Heterogeneity Of Soil Nitrogen Research Articles

Responses of Maize (Zea mays L.) Roots to Nitrogen Heterogeneity and Intraspecific Competition: Evidence from a Pot Experiment Using the ‘Root Splitting’ Approach

A heterogeneous distribution of nutrients in the soil and the root interactions of crops coexist in agroecosystems. A ‘root splitting’ approach, i.e., splitting the root system into different nutrient compartments, was used to study nutrient heterogeneity distributions and root interactions. We evaluated root foraging behavior, individual growth, and root development mechanisms in response to soil nitrogen heterogeneity, and intraspecific competition in maize. A heterogeneous distribution of nitrogen increased the foraging precision of roots at flowering and mature stages (Foraging precision > 1), and significantly increased root biomass and surface area on the intraspecific competition and no competition on the high nitrogen side. The heterogeneous distribution had no effect on yield, total root biomass, specific root length, total surface area, or average diameter. Intraspecific competition increased inter-crop competition (RII < 0) and reduced total root biomass, total plant biomass, and the root/shoot ratio. These results inform root trait development studies and provide valid evidence for optimizing and managing fertilizer application in agroecosystems, helping to maximize crop yield and nutrient use efficiency.

Litter inputs drive patterns of soil nitrogen heterogeneity in a diverse tropical forest: Results from a litter manipulation experiment

Plant functional traits affect soil nutrient cycling in many ecosystems, but high levels of diversity make it challenging to identify their influence in tropical rainforests. Here, we used a litter manipulation experiment to demonstrate that differences in litter chemistry alone are sufficient to drive changes in soil nitrogen (N) cycling within a two-year period in a lowland tropical rainforest. Previously, we used airborne imaging spectroscopy to identify ten 0.25 ha plots on the Osa Peninsula of southwestern Costa Rica, each containing 10–20 emergent trees, with relatively high or low mean canopy N content (± 0.4 standard deviations of the landscape mean; n = 5 each). Plots with high canopy N content had higher soil inorganic N concentrations, faster net N cycling rates, and greater nitrous oxide (N2O) emissions. Because abiotic conditions were similar among the plot types, we hypothesized that litter inputs drove the formation of these high and low soil N patches. We tested this hypothesis with a reciprocal litter transplant experiment. After two years of monthly treatments, litter inputs from the high canopy N plots increased soil N availability in the low canopy N plots by 30% but had no measurable effects on net N cycling rates or N2O emissions. Surprisingly, litter inputs from the low canopy N plots increased soil N availability and net nitrification in the high canopy N plots. While somewhat counterintuitive from a canopy N perspective, these results may reflect a more nuanced effect of litter chemistry. Although low canopy N plot litter had lower N content than high canopy N plot litter, it leached relatively more and higher quality soluble carbon (C), which we speculate may have had a positive priming effect, releasing N from more recalcitrant compounds. Additionally, low canopy N plot litter supported higher rates of free-living N fixation, which could have directly increased soil N availability. Overall, our results show that tropical tree assemblages with differing foliar chemistry can directly influence soil properties through litter inputs, and that this effect may be mediated not only by litter N, but also relative C solubility and chemistry.

Strong influences of stand age and topography on post-fire understory recovery in a Chinese boreal forest

Soil resource quantity and heterogeneity as well as overstory characteristics change along with stand age after fire disturbance, imposing strong influences on post-fire understory recovery. In this study, we aimed to assess how soil resource (nitrogen quantity and heterogeneity), topographic position (aspect), overstory characteristics (basal area), and stand age affected understory characteristics (cover, richness, evenness, and composition) during boreal forest succession after fire disturbance. We collected plant community and environmental data from 76 stands aged at 4 to 203 years post-fire in the boreal forest of Northeast China. We separately tested the effects of the considered factors on the characteristics of total understory, shrubs, and herbs. Total understory cover was higher at the south-facing slopes and flat locations than at north-facing slopes. Species richness of total understory, shrubs, and herbs was higher at the flat locations and south-facing slopes than at the north-facing slopes. The cover of total understory and shrubs showed increasing trends along with stand age, soil nitrogen quantity, and overstory basal area as well as decreasing trends along with soil nitrogen heterogeneity, while the cover of herbs showed reversed trends across all the three topographic positions. Understory richness showed decreasing trends along with soil nitrogen quantity as well as increasing trends along with soil nitrogen heterogeneity and overstory basal area. Total understory evenness showed flat trends along with soil nitrogen quantity, heterogeneity, and stand age as well as decreasing trends along with overstory basal area. Understory community composition was mainly affected by topographic position, stand age, and overstory basal area. During understory recovery, community composition shifted from shade-intolerant species to shade-tolerant species. Our results highlight the importance of topography and stand age in post-fire understory recovery in boreal forests of China, mediated through availability of light and soil nutrients.

