Belowground Net Primary Production Research Articles

Nitrogen Addition Decreased Respiration and Heterotrophic Respiration but Increased Autotrophic Respiration in a Cabbage (Brassica pekinensis Rupr) Experiment in the Northeast Plains

Farmland soil respiration (Rs) significantly impacts the global carbon (C) cycle. Although nitrogen (N) can promote crop growth and increase yields, its relationship with Rs and its constituents, including autotrophic respiration (Ra) and heterotrophic respiration (Rh), remains unclear. Therefore, a field study was carried out in a cabbage (Brassica pekinensis Rupr) system to probe the impact of N addition on Rs, Ra, and Rh. Five levels of N addition, including 0 kg N hm−2·yr−1 (N0), 50 kg N hm−2·yr−1 (N50), 100 kg N hm−2·yr−1 (N100), 150 kg N hm−2·yr−1 (N150), and 200 kg N hm−2·yr−1 (N200), started in March 2022. The Rs (Ra and Rh) and soil samples were measured and collected twice a month. The findings revealed the following: (1) N fertilizer enhanced Ra while reducing Rs and Rh; (2) soil temperature (ST), belowground net primary productivity (BNPP), soil inorganic N (SIN), and soil total C/total N (C/N) were the significant elements influencing Ra, and microbial biomass carbon (MBC), SIN, and microbial diversity (MD) were the primary factors influencing Rh; (3) partial least squares-path models (PLS-PM) showed that ST and SIN directly impacted Rh, while ST and BNPP tangentially influenced Ra; (4) 150 kg N hm−2·yr−1 was the ideal N addition rate for the cabbage in the region. In summary, the reactions of Ra and Rh to N fertilizer in the Northeast Plains are distinct. To comprehend the underlying processes of Rs, Ra, and Rh, further long-term trials involving various amounts of N addition are required, particularly concerning worsening N deposition.

Patterns and mechanisms of belowground carbon responses to changes in precipitation

Abstract It is well known that aboveground productivity usually increases with precipitation. However, how belowground carbon (C) processes respond to changes in precipitation remains elusive, although belowground net primary productivity (BNPP) represents more than one-half of NPP and soil stores the largest terrestrial C in the biosphere. This paper reviews the patterns of belowground C processes (BNPP and soil C) in response to changes in precipitation from transect studies, manipulative experiments, modeling and data integration and synthesis. The results suggest the possible existence of nonlinear patterns of BNPP and soil C in response to changes in precipitation, which is largely different from linear response for aboveground productivity. C allocation, root turnover time and species composition may be three key processes underlying mechanisms of the nonlinear responses to changes in precipitation for belowground C processes. In addition, microbial community structure and long-term ecosystem processes (e.g. mineral assemblage, soil texture, aggregate stability) may also affect patterns of belowground C processes in response to changes in precipitation. At last, we discuss implications and future perspectives for potential nonlinear responses of belowground C processes to changes in precipitation.

Chronic drought decreased organic carbon content in topsoil greater than intense drought across grasslands in Northern China

Grasslands are expected to experience extreme climatic events such as extreme drought due to rising global temperatures. However, we still lack evidence of how extreme drought influence soil organic carbon (SOC) content in grassland ecosystems. We experimentally imposed extreme drought in two ways – chronic drought (66 % reduction in precipitation from May to August) and intense drought (100 % reduction in precipitation from June to July) to measure the effects of these two drought types on (SOC) content across six grassland sites that spanning desert steppe, typical steppe and meadow steppe in northern China. The experiment followed a randomized complete block design with six replicates of each treatment at each site. Our results showed that both chronic and intense drought decreased SOC content in the topsoil (0–10 cm) and the loss was higher in arid grasslands (desert steppe and typical steppe). Chronic drought decreased SOC content more than intense drought, with the effect again being strongest in arid grasslands. Furthermore, the response of SOC content to extreme drought was linked with the response of net primary productivity. Specifically, the response of SOC content was negatively correlated with drought sensitivity of above-ground net primary productivity (ANPP) but positively correlated with drought sensitivity of belowground NPP (BNPP). Overall, our results suggest that shifts in grassland SOC content with future drought will depend on the types of drought as well as the productivity responses and local climatic conditions such as precipitation, temperature, and aridity. The differential extreme drought impacts described here may facilitate predictions of climate change impacts on ecosystem carbon cycling.

