 0, 5 and 20 t·ha−1, respectively) and N fertilizer addition (N0 and N1 with 0 and 50 kg·ha−1 NH4NO3, respectively) as factors, to study their effects on soil respiration rate, temperature sensitivity (Q10), soil available nutrients, and their relations in moso bamboo plantations in subtropical China from April 2014 to April 2016. We found that, irrespective of biochar addition rate, N fertilization increased Q10 on the one hand, and irrespective of N fertilization rate, lower application rate of biochar resulted in a higher Q10, on the other hand. In spite of increased Q10, combined application of biochar and N decreased soil respiration rate in both growing season and non-growing season, as well as the annual cumulative soil CO2 emissions. Annual cumulative soil CO2 emissions were found to be significantly positively correlated with soil total nitrogen (STN) (p = 0.028) in 0–10 cm soil layer, and with soil ammonium (NH4+) (p = 0.000) and soil microbial biomass carbon (MBC) (p = 0.000) in both 0–10 cm and 10–20 cm soil layer. The present study suggests that the combined application of biochar and N fertilizer can be widely used in subtropical forest ecosystems where soil N is limited, because it increases soil fertility and, at the same time, decreases soil CO2 emissions.

Regions at high latitudes and high altitudes are undergoing a more pronounced winter warming than spring warming, and such asymmetric warming will affect chilling and forcing processes and thus the spring phenology of plants. We analyzed winter chilling and spring forcing accumulation in relation to the spring phenology of three tree species (Ulmus pumila, Populus simonii, and Syringa oblata) growing in a cold region (CR) compared with trees in a warmer reference region (WR), using the Dynamic Model and the Growing Degree Hour (GDH) model. We tested that forcing rather than chilling affects the spring phenology of trees in CR (hypothesis I), and that trees in CR have both lower mean chilling and forcing temperature and thus longer accumulation periods than trees in WR (hypothesis II). The modeling results confirmed that chilling and forcing occur simultaneously during the early spring when temperature gradually increases. In line with our hypotheses, forcing played a crucial role in spring phenology in CR, but chilling and forcing combined to determine spring phenology in WR. The temperature during the chilling and forcing periods was lower and the accumulation period started earlier and ended later in CR than in WR. Moreover, the chilling accumulation was broken into two periods by the low deep winter temperature in CR, and that interruption will be removed by future strong winter warming. Future asymmetric warming, with a stronger temperature increase in winter than in spring, could decrease the forcing accumulation effects and increase the chilling effects on the spring phenology of plants in CR. This change in the balance between chilling and forcing will lead to a shift in plant phenology, which will further have major impacts on biogeochemical cycles and on ecosystem functions and services.

Heavy metal contamination and tropospheric ozone (O3) pollution often co-occur in heavy industrial urban areas, adversely affecting urban plant health. Little is known about the characteristics of growth, physiological metabolism, bioaccumulation of cadmium (Cd) and mineral nutrients in urban trees under the combination of soil Cd contamination and elevated O3 exposure. In this study, one-year-old street tree Catalpa ovata G. Don seedlings were exposed to Cd contaminated soil (0, 100, 500 mg/kg soil) with 40 µg/m3 O3 (ambient air) and 120 µg/m3 O3 (elevated O3 exposure) for 4 weeks. The results revealed that 500 mg/kg soil Cd addition alone decreased net photosynthetic rate, stomatal conductance, peroxidase activity and increased abscisic acid content and oxidative injury in the leaves of C. ovata. Furthermore, Cd soil contamination decreased leaf, stem, root and total biomass and affected Cd, Mg, Fe, and Zn contents in leaves (P 0.05). Our findings suggest that C. ovata is an appropriate tree species for urban greening and afforestation in heavy industrial urban areas with high O3 pollution in Northeast China. To ensure successful afforestation in heavy industrial areas, the long-term and large scale studies are needed to advance our understanding of the combined effects from extreme climate conditions and multi-pollutant exposure on the metabolism of mature urban trees.

