Belowground Primary Production Research Articles

Ecosystem functions in different physiognomies of Cerrado through the Rapid Ecosystem Function Assessment (REFA).

The assessment of ecosystem functions in Cerrado is important to implement practices of conservation. Recently, a 'rapid ecosystem function assessment' (REFA) for measuring ecosystem functions has been proposed and tested as a suitable method. Thus, this study aimed to assess the proxies of ecosystem functions of three physiognomies of Cerrado through REFA. This method was applied in three different preserved physiognomies of Cerrado from Northeastern, Brazil, namely: Campo Graminoide (CG), Cerrado Stricto Sensu (CSS), and Cerradão (CD). All proxies for the selected ecosystem functions differed between sites and seasons. The above- and belowground primary productivity and microbial biomass C were higher in CD than in CSS and CG. The above- and belowground secondary productivity and decomposition were higher and similar in CD and CSS as compared to CG. The principal component analysis explained 89.8% of the data variation and clustered the majority of ecosystem functions with CD, in both seasons and CSS in the wet season. The proxies of ecosystem functions measured through REFA showed differences between the physiognomies of Cerrado. Since each physiognomy of Cerrado presents different plant richness and diversity, and soil conditions, these characteristics contribute to influencing multiple ecosystem functions.

Carbon balance and soil carbon input in a poplar short rotation coppice plantation as affected by nitrogen and wood ash application

The increasing importance of short rotation coppice (SRC) plantations for bioenergy production makes it crucial to evaluate their carbon (C) sink potential and to understand which sustainable practices could increase productivity and C sequestration. This study examined the combined effect of woody ash and nitrogen (N) fertilization on the productivity, net C balance (NECB) and soil C sink capacity of a poplar SRC plantation established on a former arable land in northern Italy. Above- (ANPP) and below-ground (BNPP) primary productivity, including both root litter and rhizodeposition (Croot litter), were estimated by a combination of inventory methods, soil respiration measurements and C budgeting approaches. NECB was estimated as changes in both plant and soil C pools, and the portion of soil organic carbon (SOC) derived from poplar leaf and root litter was estimated using a combination of in-growth cores and isotopic measurements. Nitrogen application at 100 kg ha−1 increased ANPP in terms of C accumulation only in the first year, while NECB was not affected by treatments and was 9.96 Mg C ha−1 year−1 on average. Irrespective of the treatment, the plantation accumulated on average 0.7 Mg C ha−1 year−1 of SOC and the poplar-derived soil C input was 3.0 Mg ha−1 year−1. Positive NECB shows that the studied SRC resulted in an important C sink even in the first years after the establishment. However, long-term studies are needed to better assess the effect of N and ash application on C and nutrient cycles over more than one rotation period.

Spatio‐temporal dynamics and biomass of Cymodocea nodosa in Bekalta (Tunisia, Southern Mediterranean Sea)

AbstractLeaf growth, biomass and production of Cymodocea nodosa were measured from October 2006 to September 2007 in Monastir Bay (Tunisia). Shoot density showed a clear seasonal pattern, increasing during spring and summer and decreasing during fall and winter. Monthly mean shoot density ranged between 633 ± 48 and 704 ± 48 shoots∙m−2. The monthly average total biomass ranged between 560 ± 37 and 646 ± 32 g dry weight (DW)∙m−2. Total biomass varied significantly among stations and sampling times but did not show seasonal variation. Leaf plastochrone intervals varied seasonally, with an annual average of 28–30 days. Leaf productivity was highest in August (2.61 g DW∙m−2∙day−1) and lowest in February (0.35 g DW∙m−2∙day−1). Annual belowground primary production varied from 263 to 311 g DW∙m−2∙year−1. Annual leaf production was approximately equal for all the stations (from 264 to 289 g DW∙m−2∙year−1). Variability in water temperature, air temperature and salinity explained the annual variability in biological characteristics. Changes in belowground and total biomass were not correlated with seasonal variability in the environmental parameters monitored. Additionally, a literature review was conducted of C. nodosa features at other Mediterranean sites, encompassing 30 studies from 1985 to 2014.

