Dissolved organic matter (DOM) represents an important component of carbon and nutrient cycling in arctic ecosystems. In northern Alaska, DOM production and microbial activity differ among landscapes with varied glaciation histories with lower rates on younger landscapes. In addition, within the region, soil DOM concentrations vary at the scale of hillslope toposequences, with higher concentrations in upslope than streamside positions. However, it is unknown whether variation in DOM production quality among and within landscapes linked to patterns in DOM quality. To answer this question, we conducted a study of DOM biodegradability within and among hillslopes of different landscape age. We examined rates of DOM decomposition and several indices of the quality of water-extracted DOM collected from soils in the summer. A variety of methods indicated that DOM quality generally was consistent across hillslope positions and among landscape ages. For example, DOM fluorescence index, an index of quality for chromophoric DOM, did not vary significantly across all hillslope positions or landscape ages. There were no significant differences among landscape ages or hillslope positions in DOM specific UV absorbance, in rates of DOM mineralization, or in DOM decomposition, indicating that DOM quality was consistent regardless of its source or position along hillslope flow paths. This suggests that despite many potential sources of variation within and among arctic hillslopes linked to differences in vegetation, hydrology, microclimate, and microbial activity, there is little variation in growing-season soil DOM quality. Microbial processing of DOM within arctic hillslopes may lead to a convergence in growing season DOM quality resulting in little spatial variation. Approximately 10–20% of the growing season DOM is labile in tundra soils, slightly higher that the proportion that is labile in arctic rivers during the summer. 相似文献
The study of interactions between minerals, organic matter (OM) and microorganisms is essential for the understanding of soil functions such as OM turnover. Here, we present an interdisciplinary approach using artificial soils to study the establishment of the microbial community and the formation of macro-aggregates as a function of the mineral composition by using artificial soils. The defined composition of a model system enables to directly relate the development of microbial communities and soil structure to the presence of specific constituents. Five different artificial soil compositions were produced with two types of clay minerals (illite, montmorillonite), metal oxides (ferrihydrite, boehmite) and charcoal incubated with sterile manure and a microbial community derived from a natural soil. We used the artificial soils to analyse the response of these model soil systems to additional sterile manure supply (after 562 days). The artificial soils were subjected to a prolonged incubation period of more than two years (842 days) in order to take temporally dynamic processes into account. In our model systems with varying mineralogy, we expected a changing microbial community composition and an effect on macro-aggregation after OM addition, as the input of fresh substrate will re-activate the artificial soils. The abundance and structure of 16S rRNA gene and internal transcribed spacer (ITS) fragments amplified from total community DNA were studied by quantitative real-time PCR (qPCR) and denaturing gradient gel electrophoresis (DGGE), respectively. The formation of macro-aggregates (>2 mm), the total organic carbon (OC) and nitrogen (N) contents, the OC and N contents in particle size fractions and the CO2 respiration were determined. The second manure input resulted in higher CO2 respiration rates, 16S rRNA gene and ITS copy numbers, indicating a stronger response of the microbial community in the matured soil-like system. The type of clay minerals was identified as the most important factor determining the composition of the bacterial communities established. The additional OM and longer incubation time led to a re-formation of macro-aggregates which was significantly higher when montmorillonite was present. Thus, the type of clay mineral was decisive for both microbial community composition as well as macro-aggregation, whereas the addition of other components had a minor effect. Even though different bacterial communities were established depending on the artificial soil composition, the amount and quality of the OM did not show significant differences supporting the concept of functional redundancy. 相似文献
