Temperate Steppe In Inner Mongolia Research Articles

Effects of warming on soil fungal community and its function in a temperate steppe

BackgroundThe potential effects of global warming on soil fungal communities and their functions remain uncertain. To address this issue, we investigated the effects of 3-year simulated field warming on the community and function of fungi in a temperate steppe of Inner Mongolia, northern China.MethodsThe diversity and structure of the fungal community were measured by high-throughput sequencing. The functionality of fungal communities was identified by comparison with the ITS reference database.ResultsOur results showed that warming did not affect the diversity of fungi, but significantly increased the complexity of the fungal community, with fungal taxa more closely associating with each other. We observed that plant pathogens and arbuscular mycorrhizal fungi were the most abundant functional groups. Meanwhile, warming significantly decreased the relative abundance of animal pathogens.ConclusionsWarming significantly increased the complexity of the fungal community, with soil pH being the main factor affecting soil fungal function. Our findings emphasize that the response of the fungal community and its functional groups to warming has significant implications for ecosystem biogeochemical cycling.

Different responses of soil microbial respiration to nitrogen addition between surface and deep soil in a temperate steppe in Inner Mongolia

Different responses of soil microbial respiration to nitrogen addition between surface and deep soil in a temperate steppe in Inner Mongolia

Belowground Biomass Changed the Regulatory Factors of Soil N2O Funder N and Water Additions in a Temperate Steppe of Inner Mongolia

Belowground Biomass Changed the Regulatory Factors of Soil N2O Funder N and Water Additions in a Temperate Steppe of Inner Mongolia

Changes in plant species dominance maintain community biomass production under warming and precipitation addition in temperate steppe in Inner Mongolia, China

Dominant species play a crucial role in regulating plant community structure and productivity. Climate change affects community productivity by changing plant traits and resource use efficiency. However, the response of the productivity of a dominant species to warming and precipitation addition and the related effects on community biomass production in semi-arid grasslands remain unclear. We conducted a ten-year warming and precipitation addition study of a semi-arid steppe in Inner Mongolia, China. We examined the responses of community composition, biomass production, and trait and resource use efficiency of two dominant species, Leymus chinensis (rhizome grass) and Stipa krylovii. The results show that warming and precipitation increased the biomass of L. chinensis and decreased the biomass of S. krylovii. Community biomass production was unchanged under warming and precipitation from the contrasting changes in the two dominant species. Warming significantly increased the leaf area (LA) of L. chinensis and S. krylovii compared to that in ambient conditions, while it decreased the specific leaf area (SLA) and δ13C of S. krylovii. Increases in temperature stimulated biomass production of L. chinensis by affecting salicylic acid (SA) and GA (gibberellin), and they increased its competitive ability compared with that of S. krylovii. Our results highlight the different responses of L. chinensis and S. krylovii to environmental changes, which stabilised community productivity under warming and precipitation. Our study provides evidence that S. krylovii may be replaced by L. chinensis in steppe climates in the warmer and wetter future.

Ecosystem stability is determined by plant defence functional traits and population stability under mowing in a semi‐arid temperate steppe

Abstract As a common grassland management practice in many high‐latitude regions worldwide, mowing has great impacts on grassland functioning and stability. Species richness, species asynchrony and species stability have been suggested as central in responses to environmental change. Mowing can evoke plant defence system due to physical damages to plants. However, no studies have comprehensively evaluated the role of plant defence functional traits, species richness, species asynchrony and stability in ecosystem functioning under mowing regimes across timescales. In this study, we set up short‐term (4 years) and long‐term (16 years) mowing experiments with three stubble heights (control, 10 cm, 2 cm) in a temperate steppe of Inner Mongolia. We investigated the effects of mowing‐induced changes in distribution metrics associated with plant defence traits, that is mean, variance, skewness and kurtosis of trait distribution, on ecosystem stability of grassland communities using structural equation modelling. We found that grassland ecosystem stability was enhanced by increasing mowing duration and decreasing stubble height. Mowing‐induced increase in abundance and diversity of plant defence traits contributed to greater ecosystem stability by enhancing species asynchrony and population stability. Moreover, we found that mowing enhanced the abundance and diversity of plant defence traits of dominant species and contributed to population stability and species asynchrony, thus enhancing temporal stability of grassland ecosystems. These results demonstrate the important roles of plant defence traits in maintaining stability of grasslands under mowing, and highlight that, in addition to species richness, asynchrony and population stability, plant functional defence trait acts in stabilizing ecosystem functions under human‐induced environmental changes. Read the free Plain Language Summary for this article on the Journal blog.