A Landscape-Scale Assessment of Above- and Belowground Primary Production in Coastal Wetlands: Implications for Climate Change-Induced Community Shifts

Above- and belowground production in coastal wetlands are important contributors to carbon accumulation and ecosystem sustainability. As sea level rises, we can expect shifts to more salt-tolerant communities, which may alter these ecosystem functions and services. Although the direct influence of salinity on species-level primary production has been documented, we lack an understanding of the landscape-level response of coastal wetlands to increasing salinity. What are the indirect effects of sea-level rise, i.e., how does primary production vary across a landscape gradient of increasing salinity that incorporates changes in wetland type? This is the first study to measure both above- and belowground production in four wetland types that span an entire coastal gradient from fresh to saline wetlands. We hypothesized that increasing salinity would limit rates of primary production, and saline marshes would have lower rates of above- and belowground production than fresher marshes. However, along the Northern Gulf of Mexico Coast in Louisiana, USA, we found that aboveground production was highest in brackish marshes, compared with fresh, intermediate, and saline marshes, and belowground production was similar among all wetland types along the salinity gradient. Multiple regression analysis indicated that salinity was the only significant predictor of production, and its influence was dependent upon wetland type. We concluded that (1) salinity had a negative effect on production within wetland type, and this relationship was strongest in the fresh marsh (0–2 PSU) and (2) along the overall landscape gradient, production was maintained by mechanisms at the scale of wetland type, which were likely related to plant energetics. Regardless of wetland type, we found that belowground production was significantly greater than aboveground production. Additionally, inter-annual variation, associated with severe drought conditions, was observed exclusively for belowground production, which may be a more sensitive indicator of ecosystem health than aboveground production.

Ecological processes and biogeochemical cycling in salt marshes: synthesis of studies in the Bahía Blanca estuary (Argentina)

Here we offer an integrative review of biogeochemical cycling of carbon, nitrogen, phosphorus, and several metals in salt marshes of the Bahia Blanca Estuary, located in South America, which is a region underrepresented in the literature. The dominant species, Spartina alterniflora and Sarcocornia perennis, have low net aboveground primary productivity but play substantial and contrasting roles in the biogeochemical cycling of elements. S. perennis was more efficient at metal sequestration, whereas S. alterniflora was important in the immobilization of phosphorus. Because of the differences in net aboveground primary productivity between high and low marsh, plant position should be considered to evaluate the role of S. alterniflora on biogeochemical cycles. Some elements were also in high concentrations in belowground tissues but, based on our data, we could not accurately estimate net belowground primary productivity, a key process to evaluate elemental cycling in salt marshes. In spite of uncertainties in the estimations, the slower decomposition rates in S. alterniflora would be indicative of a higher contribution to the long-term storage of nutrients and metals within the marsh. Regardless shortcomings, our work represents a valuable tool for comparisons with salt marshes worldwide.

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

Abstract 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.

Above- and belowground biomass and nutrient pools of Spartina alterniflora (smooth cordgrass) in a South American salt marsh

In order to examine the role of position in the tidal range on biomass production and nutrient pools in Spartina alterniflora in an Argentinian estuary, we estimated productivity, the concentration of C, N and P in tissues and pools (concentration×biomass) of these elements in low (LM) and high (HM) zones. Aboveground biomass of S. alterniflora was higher in HM than in LM. Aboveground primary productivity was 106 and 439 g dry wt m−2 year−1 in LM and HM, respectively. Belowground biomass was similar in LM and HM. Belowground primary productivity was 526 and 744 g dry wt m−2 year−1 for LM and HM, respectively. Nutrient pools were higher in HM than in LM. Biomass and productivity values were low, which makes nutrient pools low. The lower values of the parameters analysed in LM than in HM indicate that position in the tidal range is an important factor in this system, possibly due to the effect of flooding. Moreover, this pattern is opposite to the general one observed in the northern hemisphere, meaning that studying marshes from different environments is worth doing. Because pools were higher in HM, this zone would be more important for nutrient input to the estuary.

