Productivity Of Grassland Ecosystems Research Articles

Optimization of soil hydrological properties in degraded grasslands by soil amendments

Soil amendments facilitate the restoration of degraded soil fertility and vegetation productivity. Soil hydrological functions are crucial for assessing soil degradation and restoration in grassland ecosystems. However, the manner in which soil amendments drive changes in the hydrological properties of grassland ecosystems at different soil depths remains unclear. In this study, we conducted a five-year soil amendment experiment in a semi-arid grassland of the Loess Plateau to evaluate the impact of aluminum sulfate (AS) and biochar (BC), both individually and in combination, on the hydrological properties of soil profiles. The results showed that AS significantly increased saturated water-holding capacity (SWHC) by 19.04 %, field capacity (FC) by 27.39 %, soil water storage (SWS) by 1.57 %, and saturated hydraulic conductivity (Ks) by 19.03 % in the upper soil layer (0–40 cm). BC application increased SWHC by 20.09 %, FC by 17.56 %, SWS by 12.94 %, and Ks by 16.66 % in the 0–40 cm soil layers. The combined effects of AS and BC optimized the soil hydrological properties by increasing SWHC, FC, SWS, and Ks by 25.74 %, 35.45 %, 18.47 %, and 25.80 %, respectively. These improvements were driven by significant changes in the soil organic matter, fine root biomass, total porosity, clay content, and soil bulk density. Notably, the soil amendments did not significantly affect the hydrological properties of the deep soil layer (40–80 cm). Our study demonstrated that the strategic use of AS and BC, particularly in combination, effectively enhanced soil fertility and hydrological functions, thereby increasing grassland ecosystem productivity. These findings offer critical insights for sustainable grassland management and highlight the potential of tailored soil amendments to restore and improve soil fertility and plant productivity in degraded grassland ecosystems.

Fertilizers and Manures Enhance the Bioavailability of Soil Phosphorus Fractions in Karst Grassland

Phosphorus is one of the major constraints to karst grassland productivity. Understanding the effects of different fertilization practices on soil phosphorus dynamics is essential for enhancing phosphorus bioavailability and rational management of soil phosphorus in karst grasslands. Here, we investigated the effects of fertilizers and manures on soil bioavailability of phosphorus fractions and explored the relationship between soil properties and soil phosphorus fractions. The four fertilizer application designs were as follows: control (CK; no fertilizer or manure); fertilization (F); manure application (M); fertilization and manure application (FM). The results showed that total phosphorus (TP) concentration was elevated by 23%, 1%, and 42% in F, M, and FM treatments, respectively, compared with CK. F and FM treatments enhanced the total inorganic phosphorus (Pi) concentration by 65% and 66%, respectively, while M and FM treatments enhanced the total organo-phosphorus (Po) concentration by 21% and 35%, respectively. FM treatment elevated bioavailable P, active Po, secondary mineral P, primary mineral P, and occluded P by 69%, 39%, 50%, 31%, and 41%, respectively. Fertilizers inhibited soil acid phosphatase activity, whereas alkaline phosphatase did not respond significantly to fertilizer management in low-latitude karst regions. SOM, TN, AP, and MBP are the key factors affecting the bioavailability of phosphorus fractions. The combined application of fertilizer and manure is the most beneficial measure for enhancing soil phosphorus bioavailability. This research helps deepen our understanding of soil phosphorus dynamics in the karst areas and provides a basis for further enhancement of nutrient availability and vegetation productivity of grassland ecosystems.

The effect of livestock grazing on plant diversity and productivity of mountainous grasslands in South America - A meta-analysis.

Mountainous grasslands in South America, characterized by their high diversity, provide a wide range of contributions to people, including water regulation, soil erosion prevention, livestock feed provision, and preservation of cultural heritage. Prior research has highlighted the significant role of grazing in shaping the diversity and productivity of grassland ecosystems, especially in highly productive, eutrophic systems. In such environments, grazing has been demonstrated to restore grassland plant diversity by reducing primary productivity. However, it remains unclear whether these findings are applicable to South American mountainous grasslands, where plants are adapted to different environmental conditions. To address this uncertainty, we conducted a meta-analysis of experiments excluding livestock grazing to assess its impact on plant diversity and productivity across mountainous grasslands in South America. In alignment with studies in temperate grasslands, our findings indicated that herbivore exclusion resulted in increased aboveground biomass but reduced species richness and Shannon diversity. The effects of grazing exclusion became more pronounced with longer durations of exclusion; nevertheless, they remained resilient to various climatic conditions, including mean annual precipitation and mean annual temperature, as well as the evolutionary history of grazing. In contrast to results observed in temperate grasslands, the reduction in species richness due to herbivore exclusion was not associated with increased aboveground biomass. This suggests that the processes governing (sub)tropical grassland plant diversity may differ from those in temperate grasslands. Consequently, further research is necessary to better understand the specific factors influencing plant diversity and productivity in South American montane grasslands and to elucidate the ecological implications of herbivore exclusion in these unique ecosystems.

