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Zheng J.,FuJian Forestry Vocationan Technical College | Xiong D.,State Key Laboratory of Humid Subtropical Mountain Ecology | Xiong D.,Fujian Normal University | Huang J.,State Key Laboratory of Humid Subtropical Mountain Ecology | And 11 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2012

It is increasingly recognized that tree fine roots (<2mm in diameter) are not composed of homogenous units as traditionally assumed. Instead, they include groups of individuals that differ markedly both in structure and function. Fine root respiration is a significant component of carbon cycling in forest ecosystems, however, it is commonly measured according to arbitrary diameter class. To date, few studies have focused on fine root respiration and its relationship with fine root morphology and nutrients across of different root orders, because of the numerous difficulties associated with its measurements,especially in subtropical evergreen broad-leaf forest. So in this study, intact fine root segments of six dominant tree species (Cinnamomum micranthum; Tsoongiodendron odorum Chun; Cinnamomum chekiangense; Castanopsis fabri; Altingia gracilipes; and Castanopsis carlesii) in an evergreen broadleaved forest located at the Wanmulin Nature Reserve, Jian'ou, Fujian province, were collected by excavation, separated into different root orders, and then measured for respiration rate by an Li-6400 portable photosynthesis system. We here aimed to examine the following three questions: (1) the relationship between specific root respiration (SRR) and root order; (2) the effect of root order and tree species on SRR; and (3) the relationship of SRR with specific root length (SRL) and tissue N concentration. The one-way and two- way ANOVA revealed that: tree species, root order and tree species ×root order all had significant effects on SRR (P<0. 01 for all cases). SRR ranged from 0. 625 to 1. 79 μgC·g-·1 s-1 for the lowest root order, and significantly declined with increasing root order, which was consistent for the six tree species(P<0. 01). This decline, however, differed among species, with SRR decreased most sharply for Cinnamomum chekiangense. The regression analysis showed that SRR changed systematically with root order, which could be represented by quadratic, cubic, exponential or power functions. Across all the root orders, SRR was positively correlated both with SRL and nitrogen concentration for each tree species (P<0. 01). Across all the six species, SRR was positively correlated (P<0. 01) with SRL only in the third order, and there was no correlation between SRR and nitrogen concentration in all the five root orders. When pooled by all the tree species and root orders, SRR was positively correlated both with SRL and nitrogen concentration (P<0. 01). These means that both SRL and nitrogen concentration could only reflect the intra-species but not the inter-species variations of SRR. The analysis of covariance demonstrated that: tree species had significant effected on (P <0. 01)the slope of the regression straight line which between SRR and SRL, but root order had no significant effected on slope and intercept of the regression straight line, these means the correlation between SRR and SRL was significantly affected by tree species but not by root orders, and the correlation between SRR and nitrogen concentration was significantly affected both by tree species and root orders. It is concluded that there existed evident functional heterogeneity among fine roots of different branch orders, and SRL could reflect this heterogeneity only in specific tree species. Source


Xiong L.,Fujian Normal University | Xiong L.,State Key Laboratory of Humid Subtropical Mountain Ecology | Yang Y.,Fujian Normal University | Yang Y.,State Key Laboratory of Humid Subtropical Mountain Ecology | And 7 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2015