Microbial necromass is an important source of stabilized organic matter in soil, yet the decomposition dynamics of necromass constituents have not been adequately characterized. This includes DNA, a nutrient-rich molecule that when released into the environment as extracellular DNA (eDNA) can be readily used by soil microorganisms. However, the ecological relevance of eDNA as a nutrient source for soil microorganisms is relatively unknown. To address these deficits, we performed a laboratory experiment wherein soils were amended with 13C-labeled eDNA and clay minerals known to interact with DNA (kaolinite and montmorillonite). The amount of eDNA-carbon remaining in the soil declined exponentially over time. Kaolinite amendment decreased eDNA decomposition rates and, after 30 days, retained a higher fraction of eDNA-carbon (∼70% remaining) than control or montmorillonite soils (∼40% remaining), indicating that clay mineral sorption can stabilize eDNA-derived carbon in soil. Sequencing of bacterial 16S rRNA genes showed that during the incubation the relative abundance of the added eDNA's sequence decreased by 98%, 92% and 99% in the control, montmorillonite, and kaolinite amended soils respectively. These results suggest that the fraction of eDNA-carbon that remained in the soil was incorporated into microbial biomass, firmly bound to soil constituents, or fragmented and no longer amenable to sequencing. In addition, the eDNA amendment affected the composition of the bacterial community. Specifically, the relative abundance of select phyla (Planctomycetes and TM7) and genera (e.g., Arthrobacter and Nocardioides) were elevated in soils that received eDNA, suggesting these groups may be particularly effective at degrading eDNA and using it for growth. Taken together, these results indicate that while eDNA is consumed by bacteria in soil, a fraction of eDNA material is resistant to decomposition, particularly when stabilized by soil minerals, suggesting a substantial amount of recalcitrant eDNA could accumulate over time. 相似文献
The majority of dead organic material enters the soil carbon pool following initial incorporation into microbial biomass. The decomposition of microbial necromass carbon (C) is, therefore, an important process governing the balance between terrestrial and atmospheric C pools. We tested how abiotic stress (drought), biotic interactions (invertebrate grazing) and physical disturbance influence the biochemistry (C:N ratio and calcium oxalate production) of living fungal cells, and the subsequent stabilization of fungal-derived C after senescence. We traced the fate of 13C-labeled necromass from ‘stressed’ and ‘unstressed’ fungi into living soil microbes, dissolved organic carbon (DOC), total soil carbon and respired CO2. All stressors stimulated the production of calcium oxalate crystals and enhanced the C:N ratios of living fungal mycelia, leading to the formation of ‘recalcitrant’ necromass. Although we were unable to detect consistent effects of stress on the mineralization rates of fungal necromass, a greater proportion of the non-stressed (labile) fungal necromass C was stabilised in soil. Our finding is consistent with the emerging understanding that recalcitrant material is entirely decomposed within soil, but incorporated less efficiently into living microbial biomass and, ultimately, into stable SOC. 相似文献
Multipurpose trees, the integral components of homegardens, contribute significantly to the closed nutrient cycling processes
and sustainability of the ecosystem. Although, the litter production and probable nutrient returns via litter in homegardens
have been documented, quantification and characterization of the decomposition and bioelement release from the litter have
received relatively little scientific attention. The objective of the present study is to explore the litter dynamics of six
locally important multipurpose trees (Mangifera indica L., Artocarpus heterophyllus Lamk., Anacardium occidentale L., Ailanthus triphysa Dennst., Artocarpus hirsutus L. and Swietenia macrophylla L.), in an agroforestry homegarden in Southern Kerala, India. Litterfall and nutrient additions in the six species ranged
from 383 to 868 g m−2 yr−1, nitrogen, 6.4 to 8.8, phosphorus, 0.17 to 0.42 and potassium, 1.1 to 2.8 g m−2 yr−1. The annual litter output in the homegarden was 425 kg with A. hirsutus, M. indica, A. heterophyllus and A. occidentale recording significantly higher litter and nutrient additions. Leaf litter decay studies revealed A. heterophyllus and A. occidentale to be the most labile litter species and S. macrophylla the most recalcitrant. The decay rate coefficients varied significantly among the species. Foliage decomposition rates related
to the initial chemical composition of the litter revealed best correlation with lignin. NPK release was almost complete by
