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1.
Soil microbes face highly variable moisture conditions that force them to develop adaptations to tolerate or avoid drought. Drought conditions also limit the supply of vital substrates by inhibiting diffusion in dry conditions. How these biological and physical factors affect carbon (C) cycling in soils is addressed here by means of a novel process-based model. The model accounts for different microbial response strategies, including different modes of osmoregulation, drought avoidance through dormancy, and extra-cellular enzyme production. Diffusion limitations induced by low moisture levels for both extra-cellular enzymes and solutes are also described and coupled to the biological responses. Alternative microbial life-history strategies, each encoded in a set of model parameters, are considered and their effects on C cycling assessed both in the long term (steady state analysis) and in the short term (transient analysis during soil drying and rewetting). Drought resistance achieved by active osmoregulation requiring large C investment is not useful in soils where growth in dry conditions is limited by C supply. In contrast, dormancy followed by rapid reactivation upon rewetting seems to be a better strategy in such conditions. Synthesizing more enzymes may also be advantageous because it causes larger accumulation of depolymerized products during dry periods that can be used upon rewetting. Based on key model parameters, a spectrum of life-history strategies thus emerges, providing a possible classification of microbial responses to drought.  相似文献   

2.
Grassland ecosystems contain ∼12% of global soil organic carbon (C) stocks and are located in regions where global climate change will likely alter the timing and size of precipitation events, increasing soil moisture variability. In response to increased soil moisture variability and other forms of stress, microorganisms can induce ecosystem-scale alterations in C and N cycling processes through alterations in their function. We explored the influence of physiological stress on microbial communities by manipulating moisture variability in soils from four grassland sites in the Great Plains, representing a precipitation gradient of 485-1003 mm y−1. Keeping water totals constant, we manipulated the frequency and size of water additions and dry down periods in these soils by applying water in two different, two-week long wetting-drying cycles in a 72-day laboratory incubation. To assess the effects of the treatments on microbial community function, we measured C mineralization, N dynamics, extracellular enzyme activities (EEA) and a proxy for substrate use efficiency. In soils from all four sites undergoing a long interval (LI) treatment for which added water was applied once at the beginning of each two-week cycle, 1.4-2.0 times more C was mineralized compared to soils undergoing a short interval (SI) treatment, for which four wetting events were evenly distributed over each two-week cycle. A proxy for carbon use efficiency (CUE) suggests declines in this parameter with the greater soil moisture stress imposed in LI soils from all four different native soil moisture regimes. A decline in CUE in LI soils may have been related to an increased effort by microbes to obtain N-rich organic substrates for use as protection against osmotic shock, consistent with EEA data. These results contrast with similar in situ studies of response to increased soil moisture variability and may indicate divergent autotrophic vs. heterotrophic responses to increased moisture variability. Increases in microbial N demand and decreases in microbial CUE with increased moisture variability observed in this study, regardless of the soils’ site of origin, imply that these systems may experience enhanced heterotrophic CO2 release and declines in plant-available N with climate change. This has particularly important implications for C budgets in these grasslands when coupled with the declines in net primary productivity reported in other studies as a result of increases in precipitation variability across the region.  相似文献   

3.
Water availability strongly affects soil microbial activity and community composition. In a laboratory incubation we investigated the combined effect of soil moisture potential (−10 kPa, −135 kPa, and <−1500 kPa) and plant residue addition on soil enzyme activities (protease, β-glucosidase, β-glucosaminidase and exocellulase) and phospholipid fatty acid (PLFA) profiles. Soil respiration was positively correlated with soil moisture potential and significantly increased with the addition of residue. In the unamended soil, enzyme activities were little affected by soil moisture potential, nor did they change much over time. The addition of residue, however, significantly increased enzyme activity at each moisture level. Furthermore, all four enzyme activities were considerably higher in the amended dry soil than in amended samples with a higher moisture potential. In contrast, in the amended dry soil, respiration and microbial biomass were reduced compared to the amended samples with a higher moisture potential. The low microbial biomass in the amended dry soil was mainly due to a decrease in Gram-negative bacteria, while the fungal biomass reached similar levels at all water potentials. Therefore, shifts in microbial community composition alone cannot explain the increased enzyme activities in the dry soil. Other factors, such as increased fungal activity, stronger interactions between enzymes and soil particles due to thinner water films, may have contributed to the observed effects. Our results suggest that under dry conditions, potential enzyme activities may be decoupled from microbial biomass and respiration in the presence of substrates.  相似文献   