Morphological and physiological traits of dominant plant species in response to mowing in a temperate steppe.

Mowing is a common grassland management to feed livestock during winter by harvesting hay in autumn in many high latitude regions. Trait-based approach has been used to explain the responses of plant community to disturbance resulting from environmental changes and human activities. However, few studies have focused on the mechanisms underlying responses of grassland ecosystem to mowing from perspective of plant traits. Here, we investigated the effects of mowing on plant community of a temperate steppe in Inner Mongolia of northern China by field experiments to dissect the trade-off between morphological and physiological traits in response to short-term (4 years) and long-term (16 years) mowing. Specifically, we evaluated the two strategies associated with nutrient acquisition of two dominant species in response to mowing by measuring leaf and root morphological traits and physiological traits of root carboxylate exudation, AMF colonization and soil microbial community. We found that long-term mowing, but not short-term mowing, led to an increase in species richness. In addition, mowing decreased overall plant biomass of grassland community, but enhanced and suppressed growth of forbs and grasses, respectively. However, the ratio of forbs to grasses in the community was dependent on mowing duration, such that the forbs became more dominant than the grasses under long-term mowing. Our results revealed that short-term mowing reduced soil microbial biodiversity and root colonization of AMF in the grass Stipa krylovii, while root AMF colonization and carboxylate exudation in the forb Artemisia frigida were enhanced by short-term mowing. In long-term mowing, the functional traits associated with leaf resource conservation (i.e. leaf tissue density) and root resource acquisition were reduced in the grass, while the functional traits related to leaf resource acquisition and root resource conservation were increased in the forb, highlighting the species-specific and divergence in leaf and root traits in the grass and forb of temperate steppe in response to mowing. These novel findings demonstrate that physiological and morphological strategies are main drivers for dominant species in response to mowing in temperate grasslands.

The Diversity of Soil Bacteria and Fungi Under Altered Nitrogen and Rainfall Patterns in a Temperate Steppe.

The response of soil microorganisms to altered nitrogen (N) and rainfall patterns plays an important role in understanding ecosystem carbon and nitrogen cycling processes under global change. Previous studies have separately focused on the effects of N addition and rainfall on soil microbial diversity and community composition. However, the combined and interactive impact of N addition and rainfall on soil microbial diversity and function mediated by plant and soil processes have been poorly investigated for grassland ecosystems. Here, we conducted a field experiment with simulated N addition (N addition: 10 g N m–2yr–1) and altered rainfall pattern [control, rainfall reduction (compared to control –50%); rainfall addition (compared to control + 50%)] to study their interactive effects on soil microbial diversity and function in a temperate steppe of Inner Mongolia. Our results showed that N addition and rainfall addition significantly increased soil bacterial diversity, and the bacterial diversity was positively correlated with soil microbial biomass nitrogen, inorganic nitrogen, and Stipa krylovii root exudate C:N ratio, Allium polyrhizum root exudate C and N, and A. polyrhizum root exudate C:N ratio. N addition and rainfall reduction significantly reduced fungal diversity, which correlated closely with soil microbial biomass carbon and the C:N ratio of A. polyrhizum root exudates. Bacteria were mainly eutrophic r-strategists, and the responses of bacterial function guilds to the interaction between N addition and rainfall pattern were not significant. However, the arbuscular mycorrhizal fungi (AMF), in the functional classification of fungi, were significantly reduced under the condition of N addition and rainfall reduction, and the absolute abundance of the phylum Glomeromycota increased under rainfall addition, suggesting that AMFs are sensitive to altered N and rainfall patterns over short timescales (1 year). Collectively, our results have important implications for understanding the plant–soil–microbe system of grasslands under climate change.

