Shifts in microbial community function and structure along the successional gradient of coastal wetlands in Yellow River Estuary

Soil physico-chemical properties, microbial biomass, and functional microbial diversity were investigated in two adjacent fields located in a semi-arid dryland farming region of Maharashtra state, India. In organically cultivated field (OCF) large annual inputs of composted cow manure, no tillage and no removal of crop residues is being practiced for the past 14 years. The neighboring plot which was not cultivated for the same period remained as fallow grassland (FGL) served as check for comparison. Soil samples collected from OCF had higher pH, moisture, total organic carbon and nitrogen, microbial biomass, C and N, and enzymatic activities compared to FGL soil. Microbial community structure in the two soils was assessed, using Biolog Eco and GN2 plates. OCF soil showed significant (P = 0.01) increase of microbial diversity and evenness, suggesting an improvement of functional microbial diversity. Principal component analysis (PCA) separates the two soil samples based on 10 most discriminating carbon sources for each with the maximum positive and negative scores. To the best of our knowledge this is the first study on soil quality and microbial functional diversity of soil in a semi-arid region indicating that conversion from FGL to OCF led to significant soil quality improvement due to the enhanced microbial functional diversity.

Changes in soil physico-chemical properties and microbial functional diversity due to 14 years of conversion of grassland to organic agriculture in semi-arid agroecosystem

Responses of soil microarthropods to inorganic and organic fertilizers in a poplar plantation in a coastal area of eastern China

Microbial communities are important for the functioning of the ecosystem, both in relation to direct interactions with the plants and with regard to nutrient and organic matter recycling. A study in field condition was undertaken in Kashmir valley to reveal the effect of various temperate fruit crops viz. apricot, peach, plum and cherry along with a control (no-plantation) on microbial biomass carbon (MBC), nitrogen (MBN), phosphorus (MBP) and dehydrogenase, phosphomonoesterase (acid and alkaline) and urease activities in soil at two different depths (0-20 and 21-40 cm). All the fruit crops showed a sharp decline in microbial biomass and enzyme activities with the increase in soil depth. Each of the four fruit crops showed significant (p<0.05) impact on MBC over the control and the maximum MBC was recorded in plum (1000 mg kg-1) and the lowest value was observed in control (457 mg kg-1), at the surface layer. Since there is a relationship between MBC and MBN, the similar trend was also observed in MBN as in case of MBC. For MBP, fruit crops showed any significant effect neither on surface soil, nor on subsurface soil layer over control. At the surface layer, unlike microbial biomass the highest dehydrogenase activity was observed in peach (318 mg TPF g soil-1 h-1) and the lowest value (166 mg TPF g soil-1 h-1) was attained at control plot. Maximum alkaline phosphomonoesterase activity was observed in peach (381 mg PNP g soil-1 h-1), although for acid phosphomonoesterase the highest value recorded in apricot (306 mg PNP g soil-1 hr-1), at surface soil. A significant positive correlation (p <0.01) was observed amongst MBC, MBN and MBP. Both the phosphomonoesterase activities were significantly (p <0.05) correlated with MBP in soil. It can be concluded that the influence of the studied fruit crops on the soil was not uniform, in terms of the measured parameters.

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Assessment of microbial biomass and enzyme activities in soil under temperate fruit crops in north western himalayan region

Aim

Climate change, especially the wider occurrence of extreme events, is likely to increase the intensity and frequency of insect/pathogen outbreaks (referred to as biotic disturbance), which may considerably affect plant ecophysiological traits and thus the ecosystem carbon (C) cycle. Little is known, however, about the ways in which biotic disturbance quantitatively affects ecosystem C processes, especially those that occur below ground. We reveal the general patterns of below-ground C responses to biotic disturbance from field manipulative experiments and opportunistic events.



Location

Global.



Method

We carried out a meta-analysis examining the effects of biotic disturbance on 16 variables associated with below-ground C processes, based on 64 experimental studies.



Results

Biotic disturbance significantly decreased below-ground C pools with relatively long residence times (e.g. root biomass and soil organic carbon, SOC), but increased labile C pools (e.g. microbial biomass carbon, MBC; dissolved organic carbon, DOC), soil respiration (Rs) and its components, and microbial population sizes. Compared with the neutral or positive effects of other environmental changes on below-ground C pools and fluxes, biotic disturbance had a negative effect on plant biomass and SOC but a larger positive effect on MBC, DOC and Rs.



Main conclusions

Biotic disturbance can have stronger impacts on below-ground C processes than other environmental changes, and the sensitive responses of soil labile C pools and C fluxes to biotic disturbance decrease long-term below-ground C sequestration. More research efforts are, however, needed to reduce the uncertainties in quantifying the effects of biotic disturbance and to improve forecasting of the feedback between the carbon cycle and climate.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/geb.12235

A global synthesis of below-ground carbon responses to biotic disturbance: a meta-analysis.

Soil microbial communities in an apple orchard and its adjacent boundary bush with or without infestation by violet root rot were investigated for 2 years. Effects of season (spring, summer, and fall), land-use (apple orchard and boundary bush), and violet root rot (infested and healthy) on soil microbial populations, microbial activity, and microbial community structures were determined using physiological, cytochemical, and molecular (PCR-DGGE) approaches. Seasonal fluctuations were significant ( P H ′) and evenness ( J ′) of community-level physiological profile (CLPP) in both years. However, seasonal differences of soil microbial guilds that utilize carbon substrate groups observed in the first year were not reproduced in the second year. The land-use factor differentiated the apple orchard from the boundary bush where viable bacterial population, bacterial FAME and FDA hydrolysis were significantly greater in both years. Infestation status of violet root rot, on the other hand, significantly increased bacterial FAME and FDA hydrolysis in both years. In addition, neither the land-use nor the disease infestation factor significantly influenced the utilization patterns of individual substrate guilds for the 2 years. In both years, saturated fatty acids were significantly more abundant in the orchard than in the bush soil, and monosaturated fatty acids vice versa. Principal component analyses for CLPP, FAME, and denaturing gradient gel electrophoresis (DGGE) consistently exhibited that, although the violet root rot influenced the soil microbial community structures both in the apple orchard and the boundary bush, overall magnitude of the difference in communities between the violet root rot infested and non-infested sites in the bush were greater than in the orchard, irrespective of the season. These results suggested that the seasonal and the land-use factors affected soil microbial community both quantitatively and qualitatively, whereas the impact of the violet root rot on the soil microbial community was mainly qualitative and more pronounced in the adjacent bush than in the orchard.

Shun-Iichiro Miyashita

Papers

Changes in microbial communities in an apple orchard and its adjacent bush soil in response to season, land-use, and violet root rot infestation