the end of decay in all species inspite of the initial phases of accumulation observed for nitrogen and phosphorus. Two-way
analysis of variance test revealed significant differences in the contents of the three elements as a function of species
and time elapsed. Macronutrients were released in the order K>N/P. The higher rates of decay and nutrient turnover in M. indica, A. heterophyllus and A. occidentale foliage indicated the potential of using these species’ litter as nutrient inputs in agriculture while A. triphysa, A. hirsutus and S. macrophylla perform better as organic mulches taking a longer time for decay and hence nutrient release. 相似文献
Relatively little is known about soil organic carbon (SOC) dynamics in montane ecosystems of the semi-arid western U.S. or the stability of current SOC pools under future climate change scenarios. We measured the distribution and quality of SOC in a mosaic of rangeland-forest vegetation types that occurs under similar climatic conditions on non-calcareous soils at Utah State University's T.W. Daniel Experimental Forest in northern Utah: the forest types were aspen [Populus tremuloides] and conifer (mixture of fir [Abies lasiocarpa] and spruce [Picea engelmannii]); the rangeland types were sagebrush steppe [Artemisia tridentata], grass-forb meadow, and a meadow-conifer ecotone. Total SOC was calculated from OC concentrations, estimates of bulk density by texture and rock-free soil volume in five pedons. The SOC quality was expressed in terms of leaching potential and decomposability. Amount and aromaticity of water-soluble organic carbon (DOC) was determined by water extraction and specific ultra violet absorbance at 254 nm (SUVA) of leached DOC. Decomposability of SOC and DOC was derived from laboratory incubation of soil samples and water extracts, respectively.
Although there was little difference in total SOC between soils sampled under different vegetation types, vertical distribution, and quality of SOC appeared to be influenced by vegetation. Forest soils had a distinct O horizon and higher SOC concentration in near-surface mineral horizons that declined sharply with depth. Rangeland soils lacked O horizons and SOC concentration declined more gradually. Quality of SOC under rangelands was more uniform with depth and SOC was less soluble and less decomposable (i.e., more stable) than under forests. However, DOC in grass-forb meadow soils was less aromatic and more bioavailable, likely promoting C retention through cycling. The SOC in forest soils was notably more leachable and decomposable, especially near the soil surface, with stability increasing with soil depth. Across the entire dataset, there was a weak inverse relationship between the decomposability and the aromaticity of DOC. Our data indicate that despite similar SOC pools, vegetation type may affect SOC retention capacity under future climate projections by influencing potential SOC losses via leaching and decomposition. 相似文献
The conversion of forests to agroecosystems or agroforests comes with many changes in biological and chemical processes. Agroforestry,
a tree based agroecosystem, has shown promise with respect to enhanced system nutrient accumulation after land conversion
as compared to sole cropping systems. Previous research on tropical agroforestry systems has revealed increases in soil organic
matter and total organic nitrogen in the short term. However, research is lacking on long-term system level sustainability
of nutrient cycles and storage, specifically in traditional multi-strata agroforestry systems, as data on both the scope and
duration of nutrient instability are inconclusive and often conflicting. This study, conducted in Ghana, West Africa, focused
on carbon and nitrogen dynamics in a twenty-five year chronosequence of cacao (Theobroma cacao Linn.) plantations. Three treatments were selected as on-farm research sites: 2, 15 and 25-year-old plantations. Soil carbon
(C, to a depth of 15 cm) varied between treatments (2 years: 22.6 Mg C ha−1; 15 years: 17.6 Mg C ha−1; 25 years: 18.2 Mg C ha−1) with a significant difference between the 2- and 15- and the 2- and 25-year-old treatments (p < 0.05). Total soil nitrogen in the top 15 cm varied between 1.09 and 1.25 Mg N ha−1 but no significant differences were noted between treatments. Soil nitrification rates and litter fall increased significantly
with treatment age. However, photosynthetically active radiation (PAR) and soil temperature showed a significant decrease
with age. No difference was found between decay rates of litter at each treatment age. By 25 years, system carbon sequestration
rates were 3 Mg C ha−1 y−1, although results suggest that even by 15 years, system-level attributes were progressing towards those of a natural system. 相似文献