Drought Reduces Root Respiration In Sugar Maple Forests

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/117195/1/eap199883771.pd

Anthropogenic N deposition and the fate of 15 NO 3 − in a northern hardwood ecosystem

Human activity has substantially increased atmospheric NO 3 − deposition in many regions of the Earth, which could lead to the N saturation of terrestrial ecosystems. Sugar maple ( Acer saccharum Marsh.) dominated northern hardwood forests in the Upper Great Lakes region may be particularly sensitive to chronic NO 3 − deposition, because relatively moderate experimental increases (three times ambient) have resulted in substantial N leaching over a relatively short duration (5–7 years). Although microbial immobilization is an initial sink (i.e., within 1–2 days) for anthropogenic NO 3 − in this ecosystem, we have an incomplete understanding of the processes controlling the longer-term (i.e., after 1 year) retention and flow of anthropogenic N. Our objectives were to determine: (i) whether chronic NO 3 − additions have altered the N content of major ecosystem pools, and (ii) the longer-term fate of 15 NO 3 − in plots receiving chronic NO 3 − addition. We addressed these objectives using a field experiment in which three northern hardwood plots receive ambient atmospheric N deposition (ca. 0.9 g N m −2 year −1 ) and three plots which receive ambient plus experimental N deposition (3.0 g NO 3 − -N m −2 year −1 ). Chronic NO 3 − deposition significantly increased the N concentration and content (g N/m 2 ) of canopy leaves, which contained 72% more N than the control treatment. However, chronic NO 3 − deposition did not significantly alter the biomass, N concentration or N content of any other ecosystem pool. The largest portion of 15 N recovered after 1 year occurred in overstory leaves and branches (10%). In contrast, we recovered virtually none of the isotope in soil organic matter (SOM), indicating that SOM was not a sink for anthropogenic NO 3 − over a 1 year duration. Our results indicate that anthropogenic NO 3 − initially assimilated by the microbial community is released into soil solution where it is subsequently taken up by overstory trees and allocated to the canopy. Anthropogenic N appears to be incorporated into SOM only after it is returned to the forest floor and soil via leaf litter fall. Short- and long-term isotope tracing studies provided very different results and illustrate the need to understand the physiological processes controlling the flow of anthropogenic N in terrestrial ecosystems and the specific time steps over which they operate.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42478/1/10533_2004_Article_5147148.pd

Ecological classification and analysis of the wetland ecosystems of the University of Michigan Biolo

Master of ScienceForest EcologyUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/115678/1/39015028868589.pd

Belowground carbon dynamics in northern hardwood forests: Factors controlling respiration from roots and soil microorganisms.

Terrestrial ecosystems can be important sinks for rising atmospheric carbon dioxide (CO\sb2) levels, due to enhanced carbon (C) fixation by the aboveground portions of plants. However, identifying the extent to which terrestrial ecosystems will function as net C sinks or sources in response to climate change requires knowledge of belowground C dynamics as well. To determine the effects of predicted increases in atmospheric nitrogen (N) deposition and climatic warming on the release of CO\sb2 from soils, I conducted a series of three experiments in northern hardwood forests in Michigan, USA. In the first study, I found that the specific respiration rate (g CO\sb2-C kg\sp{-1} h\sp{-1}) of fine roots ($<$2.0 mm diameter) increased exponentially with higher soil temperatures. The tissue N concentration and associated specific respiration rates of fine roots also increased at sites with high soil N availability, apparently due to the greater C costs of maintaining plant tissues high in proteins and other nitrogenous compounds. In a second experiment, I used molecular, lipid biomarker techniques, in conjunction with kinetic studies of microbial respiration, to examine the response of microbial communities to soil warming. It appears that an increase in temperature elicited shifts in soil microbial community composition and concomitant changes in microbial function (i.e., respiration). In the third study, I found that fine root biomass (kg m\sp{-2}) in the upper 10 cm of soil decreased and specific respiration rates (g CO\sb2-C kg\sp{-1} h\sp{-1}) increased with greater soil N availability. Thus, total fine root respiration (biomass x specific respiration rate, g CO\sb2-C m\sp{-2} h\sp{-1}) was relatively unaffected by soil N availability. Furthermore, total fine root respiration responded to increases in soil temperature in a manner similar to total soil respiration (g CO\sb2-C m\sp{-2} h\sp{-1}. As a result, the CO\sb2 flux from fine roots was a relatively constant proportion of total soil respiration, regardless of soil N availability or temperature. My results demonstrate that fine root and microbial respiration are responsive to changes in soil temperature and N availability, but that determining their contribution to the flux of CO\sb2 from soil requires an examination of their dynamic and often compensatory responses to environmental change.Ph.D.Biological SciencesEcologyEnvironmental scienceHealth and Environmental SciencesSoil sciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/130405/2/9722130.pd

Competitive interactions between native Spartina alterniflora and non-native Phragmites australis depend on nutrient loading and temperature.