Aboveground productivity and community stability tend to keep stable under long-term fencing and nitrogen fertilization on restoration of degraded grassland

Restoration of degraded grassland is an essential issue which has been widely concerned but not effectively resolved. Fencing and nitrogen fertilization are common and efficient restoration practices. However, there are still controversy on the effectiveness and duration of fencing and nitrogen fertilization on the restoration of degraded grassland. To estimate the effects of fencing and nitrogen fertilization on the community above-ground net primary productivity (ANPP) and stability, and explore the underlying mechanism, an 18-year (from 2003 to 2020) fencing and nitrogen fertilization (8 g N m−2 year−1) field experiment was conducted on a degraded temperate steppe in Inner Mongolia. Community ANPP and species richness were measured at the peak of plant biomass in growing season (mid-August) from 2004 to 2020. Temporal stability of community ANPP were calculated to estimate the community stability under different restoration managements. We found that both fencing and nitrogen fertilization can significantly increase the ANPP. Nevertheless, ANPP tended to keep stable rather than continuously increase with the extension of restoration duration. Long-term fencing and nitrogen fertilization significantly reduced the stability of ANPP in early stage of restoration (2004–2010), but had no significant effect on the stability of ANPP in later stage (2011–2020). Moreover, the stability of ANPP maintained stable with extension of restoration duration. Furthermore, we found that the biological factors that regulate the community stability were similar between the two restoration measures. Specifically, the stability of ANPP was regulated by species asynchrony in early phase, while, it was mediated by both species asynchrony and dominant species stability in later phase. Overall, from the perspective of community ANPP, the degraded steppe reached optimal status after approximately seven years of fencing and nitrogen fertilization, appropriate utilization after seven years' restoration may be conducive to maintain ANPP and the stability of ANPP. This study provided valuable information for better restoring and managing the degraded temperate steppes.

Effects of Fencing on Vegetation and Soil Nutrients of the Temperate Steppe Grasslands in Inner Mongolia

Grazing exclusion has been widely implemented in degraded grassland. However, the changes of plant communities and soil nutrients in response to fencing are still controversial. Thus, the effects of free grazing, 17 and 36 years of fencing on the plant biomass and litter biomass, carbon (C), nitrogen (N) and phosphorus (P) concentrations and stocks of plant, litter and soil were investigated in the temperate steppe grasslands of northern China. The results indicated that fencing increased the aboveground live biomass and litter biomass. In addition, fencing increased C, N and P stocks of aboveground live biomass, litter biomass and soil. Although root biomass and its nutrient stocks were also significantly increased by 17 years of fencing, they were decreased with fencing extending from 17 to 36 years. Moreover, there were no significant differences in aboveground live biomass and soil N and P stocks between 17 and 36 years of fencing. Litter biomass and its C, N and P stocks were positively correlated with soil C, N and P stocks. Our results demonstrated that 17 years of fencing is an effective way to restore vegetation and soil nutrients in the temperate steppe of Inner Mongolia, but a longer fencing duration has no further positive effects on biomass production and soil nutrients accumulation.

Effects of warming on the bacterial community and its function in a temperate steppe

As a significant environmental issue, global warming will have a significant impact on soil microorganisms, especially soil bacteria. However, the effects of warming on the network structure of bacterial communities and the function of ecosystems remain unclear. Therefore, we examined the effects of three-year simulated field warming on the complexity of soil bacterial communities and predicted functions in a temperate steppe of Inner Mongolia. Warming significantly increased the α-diversity of bacteria in 2018 but did not affect it in 2019 and 2020. Warming increased network complexity and stability and keystone taxa, and these bacterial taxa also associated more closely with each other, indicating that the protection of interactions between bacterial taxa is very important for the conservation of biodiversity. Warming significantly increased aerobic chemoheterotrophy, ureolysis, and chemoheterotrophy, suggesting that warming increased the ability of bacteria to decompose organic matter and the emission of greenhouse gases, such as CO2 and CH4. Collectively, warming will alter soil bacterial community structure and its potential functions, further affecting key functions in grassland belowground ecosystems.

Impacts of long-term nitrogen addition on nitrous oxide in a temperate grassland

Atmospheric nitrogen (N) deposition has increased dramatically due to increased human activities since the industrial revolution. However, it is still unclear what the responses of soil nitrous oxide (N2O) is to long-term elevated N deposition in a temperate grassland. Here, we conducted an in situ field experiment to investigate these responses to long-term high N addition on a temperate steppe in Inner Mongolia, China, from April 2017 to October 2018. Soil N2O emissions significantly increased by long-term N addition, use of structural equation modeling (SEM) showed that topsoil (0-5 cm) NH4+-N content was the most important limiting factor for N2O emission. Our results indicate that long-term high N addition showed a significantly increase in N2O emission in this temperate grassland.

