Northeast China Transect Research Articles

Biogeographic Distribution of Soil Bacteria across Precipitation Gradient in Soil Profiles

The biogeographical distribution of soil microbial diversity, driven by climate change, notably precipitation, significantly influences soil functioning in diverse ecosystems. Land-use changes can alter ecosystem services mediated by microbial diversity, particularly in near-surface soil. In this study, we investigated soil bacterial diversity across precipitation gradients in various land uses. We focused on two soil layers (10-20 cm and 40-50 cm) in seven sampling areas along the Northeast China Transect. Utilizing 16S rRNA sequencing, we obtained 897,776,803 optimized sequences. The results reveal a significant shift in bacterial community composition with changing precipitation levels. As precipitation increases, the shifts in dominant bacterial phyla were generally observed. Additionally, soil depth played a role in structuring bacterial communities, with variations observed between surface and subsurface layers. Dominant taxa (Proteobacteria, Acidobacteria, Actinobacteria, Cholloroflexi) exhibited changes in the 10-20 cm layer due to human activity's influence, while the 40-50 cm layer showed more similarity, unaffected by human activities. Notably, parent material significantly affected soil bacterial diversity patterns, underscored by distinct habitats. Such results offer insights into climate change effects and parent material influences on soil bacterial diversity, highlighting the intricate interplay between precipitation, soil depth, and bacterial distribution; enhancing our understanding of ecosystem functioning and responses to environmental changes. This study contributes to the broader comprehension of microbial ecology and underscores the importance of considering multiple factors when studying soil bacterial dynamics.

Archaeal lipids in soils and sediments: Water impact and consequences for microbial carbon sequestration

The mineral protection of microbial necromass is critical for soil carbon stabilization. The water impact on the interactions between minerals and microbial necromass, however, remains unclear due to a lack of proper methods to quantify the mineral-protected microbial necromass. Here, we used offline hydrous pyrolysis to release the archaeal necromass—isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) bound to clay minerals by heating samples at increasing temperatures (150, 200, 250, 300, and 350 °C) under argon atmosphere. The content of extractable isoGDGTs in soils reached the maximum at 200–250 °C, indicating the release of bound isoGDGTs. By investigating the free and bound isoGDGTs along a soil transect with increasing soil water content (SWC), we found that the portion of bound isoGDGTs reached up to 97% of total isoGDGTs in dry soils, and decreased with increased SWC, suggesting that SWC controls isoGDGT stabilization on clay minerals. This relationship was confirmed in the soils from the Northeast China Transect, where the proportion of bound isoGDGTs decreased with increased mean annual precipitation from 160 to 814 mm. Such a connection was further supported by the water-saturated samples of the lake and marine sediments, which have a much lower proportion of bound lipids than the soils. The decrease of bound lipid portion with increasing water content is related to the lower attachment of microbial cells to minerals in wetter soils. Microbial cells are more strongly attached to the mineral phase under drier conditions due to the thin water film on the mineral surfaces. In addition, microorganisms secrete more extracellular polymeric substances under drier conditions, which reinforces the interactions between microbial-derived organic matter and minerals. The increased microbe-mineral interactions under drier conditions offer more stable microbial legacies and stabilize organic matter in the (semi)arid regions.

Contrasting Responses of Vegetation Production to Rainfall Anomalies Across the Northeast China Transect

AbstractIncreases in rainfall variability due to climate change influence gross primary production (GPP) in drylands, with important consequences for terrestrial carbon budget. However, it is not well understood if GPP responds in heterogeneous or even contrasting ways along the temperate bioclimate gradients. Here, based on satellite observations from 2001 to 2020, we identified rainfall anomalies as the magnitude of rainfall beyond its mean of one standard deviation, and examined differential responses of GPP to rainfall anomalies across Northeast China Transect (NECT). We found wet anomalies caused major GPP increase in western arid part of NECT, and the magnitude of increased GPP declined gradually toward the eastern humid region. As a result, GPP increased in desert steppe while decreased in mesic forest in response to wet anomalies. On the contrary, dry anomalies reduced GPP across the ecosystems except for mesic forest. The meadow steppe in the transition region between semi‐arid and sub‐humid regions, which lacks of drought‐tolerant species, showed greater GPP decline in response to dry anomalies than desert and typical steppe in the arid region. The heterogeneous responses of GPP to wet and dry anomalies resulted in contrasting asymmetries in diverse biomes, showing positive asymmetry in drier region, that is, greater magnitude of GPP increase in response to wet anomalies than GPP decrease in response to dry anomalies, and negative asymmetry in wetter region, with a transition between arid and semi‐arid regions. Our findings highlight that increased rainfall variability will enhance heterogeneous and even contrasting GPP changes along temperate bioclimate gradients.