We explored the nature and impact of competitive interactions between the salt marsh foundational plant Spartina alterniflora and invasive Phragmites australis in New England under varying levels of anthropogenic influence from nutrient loading and temperature warming. Plants were grown with and without competition in mesocosms over a four-month growing season. Mesocosms were split evenly among three levels of nutrient additions and two temperatures varying by an average of ~3° C, manipulated using small greenhouses. We measured aboveground productivity as total biomass, numbers of new stems, and mean stem height. Nutrient enrichment increased all growth parameters, while competition generally reduced aboveground biomass and the production of new stems in both species. Most importantly, smooth cordgrass suffered no negative consequences of competition when no nutrients were added and temperature was elevated. The results of this study suggest that minimizing nutrient loading into coastal marshes could be an important factor in slowing the spread of common reed into the low marsh zone of New England salt marshes as global temperatures continue to warm

Fine root respiration in northern hardwood forests in relation to temperature and nitrogen availability

We examined fine-root ( \u3c 2.0 mm diameter) respiration throughout one growing season in four northern hardwood stands dominated by sugar maple (Acer saccharum Marsh.), located along soil temperature and nitrogen (N) availability gradients. In each stand, we fertilized three 50 x 50 m plots with 30 kg NO3/--N ha-1 year-1 and an additional three plots received no N and served as controls. We predicted that root respiration rates would increase with increasing soil temperature and N availability. We reasoned that respiration would be greater for trees using NO3/- as an N source than for trees using NH4/+ as an N source because of the greater carbon (C) costs associated with NO3/- versus NH4/+ uptake and assimilation. Within stands, seasonal patterns of fine-root respiration rates followed temporal changes in soil temperature, ranging from a low of 2.1 μmol O2 kg-1 s-1 at 6 °C to a high of 7.0 μmol O2 kg-1 s-1 at 18 °C. Differences in respiration rates among stands at a given soil temperature were related to variability in total net N mineralized (48-90 μg N g-1) throughout the growing season and associated changes in mean root tissue N concentration (1.18- 1.36 mol N kg-1). The hypothesized increases in respiration in response to NO3/- fertilization were not observed. The best-fit model describing patterns within and among stands had root respiration rates increasing exponentially with soil temperature and increasing linearly with increasing tissue N concentration: R = 1.347N e(0.0727T) (r2 = 0.63, P \u3c 0.01), where R is root respiration rate (μmol O2 kg-1 s-1), N is root tissue N concentration (mol N kg-1), and T is soil temperature (°C). We conclude that, in northern hardwood forests dominated by sugar maple, root respiration is responsive to changes in both soil temperature and N availability, and that both factors should be considered in models of forest C dynamics

Effect of measurement CO \u3c inf\u3e 2 concentration on sugar maple root respiration

Accurate estimates of root respiration are crucial to predicting below ground C cycling in forest ecosystems. Inhibition of respiration has been reported as a short-term response of plant tissue to elevated measurement [CO2]. We sought to determine if measurement [CO2] affected root respiration in samples from mature sugar maple (Acer saccharum Marsh.) forests and to assess possible errors associated with root respiration measurements made at [CO2]s lower than that typical of the soil atmosphere. Root respiration was measured as both CO2 production and O2 consumption on excised fine roots (≤ 1.0 mm) at [CO2]s ranging from 350 to \u3e 20,000 μl l-1. Root respiration was significantly affected by the [CO2] at which measurements were made for both CO2 production and O2 consumption. Root respiration was most sensitive to [CO2] near and below normal soil concentrations ( \u3c 1500 μl l-1). Respiration rates changed little at [CO2]s above 3000 μl l-1 and were essentially constant above 6000 μl l-1 CO2. These findings call into question estimates of root respiration made at or near atmospheric [CO2], suggesting that they overestimate actual rates in the soil. Our results indicate that sugar maple root respiration at atmospheric [CO2] (350 μl l-1) is about 139% of that at soil [CO2]. Although the causal mechanism remains unknown, the increase in root respiration at low measurement [CO2] is significant and should be accounted for when estimating or modeling root respiration. Until the direct effect of [CO2] on root respiration is fully understood, we recommend making measurements at a [CO2] representative of, or higher than, soil [CO2]. In all cases, the [CO2] at which measurements are made and the [CO2] typical of the soil atmosphere should be reported

Mean (± 1 s.e.) adjusted aboveground biomass, number of new stems, and stem height of <i>S</i>. <i>alterniflora</i> at ambient (top panels) and elevated (bottom panels) temperatures.

<p>For the graphs depicting measures of productivity at elevated temperatures (bottom panels), where significant interactive effects of competition and nutrients on biomass were detected, asterisks denote significantly different mean responses between competition levels within nutrients.</p

F-statistics and degrees of freedom (subscript) from split-plot ANOVA models of three aboveground productivity measures taken on <i>S</i>. <i>alterniflora</i> and <i>P</i>. <i>australis</i> under ambient and elevated temperatures.

<p>F-statistics and degrees of freedom (subscript) from split-plot ANOVA models of three aboveground productivity measures taken on <i>S</i>. <i>alterniflora</i> and <i>P</i>. <i>australis</i> under ambient and elevated temperatures.</p