Although seminal models of these rhizosphere processes were published and tested decades ago (Nye & Marriott, 1969 Barber & Cushman, 1981 Tinker & Nye, 2000), there has been limited progress on their integration into whole-plant models (Warren et al., 2015). Ideally, models of root-N uptake should simulate processes operating on fine spatial scales that control N flux into roots from surrounding soil – processes such as solute movement to roots through diffusion and mass flow, competition for N between plant roots and soil microbes, and kinetics of root-N uptake. Nevertheless, the potential ramifications of plant-N acquisition via diffusion or via mass flow are far reaching and include effects as diverse as plant inter- and intra-species competition, plant allocation optimization, plant water-use efficiency and growth responses to CO 2 and N fertilization.

The separation of plant-N acquisition by diffusion and by mass flow is inherently problematic, both conceptually and experimentally, and attempts to quantify the contribution of each process have arrived at more or less contrasting conclusions. This is in spite of the notion that soil-N transport processes, diffusion and mass flow, may constitute the bottleneck for plant nutrition (Nye, 1977). Furthermore, a given rate of N uptake per unit soil volume may be achieved by lower root biomass in the presence of mass flow.Īlthough the molecular underpinnings of plant-nitrogen (N) uptake and metabolism and soil turnover of N have been studied extensively, the actual processes by which plants acquire N from the soil are still poorly understood. Simulations indicate a strong impact of soil water uptake on N delivery to widely spaced roots through transpirationally driven mass flow.The results point to a benefit of root switching from high- to low-affinity N transport systems in the presence of mass flow. Root-N uptake is sensitive to the rate of mass flow for widely spaced roots with high N uptake capacity, but not for closely spaced roots or roots with low uptake capacity.We highlight a seldom considered interaction between these processes: nutrient traverses the rhizosphere more quickly in the presence of mass flow, reducing the probability of its immobilization before reaching the root surface. Processes governing N supply to roots – diffusion, mass flow, N immobilization by soil microbes – are incorporated in a model of root-N uptake.Yet, neither the MM relationship nor soil-N transport mechanisms are represented in current terrestrial biosphere models. Furthermore, soil-N transport processes that determine soil-N concentration at root surfaces are seen as a bottleneck for plant nutrition. The classic model of nitrogen (N) flux into roots is as a Michaelis–Menten (MM) function of soil-N concentration at root surfaces.Calculate the formula unit masses of ZnO, Na2O, K2C03, given atomic masses of Zn = 65 u, Na = 23 u, K = 39 u, C = 12 u, and O = 16 u.

Calculate the number of aluminium ions present in 0.051 g of aluminium oxide (Al2O3).Calculate the molecular masses of the following compounds:(a) Hydrogen sulphide, H2S(b) Carbon disulphide, CS2(Atomic masses: H = 1 u, S = 32 u, C = 12 u).Which contains more molecules, 10 g of sulphur dioxide (SO2) or 10 g of oxygen (O2)?(Atomic masses : S = 32 u O = 16 u).Calculate the mass in grams of 0.17 mole of hydrogen sulphide, H2S.(Atomic masses : H = 1 u, S = 32 u).What is the mass of 5 moles of sodium carbonate (Na2CO3)?(Atomic masses : Na = 23 u C = 12 u O = 16 u).Calculate the number of molecules present in a drop of chloroform (CHCl3) weighing 0.0239 g.(Atomic mass : C = 12 u H = 1 u Cl = 35.5 u).Calculate the formula unit masses of ( mathrm ) given atomic masses of ( Z n=65 u ), ( N a=23 u, K=39 u, C=12 u. How many moles are represented by 100 g of glucose, C6H12O6 ?(C = 12 u, H = 1 u, O = 16 u).Calculate the molecular mass of hydrogen bromide (HBr).(Atomic masses: H = 1 u Br = 80 u).Calculate the molecular mass of chloroform(CHCl3).(Atomic masses: C = 12 u H = 1 u Cl = 35.5 u).Calculate its molecular mass.(Atomic masses: C = 12 u H = 1 u O = 16 u) The molecular formula of glucose is C6H12O6.Calculate the molecular mass of ethanoic acid, CH3COOH.(Atomic masses : C = 12 u H = 1 u O = 16 u).What weight of oxygen gas will contain the same number of molecules as 56 g of nitrogen gas?(O = 16 u N = 14 u).Calculate the molecular mass of Nitric acid, HNO3.(Atomic masses: H = 1 u N = 14 u O = 16 u).

Mmass nitrogen