Fertilization Effects on Elevation Change and Belowground Carbon Balance in a Long Island Sound Tidal Marsh

We report the results of a 5-year fertilization experiment in a central Long Island Sound salt marsh, aimed at understanding the impacts of high nutrient loads on marsh elevational processes. Fertilization with nitrogen led to some significant changes in marsh processes, specifically increases in aboveground primary production and in CO2 fluxes from the soil. However, neither nitrogen nor phosphorus fertilization led to elevation loss (relative to controls), reduced soil carbon, or a decrease in belowground primary production, all of which have been proposed as links between elevated nutrient loads and marsh drowning. Our data suggest that high nutrient levels increase gross carbon loss from the sediment, but that this is compensated for by other processes, leading to no net deleterious effect of nutrient loading on carbon storage or on marsh stability with respect to sea level rise.

Restoring Ecological Function to a Submerged Salt Marsh

Impacts of global climate change, such as sea level rise and severe drought, have altered the hydrology of coastal salt marshes resulting in submergence and subsequent degradation of ecosystem function. A potential method of rehabilitating these systems is the addition of sediment‐slurries to increase marsh surface elevation, thus ameliorating effects of excessive inundation. Although this technique is growing in popularity, the restoration of ecological function after sediment addition has received little attention. To determine if sediment subsidized salt marshes are functionally equivalent to natural marshes, we examined above‐ and belowground primary production in replicated restored marshes receiving four levels of sediment addition (29–42 cm North American Vertical Datum of 1988 [NAVD 88]) and in degraded and natural ambient marshes (4–22 cm NAVD 88). Moderate intensities of sediment‐slurry addition, resulting in elevations at the mid to high intertidal zone (29–36 cm NAVD 88), restored ecological function to degraded salt marshes. Sediment additions significantly decreased flood duration and frequency and increased bulk density, resulting in greater soil drainage and redox potential and significantly lower phytotoxic sulfide concentrations. However, ecological function in the restored salt marsh showed a sediment addition threshold that was characterized by a decline in primary productivity in areas of excessive sediment addition and high elevation (>36 cm NAVD 88). Hence, the addition of intermediate levels of sediment to submerging salt marshes increased marsh surface elevation, ameliorated impacts of prolonged inundation, and increased primary productivity. However, too much sediment resulted in diminished ecological function that was equivalent to the submerged or degraded system.

Productivity and nutrient cycling in salt marshes: Contribution to ecosystem health

Abstract This study aimed to assess the contribution of different salt marsh halophytes ( Spartina maritima , Scirpus maritimus , Halimione portulacoides, Sarcocornia fruticosa, and Sarcocornia perennis ) to nutrient cycling and sequestration in warm-temperate salt marshes. Carbon, nitrogen and phosphorus concentration in plant organs and rhizosediment, as well as plant biomass were monitored every two months during one year. Results show that the C retained in the rhizosediment does not seem to be species or site specific. However, some halophytes seem to have a higher contribution to retain C from external sources, namely S. perennis and S . maritima . Regarding N, halophytes colonizing the upper and middle marsh areas had the highest NBPP (net belowground primary production) as well as the retention of N in the rhizosediment. Yet, excluding S. maritimus , all halophytes seem to contribute to the retention of N from external sources. The P retained in the rhizosediment does not seem to be species or site specific. Still, only S. maritima colonizing the lower marsh areas, which also had comparatively lower NBPP, seem to have a higher contribution to retain P from external sources. Additionally, it seems that there is no relation between plants sequestration capacity for nutrients and plant photosynthetic pathway. This work shows that nutrient cycling and accumulation processes by salt marsh halophytes contribute to reduce eutrophication (N and P retention) and also to reduce atmospheric CO 2 (C retention), highlighting salt marsh ecosystems services and the crucial role of halophytes in maintaining ecosystem functions and health.

