Kristiina A. Vogt

Production, Turnover, and Nutrient Dynamics of Above- and Belowground Detritus of World Forests

Publisher Summary Evergreen forests accumulate higher forest floor masses than deciduous in similar climatic zones. In needle-leaved forests, none of the climatic factors or latitude explains the variation in amount of aboveground litterfall mass or litterfall nitrogen (N) input. This is in contrast to the broad-leaved forests in which half of the variation in aboveground litterfall mass or litterfall N input is explained by latitude, mean annual temperature, minimum monthly mean temperature, or logarithmic transformations of precipitation. Lower total root masses were measured in cold temperate needle-leaved deciduous, Mediterranean needle-leaved evergreen, and tropical broad-leaved semi-deciduous forests while higher total mean root masses occurred in tropical broad-leaved evergreen forests. In the warm temperate zones, evergreen forests had similar mean total root masses whether broad-leaved or needle-leaved. However, deciduous forests averaged 5000 kg ha -1 less total root mass than evergreen forests. In cold temperate forests, the proportion of total detrital input to forest floor occurring as aboveground litterfall varied from 23 to 80%. Inclusion of root turnover as part of total litter input changed the calculated mean residence time of organic matter in the forest floor from 7.8 to 6.3 years in a red pine plantation and 68.6 to 15.7 years in a Pacific silver fir stand.

Review of root dynamics in forest ecosystems grouped by climate, climatic forest type and species

Patterns of both above- and belowground biomass and production were evaluated using published information from 200 individual data-sets. Data sets were comprised of the following types of information: organic matter storage in living and dead biomass (e.g. surface organic horizons and soil organic matter accumulations), above- and belowground net primary production (NPP) and biomass, litter transfers, climatic data (i.e. precipitation and temperature), and nutrient storage (N, P, Ca, K) in above- and belowground biomass, soil organic matter and litter transfers. Forests were grouped by climate, foliage life-span, species and soil order. Several climatic and nutrient variables were regressed against fine root biomass or net primary production to determine what variables were most useful in predicting their dynamics. There were no significant or consistent patterns for above- and belowground biomass accumulation or NPP change across the different climatic forest types and by soil order. Similarly, there were no consistent patterns of soil organic matter (SOM) accumulation by climatic forest type but SOM varied significantly by soil order—the chemistry of the soil was more important in determining the amount of organic matter accumulation than climate. Soil orders which were high in aluminum, iron, and clay (e.g. Ultisols, Oxisols) had high total living and dead organic matter accumulations-especially in the cold temperate zone and in the tropics. Climatic variables and nutrient storage pools (i.e. in the forest floor) successfully predicted fine root NPP but not fine root biomass which was better predicted by nutrients in litterfall. The importance of grouping information by species based on their adaptive strategies for water and nutrient-use is suggested by the data. Some species groups did not appear to be sensitive to large changes in either climatic or nutrient variables while for others these variables explained a large proportion of the variation in fine root biomass and/or NPP.

Analysis of some direct and indirect methods for estimating root biomass and production of forests at an ecosystem level

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 researchers personal preference, experiences, equipment, and/or finances.

CARBON DYNAMICS OF ROCKY MOUNTAIN DOUGLAS-FIR: INFLUENCE OF WATER AND NUTRIENT AVAILABILITY'

Changes in biomass distribution, canopy dynamics, and above- and be- lowground net primary production were examined in a Rocky Mountain Douglas-fir (Pseu- dotsuga menziesii var. glauca forest in New Mexico. Nutrient and water availability were experimentally altered by: fertilization (F), irrigation (I), carbon in the form of wood chips (WC), carbon + irrigation (WC/I), and control (C). Prior to treatment, aboveground tree biomass ranged from 238 to 369 000 kg/ha, projected leaf area index (LAI) ranged from 5.4 to 8.7 m2/m2 and aboveground net primary production (ANPP) ranged from 9200 to 11 900 kg* ha-I yr-i. Aboveground NPP was correlated positively (R2 = 0.85) with LAI before the treatments. Canopy dynamics were strongly influenced by water and nutrient availability. For trees of similar diameter, irrigated and fertilized trees supported a signif- icantly greater biomass of new twig and new foliage than control trees. During the 2-yr study leaf area index (LAI) increased by 5, 12, 18, and 24% in the C, I, WC/I, and F plots, respectively, and decreased by 3% in the WC plots. Stand level biomass distribution and production patterns were also affected by the availability of nutrients and water. Two years after the treatments were initiated, new foliage masses were 2400 (F), 2300 (WC/I), 2000 (I), 1900 (C), and 1800 (WC) kg/ha. In 1986, aboveground NPP was 33% greater in the F than WC treatment. Irrigation also increased ANPP. Fine root net primary production ranged from 1540 to 4200 kg ha-i yr-i and was significantly greater (P < .1) in the control than in the four treatments. BNPP comprised 46 (C), 32 (WC), 31 (I), 23 (WC/I), and 23 (F) % of total NPP. Total NPP was correlated positively with LAI (R2 = 0.66) and ranged from 15 360 kg ha- Iyr-I in the WC treatment to 21 140 kg ha-l yr-I in the F treatment. Many of the physiological relations between water or nutrient availability and production and carbon allocation reported in this study are consistent with results from studies on lowland Douglas-fir and other conifer forests in the Pacific Northwest. Collectively, these studies provide a mechanistic understanding of how water and nutrient availability govern production and carbon allocation of conifer forests in the western United States.

