Belowground Production Research Articles

Effects of grazing intensity and grazing exclusion on litter decomposition in the temperate steppe of Nei Mongol, China

Aims Grazing intensity and grazing exclusion affect ecosystem carbon cycling by changing the plant community and soil micro-environment in grassland ecosystems. The aims of this study were: 1) to determine the effects of grazing intensity and grazing exclusion on litter decomposition in the temperate grasslands of Nei Mongol; 2) to compare the difference between above-ground and below-ground litter decomposition; 3) to identify the effects of precipitation on litter production and decomposition. Methods We measured litter production, quality, decomposition rates and soil nutrient contents during the growing season in 2011 and 2012 in four plots, i.e. light grazing, heavy grazing, light grazing exclusion and heavy grazing exclusion. Quadrate surveys and litter bags were used to measure litter production and decomposition rates. All data were analyzed with ANOVA and Pearson’s correlation procedures in SPSS. Important findings Litter production and decomposition rates differed greatly among four plots. During the two years of our study, above-ground litter production and decomposition in heavy-grazing plots were faster than those in light-grazing plots. In the dry year, below-ground litter production and decomposition in light-grazing plots were faster than those in heavy-grazing plots, which is opposite to the findings in the wet year. Short-term grazing exclusion could promote litter production, and the exclusion of light-grazing could increase litter decomposition and nutrient cycling. In contrast, heavy-grazing exclusion decreased litter decomposition. Thus, grazing exclusion is beneficial to the restoration of the light-grazing grasslands, and more human management measures 杨丽丽等: 内蒙古温带草原不同放牧强度和围栏封育对凋落物分解的影响 749 doi: 10.17521/cjpe.2016.0051 are needed during the restoration of heavy-grazing grasslands. Precipitation increased litter production and decomposition, and below-ground litter was more vulnerable to the inter-annual change of precipitation than above-ground litter. Compared to the light-grazing grasslands, heavy-grazing grasslands had higher sensitivity to precipitation. The above-ground litter decomposition was strongly positively correlated with the litter N content (R = 0.489, p < 0.01) and strongly negatively correlated with the soil total N content (R = 0.450, p < 0.01), but it was not significantly correlated with C:N and lignin:N. Below-ground litter decomposition was negatively correlated with the litter C (R = 0.263, p < 0.01), C:N (R = 0.349, p < 0.01) and cellulose content (R = 0.460, p < 0.01). Our results will provide a theoretical basis for ecosystem restoration and the research of carbon cycling.

Above- and below-ground responses of native and invasive prairie grasses to future climate scenarios

More intense and frequent droughts, coupled with elevated temperatures, are projected for grasslands worldwide. Although it has been suggested that alterations in temperature and precipitation will increase the success of biological invasions, studies that combine these climate change scenarios are limited. These changes in climate may increase the success of non-native, invasive plant species directly, as these species often possess traits that are favored by variable climates, or indirectly through negative impacts on native vegetation or alterations in soil microbial communities, such as arbuscular mycorrhizal (AM) fungi. The goal of our research was to assess above- and below-ground production and mycorrhizal fungal abundance of functionally similar native and invasive non-native grass species under projected climate-change scenarios. We assessed plant biomass, intra-radical AM root colonization, and relative abundance of extra-radical fungal biomass of two native (Schizachyrium scoparium (Michx.) Nash, Pascopyrum smithii (Rydb.) Á.Löve) and two invasive (Bothriochloa ischaemum (L.) Keng, Bromus inermis Leyss.) grass species subjected to increased temperature and decreased soil water availability. Regardless of temperature or soil moisture, the invasive grasses in our study displayed greater seedling growth as compared with paired native species. Invasive grasses were also generally characterized by greater intra-radical colonization by AM fungi, compared with native species. Our data suggest that invasive grasses will continue to be problematic and successfully out-compete native grasses following increased temperatures and reduced water availability, as projected by climate-change models.

Can litter addition mediate plant productivity responses to increased precipitation and nitrogen deposition in a typical steppe?