Quantitative relationship between modern surface pollen and plant community at quadrat scale.

Establishing a precise relationship between modern vegetation and surface pollen is the basis and key to quantitatively reconstruct paleovegetation and paleoclimate based on pollen records. The record of plant community plots has been less considered in the statistical analysis of modern vegetation and surface pollen, which limits the quantitative estimation of its precise relationship. In this study, the quantitative relationships of compositions and quantities between modern surface pollen and plant community were analyzed, based on the Bray-Curtis dissimilarity, through the analysis of 33 surface soil samples and corresponding vegetation plots from forest, meadow steppe, typical steppe and desert steppe on the Northeast China Transect. Results showed that, in a single plot, the relationships between vegetation and pollen in compositions and quantities were different across all families and genera, dominant and common families and genera, and less common and rare families and genera, respectively, due to the differences in pollen dispersal and pollen productivity. There were significant differences among different vegetation types. The compositions of meadow steppe differed greatly, while all families and genera, dominant and common families and genera differed greatly in the quantitative relationship in forest. Less common and rare families and genera differed greatly in the compositions in meadow steppe. The vegetation-pollen relationship of different families and genera was basically the same in terms of composition and quantities. According to the Bray-Curtis dissimilarity, pollen taxa could be divided into three types: over-representative, under-representative and representative types. This dissimilarity index represented both the species composition and quantity relationship between vegetation and pollen both at quadrat scale and at specie level, which could be used as an indicator to quantitatively describe the modern vegetation-pollen relationship.

Impacts of preseason drought on vegetation spring phenology across the Northeast China Transect

Vegetation phenology is undergoing profound changes in response to the recent increases in the intensity and frequency of drought events. However, the mechanisms by which drought affects the start of the growing season (SGS) are poorly understood particularly in arid and semi-arid regions. Here, we identified varying degrees of preseason drought events and analyzed the sensitivity of the SGS to preseason drought across the Northeast China Transect (NECT). Our results showed that drought caused a delayed SGS in grassland ecosystems, but an advanced SGS within forest ecosystems. These contrasting responses to preseason drought reflected different adaptive strategies between vegetation types. The SGS was shown to be highly sensitive to short timescales drought (1–3 months) in semi-arid grasslands where annual precipitation is 200–300 mm (i.e. SAGE200–300). Biomes within this region were found to be most vulnerable out of all the ecosystems to drought. Given the frequent nature of droughts in the mid-latitudes, a drought early warning system was recommended accompanied by improved modeling of how the SGS will be affected by intensified drought under future climate change.

Surface soil n-alkane molecular and δD distributions along a precipitation transect in northeastern China

