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Fine Root Growth (fine + root_growth)
Selected AbstractsEstimating Fine Root Turnover in Tropical Forests along an Elevational Transect using MinirhizotronsBIOTROPICA, Issue 5 2008Sophie Graefe ABSTRACT Growth and death of fine roots represent an important carbon sink in forests. Our understanding of the patterns of fine root turnover is limited, in particular in tropical forests, despite its acknowledged importance in the global carbon cycle. We used the minirhizotron technique for studying the changes in fine root longevity and turnover along a 2000-m-elevational transect in the tropical mountain forests of South Ecuador. Fine root growth and loss rates were monitored during a 5-mo period at intervals of four weeks with each 10 minirhizotron tubes in three stands at 1050, 1890, and 3060 m asl. Average root loss rate decreased from 1.07 to 0.72 g/g/yr from 1050 to 1890 m, indicating an increase in mean root longevity with increasing elevation. However average root loss rate increased again toward the uppermost stand at 3060 m (1.30 g/g/yr). Thus, root longevity increased from lower montane to mid-montane elevation as would be expected from an effect of low temperature on root turnover, but it decreased further upslope despite colder temperatures. We suggest that adverse soil conditions may reduce root longevity at high elevations in South Ecuador, and are thus additional factors besides temperature that control root dynamics in tropical mountain forests. [source] Fine root dynamics in a loblolly pine forest are influenced by free-air-CO2 -enrichment: a six-year-minirhizotron studyGLOBAL CHANGE BIOLOGY, Issue 3 2008SETH G. PRITCHARD Abstract Efforts to characterize carbon (C) cycling among atmosphere, forest canopy, and soil C pools are hindered by poorly quantified fine root dynamics. We characterized the influence of free-air-CO2 -enrichment (ambient +200 ppm) on fine roots for a period of 6 years (Autumn 1998 through Autumn 2004) in an 18-year-old loblolly pine (Pinus taeda) plantation near Durham, NC, USA using minirhizotrons. Root production and mortality were synchronous processes that peaked most years during spring and early summer. Seasonality of fine root production and mortality was not influenced by atmospheric CO2 availability. Averaged over all 6 years of the study, CO2 enrichment increased average fine root standing crop (+23%), annual root length production (+25%), and annual root length mortality (+36%). Larger increase in mortality compared with production with CO2 enrichment is explained by shorter average fine root lifespans in elevated plots (500 days) compared with controls (574 days). The effects of CO2 -enrichment on fine root proliferation tended to shift from shallow (0,15 cm) to deeper soil depths (15,30) with increasing duration of the study. Diameters of fine roots were initially increased by CO2 -enrichment but this effect diminished over time. Averaged over 6 years, annual fine root NPP was estimated to be 163 g dw m,2 yr,1 in CO2 -enriched plots and 130 g dw m,2 yr,1 in control plots (P= 0.13) corresponding to an average annual additional input of fine root biomass to soil of 33 g m,2 yr,1 in CO2 -enriched plots. A lack of consistent CO2× year effects suggest that the positive effects of CO2 enrichment on fine root growth persisted 6 years following minirhizotron tube installation (8 years following initiation of the CO2 fumigation). Although CO2 -enrichment contributed to extra flow of C into soil in this experiment, the magnitude of the effect was small suggesting only modest potential for fine root processes to directly contribute to soil C storage in south-eastern pine forests. [source] Uncertainties in interpretation of isotope signals for estimation of fine root longevity: theoretical considerationsGLOBAL CHANGE BIOLOGY, Issue 7 2003YIQI LUOArticle first published online: 25 JUN 200 Abstract This paper examines uncertainties in the interpretation of isotope signals when estimating fine root longevity, particularly in forests. The isotope signals are depleted ,13C values from elevated CO2 experiments and enriched ,14C values from bomb 14C in atmospheric CO2. For the CO2 experiments, I explored the effects of six root mortality patterns (on,off, proportional, constant, normal, left skew, and right skew distributions), five levels of nonstructural carbohydrate (NSC) reserves, and increased root growth on root ,13C values after CO2 fumigation. My analysis indicates that fitting a linear equation to ,13C data provides unbiased estimates of longevity only if root mortality follows an on,off model, without dilution of isotope signals by pretreatment NSC reserves, and under a steady state between growth and death. If root mortality follows the other patterns, the linear extrapolation considerably overestimates root longevity. In contrast, fitting an exponential equation to ,13C data underestimates longevity with all the mortality patterns except the proportional one. With either linear or exponential extrapolation, dilution of isotope signals by pretreatment NSC reserves could result in overestimation of root longevity by several-fold. Root longevity is underestimated if elevated CO2 stimulates fine root growth. For the bomb 14C approach, I examined the effects of four mortality patterns (on,off, proportional, constant, and normal distribution) on root ,14C values. For a given ,14C value, the proportional pattern usually provides a shorter estimate of root longevity than the other patterns. Overall, we have to improve our understanding of root growth and mortality patterns and to measure NSC reserves in order to reduce uncertainties in estimated fine root longevity from isotope