AbstractPlant litter is a key component of grassland and plays a major role in terrestrial ecosystem processes. Global climate change has been shown to considerably alter litter inputs to soils, which may feed back to the grassland ecosystem responses to climate change. In order to explore whether litter addition could mediate above and belowground productivity responses to short‐term increases in growing‐season precipitation and nitrogen deposition, we conducted a two‐year study on water, nitrogen and litter addition in Inner Mongolia grassland. After two years of treatments, our results showed that water, nitrogen, and litter addition increased aboveground biomass (AB) and belowground net primary productivity (BNPP). Besides, litter addition increased BNPP responses to water addition. These litter addition effects could be attributed to the influence of litter on soil moisture and soil nitrogen availability, ultimately increasing belowground water use efficiency (WUEBNPP) and plant nitrogen uptake (NUPBNPP). However, litter addition suppressed the aboveground biomass (AB) responses to nitrogen addition under ambient precipitation conditions by affecting soil moisture. In conclusion, our results suggest that ecosystem responses to short‐term increases in growing‐season precipitation and nitrogen deposition could be mediated by the increased litter input caused by climate change.

Plant production and nitrogen accumulation above- and belowground in low and tall birch tundra communities: the influence of snow and litter

A vegetation transition to taller and denser deciduous shrub tundra is currently occurring in many locations across the low Arctic, and is associated with climate change. Here, we investigated if deeper snow is a mechanism for enhanced shrub growth. To determine if a moderate and climatically realistic increase in snow depth can enhance shrub productivity, we compared growth responses between ambient and experimentally deepened snow plots in low birch hummock tundra. To determine the potential influence of factors other than deepened snow that are associated with taller, denser shrubs, we also compared shrub growth between low birch hummock and tall birch-dominated tundra. Neither deciduous shrub above- nor belowground production nor nitrogen accumulation was enhanced by deepened snow. However, deciduous birch shrub new shoot production was 23× larger and total vascular shoot to belowground biomass ratios were higher in the tall birch tundra than the birch hummock (~0.7 and ~0.4, respectively), indicating that the combination of deeper snow together with other internal feedbacks greatly enhanced birch growth. Together, our results strongly suggest that the much larger litter production in tall birch ecosystems is an important internal feedback that may or may not interact with deeper snow to promote birch growth in tall shrub tundra.

Switchgrass ecotypes alter microbial contribution to deep-soil C

Abstract. Switchgrass (Panicum virgatum L.) is a C4, perennial grass that is being developed as a bioenergy crop for the United States. While aboveground biomass production is well documented for switchgrass ecotypes (lowland, upland), little is known about the impact of plant belowground productivity on microbial communities down deep in the soil profiles. Microbial dynamics in deeper soils are likely to exert considerable control on ecosystem services, including C and nutrient cycles, due to their involvement in such processes as soil formation and ecosystem biogeochemistry. Differences in root biomass and rooting characteristics of switchgrass ecotypes could lead to distinct differences in belowground microbial biomass and microbial community composition. We quantified root abundance and root architecture and the associated microbial abundance, composition, and rhizodeposit C uptake for two switchgrass ecotypes using stable-isotope probing of microbial phospholipid fatty acids (PLFAs) after 13CO2 pulse–chase labeling. Kanlow, a lowland ecotype with thicker roots, had greater plant biomass above- and belowground (g m−2), greater root mass density (mg cm−3), and lower specific root length (m g−1) compared to Summer, an upland ecotype with finer root architecture. The relative abundance of bacterial biomarkers dominated microbial PLFA profiles for soils under both Kanlow and Summer (55.4 and 53.5 %, respectively; P = 0.0367), with differences attributable to a greater relative abundance of Gram-negative bacteria in soils under Kanlow (18.1 %) compared to soils under Summer (16.3 %; P = 0.0455). The two ecotypes also had distinctly different microbial communities process rhizodeposit C: greater relative atom % 13C excess in Gram-negative bacteria (44.1 ± 2.3 %) under the thicker roots of Kanlow and greater relative atom % 13C excess in saprotrophic fungi under the thinner roots of Summer (48.5 ± 2.2 %). For bioenergy production systems, variation between switchgrass ecotypes could alter microbial communities and impact C sequestration and storage as well as potentially other belowground processes.