Biodiversity: Net primary productivity relationships are eliminated by invasive species dominance.

Experiments often find that net primary productivity (NPP) increases with species richness when native species are considered. However, relationships may be altered by exotic (non-native) species, which are hypothesized to reduce richness but increase productivity (i.e., 'invasion-diversity-productivity paradox'). We compared richness-NPP relationships using a comparison of exotic versus native-dominated sites across the central USA, and two experiments under common environments. Aboveground NPP was measured using peak biomass clipping in all three studies, and belowground NPP was measured in one study with root ingrowth cores using root-free soil. In all studies, there was a significantly positive relationship between NPP and richness across native species-dominated sites and plots, but no relationship across exotic-dominated ones. These results indicate that relationships between NPP and richness depend on whether native or exotic species are dominant, and that exotic species are 'breaking the rules', altering richness-productivity and richness-C stock relationships after invasion.

Opposing responses of temporal stability of aboveground and belowground net primary productivity to water and nitrogen enrichment in a temperate grassland

AbstractChanges in water and nitrogen availability, as important elements of global environmental change, are known to affect the temporal stability of aboveground net primary productivity (ANPP). However, evidences for their effects on the temporal stability of belowground net primary productivity (BNPP), and whether such effects are consistent between belowground and aboveground, are rather scarce. Here, we investigated the responses of temporal stability of both ANPP and BNPP to water and nitrogen addition based on a 9‐year manipulative experiment in a temperate grassland in northern China. The results showed that the temporal stability of ANPP increased with water addition but decreased with nitrogen addition. By contrast, the temporal stability of BNPP decreased with water addition but increased with nitrogen enrichment. The temporal stability of ANPP was mainly determined by the soil moisture and inorganic nitrogen, which modulated species asynchrony, as well as by the stability of dominant species. On the other hand, the temporal stability of BNPP was mainly driven by the soil moisture and inorganic nitrogen that modulated ANPP of grasses, and by the direct effect of soil water availability. Our study provides the first evidence on the opposite responses of aboveground and belowground grassland temporal stability to increased water and nitrogen availability, highlighting the importance of considering both aboveground and belowground components of ecosystems for a more comprehensive understanding of their dynamics.

Opposing effects of warming on the stability of above- and belowground productivity in facing an extreme drought event.

Climate warming, often accompanied by extreme drought events, could have profound effects on both plant community structure and ecosystem functioning. However, how warming interacts with extreme drought to affect community- and ecosystem-level stability remains a largely open question. Using data from a manipulative experiment with three warming treatments in an alpine meadow that experienced one extreme drought event, we investigated how warming modulates resistance and recovery of community structural and ecosystem functional stability in facing with extreme drought. We found warming decreased resistance and recovery of aboveground net primary productivity (ANPP) and structural resistance but increased resistance and recovery of belowground net primary productivity (BNPP), overall net primary productivity (NPP), and structural recovery. The findings highlight the importance of jointly considering above- and belowground processes when evaluating ecosystem stability under global warming and extreme climate events. The stability of dominant species, rather than species richness and species asynchrony, was identified as a key predictor of ecosystem functional resistance and recovery, except for BNPP recovery. In addition, structural resistance of common species contributed strongly to the resistance changes in BNPP and NPP. Importantly, community structural resistance and recovery dominated the resistance and recovery of BNPP and NPP, but not for ANPP, suggesting the different mechanisms underlie the maintenance of stability of above- versus belowground productivity. This study is among the first to explain that warming modulates ecosystem stability in the face of extreme drought and lay stress on the need to investigate ecological stability at the community level for a more mechanistic understanding of ecosystem stability in response to climate extremes.