4.
Boreal wetlands are characterized by a mosaic of plant communities, including forests, shrublands, grasslands, and fens, which are structured largely by changes in topography and water table position. The soil associated with these plant communities contain quantitatively and qualitatively different forms of soil organic matter (SOM) and nutrient availability that drive changes in biogeochemical cycling rates. Therefore different boreal plant communities likely contain different soil biotic communities which in turn affect rates of organic matter decomposition. We examined relationships between plant communities, microbial communities, enchytraeids, and soil C turnover in near-surface soils along a shallow topographic soil moisture and vegetation gradient in interior Alaska. We tested the hypothesis that as soil moisture increases along the gradient, surface soils would become increasingly dominated by bacteria and mesofauna and have more rapid rates of C turnover. We utilized bomb radiocarbon techniques to infer rates of C turnover and the 13C isotopic composition of SOM and respired CO2 to infer the degree of soil humification. Soil phenol oxidase and peroxidase enzyme activities were generally higher in the rich fen compared with the forest and bog birch sites. Results indicated greater C fluxes and more rapid C turnover in the surface soils of the fen sites compared to the wetland forest and shrub sites. Quantitative PCR analyses of soil bacteria and archaea, combined with enchytraeid counts, indicated that surface soils from the lowland fen ecosystems had higher abundances of these microbial and mesofaunal groups. Fungal abundance was highly variable and not significantly different among sites. Microbial data was utilized in a food web model that confirmed that rapidly cycling systems are dominated by bacterial activity and enchytraeid grazing. However, our results also suggest that oxidative enzymes play an important role in the C mineralization process in saturated systems, which has been often ignored.  相似文献   

5.
Although soil microorganisms play a central role in the soil processes that determine nutrient availability and productivity of forest ecosystems, we are only beginning to understand how microbial communities are shaped by environmental factors and how the structure and function of soil microbial communities in turn influence rates of key soil processes. Here we compare the structure and function of soil microbial communities in seven mature, undisturbed forest types across a range of regional climates in British Columbia and Alberta, and examine the variation in community composition within forest types. We collected the forest floor fermentation (F) and humus (H) layers and upper 10 cm of mineral soil at 3 sites in each of seven forest types (corresponding to seven Biogeoclimatic zones) in both spring and summer. Phospholipid fatty acid analysis was used to investigate the structure of soil microbial communities and total soil microbial biomass; potential activities of extra-cellular enzymes indicated the functional potential of the soil microbial community in each layer at each site.Multivariate analysis indicated that both structure and enzyme activities of soil microbial communities differed among the forest types, and significantly separated along the regional climate gradient, despite high local variation. Soil moisture and organic matter contents were most closely related to microbial community characteristics. Forests in the Ponderosa Pine and Mountain Hemlock zones were distinct from other forests and from each other when comparing potential enzyme activities and had the most extreme moisture and temperature values. Forest floors from the hot and dry Ponderosa Pine forests were associated with enzymes characteristic of water-stress and high concentrations of phenols and other recalcitrant compounds. The wet and cold Mountain Hemlock forests were associated with low enzyme activity.An influence of tree species was apparent at the three sites within the Coastal Western Hemlock zone; high bacterial:fungal biomass ratios were found under western redcedar (Thuja plicata) which also had high pH and base-cation levels, and under Douglas-fir (Pseudotsuga menziesii), which had high N availability. Potential activities enzymes differed among soil layers: potential activities of phenol oxidase and peroxidase were highest in mineral soil, whereas phosphatase, betaglucosidase, NAGase, sulfatase, xylosidase and cellobiohydrolase were highest in the forest floors.  相似文献   