Controlling Effects of Nanocomposite Sterilant ND-1 on the Growth of Wild Populations of Midday Gerbil (Meriones meridianus).

Grassland is not only an important part of the terrestrial ecosystem with multiple ecological functions, but also an important base for Chinese herdsmen to produce and live. However, the occurrence and spread of rodent infestation reduces the biodiversity and productivity of grassland ecosystems. It also severely threatens human life, health, and biosecurity through disease transmission. In this study, we explored the ability of the nanocomposite sterilant ND-1 to control grassland rodent populations. Semi-closed experimental and control plots were established in the desert area of Alashan, Inner Mongolia, China. In spring 2018, the nanocomposite sterile ND-1 (Nongda-1) was introduced once, and the control effect of ND-1 on the growth of the wild population of midday gerbils was measured for two years. We show that ND-1 significantly reduced the population of midday gerbils in the experimental area, with a negative population growth rate. In addition, in the second year, the ratio of female midday gerbils to sub-adults in the experimental area was significantly lower than that in the control area, which resulted in a significant difference in the sex ratio of midday gerbils. There were significantly fewer females than males, and the population growth of midday gerbils in the experimental area was significantly inhibited. ND-1 had no significant effect on the home range of midday gerbils, and sterile individuals continued to occupy the home range and consume resources. Therefore, ND-1 reduced the number of female midday gerbils during the breeding period and the sex ratio and population density and altered the age structure of the wild population. Additionally, competition between sterile and normal individuals had a significant control effect on the growth of wild populations. Our studies demonstrate the significance of ND-1 in the sustainable control of grassland rodent pests, with the potential for limiting grassland rodent damage in the future.

Effects of elevated carbon dioxide on plant growth and leaf photosynthesis of annual ryegrass along a phosphorus deficiency gradient

IntroductionSoil phosphorus (P) deficiency limits plant growth and productivity in grassland ecosystems and may moderate the growth-promoting effects of “carbon dioxide (CO2) fertilization effect”.MethodsTo evaluate the interactive effects of these two factors on the growth and physiology for annual ryegrass (Lolium multiflorum Lam.), plants were grown in controlled growth chambers with a range of P supply (0.004, 0.012, 0.02, 0.06, 0.1 and 0.5 mM) under two levels of CO2 (400 and 800 μmol mol-1, respectively).ResultsElevated [CO2] dramatically increased the aboveground biomass and net photosynthetic rates of annual ryegrass by 14.5% and 25.3% under sufficient P supply (0.5 mM), respectively, whereas decreased the belowground biomass and net photosynthetic rates under lower P supply of P0.004, P0.02, and P0.06. Two-way ANOVA results showed that CO2 × P (p < 0.001) significantly affected stomatal traits, leaf photosynthesis and biomass. The stimulation of growth and photosynthesis by elevated CO2 concentration (e[CO2]) was reduced or highly suppressed, indicating that the sensitivity of annual ryegrass to P deficiency was enhanced under e[CO2].DiscussionThese results indicated that P limitation may offset the positive effects of e[CO2] on plant growth by altering stomatal traits, leaf photochemical processes and biochemical composition in annual ryegrass.

Phosphorus Coupled with High Nitrogen Addition Exerts a Great Influence on Soil Bacterial Community in a Semiarid Grassland.