Nitrogen and phosphorus additions alter foliar nutrient concentrations of dominant grass species and regulate primary productivity in an Inner Mongolian meadow steppe

Excessive nitrogen (N) inputs shift grassland productivity from nitrogen (N) to phosphorus (P) limitation. However, how plant nutrient concentrations and stoichiometric dynamics at community and species level responding to variable soil N and P availability, and their roles in regulating net primary productivity in meadow steppe remain unclear. To address this issue, we carried out an experiment with fifteen treatments consisting of factorial combinations of N (0, 1.55, 4.65,13.95, 27.9 g N m−2 yr−1) and P (0, 5.24,10.48 g P m−2 yr−1) for three years in a meadow steppe in Inner Mongolia. We examined concentrations and stoichiometry of C (carbon), N, P in plants and soils, and their associations with plant primary productivity. Results revealed mean community N:P ratios for shoots (12.89 ± 0.98) did not exceed 14 within the control treatment, indicating that plant growth was primarily N-limited in this ecosystem. Shoot N:P ratios were significantly increased by N addition (>16 when N application rate above 4.65 g N m−2 yr−1), shifting the community from N- to P-limited whereas significantly reduced by P addition (N:P ratios <14), further aggravating N limitation. N addition increased leaf-N concentrations whereas decreased leaf C:N ratios of all four species, but only the values for two graminoid species were significantly influenced by P addition. Leaf-P concentrations significantly increased for graminoids but significantly decreased for forbs with the application of N. VPA analysis revealed that aboveground components, especially in grass leaves, explained more variation in aboveground net primary productivity (ANPP) and belowground net primary productivity (BNPP) than root and soil components. For grasses, leaf-N concentrations showed high association with ANPP, while leaf-P concentrations were associated with BNPP. These results highlight that N and P depositions could affect the leaf-nutrient concentrations of dominant grasses, and thereby potentially alter net primary productivity in meadow steppe.

Shallow-incorporated straw returning further improves rainfed maize productivity, profitability and soil carbon turnover on the basis of plastic film mulching

Ridge and furrow plastic film mulching (RFM) has improved net primary productivity (NPP) to a high level in semi-arid rainfed agricultural regions. Yet, it is unclear whether there is still a room for further improvement on NPP while stabilizing soil organic carbon through returning previous maize stover pieces. To address this issue, maize stubbles were smashed into pieces and in situ ploughed into 30 cm topsoil at a semi-arid site in northwest China from 2016 to 2017. This was done using the Pioneer 335 maize variety with three treatments (CK, ridge and furrow without mulching; RFM, ridge and furrow with plastic mulching; RFML, 3.49 t ha−1 of maize stover returning in RFM; RFMH, 5.24 t ha−1 of returning in RFM). The results indicated that maize stover returning exhibited similar trend as RFM at early cool seedling stage, raising the topsoil temperature. However, in warm and dry silking stage (2017), both stover returning rates reduced soil temperatures by 1.33 and 0.8 ◦C relative to RFM and CK (P < 0.05), respectively. The soil water storage increased significantly in RFMH by 17.3% and RFML by 28.5% relative to that of RFM, in a warm and dry growing season (2017). Critically, stover returning increased (P < 0.05) soil organic carbon and light fraction organic carbon turnover across the two growing seasons. By improving hydrothermal conditions, stover returning in RFM increased biomass accumulation and grain yield (P < 0.05), leading to higher (P < 0.05) net economic benefit, with greater above-ground biomass NPP (74.5–93.2%) and below-ground biomass NPP (88.5–89.4%), compared with CK. In conclusion, maize stover returning of stover pieces into topsoil might be a promising solution to enhance carbon turnover for higher net primary productivity on the basis of plastic film mulching in semiarid rainfed region.

Plants alter their aboveground and belowground biomass allocation and affect community-level resistance in response to snow cover change in Central Asia, Northwest China