6.
Because carbon dioxide (CO2) concentration is rising, increases in plant biomass and productivity of terrestrial ecosystems are expected. However, phosphorus (P) unavailability may disable any potential enhanced growth of plants in forest ecosystems. In response to P scarcity under elevated CO2, trees may mine deeper the soil to take up more nutrients. In this scope, the ability of deep horizons of forest soils to supply available P to the trees has to be evaluated. The main objective of the present study was to quantify the relative contribution of topsoil horizons and deep horizons to P availability through processes governed by the activity of soil micro-organisms. Since soil properties vary with soil depth, one can therefore assume that the role of microbial processes governing P availability differs between soil layers. More specifically, our initial hypothesis was that deeper soil horizons could substantially contribute to total plant available P in forested ecosystems and that such contribution of deep horizons differs among sites (due to contrasting soil properties). To test this hypothesis, we quantified microbial P and mineralization of P in ‘dead’ soil organic matter to a depth of 120 cm in forest soils contrasting in soil organic matter, soil moisture and aluminum (Al) and iron (Fe) oxides. We also quantified microbiological activity and acid phosphomonoesterase activity. Results showed that the role of microbial processes generally decreases with increasing soil depth. However, the relative contribution of surface (litter and 0–30 cm) and deep (30–120 cm) soil layers to the stocks of available P through microbial processes (51–62 kg P ha?1) are affected by several soil properties, and the contribution of deep soil layers to these stocks vary between sites (from 29 to 59%). This shows that subsoils should be taken into account when studying the microbial processes governing P availability in forest ecosystems. For the studied soils, microbial P and mineralization of P in ‘dead’ soil organic matter particularly depended on soil organic matter content, soil moisture and, to a minor extent, Al oxides. High Al oxide contents in some sites or in deep soil layers probably result in the stabilization of soil organic compounds thus reducing microbiological activity and mineralization rates. The mineralization process in the litter also appeared to be P-limited and depended on the C:P ratio of soil organic matter. Thus, this study highlighted the effects of soil depth and soil properties on the microbial processes governing P availability in the forest spodosols.  相似文献   

7.
Climate change scenarios predict increases in temperature, changes in precipitation patterns, and longer drought periods in most semi-arid regions of the world. Ecosystems in these regions are prone to land degradation, which may be aggravated by climate change. Soil respiration is one of the main processes responsible for organic carbon losses from arid and semi-arid ecosystems. We measured soil respiration over one year in two steppe ecosystems having different degrees of land degradation under three ground-covers: with vegetation, bare soil, and an intermediate situation between plants and bare soil.The largest differences in soil respiration rates between the sites were observed in spring, coinciding with the highest level of plant activity. The degraded site had drier and hotter soils with less soil water availability and a longer drought period. As a result, vegetation on the degraded site did not respond to spring rainfall events. Soil respiration showed a strong seasonal variability, with average annual rates of 1.1 and 0.8 μmol CO2 m−2 s−1 in the natural and degraded sites, respectively. We did not observe significant differences in soil respiration rates associated with ground-cover i.e., the temporal variation was much larger than the spatial variation. At both sites, soil moisture was the controlling driver of soil respiration for most of the year, when temperatures were above 20 °C and constrained the response to temperature for the few months when the temperature was below 20 °C. An empirical model based on soil temperature and soil moisture explained 90% and 72% of the seasonal variability of soil respiration on the natural and degraded sites, respectively. For the first time, this study suggests that land degradation may alter the carbon balance of these ecosystems through changes in the temporal dynamics of soil respiration and plant productivity, which have important negative consequences for ecosystem functioning and sustainability.  相似文献   

8.
Enzyme activities along a climatic transect in the Judean Desert   总被引：4，自引：0，他引：4  
Xiangzhen Li  Pariente Sarah   《CATENA》2003,53(4):349-363
Soil enzymes have an important influence on nutrient cycling. We examined spatial and temporal patterns in dehydrogenase, arylsulfatase, alkaline and acid phosphatase activities, and their relationships with organic carbon and microbial biomass nitrogen at three sites in Israel representing different climatic regions: Mediterranean (humid), mildly arid and arid. The sites were selected along a climatic transect from the Judean Mountains in the west to the Dead Sea in the east of Israel. With increasing aridity, soil organic carbon, soil microbial biomass nitrogen, dehydrogenase, phosphatase and different pools of arylsulfatase activities decreased significantly. A sharp change in enzyme activities existed between 260- and 120-mm mean annual rainfall. The arylsulfatase activity of the microbial biomass in the 0–2- and 5–10-cm soil layers usually accounted for more than 50% of the total activity, and the fraction of total activity in the 0–2-cm soil layer of the arid sites was significantly greater than that of the humid site. Dehydrogenase and total and microbial biomass arylsulfatase activities were sensitive indicators of the climatic change along the transect. At the humid and mildly arid sites, the activities of dehydrogenase were less in the winter than in the summer and spring, whereas total and microbial biomass arylsulfatase activities were less in both summer and winter. At the arid site, lower values were observed in the summer at 0–2-cm soil depth. At all sites, lower alkaline phosphatase activities at 0–2 cm were observed in the summer, but there were no significant seasonal differences in acid phosphatase activities. These different seasonal patterns of enzyme activities are attributed to the enzyme source, and specific seasonal soil moisture and temperature conditions at the studied sites. The low dehydrogenase and microbial biomass arylsulfatase activities in the winter at the humid and mildly arid sites are explained by the cold and wet soil conditions, and the low enzyme activity in the summer at the arid site is attributed to the dry and hot soil conditions.  相似文献   