Nitrogen (N) and phosphorus (P) addition, either individually or in combination, has been demonstrated to enhance plant productivity in grassland ecosystems. Soil bacterial community, which is the driver of litter decomposition and nutrient cycling, is assumed to control responses of terrestrial ecosystem structure and function to N and P addition. Using a high-throughput Illumina MiSeq sequencing platform, we conducted a 9-year field experiment of N (0, 5, 10, and 20 g N m-2 yr-1) and P (0 and 10 g P m-2 yr-1) additions in the Inner Mongolian steppes to elucidate long-term effects of N and P addition on soil bacterial richness, diversity and composition. We found that N addition reduced the relative abundance of Acidobacteria, Chloroflexi, and Nitrospirae, while increased that of Bacteroides. The results showed that the bacterial biomarker was enriched in P addition treatments, either individually or combined with N addition. Both N and P addition altered the bacterial community structure, while only N addition greatly decreased bacterial richness and diversity. More importantly, we showed that all of these effects were most significant in N3P treatment (20 g N m-2 yr-1 and 10 g P m-2 yr-1), implying that P coupled with a high-level N addition exerted a great influence on soil bacterial community. Structural equation models revealed that N and P addition had a great direct effect on soil bacterial community and an indirect effect on it mainly by changing the litter biomass. Our findings highlighted that severe niche differentiation was induced by P along with a high-level N, further emphasizing the importance of simultaneously evaluating response of soil bacterial community to N and P addition, especially in the context of increasing anthropogenic nutrient additions.

Effects of winter grazing and N addition on soil phosphorus fractions in an alpine grassland on the Qinghai-Tibet Plateau

Nutrient cycling in alpine grasslands is susceptible to climate change and anthropogenic activities, which can affect soil phosphorus (P) availability. Despite the crucial role of soil P availability in maintaining stability and productivity of grassland ecosystems, limited research has been conducted on the effects of nitrogen (N) addition and winter grazing on P transformation on the Qinghai-Tibet Plateau. In an 8-year experiment, we applied four different N addition rates (0, 25, 50, and 100 kg urea ha−1 year−1) in combination with winter grazing to investigate the effects of N addition and winter grazing on the soil P fractions. The results reveal that increasing the N addition gradually reduced the resin-Pi and NaOH-Pi contents in the soil by increasing the plant P uptake and promoting the release of carboxylates in the rhizosheath, regardless of grazing. Winter grazing decreased the NaHCO3-Pi and NaOH-Pi contents compared with the no-grazing treatment by increasing the P uptake of the plants. In contrast, neither grazing nor N addition affected the HClconc.-P or residual-P content. In the no-grazing plots, the soil NaHCO3-Po content exhibited a gradual increase in response to N addition, whereas N addition had no discernible effect on the NaOH-Po content. In the grazing plots, the NaHCO3- and NaOH-Po contents gradually decreased with N addition, which was associated with the increased acid phosphatase activity in the rhizosheath and the export of forage. Thus, we conclude that N addition promotes the dissolution of NaOH-Pi to more available inorganic P forms. Under winter grazing conditions only, the transformation of P from inorganic to organic forms gradually decreased with increasing N additions.

Root systems reserve under humid conditions of floodplain meadows of the Ob River in the subzone of the southern taiga

The results of the study of the underground phytomass of the floodplain meadow communities in the Middle Ob obtained from three permanent sample plots in the area of the Kaibasovo research station of Tomsk University (Kri-vosheinsky district of the Tomsk region) are presented. The functioning and productivity of grassland ecosystems should be carefully studied, especially in the light of ongoing climate change, as they are actively involved in the carbon cycle. However, the belowground phytomass is given much less attention in the literature than the aboveground part, despite the fact that they are equally important for the study of the cycle. The study of vegetation cover in order to analyze the biological cycle of flood-plain ecosystems, the production and destruction of plant matter in this area was practically not carried out. The goal was to assess the structure and stock of root phytomass in the meadows of the Ob floodplain. In the course of the work, the hydro-climatic conditions of the growing season of the current and previous years were characterized in order to assess their impact on root development. The reserves of underground organs in the 0-20 cm soil layer were determined, the limits of fluctuations of the total reserves of roots in the 0-20 cm layer between the sampling periods in June and August were established.
 Key words. Belowground biomass, flood, floodplain meadows, productivity, roots, Western Siberia.