Belowground plant biomass allocation in tundra ecosystems and its relationship with temperature

Climate warming is known to increase the aboveground productivity of tundra ecosystems. Recently, belowground biomass is receiving more attention, but the effects of climate warming on belowground productivity remain unclear. Enhanced understanding of the belowground component of the tundra is important in the context of climate warming, since most carbon is sequestered belowground in these ecosystems. In this study we synthesized published tundra belowground biomass data from 36 field studies spanning a mean annual temperature (MAT) gradient from −20 °C to 0 °C across the tundra biome, and determined the relationships between different plant biomass pools and MAT. Our results show that the plant community biomass–temperature relationships are significantly different between above and belowground. Aboveground biomass clearly increased with MAT, whereas total belowground biomass and fine root biomass did not show a significant increase over the broad MAT gradient. Our results suggest that biomass allocation of tundra vegetation shifts towards aboveground in warmer conditions, which could impact on the carbon cycling in tundra ecosystems through altered litter input and distribution in the soil, as well as possible changes in root turnover.

Air humidity as key determinant of morphogenesis and productivity of the rare temperate woodland fern Polystichum braunii

(1) Most ferns are restricted to moist and shady habitats, but it is not known whether soil moisture or atmospheric water status are decisive limiting factors, or if both are equally important. (2) Using the rare temperate woodland fern Polystichum braunii, we conducted a three-factorial climate chamber experiment (soil moisture (SM)×air humidity (RH)×air temperature (T)) to test the hypotheses that: (i) atmospheric water status (RH) exerts a similarly large influence on the fern's biology as soil moisture, and (ii) both a reduction in RH and an increase in air temperature reduce vigour and growth. (3) Nine of 11 morphological, physiological and growth-related traits were significantly influenced by an increase in RH from 65% to 95%, leading to higher leaf conductance, increased above- and belowground productivity, higher fertility, more epidermal trichomes and fewer leaf deformities under high air humidity. In contrast, soil moisture variation (from 66% to 70% in the moist to ca. 42% in the dry treatment) influenced only one trait (specific leaf area), and temperature variation (15°C versus 19°C during daytime) only three traits (leaf conductance, root/shoot ratio, specific leaf area); RH was the only factor affecting productivity. (4) This study is the first experimental proof for a soil moisture-independent air humidity effect on the growth of terrestrial woodland ferns. P.braunii appears to be an air humidity hygrophyte that, whithin the range of realistic environmental conditions set in this study, suffers more from a reduction in RH than in soil moisture. A climate warming-related increase in summer temperatures, however, seems not to directly threaten this endangered species.

The ecological importance of the dwarf seagrass Zostera japonica in intertidal areas on the southern coast of Korea

The intertidal seagrass Zostera japonica, which is distributed in the intertidal and shallow subtidal zones, is exposed to nutrients from over-enriched land-based discharge and storm water runoff before they can be washed out to sea. Despite its ecological importance, only a few studies have examined the ecology and physiology of Z. japonica in northeast Asia. In this study, we investigated the productivity and tissue nutrient contents of above- and below-ground tissues to evaluate the potential role of Z. japonica in carbon capture and as a nutrient sink. The average total, above-, and below-ground productivity per shoot was 0.56, 0.34, and 0.21 mg DW shoot-1 day-1, respectively. Annual leaf production was 1.5 times higher than annual below-ground production. Estimated annual whole-plant carbon, nitrogen, and phosphorus incorporation based on shoot production and tissue nutrient contents was 312.8 g C m-2 y-1, 25.7 g N m-2 y-1, and 1.6 g P m-2 y-1, respectively. These values were equivalent to 7.8 × 103 kg C y-1, 6.4 × 102 kg N y-1, and 40 kg P y-1 for all Z. japonica beds in Geoje Bay. This suggests that Z. japonica meadows can incorporate a considerable amount of carbon, nitrogen, and phosphorus in the intertidal zone. High N:P ratios of above- and below-ground tissues suggest that Z. japonica growth is probably limited by phosphorus availability in the study area.