9.
以辣椒为研究对象,研究了不同光照强度和土壤水分对辣椒叶片相对含水率（RWC）、叶绿素（Chl）含量、保护酶活性以及游离脯氨酸和丙二醛（MDA）含量的影响。结果表明：1）随着遮阴程度和土壤水分的增加,叶片RWC,叶绿素含量均呈上升趋势,土壤水分增加主要有利于叶绿素a含量的增加,遮阴主要有利于叶绿素b含量的增加。类胡萝卜素含量随遮阴程度的增加和土壤水分的降低而下降。MDA含量在干旱胁迫条件下升高,随着遮阴程度的增加呈先降后升的趋势。光照相同,在干旱和高水条件下,保护酶活性和脯氨酸含量均表现出不同程度的上升;水分条件相同,保护酶活性和脯氨酸含量均随遮阴程度的增加而下降,且保护酶对光照强度的敏感性为SOD＞CAT＞POD。2）保护类物质（脯氨酸与保护酶）与伤害类物质（MDA）均达到了极显著正相关,膜保护酶与叶绿素含量达到了极显著负相关。综合以上认为,将遮阴30%和土壤相对含水率为70%～85%作为适宜的遮阴和灌溉指标是科学合理的。  相似文献   

10.
The most favorable moisture conditions for the microbial destruction of chitin in soils are close to the total water capacity. The water content has the most pronounced effect on chitin destruction in soils in comparison with other studied substrates. It was found using gas-chromatographic and luminescent-microscopic methods that the maximum specific activity of the respiration of the chitinolytic community was at a rather low redox potential with the soil moisture close to the total water capacity. The range of moisture values under which the most intense microbial transformation of chitin occurred was wider in clayey and clay loamy soils as compared with sandy ones. The increase was observed due to the contribution of mycelial bacteria and actinomycetes in the chitinolytic complex as the soil moisture increased.  相似文献   

11.
Summary Trenching was used to reduce root activity in treeless plots in a New Mexico mixed-conifer forest to examine the effects of plant roots on soil processes. Trenching led to increases in moisture content (104%), inorganic N concentration (115%), and mass loss from cellulose (196%). In laboratory incubations, trenched soils collected in the 1st and 2nd year after trenching evolved 52% and 115% more CO2, respectively, than control soils. Amending incubated trenched and control soils with moisture and inorganic N indicated that increased soil moisture content in trenched plots could explain the increased microbial activity. Trenching also had statistically significant but inconsistent effects on net N mineralization in incubated soils. The greatest effect of trenching was to increase net N mineralization under favorable temperature and moisture conditions. Irrigation of field plots increased both CO2 evolution and net N mineralization. Overall, these data are consistent with the hypothesis that plant roots reduced microbial activity by moisture uptake during the time of the study.  相似文献   

12.
蔡庆空  李二俊  陶亮亮  王果  陈超 《土壤通报》2021,52(5):1069-1077
土壤水分作为土壤的重要组成部分,是气候、农业和生态系统的关键组成要素。快速、大面积和实时地监测土壤含水量,对旱情预报、农田灌溉和作物估产有着十分重要的作用。本文主要结合Landsat 8光学影像数据对地表土壤含水量进行反演,在温度植被干旱指数（TVDI）的地表温度－植被指数特征空间基础上引入分形覆盖度,构建地表温度－分形覆盖度特征空间,从而计算得到改进温度植被干旱指数（ITVDI）,采用研究区实测土壤含水量数据对计算的结果进行对比分析。为了分析TVDI和ITVDI与土壤体积含水量的关系,分别制作TVDI、ITVDI与土壤体积含水量的散点图并分析相关性。研究结果表明:在小麦拔节期内,研究区域大部分地区处于干旱状态,轻旱地区主要分布在研究区西部、北部以及中部的高植被覆盖地区;重旱地区主要分布在城市中心及部分裸露地面和小麦种植地区。TVDI和ITVDI与地表土壤含水量线性相关显著,两者均可表征研究区干旱的实际情况。但ITVDI引入分形植被覆盖度参数,在一定程度上避免干旱指数受到地表覆盖类型的限制,使得ITVDI与实测土壤含水量的相关性和反演精度都高于TVDI。因此,ITVDI能够更好地反映研究区域土壤含水量的状况,更适合高植被覆盖度地区土壤含水量反演。  相似文献   