Biodiversity and trophic structure of soil nematode communities are altered following woody plant invasion of grassland

Woody plant encroachment is an important land cover change in dryland ecosystems throughout the world, and frequently alters above and belowground primary productivity, hydrology, and soil microbial biomass and activity. However, there is little known regarding the impact of this geographically widespread vegetation change on the biodiversity and trophic structure of soil fauna. Nematodes represent a major component of the soil microfauna whose community composition and trophic structure could be strongly influenced by the changes in ecosystem structure and function that accompany woody encroachment. Our purpose was to characterize nematode community composition and trophic structure along a grassland to woodland chronosequence in the Rio Grande Plains of southern Texas. Research was conducted at the La Copita Research Area where woody encroachment has been documented previously. Soil cores(0-10 cm) were collected in fall 2006 and spring 2007 from remnant grasslands and woody plant stands ranging in age from 15 to 86 years, and nematodes were extracted by sugar centrifugation. Neither nematode densities (3200-13,800 individuals kg -1 soil) nor family richness (15-19 families 100 g -1 soil) were altered by woody encroachment. However, family evenness decreased dramatically in woody stands >30 years old. This change in evenness corresponded to modifications in the trophic structure of nematode communities following grassland to woodland conversion. Although root biomass was 2-5 x greater in wooded areas, root-parasitic nematodes decreased from 40% of all nematodes in grasslands to <10% in the older wooded areas, suggesting the quality (C:N or biochemical defenses) of woody plant root tissue could be limiting root-parasites. In contrast, bacterivores increased from 30% of nematodes in grasslands to 70-80% in older woody patches. This large increase in bacterivores may be a response to the 1.5-2.5x increase in soil microbial biomass (bacteria + fungi) following woody encroachment. Therefore, while energy flow through grassland nematode communities appears to be distributed nearly equally among herbivory, fungivory and bacterivory, the energy flow through nematode communities in wooded areas appears to be based primarily on bacterivory. We speculate that these shifts in nematode community composition and trophic structure could have important implications for ecosystem patterns and processes. First, the low abundance of root-parasitic nematodes (and presumably root herbivory) under woody plants may be one mechanism by which woody plants are able to establish and compete effectively with grasses during succession from grassland to woodland. Second, the large increase in bacterivores following woody encroachment likely accelerates microbial turnover and the mineralization of N, thereby providing a feedback that enables the persistence of N-rich woody plant communities.

Conservation of nitrogen increases with precipitation across a major grassland gradient in the Central Great Plains of North America

Regional analyses and biogeochemical models predict that ecosystem N pools and N cycling rates must increase from the semi-arid shortgrass steppe to the sub-humid tallgrass prairie of the Central Great Plains, yet few field data exist to evaluate these predictions. In this paper, we measured rates of net N mineralization, N in above- and belowground primary production, total soil organic matter N pools, soil inorganic N pools and capture in resin bags, decomposition rates, foliar (15)N, and N use efficiency (NUE) across a precipitation gradient. We found that net N mineralization did not increase across the gradient, despite more N generally being found in plant production, suggesting higher N uptake, in the wetter areas. NUE of plants increased with precipitation, and delta(15)N foliar values and resin-captured N in soils decreased, all of which are consistent with the hypothesis that N cycling is tighter at the wet end of the gradient. Litter decomposition appeared to play a role in maintaining this regional N cycling trend: litter decomposed more slowly and released less N at the wet end of the gradient. These results suggest that immobilization of N within the plant-soil system increases from semi-arid shortgrass steppe to sub-humid tallgrass prairie. Despite the fact that N pools increase along a bio-climatic gradient from shortgrass steppe to mixed grass and tallgrass prairie, this element becomes relatively more limiting and is therefore more tightly conserved at the wettest end of the gradient. Similar to findings from forested systems, our results suggest that grassland N cycling becomes more open to N loss with increasing aridity.