Little is known about environmental factors that mitigate or intensify drought effects on tree functioning. We hypothesized that higher nutrient availability and manipulations of the source:sink ratio can partially compensate negative drought effects when drought is not too severe, whilst too extreme drought can inhibit carbon and nutrient uptake and allocation irrespective of nutrient availability or the plant source:sink balance. We exposed three year-old Pinus sylvestris saplings during two subsequent years to drought using four different water supply regimes (from no drought to extreme drought) and released drought thereafter. Trees were exposed to two soil nutrient regimes. In addition, partial and full needle removal was performed. We assessed biomass, leaf gas exchange and tissue non-structural carbohydrates (NSCs). Extreme drought reduced stomatal conductance, photosynthesis, biomass and NSC, whereas intermediate drought levels only slightly affected biomass and NSC. Defoliation stimulated photosynthesis and fertilization increased growth and root biomass fraction, but mainly in the two intermediate drought levels. Only extreme drought pushed P. sylvestris trees to mortality. We conclude that tree mortality under severe drought periods will not be mitigated, but that the effects of low intensity drought stress could be compensated by increased nutrient availability and decreased source:sink ratio.

Brassica rapa comprises several important cultivated vegetables and oil crops. Current reference genome assemblies of Brassica rapa are quite fragmented and not highly contiguous, thereby limiting extensive genetic and genomic analyses. Here, we report an improved assembly of the B. rapa genome (v3.0) using single-molecule sequencing, optical mapping, and chromosome conformation capture technologies (Hi-C). Relative to the previous reference genomes, our assembly features a contig N50 size of 1.45 Mb, representing a ~30-fold improvement. We also identified a new event that occurred in the B. rapa genome ~1.2 million years ago, when a long terminal repeat retrotransposon (LTR-RT) expanded. Further analysis refined the relationship of genome blocks and accurately located the centromeres in the B. rapa genome. The B. rapa genome v3.0 will serve as an important community resource for future genetic and genomic studies in B. rapa. This resource will facilitate breeding efforts in B. rapa, as well as comparative genomic analysis with other Brassica species., Genomes: a new map of field mustard A detailed third-generation genome sequence has been published for Brassica rapa, which includes crops such as napa cabbage, turnips, and bok choy. Older technologies required researchers to stitch together many short sequences. Recently developed methods produce long, high-fidelity sequences. Xiaowu Wang at the Chinese Academy of Agricultural Science and the Shandong Provincial Key Laboratory of Protected Vegetable Molecular Breeding, Hongkun Zheng at Biomarker Technologies Corporation, and coworkers in China assembled the new version using 1498 sequences, compared to the 96,883 needed for the previous version. These methods provide a significant improvement in the level of detail, and permit mapping of highly repetitive regions, which were nearly impossible to map using older methods. The new sequence will aid breeding efforts, permit better comparisons with other Brassica genomes, and improve our understanding of genome evolution.

Warming and herbaceous functional group removal experiment was conducted in subalpine meadow to examine the effects of herbaceous species on Abies faxoniana seedlings by analyzing its physiological responses. The survival rate and non-structural carbohydrate content were significantly increased, but the growth and root/shoot of A. faxoniana were decreased. Seedling survival was significantly positively correlated with non-structural carbohydrate content, especially with soluble sugar. Under the treatment without warming, herbaceous species inhibited the survival of A. faxoniana, increased height growth and aboveground biomass. Grasses and forbs decreased the root length and belowground biomass of A. faxoniana. In the warming treatment, forbs increased the survival of A. faxoniana, sedges decreased root length and belowground biomass of A. faxoniana, and grasses and forbs decreased height growth and aboveground biomass of A. faxoniana. Simulated warming increased the survival of A. faxoniana seedlings, but also made it face stronger competition from herbaceous and thus inhibited its growth.通过模拟增温和功能群去除试验,研究不同功能群的草本植物在岷江冷杉幼苗更新定植过程的作用,分析其在温度升高条件下生理指标的变化.结果表明: 增温提高了岷江冷杉幼苗的存活率和植物体内非结构性碳水化合物含量,但抑制了幼苗的生长和根冠比.岷江冷杉幼苗的非结构性碳水化合物含量,尤其是可溶性糖含量与存活率呈显著正相关.不增温处理中,草本植物降低了幼苗的存活率,促进幼苗的株高生长和地上生物量积累,禾本科植物和杂类草抑制了幼苗根系生长和地下生物量的积累;增温处理中,杂类草的存在提高了幼苗的存活率,莎草科则显著抑制了幼苗根系生长和地下生物量的积累,禾本科植物和杂类草抑制了幼苗的高生长和地上生物量积累.模拟增温提高了林线树种岷江冷杉幼苗的存活率,但使其面临来自草本植物更剧烈的竞争,抑制其生长.

