Unearthing the hidden world of roots: Root biomass and architecture differ among species within the same guild (original) (raw)
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Carbon balance and management, 2015
Refined estimation of carbon (C) stocks within forest ecosystems is a critical component of efforts to reduce greenhouse gas emissions and mitigate the effects of projected climate change through forest C management. Specifically, belowground C stocks are currently estimated in the United States' national greenhouse gas inventory (US NGHGI) using nationally consistent species- and diameter-specific equations applied to individual trees. Recent scientific evidence has pointed to the importance of climate as a driver of belowground C stocks. This study estimates belowground C using current methods applied in the US NGHGI and describes a new approach for merging both allometric models with climate-derived predictions of belowground C stocks. Climate-adjusted predictions were variable depending on the region and forest type of interest, but represented an increase of 368.87 Tg of belowground C across the US, or a 6.4 % increase when compared to currently-implemented NGHGI estimates....
Tree size and climatic water deficit control root to shoot ratio in individual trees globally
Letter (not the abstract but introduction) Plants acquire carbon from the atmosphere and allocate it among different organs in response to environmental and developmental constraints (Hodge, 2004; Poorter et al., 2012). One classic example of differential allocation is the relative investment into aboveground vs belowground organs, captured by the root : shoot ratio (R :S; Cairns et al., 1997). Optimal partitioning theory suggests that plants allocate more resources to the organ that acquires the most limiting resource (Reynolds & Thornley, 1982; Johnson & Thornley, 1987). Accordingly, plants would allocate more carbon to roots if the limiting resources are belowground, that is water and nutrients, and would allocate more carbon aboveground when the limiting resource is light or CO2. This theory has been supported by recent research showing that the R : S of an individual plant is modulated by environmental factors (Poorter et al., 2012; Fatichi et al., 2014). However, understanding the mechanisms underpinning plant allocation and its response to environmental factors is an active field of research (Delpierre et al., 2016; Paul et al., 2016), and it is likely that plant size and species composition have an effect on R :S. Accounting for these sources of variation is an important challenge for modelling (Franklin et al., 2012).
Root biomass allocation in the world's upland forests
Oecologia, 1997
Because the world's forests play a major role in regulating nutrient and carbon cycles, there is much interest in estimating their biomass. Estimates of aboveground biomass based on well-established methods are relatively abundant; estimates of root biomass based on standard methods are much less common. The goal of this work was to determine if a reliable method to estimate root biomass density for forests could be developed based on existing data from the literature. The forestry literature containing root biomass measurements was reviewed and summarized and relationships between both root biomass density (Mg ha A1 ) and root:shoot ratios (R/S) as dependent variables and various edaphic and climatic independent variables, singly and in combination, were statistically tested. None of the tested independent variables of aboveground biomass density, latitude, temperature, precipitation, temperature:precipitation ratios, tree type, soil texture, and age had important explanatory value for R/S. However, linear regression analysis showed that aboveground biomass density, age, and latitudinal category were the most important predictors of root biomass density, and together explained 84% of the variation. A comparison of root biomass density estimates based on our equations with those based on use of generalized R/S ratios for forests in the United States indicated that our method tended to produce estimates that were about 20% higher.
Root biomass may to contribute a substantial proportion of the carbon sequestered in new tree plantings, particularly in regions where rainfall and/or site quality is relatively low as this may result in relatively high allocation of plant biomass below-ground to source required water or nutrients. However, root biomass is often overlooked because of difficulty with measurement. In Australia, most carbon plantings are currently mixed-species environmental or mallee eucalypt plantings on agricultural land in regions with rainfall of 250-850 mm year À1 . Here, we collated new and existing root biomass data from ca. 900 individual trees or shrubs to develop and test allometric equations for predicting root biomass based on stem diameter (of unharvested trees or shrubs) or height (of coppice harvested trees) in these plantings. Equations developed showed significant differences between groupings of species with differing growth habits or from different genera. Grouping species into categories of: (i) non-eucalypts, (ii) tree-form eucalypts, (iii) unharvested mallee eucalypts, and (iv) coppiced mallee eucalypts, provided equations with model efficiencies of 0.64-0.90. In the process of collating data across different studies, corrections were required for data consistency. Uncertainty analysis showed that although these corrections resulted in some uncertainty in the equations developed, measurement errors, particularly of stem diameter, were also important contributors to this uncertainty. We tested equations developed using data from 11 environmental and mallee planting sites where direct measurements of root biomass were made through whole-plot excavation. Site-level predictions of root biomass from individual tree allometry were effective, with an efficiency of prediction of 0.98. These results indicate that the generic allometric equations developed can be confidently applied across the Australian agricultural region with 250-850 mm year À1 rainfall to obtain accurate regional estimates of root biomass in the currently relatively young (<20 year old) environmental and mallee plantings.
