Exploration and exploitation of soil by apple, kiwifruit, peach, Asian pear and grape roots

Abstract

Measurements of root-length density (RLD) in a range of 31 apple, kiwifruit, peach, Asian pear and grape orchards were used to derive indices to describe the exploration and exploitation of rooting volumes. Orchards were of various ages and located on a range of soil types, geographic regions, management systems etc. Data were obtained from core samples of volume 1.66x 10 -4 m 3 randomly taken within a "standard volume", determined by average planting grids, of 2 m radius centred on tree stems, and 1 m depth. Root systems were described using an exploitation index, E(~b), and an exploration index, E(O). E(4) is defined as the proportion of the soil volume which contains roots at RLD greater than or equal to some specified value, q~. E(O) is defined as the proportion of the soil volume which contains roots at any RLD greater than zero. These indices are dependent on sample size, as are all volumetric or soil-coring data.Estimates of E(0) for each orchard were obtained as the proportions of cores containing any RLD>O and assessed for dependence on species. Peach trees had a significantly higher value of E(O), equal to almost 1.0, compared to the other four species where E(O) was approximately 0.8 (p<0.01) or less. There was also some variation with age. E(O) was lower for very young plants which had not fully occupied the sampled soil volume. Exploration indices for woody roots increased with rootstock age but otherwise did not explain large differences in E(~) between species for given ~b values.For example at ~b = 0.05x 104 m.m -3, E(~b) was approximately 0.45 for peach and kiwifruit, and 0.05 for apple, Asian pear and grape, whereas at ~ = 0.5× 10 4 m.m -3 the corresponding values were 0. I and almost zero. Negative exponential curves relating E(~5), scaled by dividing by E(0), to 6 were fitted for each of the 31 orchards. Exponents for these curves, k, were significantly smaller for kiwifruit and peaches than apples, grapes and Asian pears (p<0.05), and smaller for apples than grapes and Asian pears (p_<0.05). A larger k implies a rapid fall-off in E(~b) as ~ increases. Although all five species contained zero and low RLD samples, only kiwifruit and peaches contained higher RLD values and consequently have higher mean RLD. This trend was consistent across all soils, regions, sampling dates, and plant ages.The analyses demonstrate that core sampling can give useful insights into macro-scale root-system distribution, such as the proportion of a soil volume explored and how it is exploited. If positions of core samples are noted during sampling using angular direction, depth and radial distance as spatial coordinates the method can be used to describe root-system structures.

Root distribution of Fagus sylvatica in a chronosequence in western France

“…Likewise, the exploration E (1) index was defined as the number of cells having at least one root intersect in it. We calculated the latter indices by using number of fine root intersects per 100 cm 2 instead of fine root length density (Hughes et al 1995) or root surface area density (Oppelt et al 2005). These parameters are expected to yield better results than root intersects when comparisons between different species are to be made, as species-specific root lengths or areas can lead to different interpretations between surface areas and root numbers with regard to overall strategies for exploration and exploitation of resources.…”

Contrasting rooting patterns of some arid-zone fruit tree species from Botswana – I. Fine root distribution

“…Gandar and Hughes (1988) and Hughes et al (1995), we decided to use root surface area densities (RAD) instead. This decision was justified by two reasons.…”

“…Contrary to Hughes et al (1995), where independent of the size of coarse root systems a fixed 'standard soil volume' was used, we determined an 'individual soil volume', based on the spatial extension of coarse roots and the coring depth (80 cm) (cf. Oppelt et al 2000Oppelt et al , 2001.…”

“…For calculation of mean values for fine root dry weight and RAD cores without fine roots were included. In analogy to Gandar and Hughes (1988) and Hughes et al (1995), an exploitation index E(/), defined as the proportion of soil volume which contains roots at RAD>/, where / is an arbitrary threshold, was estimated for the investigated species. E(0) is the proportion of soil volume which is explored by any roots (i.e., RAD>0) and is called exploration index.…”

“…(Tiliaceae) were analysed. Motivated by the work of Gandar and Hughes (1988) and Hughes et al (1995) we have developed their exploration and exploitation index, in order to describe species-dependent differences in rooting strategies. The species investigated in this work produce fruit and are important to rural people, especially those practising subsistence dryland farming.…”