Grazing intensity changed the activities of nitrogen assimilation related enzymes in desert Steppe Plants

BackgroundNitrogen, as a limiting factor for net primary productivity in grassland ecosystems, is an important link in material cycles in grassland ecosystems. However, the nitrogen assimilation efficiency and mechanisms of grassland plants under grazing disturbance are still unclear. This study investigated Stipa breviflora desert steppe which had been grazed for 17 years and sampled the root system and leaf of the constructive species Stipa breviflora during the peak growing season under no grazing, light grazing, moderate grazing and heavy grazing treatments. The activities of enzymes related to nitrogen assimilation in roots and leaves were measured.ResultsCompared with no grazing, light grazing and moderate grazing significantly increased the activities of nitrate reductase (NR), glutamine synthetase (GS), glutamic oxaloacetic transaminase (GOT) and glutamic pyruvate transaminase (GPT) in leaves, and GS, GOT and GPT in roots of Stipa breviflora, while heavy grazing significantly decreased the activities of GS in leaves and NR in roots of Stipa breviflora. NR, GOT and GPT activities in leaves and roots of Stipa breviflora were positively correlated with nitrogen content, soluble protein, free amino acid and nitrate content.ConclusionsGrazing disturbance changed the activities of nitrogen assimilation related enzymes of grassland plants, and emphasized that light grazing and moderate grazing were beneficial for nitrogen assimilation by grassland plants. Therefore, establishing appropriate stocking rates is of great significance for material flows in this grassland ecosystem and for the stability and sustainable utilization of grassland resources.

Productivity of grassland ecosystems in the Tyva Republic, Russia

The aim of the study. The aim of the study was to estimate biological productivity of Tyva grasslands. Location and time of the study. The living and dead above- and belowground phytomass, as well as net primary production, were estimated in the montane ecosystems and depressions of the Tyva Republic, Russia. Methodology. Field and laboratory studies of the biological production by grasslands were conducted using botanical, geobotanical and ecological methods. Main results. In the montane ecosystems the aboveground phytomass production was shown to range from 1.3 to 3.6 Mg ha-1 yr-1, whereas the belowground production was evaluated as ranging 10-65 Mg ha-1 yr-1. The belowground production was found to vary widely, being associated with location of mountain ridges, slope geomorphology and grazing, but no association was found with the altitude. In depressions the average green phytomass stock changed from 0.7 to 1.9 Mg ha-1, living belowground phytomass varied 3.4 to 19.3 Mg ha-1. From the meadow steppes to the deserted ones the living above- and belowground stocks decreased 2.7 and 5.7 fold, respectively, whereas the above- and belowground production was estimated to decrease 3 and 4 times, respectively. Several indices to characterize the growth and development, hence the productivity, of herbaceous plants was proposed. The values of the indices calculated for the Tyva grasslands suggested high photosynthetic activity: all studied steppes had the same share of belowground production in the total ecosystem production, i.e. 90%. The turnover rate of the living belowground phytomass was estimated to increase from meadow steppes to the deserted ones, whereas green phytomass increment, as related to its stock, slightly decreased. Conclusions. The living belowground phytomass stock was found to exceed the green phytomass stock by 5-8 times, both in montane ecosystems and depressions. Preservation of living belowground organs during hot dry summers and cold winters, when soil freezes through, is apparently indispensable for grassland survival under any climatic conditions.

Effect of grazing exclusion on the temperature sensitivity of soil net nitrogen mineralization in the Inner Mongolian grasslands

Grazing exclusion (GE) is an efficient management practice that prevents grassland degradation. The temperature sensitivity (Q10) of soil net nitrogen (N) mineralization (Nmin) is an important parameter of N cycles, and it directly influences the feedback between the primary productivity of grassland ecosystems and climate warming. However, information remains limited about how GE affects the Q10 of Nmin in N-limited grasslands. In this study, we conducted a laboratory incubation experiment at six temperatures (−10, 0, 5, 15, 25, and 35 °C) and three soil moisture contents (15%, 25%, and 35%) for 35 days by using intact soil cores from three different GE periods grassland (0, 4 and 24 years). The results showed that long-term GE decreased the Q10 of Nmin, which was highest in GE0 (2.62), followed by GE4 (2.36) and GE24 (2.42). In addition, Q10 declined in 15% soil moisture content under all three GE treatments. Furthermore, activation energy (Ea) was negatively correlated with the substrate quality index (Q) in all three GE grasslands. These results support the carbon quality-temperature (CQT) hypothesis, showing that is can be applied to soil N mineralization in grasslands after long-term GE. This study demonstrated that GE potentially reduces the sensitivity of Nmin to increasing temperature under global warming scenarios, which might help prevent N losses in these N-limited grasslands.