Remobilization is an important mechanism of resource conservation in plants. However, our understanding of whether the responses of resource remobilization to global warming differ between deciduous and evergreen trees remains unclear. We assessed resource remobilization from leaves to 1-year-old shoots in a deciduous (Betula ermanii) and an evergreen (Quercus aquifolioides) species along elevational gradients (i.e., temperature gradient) at the end of growing season. We aimed to test the hypotheses that the reallocation rate increased with increasing elevation and that more resources were reallocated from leaves to storage tissues in deciduous species than in evergreen species. We analyzed the concentrations of non-structural carbohydrates (NSC), nitrogen (N) and phosphorus (P), and compared the differences in remobilization efficiency of NSC, N, and P between leaves and shoots within each species and between the two species along the elevational gradients. Due to the different strategies of evergreen and deciduous species in nutrients use, the deciduous species had higher N and P remobilization rate, but lower remobilization rate of sugars, starch, and NSC than the evergreen species at the end of growing season. The remobilization rate of NSC, N, and P was significantly higher in trees at their upper limits compared to lower elevations. Our results suggest that trees reallocate resources from leaves to storage tissues before leaf senescence or at the end of growing season, to increase the resource use efficiency and to adapt to the harsh alpine environments. These results contribute to better understanding of the alpine treeline phenomenon in a changing world.

The allocation and stoichiometry of plant nutrients in leaves reflect fundamental ecosystem processes, biotic interactions, and environmental drivers such as water availability. Climate change will lead to increases in drought severity and frequency, but how canopy nutrients will respond to drought, and how these responses may vary with community composition along aridity gradients is poorly understood. We experimentally addressed this issue by reducing precipitation amounts by 66% during two consecutive growing seasons at three sites located along a natural aridity gradient. This allowed us to assess drought effects on canopy nitrogen (N) and phosphorus (P) concentrations in arid and semiarid grasslands of northern China. Along the aridity gradient, canopy nutrient concentrations were positively related to aridity, with this pattern was driven primarily by species turnover (i.e., an increase in the relative biomass of N- and P-rich species with increasing aridity). In contrast, drought imposed experimentally increased N but decreased P concentrations in plant canopies. These changes were driven by the combined effects of species turnover and intraspecific variation in leaf nutrient concentrations. In addition, the sensitivity of canopy N and P concentrations to drought varied across the three sites. Canopy nutrient concentrations were less affected by drought at drier than wetter sites, because of the opposing effects of species turnover and intraspecific variation, as well as greater drought tolerance for nutrient-rich species. These contrasting effects of long-term aridity vs. short-term drought on canopy nutrient concentrations, as well as differing sensitivities among sites in the same grassland biome, highlight the challenge of predicting ecosystem responses to future climate change.

Elevation is a complex environmental factor altering temperature, light, moisture and soil nutrient availability, and thus may affect plant growth and physiology. Such effects of elevation may also depend on seasons. Along an elevational gradient of the Balang Mountain, southwestern China, we sampled soil and 2-year old leaves, 2-year old shoots, stem sapwood and fine roots (diameter

Forest fine roots contribute substantially to carbon cycling, and old growth forests have an important role in the global carbon budget. We, hence, studied temporal variation in fine root production and turnover in an old forest. Fine root dynamics were investigated, using sequential soil cores for 6 years, and related to rainfall and air temperature in a mixed mature broad-leaved Pinus koraiensis forest in northeastern China. The mass, production, mortality, and disappearance of fine roots showed intra-annual variation. Monthly live and dead fine root mass were significantly positively correlated with meteorological conditions of the previous month. Monthly fine root production was associated with air temperature of the current month. The intra-annual pattern of fine root production was similar to that of net primary production and opposite to that of leaf litterfall. Total fine root production accounted for 25 % of net primary production, and the fine root input to soil carbon was 1.2 times larger than the leaf litterfall. Our results indicate tight linkages between fine roots and meteorological conditions. The important role of fine roots in forest carbon budget suggests that forest carbon flux estimations need to take fine root dynamics into account.