Comparison of ingrowth core and sequential soil core methods for estimating belowground net primary production in grass–clover swards

AbstractEstimation of belowground net primary production (BNPP) is crucial for prediction of grassland soil organic carbon sequestration, but there are high coefficients of variation (CV) among methods of estimation. We compared accuracy and precision of two variations of the traditional soil core method and three of the ingrowth core method, over 2 years on grass–white clover swards in Germany. The ingrowth core method (5‐ to 9‐week ingrowth period) provided the most accurate BNPP estimate (471 g m−2) with the highest precision (CV: 31%), whereas the two soil core approaches resulted in underestimation and high error. Comparing results with other grassland studies, we found that reliability of the ingrowth core method was influenced by ingrowth period and sward rooting pattern related to grass phenological stages, while the precision was determined by ingrowth period and grassland productivity. We therefore recommend using the ingrowth core method for managed grasslands where belowground productivity is relatively high and installation disturbance is likely to be negligible. Using a 6‐ to 8‐week ingrowth period, the method delivers reliable and feasible BNPP estimates for temperate managed grasslands which can be applied to long‐term soil carbon budget simulation. Results from our work and other studies also indicated that standing root biomass masks seasonal pattern of rooting due to synchrony between root birth and death. The soil core method is likely to lead to underestimates and higher errors than the ingrowth core methods and thus should be avoided.

Effect of nutrient additions and site hydrology on belowground production and root nutrient contents in two wet grasslands

Belowground production can be a significant part of total plant biomass and represents a significant pool of carbon and other nutrients. Changes in root biomass and nutrient contents can influence root decomposition and nutrient turnover rates, thereby impacting ecosystem processes and functions. In-growth core bags were used in a long-term nutrient addition study to determine net belowground primary production (NBPP), root nutrient (C, N and P) percentages and stoichiometry under different nutrient treatments in two wet grasslands with either mineral or organic soil. It was hypothesized that fertilization will lead to reduced NBPP, but increased root nutrient contents, and that these differences will be greater over time. The fertilizer was added in two half doses in a growing season over seven years with NBPP and the nutrient measures sampled in years 2, 3, 5 and 7. Between-year differences in the measured parameters were tested by repeated measures ANOVA, while one-way ANOVAs were run to compare between-treatment differences in each year within each site. Linear regressions were run to relate NBPP, root nutrient content and the stoichiometric ratios to changes in site hydrology. NBPP and root nutrient contents changed over time, especially in the organic soil grassland, but were largely unaffected by the nutrient additions. Site hydrology, sometimes interacting with the nutrient treatments, appeared to be the more important factor. Prolonged flooding of the two grasslands in the latter two years of measurements led to significantly reduced NBPP, and N and P% especially in the organic soil site. The response of wet grassland belowground structures to changing hydrologic conditions, in tandem with nutrient addition, may be useful in developing management plans to deal with the expected effect of climate change on water availability at the local and regional scales.

The hidden season: growing season is 50% longer below than above ground along an arctic elevation gradient.

There is compelling evidence from experiments and observations that climate warming prolongs the growing season in arctic regions. Until now, the start, peak, and end of the growing season, which are used to model influences of vegetation on biogeochemical cycles, were commonly quantified using above-ground phenological data. Yet, over 80% of the plant biomass in arctic regions can be below ground, and the timing of root growth affects biogeochemical processes by influencing plant water and nutrient uptake, soil carbon input and microbial activity. We measured timing of above- and below-ground production in three plant communities along an arctic elevation gradient over two growing seasons. Below-ground production peaked later in the season and was more temporally uniform than above-ground production. Most importantly, the growing season continued c. 50% longer below than above ground. Our results strongly suggest that traditional above-ground estimates of phenology in arctic regions, including remotely sensed information, are not as complete a representation of whole-plant production intensity or duration, as studies that include root phenology. We therefore argue for explicit consideration of root phenology in studies of carbon and nutrient cycling, in terrestrial biosphere models, and scenarios of how arctic ecosystems will respond to climate warming.