Hydrogen isotope compositions of leaf wax long-chain n-alkanes (δDalk) buried in soils have the potential to provide records of continental paleoclimatic and paleohydrological changes. However, different factors and processes influence the δDalk signature, making interpretation of the soil isotope record complicated. The relative humidity/aridity and vegetation types (C3 vs C4 plants) are two major factors responsible for the soil δDalk variations. In most cases, the interaction between relative humidity/aridity and temperature cannot be separated. Here, we analyzed the δDalk compositions in surface soils along the Northeast China Transect (NECT), where the mean annual precipitation (MAP) varies from ca. 120 to 815 mm, yet the mean annual temperature changes little, providing a setting to test the role of relative humidity/aridity in soil δDalk variations, independent of temperature changes. At the same time, the western part of the NECT, which is mainly a grassland environment, provides a test of the effects of C3 and C4 grasses on soil δDalk changes. In the semi-humid eastern NECT region, the δDalk values and their apparent fractionation relative to precipitation exhibit a strong negative correlation with the aridity index and a close relationship with soil water content. This finding supports the idea that the soil δDalk values are mainly influenced by relative aridity and that the impact of evapotranspiration, including soil evaporation and transpiration-induced 2H enrichment of woody plant leaf water, plays a vital role in shaping soil δDalk. In the semi-arid and arid western NECT region, the δDalk values and their apparent fractionations show no relationship with any environmental factors. However, in the westernmost area, soil δDalk values tend to show a negative relationship with the increasing proportion of C4 plants. This pattern probably indicates that in the arid area the soil δDalk values vary more closely with plant types than with the environmental variables. This study provides new insights into deciphering the relationship between soil δDalk values and relative humidity/aridity, and it affirms the applicability of δDalk in paleo-hydrologic reconstructions.

Evaluating the Representation of Vegetation Phenology in the Community Land Model 4.5 in a Temperate Grassland

AbstractVegetation plays an important role in terrestrial ecosystems and affects both water and carbon cycles. It is crucial to predict vegetation phenology accurately to understand the Earth's ecosystems better. In this study, we evaluated the temperate grassland phenology simulated by the Community Land Model 4.5 for the Northeast China Transect with the Moderate Resolution Imaging Spectroradiometer leaf area index (LAI) data set. Results show that although the CLM could partly capture the seasonal patterns of LAI for temperate grasslands, shortcomings lie in a delayed end date of growing season and a problematic senescence existed in early summer. The reason is attributed to the low temperature threshold set for leaf offset and an inaccurate carbon allocation strategy for its display and storage. With the adjusted key phenology parameters, the modeled temperate grassland phenology has been substantially improved for this system: An overestimation of the growing‐season LAI as well as the annual gross primary productivity can be constrained. Meanwhile, the modified phenology would effectively change the partition of evapotranspiration in a more reasonable pattern.

Response of vegetation dynamics to climatic variables across a precipitation gradient in the Northeast China Transect

ABSTRACTThis study investigated the influence of climatic variables on the spatio-temporal variation of vegetation growth using normalized difference vegetation index (NDVI) data and climate data from 2000 to 2013 in the Northeast China Transect. Partial correlation and linear regression methods were applied to quantify the response of the growing season NDVI to climatic variables. Gradient analysis was used to investigate how the response changes across the precipitation gradient over the transect. The results show that, at the spatial scale, NDVI increases with precipitation in grassland, and the spatial sensitivity is 0.001/mm. At the temporal scale, grassland NDVI is less correlated with precipitation in wet areas where precipitation exceeds a threshold of 250 mm. The temporal sensitivity of grassland NDVI to precipitation is 0.0003–0.0006/mm. Positive correlations between NDVI and temperature dominate in forest areas, and forest NDVI is sensitive to temperature by 0.06–0.12/°C.

Ecohydrological optimality in the Northeast China Transect

Abstract. The Northeast China Transect (NECT) is one of the International Geosphere-Biosphere Program (IGBP) terrestrial transects, where there is a significant precipitation gradient from east to west, as well as a vegetation transition of forest–grassland–desert. It is remarkable to understand vegetation distribution and dynamics under climate change in this transect. We take canopy cover (M), derived from Normalized Difference Vegetation Index (NDVI), as an index to describe the properties of vegetation distribution and dynamics in the NECT. In Eagleson's ecohydrological optimality theory, the optimal canopy cover (M*) is determined by the trade-off between water supply depending on water balance and water demand depending on canopy transpiration. We apply Eagleson's ecohydrological optimality method in the NECT based on data from 2000 to 2013 to get M*, which is compared with M from NDVI to further discuss the sensitivity of M* to vegetation properties and climate factors. The result indicates that the average M* fits the actual M well (for forest, M* = 0.822 while M = 0.826; for grassland, M* = 0.353 while M = 0.352; the correlation coefficient between M and M* is 0.81). Results of water balance also match the field-measured data in the references. The sensitivity analyses show that M* decreases with the increase of leaf area index (LAI), stem fraction and temperature, while it increases with the increase of leaf angle and precipitation amount. Eagleson's ecohydrological optimality method offers a quantitative way to understand the impacts of climate change on canopy cover and provides guidelines for ecorestoration projects.

