Belowground Net Primary Production Research Articles

Carbon budget of the Harvard Forest Long‐Term Ecological Research site: pattern, process, and response to global change

AbstractHow, where, and why carbon (C) moves into and out of an ecosystem through time are long‐standing questions in biogeochemistry. Here, we bring together hundreds of thousands of C‐cycle observations at the Harvard Forest in central Massachusetts, USA, a mid‐latitude landscape dominated by 80–120‐yr‐old closed‐canopy forests. These data answered four questions: (1) where and how much C is presently stored in dominant forest types; (2) what are current rates of C accrual and loss; (3) what biotic and abiotic factors contribute to variability in these rates; and (4) how has climate change affected the forest’s C cycle? Harvard Forest is an active C sink resulting from forest regrowth following land abandonment. Soil and tree biomass comprise nearly equal portions of existing C stocks. Net primary production (NPP) averaged 680–750 g C·m−2·yr−1; belowground NPP contributed 38–47% of the total, but with large uncertainty. Mineral soil C measured in the same inventory plots in 1992 and 2013 was too heterogeneous to detect change in soil‐C pools; however, radiocarbon data suggest a small but persistent sink of 10–30 g C·m−2·yr−1. Net ecosystem production (NEP) in hardwood stands averaged ~300 g C·m−2·yr−1. NEP in hemlock‐dominated forests averaged ~450 g C·m−2·yr−1until infestation by the hemlock woolly adelgid turned these stands into a net C source. Since 2000, NPP has increased by 26%. For the period 1992–2015, NEP increased 93%. The increase in mean annual temperature and growing season length alone accounted for ~30% of the increase in productivity. Interannual variations in GPP and NEP were also correlated with increases in red oak biomass, forest leaf area, and canopy‐scale light‐use efficiency. Compared to long‐term global change experiments at the Harvard Forest, the C sink in regrowing biomass equaled or exceeded C cycle modifications imposed by soil warming, N saturation, and hemlock removal. Results of this synthesis and comparison to simulation models suggest that forests across the region are likely to accrue C for decades to come but may be disrupted if the frequency or severity of biotic and abiotic disturbances increases.

Warming of alpine tundra enhances belowground production and shifts community towards resource acquisition traits

AbstractClimate warming is expected to stimulate plant growth in high‐elevation and high‐latitude ecosystems, significantly increasing aboveground net primary production (ANPP). However, the effects of simultaneous changes in temperature, snowmelt timing, and summer water availability on total net primary production (NPP)—and elucidation of both above‐ and belowground responses—remain an important area in need of further study. In particular, measures of belowground net primary productivity (BNPP) are required to understand whether ANPP changes reflect changes in allocation or are indicative of a whole plant NPP response. Further, plant functional traits provide a key way to scale from the individual plant to the community level and provide insight into drivers of NPP responses to environmental change. We used infrared heaters to warm an alpine plant community at Niwot Ridge, Colorado, and applied supplemental water to compensate for soil water loss induced by warming. We measured ANPP, BNPP, and leaf and root functional traits across treatments after 5 yr of continuous warming. Community‐level ANPP and total NPP (ANPP + BNPP) did not respond to heating or watering, but BNPP increased in response to heating. Heating decreased community‐level leaf dry matter content and increased total root length, indicating a shift in strategy from resource conservation to acquisition in response to warming. Water use efficiency (WUE) decreased with heating, suggesting alleviation of moisture constraints that may have enabled the plant community to increase productivity. Heating may have decreased WUE by melting snow earlier and creating more days early in the growing season with adequate soil moisture, but stimulated dry mass investment in roots as soils dried down later in the growing season. Overall, this study highlights how ANPP and BNPP responses to climate change can diverge, and encourages a closer examination of belowground processes, especially in alpine systems, where the majority of NPP occurs belowground.