Biodiversity and the productivity and stability of ecosystems

Attempts to unveil the relationships between the taxonomic diversity, productivity and stability of ecosystems continue to generate inconclusive, contradictory and controversial conclusions. New insights from recent studies support the hypothesis that species diversity enhances productivity and stability in some ecosystems, but not in others. Appreciation is growing for the ways that particular ecosystem features, such as environmental variability and nutrient stress, can influence biotic interactions. Alternatives to the diversity-stability hypothesis have been proposed, and experimental approaches are starting to evolve to test these hypotheses and to elucidate the mechanisms underlying the functional role of species diversity.

Fine root dynamics following single and multiple disturbances in a subtropical wet forest ecosystem

1 Live and dead fine root biomass and rates of root decomposition were studied prior to and immediately following a localized disturbance (experimental gap creation) and a landscape-level disturbance (Hurricane Hugo) in a lower montane subtropical wet forest in Puerto Rico. The effects of the hurricane on the previously disturbed environment (experimental gaps) were also examined to determine the effects of a multiple disturbance regime. 2) A 40% decline in fine live roots occurred two months following gap creation. Six months following the hurricane, high fine root mortality resulted in a decline of 70-77% of the initial fine live root biomass in the experimental gaps; a similar decline occurred in the control forest

Respiration from the Organ Level to the Stand

Publisher Summary Respiration is a major factor in plant, stand, or ecosystem energy budgets, estimated to consume anywhere from 30–70% of total carbon fixed. Respiration has been an area of particular interest and concern recently because of the possibility that C02-induced global warming might lead to substantial increases in respiration in temperate and boreal ecosystems that could decrease net primary productivity This chapter focuses on respiration. It describes dark respiration as a process by which glucose is enzymatically combined with oxygen to liberate chemical energy and CO2. Most respiration in trees is through the normal cytochrome-mediated pathway, but there is an alternative. Cyanide-resistant or salicylhydroxamic acid-sensitive respiration is a nonphosphorylating respiration pathway that generates only 40–50% as much chemical energy per glucose oxidized. When the respiration costs of producing plant tissue are estimated from tissue analyses, any ATP required for synthesis is produced by cytochromemediated respiration. Photorespiration is a by-product of photosynthesis in C3 plants in which ribulose bisphosphate carboxylase/oxygenase binds to O2 instead of CO2. It manifests as a reduction in the rate of photosynthesis. Considerable effort has been put into developing techniques for scaling individual measurements up to stand level. This chapter focuses on these scaling techniques and how they deal with known sources of variation in respiration.

Decay rate and substrate quality of fine roots and foliage of two tropical tree species in the Luquillo Experimental Forest, Puerto Rico

Decomposition rates, initial chemical composition, and the relationship between initial chemistry and mass loss of fine roots and foliage were determined for two woody tropical species, Prestoea montana and Dacryodes excelsa, over a gradient of sites in two watersheds in the Luquillo Experimental Forest, Puerto Rico. At all locations, fine roots decayed significantly more slowly than foliage during the initial 6 months.Substrate quality of the initial tissue showed marked differences between roots and foliage when using cell wall chemistry, secondary chemistry and total elemental analysis as indices. Quantity of acid detergent fiber (ADF) (non-digestible cell wall fiber) and lignin content were higher for roots than leaves: D. excelsa roots had 55.3% ADF and 28.7% lignin while leaves had 36.2% ADF and 11.8% lignin; P. montana roots had 68.0% ADF and 26.8% lignin while leaves had 48.5% ADF and 16.1% lignin. Aluminum concentrations were higher in fine roots (843 mg kg−1 in D. excelsa, 1500 mg kg−1 in P. montana) than leaves (244 mg kg−1 in D. excelsa, 422 mg kg−1 in P. montana), while calcium concentrations were higher in foliage (5.5 mg g−1 in D. excelsa, 7.8 mg g−1 in P. montana) than roots (3.4 mg g−1 in D. excelsa, 3.1 mg g−1 in P. montana). Nitrogen did not show any trend with tissue or species type. A linear model between mass remaining after 6 months and initial tissue chemistry could be developed only for calcium (r2=0.64).

Belowground responses as indicators of environmental change

Abstract This paper discusses when and under what circumstances belowground parameters become advantageous to monitor as sensitive, early indicators of an environment being exposed to anthropogenic stress. The following specific belowground attributes are presented as useful parameters to monitor because they are sensitive to stress and should be influenced prior to the occurrence of visible aboveground symptoms: fine root biomass and turnover, mycorrhizal biomass and species of fungi colonizing the roots, secondary defensive chemical production in roots, carbohydrate reserves in roots, and nutrient and/or trace element concentrations and ratios in roots.

STRUCTURAL AND FUNCTIONAL RESPONSES OF A SUBTROPICAL FOREST TO 10 YEARS OF HURRICANES AND DROUGHTS

Little is known about ecosystem-level responses to multiple, climatic disturbance events. In the subtropical forests of Puerto Rico, the major natural disturbances are hurricanes and droughts. We tested the ecosystem-level effects of these disturbances in sites with different land use histories. From 1989 to 1992, data were collected to determine the effects of Hurricane Hugo and two droughts on litterfall inputs, fine-root biomass, and decomposition rates in three topographic locations (stream, riparian, upslope) within two watersheds. From 1994 to 1998, we added a third watershed and an experiment in which coarse-wood levels were manipulated to simulate hurricane inputs. Data were collected on tree and palm growth rates, litterfall inputs, fine-root biomass, and decomposition rates. From 1994 to 1998, four hurricanes and three droughts were recorded. Measured parameters had unique responses and recovery rates to hurricanes and droughts. Litterfall inputs returned to long-term mean rates within one month...