Spatiotemporal patterns of vegetation phenology change and relationships with climate in the two transects of East China

Changes in vegetation phenology due to global climate change directly impact the dynamic balance of terrestrial carbon and nutrients and the biodiversity pattern, and send feedbacks to climate system. It is crucial to understand spatiotemporal patterns and mechanisms of vegetation phenology change and their relationship with climatic change. In this paper, we quantified the spatiotemporal patterns of start and end of growing season for seven vegetation types in Northeast China Transect (NECT) and North–South Transect of East China (NSTEC) during 2001–2013 using MODIS Enhanced Vegetation Index (EVI). The integral of EVI during growing season was also calculated as an additional phenological index. We then proceeded to analyze the relationship between the three phenological metrics and climate variables including daytime and nighttime temperature and precipitation. To study the temporal phenological trend of deciduous broadleaved forest in northeast China, we identified stands of deciduous broadleaved forest without land cover changes during 2001–2013 and derived the slopes of temporal changes in phenological metrics. Regression was applied to quantify the relationship between phenological trends and trends of climate variables.The vegetation types along the two transects in eastern China have distinctly different phenological characteristics and the strength of climate modulations on phenology varies among vegetation types. The study of temporal trend of phenological changes of the deciduous broadleaved forest in northeast China revealed that nighttime temperature is the most important driver. Increasing in nighttime temperature in spring tends to advance the start of growing season, while increasing in nighttime temperature during growing season tends to delay the growing season. Cold daytime prior to growing season also favors advanced start of growing season. On the other hand, summer nighttime temperature tends to bring down, whereas precipitation tends to enhance, the maximum EVI and hence the EVI integral as the latter is mostly determined by maximum EVI and to a less extent by length of growing season.

Evapotranspiration dynamics over a temperate meadow ecosystem in eastern Inner Mongolia, China

Ecosystem evapotranspiration links surface energy and water balance, which is very important to the forming and evolution of regional climate. To understand the evapotranspiration dynamic over the temperate meadow in Inner Mongolia grassland, a long-term continuous measurement of water vapour flux was conducted using eddy covariance technique from 2008 to 2013. The results showed that the seasonal variation of daily evapotranspiration displayed a unimodal pattern with maximum value of 6.45 mm day−1. The mean value of annual evapotranspiration (ET) was 650 mm with 72 % occurring during the growing season from May to September. The annual evapotranspiration was larger than the annual precipitation (P), while less than the annual evaporation (E). The ET/P reached up to 1.91, while the ET/E was only 0.60. The evapotranspiration was not limited by precipitation due to additional water supply from surrounding dunes. The daily evapotranspiration was mainly driven by atmospheric moisture demand in the growing season with high Priestley–Taylor parameter, averaged 1.04. The daily evapotranspiration presented positive correlation with net radiation, and the correlation was affected by water vapour pressure deficit. The net radiation and water vapour pressure deficit controlled the evapotranspiration process together. The study site had the largest annual evapotranspiration and ET/P compared with the other ecosystems along the transection of Northeast China Transect, International Geosphere Biosphere Programme. The harvest activity could increase the albedo and then decrease the available energy of the surface, eventually reducing the monthly evapotranspiration as much as 33.98 % in September.

Soil gross nitrogen transformations along the Northeast China Transect (NECT) and their response to simulated rainfall events.