Carbon Balance in Salt Marsh and Mangrove Ecosystems: A Global Synthesis

Mangroves and salt marshes are among the most productive ecosystems in the global coastal ocean. Mangroves store more carbon (739 Mg CORG ha−1) than salt marshes (334 Mg CORG ha−1), but the latter sequester proportionally more (24%) net primary production (NPP) than mangroves (12%). Mangroves exhibit greater rates of gross primary production (GPP), aboveground net primary production (AGNPP) and plant respiration (RC), with higher PGPP/RC ratios, but salt marshes exhibit greater rates of below-ground NPP (BGNPP). Mangroves have greater rates of subsurface DIC production and, unlike salt marshes, exhibit active microbial decomposition to a soil depth of 1 m. Salt marshes release more CH4 from soil and creek waters and export more dissolved CH4, but mangroves release more CO2 from tidal waters and export greater amounts of particulate organic carbon (POC), dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC), to adjacent waters. Both ecosystems contribute only a small proportion of GPP, RE (ecosystem respiration) and NEP (net ecosystem production) to the global coastal ocean due to their small global area, but contribute 72% of air–sea CO2 exchange of the world’s wetlands and estuaries and contribute 34% of DIC export and 17% of DOC + POC export to the world’s coastal ocean. Thus, both wetland ecosystems contribute disproportionately to carbon flow of the global coastal ocean.

Shifting biomass allocation determines community water use efficiency under climate warming

Understanding how net primary production (NPP) and its allocation respond to climate warming is of fundamental importance in predicting ecosystem carbon (C) cycle and C-climate feedback. Especially, the optimal partitioning theory suggests that plants preferentially allocate photosynthates toward the above- or below-ground parts to acquire the limiting resources to maximize their growth rate and optimize resource use under environmental change. However, it remains elusive on how NPP allocation changes and regulates community water-use efficiency (WUEc) under climate warming. In this study, we conducted a manipulative warming experiment with three levels of warming treatments (control, + 1.5 °C and + 2.5 °C) to explore the response of NPP allocation and its regulation on WUEc in an alpine meadow. Results showed that above-ground NPP (ANPP) and below-ground NPP (BNPP) responded differently to warming. On average, W1.5 (+ 1.5 °C) and W2.5 (+ 2.5 °C) treatments increased BNPP by 28.98% and 33.28% and increased NPP by 20.05% and 38.70%, respectively, across 4 years. Whereas no consistent warming effect on ANPP was observed across years. The fraction of BNPP to total NPP (fBNPP) responded positively to warming under low ambient temperature and community biomass while it responded negatively under high ambient temperature and community biomass. Notably warming-induced changes in fBNPP negatively correlated with warming-induced changes in WUEc. These results suggested that warming effect on NPP allocation was largely contextually dependent and implied important biological regulation on WUEc. The emerging trade-offs between NPP allocation and WUEc reflect adaptation strategy of plant community under climate change.

The importance of extreme rainfall events and their timing in a semi‐arid grassland

Abstract Climate change is intensifying the hydrologic cycle globally, increasing both the size and frequency of extreme precipitation events, or deluges. Arid and semi‐arid ecosystems are expected to be particularly responsive to this change because their ecological processes are largely driven by distinct soil moisture pulses. However, since soil moisture, air temperature and plant phenology vary throughout the growing season, deluges will likely have differing impacts on these systems depending on when they occur. We conducted a field experiment to assess how the seasonal timing (early, middle or late growing season) of a single deluge (70‐mm precipitation event) altered key ecological processes in the semi‐arid shortgrass steppe of North America. Regardless of timing, a single deluge stimulated most ecosystem processes, but a deluge at mid‐season caused the greatest increase in soil respiration, canopy greenness, above‐ground net primary production (ANPP) and growth and flowering of the dominant plant species Bouteloua gracilis. In contrast, below‐ground net primary production (BNPP) was insensitive to deluge timing, with a consistent BNPP increase in all the deluge treatments that was almost twice as large as the ANPP response. This BNPP response was largely driven by enhanced root production at the 10–20 cm, rather than 0–10 cm, soil depth. Synthesis. In a semi‐arid ecosystem, a single deluge can have season‐long impacts on many ecosystem processes, but responses can be mediated by event timing. Therefore, predicting responses of semi‐arid ecosystems to more dynamic precipitation regimes, and subsequent impacts on the global carbon budget, will require knowledge of how deluge magnitude, frequency and timing are being altered by climate change.