13.
The purpose of this experiment was to evaluate whether soil storage and processing methods significantly influence measurements of potential in situ enzyme activity in acidic forest soils. More specifically, the objectives were to determine if: (1) duration and temperature of soil storage; (2) duration of soil slurry in buffer; and (3) age of model substrates significantly influence the activity of six commonly measured soil extracellular enzymes using methylumbelliferone (MUB)-linked substrates and l-dihydroxyphenylalanine (l-DOPA). Soil collected and analyzed for enzyme activity within 2 h was considered the best measure of potential in situ enzyme activity and the benchmark for all statistical comparisons. Sub-samples of the same soil were stored at either 4 °C or −20 °C. In addition to the temperature manipulation, soils experienced two more experimental treatments. First, enzyme activity was analyzed 2, 7, 14, and 21 days after collection. Second, MUB-linked substrate was added immediately (i.e. <20 min) or 2 h after mixing soil with buffer. Enzyme activity of soil stored at 4 °C was not significantly different from soil stored at −20 °C. The duration of soil storage was minimal for β-glucosidase, β-xylosidase, and peroxidase activity. N-acetyl-glucosaminidase (NAGase), phosphatase, and phenol oxidase activity appeared to change the most when compared to fresh soils, but the direction of change varied. Likewise, the activities of these enzymes were most sensitive to extended time in buffer. Fluorometric MUB and MUB-linked substrates generally had a 3-day shelf life before they start to significantly suppress reported activities when kept at 4 °C. These findings suggest that the manner in which acidic forest soils are stored and processed are site and enzyme specific and should not initially be trivialized when conducting enzyme assays focusing on NAGase, phosphatase, and phenol oxidase. The activities of β-glucosidase, β-xylosidase, and peroxidase are insensitive to storage and processing methods.  相似文献   

14.
Factors determining C turnover and microbial succession at the small scale are crucial for understanding C cycling in soils. We performed a microcosm experiment to study how soil moisture affects temporal patterns of C turnover in the detritusphere. Four treatments were applied to small soil cores with two different water contents (matric potential of ?0.0063 and ?0.0316 MPa) and with or without addition of 13C labelled rye residues (δ13C=299‰), which were placed on top. Microcosms were sampled after 3, 7, 14, 28, 56 and 84 days and soil cores were separated into layers with increasing distance to the litter. Gradients in soil organic carbon, dissolved organic carbon, extracellular enzyme activity and microbial biomass were detected over a distance of 3 mm from the litter layer. At the end of the incubation, 35.6% of litter C remained on the surface of soils at ?0.0063 MPa, whereas 41.7% remained on soils at ?0.0316 MPa. Most of the lost litter C was mineralised to CO2, with 47.9% and 43.4% at ?0.0063 and ?0.0316 MPa, respectively. In both treatments about 6% were detected as newly formed soil organic carbon. During the initial phase of litter decomposition, bacteria dominated the mineralisation of easily available litter substrates. After 14 days fungi depolymerised more complex litter compounds, thereby producing new soluble substrates, which diffused into the soil. This pattern of differential substrate usage was paralleled by a lag phase of 3 days and a subsequent increase in enzyme activities. Increased soil water content accelerated the transport of soluble substrates, which influenced the temporal patterns of microbial growth and activity. Our results underline the importance of considering the interaction of soil microorganisms and physical processes at the small scale for the understanding of C cycling in soils.  相似文献   