Climate changes are predicted to increase extreme rainfall events in semiarid and arid region in Northern Hemisphere. Nutrient cycles will be affected by the precipitation changes but so far only very little is known how soil N transformations may respond. Here we investigated gross soil N transformation rates and their response to simulated rainfall events across Northeast China Transect (NECT). The results showed that gross N mineralisation rate, nitrification rate and nitrification to mineralisation ratio significantly increased as the humidity index decreased along NECT, resulting in NO3− as the predominant inorganic N form. These characteristics could increase the risk of NO3− losses but at the same time reduce the risk of N losses via volatilization in the semiarid and arid region. The soil-plant ecosystems have developed effective N conservation strategies in the long term with respect to the prevailing climate in arid region. However, compared to humid soils more dramatic changes of soil N transformation rates are likely to occur in arid soils, after sudden soil moisture increases. Soil N conservation mechanisms in arid regions were drastically affected when the heavy rainfall frequently occurred. Arid ecosystems are expected to be more vulnerable than humid ecosystems in response to extreme rainfall events.

Spatial and temporal characteristics of droughts in the Northeast China Transect

In this study, drought trends and change magnitudes of the Northeast China Transect (NECT) were analyzed using the Mann–Kendall test and Theil–Sen’s slope estimator. Meteorological data from 20 meteorological stations of NECT region from 1957 to 2012 were used. Results demonstrated that five stations had significant negative trends in precipitation. The magnitudes of the significant negative trends at the 95 % confidence level varied from −2.41 ± 1.05 mm year−1 at Tonghe station to −1.11 ± 0.51 mm year−1 at Qianguoerluosi station. Analysis of the seasonal precipitation series showed a mix of negative and positive trends. Many stations also exhibited strong contrasting seasonal trends that counterbalanced one other at the yearly level. In addition, cluster analysis based on discrete wavelet transform (DWT) was applied to the standard precipitation index (SPI) series. Results revealed three different and spatially well-defined subregions (east, center and west regions of NECT). Due to the decrease in precipitation from the east to the west, land use varies from forest regions in the east, to agriculture in the center, to pastoral areas in the west. Characteristics of drought events for each representative station of different subregions are explored using temporal evolution of the SPI values. Results showed that severe or extreme droughts occurred in 2001, 2003 and 2008 in Tonghe, 1980 and 2007 in Tongliao and 2005–2007 in East Ujimqin Banner. Results indicate that clustering analysis based on DWT has great potential for examining spatial coherence of regional drought, which was consistent with not only the precipitation spatial distribution but also the characteristics of land use in the study area. This study not only provides important information on drought variability in the NECT, but also provides useful information for improving water management strategies and planning agricultural practices.

Validating a Dynamic Global Vegetation Model with Remotely Sensed Vegetation Index

The present study aims to evaluate the ability of IBIS model to capture the difference in vegetation characteristics among six major biomes in the Northeast China Transect and to calibrate the simulated LAI by IBIS, using the product of MODIS LAI (Leaf Area Index). The results showed that IBIS simulated a little lower growing season LAI over temperate evergreen conifer forest and boreal evergreen forest, while it overestimated LAI relative to MODIS in non-growing season. IBIS performed poorly on LAI over savanna, grassland and shrub land, compared with MODIS and it nearly simulated higher LAI throughout the year. Based on regression analysis, the simulating LAI by IBIS (Integrated Biosphere Simulator) presented a significant linear correlation with that from MODIS over temperate evergreen conifer forest in spring and winter, boreal evergreen forest throughout the year and grassland from summer to early autumn. Therefore, it was help to adjust the model parameters over these plant functional types to calibrate the estimated LAI in a large spatial scale.

Soil pH was the main controlling factor of the denitrification rates and N2/N2O emission ratios in forest and grassland soils along the Northeast China Transect (NECT)