Dissolved organic carbon (DOC) is a mixture of organic compounds with varying molecular sizes and weights. In forest ecosystems, litterfall is a major aboveground resource of DOC, which supplies soils with carbon as a crucial component of terrestrial biogeochemical cycles. During the migration of litterfall-derived DOC from topsoils to subsoils, soils might retain, transform, or release DOC, depending on the chemical nature of DOC and its interactions with soil surfaces. These physicochemical processes contribute considerably to soil organic carbon (SOC) accumulation. It is generally accepted that soil properties have a great influence on the interaction between soil surface and DOC, with Fe/ Al oxides constraining DOC losses and high SOC content being usually negatively correlated to DOC sorption. However, an inconsistency still remains regarding the extent to which soils properties impact DOC movement. In some cases topsoils rich in SOC might demonstrate higher DOC retention capacity. Although subsoils with abundant Fe/ Al oxides are considered to have a stronger DOC retention capacity, relatively lower SOC content is often found in subsoils, and direct evidence for their higher carbon sequestration potential is rare. One reason for this maybe the amount of DOC from aboveground litterfall, which is not sufficient and little DOC can reach subsoils. Another reason might be that highly sorptive DOC is preferentially absorbed by topsoils, and DOC that reaches subsoils has a weak affinity for soil surfaces. Supplying individual soil horizons with a common DOC solution is thus a good way to differentiate their carbon sequestration capacities. Natural Castanopsis carlesii forests are dominant evergreen broad-leaf forests in mid-subtropical China, and interaction between litterfall derived DOC and red soil (Ferralic Cambisols, World Reference Base) is now recognized as one of the most important mechanisms of C sequestration in this region. To solve inconsistencies about factors controlling DOC translocation in soils and to provide direct information to differentiate carbon sequestration potential between soil horizons, a 200-year-old natural Castanopsis carlesii forest without human interference was selected for undecomposed litter collection and soil sampling at the depth of 0—10 cm, 10—20 cm, 20—40 cm, 40—60 cm, 60—80 cm, 80—100 cm from each of the three profiles in the site. After extracting DOC from the collected litter with ultrapure water, we supplied individual soil cores with the common DOC in the laboratory. We not only analyzed the influences of soil properties on DOC interception, but also studied the changes in structural composition of DOC before and after leaching. The results showed that: (1) DOC interception in subsoils was greater than that in topsoils. Hydrophilic and hydrophobic DOC competed for binding sites on soil surfaces, and aromatic compounds and macromolecular substances of hydrophob c components were preferentially adsorbed by soils; (2) infrared spectrum suggested that hydrophobic materials such as aromatic substances and ethers were much more ready to be adsorbed than alkane materials, while indigenous hydrophilic substances such as phenols, alcohols could be displaced by hydrophobic components of DOC; (3) there was significant positive correlation between DOC interception and the content of clay and free iron oxide and significant negative correlation between DOC interception and the content of sand and soil organic carbon. Soil organic carbon content was the key factor affecting DOC interception in different soil horizons in natural Castanopsis carlesii forest. © 2015 Ecological Society of China. All Rights Reserved. Source


Xiong D.,State Key Laboratory of Humid Subtropical Mountain Ecology | Xiong D.,Fujian Normal University | Huang J.,State Key Laboratory of Humid Subtropical Mountain Ecology | Huang J.,Fujian Normal University | And 8 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2012

Fine roots play an important role in the function of individual plants. Recent studies indicated large heterogeneity in architecture, morphology, anatomy, physiology, and longevity within the fine root pool which can be systematically described by branching order. To date, while it is remarkable how little we know about the architecture and morphology in fine roots of subtropical evergreen broad-leaf forest. So in this study intact fine root segments of six dominant tree species (Cinnamomum micranthum, CIM; Tsoongiodendron odorum Chun, TOC; Cinnamomum chekiangense, CIC; Castanopsis fabri, CAF; Altingia gracilipes, ALG; and Castanopsis carlesii, CAC) were collected by excavation in an evergreen broadleaved forest located at the Wanmulin Nature Reserve, Jian′ou, Fujian province. Individual roots were dissected according to the branching order, starting from the distal end of the root system that was numbered as the first order and then increasing sequentially with each branch from the first order to fifth order roots. Then, fine root samples were scanned by the Espon scanner, used Win-RHIZO system to analyze root architecture and morphology. We attempted to address the following questions: (1) the effect of root order and tree species on fine root architecture and morphology; and (2) the relationship between specific root length, tissue density and diameter across root order and tree species. The result showed that: for CIM, ALG and CAC, the branching ratios (Rb) was higher between the first two root orders (over 4) than between the other orders (about 3); while for TOC, CIC and CAF, Rb were higher between the third and forth orders than between the other orders (about 3), with the highest Rb value of 8. 65 between the third and forth orders of CIC. For all species, 70% to 90% of total root number comprised the first two orders. Root diameter, length, and tissue density increased and specific root length (SRL) decreased with increase in order for all species. Though there was no consistent changed with root order, root biomass was mainly concentrated in the higher root orders. The ANOVA demonstrated that both tree species (P<0. 05 for all cases) and tree species ×branching level (P<0. 01 for all cases) had significant effect on Rb. The branching level had significant effect on Rb for CIC and CAC (P <0. 01) and for the other four species (P < 0. 05). Tree species had significant effect on root length, diameter, biomass (P<0. 01) and SRL (P<0. 05), but had no significant effect on tissue density (P>0. 05). The tree species ×root order interaction had significant effect on root length, diameter, biomass (P<0. 01) and tissue density (P<0. 05), but had no significant effect on SRL (P<0. 01). Though root order had no consistent effect on root length, diameter, SRL and biomass, it had significant effect on tissue density for all species (P <0. 01). The variations in SRL of the first to the forth orders among species were mainly caused by tissue density, while those of the fifth order caused by root diameter. A trade-off between root diameter and tissue density occured in the first order. For individual species, changes in root number, diameter, length, SRL, tissue density and biomass with root order can be represented by exponential, linear, quadratic, cubic or power functions. Source