Towards a predictive understanding of belowground process responses to climate change: have we moved any closer?

Summary 1. Belowground processes, including root production and exudation, microbial activity and community dynamics, and biogeochemical cycling interact to help regulate climate change. Feedbacks associated with these processes, such as warming-enhanced decomposition rates, give rise to major uncertainties in predictions of future climate. 2. Uncertainties associated with these processes are more likely to be reduced if two key challenges can be met: increasing interdisciplinarity among researchers, and measuring belowground ecosystem structure and function at relevant spatial and temporal scales. For instance, recognizing the relationship between belowground primary production and soil respiration enhances modelling of global-scale C cycle temperature responses. At the opposite end of the spectrum, applying genomic techniques at the scale of microns improves mechanistic understanding of root‐microbe interactions. 3. Progress has been made in understanding interactions of belowground processes with climate change, although challenges remain. We highlight some of these advances and provide directions for key research needs in this Special Feature of Functional Ecology, which results from a symposium that was convened at the Soil Science Society of America National Meeting in November, 2006.

Assessing nitrogen fluxes from roots to soil associated to rhizodeposition by apple (Malus domestica) trees

The mass transfer from root to soil by means of rhizodeposition has been studied in grasses and forest trees, but its role in fruit trees is still unknown. In this study, N fluxes from roots to soil were estimated by applying a 15N mass balance technique to the soil–tree system. Apple (Malus domestica) trees were pre-labelled with 15N and then grown outdoors in 40 L pots for one vegetative season in (1) a coarse-textured, low organic matter soil, (2) a coarse-textured, high organic matter soil, and (3) a fine-textured, high organic matter soil. At tree harvest the 15N abundance of the soils was higher than at transplanting, but the total amount of 15N present in the tree–soil system was similar at transplanting and tree harvest. The soils had a strong effect on N fluxes from and to the soil. In the fine-textured soil, 11% of the total plant-derived nitrogen was transferred to the soil, compared with 2–5% in the two coarse-textured soils. Rhizodeposition was higher in the fine soil (18% of the primary production) than in the coarse-textured soils, whereas higher soil organic matter depressed rhizodeposition. Nitrogen uptake was almost double in the coarse-textured, high organic matter soil versus the other soils. Our results indicate that belowground primary productivity is significantly underestimated if based on root production data only. Rhizodeposition represents a major process, whose role should not be underestimated in carbon and nitrogen cycles in orchard ecosystems.

Aboveground and belowground productivity ofSpartina alterniflora (Smooth Cordgrass) in natural and created Louisiana salt marshes

In Louisiana, salt marshes are being created in an effort to offset the large loss of such habitat that has occurred over the last 50 yr. Primary productivity is an important function and indicator of success for salt marsh creation and restoration projects. The aim of this study was to determine whether the aboveground and belowground productivity of the dominant salt marsh grassSpartina alterniflora in created marshes in southwest Louisiana began to approximate productivity levels in natural marshes, over time. Net annual aboveground primary productivity (NAPP) was measured by a harvest technique, while the ingrowth core method was used to estimate net annual belowground primary productivity (NBPP). NAPP levels were similar to those found in other, Louisiana salt marshes, while NBPP levels were similar to or higher than the reported range forS. alterniflora studied along the Atlantic and Gulf of Mexico coasts. NAPP tended to decrease as the created marshes aged, but the levels in the oldest, 19 year old, created marsh were still well above values measured in the, natural marshes. It was estimated that it would take 35 yr after marsh creation for NAPP in the created marshes to become equivalent to that in natural marshes. NBPP in the created marshes became equivalent to levels found in the natural marshes after 6–8 yr, but then belowground production increased with marsh age, reaching an asymptote that surpassed natural marsh levels. Equivalency in primary productivity has not been reached in these marshes. Elevation also affected productivity, as higher elevational sites with greater topographic heterogeneity had significantly lower aboveground and belowground biomass levels than those with elevations closer to mean sea level. This underscores the need to construct marshes so that their mean elevation and degree of topographic heterogeneity are similar to natural marshes.