The Northeast China Transect (NECT) is a mid-latitude terrestrial transect in the International Geosphere-Biosphere Programme. Its major environmental gradient is precipitation, which gradually decreases from the eastern mountainous region to the western pastoral area. In this investigation, a series of forest and grassland soils were sampled along the NECT, and the denitrification rate and nitrogen/nitrous oxide (N2/N2O) ratio were studied under laboratory conditions by the acetylene inhibition method. Forest soils were all acidic, with soil pH values ranging from 4.3 to 5.9 and soil organic carbon ranging from 32.0 to 54.7 g kg−1. Soil pH for grassland soils was approximately neutral, ranging from 6.1 to 7.8, while soil organic carbon ranged from 14.8 to 32.2 g kg−1. The highest denitrification rates (average 1.1 ± 0.2 mg N kg−1 h−1) were in grassland soils in the western part of the NECT, while the lowest were in forest soils (average 0.25 ± 0.1 mg N kg h−1) in the eastern part of the NECT. The denitrification rate increased linearly from east to west along the NECT (p < 0.01). Nitrous oxide was the main component of gas products of denitrification in forest soils, while N2 was the dominant denitrification product in grassland soils. The ratio of N2/N2O increased linearly from east to west along the NECT (p < 0.01). Soil pH was the best predictor of the denitrification rate and of the N2/N2O ratio in grassland and forest soils along the NECT.

The Vegetation Coverage Dynamic Coupling with Climatic Factors in Northeast China Transect

Based on SPOT-VGT images and meteorological data, this paper applied an integrated method to investigate the vegetation dynamic and its response to climate factors during 1998-2008 in Northeast China Transect, one of 15 ecological transects listed in the International Geosphere-Biosphere Programme. The main findings are as follows: (1) The NDVI time series presented nonlinear patterns that vary with timescales. The series fluctuated greatly at the smallest timescale (20 days), showing no salient trend, whereas a trend manifested itself more and more with the increase of time scale and finally stabilized at the 320-day scale. Little difference was found between vegetation types about the NDVI periodicity, as they occurred on either a 280-day or a 290-day cycle. (2) NDVI exhibited a significant correlation with temperature, precipitation, and sunshine hours. Overall, the correlation between NDVI and temperature was the highest, followed by precipitation, sunshine hours, and relative humidity. For different vegetation types, the correlations between NDVI and climate variables diversified, increasing from desert steppe to typical steppe, meadow steppe, and forest. (3) The periodicity of temperature and precipitation occurred in either a 280-day or 290-day cycle, which was approximately coincident with that of NDVI. This further supported the significant relationship between NDVI and these two climate factors. (4) At all the time scales under examination, NDVI and temperature and precipitation are significantly, positively correlated, especially at the 160-day scale, which can be regarded as the most suitable time scale for investigating the responses of vegetation dynamics to climate factors at most stations.

Controls on soil organic carbon and nitrogen in Inner Mongolia, China: A cross-continental comparison of temperate grasslands

[1] Most global ecosystem models assume that controls over soil organic matter are alike in climatically similar regions. In this study, we tested the generality of controls over soil organic carbon (SOC) and soil organic nitrogen (SON) in temperate grasslands. We measured organic matter pools in Inner Mongolia, China, along the Northeast China Transect, and analyzed the relationship of SOC and SON to climate, soil texture, and land use variables. We then compared our data to values simulated by a regression model developed in the U.S. Great Plains and also to Century model simulations. We found that, as in the U.S. Great Plains, climate and soil texture variables could explain a large proportion of variation in observed SOC and SON, but a regression model developed in the Great Plains overestimated SOC and underestimated SON in Inner Mongolia. Using Century, we found that simulated SOC and SON values were sensitive to both inclusion of altered land use and changes in N deposition and that the model that best fit our data included higher-intensity grazing and N deposition values higher than that in the Great Plains. This model also produced aboveground net primary production (ANPP) values comparable with values observed in the literature for Inner Mongolian grasslands, but these values were higher than ANPP predicted by previously published regression models. These results suggest that different controls over SOC and SON cycling in Inner Mongolia may affect our ability to predict SOC and SON pool sizes using relationships in other regional models.