15.
Respiration rate of soils manured by seabirds and seals on sub-Antarctic Marion Island (47°S, 38°′E) is considerably higher than that of unmanured soils, and the main objective of this study was to determine whether this is caused by an enhanced supply of inorganic nutrients (N and P) or organic C substrates, or both. The effect of soil moisture content was also investigated. Soils from five habitats were studied: Mesic fellfield, Dry mire, Closed fernbrake, Coastal herbfield and Cotula herbfield. The latter two are strongly influenced by manuring. Respiration rate increased with soil moisture content up to full water holding capacity, and the response of respiration to moisture increased strongly with temperature (especially above 10 °C). Respiration Q10 increased with soil moisture content. Glucose addition markedly stimulated soil respiration rate in all the soils, despite the fact that they all possessed substantial concentrations of organic C, a wide range of N and P concentrations and a 2-fold variation in C:N ratio. This suggests that the primary factor limiting soil respiration on the island is the supply of labile carbon substrate. Soil N and P status is also important, since adding glucose with N and/or P to soils with low N and P concentrations resulted in a significantly greater stimulation of respiration rate than adding glucose alone. In fact, for the Mesic fellfield and Dry mire soils (especially poor in N and P) adding N and P stimulated respiration rate even without added glucose. For soils with adequate endogenous concentrations of N and P (the Coastal herbfield and Cotula herbfield soils), adding further N and P did not stimulate respiration, and adding N and P with glucose did not enhance respiration more than adding glucose alone. It is proposed that manuring results in a whole syndrome of consequences for soil respiration rate, including increased litter input and root exudation due to higher primary production, higher quality of litter and soil organic matter, larger, more active and more diverse soil microbial populations and larger numbers of microbivores that stimulate microbial activity and turnover.  相似文献   

16.
Changes in mean global air temperature and precipitation patterns, leading to longer drought periods and more extremely dry years, are predicted. The objective of this work was to assess whether a long period of severe drought can affect the growth and activity of the microbiota of a semiarid soil, as well as the effect of organic amendments on soil resistance and resilience to this severe drought. A soil incubation experiment was carried out over 60 days, under controlled conditions (25 °C and 60/80% day/night relative humidity), with two treatments: unamended (US) and amended (AS) with manure compost (100 t ha−1). Two levels of irrigation were imposed: (1) well-watered (MUS and MAS), the soil being maintained at 60% of its water-holding capacity (WHC), and (2) dry, without irrigation (DUS and DAS). Then, a single level of irrigation was established for 37 days, dry soils being irrigated under the same conditions than well-watered soils, to assess soil resilience to this period of drought. Under well-watered conditions, the soil water-soluble nitrogen contents were 73 and 88% higher, the microbial biomass carbon 63 and 48% higher, alkaline phosphomonoesterase activity 46 and 32% higher, β-glucosidase activity 16 and 25% higher and urease activity 30 and 19% higher for the US and AS treatments, respectively, compared with the dry conditions at the end of the experimental period. Furthermore, the organic amendment helped the soil to retain moisture and encouraged the growth and activity of soil microbial populations. However, a 2-month drought seems insufficient to destroy the native microbial biomass in the arid soil used in this study, indicating that it is well adapted to adverse climate conditions. Thus, microbiological and biochemical parameters experienced a rapid recovery after soil rewetting, DUS and DAS showing values similar to MUS and MAS, after rewetting, highlighting the resilience of this type of soil against drought stress.  相似文献   

17.
Three semiarid Mediterranean patchy landscapes were investigated to test the existence of a microsite effect (i.e. plant canopy vs. inter-canopy) on soil microbial communities. Surface soil samples were independently taken from both microsites under naturally changing conditions of humidity and temperature through the year. In gypsiferous soils covered with a shrub steppe, improved physical and chemical soil properties were registered underneath the plant canopy, where the densest and most active microbial communities were also detected (e.g. microbial biomass C averaged 531 and 202 mg kg−1 in canopy and inter-canopy areas, respectively). In calcareous perennial tussock grasslands, either growing on soils over limestones or alluvial deposits, the microsite effect was not so marked. Soil humidity, temperature and total organic C were homogeneously distributed over the landscape conditioning their uniform microbial activity under field moisture conditions (ATP content averaged 853 and 885 nmol kg−1 in canopy and intercanopy areas, respectively). However, readily mineralizable C and microbial biomass C were preferentially accumulated in soils underneath the tussocks determining their larger potential microbial activity (e.g. C hydrolysis capacity under optimal conditions). In conclusion, plant clumps either functioned as microbial hotspots where enhanced microbially driven ecosystem processes took place or as microbial banks capable of undergoing a burst of activity under favourable climatic conditions. Our results provide experimental evidence of a non-patchy distribution of certain soil microbial properties in semi-arid Mediterranean patchy ecosystems.  相似文献   