Theoretical and observational studies have suggested that environmental variations would change compositional similarity between plant communities. However, this topic has rarely been examined via experiments involving direct manipulation of resources utilized by plant communities. A 9-year field manipulation experiment was conducted to examine the effects of nitrogen addition and increased water on community similarity between a steppe and an old field in the semiarid region of northern China. Over the experimental period, nitrogen addition reduced community similarity between the steppe and the old field, whereas water addition enhanced community similarity. These treatment effects were closely related to changes in diversity characteristics as well as abundance of functional groups and dominant species of plant communities. These results highlight the importance of resource availability in regulating the trajectory of ecosystem succession, and suggest that the increase in atmospheric nitrogen deposition in northern China will contribute to divergence between the steppe and the old field, whereas the increase in growing-season precipitation may encourage convergence between the two grasslands with respect to species composition during succession. Thus the decrease in community similarity caused by nitrogen enrichment may be counteracted, at least partially, by precipitation increase under changing atmosphere and climate.

Nitrogen (N) and phosphorus (P) play vital roles in plant growth and development. Yet how climate regimes and soil fertility influence plant N and P stoichiometry is not well understood, especially in the belowground plant parts. Here we investigated plant aboveground and belowground N and P concentrations ([N] and [P]) and their stoichiometry in three dominant genera along a 2200 km long climatic gradient in northern China. Results showed that temperature explained more variation of [N] and [P] in C4 plants, whereas precipitation exerted a stronger influence on [N] and [P] in C3 plants. Both plant aboveground and belowground [N] and [P] increased with decreasing precipitation, and increasing temperatures yet were negatively correlated with soil [N] and [P]. Plant N:P ratios were unrelated with all climate and soil variables. Plant aboveground and belowground [N] followed an allometric scaling relationship, but the allocation of [P] was isometric. These results imply that internal processes stabilize plant N:P ratios and hence tissue N:P ratios may not be an effective parameter for predicting plant nutrient limitation. Our results also imply that past positive relationships between plant and nutrient stocks may be challenged under changing climatic conditions. While any modeling would need to be able to replicate currently observed relationships, it is conceivable that some relationships, such as those between temperature or rainfall and carbon:nutrient ratios, should be different under changing climatic conditions.

We examined the gene expression profiles of the 5-hydroxytryptamine signaling pathway in the regenerating liver and 8 types of liver cells during rat liver regeneration, and explored expression differences in 5-hydroxytryptamine signaling pathway genes at the level of tissues and cells, as well as the role of the pathway on liver regeneration. Eight types of rat regenerating liver cells were isolated using Percoll density-gradient centrifugation and immunomagnetic bead methods. Rat Genome 230 2.0 Array was used to detect expression changes in 5-hydroxytryptamine signaling pathway genes. The results showed that 26, 47, 8, 21, 16, 19, 22, 27, and 20 genes changed significantly in hepatocytes, biliary epithelial cells, hepatic stellate cells, oval cells, sinusoidal endothelial cells, Kupffer cells, pit cells, dendritic cells, and the regenerating liver, respectively. Synthetic effects of 5-hydroxytryptamine signaling pathway genes in 8 types of liver cells showed that 26 genes were expressed significantly; the expression trends of 10 genes were the same in the regenerating liver, while others were different. Based on the gene expression profiles of the 8 types of liver cells, 5-hydroxytryptamine promoted hepatocyte proliferation through the RAS and STAT3 signaling pathways, proliferation and differentiation of sinusoidal endothelial cells through the STAT3 signaling pathway, and proliferation and apoptosis of pit cells through the AKT3 signaling pathway. There were large differences in genes involved in 5-hydroxytryptamine signaling at the tissue and cellular levels; thus, liver regeneration should be studied in-depth at the cellular level to reveal the molecular mechanism of liver regeneration.