Asymmetric responses of soil respiration in three temperate steppes along a precipitation gradient in northern China revealed by soil-monolith transplanting experiment

Responses and feedbacks of ecosystem carbon (C) cycling in the terrestrial biosphere to climate change pose the major challenge for Earth System Model projections. However, whether ecosystem C cycling among diverse vegetation types shows different sensitivities and the associated underlying mechanisms remain elusive. As part of a 5-year (2014–2018) soil monolith transplant experiment, this study was designed to examine the influences of night warming, decreased precipitation, and increased precipitation on soil respiration in the three temperate steppes (i.e. desert, typical, and meadow steppes) along a precipitation gradient on the Mongolian Plateau. Over the 5 years, night warming had no effect on soil respiration in any of the three steppes. Decreased precipitation reduced soil respiration, whereas increased precipitation stimulated it in each steppe. In addition, the sensitivity of soil respiration to increased precipitation was larger than that to decreased precipitation, suggesting a positive asymmetry of soil respiration in response to changing precipitation. The soil respiration responses were predominately determined by both soil water availability and belowground net primary productivity in the desert and typical steppes, but by soil total C alone in the meadow steppe. These findings not only improve mechanistic understanding on the responses of soil respiration in various grassland ecosystems, but also facilitate the extrapolation from local to regional scale for the robust projections of terrestrial C-climate change feedbacks.

Global patterns and climatic controls of belowground net carbon fixation

Carbon allocated underground through belowground net primary production represents the main input to soil organic carbon. This is of significant importance, because soil organic carbon is the third-largest carbon stock after oceanic and geological pools. However, drivers and controls of belowground productivity and the fraction of total carbon fixation allocated belowground remain uncertain. Here we estimate global belowground net primary productivity as the difference between satellite-based total net primary productivity and field observations of aboveground net primary production and assess climatic controls among biomes. On average, belowground carbon productivity is estimated as 24.7 Pg y-1, accounting for 46% of total terrestrial carbon fixation. Across biomes, belowground productivity increases with mean annual precipitation, although the rate of increase diminishes with increasing precipitation. The fraction of total net productivity allocated belowground exceeds 50% in a large fraction of terrestrial ecosystems and decreases from arid to humid ecosystems. This work adds to our understanding of the belowground carbon productivity response to climate change and provides a comprehensive global quantification of root/belowground productivity that will aid the budgeting and modeling of the global carbon cycle.

Ojos que no ven... ¿Qué podemos hacer para incluir más a la fracción subterránea en estudios de vegetación?

Conocer la estructura y el funcionamiento de la fraccion subterranea de la vegetacion es fundamental para comprender numerosos procesos que ocurren en distintos niveles de organizacion. Sin embargo, dicha fraccion fue menos estudiada que su contraparte aerea, principalmente por el gran esfuerzo que demanda muestrearla a campo y procesarla en el laboratorio. En la XXVIII Reunion Argentina de Ecologia (Mar del Plata, 2018) se realizaron dos simposios sobre la importancia de conocer las raices en estudios ecologicos. De los simposios surgio la necesidad de 1) cuantificar los estudios que hayan evaluado las fracciones subterranea y aerea de la vegetacion, y 2) determinar las metodologias empleadas y las variables de la fraccion subterranea registradas en sistemas naturales (i.e., pastizales, estepas, bosques, arbustales y desierto) y antropizados (i.e., pasturas y cultivos) en seis provincias fitogeograficas de la Argentina y en dos regiones geomorfologicas de Uruguay. Se registraron 933 estudios publicados entre 1990 y 2019. El 57% y el 23% correspondieron a estudios exclusivos de la fraccion aerea y de la subterranea, respectivamente, con un incremento exponencial en el tiempo de ambas fracciones. En la actualidad existe una tendencia a incorporar el compartimiento subterraneo en estudios ecologicos. Mediante un analisis sistematico se encontro que se emplearon seis metodos de muestreo (barreno, ruleros, planta entera, monolitos, rhizotron y estimacion de la biomasa subterranea a partir de la biomasa aerea) para evaluar cuatro variables (biomasa subterranea, productividad primaria neta subterranea, algunos atributos radicales y tasa de descomposicion radical). El metodo mas empleado fue el del barreno y la variable mas evaluada fue la biomasa subterranea. Proponemos fomentar la colaboracion entre equipos de investigacion y establecer comparaciones metodologicas para comprender los alcances de los resultados y obtener estimaciones mas confiables sobre las consecuencias del cambio en el uso del suelo.