It is important to elucidate the changing distribution pattern of net primary productivity (NPP) to mechanistically understand the changes in aboveground and belowground ecosystem functions. In water-scarce desert environments, snow provides a crucial supply of water for plant development and the spread of herbaceous species. Yet uncertainty persists regarding how herbaceous plants' NPP allocation responds to variation in snow cover. The goal of this study was to investigate how variation in snow cover in a temperate desert influenced the NPP allocation dynamics of herbaceous species and their resistance to environmental change in terms aboveground and belowground productivity. In the Gurbantunggut Desert, wintertime snow cover depth was adjusted in plots by applying four treatments: snow removal (−S), ambient snow, double snow (+S), and triple snow (+2S). We examined their species richness, aboveground NPP (ANPP), belowground NPP (BNPP), and the resistance of ANPP and BNPP. We found that species diversity of the aboveground community increased significantly with increasing snow cover and decreased significantly Pielou evenness in plots. This resulted in greater ANPP with increasing snow cover; meanwhile, BNPP first increased and then decreased with increasing snow cover. However, this productivity in different soil layers responded differently to changed snow cover. In the 0–10 cm soil layer, productivity first rose and then declined, while it declined linearly in both the 10–20 cm and 20–30 cm soil layers, whereas in the 30–40 cm soil layer it showed an increasing trend. Belowground resistance would increase given that greater snow cover improved the BNPP in deeper soil and maintained the resource provisioning for plant growth, thus improving overall belowground stability. These results can serve as a promising research foundation for future work on how the functioning of desert ecosystems becomes altered due to changes in plant community expansion and, in particular, changes in snow cover driven by global climate change.

Different nitrogen saturation thresholds for above-, below-, and total net primary productivity in a temperate steppe.

Identifying the thresholds for the positive responses of total net primary productivity (NPP) to nitrogen (N) enrichment is an essential prerequisite for predicting the benefits of N deposition on ecosystem carbon sequestration. However, the responses of below-ground NPP (BNPP) to N enrichment are unknown in many ecosystems, which limits our ability to understand the carbon cycling under the scenario of increasing N availability. We examined the changes in above-ground NPP (ANPP), BNPP, and NPP of a temperate meadow steppe across a wide-ranging N addition gradient (0, 2, 5, 10, 20, and 50 g N m-2  year-1 ) during 5 years. Both ANPP and NPP increased nonlinearly with N addition rates. The N saturation threshold for ANPP (TA ) and NPP (TN ) was at the rate of 13.11 and 6.70 g N m-2  year-1 , respectively. BNPP decreased with increasing N addition when N addition rates ˃5 g N m-2  year-1 , resulting in much lower TN than TA . Soil N enrichment played a key role in driving the negative impacts of high N addition rates on BNPP, and consequently on the earlier occurrence of N saturation threshold for NPP. Our results highlight the negative effects of soil N enrichment on NPP in natural grasslands super-saturated with N. Furthermore, by considering ANPP and BNPP simultaneously, our results indicate that previous findings from above-ground might have over-estimated the positive effects of N deposition on primary productivity.

The Sensitivity of Belowground Ecosystem to Long‐Term Increased Nitrogen Deposition in a Temperate Grassland: Root Productivity, Microbial Biomass, and Biodiversity

AbstractStudies exploring ecosystem vulnerability to nitrogen (N) enrichment have mostly focused on aboveground components of ecosystems. However, the sensitivity of the belowground ecosystem to increasing N deposition remains unclear. We estimated responses of belowground net primary productivity (BNPP), soil microbial biomass N (MBN), N mineralization, nitrification, and 16S rRNA gene based bacterial diversity to elevated N inputs. The study was based on a long‐term N deposition experiment with monthly N applications at nine rates ranging from 0 to 50 g N m−2 yr−1 in a temperate grassland. BNPP, MBN, and microbial diversity showed non‐linearities across the N gradient. In both post‐hoc test and regression tree model, the significant decrease of BNPP relative to the control started at the 10 g N m−2 yr−1 rate (the 53% decrease), whereas in Bayesian regression model, the decrease started at the 5 g N m−2 yr−1 rate (the 39% decrease) in year 6. We therefore estimated a critical load range of 5–10 g N m−2 yr−1 for BNPP. Regression tree model, Bayesian regression, and post‐hoc test consistently suggested that the detrimental effects on MBN might occur above ∼10 g N m−2 yr−1 addition rate. Bacterial diversity and the relative abundance of dominant phyla declined when N addition rate exceeded 5 or 10 g N m−2 yr−1. The impacts of N deposition on the root‐microbe system strongly depended on the interannual fluctuation in precipitation. The responses of the sensitive belowground indicators are vital to help minimize the detrimental impacts of anthropogenic N inputs.

