C:N:P stoichiometry and nutrient limitation of the soil microbial biomass in a grazed grassland site under experimental P limitation or excess

Abstract

Introduction: The availability of essential nutrients, such as nitrogen (N) and phosphorus (P), can feedback on soil carbon (C) and the soil microbial biomass. Natural cycles can be supplemented by agricultural fertiliser addition, and we determined whether the stoichiometry and nutrient limitation of the microbial biomass could be affected by an unbalanced nutrient supply.Methods: Samples were taken from a long-term trial (in effect since 1968) with annual applications of 0, 15 and 30 kg P ha −1 with constant N and potassium. Soil and microbial biomass CNP contents were measured and nutrient limitation assessed by substrate-induced respiration. Linear regression and discriminant analyses were used to identify the variables explaining nutrient limitation. Results: Soil and biomass CNP increased with increasing P fertiliser, and there was a significant, positive, correlation between microbial biomass P and biomass C, apart from at the highest level of P fertilisation when the microbial biomass was over-saturated with P. The molar ratios of C:N:P in the microbial biomass remained constant (homeostatic) despite large changes in the soil nutrient ratios. Microbial growth was generally limited by C and N, except in soil with no added P when C and P were the main limiting nutrients. C, N and P, however, did not explain all the growth limitation on the soils with no added P. Conclusions: Increased soil C and N were probably due to increased net primary production. Our results confirm that C:N:P ratios within the microbial biomass were constrained (i.e. homeostatic) under near optimum soil conditions. Soils with no added P were characterised by strong microbial P limitation and soils under high P by over-saturation of microorganisms with P. Relative changes in biomass C:P can be indicative of nutrient limitation within a site.

Soil properties and not inputs control carbon : nitrogen : phosphorus ratios in cropped soils in the long term

“…This introduction shows that there is already a significant body of information on the C, N, and P relationships in soils, and it illustrates how this knowledge is used. However, as pointed out by Mulder et al (2013), we lack information on P (i) because of an overall lack of data on P and (ii) because of the different methods used to measure microbial and organic P. Furthermore, although published papers consider soils from agricultural systems (Kirkby et al, 2011;Hartman and Richardson, 2013;Xu et al, 2013), the impacts of agricultural practices are very rarely studied (Mulder et al, 2013;Griffiths et al, 2012). These should, however, be considered as agricultural systems can receive large amounts of C, N, and P through net photosynthesis, symbiotic N 2 fixation, and organic and mineral fertilizer additions, as well as through seeds and wet and dry atmospheric deposition.…”

“…In the studies by Fanin et al and Heuck et al, changes in microbial C : N : P ratios were partly accompanied by changes in microbial community structure. Griffiths et al (2012) and Chen et al (2014) showed that different P fertilization regimes did not modify the C : N : P ratio of soil microorganisms in the long term on a grazed pasture, while they strongly modified the microbial P and C concentrations and the soil microbial community composition. Finally, Mouginot et al (2014) showed that the N : P ratios of fungi and bacteria isolated from grassland leaf litter were similar, whereas the C : N and C : P ratios were higher in fungi than in bacteria, which is in line with observations of higher P concentrations in bacteria than in fungi made by Bünemann et al (2008aBünemann et al ( , 2011.…”

Sensitivity analysis of six soil organic matter models applied to the decomposition of animal manures and crop residues

“…Microbial biomass C was initialised at 2% of soil C (Blagodatskaya and Kuzyakov, 2008;Wutzler and Reichstein, 2013). The microbial biomass C to N ratio was let to vary between 4 and 12 (Hassink, 1994;Friedel and Gabiel, 2001;Cleveland and Liptzin, 2007;Griffiths et al, 2012), by changing the N content of the pool B.…”

“…The six models were subjected to global SA, highlighting the contribution of model parameters on the variation of CO2 emissions and SMN concentration at different stages of SOM decomposition, from 3 to 189 days after soil amendment with animal manures or crop residues, under constant soil temperature and soil water content. Blagodatskaya and Kuzyakov (2008); b, Cavalli and Bechini (2011);c, Cavalli et al (2015); d, Cleveland and Liptzin (2007); e, Friedel and Gabiel (2001); f, Griffiths et al (2012); g, Hadas et al (1998); h, Hadas et al (2004); i, Henriksen and Breland (1999); j, Kätterer and Andrén (2001); k, Morvan et al (2006); l, Peters and Jensen (2011); m, Petersen et al (2005a); n, Petersen et al (2005b); o, Wutzler and Reichstein (2013); p, calculated according to Eq. 10; q, calculated according to Eq.…”

Allelopathic effects of humus forest soil of Hippophae rhamnoides, Caragana korshinskii and Amorpha fruticosa on medicinal plants

“…Record the volume of ferrous sulfate from flask used in the titration and calculate the C content of soil samples. Available potassium (K) was determined with 1.0 mol·L -1 NH 4 A c extraction by a flame photometer method; available phosphorus (P) was determined with 0.5 mol·L -1 sodium hydrogen carbonate extraction by a UV-Vis spectrophotometer method; alkaline nitrogen (N) was determined with magnesium oxide by alkaline hydrolysis diffusion method (Bao, 2005;Griffiths et al, 2012). All treatments in this study were replicated 3 times.…”