Root to shoot and carbon to nitrogen ratios of maize and soybean crops in the US Midwest

Abstract Root traits are important to crop functioning, yet there is little information about how root traits vary with shoot traits. Using a standardized protocol, we collected 160 soil cores (0−210 cm) across 10 locations, three years and multiple cropping systems (crops x management practices) in Iowa, USA. Maximum root biomass ranged from 1.2 to 2.8 Mg ha−1 in maize and 0.86 to 1.93 Mg ha−1 in soybean. The root:shoot (R:S) ratio ranged from 0.04 to 0.13 in maize and 0.09 to 0.26 in soybean. Maize produced 27 % more root biomass, 20 % longer roots, with 35 % higher carbon to nitrogen (C:N) ratio than soybean. In contrast, soybean had a 47 % greater R:S ratio than maize. The maize R:S ratio values were substantially lower than literature values, possibly due to differences in measurement methodologies, genotypes, and environment. In particular, we sampled at plant maturity rather than crop harvest to minimize the effect of senescence on measurements of shoots and roots. Maximum shoot biomass explained 70 % of the variation in root biomass, and the R:S ratio was positively correlated with the root C:N measured in both crops. Easily-measured environmental variables including temperature and precipitation were weakly associated with root traits. These results begin to fill an important knowledge gap that will enable better estimates of belowground net primary productivity and soil organic matter dynamics. Ultimately, the ability to explain variation in root mass production can be used to improve C and N budgets and modeling studies from crop to regional scales.

How plastic mulching affects net primary productivity, soil C fluxes and organic carbon balance in dry agroecosystems in China

Agricultural soil management has a great potential to reduce the anthropogenic emissions of carbon (C), mainly via increasing soil organic carbon (SOC) sequestration. The global use of agricultural plastic mulches has emerged as a widespread soil management practice due to its apparent economic benefits, especially in the dry croplands of China. However, the integrated effects of plastic mulching in China’s drylands on net primary productivity (NPP) of staple crops (i.e. maize, wheat, and potato), SOC stocks, and C emissions have rarely been assessed quantitatively. We conducted a meta‒analysis of nationwide dataset and found that compared with traditional non‒mulching farming, plastic mulching on average increased national aboveground NPP by 1.41 Mg C ha−1 y−1, while it led to rising soil CO2 emissions (437 kg C ha−1 y−1 higher than non‒mulching) because of stimulated microbial metabolism, such as higher microbial biomass C and extracellular enzyme activities. Critically, plastic mulching not only enhanced crop‒sourced C inputs into the soil by 0.24 Mg C ha−1 y−1 through improving belowground NPP, but also facilitated soil CH4 absorption by 0.25 kg C ha−1 y−1 across the entire dataset. As a result, a significant increase in SOC storage under plastic mulching was estimated as 0.012 Mg C ha−1 y−1, and crop types, N input, and precipitation seems to be the strongest predictors explaining variability in mulching‒driven SOC sequestration. These results suggest that plastic mulching in dry agroecosystems can have a distinct potential to curtail the anthropogenic emissions of C through significant increases in both SOC sequestration and crop C fixation.

High Below-Ground Productivity Allocation of Alpine Grasslands on the Northern Tibet.

The allocation of net primary production (NPP) between above- and belowground components is a key step of ecosystem material cycling and energy flows, which determines many critical parameters, e.g., the fraction of below ground NPP (BNPP) to NPP (fBNPP) and root turnover rates (RTR), in vegetation models. However, direct NPP estimation and partition are scarcely based on field measurements of biomass dynamics in the alpine grasslands on the Northern Tibetan Plateau (NTP). Consequently, these parameters are unverifiable and controversial. Here, we measured above- and belowground biomass dynamics (monthly from May to September each year from 2013 to 2015) to estimate NPP dynamics and allocations in four typical alpine grassland ecosystems, i.e., an alpine meadow, alpine meadow steppe, alpine steppe and alpine desert steppe. We found that NPP and its components, above and below ground NPP (ANPP and BNPP), increased significantly from west to east on the NTP, and ANPP was mainly affected by temperature while BNPP and NPP were mainly affected by precipitation. The bulk of BNPP was generally concentrated in the top 10 cm soil layers in all four alpine grasslands (76.1% ± 9.1%, mean ± SD). Our results showed that fBNPP was significantly different among these four alpine grasslands, with its means in alpine meadow (0.93), alpine desert steppe (0.92) being larger than that in the alpine meadow steppe (0.76) and alpine steppe (0.77). Both temperature and precipitation had significant and positive effects on the fBNPP, while their interaction effects were significantly opposite. RTR decreased with increasing precipitation, but increased with increasing temperature across this ecoregion. Our study illustrated that alpine grasslands on the NTP, especially in the alpine meadow and alpine desert steppe, partitioned an unexpected and greater NPP to below ground than most historical reports across global grasslands, indicating a more critical role of the root carbon pool in carbon cycling in alpine grasslands on the NTP.