Linkages between changes in plant and mycorrhizal fungal community composition at high versus low elevation in alpine ecosystems.

Arbuscular mycorrhizal fungi (AMF) play an important role in maintaining plant diversity and productivity in grassland ecosystems. However, very few studies have investigated how AMF and plant communities co-vary between contrasting environments in natural ecosystems. Intensive sampling (50 soil samples) was conducted in natural open grasslands at both 3570 and 4556 m on Mount Segrila on the Southeast Tibetan Plateau. We used 454-pyrosequencing to investigate soil AMF communities and to explore relationships between AMF diversity and plant richness, productivity and community composition. AMF diversity was negatively correlated with plant richness at 3570 m but positively at 4556 m. Differences in AMF community composition between elevations were attributable to plant community composition, soil pH and available phosphorus concentration. The AMF community was more phylogenetically clustered at the higher elevation than the lower elevation. However, greater phylogenetic clustering (under dispersion) of AMF communities at the two elevations was positively correlated with above-ground biomass. Our results indicate that plant community composition and environmental filtering are the primary drivers structuring the AMF community. Phylogenetic relatedness may be important in explaining the function of AMF communities in alpine ecosystems.

Climate Benefits of Increasing Plant Diversity in Perennial Bioenergy Crops

Bioenergy from perennial grasses mitigates climate change via displacing fossil fuels and storing atmospheric CO2 belowground as soil carbon. Here, we conduct a critical review to examine whether increasing plant diversity in bioenergy grassland systems can further increase their climate change mitigation potential. We find that compared with highly productive monocultures, diverse mixtures tend to produce as great or greater yields. In particular, there is strong evidence that legume addition improves yield, in some cases equivalent to mineral nitrogen fertilization at 33–150 kg per ha. Plant diversity can also promote soil carbon storage in the long term, reduce soil N2O emissions by 30%–40%, and suppress weed invasion, hence reducing herbicide use. These potential benefits of plant diversity translate to 50%–65% greater life-cycle greenhouse gas savings for biofuels from more diverse grassland biomass grown on degraded soils. In addition, there is growing evidence that plant diversity can accelerate land restoration.

Responses of grassland ecosystem productivity to altered precipitation regime: A review.

Under global change scenario, precipitation pattern has significantly changed, mainly in the aspects of annual precipitation amount, precipitation seasonal distribution and precipitation event characteristics (size of individual precipitation event, periods length between two precipitation events, and number of precipitation events in a year), which combined to affect various processes of terrestrial ecosystems, especially productivity. Grassland ecosystem is one of the most sensitive ecosystems to the changes of precipitation regime. Therefore, it is necessary to clarify the responses of productivity to altered precipitation regime in grasslands. In this study, I firstly reviewed the responses of grassland productivity to each characteristic of the altered precipitation regime. Then, I summarized the methods that employed in the study of productivity-precipitation relationship, including long-term observations, manipulative field experiments, and modelling. Finally, I came up with several theoretical and methodological problems that needed to be solved in the future. This work would facilitate the understanding of how grasslands response to the global climate change, with implications for grassland management in the context of climate change.

Nodulation and biological nitrogen fixation (BNF) in forage peanut (Arachis pintoi) cv. Belmonte subjected to grazing regimes