Evidence of a universal scaling relationship for leaf CO2 drawdown along an aridity gradient

The leaf carbon isotope ratio (δ(13) C) of C3 plants is inversely related to the drawdown of CO2 concentration during photosynthesis, which increases towards drier environments. We aimed to discriminate between the hypothesis of universal scaling, which predicts between-species responses of δ(13) C to aridity similar to within-species responses, and biotic homoeostasis, which predicts offsets in the δ(13) C of species occupying adjacent ranges. The Northeast China Transect spans 130-900 mm annual precipitation within a narrow latitude and temperature range. Leaves of 171 species were sampled at 33 sites along the transect (18 at ≥ 5 sites) for dry matter, carbon (C) and nitrogen (N) content, specific leaf area (SLA) and δ(13) C. The δ(13) C of species generally followed a common relationship with the climatic moisture index (MI). Offsets between adjacent species were not observed. Trees and forbs diverged slightly at high MI. In C3 plants, δ(13) C predicted N per unit leaf area (Narea) better than MI. The δ(13) C of C4 plants was invariant with MI. SLA declined and Narea increased towards low MI in both C3 and C4 plants. The data are consistent with optimal stomatal regulation with respect to atmospheric dryness. They provide evidence for universal scaling of CO2 drawdown with aridity in C3 plants.

Anthropogenic and climatic impacts on surface pollen assemblages along a precipitation gradient in north‐eastern China

ABSTRACTAim To understand the scenarios of ‘anthropogenic biomes’ that integrate human and ecological systems, we need to explore the impacts of climate and human disturbance on vegetation in the past and present. Interactions among surface pollen, modern vegetation and human activities along climate and land‐use gradients are tested to evaluate the natural and anthropogenic forces shaping the modern vegetation, and hence to aid the reconstruction of vegetation and climate in the past. This in turn will help with future predictions.Location The North‐east China Transect (NECT) in north‐eastern China.Methods We analysed 33 surface pollen samples and 213 quadrats across four vegetation zones along the moisture/land‐use gradients of the NECT. Detrended correspondence analysis (DCA) and redundancy analysis (RDA) of 52 pollen taxa and three environmental variables were used to distinguish anthropogenic and climatic factors that affect surface pollen assemblages along the NECT.Results The 33 surface samples are divided into four pollen zones (forest, meadow steppe, typical steppe and desert steppe) corresponding to major vegetation types in the NECT. Variations in pollen ratios of fern/herb (F/H), Artemisia/Chenopodiaceae (A/C) and arboreal pollen/non‐arboreal pollen (AP/NAP) represent the vegetation and precipitation gradient along the NECT. DCA and RDA analyses suggest that surface pollen assemblages are significantly influenced by the precipitation gradient. Changes in the abundance of Chenopodiaceae pollen are related to both human activities and precipitation.Main conclusions Surface pollen assemblages, fossil pollen records, archaeological evidence and historical documents in northern China show that a large increase of Chenopodiaceae pollen indicates human‐caused vegetation degradation in sandy habitats. The A/C ratio is a good indicator of climatic aridity, but should be used in conjunction with multiple proxies of human activities and climate change in the pollen‐based reconstruction of anthropogenic biomes.

Exploring the effects of water on vegetation change and net primary productivity along the IGBP Northeast China Transect

To understand the mechanisms underlying the effects of climate variation, especially the effects of water on vegetation, vegetation type and distribution as well as climate data and soil type were used to simulate present vegetation distributions and net primary productivity (NPP) under present and future climate scenarios SRES-A2 and SRES-B2. A natural vegetation NPP model was also applied to calculate future vegetation NPP. The results showed that water played a dominant role not only in the distribution of vegetation, but also in the rate of change in the vegetation area. Analysis of NPP showed that precipitation had more effects on the amount of biome NPP than temperature did. Different effects were observed for the rate of change in NPP. In cases where biomes remain unaltered, the variation in annual precipitation could account for 39% of the variation in NPP. In cases where biomes changed, 45% of NPP was caused by temperature variation. Regarding the variation in transect production, −2.85% resulted from the change in vegetation structure when compared with present NPP, and 7.69% from the climate change under scenario SRES-B2; these values were −7.4 and 19.56%, respectively, under scenario SRES-A2. The results showed water served as a dominant factor controlling the vegetation distributions and NPP. However, temperature became determinant where the biomes changed, impacting the rate of change in vegetation NPP when the climate changed. The results also showed that water would have a positive effect on transect production, and the structure of vegetation had a negative effect under the projected future climate.