Nitrogen controls the net primary production of an alpine Kobresia meadow in the northern Qinghai-Tibet Plateau.

Net primary production (NPP) is a fundamental property of natural ecosystems. Understanding the temporal variations of NPP could provide new insights into the responses of communities to environmental factors. However, few studies based on long‐term field biomass measurements have directly addressed this subject in the unique environment of the Qinghai‐Tibet plateau (QTP). We examined the interannual variations of NPP during 2008–2015 by monitoring both aboveground net primary productivity (ANPP) and belowground net primary productivity (BNPP), and identified their relationships with environmental factors with the general linear model (GLM) and structural equation model (SEM). In addition, the interannual variation of root turnover and its controls were also investigated. The results show that the ANPP and BNPP increased by rates of 15.01 and 143.09 g/m2 per year during 2008–2015, respectively. BNPP was mainly affected by growing season air temperature (GST) and growing season precipitation (GSP) rather than mean annual air temperature (MAT) or mean annual precipitation (MAP), while ANPP was only controlled by GST. In addition, available nitrogen (AN) was significantly positively associated with BNPP and ANPP. Root turnover rate averaged 30%/year, increased with soil depth, and was largely controlled by GST. Our results suggest that alpine Kobresia meadow was an N‐limited ecosystem, and the NPP on the QTP might increase further in the future in the context of global warming and nitrogen deposition.

Precipitation-use efficiency may explain net primary productivity allocation under different precipitation conditions across global grassland ecosystems

Conclusions made regarding plant biomass allocation, trade-off patterns and aboveground/belowground biomass without considering the existence of perennials in grassland ecosystems are under fierce debate. This study focused on this issue and brings clarity to allocation patterns; 217 samples were collected across different grassland ecosystems worldwide that contained the mean values of aboveground and belowground net primary productivity (ANPP and BNPP). Based on the relationships between BNPP to ANPP ratio and mean annual precipitation (MAP), the change point was found to divide the habitats into precipitation-limited and precipitation-unlimited conditions. The results show that overall benefits pointed to ANPP (0.04) and pointed to BNPP (0.13) under different precipitation conditions, respectively. Our findings add BNPP to the calculation of precipitation-use efficiency (PUE) and confirm that PUE may explain the net productivity allocation patterns and trade-offs of ANPP and BNPP under precipitation-limited conditions. The study highlights production allocation and trade-off patterns under unlimited/limited precipitation backgrounds across global grassland ecosystems and connects PUE with the distribution of productivity, which should benefit our understanding of the complicated mechanisms of ecological processes.

Asymmetry in above- and belowground productivity responses to N addition in a semi-arid temperate steppe.

Nitrogen (N) enrichment often increases aboveground net primary productivity (ANPP) of the ecosystem, but it is unclear if belowground net primary productivity (BNPP) track responses of ANPP. Moreover, the frequency of N inputs may affect primary productivity but is rarely studied. To assess the response patterns of above- and belowground productivity to rates of N addition under different addition frequencies, we manipulated the rate (0-50gNm-2 year-1 ) and frequency (twice vs. monthly additions per year) of NH4 NO3 inputs for six consecutive years in a temperate grassland in northern China and measured ANPP and BNPP from 2012 to 2014. In the low range of N addition rates, BNPP showed the greatest negative response and ANPP showed the greatest positive responses with increases in N addition (<10gNm-2 year-1 ). As N addition increased beyond 10gNm-2 year-1 , increases in ANPP dampened and decreases in BNPP ceased altogether. The response pattern of net primary productivity (combined above- and belowground; NPP) corresponded more closely to ANPP than to BNPP. The N effects on BNPP and BNPP/NPP (fBNPP ) were not dependent on N addition frequency in the range of N additions typically associated with N deposition. BNPP was more sensitive to N addition frequency than ANPP, especially at low rates of N addition. Our findings provide new insights into how plants regulate carbon allocation to different organs with increasing N rates and changing addition frequencies. These root response patterns, if incorporated into Earth system models, may improve the predictive power of C dynamics in dryland ecosystems in the face of global atmospheric N deposition.