Landscape versus ungulate control of gross mineralization and gross nitrification in semi-arid grasslands of Yellowstone National Park

Grazers have marked effects on decomposition and N cycling processes, generally resulting in increased net N mineralization. Within landscapes, topographic and edaphic gradients also affect these microbial processes. The objective of this study was to evaluate the effects of grazers on N cycling processes in a landscape context that encompassed a wide range of environmental conditions in order to increase our mechanistic understanding of these processes and provide a stronger basis for management and assessment of grassland ecosystems. This study was conducted on a series of 37–41-year-old grazing exclosures on the northern winter range of Yellowstone National Park. We measured gross and net mineralization, nitrification and immobilization in grazed and ungrazed plots in upland and bottomland landscape positions by 15N pool dilution in a laboratory incubation with intact cores. There were no significant differences in either gross mineralization, immobilization, gross nitrification or NO3− immobilization between grazed and ungrazed plots in a paired t-test using all plots (P=0.52, P=0.32, P=0.91 and P=0.93, respectively). These results were unexpected, because previous reports indicated that grazers increased soil N dynamics, including net N mineralization, in Yellowstone grassland, and suggest that herbivore regulation of N processes may accumulate over a longer time scale than was measured in this study (24 h). Instead, we found that landscape position was the dominant factor controlling both mineralization and immobilization rates, with higher rates located at the bottoms of the slopes (32.9 and 33.4 μg N g soil−1 d−1, respectively), compared to the upland sites (4.4 and 3.2 μg N g soil−1 d−1, respectively). Gross mineralization and immobilization rates were highly correlated with soil C and N content, while gross nitrification was not. Turn over times for NH4+ and NO3− pools averaged 1.2 days for the NH4+ pool and 2.25 days for the NO3− pool. There was no apparent effect of grazers on turnover times, nor were there any significant correlations between turnover times and soil C and N pools, slope position, or soil water content. Previous modeling to understand how herbivores affect N cycling suggested that stimulation of net mineralization was most likely due to grazers suppressing immobilization by reducing belowground primary productivity and organic matter inputs to the soil. Our results do not suggest that grazers suppress immobilization. If anything, they suggest that grazers enhance this process, especially in the more mesic components of the landscape. Landscape position effects on N cycle processes were much stronger than grazer effects in this study, and appear to be driven by soil C and N contents.

Does the timing of litter inputs determine natural abundance of 13C in soil organic matter? Insights from an African tiger bush ecosystem

We investigated total primary production and natural abundance of (13)C in soil and plants in the landscape of tiger bush, Niger. Tiger bush is viewed as a natural cyclic succession of several types of vegetation (grasses, living trees and senescent vegetation) occurring over very small areas, on soils with similar chemical and physical characteristics. Under the pioneer front, production was 130gm(-2)year(-1) of which 23% came from C4 plants; under the thicket of mature trees, grass production was 190gm(-2)year(-1) (all C3 grasses) and under senescent vegetation, 40gm(-2)year(-1) of which 1.5% came from C4 plants. Total above- and belowground primary production was estimated to be 890-4880gm(-2)year(-1) of which 0.4-0.5% was contributed by C4 plants. From 29 to 45% of the soil organic carbon originated from C4 plants even though the contribution of C4 grasses to total primary production did not exceed 0.5%. We suggest that the order in which the different sources of organic matter entered the soil could lead to the overlabelling of soil organic matter with a C4 print. Because all C4 plants are grasses located in the pioneer front of tiger bush bands, their C4 organic matter enters the soil first and fixes onto clays. The C3 organic matter enters the soil several years later and is also fixed by the clays but in a lower proportion. Therefore it is less protected from microbial activity and quickly decomposes. We postulate that the repetition of this pattern over many decades (incorporation of a pure C4 material to soil, followed by the incorporation of a C3-dominated material), leads to the overaccumulation of C4 compounds on the most protective sites.