Mercury accumulation in soil from atmospheric deposition in temperate steppe of Inner Mongolia, China

Mercury (Hg) is a toxic and persistent pollutant and has long-term impacts on ecological systems and human health. Coal-fired power plants (CFPPs) are the main source of anthropogenic Hg emission, and the emitted atmospheric Hg is deposited to the surrounding environments which causes soil pollution. To assess the effects of atmospheric Hg from CFPPs in China on the temperate steppe, Hg contents in the topsoil and subsoil were analyzed for samples collected from 80 sites in central Inner Mongolia during 2012–2015. The average content of Hg in topsoil and subsoil were 14.9 ± 10.4 μg kg−1 and 8.9 ± 5.8 μg kg−1, respectively. The principal components analysis (PCA) indicated that the soil organic matter content and atmospheric deposition were the main factors determining soil Hg content in Inner Mongolia. We used the power plant impact factor (PPIF) to evaluate the impacts of the surrounding CFPPs. The PPIF results showed the most positive correlation with Hg content in topsoil at more than 400 km distances, indicating that the contribution of the long-range transport of Hg emitted from CFPPs is regional in scale. Considering the potential of Hg accumulation in soil, long-term and regional measurements of soil Hg and stricter emission-limit standards for power plants should be implemented to control soil Hg pollution in China.

Effects of nitrogen addition on above-and belowground litter decomposition and nutrient dynamics in the litter-soil continuum in the temperate steppe of Inner Mongolia, China

Anthropogenic activities have increased nitrogen (N) inputs to grassland ecosystems, greatly affecting ecosystem carbon cycling. To investigate the litter decomposition and nutrient dynamics for different litter types under N addition, we conducted a 2-year litter bag experiment at N addition rates ranging from 0 to 25 g N m−2 yr−1. The decomposition rates (k) of Leymus chinensis and Stipa grandis were both highest in the 25 g N m−2 yr−1 treatment, whereas decomposition of mixed litter (aboveground) was highest in the 10 g N m−2 yr−1 (N10) treatment. The decomposition rate of all the aboveground litter was significantly positively correlated with the NO3−–N:NH4+–N ratio. Mixed litter and mixed roots exhibited net C, N, and P release in all treatments. Nitrogen addition promoted N immobilization and slowed P release for S. grandis. For L. chinensis, net P immobilization occurred in most N-addition treatments except for N10 in the first year, followed by a net P release. Soil C:N and C:P ratios were significantly negatively correlated with the litter C:N and C:P ratios, respectively, of L. chinensis. This result may indicate that the N release and P immobilization during decomposition of L. chinensis litter were the main factors influencing the soil stoichiometric ratios.

Aboveground net primary productivity not CO2 exchange remain stable under three timing of extreme drought in a semi-arid steppe.

Precipitation patterns are expected to change in the semi-arid region within the next decades, with projected increasing in extreme drought events. Meanwhile, the timing of extreme drought also shows great uncertainty, suggesting that the timing of drought, especially during growing season, may subsequently impose stronger stress on ecosystem functions than drought itself. However, how the timing of extreme drought will impact on community productivity and carbon cycle is still not clear. In this study, three timing of extreme drought (a consecutive 30-day period without precipitation event) experiments were set up separately in early-, mid- and late-growing season in a temperate steppe in Inner Mongolia since 2013. The data, including soil water content (SWC), soil temperature (ST) chlorophyll fluorescence parameter (Fv/Fm), ecosystem respiration (Re), gross primary productivity (GPP), net ecosystem carbon absorption (NEE) and aboveground net primary productivity (ANPP) were collected in growing season (from May to September) of 2016. In this study, extreme drought significantly decreased SWC during the drought treatment but not for the whole growing season. Extreme drought decreased maximum quantum efficiency of plant photosystem II (Fv/Fm) under “optimum” value (0.75~0.85) of two dominant species (Leymus chinensis and Stipa grandis). While ANPP kept stable under extreme drought treatments due to the different responses of two dominant species, which brought a compensating effect in relative abundance and biomass. In addition, only early-growing season drought significantly decreased the average Re (P < 0.01) and GPP (P < 0.01) and depressed net CO2 uptake (P < 0.01) than mid- and late-growing season drought. ST and SWC influenced the changes of GPP directly and indirectly through photosynthetic ability of the dominant species by path analysis. Our results indicated that the timing of drought should be considered in carbon cycle models to accurately estimate carbon exchange and productivity of semi-arid grasslands in the context of changing climate.