Simulating Rangeland Ecosystems with G-Range: Model Description and Evaluation at Global and Site Scales

Rangeland ecosystems and their roles in providing ecosystem services are vulnerable to changes in climate, CO2 concentration, and management. These drivers forcing widespread changes in rangeland ecosystem processes and vegetation dynamics create two-way interactions and feedback loops between biogeochemistry and vegetation composition. To support spatial simulation and forecasting in the global rangelands, the G-Range global rangelands model couples biogeochemical submodels from the CENTURY soil organic matter model with dynamic populations’ submodels for herbs, shrubs, and trees. Here is presented a model description for G-Range, including novel elements of G-Range and implementation of CENTURY code. An initial evaluation of G-Range at global and site scales follows. G-Range outputs for net primary productivity (NPP) and vegetation cover (herbs, shrubs, trees, bare ground) were evaluated against global MODIS layers at global and site scales, and aboveground and belowground NPP were compared with field data from globally distributed sites. Most model outputs evaluated were within the range of a priori benchmarks for tolerable absolute or relative error (two benchmarks per output, at two scales, for five outputs of NPP and vegetation cover). Trade-offs in model fit among variables, datasets, and scales indicated practical constraints on improving model fit with respect to the selected evaluation datasets, especially field NPP versus MODIS NPP. The relative effects of multiple drivers of rangeland vegetation change were the greatest sources of uncertainty in model outputs. G-Range is best suited to scenario analysis of large-scale and long-term impacts of climate, CO2, and management on rangeland ecosystem processes and vegetation, as well as ecosystem services, such as production of forage and browse and carbon sequestration.

Yield potential and nitrogen dynamics of no-till silage maize (Zea mays L.) under maritime climate conditions

Abstract In intensive dairy farming in Northwest Europe resource-efficiency of forage production based on permanent grassland in combination with continuous maize is undermined by high nitrogen surpluses. With respect to the paradigm of ecological intensification (EI), a field experiment was set up in northern Germany to answer the question of whether rotational fodder production including silage maize (Zea mays L.) and grassland combined with no-till soil cultivation represents an alternative to conventional tillage. A 10-year-old grassland sward was converted to maize in two ways: (i) with conventional tillage (CT) and (ii) with no-tillage (NT). There were two rates of N-fertilization: fertilized (N1), (grassland 380 kg N ha−1, maize 90 kg N ha−1) and unfertilized (N0). Aboveground net primary production (ANPP) was not significantly different in N1 treatments, with average maize yields of 18 (NT) and 21 t ha−1 (CT). Belowground net primary production (BNPP) showed similar biomass production in NT and CT. N-release from the old sward made additional fertilization unnecessary in the first year. A beginning differentiation between both tillage systems in the second year showed a significant decline in N-yield and N-release in NT N0 treatments. However, crop performance and N-release in N1 treatments continued to be comparable to CT. In terms of N leaching, tillage intensity had no clear effect on drainage N-losses. We conclude that due to comparable yields in both tillage treatments, no-till maize cropping following several years of grassland leys can contribute to EI by saving N-fertilizer input.