Global depth distribution of belowground net primary productivity and its drivers

AbstractAimThis study aimed to infer the allocation of belowground net primary productivity (BNPP) to sequential soil depths down to 2 m across the globe at a 1 km resolution and assess underlying environmental drivers.LocationGlobal.Time PeriodContemporary (1932–2017).Major Taxa StudiedTerrestrial plants.MethodsGlobal datasets including field net primary production (NPP, i.e., the difference between plant assimilated and respired carbon) from 725 soil profiles, root biomass and its depth distribution from 559 soil profiles were compiled and used to infer the depth distribution of BNPP across the globe and digitally map depth‐resolved BNPP globally at 1 km resolution. Drivers of the depth distribution of BNPP were evaluated using machine learning‐based models.ResultsGlobal average BNPP allocated to the 0–20 cm soil layer is estimated to be 1.1 Mg C ha−1 yr−1, accounting for ~60% of total BNPP. Across the globe, the depth distribution of BNPP varies largely, and more BNPP is allocated to deeper layers in hotter and drier regions. Edaphic, climatic and topographic properties (in order of importance) explain &gt;80% of such variability; and the direction and magnitude of the influence of individual properties are soil depth‐ and biome‐dependent.Main ConclusionsThe findings suggest that mean annual temperature and precipitation are the two most important factors regulating BNPP across the globe. Soil properties such as soil actual evaporation and total nitrogen also play a vital role in regulating the depth distribution of BNPP. The maps of BNPP provide global benchmarks of depth‐resolved BNPP for the prediction of whole‐profile soil carbon dynamics across biomes.

As above, not so below: Long-term dynamics of net primary production across a dryland transition zone.

Drylands are key contributors to interannual variation in the terrestrial carbon sink, which has been attributed primarily to broad-scale climatic anomalies that disproportionately affect net primary production (NPP) in these ecosystems. Current knowledge around the patterns and controls of NPP is based largely on measurements of aboveground NPP (ANPP), particularly in the context of altered precipitation regimes. Limited evidence suggests belowground NPP (BNPP), a major input to the terrestrial carbon pool, may respond differently than ANPP to precipitation, as well as other drivers of environmental change, such as nitrogen deposition and fire. Yet long-term measurements of BNPP are rare, contributing to uncertainty in carbon cycle assessments. Here, we used sixteen years of annual NPP measurements to investigate responses of ANPP and BNPP to several environmental change drivers across a grassland-shrubland transition zone in the northern Chihuahuan Desert. ANPP was positively correlated with annual precipitation across this landscape; however, this relationship was weaker within sites. BNPP, on the other hand, was weakly correlated with precipitation only in Chihuahuan Desert shrubland. Although NPP generally exhibited similar trends among sites, temporal correlations between ANPP and BNPP within sites were weak. We found chronic nitrogen enrichment stimulated ANPP, whereas a one-time prescribed burn reduced ANPP for nearly a decade. Surprisingly, BNPP was largely unaffected by these factors. Together, our results suggest that BNPP is driven by a different set of controls than ANPP. Furthermore, our findings imply belowground production cannot be inferred from aboveground measurements in dryland ecosystems. Improving understanding around the patterns and controls of dryland NPP at interannual to decadal scales is fundamentally important because of their measurable impact on the global carbon cycle. This study underscores the need for more long-term measurements of BNPP to improve assessments of the terrestrial carbon sink, particularly in the context of ongoing environmental change.

Drought is threatening plant growth and soil nutrients of grassland ecosystems: A meta-analysis.

As a widespread direct effect of global warming, drought is currently wreaking havoc on terrestrial ecosystems' structure and function, however, the synthesized analysis is lacked to explore the general rules between drought changes and main functional factors of grassland ecosystems. In this work, meta-analysis was used to examine the impacts of drought on grassland ecosystems in recent decades. According to the results, drought greatly reduced aboveground biomass (AGB), aboveground net primary production (ANPP), height, belowground biomass (BGB), belowground net primary production (BNPP), microbial biomass nitrogen (MBN), microbial biomass carbon (MBC) and soil respiration (SR), and increased dissolved organic carbon (DOC), total nitrogen (TN), total phosphorus (TP), nitrate nitrogen (NO3--N), and the ratio of microbial biomass carbon and nitrogen (MBC/MBN). The drought-related environmental factor mean annual temperature (MAT) was negatively correlated with AGB, height, ANPP, BNPP, MBC, and MBN, however, mean annual precipitation (MAP) had positive effect on these variables. These findings indicate that drought is threatening the biotic environment of grassland ecosystem, and the positive steps should be taken to address the negative effects of drought on grassland ecosystems due to climate change.