Increased snowfall weakens complementarity of summer water use by different plant functional groups.

Winter snowfall is an important water source for plants during summer in semiarid regions. Snow, rain, soil water, and plant water were sampled for hydrogen and oxygen stable isotopes analyses under control and increased snowfall conditions in the temperate steppe of Inner Mongolia, China. Our study showed that the snowfall contribution to plant water uptake continued throughout the growing season and was detectable even in the late growing season. Snowfall versus rainfall accounted for 30% and 70%, respectively, of the water source for plants, on the basis of hydrogen stable isotope signature (δD) analysis, and accounted for 12% and 88%, respectively, on the basis of oxygen stable isotope signature (δ18O) analysis. Water use partitioning between topsoil and subsoil was found among species with different rooting depths. Increased snowfall weakened complementarity of plant water use during summer. Our study provides insights into the relationships between precipitation regimes and species interactions in semiarid regions.

Effects of Stimulated Nitrogen Deposition on the Bacterial Community Structure of Semiarid Temperate Grassland

With the development of economics, the deposition of available nitrogen in the terrestrial ecosystem is increasing dramatically due to anthropic activities, which negatively impacts the sustainability of the ecosystem ecology. In this study, the effect of long-term stimulated nitrogen deposition[with nitrogen addition of 0, 1, 4, 8, and 32 g·(m2·a)-1] on the microbial community structure of soil was investigated in a temperate steppe in Inner Mongolia using a pyrosequencing technique targeting the bacterial 16S rRNA gene. The results show that the available nitrogen in soil increases with increasing nitrogen addition, resulting in the decrease of the soil pH. The results of pyrosequencing indicate that soil bacterial OTU (operational taxonomy unit) numbers increase with increasing nitrogen deposition, while bacterial α diversity indices show an initial increase and subsequent decrease. Non-metric multidimensional scaling (NMDS) analysis indicates that the bacterial community structure significantly varies among treatments, which can be largely attributed to the changes in the soil pH and nitrogen content due to nitrogen deposition. At the class level, the relative abundance of different bacterial groups shows a varying trend depending on the nitrogen deposition. This study indicates that long-term nitrogen deposition significantly impacts the bacterial community by changing the soil properties.

Responses of plant 15N natural abundance and isotopic fractionation to N addition reflect the N status of a temperate steppe in China

Elevated anthropogenic nitrogen (N) deposition could alter N status in temperate steppe. However, threshold observations of N status change from N limit to N saturation by far are not conclusive in these ecosystems. Research on the natural abundance of ¹⁵N (δ¹⁵N) could greatly help provide integrated information about ecosystem N status. The goal of this study was to investigate the suitability of measurements of δ¹⁵N of major ecosystem N pools and several key species, plant ¹⁵N fractionation, together with key vegetation and soil indicators in response to N fertilization as a tool to identify the N status in a temperate steppe in Inner Mongolia. We carried out a N addition experiment during 2011–14 on a Stipa krylovii steppe in Inner Mongolia, Northern China. We investigated the response of several key N transformation processes, vegetation and soil properties to N addition. Aboveground biomass and belowground biomass (BGB) δ¹⁵N, root and foliar δ¹⁵N of three dominant species (Artemisia frigida, S. krylovii and Leymus chinensis), δ¹⁵N of soil total N and soil KCl-extractable NO₃⁻-N were determined. The responses of isotope fractionation during plant N uptake and reallocation to N addition were also determined. Our results suggest that the N addition rate of 5g N m⁻² yr⁻¹ could be regarded as threshold of early N saturation in this S. krylovii steppe as indicated by an increase in plant fractionation and a decrease in plant δ¹⁵N. When N input rate is >10 g N m–² yr–¹, increased N deposition can lead to an apparent reduction in species richness and BGB as well as an increase in NO₃⁻ in extractable soil pools <30-cm soil profile. With N addition, S. krylovii and A. frigida undergo earlier N status shift from N limitation toward N excess compared with L. chinensis, contributing to L. chinensis out-competing other species. Overall, this study provides a better understanding of N status change in temperate steppe based on isotope evidence and several other functional variables and contributes to predicting the responses of temperate steppe to future global N deposition scenario.