Quantifying above‐ and belowground biomass carbon loss with forest conversion in tropical lowlands of Sumatra (Indonesia)

Natural forests in South-East Asia have been extensively converted into other land-use systems in the past decades and still show high deforestation rates. Historically, lowland forests have been converted into rubber forests, but more recently, the dominant conversion is into oil palm plantations. While it is expected that the large-scale conversion has strong effects on the carbon cycle, detailed studies quantifying carbon pools and total net primary production (NPPtotal ) in above- and belowground tree biomass in land-use systems replacing rainforest (incl. oil palm plantations) are rare so far. We measured above- and belowground carbon pools in tree biomass together with NPPtotal in natural old-growth forests, 'jungle rubber' agroforests under natural tree cover, and rubber and oil palm monocultures in Sumatra. In total, 32 stands (eight plot replicates per land-use system) were studied in two different regions. Total tree biomass in the natural forest (mean: 384Mgha(-1) ) was more than two times higher than in jungle rubber stands (147Mgha(-1) ) and >four times higher than in monoculture rubber and oil palm plantations (78 and 50Mgha(-1) ). NPPtotal was higher in the natural forest (24Mgha(-1) yr(-1) ) than in the rubber systems (20 and 15Mgha(-1) yr(-1) ), but was highest in the oil palm system (33Mgha(-1) yr(-1) ) due to very high fruit production (15-20Mgha(-1) yr(-1) ). NPPtotal was dominated in all systems by aboveground production, but belowground productivity was significantly higher in the natural forest and jungle rubber than in plantations. We conclude that conversion of natural lowland forest into different agricultural systems leads to a strong reduction not only in the biomass carbon pool (up to 166MgCha(-1) ) but also in carbon sequestration as carbon residence time (i.e. biomass-C:NPP-C) was 3-10 times higher in the natural forest than in rubber and oil palm plantations.

Effects of Potassium Sulfate on Adaptability of Sugarcane Cultivars to Salt Stress under Hydroponic Conditions

The effect of potassium sulfate (K2SO4) on adaptability of sugarcane to sodium chloride (NaCl) stress was investigated under hydroponic conditions. Two sugarcane cultivars, differing in salinity tolerance, were grown in half strength Johnson's solution at 80 mM NaCl with 0, 2.5 and 5.0 mM potassium (K) as K2SO4. Salinity disturbed above and below-ground dry matter production in both sugarcane cultivars. However, salt sensitive cultivar showed more reduction in shoot dry matter and higher root:shoot ratio compare to the salt tolerant cultivar under. Application of K significantly (p < 0.05) improved dry matter production in both sugarcane cultivars. The concentration of Na was markedly increased with increasing salinity; however, the application of K reduced its uptake, accumulation and distribution in plant tissues. Salinity induced reduction in K concentration, K-uptake, K utilization efficiency (KUE) and K:Na ratio in both sugarcane cultivars was significantly improved with the addition of K to the saline growth medium.

The influence of boreal tree species mixtures on ecosystem carbon storage and fluxes

Plant species mixtures are often seen as being able to achieve higher productivity and carbon (C) sequestration than their single-species counterparts, but it is unclear whether this is true in natural forests. Here, we investigated whether naturally-regenerated mixtures of common North American boreal tree species were more productive and stored more C than single-species stands. We also examined how closely the different C pools and fluxes were interrelated and whether these relationships varied with species composition. Single- and mixed-species stands of trembling aspen, black spruce and jack pine on mesic sites were selected in two regions of the Canadian boreal forest to assess aboveground and belowground productivity and C storage. Although previous studies conducted in these stands found synergistic effects of tree species mixtures on specific C pools and fluxes, such as higher organic layer C stocks and higher fine root productivity in some mixtures, no effects were detected on combined C pools or fluxes at the ecosystem level in the current study. Aspen abundance was linked with higher aboveground tree productivity, higher aboveground living biomass and higher soil heterotrophic respiration, indicating that aspen acts as a key driver of ecosystem C storage and fluxes in these natural forest ecosystems, more so than species richness. However, our results do not rule out the possibility of increased productivity and C storage in mixed stands under environmental conditions or stand developmental stages that are different from the ones studied here. Furthermore, when the entire forest ecosystem is considered (not only tree parts), synergistic effects of tree species mixtures may be more difficult to observe because the beneficial effect of species mixing on one specific C pool may be counterbalanced by a negative effect on another pool.