data. [source] Environmental control of fine root dynamics in a northern hardwood forestGLOBAL CHANGE BIOLOGY, Issue 5 2003GERALDINE L. TIERNEY Abstract Understanding how exogenous and endogenous factors control the distribution, production and mortality of fine roots is fundamental to assessing the implications of global change, yet our knowledge of control over fine root dynamics remains rudimentary. To improve understanding of these processes, the present study developed regression relationships between environmental variables and fine root dynamics within a northern hardwood forest in New Hampshire, USA, which was experimentally manipulated with a snow removal treatment. Fine roots (< 1 mm diameter) were observed using minirhizotrons for 2 years in sugar maple and yellow birch stands and analyzed in relation to temperature, water and nutrient availability. Fine root dynamics at this site fluctuated seasonally, with growth and mortality peaking during warmer months. Monthly fine root production was strongly associated with mean monthly air temperature and neither soil moisture nor nutrient availability added additional predictive power to this relationship. This relationship exhibited a seasonal temperature hysteresis, which was altered by snow removal treatment. These results suggest that both exogenous and endogenous cues may be important in controlling fine root growth in this system. Proportional fine root mortality was directly associated with mean monthly soil temperature, and proportional fine root mortality during the over-winter interval was strongly related to whether the soil froze. The strong relationship between fine root production and air temperature reported herein contrasts with findings from some hardwood forest sites and indicates that controls on fine root dynamics vary geographically. Future research must more clearly distinguish between endogenous and exogenous control over fine root dynamics in various ecosystems. [source] Effects of water and nutrient availability on fine root growth in eastern Amazonian forest regrowth, BrazilNEW PHYTOLOGIST, Issue 3 2010Tâmara Thaiz Santana Lima Summary ,Fine root dynamics is widely recognized as an important biogeochemical process, but there are few data on fine root growth and its response to soil resource availability, especially for tropical forests. ,We evaluated the response of fine root dynamics to altered availability of soil water and nutrients in a 20-yr-old forest regrowth in eastern Amazonia. In one experiment the dry season reduction in soil moisture was alleviated by irrigation. In the other experiment, nutrient supply was reduced by litter removal. We used the ingrowth core technique to measure fine root mass growth, length growth, mortality and specific root length. ,Dry-season irrigation had no significant effect on mass and length of live and dead roots, whereas litter removal reduced mass and length of live roots. For both irrigation and litter removal experiments, root growth was significantly greater in the dry season than in the wet season. ,Increased root growth was associated with decreased soil water availability. However, root growth did not increase in response to nutrient reduction in litter removal plots. Overall, our results suggest that belowground allocation may differ according to the type of soil resource limitation. [source] Size and Structure of Fine Root Systems in Old-growth and Secondary Tropical Montane Forests (Costa Rica)BIOTROPICA, Issue 2 2003Dietrich Hertel ABSTRACT The fine root systems of three tropical montane forests differing in age and history were investigated in the Cordillera Talamanca, Costa Rica. We analyzed abundance, vertical distribution, and morphology of fine roots in an early successional forest (10,15 years old, ESF), a mid-successional forest (40 years old, MSP), and a nearby undisturbed old-growth forest (OGF), and related the root data to soil morphological and chemical parameters. The OGF stand contained a 19 cm deep organic layer on the forest floor (i.e., 530 mol C/m2), which was two and five times thicker than that of the MSF (10 cm) and ESF stands (4 cm), respectively. There was a corresponding decrease in fine root biomass in this horizon from 1128 g dry matter/m2 in the old-growth forest to 337 (MSF) and 31 g/m2 (ESF) in the secondary forests, although the stands had similar leaf areas. The organic layer was a preferred substrate for fine root growth in the old-growth forest as indicated by more than four times higher fine root densities (root mass per soil volume) than in the mineral topsoil (0,10 cm); in the two secondary forests, root densities in the organic layer were equal to or lower than in the mineral soil. Specific fine root surface areas and specific root tip abundance (tips per unit root dry mass) were significantly greater in the roots of the ESF than the MSF and OGF stands. Most roots of the ESF trees (8 abundant species) were infected by VA mycorrhizal fungi; ectomycorrhizal species (Quercus copeyemis and Q. costaricensis) were dominant in the MSF and OGF stands. Replacement of tropical montane oak forest by secondary forest in Costa Rica has resulted in (1) a large reduction of tree fine root biomass; (2) a substantial decrease in depth of the organic layer (and thus in preferred rooting space); and (3) a great loss of soil carbon and nutrients. Whether old,growth Quercus forests maintain a very high fine root biomass because their ectomycorrhizal rootlets are less effective in nutrient absorption than those of VA mycorrhizal secondary forests, or if their nutrient demand is much higher than that of secondary forests (despite a similar leaf area and leaf mass production), remains unclear. [source] | ||||||||||