Extreme-duration drought impacts on soil CO2 efflux are regulated by plant species composition

Long-duration drought can alter ecosystem plant species composition with subsequent effects on carbon cycling. We conducted a rainfall manipulation field experiment to address the question: how does drought-induced vegetation change, specifically shrub encroachment into grasslands, regulate impacts of subsequent drought on soil CO2 efflux (Rs) and its components (autotrophic and heterotrophic, Ra and Rh)? We conducted a two-year experiment in Inner Mongolia plateau, China, using constructed steppe communities including graminoids, shrubs and their mixture (graminoid + shrub) to test the effects of extreme-duration drought (60-yr return time) on Rs, Rh and Ra. Our results indicated that extreme-duration drought reduced net primary production, with subsequent effects on Rs, Rh and Ra in all three vegetation communities. There was a larger relative decline in Ra (35–54%) than Rs (30–37%) and Rh (28–35%). Interestingly, we found Rs in graminoids is higher than in shrubs under extreme drought. Meanwhile, Rh declines were largest in the shrub community. Although Ra and Rh both decreased rapidly during drought treatment, Rh recovered quickly after the drought, while Ra did not, limiting the Rs recovery. This study suggests that plant species composition regulates several aspects of soil CO2 efflux response to climate extremes. This regulation may be limited by above- and below-ground net primary production depending on soil water availability. The results of this experiment address a critical knowledge gap in the relationship between soil respiration and plant species composition. With shrub encroachment into grasslands, total soil respiration is reduced and can partly offset the effect of reduction in productivity under drought stress.

Effects of climate warming on carbon fluxes in grasslands-A global meta-analysis.

Climate warming will affect terrestrial ecosystems in many ways, and warming-induced changes in terrestrial carbon (C) cycling could accelerate or slow future warming. So far, warming experiments have shown a wide range of C flux responses, across and within biome types. However, past meta-analyses of C flux responses have lacked sufficient sample size to discern relative responses for a given biome type. For instance grasslands contribute greatly to global terrestrial C fluxes, and to date grassland warming experiments provide the opportunity to evaluate concurrent responses of both plant and soil C fluxes. Here, we compiled data from 70 sites (in total 622 observations) to evaluate the response of C fluxes to experimental warming across three grassland types (cold, temperate, and semi-arid), warming methods, and short (≤3years) and longer-term (>3years) experiment lengths. Overall, our meta-analysis revealed that experimental warming stimulated C fluxes in grassland ecosystems with regard to both plant production (e.g., net primary productivity (NPP) 15.4%; aboveground NPP (ANPP) by 7.6%, belowground NPP (BNPP) by 11.6%) and soil respiration (Rs) (9.5%). However, the magnitude of C flux stimulation varied significantly across cold, temperate and semi-arid grasslands, in that responses for most C fluxes were larger in cold than temperate or semi-arid ecosystems. In semi-arid and temperate grasslands, ecosystem respiration (Reco) was more sensitive to warming than gross primary productivity (GPP), while the opposite was observed for cold grasslands, where warming produced a net increase in whole-ecosystem C storage. However, the stimulatory effect of warming on ANPP and Rs observed in short-term studies (≤3years) in both cold and temperate grasslands disappeared in longer-term experiments (>3years). These results highlight the importance of conducting long-term warming experiments, and in examining responses across a wide range of climate.

Impacts of mixed-grazing on root biomass and belowground net primary production in a temperate desert steppe.

The impacts of large herbivores on plant communities differ depending on the plants and the herbivores. Few studies have explored how herbivores influence root biomass. Root growth of vegetation was studied in the field with four treatments: sheep grazing alone (SG), cattle grazing alone (CG), mixed grazing with cattle and sheep (MG) and no grazing (CK). Live and total root biomasses were measured using the root ingrowth core and the drilling core, respectively. After 2 years of grazing, total root biomass showed a decreasing trend while live root biomass increased with time during the growing seasons. Belowground net primary production (BNPP) among the treatments varied from 166 ± 32 to 501 ± 88 g m−2 and root turnover rates (RTR) varied from 0.25 ± 0.05 to 0.70 ± 0.11 year−1. SG had the greatest BNPP and RTR, while the CG had the smallest BNPP and RTR. BNPP and RTR of the MG treatment were between those of the CG and SG treatments. BNPP and RTR of the CK were similar to MG treatment. Compared with other treatments, CG had a greater impact on dominant tall grasses species in communities. SG could decrease community diversity. MG eliminated the disadvantages of single-species grazing and was beneficial to community diversity and stability.