Rapid Root Decomposition Decouples Root Length from Increased Soil C Following Grassland Invasion

Plant invasion often increases stand biomass, but higher tissue quality (for example, less lignin and more nutrients) in invasive species might accelerate litter decomposition. This mechanism may minimize increases in soil carbon (C) sequestration despite higher production. Our knowledge about invasion and tissue quality is based on shoots, but roots contribute 50–90% of biomass in vegetation types such as semiarid grasslands. Here we investigate root decomposition rates and tissue quality in the widespread invasive grass Agropyron cristatum, which doubles root mass but not soil C in the Great Plains of North America. Root length was significantly greater beneath Agropyron than native grassland 7 years after minirhizotron installation. However, CO2 evolution from decomposing roots was twice as much for Agropyron roots as for native grass roots (P < 0.05). CO2 evolution from decomposing native grass roots was not significantly different from controls with no root tissue added, suggesting that Agropyron invasion can convert grassland soil to a source of CO2 to the atmosphere. Rapid root decomposition was associated with significantly lower lignin content in Agropyron roots than native grass roots, although root N and lignin:N ratios did not differ. We present the first report of root decomposition rates associated with plant invasion. Increases in root length were accompanied by increased root decomposition rates of low-lignin tissue, such that invasion-driven enhanced productivity did not enhance soil C sequestration. Among-species differences in root tissue quality and decomposition rates could influence soil C dynamics during invasions of systems dominated by belowground production, such as tundra, boreal forests, and semiarid grassland.

Impact of nitrogen deposition on forest and lake food webs in nitrogen-limited environments.

Increased reactive nitrogen (Nr ) deposition has raised the amount of N available to organisms and has greatly altered the transfer of energy through food webs, with major consequences for trophic dynamics. The aim of this review was to: (i) clarify the direct and indirect effects of Nr deposition on forest and lake food webs in N-limited biomes, (ii) compare and contrast how aquatic and terrestrial systems respond to increased Nr deposition, and (iii) identify how the nutrient pathways within and between ecosystems change in response to Nr deposition. We present that Nr deposition releases primary producers from N limitation in both forest and lake ecosystems and raises plants' N content which in turn benefits herbivores with high N requirements. Such trophic effects are coupled with a general decrease in biodiversity caused by different N-use efficiencies; slow-growing species with low rates of N turnover are replaced by fast-growing species with high rates of N turnover. In contrast, Nr deposition diminishes below-ground production in forests, due to a range of mechanisms that reduce microbial biomass, and decreases lake benthic productivity by switching herbivore growth from N to phosphorus (P) limitation, and by intensifying P limitation of benthic fish. The flow of nutrients between ecosystems is expected to change with increasing Nr deposition. Due to higher litter production and more intense precipitation, more terrestrial matter will enter lakes. This will benefit bacteria and will in turn boost the microbial food web. Additionally, Nr deposition promotes emergent insects, which subsidize the terrestrial food web as prey for insectivores or by dying and decomposing on land. So far, most studies have examined Nr -deposition effects on the food web base, whereas our review highlights that changes at the base of food webs substantially impact higher trophic levels and therefore food web structure and functioning.

Coastal wetland response to sea level rise in Connecticut and New York

The persistence of salt marshes in the landscape depends on their ability to accommodate rising sea level and minimize additional flooding stress. We use sediment cores and water level data from 14 marshes in Connecticut and New York to evaluate how marsh accretion, mineral and organic accumulation, carbon storage, and hydroperiod have changed from 1900 to 2012. We observe a regional acceleration in marsh accretion beginning around 1940, although marsh accretion did not reach parity with sea level rise for several additional decades. Despite a rise in marsh accretion from 1.0 mm yr−1 circa 1900 to 3.6 mm yr−1 at present, the marsh surface has lost elevation relative to tidal datums. Declining relative elevations have led to increased tidal flooding, particularly in high marsh settings. As flooding increased, organic matter accumulation accelerated at all marshes. Accelerating mineral deposition was only observed in areas of short-form Spartina alterniflora. Mineral and organic sediment accumulation co-limit accretion, but organic accumulation was the stronger limiting factor, suggesting that marsh response to sea level rise in the region is sensitive to processes affecting rates of belowground production and decomposition. Marsh carbon storage over the period of study averaged 84 g C m−2 yr−1, increasing as accretion accelerated. If marshes remain spatially intact as sea levels rise, these results suggest that marshes have the capacity to become even greater C sinks.

