Soil Chemical Analysis

Well-constrained carbon:nitrogen:phosphorus (C:N:P) ratios in planktonic biomass, and their importance in advancing our understanding of biological processes and nutrient cycling in marine ecosystems, has motivated ecologists to search for similar patterns in terrestrial ecosystems. Recent analyses indicate the existence of “Redfield-like” ratios in plants, and such data may provide insight into the nature of nutrient limitation in terrestrial ecosystems. We searched for analogous patterns in the soil and the soil microbial biomass by conducting a review of the literature. Although soil is characterized by high biological diversity, structural complexity and spatial heterogeneity, we found remarkably consistent C:N:P ratios in both total soil pools and the soil microbial biomass. Our analysis indicates that, similar to marine phytoplankton, element concentrations of individual phylogenetic groups within the soil microbial community may vary, but on average, atomic C:N:P ratios in both the soil (186:13:1) and the soil microbial biomass (60:7:1) are well-constrained at the global scale. We did see significant variation in soil and microbial element ratios between vegetation types (i.e., forest versus grassland), but in most cases, the similarities in soil and microbial element ratios among sites and across large scales were more apparent than the differences. Consistent microbial biomass element ratios, combined with data linking specific patterns of microbial element stoichiometry with direct evidence of microbial nutrient limitation, suggest that measuring the proportions of C, N and P in the microbial biomass may represent another useful tool for assessing nutrient limitation of ecosystem processes in terrestrial ecosystems.

https://www.cfc.umt.edu/research/biogeochemistry/files/publications/BGC_85_232%20copy.pdf

C:N:P stoichiometry in soil: is there a “Redfield ratio” for the microbial biomass?

Global biogeochemical models have improved dramatically in the last decade in their representation of the biosphere. Although leaf area data are an important input to such models and are readily available globally, global root distributions for modeling water and nutrient uptake and carbon cycling have not been available. This analysis provides global distributions for fine root biomass, length, and surface area with depth in the soil, and global estimates of nutrient pools in fine roots. Calculated root surface area is almost always greater than leaf area, more than an order of magnitude so in grasslands. The average C:N:P ratio in living fine roots is 450:11:1, and global fine root carbon is more than 5% of all carbon contained in the atmosphere. Assuming conservatively that fine roots turn over once per year, they represent 33% of global annual net primary productivity.

https://www.pnas.org/content/pnas/94/14/7362.full.pdf

A global budget for fine root biomass, surface area, and nutrient contents

Root turnover is a critical component of ecosystem nutrient dynamics and carbon sequestration and is also an important sink for plant primary productivity. We tested global controls on root turnover across climatic gradients and for plant functional groups by using a database of 190 published studies. Root turnover rates increased exponentially with mean annual temperature for fine roots of grasslands (r2 = 0.48) and forests (r2 = 0.17) and for total root biomass in shrublands (r2 = 0.55). On the basis of the best-fit exponential model, the Q10 for root turnover was 1.4 for forest small diameter roots (5 mm or less), 1.6 for grassland fine roots, and 1.9 for shrublands. Surprisingly, after accounting for temperature, there was no such global relationship between precipitation and root turnover. The slowest average turnover rates were observed for entire tree root systems (10% annually), followed by 34% for shrubland total roots, 53% for grassland fine roots, 55% for wetland fine roots, and 56% for forest fine roots. Root turnover decreased from tropical to high-latitude systems for all plant functional groups. To test whether global relationships can be used to predict interannual variability in root turnover, we evaluated 14 yr of published root turnover data from a shortgrass steppe site in northeastern Colorado, USA. At this site there was no correlation between interannual variability in mean annual temperature and root turnover. Rather, turnover was positively correlated with the ratio of growing season precipitation and maximum monthly temperature (r2 = 0.61). We conclude that there are global patterns in rates of root turnover between plant groups and across climatic gradients but that these patterns cannot always be used for the successful prediction of the relationship of root turnover to climate change at a particular site.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1469-8137.2000.00681.x

Global patterns of root turnover for terrestrial ecosystems

Root decomposition represents a significant C flux in terrestrial ecosystems. Roots are exposed to a different decomposition environment than aboveground tissues, and few general principles exist regarding the factors controlling rates of root decay. We use a global dataset to explore the relative importance of climate, environmental variables, and litter quality in regulating rates of root decomposition. The parameters that explained the largest amount of variability in root decay were root Ca concentrations and C:N ratios, with a smaller proportion explained by latitude, mean annual temperature, mean annual precipitation, and actual evapotranspiration (AET). Root chemistry and decay rates varied by plant life form (conifer, broadleaf, or graminoid). Conifer roots had the lowest levels of Ca and N, the highest C:N and lignin:N ratios, and decomposed at the slowest rates. In a stepwise multiple linear regression, AET, root Ca, and C:N ratio accounted for approximately 90% of the variability in root decay rates. Root chemistry appeared to be the primary controller of root decomposition, while climate and environmental factors played secondary roles, in contrast to previously established leaf litter decomposition models.

Global patterns in root decomposition: comparisons of climate and litter quality effects.

/pdf/transdermal-drug-delivery-system-a-review-6tve6k66z7.pdf

Transdermal Drug Delivery System: A Review

Effect of organic amendments of soil on growth and productivity of three common crops viz. Zea mays, Phaseolus vulgaris and Abelmoschus esculentus

We examined the effects of treefall gap size and soil properties on microbial biomass dynamics in an undisturbed mature-phase humid subtropical broadleaved forest in north-east India Canopy gaps had low soil moisture and low microbial biomass suggesting that belowground dynamics accompanied changes in light resources after canopy opening High rainfall in the region causes excessive erosion/leaching of top soil and eventually soil fertility declines in treefall gaps compared to understorey Soil microbial population was less during periods when temperature and moisture conditions are low, while it peaked during rainy season when the litter decomposition rate is at its peak on the forest floor Greater demand for nutrients by plants during rainy season (the peak vegetative growth period) limited the availability of nutrients to soil microbes and, therefore, low microbial C, N and P Weak correlations were also obtained for the relationships between microbial C, N and P and soil physico–chemical properties Gap size did influence the microbial nutrients and their contribution to soil organic carbon, total Kjeldhal nitrogen and available-P Contribution of microbial C to soil organic carbon, microbial N to total nitrogen were similar in both treefall gaps and understorey plots, while the contribution of microbial P to soil available-P was lower in gap compared to the understorey These results indicate that any fluctuation in microbial biomass related nutrient cycling processes in conjunction with the associated microclimate variation may affect the pattern of regeneration of tree seedlings in the gaps and hence be related with their size

Ayyanadar Arunachalam

Papers

Transdermal Drug Delivery System: A Review

Effect of organic amendments of soil on growth and productivity of three common crops viz. Zea mays, Phaseolus vulgaris and Abelmoschus esculentus

Influence of gap size and soil properties on microbial biomass in a subtropical humid forest of north-east India

Dynamics of soil microbial biomass C, N and P in disturbed and undisturbed stands of a tropical wet-evergreen forest

Seasonal dynamics of microbial biomass C, N and P during regrowth of a disturbed subtropical humid forest in north-east India