Xiong D.,State Key Laboratory of Humid Subtropical Mountain Ecology | Xiong D.,Fujian Normal University | Huang J.,State Key Laboratory of Humid Subtropical Mountain Ecology | Huang J.,Fujian Normal University | And 10 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2012

Fine roots, commonly defined as roots < 2 mm in diameter, are often treated as a homogeneous mass compartment. However, this approach ignores the distinct branching structure of fine root systems, roots of different branch orders play different roles in belowground carbon and nutrient cycling. To date, it is remarkable how little we know about the chemical properties in fine root and the correlation between fine root and leaf in chemical properties, especially in subtropical evergreen broadleaved forest. So, in this study, intact fine root segments and leaves of six dominant tree species (Cinnamomum micranthum; Tsoongiodendron odorum Chun; Cinnamomum chekiangense; Castanopsis fabri; Altingia gracilipes; and Castanopsis carlesii) were sampled in an evergreen broadleaved forest located at the Wanmulin Nature Reserve, Jian'ou, Fujian province. We focused on: (1) the relationship between branch order and root nutrient concentrations; (2) the correlation between the chemical and morphological traits of fine root and between the chemical traits of root and leaf; (3) the effect of root order and tree species on root chemical traits. For Cinnamomum micranthum, C content increased as root order increased, while there was no distinct trend for the other five species. There was a negative relationship between root branch order and N and P concentration, and a positive relationship between root branch order and C/ N ratios for the six tree species, while the N/ P ratios had no distinct pattern with branch order. The one-way ANOVA demonstrated that tree species had significant effect on C,N,P concentration, C/ N ratio, and N/ P ratio (P < 0.01). Though root order had significant or marked effect on N,P concentration and C/ N ratio (P<0. 01, P<0. 05), it had no significant effect on C concentration and N/ P ratio (P>0. 05) for the six tree species. The two-way ANOVA showed that tree species ×root order interaction had significant or marked effect on C,N,P concentration and C/ N ratio (P<0. 01, P<0. 05), while it had no effect on N/ P ratio (P>0. 05). The analysis of correlation revealed that variation in C/ N ratio was determined by N concentration in the lower root order and by C concentration in the highest root order, and the variation in N/ P ratio was determined by N concentration. Among tree species, C concentration was coupled with N concentration in the higher root order and the N concentration coupled with P concentration in the lower root order. Specific root length was correlated with N and P concentrations as well as C/ N ratio (P <0. 01), but had no significant correlation with C concentration and N/ P ratio for the six tree species. The comparison among first root order, bulk fine root and leaf for the six tree species indicated that, while there was no significant correlation, N,P concentration and N/ P ratio of the first root order were more similar to those of leaf than those of bulk fine root. It concludes that there was large heterogeneity in nutrient traits among different root orders for these subtropical evergreen broadleaved species, especially N and P concentrations, and the root tip to some extent can serve as an analogue to leaf with regard to nutrient traits. Source


Huang J.,State Key Laboratory of Humid Subtropical Mountain Ecology | Huang J.,Fujian Normal University | Ling H.,State Key Laboratory of Humid Subtropical Mountain Ecology | Ling H.,Fujian Normal University | And 10 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2012

Fine roots production and turnover is a significant component of the carbon cycle in forest ecosystems. Fine root survivorship was monitored by minirhizotrons during two successive years in two subtropical evergreen broadleaved forests (Altingia grlilipes, ALG; and, Castanopsis carlesii, CAC) in Wanmulin Natural Reserve, Jian-ou, Fujian province. Root longevity was estimated by the Kaplan-Meier method and differences among single factors, including fine root diameter (d< 0. 3 mm, 0. 30. 05). With the increase of root order, mean fine root longevity of ALG and CAC were increased significantly (P<0. 01). Mean fine root of ALG′s first order and higher order were (267±8) d and (559±32) d, respectively, While CAC′s were (247±10) d and (425±41) d. The number of fine root in ALG and CAC was decreased with root order increased. With the addition of number of neighbor root, mean fine root longevity of ALG and CAC were increased significantly (P<0. 01). Furthermore, mean fine root longevity of ALG in 00. 05). According to the size of impact on root longevity, these factors can be ranked as: root order, season of birth, root diameter, and number of neighbor root. Soil depth had the weakest effect in ALG while had no effect in CAC (P>0. 05). Source

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