Productivity of grassland ecosystems is highly dependent on the availability of nitrogen (N) from the soil and/or biological fixation (BNF) from the atmosphere. However, the high cost of N-fertilizers and the increasing awareness of the need for sustainable nutrient alternative sources have increased the strategic importance of the BNF. Defoliation interferes with plant growth and also with BNF in legumes, since it modifies the leaf area and the availability of energy to plants. In spite of the potential advantages of forage legumes to pastures, current knowledge regarding the effects of grazing management on BNF is scarce. In order to evaluate the effect of grazing management on aerial and root mass, nodulation and BNF in forage peanut (Arachis pintoi cv. Belmonte), two experimental protocols based on the continuous and intermittent (rotational grazing) stocking methods were used. In the continuous stocking protocol, treatments corresponded to four grazing intensities represented by four management heights - 5, 10, 15 and 20 cm. In the intermittent stocking protocol, treatments corresponded to combinations between two pre- (95% and maximum canopy light interception during regrowth – LI95% and LIMax, respectively) and two post-grazing (post-grazing heights equivalent to 40 and 60% of the pre-grazing height) conditions. It was hypothesized that hard grazing, represented by low management heights under continuous stocking or low post-grazing heights under intermittent stocking, causes reduction in root mass and nodulation interfering with the balance between root and aerial, with negative impacts on BNF. Under continuous stocking, greater number of nodules was associated with lower nodule mass and vice-versa throughout the year. Swards managed at 5 and 10 cm had greater root and nodule mass than those managed at 15 and 20 cm. However, greater BNF (%Ndfa and BNF) was recorded on swards managed at 15 and 20 cm relative to those managed at 5 and 10 cm. Under intermittent stocking, the combinations between frequencies and severities of grazing did not affect root mass or nodule number at both pre- and post-grazing conditions. Overall, swards managed with the LIMax target showed greater BNF than those managed with the LI95% target. For swards managed with the same LI target (LI95% or LIMax), hard grazing (40% of the pre-grazing height) resulted in lower %Ndfa and BNF during early and late spring and summer II. For both grazing methods, the range of management targets used did not result in negative impacts on root mass or nodulation. Regardless of grazing method, BNF was determined by aerial biomass, indicating that moderate intensities of grazing would be adequate for optimizing BNF.

The optimal Redfield N: P ratio caused by fairy ring fungi stimulates plant productivity in the temperate steppe of China

Abstract The Redfield ratio (or stoichiometry) is widely used as a reference to differentiate between nitrogen (N) and phosphorus (P) limitations in plankton and in the deep oceanic waters. Whether the Redfield ratio is applicable to plant and soil fungal growth is rarely considered. Fairy rings (FRs) caused by Agaricus gennadii can influence plant productivity and soil nutrient composition. However, the internal mechanisms associated with the optimal Redfield N: P ratio remain unclear. Changes in plant and soil stoichiometry in three concentric zones of FRs occurring in the temperate steppe of China, namely outside the ring (Out), on the ring (On), and inside the ring (In), were assessed in order to confirm the effects of FR fungi on plants and soil and explain the mechanisms using nutrient stoichiometry. We observed a significantly higher aboveground biomass only in the On zone. The plant N: P ratio was 14.5, 10.4, and 7.3 in the Out, On, and In zones, respectively. This indicates that the limiting element of the aboveground biomass was P in the Out zone and N in the In zone, while the On zone possessed an optimal plant N: P ratio and relatively high aboveground biomass. As with the plant N: P ratio, the On and In zones displayed a significantly lower soil inorganic N: available P ratio than the Out zone. The plant N: P ratio was highly positively correlated with the soil inorganic N: available P ratio. Our results suggest that FR fungi with low N: P ratio shift the soil ecosystem from P- to N-limited, thereby accelerating the uptake of soil N by plants. As with the plant N: P ratio, the soil inorganic N: available P ratio can also be used to evaluate whether N or P is more limiting for plant production in grassland ecosystems.

Phytolith-occluded organic carbon as a mechanism for long-term carbon sequestration in a typical steppe: The predominant role of belowground productivity

Phytolith-occluded organic carbon (phytOC) has recently been demonstrated to be an important terrestrial carbon (C) fraction resistant to decomposition and thus has potential for long-term C sequestration. Existing studies show that plant leaves and sheath normally have high phytOC concentration, thus most of phytOC studies are limited to the aboveground plant parts. Grassland communities comprise herbaceous species, especially grasses and sedges which have relatively high concentrations of phytoliths, but the phytOC production from grassland, especially from its belowground part, is unknown. Here we determined the phytOC concentration in different parts of major plant species in a typical steppe grassland on the Mongolian Plateau, and estimated the phytolith C sequestration potential. We found that the phytOC concentration of major steppe species was significantly (p<0.05) higher in belowground (0.67gkg−1) than aboveground biomass (0.20gkg−1) and that the belowground net primary productivity (BNPP) was 8–15 times the aboveground net primary productivity (ANPP). Consequently, the phytOC stock in belowground biomass (12.50kgha−1) was about 40 times of that in aboveground biomass (0.31kgha−1), and phytOC production flux from BNPP (8.1–15.8kgha−1yr−1) was 25–51 times of that from ANPP. Our results indicate that BNPP plays a dominant role in the biogeochemical silica cycle and associated phytOC production in grassland ecosystems, and suggests that potential phytolith C sequestration of grasslands may be at least one order of magnitude greater than the previous estimation based on ANPP only. Our results emphasize the need for more research on phytolith and phytOC distribution and flux in both above and below ground plant parts for quantifying the phytolith C sequestration.