Journal of Forest Planning, 2003
Root biomass can represent a significant proportien of the total ecosystem biomass, although the difficulty in extracting the reots is eften a limit{ng factor when estimating the belowground biomass. The objective of this study is to create equations to estimate the roet variables from other tree variables for mizunara oak CQuercus crisPttla BLuME) in broad-leaved secondary forests, First, experimenta1 plots were established ln secondary forests dominated by mizunara oak and sample oak trees were felled just outside the plots. 'ihe biomass of each tree orgaii was measured and other reot variables such as root length, area and volume were also measured. Then, allocatien of the four root variables by root diameter classes was described, Regression equations by power functien were created between the four root variables and root diameter to estimate the missing root parts by root diameter classes ancl for the total reot systern. Root variables for missing parts were estimated frorn the diameter of broken root ends with regression equations between the four root variables and roet diameter for tetal root system. Finally, allometric regressions between root variables and ether tree variab]es were analyzed both by root diameter classes and for the tetal roet system. Diameter at beast height (DBH) preved to be a geod predictor of root variab]es fer different reot classes and for the tota1 root system, Diarneter at stump height (DSH) can be a usefu1 estimator if branching starts at DBH as it also shows high correlation with root systems. Kdywords: missing root, roet area, roet blomass, roet length, root volume water or nutrient uptake asOHM, 1979), Because it is difficult to classLly reots in the sarne way as to classify the abeveground parts, KARTzuMI (1974a) attempted to classify roets mechanically into six parts and BOHM (1979) reported that the common practice ef dividing tree roots into classes with different diameters is on aid to obtain information on the amount of fine, small, medium, and large reots in a reot system. Furthermore, VoGT (1989) $uggested that reot systems could be divided into several diameter classes based on their funct{on in tihe support, storage, transport and uptake J fon Rann. 9:85-95ceO03) NII-Electronic
Carbon allocation between tree root growth and root respiration in boreal pine forest
Oecologia, 2002
Soil respiration, i.e. respiration by mycorrhizal roots and by heterotrophic organisms decomposing above-and below-ground litters, is a major component in ecosystem carbon (C) balances. For decades, the paradigm has been that the biomass of fine roots of trees turns over several times a year, which together with large inputs of above-ground litter leaves little room for the contribution from root respiration. Here, we combine the results of a recent tree girdling experiment with the C budget of the classic Swedish Coniferous Forest (SWECON) project, in which root growth and turnover were estimated to be high. We observe that such a high rate of root turnover requires an unlikely high C use efficiency for root growth, and is not consistent with the 1:1 relation between root: heterotrophic respiration obtained in the girdling experiment. Our analysis suggests that 75% of the C allocated to roots is respired, while 25% is used for growth, and hence that root growth and turnover were grossly overestimated in the SWECON study.
Plant and Soil, 1998
The relationship of global climate change to plant growth and the role of forests as sites of carbon sequestration have encouraged the refinement of the estimates of root biomass and production. However, tremendous controversy exists in the literature as to which is the best method to determine fine root biomass and production. This lack of consensus makes it difficult for researchers to determine which methods are most appropriate for their system. The sequential root coring method was the most commonly used method to collect root biomass data in the past and is still commonly used. But within the last decade the use of minirhizotrons has become a favorite method of many researchers. In addition, due to the high labor-intensive requirements of many of the direct approaches to determine root biomass, there has been a shift to develop indirect methods that would allow fine root biomass and production to be predicted using data on easily monitored variables that are highly correlated to root dynamics. Discussions occur as to which method should be used but without gathering data from the same site using different methods, these discussions can be futile. This paper discusses and compares the results of the most commonly used direct and indirect methods of determining root biomass and production: sequential root coring, ingrowth cores, minirhizotrons, carbon fluxes approach, nitrogen budget approach and correlations with abiotic resources. No consistent relationships were apparent when comparing several sites where at least one of the indirect and direct methods were used on the same site. Until the different root methods can be compared to some independently derived root biomass value obtained from total carbon budgets for systems, one root method cannot be stated to be the best and the method of choice will be determined from researcher's personal preference, experiences, equipment, and/or finances.
Comparison of direct and indirect methods for studying root dynamics of forests
Plant and Soil
The relationship of global climate change to plant growth and the role of forests as sites of carbon sequestration have encouraged the refinement of the estimates of root biomass and production. However, tremendous controversy exists in the literature as to which is the best method to determine fine root biomass and production. This lack of consensus makes it difficult for researchers to determine which methods are most appropriate for their system. The sequential root coring method was the most commonly used method to collect root biomass data in the past and is still commonly used. But within the last decade the use of minirhizotrons has become a favorite method of many researchers. In addition, due to the high labor-intensive requirements of many of the direct approaches to determine root biomass, there has been a shift to develop indirect methods that would allow fine root biomass and production to be predicted using data on easily monitored variables that are highly correlated to root dynamics. Discussions occur as to which method should be used but without gathering data from the same site using different methods, these discussions can be futile. This paper discusses and compares the results of the most commonly used direct and indirect methods of determining root biomass and production: sequential root coring, ingrowth cores, minirhizotrons, carbon fluxes approach, nitrogen budget approach and correlations with abiotic resources. No consistent relationships were apparent when comparing several sites where at least one of the indirect and direct methods were used on the same site. Until the different root methods can be compared to some independently derived root biomass value obtained from total carbon budgets for systems, one root method cannot be stated to be the best and the method of choice will be determined from researcher's personal preference, experiences, equipment, and/or finances.