Temporal changes in biomass production across different plant communities in alpine meadows of Tungnath, Garhwal Himalaya

We studied temporal changes in biomass and net primary productivity of alpine grasslands at Tungnath in Garhwal Himalaya. Five different communities with similar elevations were taken for investigation. The above-ground biomass samples were harvested as close to the ground as possible. Similarly, below-ground biomass samples were collected from harvesting monoliths (25 x 25 x 30 cm). Aboveground net primary production was determined as the sum of positive changes in biomass and belowground net primary production was calculated as the difference between peak belowground biomass and preceding minimum biomass. The live shoot biomass increased from May till September in all communities except Trachydium roylei and Polygonum, which peaked in August. The dead shoot and litter biomass first decreased and peaked in all communities in October. Belowground biomass first decreased and then increased towards the end of the growing season. The belowground to aboveground biomass ratio ranged between 0.61-3.08. The aboveground net productivity ranged between 454.8-294.3 g m-2, and the belowground net productivity ranged between 346.3-102.4 g m-2.

Responses of terrestrial ecosystem productivity and community structure to intra-annual precipitation patterns: A meta-analysis.

The productivity and community structures of terrestrial ecosystems are regulated by total precipitation amount and intra-annual precipitation patterns, which have been altered by climate change. The timing and sizes of precipitation events are the two key factors of intra-annual precipitation patterns and potentially drive ecosystem function by influencing soil moisture. However, the generalizable patterns of how intra-annual precipitation patterns affect the productivity and community structures of ecosystems remain unclear. We synthesized 633 observations from 17 studies and conducted a global meta-analysis to investigate the influences of intra-annual precipitation patterns on the productivity and community structures of terrestrial ecosystems. By classifying intra-annual precipitation patterns, we also assess the importance of the magnitude and timing of precipitation events on plant productivity. Our results showed that the intra-annual precipitation patterns decreased diversity by 6.3% but increased belowground net primary productivity, richness, and relative abundance by 16.8%, 10.5%, and 45.0%, respectively. Notably, we found that the timing uniformity of precipitation events was more important for plant productivity, while the plant community structure benefited from the increased precipitation variability. In addition, the relationship between plant productivity and community structure and soil moisture dynamic response was more consistent with the nonlinear model. The patterns of the responses of plant productivity and community structure to altered intra-annual precipitation patterns were revealed, and the importance of the timing uniformity of precipitation events to the functioning of production systems was highlighted, which is essential to enhancing understanding of the structures and functions of ecosystems subjected to altered precipitation patterns and predicting their changes.

Türkiye'nin Orta Karadeniz Bölgesi Ova Çayır Vejetasyonunda Hayvan Otlatılan Bir Alan ve Hayvan Otlatılmayan Korunmuş Bir Komşu Arazinin Yeraltı Biyokütlesi ve Verimliliği

The subject of this study is to determine the below-ground plant biomass and annual below-ground net primary production of lowland meadows in the Central Black Sea region. This study calculated the annual average amount of below-ground plant biomass, its seasonal distribution, annual primary production, and turnover values in the ungrazed and grazed meadow stands. Below-ground plant biomass, below-ground net primary production, and turnover of grazed stands were higher than in ungrazed stands. This turnover value shows that root biomass is renewed faster in grazed areas. Grazing, annual rainfall, and soil characteristics may have led to these different results.

Above- and belowground net-primary productivity: A field-based global database of grasslands.