Seagrass metabolism across a productivity gradient using the eddy covariance, Eulerian control volume, and biomass addition techniques

AbstractThe net ecosystem metabolism of the seagrass Thalassia testudinum was studied across a nutrient and productivity gradient in Florida Bay, Florida, using the Eulerian control volume, eddy covariance, and biomass addition techniques. In situ oxygen fluxes were determined by a triangular Eulerian control volume with sides 250 m long and by eddy covariance instrumentation at its center. The biomass addition technique evaluated the aboveground seagrass productivity through the net biomass added. The spatial and temporal resolutions, accuracies, and applicability of each method were compared. The eddy covariance technique better resolved the short‐term flux rates and the productivity gradient across the bay, which was consistent with the long‐term measurements from the biomass addition technique. The net primary production rates from the biomass addition technique, which were expected to show greater autotrophy due to the exclusion of sediment metabolism and belowground production, were 71, 53, and 30 mmol carbon m−2 d−1 at 3 sites across the bay. The net ecosystem metabolism was 35, 25, and 11 mmol oxygen m−2 d−1 from the eddy covariance technique and 10, −103, and 14 mmol oxygen m−2 d−1 from the Eulerian control volume across the same sites, respectively. The low‐flow conditions in the shallow bays allowed for periodic stratification and long residence times within the Eulerian control volume that likely reduced its precision. Overall, the eddy covariance technique had the highest temporal resolution while producing accurate long‐term flux rates that surpassed the capabilities of the biomass addition and Eulerian control volume techniques in these shallow coastal bays.

Do Two Graminoids, the Invasive Phalaris arundinacea and the Native Scirpus microcarpus, Have Similar Ecosystem Effects in a Wetland?

Invasive species have been documented to have widespread ecosystem impacts, but these effects are dependent on characteristics of the environment and potentially on similarity in traits between the invasive and replaced native species. We compared the ecosystem effects of two graminoid wetland species with similar traits, the highly invasive Phalaris arundinacea L. (Poaceae family) and the native Scirpus microcarpus J. Presl &amp; C. Presl. (Cyperaceae family). Both species had naturally established in monoculture patches in close proximity to each after agricultural abandonment over at least two decades ago in an Oregon, USA marsh. We compared seasonally the effects of the two species in paired patches on a broad suite of ecosystem soil responses. The two communities differed in a number of ecosystem processes and characteristics, such as belowground productivity, soil temperature, soil texture, soil pH, CH4 production, and aspects of the N cycle. However, these species‐level effects were secondary to strong controls of season and edaphic factors. We demonstrate that an invasive introduced species can have widespread ecosystem effects when compared with a relatively similar native species, but these effects may be moderate compared with natural environmental controls over ecosystem processes.

Flowering and biomass allocation in U.S. Atlantic coast Spartina alterniflora.

Salt marshes are highly productive and valuable ecosystems, providing many services on which people depend. Spartina alterniflora Loisel (Poaceae) is a foundation species that builds and maintains salt marshes. Despite this species' importance, much of its basic reproductive biology is not well understood, including flowering phenology, seed production, and the effects of flowering on growth and biomass allocation. We sought to better understand these life history traits and use that knowledge to consider how this species may be affected by climate change. We examined temporal and spatial patterns in flowering and seed production in S. alterniflora at a latitudinal scale (along the U.S. Atlantic coast), regional scale (within New England), and local scale (among subhabitats within marshes) and determined the impact of flowering on growth allocation using field and greenhouse studies. Flowering stem density did not vary along a latitudinal gradient, while at the local scale plants in the less submerged panne subhabitats produced fewer flowers and seeds than those in more frequently submerged subhabitats. We also found that a shift in biomass allocation from above to belowground was temporally related to flowering phenology. We expect that environmental change will affect seed production and that the phenological relationship with flowering will result in limitations to belowground production and thus affect marsh elevation gain. Salt marshes provide an excellent model system for exploring the interactions between plant ecology and ecosystem functioning, enabling better predictions of climate change impacts.