Effects of herbivore assemblage on the spatial heterogeneity of soil nitrogen in eastern Eurasian steppe

Abstract The spatial heterogeneity of soil limiting resources is one of the most important factors maintaining biodiversity and ecosystem functions. There is a general concern that herbivore grazing plays a central role in modifying soil resources heterogeneity. However, most studies have examined how large herbivores as a group affect soil heterogeneity. There is limited knowledge about how assemblages of different herbivore species may influence soil heterogeneity, and whether the herbivore assemblage effects might vary with grassland types. Here we conducted a 4‐year grazing experiment to examine the effects of different herbivore assemblages (no grazing; cattle grazing; sheep grazing; and mixed grazing of cattle and sheep) on the spatial heterogeneity of soil N availability across three types of grasslands (meadow steppe, typical steppe and desert steppe) in eastern Eurasian steppe. The results showed that all the herbivore grazing increased the heterogeneity of soil N availability in the three grasslands with different precipitation (only cattle grazing and mixed grazing of cattle and sheep in meadow steppe did not reach a statistically significant level). The consistently increased heterogeneity of soil N availability was primarily due to the effect of animal excreta addition, which weakened in drier grasslands, likely because of the slower excreta decomposition. Moreover, sheep excreta contributed more to soil N heterogeneity than that of other herbivore assemblages, and the effect was statistically significant in meadow steppe and typical steppe with relative high precipitation. Synthesis and applications. Our study indicates that sheep could have larger potential to maintain and enhance grassland heterogeneity than cattle especially in grassland ecosystems with high precipitation. We therefore suggest that managing above‐ground herbivore species is important for conserving and promoting grassland soil heterogeneity, and that the management should also take into account local environmental conditions such as precipitation.

Relationship between Pinus taiwanensis seedling regeneration and the spatial heterogeneity of soil nitrogen in Daiyun Mountain, southeast China

• Regeneration of Pinus taiwanensis seedling conforms aggregated distribution. • Soil nitrogen shows mosaic-type distribution. • Regeneration of P. taiwanensis seedling prefers habitat with high soil nitrogen. Forest soil plays vital importance on plant community pattern formation, ecosystem productivity and ecological restoration. The relationship between the regeneration of Pinus taiwanensis seedling and the heterogeneity of soil nitrogen (N) in Daiyun Mountain National Nature Reserve (DYMNNR) were determined using geo-statistics method and geographic information system (GIS) technology. The results showed the regeneration of P. taiwanensis seedlings conformed aggregated distribution. The contents of soil total nitrogen (TN), available nitrogen (AN), nitrate nitrogen (NO 3 − -N) and ammonium nitrogen (NH 4 + -N) presented moderate variability. The optimum semivariance model for TN and AN were spherical model, while those of NO 3 − -N and NH 4 + -N were exponential model. The N heterogeneity mainly dominated by spatial autocorrelation ranging from 11.06 to 21.30 m. The distribution of TN, AN, NO 3 − -N and NH 4 + -N was anisotropic, and an obvious mosaic pattern of distribution appeared with zonal and patchy characteristics. High levels of N all appeared in the central, south central, and southeast directions of the study plot, while lower levels of TN and AN distributed in the southwest and north central directions. Low levels of NO 3 − -N and NH 4 + -N were mainly located in the eastern and western directions of the study plot, respectively. Higher N resulted in better survival possibility for P. taiwanensis seedlings, which displayed obvious habitat preferences. This study provides guidance relating to soil sampling design and the practice of natural management of P. taiwanensis forest.

Root plasticity of native and invasive Great Basin species in response to soil nitrogen heterogeneity

Soil nutrients are heterogeneously distributed in natural systems. While many species respond to this heterogeneity through root system plasticity, little is known about how the magnitude of these responses may vary between native and invasive species. We quantified root morphological and physiological plasticity of co-occurring native and invasive Great Basin species in response to soil nitrogen heterogeneity and determined if trade-offs exist between these foraging responses and species relative growth rate or root system biomass. The nine study species included three perennial bunchgrasses, three perennial forbs, and three invasive perennial forbs. The plants were grown in large pots outdoors. Once a week for 4 weeks equal amounts of 15NH4 15NO3 were distributed in the soil either evenly through the soil profile, in four patches, or in two patches. All species acquired more N in patches compared to when N was applied evenly through the soil profile. None of the species increased root length density in enriched patches compared to control patches but all species increased root N uptake rate in enriched patches. There was a positive relationship between N uptake rate, relative growth rate, and root system biomass. Path analysis indicated that these positive interrelationships among traits could provide one explanation of how invasive forbs were able to capture 2 and 15-fold more N from enriched patches compared to the native grasses and forbs, respectively. Results from this pot study suggest that plant traits related to nutrient capture in heterogeneous soil environments may be positively correlated which could potentially promote size-asymmetric competition belowground and facilitate the spread of invasive species. However, field experiments with plants in different neighbor environments ultimately are needed to determine if these positive relationships among traits influence competitive ability and invader success.

Biodiversity and ecosystem functioning: reconciling the results of experimental and observational studies

Biodiversity and ecosystem functioning research has been some of the most controversial of the last decade but rapid progress has been made by deriving hypotheses from the differing view points and challenging them with appropriate experimental and analytical tests (Loreau et al. 2001). Here we address some recent criticisms of the BIODEPTH project (Thompson et al. 2005) and show that: 1. While legume species play an important role in the BIODEPTH results, patterns are not generally consistent with the multispecies sampling effect for legumes proposed by Huston & McBride (2002) as suggested in Thompson et al. (2005). 2. The BIODEPTH results are also not consistent with transient biodiversity effects. Levels of species diversity were generally maintained over the 3 years of the project (i.e. little competitive exclusion) and diversity-productivity relationships in BIODEPTH generally strengthened during the experiments.

