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© iForest -Biogeosciences and Forestry IntroductionSoil health and quality may be successfully monitored through the use of two microbial indexes: (i) the microbial biomass, which is defined by the living component of soil organic matter, excluding the macrofauna and plant roots; and (ii) soil microbial respiration (basal respiration), which is described by the respiration without the addition of an organic substrate to soil (Jenkinson & Ladd 1981, Alef 1995, Sparling 1997. The microbial biomass is small and labile as compared with other ecosystem components; however, because of its key role in the mineralization of nutrients such as C, N, P and S, it is considered a reliable indicator of changes in soil characteristics (Jenkinson & Ladd 1981, Powlson et al. 1987, Balota et al. 2003. Balota et al. (2013) report that changes in the microbial properties of soil may lead to important changes in soil quality, thus affecting nutrient cycling and plant development. Haris (2003) clearly affirmed that the microbial community serves as an indicator of the re-establishment of connections between ecological functions of the biota in disturbed ecosystems. Despite the large variations in mineralogy, soil texture and land use type, extreme environments usually show low organic matter and very low microbial biomass contents, which indicate poor soil quality and limited site productivity (Sparling 1997, Guénon et al. 2013.Soil basal respiration is a well-established parameter to be measured through the decomposition process, and it is defined as the overall activity or energy spent by the indigenous microbial pool (Anderson & Domsch 1990, Sparling 1997. Insam et al. (1991) argued that soil basal respiration reflects the availability of slow-flowing C for microbial permanence and is a measure of basic turnover rates in soil.Robinia pesudoacacia L. (black locust or false acacia) is a deciduous, broad-leaved, light-demanding, medium-sized pioneer tree ranging in height 20-25 m. Black locust is regarded as an invasive, non-indigenous species in many parts of Europe, such as Germany, Italy and Turkey (Ansin & Özkan 1997, Cierjacks et al. 2013. It is well-adapted to grow on different types of soil and environmetal conditions, though it avoids compacted or wet soils. Indeed, its demand for aerated soil is the reason why black locust can be primarily found in disturbed sites from poor to fertile soils (Sabo 2000, Cierjacks et al. 2013. Black locust shows a rapid growth and adaptability, for it has been utilized for soil conservation or fuel wood, as well as for early reforestation of barren soils at disturbed sites (Landgraf et al. 2005, Keskin & Makineci 2009, Noh et al. 2010). However, in Turkey it has been long cultivated as an ornamental plant and it can be currently found in schoolyards, roadsides or other marginal lands (Ansin & Özkan 1997). This tree species is characterized by an extensive root system (Zhou & Shangguan 2005) nodulated by diverse nitrogen-fixing Rhizobium communities, providing the host with an advantage over na...

Purpose Due to climatic and topographic conditions, soil erosion is a major problem in Turkey; approximately 86% of the land is suffering from some degree of erosion. This study investigated the relationship between bare soil slope length and the erosion-induced degradation of soil quality and the loss of carbon (C) and nitrogen (N) from the microbial biomass in eroded sediment in the Western Black Sea Region of Turkey. Materials and methods Six erosion study plots were constructed at an altitude of 146 m with a mean slope of 30%. Each plot had a width of 1.87 m and two slope lengths (5.5 and 11.0 m) with the long axis oriented downslope. Runoff and sediments were collected in two tanks arranged in series at the base of each plot. Microbial biomass carbon (C mic ) and nitrogen (N mic ) were estimated using the chloroform-fumigation extraction method. Moreover, basal respiration was determined by quantifying the carbon dioxide (CO 2 ) released in the process of microbial respiration during 7 days of incubation. Results and discussion Data from six field runoff plots with two slope lengths (5.5 and 11.0 m) revealed that short slopes had more runoff per unit area than long slopes. In contrast, the total soil loss per unit area increased with increasing slope length. The estimated total annual losses of microbial C and N were 641.72 and 106.90 g ha −1 year −1 , respectively, for short slopes and 814.32 and 153.46 g ha −1 year −1 , respectively, for long slopes. Microbial communities of eroded sediment in long slopes are energetically more efficient (lower qCO 2 ) with correspondingly higher C mic /C org ratios (increased biomass) compared to short slopes. Conclusions The present study demonstrated that increased soil loss results in increased C mic /C org percentages and decreased qCO 2 . Moreover, the eroded sediment from long slopes exhibited a healthier eco-physiological profile compared to sediment from short slopes.

Purpose The literature indicates that the presence and activity of microbial biomass could be potential indicators of other changes in mineral soils, making it useful for monitoring and assessing the relationships between plants and soil and their effects on the health and quality of the soil. Therefore, the aim of the study was to determine whether if there were any changes in the C and N content or the basal respiration of microbial biomass in soils under black locust trees (Robinia pseudoacacia L.) between 2013 and 2014. Materials and methods Samples of topsoil (0-6.5 cm) under the black locust were collected randomly from 12 different locations in 2013, and 12 samples were taken from the same locations in 2014. The C and N contents of the microbial biomass were determined by the chloroform fumigation extraction method. Basal respiration was determined by the sodium hydroxide (NaOH) trap method. Results and discussionThe results demonstrated that the average C content of microbial biomass (C mic ) increased by about 55 % in soils under black locust and that the average N content (N mic ) of microbial biomass N increased by about 59 %. Both the C mic and N mic values were significantly affected by the temporal variation (P<0.05). The average basal respiration was lower in 2013 than in 2014, i.e., 0.303 and 0.526 μg CO 2 -C g −1 h −1 , respectively; this difference from 2013 to 2014 was statistically significant (P<0.05). Related to substrate (glucose, protein, carbohydrate, etc.) quality, the average C mic /C org (%) of the soils was significantly (P<0.05) lower in 2013 (5.18 %) than in 2014 (6.86 %). Similarly, the metabolic quotient (qCO 2 ), on average, also was lower in 2013 (0.96 mg CO 2 -C g −1 C mic h −1 ) than in 2014 (1.10 mg CO 2 -C g −1 C mic h −1 ); however, the difference in the values for the two years was not statistically significant (P>0.05). Conclusions Thus, it was concluded that the effect of black locust on the C and N content and basal respiration of the microbial biomass was due to the combined result of changing microclimatic conditions and soil characteristics, including the temperature, moisture content, pH, organic C, and total N in the soil. Therefore, this tree is an appropriate and valuable species where poor ecological conditions exist because of its rapid growth rate and its positive effect on the health and quality of soil.

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