青藏高原两种植被类型净初级生产力与气候因素的关系及周转值分析

PDF HTML阅读 XML下载 导出引用 引用提醒 青藏高原两种植被类型净初级生产力与气候因素的关系及周转值分析 DOI: 10.5846/stxb201808301852 作者: 作者单位: 中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41730752，31700395，31770532，31400483）；海南州小流域的综合治理及示范（2019-ST-152） The response of net primary productivity of two different vegetation types to climatic factors and root turnover analysis on the Qinghai-Tibet Plateau Author: Affiliation: Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:基于2008-2016年青海海北站9年净初级生产力及气候因子监测数据，分析了青藏高原高寒小嵩草草甸和高寒金露梅灌丛两种植被净初级生产力年际动态，并探讨了气候因子对其影响及其不同土层深度根系周转值特征。结果表明：（1）年际尺度上，小嵩草草甸地上净初级生产力表现为显著增加趋势，增幅为7.02 g m-2 a-1，而金露梅灌丛地上净初级生产力相对较为稳定；对于其地下净初级生产力和总生产力，小嵩草草甸和金露梅灌丛均表现为增加趋势（P > 0.05），9年间小嵩草草甸地上、地下和总净初级生产力平均值分别为（217.55±9.95）、（1882.75±161.33）g m-2 a-1和（2100.30±163.38）g m-2 a-1，金露梅灌丛地上、地下和总净初级生产力9年间平均值分别为（256.27±11.4）、（1614.31±173.03）g m-2 a-1和（1870.58±177.93）g m-2 a-1。（2）不同植被类型地上净初级生产力对气候因素响应不同，金露梅灌丛地上净初级生产力主要受温度影响，而温度对小嵩草草甸地上净初级生产力无显著影响。此外，降水不是限制高寒生态系统草地地上净初级生产力主要因子，相比于降水影响，高寒生态系统地上净初级生产力更受温度调控。（3）年均温和年降水对金露梅灌丛和小嵩草草甸地下净初级生产力均无显著影响（P > 0.05），表明高寒生态系统，其地下生产力受外界气候条件变化影响微弱，是一个稳定的碳库。（4）两种植被类型其根系周转值均随着土壤深度的增加呈逐渐增加趋势，且高寒灌丛根系周转值明显高于高寒草甸根系周转值。研究表明，在全球气候变暖背景下将会增加金露梅灌丛地上净初级生产力，而对小嵩草草甸地上净初级生产力无显著影响。 Abstract:Based on nine years (from 2008 to 2016) of monitoring data of net primary productivity (NPP) and climatic factors at Haibei Station, the interannual NPP dynamics of alpine Kobresia pygmaea meadow and alpine Potentilla fruticosa shrubs were analyzed. In addition, the effects of climatic factors on NPP and the characteristics of root turnover across different soil layers were also assessed. The results showed that (1) on an interannual scale, the aboveground net primary productivity (ANPP) of Kobresia pygmaea meadow showed a significant increasing trend (7.02 g m-2 a-1), but the ANPP of Potentilla fruticosa shrubs remained relatively stable. Both belowground net primary productivity (BNPP) and total net primary productivity (NPP) of the two vegetation types showed a slight increase (P>0.05). The average ANPP, BNPP, and NPP for the Kobresia pygmaea meadow were (217.55±9.95) g/m2, (1882.75±161.33) g/m2 and (2100.30±163.38) g/m2, respectively. The average ANPP, BNPP, and NPP for Potentilla fruticosa shrubs were (256.27 ±11.4) g/m2, (1614.31 ±173.03) g/m2, and (1870.58±177.93) g/m2, respectively. (2) The ANPP of the vegetation types responded differently to climatic factors. The mean annual air temperature had a significant effect on ANPP for Potentilla fruticosa shrubs, but no significant impact on the ANPP of Kobresia pygmaea meadow. Furthermore, precipitation was not a key factor limiting the NPP of grassland in alpine ecosystems; temperature exerted a stronger effect on the ANPP of alpine ecosystems compared with precipitation. (3) The mean annual air temperature and mean annual precipitation showed no notable effect on the BNPP, indicating that the BNPP was less affected by external climatic factors than the ANPP. (4) Root turnover increased with soil depth and the root turnover of Potentilla fruticosa shrubs was higher than that of Kobresia pygmaea meadow. Our study implies that the ANPP of Potentilla fruticosa shrubs will increase with climate change, but no significant change is expected for the ANPP of Kobresia pygmaea meadow. 参考文献 相似文献 引证文献