Spatial heterogeneity of soil nitrogen in a subtropical forest in China

Spatial variability of soil total nitrogen (N), available N (KCl extractable NH4 and NO3 ), and spatial patterns of N mineralization and nitrifi- cation at a stand scale were characterized with geostatistical and univariate analysis. Two extensive soil spatial samplings were conducted in an ever- green broadleaf forest in Sichuan province, south- western China in June and August 2000. In a study area of 90 · 105 m 2 , three soil samples were collected from each 5 · 5m 2 plot (n = 378) in June and August, and were analyzed for total N and available N contents. Net N mineralization and nitrification were measured by in situ core incuba- tion and the rates were estimated based on the

Effects of soil nutrient heterogeneity on the growth of plants under the various distributions and levels of nutrients in Zoysia japonica Steud.

AbstractAn experiment was carried out to analyze the effects of soil nitrogen heterogeneity in containers on the growth of a clonal plant of Zoysia japonica Steud. The overall soil nitrogen supply in the containers, their distribution and their interactions significantly affected the dry matter production of Zoysia japonica plants. Dry matter production in Zoysia japonica was benefited from heterogeneous nitrogen distributions when the overall soil nitrogen supply in the containers was relatively low. When the overall soil nitrogen was relatively high, stolon production was substantially higher in homogeneous soil nutrients. In heterogeneous distributions of nutrients, the positions of rich soil bands close to the initial Zoysia ramets positively affected the stolon production. The earlier Zoysia clones acquired abundant nitrogen from rich soil bands, the more they increased dry matter production in low nitrogen levels.

Forest structure and tree species distribution in relation to topography‐mediated heterogeneity of soil nitrogen and light at the forest floor

We investigated the patterns of soil nitrogen (N) and forest floor light availability, forest structure and tree species distribution along a topographic gradient on a 200‐m mountain slope in a cool‐temperate deciduous broad‐leaved forest in Japan. Rates of soil N mineralization and nitrification decreased from lower to upper slope positions, revealing that N availability decreased up the slope. Maximum tree height and above‐ground biomass were greater on the lower than the upper parts of the slope. Canopy openness, an index of light availability at the forest floor, increased up the slope. Tree species could be placed into three groups according to their distribution patterns on the slope. ‘Ridge’ and ‘valley’ species were distributed on the upper and lower parts of the slope, respectively, whereas ‘uniform’ species were distributed over the entire slope. Topography‐mediated resource gradients of soil N and light may be important determinants of species distribution patterns and forest regeneration, and the results of this study imply that the determinants of the regeneration process differ between the lower and upper parts of a slope. The former may be relatively light limited and the latter may be soil N limited. Valley species may have a greater ability to compete for light, whereas ridge species have a greater ability to compete for soil N. The broad distribution of uniform species probably reflects an ability to effectively compete for both light and soil N.

Reciprocal transport between ramets increases growth of Fragaria chiloensis when light and nitrogen occur in separate patches but only if patches are rich.

Fragaria chiloensis is a stoloniferous perennial herb that grows on coastal sand dunes where scattered shrubs create small patches of lower photon flux density (PFD) but higher soil nitrogen availability. The potential effects of resource transport between ramets when PFD and soil nitrogen are negatively associated in space were tested by comparing the growth of pairs of ramets in which the vascular connection between ramets was either severed or left intact. One ramet in each pair was given high PFD but a low level of soil nitrogen and the other ramet was given low PFD but high N. The analogous effects of resource transport likely to be realized in nature were tested by substituting a more realistic medium soil nitrogen level in place of the high level. Results suggested that connected ramets exchanged carbon and nitrogen under both regimes of soil nitrogen heterogeneity. In the low versus high nitrogen regime, connected ramets had higher combined dry biomass and different patterns of dry mass partitioning from those of severed ramets; effect of connection was greater on ramets given low PFD and high N and on younger ramets. In the low versus medium nitrogen regime, connected ramets had different patterns of partitioning only. Apparent reciprocal resource transport between ramets can enhance the growth of ramets with complementary resource deficiencies, but may affect growth in dry mass only when maximum resource levels are high.

Pocket gophers (Geomys bursarius), vegetation, and soil nitrogen along a successional sere in east central Minnesota.

Pocket gophers (Geomys bursarius: Geomyidae Rodentia) are shown to affect soil resources and thus, indirectly, vegetation. Gophers reduce average soil nitrogen near the surface and increase point-to-point heterogeneity of soil nitrogen by moving nitrogen-poor subsurface soil to the soil surface. Data from 22 old fields at Cedar Creek Natural History Area, Minnesota, USA show correlations of soil nitrogen, vegetation, and gopher mounds that are consistent with this indirect mechanism by which gophers affect local species composition and old field succession.