Seasonal timing regulates extreme drought impacts on CO2 and H2O exchanges over semiarid steppes in Inner Mongolia, China

Climate models predict a substantial increase in the frequency of extreme drought, suggesting subsequent impacts on the carbon (C) and water cycles. Although many studies have investigated the impacts of extreme drought on ecosystem functioning, it remains unknown how the timing of extreme drought within a growing season may affect carbon and water cycling. Here we conducted a 3-year field experiment to investigate the influence of seasonal drought timing on ecosystem carbon and water exchange by excluding rainfall (for consecutive 30 days) during three periods of the growing season (May–June, July–August and August–September) in fenced and grazed sites of a semiarid temperate steppe in Inner Mongolia, China. In the fenced steppe, extreme drought reduced growing-season net CO2 uptake regardless of drought timing, while in the grazed steppe, early-growing season drought caused relatively larger reductions to net CO2 uptake than drought imposed later in the season. The effect of extreme drought on evapotranspiration (ET) was similar to that of CO2 exchange at the fenced site, with consistent reductions of seasonally-integrated ET for all treatments compared with the ambient condition. In contrast, at the grazed site, the response of ET to extreme drought was more variable, possibly due to the absence of litter and greater bare ground. Surprisingly, both gross and net carbon uptake declined with increasing ET at the grazed site, while the fenced site showed the positive water-carbon linkage typically seen in semiarid ecosystems. The different responses of CO2 and water exchanges for the fenced and grazed sites were regulated predominately by soil temperature and soil water content. Together, our results show that drought timing within the growing season can significantly alter drought impacts on ecosystem water and CO2 exchanges, and that grazing management may further mediate the response.

Dynamics of Land Cover Change from 2001 to 2013 in China

In order to explore spatial-temporal land cover dynamics in China, we use MODIS data from 2001 to 2013 to statistic the percent of land coverage change and analyze the spatial pattern of land cover change in each natural regions. The results show that: (1) From 2001 to 2013, forest, arable land and water are increasing, and annual growth rates are 1.81%, 0.66% and 0.36% respectively. Shrubs, grassland and unused land are decreasing, and the average annual reduction rates are 2.61%, 0.51% and 0.63%. (2)In A (humid, semi-humid region in Northeast), B (warm temperate humid, semi-humid region in North China) and E (temperate steppe in Inner Mongolia) regions, the major land cover change is from grassland to arable land; in C (subtropical humid region in South and central China) and D (Tropica humid l region in South China) regions, the major land cover change is from grassland to forest; in the F (temperate and warm temperate desert region in Northwest) and G (Tibetan Plateau) regions, the major land cover change is from unused land to grassland. (3) In the Northeast China, arable land area increased; in the Tibetan plateau and northwest arid region, the utilization of unused land area increased; in central and south China, forest increased.

Responses of Soil Ammonia Oxidizers to Simulated Warming and Increased Precipitation in a Temperate Steppe of Inner Mongolia

Soil ammonia oxidizers, as key players for the ammonia oxidation process in soil N cycling, could respond, adapt, and give feedback to global change. In this research, soil samples were collected from a long-term field experiment with increased precipitation and warming in a temperate steppe of Inner Mongolia. We analyzed the responses of the abundance, diversity, and community structure of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) to warming and increased precipitation using quantitative real-time PCR, terminal restriction fragment length polymorphism (T-RFLP), and clone library. The results showed that increased precipitation significantly stimulated soil pH and warming significantly reduced soil respiration (SR). No significant difference was detected regarding the abundances of amoA genes across all treatments, whereas increased precipitation significantly affected the community structure of soil AOB. However, the interactive effect between warming and increased precipitation had no significant influence on the community structure of soil ammonia oxidizers. The result of the structural equation model indicated that the plant diversity and community structures of soil ammonia oxidizers were significantly correlated, suggesting that there were certain relationships among climate change, microbes, and plants. In conclusion, this study confirmed that soil microorganisms had the ability to adapt to climate change, which could provide important information for predicting future changes in ecosystems.