Net primary productivity (NPP) over global grasslands is crucial for understanding the terrestrial carbon cycling and for the assessments of wild herbivores food security. During the past few decades, numerous field investigations have been conducted to estimate grassland NPP since the measuring criterion released by the International Biological Program. However, a comprehensive NPP database, particularly for belowground NPP (BNPP), in global grasslands is rare to date. Here, field NPP measurements from 438 publications (1957-2018) in global grasslands were collected, critically filtered, and incorporated in a comprehensive global database with observations for aboveground NPP (ANPP), BNPP, total NPP (TNPP), and BNPP fraction (fBNPP ). Associated information on geographical locations, climatic records, grassland types, land use patterns, manipulations subjected to manipulative experiments, sampling year of study sites, as well as NPP measurement methods are also documented. This database included 2985 entries from 1785 study sites. Among them, 806 entries contained paired data of ANPP and BNPP, resulting in the 806 fBNPP data. The study sites encompassed global grasslands with latitudinal range of 54.5° S~78.9° N, longitudinal range of 157.4° W~175.8° E, and altitudes from 0 to 5168 m above sea level, covering broad climatic gradients (-17.6 to 28.8°C in mean annual temperature and 63-2052 mm in mean annual precipitation). This global database is the world's largest paired data of ANPP and BNPP field measurements in grasslands. It can be used to study the spatio-temporal patterns of NPP and its allocation, evaluate the responses of above- and below-ground carbon components to future global changes, and validate the NPP estimation by empirical or process-based models in global grasslands. The database can be freely used for noncommercial applications. We kindly request users cite this data paper when using the database, respecting all the hard work during data compilation.

Stronger fertilization effects on aboveground versus belowground plant properties across nine U.S. grasslands.

Increased nutrient inputs due to anthropogenic activity are expected to increase primary productivity across terrestrial ecosystems, but changes in allocation aboveground versus belowground with nutrient addition have different implications for soil carbon (C) storage. Thus, given that roots are major contributors to soil C storage, understanding belowground net primary productivity (BNPP) and biomass responses to changes in nutrient availability is essential to predicting carbon-climate feedbacks in the context of interacting global environmental changes. To address this knowledge gap, we tested whether a decade of nitrogen (N) and phosphorus (P) fertilization consistently influenced aboveground and belowground biomass and productivity at nine grassland sites spanning a wide range of climatic and edaphic conditions in the continental United States. Fertilization effects were strong aboveground, with both N and P addition stimulating aboveground biomass at nearly all sites (by 30% and 36%, respectively, on average). P addition consistently increased root production (by 15% on average), whereas other belowground responses to fertilization were more variable, ranging from positive to negative across sites. Site-specific responses to P were not predicted by the measured covariates. Atmospheric N deposition mediated the effect of N fertilization on root biomass and turnover. Specifically, atmospheric N deposition was positively correlated with root turnover rates, and this relationship was amplified with N addition. Nitrogen addition increased root biomass at sites with low N deposition but decreased it at sites with high N deposition. Overall, these results suggest that the effects of nutrient supply on belowground plant properties are context dependent, particularly with regard to background N supply rates, demonstrating that site conditions must be considered when predicting how grassland ecosystems will respond to increased nutrient loading from anthropogenic activity.

Below‐ground net primary productivity stability in response to a nitrogen addition gradient in an alpine meadow

Abstract Temporal stability of ecosystem productivity is important for providing reliable ecosystem services under global changes. Great efforts have been made to explore the response of above‐ground net primary productivity (ANPP) stability to nitrogen (N) enrichment, yet how it affects below‐ground net primary productivity (BNPP) stability remains elusive, which hinders a comprehensive understanding of ecosystem stability from the view of a whole system. Here, using a field manipulative experiment with six N addition rates (0, 2, 4, 8, 16, 32 g N m−2 year−1), we explored the response patterns and drivers of BNPP stability in the topsoil (0–20 cm) and subsoil (20–40 cm) in the alpine meadow. The results showed that BNPP stability at both soil depths showed a unimodal response to increasing N addition rates. Specifically, for both the topsoil and subsoil, low‐level N addition significantly promoted BNPP stability, while high doses of N addition had no significant impact on BNPP stability, suggesting that current low level of N deposition likely benefits the stable provision of below‐ground functioning. Furthermore, dominant species stability and species richness contributed most to the changes in BNPP stability in the topsoil, whereas only dominant species stability was the dominant driver of BNPP stability in the subsoil. This study is among the first to illuminate the main mechanisms underlying the responses of BNPP stability to N enrichment at various soil depths, which will advance our current understanding of N addition effects on below‐ground processes and benefit the sustainable provision of ecosystem functioning in the context of atmospheric N deposition. Read the free Plain Language Summary for this article on the Journal blog.