Plant diversity effects on grassland productivity are robust to both nutrient enrichment and drought.

Global change drivers are rapidly altering resource availability and biodiversity. While there is consensus that greater biodiversity increases the functioning of ecosystems, the extent to which biodiversity buffers ecosystem productivity in response to changes in resource availability remains unclear. We use data from 16 grassland experiments across North America and Europe that manipulated plant species richness and one of two essential resources—soil nutrients or water—to assess the direction and strength of the interaction between plant diversity and resource alteration on above-ground productivity and net biodiversity, complementarity, and selection effects. Despite strong increases in productivity with nutrient addition and decreases in productivity with drought, we found that resource alterations did not alter biodiversity–ecosystem functioning relationships. Our results suggest that these relationships are largely determined by increases in complementarity effects along plant species richness gradients. Although nutrient addition reduced complementarity effects at high diversity, this appears to be due to high biomass in monocultures under nutrient enrichment. Our results indicate that diversity and the complementarity of species are important regulators of grassland ecosystem productivity, regardless of changes in other drivers of ecosystem function.

Contrasting responses of gross primary productivity to precipitation events in a water-limited and a temperature-limited grassland ecosystem

The impact of global climate change on precipitation regimes may bring about significant consequences to the productivity of grassland ecosystems. This study reports the effects of the characteristics of precipitation events (PEC, e.g., size, frequency, interval, and seasonal distribution of precipitation events) on gross primary productivity (GPP) based on long-term measurements of net ecosystem CO2 exchange and evapotranspiration by the eddy covariance technique in a water-limited temperate steppe in Inner Mongolia and a humid but temperature-limited alpine meadow in Tibet, China. We determined that the predominant characteristics of precipitation events that affected GPP differed remarkably between these two ecosystems. The number of heavy precipitation events (>10mmday−1) was the most important PEC to impact GPP in the temperate steppe. Years with more frequent heavy precipitation events favored higher GPP. However, in contrast with the case in the temperate steppe, precipitation interval was the factor that affected GPP most in the alpine meadow. GPP was higher as the precipitation intervals lengthened or their distribution shifted to fewer but longer intervals (concentrated distribution). Additionally, the mechanisms for the effects of PEC on GPP also differed between these two ecosystems. Compared with small events, heavy precipitation events recharged deeper soil layers in the temperate steppe, which was biologically more meaningful for plant transpiration (i.e., an increase in the ratio of transpiration to evapotranspiration), relief from drought stress (an increase in the duration of high soil water content), and thereby higher GPP. In contrast, mean air temperature was higher in the alpine meadow when the precipitation intervals increased or their distribution was more concentrated, leading to a longer period of higher temperature that was favorable to higher GPP. Our results imply that soil water is not the exclusive means of revealing the mechanism of precipitation affecting productivity; the corresponding changes in temperature along with precipitation events may also play a substantial role in temperature-limited grasslands.

Short-term rather than long-term exclusion of grazing increases soil bacterial diversity in an Inner Mongolian steppe

Cessation of grazing is an important management practice in restoration of grassland ecosystem productivity and function. However, little is known about the effects of long-term exclusion of grazing on soil bacterial community structure and diversity in grassland ecosystems. This study utilized three grassland sites over two consecutive years (2004 and 2005) in a semi-arid Inner Mongolia steppe; there were a free grazing site (FG), fenced site since 1999 (UG99) and fenced site since 1979 (UG79). Soil moisture content, organic carbon (C) and nitrogen (N), NH4+–N and NO3-–N concentrations were measured across the treatments. Bacterial community structure and diversities were assessed with PCR amplification of genomic DNA extracted from soils and following denaturing gradient gel electrophoresis (DGGE) separation. Results showed that the UG99 soil had higher moisture, organic C, organic N and NH4+–N concentrations than the other soils. Principal components analysis of DGGE patterns showed that soil bacterial community structure sampled in 2004 was different from that in 2005, and the UG99 soil was significantly different from the FG and UG79 soils across the two consecutive years. In addition, the UG99 soil had significantly higher bacterial diversity and evenness compared with the FG and UG79 soils. These results indicate that long-term exclusion of grazing decreases bacterial diversity, which has significant implication for grassland ecosystem management.