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Aims: More sustainable agricultural systems, which contribute to C sequestration and biological N fixation, require accurate quantification of plant C and N inputs into soils. This has to be conducted under field conditions, as there are serious shortcomings to pot-based experiments, which have dominated studies on rhizodeposition estimation in the past. Therefore, amounts of below-ground plant C, N, and especially the rhizodeposition of peas were quantified in the field more accurately, with particular emphasis on their transfer into different soil compartments during vegetation. Methods: Pea (Pisum sativum L.) plants were labelled with multiple pulses of 13C-glucose and 15N urea using the cotton wick method. Plants were harvested at four dates depending on plant development. Representative soil samples were taken at harvest with a special drilling tool, considering the spatial distribution of pea roots. Results: Our results indicate that the quantity of C and N rhizodeposition did not change between flowering and maturity. About one third of the C and N rhizodeposits were present in microbial biomass and extractable C or the inorganic N pool of soil. When comparing this field study to a former pot experiment, a higher root-to-shoot ratio was detected; also the rhizodeposition-to-root ratio was altered in the field, questioning the assumption that results from pot experiments can be transferred to field conditions. Conclusions: Due to a higher below-ground C (BGC) and N (BGN) input compared to pot experiments, studies aiming at quantifying BGC and BGN input will have to be conducted under field conditions. [ABSTRACT FROM AUTHOR]

Aims: Radiata pine ( Pinus radiata D. Don) plantations are widely used to control erosion in New Zealand. However, other species with similar growth but longer rotation lengths and ability to coppice may offer future alternatives to radiata pine. Comparing performance of alternative species to radiata thus becomes important if policy is to be developed to promote them. Methods: The below-ground characteristics (roots) of young redwood ( Sequoia sempervirens (D. Don) Endl.) trees from two established plantations in New Zealand were examined and compared with those of radiata pine, and selected poplar and New Zealand native species. Results: Roots with diameters less than 10 mm comprised over 99 % of total root length in 3-yr-old trees and 98 % of total root length in 4-yr-old trees. For roots greater than 2 mm in diameter, total root length of young redwood trees was greater than that of young radiata pine, poplar and the best performing New Zealand native plant. Total root length at a given root collar diameter for young (1-4 year old) redwood trees was significantly greater than for radiata pine trees. Roots of redwoods were finer and more numerous than for radiata but the below-ground biomass for a given root collar diameter showed no statistical difference between the two species. Conclusions: Redwood, because of its comparable growth rate and the production of many fine lateral roots, has the potential to become a keystone erosion-control species in New Zealand, especially on steep lands where there is an increased risk of post-harvest landsliding associated with moderate to severe rainstorm events. [ABSTRACT FROM AUTHOR]

Data on the distribution of root biomass are critical to understanding the ecophysiology of vegetation communities. This is particularly true when models are applied to describe ecohydrology and vegetation function. However, there is a paucity of such information across continental Australia. We quantified vertical and horizontal root biomass distribution in a woodland dominated by Angophora bakeri and Eucalyptus sclerophylla on the Cumberland Plains near Richmond, New South Wales. The site was characterised by a duplex (texture contrast) soil with the A horizon (to 70 cm) consisting of loamy sand and the B horizon (to > 10 m) consisting of sandy clay. The topsoil had a smaller bulk density, a smaller water holding capacity but a larger organic component and a larger hydraulic conductivity in comparison to the subsoil. Root biomass was sampled to 1.5 m depth and declined through the soil profile. Whilst total biomass in the B horizon was relatively small, its contribution to the function of the trees was highly significant. Coarse roots accounted for approximately 82% of the root mass recovered. Lateral distribution of fine roots was generally even but coarse roots were more likely to occur closer to tree stems. Variation in tree diameter explained 75% of the variation in total below-ground biomass. The trench method suggested the belowground biomass was 6.03 ± 1.21 kg m−2 but this method created bias towards sampling close to tree stems. We found that approximately 68% of root material was within a 2 m radius of tree stems and this made up 54% of the total number of samples but in reality, only approximately 5 to 10% of the site is within a 2 m radius of tree stems. Based on these proportions, our recalculated belowground biomass was 2.93 ± 0.59 kg m−2. These measurements provide valuable data for modeling of ecosystem water use and productivity. [ABSTRACT FROM AUTHOR]

The aim of this controlled environment experiment was to quantify the distribution of leaf-fed-15N and canopy fed-13C within nodulating, non-nodulating or N fertilized non-nodulating Cicer arietinum L. and in their surrounding rhizosphere soil, excluding soil + root respiration. Nodulating chickpea partitioned 32% of its total N and 27% of its total recoverable C below-ground, of which only 50% of N and 36% of C were in the clean root fraction. Non-nodulating chickpea allocated equal recoverable C but slightly less N (28%) below-ground but lost less C from plant induced below-ground respiration. The importance of this below-ground partitioning for crop systems C and N balances is highlighted by their large (45% and 33%, for N and C, respectively) contribution to the total plant derived residue (recyclable) fraction. Recovered 15N and 13C were greater ( P < 0.05) in the outer-rhizosphere (459 µg 15N and 3.2 mg 13C core−1) than in the inner-rhizosphere soil (detached from roots during freeze-drying; 18 µg 15N and 67 µg 13C core−1) in relation with the relative size of these compartments. This highlights the significance of the outer-rhizosphere soil when estimating C and N budgets and quantifying rhizodeposition, and the benefit of a double (15N, 13C) isotope approach to determine this flow against large background soil C and N pools. [ABSTRACT FROM AUTHOR]