Belowground Primary Production by Carbon Isotope Decay and Long-term Root Biomass Dynamics

The isotope decay method of estimating belowground net primary production (BNPP) has the potential to overcome the assumptions and biases associated with traditional methods. Isotope loss through in situ decomposition after pulse-labeling is considered the inverse of production, and turnover times are estimated by regression to time of zero remaining isotope. Method development and estimates of production were previously published using 4 years of data, which showed a clear linear loss rate over time. A slow, distinctly different phase in isotope loss developed 5–10 years postlabeling. We assess reasons for the two-phase loss functions and the implications for estimates of BNPP and compare the isotope decay method with standard coring methods over a 13-year period. Reasons for the two-phase dynamics of carbon 14 (14C) loss could include various biological and/or methodological factors. Results suggest that 14C in soil embedded in roots as they grow, a small proportion of roots that live for a much longer time than the majority of roots, and method of separating roots from soil organic matter may influence estimates of BNPP by isotope methods. Remobilization of label in structural tissue or reuptake of label from the soil did not appear to be responsible for the slow, second phase of loss dynamics. Isotope decay produced more reliable estimates than standard coring methods. Estimates using harvest sum of increments were zero in 6 of 13 years. Thirteen years of root biomass data showed no predictable trend over winter or consistent seasonal pattern, although longer-term cycles were evident. Aboveground:belowground ratios were generally smaller during dry periods, but root biomass was not as responsive as aboveground biomass to annual precipitation.

Primary production and management of seasonally flooded prairie marshes harvested for wild hay

Experimental spring-flooded and nonflooded water regimes were applied to prairie marshes dominated by whitetop grass (Scolochloa festucacea) in Manitoba, Canada, to examine their effects on aboveground and belowground primary production and to evaluate flooding management for wild hay production. Spring flooding increased marsh aboveground and belowground production. Annual and perennial forbs comprised a greater portion of aboveground production in nonflooded marsh. Two methods (soil coring and ingrowth into mesh bags) showed earlier commencement of belowground growth and greater belowground production in flooded marsh. Higher rhizome ingrowth in flooded marsh indicated that spring flooding increased plants' ability to replenish belowground reserves. The percentage of plant production allocated aboveground was greater in flooded marsh, but shifts in allocation were small compared with the absolute increases in production caused by flooding and could not account for the observed differences in aboveground production between flooding regimes. The strong plant growth response to flooding indicates that management that conserves or mimics the natural spring-flooded hydrologic regime can increase whitetop forage production and control invasion by undesirable species. Key words: belowground, hydrologic regime, prairie marsh, primary production, rhizomes, roots.

Above- and below-ground net primary production of four barley (Hordeum vulgare L.) cultivars in western Canada

Information on above- and below-ground primary production for a wide range of agro-ecosystems is needed. The objective of this study was to quantify the shoot and root mass, shoot mass/root mass ratios, and root lengths of four barley (Hordeum vulgare L.) cultivars (Abee, Bonanza, Harrington and Samson) grown in a Black Chernozem in north-central Alberta. The cultivars were grown using a randomized complete block design with three replicates and were sampled at the tillering, stem-extension, heading, and ripening stages. Root mass and root lengths from soil cores were measured. The results showed that (1) shoot mass and root mass of Harrington and Bonanza were not different from those of Abee and Samson, but those of Abee were significantly greater than those of Samson, indicating that the below-ground input of organic matter could be a function of specific cultivar; (2) root mass increased rapidly until the heading stage, and shoot mass increased at a higher rate than roots between the heading and ripening stages, producing a widening of shoot/root ratios with time; and (3) decomposition of very small roots may have contributed to a more rapid decrease in root length than in root mass after the heading stage.Key words: Barley (Hordeum vulgare L.) cultivars, Typic Cryoboroll, root mass, root lengths, shoot/root ratio, soil organic matter