18.
Soil microbes are an essential component of most terrestrial ecosystems; as decomposers they are responsible for regulating nutrient dynamics, and they also serve as a highly labile nutrient pool. Here, we evaluated seasonal variations in microbial biomass carbon (MBC) and nitrogen (MBN) as well as microbial activity (as qCO2) for 16 months with respect to several factors relating to soil moisture and nutrients under different land management practices (plant residue application, fertilizer application) in both clayey (38% clay) and sandy (4% clay) croplands in Tanzania. We observed that MBC and MBN tended to decrease during the rainy season whereas they tended to increase and remain at high levels during the dry season in all treatment plots at both of our test sites, although soil moisture did not correlate with MBC or MBN. qCO2 correlated with soil moisture in all treatment plots at both sites, and hence soil microbes act as decomposers mainly during the rainy season. Although the effect of seasonal variation of soil moisture on the dynamics of MBC, MBN, and qCO2 was certainly greater than that attributable to plant residue application, fertilizer application, or soil texture, plant residue application early in the rainy season clearly increased MBC and MBN in both clayey and sandy soils. This suggests that plant residue application can help to not only counter the N loss caused by leaching but also synchronize crop N uptake and N release from soil microbes by utilizing these microbes as an ephemeral nutrient pool during the early crop growth period. We also found substantially large seasonal variations in MBC and MBN, continuously high qCO2, and rapid turnover of soil microbes in sandy soil compared to clayey soil. Taken together, our results indicate that soil microbes, acting as both a nutrient pool and decomposers, have a more substantial impact on tropical sandy soil than on clayey soil.  相似文献   

19.

Background

Ridge and furrow (RIFU) systems and associated soils are a widespread legacy of medieval agriculture, are archives of historical land use, and might affect recent ecosystems. Open questions about RIFU formation and potential legacy effects still exist, especially related to physical soil properties.

Aims

Our aims were (1) to characterize the soil properties of RIFU soils and (2) to compare the drought sensitivity and the growth resistance in extremely dry years of trees growing on ridges and furrows, respectively.

Methods

We studied soil physical (bulk density, saturated soil hydraulic conductivity, and texture) and chemical (soil pH, soil organic matter, and nitrogen content) properties and the climate sensitivity of tree growth on RIFU systems for three study sites in Prignitz, Germany.

Results

RIFU systems showed a high spatial heterogeneity of soil stratigraphy due to ridge construction and increased accumulation of soil moisture and organic matter in furrows due to post-abandonment pedogenesis. Slight spatial differences in soil physical properties were found, with increased air capacity in ridge soils and higher available water contents in furrow soils. No differences in drought sensitivity were observed for trees growing on ridges and furrows, except for a wet site, where trees in furrows showed a higher sensitivity. Resistance in dry years tended to be similar or increase from furrows to ridges.

Conclusions

The results reflect a spatial differentiation of stratigraphy and post-abandonment pedogenesis on abandoned RIFU systems and suggest an adaption to different moisture conditions through RIFU construction. Differences in drought sensitivity of tree growth with relative land surface could only be detected for one of the three sites, where trees were found to be less drought sensitive on ridges.  相似文献   

20.
Effect of severe drought events in combination with organic amendments (municipal solid waste, MSW, sheep manure, SM, and cow manure, CM) on soil dehydrogenase, urease, β‐glucosidase and phosphatase activities and microbial community by analyzing phospholipid fatty acids was studied under controlled laboratory conditions for one year. Two levels of irrigation were used: (1) watered soils, where the soils were maintained at 60% of their water holding capacity through the experiment, and (2) non‐watered soils, without irrigation through the experiment. The severe drought conditions negatively affected the soil enzymatic activities and total bacterial and fungal PLFA concentrations. The application of organic amendments to the soil subjected to severe drought increased soil water retention and encouraged the growth and activity of soil microbial populations. However, the chemical composition of the organic matter applied to the soil also strongly influenced soil moisture. In non‐watered soils and compared with the unamended soil, the dehydrogenase activity was 71 · 3%, 60 · 9% and 38 · 6% higher in the soil with SM, CM and MSW, respectively. Urease activity was 60 · 6%, 51 · 5% and 37% higher in the soil with SM, CM and MSW, respectively. β‐glucosidase and phosphatase activities had a similar trend. Water retention was higher when the organic wastes applied to the soils had a higher content of humic acids than fulvic acid contents. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

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